Orienting Toleranced Parts

Submitted to the International Journal of Robotics Research, December 1998

Srinivas Akella and Matthew T. Mason

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 the orienting process to develop systems that can orient toleranced polygonal parts. We present a shape uncertainty model and discuss the nondeterminism in the orienting process that arises from shape uncertainty for a conveyor-based parts orienting system. The variations in part shape are characterized by the tolerance model and the part's nominal shape. We show that sensor-based and sensorless orienting plans can exist for polygonal parts with shape uncertainty. We present implemented planners that generate orienting plans for the entire variational class of part shapes given a nominal part shape and shape uncertainty bounds. These plans use both deterministic and nondeterministic actions to orient the parts, and we describe experiments to demonstrate them.