1 Centre for Autonomous Systems, Faculty of Engineering and Information Technology, University of Technology, Sydney.
2 Wyss Institute for Biologically Inspired Engineering, School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts.
Soft Robot. 2017 Sep;4(3):202-210. doi: 10.1089/soro.2016.0053. Epub 2017 May 16.
Undulatory motion of the body is the dominant mode of locomotion in fishes, and numerous studies of body kinematics and muscle activity patterns have provided insights into the mechanics of swimming. However, it has not been possible to investigate how key parameters such as the extent of bilateral muscle activation affect propulsive performance due to the inability to manipulate muscle activation in live, freely swimming fishes. In this article we extend previous work on passive flexible mechanical models of undulatory propulsion by using actively controlled pneumatic actuators attached to a flexible foil to gain insight into undulatory locomotion and mechanisms for body stiffness control. Two soft actuators were attached on each side of a flexible panel with stiffness comparable to that of a fish body. To study how bilateral contraction can be used to modify axial body stiffness during swimming, we ran a parameter sweep of actuator contraction phasing and frequency. Thrust production by the soft pneumatic actuators was tested at cyclic undulation frequencies ranging from 0.3 to 1.2 Hz in a recirculating flow tank at flow speeds up to 28 cm/s. Overall, this system generated more thrust at higher tail beat frequencies, with a plateau in thrust above 0.8 Hz. Self-propelled speed was found to be 0.8 foil lengths per second or ∼13 cm/s when actuated at 0.55 Hz. This active pneumatic model is capable of producing substantial trailing edge amplitudes with a maximum excursion equivalent to 1.4 foil lengths, and of generating considerable thrust. Altering the extent of bilateral co-contraction in a range from -22% to 17% of the cycle period showed that thrust was maximized with some amount of simultaneous left-right actuation of ∼3% to 6% of the cycle period. When the system is exposed to water flow, thrust was substantially reduced for conditions of greatest antagonistic overlap in left-right actuation, and also for the largest latencies introduced. This experimental platform provides a soft robotic testbed for studying aquatic propulsion with active control of undulatory kinematics.
身体的波动运动是鱼类主要的运动模式，大量的身体运动学和肌肉活动模式的研究为游泳的力学提供了深入的了解。然而，由于无法在活体、自由游动的鱼类中操纵肌肉活动，因此无法研究关键参数（如双侧肌肉激活的程度）如何影响推进性能。在本文中，我们通过使用附着在柔性箔片上的主动控制气动致动器来扩展以前关于波动推进的被动柔性机械模型的工作，以深入了解波动运动和身体刚度控制的机制。两个软致动器附着在具有与鱼体相当的刚度的柔性面板的每一侧。为了研究双侧收缩如何在游泳过程中用于改变轴向身体刚度，我们对致动器收缩相位和频率进行了参数扫描。在循环波动频率为 0.3 至 1.2 Hz 的范围内，在流速高达 28 cm/s 的再循环流槽中测试了软气动致动器的推力产生。总体而言，该系统在较高的尾拍频率下产生更大的推力，在 0.8 Hz 以上的推力出现平台。当以 0.55 Hz 致动时，自推进速度被发现为每秒 0.8 个箔片长度或约 13 cm/s。这种主动气动模型能够产生具有最大偏移量等效于 1.4 个箔片长度的大量尾缘振幅，并产生相当大的推力。在 22%至 17%的周期内改变双侧共收缩的程度表明，当左右同时激活约 3%至 6%的周期时，推力达到最大。当系统暴露于水流时，在左右致动的最大拮抗重叠的条件下，以及在引入最大延迟的条件下，推力会大大降低。这个实验平台为研究具有波动运动主动控制的水下推进提供了一个软机器人测试平台。
