Machine, Link, Pair, Kinematic Chain

1. Ms.Viddya S. Patil
Assistant Professor
Department of Mechanical Engineering
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Sharad Institute of Technology, College of
Engineering, Yadrav- Ichalkarnji
Department of Mechanical Engineering
Lecture 2:
Introduction to Machine
Fundamentals of Mechanical
Engineering

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Content
1. What is Machine?
2. Link
3. Pair
4. Kinematic chain
5. Different motions involved in Mechanism

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1. What is Machine?
 A device that transmits and modifies energy to perform a specific task. This energy can be
mechanical, electrical, thermal, or any other form, but the machine ultimately converts it into
useful mechanical work
 Composed of interconnected components, each with its own function. These components include
gears, levers, bearings, shafts, springs, and so on.
 Designed to achieve a specific motion or force transformation. This could involve changing the
direction of force, amplifying its magnitude, or converting one type of motion into another.
 Focused on practical applications. Examples include engines, turbines, pumps, robots, vehicles,
and countless other devices used in various industries.
 Defined input and output: A machine receives an input (energy, material) and produces a desired
output (work, product).
 Controlled process: The machine's components and mechanisms work together in a controlled
manner to achieve the desired outcome.

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CLASSIFICATION OF MACHINES
1. Machines for generating mechanical energy
- Converts other forms of energy into mechanical work
Examples: Steam engines, Steam turbines, I. C. engines, gas turbines, water
turbines etc.
2. Machines for transmitting mechanical energy into other form of energy
- Known as converting machines
Examples: Electric generators, air or hydraulic pumps, etc.
3. Machines for utilizing mechanical energy in the performance of useful work.
Examples: Lathe, and other machine tools, etc.

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Examples of machines in mechanical
engineering:
 Internal combustion engine
(converts chemical energy into
mechanical work)
 Wind turbine (converts wind
energy into electrical energy)
 Robotic arm (converts electrical
signals into precise movements)
 Hydraulic press (uses fluid
pressure to exert large forces)
 Conveyor belt (transports
materials efficiently)

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2. Link
Link-A link is a rigid body within a machine that connects other parts and transmits forces and motion.
A link is defined as a single part which can be a resistant body or a combination of resistant bodies having
inflexible connections and having a relative motion with respect to other parts of the machine. A link is also
known as kinematic link or element.
The frame of any machine is considered as single link as there is no relative motion between the various parts of
the frame. As shown in slider crank mechanism shown below, the frame is considered as one link (link 1) as
there is no relative motion in frame itself. The crank here is link 2 & connecting rod is again single link (link 3).
The slider or piston is link 4 as there is no relative motion it. In this way, many complex mechanisms can be
describe by simple configuration diagram by considering the definition of a link.

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1. The links can also be classified into Rigid, Flexible, Fluid according to its nature
i). Rigid link – Rigid link is the link which do not deform while transmitting the motion e.g. connecting
rod, lever.
ii). Flexible link – Flexible link is the link which deform while transmitting the motion but does not
affect its function of transmitting motion. eg. chain , belt, rope etc.
iii). Fluid link – Fluid link is the link which uses the fluid pressure to transmit the motion e.g. oil in
hydraulic system, air in pneumatic system, hydraulics jack, brakes and lifts.
Types of Links can be classified into Binary, Ternary, and Quaternary etc. depending upon its ends on
which revolute or turning pairs can be placed.
a] Binary link - Having two connection
b] Ternary link - Having three connections
c] Quaternary link - Having four connection
Types of links-

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A kinematic pair is a connection between rigid bodies, which permits relative motion between them. When two
links are connected in such a manner that relative motion between them take place in a definite way then it is
called kinematic pair.
When the links are supposed to be rigid in kinematics, then, there cannot be any change in the relative positions
of any two chosen points on the selected link.
CLASSIFICATION OF PAIRS
Kinematic pairs can be classified according to
a) Type of contact between elements
b) Type of relative motion
c) Nature of constraint or Type of closure
A) Type of contact between elements
i) Lower Pairs: A pair of links having surface or area contact between the members is known as a lower pair. The
surfaces in contact of the two links are similar.
Examples: Nut turning on a screw, shaft rotating in a bearing
ii) Higher Pair: When a pair has a point or line joint contact between the links, it is known as a higher pair. The
contact surfaces of the two links are dissimilar.
Examples: Wheel rolling on a surface, cam and follower pair, tooth gears, ball and roller bearings, etc.
Kinematic pair or Pair

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b) Type of relative motion
i) Sliding Pair: When two pairs have sliding motion relative to each
other. Examples: piston and cylinder, rectangular rod in rectangular
hole.
ii) Turning Pair: When one element revolves around another element it
forms a turning pair. Examples: shaft in bearing, rotating crank at
crank pin.
iii) Screw Pair: This is also known as helical pair. In this type of pair two
mating elements have threads on it or its relative motion takes place
along a helical curve. Examples: Nut and screw pair as shown in
figure, Screw jack
iv) Rolling Pair: When one element is free to roll over the other one.
Examples: Ball and rolling as shown in figure, motion of wheel on
flat surface
v) Spherical pair: When one element move relative to the other along a
spherical surface. Examples: Ball and socket joint

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C) Nature of constraint or Type of closure
i) Closed pair: One element is completely surrounded by the other.
Examples: Nut and screw pair
ii)Open Pair: When there is some external mean has been applied to prevent them from separation.
Examples: cam and follower pair

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Kinematic Chain
When two or more kinematic pairs are joined together, they form kinematic chain.
A kinematic chain may be defined as a combination of kinematic pairs, joined in such a way that each link
forms a part of two pairs and the relative motion between the links or elements is completely or successfully
constrained. When the kinematic pairs are coupled in such a way that the last link is joined to the first link to
transmit definite motion (i.e. completely or successfully constrained motion), it is called a kinematic chain.
Types of Kinematic chain-
i) Four Bar Chain- ii) Single Slider Crank Chain iii) Double Slider Crank Chain

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Different motions involved in Mechanism
i) Completely Constraint- Moves in a definite direction iii) Successfully Constraint-Motion is not completed by itself but
by some other means.
ii) Incompletely Constraint-Moves in all direction.

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Relation between Links, Pairs and Joints
L = 2p-4
J =(3/2) L – 2
L = No of Links
P = No of Pairs
J = No of Joints
L.H.S > R.H.S = Locked chain
L.H.S = R.H.S = Constrained Kinematic Chain
L.H.S < R.H.S = Unconstrained Kinematic Chain

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This video is prepared for academic use only.