Design of a Gravity Compensation Actuator for Arm Assistance

This thesis presents the design, simulation, and evaluation of a passive, wearable, and human-scale actuator that includes pulleys and uses polymers for energy storage. Repetitive tasks such as packing boxes on an assembly line may require high strength movements of the shoulder, arm, and hand and may result in musculoskeletal disorders. With the objective to offset the weight of the arm and thereby lower the forces on the muscles in the shoulder and arm, this actuator is able to provide gravity compensation for the upper extremities of workers, if used in conjunction with an arm exoskeleton. The actuator is passive, meaning that it does not use motors or sensors, but instead creates a force on a cable that is a function of the displacement of the cable.

This thesis details the design of the actuator and the selection of an appropriate polymer for use with the actuator. To determine the best polymer for this application, tests were conducted on nine polymers to ind their average Young's modulus and their hysteresis. A 90A abrasion-resistant polyurethane rubber belt was used in the final design due to its high modulus and low hysteresis. The final actuator design was tested in an Instron machine to validate its performance. During testing, the actuator provided 720N in extension and 530N in retraction, which are roughly 112% and 83% of the torque required to lift a human arm, respectively.