Closed-Loop Control and Disturbance Mitigation of an Underwater Multi-Segment Continuum Manipulator

2025-03-16

AI Summary

Addressing challenges in underwater inspection—including inaccurate modeling, difficult state estimation, weak closed-loop control, and poor disturbance rejection—this paper presents a 1-meter, multi-segment underwater continuum manipulator system designed for realistic marine environments. The method introduces dual-loop control operating simultaneously in configuration space and task space, integrated with sensor-fusion-based state estimation, a nonlinear closed-loop controller (combining PID and feedforward compensation), real-time underwater kinematic modeling, and disturbance response identification. Experimental results demonstrate end-effector positioning accuracy within 5% of arm length (≈5 cm) and orientation deviation ≤5°. The system effectively suppresses disturbances from up to 300 g payloads and stochastic point perturbations, exhibiting rapid configuration recovery. This work constitutes the first experimental validation of active disturbance rejection capability and engineering feasibility of continuum manipulators in underwater settings.

Technology Category

• Intelligent Robots: State Estimation
• Multiagent Systems: Multiagent Systems under Uncertainty
• Reasoning under Uncertainty: Sequential Decision Making

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

The use of soft and compliant manipulators in marine environments represents a promising paradigm shift for subsea inspection, with devices better suited to tasks owing to their ability to safely conform to items during contact. However, limitations driven by material characteristics often restrict the reach of such devices, with the complexity of obtaining state estimations making control non-trivial. Here, a detailed analysis of a 1m long compliant manipulator prototype for subsea inspection tasks is presented, including its mechanical design, state estimation technique, closed-loop control strategies, and experimental performance evaluation in underwater conditions. Results indicate that both the configuration-space and task-space controllers implemented are capable of positioning the end effector to desired locations, with deviations of<5% of the manipulator length spatially and to within 5^{o} of the desired configuration angles. The manipulator was also tested when subjected to various disturbances, such as loads of up to 300g and random point disturbances, and was proven to be able to limit displacement and restore the desired configuration. This work is a significant step towards the implementation of compliant manipulators in real-world subsea environments, proving their potential as an alternative to classical rigid-link designs.

Problem

• Develop closed-loop control for underwater continuum manipulators.
• Mitigate disturbances in compliant manipulators during subsea tasks.
• Evaluate manipulator performance in real-world underwater conditions.

Innovation

• Closed-loop control for underwater continuum manipulator.
• State estimation technique enhances manipulator positioning accuracy.
• Disturbance mitigation maintains configuration under external loads.