Max Planck ETH Center for Learning Systems researchers Thomas Buchner (right) and Toshihiko Fukushima with their robotic leg system. [Photo by Wolfram Scheible for the Max Planck Institute for Intelligent Systems]
The researchers say the leg — inspired by living creatures — can jump across different terrains with both agility and energy efficiency. Without the need for complex sensors, they say the leg can perform high jumps and fast movements and detect and react to obstacles, all while delivering more energy efficiency than a conventional robotic leg.
ETH Zurich’s Robert Katzschmann and Christoph Keplinger from MPI-IS led the Max Planck ETH Center for Learning Systems (CLS) research partnership. Doctoral students Thomas Buchner and Toshihiko Fukushima served as co-first authors of the team’s publication in Nature Communications.
“The field of robotics is making rapid progress with advanced controls and machine learning; in contrast, there has been much less progress with robotic hardware, which is equally important,” Keplinger said in a post on the ETH Zurich website. “This publication is a powerful reminder of how much potential for disruptive innovation comes from introducing new hardware concepts, like the use of artificial muscles.”
The robotic leg works according to the same principle as human legs when jumping. [Image courtesy of ETH Zurich]
“As soon as we apply a voltage to the electrodes, they are attracted to each other due to static electricity,” Buchner said. “Similarly, when I rub a balloon against my head, my hair sticks to the balloon due to the same static electricity.”
Pairs of the actuators attached to a skeleton deliver the same paired muscle movements seen in living creatures, the researchers say. As one muscle shortens, the other lengthens. The team used a computer code that communicates with high-voltage amplifiers to control which actuators contract and which extend.
According to the researchers, this method is far more energy-efficient than a conventional robotic leg powered by an electric motor. They say a motorized leg consumers more energy if it has to hold a bent position. Meanwhile, the temperature in an electro-hydraulic leg remains the same because the artificial muscle is electrostatic and doesn’t unnecessarily convert energy into heat.
Meanwhile, the leg can jump because it can lift its own weight explosively. It has a high degree of adaptability, the researchers say, which is important in soft robotics.
“It’s no different with living creatures. If we can’t bend our knees, for example, walking on an uneven surface becomes much more difficult,” Katzschmann said. “Just think of taking a step down from the pavement onto the road.”
Electro-hydraulic actuator research is still a young field and, while they are unlikely to aid heavy machinery on construction sites, they offer specific advantages over electric motors, the team said. Still, the researchers feel they have a long way to go.
“Compared to walking robots with electric motors, our system is still limited,” Katzschmann said. “The leg is currently attached to a rod, jumps in circles and can’t yet move freely. 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.”
