Tight-Space Maneuvering of a Hybrid-Driven Robotic Fish Using Backstepping-Based Adaptive Control

Precise path-following control in tight space is a great challenge for underwater operation. To this end, this article proposes a 3-D path-following control system for a miniature robotic fish. Aiming at achieving higher maneuverability, a newly designed miniature hybrid-driven robotic fish is presented for maneuvering in a tight space, owning both fish-like and propeller-based motion modes. On this basis, a novel 3-D path-following control framework is proposed, including a navigation strategy, a depth controller, a heading controller, and a nonlinear mapping process, ensuring reliable 3-D path-following performance. More importantly, a gliding-oscillating-strategy-based backstepping-adaptive control method is provided to attenuate the jitter of the tracking error, which exhibits both low sensitivity to the hydrodynamic parameters and ideal match to the 3-D path tracking of a single-jointed robotic fish. Extensive comparative simulations and aquatic experiments are carried out, e.g., flexible swimming among obstacles in tight space and 3-D path-following tasks with imprecise hydrodynamic parameters. The obtained results verify the effectiveness of the designed prototype and the proposed methods, providing valuable insight for the new-type underwater platform design and underwater operations in tight space.