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SIMPLE MECHANISM
Explain the term kinematic link? Give the classification of kinematic links?
Ans) Kinematic link: Each part of a machine which moves relative to some other part is called a
kinematic link.
Types of links:
Rigid Link: It is one which does not undergo any deformation while transmitting motion.
Example: The deformation of a connecting rod and crank of a reciprocating steam engine is
can be considered as rigid links.
Flexible Link: It is one which is partly deformed in a manner not to affect the transmission of
motion.
Example: Belts, ropes, chain drives & wires are flexible links.
Fluid Link: It is one which is formed by having a fluid & the motion is transmitted through the
fluid by pressure or compression only.
Example: Hydraulic presses, jacks and brakes.
What is a kinematic pair? Explain different types of kinematicpairs?
Ans) Kinematic pair: The two links of a machine when in contact with each other are said to form a
kinematic pair.
Classification of kinematic pairs:
(a) According to nature of relative motion:
Sliding Pair: If one link of a pair has a sliding motion relative to other, then the pair is
called as sliding pair.
Example: Rectangular rod in a rectangular hole.
Turning Pair / Revolving Pair: If one link of a pair has a revolving motion relative to the
other, then the pair is called as turning pair.
Example: Circular shaft revolving in a bearing.
Rolling Pair: If one link of a pair has a rolling motion relative to the other, then the pair is
called as rolling pair.
Example: Ball & roller bearings, and a rolling wheel on a flat surface.
Screw Pair / Helical Pair: If two mating links of a pair have a turning as well as sliding
motion between them, then the pair is called as screw pair.
Example: Lead Screw & the Nut of a Lathe.
Spherical Pair: When one link in the form of a sphere turns inside a fixed link, then the
obtained pair is called as spherical pair.
Example: Ball & Socket Joint.
(b) According to nature of contact:
Lower Pair: A pair of links having surface or area contacts between the members is
called as lower pair.
Example: All pairs of Slider crank mechanism, nut turning on a screw, and shaft
rotating in bearing.
Higher Pair: A pair of links having a point or line contact between the members is called as
higher pair.
Example: Wheel rolling on a surface, cam & follower, and tooth gears.
(c) According to the nature of mechanical constraint or type of closure:
Closed pair / Self closed pair: When the elements of a pair are held together
mechanically, then the pair is called as closed pair
Example: All Lower pairs & some higher pairs.
Unclosed / forced closed pairs: When two links of a pair are in contact either due to force
of gravity or some spring action, then the pair is called as unclosed pair.
Example: Cam & Follower pairs.
Define Kinematic chain. Give the classification of joints in a chain?
Ans) Kinematic Chain: When the kinematic pairs are coupled in such a way that last link is joined
to the first link to transmit definite motion, it is called as kinematic chain.
Number of joints in a chain: J = (3 /2) L - 2
Types of joints:
Binary Joint: If two links are joined at the same connection, it is called a binary joint.
Example: A joint with two binary joints named B as shown in the below figure.
Ternary Joint: If three links are joined at a connection, it is known as a ternary joint.
Example: Ternary links are named T as shown in the below figure.
Quaternary Joint: If four links are joined at a connection, it is known as quaternary
joint.
Define Inversion of mechanism
Ans) Inversion is the method of obtaining different mechanisms by fixing different links in a
kinematic chain.
What are the types of Kinematic Chains?
Ans) Types of kinematic Chains are (i) Four Bar Chain / Quadric Cycle Chain, (ii) Single Slider Crank
Chain, (iii)Double Slider Crank Chain.
