Adaptive disturbance observer-based fixed-time prescribed performance sliding-mode control of uncertain robot manipulators

This paper studies the fixed-time prescribed performance trajectory tracking issue of robot manipulators under uncertainties, actuator faults, and external disturbances. First, an adaptive disturbance observer (ADO) is developed, which does not need the exact upper bound information of unknown lumped disturbance and its derivative to effectively estimate the unknown lumped disturbance. Then, a novel fixed-time prescribed performance function (FTPPF) that can converge to a small region in a fixed time is proposed as the preset bound of tracking errors. Furthermore, a sliding surface that uses the prescribed performance tracking error is designed. Afterward, a nonsingular fixed-time prescribed performance terminal sliding-mode control (FTPPTSMC) combined with ADO is developed, to assure the transient and steady-state performance of the robot manipulator. The proposed FTPPTSMC can guarantee that the position tracking errors always keep within the prescribed performance bound and converge to a preset small region in a fixed time by the proposed FTPPF, asymptotically converging to the origin. Finally, the effectiveness of the proposed FTPPTSMC scheme for the robot manipulator is verified by simulations and experiments.