Autodesk_Inventor_Pro_2008_Dynamic_Simulation_and_Stress_Analysis

Autodesk Inventor

®

™

Professional 2008

Dynamic Simulation and Stress Analysis Autodesk Official Training Courseware (AOTC)

46206-050008-1700A August 2007

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Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi Chapter 1: Introduction to Engineering Analysis . . . . . . . . . . . . . . . . . . . . 1 Lesson: Dynamic Simulation Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 About Dynamic Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Dynamic Simulation Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Creating Dynamic Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Exercise: Review a Cam Valve Simulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Lesson: Stress Analysis Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 About Stress Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Stress Analysis User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Performing a Stress Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Exercise: Perform a Basic Stress Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Chapter Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Chapter 2: Dynamic Simulation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Lesson: Creating Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 About Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Joint Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Guidelines for Creating Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Creating Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 About Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Repairing Redundant Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Exercise: Create Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Exercise: Create a Nonredundant Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 Lesson: Environmental Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Setting Initial Positions of Joints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 Applying Joint Torques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Applying Imposed Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Applying External Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Applying Friction and Gravity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 About the Input Grapher. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Using the Input Grapher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Exercise: Define Environmental Constraints . . . . . . . . . . . . . . . . . . . . . . . . . 86

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Lesson: Running Simulations and Analyzing Results . . . . . . . . . . . . . . . . . . . . . . 96 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Running Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 About the Output Grapher. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Using the Output Grapher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 Reviewing and Analyzing Simulation Results . . . . . . . . . . . . . . . . . . . . . . . 105 Exercise: Calculate the Driving Torque of the Wiper Assembly . . . . . . 107 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

Chapter 3: Stress Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 Lesson: Creating Loads and Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 About Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Types of Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 About Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Types of Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Exercise: Create Loads and Constraints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Lesson: Running an Analysis and Analyzing Results . . . . . . . . . . . . . . . . . . . . . 129 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Setting Up and Running the Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Revising Models and Stress Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Reviewing and Interpreting Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . 134 Animating and Reporting Analysis Results. . . . . . . . . . . . . . . . . . . . . . . . . . 138 Performing a Convergence Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Stress Analysis Files. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Exercise: Determine Enforced Displacement . . . . . . . . . . . . . . . . . . . . . . . 147 Exercise: Perform an In-Place Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 Lesson: Sharing Dynamic Simulation Results with Stress Analysis. . . . . . . . 156 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 About Sharing Dynamic Simulation Results with Stress Analysis. . . . . 157 Exporting Motion Loads to Stress Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . 159 Exercise: Simulate and Analyze a Glass Lever Mechanism . . . . . . . . . . . 161 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166

Chapter 4: Engineering Problems and Solutions . . . . . . . . . . . . . . . . . . 167 Lesson: Solving Design Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 Design Problem 1: Calculate the Stress on a Wheelie Bar . . . . . . . . . . . 170 Design Problem 2: Calculate the Maximum Acceleration of a Cross Subassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 Design Problem 3: Validate the Robustness of an Arm Linkage. . . . . . 179 Design Problem 4: Create a Cam Part from Motion Outputs. . . . . . . . . 184 Design Problem 5: Size a Spring for a Bike Suspension. . . . . . . . . . . . . . 190 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196

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Appendix A: Additional Support and Resources . . . . . . . . . . . . . . . . . . 197 Courseware from Autodesk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Autodesk Services & Support. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Autodesk Subscription. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Autodesk Consulting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Autodesk Partners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Autodesk Authorized Training Centers . . . . . . . . . . . . . . . . . . . . . . . . . . . . Autodesk Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Useful Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Acknowledgements The Autodesk Official Training Courseware (AOTC) team wishes to thank everyone who participated in the development of this project, with special acknowledgement to the authoring contributions and subject matter expertise of Ron Myers and CrWare, LP. CrWare, LP began publishing courseware for Autodesk Inventor in 2001. Since that time, the company has grown to include full-time authors and subject matter experts, each with a unique set of industry experiences and talents that enables CrWare to create content that is both accurate and relevant to meet the learning needs of its readers and customers. The company’s Founder and General Partner, Ron Myers, has been using Autodesk products since 1989. During that time, Ron Myers worked in all disciplines of drafting and design, until 1996 when he began a career as an Applications Engineer, Instructor, and Author. Ron Myers has been creating courseware and other training material for Autodesk since 1996 and has written and created training material for AutoCAD, Autodesk Inventor, AutoCAD Mechanical, Mechanical Desktop, and Autodesk Impression.

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Acknowledgements

Introduction Welcome to the Autodesk Inventor Professional 2008: Dynamic Simulation and Stress Analysis Autodesk Official Training Courseware (AOTC), training courseware for use in Authorized Training Center (ATC®) locations, corporate training settings, and other classroom settings. Although this courseware is designed for instructor-led courses, you can also use it for self-paced learning. The courseware encourages self-learning through the use of the Autodesk® Inventor™ Professional 2008 Help system. This introduction covers the following topics: ■ ■ ■ ■ ■ ■ ■ ■ ■

Course objectives Prerequisites Using this courseware CD contents Completing the exercises Installing the exercise data files from the CD Projects Notes, tips, and warnings Feedback

This courseware is complementary to the software documentation. For detailed explanations of features and functionality, refer to the Help system in the software.

Course Objectives After completing this course, you will be able to: ■

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Describe the Dynamic Simulation and Stress Analysis environments and the major components of the user interface, and describe and create dynamic simulations and stress analysis results. Create a dynamic simulation of a mechanism using joints and environmental constraints, and eliminate redundancy in the design. Use the Stress Analysis environment to determine stress, deformation, and natural frequencies on parts. Solve engineering and design problems using Dynamic Simulation and/or Stress Analysis.

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Prerequisites This course is designed for experienced Autodesk® Inventor™ users who want to learn about the tools and workflows in Autodesk Inventor Professional 2008 for simulating the operation of mechanisms and motorized assemblies and predicting part stress and deflection. It is recommended that you have: ■ ■

A working knowledge of parametric part and assembly design using Autodesk Inventor. A working knowledge of Microsoft® Windows® 2000, or Microsoft® Windows® XP.

Using This Courseware The lessons are independent of each other. However, we recommend that you complete these lessons in the order that they are presented unless you are familiar with the concepts and functionality described in those lessons. Each chapter contains: ■

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Lessons Usually two or more lessons in each chapter. Exercises Practical, real-world examples for you to practice using the functionality you have just learned. Each exercise contains step-by-step procedures and graphics to help you complete the exercise successfully.

CD Contents The CD attached to the back cover of this book contains all the datasets you need to complete the exercises in this course.

Completing the Exercises You can complete the exercise in two ways: using the book or onscreen. ■

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In the book Follow the step-by-step exercises in the book. Onscreen Click the AOTC AIP 2008 Dynamic Simulation and Stress Analysis icon on your desktop, installed from the CD, and follow the step-by-step exercises on screen. The onscreen exercises are the same as those in the book. The onscreen version has the advantage that you can concentrate on the screen without having to glance down at your book.

Introduction

After launching the onscreen exercises, you might need to alter the size of your application to align both windows.

Installing the Exercise Data Files from the CD To install the data files for the exercises: 1.

Insert the courseware CD.

2.

When the setup wizard begins, follow the instructions on screen to install the data.

3.

If the wizard does not start automatically, browse to the root directory of the CD and doubleclick Setup.exe.

Unless you specify a different folder, the exercise files are installed in the following folder: C:\Documents and Settings\All Users\Autodesk Learning\AIP 2008\ Dynamic Simulation and Stress Analysis After you install the data from the CD, this folder contains all the files necessary to complete each exercise in this course. You can also use the Autodesk Learning shortcut on your desktop to quickly access the datasets for each AOTC course on your system.

Projects Most engineers work on several projects at a time, and each project might consist of a number of files. You can use Autodesk Inventor projects to organize related files and maintain links between files. This courseware has a project file that stores the paths to all the files related to the exercises. When you open a file, Autodesk Inventor uses the paths in the current project file to locate other required files. To work on a different project, you make a new project active in the Project Editor.

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Follow the instructions below to locate the Dynamic Simulation and Stress Analysis project file for this courseware and make it active. 1.

Start Autodesk Inventor Professional.

2.

If the Autodesk Inventor New or Open dialog box does not appear, click File menu > Projects.

3.

At the bottom of the Projects dialog box, click Browse. ■

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Browse to C:\Documents and Settings\All Users\Autodesk Learning\AIP 2008\ Dynamic Simulation and Stress Analysis. Click Dynamic Simulation and Stress Analysis.ipj. Click Open. Click Done.

Notes, Tips, and Warnings Throughout this courseware, notes, tips, and warnings are called out for special attention.

Notes contain guidelines, constraints, and other explanatory information.

Tips provide information to enhance your productivity.

Warnings provide information about actions that might result in the loss of data, system failures, or other serious consequences.

Feedback We always welcome feedback on Autodesk Official Training Courseware. After completing this course, if you have suggestions for improvements or if you want to report an error in the book or on the CD, please send your comments to [email protected].

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Introduction

Chapter

1 Introduction to Engineering Analysis Chapter1:

This chapter introduces you to the Dynamic Simulation and Stress Analysis environments. You learn how to use dynamic simulation and stress analysis to analyze designs and identify their successes and flaws before you build costly physical prototypes.

Objectives After completing this chapter, you will be able to: ■

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Describe the Dynamic Simulation environment and the processes you use to create simulations to evaluate motions in an assembly. Describe the Stress Analysis environment and the processes you use to create and analyze designs.

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Lesson: Dynamic Simulation Overview Overview This lesson describes the Dynamic Simulation environment, and its interface and tools. The lesson also describes the processes you use to create simulations to evaluate motions in an assembly, to size actuators, to determine bearings, and to compute stresses in parts. Proving the validity of your designs before you build saves time and money by eliminating costly reworking and alterations after the build process has begun. Simulation data serves as a valuable presentation tool for customers to assure them that you are providing a design that meets their requirements. The integration of Dynamic Simulation with Autodesk® Inventor™, and the Dynamic Simulation evaluation mechanisms, provide you with valuable tools to test, refine, and prove your designs.

Objectives After completing this lesson, you will be able to: ■ ■ ■

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Describe the Dynamic Simulation environment. Identify the Dynamic Simulation interface, its tools, and its unique browser nodes. Describe the basic process for creating a dynamic simulation.

Chapter 1: Introduction to Engineering Analysis

About Dynamic Simulation Dynamic Simulation is an environment included in Autodesk® Inventor™ Professional. Dynamic Simulation is used to simulate and analyze dynamic characteristics of an assembly under various load conditions. You can also export load conditions at any motion state to the Stress Analysis environment to see how parts respond from a structural view to dynamic loads at any point in the assembly’s range of motion. In addition, you have the option to transfer multiple load conditions simultaneously in the assembly’s range of motion to the Stress Analysis environment. This option enables you to validate and compare designs without the need to go back to Dynamic Simulation to transfer loads again. In the following illustration, an assembly is shown in the Dynamic Simulation environment.

Definition of Dynamic Simulation A dynamic simulation simulates the dynamic motion in an assembly. The Dynamic Simulation environment automatically converts assembly constraints between components into mechanical joints. You also have the option to define mechanical joints between components manually. After the joints have been finalized, forces, accelerations, or velocities need to be applied to them where applicable to reproduce real-world conditions. You can use the results of the simulation to determine the integrity of a design, calculate the amount of force required to produce a desired motion, or view the effect of natural forces such as gravity and friction on the mechanism.

Lesson: Dynamic Simulation Overview

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In the following illustration, an assembly is in the middle of a simulation with the Output Grapher displaying force data used to perform stress analysis on a component.

Starting Dynamic Simulation Within Autodesk Inventor Professional, you can access Dynamic Simulation only from an assembly file. You must click the Application’s menu and then click Dynamic Simulation.

Example of Dynamic Simulation You have designed a windshield wiper assembly that is ready to be manufactured. Before the design is complete, you must determine the amount of driving torque required to rotate the drive arm at a velocity of 180 degrees per second. In Dynamic Simulation, you define the mechanism and impose the velocity on the drive arm. Using the Output Grapher, you can graph the torque curve for the drive arm. You can then extract the maximum drive torque on the drive arm, which you use to select the proper motor for the assembly.

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In the following illustration, the drive arm for the wiper assembly is shown to the left of the Output Grapher.

Dynamic Simulation Interface The Dynamic Simulation environment uses the same major interface components that you use in the part or assembly environments, including the graphics window, panel bar, and browser. The tools presented on the panel bar, and the elements in the browser, are specific to the Dynamic Simulation environment. Additionally, the Dynamic Simulation panel bar contains controls to run simulations and set their time parameters.

Graphics window

Dynamic Simulation browser

Dynamic Simulation panel bar

Simulation Panel Lesson: Dynamic Simulation Overview

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Dynamic Simulation Panel Bar The Dynamic Simulation panel bar is divided into four sections according to the types of operations that they perform.

Tools to create joints and the forces applied to them Tools to simulate or to use the simulation output Tool to set the simulation environment settings Parameters tool to access assembly parameters

Dynamic Simulation Browser The Dynamic Simulation browser provides a set of groups and nodes that are unique to the Dynamic Simulation environment. Components are classified as Grounded or Mobile. Joints are grouped by category, as are external loads and traces. In the browser you access the shortcut menus to open joint properties, edit and delete joints, lock degrees of freedom, and control the display of joints.

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The unique nodes in the Dynamic Simulation browser are shown in the following illustration.

Simulation Panel The Simulation Panel is used to run a simulation. With this tool, you control the simulation time, how many time steps are calculated, and the speed at which the simulation runs. The Simulation Panel is synchronized with the mechanism in the graphics window and the Output Grapher, so that you can see the position of the mechanism and the resultant force in the Output Grapher at any time step that you choose. In the UI, the Simulation Panel is located below the Dynamic Simulation browser. In the following illustration, the Simulation Panel is shown with the slider at 50%, halfway through the simulation.


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Creating Dynamic Simulations With dynamic simulation, the intent is to build a functional mechanism, and then add dynamic, realworld influences of various kinds of loads to create a true kinematic chain. You then run the simulation to see how the joints, loads, and component structures interact as a moving dynamic mechanism. In the following illustration, the Input Grapher is open to adjust properties of a joint.

Process: Creating Dynamic Simulations The following steps provide an overview of the process of creating dynamic simulations of your assembly designs.

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1.

Open an assembly file in Autodesk Inventor Professional.

2.

Click Applications menu > Dynamic Simulation.

3.

Create standard joints by converting existing assembly constraints automatically and/or manually in order to create degrees of freedom.

4.

Create other types of joints like contacts, rolling/sliding, or spring, to further constrain your mechanism.

5.

Define the physical environment in the joint properties and apply forces by using the Input Grapher.

6.

Run the dynamic simulation to see how joints, loads, and component structures interact.

7.

Use the Input Grapher to apply joint forces and external forces.

8.

Use the Output Grapher to analyze and export results.

9.

Transfer loads on a part to be analyzed by Stress Analysis to study the effect of the loads on the part.

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Exercise: Review a Cam Valve Simulation In this exercise, you run a simulation of a cam valve assembly with and without friction to determine the torque required to overcome the spring resistance and the friction force.

2.

Click Applications menu > Dynamic Simulation. Click OK in the Dynamic Simulation warning dialog box alerting you that legacy contact joints will be merged to the new format.

3.

On the Simulation Panel, click Run or Replay Simulation, and view the simulation.

At the beginning of the simulation you notice that the valve is bouncing. You will correct this and run the simulation again.

The completed exercise

Completing the Exercise

4.

On the Simulation Panel, click Activate Construction Mode.

5.

In the Dynamic Simulation browser, expand the Contacts Joints node. Right-click nº4 : 2D Contact (Cam:1, Valve:1). Click Properties.

6.

In the nº4 :2D Contact (Cam:1, Valve:1) dialog box, for Restitution, enter 0. Click OK.

7.

On the Simulation Panel, click Run and view the simulation. The valve does not bounce.

To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 1: Introduction to Engineering Analysis. Click Exercise: Review a Cam Valve Simulation.

1.

Open CamValve.iam.


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8.

9.

On the Dynamic Simulation panel bar, click Output Grapher. Resize the Output Grapher and zoom and pan in the CamValve assembly to view both, as shown.

11.

In the Output Grapher, click Save. Save the file as CamValve.iaa.

12.

On the Simulation Panel, click Activate Construction Mode.

In the Output Grapher, double-click the dashed line at 0.25 (1). The timeline (2) is displayed, and the cam (3) position updates to show its position at that point of the simulation.

In the next two steps you add a coefficient of friction to calculate the effect on the torque required to rotate the cam and overcome the spring force and friction force.

10.

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To cycle through the simulation, use the right and left arrow keys on the keyboard to step forward and backward in the simulation. Cycle through the simulation to 1.00 to show the cam at the end of the simulation.

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13.

In the Dynamic Simulation browser, for Contacts, right-click nº4 :2D Contact (Cam:1, Valve:1). Click Properties.

14.

In the nº4 :2D Contact (Cam:1, Valve:1) dialog box, for Friction, enter 0.15. Click OK.

15.

On the Simulation Panel, click Run or Replay Simulation, and view the simulation. The Output Grapher is still open, so you see the graph being generating as the simulation is running.

19.

In the Dynamic Simulation - Properties dialog box, click OK. Your graph in the Output Grapher changes to red.

20.

On the Output Grapher toolbar, click Import Simulation.

In the next step, you change the color of the newly generated curve. When you compare the saved graph curve with this new one, you can distinguish between the two of them. 16.

In the Output Grapher, right-click the Ukin[2.1]/N mm column heading. Click Curve Properties.

17.

In the Dynamic Simulation - Properties dialog box, click the color box.

18.

In the Color dialog box, click the red color swatch and click OK.


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22.

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In the Dynamic Simulation - Load file dialog box, select CamValve.iaa and click Open. The CamValve.iaa node is added to the Output Grapher tree, as shown.

In the Output Grapher tree, expand the CamValve.iaa node. Expand nº2 :Revolution (Support:1, Cam:1). Expand Driving Force and select Ukin[2.1].

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23.

The Output Grapher now shows the graphs of the driving force without friction (blue) and with friction (red), to compare the difference in force required for each situation. A new column also appears to display the numerical values.

24.

Close the file. Do not save changes.

Lesson: Stress Analysis Overview Overview This lesson introduces you to the concept and overall process for performing a stress analysis in Autodesk Inventor Professional. In a typical product design cycle, you may need to examine how your design will perform under certain real-world conditions. When the product will be exposed to forces, loads, and constraints during normal use, it is important that you design the product to function properly to withstand these forces, loads, and constraints. In the following illustration, the results of a stress analysis indicate how the part would be deformed under specific load and constraint conditions.

Objectives After completing this lesson, you will be able to: ■ ■

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Describe stress analysis and how you can use it to validate your designs. Describe how the Stress Analysis environment is integrated into the Autodesk Inventor user interface. Explain how to perform basic stress analysis. Perform a basic stress analysis and review the results.

Lesson: Stress Analysis Overview

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About Stress Analysis Stress Analysis enables you to estimate the deformation, stress, and natural frequencies of your parts as they are placed under certain load and constraint conditions. The process helps you to create better parts by indicating areas of your models that require further attention. You can reduce the number of design-test-redesign cycles by using Stress Analysis early in the design cycle to find and fix your models before you build the first prototype. For most components, you can consider a physical test of the final part to ensure that it meets the performance criteria. You can even use Stress Analysis to help design the test by identifying locations of high stress or deformation. You use the test results to fine-tune your stress analysis so that you can predict the stress on similar parts with greater accuracy. Testing also builds confidence in your stress analysis methods and results.

Definition of Stress Analysis Stress Analysis uses a technique called finite element analysis (FEA) to calculate the deformation, stress, and mode shapes of a model. Finite element analysis is an approximation method that estimates the behavior of a model. If a model has simple geometry, it is straightforward to solve for stress and deflection manually by using available equations. However, most models have complex geometry, and equations to predict the stress, deflections, or mode shapes are typically unavailable. In finite element analysis, the model is subdivided into a number of pieces called elements, which have simple shapes that have available solutions. The solutions for each element are combined to obtain the behavior of the entire model. The process of generating the elements in finite element analysis is called meshing, and the resulting set of connected elements is called the mesh.

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In the following illustration, the original and meshed models for a bracket are shown.

The size of each element in the mesh determines the resolution of the results. The smaller the elements, the more accurate the numerical results, but the model takes longer to process. In areas of the model where the stress is fairly constant, large elements are adequate; however, where the stress changes rapidly, such as near a stress concentration, smaller elements are required.

Example of Stress Analysis In the following illustration, deformation results are shown for a stress analysis on a metal bracket.


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Potential Uses for Stress Analysis You use Stress Analysis to identify: ■

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Portions of your models that are highly stressed and may lead to part failure during the prototype or production phase. Areas that carry little load, which may warrant a change in geometry to save weight or material. Components that deform beyond an allowable limit and that may need to be stiffened through model or material changes. Parts with modal frequencies near the operating frequency that may result in excess wear or noise.

Stress Analysis Assumptions You use Stress Analysis to solve linear static problems. Although many engineering components can be analyzed using Stress Analysis, there may be situations where linear static analysis assumptions do not apply. Linear static stress analysis assumptions include the following: ■

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The deflection and stress are linearly proportional to the load. If you double the load, the deflection and stress double. Material properties are linear. The stress-strain curve is a straight line, with the stress remaining proportional to the strain. There is no yielding of the material. The loading is static and is applied slowly. Dynamic loading effects such as sudden load application or impact are not considered. Temperature has no effect on the part geometry or material properties. The deformation of the part is small when compared to the dimensions of the part. Large deflection requires a nonlinear analysis to account for changing part and load geometry and is not considered in linear analysis. Other nonlinear effects such as buckling are not considered.

If you have a problem for which these assumptions are not valid, you should either upgrade to a full analysis package such as ANSYS DesignSpace®, or pass the problem on to an analyst with the appropriate knowledge and software to manage it.

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Stress Analysis User Interface The Stress Analysis environment uses all of the interface elements you are familiar with in the assembly and part modeling environments. In the following illustration a part is shown in the Stress Analysis environment. Specific stress analysis tools and features are shown in the panel bar, browser, and graphics window.

Activating the Stress Analysis Application Before you can access stress analysis tools, you must activate the Stress Analysis application. You do this with the Applications menu.

Access Stress Analysis

Menu: Applications > Stress Analysis


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Stress Analysis Panel Bar The Stress Analysis panel bar is displayed automatically when the Stress Analysis application is activated. The Stress Analysis panel bar provides the tool set for the Stress Analysis environment. You use the Applications menu to switch between the Stress Analysis and part environments.

