Dynamic Modeling of the Tuna-Inspired Robotic Fish Based on the Elastic-Damping Mechanism

Compliant passive mechanism has been widely employed in the development of bioinspired aquatic robots that imitates the variable stiffness of fish muscles. However, the existing compliant passive mechanism cannot produce excellent propulsion performance in a wide frequency range. To solve this problem, this paper proposes a novel modeling method for a tuna-inspired robotic fish with passive compliant joint. The passive compliant joint is developed composed of double torsion springs and damping liquid, attempting to implement on the robotic fish to achieve high swimming performance. In order to analyze the motion of the passive joint, a hydrodynamic-twisting-damping torque (HTDT) model is proposed. A dynamic model based on Kane equation is established and indicates that the compliant joint could affect the torque transmitted to the caudal fin to improve the swimming speed of the robotic fish. The particle swarm optimization (PSO) algorithm is further employed to optimize the joint parameters for an enhanced velocity performance. The obtained simulation results suggest that the proposed robotic fish model can reach to a speed of 2.32 m/s, exhibiting an excellent swimming performance. The dynamic model established by this study can make a guideline for the development of robotic fishes with the compliant passive joint.