Zero-offset calibration using a screw theory

Abstract

In this paper, we propose an algorithm to easily correct zero-offset in robotic manipulators by identifying screw information. The proposed algorithm improves the accuracy of the robot even if there may be errors in the other geometric parameters. To identify the screw information, the robot is made to create a circular trajectory by rotating a certain joint, while other joints being fixed, and then its endpoints are measured by a laser tracker. The screw information such as rotation axis and a point along the axis is computed through a least-square circle fit. By comparing the resulting screw information from the measurement and that from the kinematic model, we determine the amount of zero-offset in the least square sense. Thus we can enhance the position accuracy by compensating for the determined zero-offset associated with the kinematic model. We show the effectiveness of the proposed algorithm via experimentation using a dual arm robot manipulator.