ACCELERATION IN ACCELERATION IN

MECHANISMSMECHANISMS

Topic

CONTENTS

1) Define mechanism2) Acceleration diagram for a link3) Acceleration of a point on a link4) Acceleration in the slider crank mechanisms5) 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 mechanical transformations in a machine. This

transformation could be any of the following.

1)It may convert one speed to another speed.

2)It may convert one force to another force.

3)It may convert one torque to another torque.

4)It may convert force into torque.

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

6)It may convert angular motion into linear motion.

7)It may convert linear motion into angular motion.

EXAMPLE OF MECHANISM

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Can crusher

Simple press

Rear-window wiper

EXAMPLE OF MECHANISMS

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Conceptual design for an exercise machine

Rowing type exercise machine

EXAMPLE OF MECHANISM

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

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

CONSIDER THE NEXT MECHANISM USED IN SHAPING MACHINES AND ALSO KNOWN AS THE WHITWORTH QUICK- RETURN MECHANISM.

ACCELERATION 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 may be relative or absolute.

INERTIA FORCE

One of the 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 = mass x acceleration F = M a

Torque = moment of inertia x angular acceleration T = Iα

ACCELERATION DIAGRAM FOR A LINK

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

1. 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 COMPONENT

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

TANGENTIAL COMPONENT

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

ACCELERATION OF A POINT ON A LINK

THE SLIDER-CRANK MECHANISM

Another mechanism that is commonly encountered 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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In-line slider crank mechanism

The mechanism has a stroke B1B2 equal twice the crank length r2.

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

ACCELERATION DIAGRAM FOR SLIDER CRANK 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