Types of Kinematic Pairs

Kinematic Pair Definition and Types

Kinematic pair Definition	The two links or elements of a machine, when in contact with each other, are said to form a pair. If the relative motion between them is completely or successfully constrained (i.e., in a definite direction), the pair is known as a kinematic pair.
Types of Kinematic Pairs
1. According to the type of relative motion between the elements:	Sliding pair: When the two elements of a pair are connected in such a way that one can only slide relative to the other, the pair is known as a sliding pair. Turning pair: When the two elements of a pair are connected in such a way that one can only turn or revolve about a fixed axis of another link, the pair is known as turning pair. Rolling pair: When the two elements of a pair are connected in such a way that one rollover another fixed link, the pair is known as rolling pair/li> Screw pair: When the two elements of a pair are connected in such a way that one element can turn about the other by screw threads, the pair is known as screw pair. Spherical pair: When the two elements of a pair are connected in such a way that one element (with spherical shape) turns or swivels about the other fixed element, the pair formed is called a spherical pair
2. According to the type of contact between the elements:	Lower pair: When the two elements of a pair have a surface contact when relative motion takes place and the surface of one element slides over the surface of the other, the pair formed is known as lower pair. Higher pair: When the two elements of a pair have a line or point contact when relative motion takes place and the motion between the two elements is partly turning and partly sliding, then the pair is known as higher pair.
3. According to the type of closure:	Self-closed pair: When the two elements of a pair are connected together mechanically in such a way that only required kind of relative motion occurs, it is then known as self closed pair. The lower pairs are self closed pair. Force-closed pair: When the two elements of a pair are not connected mechanically but are kept in contact by the action of external forces, the pair is said to be a force-closed pair. The cam and follower is an example of force closed pair, as it is kept in contact by the forces exerted by spring and gravity.