Fixed time robust control for tower cranes with unmatched disturbances and input saturation

To address the challenging problem of fixed-time anti-sway and positioning control for tower cranes with uncertain disturbances and input saturation, a novel fixed-time anti-saturation robust algorithm is proposed. First, on the basis of a newly designed fixed-time convergence system, a fixed-time disturbance observer (FTDO) is developed to estimate the matched and unmatched disturbances. Then, an anti-saturation compensator is employed to deal with the input saturation and make the control input leave the saturated region rapidly. Upon which, a novel non-singular fast terminal sliding mode surface is presented. Furthermore, in order to ensure the stability of each subsystem, a hierarchical sliding mode surface taking into account unmatched disturbances and input saturation is designed. Finally, the FTDO based hierarchical sliding mode control law is introduced to improve the transient control performance and robustness of tower cranes. The fixed-time convergence of the closed-loop system is proved by Lyapunov technique. Numerical simulations for four scenarios demonstrate the validity of the presented control scheme and fastest convergence speed in comparison to the recently proposed fixed-time control methods.