Development of an Efficient Stiffness Modulation Mechanism in Fish-like Robots for Enhanced Swimming Performance

Abstract

Drawing inspiration from the ability of fish to maintain efficient swimming over a wide range of speeds by tuning the stiffness of their tails, researchers have explored stiffness adjustment mechanisms in fish-like robots. Typically, existing mechanisms require extra actuators or power sources only for tuning stiffness, resulting in additional energy consumption and more complex structures. To address this, our study introduces an innovative fishtail featuring an online stiffness modulation mechanism that does not require additional actuators or power sources solely for stiffness adjustment. Through model-based simulations and experimental testing, we evaluated the effectiveness of the proposed method. The results demonstrate that the designed mechanism enables efficient swimming across a broader frequency range (0–4 Hz) compared to most servo-actuated platforms with adjustable stiffness reported in existing studies. The robot achieves a maximum average speed of 1.4 BL/s and a minimum cost of transport of 9.5 J/(m•kg).