Design and Control of an Actuated Prosthetic Elbow to Restore Arm Swing for Persons with Upper Limb Absence

Dynamic balance in human locomotion relies on the regulation of whole-body angular momentum. Asymmetry in upper extremity body mass and motion that occurs from upper limb absence disrupts this regulation. Conventional transhumeral prostheses do not restore controlled arm swing, leaving this asymmetry unresolved. This project aimed to develop an actuated prosthetic elbow that mimics natural elbow rotations to restore arm swing during walking. Two prototypes with contrasting designs were fabricated and tested. Prototype 1, featuring a direct drive motor, tracked arm swing trajectories based on able-bodied data with less than 5 % position error. It enabled evaluation of predicted elbow torque requirements, showing that a double-pendulum dynamic model overestimates torque needs. This finding supports using smaller, lighter direct drive motors for natural arm swing. While Prototype 1 performed well, its motor was too large for practical integration. Prototype 2 successfully fit the drive and control system into a standard prosthetic envelope for enhanced applicability. Testing revealed that gearbox friction hindered control, and successful operation required synchronizing elbow movement with natural arm swing frequency. Despite using the same control system, both prototypes produced notably different outcomes. These results highlight potential for future designs incorporating a small direct drive motor to match Prototype 1's performance while maintaining Prototype 2's compact form.