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In this paper, the tracking control problem of underwater robot manipulators is investigated under the influence of the lumped disturbances, including unknown ocean current disturbances and parameter uncertainties. The proposed novel continuous nonsingular finite–time (CNFT) control method is twofold. Firstly, the modified adaptive super–twisting algorithm (ASTA) is proposed with a nonsingular fast terminal sliding mode (NFTSM) manifold to guarantee the finite–time convergence both in the sliding mode phase and the reaching phase. Secondly, a higher–order super–twisting disturbance observer (HOSTDO) is exploited to attenuate the effects of the lumped disturbances. Considering the time–varying gain matrix of the closed–loop control system, the bounded stability is strictly proved via the Lyapunov theory. Hence, the superiority of the proposed controller is singularity–free, fast convergence, chattering–free, high steady–state tracking performance, and good robustness by resorting to the methods of CNFT control and ASTA in combination with a disturbance observer. Finally, numerical simulations are conducted on a two degree–of–freedom (DOF) underwater robot manipulator to demonstrate the effectiveness and high tracking performance of the designed controller.

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This article studies the trajectory tracking control of underactuated underwater vehicles using control moment gyros through a biologically inspired approach based on homeomorphism transformation and Lyapunov functions in the horizontal plane. First, a series of assumptions and simplifications need to be made to build the kinematic and dynamic equations of the underwater vehicle under a single-frame pyramid configuration structured with four control moment gyros. Second, the error dynamics analysis of the submarine based on the control moment gyros is derived from the equations, and a tracking control algorithm is proposed to demonstrate the feasibility and stabilization of this tracking control scheme from theoretical analysis. Finally, the numerical simulation results are given for verifying the effectiveness and feasibility of the rendered control law.

This paper focuses on the attitude tracking control of the autonomous underwater vehicle (AUV) using control moment gyros (CMGs) with the lumped nonlinearities including model uncertainty, coupling dynamic property, external disturbance, and input saturation. To describe the attitude of the AUV without singularities, quaternions are used to describe its translational and rotational motion. A finite-time convergent extended state observer (FTCESO) in conjunction with the sliding mode control (SMC) approach is exploited to design the tracking controller for the closed-loop system with the finite-time convergence. Meanwhile, in order to release the burden of the observer, the anti-windup compensator is utilized to handle the nonlinearity of input saturation. A switch function is considered to make a switch between the robust controller and the constant-rate reaching law. Subsequently, with consideration of the inherent singularity problem of actuator dynamics, the constrained steering logic is implemented to avoid this issue without introducing other torque errors in theory. Finite-time stability of the attitude tracking system is guaranteed by the Lyapunov-based approach. Finally, the simulation results validate the attitude tracking performance of the CMG-based AUV with the proposed control strategy, when it is subject to the stated nonlinear uncertainties. INDEX TERMS Autonomous underwater vehicle, control moment gyros, attitude tracking control, extended state observer, input saturation.