Kinematic Pairs

Kinematic Pairs


Kinematic Pairs

A kinematic pair is a connection between two bodies that imposes constraints on their relative movement. Franz Reuleaux introduced the kinematic pair as anew approach to the study of machines that provided an advance over the notion of elements consisting of simple machines.
There are three general types of Kynematic Pairs:
Lower pair: A lower pair isan ideal joint that constrains contact between a point, line or plane in the moving body to a corresponding point line or plane in the fixed body. A lower pair is one in which there occurs a surfaceor area contact between two members, e.g. nut and screw, universal joint used to connect two propeller shafts.
* A revolute pair, or hinged joint, requires a line in the moving body to remainco-linear with a line in the fixed body, and a plane perpendicular to this line in the moving body maintain contact with a similar perpendicular plane in the fixed body. This imposes five constraints onthe relative movement of the links, which therefore has one degree of freedom.
* A prismatic joint, or slider, requires that a line in the moving body remain co-linear with a line in the fixed body,and a plane parallel to this line in the moving body maintain contact with a similar parallel plan in the fixed body. This imposes five constraints on the relative movement of the links, whichtherefore has one degree of freedom.
* A screw pair requires cut threads in two links, so that there is a turning as well as sliding motion between them. This joint has one degree of freedom.
* Acylindrical joint requires that a line in the moving body remain co-linear with a line in the fixed body. It is a combination of a revolute joint and a sliding joint. This joint has two degrees offreedom.
* A spherical joint, or ball joint, requires that a point in the moving body maintain contact with a point in the fixed body. This joint has three degrees of freedom.
* A planar joint...