Ans :
KINEMATIC PAIRS
|__ Spherical Pair
A) Kinematic pairs according to the relative motion
Sliding pair: “When relative motion between two elements of a pair takes place in the form of PURE SLIDING, then the pair is called sliding pair.”
Example, a rectangular bar in a rectangular hole, the piston and cylinder of an engine, the cross-head and guides of a steam engine, the ram and its guides of a steam engine, the ram and its guides in a shaper, the tail-stock on the lathe bed etc.
Turning pair: “When relative motion between two elements of a pair takes place in the form of PURE TURNING only, then the pair is called turning pair.”
Example, a shaft with a collar at both ends revolving
in a circular hole. The collars prevent the sliding motion of the shaft in the bearing.
Rolling pairs: “When two elements are so connected that one is constrained to roll on another element which is fixed, they from a rolling pair. “
Example Ball and roller bearings, a wheel rolling on a flat surface etc. are examples of rolling pairs.
Screw (or helical) pair: “When one element turns about the other element by means of threads, they form a screw pair.” The motion in this case is a
combination of sliding and turning.
Example the lead screw of a lathe with a nut, a bolt with a nut, Screw and nut of screw jack are some examples of screw pairs.
Spherical pair: “When one element in the form of sphere turns about the other element which is fixed they form a spherical pair.”
Example-the ball and socket joint, a pen stand, the mirror attachment of vehicles etc, are some examples of spherical pairs.
B) Kinematic pairs according to the type of contact.
Lower pair: “When the two elements of a pair have surface(area) contact while in motion the pair is called a lower pair.”
All sliding pairs, turning pairs and screw pairs form lower pair. for example, a nut turning on a screw, a shaft rotating in a bearing, an universal joint, all pairs of a slider crank mechanism, a pantograph etc.
Higher pair: “When the two elements have point or line contact while in
motion then the pair is known as higher pair.”
Belt, rope and chain drives, gears, the cam and follower ball and roller bearings, a wheel rolling on a surface etc all etc. All form higher pairs.
C) Kinematic pairs according to the type of mechanical constraint
Closed pair: When the two elements of pair are held together mechanically
in such a manner the only the required type of relative motion occurs, they are
called a close pair. All lower pairs and some higher pairs
(for example, the enclosed cam and follower) are closed pairs.
Open pair: When the two elements of a pair are not held mechanically
and are held in contact by the action of external forces, the pair is called an
unclosed pair. for example, the can and spring loaded follower pair.