Configurable Pneumatic Soft Actuators for Multi-Directional Wrist Rehabilitation

Due to their inherent compliance and safe interac- tion with their environment, soft robots play a significant role in wrist rehabilitation. However, current designs lack bending in multiple directions and have limited payload capacity. This article aims to explore various configurations of pneumatic soft fingers, specifically targeting the different bending directions of the wrist joint. A pair of parallel-connected soft actuators is mounted on the index and ring fingers to achieve extension and flexion movements by simultaneously pressurizing both actuators. Pronation and supination are achieved by activating two diagonally positioned actuators, while radial and ulnar motions are accomplished through two side-connected actuators attached to the little finger and thumb. A nonlinear static analysis based on the Yeoh model is conducted to validate the design while concerning its bending and deflection. A series of experiments is carried out to verify the bending and payload capacity of the pneumatic soft finger. The results show that it achieves a bending angle of 270◦, while carrying a payload of 200 g. Moreover, the effectiveness of soft design is validated by bending a 660 g metal frame, which is designed to mimic a human hand, in multiple directions. Finally, four soft fingers were employed to successfully perform flexion deviation on a real human hand. This paper represents the initial phase of utilizing pneumatic soft fingers to achieve multiple wrist- bending movements.