Device Gives New Meaning to "Power Walking"

[David Farber <dave () farber net>]

________________________________________
From: Kurt Albershardt [kurt () nv net]
Sent: Saturday, February 09, 2008 1:24 PM
To: David Farber
Subject: Device Gives New Meaning to "Power Walking"

<http://sciencenow.sciencemag.org/cgi/content/full/2008/207/1>
Device Gives New Meaning to "Power Walking"

By Devin Powell
ScienceNOW Daily News
7 February 2008

The latest fad in self-powered wrist wear is the kinetic watch, a device that converts the momentum of a swinging arm 
into milliwatts. But researchers have unveiled a new accessory for your knees that puts the trendy timepiece to shame. 
Generating more than 1000 times more energy, the "Biomechanical Energy Harvester" may provide a green way to power the 
portable devices of the future.

Every time you take a step, you use two different groups of powerful muscles connected to the knee. The first group 
pushes to kick the lower leg out. Just before full extension, the second group pulls to put the brakes on. But for Max 
Donelan, director of the Simon Fraser University Locomotion Laboratory in Burnaby, Canada, and his colleagues, this 
braking process is just useful energy going to waste. His team has created a modified knee brace with a drive train 
that converts the mechanical
energy into electricity. "A similar principle is used in hybrid cars to make electricity when you press the brakes; 
it's called generative braking," says Donelan.

Six volunteers wore the braces while they walked on treadmills. Embedded sensors detected the angle and velocity of 
their legs, switching the device on only during the braking phase of each swing. As the team reports tomorrow in 
Science, the braces produced 5 watts of power--enough to run 10 cell phones. And although it took a bit more effort to 
swing the added weight of the brace--the prototype weighs 1.6 kg--the walkers didn't have to work harder when the 
power-harvesting mechanism was turned
on. The amount of oxygen they consumed--a measure of metabolism and effort--didn't increase. "Our generator actually 
helps your muscles out," says Donelan, "by decelerating your limbs for you."

If the researchers can lighten the load of the device, the first users will likely be people whose lives depend on 
reliable, portable power: patients with insulin pumps, for example. Douglas Weber, a team member and mechanical 
engineer at the University of Pittsburgh School of Medicine in Pennsylvania, believes that it will also be incorporated 
into the design of cutting-edge neuroprostheses--artificial limbs directly controlled by brainwaves and deep-brain 
stimulators for Parkinson's disease
patients. Eventually, the device might prove useful for anyone off the main power grid: soldiers, relief workers, 
hikers, even normal folks with cell phones and personal digital assistants.

...

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