Robot Control Theory Applied To Improve Prosthetic Legs

Robot Control Theory Applied To Improve Prosthetic Legs
(Image source)
Researchers applied robot control theory to enable powered prosthetics to dynamically respond to the wearer's environment and help amputees walk. In the study published in the journal IEEE Transactions on Robotics, wearers of the robotic leg could walk on a moving treadmill almost as fast as an able-bodied person.
 
Humanoid robots can walk, run, jump and climb stairs autonomously, but modern prosthetics limit similar actions in humans. While prosthetics have been made lighter and more flexible, they fail to mimic the power generated from human muscles in able-bodied individuals. Powered prostheses, or robotic legs, have motors to generate force, but lack the intelligence to stably respond to disturbances or changing terrain.
 
Control engineers view the human gait cycle through the lens of time - the interval at which each movement in the walking cycle needs to occur. The researchers proposed a new way to view and study the process of human walking: measuring a single variable that represents the motion of the body. In this study, that variable was the center of pressure on the foot, which moves from heel to toe through the gait cycle.
 
The researchers first tested the theory on computer models, and then with three above-knee amputee participants at the Rehabilitation Institute of Chicago, an affiliate of Northwestern University. They implemented the algorithms with sensors measuring the center of pressure on a powered prosthesis. Inputted with only the user's height, weight and dimension of the residual thigh into the algorithm, the prosthesis was configured for each subject in about 15 minutes. Subjects then walked on the ground and on a treadmill moving 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", one of the researchers said.
 
The participants were able to move at speeds of more than 1 meter per second; the typical walking speed of fully able-bodied people is about 1.3 meters per second. The participants also reported exerting less energy than with their traditional prostheses.
 
Current powered prosthetic devices require a team of physical rehabilitation specialists spending significant amounts of time tuning hundreds of knobs and training each powered leg to the individual wearer. The next step in the research will be to compare results of experiments with robotic legs using both the time paradigm and center of pressure paradigm.