Types of Kinematic Pairs:
Kinematic
pairs can be classified according to
i) Nature of
contact.
ii) Nature of
mechanical constraint.
iii) Nature of
relative motion.
i) Kinematic pairs according to nature of contact:
a) Lower
Pair: A pair of links having surface or area contact between the members is
known as a lower pair. The contact surfaces of the two links are similar.
Examples:
Nut turning on a screw, shaft rotating in a bearing, all pairs of a
slider-crank mechanism, universal joint.
b) Higher
Pair: When a pair has a point or line 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.
ii) Kinematic pairs according to nature of
mechanical constraint.
a) Closed
pair: When the elements of a pair are held together mechanically, it is known
as a closed pair. The contact between the two can only be broken only by the
destruction of at least one of the members. All the lower pairs and some of the
higher pairs are closed pairs.
b) Unclosed
pair: When two links of a pair are in contact either due to force of gravity
or some spring action, they constitute an unclosed pair. In this the links are
not held together mechanically. Ex.: Cam and follower pair.
iii) Kinematic pairs according to nature of
relative motion.
a) Sliding
pair: If two links have a sliding motion relative to each other, they form a
sliding pair. A rectangular rod in a rectangular hole in a prism is an example
of a sliding pair.
b) Turning
Pair: When on link has a turning or revolving motion relative to the other, they
constitute a turning pair or revolving pair.
c) Rolling
pair: When the links of a pair have a rolling motion relative to each other,
they form a rolling pair. A rolling wheel on a flat surface, ball ad roller
bearings, etc. are some of the examples for a Rolling pair.
d) Screw
pair (Helical Pair): if two mating links have a turning as well as
sliding motion between them, they form a screw pair. This is achieved by
cutting matching threads on the two links.
The lead
screw and the nut of a lathe is a screw Pair
e)
Spherical pair: When one link in the form of a sphere turns inside
a fixed link, it is a spherical pair. The ball and socket joint is a spherical
pair.
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