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DIPLOMA IN Mechnical Engineering
2011-
2012
Mr.Vaibhav V Naik
Mechanical
Engineering
2011-2012
FUNDAMENTALS AND TYPEOF MECHANISM
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Fundamental and types of mechanism
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THEORY OF MACHINE
Theory of machine is Branch of engineering science which deals with thestudy of relative motion and forces between the various machine elements
:
Figure: Diagram of Theory of Machine
1. Statics
It is the branch of theory of machine, which deals with the forces and itseffect on the machine part while the latter is at rest.
2. Dynamics of machine
It is the branch of theory of machine, which deals with the forces and
effect of forces on the machine component when they act on them.
3. Kinetics
It is the branch of theory of machine, which deals with the inertia forces,
which are formed due to combined action of mass and motion of
machine elements.
4. Kinematics of machine
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
THEORY OF MACHINE
KINEMATICSDYNAMICS KINETICSSTATICS
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It is the branch of theory of machine, which deals with the relative motion
between the various parts of the machine, without considering the forces
1. Kinematic Link
a. Links are individual parts of a mechanism.b. Each parts of a machine which has a relative motion to some other parts isknown as Kinematic link.
Characteristics of the Kinematic link
1. It should have relative motion and
2. It should be a resistant body
Classification of the LINK
A. Depending upon the nature of the resistant bodies
1. Rigid link.
2. Flexible link.
3. Fluid link.
B. Depending upon the points at which the link is attached to mechanism
1. Binary link
2. Ternary link
3. Quaternary link
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A. Depending upon the nature of the resistant bodies
1. Rigid link
The links which do not undergo appreciable transformation while transmitting
the required motion and forces is known as rigid link.
Example:
a. Piston,
b. Connecting Rod of Steam engine.
2. Flexible Link
The links which are partly deformed transformation while transmitting the
required motion and forces in such a way that they don effect the required
transmission of motion is known as Flexible link.
Example:
a. Chain,
b. Belt and Spring
3. Fluid Link
The link which transmit the motion by fluid pressure as compression are
called fluid link.
Example:
a. Liquid used in Hydraulic presses
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B. Depending upon the points at which the link is attached to mechanism
1. Binary linkThe link which is attached to two points in the mechanism is called Binary
link.
2. Ternary linkThe link which is attached to three points in the mechanism is called Ternary
link.
3. Quaternary linkThe link which is attached to four points in the mechanism is called
Quaternary link.
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2. Kinematic Pair
The two links of the machine when in contact with each other are said to
form a pair if the relative motion between them is successfully constrained.
CLASSIFICATION OF KINEMATIC PAIR
A. According to the relative motion between them
1. Sliding pair. S
2. Turning pair.
3. Rolling pair.
4. Screw pair.
5. Spherical pair.
B. According to Nature of the contact
1. Lower pair.
2. Higher pair.
C. According to type of closure
1. Self closed pair.
2. Force closed pair.
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A. According to the relative motion between them
1. Sliding pair.
A sliding pair is said to be formed by two links such a manner that one link is
constrained to have a sliding motion relative to other link.
Example:
1. Piston and Cylinder,
2. Cross head and guides of Steam engine.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Sliding Pair
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2. Turning pair
A turning pair is said to be formed by two links such a manner that one link is
constrained to turn or revolve relative to other link.
Example:
Shaft with collar in circular hole.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Turning Pair
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3. Rolling pair.
A Rolling pair is said to be formed by two links such a manner that one link isconstrained to have a rolling motion over the other link.
Example:
Ball bearing forms Rolling pair.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Rolling Pair
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4. Screw pair.
When the two elements of pairs are connected in such a way that one
element can turn about the other by means of screw threads is known as
Screw Pair.
Example:
Bolt and nut is example of Screw Pair.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Screw Pair
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5. Spherical pair.
When the two elements of pairs are connected in such a way that one
element turn or swivels about the other fixed element, the pair formed is
known as Screw Pair.
Example:
Ball and socket is example of Spherical Pair.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure:Spherical Pair
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B. According to Nature of the contact
1. Lower pair.
When the two element of a pair have a surface contact when the relative
motion takes place and the surface of one element slides over the other, the
pair forced is known as lower pair.
