Disturbance Observer-based Trajectory Following Control of Robot Manipulators

Abstract

Robotic manipulators are usually subject to different types of disturbances. If the effects of such disturbances are not taken into account, it can lead to unsatisfactory tracking performance of the robot and may even destabilize the robot control system. In this paper a novel nonlinear disturbance observer-based controller is designed for robotic manipulators. Previous disturbance observer-based controllers which are designed for robotic systems undergo the restricting assumption that the external disturbance is constant. In this paper a novel two-stage procedure is proposed to design a disturbance observer that improves disturbance attenuation ability of current disturbance observer-based controllers. The proposed method can cope with non-constant disturbance. Furthermore, it is shown that even for the fast time varying disturbance, the controller achieves satisfactory tracking performance. The proposed controller guarantees semi-global asymptotic position and velocity tracking and moreover, removes restrictions of previous studies on the number of degrees of freedom (DOFs), joint types, and manipulator configuration. The effectiveness of the proposed method is verified against different types of external disturbance applied on the robot manipulator and the results are compared with the results of previous methods. Furthermore, the results support the theoretical conclusions.