New Improvements for Prosthetic Legs: Scientists Learn from Robots

There may be some new improvements for prosthetic legs. Scientists have applied robot control theory to enable powered prosthetics to dynamically respond to the wearer's environment and help amputees walk.

"We borrowed from robot control theory to create a simple, effective new way to analyze the human gait cycle," said Robert Gregg, lead author of the new paper, in a news release. "Our approach resulted in a method for controlling powered prostheses for amputees to help them move in a more stable, natural way than current prostheses."

Human robots can actually run, jump and climb stairs autonomously. Yet modern prosthetics limit similar actions in humans. While prosthetics have been made lighter and more flexible over time, they fail to mimic the power generated from human muscles in able-bodied individuals.

In this particular study, Gregg proposed a new method to view and study the process of human walking. He suggested measuring a single variable that represents the motion of the body. More specifically, the variable was the center of pressure on the foot, which moves from heel to toe through the gait cycle.

"The gait cycle is a complicated phenomenon with lots of joints and muscles working together," said 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."

First, Gregg tested his theory on computer models. Then, he applied it to three above-knee amputee participants. More specifically, he implemented his algorithms with sensors measuring the center of pressure on a powered prosthesis. Each prosthesis was configured for each subject in about 15 minutes, and then the volunteers spent time walking on the ground and then on a treadmill. In the end, they were able to move at speeds of 1 meter per second; that's almost as fast as the typical walking speed of fully able-bodied people of 1.3 meters per second.

The new approach could help those using prostheses in the future. The next step is to compare results of experiments with robotic legs using both the time paradigm and center of pressure paradigm.

The findings are published in the journal IEEE Transactions on Robotics.