# Super-Twisting Sliding Mode Trajectory Tracking Control of an Underwater Manipulator Subject to Input Saturation Constraints

## TL;DR

A new control method improves underwater robot arm tracking accuracy and reduces chattering in complex environments.

## Contribution

A super-twisting sliding mode controller with ESO and anti-saturation system is proposed for underwater manipulators.

## Key findings

- Input saturation compensation significantly improves tracking robustness.
- Chattering is substantially suppressed without sacrificing robustness.
- Higher trajectory tracking accuracy and faster recovery after saturation are achieved.

## Abstract

What are the main findings?
A super-twisting sliding mode controller with ESO is proposed for underwater manipulators.Input saturation compensation significantly improves tracking robustness.

A super-twisting sliding mode controller with ESO is proposed for underwater manipulators.

Input saturation compensation significantly improves tracking robustness.

What are the implications of the main findings?
Robust and accurate trajectory tracking is achieved under actuator saturation.Chattering is substantially suppressed without sacrificing robustness.

Robust and accurate trajectory tracking is achieved under actuator saturation.

Chattering is substantially suppressed without sacrificing robustness.

To address the trajectory tracking problem of underwater manipulators operating in complex marine environments with strong multi-degree-of-freedom coupling, pronounced nonlinearities, and actuator saturation constraints, this paper proposes a super-twisting sliding mode control scheme integrated with an extended state observer and an anti-saturation auxiliary system. A dynamic model of the underwater manipulator incorporating major hydrodynamic effects (added mass and drag) is first established. Based on this model, a super-twisting sliding mode controller is designed to achieve fast convergence of the tracking errors while effectively alleviating the chattering phenomenon associated with conventional sliding mode control. An improved extended state observer is then introduced to estimate unmodeled dynamics and external time-varying disturbances in real time, providing feedforward compensation to enhance system robustness. To explicitly handle actuator output limitations, an anti-saturation auxiliary system is further developed to dynamically regulate the control input and mitigate the adverse effects of saturation. Comparative simulation studies conducted on the Oberon7 underwater manipulator demonstrate that the proposed control strategy achieves higher trajectory tracking accuracy, improved disturbance rejection capability, and faster recovery after saturation release compared with conventional control methods. These results indicate that the proposed approach offers an effective and reliable solution for high-precision trajectory tracking control of underwater manipulators under input saturation constraints.