Fast Swimming Robot Fish Under Countercurrent, Complex Trajectory, and Heavy Load Environments

ABSTRACT The present study proposes a new design for a robot fish which is propelled by periodic vibrations of a flexible‐soft coupled beam. This unique, flexible‐soft coupled beam can display the first and second‐order mode oscillations, which are capable of effectively mimicking the swings of the fish tail, resulting in fast swimming of the robot fish. Firstly, the nonlinear dynamic model for the coupled beam is established based on the absolute node coordinate formulation. The effect of length and stiffness parameters on natural frequency and mode shape of the coupled beam is explored to obtain the linear dynamic characteristics of the fish tail. To reach the maximum vibration amplitude, the optimal values for position, frequency, and magnitude of the applied force and the length and stiffness parameters are determined. In the following, the control system uses a communication mode to receive signals from a wireless communication module, and an inertial sensor is designed. The fuzzy PID algorithm is employed to control vibrations of the coupled beam to realize the swimming forward and turning around of the robot fish. Finally, through 3D printing and the opening mold technique, the robot fish is fabricated with an overall size of 130 × 125 × 70 mm 3 . Swimming experiments are performed to display the propulsion speed and force of the robot fish. It shows that the swimming speed of 1.17 BL/s can be achieved, which is much higher than most of the previously designed robot fish in BCF mode. In addition, the experiments indicate that the robot fish has an excellent swimming performance even in countercurrent, complex trajectories, and heavy load environments. The present study offers a delicate design and a precise theory of the flexible‐soft coupled beam‐based fish tail for fast swimming of the robot fish.