Turning motion direction of fish robot driven by non-uniform flexible pectoral fins

Flexible fins own outstanding advantages in robotic fish locomotion, especially in high propulsive efficiency. This paper proposes a mechanism for changing the moving direction of fish robots in two-dimensional planes using flexible pectoral fins. Firstly, a mathematical model of the fish robot equipped with non-uniform flexible pectoral fins is introduced. In this model, the influences of fluid inertia, and drag of the surrounding fluid exerting on the fin surface is considered as the Morison force. Based on the energetic method, the Assume Mode Method (AMM) and Rayleigh-Ritz method, the solution for the body motion and deformation of the points on the flexible fins is derived. Secondly, the mechanism for steering the direction of robot swimming motion is proposed. Due to the complex influence of lift forces which are generated by pectoral fins on the robot orientation, a fuzzy logic controller is designed to stabilize the angle trajectory of the fish robot. Finally, the numerical simulations, the movement performances, and the control effectiveness are illustrated.