‘Avatar’ research could lead to improved systems for locomotion

Researchers at North Carolina State University are making use of an “avatar”-like bio-robotic motor system to better understand the physiology of the human body during locomotion.

According to a university press release, the system makes use of a real muscle and tendon as well as a computer-controlled nerve stimulator that functions as the avatar’s spinal cord. The goal of the research is to create robotic devices that combine human and machine functions in an effort to improve locomotion. The research is described by Gregory S. Sawicki, PhD, associate professor in the North Carolina State (NC State) and University of North Carolina-Chapel Hill Joint Department of Biomedical Engineering, and Benjamin D. Robertson, a postdoctoral researcher at Temple University, in Proceedings of the National Academy of Sciences.

Gregory S. Sawicki is working with a bio-robotic motor system to create robotic devices that improve locomotion.

Source: Hall M, NC State University


Sawicki and Robertson found they were able to predict neural control strategies resulting in spring-like behavior when the mass, stiffness and leverage of the ankle’s primary muscle-tendon unit were known.

“We tried to build locomotion from the bottom up by starting with a single muscle-tendon unit, the basic power source for locomotion in all things that move,” Sawicki stated in the release. “We connected that muscle-tendon unit to a motor inside a custom robotic interface designed to simulate what the muscle-tendon unit ‘feels’ inside the leg, and then electrically stimulated the muscle to get contractions going on the benchtop.”

The researchers found that the leg’s “springy” behavior during locomotion is likely caused by resonance tuning, a mechanism Sawicki noted works similarly to a slinky toy.

“When you get it oscillating well, you hardly have to move your hand — it’s the timing of the interaction forces that matters,” he stated, adding, “In locomotion, resonance comes from tuning the interaction between the nervous system and the leg so they work together. It turns out that if I know the mass, leverage and stiffness of a muscle-tendon unit, I can tell you exactly how often I should stimulate it to get resonance in the form of spring-like, elastic behavior.”

The findings could lead to improved exoskeleton designs and prosthetic systems, according to the release.

“In the end, we found that the same simple underlying principles that govern resonance in simple mechanical systems also apply to these extraordinarily complicated physiological systems,” Robertson stated.

Reference: Sawicki G, et al. P Natl Acad Sci USA. 2015;doi: 10.1073/pnas.1500702112.

Disclosures: The researchers report funding from NC State University and Grant No. 2011152 from the U.S.-Israel Binational Science Foundation.

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