Local POE model for robot kinematic calibration

A robot kinematic calibration method based on the local frame representatio n of the product-of-exponentials (Local POE) formula is introduced. In this method, the twist coordinates of the joint axes are expressed in their res pective local (body) frames. The advantages of this new approach are threef olds: (1) revolute and prismatic joints can be uniformly expressed in the t wist coordinates based on the line geometry; (2) the twist coordinates of t he joint axes can be set up with simple values because the local frames can be arbitrarily defined on the links; (3) the kinematic parameters describe d by the twist coordinates vary smoothly that makes the method robust and s ingularity-free. By assuming that the kinematic errors exist only in the re lative initial poses of the consecutive link frames, the kinematic calibrat ion models can be formulated in a simple and elegant way. The calibration p rocess then becomes to re-define a set of new local link frames that are ab le to reflect the actual kinematics of the robot. This method can be applie d to robot manipulators with generic open chain structures (serial or tree- typed). The simulation and experiment results on a 4-DOF SCARA type robot a nd a 5-DOF tree-typed modular robot have shown that the average positioning accuracy of the end-effector increases significantly after calibration. (C ) 2001 Elsevier Science Ltd. All rights reserved.