This Spring-Powered Exoskeleton Improves Inefficient Human Walking

Springs are lighter and less power-hungry than motors.

Apr 1 2015, 5:14pm

​Image: Stephen Thrift

Robotic exoskeletons could very well make us stronger and faster one day. But if you don't want to deal with the power requirements and repair headaches that come with advanced robotics, you could opt for a spring-powered exoskeleton that gets the job done instead.

Researchers at Carnegie Mellon University—the same school helping Uber develop autonomous vehicles—were frustrated with the bulky design and huge power demands of robotic, motorized exoskeletons. In order to maximize the benefit of an ability-boosting prosthetic, they needed something lighter. So, they took inspiration from how the human calf and heel interact naturally and built an exoskeleton that uses springs instead of motors.

"Recent ultrasound imaging studies show that calf muscles act more like clutches than motors during walking, holding one end of the Achilles tendon as it is stretched and recoils," Steve Collins, the lead author of a paper describing the system, explained. "You could say that the design is bio-inspired—nature finds simple, elegant solutions to these types of problems."

When you use a complicated series of motors to assist your walking, what you're really doing is using an external energy source to replace the energy your body would be using otherwise. To make walking easier without external power, you have to make walking itself more efficient. That's not easy, since humans have been walking for a very long time now. We're pretty good at it, for the most part.

The researchers' exoskeleton accomplishes this by essentially performing the function of the calf muscles, which consume energy to move you around, but with simple spring-loaded efficiency. The spring is kept taut when the wearer's foot is on the ground with a clutch at the top of the calf, and releases when it's in the air, giving the motion of walking an external boost.

According to the researchers, the exoskeleton resulted in a 7 percent reduction in the amount of energy the wearer used. This is comparable to the energy reduction in pneumatic systems—a 2013 study found a 6 percent energy reduction in one system—and is equivalent to taking off an eight pound backpack.

"This could make a big difference for people who walk a lot in their occupations, such as nurses or soldiers, and for people whose energy cost is already elevated because of disability," Collins told me. "Of course, we still need to perform quite a bit of science and engineering before such products are ready for everyday life."

According to Collins, his team is working on similar spring-powered systems for people with disabilities from stroke or aging, and devices that will work on the knees and hips. The idea is that spring-powered exoskeletons will reduce the energy cost of movement in those areas, like they did for the leg in these experiments.

While robots and jetpacks tantalize us with a sci-fi future full of mechanical exoskeletons that let you run a marathon or flip a car with ease, spring-loaded systems remind us that simpler approaches are sometimes just as effective, even in the future.