Stress Analysis Browser The Stress Analysis browser lists the loads, constraints, and results of an analysis. You use the browser to edit or delete existing loads and constraints, and to select the results you want to display.

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Stress Analysis Display Tools In the Stress Analysis environment, you use tools on the Standard toolbar to control the display of input and results.

Select the desired contour setting. Use these options to toggle the display of Elements, Boundary Conditions, Maximum Stress/Displacement Point, and Minimum Stress/Displacement Point. Select a deformation scale in the list to exaggerate the visual results.

Stress Analysis Options in the Part Environment After you perform a stress analysis, you may need to modify geometry in identified areas of concern. While you are working in the part environment, the Standard toolbar contains tools that enable you to update the stress analysis and display the last stress result item. Using these tools, you can identify areas of the model that require edits to address problems identified by the stress analysis. After making the changes, you can update the analysis to see the effects of your changes.

Click to update the stress analysis to incorporate changes in the part model. Click to display the results of the last stress analysis result item.


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Performing a Stress Analysis The process of performing a stress analysis involves several steps, some of which must be repeated as you refine the model geometry based on the analysis results. When you perform a stress analysis, your goal is to simulate real-world conditions on your part by duplicating forces, loads, and constraints in the design environment. In the following illustration, Equivalent Stress results are shown on a simple part model.

Process: Performing a Stress Analysis The following steps describe the process of performing a stress analysis. 1.

Click Applications menu > Stress Analysis.

2.

Add loads to your model that represent the actual loading conditions that will occur. ■

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You can add forces, moments, pressure, bearing, and body loads such as gravity and acceleration. Specify the load directions using geometry on the part or on other parts in the assembly.


3.

Add constraints that represent the physical connection of the part to other parts in the design. For example, use a constraint where the part is bolted or welded, or where it contacts other components.

4.

Set the analysis options. In the Stress Analysis dialog box, select the type of analysis and the mesh size.

5.

Analyze the model: ■

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6.

View the results. ■

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7.

When the analysis is complete, the results are displayed graphically on the model. You can view contours for stress, deformation, factor of safety, or the different mode shapes. You can also display or hide the mesh, loads, or constraints; change the display range for contours; and display or hide minimum and maximum markers.

Refine the model: ■

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8.

When you finish applying loads and constraints, click the Stress Analysis Update tool to analyze the model. The Solution Status dialog box shows the analysis progress.

If there are areas of concern, return to the part environment, display the results of the analysis on the model to guide your changes, make appropriate model changes, and then update the stress analysis. Repeat this cycle until you are satisfied with the model’s results.

Document the results: ■

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Create a report that summarizes the input values and results, including images of the results. The report is in HTML format, so you can share it with others on the design team and include it in documentation.


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Guidelines Keep the following guidelines in mind when performing a stress analysis. ■ ■

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If your part is a component of an assembly, either edit the part in place or open the part separately. To analyze a series of rigidly connected components in an assembly, create a derived part and then analyze the derived part. Suppress features that do not affect the results, especially if the features are small. Typical features that you want to suppress include small cosmetic rounds, chamfers on outside corners, and small holes or other features in areas where the stress will be low and which do not contribute to the stiffness of the model. Small features increase the number of elements and can significantly increase solution time. If you are interested in converging the stress results, make sure that inside corners in the area of interest have fillets. Sharp inside corners result in infinite stress, and the stress results will not converge. The processing time depends on the size of the model and of the mesh. You typically analyze several times at decreasing mesh sizes to prove that the results are converged. When you are confident that the model performs correctly, select Result Convergence to automatically converge on a result.

Using Autodesk Inventor Although you must have Autodesk Inventor Professional software to perform a stress analysis and view analysis results, you can open and edit a part that contains Stress Analysis results with the Autodesk Inventor application. If you modify the part in an Autodesk Inventor application and then open it in Autodesk Inventor Professional software, the stress results must be updated so that they reflect the changes. You may need to edit loads and constraints if the geometry to which they were attached was modified.

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Exercise: Perform a Basic Stress Analysis In this exercise, you determine the stress and deformation of a plate with an end load. You apply loads and constraints, run an analysis, and view the results. You add a hole to the plate and determine the hole’s effects on the results. You perform a convergence study to determine whether the mesh size is adequate.

1.

Open Stress_SteppedPlate.ipt.

2.


NOTE: The first part of this problem is a simple example with a known solution. Whenever you run a new analysis type, run a simple test case to familiarize yourself with the input values and other program settings. ■

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3.

Because no material was set for the model, the Choose Material dialog box is displayed. From the Material list, select Steel, Mild. Click OK.

On the panel bar, click Force. ■

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Move the cursor over edges, vertices, and faces on the plate to display the allowed selections. Click the right end face of the plate.

The force is applied with its default direction perpendicular to and toward the selected face. The completed exercise

Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 1: Introduction to Engineering Analysis. Click Exercise: Perform a Basic Stress Analysis.


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4.

In the Force dialog box: ■

7.

Confirm the appearance of the constraint in the browser.

8.

To adjust the Stress Analysis Settings:

Click the Flip Force button to make the force arrow point away from the face. For Magnitude, enter 5000 N. Click OK.

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5.

Confirm the appearance of the force element in the browser.

9.

6.

Add a constraint to the part: ■

On the panel bar, click the Fixed Constraint tool. Select the face at the left end of the plate. Click OK.

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On the panel bar, click the Stress Analysis Settings tool. In the Stress Analysis Settings dialog box, make sure that Stress Analysis is selected in the Analysis Type list. Click Preview Mesh to view the finite element mesh. Click OK.

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On the Standard toolbar, click the Stress Analysis Update tool. When the analysis is complete, the equivalent stress is displayed on the deformed model.

As expected, the stress is highest at the fillets. The result is close to the theoretical stress of about 56 MPa (using a stress concentration factor of 1.6). NOTE: In this analysis, the analysis result matched the theoretical result on the first run because the model loading and geometry are simple. Never consider an analysis complete after just one run. You must always perform a convergence study to confirm that the results of several runs are converged. 10.

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Confirm that the reaction force in the X direction is -5000 N. Click OK to close the dialog box.

The lowest safety factor is 3.7214, which is equal to the yield strength of the material (207 MPa) divided by the maximum stress (55.6243 MPa). 17.

On the Standard toolbar, in the Deformation Scale list, select 2:1 Automatic.

On the Standard toolbar, in the Deformation Scale list, select Actual.

To change the force magnitude: ■

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The deformed shape changes. Remember that the deformation is exaggerated. 12.

In the browser, double-click Safety Factor. The safety factor contours are displayed on the model.

In the browser, right-click Fixed Constraint 1. Click Reaction Forces. In the Reaction Forces dialog box: ■

11.

The contours are parallel because the plate is loaded uniformly across the end. The contours are farther apart in the wider area of the plate and closer together in the narrower area because the plate deforms more per unit length in the narrower area. The result matches the theoretical estimate of 0.011 mm.

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In the browser, right-click Force 1. Click Edit. In the Edit Force dialog box, for Magnitude, enter 6000 N. Click OK.

18.

In the browser, notice that the icons in front of the results have lightning bolts, indicating that the results need to be updated.

19.

Click the Stress Analysis Update tool.

20.

View the stress, deformation, and safety factor. The stress and deflection values should be approximately twenty percent greater than the previous values.

Notice that the actual deformation is very small. 13.

Return the deformation style to the default value of 1:1 Automatic.

14.

On the Standard toolbar, turn the display tools on and off and notice the effects.

15.

In the browser, double-click Deformation. The deformation contours are displayed on the model.


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21.

In the browser, expand Features. Right-click Hole1. Click Unsuppress Features. Notice that the results need updating.

22.

On the Standard toolbar, click the Stress Analysis Update tool to rerun the analysis. View the results.

The stress has decreased slightly, and the deformation is unchanged at 0.0159 mm. Because the percentage of change in stress is very small between the runs, the mesh size is probably adequate to predict the stress in the model. You now try automatic convergence. The analysis may take several minutes. 25.

To use Results Convergence: ■ ■

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26.

Click the Stress Analysis Update tool to rerun the analysis. The stress has decreased slightly again. ■

The maximum stress is now 141.44 MPa and is located near the hole. The maximum deformation is 0.0159 mm.

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23.

Click the Stress Analysis Settings tool. ■

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Click the Stress Analysis Update tool to rerun the analysis.

27.

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On the Standard toolbar make sure the Element Visibility button is selected. This causes the mesh to be displayed. Notice that the mesh is much finer near the hole.

In the Stress Analysis Settings dialog box, change the Mesh Relevance slider to 100. Click Preview the Mesh. In the warning dialog box, click OK. In the Stress Analysis Settings dialog box, click OK.

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24.

Click the Stress Analysis Settings tool. In the Stress Analysis Settings dialog box, under Mesh Control, select the Results Convergence check box. Click OK.

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Chapter Summary This chapter introduced you to the Dynamic Simulation and Stress Analysis environments. You learned how to use dynamic simulation and stress analysis to analyze designs and identify their successes and flaws before you build costly physical prototypes. Having completed this chapter, you can: ■

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Describe the Dynamic Simulation environment and the processes you use to create simulations to evaluate motions in an assembly. Describe the Stress Analysis environment and the processes you use to create and analyze designs.

Chapter Summary

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Chapter

2 Dynamic Simulation

Chapter2:

In this chapter, you learn how to define relationships between components by describing how parts move in relationship to one another, and how to identify and avoid redundancy in a simulation design. You learn how to identify the starting conditions of joints, as well as motion or force values which define the environment under which the mechanism runs. You also learn how to run a simulation and use the Output Grapher to review and analyze the simulation results.


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Create joints that define the relationships between components in a mechanism while avoiding redundancy. Create environmental constraints for a simulation. Run a simulation, then use the Output Grapher to review and analyze the results.

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Lesson: Creating Joints Overview This lesson describes joints, their use in describing how a mechanism works, and their importance in the dynamic simulation process. This lesson also describes redundancy in Dynamic Simulation mechanisms, and how to create nonredundant models. You learn how to define redundancy, how redundancies occur, and how redundancies can be repaired. To simulate dynamic motion in an assembly, you need to design mechanical joints between components in an assembly. Joints define the relationships between components in a mechanism by describing how parts move in relationship to one another, as well as determining the types of active and reactive forces that act on the mechanism to control its movements. In mechanism theory, redundancy occurs when too many unknowns exist in a simulation, resulting in the existence of infinite solutions when only one solution is needed. In the following illustration, a Spring/Damper/Jack joint is being applied to a cam valve assembly.

Objectives After completing this lesson, you will be able to: ■ ■ ■ ■ ■ ■

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Describe joints and their importance in Dynamic Simulation. Identify joint types and where particular joints should be used. Describe the guidelines for creating joints. Create different types of joints based on mechanism or simulation requirements. Explain redundancy and how redundancies occur in dynamic simulations. Repair redundancies in joints.

Chapter 2: Dynamic Simulation

About Joints In Dynamic Simulation, creating joints of types such as revolution, planar, and spherical is how you manage degrees of freedom for components. Unlike assembly constraints, which restrict degrees of freedom, joints add degrees of freedom. Joints are used to provide motions to components, which along with component inertial property, friction, gravity, and other imposed forces, provide Dynamic Simulation with the information needed to generate the simulation and graph the results. In the following illustration, a revolution joint is being applied to the cam, which provides the freedom to rotate within the hole on the support component.

Definition of Joints A joint is a relationship between assembly components that determines how they move or react to one another within a mechanism. You can create joints automatically in the Dynamic Simulation environment by converting existing and new assembly constraints, or manually by using the Insert Joint tool.

Lesson: Creating Joints

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In the following illustration, the spring joint imposes a force on the valve, causing the valve to maintain contact with the cam surface.

Differences Between Assembly Constraints and Joints Degrees of freedom (DOF) for components are managed differently in the assembly environment as compared to the Dynamic Simulation environment. In the assembly environment, unconstrained and nongrounded parts, by default, have six degrees of freedom: three rotational, and three translational. When you add assembly constraints, you restrict degrees of freedom. For instance, adding an insert constraint to a cylindrical component restricts five degrees of freedom, and allows the component to rotate only around one axis. In Dynamic Simulation, all parts, by default, have zero degrees of freedom. Even parts that are not grounded in the assembly environment have zero degrees of freedom in Dynamic Simulation. Adding a revolution joint to a component in Dynamic Simulation creates one degree of freedom, freeing the part to rotate around the selected rotation axis.

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Example of Joints You have designed a cam valve assembly. You use a spring to ensure that the valve maintains contact with the cam during the cycle, and a contact joint to manage the contact between the cam and the valve. Due to contact friction, power is lost during the motion. You use Dynamic Simulation to determine the loss in power. The first step you take to run the simulation is to convert assembly constraints and insert joints to define the mechanism. Now you are set to run the dynamic simulation. In the following illustration, the cam valve assembly is shown before the joints were applied (1) and in the middle of a simulation after creation of the required joints (2).

Joint Types The first step in building a mechanism in Dynamic Simulation is to create joints. The different categories of joints include standard, rolling, sliding, contact, and force. Standard joints can be automatically created from assembly constraints to create degrees of freedom, or manually if no assembly constraints are present. Rolling, sliding, and contact joints are special joints that are created in addition to standard joints to restrict and create specific motion. Force joints like spring, damper, and jack create an action/reaction force between two components in an assembly. The following illustration displays the Joints Table, where you select the joint to insert. The upper part of the dialog box displays buttons representing the categories of joints: standard joints, rolling joints, sliding joints, 2D contact joints, and force joints. When you click a category button in the upper window, the lower window updates to display buttons representing the available joints that fit the chosen category. Select the button for the joint you want to use and click OK to create the joint.


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Standard Joints: Create Degrees of Freedom The joints in the following table create degrees of freedom. These joints must be the first joints that are created in an assembly in order to create the degrees of freedom between components. Button

Description Revolution Joint Use this joint to create a relationship between the cylindrical faces and cylindrical axes of two components. This joint authorizes rotation around the Z axis of the joint coordinate system. The angular value of the rotational degree of freedom is measured between the first coordinate system X axis and the second coordinate system X axis. Prismatic Joint Use the prismatic joint to constrain the edge of one component to the edge of a second component. This joint authorizes translation along the Z axis of the joint coordinate system. The value of the translational degree of freedom is measured between the first coordinate system origin and the second coordinate system origin. Cylindrical Joint Use this joint to constrain the axes of two cylindrical components to allow the component that is chosen second to move back and forth along the axis of the first component. This joint authorizes translation along the Z axis of the joint coordinate system and rotation around the Z axis of the joint coordinate system. The value of the translational degree of freedom is measured between the first coordinate system origin and the second coordinate system origin. The angular value of the rotational degree of freedom is measured between the first coordinate system X axis and the second coordinate system X axis.

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Button

Description Spherical Joint This joint is used for a ball-and-socket type movement. This joint authorizes three rotations between the joint’s coordinate systems. The two joint coordinate system origins always remain coincident. Planar Joint Use the planar joint to constrain a planar face on one component to a planar face on a second component. The first selected component is the reference component and remains stationary. The second component can move freely on the selected face of the reference component. Use the planar joint to constrain a planar face on one component to a planar face on a second component. This joint authorizes two translations along the X and Z axis and one rotation around the Y axis of the joint coordinate system. The value of the translational degree of freedom is measured between the first coordinate system origin and the second coordinate system origin. The angular value of the rotational degree of freedom is measured between the first coordinate system X axis and the second coordinate system X axis. Point - Line Joint This joint constrains the center point of a spherical component to the axis of a cylindrical feature or a point on a line. This joint authorizes one translation along the Z axis and three rotations between the two joint coordinate systems. The value of the translational degree of freedom is measured between the first coordinate system origin and the second coordinate system origin. The origin of the second coordinate system always stays on the Z axis of the first coordinate system. Line - Plane Joint This joint constrains the line edge of a component to a planar face on a reference component. This joint authorizes two translations along the X and Z axis and two rotations between the two-joint coordinate system. The value of the translational degree of freedom is measured between the first coordinate system origin and the second coordinate system origin. The Z axis of the second coordinate systems always stays on the XZ plane of the first coordinate system. Point - Plane Joint This joint constrains a single point of a component to a planar face on a reference component. This joint authorizes two translations along the X and Z axis and three rotations between the two joint coordinate system. The value of the translational degrees of freedom is measured between the first coordinate system origin and the second coordinate system origin. The origin of the second coordinate system always stays on the XZ plane of the first coordinate system. Spatial Joint This joint creates a space relationship between two moving components. This joint authorizes three translations along the X, Y and Z axes and three rotations between the two joint coordinate systems. The value of the translational degrees of freedom is measured between the first coordinate system origin and the second coordinate system origin. Welding Joint Use the welding joint when multiple components need to function as one. This joint displays as a welded group in the Dynamic Simulation browser. Unlike the weld feature, Dynamic Simulation provides reaction forces and torques for this joint as output results.


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Rolling Joints: Restrict Degrees of Freedom The rolling joints in the following table restrict degrees of freedom. Button

Description Rl Cylinder on Plane Joint This joint constrains a rotating cylinder face without sliding to a flat face on a second component. The relative motion between the two components must be 2D. Use for gear and a rack or for a cylinder that rolls on a plane. This joint must be created using the primitive cylinder and plane of the rack. If you use Design Accelerator, the primitive surfaces are automatically created, you simply must make them visible and use them to create the joint. If not, you can use, for instance, sketches on each component that contains the primitive circle for the gear and the primitive line for the rack. Rl Cylinder on Cylinder Joint This joint constrains the rotating cylindrical face of one component to the rotating cylindrical face of a second component without sliding. The relative motion between the two components must be 2D. This joint must be created using the cylinder edges or the sketched pitch diameters of gears. If you use Design Accelerator to create gears, the primitive surfaces are automatically created, you simply must make them visible and use them to create the joint. For other gears, you can use sketches on each component that contain the circle representing the pitch diameter for each gear. Rl Cylinder in Cylinder Joint This joint constrains the rotating cylindrical face of one component inside the rotating cylindrical face of a second component without sliding. The relative motion between the two components must be 2D. This joint must be created using the edge of the cylinders or sketches of the pitch diameter of gears. If you use Design Accelerator to create gears, the primitive surfaces are automatically created, you simply must make them visible and use them to create the joint. If not, you can use, for instance, sketches on each component that contains the primitive circles for each gear. Rl Cylinder Curve Joint Use this joint for a rotating cylinder face that maintains contact with a rotating cam face. The relative motion between the two components must be 2D. Use the edges, faces, or sketches of the two components for selection. Belt Joint This joint is used to constrain a belt to two rotating cylindrical components.

Rl Cone on Plane Joint This joint constrains a rotating conical face to the flat face of a second component. If you use Design Accelerator to create gears, the primitive surfaces are automatically created, you simply must make them visible and use them to create the joint. If not, you can use, for instance, sketches on each component that contains the primitive circles for each gear. Rl Cone on Cone Joint This joint constrains a rotating conical face to the conical face of a second component. If you use Design Accelerator to create gears, the primitive surfaces are automatically created, you simply must make them visible and use them to create the joint. If not, you can use, for instance, sketches on each component that contains the primitive circles for each gear.

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Button

Description Rl Cone in Cone Joint This joint constrains the face of a conical rotating component to the inside conical face of a second stationary component. Screw Joint Use this joint to construct a relationship between a component that screws into a second component. You create a cylindrical joint between the two components and the thread pitch to indicate the amount of travel per rotation. Worm Gear Joint Use this joint to constrain a worm gear component to a helical gear component. If you use Design Accelerator, the primitive surfaces are automatically created, you simply must make them visible and use them to create the joint. If not, you can use, for instance, sketches on each component that contains the primitive circles for each gear.

Sliding Joints: Restrict Degrees of Freedom The sliding joints in the following table restrict degrees of freedom. Button

Description Sl Cylinder on Plane Joint Use this joint to constrain a cylindrical face to a plane so that it slides without rotating. The relative motion between the two components must be 2D. Sl Cylinder on Cylinder Joint Use this joint to constrain a cylindrical face to slide on a cylindrical face. The relative motion between the two components must be 2D. Sl Cylinder in Cylinder Joint Use this joint to constrain a cylindrical face to slide inside a cylindrical face. The relative motion between the two components must be 2D. Sl Cylinder Curve Joint Use this joint to constrain the cylindrical face to slide on a face of a cam. The relative motion between the two components must be 2D. Sl Point Curve Joint This joint constrains a point on one component to stay on a curve defined by a face, edges, or sketches. The relative motion between the two components must be 2D.


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2D Contact Joint: Restrict Degrees of Freedom The 2D contact joint in the following table restricts degrees of freedom. Button

Description 2D Contact Joint This joint creates a contact between a curve on one component and curve on another. The relative motion between the two components must be 2D. The curves can be defined by selecting a face, an edge, or a sketch. Unlike rolling and sliding joints, the contact could be nonpermanent during the simulation.

Force Joints: Create an Action/Reaction Force The force joints in the following table create an action/reaction force. Button

Description Spring/Damper/Jack Joint Use this joint when you need to create a spring force, a damping force like a shock absorber, or a jack force that lifts or lowers. 3D Contact Joint This joint, based on spring-damper forces between the parts, detects the interference on the entire faceted surface of the parts. This joint works only with part occurrences. A subassembly is not completely taken into account if a single part is selected.

Guidelines for Creating Joints The most important step in creating joints is determining which joints should be created for the intended simulation. After you determine the necessary joints for your mechanism, your joints must be created in the proper order, standard joints first and then others, like contact, rolling/sliding, and spring joints. Correct creation of joints ensures that the mechanism works as intended and that the simulation can be run. Use the following as guidelines for creating joints. ■

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The number of joints in a mechanism can affect Dynamic Simulation performance. For components and subassemblies that function as a unit, consider using the welded joint in Dynamic Simulation, or restructure as a subassembly in the assembly environment. These actions cause Dynamic Simulation to treat the welded group and the subassembly as a single entity during the simulation, which optimizes simulation time. You can simplify the standard joint creation process by automatically creating multiple joints at once, from all existing and new assembly constraints, or converting joints automatically from assembly constraints one by one. After converting assembly constraints, you can manually create any remaining joints that are required including rolling, sliding, or 2D contact joints.


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If you are unsure of which joint to use, click the Joints Table button in the Insert Joints dialog box to open the Joints Table, which shows visual representations of the joints and how they affect the selected components. Be sure to close the Joints Table when you are finished, because you cannot select any geometry with the Joints Table open. When you create a joint between components that are not in place, you need to specify the Z axis, origin, and X axis (the coordinate system) on each component to align and create a relationship between the two components. Adjust the alignment of the X and Z axes of the coordinate systems on your selected components to control how the components’ positions are adjusted when the coordinate systems are aligned.

