ANN ARBOR – The National Institutes of Health has awarded the University of Michigan $1.7 million to develop a special powered exoskeleton designed for the lower limbs.
U-M’s team aims to create a modular exoskeletal system for use on one or more leg joints -- a less bulky alternative to full-body suits. According to a U-M release, one in eight Americans lives with a mobility disability that makes it extremely challenging for them to walk or climb stairs.
The project will last three years and will focus on the elderly who have experienced an age-related decline in mobility and workers whose job is to lift and lower objects.
“Imagine adding a small motor to a bicycle—the rider still pedals, but there’s that extra power to get up hills without breaking too much of a sweat,” project lead Robert Gregg, associate professor of electrical and computer engineering said in a release.
“Similarly, we can take the conventional ankle, hip or knee braces used today, add a self-contained specialized motor and gear system, and provide power at a specific joint to increase mobility.”
Unlike conventional braces, which cannot actively assist a person’s joints during strenuous activities, state-of-the-art exoskeletons help to replace the total function of a limb.
However, accurately predicting the user’s intent is a great limitation of exoskeletons.
“There is a continuum of human movement possibilities, from jumping jacks to walking up a slightly different incline. If the exoskeleton recognizes the wrong activity, then it’s getting in the way of the human,” Gregg said in a release.
To solve the issue, Gregg and his team plan on developing a new control algorithm for the system, as well as an updated motor and transmission.
The challenging part of designing a new motor is how to deliver enough torque while still being a lightweight device, said Gregg.
He said his team will proceed using flat motors originally used in drones, which are being used in the Open Source Leg project by assistant professor of mechanical engineering Elliott Rouse.
The team is will work on developing a “task invariant” control algorithm to control both the motor and transmission, which, according to a news release “will not rely on knowing the task the user is trying to complete in order to effectively provide assistance.”
“You have to make sure that when you tell the motor what to do, it’s not fighting the human, but that’s a big challenge because you don’t always know the human’s intent,” Gregg said in a statement.
To address the issue, Gregg said the algorithm will work on changing how a person moves as opposed to predicting their intent.
“With this method, we may compensate for gravity: no matter where you move, the motor can assist with that,” Gregg said in a statement. “Another example is inertia: no matter where you move, the motor can compensate for limb inertia to make movement easier.”
The team will work with certified prosthetist orthotist at U-M’s Orthotics and Prosthetics Center, Alicia Foster, and associate professor of physical medicine and rehabilitation, Chandramouli Krishnan, on the project.
The team hopes to develop a low-cost system that would be easily added to existing knee, hip and ankle orthoses.