Example:
a. The motion of piston and cylinder in the engine.
b. Shaft rotating in a bearing and
c. Nut turning on a screw.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Lower Pair
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2. Higher pair.
When the two element of a pair have a line or point contact when therelative motion takes place and the motion between the two element is
partially turning and partly sliding then the pair formed is know as Higher
pair.
Example:
The motion of cam and follower
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Higher Pair
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C. Kinematic pairs according to nature of mechanical constraint
1. Self Closed pair
When the elements of a pair are held together mechanically in such a way
that only the required kind of relative motion occurs , all the lower pairs and
some of the higher pairs are closed pairs.
Example:
The lower pair is known as closed pair.
2. Force Closed pair or Unclosed pair
When two links of a pair are not connected mechanically but kept in contact
either due to force of gravity or some spring action, they constitute an
unclosed pairs.
Example:
The motion of cam and follower
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TYPE OF CONSTARINED MOTIONS.
1. Completely constrained motion.
2. Incompletely constrained motion.
3. Successfully constrained motion.
1. Completely constrained motion.
When the motion between a pair is limited to definite direction irrespective of
the direction of force applied, then the motion is said to be a completely
constrained motion.
Example:
1. The motion of the square bar in square hole.
2. The motion of shaft with collars at each end in a circular hole.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Complete Constrained Motion
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2. Incompletely constrained motion.
When the motion between a pair can take place in more than one direction,
then the motion is said to be a completely constrained motion.
Example:
1. The motion of the circular bar in circular hole.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Incomplete Constrained Motion
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3. Successfully constrained motion
When the relative motion between the link is not completely constrained by
itself but it is made by some other means is called successfully constrained
motion.
Example:
1. Shaft in Footstep Bearing
2. The motion IC engine valve and piston in reciprocating inside an engine
cylinder.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Successfully Constrained Motion
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3. Kinematic Chain
When the kinematic pairs are coupled in such a way that the last linked is
joined the first link to transmit the definite motion it is called a kinematic chain.
To determine the given assemblage of links forms the kinematic chain
or not:
The two equations are:
1. l = 2p - 4
2. J = 3/2 * l - 2
l = number of links
p = number of pairs
j = number of joints
Three possible cases are
1. If L.H.S=R.H.S then it is Constrained kinematic chain
2. If L.H.S>R.H.S then it is Locked Chain
3. If L.H.S
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1. Arrangement of three links
2. Arrangement of four links
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure :Three Links
Figure :Four Links
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3. Arrangement of five links
4. Arrangement of six links
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure :Five Links
Figure :Sic Links
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FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
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Types of Joints in the Chain
1. Binary joints
When the two links are joined at the same connections, the joint is known
as binary joint
W.Kliens criterion of constraint
l = number of links
h = number of higher pairs
j = number of binary joints
j=4; l=4; h=0
j+h/2 = 3/2*l - 2
4+0 = 3/2*4 - 2
4 = 4
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Binary Joints
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L.H.S=R.H.S
2. Ternary Joints
When the three links are joined at the same connections, the joint is
known as ternary joints.
A.W.Kliens criterion of constraint
l = number of links
h = number of higher pairs
j = number of binary joints
j=7; l=6; h=0
j+h/2 =3/2*l 2
7+0 =3/2*6 2
7 =7
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Ternary Joints
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L.H.S=R.H.S
3. Quaternary Joints
When the four links are joined at the same connections, the joint is knownas Quaternary joints.
W.Kliens criterion of constraint
l = number of links
h = number of higher pairs
j = number of binary joints
j=12; l=9; h=0
j+h/2 = 3/2*l 2
12+0 = 3/2*9 2
12 = 11.5
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Quaternary Joints
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L.H.S>R.H.S
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Types of Kinematic chain
1. Four bar chain
2. Single slider crank chain.
3. Double slider crank chain
Inversion of the following types
1. Four bar chain
a) Beam engine.
b) Coupling rod of Locomotives.
c) Watts indicator mechanism.
d) Pantograph.
2. Single slider crank chain .
a) Pendulum pump or Bull engine.
b) Oscillating cylinder engine.
c) Rotary IC engine.
d) Crank and slotted lever quick return mechanism.
e) With worth quick return mechanism.
