Neurobionics Lab

Motivation:

It was desired to extend the capabilities of the Variable Stiffness Orthosis (VSO) to allow for decoupled energy storage and return (DESR), similar to the Decoupled Energy Storage and Return VSPA Foot. For users with foot drop or other conditions of ankle weakness/disability, storing energy in one part of the gait cycle for use in another part of the gait cycle can provide increased push off power (capturing energy at heel strike for use at push off for example). Additionally, since a DESR module is comprised of two cam profiles, instead of one, it can allow for two separate device equilibrium angles. Since it can be desirable to have a more dorsiflexed ankle equilibrium during swing but a more plantarflexed equilibrium during standing, for safety and comfort respectively, this feature of the DESR module has the potential to be an improvement for AFO users.

Approach:

With its two separate cam profiles, the DESR module allows for loading and unloading the VSO’s spring along distinct torque-angle relationships. Distinct torque-angle relationships encoded in two separate cams can allow for multiple ankle equilibrium angles, energy recycling between gait phase, and differing the rates of energy storage and return. The DESR module switches between cams by dividing the cam profiles into dynamic and static parts, which correspond to regions of the full torque-angle relationship. When the static cam profile (gray) is loaded by the cam follower, the dynamic cam profiles are unloaded (blue and red). In this state, passive, permanent magnets switch the cam profiles at predetermined ankle angles. This switching allows the DESR module to harvest energy from one region of the gait cycle (region one) as spring preload for use later in the gait cycle (region 2), comprising of entirely passive components.

Optimization:

The DESR modules can be optimized for any biomechanical objective, using an optimization tool. This tool was validated through the design of DESR modules that maximize energy recycling or swing angle of the foot for both able-bodied users of VSO and users with foot drop. The tool is rooted in a genetic algorithm and can be easily parameterized for different populations.

Contributors: Nikko Van Crey, Emily Bywater, Hemanth Aroumougam, Elliott Rouse

Publications:

Van Crey, N. Lam, D.J., Bywater, E.A., Shepherd, M., and Rouse, E.J. “The Variable Stiffness Orthosis: Customizable Mechanics for Assistance and Rehabilitation.” Authorea Preprints (2024).

Bywater, Emily A., Nikko Van Crey, and Elliott J. Rouse. “Optimizing the Mechanics of a Variable-Stiffness Orthosis With Energy Recycling to Mitigate Foot Drop.” IEEE Transactions on Medical Robotics and Bionics (2024).