Implementation and Validation of a Data-Driven Variable Impedance Controller on the Össur Power Knee.

While prototype prostheses and control algorithms have demonstrated compelling clinical benefits in research laboratories, studies with commercially-available robotic prostheses have often failed to demonstrate similar benefits for users, limiting their adoption into mainstream clinical practice. This work is a step towards addressing this shortcoming by presenting the implementation of a phase-based variable impedance controller on the commercially-available Össur Power Knee ${ }^{\text {TM }}$ for walking and sit/stand tasks. We show that, through preliminary experiments with $\mathrm{N}=4$ high-mobility above-knee prosthesis users, the Power Knee under our controller can produce clear clinical benefits compared to the users' prescribed prostheses. In sitting and standing, users demonstrated generally increased leg-loading symmetry and speed with the Power Knee, indicating easier motions with less over-use of the sound limb. In walking, users demonstrated improved gait with the Power Knee, including increases in toe clearance and early-stance knee flexion. These positive results are similar to our previous work on prototype hardware, demonstrating our controller's hardware generalization and its potential for generating clinical benefits with commercial prostheses. These results are a step towards a promising future in which commercially-available robotic prostheses provide users with concrete clinical benefits.