Mechnical Design Systems Laboratory, Hiroshima University

There would be various advantages if industrial robots can be applied to machining operations like NC machine tools. One critical issue is that machining operations would require a robot to have not only high positioning repeatability, but also "absolute" positioning accuracy, or the "volumetric accuracy," over the entire workspace. This paper first presents a method to measure the 2D positioning accuracy of a SCARA-type robot over the entire workspace. The proposed scheme measures multiple paths both in X and Y directions by using a laser interferometer. An optical square is used to ensure the parallelism or the perpendicularity of multiple paths. Secondly, this paper proposes a scheme to identify the angular positioning deviation of each rotary axis from the measured trajectories. The kinematic model with not only link length errors and rotary axis angular offsets, but also the identified "error map" of each rotary axis, is proposed. Its modeling accuracy is experimentally validated.

Keywords: Calibration, Industrial robot, Laser Interferometer