Friction is the essential mediator of terrestrial locomotion, yet in robotic systems it is almost always treated as a passive property fixed by surface materials and conditions. Here, we introduce ultrasonic lubrication as a method to actively control friction in robotic locomotion. By exciting resonant structures at ultrasonic frequencies, contact interfaces can dynamically switch between "grip" and "slip" states, enabling locomotion. We developed two friction control modules, a cylindrical design for lumen-like environments and a flat-plate design for external surfaces, and integrated them into bio-inspired systems modeled after inchworm and wasp ovipositor locomotion. Both systems achieved bidirectional locomotion with nearly perfect locomotion efficiencies that exceeded 90%. Friction characterization experiments further demonstrated substantial friction reduction across various surfaces, including rigid, soft, granular, and biological tissue interfaces, under dry and wet conditions, and on surfaces with different levels of roughness, confirming the broad applicability of ultrasonic lubrication to locomotion tasks. These findings establish ultrasonic lubrication as a viable active friction control mechanism for robotic locomotion, with the potential to reduce design complexity and improve efficiency of robotic locomotion systems.

翻译：摩擦力是陆地运动的关键媒介，然而在机器人系统中，它几乎总是被视为由表面材料和条件决定的被动属性。本文提出超声润滑作为一种在机器人运动中主动控制摩擦力的方法。通过以超声频率激励谐振结构，接触界面可以在"抓握"和"滑移"状态之间动态切换，从而实现运动。我们开发了两种摩擦控制模块：适用于类腔道环境的圆柱形设计和适用于外部表面的平板设计，并将其集成到仿尺蠖和黄蜂产卵器运动模式的仿生系统中。两个系统均实现了双向运动，且运动效率接近完美，超过90%。摩擦特性实验进一步证明，该方法能在干湿条件下，在不同粗糙度的刚性、柔软、颗粒状及生物组织界面上实现显著的摩擦力降低，证实了超声润滑在运动任务中的广泛适用性。这些发现确立了超声润滑作为机器人运动可行的主动摩擦控制机制，具有降低机器人运动系统设计复杂度并提高效率的潜力。