Adaptive Integral Sliding Mode Control for Attitude Tracking of Underwater Robots With Large Range Pitch Variations in Confined Space

TL;DR

This paper tackles attitude control for underwater robots operating in confined spaces with large-range pitch variations. It introduces an adaptive integral sliding mode control (AISMC) that fuses integral sliding mode (ISMC) with adaptive switching gains to improve tracking accuracy and robustness amid unknown disturbances and complex turbulence. Lyapunov-based analysis establishes stability, and extensive experiments on a BlueROV2 Heavy demonstrate that AISMC significantly reduces tracking errors and chattering compared with PID and conventional SMC, particularly under large pitch excursions. The work advances reliable attitude control for constrained-environment operations, enabling more versatile underwater tasks such as navigation through narrow passages and stationary station-keeping under disturbance.

Abstract

Underwater robots play a crucial role in exploring aquatic environments. The ability to flexibly adjust their attitudes is essential for underwater robots to effectively accomplish tasks in confined space. However, the highly coupled six degrees of freedom dynamics resulting from attitude changes and the complex turbulence within limited spatial areas present significant challenges. To address the problem of attitude control of underwater robots, this letter investigates large-range pitch angle tracking during station holding as well as simultaneous roll and yaw angle control to enable versatile attitude adjustments. Based on dynamic modeling, this letter proposes an adaptive integral sliding mode controller (AISMC) that integrates an integral module into traditional sliding mode control (SMC) and adaptively adjusts the switching gain for improved tracking accuracy, reduced chattering, and enhanced robustness. The stability of the closed-loop control system is established through Lyapunov analysis. Extensive experiments and comparison studies are conducted using a commercial remotely operated vehicle (ROV), the results of which demonstrate that AISMC achieves satisfactory performance in attitude tracking control in confined space with unknown disturbances, significantly outperforming both PID and SMC.

Figures (8)

• Figure 1: AISMC attitude closed-loop control framework for underwater robots, enabling a wide range of pitch variations in confined space.
• Figure 2: A top view snapshot of the experimental setup. The water tank measures 1 m $\times$ 1 m$\times$ 1.3 m. Camera #1 perceives the horizontal positions of the robot, for real-time feedback control. Camera #2 is employed for recording the experiment from the underwater perspective only. Fathom-X Tether Interface Board facilitates the communication between the robot and upper computer via tethered connections. The confined space provides a testing environment of significant flow disturbances during robot attitude adjustments.
• Figure 3: Illustration of the BlueROV2 Heavy, the robot motion states, and the relevant coordinate reference frames.
• Figure 4: The robot undergoing large pitch variations controlled by AISMC in Task #3.
• Figure 5: Attitude tracking performance in Task #1. "Ref" denotes the reference trajectory, "Sim" represents the results of AISMC simulation, and the remaining curves show the experimental results of different controllers. Similarly for Fig. \ref{['fig6']} and Fig. \ref{['fig7']}.