Example of Applying Guidelines to Create a Joint You create a revolution joint on the cam valve assembly. When you select the face and edges to create the joint, the Z axis for the coordinate system on the cam component is pointing in the opposite direction of the Z axis of the coordinate system on the support. If you apply the joint, the cam flips to align the origin point and the axes of its coordinate system with that of the support component’s origin point and axes. In the Insert Joints dialog box, you invert the Z axes of the coordinate system on the cam before applying the joint. In the following illustration, on the left, the Z axis of the cam (1) is pointing in the opposite direction of the Z axis on the support (2). On the right, the Z axis on the cam (3) has been inverted and now is pointing in the same direction as the Z axis on the support.

Creating Joints When you create joints, you must determine whether the components are already aligned or not. If you are creating the joints between parts that are not initially aligned, it may be necessary to adjust the orientation of the axes and origin for the coordinate systems of the selected geometry on your components. If components are already in place, then it is easier to make use of the automatic conversion/update of assembly constraints to joints.


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In the following illustration, all components that are in place and have been constrained in the assembly environment will have their constraints automatically converted to the appropriate joints. This is achieved by selecting the Automatically Update Translated Joints button as shown.

Access Insert Joint

Panel Bar: Dynamic Simulation Toolbar: Dynamic Simulation

Access Convert Assembly Constraints

Panel Bar: Dynamic Simulation Toolbar: Dynamic Simulation

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Procedure: Updating Existing Assembly Constraints Automatically The following table lists the steps to automatically convert all existing and new assembly constraints to standard joints in Dynamic Simulation. 1.

On the Dynamic Simulation panel bar, click Dynamic Simulation Settings.

2.

In the Dynamic Simulation Settings dialog box, select the Automatically Update Translated Joints option.

3.

Click OK. All existing constraints are displayed in the Dynamic Simulation browser under the Standard Joints group.

4.

To create a new joint between two components in position, press SHIFT+C on your keyboard to start the Place Constraint tool. Use standard procedures to create the required constraints.

5.

As soon as you click OK, the newly created constraints are converted to joints as illustrated.


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NOTE: If you use the Automatically Update Translated Joints option, the Standard Joint Types and Convert Assembly Constraints tools are disabled. However you still can create standard joints by using assembly constraints within the Dynamic Simulation environment by pressing SHIFT+C on the keyboard.

Procedure: Converting Assembly Constraints The following table lists the steps to convert existing assembly constraints to standard joints by manually selecting constraints one by one in Dynamic Simulation. The benefit of this method over the automatic update method is that you can manipulate the type of joint created from existing constraints.

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1.

On the Dynamic Simulation panel bar, click Convert Assembly Constraints.

2.

In the graphics window, select the parts with constraints that you want to convert. The Convert Assembly Constraints dialog box is displayed showing the assembly constraints between the two components.

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3.

In the Convert Assembly Constraints dialog box, select the assembly constraints you want to convert (1 and 2). The dialog box updates to show the joint that will be created (3).

4.

Click OK. The new constraint is displayed in the Dynamic Simulation browser under the Standard Joints group.

Procedure: Inserting Standard Joints The following table lists the steps to insert a standard joint in Dynamic Simulation. 1.

On the Dynamic Simulation panel bar, click Insert Joint.

2.

In the Insert Joint dialog box, click the Display Joints Table button.


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3.

In the Joints Table dialog box, select the Standard Joints category (1). Select the joint you want to create (2). In the Joints Table dialog box, click OK.

4.

To place the first joint coordinate system, select geometry (1) to create the coordinate system. Select a circular edge (2) or point to set the origin for the first coordinate system.

5.

To place the second joint coordinate system, select geometry (1) to create the coordinate system. Select a circular edge (2) or point to set the origin for the second coordinate system. If necessary, click Switch Z or Switch X to adjust the direction of the axes to control the second component orientation when the joint is created.

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6.

In the Insert Joint dialog box, click OK. The origin of the second joint coordinate system is moved to the origin of the first joint coordinate system and axes of the second coordinate system align with the corresponding axes of the first coordinate system. Degree(s) of freedom are created between the two joint coordinates systems depending on the joint type. In this example, you have created a revolution joint, so a rotational degree of freedom is created around the Z axis.

Procedure: Inserting Rolling Joints The following table lists the steps to insert a rolling joint in Dynamic Simulation. 1.


2.

In the Insert Joint dialog box, click Display Joints Table.

3.

In the Joints Table dialog box, select the Rolling Joints category (1). Select the joint you want to create (2). In the Joints Table dialog box, click OK.


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4.

To place the first rolling joint cylinder face, select a part edge, visible sketch, or surface (1) to determine the radius. Select a circular edge (2) or point to set the center point for the first cylinder face. In case of rolling joints, you have access to two different modes: two constraints (rolling and tangency), and one constraint (rolling). The twoconstraints mode makes the two-cylinder face tangent and causes rolling without sliding. If the two cylinders are already tangent, use the oneconstraint mode.

5.

To place the second rolling joint cylinder face, select a part edge, visible sketch, or surface (1) to determine the radius. Select a circular edge (2) or point to set the origin for the second cylinder face.

6.

In the Insert Joint dialog box, click OK. The joint is created and it is displayed under the Rolling Joints node in the Dynamic Simulation browser.

Procedure: Inserting Sliding Joints The following table lists the steps to insert a sliding joint in Dynamic Simulation.

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1.


2.


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3.

In the Joints Table dialog box, select the Sliding Joints category (1). Select the joint you want to create (2). In the Joints Table dialog box, click OK.

4.

Make your selections for the first component. Selecting the plane on the first component, as shown, sets the plane on which the second component will slide.

5.

Make your selections for the second component. Select the cylindrical face that will slide on the plane selected in the first component.

6.

In the Insert Joint dialog box, click OK. The joint is created and it is displayed under the Sliding Joints node in the Dynamic Simulation browser.


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Procedure: Inserting 2D Contact Joints The following table lists the steps to insert a 2D contact joint in Dynamic Simulation.

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1.


2.


3.

In the Joints Table dialog box, select the 2D Contact Joints category (1). Select the joint you want to create (2). In the Joints Table dialog box, click OK.

4.

Select a part edge (1) or visible part sketch on the first component, and a part edge or visible part sketch (2) on the second component.

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5.

Whenever you create a 2D contact joint, it is important to check the Z normal direction of the curve component. In the Dynamic Simulation browser, under Contacts, right-click the 2D contact joint you just created and select Properties in the shortcut menu.

6.

The Z normal axis (1) on a disk curve should always point toward the air. The selected curve is a cam, which means that the material is on the inside and the air is on the outside. Click Invert Normal (2) to invert the normal direction of the first component. Click OK.

Procedure: Inserting Force Joints The following table lists the steps to insert a force joint in Dynamic Simulation. 1.


2.

In the Insert Joint dialog box, click Display Joints Table. The Joints Table dialog box is displayed.


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3.

In the Joints Table dialog box, select the Force joints category (1). Select the joint you want to create (2). In the Joints Table dialog box, click OK.

4.

Select part edges, part corner points, user work points, or circular edges to set the extremities of the force joint. In this example, select a circular edge (1) on the first component and a circular edge (2) on the second component. When you select a circular edge, the center of the arc is automatically selected.

5.

In the Insert Joint dialog box, click OK. The force joint is created. By default the joint is not active. Also, you need to specify the force for the joint as well as any other parameters to describe the joint.

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6.

In the Dynamic Simulation browser, under the Force Joints node, right-click the newly created force joint and select Properties in the shortcut menu.

7.

A properties dialog box is displayed with the joint name in the title bar. To activate the joint, select Active Joint. Enter the desired values in the edit boxes. Click OK.

8.

Notice that the joint properties are applied and the joint display updates in the graphics window.


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About Redundancy When you constrain components in Autodesk® Inventor™ assembly files, all measurements are at the nominal values. Thus you can apply constraints without consideration for manufacturing tolerances or clearances. In reality these tolerances or clearances are necessary for assembling components together and providing flexibility in the kinematic loop, as explained and illustrated by the following illustrations.

No manufacturing clearance exists between the pin and hole. This means it is sometimes difficult to assemble components and therefore clearance is necessary.

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In Dynamic Simulation, this lack of flexibility in joints creates redundancies, meaning multiple solutions exist in the joint due to the lack of degrees of freedom. Therefore, you need to increase degrees of freedom between joints to relate to the reality of clearances between parts, as shown in the following illustration.

Manufacturing clearance between the pin and hole. This clearance allows some angular movement between the pin and hole in addition to rotation. In the following illustration, a revolution joint is being changed to a point-line joint, adding degrees of freedom to eliminate redundancies in the joint.


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Definition of Redundancy Redundant joints are those that cause a mechanism to be overconstrained. Redundancy occurs in mechanisms when no provision exists for the clearances that occur in real-life mechanisms. In the assembly environment, components are made to nominal values that enable the assembly to be constrained using exact measurements. Due to machining imperfections and tolerances, real-life mechanisms are not entirely perfect, and thus these clearances provide flexibility to keep the mechanism from binding. NOTE: When you run a simulation for a redundant model, the Output Grapher is yellow as shown in the following illustration.

Yellow background indicates a redundant condition.

Example of Redundancy and Repair In a typical four bar linkage, if you start applying revolution joints from (1) to (4), you achieve the following joint configuration. Revolution joint Revolution joint Revolution joint Revolution joint

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As soon as you apply a revolution joint to Joint four (4), the mechanism is considered to be overconstrained. You are notified of this condition, and informed about using the Repair Redundancies command to fix the problem.

This warning indicates that manufacturing tolerances or clearances have not been taken into account in the assembly, and thus do not reflect a real-life situation. Joint four (4) needs to be resolved in order to remove redundancy from the assembly. In other words, this means that more degrees of freedom are required for Joint four (4). One possible solution is to use Repair Redundancies on the joint. This achieves the results shown in the illustration on the left. However, this model is not unique because it was dependent on the workflow of the designer in creating joints (1) through to (4). Another possible nonredundant model is shown in the illustration on the right.

Revolution joint

Revolution joint

Revolution joint

Spherical joint

Revolution joint

Revolution joint

Point-Line joint

Cylindrical joint

While the results may be slightly different, both these solutions are correct and provide correct simulation results regarding the dynamics of the model, including inertial loads. However, you should be aware that if you are interested in analyzing the reactions at the joints (or need to transfer loads for stress analysis), the results are not unique. For example, the point-line joint has no reaction in the Z direction, whereas the revolution joint has reaction in the Z direction. Different joints create different reaction forces/torques that you should be aware of. If you want to study the reaction forces and torques, then place the extra degree joints on the weakest joints or in the joints where you intend to put clearances in the real mechanism.


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Repairing Redundant Models When a mechanism contains redundancies, you can use a tool in the Dynamic Simulation environment to automatically repair them. In the following illustration, the Repair Redundancies dialog box shows the joint with the redundancies and suggested repair.

Repairing Redundancies Defined Repairing redundancies is accomplished by editing the joint that contains the redundancies and changing it to one that has additional degrees of freedom. For example, you change a revolution joint, which has only one degree of freedom, to a cylindrical joint, which has two degrees of freedom. The Dynamic Simulation environment also has a Repair Redundancies tool that monitors your joints and suggests repair options.

Process: Repairing Redundant Models The following steps give an overview for repairing redundant models.

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1.

Create the joints to define your mechanism.

2.

Upon receiving a warning that the mechanism is overconstrained, click OK.

3.

In the browser, right-click the joint with the redundancies and select the Repair Redundancies tool.

4.

Click OK in the Repair Redundancies dialog box to accept the edits suggested.

5.

The Repair Redundancies tool works only on manually created joints. If the joint was created by converting assembly constraints, you must edit the redundant joints manually.

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Exercise: Create Joints In this exercise, you create joints to add degrees of freedom to components in an assembly. First, you create two revolution joints by converting assembly constraints and by using the Insert Joint tool. Next, you create two 2D contact joints to control the relationship between the two revolving subassemblies. Finally, you impose motion on the joints to see the effect in the assembly.

2.

In the browser, expand frame:1 to see the two Mate constraints. In the following steps you convert these constraints to create degrees of freedom between the frame and the cross components.


3.

To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 2: Dynamic Simulation. Click Exercise: Create Joints.


4.

In the Dynamic Simulation browser, notice that all of the subassemblies are shown under the Grounded node because no joints have been applied.

5.

To automatically update the assembly constraints to a standard joint, on the Dynamic Simulation panel bar, click Dynamic Simulation Settings.


Update Constraints Automatically In this portion of the exercise, you convert existing assembly constraints into a revolution joint. 1.

Open GenevaDrive.iam.


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6.

7.

In the Dynamic Simulation Settings dialog box, click the Automatically Update Translated Joints check box. Click OK.

In this portion of the exercise, you manually create a revolution joint between two components using assembly constraint commands. 1.

With the Dynamic Simulation application still active, press SHIFT+C to activate the Place Constraint dialog box.

2.

Select the Insert Constraint option. For the first component, select the edge as shown.

In the Dynamic Simulation browser: ■

Notice the subassemblies have a prefix added to signify that they have had joints applied to them. Because the frame assembly is grounded in the assembly environment, it remains in the Grounded group in the Dynamic Simulation browser. A Mobile Groups node is added and the cross subassembly is placed in that group. A Standard Joints node is added and the newly created Revolution joint is placed there as a result of existing assembly mate constraints.

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NOTE: The number of joints created is not necessarily the same as the number of assembly constraints.

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Create a Standard Joint

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3.

On the keyboard press and hold the F4 key and rotate the view as shown, to expose the bottom of the rotor subassembly.

4.

For the second component, select the edge as shown. Click OK.

5.

On the keyboard, press F6 to return to the isometric view to see the results of the new rotation joint.

Create 2D Contact Joints In this portion of the exercise, you create two 2D contact joints between the cross and rotor subassemblies and set the initial position of the rotor subassembly. 1.

In the graphics window, right-click the cross subassembly. Click Open.


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2.

Notice the geometry in the cross.iam file. You use the work plane and the projected edges to create the 2D contact joint.

3.

On the keyboard, press CTRL+TAB to switch back to the GenevaDrive.iam file.

4.


5.


6.

In the Joints Table dialog box: ■

Click 2D Contact Joints (1). Click 2D Contact Joint (2). Click OK.

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7.

On the cross assembly, click the projected loop, as shown.

8.

On the rotor assembly, click the edge on the cylindrical face, as shown. Click OK. When the joint is applied, this edge cannot penetrate in the projected loop during simulation. This joint drives the cross subassembly.

The Z axis for the coordinate system of the projected loop must be inverted for the joint to function properly. In its present orientation, it functions as a hole and not a perimeter edge. 9.

To invert the Z axis, in the Dynamic Simulation browser, under Contacts, rightclick n°3 : 2D Contact (cross:1, rotor:1). Click Properties.

Next, you set up the initial state of the rotor relative to the cross. This is to make sure that the two components are not interfering at start of the simulation. 11.

In the Dynamic Simulation browser, under Standard Joints, right-click n°2 :Revolution (frame:1, rotor:1). Click Properties.

12.

In the n°2 :Revolution (frame:1, rotor:1) dialog box: ■ ■

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10.

Click the Dof 1 (R) tab (1). Confirm that Edit Initial Conditions is selected (2). For Position, enter 60 deg (3). Click OK.

In the n°3 : 2D Contact (cross:1, rotor:1) dialog box: ■ ■

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Click Invert Normal (1). Notice that the Z axis (2) is now pointing away from the cross assembly. Click OK.

13.

On the Dynamic Simulation panel bar, click Insert Joint. In the Insert Joint dialog box, select 2D Contact in the Joint Type list.


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14.

For the first loop, on the cross subassembly, select the radius edge as shown.

15.

For the second loop, on the rotor subassembly, select the radius edge as shown. Click OK.

You must invert the Z axes for the coordinate systems of the cross subassembly in order for the joint to function properly. In its present orientation it acts as a hole and not perimeter edge.

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16.

To invert the Z axes, in the Dynamic Simulation browser, for Contacts, right-click n°4 :2D Contact (cross:1, rotor:1). Click Properties.

17.

Notice the position of the Z axis (1) for the cross subassembly. In the n°4 :2D Contact (cross:1, rotor:1) dialog box, click the left Invert Normal button (2) for the cross subassembly.

18.

Confirm that the Z axis is inverted, as shown. Click OK.

3.

In the Dynamic Simulation browser, notice the icon for the n°2 :Revolution (frame:1, rotor:1) joint. A # symbol was added to signify that motion was applied to the joint.

4.

Next you apply gravity to the assembly. In the browser, under External Loads, doubleclick Gravity. In the Gravity dialog box:

Run the Simulation Before you can run the simulation, you must impose a motion on the rotor and apply gravity to the assembly. 1.

In the Dynamic Simulation browser, under Standard Joints, right-click n°2 :Revolution (frame:1, rotor:1). Click Properties.

2.

In the n°2 :Revolution (frame:1, rotor:1) dialog box: ■ ■ ■ ■ ■

■ ■

Click the Dof 1 (R) tab (1). Click Edit Imposed Motion (2). Select Enable Imposed Motion (3). Select Velocity (4). Click the arrow and select Constant Value (5). Enter 360 deg/s in the edit box (6). Click OK.

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Clear the Suppress option. Select Components. For Coordinates, for g[X], enter 0 m/s^2. For Coordinates, for g[Y], enter -9.81 m/s^2. For Coordinates, for g[Z], enter 0 m/s^2. Click OK.


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5.

To run the simulation, on the Simulation Panel: ■

Under Final Time, enter 2 s (1). In Time Mode, Images =, enter 60 (2). Click Run or Replay Simulation (3).

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6.

View the simulation. The rotor makes two revolutions and drives the cross subassembly when the pin engages the slots.

7.

Close all files. Do not save changes.

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Exercise: Create a Nonredundant Model In this exercise, you create joints in a windshield wiper assembly. Some of the joints that you create contain redundancies. Although you can simulate a redundant model in the Dynamic Simulation environment, it is not advisable to do so. You repair the redundancies and test the joints to confirm the wiper subassembly movement.


Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 2: Dynamic Simulation. Click Exercise: Create a Nonredundant Model.

Create Revolution Joints for the Wiper Assemblies In this portion of the exercise, you create revolution joints between the wiper subassemblies and the bearings subassembly. 1.

Open WiperAssemblyNRM.iam.

2.


3.

Use zoom and pan to adjust the view as shown.

The Brush_asm_left and the Complete_wiper_left_asm subassemblies must move as a unit. In the next step, you weld the two subassemblies together.


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4.

5.

On the keyboard, press and hold CTRL. In the Dynamic Simulation browser, click the Brush_asm_left and Complete_wiper_left_asm subassemblies. Right-click Brush_asm_left:1. Click Weld Parts.

In the Dynamic Simulation browser, notice that n°1 :Welded group1 is added beneath the Grounded node.

With the two subassemblies welded, you now create the joints to add degrees of freedom to the wiper assembly mechanism.

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6.

On the keyboard, press ALT+] to turn on the visibility of the user work planes.

7.

On the Dynamic Simulation panel bar, click Insert Joint. The Insert Joint dialog box is displayed and the Revolution Joint is active.

8.

In the graphics window, click the tubular component (1) to set the rotation axis, and the work plane (2) to set the origin for the coordinate system, as shown.

9.

On the keyboard, press and hold F4 and rotate views as shown.

10.

In the Insert Joint dialog box, under Component 2, click the button, as shown.

11.

Click the circular edge twice, as shown, to set the rotation axis and the origin for the coordinate system on the welded assembly.

12.

Click OK.

13.

On the keyboard, press F6 to return to the isometric view.


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14.

Zoom in to the view as shown.

The Complete_wiper_right_asm and the Bearings subassemblies currently are in the proper orientation. Next, you create a revolution joint by converting assembly constraints. 15.

On the Dynamic Simulation panel bar, click Convert Assembly Constraints. The Convert Assembly Constraints dialog box is displayed.

16.

In the graphics window, click as shown to select Part 1.

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17.

In the graphics window, click as shown to select the subassembly.

18.

Select the constraint as shown. A revolution joint is displayed.

19.

Click OK to create a revolution joint. On the keyboard, press HOME to zoom all.

2.

In the graphics window, place the cursor (1) over the Complete_wiper_left_asm as shown. Press and hold the left mouse button and drag in the direction shown (2).

3.

Position the wiper blade so that it is close to parallel, as shown.

4.

Using the Zoom and Rotate tools, position the view as shown to see the back side of the repositioned wiper blade.

Repair Redundant Joints In this portion of the exercise, you create revolution joints between the Inter_Crank and the wiper subassemblies. Because using only revolution joints to build the four-bar linkage leads to redundancies, you use the Repair Redundancies tool to analyze and repair the problem. 1.

On the keyboard, press ALT+] to turn off the user work planes. Zoom in to the wiper subassemblies, as shown.

Next, you align the wiper assemblies so that they are nearly parallel.

Before you create the revolution joint, you must reposition the Inter_Crank to view the hole for the pivot.


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5.

In the graphics window, place the cursor on the part. Press and hold the left mouse button and drag to a new location, as shown.

8.

Click the circular edge (1) twice to set the coordinate system for the first component and its origin. Notice the orientation of the X axis (2) and the Z axis (3).

9.


Now you create a revolution joint between the Inter_Crank and the Complete_wiper_left_asm. 6. 7.

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On the Dynamic Simulation panel bar, click Insert Joint. In the Insert Joint dialog box, the Revolution joint is active.

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10.

Click the circular edge (1) twice to set the coordinate system for the first component and the origin for the coordinate system. Notice the orientation of the X axis (2) and the Z axis (3).

The Z axes are pointing in the same direction, so the components maintain their current orientation. The X axes are pointing in nearly opposite directions, which will cause the Inter_Crank part to rotate so that its X axis matches the direction of the X axis on the Complete_wiper_left_asm subassembly. Next, you reverse the direction of the Complete_wiper_left_asm X axis to minimize the rotation. 11.

In the Insert Joint dialog box, under Component 2, click X Axis (1). The X axis (2) for the Complete_wiper_left_asm subassembly reverses direction.

12.

Click OK. The joint is created.

Now you create a revolution joint between the other end of the Inter_Crank component and the Complete_wiper_right_asm subassembly. 13.

On the Dynamic Simulation panel bar, click Insert Joint. The Insert Joint dialog box is displayed with the Revolution Joint active.

