Adaptive Fractional-Order Fast-Terminal-Type Sliding Mode Control for Underwater Vehicle-Manipulator Systems

This article proposes an adaptive fractional-order fast-terminal-type sliding mode control method to solve the trajectory tracking problem of the underwater vehicle-manipulator system in the presence of large dynamic uncertainties and strong external disturbances. For improving the control continuity and accuracy of the conventional sliding mode control method, a modified fractional-order sliding mode control scheme with a novel fractional-order sliding manifold and a fast-terminal-type reaching law is proposed. In addition, an auto-tuning law of switching gains is presented and combined with the fractional-order sliding mode control scheme to overcome the problem that the fixed switching gain may lead to obvious tracking performance degradation under complicated lumped disturbances. Finally, the superiorities of the proposed adaptive fractional-order fast-terminal-type sliding mode control method are verified through a series of comparative simulations of a 6-degrees-of-freedom (DOF) UVMS carrying a 6DOF manipulator.