A metabolically efficient leg brace

Abstract

Locomotion assistive devices can be broadly classified as either being passive or powered. Both have been created to aid in the leg's generation of a ground reaction force which supports the torso during locomotion, yet their inherent design has limited their functional growth to date. While many differing gait simulations have demonstrated stable solutions for lossless gait cycles, passive orthoses only diminish the user's impediment, and though powered gait exoskeletons can augment strength and endurance, they are limited by their energy demanding actuators. In response to these two extremes, an energy efficient locomotion assist device was developed from the basis of lossless gait models that did not require external power, and augmented locomotion by harvesting the inherent energy associated with the gait cycle. The simplest anthropomorphic leg can be modeled with a peg-leg shank, a knee, a thigh and a point mass for the head, arms and torso. Using a tuned non-linear hardening torsion spring at the knee joint, the torso support that is required between the ground and pelvis for lossless gait simulations can be generated; allowing the close physical realization of the theoretical. It was found that a single torsion spring can generate the leg thrusts necessary for a realistic range of walking and running gait velocities without the addition of any external power. While frictional losses do inhibit the locomotion assist device's efficiency, since the device functions in parallel with the user's leg, any losses can be supplemented with minimal muscular activity. These results give strong indication that a new avenue of gait assistive and gait augmenting devices that require minimal actuation energy is feasible.