Many biological systems synchronize their movement through physical interactions. By far, the most well-studied examples concern physical interactions through a fluid: Beating cilia, swimming sperm and worms, and flapping wings all display synchronization behavior through fluid mechanical interactions. However, as the density of a collective increases, individuals may also interact with each other through physical contact. In the field of “active matter” systems, it is well known that inelastic contact between individuals can produce long-range correlations in position, orientation, and velocity. In this work, we demonstrate that contact interactions between undulating robots yield novel phase dynamics such as synchronized motions. We consider undulatory systems in which rhythmic motion emerges from time-independent oscillators that sense and respond to an undulatory bending angle and speed. In pair experiments, we demonstrate that robot joints will synchronize to in-phase and antiphase oscillations through collisions, and a phase-oscillator model describes the stability of these modes. To understand how contact interactions influence the phase dynamics of larger groups, we perform simulations and experiments of simple three-link undulatory robots that interact only through contact. Collectives synchronize their movements through contact as predicted by the theory, and when the robots can adjust their position in response to contact, we no longer observe antiphase synchronization. Lastly, we demonstrate that synchronization dramatically reduces the interaction forces within confined groups of undulatory robots, indicating significant energetic and safety benefits from group synchronization. The theory and experiments in this study illustrate how contact interactions in undulatory active matter can lead to novel collective motion and synchronization.

中文翻译：

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通过接触实现波动运动的集体同步

许多生物系统通过物理相互作用同步它们的运动。到目前为止，研究得最充分的例子涉及通过流体的物理相互作用：搏动纤毛、游泳的精子和蠕虫以及拍打翅膀都通过流体机械相互作用表现出同步行为。然而，随着集体密度的增加，个体之间也可能通过身体接触进行互动。在“活性物质”系统领域，众所周知，个体之间的非弹性接触可以产生位置、方向和速度的长程相关性。在这项工作中，我们证明了起伏机器人之间的接触相互作用产生了新的相位动力学，例如同步运动。我们考虑波动系统，其中有节奏的运动从独立于时间的振荡器中产生，这些振荡器感知并响应波动的弯曲角度和速度。在配对实验中，我们证明机器人关节将通过碰撞同步到同相和反相振荡，并且相位振荡器模型描述了这些模式的稳定性。为了了解接触相互作用如何影响较大群体的相位动力学，我们对仅通过接触相互作用的简单三连杆波动机器人进行了模拟和实验。正如理论所预测的那样，集体通过接触来同步他们的运动，当机器人可以根据接触调整自己的位置时，我们就不再观察到反相同步。最后，我们证明同步极大地减少了波动机器人的受限群体内的相互作用力，表明群体同步具有显着的能量和安全益处。本研究中的理论和实验说明了波动活动物质中的接触相互作用如何导致新的集体运动和同步。