Grip as Needed, Glide on Demand: Ultrasonic Lubrication for Robotic Locomotion
This work provides a new active friction control paradigm for robotic locomotion, potentially reducing design complexity and improving efficiency for robots operating in varied environments.
The authors introduce ultrasonic lubrication as an active friction control method for robotic locomotion, enabling dynamic switching between grip and slip states. Their bio-inspired inchworm and wasp ovipositor robots achieved bidirectional locomotion with over 90% efficiency, and friction reduction was demonstrated across diverse surfaces and conditions.
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.