Prediction of the Slop in General Spatial Linkages

This paper reviews techniques for assessing how joint clearances affect the precision of multiloop, multifreedom linkages. Slop, or backlash, arises from the small movements as joint clearances are taken up and, as these movements are generally uncontrolled, the precise location of bodies in the linkage becomes uncertain. This is particularly important when such linkages are used as robot manipulators, where the location of the end effector is of interest. A new analytic technique, which is more widely applicable than previous techniques, is presented and demonstrated by way of the Melbourne dextrous finger. We assume that the joints in the linkage are frictionless, and we seek the maximum free movement, bounded by nominal joint clearances, of some body of interest. Theoretical results are compared with experimental measurements collected using a photogrammetric technique. KEY WORDS—mechanism analysis, parallel manipulators, backlash, mechanism precision, spatial kinematic chains, robot hands