A systematic approach to identify the error motion of anN-degree of freedom manipulator

A generalised calibration technique for identifying the joint geometric parameters of an N-degrees-of-freedom (d.o.f.) robot manipulator model is presented. The technique is analogous to the synthesising calibration method applied in the calibration of coordinate measuring, machines. It describes the state of each joint by six d.o.f. and assumes rigid-body motion. The initial step in the calibration involves locating the axis of motion of each joint; the axes are then used to extract the kinematic parameters, introduced by Denavit-Hartenberg (D-H). In order to derive the generalised manipulator kinematic equation, the robot model is modified to include the six error motion components associated with each axis. The paper also addresses the problem of identifying the error motion components of each joint, on the basis of a set of measurement of three noncollinear points at the robot end-effector at various joint configurations. Because the technique is based on axis-by-axis calibration, other non-geometric errors such as joint backlash and gear transmission error may also be revealed.