A Novel Jamming Structure With Interlocking Mechanism Towards Applications in Wearable Robots

Abstract

The adoption of variable stiffness actuators allows robots to take advantages of both rigid and soft structures. Jamming based variable stiffness structures are receiving increased attentions due to advantages of light weight, easy fabrication, and so on. However, the maximum bending stiffness and stiffness variation ratio achieved by most existing jamming structures are relatively small and unable to provide sufficient assistance to human joints when used in wearable robots. In this study, we proposed a novel jamming structure called gear jamming. Be different from most existing jamming structures that adopt frictional effects between internal components for resistance generation, the proposed jamming structure relies on an interlocking mechanism consisting of a series of gear-shape components and two layers distributed with teeth. A geometrical model was built to provide guidance for structure design, and experiments were performed to investigate effects of different factors on bending stiffness. A stiffness variation ratio up to 29.09 folds was achieved with the structure when the vacuum pressure increased from 0 to 90 kPa. To evaluate its performance for human joint assistance, a 64-g prototype was worn on subject's wrist to assist static holding of a 3-kg weight under a low vacuum pressure (30 kPa). Muscular activities of three representative muscles on the forearm reduced by 74.31±5.24%, 39.31±11.03%, and 71.48±3.00% in average over five subjects when compared to the condition without wearing the gear jamming prototype, which implied the promise of applying the proposed gear jamming structure in wearable robots.