14.

Click the circular edge (1) twice, to set the coordinate system for the first component and the origin for the coordinate system. Notice the direction of the X axis (2) and the Z axis (3) for the coordinate system.


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15.

16.

17.

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With the Z axes and the X axes for the two components pointing in opposite directions, one of the components will try to flip to match the Z axis of the other component and rotate to match the X axis, causing the joint to fail. Next, you reverse the direction of the X and Z axes of Component 2 to create a successful joint. 18.

In the Insert Joint dialog box, under Component 2, click Z Axis (1), and the Z axis (2) reverses direction in the graphics window. Under Component 2, click X Axis (3), and the X axis reverses direction in the graphics window (4).

19.

Click OK. A warning box is displayed stating that the mechanism is overconstrained by three degrees. Click OK.

20.

In the Dynamic Simulation browser, in the Standard Joints group, notice that the n°4 :Revolution (Inter_Crank:1, Complete_wiper_right_asm:1) joint is shown with an icon indicating that it has redundancies.

In the graphics window, pan over to the end of the Complete_wiper_right_asm, as shown.

Click the circular edge (1) twice to set the coordinate system for the second component and the origin for the coordinate system. Notice the direction of the X axis (2) and the Z axis (3) for the coordinate system.

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24.

In the dialog box, notice that the problem areas with the joint are highlighted with an orange background. For your joint: ■

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Tz denotes a Translational redundancy preventing movement along the Z axis of the joint. Rx denotes a rotational redundancy preventing rotation around the X axis of the joint. Ry denotes a rotational redundancy preventing rotation around the Y axis of the joint. In the Final Joints column, next to the redundant constraints, is a joint that can repair the redundancies.

Next, you repair the redundancies in the revolution joint. 21.

In the Dynamic Simulation browser, click the n°4 :Revolution (Inter_Crank:1, Complete_wiper_right_asm:1) node.

22.

On the Dynamic Simulation panel bar, click Repair Redundancies.

23.

Notice that the Repair Redundancies dialog box is displayed. In the graphics window, the coordinate system glyphs for the joint are displayed.

25.

Click OK to apply the Point-Line joint solution. In the Dynamic Simulation browser, notice that the joint is updated and the redundancy icon is gone.


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26.

At the keyboard, press F6 to return to the isometric view.

In the next step you test the joints to verify that they work correctly. 27.

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In the graphics window, place the cursor (1) over the Complete_wiper_left_asm as shown. Press and hold the left mouse button and drag in the direction shown (2).

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28.

Notice that the wiper subassemblies are linked together through the joints you have created and move together as shown.

29.


Lesson: Environmental Constraints Overview This lesson describes environmental constraints and how you apply them in Dynamic Simulation. To run a simulation, you must define the virtual environment that simulates the reality in which the mechanism behaves or functions. The initial joints that have been automatically transferred from existing Inventor assembly constraints, or manually created within Dynamic Simulation, define the degrees of freedom. You create environmental constraints to define the initial starting conditions of a joint, simulate realistic friction for joints, and manipulate imposed motion of the joints. Examples of external environmental constraints that can be applied to the design or assembly include forces, torques, friction, and gravity. These environmental constraints define what joints and assemblies do during the simulation. Environmental constraints provide Dynamic Simulation with the information necessary to calculate the simulation. In the following illustration, a resistant force has been applied to the windshield wiper blades. During the simulation the force is displayed as arrows pointing in the direction of the resistance, as shown.

Objectives After completing this lesson, you will be able to: ■ ■ ■ ■

Define initial positions of joints. Define joint torques. Define imposed motions and apply them to joints. Define external forces and apply them to joints.

Lesson: Environmental Constraints

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Explain friction and gravity and how to apply their effects on your mechanism and assembly designs. Identify the Input Grapher, its tools, and its options for fine-tuning your environmental constraints. Use the Input Grapher to refine your imposed motions and joint torques, as well as the way they are applied during your simulation. Impose motion and resistive force in a mechanism, and use the Input Grapher to control the effect of resistive force during the simulation.

Setting Initial Positions of Joints After you constrain a mechanism using joints, it is sometimes necessary to set the initial position of a joint. Depending on the type of joint, the position could either be a translational or rotational position. For example, for a revolution joint, you should generally be able to set the initial position by defining the angle in degrees. In the following illustration, an initial position of a revolution joint is being set to -20 degrees.

Description of Initial Position of Joints The initial position of a joint can be rotational, translational, or both depending on the joint. For more complicated joints, for example a point line joint, one translational and three rotational positions need to be defined to set the initial position of the joint. You can define an initial joint position with a constant value only.

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Process: Applying Initial Positions The following steps describe the process for defining the initial position of a joint in a dynamic simulation. 1.

In the Dynamic Simulation environment, apply the joints to define the mechanism.

2.

Edit the properties of the joint to which you want to impose the motion.

3.

Click the DOF tab that corresponds to the degree of freedom that you want to define for the initial position.

4.

On the DOF tab, use the edit box to enter a constant value.

5.

Click OK to apply the initial position.

Applying Joint Torques After you constrain a mechanism using joints, it is sometimes useful to apply damping or friction to a joint to create a resistance that simulates what occurs in real joints. In the following illustration, damping is being applied to a joint.

Description of Joint Torques A joint torque can be defined by applying damping or elastic stiffness, and/or by specifying a value for a coefficient of friction. You can define joint torques with a constant value throughout the time range of the simulation, or you can use the Input Grapher to apply different values that may occur at designated times during the simulation.


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Process: Applying Joint Torques The following steps describe the process for adding imposed motion to a joint in a dynamic simulation. 1.


2.


3.

Click the DOF tab that corresponds to the degree of freedom you are adding the motion to.

4.

On the DOF tab, enable the joint torque and use the edit box to enter a constant value, or use the Input Grapher to define different values along the simulation timeline.

5.

Click OK to apply the imposed motion.

Applying Imposed Motion After you constrain a mechanism using joints, it is necessary to define the movement of the joints. For a joint with a rotational or translational degree of freedom you impose a velocity, acceleration, or position motion. Combined with the time of the simulation, which is set in the Dynamic Simulation panel bar, you control the total amount of movement in the joint. In the following illustration, an imposed motion is being applied to a joint, defining its velocity.

Description of Imposed Motion Imposed motion is the position, velocity, or acceleration applied to a joint that has a rotational or translational degree of freedom. You can define imposed motion with a constant value throughout the time range of the simulation, or you can use the Input Grapher to apply different values that may occur at designated times during the simulation.

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Process: Applying Imposed Motion The following steps describe the process for adding imposed motion to a joint in a dynamic simulation. 1.


2.


3.

Click the DOF tab that corresponds to the degree of freedom you are adding the motion to.

4.

On the DOF tab, enable the imposed motion and use the edit box to enter a constant value, or use the Input Grapher to define different values along the simulation timeline.

5.

Click OK to apply the imposed motion.

Applying External Forces When a mechanism is going through its motions, various forces affect the movement, such as gravity, friction, or drag. Sometimes these forces are resistive, or opposed to the motion, and sometimes external forces are driving forces and help the motion. You define these forces in the Dynamic Simulation environment to further ensure that the simulation takes into account all factors that control movement in the simulation. In the following illustration, an external force is shown being applied to point on a windshield wiper blade with an arrow defining the direction of the force.


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Description of Applying External Forces In the Dynamic Simulation environment, external forces are forces that you apply to account for gravity, friction, drag and any other type of force that resists movement or aids movement. External forces do not have to be exact, but can reflect the maximum amount of resistance that you want the mechanism to overcome.

Process of Applying External Forces The following steps describe the process for adding external forces to a joint in a dynamic simulation. 1.

In the Dynamic Simulation environment, use the Force or Torque tool to place an external force.

2.

Define the location for the external force.

3.

Define the direction of the external force.

4.

Designate whether the direction of the external force is fixed or associative.

5.

Designate whether the force will display during the simulation, and the size and color of the symbol.

6.

Apply the external force to the joint.

Applying Friction and Gravity Friction and gravity are forces that affect a mechanism or joint evenly. The effect of gravity occurs in a single direction relative to the entire mechanism. Friction occurs on all contact surfaces of a joint, defining the resistance of the two components that comprise the joints as they rub against each other during motion.

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In the following illustration, gravity is being applied to the mechanism, with the arrow defining the direction of gravity and the dialog box defining the magnitude.

Description of Applying Friction Applying friction defines the resistant force in a joint caused by component surfaces rubbing against each other. Friction is defined by entering a coefficient value equal to the percentage of extra force required to overcome this condition.

Description of Applying Gravity Applying gravity defines the effect of gravity on the mechanism. Gravity can resist or aid a mechanism depending on its relationship to the mechanism. If a mechanism is lifting against gravity, more driving force is required to overcome the gravitational force. If a lifter lowers in the direction of gravity, gravity works as a driving force helping the mechanism.

Process: Applying Friction The following steps provide an overview of how to apply friction. 1.

In the Dynamic Simulation browser, right-click the joint you want to add the friction to and click Properties in the shortcut menu.

2.

In the Properties dialog box, click the DOF you want to add the coefficient of friction to.

3.

Depending on whether the DOF is rotational or translational, click Edit Joint Torque for rotational and Edit Joint Force for translational.


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4.

Select the check box to enable the joint force.

5.

For a translational DOF tab, edit the coefficient of friction. For a rotational DOF tab, edit the coefficient of friction and the radius distance from the joint where the friction will be calculated.

6.

Click OK to apply the friction values.

Process: Applying Gravity The following steps provide an overview of how to apply gravity. 1.

In the Dynamic Simulation browser, right-click Gravity and select Define Gravity on the shortcut menu.

2.

Activate gravity.

3.

Select whether the gravity will be defined relative to an entity or to global coordinates.

4.

If defined by an entity, select a component face and the direction relative to the face. Enter the value for gravity and click OK.

5.

If defined by an entity, select a component face and the direction relative to the force. Enter the value and click OK.

6.

If defined by coordinates, enter the gravity values for the X, Y, and Z axes. Click OK.

About the Input Grapher The Input Grapher is used to define the laws of dynamic actions (movement law, joint forces, and external forces) using a graphical interface. This interface proposes simple laws, like Constant and Sine, and other more developed options, like Ramps and Spline. You can also combine laws in time sectors. In the following illustration, the Input Grapher is shown with the ramp up from 0 deg/s velocity up to full speed, and the ramp back down to 0 deg/s.

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Definition of the Input Grapher The Input Grapher is a graphical interface that you use to define the imposed motions when a constant value is not applied to the motion. The Input Grapher provides tools to separate the simulation time range into sectors, each of which can have its own laws controlling the motion in that sector. In the following illustration, the ramp up sector of the velocity is shown. When you activate a sector, it is shaded as shown.

Example of the Input Grapher In the course of designing your windshield wiper mechanism, you need to calculate the driving torque needed to move the wipers. Because the wipers do not immediately go from 0 deg/s velocity at start to the 180 deg/s velocity required, you use the Input Grapher to define the time periods for ramp up, constant velocity, and ramp down back to 0 deg/s at the end of the simulation. Also, you need to define the change in direction of the external force on the wiper blades as the wipers reverse direction. The Input Grapher provides the interface to set the rules for the external force reversal. In the following illustration, the transition of the external force is shown reversing with the cubic ramp law controlling the transition of the force.


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Using the Input Grapher The Input Grapher can be accessed from any external force or imposed motion to fine-tune the way that the motion or force is applied. You can define the values as a function of any of the mechanism’s variables, apply user parameters, and create equations. In the illustration, the function is shown being changed to velocity as the reference.

Description of the Using the Input Grapher In the following illustration, the Input Grapher is displayed with its sections labeled.

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The graph area displays the results of the values applied to the designated motion or force. In this area, you define the parameters for the highlighted sector in the graph. Starting Point defines the values at the beginning of the chosen time sector, and Ending Point defines the values at the end of the chosen time sector. Property of the Select Sector defines the law applied to the highlighted sector in the graph. The reference button opens the mechanism’s variables browser where you can select a different reference for the context of defining the motion or force.

Process: Using the Input Grapher The following steps provide an overview of how to use the Input Grapher. 1.

Access the Input Grapher by editing the properties of the selected joint.

2.

Select the DOF tab for the joint degree of freedom you want to edit.

3.

Select the joint force or Imposed Motion button depending on the value you want to edit.

4.

Confirm that the imposed force or motion is active, then select Position.

5.

From the Force edit box, access the Input Grapher.

6.

In the Input Grapher, select the reference for the values you will define.

7.

Add time sectors as required to define changes in the values.

8.

Define the start and end values for each time sector and the law to apply to each sector.

9.

Click OK to apply the changes and exit the grapher.


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Exercise: Define Environmental Constraints In this exercise you create joints in a wiper assembly to drive the wiper arms. You impose motion on the drive arm and add resistive force to the wiper blades to simulate the friction of the blade on the windshield. Finally you use the Input Grapher to define the resistive force so that it is always opposed to the wiper motion.

3.

Use the Rotate, Pan, and Zoom tools to orient your view to match the following illustration.

First, you create a joint to control the rotation of the Motor_Crank_Asm (1). This subassembly is attached to the wiper motor and drives the Crank_motor2 component (2), which drives the wiper subassemblies (3). 4. The completed exercise

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Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 2: Dynamic Simulation. Click Exercise: Define Environmental Constraints.

Create the Drive Arm Joints In this portion of the exercise, you define the joints that connect the drive arm to the cranks that move the wiper subassemblies. 1.

Open WiperAssemblyDEC.iam. NOTE: For this exercise you can continue to work on the earlier exercise WiperAssemblyNRM.iam if it is complete and still opened.

2.

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To insert a joint:

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5.

On the Dynamic Simulation panel bar, click Insert Joint. In the Insert Joint dialog box, expand the Joint list and select Cylindrical.

To set the Z axis (axis of rotation) of component 1, click in the hole of the Motor_Crank_Asm as shown.

6.

7.

8.

In the Insert Joint dialog box, under Component 2, click the button for the Z axis, as shown.

9.


10.

In the Insert Joint dialog box, expand the joint list and select Revolution.

11.

To set the Z axis (axis of rotation) of component 1, click the circular edge twice. The first click sets the Z axis for the first coordinate system, and the second click sets the origin for the coordinate system.

12.

In the Insert Joint dialog box, under Component 2, click the button for the Z axis as shown.

To set the Z axis (axis of rotation) of component 2, select the work axis, as shown.

Click OK to apply the joint. The cylindrical joint enables the Motor_Crank_Asm to rotate freely around the work axis, as well as to move along the work axis.

Now, you create the joints to connect the Crank_motor2 to the Motor_Crank_Asm and the Complete_wiper_left_asm, completing the mechanism.


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13.

14.

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To set the Z axis (axis of rotation) of component 2, click the circular edge twice. The first click sets the Z axis for the second coordinate system, and the second click sets the origin for the coordinate system.

15.

Click Apply to apply the joint. The Crank_motor2 now moves to the correct position, as shown, to make the joint. The dialog box remains open.

16.

In the Insert Joint dialog box, expand the Joint list. Select Spherical.

17.

To set the spherical point of component 1, click the circular edge (1) twice. The first click selects the center point of the circular edge as the point for component 1, and the second click sets the Z axis for the coordinate system. Notice the direction of the Z axis (2) for the component 1 coordinate system.

18.

In the Insert Joint dialog box, under Component 2, click the button for the Point, as shown.

In the Insert Joint dialog box, under Component 2, click Switch X, as shown, to reverse the direction of the coordinate system X axis. This enables the minimal rotation of the link when the joint is created.

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20.

To set the spherical point of component 2, click the circular edge (1) twice. The first click selects the center point of the circular edge as the point for component 2, and the second click sets the Z axis for the coordinate system. Notice that the Z axis for the component 2 coordinate system is pointing in the opposite direction of the Z axis (2) of the component 1 coordinate system.

21.

Click OK to create the joint.

22.

On the keyboard, press F6 to return to the isometric view.

In the Insert Joint dialog box, under Component 2, click Switch Z to reverse the direction of the coordinate system Z axis. This causes the Z axis of component 2 to match the Z axis of component 1.


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Impose Motion and Add External Forces

3.

In this portion of the exercise, you impose motion on the Motor_Crank_Asm to simulate the wiper motor driving the wipers. Then you add a resistant force to the wipers to simulate the wiper blade rubbing against the windshield as it turns. 1.

2.

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Zoom in on the view to match the following illustration.

Next, you set the starting conditions for your assembly.

In the n°5 :Cylindrical (Motor_Crank_Asm:1, Bearings:1) dialog box:

4.

In the Dynamic Simulation browser, rightclick n°5 :Cylindrical (Motor_Crank_Asm:1, Bearings:1). Click Properties.

Click the Dof 1 (R) tab. (1) Confirm that Edit Initial Conditions is selected. (2) For Position, enter -15 deg. (3) Click OK.

Notice that the -15 deg is placed between the X axis (1) of component 1 in the cylindrical joint and the X axis (2) of component 2.

Now, you impose motion on the cylindrical joint to see the mechanism in action. 5.

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6.

In the n°5 :Cylindrical (Motor_Crank_Asm:1, Bearings:1) dialog box: ■ ■ ■ ■ ■

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8.

Click the Dof 1 (R) tab. (1) Click Edit Imposed Motion. (2) Select Enable Imposed Motion. (3) Under Driving, select Velocity. (4) Click the arrow and select Constant Value in the shortcut menu. (5) In the edit window, enter 180 deg/s. (6) Click OK.

In the Simulation Panel, click the Construction Mode button. You can make edits only in the construction mode.

Next, you add a resistive force to the left wiper arm to simulate friction between the wiper blade and the windshield. In the case of the wiper blade, the resistive force must be calculated in each direction due to the back and forth motion of the wipers. 9.

Zoom in on the view to match the following illustration.

10.

On the Dynamic Simulation panel bar, click Force.

Next you run the simulation using the velocity value that you just set. Because the velocity is set to 180 deg/s, it will take two seconds to make a full revolution. 7.

In the Simulation Panel: ■

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In the Final Time window, enter 4s (1) and press TAB. This simulates two full revolutions. In Time Mode, Images =, the value should change to 400. (2) This determines the number of total images generated during the simulation. Click Run (3) or Replay Simulation to view.

The Motor_Crank_Asm makes two complete revolutions, driving the wiper arms back and forth for two cycles.


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11.

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For the location of the force, click the work point on the wiper blade, as shown.

Notice that the glyph shown in the following illustration is placed at the location of the force.

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13.

For the force direction, click the flat surface of the wiper arm, as shown.

14.

Notice that the glyph shown in the following illustration displays the direction of the force.

15.

In the Force dialog box: ■ ■

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17.

For Magnitude, enter 5N. (1) Click Associative Load Direction. (2) This option causes the force to maintain its relationship to the location point. Select Display. (3) This displays the force direction when you run a simulation. Click OK.

In the Simulation Panel, click Run or Replay Simulation. Notice that the force arrow is displayed on the wiper blade during the simulation, as shown.

The resistive force maintains the same direction on the wiper throughout the simulation. The resistive force of the wiper should always be opposite the motion. You use the Input Grapher to change the direction of the force when the wiper changes direction. 16.

In the Dynamic Simulation browser, notice that the Force is added beneath the External Loads node.

18.

In the Simulation Panel, click Activate Construction Mode.

19.

In the Dynamic Simulation browser, rightclick Force1 (Force on Brush:1). Click Edit Force.


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20.

In the Force dialog box, click the arrow in the Magnitude edit window. Click Input Grapher.

23.

In the Magnitude dialog box: ■ ■ ■ ■

21.

For X1, enter -1 deg/s. For Y1, enter 5 N. For X2, enter 1 deg/s. For Y2, enter -5 N.

In the Magnitude dialog box, click Select Reference.

Between -1 deg/s velocity and 1 deg/s velocity, the resistant force reverses itself, avoiding a discontinuity or immediate switch in the resistive force. 24.

22.

In the Select Reference dialog box: ■

Expand n°1 :Revolution (Bearings:1, Welded group1). Expand Velocities. Select v[1.1].

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In the Magnitude dialog box, notice that the graph updates to reflect the values in the Starting Point and the Ending Point. The ramp area is shaded in the graph.

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To create a smooth transition in the resistive force, you can change the ramp from a linear ramp to a cubic ramp.

25.

In the Magnitude dialog box: ■ ■ ■

26.

28.

Expand the list of available laws. (1) Select Cubic Ramp. (2) Click Replace the Current Law. (3)

In the Magnitude dialog box, notice that the graph updates to reflect the cubic ramp. Click OK.

Because both wiper blades rub against the windshield, you need to repeat steps 10 through 27 for the right wiper. 29.

27.

In the Simulation Panel, click Run or Replay Simulation to view the simulation. This time you see the resistive force arrow direction reverse when the wiper reverses, as shown.


In the Force dialog box, click OK.


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Lesson: Running Simulations and Analyzing Results Overview This lesson describes the process of running a simulation and analyzing or interpreting the results. After all joints, external forces, and imposed motions are defined, you use the Simulation Panel to run the simulation. While running the simulation, you can use the Output Grapher to view a graphical representation of the results. The ultimate goal of a simulation is to provide the feedback that you need to adjust and refine your design to meet specific design requirements. To ensure that your simulation is accurate and provides you with the appropriate technical feedback, you need to know how to use the Simulation Panel to set up and run the simulation, and how to use the Output Grapher to interpret the results. In the following illustration, the Output Grapher is used to analyze the results of a simulation.

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Describe how to set up and run a simulation using the Simulation Panel. Describe the Output Grapher. Use the Output Grapher to view and export graphical and numeric results of your simulation. Review and analyze your simulation results to determine whether your mechanism will perform as designed. Run a simulation to calculate the driving torque of a component in an assembly.

Running Simulations After all joints, external forces, and imposed motions are defined, you run the simulation to view the results. You use the Simulation Panel to run the simulation, stop it at any point, or play it in a continuous loop. While running the simulation, you can open the Output Grapher to view a graphical representation of a selected variable in a graphical or numeric format. Results can be exported to FEA for stress analysis of individual components. In the following illustration, a simulation is running with the Output Grapher open showing the synchronization with the current time step in the Simulation Panel, and the assembly in the graphics window.

Lesson: Running Simulations and Analyzing Results

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Description of Running Simulations Running a simulation in Dynamic Simulation is the act of calculating the values of the joints in a mechanism. When you run a simulation, your mechanism moves according to the joints, imposed motions and torques, and external forces you have applied to it.

