State Key Laboratory of Management and Control for Complex Systems, Institute of Automation, CAS, Beijing 100190,People's Republic of China.
School of Artificial Intelligence, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
Bioinspir Biomim. 2022 Sep 13;17(6). doi: 10.1088/1748-3190/ac84b6.
Undulation regulation in a robotic fish propelled by a passive flexible tail is more similar to that of a natural fish than with a rigid tail, owing to the smooth curvature of the flexible tail. Moreover, it has been observed that fish change the stiffness of their bodies to adapt to various swimming states. Inspired by this, a stiffness optimization scheme is explored for a novel elastic tail, which can improve the performance of the robotic fish. Spring steels are used as passive flexible joints of the fishtail; these can be easily expanded into multi-joint structures and the joint stiffness can be altered by changing the joint size. In this study, the Lagrangian dynamic method is employed to establish a dynamic model of the robotic fish in which passive flexible joints are simplified by a pseudo-rigid-body model. In addition, the hydrodynamics of the head and tail are analyzed using the simplified Morison equation and quasi-steady wing theory, respectively. Furthermore, to determine unknown hydrodynamic parameters in the dynamic model, a parameter identification method is applied. The results show that the identified simulation speeds fit the experimental speeds well within a wide range of stiffness values. Finally, to improve performance, the influence of joint stiffness and frequency on swimming speed is investigated based on the identified dynamic model. At each frequency, the optimal joint stiffness distribution is one that reduces the stiffness from the front to the rear. At the maximum driving frequency of 2.5 Hz, the optimal swimming speed is 0.3 body lengths per second, higher than that when rigid joints are used.
与刚性尾鳍相比，被动柔性尾鳍推动的机器鱼的波动调节更类似于天然鱼，这要归功于柔性尾鳍的平滑曲率。此外，人们已经观察到鱼会改变身体的刚度以适应各种游动状态。受此启发，探索了一种新颖弹性尾鳍的刚度优化方案，这可以提高机器鱼的性能。机器鱼尾鳍的被动柔性关节采用弹簧钢制成；这些关节很容易扩展成多关节结构，并且通过改变关节尺寸可以改变关节刚度。在这项研究中，采用拉格朗日动力学方法建立了机器鱼的动力学模型，其中通过伪刚体模型简化了被动柔性关节。此外，分别使用简化的莫里森方程和准定常机翼理论分析了头部和尾部的水动力。此外，为了确定动力学模型中的未知水动力参数，应用了参数识别方法。结果表明，在广泛的刚度值范围内，识别的模拟速度与实验速度非常吻合。最后，为了提高性能，基于所识别的动力学模型研究了关节刚度和频率对游动速度的影响。在每个频率下，最佳的关节刚度分布是从前到后减小刚度的分布。在最大驱动频率 2.5 Hz 时，最佳游动速度为 0.3 个体长/秒，高于使用刚性关节时的速度。
