Trajectory Tracking Control of Rowing Pectoral Fin-Actuated Robotic Fish

Robotic fish has received increasing attention in the last few decades, as they hold strong promise in a myriad of applications. Efficient and precise control of these robots, particularly accurate trajectory control, has become essential in many of these applications. This article proposes a dual-loop backstepping-based trajectory tracking control approach for a robotic fish actuated by rowing pectoral fins. While rowing pectoral fin-based locomotion is important for maneuvering, the range constraints of fin movement pose significant challenges in the control of robotic fish, including potentially preventing the robot from generating the thrust needed to maneuver in a desired direction. To overcome these challenges, we propose a dual-loop controller, designed based on an averaged dynamic model of the robot. In particular, an outer-loop backstepping-based controller finds the needed force and moment inputs for the robot to track the desired trajectory, while the inner loop determines the optimal fin-beat parameters such that the resulting fin-generated forces and moment are close to their desired values. Experimental results are presented to show the efficacy of the proposed control scheme, where the robot is commanded to track a trajectory with variable linear and angular velocities. Comparing to a well-tuned proportional–integral–derivative controller, the proposed control scheme shows a distinct advantage in tracking desired orientations in addition to tracking desired positions.