This article explores a set of locomotion optimization methods for a novel tendon-driven robotic fish. With the typical features of the dual tendon driving active tail and variable stiffness passive caudal fin, a fully functioning tendon-drive robotic fish is developed. Next, a practical dynamic model for the tendon-driven robotic fish is established with full consideration of variable stiffness passive caudal fin, and the model parameters are accurately identified via data-driven methods. More importantly, to improve the motion performances, an asymmetric central pattern generator is particularly proposed, and an adjustment rule of passive stiffness is explored to fit different motion states of the robotic fish. Finally, extensive simulations and aquatic experiments verify the feasibility of the proposed prototype and locomotion optimization methods. The obtained results show that the improvements of steering radius and forward swimming velocity are 36.3% and 29%, respectively. At present, our robotic fish can achieve maximum forward swimming as 1.04 BL/s (BL for the body length), maximum turning rate as 153.3 $^\circ$ /s, and the minimum turning radius reaches to 0.31 BL, providing a valuable reference for bioinspired research of aquatic mechanical design and locomotion control.

中文翻译：

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具有可变被动尾鳍的肌腱驱动机器鱼的运动优化

本文探索了一组用于新型肌腱驱动机器鱼的运动优化方法。利用双肌腱驱动主动尾部和变刚度被动尾鳍的典型特征，开发了功能齐全的肌腱驱动机器鱼。接下来，在充分考虑可变刚度被动尾鳍的情况下，建立了肌腱驱动机器鱼的实用动力学模型，并通过数据驱动方法准确识别模型参数。更重要的是，为了提高运动性能，特别提出了一种非对称中心模式发生器，并探索了被动刚度的调整规则以适应机器鱼的不同运动状态。最后，广泛的模拟和水生实验验证了所提出的原型和运动优化方法的可行性。所得结果表明，转向半径和前泳速度分别提高了36.3%和29%。目前，我们的机器鱼最大前泳速度可达1.04 BL/s（BL为体长），最大转身速度为153.3 $^\circ$ /s，最小转弯半径达到0.31 BL，为水上机械设计和运动控制的仿生研究提供了有价值的参考。