Improved non-singular fast terminal sliding mode control for 4DOF ship-mounted rotary cranes

Abstract

The precise control of ship-mounted rotary cranes is critically challenged by their inherent underactuation, strong nonlinear coupling between boom motion and payload swing, and persistent wave-induced ship disturbances. While advanced control strategies (e.g., sliding mode control, adaptive control) have been developed, many existing designs either rely on model linearization, lack rigorous finite-time stability guarantees for the fully coupled system, or exhibit limited robustness against compound time-varying disturbances. To address these gaps, this paper proposes a novel adaptive non-singular fast terminal sliding mode (ANFTSM) controller. Its core innovation is a newly constructed sliding surface that explicitly integrates errors from both actuated and underactuated states, ensuring the finite-time convergence of all system variables. Enhanced robustness is achieved through adaptive laws that estimate and compensate for unknown friction and wind disturbances in real time, without requiring prior knowledge of disturbance bounds. Importantly, the controller is derived directly from the full nonlinear dynamics, forgoing any linearization, and its global stability is rigorously proven via Lyapunov theory. Extensive comparative experiments demonstrate that the proposed controller outperforms established benchmarks (PD-SMC, OFC, BBC). Under nominal conditions, it achieves the fastest convergence times (8.06 [s] for luffing, 8.56 [s] for rotation) and superior swing suppression, limiting the maximum radial sway to merely 2.05 [deg]. Furthermore, it maintains excellent robustness against significant parameter variations (e.g., load mass, cable length) and non-zero initial swing angles. These performance gains are accomplished with the lowest total control effort (70 [N · m · s]) among all compared methods, confirming its superior energy efficiency alongside outstanding control performance.