Adaptive PID actuator fault tolerant control of single-link flexible manipulator

Actuator faults may cause performance degradation of a system and may sometimes even lead to instability. This paper deals with the fault tolerant control problem of a single-link flexible manipulator under a loss of actuator effectiveness. The proposed control scheme uses an adaptive proportional–integral–derivative (APID) controller, which may automatically online tune the three control gains, kp, ki, and kd. The adaptation laws of the APID controller are derived in the sense of the Lyapunov function, so that the stability of the closed-loop system may be guaranteed. The main advantage of the proposed methodology is that no prior offline learning or manual retuning of the PID controller is required to accommodate the actuator fault. In addition, the proposed APID controller does not require any knowledge of the fault magnitude in advance. The effectiveness and feasibility of the proposed approach is tested for the hub angular position and tracking control of a single-link flexible manipulator under both faulty and fault-free conditions. The results demonstrate that the approach is valid, leading to an accurate fault reconstruction, a better transient and good tracking performance, and significantly improved upon previous approaches in terms of errors with respect to the corresponding traditional fixed-gain PID controller.