Researchers at Oregon State University (OSU), Corvallis, have outlined the specific interaction between the ankle, knee, muscles, and tendons. Their work improves the understanding of a leg moving forward in a way that maximizes motion while using minimal amounts of energy. The research could find some of its earliest applications in improved prosthetic limbs, they said, while a more complete grasp of these principles could lead to walking or running robots that are far more agile and energy efficient than anything that exists today. Their work was published December 20, 2013, in The Journal of Experimental Biology.
“Human walking is extraordinarily complex and we still don’t understand completely how it works,” said Jonathan Hurst, PhD, an OSU assistant professor of mechanical engineering and an expert in legged locomotion in robots. “When we fully learn what the human leg is doing,” Hurst added, “we’ll be able to build robots that work much better.”
Researchers have long observed some type of high-power push off when the leg leaves the ground, but didn’t really understand how it worked. Now they believe they do. The study concluded there are two phases to this motion. The first is an “alleviation” phase in which the trailing leg is relieved of the burden of supporting the body mass. Then in a “launching” phase the knee buckles, allowing the rapid release of stored elastic energy in the ankle tendons, like the triggering of a catapult.
“We calculated what muscles could do and found it insufficient, by far, for generating this powerful push off,” said Daniel Renjewski, PhD, a research associate in the OSU Dynamic Robotics Laboratory. “So we had to look for a power-amplifying mechanism. The coordination of knee and ankle is critical. And contrary to what some other research has suggested, the catapult energy from the ankle is just being used to swing the leg, not add large amounts of energy to the forward motion.”
Walking robots don’t do this. Many of them use force to “swing” the leg forward from something resembling a hip point. It can be functional, but it’s neither energy efficient nor agile. In addition, for more widespread use of mobile robots, energy use is crucially important, the researchers said.
“We still have a long way to go before walking robots can move with as little energy as animals use,” Hurst said. “But this type of research will bring us closer to that.”
Robots with the ability to walk and maneuver over uneven terrain could ultimately find applications in prosthetic limbs, an exoskeleton to assist people with muscular weakness, or use in the military, disaster response, or any dangerous situation.