Unpowered exoskeleton springs into action

Pittsburgh, Pennsylvania and Raleigh, North Carolina – Sometimes a very complex problem has a surprisingly simple solution.

The problem: trying to improve upon millions of years of evolutionary efficiency of human locomotion. The solution: a mechanical clutch that fits in the palm of your hand.

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. 

Since at least 1890, engineers have tried unsuccessfully to develop machines that make walking easier. A prominent example is HULC, a DARPA-funded project that started in 2000 and spent millions of dollars on what was intended to be a powered super-suit for soldiers (think of an Ironman-esque armor). It was so heavy and required so much energy to power it that DARPA recently abandoned the project.

According to an article published in Nature this week, Carnegie Mellon University’s Steve Collins and his collaborator Greg Sawicki at North Carolina State University have discovered a way to make humans more efficient at walking.

They have developed a 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.  

But why do we want to make walking easier in the first place? If by spending less energy on walking we burn fewer calories, wouldn’t most of us want to make walking more difficult?

The answer for many is ‘no.’ Collins, a mechanical engineer and roboticist, explains:

“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? Click here to watch

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.

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.’” 

Collins runs the Experimental Biomechatronics Lab at Carnegie Mellon University. He is an assistant professor in the Department of Mechanical Engineering with a courtesy appointment in the Robotics Institute.

Source: Carnegie Mellon University & North Carolina State University