Design and Modeling of a Robotic Fish With Modular Adaptive Variable Stiffness Passive Joint

Fish in nature adjust their body stiffness in different flow environments to improve their swimming speed and efficiency, providing new ideas for developing bionic robotic fish. However, the existing variable stiffness fish-like tail structures currently require additional driving sources, which increases the complexity of the design and control of the robotic fish. Therefore, this article proposes a robotic fish with modular adaptive variable stiffness passive joint (MAVSPJ), which can achieve stiffness adaptive change without any driving sources. Then, a dynamic model of the robotic fish with MAVSPJ is established, and a customization design method for stiffness adaptive variation is proposed. Finally, the swimming performance of the designed tail with MAVSPJ is tested through extensive experiments. The results indicate that the designed tail with MAVSPJ can effectively achieve stiffness adaptive changing process, thereby improving the swimming performance of the robotic fish over a wide frequency range. This article provides valuable insights into the design of variable stiffness robotic fish.