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Power Suit OPEN ACCESS

Soldiers Carry More Equipment than Ever. A New Type of Flexible Support System May Help Them Shoulder That Load.

[+] Author Notes

Tom Gibson, P.E is a consulting mechanical engineer specializing in machine design and green building and a freelance writer specializing in engineering, technology, and sustainability. Based in Milton, Pa., Gibson publishes the online magazine Progressive Engineer.

Mechanical Engineering 139(07), 38-41 (Jul 01, 2017) (4 pages) Paper No: ME-17-JUL2; doi: 10.1115/1.2017-Jul-2

This article explores the research and development work of developing exoskeletons that would assist soldiers in carrying heavy loads across long distances. Much of the funding for soft exoskeletons has come through Defense Advanced Research Projects Agency (DARPA), which has the goal of helping soldiers walk long distances while carrying a heavy load. An exosuit that reduces the physical toll on soldiers can improve the Army’s war-fighting capability. The exosuits are robotic external skeletons made of soft, lightweight, and flexible material so that people can wear them like the Spandex athletic wear. Once these suits exit the lab, they could support soldiers as they walk or increase their endurance. Flexible powered suits could provide assistance during walking, hiking, running, and other sporting activities. Similar suits could be programmed to compensate for the limited strength and coordination of someone recovering from an injury or managing with a debilitating illness. The slimmer profile of the soft exosuits will enable them to be more seamlessly incorporated in work settings.

People are soft. That's not a moral indictment, it's just a physiological fact.

That softness makes encasing humans in hard, rigid machines problematic.

“When you use hard structures with soft tissues, you end up with things like abrasions, blisters, and bruises,” said Angela Boynton, a mechanical engineer at the Aberdeen Proving Ground in Maryland.

Boynton works on a team dedicated to developing exoskeletons that would assist soldiers in carrying heavy loads across long distances. There are many challenges involved with that project— creating durable miniaturized motors and lightweight power packs—but perhaps the greatest stumbling block is human frailty.

“The goal is actually to wear these for 72 hours,” Boynton said. “You can’t have a suit that is causing blisters and bruises on the person.”

Engineers at the Harvard Biodesign Lab believe they have the answer to matching a powerful exosuit to a squishy human: Make the suit soft, as well.

The exosuits are robotic external skeletons made of soft, lightweight, and flexible material so that people can wear them like the Spandex athletic wear.

Once these suits exit the lab, they could support soldiers as they walk or increase their endurance. Ultimately, it is hoped that exosuits will one day assist people with injuries or disabilities that impair their mobility, or enable workers to spend the day on a factory floor without fatigue.

The mental model for powered exoskeletons is Iron Man, the fictional superhero who wears a suit of battle armor bristling with weapons. For decades, engineers working toward a more modest goal—helping people who are fully paralyzed with a spinal cord injury walk again—have followed a similar path. Hard surfaces would enable engineers to attach powerful motors and actuators, and rigid joints would provide support for the weight of that equipment and the necessary power supply.

 

Grahic Jump Location 

Each assumption led to a choice that made the suits bigger and more cumbersome.

When Conor Walsh was an undergraduate mechanical engineering student at Trinity College in Dublin, Ireland, he saw a magazine article about a project funded by the Defense Advanced Research Projects Agency, or DARPA, to develop a set of powered rigid leggings.

“I think I was in my junior year, and it was the coolest thing ever,” he recalled.

Within a few years, as a graduate student at the Massachusetts Institute of Technology in Cambridge in the mid-2000s, Walsh was using DARPA money to build hard exoskeletons of his own. In spite of making some progress, it was slow going.

By the time he started working at Harvard's Wyss Institute for Biologically Inspired Engineering, Walsh realized that he needed to take things in a new direction. Instead of making everything bigger and more power-hungry, the key was to ask the suit to do less.

“We’re coming from an entirely different perspective and developing systems that don’t give as much resistance, so they’re not quite as powerful,” Walsh said. Rather than doing the walking for the wearer— physically picking up her legs and carrying them forward into a step—the suit could simply add support or power to the step the user is already taking. That radically reduces the size and complexity of the suits, even if it limits the applicability.

A powered exosuit developed at Harvard (left) is being tested by the U.S. Army as a way to help soldiers.

Photos: Harvard University (opposite), Tom Faulkner, RDECOM (above).

Grahic Jump LocationA powered exosuit developed at Harvard (left) is being tested by the U.S. Army as a way to help soldiers.Photos: Harvard University (opposite), Tom Faulkner, RDECOM (above).

Technicians at the U.S. Army's Aberdeen Proving Ground in Maryland adjust the soft exosuit before a soldier tests it. The device, made of flexible straps and cables, is designed to boost power and endurance while walking.

