Switching PD-based sliding mode control for hovering of a tilting-thruster underwater robot

Area of Science:

• Robotics
• Control Systems
• Ocean Engineering

Background:

• Underwater robots require precise control for stable hovering.
• Tilting thruster speed is critical for maintaining stability in 6-DOF motion.
• Traditional Proportional-Derivative (PD) control has limitations at lower tilting speeds.

Purpose of the Study:

• To develop an advanced control method for stable 6-DOF hovering of underwater robots.
• To enhance hovering performance at reduced thruster tilting speeds.
• To address the limitations of existing PD control methods.

Main Methods:

• A switching Proportional-Derivative-based Sliding Mode Control (PD-SMC) method was developed.
• The method combines PD control with sliding mode control principles.
• A sigmoid function replaced the sign function in sliding mode control to mitigate chattering.

Main Results:

• Simulations demonstrated PD-SMC effectiveness for tilting durations up to 1500 ms, compared to 600 ms for PD control.
• Experimental results confirmed superior hovering performance of PD-SMC over PD control.
• The proposed method ensures stable hovering even at significantly lower thruster tilting speeds.

Conclusions:

• The PD-SMC method offers a robust solution for stable underwater robot hovering.
• This control strategy significantly expands the operational range concerning thruster tilting speed.
• The findings present a substantial advancement in underwater robot control technology.