Fixed-Time Fault-Tolerant Control of Robotic Manipulators with Actuator Faults Based on Fixed-Time Extended State Observer

This paper proposes a fixed-time fault-tolerant controller for n-DOF robotic manipulators with actuator partial loss of effectiveness (LOE) faults, external disturbances, and unknown nonlinearities. A novel fixed-time extended state observer (FxTESO) is designed to estimate joint velocities and lumped uncertainty, and the estimation error can theoretically be arbitrarily small by increasing the bandwidth. An adaptive law is designed to estimate an upper bound related to FxTESO error, which can enhance the controller robustness. The proposed controller can guarantee practical fixed-time stability of the manipulator, and require no velocity measurement and prior information about lumped uncertainty. The comparative experiments with the other state-of-the-art controllers on a 4DOF manipulator under different external disturbances and actuator faults verify the superiority of the proposed controller.