18653229 Acceleration in Mechanisms
Transcript of 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