AMP-CAD: Automatic assembly motion planning using CAD models of parts

Abstract Assembly with robots involves two kinds of motions, those that are point-to-point and those that are force/torque guided, the former kind of motions being faster and more amenable to automatic plannning and the latter being necessary for dealing with tight clearances. In this paper, we describe an assembly motion planning system that, given CAD models of the parts and a description of the assembly operation, automatically figures out which motions should be point-to-point and which motions should be force/torque guided. Our planner uses graph search over a potential field representation of parts to calculate candidate assembly paths. Given the tolerances of the parts and other uncertainties, these paths are then analyzed for the likelihood of collisions. Subsequently, the path segments that are prone to collisions are marked for execution under force/torque control. The calculation of the various motions is facilitated by an object-oriented and feature-based assembly representation. An integral part of the assembly motion planner is the execution unit. Residing in this unit is knowledge of the different types of automatic EDR error detection and recovery) strategies. Therefore, during the execution of a force/torque guided motion, this unit invokes the EDR strategies appropriate to the geometric constraints relevant to the motion. This system. called AMP-CAD, has been experimentally verified using a Cincinnati Milacron T 3 -726 robot and a Puma 762 robot on a variety of assemblies.