Elasto-geometrical calibration of an industrial robot under multidirectional external loads using a laser tracker

This paper presents an elasto-geometrical calibration method for improving the position accuracy of an industrial robot (ABB IRB 1600). Geometric parameter errors and joint stiffness parameters are identified through measuring the position of the robot's end-effector in several robot configurations using a laser tracker. Contrary to previous works, robot's position errors are measured under a wide range of external forces and torques for each robot configuration. A 6-DOF cable-driven parallel robot is employed to automatically apply the desired load on the end-effector of the ABB robot. Before the experiment, an observability analysis is performed in order to improve the robustness of the calibration process with respect to measurement noise and unmodeled errors. Accordingly, an optimal set of robot configurations and external loads is selected for the calibration process. The measured position errors of the ABB robot for this selected set are used to identify the real robot's elasto-geometrical parameters. Finally, the calibration efficiency is evaluated for a number of random combinations of robot configurations and external loads. The experimental results revealed that the proposed elasto-geometrical calibration approach is able to reduce the maximum position error to 0.960 mm, while a customary kinematic calibration can reduce the maximum position error only to 2.571 mm.