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Lower-leg amputees to test new balance recovery technology

19 November 2015

A robotic leg prosthesis promises to help users recover their balance following a stumble, by using techniques based on the way human legs are controlled.

Lower-leg amputees are set to test Carnegie Mellon’s balance recovery technology (photo: Carnegie Mellon University)

Hartmut Geyer, assistant professor of robotics at Carnegie Mellon University, claims a control strategy devised by studying human reflexes and other neuromuscular control systems has shown promise in simulation and in laboratory testing, producing stable walking gaits over uneven terrain and better recovery from trips and stumbles. Over the next three years, this technology will be further developed and tested using volunteers with above-the-knee amputations.

“Powered prostheses can help compensate for missing leg muscles, but if amputees are afraid of falling down, they won’t use them,” Geyer says. “Today’s prosthetics try to mimic natural leg motion, yet they can’t respond like a healthy human leg would to trips, stumbles and pushes. Our work is motivated by the idea that if we understand how humans control their limbs, we can use those principles to control robotic limbs.”

Those principles might aid not only leg prostheses, but also legged robots. Geyer’s latest findings applying the neuromuscular control scheme to prosthetic legs and, in simulation, to full-size walking robots, were presented recently at the IEEE International Conference on Intelligent Robots and Systems in Hamburg, Germany.

Geyer has studied the dynamics of legged walking and motor control for the past decade. Among his observations is the role of the leg extensor muscles, which generally work to straighten joints. He says the force feedback from these muscles automatically responds to ground disturbances, quickly slowing leg movement or extending the leg further, as necessary.

Geyer’s team has evaluated the neuromuscular model by using computer simulations and a cable-driven device about half the size of a human leg, which they have dubbed Robotic Neuromuscular Leg 2.

The researchers found that the neuromuscular control method can reproduce normal walking patterns and that it effectively responds to disturbances as the leg begins to swing forward as well as late in the swing. More work will be necessary, however, because the control scheme doesn’t yet respond effectively to disturbances at mid-swing.

Powered prosthetics have motors that can adjust the angle of the knee and ankle during walking, allowing a more natural gait. These motors also generate force to compensate for missing muscles, making it less physically tasking for an amputee to walk and enabling them to move as fast as an able-bodied person.

About half of the US amputee population reports a fear of falling and large numbers say the inability to walk on uneven terrain limits their quality of life. According to Geyer, robotic prosthetics is an emerging field that provides an opportunity to address these problems with new prosthetic designs and control strategies.


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