Fixed-time fractional second-order sliding mode control for robotic systems with actuator faults

A fixed-time fractional second-order sliding mode active fault-tolerant control scheme is proposed for robotic systems with actuator faults. The actuator faults are first estimated via a fixed-time fault observer. Adopting a fractional-order sliding mode surface and introducing a double-power reaching law, a fixed-time fractional second-order sliding mode controller is obtained to achieve active fault-tolerant control of robotic systems. Subsequently, an adaptive law is designed to deal with the fault estimation error. It is mathematically proved that the position tracking error can achieve a fixed-time convergence with the proposed scheme. Simulations show that compared with integer-order finite-time sliding mode control schemes, the proposed control scheme can enhance the fault compensation ability, improve tracking accuracy, and accelerate system response within a fixed time while effectively mitigating chattering.