Adaptive non-singular fixed-time sliding mode control of moving-base underwater flexible manipulators

This paper presents a composite controller for trajectory tracking of moving-base underwater flexible manipulators (UFM). Firstly, a dynamics model of the moving-base UFM is established, and the model is decomposed into a slow-varying subsystem and a fast-varying subsystem by using the singular perturbation method. Then, an adaptive non-singular fixed-time sliding mode controller based on a high-order sliding mode observer is proposed for the slow-varying subsystem. In this controller, the high-order sliding mode (HOSM) observers are used to estimate and compensate for lumped disturbances, and adaptive super-twisting algorithm is used to reduce sliding mode chattering, which overcomes the disadvantage that the traditional adaptive method is prone to overestimation. To further suppress the system chattering, a HOSM observer is used to obtain the flexible mode derivatives for the fast-varying subsystem to achieve the suppression of vibration modes. The main advantages of this controller are its non-singularity, fast finite-time convergence and good vibration suppression. Extensive simulation results have validated the effectiveness of the proposed control method.