Double-Loop Fractional Integral Sliding Mode Trajectory Tracking Control for an Underwater Manipulator

A double-loop fractional integral sliding mode control (DLFISMC) strategy is designed to solve the trajectory tracking problem of an underwater manipulator with bounded external disturbance, which is composed of the outer loop position control and the inner loop velocity one. On the basis of the fractional theory and the stability method, the sliding mode surfaces and the reaching laws are designed respectively. In addition, an auxiliary is introduced to the inner loop controller to estimate the external disturbance. The Lyapunov theory can ensure the finite-time convergence and stability of the closed-loop system. The simulation results from a 6 degree of freedom (DOF) underwater manipulator validate the higher precision tracking performance and better robustness of the proposed control system against the external disturbance.