1. The document discusses various mechanisms including quick return motion mechanisms, straight line motion mechanisms, intermittent motion mechanisms, and steering gear mechanisms. 2. Specific mechanisms covered include the drag link mechanism, Whitworth mechanism, crank and slotted lever mechanism, Peaucellier's mechanism, Geneva wheel mechanism, ratchet and pawl mechanism, and Ackerman steering gear mechanism. 3. Key aspects of each mechanism such as their working principles, components, and applications are described.

1. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 1
Mechanisms:
Syllabus: Quick return motion mechanisms-Drag link
mechanism, Whitworth mechanism and Crank and slotted lever
Mechanism.
Straight line motion mechanisms Peaucellier's mechanism and
Robert's mechanism.
Intermittent Motion mechanisms -Geneva wheel mechanism
and Ratchet and Pawl mechanism. Toggle mechanism,
Pantograph, Ackerman
steering gear mechanism
UNIT - 2
SantoshA Goudar,B.E,M.Tech,(Ph.D).,
Asst.Professor,
MechanicalDepartment,
AIET,Moodbidri
1
1. Quick return motion mechanisms
a. Drag link mechanism,
b. Whitworth mechanism and
c. Crank and slotted lever Mechanism
2
a. Drag link mechanism
3
• This mechanism is obtained when the shortest
link is fixed and it is also called as double-crank-
mechanism, drag crank mechanism.
• The unique features of this linkage are
(a) there is no dead-centre phase,
(b) Links 2 and 4 both rotate and
(c) either 2 or 4 can be the driver link
• If the link-2 rotates with a uniform speed, link-4
will rotate with a non-uniform speed.
4

2. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 2
• When the point C moves through
the Arc C'CC" the link-4 moves through 180°
whereas Link-2 has moved through an angle 'α'.
• However, if the link-4 further moves from point
C" to C' it covers 180°, whereas the link-2 moves
through an angle 'β'.
• Since the angle 'α' is much larger than 'β' it is
evident that even when link-4 has moved through
the same angle i.e. 180° in both the cases
5
b. Whitworth mechanism
6
• When the driving crank CA moves from the
position CA1 to CA2 (or the link DP from the
position DP1 to DP2) through an angle α in the
clockwise direction, the tool moves from the
left hand end of its stroke to the right hand
end.
• Now when the driving crank moves from the
position CA2 to CA1 (or the link DP from DP2
to DP1 ) through an angle β in the clockwise
direction, the tool moves back from right hand
end of its stroke to the left hand end.
7
• The time taken during the left to right
movement of the ram (i.e. during forward or
cutting stroke) will be equal to the time taken
by the driving crank to move from CA1 to CA2.
Similarly, the time taken during the right to
left movement of the ram (or during the idle
or return stroke) will be equal to the time
taken by the driving crank to move from CA2
to CA1.
8

3. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 3
• Since the crank link CA rotates at uniform
angular velocity therefore time taken during
the cutting stroke (or forward stroke) is more
than the time taken during the return stroke.
• Quick return ratio:
The ratio between the time taken during the
cutting and return strokes is given by,
• This mechanism is mostly used in shaping and
slotting machines.
9
c. Crank and slotted lever Mechanism
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• In this mechanism link 3 is fixed. The slider
(link 1) reciprocates in oscillating slotted lever
(link 4) and crank (link 2) rotates.
• The ram with the cutting tool reciprocates
perpendicular to the fixed link 3 and AP1 and
AP2 are extreme positions.
• The forward or cutting stroke occurs when the
crank rotates from the position CB1 to CB2 (or
through an angle β) in the clockwise direction.
• The return stroke occurs when the crank
rotates from the position CB2 to CB1 (or
through angle α) in the clockwise direction.
11
• Since the crank has uniform angular speed,
therefore,
• Since the tool travels a distance of R1 R2 during cutting
and return stroke, therefore
Length of stroke
12

4. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 4
Straight line motion mechanisms
• The mechanisms that permits only relative
motion of an oscillatory nature along a
straight line. The mechanisms used for this
purpose are called straight line mechanisms.
• There are mainly two types of Straight line
motion mechanisms.
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1. Exact straight line motion
a. Peaucellier mechanism.
b. Hart’s mechanism.
c. Scott Russell’s Mechanism
2. Approximate straight line motion
a. Watt’s mechanism.
b. Modified Scott-Russel mechanism
c. Grasshopper mechanism
d. Tchebicheff’s mechanism.
e. Roberts mechanism
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Condition for generating Exact straight
line motion
• Let O be a point on the
circumference of a circle of
diameter OP
• Let OA be any chord and B is a
point on OA produced, such that
OA × OB = constant
• Then the locus of a point B will
be a straight line perpendicular to
the diameter OP
15
Proof:
Draw BQ perpendicular to OP produced. Join AP.
The triangles OAP and OQB are similar.
But OP is constant as it is the diameter of a circle,
therefore, if OA × OB is constant, then OQ will be
constant. Hence the point B moves along the straight
path BQ which is perpendicular to OP.
16

5. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 5
Peaucellier mechanism.
17
• It consists of a fixed link OO1 and the other
straight links O1A, OC, OD, AD, DB, BC and CA
are connected by turning pairs at their
intersections
• The pin at A is constrained to move along the
circumference of a circle with the fixed
diameter OP, by means of the link O1A
• In Fig., AC = CB = BD = DA ; OC = OD ; and
OO1 = O1A
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PROOF:
• It may be proved that the product OA × OB
remains constant, when the link O1A rotates.
• Join CD to bisect AB at R.
• Now from right angled triangles ORC and BRC,
we have,
19
Since OC and BC are of constant length,
therefore the product OB × OA remains
constant. Hence the point B traces a straight
path perpendicular to the diameter OP.
20

6. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 6
Robert's mechanism
21
• It is also a four bar chain mechanism, which,
in its mean position, has the form of a
trapezium.
• In fig., OO1 is fixed, OA=O1B , AP= PB, PQ is
perpendicular to AB, and here Q is tracing
point
• If the mechanism is displaced as shown by the
dotted lines in Fig., the point Q will trace out
an approximately straight line
22
Intermittent Motion mechanisms
1. Geneva wheel mechanism
2. Ratchet and Pawl mechanism
23
1. Geneva wheel mechanism
2
1
24

7. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 7
• A Geneva mechanism translates a continues
rotation into an intermittent rotary motion .
• A Geneva wheel consists of a driving wheel 1
carrying a pin P which engages in a slot of
driven member 2 as shown in figure.
• A member 2 is turned 1/4th of revolution for
each rotation of plate1
• The angle β is half the angle turned through
by member 2 during indexing period
• This mechanism is used in preventing over
winding of main spring in clock and watch
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2. Ratchet and Pawl mechanism
2- Ratchet Wheel
3 – Driving Pawl
4 – Pawl Lever
5- Supplementary Pawl
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• This mechanism is used to produce intermittent
circular motion from oscillating member.
• A ratchet consists of ratchet wheel, driving pawl
shown in fig.
• The driving pawl is held against the wheel by a
spring or gravity.
• As the pawl lever is raised, the driving pawl drives
the wheel in counter-clockwise rotation.
• A supplementary pawl is used to prevent the
ratchet from reversing.
• Ratchets are used in feed mechanisms, lifting
jacks, clocks, watches and counting devices.
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Steering Gear Mechanism
• The steering gear mechanism is used for changing
the direction of two or more of the wheel axles
with reference to the chassis, so as to move the
automobile in any desired path.
• In automobiles, the front wheels are placed over
the front axle & The back wheels are placed over
the back axle
• The steering is done by means of front wheels
only, The back wheels remain straight and do not
turn
28

8. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 8
29
• In order to avoid skidding, the two front
wheels must turn about the same
instantaneous centre ‘I’ which lies on the axis
of the back wheels.
Condition for correct steering:
• The condition for correct steering is that all
the four wheels must turn about the same
instantaneous centre.
• While turning to the left side, axes of the front
and the rear wheels meet at ‘I’.
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Let,
a = Wheel track,
b = Wheel base
c = Distance between the pivots A and B of the
front axle
Θ=The angle by which the inner wheel is turned;
φ=The angle by which the outer wheel is turned;
(Θ > φ),
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This is the fundamental equation for correct
steering. If this condition is satisfied, there will
be no skidding of the wheels, when the vehicle
takes a turn
32

9. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 9
Ackerman steering gear mechanism
33
Ackerman steering gear taking left turn.
34
• In Ackerman steering gear, the mechanism ABCD
is a four bar crank chain, as shown in Fig.
• The shorter links BC and AD are of equal length
and are connected by hinge joints with front
wheel axles. The longer links AB and CD are of
unequal length.
• The following are the only three positions for
correct steering.
1. When the vehicle moves along a straight path,
the longer links AB and CD are parallel and the
shorter links BC and AD are equally inclined to
the longitudinal axis of the vehicle, as shown by
firm lines in Fig.
35
2. When the vehicle is steering to the left, the
position of the gear is shown by dotted lines in
Fig.. In this position, the lines of the front wheel
axle intersect on the back wheel axle at I, for
correct steering
3. When the vehicle is steering to the right, the
similar position may be obtained.
• In order to satisfy the fundamental equation
for correct steering (cot φ – cot θ = c / b) , the
links AD and DC are suitably proportioned.
• The value of θ and φ may be obtained either
graphically or by calculations.
36
θ φ
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10. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 10
Toggle mechanism
37
tan2
F
P 
Or
38
Pantograph
• A pantograph is an instrument used to
reproduce to an enlarged or a reduced scale
and as exactly as possible the path described
by a given point
39
• It consists of a jointed parallelogram ABCD as
shown in Fig. It is made up of bars connected
by turning pairs.
• The bars BA and BC are extended to O and E
respectively, such that
OA/OB = AD/BE
• Thus, for all relative positions of the bars, the
triangles OAD and OBE are similar and the
points O, D and E are in one straight line
40

11. IV 'B' Sec Mechanical Department KOM Notes-2016
Santosh A. Goudar, B.E M.Tech (Ph.D.,)
Asst. Professor,Mechanical Department, AIET, Moodbidri 11
• It may be proved that point E traces out the
same path as described by point D.
• From similar triangles OAD and OBE, we find
that OD/OE = AD/BE
• Let point O be fixed and the points D and E
move to some new positions D′ and E′. Then
OD/OE = OD′/OE′
• A little consideration will show that the
straight line DD′ is parallel to the straight line
EE′.
41
• if E is constrained to move in a straight line,
then D will trace out a straight line parallel to
the former.
• A pantograph is mostly used for the
reproduction of plane areas and figures such
as maps, plans etc., on enlarged or reduced
scales. It is also used to guide cutting tools
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