While trips and stumbles leading to falls can be common for amputees using leg prosthetics, a new robotic leg prosthesis being developed at Carnegie Mellon University promises to help users recover their balance by using techniques based on the way human legs are controlled.

Fig. 1 – The Robotic Neuromuscular Leg 2 is a cable-driven device that can help determine force feedback testing.
Hartmut Geyer, Assistant Professor of Robotics, explains that 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 shoves.

Over the next three years, as part of a $900,000 National Robotics Initiative study funded by the National Science Foundation, this technology will be further developed and tested using volunteers with above-the-knee amputations.

The collaborative project includes colleagues from the Department of Mechanical Engineering and Robotics, as well as a certified prosthetist orthotist and instructor in the Department of Rehabilitation Science and Technology at the University of Pittsburgh.

“Powered prostheses can help compensate for missing leg muscles, but if amputees are afraid of falling down, they won’t use them,” Geyer said. “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 apply the neuromuscular control scheme to prosthetic legs and, in simulation, to full-size walking robots. His observations include 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, called the Robotic Neuromuscular Leg 2. (See Figure 1)

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. 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.

For more information, visit www.cmu.edu/news.