Design of a quasi-passive parallel leg exoskeleton to augment load carrying for walking

Abstract

Biomechanical experiments suggest that it may be possible to build a leg exoskeleton to reduce the metabolic cost of walking while carrying a load. A quasi-passive, leg exoskeleton is presented that is designed to assist the human in carrying a 75 lb payload. The exoskeleton structure runs parallel to the legs, transferring payload forces to the ground. In an attempt to make the exoskeleton more efficient, passive hip and ankle springs are employed to store and release energy throughout the gait cycle. To reduce knee muscular effort, a variable damper is implemented at the knee to support body weight throughout early stance. In this thesis, I hypothesize that a quasi-passive leg exoskeleton of this design will improve metabolic walking economy for carrying a 751b backpack compared with a leg exoskeleton without any elastic energy storage or variable-damping capability. I further anticipate that the quasi-passive leg exoskeleton will improve walking economy for carrying a 751b backpack compared with unassisted loaded walking. To test these hypotheses, the rate of oxygen consumption is measured on one human test participant walking on a level surface at a self-selected speed. Pilot experimental data show that the quasi-passive exoskeleton increases the metabolic cost of carrying a 751b backpack by 39% compared to carrying 75 lbs without an exoskeleton. When the variable-damper knees are replaced by simple pin joints, the metabolic cost relative to unassisted load carrying decreases to 34%, suggesting that the dampening advantages of the damper knees did not compensate for their added mass.

(cont.) When the springs are removed from the aforementioned pin knee exoskeleton, the metabolic cost relative to unassisted load carrying increased to 83%. These results indicate that the implementation of springs is beneficial in exoskeleton design.