In-Situ Measurement of Multi-Axis Torques Applied by Wearable Soft Robots for Shoulder Assistance

While a number of wearable soft robotic devices have been proposed to assist the shoulder, limited efforts have been made to quantify the amount of torque they apply to the body. Most work to-date has assessed soft actuator performance with simple benchtop experiments that may not be representative of the boundary conditions on the human body. We propose a new methodology to measure torques directly in-situ on the body and then use this technique to make a detailed comparison of two versions of a soft wearable shoulder assistance robot. The impact of a number of factors are considered, such as actuator design, garment anchoring, material hysteresis, arm pose, and inflation pressure. Many of these factors are not present on the benchtop and are found to significantly affect torque production. We compare results obtained on a simple benchtop test fixture with two on-body settings: an idealized mannequin and actual human subjects. The mannequin and human results were similar, but differed significantly from the benchtop, further motivating the need for on-body testing. Moving forward, we believe that the ability to directly quantify device performance in-situ will be critical to develop new design, modeling, and control strategies for wearable robots.