Study on robot calibration using a laser tracking system (1st report) - Estimation of robot accuracy and consideration on disadvantage of joint axis estimating method

Abstract

Aiming at realizing off-line programming, many researches of improving robot's accuracy by calibrating the kinematic parameters of a robot are being carried out now. For an effective calibration it is necessary to measure the position of the tip of a robot arm precisely in a comparatively wide area. Although a laser tracking system is regarded as the most practical measuring system for this purpose in ISO 9283, there is no report yet which actually applies this system to the robot calibration. In this paper a 6-DOF articulated robot is calibrated by using a laser tracking system according to the joint axis estimating method and the effectiveness of this system is certified. A method of estimating the accuracy which refers to the robot base coordinate system is proposed. It is proved experimentally that the accuracy of the robot before calibration is worse than 3mm. The robot after calibration is positioned to the limited grid which is in the area near the initial pose of the calibration and to the wide grid. The accuracy in the limited grid is improved to be 0.27mm by the calibration, however the accuracy in the wide grid is worse compared with that in the limited grid. From this result it is proved that the joint axis estimating method is not so effective except for the neighborhood of the initial pose.