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Non-Powered Ankle Exoskeleton Can Mimic Calf Muscles, May Assist Post-Stroke Walking

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The walking assist clutch was developed as a non-powered exoskeleton that reduces the energy expended for walking. (Image courtesy of UNC Chapel Hill.)

The walking assist clutch was developed as a non-powered exoskeleton that reduces the energy expended for walking. (Image courtesy of UNC Chapel Hill.)

Recovery from stroke or orthopedic injury may get a big assist from a lightweight, unpowered exoskeleton designed to be worn on the ankle that reduces the energy needed to walk by approximately 7%, or the equivalent of removing a 10-pound weight. This new technology that effectively makes humans more efficient at walking was developed by Carnegie Mellon University’s Steve Collins, assistant professor of mechanical engineering, and North Carolina State University assistant professor of biomedical engineering Greg Sawicki.

The wearable exoskeleton—called the walking assist clutch—is described in a media release from Carnegie Mellon University as a wearable boot-like apparatus that, when attached to the foot and ankle, reduces the energy expended in walking by around 7%. That reduction is equated with the removal of a 10-pound backpack. Furthermore, the release notes, the device requires no power source—so there are no batteries to recharge or replace—and is made to be affordable to users.

Collins, who is a roboticist, notes that the device could be a boon to individuals whose jobs require them to spend considerable amounts of time walking. The technology also has application, however, to individuals affected by injury or a movement disability.

For example, the release notes, an individual recovering from a stroke could regain the ability to walk with the assistance of the device, or a child with a developmental delay may find taking steps is done more easily. For someone needing rehabilitation, devices based on this technology could be life-changing, according to the release.

Although Collins cautions against being too speculative, he is optimistic. “Someday soon we may have simple, lightweight, and relatively inexpensive exoskeletons to help us get around, especially if we’ve been slowed down by injury or aging.”

Collins demonstrates the device in an online video.

Walking Assist Clutch Mechanism

The functional action of the device is relatively simple. The device is designed to use a spring that acts like the Achilles’ tendon and a clutch that mimics the calf muscles. The difference is that the spring and clutch do not expend any energy as tendons and muscles do.

“The unpowered exoskeleton works in parallel with your muscles, thereby decreasing muscle force and the metabolic energy needed for contractions,” says Greg Sawicki, a biomedical engineer at North Carolina State University and co-author of the article.

The device is designed to reduce the load placed on the calf muscles and the spring stores and releases elastic energy. The clutch engages the spring while the foot is on the ground, disengaging it while the foot is in the air.

While muscles waste energy in producing force, this simple device is said to do so passively.

Collins concluded, “We asked ourselves years ago, ‘Is there a way to assist a human in the task of walking by reducing their own energy use without needing an additional energy source?’ The answer to this question, it turns out, is ‘yes.’ ”

[Source: Carnegie Mellon University]