Background:
Upper extremity hemiparesis (one-sided weakness) affects roughly 50% of stroke survivors. Weakness in shoulder movement can limit individuals’ ability to perform daily activities for years post-stroke. Exosuits are soft wearable devices that offer mechanical support to limb motion. Powered tendon-driven exosuits use cables to transmit tension from actuator to limb, proven to reduce muscular demand on the deltoid muscle. Robot-assisted rehabilitation is proven more effective than traditional therapy for long term upper extremity rehabilitation.
Objective:
Develop a tendon-driven exosuit that assists shoulder flexion while remaining comfortable, lightweight, and adjustable for users.
Methodology:
I focused on the mechanical design of the exosuit—developing early concept sketches (Fig. 6), translating them into detailed CAD models of key components, and 3D printing and assembling these components.
Assembly features a backplate-mounted motor and pulley drive connected to a spool tied to a Bowden cable (Fig. 1); which is routed through a shoulder piece to an arm anchor point (Fig. 4, 5); and adjustable harness straps around the torso with a buckle. The motor spools the cable (Fig. 2, 3), which lifts the upper arm and assists the shoulder. The backplate and shoulder piece were designed to have minimal surface area and ergonomic curvature but sufficient width to keep harness straps around the shoulders from the harness slots, based on NASA anthropometric data and mockups on mannequins.
Based on typical shoulder assistance forces required by patients, I researched the optimal motor for the exosuit, balancing size and power requirements. The pulley drive ratio was designed to offer the greatest force output within the size limit of the backplate. I designed the main components to fit together in the smallest ergonomic design profile possible.
I then optimized these components for 3D printing and integration with traditional assembly hardware. Based on preliminary fit and mechanical alignment, I designed and printed a second iteration of the shoulder piece (Fig. 4).
Key Results:
Preliminary assembly testing on a model user confirmed that the exosuit reliably elevates the arm and can be comfortably worn and adjusted to individual body dimensions. The 3D-printed components, including the backplate and shoulder piece (featuring a spherical bearing for smooth cable routing), successfully met the design specifications for ergonomics and housing the required electro-mechanical components for force transfer. The mechanical assembly demonstrated proper interfacing, with the Bowden cable routing effectively transmitting force from the back-mounted motor to the arm anchor point.
Conclusion:
The mechanical design and prototyping of the tendon-driven exosuit have validated the feasibility of a lightweight, adjustable, body-mounted actuation system for shoulder movement assistance. My contributions—encompassing CAD development, optimal component ratio determination, and successful integration of 3D-printed parts—establish a solid foundation for further work. Future work by the lab involves identifying the optimal harness straps and integrating sensor feedback to fully realize a user-driven control system.