Simulation Panel You use the Simulation Panel to set up and run the dynamic simulation of the assembly. The panel has several buttons that enable you to control the simulation time and accuracy. In addition it provides visual feedback on the progress of the simulation of the assembly. It is the most important part of the simulation process because it controls the accuracy of the simulation.

Simulation construction After playing the simulation, click to enter construction mode to mode continue editing the simulation.

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Player controls

Click the various buttons to control playback of the simulation.

Final time

Enter the final simulation time.

Images

Enter the number of images to create for the simulation. More images result in a more accurate simulation, but also take longer to solve the simulation.

Filter

Normally set to 1. If the value is changed to 10, then the simulation ignores images between 1 to 10.

Simulation time

Read-only value depicting the time step in the simulation.

Percentage of realized simulation

Read-only value that displays the percentage of simulation completed.

Real time

Read-only field that displays the actual time that has elapsed during the simulation.


Player Controls

Rewind to the beginning of simulation

Returns the simulation back to its starting condition. This button is available only after the simulation has started or when the slider is moved from 0%.

Stop current simulation

Stops the simulation.

Run or replay simulation

Runs the simulation forward from the current step. If the simulation is at the end point, or the slider set to 100%, this button has no effect.

Deactivate screen refresh at each time step

Prevents the screen refresh at each time step. This speeds up the simulation and depending on your computer may or may not be noticeable.

Forward to end of simulation

Advances to the end of simulation. This button is available only when the simulation has not started or when the slider is set to less than 100%.

Play current simulation in continuous loop

Plays the simulation all the way through, returns to the beginning and starts over again. The simulation continues to repeat until you stop it.

Process: Running a Simulation The following steps provide an overview of the process of running a simulation. 1.

In the Dynamic Simulation environment, define the joints, external torques and forces, and imposed motions to define the mechanism.

2.

Use the Simulation Panel to run the simulation.

3.

If required, open the Output Grapher to see a graphical representation of the selected variables in the mechanism.


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About the Output Grapher When your simulation is prepared and running, you need a way to use the data that is generated. The Output Grapher enables you to view the results of any of the variables in the simulation using a graphical interface. Data from the Output Grapher can be output to Microsoft® Excel, or to an IAA file that can be imported back into the Output Grapher to compare with a set of values from a new simulation with different forces or motions. In the following illustration, a mechanism is shown with the Output Grapher open. The time step is set to the maximum force in the simulation.

Definition of the Output Grapher The Output Grapher is a tool in Dynamic Simulation that generates graphs and numerical values for all the input and output variables of a simulation, both during and after the simulation completes. You can have more than one Output Grapher open simultaneously. The Output Grapher is synchronized to the mechanism. You can access any time step in the simulation, and the mechanism displays the state of joints at that time step.

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In the following illustration, the synchronization between the Output Grapher and mechanism is shown. The time step in the graph (1) is highlighted in the values area, (2) while the position of the wipers (3) is shown at that time step.

Example of the Output Grapher In your cam and follower assembly, you want to compare the driving force on the cam when two different contact values are applied between the follower and cam. You run the simulation with the first value applied. In the Output Grapher, you display the graph of the cam driving force and save the results. You edit the contact properties between the cam and follower and rerun the simulation. You display the graph of the second simulation and then import the saved IAA file from the first simulation. You then display the driving force value of the first simulation so that you can compare the values.


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In the following illustration, the graph shows the driving force (1) for the second cam force and the original cam force (2).

Using the Output Grapher The Output Grapher provides many options and controls to display and export the results of your simulation. Simulation results can be exported to Microsoft® Excel, to FEA for stress analysis, or imported into a different simulation to perform comparison studies. The Output Grapher can be open during a simulation to generate the graph as the simulation runs, or you can open it after the simulation to see the final results.

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In the following illustration, the results of a simulation have been exported from the Output Grapher to Microsoft® Excel, creating a page for the graphical results and a page for the numeric results.

Description of the Output Grapher In the following illustration, the Output Grapher is displayed with its sections labeled.


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Output Grapher Tree

Here you have access to all the variables from the simulation. Variables selected here have their values displayed in the graph and the time column.

Graphic Area

The graphs of the selected variables are displayed here. Doubleclick in this area to set a time step in the graph that is synchronized to the Time column, the display of the mechanism in the graphics window, and the slider in the Simulation Panel.

Time Column

Contains a column for the time steps. The number of steps matches the time mode images in the Simulation Panel. Each of the variables selected in the tree has a column.

Load Transfer Column

Select single or multiple time steps to transfer loads to FEA.

Process: Using the Output Grapher The following steps provide an overview of the process for using the Output Grapher.

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1.

In Dynamic Simulation, create your joints and set your environmental constraints.

2.

Run the simulation and open the Output Grapher during the simulation or after the simulation has finished.

3.

In the selection tree, select the variables that you want displayed in the grapher.

4.

Double-click in the graph to set the current time. Step back and forth in the grapher using the right and left arrow keys on your keyboard.

5.

To find the maximum value on a curve, right click anywhere on the chosen tabular column and select Search Max.

6.

To find the minimum value on a curve, right click anywhere on the chosen tabular column and select Search Min.

7.

To save the graph curve, with the Grapher open save the assembly file. The results of the simulation are saved in a file with the same name as the assembly file and an extension of .iaa.

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Reviewing and Analyzing Simulation Results After you have run the simulation, you must review and analyze the results. Dynamic Simulation uses the joints you define, the external forces, and the imposed forces and torques to calculate the various drive forces and torques, accelerations, and velocities in your mechanism. The Output Grapher acts as the repository and organizer of the simulation results. In the following illustration, the driving force of a revolution joint and the moment of the prismatic joint are shown in the Output Grapher to compare their relationship.

Reviewing and Analyzing Simulation Results Reviewing and analyzing simulation results using the Output Grapher gives you graphical and numeric feedback for a specific joint. You can view the driving force on revolutions and motions, and positions of components during the simulation, as well as velocities, accelerations, and moment forces. Some results, specifically moments and forces, can be exported to FEA to perform stress analysis calculations on parts.


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Process: Reviewing and Analyzing Simulation Results The following steps describe how to review and analyze results in Dynamic Simulation.

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1.

In the Dynamic Simulation environment, define your mechanism using Automatic Update of Constraint joints, or converted assembly constraints and/or inserted joints. Define the start position and the imposed motion, imposed forces and torques, and external forces.

2.

In the Simulation Panel, enter the settings for the simulation and then run the simulation.

3.

Open the Output Grapher.

4.

In the Output Grapher, selection tree, expand the joint that you are analyzing.

5.

Expand the folder for the type of results you want to review.

6.

Click the node that you want the grapher to display.

7.

Find the time step, and minimum or maximum value in the graph, or export the file to Microsoft® Excel for later use. Then save the results for import into another simulation, and save the file with the Output Grapher open.

8.

Import results from another simulation for comparison.

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Exercise: Calculate the Driving Torque of the Wiper Assembly In this exercise, you use Dynamic Simulation on the wiper assembly to calculate the driving torque required to move the wipers so that you can size the wiper motor. You then use the Output Grapher to plot the graph and review the results.

1.

Open WiperAssemblySDP.iam.

2.

Click Applications menu > Dynamic Simulation. First you impose a velocity on the Motor_Crank_Asm. The wiper assembly is fully constrained and a force of 5 N has been added to each wiper blade assembly to simulate the drag of the blade on the windshield.


Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 2: Dynamic Simulation. Click Exercise: Calculate the Driving Torque of the Wiper Assembly.

3.



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4.

In the n°5 :Cylindrical (Motor_Crank_Asm:1, Bearings:1) dialog box: ■

Click the Dof 1 (R) tab. (1) Click Edit Imposed Motion. (2) Select Enable Imposed Motion. (3) Under Driving, select Velocity. (4) Click the arrow next to the edit window. Click Constant Value. (5) In the edit window, enter 180 deg/s. (6) Click OK.

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Next, you run the simulation to see the wiper assembly in motion. Because the velocity is 180 degrees per second, you set the simulation to run for two seconds so that the Motor_Crank_Asm makes one complete revolution. 5.

7.

In the Simulation Panel:

If the Output Grapher is minimized, resize it by placing your cursor at a corner of the title bar, as shown. When the double-ended arrow is displayed, press and hold the left mouse button and drag to resize the Output Grapher.

Next, you select the variable to view in the Output Grapher. 8.

In the Output Grapher browser: ■

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For Final Time, enter 2 s. (1) For Time mode, enter 200. (2) Click Run or Replay Simulation. (3)

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Expand n°5 :Cylindrical (Motor_Crank_Asm:1, Bearings:1). Expand Driving Force. Select Ukin[5.1].

Next, you open the Output Grapher to view the driving torque on the Motor_Crank_Asm. 6.

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On the Dynamic Simulation panel bar, click Output Grapher.

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Now, you find the maximum torque required to rotate Motor_Crank_Asm at the specified velocity.

9. 10.

12.

In the Values window, right-click anywhere in the Ukin[5.1] column. Click Search Max.

Challenge Task Now try increasing the force to 10 N on each wiper to determine the size of the motor required by this change.

View the grapher. In the Values window the maximum driving torque is highlighted, and in the graph the time bar displays the correct time. You also notice that the assembly is synchronized to the grapher, and the mechanism shows the position of the wipers at maximum drive torque. The maximum driving torque required to move the wipers is 4148 N mm. The torque of the motor required to drive the windshield wipers must at least equal this value.

Tips ■ ■

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13.

11.

Right-click Force1 to edit the force value. Double-click the Input Grapher in the value box. Change both the starting and ending point force values from 5 to 10 and from -5 to -10 respectively. Click OK twice. Repeat the above steps for Force2. Run the simulation. Search max value approx (8292N).


In the Simulation Panel, click Activate Construction Mode.


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Chapter Summary Dynamic Simulation enables you to simulate functional assemblies while generating sophisticated engineering data. With this data, you can determine how your design will perform in real-world situations, while reducing the need for expensive prototypes. Having completed this chapter, you can: ■

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Create joints that define the relationships between components in a mechanism while avoiding redundancy. Create environmental constraints for a simulation. Run a simulation, then use the Output Grapher to review and analyze the results.


Chapter

3 Stress Analysis

Chapter3:

In this chapter, you learn how to analyze parts to determine stress, deformation, and natural frequencies. You also learn how to use results from the Dynamic Simulation environment to accurately place loads in the Stress Analysis environment.


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Create loads and constraints to simulate the real-world conditions in which your designs are expected to perform. Set up and run stress analyses and review the results; animate those results and perform convergency studies to achieve the greatest accuracy. Perform a finite element analysis on a component in the Stress Analysis environment using loads calculated in the Dynamic Simulation environment.

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Lesson: Creating Loads and Constraints Overview This lesson describes loads and constraints and how to create them to simulate the real-world conditions in which your designs will be expected to perform. To accurately simulate the stresses that occur on a part, stress analysis applications must be able to simulate real-world conditions. Two conditions that must be simulated are loads, which are external forces that act upon the part, and constraints, which are virtual conditions that act against forces by constraining degrees of freedom for the part. In the following illustration, a simple rocker arm design illustrates how loads and constraints work in a simple mechanism. Forces (1) are applied to the component through the pushrod mechanism, while constraints (2) restrict the available degrees of freedom. The combination of these conditions simulates real-world effects that are exerted on the mechanism.


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Describe loads and how they are used in the Stress Analysis environment. Identify the types of loads that can be applied to parts and explain how to create them. Describe constraints and how they are used in the Stress Analysis environment. Identify the types of constraints that can be applied to parts and explain how to create them.

Chapter 3: Stress Analysis

About Loads Loads represent the external forces that are exerted on a part. During normal use, the component is expected to withstand these loads and continue to perform as intended. The goal of performing a stress analysis is to determine how these loads affect the part and then, if necessary, adjust the design to withstand these loads. In the following illustration, a load is being placed on the component at the location and direction indicated by the arrow. (1) After the appropriate constraints are applied, a stress analysis reveals the equivalent stress on the component as a result of the load that is applied. (2)

Definition of Loads A load can be defined as an external force that is exerted on a component directly or indirectly. Loads can occur in various locations on the part, and their magnitude and types are also variable. The Stress Analysis environment in Autodesk® Inventor™ supports the following types of loads: ■ ■ ■ ■ ■ ■

Force Pressure Bearing Moment Body Motion

Lesson: Creating Loads and Constraints

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In the following illustration, bearing loads (1) have been added to each arm of the centrifuge rotor. A body load specifying a rotational velocity of 4500 rpms has also been applied. The resulting stress analysis shows the amount of deformation that would occur on the component.

Example of Loads Exerted on a Part In the following illustration, a bearing load is being applied to the surface of the hole. (1) The load direction is set by selecting an edge of a connecting part. (2) The preview arrow (3) indicates the direction of the load being created.

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Types of Loads You create loads by specifying a force, moment, pressure, bearing force, acceleration, gravity, or rotational velocity. Loads can be applied to vertices, edges, or faces of the part. With many loads, you can specify the direction by selecting model geometry or by specifying the individual X,Y,Z components of the load.

Applying Loads To apply a load, click a load tool on the Stress Analysis panel bar and specify the geometry, magnitude, and if applicable, the direction.

Load Direction Some types of loads require you to specify a load direction. The following illustrations give examples of how the load directions can be specified.

Load normal to face

Load aligned to work axis

Load aligned to other part edge

The load is parallel to the selected edge or normal to the selected face. If you need to orient the load in a direction that cannot be specified using existing model geometry, you can specify the load’s components in the X,Y, and Z directions. Alternatively, you can create a work plane or work axis and then use the work feature to orient the load, as shown in this illustration. To orient a load, you can select a part edge or face on the part itself or from another part in the assembly.


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Force Loads You can apply a force to a vertex, edge, or face on a part. You specify the direction by X, Y, Z components, by selecting a planar face, work plane, edge, or work axis, or by selecting two vertices on either the part itself or on another part in the assembly. If you select a planar face or work plane to orient the force, the force is aligned normal to the selected geometry.

When you select geometry to apply the force, all selections must be of the same type. For example, you can select four different faces but not two edges and two faces. The total force is evenly divided among the selected geometry.

Apply forces to faces rather than to edges or vertices to avoid stress singularities.

Pressure Loads You can apply a pressure to a face. The pressure’s direction is always normal to the selected faces and is directed toward the faces by default. Enter a negative magnitude to reverse the direction so that the pressure is directed away from the faces.

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Bearing Loads You can apply a bearing load to an inside or outside cylindrical face. You specify the direction using X, Y, Z components or by selecting a planar face, work plane, edge, or work axis on the part itself or on another part in the assembly.

The component of the bearing load that is radial (perpendicular to the circular face), is distributed over the projected area of the face, as shown in the following illustration.


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You normally use a bearing load to apply a load where a bolt, shaft, or pin makes contact with the part. If the pin or shaft is a tight fit, you can assume that the contact area is the full surface. When the pin or shaft is a loose fit, the contact area is smaller, and you might want to split the face and apply the bearing load to a smaller section of the cylindrical face.

Moment Loads Moment loads take into account bending and twisting of components. You can apply a moment load to faces. You specify the direction by using X, Y, Z components or by selecting a planar face.

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Body Loads Body loads include loading due to gravity and acceleration and apply to the entire part, not to specific areas of the part. You apply gravity to incorporate the part’s weight into the analysis. You can set the direction as the X, Y, or Z part axis. You apply linear acceleration or rotational velocity to determine the effect of accelerating the entire part. You specify the direction by selecting a planar face, work plane, linear edge, or work axis.

Motion Loads Motion loads are created from joints from within the Dynamic Simulation environment and not from the Stress Analysis environment. The motion loads are automatically converted from reaction forces on the joints and applied as bearing loads, torque, and moments on the faces of the joints. If a part to be analyzed has three connecting parts (or three joints), then you need to specify the three faces on the part as shown in the following illustration. The dialog box is displayed when you select the part to be exported to FEA. The only loads that cannot be created from motion loads are pressure. When you are in the Stress Analysis environment, a Motion Loads button is displayed in the Loads area. When you click Motion Loads, all the bearing loads and moments are automatically applied to the specified faces.


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Enforced Displacement You can apply a fixed displacement to a vertex, edge, or face in order to calculate the force required to deform the part or the resulting stress. You specify a displacement by applying a fixed constraint and then specifying the displacement in the constraint components. Enforced displacement loads are useful to determine how much force is required to close the gap between two parts or to deform a part a given distance.

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Guidelines for Applying Loads You may not always have geometry at a location where you want to apply a load. To add a load to an area of the model that does not have a face, edge, or vertex, you split a face of the model using the Split tool and then apply the load to the new face. If you specify the components of a load while editing a part in place, remember that the toplevel assembly’s coordinate system is displayed, and not the part’s. The force components that you enter must be in the part coordinate system. These can be difficult to determine while you are in the assembly.

To specify the components or magnitude of a force, you can enter an equation in which you make calculations or reference other parameters.

Summary of Load Types The following table summarizes the available loads, the geometry to which you can apply the load, and the methods you can use to specify the load’s direction. Load

Can Be Applied To

Specify Direction Using

Force

Vertex Edge Face

Components Planar face or work plane Edge or work axis Two vertices

Pressure

Face

Pressure is always normal to the face

Bearing Load

Face (cylindrical only)

Components Planar face or work plane Edge or work axis

Moment

Face

Components Planar face or work plane Edge or work axis

Body Loads

Acts on the whole body

Planar face or work plane Edge or work axis

Motion Loads

Face

Generated automatically by Dynamic Simulation

Enforced Displacement

Vertex Edge Face

Components


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About Constraints You use constraints to model how the part is restrained from motion. You typically place a constraint where the part is connected to or makes contact with other rigid components. Using one or more fixed, pin, or frictionless constraint, you must constrain the model so that it cannot translate or rotate in any directions. In the following illustration, a pin constraint is being added to the rocker arm where it swivels on the shaft component.

Definition of Constraints Constraints are used to define how components would be fixed in a real-world assembly. These constraints can be controlled by varying the fixing directions in the X,Y,and Z axes or radial, axial, and tangential directions for cylindrical components. The Stress Analysis environment in Autodesk Inventor supports the following types of constraints: ■ ■ ■

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Fixed Pin Frictionless


In the following illustration, a pin constraint is being applied to one of the cylindrical faces (1) of the connecting arm. The tangential direction is free to move as it would in reality.

Example of Constraints In the following illustration, a frictionless constraint is applied to the rocker. (1) This enables the rocker to move in the indicated direction. (2)


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Types of Constraints To apply a constraint, you click a constraint tool on the Stress Analysis panel bar and specify the geometry to constrain.

Fixed Constraints A fixed constraint restricts the translation of the constrained geometry in one, two, or three directions. Use a fixed constraint to model rigid connection points to other components. Fix all three directions when you know that the part is fully fixed to a rigid support, such as where an edge or face of the part is welded or bonded to another part. Use components of the fixed constraint to fix or release motion in specific directions. If the face of a part contacts another part and the faces are not fully attached, either apply a fixed constraint and release the in-plane motion directions, or use a frictionless constraint. You can also use the components of the fixed constraint to specify a displacement for the constrained geometry.

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Pin Constraints You use a pin constraint to prevent a cylindrical surface on the part from moving radially, tangentially, or axially. You typically use pin constraints where holes are supported by bearings or pins. You can select which directions to fix with respect to the cylindrical surface. For a bearing or pin, you free the tangential direction to enable the surface to rotate freely.

Frictionless Constraints A frictionless constraint enables a surface to freely slide along a plane or surface but prevents the surface from moving normal to itself. You use frictionless constraints to model face-to-face and surface-to-surface contact between parts where one part can slide on the other. Most surfaces in contact are not entirely frictionless. Furthermore, frictionless constraints give conservative results because the friction’s contribution to the overall model stiffness is not included.

Frictionless constraints are also used to model symmetry boundary conditions. When a model’s loading and geometry are symmetric, you can analyze a portion of the model to save analysis time. You use frictionless constraints on all of the symmetry surfaces in the model. For example, consider a rotor for a swing-bucket centrifuge rotating at 4500 rpm, and a pin constraint applied in the hole in the middle. Because the load, constraints, and model are symmetric, you can analyze a section instead


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of the entire model. You apply the load and constraints as you would for the entire model and then apply frictionless constraints to the faces on the cut planes, as indicated by the arrows in the following illustration.

Guidelines for Applying Constraints Before you perform a stress analysis, you must fully constrain the model so that you prevent translation and rotation in all directions. If you fail to constrain the model fully, an error message is displayed, and the analysis does not proceed.

When you use frictionless or pin constraints, potential may exist for rigid body motion, even though rigid body motion is not possible based on the combination of constraints. Weak springs are automatically added to the model to prevent rigid body motion. If the boundary conditions prevent rigid body motion, the springs do not affect the result. When the analysis is complete, you should check that the deformed model and the reaction forces are reasonable.

Selecting the wrong type of constraint or overconstraining the model are frequent mistakes in finite element analysis. The constraints that you choose and where you apply them significantly affect the results. Make sure that you understand how the part interacts with other parts in the assembly. If you are uncertain about which constraint to apply, run a sensitivity analysis to determine how sensitive the result is to the type of constraint.

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Exercise: Create Loads and Constraints In this exercise, you create the required loads and constraints to determine the stress and deformation of a rotor for a swing-bucket centrifuge rotating at 4500 rpm.

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5.

Preview the mesh. Click OK.

On the panel bar, click the Body Loads tool. ■ ■

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Under Rotational Velocity, select Enable. Click the Select Rotational Direction arrow. Move the cursor over the top face of the hub until the load arrow is displayed. Click to set the direction. Under Rotational Velocity, for Magnitude, enter 4500 rpm. Click OK.


Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 3: Stress Analysis. Click Exercise: Create Loads and Constraints.

1.

Open Stress_CentrifugeRotor.ipt.

2.

Change the material to Aluminum-6061.

3.


4.

On the panel bar, click the Stress Analysis Settings tool. ■

In the Stress Analysis Settings dialog box, make sure that Stress Analysis is selected from the Analysis Type list.

6.

Apply a pin constraint to the inner circular surface of the hub. Constrain all three directions by selecting the check boxes.

NOTE: A pin constraint with all three directions constrained is equivalent to a fixed constraint.


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7.

On the panel bar, click the Bearing Load tool. ■

Select the two holes (1) on either side of the cutout that is aligned with the positive X axis. Click the Select Bearing Load Direction button. Select the edge of the slot (2) to orient the forces in the positive X axis direction. For magnitude, enter 1600 N. Click OK.

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NOTE: The magnitude was calculated based on the rotational velocity, mass of the swing buckets and contents, and swing radius.

10.

