High-precision Closed-loop Robust Control of Industrial Robots Based on Disturbance Observer

Industrial robots have high repeatable positioning accuracy but their absolute positioning accuracy is relatively low, which limits their application in high-precision machining. Traditional methods to improve absolute positioning accuracy include geometric parameter calibration and off-line error compensation, but their absolute positioning error is hundreds of microns and cannot meet the requirements. Online compensation is a more effective method, but most of the relevant researches are based on simple PID control, which is difficult to achieve accurate trajectory tracking in complex conditions. Thus, a high-precision robust control method is proposed to improve the control precision and robustness in online compensation. The method uses a laser tracker to measure the robot’s terminal position in real time and identifies the external disturbance through a second-order disturbance observer. On this basis, a sliding mode controller is designed to complete the robot’s robust control. The boundness of observation error of disturbance observer and the asymptotic stability of closed-loop system are proved by Lyapunov method. The proposed method is validated on a COMAU robot, experimental results show that the root-mean-square value of tracking error module in Cartesian space is 0.037 mm when the proposed control method is used for online compensation, which is only 39% of PID based online compensation method. © 2022 Editorial Office of Chinese Journal of Mechanical Engineering. All rights reserved.