Upper Limb Exoskeleton Supporting Shoulder Flexion Exercises for Rehabilitation: Mechanical Design and System Characterization

The shoulder rehabilitation program requires significant time and effort to complete. Patients sometimes need to perform specific exercises by themselves. Exoskeleton robots could help patients perform repetitive tasks correctly while requiring less monitoring from therapists. The level of assistive and resistive moments can be adaptive against the phase and across the patients. The motion data during training can be recorded to improve the rehabilitation outcome. This paper aims to design and build a prototype of an exoskeleton supporting the shoulder and the elbow joints during upper extremity exercise on a sagittal plane. A parallelogram four-bar linkage structure was applied so that the motor driving the elbow joint can be located concentrically to the shoulder motor at the non-moving base, which reduces the moving inertia of the upper arm limb. Two identical brushless DC motors with integrated controller and planetary gearbox were applied for both joints. For lightweight structure, the exoskeleton links were built from octagon carbon fiber tubes with 3D printed custom parts with full bearing support for the joints. The design allows adjustment of the exoskeleton links' length to comply with the body limb segments of a wearer. The workspace of the built prototype was validated to confirm the range of motion covering flexion and extension of the shoulder and the elbow joints. Experiments were conducted to evaluate the effect of gravity and to estimate the mass moment of inertia of the exoskeleton at different configurations of shoulder and elbow joint angles to further improve impedance control for physical human- ro bot interaction.