Review the deformation and safety factor. The stress is far below the yield point for the material. The highest stress is at the load connection point, but the stress at that point is not accurate because the load connection was not modeled in detail. Because the stress is low in the rest of the arm and no stress singularities or critical locations are apparent, you do not perform a stress convergence study. You now increase each force to 2000 Newtons using the Parameters dialog box.

8.

Repeat the previous step for each of the other slots. Make sure that the forces point out from the center of the part.

9.

On the Standard toolbar click Stress Analysis Update. When the analysis is complete, the equivalent stress is displayed on the deformed model.

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11.

On the panel bar, click Parameters. In the Parameters dialog box. under either Model Parameters or Stress Analysis Parameters, change all of the 1600 N entries to 2000 N and click Done.

12.

On the Standard toolbar, click Stress Analysis Update to update the analysis and view the results.

13.

Save and close the file.

Lesson: Running an Analysis and Analyzing Results Overview This lesson describes how to run a stress analysis and analyze the results for quality and performance. After you have applied loads and constraints, it is time to run a stress analysis and analyze the results. To effectively use the resulting data, you typically run multiple analyses as you refine the design. Understanding how to access and analyze the results enables you to effectively change the design to ensure desired performance. The following illustration shows an equivalent stress plot of a rocker arm indicating areas of high stress. Other result plots include deformation and factor of safety.


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Set up and run a stress analysis. Revise models and stress analysis loads and constraints, and rerun an analysis to determine the results. Review and interpret the stress analysis results. Animate and report analysis results. Perform a convergence study. Describe and identify the types of files that are created when you perform a stress analysis.

Lesson: Running an Analysis and Analyzing Results

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Setting Up and Running the Analysis Before you run the analysis, you should confirm the default settings that are selected in the Stress Analysis Settings dialog box. If necessary you should then revise them based on the type of analysis you require and the relevant mesh control. During a typical analysis process, you may change the settings several times as you refine the component’s design and change other analysis properties such as constraints and loads.

Access Stress Analysis Settings

Panel Bar: Stress Analysis Toolbar: Stress Analysis

Access Stress Analysis Update

Toolbar: Standard

Analysis Type You use the Analysis Type list to select a stress analysis, a modal analysis, or both. If the model on which you run a modal analysis has loads, the natural frequencies are calculated for the stressed model.

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Term

Definition

Stress Analysis

Determines the strength of components and enables you to optimize designs by indicating areas of stress and potential failure.

Modal Analysis

Determines the natural frequencies of the component. This type of analysis is useful when the component is part of an assembly.

Mesh Control The Mesh Control settings determine the mesh size. On the Mesh Relevance slider, you can set the average overall mesh size. The default setting of zero is a good starting point for most analyses. You use a higher number for a smaller mesh size, providing a more accurate answer but increasing analysis time. You use lower settings to perform a quick analysis to ensure that the model, loads, and constraints are correctly applied before you run an analysis with a smaller mesh. If Result Convergence is selected, the mesh is automatically refined. This significantly increases analysis time but generally provides a more accurate result.


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Running the Analysis Click the Stress Analysis Update tool to run the analysis. The ANSYS Solution Status dialog box displays the progress of the analysis.

Process: Setting Up and Running the Analysis The following steps give an overview of the process of setting up and running the analysis. 1.

With the Stress Analysis application activate, click the Stress Analysis Settings button on the panel bar.

2.

Select the type of analysis and adjust the mesh relevance slider based on the current analysis and your requirements.

3.

Run the analysis by clicking the Stress Analysis Update button on the Standard toolbar.

Revising Models and Stress Analysis Based on the result of an analysis, you may need to make changes to the part or to the applied loads and constraints and then rerun the analysis.

Editing Loads and Constraints To edit a load or constraint, right-click it in the Stress Analysis browser and click Edit.

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Loads are stored as user parameters, so you can edit their magnitudes using the Parameters tool. You use this method to change the value of multiple loads, or for automation using VBA or another automation tool.

Results You edit the part geometry by changing the model parameters or by switching to the part environment. In the part environment, you can display the last stress result item on the part to guide your model changes.

When you change the part or other values that affect the stress results, the icons in the Results folder of the Stress Analysis browser change to indicate that the results are out of date. Click the Stress Analysis Update tool to rerun the analysis.


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Process: Revising Models and Stress Analysis The following steps give an overview of revising the model and stress analysis. 1.

Edit loads or constraints based on the stress analysis requirements.

2.

Switch to the part environment and make design changes as required, based upon the stress analysis results.

3.

Update the stress analysis and continue to revise the design and analysis.

Reviewing and Interpreting Analysis Results When you view and interpret analysis results, you should remember that finite element analysis approximates the actual stress and deflection. The result is sensitive to many factors, including: ■ ■ ■ ■ ■

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Material properties Model geometry Mesh density (element size) Type of loads and how and where they are applied Types of constraints and how and where they are applied


If any input value is incorrect, the result may look reasonable but can be meaningless. Incorrect loads and constraints cause many errors in finite element analysis. The real-world interaction between one part and another needs to be approximated, and incorrect assumptions can lead to errors in the result. You learn by experience to approximate the actual conditions with available loads and constraints. Finite element analysis identifies problems early in the design cycle, which helps you make better products. If you are designing a critical component, you should test the actual part to ensure that it meets the performance criteria. You can use the test result to fine-tune your stress analysis to predict stress on similar parts with greater accuracy.

Viewing Results When the analysis is complete, the result is displayed graphically on a deformed model. To view a different result, double-click the result in the Results folder in the Stress Analysis browser.

Several terms and values are displayed as results of a stress analysis. The equivalent stress is a combination of all of the stresses. It is also known as Von Mises stress. For ductile materials, you compare the equivalent stress to the yield strength of the material to estimate whether the material will yield. The safety factor is equal to the yield strength of the material divided by the equivalent stress. If the safety factor is greater than 1, the yield strength is greater than the equivalent stress, and the part should not yield. The results are typically displayed on a deflected shape. Actual deformations are normally small, so the default display setting greatly exaggerates the deformation. If you are concerned about actual deformation (for example, to assess whether the part would make contact with another part), you should be sure to view both the actual deformed shape and the deformation contours.


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Results Deformation The following illustration shows the exaggerated (left) and actual (right) deformed shape of a bracket. From the exaggerated deformation, you might conclude that the side of the bracket deforms beyond the back of the bracket, making contact with the component to which the bracket is mounted. However, the actual deformed shape on the right shows that the side of the bracket deforms very little.

You change the deformation scale with the Deformation Style list on the Standard toolbar.

Reaction Forces The constraints resist external loading by generating reaction forces. To view the reaction forces at a constraint, right-click the constraint and click Reaction Forces.

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Color Bar The color bar relates the colors of contoured results to numerical values. You can adjust the color bar to ignore extreme results such as a stress singularity or to give more detail in a specific range of values. To adjust the color bar, click the Color Bar tool on the Stress Analysis panel bar. In the Color Bar dialog box, you can: ■ ■ ■

Clear the Automatic check boxes to specify a range of stress values of interest to you. Change the color styles from color to monochrome. Orient the position of the color bar in the graphics window in standard or compact form.

Each result item maintains its own color bar, so the changes that you make, for example to the equivalent stress color bar, do not affect the deformation or safety factor color bars.

Parameters The result of a stress or modal analysis is saved as both stress analysis parameters and reference parameters. You can view the result in the Parameters dialog box or read the parameters using VBA or another automation tool.


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Stress Singularities Stress singularities can occur in models where you simplified loads, constraints, or model geometry. In theory, the stress at a singularity is infinite, resulting in an unrealistically high stress. You should be aware of singularities so that you can correctly interpret analysis results. An example of a singularity is when you apply a force or a fixed constraint to a vertex or edge of a model. Because a point or edge has an area equal to zero, the theoretical stress is infinite. As shown in the following illustration, the stress reported by finite element analysis is large at point loads.

A point or edge load is unusual in real models, but these loads are convenient for stress analysis and work well if the result is interpreted correctly. If the area of interest in the model is located away from the load, you can ignore the unrealistically high stresses reported at the load. If the singularity is at the area of interest, you need to model that area in more detail. If you perform a convergence study, the stress at the singularity never converges, because the theoretical stress is infinite. Monitor the stress at the area of interest and not at the stress singularity. Another common cause of stress singularities is models with sharp internal corners. Because sharp internal corners have infinite stress, the stress never converges on an answer. Most models have a fillet in the corner, especially if the corner is in an area where high stresses are expected. If the sharp corner is in an area of concern, add a fillet to better approximate the real component. If the corner is not in an area of concern, either add a fillet or ignore the unrealistic high stress reported at the singularity. You can adjust the color bar so that you ignore the unrealistic stresses at a singularity. Although you can ignore stress singularities when you perform a manual mesh convergence, you cannot perform an automatic convergence if the model contains singularities.

Animating and Reporting Analysis Results When a simulation is complete, you have two additional tools for interpreting and communicating the results: animation and report generation. The Animation tool enables you to better understand the behavior of the component under a specific loading condition. The Report tool enables you to communicate your designs and results effectively without needing Inventor or Inventor Professional. The report automatically includes a copy of all the result plots and data in a compact HTML file, making it an excellent medium for communicating results through the Internet or intranet.

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The following illustration is part of an HTML report generated in the stress analysis environment showing a summary of maximum results and an equivalent stress plot.

Animate Results You use the Animate Results tool to see how the part reacts under load by animating the deformed model. The animation uses the current deformation scale. You can view the animation on screen, or save it to an AVI file to include in reports or share with team members.

Access Animate Results



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In the following illustration, four images are shown to simulate the animated results of the analysis. Using standard media player controls you can play, pause, stop, and record the animated results.

Generating Reports When an analysis is complete, you use the Report tool to generate an HTML report of the result. The report includes: ■ ■ ■ ■

■

Loads. Constraints. Material properties. Tabular results, such as maximum and minimum stress, deformation, safety factor, and modal frequencies. Graphical results, such as equivalent stress, deformation, safety factor, and mode shapes.

Access Report


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In the following illustrations, different areas of the report are shown to illustrate the types of information the reports contain.

The report is in HTML format and includes several linked files. To distribute or move the report, include the report file itself and all of the linked files. You can find the location of the report in your web browser’s address bar. You can edit a report by opening it in an HTML editor or word processor. Use Microsoft® Word to embed the images in the document and save the report as a single document to share with others, or to incorporate into other documents. The same name and location are used for all reports. If you want to keep a report, copy the report and its associated files to another folder so that they are not overwritten when you generate the next report.


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Performing a Convergence Study The number, size, and distribution of elements in a model are critical to the success of your analysis. In finite element analysis, there is a trade-off between accuracy and speed of solution. For greater speed, you should use fewer elements. For greater accuracy, you must use more elements. To ensure that your analysis results are accurate, you need to perform a convergence study to determine the optimum mesh size for your design. The appropriate distribution of elements is also important to avoid wasting solution time solving for many small elements where a few large elements suffice. In areas of the model where stress is fairly continuous or changes minimally, large elements can adequately model the stress distribution. In areas of the model where the stress changes rapidly, such as near a stress concentration, small elements are required.

Stress Analysis Settings You use the Mesh Relevance slider in the Stress Settings dialog box to set the global mesh size.

You typically perform two or more runs to determine the best mesh size. You can manually perform a convergence study by running the analysis at several different mesh relevance settings, such as 0, 50, and 100. To run automatic convergence, select Result Convergence and run the analysis. The model is meshed using the global mesh size that you set on the Mesh Relevance slider. When the analysis is complete, the software calculates the change in stress (error norm) for each element. If the change in stress is large, the element is divided into four elements for the next run. After the next analysis, if the results have changed less than 10%, the model is considered to have converged. If not, the elements with high error norm are again divided and the analysis is rerun. There is a maximum of three analyses. If the model fails to converge, a warning message is displayed. When this occurs, check for and correct singularities in the model. Automatic convergence can produce much finer mesh than you can achieve using the manual Mesh Relevance slider, but it can take much longer to converge on an answer.

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The following illustration shows differences in mesh size with manual meshing and using automatic convergence.

Mesh Relevance = -100

Mesh Relevance = 100

Automatic Convergence

Convergence Study Graphs The following illustrations show stress results that are converging on a value (the left graph) and values that are not converging (the right graph).

In the left graph, it is clear that the results are converging on a value and that a further decrease in mesh size will not make a significant difference to the answer. If the results have not converged, as in the right graph, there is a problem in the model and you need to examine the results closely before you use them. Nonconverging results are normally due to stress singularities caused by modeling simplifications or errors. If the stress singularity is not in the area of interest, you can ignore the high stress and use the results at the area of interest.

Process: Performing a Convergence Study The following steps outline how to perform a convergence study to determine the optimum mesh size for a model. 1.

Start with a coarse mesh (few large elements) and run the analysis.

2.

View the deformation to determine whether constraints and loads are correctly applied.

3.

Record the result (stress, deformation, or modal frequency) in the area of interest.

4.

Re-mesh with a smaller mesh in the area of high stress gradient.


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5.

Run the analysis again and record the result in the area of interest.

6.

Re-mesh with a smaller mesh in the area of high stress gradient.

7.

Run the analysis again and record the result in the area of interest.

8.

Plot or tabulate the results to determine if they are converging. Typically, if the result changes less than 10% between runs, the model is considered to have converged.

Convergence Study Guidelines Results convergence can take a long time to run, so it is best to do last, after you understand the analysis behavior and have performed all design iterations. In most cases, only the end quantity changes in the converged answer, and not the area where the high stress occurs and how the part deflects. Deformation and mode shape typically converge quickly and without problem. Because deformation is not affected by small geometric features, larger elements adequately model deformation, and few runs are required to converge on a result. Stress results typically take more steps to converge and may not converge at all if singularities are present. If the high stress is concentrated in a small area, numerous small elements are required to adequately model the stress distribution, which typically takes several steps before the results converge. Avoid the tendency to select a fine mesh and run only one analysis. It is impossible to determine whether the results converge unless you run several analyses.

If you run out of disk space during results convergence, change the %TEMP% or %TMP% system variable to point to a drive with more free space. To access these variables, right-click My Computer, click Properties, click the Advanced tab, and click Environment Variables.

Stress Analysis Files When you add stress analysis information to a part and then save the part file, new files are created to hold the stress analysis input and results. The file names begin with the same name as the part file but have different extensions. By default, the files are created in the same location as the part file, with some files being stored in subfolders within that location.

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Stress Analysis Settings Dialog Box Select the Create OLE Link to Result Files option to create OLE links between the part file and the result files that are generated.

OLE Linked Result Files In the following illustration, result files are displayed under the 3rd Party node in the browser. These files are automatically created and linked when the part file is saved. The *_Structure files are displayed only when Analysis Type is set to Stress Analysis or Both, while the *_Modal file is displayed only when the Analysis Type is set to Modal or Both.


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Storage Locations The following illustration shows the analysis result file storage locations.

The primary result file *.ipa is created in the same folder as the part file to which it is linked. Additional result files are stored in a subfolder that uses the same name as the part file to which they are linked.

File Management The analysis result files contain the analysis settings, loads, and results. The IPT file also contains a copy of the analysis settings and loads, but it does not contain the results. The IPT and result files each contain references to each other. You manage these files in a similar manner to managing other Autodesk Inventor files. If you move or rename one of the files and not the others, you see a prompt to resolve the file link errors when you open the part or when you switch to the Stress Analysis environment. To resolve the link, you can locate the files or, if you know that the files are missing or deleted, skip the file to continue. If you skip the file, the loads and settings are still available, because copies are stored in the IPT file. To update the results, update the analysis. When you save the part file, new result files are generated. If you use Autodesk® Vault storage, the result files are treated as children of the part file. Autodesk Vault retrieves and checks in the result files at the same time as the part file when requested to do so.

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Exercise: Determine Enforced Displacement In this exercise, you determine the force required to displace a cantilever snap fit a known distance. You also determine the stress and safety factor.

2.

Click Applications menu > Stress Analysis. Because no material was set for the model, the Choose Material dialog box is displayed. ■ ■

From the Material list, select Nylon-6/6. Click OK.

The Stress Analysis panel bar is displayed. There are no loads or constraints, so the Stress Analysis Update tool is disabled. 3.

On the panel bar, click the Fixed Constraint tool. ■ ■ ■

Click the face at the left end of the beam. Click OK. Notice that the fixed constraint is added to the browser.


Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 3: Stress Analysis. Click Exercise: Determine Enforced Displacment.

4.

Click the Fixed Constraint tool. ■ ■

1.

Open Stress_CantileverSnapFit.ipt.

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Click the face on the back of the hook. Expand the Fixed Constraint dialog box. Select Use Components. Select the check box next to Y and enter -4mm. Notice that the displacement is negative because the tip must deflect down. Click OK.


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NOTE: You could also apply the constraint to the top edge instead of the face. Because the area of the edge is zero, the reported stress will be unrealistically high at the edge. 5.

The stress distribution in the beam looks reasonable. The stress is not uniform at the fixed end because the fixed constraint prevents the beam from shrinking laterally as a result of the Poisson effect. 7.

The force required to displace the edge is listed.

Click the Stress Analysis Settings tool. In the Stress Analysis Settings dialog box, ensure that: ■

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For Analysis Type, Stress Analysis is selected. Mesh Relevance is 0. The Result Convergence check box is clear.

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In the browser, right-click Fixed Constraint 2. Click Reaction Forces.

Click OK to close the Reaction Forces dialog box.

In the dialog box, click OK. 6.

On the Standard toolbar, click the Stress Analysis Update tool. When the analysis is complete, the equivalent stress is displayed on the deformed model.

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8.

In the browser, double-click Deformation.

9.

On the Standard toolbar, select 1:1 Automatic in the Deformation Style list.

10.

View the model from the front and confirm that the snap fit deflects the correct amount.

12.

Adjust the color bands so that you can determine the stress on the top of the beam, near the fixed end. ■ ■

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11.

On the panel bar, click Color Bar. In the Color Bar dialog box, clear the Automatic option. Enter 5.00e+001 MPa. Click OK.

Reanalyze the model using a mesh relevance of approximately 50 and again with a mesh relevance of 100. Confirm that the stress has converged. The following illustration shows the stress for a mesh relevance of 100. 13.

On the panel bar, click the Stress Analysis Settings tool. ■ ■

Set the Mesh Relevance to 0. Select Result Convergence and click OK.

14.

Run the analysis. This may take several minutes.

15.

Turn on the mesh display to see the resulting mesh.

As you increase the mesh size, the maximum stress at the corners of the fixed end increases because there is a stress singularity at the corner.


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16.

Adjust the color bars to determine the stress on the top face of the beam near the fixed end.

The factor of safety plot shows a value of 1.2. There is very little option to reduce weight based on achieving a factor of safety of 1. Another option is to use a stronger material and then reduce weight. 17.

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Save and close the file.

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Exercise: Perform an In-Place Analysis In this exercise, you perform an in-place analysis of a part in an assembly. You add a bearing load using another part in the assembly to align the load. You also use pin and frictionless constraints.



1.

Open Stress_RockerArm.iam.

To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 3: Stress Analysis. Click Exercise: Perform an InPlace Analysis.


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2.

To suppress fillets on the Rocker Arm part: ■

6.

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In the browser, right-click Rocker Arm. Click Edit. In the browser, right-click ExteriorFillets. Click Suppress Features.

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4.

On the panel bar, click the Pin Constraint tool.

On the panel bar, click the Bearing Load tool.

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Select the two cylindrical surfaces that contact the bearings. Click OK.

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Select the hole where the hydraulic cylinder is attached. For Magnitude, enter 20000 N. Click the Set Bearing Load Direction button. Click the edge of the hydraulic cylinder to orient the force. If the force points toward the cylinder, click Flip Bearing Load to make the force point away from the cylinder. Click OK to close the Bearing Load dialog box.

On the panel bar, click the Frictionless Constraint tool. ■

Select the flat face. Click OK.

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On the panel bar, click the Stress Analysis Settings tool. In the Stress Analysis Settings dialog box, confirm the following: ■ ■ ■

The analysis type is Stress Analysis. Mesh Relevance is approximately 0. Result Convergence is cleared.

Click OK to close the Stress Analysis Settings dialog box. 8.

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On the Standard toolbar, click the Stress Analysis Update tool.

9.

13.

When the analysis is complete, the equivalent stress is displayed on the deformed model.

In the browser, right-click Hyd_Ram_Pin. Select Properties. ■ ■ ■

10.

Click the Occurrence tab. Change the X Offset to -500 mm. Click OK.

14.

On the Standard toolbar, click Update.

15.

Edit the rocker arm in place. Activate the Stress Analysis application.

16.

Zoom in to the right end where the hydraulic cylinder is attached. Notice that the force direction does not update to reflect the change in position of the component.

17.

In the browser, right-click Bearing Load. Click Edit.

On the panel bar, click Animate Results. ■

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In the Animation dialog box, click Play. With the animation still running, view the model from the front. Zoom in to the left end. Confirm that the face slides left and right and does not move up or down.

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18.

11.

With the animation still running, zoom out to display the entire model. When you understand how the model deforms, click OK.

12.

Return to the top-level assembly.

Set the force direction. Close the Edit Bearing Load dialog box.

Rerun the analysis and view the result.


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19.

In the browser, double-click the Safety Factor result.

According to the factor of safety plot, you can reduce weight if you are trying to achieve a factor of safety value of 2. 20.

Return to the part environment. On the Standard toolbar, click the Last Displayed Stress Result Item as shown.

22.

Return to the Stress Analysis environment. On the Standard toolbar, click Stress Analysis Update.

23.

In the browser, double-click the Safety Factor result.

This result is useful because it enables you to edit features based on stress results. 21.

Create a cutout using the following dimensions.

Even though you have reduced the weight, the factor of safety remains unaltered and stress has remained the same. You can try the next challenge step or go straight to the last step.

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24.

Challenge Task

26.

Alter the position of the small hole away from the big hole as shown in the following illustration.

27.

Update the analysis. As a result of moving the hole further away, you have achieved your goal.

28.

Save and close all files.

Now see if you can remove further material without going below a factor of safety of 2. A sample is shown.

TIP: Reduce thickness of material in the region of the hole cutouts. Use a thickness of 6 mm. 25.

Run a results convergence to see if the results have converged.

As a result of performing a results convergence, the factor of safety plot has reduced to less than 2. If it is greater than 2, then you do not need to proceed to next step. Go straight to the last step.


