Powered lower leg prostheses have gotten rather complicated lately, utilizing multiple motors to produce motion within the devices’ joints. While this capability can lead to a natural walking gait, it can also lead to awkward device behavior when moving over unusual terrain, going up and down stairs, and trying to walk as fast as possible. Researchers at University of Texas at Dallas have been working on translating techniques used to control walking robots for use in powered prostheses in order to produce a natural and speedy walking gait even in unusual conditions.
The team wanted to rely on a single variable to adjust the motor activity of a prosthetic leg. They focused on the center of pressure that the body applies to the foot as the person is walking. With each step this spot moves from the back to the front of the foot as the person steps on the heel and shifts the body to move the weight toward the toes. Interestingly, this variable defines exactly where the person is during a walking gait and the prosthetic has everything it need to figure out what to do next.
The investigators then developed control software that takes as input the person’s height, weight, and the measurements of the remaining stump. This was tested on three above-the-knee amputees at the Rehabilitation Institute of Chicago for whom the software was customized within about fifteen minutes. The patients were then asked to walk on the ground and also use a treadmill that would speed up without the software being notified of the change. The three amputees were able to walk nearly as fast as healthy people and reported having to exert themselves less than when using traditional control software.