Abstract
The complexity of the marine environment results in a low grasping success rate for underwater robot manipulators, coupled with a high damage rate that leads to grasping injuries and slippage of underwater targets. Consequently, precise real-time control of contact forces between the end-effector and targets becomes critically necessary. Currently, Active Disturbance Rejection Control (ADRC) has been applied to underwater manipulators. While this method effectively filters underwater disturbances in position-control systems, it struggles to achieve precise force control on the contact forces between the manipulator's end-effector and targets. Therefore, this paper proposes a PID-ADRC tandem control strategy that integrates the external PID force control loop with the active disturbance rejection position control in series, forming a composite tandem control structure without disrupting the position inner loop. When the underwater target is not in contact, ADRC is employed to achieve high-precision position tracking. Upon contact with the target, the system automatically switches to PID-ADRC force control, in which system model uncertainties, fluid resistance, and contact force disturbances are treated as a total perturbation, enabling real-time estimation and compensation via an extended state observer (ESO). This approach enhances system robustness without requiring accurate modeling.