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Lesson: Sharing Dynamic Simulation Results with Stress Analysis Overview This lesson describes how to transfer reaction loads of joints from the Dynamic Simulation environment into the Stress Analysis environment. It also illustrates how to apply motion loads in the Stress Analysis environment. Performing FEA on a component using loads calculated in the Dynamic Simulation environment provides a realistic view of how the component will perform in real-life conditions. In the following illustration, Stress Analysis was used to test an arm, and the display was set to Safety Factor.


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Describe how Dynamic Simulation and Stress Analysis can work together to validate part designs. Export Dynamic Simulation results to FEA.


About Sharing Dynamic Simulation Results with Stress Analysis Performing stress analysis on a component requires you to choose where the loads should be applied, which types of loads should be applied, and the magnitude of the loads to calculate stresses. To eliminate guesswork and save time, you can use the Dynamic Simulation environment to calculate the types of forces and magnitude of forces on the component, and then export the required loads directly to FEA. If the stress analysis exposes problem areas with a component, you can quickly return to the part environment, edit the design, and return to the Stress Analysis environment to test the effect of the edits. In the following illustration, a component is shown in the Stress Analysis environment with motion loads that were exported from the Dynamic Simulation environment. The symbols designate the location of the loads and the type of load to be applied.

Definition of Sharing Dynamic Simulation Results with Stress Analysis Solving design problems with Dynamic Simulation and Stress Analysis is a two-step process that ensures that components in an assembly withstand the forces and motions applied to them during the proposed life of the mechanism. You can use Dynamic Simulation to calculate the types of forces as well as the magnitude of the forces, and export that information to be used for stress analysis. In the Stress Analysis environment the exported forces, or motion loads, are then applied to the component and the results are displayed according to the output that you require.

Lesson: Sharing Dynamic Simulation Results with Stress Analysis

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In the following illustration, the Output Grapher is displaying the time cycle showing the time step chosen to be exported (1) to Stress Analysis. The steps that are chosen for export appear under the Time Steps node (2).

Example In the course of designing a window glass lift mechanism, the design of one of the arms has come into question. To test the ability of the arm to withstand the stresses of lifting and lowering the window glass, you use Dynamic Simulation to place the joints, add the required velocity to the mechanism, and then calculate the motion loads. After the simulation has run, you use the Output Grapher to export the loads to FEA. In Stress Analysis, you apply the motion loads to the component and perform a stress analysis update to view the results. Upon changing the display to Safety Factor, you see that in several areas the safety factor is less than the customer-mandated safety factor of four. With this information, you can modify the component design and quickly repeat the process to see the effect of your modifications. In the following illustration, the stress analysis has been completed and the part displayed with contour colors that correspond to the color bar on the left.

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Exporting Motion Loads to Stress Analysis After you calculate reaction forces and torques in joints in Dynamic Simulation, you can easily export these values to Stress Analysis as input values to test and validate a part. This method of analyzing a part is accurate because Dynamic Simulation provides the magnitude of the forces and torques that the part experiences in the mechanism during the motion. In the following illustration, a simulation is running, and the forces designated for stress analysis are indicated by arrows. These arrows display the direction and magnitude of the forces.

Process: Exporting Motion Loads to Stress Analysis The following steps describe the process of sharing Dynamic Simulation results with Stress Analysis. 1.

In the Dynamic Simulation environment, create joints for the mechanism using the Automatic Update of Constraints or Convert Assembly Constraints and Insert Joint tools.

2.

Run the simulation to calculate the motion loads.

3.

Use the Output Grapher to determine the time step you will use by clicking in the Export FEA column.

4.

Click Export to FEA in the panel bar. Designate the joint faces whose motion loads will be exported to FEA.

5.

Perform an in-place edit of the part.

6.

Enter the Stress Analysis environment.

7.

Apply the motion loads.

8.

Perform a stress analysis update to calculate the stresses.

9.

If testing reveals an area of concern, return to the part modeling environment (or suppress features within the Stress Analysis environment if applicable).


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10.

Make necessary edits to the part.

11.

Rerun the Stress Analysis.

12.

Enter the Dynamic Simulation environment and rerun the dynamic simulation to verify inertial and reaction loads.

Guidelines The following list describes some basic guidelines for sharing Dynamic Simulation results with Stress Analysis. ■

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Because selection can be difficult when the entire assembly is visible, isolate the part in the assembly environment. Return to the Dynamic Simulation environment and designate the part faces for FEA testing before you run the simulation. Because it can be difficult to find the time step where you have the maximum peak stresses during the motion, it is recommended that you export several time steps and compare the results.


Exercise: Simulate and Analyze a Glass Lever Mechanism In this exercise, you run a simulation of a glass lever mechanism. You then use the simulation results to export the maximum loads to the Stress Analysis environment to validate the robustness of a part. The initial results indicate that the original design achieves a factor of safety below 1, which indicates that the part has failed.

1.

Open WindowGlassLeverFEA.iam.

The joints for this mechanism have already been created. You designate the load bearing faces on the second arm component. These are the faces that will be used by Stress Analysis to apply the reaction forces and torques in the joints determined by Dynamic Simulation. The completed exercise

2.


3.

In the Simulation Panel, click Run or Replay Simulation.

Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 3: Stress Analysis. Click Exercise: Simulate and Analyze a Glass Lever Mechanism.

After the simulation is complete, you open the Output Grapher to find the time step for the maximum force on the arm. You use this time step to test the part in FEA. 4.

In the Dynamic Simulation browser, click Output Grapher.


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5.

In the Output Grapher browser: ■

7.

In n°3 :Revolution (Main Arm asm:1, Second Arm:1), expand Force. Select fr[3.1] (1). In n°4 :Welding (Pin:1, Second Arm:1), expand Force. Select fr[4.0] (2). In n°5 :Welding (Upper_Pin:1, Second Arm:1), expand Force. Select fr[5.0] (3).

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When the search max load is highlighted, select the box as indicated by (1). This action transfers the loads to the Stress Analysis environment as indicated by (2).

NOTE: You can transfer multiple loads to Stress Analysis.

6.

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Right-click the column heading for fr[3.1] (N). Click Search Max. The time bar on the graph moves to the time step highlighted in the Time Viewer, as shown.

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8.

Close the Output Grapher and reset the simulation to the start position by clicking the Rewind button or dragging the time slider to 0.00 seconds.

9.

On the Dynamic Simulation panel bar, click Export to FEA.

10.

Select the Second Arm as shown. This action enables you to transfer the loads to this part to perform stress analysis. Click OK.

11.

Highlight Joint No. 3 if not already highlighted. Select the load bearing surface as shown. This is the surface where the loads will be transferred to.

12.

Next highlight Joint No. 4. Select the load bearing surface as shown.

13.

Next highlight Joint No. 5. Select the load bearing surface as shown. Click OK.

14.

Click Applications menu > Assembly.

15.

In the Model browser, right-click Second Arm:1. Click Edit.

16.


17.

On the Stress Analysis panel bar, click Motion Loads. In the Motion Loads information box, click OK. Notice the symbols added to the part at the locations where the loads will be calculated, as shown.


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18.

On the Standard toolbar, click Stress Analysis Update. After a few moments the part updates to show the effect of the stress on the Second Arm:1 at the selected time step of the simulation.

20.

On the Standard toolbar, in the Deformation Scale list, select Actual.

21.

Notice that the display updates to show the actual amount of deformation in the part.

NOTE: Due to the complex calculations required, this update may take several minutes to complete.

The results in the graphics window display the equivalent stress on the arm. The color contours correspond to the values defined by the color bar. Equivalent stress can be used to obtain a reasonable estimation of fatigue failure, especially in cases of repeated tensile and tensile-shear loading. 19.

In the graphics window, use the Rotate and Zoom tools so that your view matches the following illustration.

NOTE: The amount of flex shown is not the true amount of change in the part, but a scaled representation. Next, you change the scale to see the actual amount of deformation of the part.

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Next you change the display to view the safety factor for the part. The safety factor identifies the areas of the model that are likely to fail under load. 22.

In the Model browser, for Second Arm:1, under Results, double-click Safety Factor. Notice that the view updates with a new color bar and the part display updates to reflect the safety factor values. The red areas highlight where the part’s safety factor is 1 or less and indicates areas where failure is likely to occur.

NOTE: You may need to rotate your view to see the areas that are likely to fail.

The part has a minimum factor of safety of 0.635. This means it has gone beyond the elastic limit and the part has failed. 23.

On the Standard toolbar, click Return.

24.



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Chapter Summary Stress Analysis enables you to visualize how your design will perform and helps to identify areas in the design that may need improvement. Like any simulation application, the result accuracy for Stress Analysis is completely dependent on the accuracy of the information that is given for loads and constraints. By using information gathered from the results of your dynamic simulation, the accuracy of your stress analysis is enhanced and the process is streamlined. Having completed this chapter, you can: ■

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Create loads and constraints to simulate the real-world conditions in which your designs are expected to perform. Set up and run stress analyses and review the results; animate those results and perform convergency studies to achieve the greatest accuracy. Perform a finite element analysis on a component in the Stress Analysis environment using loads calculated in the Dynamic Simulation environment.


Chapter

4 Engineering Problems and Solutions Chapter4:

This chapter offers you a chance to practice using the tools and techniques you have learned in previous chapters to solve real-world engineering and design problems.

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Lesson: Solving Design Problems Overview Designers are required to solve many different engineering problems throughout a typical design. At any point during the design process, a designer may ask one or more of the following questions: ■ ■ ■ ■

Do the parts fit together properly? Do the parts move well together? Is there an unknown interference between parts? Do the parts follow the intended path?

Even though most of these questions can be answered using the standard design tools offered in the Autodesk® Inventor™ software, there may be other questions which cannot. For example, most designers also want to know: ■ ■ ■ ■

What is the machinery time cycle? Is the actuator powerful enough? Is the link robust enough? Can you reduce weight without sacrificing integrity?

All these questions can be answered by building a digital prototype using Dynamic Simulation and Stress Analysis. By combining the design tools available in the standard Autodesk Inventor software with the Dynamic Simulation and Stress Analysis capabilities in the Autodesk® Inventor™ Professional software, designers can quickly build and validate an optimum product that enables them to complete the tasks identified in the following illustration.

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Size bearings using reactions.

Find peak stresses using motion loads.

Size actuators using reaction loads.

Evaluate the global motion and time cycle.

Chapter 4: Engineering Problems and Solutions

This lesson contains a collection of real-world engineering design problems. Each design problem is unique and offers a recommended approach or workflow for solving the problem using Dynamic Simulation and/or Stress Analysis. These engineering design problems include: 1. 2. 3. 4. 5.

Calculating the stress on a wheelie bar. Calculating the maximum acceleration of a cross subassembly. Validating the robustness of an arm linkage. Creating a cam part from motion outputs. Sizing a spring for a bike suspension.

Objectives After completing this lesson, you will be able to: ■

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Use Stress Analysis to apply boundary conditions and analyze an initial design. Based on the initial stress analysis results, revise the design in the part environment for reanalysis. Use Dynamic Simulation to define realistic contact mechanisms incorporating frictional and restitutional properties. Use Dynamic Simulation to export motion loads to Stress Analysis. In Stress Analysis, apply the motion loads and perform a stress analysis to view initial results and modify geometry to satisfy design criteria. Use Dynamic Simulation to trace the motion of a component during the simulation and then use this trace curve to create a part. Use Dynamic Simulation to identify the length, stiffness, and tension requirements of a spring for a bike suspension.

Lesson: Solving Design Problems

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Design Problem 1: Calculate the Stress on a Wheelie Bar Design problem – Optimizing a design can become a lengthy process, especially when designers and analysts are working in isolation or when a physical prototype is required to test the initial design. This task becomes more challenging and tedious when you need to revise the design.

Set the Boundary Conditions for the Wheelie Bar 1.

Open Stress_WheelieBar.ipt.

2.


3.

The wheelie bar assembly must be designed to withstand a total load of 700 N because there are two brackets and the force is divided between them. The force of 350 N needs to be applied at 10 degrees from the vertical position.

Design solution – Using Stress Analysis you can easily apply boundary conditions, including forces and constraints, to analyze the initial design using a digital prototype. Based on the initial stress analysis results, you can easily make changes to the component in the part environment for reanalysis. In this exercise, you do the following: 1. Set boundary conditions for the wheelie bar. 2. Perform an initial analysis of the wheelie bar to check for strength and deflection. 3. Make design changes to the wheelie bar and then reanalyze.

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Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 4: Engineering Problems and Solutions. Click Design Problem1: Calculate the Stress on a Wheelie Bar.

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On the panel bar, click the Force tool. Select the upper hole (1) on the right side of the part. In the Force dialog box, expand the dialog box. Select Use Components. In the Fy field, enter -350N*sin(80deg). Make sure the Fx and Fz values are set to 0. Click OK.

4.

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5.

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The wheelie bar is supported by the bolt through the axle and needs to be fully constrained using the fixed constraint at the bolt hole.

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Click Applications menu > Part. Split both faces top and bottom equally as shown.

On the panel bar, click the Fixed Constraint tool. Select the bolt hole and click OK.

The wheelie bar is also prevented from rotating around the bolt hole because the bar fits tightly over the frame rail. When a force is applied, the wheelie bar bends down and tries to rotate around the bolt hole. Although the constraint on the bolt prevents rigid body rotation, it does not prevent the bar from deforming into the space occupied by the frame rail. To prevent rotation, you need to fix the Y direction on the faces that make contact with the top and bottom of the frame rail using frictionless constraints.

6.

To constrain the split faces: ■

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Click Applications menu > Stress Analysis. On the panel bar, click the frictionless constraint. Select the top and bottom split faces as shown. Click OK.

You constrain only half of each face because the other half must be free to pull away from the frame rail as the wheelie bar deforms. TIP: Sketch a line on each face and then split each face using the sketched line.


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Perform an Initial Analysis of the Wheelie Bar

Make Design Changes to the Wheelie Bar 1.

1.

On the panel bar, click the Stress Analysis Setting tool. ■

Set Mesh Relevance to 0 if it is not already set. Clear the Result Convergence check box if it is selected. Click OK.

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2.

On the Standard toolbar, click Stress Analysis Update.

3.

In the browser, double-click Safety Factor. The factor of safety is approx 1.4.

In the browser, expand the Features folder. ■ ■

2.

Right-click Fillet3. Click Unsuppress Features.

On the Standard toolbar, click the Stress Analysis Update button. ■

In the browser, in the Results folder, double-click Safety Factor.

Even though the factor of safety has increased, it is still less than 2. The design requires additional alterations. 4.

The design target is 2. Therefore the component has failed. While design alterations are required, first you create a report. ■

On the panel bar, click Report. Minimize the report. Do not close the report.

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3.

Click Applications menu > Part.

4.

Add the rib to wheelie bar as shown.

5.

On the panel bar, click Fillet. ■

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8.

Add 4 mm radius fillets to the four edges as shown. Click OK.

6.


7.

On the Standard toolbar, click Stress Analysis Update to rerun the analysis.

In the browser, double-click Safety Factor to display the results.

Because the factor of safety is greater than 2, you can conclude that the component is safe for operation based on the design criteria. 9.

On the panel bar, click Report to generate a new report. Compare the results with the original report.

10.



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Design Problem 2: Calculate the Maximum Acceleration of a Cross Subassembly Design Problem – Traditionally, the ability to accurately study complex contact mechanisms could be achieved only by either building a physical prototype or through extensive research and development. The major disadvantage of these methods is that they are both time-consuming and costly.

Apply 2D Contacts Between the Cross Subassembly and Rotor 1.

Open GenevaDriveSDP.iam.

Design Solution – Using Dynamic Simulation, you can easily create realistic contact mechanisms that incorporate frictional and restitutional properties. This enables you to simulate realistic conditions and analyze mechanisms confidently and efficiently. In this exercise, you do the following: 1. Apply 2D contacts between the cross subassembly and rotor, including specifying frictional and restitution properties. 2. Apply rotational velocity to the rotor. 3. Determine maximum acceleration of the cross subassembly.


Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 4: Engineering Problems and Solutions. Click Design Problem 2: Calculate the Maximum Acceleration of a Cross Subassembly.

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The joints for the Geneva drive have already been applied. First you apply a coefficient of friction to the contact joints between the cross and rotor subassemblies. 2.

Click Applications menu > Dynamic Simulation. In the Dynamic Simulation dialog box, read the message about migrating legacy joints and click OK.

3.

In the Dynamic Simulation browser, rightclick n°3 : 2D Contact (cross:1, rotor:1). Click Properties.

4.

In the n°3 :2D Contact (cross:1, rotor:1) dialog box: ■ ■ ■

5.

For Restitution, enter 0. For Friction, enter 0.15. Click OK.

Apply Rotational Velocity on the Rotor 1.

In the Dynamic Simulation browser, rightclick n°2 :Revolution (frame:1, rotor:1). Click Properties.

2.

In the n°2 :Revolution (frame:1, rotor:1) dialog box:

In the Dynamic Simulation browser, rightclick n°4 :2D Contact (cross:1, rotor:1). Click Properties.

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6.

Click the Dof (1) R tab. (1) Click Edit Imposed Motion. (2) Select Enable Imposed Motion. (3) Select Velocity. (4) Click the arrow next to the edit window. Click Constant Value. (5) In the edit window, enter -360 deg/s. (6) Click OK.

In the n°4 :2D Contact (cross:1, rotor:1) dialog box: ■ ■ ■

For Restitution, enter 0. For Friction, enter 0.15. Click OK.


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3.

In the Dynamic Simulation browser, notice that the revolution joint n°2 :Revolution (frame:1, cross:1) has a hash mark (#) added to the icon, signifying that a force has been imposed on the joint.

Determine Maximum Acceleration of Rotor 1.

In the Simulation Panel: ■ ■ ■

4.

In the browser, right click n°4 :2D Contact (cross:1, rotor:1). Click Properties. In the n°4 :2D Contact (cross:1, rotor:1) dialog box: ■

Click Invert Normal as shown (1). Click OK.

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Next, you run the simulation to view the resulting forces in the graphics window.

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For Final time, enter 2 s. (1) For Time Mode, enter 200. (2) Click Run or Replay Simulation. (3)

Next, you open the Output Grapher to view the results. 2.

On the Dynamic Simulation panel bar, click Output Grapher.

3.

If the Output Grapher is minimized, expand it by placing your cursor on the corner of the title bar as shown. Hold down your left mouse button and drag to resize.

When the Output Grapher is visible, you select the information you wish to display. For this simulation, you want to determine the acceleration of the cross as the rotor rotates at one turn per second. Then you determine the maximum acceleration and the point at which it occurs. 4.

6.

In the Graphics area of the Output Grapher, a graph of the items selected in the browser is displayed. The graph displays the time (1) divided in 0.25 second increments, and the acceleration (2) measured in degrees per second.

In the Output Grapher browser: ■ ■ ■

Under Positions, clear p[1.1]. Expand Accelerations. Select a[1.1].

Next, you use the Output Grapher to determine the maximum acceleration of the cross and the point at which this acceleration occurs. 7. 5.

Right-click anywhere in the a[1.1] column. Click Search Max.

Notice that the Output Grapher updates to display the information that you selected. In the Values area, two columns are displayed: ■

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Time (1): The total time of the simulation is divided by the number of images specified in the Simulation Panel. a[1.1] (2): This column displays the acceleration value in relation to the time.


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8.

In the Output Grapher: ■

The maximum acceleration is highlighted in the Values area. (1) The time bar displays on the graph showing the time of the maximum acceleration. (2) The assembly updates to show the position of the rotor subassembly at maximum acceleration. (3)

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9.

Close the Output Grapher. In the Simulation Panel, click Activate Construction Mode.

10.


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Design Problem 3: Validate the Robustness of an Arm Linkage Design Problem – In the course of designing a window glass lift mechanism, the designer needs to verify that one of the arms can withstand the stresses of lifting and lowering the window glass. Developing a physical prototype would be costly and timeconsuming. Relying only on engineering experience could introduce a significant element of risk or introduce an overdesign scenario. Design Solution – Using Dynamic Simulation, you can simulate the mechanism and export the motion loads to Stress Analysis. In Stress Analysis, you can apply the motion loads to the component and perform a stress analysis to view initial results. Based on these results, you can modify the part geometry to satisfy the design criteria.

Perform Initial Analysis of Second Arm In this portion of the exercise, you calculate the stresses in the second arm component. After performing the stress analysis, you view the equivalent stress, safety factor, and deformation for the component and then generate a report for comparison. 1.

Open WindowGlassLeverFEA-DP3.iam.

2.

In the browser, right-click Second Arm. Click Edit.

3.


In this exercise, you do the following: 1. Conduct an initial analysis of the second arm using motion loads exported from Dynamic Simulation. 2. Modify the second arm design and reanalyze.

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On the panel bar, click Motion Loads. Click OK.

Notice that the loads have already been transferred from the Dynamic Simulation environment.

Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 4: Engineering Problems and Solutions. Click Design Problem 3: Validate the Robustness of an Arm Linkage.


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4.

On the Standard toolbar, click Stress Analysis Update. After a few moments the part updates to show the effect of the stress on the connecting arm at the selected time step of the dynamic simulation. NOTE: Due to the complex calculations required, this update may take several minutes to complete.

Next, you change the view to determine the total deformation of the part. 6.

In the browser, under the Results folder, double-click Deformation. Notice the color bar on the left. It shows that the maximum deformation of the part is 7.2716 mm and the minimum deformation is 0.

Equivalent stress can be used to obtain a reasonable estimation of fatigue failure, especially in cases of repeated tensile and tensile-shear loading. Next you change the display to view the safety factor for the part. The safety factor identifies the areas of the model that are likely to fail under load. 5.

In the browser, under the Results folder, double-click Safety Factor. Notice that the view updates with a new color bar, and the part display updates to reflect the safety factor values. The red areas highlight where the part’s safety factor is 1 or less and indicate areas where failure is likely to occur. The part has a minimum factor of safety of 0.635. This means it has gone beyond the elastic limit and that the part has failed.

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Next, you generate a report that displays all of the stresses, the deformation, and safety factors on a single HTML page.

7.

On the panel bar, click Report. A Microsoft® Internet Explorer window opens displaying a page with part information on tables, and images of the different types of stresses and their associated color bars. ■ ■

1.

In the browser, under Second Arm:1, expand the Features folder. ■

Right-click Fillet2. Click Unsuppress Features.

Minimize the report window. Do not close the report.

Modify Second Arm Design In this portion of the exercise, you make changes to the second arm and rerun the stress analysis to see the effect of the changes. The part had an initial safety factor value of less than 1, and the simulation indicates that the part would fail under normal use. You make changes to the design in order to increase the safety factor to an acceptable value. Finally you generate a report of the stress analysis to compare with the original version of the part.

