Kinematic coupling

Kinematic coupling describes fixtures designed to exactly constrain the part in question, providing precision and certainty of location.

An alternative design consists of three hemispheres on one part that fit respectively into a tetrahedral dent, a v-groove, and a flat.

The benefit of this design is that the center of rotation is located at the tetrahedron, however, it suffers from contact stress problems in high-load applications.

Also, the Maxwell coupling is thermally stable due to this symmetry as the curved surfaces can expand or contract in unison in the v-grooves.

[2] The reproducibility and the precision of a kinematic coupling come from the idea of exact constraint design.