A New Technique for Clearance Influence Analysis in Spatial Mechanisms

This paper presents a technique for assessing the influence that clearance in the kinematic pairs of a mechanism has on accuracy. The technique works for both planar and spatial, open-, and closed-chain mechanisms, but not for overconstrained mechanisms. It can be defined deterministic, because it precisely determines the actual pose of the link of interest, and does not rely on probability density functions. The most innovative aspect is that, unlike other existing techniques, knowledge of the forces acting on the mechanism is not needed; on the contrary, given a mechanism configuration, the maximum pose error of the link of interest—that is, the maximum displacement of the link of interest caused by clearance take-up—is directly determined. In this way, a problem which is intrinsically kinematic is solved by a kinematic method, rather than by a kinetostatic one as usually done in the literature. This allows for a more general approach to the clearance problem, as it removes one of the inputs (the external load) usually required for a kinetostatic analysis. The numerical effectiveness of the method is shown on a pure translational parallel manipulator.