In a video released by its developers, a robotic leg equipped with artificial muscles could be seen hopping through grass, sand, gravel, and small rocks.
Uneven terrain is not an obstacle for the robotic leg, which is powered by artificial “electro-hydraulic” muscles and was developed by researchers at ETH Zurich and the Max Planck Institute for Intelligent Systems.
According to the developers, it is in fact the first robotic leg with artificial muscles that can automatically adapt to different terrain, as demonstrated in the video clip accompanying the publication of research.
The system is more energy efficient than electric motors, enabling high jumps and fast movements without complex sensors, researchers said.
“Typically, electric motor-driven robots need heat management which requires additional heat sinks or fans for diffusing the heat to the air. Our system doesn’t require them,” said Toshihiko Fukushima, one of the study’s co-first authors.
Imitating human legs
Scientists said “living creatures” inspired their research and the robotic leg works according to the same principle as human legs when jumping.
According to ETH Zurich, an extensor and a flexor muscle, like those in humans and animals, ensure that the robotic leg can move in both directions.
These electro-hydraulic actuators – dubbed HASELs by researchers – are attached to the skeleton by tendons. The actuators are oil-filled plastic bags similar to those used to make ice cubes.
About half of each bag is coated on either side with a black electrode made of a conductive material, which electrically charges the same way “when I rub a balloon against my head,” according to Thomas Buchner, another co-first author of the study.
Buchner explained that “as soon as we apply voltage to the electrodes, they are attracted to each other due to static electricity.”
With the increase of the voltage, the electrodes come closer and push the oil in the bag to one side, imitating muscle movement: as one muscle shortens, its counterpart lengthens.
Soft robotics breakthrough
Electric motors, a technology invented 200 years ago, are still predominantly used in robotics. By contrast, the field of electrohydraulic actuators emerged only around six years ago.
While electro-hydraulic actuators are unlikely to be used in heavy machinery on construction sites, the emerging technology opens up new possibilities in fields like soft robotics, according to Robert Katzschmann, who led the study.
The advantages are “particularly evident” in applications such as grippers – or robot hands – where high precision is required to handle objects such as a ball or an egg.
“Compared to walking robots with electric motors, our system is still limited. The leg is currently attached to a rod, jumps in circles, and can’t yet move freely,” Katzschmann said, adding that overcoming limitations will open doors to developing “real” walking robots.
“If we combine the robotic leg in a quadruped robot or a humanoid robot with two legs, maybe one day, when it is battery-powered, we can deploy it as a rescue robot,” he said.
The paper detailing the results of the study was published in Nature Communications.
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