2.

Notice the ribs in each of the openings. These were created and suppressed in the event that the part would need extra strength.

Next, you perform a stress analysis on the revised part. 3.

On the Standard toolbar, click Stress Analysis Update. The initial view displays the equivalent stress values for the Second Arm:1.


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4.

You recall the deformation values to compare with the original version of the part. ■

6.

■

In the browser, under the Results folder, double-click Deformation. Notice the minimum and maximum values for the deformation of the part.

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The safety factor is to close to 1 at a value of approx 1.0451.

■

The maximum deformation is now 3.0968.

7. 5.

In the browser, double-click Safety Factor. Notice that minimum factor of safety is now greater than 1.

To reduce the stress, you alter the fillet size around the high stress area. ■

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8.

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In the browser, double-click Equivalent Stress. Zoom in to the model to see the maximum stress area around the fillet, as shown.

In the browser, in the Features Folder, right-click Fillet2. Click Edit Feature. In the Fillet dialog box, change the radius from 2 to 4 mm. Click OK.

On the Standard toolbar, click Stress Analysis Update to rerun the analysis. The stress has reduced from 263MPa to 234MPa. The maximum stress has moved to the back fillet as shown.

9.

10.

In the browser, double-click Safety Factor. The factor of safety has increased again to 1.1725.

11.

Challenge Task: If you want to further increase the factor of safety, then you can add further ribs or alter other geometry.

12.


13.


Finally, you generate a report of the stress values to compare with the original version of the part. ■

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On the Stress Analysis panel bar, click Report. A second Microsoft® Internet Explorer window is displayed with an HTML page showing a report of the revised part statistics and the results of the stress analysis. Compare the latest report to the initial report. Save these reports for comparison purposes and as a record to show that the analysis was performed.


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Design Problem 4: Create a Cam Part from Motion Outputs Design Problem – Designing a cam is often a tedious process, especially if you approach the problem using data generated from mathematical expressions and equations from several different sources. The task becomes even more challenging when you need to revise the cam design as a result of a change in your mechanism and/or function.

Create Joints Automatically from Assembly Constraints In this portion of the exercise, you convert all assembly constraints to joints. 1.

Open Cam_To_Build.iam.

2.


3.

In the Dynamic Simulation browser, notice that all of the subassemblies are shown under the Grounded node because no joints have been applied.

Design Solution – Using Dynamic Simulation, you can easily create a cam by tracing the motion of a component during the simulation. You can then use this trace curve to easily create a cam part. This process also simplifies the task of revising or replacing your cam part as a result of a change in your mechanism design. In this exercise, you do the following: 1. Create joints automatically from existing assembly constraints. 2. Set the initial closed position of the valve. 3. Import time and position data for the follower from a text file using the Input Grapher. 4. Create a trace of the follower relative to the shaft. 5. Export the trace of the follower to a sketch to create the cam. 6. Create the 3D cam part from exported trace data in the part environment.


Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 4: Engineering Problems and Solutions. Click Design Problem 4: Create a CAM Part from Motion Outputs.

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4.

To automatically update the assembly constraints to a standard joint: ■

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5.

6.

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On the panel bar, click Dynamic Simulation Settings. In the Dynamic Simulation Settings dialog box, select Automatically Update Translated Joints. Click OK.

In the browser, notice that all of the assembly constraints are translated into joints. All are shown below the Standard Joints folder.

In the graphics window, place the cursor (1) over the C06:1 valve as shown.

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Press and hold the left mouse button and drag in the direction as shown (2). Click Undo after you have checked the mechanism to enable the mechanism to go to its original position.

In the next section, you set the initial position of the C06:1 valve to its closed position.

Set the Initial Closed Position of the Valve 1.


2.

On the panel bar, click Constraint. ■

■ ■

In the Place Constraint dialog box, under Solution, click Flush. Select the two faces as shown. Click OK.

In the next step, you test the joints to verify that the initial mechanism is working correctly.


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3.

The flush constraint was used only to move the C06:1 component to its closed position. Now suppress the Flush:4 constraint as shown. In the browser, right-click the Flush constraint. Click Suppress.

Notice that this offset resets the position value to 0 for the current position of the nº 2 Prismatic (Ground:1, C06:1) joint.

Import Time/Position Data of Follower from a Text File Using the Input Grapher

4. 5.

Click Applications menu > Dynamic Simulation. In the browser, expand the Standard Joints node. ■

Right-click nº 2 Prismatic (Ground:1, C06:1). Click Properties. In the nº 2 Prismatic (Ground:1, C06:1) dialog box, click the Dof 1 (T) tab. (1) Right-click in the Position window. Click Set Offset. (2) Click OK.

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1.

In the browser, right-click nº 2 Prismatic (Ground:1, C06:1). Click Properties.

2.

In the nº 2 Prismatic (Ground:1, C06:1) dialog box: ■ ■ ■ ■ ■ ■

Click the Dof 1 (T) tab. (1) Click Edit Imposed Motion. (2) Select Enable Imposed Motion. (3) Select Position. (4) Select Input Grapher. (5) Click in the edit box. (6)

3.

When the Input Grapher is displayed, for the law of motion, select Spline as shown.

6.

In the browser, right-click nº 6 Revolution (Ground:1, Shaft:1). Click Properties. In the nº 6 Revolution (Ground:1, Shaft:1) dialog box: ■ ■ ■ ■ ■ ■ ■

4.

Click the Dof 1 (R) tab. (1) Click Edit Imposed Motion. (2) Select Enabled Imposed Motion. (3) Select Velocity. (4) Select Constant Value. (5) In the edit box, enter 360 deg/s. (6) Click OK.

In the Input Grapher: ■ ■ ■

■ ■

Click Replace the Current Law. (1) Click Load a Spline. (2) Navigate to the location of your student dataset files. Select Cam_To_Build.txt. (3) Click Open. Make sure X1 = 0 and X2 = 1.

Create a Trace of the Follower Relative to the Shaft

5.

1.

In the browser, right-click Traces. Click Add Trace.

2.

Select the circular edge of the follower C3:1 as shown.

Click OK twice.


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3.

Choose the shaft as the reference geometry.

2.

In the browser, right-click Trace C3:1. Click Export to Sketch. Select the shaft as shown. A sketch with the trace is created on the selected component.

4.

Click the Trajectory color swatch. In the Color dialog box, select Pink. Click OK. In the Trace dialog box, click OK.

Export the Trace of the Follower to a Sketch to Create a Cam 1.

Run the simulation.

Create a Cam Part from the Exported Trace

The following trace is produced at the end of the simulation.

1.


NOTE: Do not restart the simulation.

2.

In the browser, double-click Shaft:1 to edit the part.

3.

Double-click Sketch11 to edit the sketch. ■

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On the panel bar, click Offset. Select the exported sketch. Offset the new sketch toward the inside of the existing sketch geometry. Place a 5 mm dimension between two curves.

4.


5.

Extrude the profile using a mid-plane extrusion to a depth of 15 mm.

6.

Change the cam feature color to pink. ■

■

■

In the browser, right-click the new feature. Click Properties. In the Feature Properties dialog box, in the Feature Color Style list, select Pink. Click OK.

7.


8.


9.

In the Simulation Panel, click Construction Mode.

10.

Rerun the simulation.

11.



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Design Problem 5: Size a Spring for a Bike Suspension Design Problem – In order for a bike suspension to function properly, you need to ensure that the spring has enough stiffness and travel to overcome a known force exerted on the rear wheel and frame. The frame design with the appropriate joints and environmental constraints is known, and has already been defined. To complete the design, you need to determine the stiffness and length (or travel) of the spring.

Convert Assembly Constraints to Joints Automatically 1.

Open Bike_Suspension.iam.

2.


3.

In the browser, notice that all of the joints have been created automatically.

Design Solution – Using Dynamic Simulation, you can easily create and define a mechanism that accurately represents the realistic behavior of forces. With these actions, you can easily identify the appropriate spring length, stiffness, and tension, all of which are required to ensure a properly functioning bike suspension design. In this exercise, you do the following: 1. Convert assembly constraints to joints automatically. 2. Create an external force on the rear axis using the Input Grapher. 3. Run the unknown force to determine the equilibrium state of the mechanism. 4. Determine the spring length and plot the spring behavior.


Completing the Exercise To complete the exercise, follow the steps in this book or in the onscreen exercise. In the onscreen list of chapters and exercises, click Chapter 4: Engineering Problems and Solutions. Click Design Problem 5: Size a Spring for a Bike Suspension.

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This is because the Automatically Update Translated Joints option is selected in the Dynamic Simulation Settings.

In the next step you test the joints to verify that the initial mechanism is working correctly. 4.

In the graphics window, place the cursor (1) over the Oscillating Arm:1 as shown. Press and hold the left mouse button and drag in the direction as shown. (2) 2.

Notice that Trace1 is added in the browser.

NOTE: This export of trajectory data for the force enables you to select X, Y, Z data in the Output Grapher. 3.

On the panel bar, click Force. Select the endpoint of the Oscillating Arm:1. (1) ■

5.

On the Standard toolbar, click Undo to return the mechanism to its original position.

■

■

Select the axis for direction. (2) Expand the Force dialog box. Select the Display option. (3) For Scale, enter 0.0001.

Create an External Force on the Rear Axis Using the Input Grapher 1.

In the browser, right-click Traces. Click Add Trace. ■

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Select the endpoint of the Oscillating Arm:1. (1) Clear Display Trace Value for the Trajectory check box. (2) Select Output Trace Value for the Trajectory check box. (3) Click OK.


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4.

In the Force dialog box, from the value edit box, select Input Grapher.

5.

In the Magnitude dialog box, click Select Reference. (1) ■

6.

In the Magnitude dialog box, enter the following coordinates: X1 = 0 mm, Y1 = 500 N, X2 = 100 mm, Y2 = 2000 N.

In the Select Reference dialog box, expand Trace1. Select the Z coordinate of Trace1 (Oscillating Arm). (2)

■

NOTE: These actions create a linear behavior between 0 mm and 100 mm. Beyond these points the value is constant, which you need to change so that the whole motion is linear even beyond these points. 7.

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Click the Next Sector button.

8.

■

In the Magnitude dialog box, under the Out of Definition area, select On the Right of the Last Point. (1) Select Constant Slope. (2)

■ ■ ■ ■

9.

From the Joint list, select Revolution (Frame:1, Oscillating Arm:1). (4) For Final Position, enter -10 deg. (5) For # of steps, enter 20. (6) Expand the dialog box. Select Display. (7) For Scale, enter 0.0001. (8)

In the Magnitude dialog box, under the Out of Definition area, select On the Left of the First Point. (1) Select Constant Slope. (2)

2.

10.

Click OK to close the Magnitude dialog box.

11.

Click OK to close the Force dialog box.

Click OK.

Run the Unknown Force In this portion of the exercise, you calculate the required jack (or compression force of the spring) for a set of specified positions to keep the mechanism in static equilibrium when the force is applied. 1.

On the panel bar, click Unknown Force. ■

■

■

In the Unknown Force dialog box, select Jack. (1) For Location 1, select the point as shown. (2) For Location 2, select the point as shown. (3)

NOTE: The results for the unknown force are given as a function of the step number rather than as a function of time. The unknown force is accessible in the Unknown Force folder. 3.

Close the Output Grapher.


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Determine the Spring Length and Plot the Spring Behavior 1.

On the Simulation Panel, click Construction mode.

2.

In the browser, right-click Traces. Click Add Trace. ■

Select a point as shown. (1) Clear the Display Trace Value check box for Trajectory. Select the Output Trace Value check box for Trajectory. Click Apply.

■

■

■

3.

Select a point as shown. (2)

4.

On the panel bar, click Unknown Force. Click OK.

5.

In the Output Grapher, click the New Curve icon.

6.

Using Windows® Explorer, browse to the location of your dataset files and open formula.txt.

7.

Select and copy all text.

NOTE: Make sure you select the small circle. ■

Clear the Display Trace Value check box for Trajectory. Select the Output Trace Value check box for Trajectory. Click OK.

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194

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8.

For Name, enter Spring_Length. Paste the selected text in the equation field.

11.

Right-click Spring_Length. Click Set as Reference.

9.

Click OK.

12.

The jack force is displayed as a function of the spring’s length.

NOTE: This formula defines the distance between the two selected points. Where:

10.

A new variable is created in User Variables folder. Clear the selection for Spring_Length.

NOTE: The graph has a minimum value of 1094 N which is the preload, and a maximum value of 6161 N to react against the applied force to gain equilibrium. From the curve, you can manually calculate the gradient to give you a value for the stiffness of the spring (or jack). The maximum spring length is 373.7 mm. Calculation of the gradient: K (Spring Stiffness) = (6161 - 1094) / (373.7 284.5) = 5067 / 89 = 56.8 N/ mm NOTE: Actual values may vary. 13.



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Chapter Summary This chapter offered you a chance to practice using the tools and techniques you learned in previous chapters to solve real-world engineering and design problems. Because each design problem was unique, different workflows and approaches were required to solve these problems. Having completed this chapter, you can: ■

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Use Stress Analysis to apply boundary conditions and analyze an initial design. Based on the initial stress analysis results, revise the design in the part environment for reanalysis. Use Dynamic Simulation to define realistic contact mechanisms incorporating frictional and restitutional properties. Use Dynamic Simulation to export motion loads to Stress Analysis. In Stress Analysis, apply the motion loads and perform a stress analysis to view initial results and modify geometry to satisfy design criteria. Use Dynamic Simulation to trace the motion of a component during the simulation, and then use this trace curve to create a part. Use Dynamic Simulation to identify the length, stiffness, and tension requirements of a spring for a bike suspension.


Appendix

A Additional Support and Resources

ApendixA:

A variety of resources are available to help you get the most from Autodesk® software: ■ ■ ■ ■ ■ ■ ■

Courseware from Autodesk (AOTC, AOCC, AATC) Autodesk Services and Support Autodesk Subscription Autodesk Consulting Autodesk Partners Autodesk Authorized Training Centers (ATC®) Autodesk Certification

197

Courseware from Autodesk Autodesk publishes dozens of courseware titles every year designed to help users at all levels of expertise improve their productivity with Autodesk software. Courseware from Autodesk is the preferred classroom training material for Autodesk Authorized Training Centers (ATC) and Resellers. The same training materials are also well-suited for self-paced, standalone learning. Autodesk offers three brands of Courseware: Autodesk Official Training Courseware (AOTC) is developed by Autodesk for hands-on learning covering the most important software features and functionality. Autodesk Official Certification Courseware (AOCC) covers the knowledge and skills assessed on the Certified User and Certified Expert examinations. Autodesk Authorized Training Courseware (AATC) is created in cooperation with leading Autodesk partners, and includes a growing number of local-language titles.

Experience Real-world, Hands-on Learning Students simulate real-world projects and work through hands-on, job-related exercises. Most titles include a trial version of the software.

Reaching All Levels Autodesk has courseware titles to fit a wide range of skill levels. Beginners, advanced users, and those looking for transitioning and migration materials will find a title that fits their needs: ■ ■ ■ ■

Essentials titles teach the basics. Transition titles help smooth the way of upgrades and migrations. Advanced titles focus on advanced skills to improve productivity. Solution Series apply a process-based approach to real-world projects.

Role-specific Learning Paths Autodesk Courseware fits into a wide range of role-based Learning Paths so you can focus your training on skills and certifications that are most important to your job – and career. Within each Learning Path, you’ll find a series of courses that follow a natural progression and build on each other, delivering a powerful synergy of both theory and practical skills. Like a roadmap, each Learning Path provides you with a clear and effective route to your career destination. To embark on your personal learning path, talk with your local Autodesk Authorized Training Center www.autodesk.com/atc. An ATC instructor can lead you through the steps to improve your product knowledge and map the way to gaining Autodesk Certification www.autodesk.com/certification.

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Appendix A: Additional Support and Resources

Available for Most Autodesk Products ■

AutoCAD® Architecture (former Autodesk® Architectural Desktop)

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Autodesk® Productstream®

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AutoCAD® MEP (former Autodesk® Building Systems)

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Autodesk® Vault

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Revit® Architecture (former Autodesk® Revit® Building)

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AutoCAD®

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Revit® MEP (former Autodesk® Revit® Systems)

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AutoCAD LT®

■

Revit® Structure (former Autodesk® Revit® Structure)

■

Autodesk® VIZ

■

AutoCAD® Civil 3D® (former Autodesk® Civil 3D®)

■

AutoCAD® Map 3D (former Autodesk Map® 3D)

■

AutoCAD® Land Desktop (former Autodesk® Land Desktop)

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AutoCAD® Raster Design (former Autodesk® Raster Design)

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Autodesk® FMDesktop™

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Autodesk® 3ds Max®

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AutoCAD® Electrical

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Autodesk® Combustion®

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AutoCAD® Mechanical

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Autodesk® Fire®

■

Autodesk® Inventor™ (not a stand-alone product)

■

Autodesk® Smoke®

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Autodesk® Inventor™ Professional

Digital Site License Delivering training for a large number of students? A Courseware Digital Site License enables you to print courseware yourself to flexibly meet your training schedules and enrollment levels. Contact your Autodesk Reseller or inquire directly with Autodesk for more information.

Finding Courseware Courseware can be found in training classes offered by Autodesk Authorized Training Centers, Autodesk Resellers, or may be purchased directly from the Autodesk eStore (North America only). To find up-to-date information on the latest official Autodesk courseware titles, visit www.autodesk.com/aotc and browse the Courseware Catalog for titles and topics.

Feedback Encouraged If you have comments, suggestions for future titles, or general inquiries about Autodesk courseware, please email [email protected]. We value your feedback!


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Autodesk Services & Support Accelerate return on investment and optimize productivity with innovative purchase methods, companion products, consulting services, support, and training from Autodesk and Autodesk authorized partners. Designed to get you up to speed and keep you ahead of the competition, these tools help you make the most of your software purchase—no matter what industry you’re in. To learn more, visit www.autodesk.com/servicesandsupport.

Knowledge Base Search the support database for answers, hot fixes, tips, and service packs. Access the knowledge base from the main Autodesk Services & Support page at www.autodesk.com/servicesandsupport.

Contact a Reseller Get in touch with a reseller near you for information on product support programs that fit your needs. Find a reseller near you with our reseller locator at www.autodesk.com/reseller.

Discussion Groups Ask questions and share information in peer-to-peer forums. For more information visit the Discussion Groups area at www.autodesk.com/discussion.

Autodesk Subscription Ensure competitive advantage by keeping your design tools—and your design skills—up to date easily and cost-effectively with Autodesk® Subscription. Simplify your technology upgrades and boost your design productivity with the complete software, support, and training package from Autodesk Subscription. With Autodesk Subscription you get the latest releases of your Autodesk software, incremental product enhancements, personalized web support direct from Autodesk technical experts, and self-paced training (e-Learning) to help extend your skills. And with access to a range of exclusive community resources and members-only privileges, you can use the power of your design tools to the fullest and make the most of your technology investment. For more information visit www.autodesk.com/subscription.

Autodesk Consulting Make the most of your software investment with Autodesk Consulting. Get access to Autodesk technical and project management professionals, a global network of technical experts. For more details visit www.autodesk.com/consulting.

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Autodesk Partners Developer Center The Developer Center was created for developers seeking proven tools and technologies to produce superior design solutions. Whether you plan to customize existing Autodesk software or develop a completely new application, Autodesk is committed to making technology that is accessible to you. For more information visit www.autodesk.com/developer.

Autodesk Sparks Sparks developers leverage Autodesk Media and Entertainment’s strong technical and market expertise to deliver integrated, creative and workflow solutions to the post-production community. For more information visit www.autodesk.com/sparks.

Reseller Center Autodesk resellers understand your design processes and business requirements, and specialize in all kinds of industries and applications. You can maximize your productivity with Autodesk software with Reseller services, from implementation and customization to learning and training. To learn more and find a reseller near you, visit www.autodesk.com/resellers.

Partner Products & Services Autodesk works together with thousands of software development partners from around the world. In the Partner Products & Services catalog, you can search for and find detailed information on Autodesk partners around the world that further enhance our broad range of fully integrated and interoperable solutions, for every design profession you can imagine. For more information visit www.autodesk.com/partnerproducts.

Autodesk Authorized Training Centers Be more productive with Autodesk Software. Get trained at an Autodesk Authorized Training Center (ATC®) with hands-on, instructor-led classes to help you get the most from your Autodesk Products. Autodesk has a global network of Authorized Training Centers offering Autodesk-approved training of the highest quality. Every day, thousands of our customers are taught how to realize their ideas, faster, with Autodesk® software. You can perform smarter and better with Autodesk software products when you turn to an Authorized Training Center. ATCs are carefully selected and monitored to ensure you receive highquality, results-oriented learning. An ATC® is your best source for Autodesk-authorized classes, tailored to meet the needs and challenges facing today’s design professionals.

Find an Authorized Training Center With nearly 2000 ATCs around the world, there is probably one close to you. Visit the ATC locator at www.autodesk.com/atc to find an Autodesk Authorized Training Center near you.


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Autodesk Certification Gain a competitive edge with Autodesk Certification. Autodesk certifications validate that you have the knowledge and skills required to use Autodesk products. Demonstrate your software skills to prospective employers, advance your career opportunities, and enhance your credibility.

End-to-End Certification Solution Each solution includes the necessary components to help you independently validate your product skills. Application Proficiency Examination measures your readiness for Certification. Assess your skills on your schedule, anytime, using an on-line test to measure your knowledge of an Autodesk product. Autodesk Official Certification Courseware (AOCC) covers the knowledge and skills assessed on the Certified User and Certified Expert examinations. Autodesk Certified User Examination validates your core knowledge of an Autodesk application. Autodesk Certified Expert Examination validates that you can use the application to perform complex tasks typically associated with a power user.

Certification Benefits ■ ■ ■ ■

Immediate feedback on your certification status An Electronic Certificate with a unique serial number The right to use an official Autodesk end User Certification logo The option to display your certification status in the Autodesk Certified User database

For more information: Visit www.autodesk.com/certification to learn more and to take the next steps to get certified.

Useful Links

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Courseware: www.autodesk.com/aotc

Consulting: www.autodesk.com/consulting

Certification: www.autodesk.com/certification

Discussion Groups: discussion.autodesk.com

Find a Reseller: www.autodesk.com/reseller

Blogs: www.autodesk.com/blogs

Find an Authorized Training Center: www.autodesk.com/atc

Communities: www.autodesk.com/community

Services & Support: www.autodesk.com/servicesandsupport

Student Community: students.autodesk.com

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