Design tradeoffs in the development of a wearable soft exoskeleton for upper limb mobility disorders

This paper investigates the tradeoffs between design variables important for the development of a mobility support soft exoskeleton for horizontal shoulder adduction. The soft exoskeleton utilizes discreet shape memory alloy (SMA) spring actuators to generate the required torque to move the arm segment, while preserving the qualities of a soft, wearable garment solution. A pilot benchtop test involving varying power input, actuator anchor position, actuator orientation, and added weight, was investigated to evaluate their effects against the degree of motion the soft exoskeleton allows. The results show that the power input, actuator anchor position, and simulated limb weight each affect the ultimate horizontal adduction angle the exoskeleton is able to induce. Further, the project highlights a crucial point in regard to the tradeoffs between functionality and wearability: when actuator orientation was investigated, we found a decrement in functionality (as measured by maximum achievable horizontal adduction angle) when the actuators were constrained close to the body. This shows that when aiming to improve the hypothetical system’s wearability/usability, the effective torque that can be generated is reduced. Together these findings demonstrate important design considerations while developing a wearable, soft exoskeleton system that is capable of effectively supporting movement of the body while maintaining the comfort and discreetness of a regular garment.