Expected force adaptive variable impedance control of underwater manipulator in uncertain environment

Abstract Addressing challenges in underwater manipulator operations, including unknown environments, hydrodynamic disturbances, and dynamic force tracking, this study proposes a novel adaptive variable impedance control (AVIC) framework. Firstly, the framework employs a sliding mode controller (SMC) for end-effector position control, augmented by a nonlinear disturbance observer for real-time compensation of system uncertainties and underwater disturbances. Secondly, an AVIC strategy is developed, integrating parameter identification and force-tracking error feedback to adjust impedance parameters dynamically. Unlike conventional constant impedance control, which requires precise knowledge of the environment and exhibits limited adaptability to dynamic forces, the proposed method utilizes force-position coupling analysis to optimize impedance parameters and trajectory compensation concurrently. The position correction term, derived from the force-tracking error, dynamically modifies the reference trajectory via the SMC, achieving synergistic optimization of position tracking and dynamic contact force control. Lyapunov stability analysis proves the stability of the closed-loop system. Comparative simulations demonstrate a significant performance improvement of the proposed control law. Compared to PID position control, it reduces the settling time by 64.18% and decreases position error by 94.44%. When evaluated against constant impedance control and variable damping impedance control, the proposed method reduces force overshoot by 83.68% and 79.88%, respectively, and shortens force settling time by 57.62% and 48.35%, respectively. Moreover, it exhibits enhanced robustness to variations in environmental parameters. Simulation experiments confirm the control law’s superior transient performance and minimize steady-state error in tracking dynamic contact forces.