BASICS OF MECHANISMS

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Single Slider Crank Chain In a four
bar kinematic chain there are four revolute
pairs. If one of this pairs is changed as
prismatic/sliding pair that kinematic chain is
called single slider crank chain. Link 1
Fixed Link Link 3 Connecting Rod
Link 2 Crank Link 4
Slider / Piston

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Inversions of Single Slider Crank Chain
As there are four links, fixing each link in
turn, four inversions can be obtained.
In the first inversion, where the link
with one revolute pair and one prismatic pair is
fixed. Example 1) I.C. Engine mechanism, in
which the fourth link piston is the input and
the crank is output. 2) In air compressor, in
which the second link crank is the input and the
piston is the output.

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Second Inversion of Single Slider Crank Chain
Second link in the original chain, ie., crank
with two revolute pairs is fixed, second
inversion is obtained.
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Examples for the Second Inversion 1. Whitworth
Quick Return Mechanism 2. Rotary Engine
Mechanism

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Third Inversion of Single Slider Crank Chain
Third link of the original chain, ie.,
Connecting Rod with two revolute pairs (length of
this link is more than crank) is fixed to obtain
third inversion.
Example 1. Oscillating
Cylinder Mechanism 2. Crank
and slotted lever quick return
mechanism
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Crank and Slotted Lever Quick Return Mechanism

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Fourth Inversion of Single Slider Crank Chain
In the original chain, if the fourth link
with revolute pair and prismatic pair is fixed,
then the fourth inversion is obtained.
Example Hand Pump
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Double Slider Crank Chain
This Chain has two revolute pairs and two
prismatic pairs. The first inversion is with a
link with revolute pair and prismatic pair is
fixed. Example Scotch Yoke Mechanism, which is
also called as Sinusoidal Generator.
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The Second inversion of the double slider crank
chain is obtained when the link with two
prismatic pairs is fixed. Example Elliptic
Trammel
X BC cos?
Y AC sin?
(X / BC) cos?
(Y / AC)
sin? (X2 / BC2)
cos2? (Y2 / AC2)
sin2?
(X2 / BC2) (Y2 / AC2) cos2? sin2?
(
1
Equation for
Ellipse.


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Third inversion of the double slider crank chain
is obtained when the link two revolute pairs is
fixed. Example Oldham coupling, which is used to
connect two parallel misaligned shafts.

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Straight Line Mechanisms
1.Chebyshev Straight Line Mechanism L1 2
Units, L 2 L 4 2.5 Units, L 3 1 Unit
P is the mid-point
of L 3 This is a
Double-Rocker Mechanism


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2. Hoekens Straight Line Mechanism L 1 2
Units, L 2 1 Unit, L 3 L 4 2.5 Units
Coupler point location from A is 5 units
This is a Crank-Rocker Mechanism

L 3
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3.Roberts Straight Line Mechanism L1 2
Units, L2 L3 L4 1
Unit Coupler Point P is 1 unit each from both pin
joint centres of coupler. This is a
non-Grashofian Double Rocker.
L 3
L1
L1
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4. Watts Straight Line Mechanism
L1 L3 2 Units, L2 1
Units Fixed link length is 4 units, and the
coupler point P is mid point of the
coupler. This is, also, a non-Grashofian Double
Rocker mechanism.

L1
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5.Peaucellier Exact Straight Line Mechanism
L1 L2 , L3 L4 ,
L5 L6 L7 L8 Free end point of the
Rhombus will trace Exact Straight Line If, L1
? L2 , then the same point will trace a circular
arc with very large radius, much larger than
the link lengths.

L1
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Ratchet and Pawl
RATCHET is a device that allows rotary or
linear motion in only one direction. It can be
used to move a toothed wheel one tooth at a time.
The part which is used to move the ratchet is
known as the PAWL. Motion developed by a ratchet
is intermittent motion. They are also used in the
freewheel mechanism of bicycle, clocks,
screwdrivers, jacks, and hoists. ESCAPEMENTS
are generally used in clocks with mechanical
motions. In clocks the escapement controls the
spring driven clock mechanism such that it moves
in regulated steps controlled by a pendulum or an
oscillating arm.
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• Ratchets and Escapements

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• Animation of Ratchet and Pawl Mechanism

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• Indexing Mechanisms
• A simple index
  mechanism consists
• of a hold or a
  hook that catches a pin on
  on an index wheel. The Clutch slips
• until a
  solenoid pulls the hold away,
• which frees
  the wheels to turn.
• Geneva
  Mechanisms are often used
• in machine
  tools. They are capable
• of indexing
  or partially rotating some
• part of a
  machine. In cinema projectors Geneva stop is used
  to move the film on one frame at a time.

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Animation of Indexing Mechanisms
External Geneva Wheel Internal
Geneva Wheel
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• Animation Contd

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• Double Slider Driven Geneva Mechanism
• The pin at the mid point of the green link, which
  moves in a circular path, drives a Geneva
  mechanism used to provide intermittent motion.

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• Rocking Mechanisms
• 1.Crank Rocker Mechanism
• 2.Quick Return Mechanism
• 3. Cam and Oscillating
• Follower Mechanism
• n 4. Toothed Rack System
• (1)
  (2)
• (3)
  (4)
  

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Offset Slider Mechanism
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ACKNOWLEDGMENT

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  pre-historic days to to-day, who have registered
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