Backstepping Control of Gliding Robotic Fish for Trajectory Tracking in 3D Space

Autonomous underwater gliders have become valuable, energy-efficient tools for a myriad of applications including ocean exploration, fish tracking, and environmental sampling. Many applications, such as, exploring a large area of underwater ruins or navigating through a coral reef, would benefit from fine trajectory tracking. However, trajectory tracking control of underwater gliders is particularly challenging due to their under-actuated, nonlinear dynamics. Taking gliding robotic fish as an example, in this work we propose a backstepping-based controller for the gliding motion to track a desired reference for the pitch angle and position in the 3D space. In particular, the challenge of under-actuation is addressed by exploiting the coupled dynamics and introducing a new modified error term that combines pitch and horizontal position tracking errors. The effectiveness of the proposed control scheme is demonstrated via simulation and its advantages are shown via comparison with a PID controller.