Energy Harvesting Backpack
Rome’s major results were that (1) the backpack generated more electrical energy (4-7 Watts) during human locomotion than other human energy harvesting methods (example: piezoelectric shoe compression << 1 W) and (2) that the metabolic cost of carrying the oscillating load and generating electricity was less than expected using the backpack. For reference, cell phones typically use about 0.6 W. Using a combination of modeling and human subject experiments, we are exploring the underlying biomechanics of the energy harvesting backpack that may enable us to locomote at a lower metabolic cost than expected. This project is in line with my interests in human-machine interfaces and how to better couple or attach orthotic devices to the human body. Currently, I am acting in an advisory capacity for this project as it is being pursued by some of our ambitious undergraduate researchers (Yiqi Gao, Jeremy Brown).
Our hypotheses are based on our passive-dynamic walking models/simulations depicted below.
Energy harvesting backpack
In theory, single support (inverted pendulum) allows body weight to be supported with very little muscle effort (Kuo 2005). Experimental evidence suggests double support (transitioning from one leg to the other) is more metabolically costly.
For the oscillating payload, the force exerted by the load is reduced during the metabolically expensive double-support (mass-redirection) phase (Kuo 2005). Therefore, we hypothesize that proper phasing of the oscillating load may reduce the metabolic cost of carrying a given load
The human energy harvesting backpack was invented by Larry Rome at the University of Pennsylvania . In the proposed design, the backpack load is suspended via springs from the backpack frame. The frame in turn is attached to the human torso much like any other backpack. During normal human walking the hips (and consequently backpack frame) follow a sinusoidal motion, rising and falling throughout the gait cycle. This natural frequency of walking drives the backpack’s spring-mass system; (force) x (displacement) = (mechanical work or energy). This mechanical energy, generated as the backpack load oscillates up and down, can then be converted (at some fractional efficiency) to electrical power.
