Orienting Toleranced Polygonal Parts

Abstract

Parts manufactured to tolerances have variations in shape. Most previous work in robotic manipulation assumes that parts do not have shape variations. Orienting devices such as bowl feeders often fail due to variations in part shape. We study the effects of uncertainty in part shape on orienting to develop systems that can orient toleranced polygonal parts. We present a tolerance model in which the part center of mass and vertices lie in circular uncertainty zones around their nominal positions. The variations in part shape are characterized by the tolerance model and the part’s nominal shape. We describe the nondeterminism that arises due to part shape uncertainty for a conveyor-based orienting system and show that sensor-based and sensorless orienting plans can exist for toleranced polygonal parts. We present implemented planners that generate orienting plans for the entire variational class of part shapes given a nominal part shape and tolerance bounds. These plans use both deterministic and nondeterministic actions to orient the parts, and we describe experiments to demonstrate them.