Nonlinear Antiswing Control of Offshore Cranes With Unknown Parameters and Persistent Ship-Induced Perturbations: Theoretical Design and Hardware Experiments

In practical applications, offshore cranes are widely utilized on large scale ships to accomplish the tasks of transferring cargos from one ship to another or between ships and harbors. Compared with traditional land-fixed cranes, offshore cranes work in noninertial (ship) frames and their movements are significantly influenced by such complicated disturbances as sea waves, etc. Hence, the control issue of offshore cranes presents much more challenges. At present, existing controllers for offshore cranes are designed based upon linearized dynamics, and they need the accurate values of the plant parameters. However, the values of the parameters, including cargo/jib masses, are usually difficult to measure or even unknown, which makes exact gravitational force compensation difficult and unavoidably results in positioning errors for luffing and hoisting/lowering control. To deal with these practical issues, we suggest a novel model-parameter-free control approach to achieve effective control for underactuated offshore crane systems. By constructing an elaborate storage function, we provide a complete Lyapunov-based stability analysis. As far as we know, this paper provides the first control strategy to asymptotically regulate an offshore crane system subject to parametric uncertainties and ship-induced perturbations, which is developed without simplifying the original nonlinear dynamic equations. At last, a series of experimental results, carried out on a self-built offshore crane hardware platform, are presented to validate the effectiveness and robustness of the presented control scheme.