Tool Locating Behavior
Kinematic couplings are an example of exact constraint design principles put to use. Here, the carriage and tool represent two independent entities that will disconnect and reconnect numerous times. Each reconnection must repeat to the same position relative to each other regardless of the cycle. By exact constraint design principles, the (six) degrees of freedom of the free tool plate are constrained by the same number of constraints. Doing so joins the two entities in such a way that they can neither bind nor wiggle. They only fit together one way.
The Maxwell Coupling is a mechanical design pattern for fully constraining two entities with six points of contact. In the ideal case, the two entities join together and infinitesimally small points. This principle puts a high stress on a small surface area, so, in practice stiff materials such as steel are used to form the coupling points.