Disturbance Observer-based Trajectory following Control of Nonlinear Robotic Manipulators

Robotic manipulators are highly nonlinear and coupled dynamic systems, which may be subject to different types of unknown disturbances such as joint frictions and end-effector external payloads. Such disturbances, when unaccounted for, cause poor tracking performance of the robot and may even destabilize the robot control system. In this paper we propose a novel nonlinear control scheme for robotic manipualtors subject to disturbances using the concept of disturbance observer-based control by modifying the disturbance observers proposed in [1] and [2]. The proposed control scheme and disturbance observer guarantee global asymptotic position and disturbance tracking and remove the previous restrictions on the number of degrees of freedom (DOFs), joint types, or manipulator configuration. Computer simulations are presented for a 4-DOF SCARA manipulator to show the effectiveness of the proposed disturbance observer-based control scheme.