Velocity-free practical fixed/predefined-time fault-tolerant tracking control of manipulators

How to maintain performance and avoid instability when encountering velocity-free measurement and actuator failures in dynamically changing environments is challenging. Through employing an embedded function, a new fixed/predefined-time criteria is introduced. Due to more adjustable parameters for the size of compact set and settling time, the scheme is more general for facilitating the control design, and can converge to a smaller residual set. It can achieve a reduction in the overall trajectory tracking error with the presence of disturbance and uncertainties. Subsequently, a practical fixed/predefined-time fault-tolerant tracking control of manipulators without velocity measurement and under actuator faults is proposed Based on a state observer, it achieves predefined-time estimation of joint angular velocity using only the signals from position sensors. A predefined-time observer is used for estimate the upper bound of lumped disturbance, and another one is used to compensate for actuator faults and saturation. Finally, the proposed control method is verified through trajectory tracking of manipulators.