Design and Preliminary Evaluation of a Wearable Passive Cam-Based Shoulder Exoskeleton

Area of Science:

• Biomechanical Engineering
• Rehabilitation Technology
• Human Movement Science

Background:

• Passive exoskeletons offer a practical and affordable approach for continuous, home-based movement assistance.
• A clinical need exists for effective, non-intrusive assistive devices for shoulder movement.
• Wearable assistive devices can improve quality of life and functional independence.

Purpose of the Study:

• To design, fabricate, and evaluate a wearable, passive, cam-driven shoulder exoskeleton (WPCSE) prototype.
• To validate the mechanical output of the WPCSE against a theoretical model.
• To assess the impact of the WPCSE on muscle activity and shoulder kinematics in able-bodied subjects.

Main Methods:

• Development of a novel modular spring-cam-wheel mechanism for customizable assistive force generation.
• Benchtop experiments to validate the mechanical output of the WPCSE prototype against theoretical predictions.
• Pilot biomechanics study involving eight able-bodied subjects performing shoulder elevation and adduction/abduction movements.

Main Results:

• The spring-cam-wheel module closely matched theoretical moments, but the full WPCSE exhibited deviations (up to 30% lower/120% higher) due to friction.
• A WPCSE prototype, compensating for ~25% of gravitational shoulder elevation moment, showed a trend towards reduced muscle activity (EMG).
• The WPCSE did not constrain or impede tested shoulder movements, demonstrating functional compatibility.

Conclusions:

• The WPCSE prototype provides proof-of-concept for assisting shoulder movements against gravity.
• The device's modular design allows for customized assistance, addressing individual needs.
• Further research and optimization are warranted to mitigate friction and enhance assistive performance for clinical application.