Robotic Control Theory Turns Prostheses Into Bionics
A professor at the University of Texas at Dallas, along with researchers from the Rehabilitation Institute of Chicago, Northwestern University and the University of New Brunswick, applied robot control theory to enable powered prosthetics to respond to the environment and actively aid locomotion.
“We borrowed from robot control theory to create a simple, effective new way to analyze the human gait cycle,” says Dr. Robert Gregg, lead author of the research paper. “Our approach resulted in a method for controlling powered prosthesis for amputees to help them move in a more stable, natural way than current prostheses.”
Conventional prosthetics cannot reproduce the power output or compensation of typical human muscles, unlike humanoid robots that are able to run, jump and balance.
The team studied the gait cycle — each phase of walking movement — and implemented algorithms to allow the prosthetic to support a natural gait.
“The gait cycle is a complicated phenomenon with lots of joints and muscles working together,” says Gregg. “We used advanced mathematical theorems to simplify the entire gait cycle down to one variable. If you measure that variable, you know exactly where you are in the gait cycle and exactly what you should be doing.”
The variable used was the center of pressure on the foot, which moves from heel to toe during a stride.
After testing on computer models, the theory was tested on three amputees at the Rehabilitation Institute of Chicago using only height, weight and dimension of residual thigh to quickly configure the prosthesis for each subject. Each user then walked on the ground and a treadmill at increasing speeds.
“We did not tell the prosthesis that the treadmill speed was increasing. The prosthesis responded naturally just as the biological leg would do,” says Gregg.
Participants were able to use less energy than with their traditional prostheses and were able to walk at speeds very close to able-bodied individuals. Also, the 15-minute setup time drastically reduces the extensive fine tuning and training that goes into using traditional prostheses explained Gregg.
“Our approach unified multiple modes of operation into one and resulted in technology that could help people in the future,” he says.
The study was funded by the U.S. Army Medical Research Acquisition Activity, the Burroughs Wellcome Fund, and the National Institute of Child Health and Human Development.
