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COSMOSMotion Essentials Training COSMOSMotion 2007
Image courtesy of National Optical Astronomy Observatory, operated by the Association of Universities
About this course
Prerequisites
Course Design Philosophy
Using this book
A note about about files
Conventions used in this book
Class Introductions
2
About this course
Prerequisites
Course Design Philosophy
Using this book
A note about about files
Conventions used in this book
Class Introductions
2
Design Validation Products COSMOSWorks Adv. Professional Designer
COSMOSFloWorks Flow Simulation
Professional Drop Test
Static Vibration & Buckling
Fatigue
Nonlinear
Thermal
Optimization
Post-dynamics
COSMOSEMS Electromagnetic
COSMOSMotion
3
What is Motion Simulation ?
Study of moving systems or mechanisms
Motion of a system is determined by – Mechanical joints connecting the parts – The mass and inertia properties of the components – Applied forces to the system (Dynamics) – Driving motions (Motors or Actuators) – Time
4
Mechanism types
Kinematic System – Movement of part(s) under enforced or constrained motion – Fully controlled and only one possible motion result irrespective of force and mass – Zero degree of freedom
Dynamic System – Movement of part(s) under free motion subject to forces – Partially controlled and infinite number of results depending on forces – Greater than zero degrees of freedom
5
Understanding Basics
Mass and Inertia – Newton’s First Law – Conservation of momentum
Degrees of freedom – Rigid body – Grounded parts – Moving parts
Constraints – Restrictions placed on a part’s movement in specific degrees of freedom – Mechanical joints are connections that restrict the movement of one part to another
Joint motion
Gravity
Pendulum restrained to pivot about mounting point
y x
6
Constraint Mapping
Mapping of SolidWorks assembly mates (constraints) to COSMOSMotion joints. 100+ ways of defining SolidWorks mates. Basic constraint types are merged to simplified mechanical joints. – One Orthogonal Concentric mate in SolidWorks becomes a Concentric joint. – One Coincident and One Orthogonal Concentric mates in SolidWorks becomes a Revolute joint. – One Point to Point coincident mate in SolidWorks becomes a spherical joint 7
User Interface
Motion toolbar
Pull down menu Intellimotion browser Intellimotion builder
8
User Interface
Motion toolbar
Pull down menu Intellimotion browser Intellimotion builder
9
Lesson 1 Governor Mechanism
Image courtesy of National Optical Astronomy Observatory, operated by the Association of Universities
Image courtesy of National Optical Astronomy Observatory, operated by the Association of Universities
Lesson 3 Topics
Review basic joint types in COSMOSMotion
Create Mechanical Joints
Apply motion to a joint Create and review results
20
Lesson 3: Basic Joint Types
Joints used to constrain the relative motion of a pair of rigid bodies by physically connecting them. Joint Primitives used to enforce standard geometric constraints
21
Lesson 3: Joint definition
Location
Direction
22
Lesson 3 Results
Torque required to drive the mechanism
23
Lesson 4 Coupler
Image courtesy of National Optical Astronomy Observatory, operated by the Association of Universities
Lesson 4 Topics
Simulate motion of gears using joint couplers Joint coupler to associate the movement of one joint with another Modeling gear-mate from SolidWorks model Conversion Convert RPM to deg/s 1 RPM = 1 min = 100 RPM =
360 degree 60 s 600 deg/s
25
Lesson 4: Couplers
Any one of the following joint combinations will create a coupler: – – – – – –
Image courtesy of National Optical Astronomy Observatory, operated by the Association of Universities
Lesson 5 Topics
Create springs and damper entities in COSMOSMotion Attach different parts together to move them as a single entity Constrain the motion of a cylindrical joint to achieve correct mechanism behavior Modify springs and dampers to achieve desired design goals
30
Lesson 5 Attaching Parts
Physically attach one part to another Two parts will be welded or rigidly connected to one another. No relative motion between the two parts Initial orientation between the two parts will be locked and will be maintained throughout the simulation
31
Lesson 5: Springs Tr a n s l a t i o n a l Sp r i n g F o r c e = -k (X - X 0 )n + F 0
Where: k = Spring stiffness coefficient (always > 0) X = Current distance between the spring connection points
X 0 = Reference length of the spring (Free length) n = Exponent defining spring character istic
F 0 = Reference force of the spring (preload) Positive force repels the two parts. Negative force attracts the two parts.
S i m i l a r f o r c e ex p r e s s i o n a p p l i e s t o T o r s i o n a l S p r i n g s 32
Lesson 5: Dampers Tr a n s l a t i o n a l D am p e r F o r c e = c*v n
Where: c - Translational damping coefficient v - Current relative velocity between parts at the attachment points n - Exponent.
