Inspired by the snap-through action of a steel hairclip, we propose a design method for in-plane prestressed mechanisms that exhibit biomimetic morphing and high locomotion performance. Compliant bistable flapping mechanisms are fabricated using this method and are mounted on our untethered soft robotic fish. Using this mechanism, we achieve life-like undulation with a Strouhal number (1) of St = 0.28 and a velocity of 2.03 body lengths per second (43.6 cm/s), a three-fold improvement over past compliant fish robots. A tethered pneumatic version indicates that this mechanism is compatible with soft actuators. We study the mechanism both computationally and experimentally and suggest that elastic instability may offer a path to overcome the speed challenge of soft and compliant robots.

翻译：受钢制发夹弹跳动作的启发，我们提出了一种面向面内预应力机构的设计方法，该机构可实现仿生变形并具有高运动性能。利用该方法制备了柔性双稳态扑翼机构，并将其安装在无系绳软体机器鱼上。通过该机构，我们实现了类生物波动，斯特劳哈尔数 St = 0.28，游速达到每秒2.03倍体长（43.6 cm/s），性能较以往柔性机器鱼提升三倍。系留气动版本实验表明该机构与软体执行器兼容。我们通过计算与实验方法研究该机构，并指出弹性失稳或许能为克服软体及柔性机器人速度难题提供一条新路径。