# A low-power ankle-foot prosthesis for push-off enhancement

## TL;DR

This paper introduces a low-power robotic module that enhances the push-off of passive ankle-foot prostheses, improving gait and energy return for amputees.

## Contribution

The novel low-power active prosthetic module enhances energy return by augmenting off-the-shelf passive prostheses with parallel elastic actuation.

## Key findings

- The module increased dorsiflexion peak by 15.2% and 41.6% for two amputees during treadmill walking.
- Energy return improved by 26% and 45% for the two subjects, with a 2% increase in cadence observed.
- The control strategy adapts to user cadence and loading conditions for optimal energy return timing.

## Abstract

Passive ankle-foot prostheses are light-weighted and reliable, but they cannot generate net positive power, which is essential in restoring the natural gait pattern of amputees. Recent robotic prostheses addressed the problem by actively controlling the storage and release of energy generated during the stance phase through the mechanical deformation of elastic elements housed in the device. This study proposes an innovative low-power active prosthetic module that fits on off-the-shelf passive ankle-foot energy-storage-and-release (ESAR) prostheses. The module is placed parallel to the ESAR foot, actively augmenting the energy stored in the foot and controlling the energy return for an enhanced push-off. The parallel elastic actuation takes advantage of the amputee’s natural loading action on the foot’s elastic structure, retaining its deformation. The actuation unit is designed to additionally deform the foot and command the return of the total stored energy. The control strategy of the prosthesis adapts to changes in the user’s cadence and loading conditions to return the energy at a desired stride phase. An early verification on two transtibial amputees during treadmill walking showed that the proposed mechanism could increase the subjects’ dorsiflexion peak of 15.2% and 41.6% for subjects 1 and 2, respectively, and the cadence of about 2%. Moreover, an increase of 26% and 45% was observed in the energy return for subjects 1 and 2, respectively.