Bristol Composites Institute (BCI), School of Civil, Aerospace and Design Engineering, University of Bristol , Bristol BS8 1TR, UK.
Exeter Technologies Group (ETG), Department of Engineering, University of Exeter , Exeter EX4 4PY, UK.
J R Soc Interface. 2024 Sep;21(218):20240148. doi: 10.1098/rsif.2024.0148. Epub 2024 Sep 4.
Biology is a wellspring of inspiration in engineering design. This paper delves into the application of elastic instabilities-commonly used in biological systems to facilitate swift movement-as a power-amplification mechanism for soft robots. Specifically, inspired by the nonlinear mechanics of the hummingbird beak-and shedding further light on it-we design, build and test a novel, rapid-response, soft end effector. The hummingbird beak embodies the capacity for swift movement, achieving closure in less than [Formula: see text]. Previous work demonstrated that rapid movement is achieved through snap-through deformations, induced by muscular actuation of the beak's root. Using nonlinear finite element simulations coupled with continuation algorithms, we unveil a representative portion of the equilibrium manifold of the beak-inspired structure. The exploration involves the application of a sequence of rotations as exerted by the hummingbird muscles. Specific emphasis is placed on pinpointing and tailoring the position along the manifold of the saddle-node bifurcation at which the onset of elastic instability triggers dynamic snap-through. We show the critical importance of the intermediate rotation input in the sequence, as it results in the accumulation of elastic energy that is then explosively released as kinetic energy upon snap-through. Informed by our numerical studies, we conduct experimental testing on a prototype end effector fabricated using a compliant material (thermoplastic polyurethane). The experimental results support the trends observed in the numerical simulations and demonstrate the effectiveness of the bio-inspired design. Specifically, we measure the energy transferred by the soft end effector to a pendulum, varying the input levels in the sequence of prescribed rotations. Additionally, we demonstrate a potential robotic application in scenarios demanding explosive action. From a mechanics perspective, our work sheds light on how pre-stress fields can enable swift movement in soft robotic systems with the potential to facilitate high input-to-output energy efficiency.
生物学是工程设计灵感的源泉。本文探讨了弹性不稳定性在工程设计中的应用，这些不稳定性在生物系统中被广泛用于促进快速运动，作为软机器人的功率放大机制。具体来说，受蜂鸟喙的非线性力学启发，并对其进行了进一步的研究，我们设计、制造和测试了一种新型的快速响应软末端执行器。蜂鸟喙具有快速运动的能力，能够在不到[Formula: see text]的时间内完成闭合。以前的工作表明，通过肌肉驱动喙根部的快速运动来实现快速运动。我们使用非线性有限元模拟和连续算法，揭示了蜂鸟喙启发结构的平衡流形的代表性部分。探索涉及到应用一系列由蜂鸟肌肉施加的旋转。特别强调的是确定和调整鞍结分岔沿流形的位置，在该位置弹性不稳定性触发动态快速运动。我们展示了序列中中间旋转输入的至关重要性，因为它导致弹性能量的积累，然后在快速运动时爆炸性地释放为动能。受我们的数值研究的启发，我们使用一种柔顺材料（热塑性聚氨酯）制造了一个原型末端执行器，并对其进行了实验测试。实验结果支持了数值模拟中观察到的趋势，并证明了仿生设计的有效性。具体来说，我们测量了软末端执行器向摆锤传递的能量，改变了预定旋转序列中的输入水平。此外，我们还展示了在需要爆炸动作的场景中的潜在机器人应用。从力学角度来看，我们的工作揭示了预加应力场如何使软机器人系统能够快速运动，并有可能提高输入到输出的能量效率。
