A Computation for Robots to Orient and Position Hand-Held Workpieces

Abstract

A computation is presented which enables robots with six degrees of freedom to orient and position workpieces against fixtures. It is assumed that the robot can grasp a single workpiece and that a vision system can determine the three-dimensional locations of three feature points on that workpiece. A feature point is a unique point on a workpiece, such as the apex of a cone, which may be located visually by examining neighboring edges or surfaces. The spatial relation between workpiece and fixture which is to be the goal of arm motion is specified by measurements taken as the workpiece is held with the correct posture by a programmer. These measurements are the spatial locations of three noncollinear feature points on the workpiece and three noncollinear feature points on the fixture. The computation presented adjusts for relative motion between fixture and robot if the vision system keeps track of the three feature points on the fixture. The solution to the equations presented is a set of arm link parameters which satisfy the goal of relative workpiece placement. The general form of the equations permits application of the computation to robots with different kinematic configurations.