Mechnical Design Systems Laboratory, Hiroshima University

Industrial robots generally have lower “absolute” positioning accuracy compared to its repeatability. To improve its positioning accuracy over the entire workspace, many previous research works presented a calibration scheme for link lengths and rotary axis angular offsets. Even when these errors are compensated, in many cases a robot's positioning error is still roughly 10 to 100 times larger than typical machine tools. The purpose of this research is to propose a new kinematic model and its calibration scheme to further improve the absolute position accuracy over the entire workspace. To simplify the problem, this paper only targets the 2D positioning accuracy by a SCARA type robot. The proposed model contains 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 error maps can be identified by measuring the 2D position trajectory of the robot’s end effector by using a laser tracker. Its modelling accuracy is experimentally validated.

Keywords: Calibration, Kinematics model, Industrial robot