Abstract: The flexible coordinate measurement system which consists of universal industrial robot and visual sensor is a very important application of visual inspection technology in the area of industrial online measurement. The positioning error of the industrial robot is the most major factor which affects system measurement accuracy due to robot’s complex mechanical structure and control process, but it can be compensated by modifying the link parameters. The positioning error compensation model of tool center point (TCP) on the basis of the relative positioning accuracy is derived by means of modified Denavit-Hartenberg kinematics convention, which can avoid accuracy loss in the transformation among different coordinate frames. Pertinent study on compliance errors related to robot’s postures is carried out. By establishing the elastic torsion spring model of flexible joints, compliance errors are divided into two parts, the compliance error from external load and that from manipulator gravity, to be compensated separately. A laser tracker is used as high precision measurement equipment in the calibration process to simplify the operation so that the three dimension coordinates of TCP can be acquired in the single point measurement mode. After compensation, the root-mean-square error of calibration points is reduced from 1.230 2 mm to 0.428 8 mm and that of validation points from 0.723 6 mm to 0.505 4 mm.

Key words: Compliance error, Industrial robot, Laser tracker, Positioning error, Relative positioning accuracy