Simple unpowered walking assist clutch is like removing a 7-20 pound backpack by putting a spring in your step

For over a century, scientists have tried to make it easier for people to walk. Evolution has shaped an extremely efficient human gait, but even with Mother Nature’s improvements we still spend more energy walking than on any other activity.

The solution: a mechanical clutch that fits in the palm of your hand.

It is lightweight, unpowered, wearable exoskeleton (the walking assist clutch) to reduce the energy cost of human walking. This wearable boot-like apparatus, when attached to the foot and ankle, reduces the energy expended in walking by around 7%.

If a 7% improvement in walking with a robotic exoskeleton doesn’t seem very impressive, consider that it is approximately equivalent to removing a 10-pound backpack. And, given this device’s simplicity, it would be extremely low-cost to produce. (Keep in mind that the Bionic Man’s 60 MPH hardware came with a six million dollar price tag.)

The walking assist clutch is also lightweight and requires no power source, so there are no batteries to recharge or replace.

The HULC, lower body exoskeleton was so heavy and required so much energy to power it that DARPA recently abandoned the project.

The exoskeleton comprises rigid sections attached to the human shank and foot and hinged at the ankle. A passive clutch mechanism and series spring act in parallel with the calf muscles and Achilles tendon.

Nature – Reducing the energy cost of human walking using an unpowered exoskeleton

“Think of nurses, emergency response workers, soldiers or the millions of other people who walk many hours a day—7% would make a difference to them.”

In other words, that added 7% efficiency would help them go the proverbial extra mile.

Another population that might benefit from this technology includes those with disabilities or recovering from injuries.

Imagine someone recovering from a stroke who can walk again with her granddaughter in the park, or a child with a developmental delay taking steps more easily. For someone needing rehabilitation, devices based on this technology could be life-changing.

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.”

So how exactly does the walking assist clutch work?

The device uses 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 the way 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 reduces 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 does so passively.

This image shows walking with a passive-elastic ankle exoskeleton. An unpowered clutch engages a spring in parallel with the Achilles tendon when the foot is on the ground, offloading the calf muscles and making walking easier. Image credit: Stephen Thrift / North Carolina State University.

With efficiencies derived from evolution, growth and learning, humans are very well-tuned for locomotion1. Metabolic energy used during walking can be partly replaced by power input from an exoskeleton, but is it possible to reduce metabolic rate without providing an additional energy source? This would require an improvement in the efficiency of the human–machine system as a whole, and would be remarkable given the apparent optimality of human gait. Here we show that the metabolic rate of human walking can be reduced by an unpowered ankle exoskeleton. We built a lightweight elastic device that acts in parallel with the user’s calf muscles, off-loading muscle force and thereby reducing the metabolic energy consumed in contractions. The device uses a mechanical clutch to hold a spring as it is stretched and relaxed by ankle movements when the foot is on the ground, helping to fulfill one function of the calf muscles and Achilles tendon. Unlike muscles, however, the clutch sustains force passively. The exoskeleton consumes no chemical or electrical energy and delivers no net positive mechanical work, yet reduces the metabolic cost of walking by 7.2 ± 2.6% for healthy human users under natural conditions, comparable to savings with powered devices. Improving upon walking economy in this way is analogous to altering the structure of the body such that it is more energy-effective at walking. While strong natural pressures have already shaped human locomotion, improvements in efficiency are still possible. Much remains to be learned about this seemingly simple behavior.

18 pages of supplemental information

SOURCES- Carnegie Mellon, Nature, Youtube

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