Servo - January 2016

BETTER BALANCE FOR BOTS (AND HUMANS)

Trips and stumbles too often lead to falls for amputees using leg prosthetics, but a 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.

Hartmut Geyer, assistant professor of Robotics, said 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 through the National Science Foundation, this technology will be further developed and tested using volunteers with above-the-knee amputations.

Joining Geyer on the research team are Steve Collins, associate professor of Mechanical Engineering and Robotics, and Santiago Munoz, 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, 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.

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, he noted, because the control scheme doesn’t yet respond effectively to disturbances at mid-swing.

More than a million Americans have had a leg amputation and that number is expected to quadruple by 2050, Geyer said. About half of the amputee population reports a fear of falling, and large numbers say the inability to walk on uneven terrain limits their quality of life.

STEPPIN’ OUT As witnessed at the DARPA Robotics Challenge Finals, walking isn’t easy for robots. However, the Chinese robot Xingzhe No.1 recently walked for 54 hours straight, taking 360,000 steps that covered 83.28 miles, setting the world record for furthest distance walked by a quadruped robot.