A new knee brace developed by researchers at the University of Michigan and Simon Fraser University generates electricity when a user is walking.
“The trick we were after was really to copy the idea of regenerative braking in cars, where instead of just throwing energy away when you’re braking, we tried to use a generator to get power out of that — electrical power,” says Arthur Kuo, associate professor of mechanical engineering at the University of Michigan. The knee generator uses the motion of the knee braking itself before the next stride begins to capture that expended energy.
The 3.5-lb device looks similar to a knee brace with a housing attached at the joint. It is made of an aluminum chasse and uses steel gears with plastic bushings and steel shafts; any parts that were unavailable for purchase were CNC machined. The generator uses a three-phase permanent-magnet motor made for robotics as well as a mechanical clutch to engage and disengage the power-generation system.
Besides using the mechanical clutch, the knee generator uses a real-time control system built in the Mathworks’Simulink and run in Real-Time Windows Target, which opens and closes a switch on the power-generating circuit to engage and disengage power generation. “So you can imagine if the switch is open then there’s a resistance caused by the friction in the gear train and the generator, but not as much resistance because there is no back EMF,” says Max Donelan, assistant professor of kinesiology at Simon Fraser University.
Tests were recently conducted to determine the efficiency of the device. According to a University of Michigan release, the device requires less than 1W of metabolic energy to generate 1W of electricity and was tested at a rate of 2.2 mph. According to Kuo, the research team is looking into using a cable-driven system in order to place the device closer to the hips where the user would not notice the weight as much.
Kuo says the research team has already started partnering up with medical device companies. Potential applications include use in powered prosthetic knees, pacemakers and insulin pumps. “Essentially what we’re interested in doing for any implantable device is to try to decrease the number of times you have to replace the batteries,” he says.
Other uses could be for the military to help supplement the batteries used by soldiers in the field and to provide some power source to people in developing countries without any electricity. “About 1.6 billion people don’t have an electricity supply. Also, for those people, a lot of times they spend a lot of effort going to get water every day; that’s a big chore,” says Kuo. “So what if you could generate some electricity while you are going to get the water and then that could power the LED head lamp, the radio, the water purifier or a variety of devices.