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'Spring-mass' technology heralds the future of walking robots

28 October 2015

Researchers claim the most realistic robotic implementation of human walking dynamics, which may ultimately allow human-like versatility and performance.

ATRIAS walking robot is put through its paces (courtesy of Oregon State University)

The system is based on a concept called 'spring-mass' walking that was theorised less than a decade ago, and combines passive dynamics of a mechanical system with computer control. It provides the ability to blindly react to rough terrain, maintain balance, retain an efficiency of motion and essentially walk like humans do.

The findings on spring-mass walking have been reported for the first time in IEEE Transactions on Robotics, by engineers from Oregon State University (OSU) and Germany. Their work is supported by the US National Science Foundation, the Defense Advanced Research Projects Agency (DARPA) and the Human Frontier Science Program.

The technologies developed at OSU have evolved from intense studies of both human and animal walking and running, to learn how animals achieve a fluidity of motion with a high degree of energy efficiency. Animals combine a sensory input from nerves, vision, muscles and tendons to create locomotion that researchers have now translated into a working robotic system.

The system is also efficient. Studies done with their ATRIAS robot model, which incorporates the spring-mass theory, showed that it’s three times more energy-efficient than any other human-sized bipedal robots.

“I’m confident that this is the future of legged robotic locomotion,” says Jonathan Hurst, an OSU professor of mechanical engineering and director of the Dynamic Robotics Laboratory in the OSU College of Engineering.

“We’ve basically demonstrated the fundamental science of how humans walk. Other robotic approaches may have legs and motion, but don’t really capture the underlying physics. We’re convinced this is the approach on which the most successful legged robots will work. It retains the substance and science of legged animal locomotion, and animals demonstrate performance that far exceeds any other approach we’ve seen. This is the way to go.”

“Robots are already used for gait training, and we see the first commercial exoskeletons on the market,” says lead author, Daniel Renjewski from the Technische Universitat Munchen. “However, only now do we have an idea how human-like walking works in a robot. This enables us to build an entirely new class of wearable robots and prostheses that could allow the user to regain a natural walking gait.” 

The robots being constructed at OSU are designed to mimic the 'spring-legged' action of bipedal animals. With minor variations, muscles, tendons and bones form a structure that exhibits most of the required behaviour, and conscious control just nudges things a little to keep it going in the right direction. The effort is smooth and elastic, and once understood, can be simulated in walking robots by springs and other technology.

ATRIAS, the human-sized robot most recently created at OSU, has six electric motors powered by a lithium polymer battery that is substantially smaller than the power packs of some other mobile robots. It can take impacts and retain its balance. It can walk over rough and bumpy terrain.

In continued research, work will be done to improve steering, efficiency, leg configuration, inertial actuation, robust operation, external sensing, transmissions and actuators, and other technologies.

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