18653229 Acceleration in Mechanisms

5/23/2018 18653229 Acceleration in Mechanisms

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CCELER TIONINMECH NISMS

Topic


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CONTENTS

1) Define mechanism

2) Acceleration diagram for a link3) Acceleration of a point on a link

4) Acceleration in the slider crank mechanisms

5) Coriolis component of acceleration


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INTRODUCTION

The acceleration analysis plays a very importantrole in the development of machines and

mechanisms.


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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.


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EXAMPLEOFMECHANISM

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Can crusher

Simple press

Rear-window wiper


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EXAMPLEOFMECHANISMS

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Conceptual design for an

exercise machine

Rowing type exercise machine


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EXAMPLEOFMECHANISM

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.


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CONSIDERTHENEXTMECHANISMUSEDINSHAPING

MACHINESANDALSOKNOWNASTHEWHITWORTH

QUICK- RETURNMECHANISM.


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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.


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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

Newtons second law.

Force = mass x acceleration F = M a

Torque = moment of inertia x angular acceleration T = I


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ACCELERATIONDIAGRAMFORALINK


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ACCELERATIONOFAPARTICLEWHOSEVELOCITYCHANGESBOTHIN

MAGNITUDEANDDIRECTIONATANYINSTANTHASTHEFOLLOWINGTWO

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.


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CENTRIPETALORRADIALCOMPONENT

This radial component of acceleration acts

perpendicular to the velocity VBA, In o ther words , i t

acts parallel to the l ink AB .


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TANGENTIALCOMPONENT

This tangential component of acceleration acts parallel to

the velocity VBA. In other words, itactsperpendicular to

the link AB.


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ACCELERATIONOFAPOINTONALINK


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THESLIDER-CRANKMECHANISM

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 onesliding joints.

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SLIDER-CRANKMECHANISMKen

Youssefi

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UCBerkele

y

In-line slider crank mechanism

The mechanism has a stroke

B1B2equal twice the cranklength r2.

Locations B1 and B2are calledthe extreme positions (limiting)

of the slider


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ACCELERATIONDIAGRAMFORSLIDERCRANK

MECHANISM


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CORIOLISCOMPONENTOF

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 whenthey are viewed from a rotating

reference frame.


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CORIOLISCOMPONENTOFACCELERATION


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THECORIOLISCOMPONENTOF

ACCELERATIONISPRESENTIN

(a) 4-bar mechanisms with 4 turning pairs

(b) shape mechanism

(c) slider-crank mechanism

(d) Scotch Yoke mechanism

18653229 Acceleration in Mechanisms

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