Adaptive robust tracking control of an underwater vehicle-manipulator system with sub-region and self-motion criteria

This paper proposes an adaptive robust control scheme for an Underwater-Vehicle Manipulator System (UVMS). The proposed controller enables the tracking of the intersection of multiple local sub-regions that are assigned for each subsystem of a UVMS under the influence of modelling uncertainties as well as additive disturbances. The presence of variable ocean currents creates hydrodynamic forces and moments that are not well-known or predictable, even though they are bounded. Therefore, the control task of tracking a prescribed sub-region trajectory is challenging due to these additive bounded disturbances. In the presented adaptive control law, a least-squares estimation algorithm is utilized rather than gradient-type approach. The use of the self-motion due to the kinematically redundant system allows performance of multiple subtasks (e.g., maintaining manipulability and avoidance of mechanical joint limits). The asymptotically sub-region and sub-task tracking are ensured using the proposed control law despite the parametric uncertainty of the UVMS and external additive disturbances. The stability analysis is carried out using the Lyapunov-type approach. The simulation results illustrate the validity of the proposed control scheme.