Acceleration in Mechanisms

Topic

ACCELERATION IN MECHANISMS

CONTENTS 1) 2) 3) 4) 5)

Define mechanism Acceleration diagram for a link Acceleration of a point on a link Acceleration in the slider crank mechanisms Coriolis component of acceleration

INTRODUCTION The acceleration analysis plays a very important role in the development of  machines and mechanisms.

MECHANISM A mechanism is used to produce mechanicall transformations in a machine. mechanica This transformation transformati on could be any of the following. 3)It

may convert one speed to another speed.

4)It

may convert one force to another force.

5)It

may convert one torque to another torque. 6)It

may convert force into torque.

7)It

may convert one angular motion to another angular motion. 8)It

may convert angular motion into linear motion. 9)It

may convert linear motion into angular

EXAMPLE OF MECHANISM

Can crusher Simple press

Rear-window wiper 6

EXAMPLE OF MECHANISMS

Rowing type exercise machine Conceptual design for an exercise machine 7

EXAMPLE OF MECHANISM •

A good example is a crank, connecting rod rod and piston mechanism.

•

If the crank is turned, turned, angular motion is converted into linear motion of the piston and input torque is transformed into force on the piston.

SHAPING MACHINES AND ALSO KNOWN AS  THE WHITWOR WHITWORTH TH QUICK QUICK-- RETURN RE TURN MECHANISM.

ACCELERATION ACCELERA TION DIAGRAMS It is important to determine the acceleration of links because acceleration produces inertia forces in the link which stress the component parts of the mechanism.  Accelerations Accelerations may be relative or absolute. 

INERTIA FORCE 

One of the reasons reasons for finding the acceleration of links is to calculate the inertia force needed to accelerate or decelerate it. This is based on Newton’s second law.



Force Force = mass x acceleration accele ration F = M a

 Torque = moment of inertia x angular acceleration T = Iα

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ACCELERATION ACCELERA TION DIAGR DIAGRAM AM FOR FOR A LINK 

ACCELERATION OF A PARTICLE ACCELERATION PARTICLE WHOSE VELOCITY CHANGES BOTH IN MAGNITUDE AND DIRECTION AT ANY INSTANT HAS THE FOLLOWING TWO COMPONENTS :

 The centripetal or radial component, which is perpendicular to the velocity of the particle at the given instant. 2. The tangential component, which is parallel to the velocity of the particle at the given instant.

CENTRIPETAL OR RADIAL CENTRIPETAL COMPONENT

This radial component of acceleration acts perpendicular to the velocity VBA , In other  words, it acts it acts parallel  parallel to the link AB.

 TANGENTIAL COMPONENT  This tangential component of acceleration acts parallel to the velocity VBA. In other words, it acts it acts  perpendicular to the link AB.



ACCELERATION OF A POINT ON A LINK 

THE SLIDER-CRANK  MECHANISM Another mechanism that is commonly encountered encountere d is a slider crank. This mechanism also consists of a combination of four links, with one being designated as the frame. This mechanism, however, is connected by three pin joints and one sliding joints.

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SLIDER-CRANK MECHANISM The mechanism has a stroke stroke B1B2 equal twice the crank length r 2.

K   e n Y   o  u  s   s   e f   i  

Locations B1 and B2 are called the extreme positions (limiting) of the slider 

 U  C  B   e r  k   e l    e  y 

In-line slider crank mechanism 18

ACCELERATION DIAGR ACCELERATION DIAGRAM AM FOR FOR SLIDER S LIDER CRANK CR ANK MECHANISM

CORIOLIS COMPONENT OF ACCELERATION When a point on one link is sliding along another rotating link, such as in quick return motion mechanism, then the Coriolis component of the acceleration must be calculated. OR

the Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating reference frame.

CORIOLIS COMPONENT OF ACCELERATION

THE CORIOLIS COMPONENT OF ACCELERATION IS PRESENT IN (a) 4-bar mechanisms with 4 turning pairs (b) shape mechanism (c) slider-crank mechanism (d) Scotch Yoke mechanism