S i m i l a r f o r c e ex p r e s s i o n a p p l i e s t o To r s i o n a l D am p e r s 33
Lesson 5: Results
gas_piston-1 not only translates along gas_cylinder-1 but also rotates. The rotation needs to be prevented
34
Lesson 5: Results Spring stiffness: 1 N/mm Damper Co-efficient: 5 N (sec/mm)
Velocity goal is satisfied Door does not stop in 30 seconds
Should we increase or decrease spring stiffness? 35
Lesson 5: Results Spring stiffness: 2 N/mm Damper Co-efficient: 10 N (sec/mm)
Velocity goal is satisfied Door stops in 30 seconds
36
Lesson 6 Hatchback Mechanism
Image courtesy of National Optical Astronomy Observatory, operated by the Association of Universities
Lesson 6 Topics
Create an Action Only force to simulate an
Change the mass properties of a part
Use Impact forces to control two parts from interfering each other
38
Lesson 6: Forces
Affect the dynamic behavior of a mechanism Do not prohibit or prescribe motion and so do not add or remove degrees-of-freedom from your model. Force Entities – – – – – – –
Translational and Torsional Springs Translational and Torsional Dampers Action-Only Forces/Moments Action-Reaction Forces/Moments Impact Forces Flexible Connectors Gravity
39
Lesson 6: Force Definition
Force Type – Whether the loading is a force or a moment.
Location
Direction – Along an axis defined by an edge, plane or cylindrical surface. – Along the line-of-sight between two points
Magnitude – Enter a pre-defined function expression (step, harmonic, spline). – Enter an equation directly into the Function Expression field using the library of built-in COSMOSMotion functions.
Intermittent force that is dependent on relative distance between two components). Impact forces are used to simulate the collision between two parts. As two parts approach within a specified distance, the impact force becomes active, and a force specified by the impact parameters is applied to both of the colliding parts. The collision is dependent on the materials and geometry of the bodies colliding.
44
Lesson 6: Impact Parameters
Impact Force = Spring Force + Damping Force Stiffness: Depends on material properties and curvature of interacting surfaces
Exponent: Determines impact force characteristic
Max Damping: Simulates energy loss in collision
Penetration: Depth at which maximum damping occurs. Length: distance at which the impact force is activated (parts contact)
45
Lesson 6: Impact Parameters Good numbers for impact parameters: Stiffness:
10000 lb/in
10000 N/mm
Exponent:
1.1-1.3
1.1-1.3
Damping:
0.1-100 lb-s/in
1-100
Penetration:
0.0001 in
0.01 mm
Height of Piston:
0.95 in
Impact Distance 1 in 0.95 in 0.9 in 0.85 in 1.3 in
Clearance Distance 0.05 0 -0.05 -0.15 0.35
in in in in in
Components interfere
This values are linearly proportionaly due to the exponent input.
d cannot be specified as 0 46
Lesson 6: Results Translational displacement of the concentric joint between the piston and cylinder parts
Notice that the displacement is held at 8 inches which means that the impact force does not allow further translation between the parts
47
Lesson 6: Results
Magnitude of the impact force applied
48
Lesson 7 Contacts
Image courtesy of National Optical Astronomy Observatory, operated by the Association of Universities
Lesson 7 Topics Apply Point to curve contact
Apply Curve to curve contact
Apply 3D Contact
50
Lesson 7: Understanding Contacts Point-curve - Restricts a point on one rigid Point-curve body to lie on a curve on a second rigid body.
Curve-curve - Constrains one curve to Curve-curve remain in contact with a second curve.
Intermittent curve-curve curve-curve - Applies a force to prevent curves from penetrating each other. Only active if the parts are touching
3D Contact – Applies a force to prevent bodies from penetrating each other. Only active if the parts are touching
51
Lesson 7: Impact Forces Vs Contacts Contact is similar to an impact force in that the material properties of the parts are used to define the contact parameters.
Contact differs from an impact force since any point along a curve or geometry is used in the contact
Contact simulates friction forces between parts.
52
Lesson 7: 3D Contact
Surface Representation of parts: – Tessellated Geometry
Faster but less accurate in certain contact situations like point to surface or multiple contacts
– Precise Geometry
Longer simulation time but produces accurate results
Contact Containers
53
Lesson 8 Railcar Mechanism
Image courtesy of National Optical Astronomy Observatory, operated by the Association of Universities
Lesson 8: Topics
Apply Gravity force to the mechanism
Create an Action-Reaction force to accelerate the railcar
Learn some advanced plotting techniques in COSMOSMotion
55
Lesson 8: Action Reaction Force
56
Lesson 8: Results Probing translational velocity plot of body-1
57
Lesson 8: Results Plotting multiple plots in the same XY graph
58
Lesson 8: Results Replacing X axis time scale with a desired results quantity
59
Lesson 9 Floor Jack Mechanism
Image courtesy of National Optical Astronomy Observatory, operated by the Association of Universities
Lesson 9 Topics Apply motion to a part
Use different types of motion functions
Make a design change and study mechanical advantage
61
Lesson 9: Part Motion
62
Lesson 9: Function Types Constant
Step Function
d0 = Initial value of displacement d1 = Final value of displacement t0 = Start step time t1 = Final step time
Harmonic
Amplitude; Frequency; Time Offset; Phase Shift; Average
63
Lesson 9: Function Types Spline
–You can use your own motion data to control your mechanism by importing data points. –To import data points, they must be in a .TXT or .CSV file format. –You may import an unlimited number of data points.
