A novel reaching-law-based sliding mode control for the joint of a deep-sea hydraulic manipulator

This paper proposes a novel sliding mode control method aimed at achieving high-precision control of a deep-sea hydraulic manipulator (DHM). Initially, we present a multivariable sliding mode reaching law based on a time-varying gain. Real-time online updating of the reaching law gain is implemented to balance chattering suppression and system convergence time. Subsequently, a nonsingular terminal sliding mode control method is developed, which, in conjunction with the nonsingular terminal sliding mode surface and reaching law design, effectively mitigates the negative effects stemming from uncertainties and unknown nonlinearities for precise DHM control. Third, this paper establishes a mechanism model for sliding mode reaching law gain and bandwidth, as well as the convergence time of the sliding mode control method, through a combination of Lyapunov stability theory and the system discrete method. This lays the foundation for parameter adaptive gain adjustment. Finally, the effectiveness and practicability of the proposed method are validated through simulations and experiments.