Effects of caudal fin stiffness on optimized forward swimming and turning maneuver in a robotic swimmer
Effects of caudal fin stiffness on optimized forward swimming and turning maneuver in a robotic swimmer
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DOI：
10.1088/1748-3190/ad2f42
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发表时间：
2024-05-01
影响因子：
3.4
通讯作者：
Cheng，Bo
中科院分区：
文献类型：
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作者：
Deng，Hankun;Li，Donghao;Cheng，Bo
在动物和机器人体尾鳍型游泳者中，水动力推力主要由尾鳍产生，尾鳍的刚度对推力和游泳效率都有很大的影响。尾鳍僵硬也影响运动控制和所产生的与最佳游泳性能相对应的游泳步态；然而，它们之间的关系仍然很少被研究。在这里，我们使用磁力、模块化、波动机器人(μBot)，测试了尾鳍刚度对前向游泳和转弯机动的影响。我们开发了六个尾鳍，它们的硬度相差三个数量级以上。对于装有尾鳍的μ机器人(以及没有尾鳍的μ机器人)，我们在实验中应用强化学习来优化运动控制，以最大化前进游泳速度或最终航向改变。μ机器人的运动控制是由一个用于前向游泳的中央模式发生器或由一系列用于转弯机动的参数化方波来产生的。在前向游泳中，尾鳍刚度的变化导致了3种运动频率和游泳步态的优化，包括无尾鳍(4.6 Hz)、10−4Pam4(∼10.6 Hz)和10−4Pam4(∼8.4 Hz)。而游泳速度随步态的不同而独立变化，在0.2 3×10−4Pam4时达到最大值，无尾鳍的μ机器人速度最低。在转弯机动中，尾鳍刚度对头部初始转向和后坐的幅值以及最终的航向变化都有很大的影响。除无尾鳍的μ机器人外，对转向运动程序的影响相对较小。优化的前向游泳和转体动作具有相同的尾鳍硬度以及相似的脚柄和尾鳍运动模式，这表明μ机器人游泳的形式和功能关系简单。
In animal and robot swimmers of body and caudal fin (BCF) form, hydrodynamic thrust is mainly produced by their caudal fins, the stiffness of which has profound effects on both thrust and efficiency of swimming. Caudal fin stiffness also affects the motor control and resulting swimming gaits that correspond to optimal swimming performance; however, their relationship remains scarcely explored. Here using magnetic, modular, undulatory robots (μBots), we tested the effects of caudal fin stiffness on both forward swimming and turning maneuver. We developed six caudal fins with stiffness of more than three orders of difference. For a μBot equipped with each caudal fin (and μBot absent of caudal fin), we applied reinforcement learning in experiments to optimize the motor control for maximizing forward swimming speed or final heading change. The motor control of μBot was generated by a central pattern generator for forward swimming or by a series of parameterized square waves for turning maneuver. In forward swimming, the variations in caudal fin stiffness gave rise to three modes of optimized motor frequencies and swimming gaits including no caudal fin (4.6 Hz), stiffness< 10− 4 Pa m 4 (∼ 10.6 Hz) and stiffness> 10− 4 Pa m 4 (∼ 8.4 Hz). Swimming speed, however, varied independently with the modes of swimming gaits, and reached maximal at stiffness of 0.23× 10− 4 Pa m 4, with the μBot without caudal fin achieving the lowest speed. In turning maneuver, caudal fin stiffness had considerable effects on the amplitudes of both initial head steering and subsequent recoil, as well as the final heading change. It had relatively minor effect on the turning motor program except for the μBots without caudal fin. Optimized forward swimming and turning maneuver shared an identical caudal fin stiffness and similar patterns of peduncle and caudal fin motion, suggesting simplicity in the form and function relationship in μBot swimming.