3. Double slider crank chain.
a) Elliptical trammel
b) Scotch yoke mechanism.
c) Oldhams coupling.
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3. MECHANISM
a. When one of the links of a kinematic chain is fixed, the chain is known as
mechanism.
b. It may be used for transmitting or transforming motion.
Example:
1. Engine indicator,
2. Typewriter.
Types of Mechanism
a. Simple mechanism (a mechanism with four links)
b. Compound mechanism (a mechanism with more than four link)
Differentiate between Machine and Mechanism
NO MACHINE MECHANISM
1. It is like the human body, ittransforms energy into usefulwork.
It is like a frame work and has adefinite motion between variouslinks.
2 It relates to energy only. It relates to motion.
3 It has many link. It also has many links.
4 Ex: lathe, shaper. Ex. watt indicator,typwriter
5
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4. Structure
It is the assemblage of a number of resistant bodies having no relative motion
between then and meant for carrying loads having a straining action.
Example:
1. A Railway bridge.
2. Roof Trusses
3. bridges,
4. buildings
5. machine frames
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Structure
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Differentiate between Machine and Structure.
NO MACHINE STRUCTURE
1 Has relative motion between themembers
Has no relative motion
2 Transforms available energy intopossible work.
Does not transform.
3 Members are meant to transmitmotion and forces.
Members are meant to acceptload
4 Example Shaper, lathe Example :Bridge.
5. Inversion
The method of obtaining the different mechanism by fixing the different links in
a kinematic chain is known as inversion of the mechanism.
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Important Terminologies and Definition
1. Machine
It is device which takes in the available energy and converts it into usefulwork.
When the mechanism is required to transmit the power or to do someparticular type of work, it then becomes a Machine.
Example: Shaper, Lathe machine
2. Mechanics( Theory of Machine)
Branch of engineering which deals with the relative motion and forces
between the various machine elements.
Kinematics of machine
Deals with the relative motion without considering the forces
Dynamics of machine
Deals with the forces and effect of forces on the machine component
when they act on them.
3. Kinetics of machine
Deals with the forces, which are formed due to combined action ofmass and motion of machine elements.
4. Statics
Deals with the forces and its effect on the machine part while the latteris at rest.
5. Resistant body Abody is said to be resistant body if it is able to transmit the forces with the
least possible deformation.
Example: spring, belt oils in hydraulic presses
6. Kinematic Link
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Links are individual parts of a mechanism.
Each parts of a machine which has a relative motion to some otherparts is known as Kinematic link.
7. Kinematic Chain
When the kinematic pairs are coupled in such a way that the last linked isjoined the first link to transmit the definite motion it is called a kinematic chain.
8. Kinematic Pair
The two links of the machine when in contact with each other are said to forma pair if the relative motion between them is successfully constrained.
9. Inversion
The method of obtaining the different mechanism by fixing the different links ina kinematic chain is known as inversion of the mechanism.
10.Structure
It is the assemblage of a number of resistant bodies having no relative motionbetween then and meant for carrying loads having a straining action.
Example: a railway bridge.
11.Mechanism
When one of the links of a kinematic chain is fixed, the chain is known as
mechanism.
It may be used for transmitting or transforming motion.
Example: Engine indicator, Typewriter.
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Grashof's Law
The sum of the length of shortest and longest link must be equal or less
than the sum of the length of the other two link length, if there is to be a
continuous relative motion between the two links.
According to Grashofs law
s + l < p + q
l = length of the longest link.
s = length of the shortest link.
p & q = length of the other two
links
In a four-bar linkage, we refer to the line segment between hinges on a given link
as a bar where:
s = length of shortest bar
l = length of longest bar
p, q = lengths of intermediate bar
Grashof's theorem states that a four-bar mechanism has at least one revolving
link if
s + l p + q (2)
The inequality (1) is Grashof's criteria
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The Link opposite to the frame is called Coupler Link and the link which are
hinged to the frame are called side link.
The link which is free to rotate through 3600 with respect to second link will be
said to revolve relative to the second link (not necessarily a frame).
If it is possible for all four bar to become simultaneously aligned, such a state
is called change point.
From the table we can see that for a mechanism to have a crank, the sum of the
length of shortest and longest link must be equal or less than the sum of the
length of the other two link.
