Soft Wrist Exosuit Actuated by Fabric Pneumatic Artificial Muscles

Recently, soft actuator-based exosuits have gained interest, due to their high strength-to-weight ratio, inherent safety, and low cost. We present a novel wrist exosuit actuated by fabric pneumatic artificial muscles that has lightweight wearable components (160 g) and can move the wrist in flexion/extension and ulnar/radial deviation. We derive a model representing the torque exerted by the exosuit and demonstrate the use of the model to choose an optimal design for an example user. We evaluate the accuracy of the model by measuring the exosuit torques throughout the full range of wrist flexion/extension. We show the importance of accounting for the displacement of the mounting points, as this helps to achieve the smallest mean absolute error (0.283 Nm) compared to other models. Furthermore, we present the measurement of the exosuit-actuated range of motion on a passive human wrist. Finally, we demonstrate the device controlling the passive human wrist to move to a desired orientation along a one and a two-degree-of-freedom trajectory. The evaluation results show that, compared to other pneumatically actuated wrist exosuits, the presented exosuit is lightweight and strong (with peak torque of 3.3 Nm) but has a limited range of motion.

I. Introduction

Upper limb wearable assistive devices can be useful in a variety of scenarios. Healthy people can benefit from physical assistance to avoid fatigue and muscle strain during repetitive tasks or to augment their natural physical abilities [1], and the physically impaired can benefit from assistance for activities of daily living [2], or assistance and resistance during rehabilitation exercises [3]. Especially over the last decade, soft wearable assistive devices, also known as soft exosuits, have attracted much interest from the research community. The term “soft exosuits” is used as a collective term for wearable robotic devices made from compliant materials [4]. They wrap around the user’s body and rely on its structural integrity instead of an additional rigid frame to transfer reaction forces between body segments [5]. Compared to their rigid counterparts where the joints are motorized, soft exosuits have potential to solve several design and control challenges, including achieving a high strength-to-weight ratio, inherent safety, comfort, and low cost, as well as avoiding joint misalignment between the body and the wearable device [6].