A nonlinear disturbance observer using delayed estimates - its application to motion control of an underwater vehicle-manipulator system

This paper presents a control design method with a new nonlinear disturbance observer using delayed estimates for motion control of an underwater vehicle-manipulator system (UVMS). In recent years, application of an underwater vehicle has been expected in various fields. Since modeling unknown hydrodynamic forces is difficult, nonlinear disturbance observers have been proposed in the aim of decreasing disturbances due to hydrodynamic forces. In this paper, we propose a new disturbance observer by combining a conventional disturbance observer and time delay control, and attempt to apply it to motion control of a UVMS. Further, an analysis of ultimate boundedness and numerical simulations are conducted to evaluate the proposed control system. The respective analysis and simulation results show that the proposed disturbance observer exhibits faster convergence and less estimation errors than the conventional one and hence the control system based on it can perform successful motion control.