Adaptive hierarchical sliding mode controller for tower cranes based on finite time disturbance observer

Summary A finite time disturbance observer (FTDO) based adaptive hierarchical sliding mode control (AHSMC) is proposed for 4‐DOF tower crane systems with unknown external disturbances. More specifically, to overcome the unknown disturbances, an FTDO combined with the designed adaptive observation error is presented to estimate both matched and unmatched disturbances. Then a new error dynamics taking into account the unmatched disturbances is defined, based on which, a novel nonsingular fast terminal sliding mode (FTSM) surfaces is designed to improve the convergence of system states. Finally, in order to ensure the stability of each subsystem, an AHSMC law incorporating the suggested FTSM‐type reaching law is presented to realize the anti‐sway and positioning control of tower crane system. The finite‐time stability analysis of the closed‐loop system is derived by Lyapunov technique, and simulation results verify the effectiveness of the presented control strategy.