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

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.

Improving Walking Energy Efficiency in Transtibial Amputees Through the Integration of a Low-Power Actuator in an ESAR Foot

“…The estimated energy injected by the actuator was computed by means of an offline kinetic model [17] and is shown in Fig. 7.…”

“…The stroke regulation was changed at each iteration, spanning the whole available range. For each tested stroke regulation, the energy injected by the actuator was computed offline by means of the kinetic model described in detail in the Supplementary Materials of our previous publication [17]. The model provides an estimate of the energy injected by the actuator by combining benchtests and experimental walking data.…”

“…To increase the energy storing capability of an off-the-shelf ESAR foot, we designed a semi-active prosthesis, namely the Wearable Robotics Laboratory Transtibial Prosthesis (WRL TTP) [17] embedding a low-power actuator in parallel to an ESAR foot (Fig. 1).…”

A Locomotion Mode Recognition Algorithm Using Adaptive Dynamic Movement Primitives

“…The transtibial amputee subject was requested to wear the Wearable Robotics Laboratory TransTibial Prosthesis (WRL TTP), a semi-active ankle-foot prosthesis designed to enhance the push-off during walking [28]. During experimentations, the WRL TTP did not provide additional power to the user and acted as a passive energy-storage-and-return foot.…”