Tolerancing kinematic couplings

This paper presents a method for allocating tolerances to dimensions in kinematic couplings, which are exact constraint devices used to locate one object with respect to another. The objective is to reduce the manufacturing cost without exceeding limits on the variation of the coupled position and orientation. The allocation procedure uses parametric models of the contacting surfaces and a solution for the resting position of the coupled body. A multivariate error analysis provides a relation between variation in manufactured dimensions and variation in the position and orientation of the coupled body. Optimal tolerances are then determined using a non-linear constrained optimization algorithm that minimizes the manufacturing cost while satisfying constraints on the variation of the coupled position and orientation. The method provides a useful tool when designing mass-produced kinematic couplings intended for applications where coupled bodies are exchanged.