Gait Event Detection with Proprioceptive Force Sensing in a Powered
Knee-Ankle Prosthesis: Validation over Walking Speeds and Slopes
Abstract
Many powered prosthetic devices use load cells to detect ground
interaction forces and gait events. These sensors introduce additional
weight and cost in the device. Recent proprioceptive actuators enable an
algebraic relationship be?tween actuator torques and ground contact
forces. This paper presents a proprioceptive force sensing paradigm
which esti?mates ground reaction forces as a solution to detect gait
events without a load cell. A floating body dynamic model is obtained
with constraints at the center of pressure representing foot-ground
interaction. Constraint forces are derived to estimate ground reaction
forces and subsequently timing of gait events. A treadmill experiment is
conducted with a powered knee-ankle prosthesis used by an able-bodied
subject walking at various speeds and slopes. Results show accurate gait
event timing, with pooled data showing heel strike detection lagging by
only 6.7 ± 7.2 ms and toe off detection leading by 30.4 ± 11.0 ms
compared to values obtained from the load cell. These results establish
proof of concept for predicting gait events without a load cell in
powered prostheses with proprioceptive actuators.