Many exoskeletons are designed to help people with walking, and a few devices can assist with running. No untethered device has been able to efficiently handle both gaits — until now. Researchers at Harvard University and the University of Nebraska Omaha have developed a lightweight exosuit that can assist the wearer with both walking and running.

A team from Harvard’s Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Sciences (SEAS), as well as from the University of Nebraska Omaha, shared its research today in Science Robotics.

“In the past five years, our group and others have shown how ankle exoskeletons can help with walking,” said Conor Walsh, a core faculty member of the Wyss Institute, the Gordon McKay Professor of Engineering and Applied Sciences at SEAS, and founder of the Harvard Biodesign Lab. “More recently, we’ve explored running, in one case, with passive hip systems.”

“One of the remaining challenges is a single device to help with more than one activity. For the first time, we can help with more than one,” he told The Robot Report. “A related breakthrough is that the system automatically detects if a person is walking or running and dynamically adjusts the level of its assistance.”

DARPA and development team

“This is the culmination of a multiyear effort,” said Walsh. “We’ve been working on soft exosuits since at least 2012, and we’ve developed many types of systems to help with walking and rehabilitation for stroke survivors.”

The study was founded by the U.S. Defense Advanced Research Projects Agency’s (DARPA) former Warrior Web Program, the National Science Foundation, and the Wyss Institute.

“The past few years have been the final phase of the DARPA program,” Walsh said. “We looked at people going different speeds, running around in rough terrain, and going up an incline.”

Similar technology is used in a medical version of the exosuit to assist stroke patients with both the hip and ankle during walking. It is commercially available through ReWalk Robotics.

While much of the work was done at Harvard, Philippe Malcom, an assistant professor at the University of Nebraska Omaha, led the biomechanical analysis in the paper, said Walsh.

Jinsoo Kim, a SEAS graduate student, was co-first author with Giuk Lee, Ph.D., a former postdoctoral fellow on Walsh’s team and now assistant professor at Chung-Ang University in Seoul, South Korea.

Other authors on the study are past and present members of Walsh’s team, including data analyst Roman Heimgartner; research fellow Dheepak Arumukhom Revi; control engineer Nikos Karavas, Ph.D.; functional apparel designer Danielle Nathanson; robotics engineer Ignacio Galiana, Ph.D.; robotics engineer Asa Eckert-Erdheim; electromechanical engineer Patrick Murphy; engineer David Perry; software engineer Nicolas Menard, and graduate student Dabin Kim Choe.

“The project has been a big team effort, with multiple disciplines — textiles, biomechanics, robotics — working together for many years,” said Walsh. “The paper and results are really nice, but we’re excited about learning about one another’s expertise and working to a common goal.”

Related content: See The Robot Report August 2019 issue on exoskeletons.

Focus on the hip

“We started with understanding the biomechanics of different gaits — the body and legs behave fundamentally differently,” Walsh said. “We used three different IMUs [inertial measurement units] to detect different walking patterns for a classification algorithm that’s 99% accurate.”

Although walking and running are different, both involve an extension of the hip joint that begins when the foot touches the ground. This requires the expenditure of energy to propel the body and became the focus for the wearable robotic device.

The team’s latest exosuit is designed to be lighter and simple and includes textile belts at the waist and thighs. The device weighs a total of 5kg (11 lb.), and more than 90% of its weight is close to the wearer’s center of mass.

The portable exosuit has a mobile actuation system at the lower back with cables controlled by an algorithm that can detect the transition between gaits.

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The Robot Report has launched the Healthcare Robotics Engineering Forum, which will be on Dec. 9-10 in Santa Clara, Calif. The conference and expo focuses on improving the design, development and manufacture of next-generation healthcare robots. Learn more about the Healthcare Robotics Engineering Forum.

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Exosuit enhances efficiency

A major challenge was tuning the algorithm to distinguish between gait speeds and change its actuation cycles for the right amount of assistance at the right time.

“We tested the hardware and control algorithm extensively in the lab and outside,” explained Walsh. “Tests showed that we could reduce the energetics of walking and running and that it worked robustly.”

In treadmill-based tests, users reduced their metabolic rates when walking by an average of 9.3% and of running by 4% compared with when they were not wearing the device.

“Those reductions are still relatively modest, but others have shown more for only one gait or the other,” Walsh said. “Metabolic reduction is like offloading weight. This was like taking 5.5kg [12.1 lb.] or 7.5kg [16.5 lb.] off a person.”

“About a year ago, we published a paper for a multi-joint system at the hip and ankle,” he added. “It could get a 16% reduction, but only for helping walking. Running is much more dynamic, and we wanted minimal weight.”

“The focus of this paper is on exosuits to augment normal human performance — for hikers, soldiers, and factory workers,” said Walsh. “We do have ongoing collaboration with ReWalk to explore where a hip device can be useful for stroke, multiple sclerosis, or Parkinson’s patients. The expertise developed here could eventually feed into medical devices.”

The research team is continuing to work on further reducing the exosuit’s weight, personalizing assistance, and improving its ease of use.