Calibration and Compensation of Rotary Axis Angular Positioning Deviations on a SCARA-Type Industrial Robot Using a Laser Tracker

In general, the “absolute” positioning accuracy of industrial robots is significantly lower than its repeatability. In the past research, in order to improve a robot’s positioning accuracy over the entire workspace, the compensation for the link length errors and the rotation axis angle offsets are often employed. However, the positioning error of the compensated industrial robot is still much higher than that of a typical machine tool. The purpose of this study is to propose a new kinematic model and its calibration scheme to further improve the absolute positional accuracy of an industrial robot over the entire workspace. In order to simplify the problem, this study only targets the 2D positioning accuracy of a SCARA-type robot. The proposed model includes not only link length errors and rotary axis angular offsets but also the “error map” of the angular positioning deviation of each rotary axis. The angular error deviation of each rotary axis is identified by measuring the robot’s end-effector position by a laser tracker at many positions. To verify the validity of the identified model, the effectiveness of the compensation based on it is also investigated.