However this condition is necessary but not sufficient. Mechanism satisfying this
condition falls into following three categories.
1) When the shortest link is the side link, the mechanism is crank rocker
mechanism. The shortest link is the CRANK in the mechanism.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Case Criterion Shortest link Category
1 s+l < p+q frame double crank
2 s+l < p+q slide crank rocker
3 s+l < p+q coupler double rocker
4 s+l = p+q any change point
5 s+l < p+q any triple rocker
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2) When the shortest link is the Frame, the mechanism is double crank
mechanism.
3) When the shortest link is the coupler link, the mechanism is Double rocker
mechanism
Inversion of the following types
1. Four bar chain
a. Beam engine.
b. Coupling rod of Locomotives.c. Watts indicator mechanism.
d. Pantograph.
2. Single slider crank chain .
a. Pendulum pump or Bull engine.
b. Oscillating cylinder engine.
c. Rotary IC engine.
d. Crank and slotted lever quick return mechanism.
e. Whit worth quick return mechanism.
3. Double slider crank chain.
a. Elliptical trammel
b. Scotch yoke mechanism.
c. Oldhams coupling.
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INVERSION OF FOUR BAR CHAIN MECHANISM
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a. BEAM ENGINE
1. Beam engine is also called as Crank and lever mechanism.
2. It consist of four link
a. Link A Frame
b. Link AB Crank
c. Link BC Coupler
d. Link CELever
3. In this mechanism, when the crank rotated about the fixed centre A,
the lever oscillates about the fixed center D.
4. The end E of the lever CDE is connected to piston rod which
reciprocates due to the rotation of the crank.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Beam Engine
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5. Purpose: Convert rotary motion into reciprocating motion.
b. Coupling rod of locomotive
1. The coupling rod of the locomotive consists of four links as shown in figure.
2. It consist of four link
a. Link AD frame
b. Link AB crank
c. Link BC connecting rod
d. Link CDcrank3. In this mechanism, the link AB and BC act as crank and are connected to
the respective wheel.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Coupling Rod of locomotive
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4. The link CD act as a coupling rod and the link AB is fixed in order to
maintain a constrain motion between them.
5. Purpose: meant for transmitting rotary motion from one wheel to another
wheel.
c. Watts indicator mechanism
A watt indicator mechanism has a four link as shown in figure.
1. The four links are fixed link at A, link AC, link CE, and link BFD.
2. It may be noted that BF and FD forms one link because two parts have no
relative motion between them.
3. The link CE and BFD act as lever.
4. The displacement of link BFD is directly proportional to the pressure of gas
or steam which acts on the indicator plunger.
5. On any small displacement of the mechanism, the tracing point E at the end
of the link CE traces out approximately straight line.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Watts Indicator Mechanism
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6. The initial position of the mechanism is shown in full line whereas the dotted
lines shows the position of mechanism when the gas or steam pressure acts
on the indicator plunger.
d. Pantograph
A pantograph is an instrument used to reproduce an enlarged or reduce scale
and as exactly as possible the path described by a given point.
1. It is a based on four based kinematic chain.
2. It consists of jointed parallelogram ABCD.
3. It is made up of bar connected by turning pair. It has a four turning pair.
4. Link BA and BC are extended to O and E respectively such that
OA/OE = AD/BE.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Pantograph
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5. For all relative position of bars the triangle OAD and OBE are similar and
the point O,D,E are in straight line.
6. The point E describes the same path as described by point D.
INVERSION OF SINGLE SLIDER CRANK CHAIN
MECHANISM
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a. Pendulum pump or Bull engine.
1. In this mechanism, the inversion is obtained by fixing the link 4 or cylinder
(sliding pair).
2. It consist of four link
a. Link 1 Piston rod
b. Link 2 AB-Crank
c. Link 3 -BC -connecting rod
d. Link 4 Cylinder.
3. In this case, the crank rotates the connecting rod oscillates about the pin
pivoted to the fixed link.
4. The piston attached to the piston rod reciprocates inside the cylinder.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Pendulum pump or Bull engine
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b. Oscillating cylinder engine.
1. In this mechanism, the inversion is obtained by fixing the link 3 or
connecting rod (turning pair).
