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
AI summary
Problem
Existing underwater manipulators lack sufficient compliance and safe interaction capabilities, struggling with hydrodynamic disturbances that cause inaccurate force measurement and dangerous contact force overshoot.
Approach
The system integrates a 6-axis force/torque sensor with a control framework that uses an unknown dynamics estimator and super-twisting sliding mode control for precise motion, paired with a variable admittance controller and adaptive feedback for compliant force regulation.
Key results
- Accurate underwater force estimation compensates for flow-induced sensor drift
- Robust position controller significantly improves trajectory tracking under varying flows
- Variable admittance controller ensures stable contact force tracking with minimal overshoot
- Successful underwater thickness measurement validates practical inspection capability
Why it matters
This work enables safe, reliable robotic inspection of aging underwater hydraulic infrastructure, reducing diver risk and improving maintenance accuracy in complex flow environments.
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 con- troller, 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 damp- ing 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.