Finite-Time Observer Based Prescribed Performance Robust Control for Position Stabilization of Offshore Gangway Ends

Consider an offshore gangway subject to mathematical model parameter uncertainties and disturbance uncertainties. A finite-time observer (FTO) is designed to estimate the motion states of the gangway end (GE) and the total uncertain nonlinear disturbances lumped by the parameter uncertainties and disturbance uncertainties. The bandwidth of the FTO is a function of the GE position estimation error and a prescribed performance function and is time-varying, and thus our designed FTO does not rely on the bounds of the derivatives of the total uncertain nonlinear disturbances compared with conventional FTOs. Whereby, according to the idea of the active disturbance rejection control, we develop a prescribed-performance robust control law (PPRCL) for GE position stabilization such that the position stabilization error can converge into a prescribed tolerance steady-state band in a finite settling time. Simulation results with comparisons show the robustness and the advantage of our developed PPRCL.