Worm gear mechanism with switchable backdrivability

Abstract

A worm gear has the advantages of a large reduction ratio and non-backdrivability. Because of this non-backdrivability, it can maintain a joint angle without energy consumption. Today, many robots have large workspaces that extend into the living spaces of humans, and they are required to work cooperatively with humans. In such cases, backdrivability is necessary to achieve high compliance for robots. Compliance helps robots perform cooperative tasks with humans, and protects its mechanisms and humans in the case of a collision. However, a worm gear cannot be backdriven because of the friction between tooth surfaces. Therefore, we have developed a worm gear mechanism that can switch its backdrivability using vibration that reduces friction. In this paper, we present a dynamic model of the worm gear to analyze the friction-reduction phenomenon caused by vibrations. We discuss the change in the effectiveness of the backdrivability with the change in the vibration direction. Finally, we experimentally confirm the certainty of the analysis.