2. It consist of four link
e. Link 1 -AB- Piston rod
f. Link 2 -BD-Crank
g. Link 3 -AD -Connecting rod
h. Link 4 Cylinder.
3. The link 3 (AD-connecting rod) is corresponds to the connecting rod of the
reciprocating steam engine mechanism.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Oscillating Cylinder Engine
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4. When the link 2 rotates (BD-Crank) rotates, the piston attached to the
piston rod reciprocates and the cylinder oscillates about the pin pivoted to
the fixed link at A.
d. Rotary IC engine.
1. In this mechanism, the inversion is obtained by fixing the link 2 or crank.
2. It consist of four link
a. Link 1 - Cylinder.
b. Link 2 -Fixed Crank
c. Link 3 -Piston
d. Link 4 Connecting rod
3. The link 4 (AD-connecting rod) rotates, the piston reciprocates inside the
cylinder forming link1.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Rotary IC Engine
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a. Crank and slotted lever quick return mechanism
1. In this mechanism, the inversion is obtained by fixing the link 3 or turning
pair.
2. It consist of four link
a. Link 1 -Slider
b. Link 2 Driving Crank
c. Link 3 -Fixed link
d. Link 4 Slotted lever or Slotted bar
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Crank and slotted lever quick return mechanism
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3. The driving crank BC revolves with uniform angular speed about fixed
centre.
4. The sliding bock is attached to crank pin at B slides in the slotted bar AP
and thus causes AP to oscillate about the point A.
5. A short link PQ transmits the motion from AP to the Ram to which the
cutting tool is fixed
6. The motion of the tool is constrained along the line produced
b. Whitworth quick return mechanism.
1. In this mechanism, the inversion is obtained by fixing the link 3 or
turning pair.
2. It consist of four link
a. Link 1 -Slider
b. Link 2 - Crank
c. Link 3 -Fixed link
d. Link 4 Slotted lever
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Withworth Quick Return mechanism
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3. The driving crank BC revolves with uniform angular speed about fixed
centre.
4. The sliding bock is attached to crank pin at B slides in the slotted bar AP
and thus causes AP to oscillated about the point A.
5. A short link PQ transmits the motion from AP to the Ram to which the
cutting tool is fixed
6. The motion of the tool is constrained along the line produced.
INVERSION OF DOUBLE SLIDER CRANK CHAIN
MECHANISM
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
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a. Elliptical trammel
1. In this mechanism, the inversion is obtained by fixing the link 4 or slotted
plate.
2. It consist of four link
a. Link 1 Sliders
b. Link 2 Bar
c. Link 3 Sliders
d. Link 4 Slotted Plate
3. The looted plate has two grooves cut in it at right angles to each other.
4. The link 1 and known as a sliders and form sliding pair with the link 4.
5. The link AB is a bar which forms the turning pair with the links 1 and link 3.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Elliptical trammel
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6. When the link 1 and link 3 slides along the respected grooves ,any point of
the link 2 such as point P traces out the ellipse on the surface.
b. Scotch yoke mechanism.
1. In this mechanism, the inversion is obtained by fixing link 1 or link3.
2. It consist of four link
e. Link 1 Fixed Link
f. Link 2 Crank
g. Link 3 Slider
h. Link 4 Frame (Piston and Cylinder arrangement )
3. When the link 2 rotates about the about B as a centre the link 4
reciprocates.(Piston reciprocates inside the cylinder)
4. The fixed links guides the frame
.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
Figure: Scotch Yoke Mechanism
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c. Oldhams coupling.
1. In this mechanism, the inversion is obtained by fixing link 2.
2. It consist of four link
a. Link 1 Flanges
b. Link 2 Supporting Frame
c. Link 3 Flanges
d. Link 4 Intermediate Piece.
3. The flanges (link 1 and link 3) forms turning pair with the link 2.
FUNDAMENTALS AND TYPES OF MECHANIISM Vaibhav Vithoba Naik
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4. When the driving shaft is rotated, the flange (link 1) causes the
intermediated piece (link 4) to rotate at the same angle through which
the flange (link 1) is rotated.
5. It further rotates the flange (link 3) at the same angle through which the
flange (link 1) is rotated. Hence link 1,3,4, have same angular velocity.
6. A little consideration there is a sliding motion between link 4 and link 1
and 3.