Robust Admittance Control of an Electric Underwater Manipulator for Precise Motion and Safe Contact Inspection of Hydraulic Structures
Fei Wang, Haixin Liu, Lin Cao, Shitong Hou, Guangming Song, Aiguo Song
Abstract
Inspection of hydraulic structures is crucial for ensuring the reliability and safety of infrastructures. Although underwater manipulators are essential tools, existing systems often lack sufficient compliance and safe interaction capabilities. This study develops a novel underwater manipulator system with a robust admittance control framework designed specifically for safe contact inspection tasks. The manipulator integrates a 6-axis force/torque sensor for contact force measurement and an ultrasonic detector for structural inspection. An underwater force estimation algorithm is implemented to ensure accurate force measurement under varying flow conditions. The proposed robust admittance control strategy comprises an inner-loop position controller, enhanced by an unknown system dynamics estimator and super-twisting sliding mode control, to counteract hydrodynamic disturbances and improve trajectory tracking accuracy. An outer-loop variable admittance controller, incorporating variable damping mechanism and adaptive feedback compensation, ensures compliant interactions and precise force control with minimal overshoot. Extensive experiments, including force measurement, motion and contact force control, and underwater thickness measurement, demonstrate the system's excellent performance, validating its effectiveness for hydraulic structure inspection tasks.