Fine motion planning through constraint network analysis

Flexible assembly machines may be improved and costs reduced by relating constraints on part fixturing accuracy and employing compliant devices in assembly effectors. An effector-mounted remote center compliance (RCC) device that corrects for spatial misalignments of prismatic parts of general cross section has recently been demonstrated. This spatial RCC was designed by planning for the possible fine motion assembly contact states given a range of initial position and orientation uncertainty between the mating parts. These fine motion contact states are arranged in a constraint network in the fashion of a Petri-net controller. However, the control transitions are mediated by compliances reacting to contact forces rather than from force sensing and discrete event controller schemes. A path through the constraint network of a square peg and hole task is found from initial to final assembly states. This path defines a single compliance relationship that is realized with a practical assembly device. Extensions of this design technique to other assembly tasks is discussed.