A Novel Variable Stiffness Underwater Biomimetic Propulsion Mechanism

After billions of years of evolution, fish have excellent swimming abilities and are research focus in the field of biomimetics. Currently, there is still a significant gap in swimming performance between robotic fish and real fish. A key factor is that real fish can change their body stiffness independently, but most robotic fish lack this ability. To overcome this bottleneck, we developed an underwater biomimetic propulsion mechanism based on the layer-jamming structure. By controlling the vacuum pressure in the inner cavity of the soft film, its stiffness can be adjusted over a wide range without changing the external shape of the mechanism. To analyse the stiffness change process of the propulsion mechanism, theoretical explanation and finite simulation were carried out, and its variable stiffness ability was verified by deflection tests and oscillation tests in water with one end fixed. The proposed variable stiffness propulsion mechanism will provide new ideas for the development of underwater biomimetic robots, and also provide a platform for exploring the relationship between fish body stiffness and swimming performance.