Types ans links and pairs with illustrative example.

1. THEORY OF MACHINES
(DME 5201)
UNIVERSITY POLYTECHNIC
GLA UNIVERSITY,
MATHURA
LECTURE 1-2

2. MODULE -1 : Contents
Review and Basics
Definition of statics, kinetics, kinematics and dynamics, Rigid body
and resistant body
Mechanism &
Machines
Links , Kinematics pairs and their types, Kinematics pairs- types;
Degree of freedom, Kinematics chain and their types, Constrained
motion and mechanisms
Inversion OF
Mechanisms
Classification of mechanisms ; Equivalent mechanism, Laws of
inversion of mechanisms, Single slider crank chain and its
inversions, Quick return mechanism, pantograph
Clutches
Introduction of clutches and its working principle, Single plate
Clutch, Multi-plate clutch, Cone clutches
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3. Basics Definitions• Statics-the branch of mechanics concerned with bodies at rest and forces in
equilibrium.
• Kinetics-the branch of classical mechanics that is concerned with the relationship
between motion and its causes, specifically, forces and torques.
• Kinematics-the branch of mechanics concerned with the motion of objects
without reference to the forces which cause the motion.
• Dynamics-the branch of mechanics concerned with the motion of bodies under
the action of forces
• Rigid body- A rigid body (also known as a rigid object) is a solid body in which
deformation is zero or so small it can be neglected. The distance between any two
given points on a rigid body remains constant in time regardless of external forces
exerted on it.
• Resistant body- A body is said to be a resistant body, if it does not deform for
the purpose for which it is made.
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4. Note:
• Resistant bodies may be solid, liquid (as in hydraulic
jack) or isochoric gases(as in pnumatic brakes of
trucks).
• All the rigid bodies are resistant bodies.
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5. • Link- A component forming a part of a chain; generally rigid
with provision at each end for connection to two other links
• KINEMATIC LINK- Each part of a machine, that
undergoes relative motion with respect to some other part, is
called kinematic link.
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6. TYPES OF KINEMATIC LINK
Based on rigidity, kinematic links can be broadly classified into
three types. They are:
• Rigid link
• Flexible link and
• Fluid link
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7. Rigid Link
 Rigid links are those
kinematic links that do not
undergo any change of shape
when transmitting motion.
 In reality, no rigid links exist.
 Example-crankshafts,
connecting rod and cam
followers
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8. Flexible Link
• A flexible link is a resistant kinematic
link that undergoes partial
deformation when transmitting
motion.
• Deformation does not affect the
effectiveness of transmission.
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9. Fluid Link
• A fluid link makes use of a fluid (liquid
or gas) to transmit motion, by means
of pressure.
• Fluid links always undergo
deformation when transmitting
motion.
• Example: Pneumatic punching
presses, hydraulic jacks and hydraulic
brakes.
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10. KINEMATIC PAIR
• A kinematic pair is a joint which
is formed by the contact
between two bodies and allows
relative motion between them.
• The contact element on a body,
which joins to form a kinematic
pair, is called pairing element.
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11. TYPES OF KINEMATIC PAIRS
• ON THE BASIS OF TYPE OF CONTACT
– Lower Pair
– Higher Pair
• ON THE BASIS OF RELATIVE MOTION
– Sliding Pair
– Turning Pair
– Screw Pair
– Spherical Pair
– Rolling Pair
• ON THE BASIS OF CLOSURE
– Self Closed
– Force Closed
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12. ON THE BASIS OF TYPE OF CONTACT
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13. LOWER PAIRS
• Surface contact between
links
• Example: A block is sliding
on a surface , prism into a
triangular hole
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14. HIGHER PAIRS
• Higher pairs (joints) have
either a line contact or
a point contact.
• Example: cam mechanisms,
gear trains, ball and roller
bearings and roll-slide joints,
etc.
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15. ON THE BASIS OF RELATIVE MOTION
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16. SLIDING PAIR
• One link slides on the
other link.
• Contact is surface
contact.
• They form lower pair.
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17. TURNING PAIR
• One link turns about
another link or both links
turn about a common joint.
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18. SCREW PAIR
• Contact is like screw threads.
• A screw pair consists of links that have both
turning and sliding motion relative to each
other.
• Example: Nut and Bolt
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19. SPHERICAL PAIR
• In a spherical pair, a spherical
link turns inside a fixed link.
• A spherical pair has three
degrees of freedom
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20. ROLLING PAIR
• In a rolling pair, one element
undergoes rolling motion with
respect to the other.
• Example: Bicycle tyre on the
ground.
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21. ON THE BASIS OF CLOSURE
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22. Self Closed Pairs : Whenever two
elements of pair are held together
mechanically in such a way that only
required the type of relative motion occurs
called Self closed pair or closed pair.
• Example- all lower pairs
Force Closed Pairs : Whenever two
elements of pair are not held together
mechanically but are kept in contact by the
action of external forces the pair is said to
be Force closed pair or Un-closed pair.
• Example- cam and follower
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