Disturbance observer-based fractional-order sliding mode control for free-floating space manipulator with disturbance

This paper proposes a fractional-order sliding mode control scheme based on disturbance observer for tracking control of free-floating space manipulators (FFSM), regarding system uncertainties and disturbances. To mitigate the effect of disturbance, a fast fractional-order disturbance observer (FFODOB) is proposed, which can estimate the disturbances in finite time. It relaxes the assumption of first-order differentiable of the disturbances, which is common in many existing disturbance observers, to continuous but not necessarily differentiable, making it more suitable for practical applications. Besides, a new fractional-order nonsingular terminal sliding mode (FONTSM) controller is designed, in which, a fractional-order integral term is introduced into the conventional nonsingular terminal sliding mode surface. The presented FONTSM improves the transient response and tracking precision of FFSM. Stability of the closed-loop system and finite-time convergence are proved theoretically. Simulations are performed for different situations, and the results demonstrate the effectiveness and superiorities of the proposed methods over the existing methods.