Photos: Tom Faulkner, RDECOM (above), Harvard Univ. (opposite)

Grahic Jump LocationTechnicians at the U.S. Army's Aberdeen Proving Ground in Maryland adjust the soft exosuit before a soldier tests it. The device, made of flexible straps and cables, is designed to boost power and endurance while walking.Photos: Tom Faulkner, RDECOM (above), Harvard Univ. (opposite)

Walsh's team had to design new sensors that integrate into wearable garments, measuring not the change in the angle of the joints directly, but the amount of stretch in the legs that relates to the motion around the joint.

“They’re more suited for people who can walk but just not very well,” Walsh said, “such as someone who has suffered a stroke or an elderly person.”

By 2014, his team at Harvard had secured a multimillion-dollar grant via DARPA's Warrior Web program to develop the concept of soft exosuits, and Walsh had founded the multidisciplinary Harvard Biodesign Lab to study ways to bring together robots and people. In addition to the sorts of engineers one would expect in a robotics lab, the Biodesign Lab employs a physical therapist, two apparel designers, and a pattern maker. The fashion school-trained lab members assist the engineers by trying different patterns of fabric, strapping, and webbing to find combinations that are both comfortable and capable of transmitting large forces to the person's body.

The result is a suit made of nylon, polyester, and Spandex that straps around the user's hips and thighs and connects to boots at the heel.

Rigid exoskeletons usually include sensors such as encoders or potentiometers in robotic joints that track joint angles, but those sensors are not compatible with soft structures. Walsh's team had to design new sensors that integrate into wearable garments, measuring not the change in the angle of the joints directly, but the amount of stretch in the legs—between the hip and the back of the thigh, or from the front of the thigh to the top of the shin—that relates to the motion around the joint. In addition, they use other off-the-shelf sensor technologies such as gyros, pressure sensors, and inertial measurement units.

When the user starts to walk, a computer processor tracks the gait and signals a system of motors and pulleys on cables strapped at the hips. The cables, sliding through sheaths much like the brake and shifting cables on a bicycle, pull to provide bursts of power at just the right moment to work with—not in place of— the wearer's muscles.

The software is flexible enough to change the timing and force of the pulls depending on the user or on the type of task being performed.

A different system was developed for assisting arms and hands. Instead of cables, the team built fluidbased actuators driven by a small pump worn at the user's waist or mounted on a wheelchair. Flexible tubes go to the actuators made from soft silicone that mount on the hands. One advantage of pneumatic or hydraulic actuators is that because they are mounted at the waist or in a backpack, they don’t add weight to the extremities being assisted.

“They’ve shown that you can apply big enough moments about the joints to provide people with a benefit,” said Steve Collins, an associate professor of mechanical engineering at Carnegie Mellon University in Pittsburgh and director of the school's Experimental Biomechatronics Laboratory, who is familiar with the work in the Harvard Biodesign Lab. “With their soft exoskeleton, they can reduce energy costs of walking by about the same amount as hard exoskeletons.”

Much of the funding for soft exoskeletons has come through DARPA, which has the goal of helping soldiers walk long distances while carrying a heavy load. An infantryman on the march can be expected to haul a rifle and sidearm, ammunition for each, grenades, body armor, water, extra batteries, and more—as much as 100 pounds in some cases. Carrying that weight fatigues soldiers and contributes to some of the chronic injuries reported by servicemen returning from combat.

An exosuit that reduces the physical toll on soldiers could improve the Army's war-fighting capability.

At the Aberdeen Proving Ground, Angela Boynton says her group has worked closely with Walsh and his team for the last several years. The Harvard team has visited Aberdeen a half-dozen times with different generations of their exosuits, and Boynton's Army engineers have evaluated and critiqued each system.

“I always try the suits on when they come, and the soldiers will, too.” Boynton said. “We go through the woods in it and then provide feedback to Conor and his team about any issues.”

How well do they work? “They’ve been very comfortable to wear,” Boynton said. “The actuation the system provides is awkward at first, but after you walk in them awhile, it gets to be a more natural feel. They’re still working on some things with uneven terrain, but they’re comfortable over a long period of time carrying a load.”

“The advantages are that you don’t have these heavy, bulky rigid elements that could cause a large penalty when you put the device on, that could interfere with other things you want to wear like clothing or footwear,” Collins said. “You don’t have these big sharp things that could jam into your body.”

An exosuit that reduces the physical toll on soldiers could improve the Army's war-fighting capability.

But Walsh sees applications beyond the military. For instance, flexible powered suits could provide assistance during walking, hiking, running, and other sporting activities. Similar suits could be programmed to compensate for the limited strength and coordination of someone recovering from an injury or managing with a debilitating illness.

The slimmer profile of the soft exosuits will enable them to be more seamlessly incorporated in work settings. “You’re going to see more and more industrial applications where people in factories are using it to help them perform their jobs better and safer,” Walsh said.

Too often, we associate softness with weakness. But in the case of Conor Walsh's soft robotics, it is their very flexibility that gives them so much strength—and potential.

Copyright © 2017 by ASME
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