For the last 70 years, researchers have been developing robots that are powered by motors — a technology that is some 200 years old.
While these robots have arms and legs and can walk around, they often lack the mobility and fluidity of movement of humans. Why?
Because they don’t have muscles.
Researchers at ETH Zurich and the Max Planck Institute for Intelligent Systems say they’ve made a breakthrough, by building a robotic leg powered by artificial muscles rather than electronic motors. The robotic limb, inspired by humans and animals in nature, can jump across terrains such as pebbles and sand and evade obstacles. It can also perform high jumps and fast movements without the need for complex sensors.
The leg is also much more energy-efficient than motor-powered robots, say the researchers in a statement, adding that, while the technology is still new, it could open up new possibilities for future humanoid robots to be powered by artificial muscles.
The research is set to be published in scientific journal Nature Communications and was authored by doctoral students Thomas Buchner and Toshihiko Fukushima.
What are artificial muscles?
The robotics sector has been getting a lot of attention from investors this year, with Goldman Sachs forecasting the global market for humanoid robots to reach $38bn by 2035.
Startups in Europe building humanoid robots include Norwegian AI startup 1X, and Swiss startups (and ETH spinouts) ANYbotics, which is building a four-legged robot for use in industrial applications, and Mimic, which is developing AI-powered robotic hands.
But the ETH and Max Planck researchers say that, unlike conventional robotic limbs, its leg mirrors how real-life humans and animals move, with an “extensor and a flexor” muscle that can move it in both directions. These artificial muscles are called electro-hydraulic actuators (dubbed HASELS by the researchers) which are attached to the skeleton by tendons. This is different to conventional robotic legs which are instead driven by electromagnetic rotary motors, the researchers say.
The artificial muscles are essentially plastic bags filled with oil, like those used to make ice cubes. Roughly half of each bag is coated on both sides with a black electrode made out of conductive material.
“As soon as we apply a voltage to the electrodes, they are attracted to each other due to static electricity. Similarly, when I rub a balloon against my head, my hair sticks to the balloon due to the same static electricity,” explains Büchner in the statement. When you increase the voltage, the electrodes come closer together and push the oil in the bag to one side which makes the bag shorter.
These actuators essentially work the same as muscle pairs in humans: as one muscle shortens, the other lengthens.
New possibilities
It’s still early days for the field of artificial muscles (electro-hydraulic actuators) which only emerged six years ago — and the researchers admit that there’s still a way to go until their technology is outperforming the most advanced humanoid robots on the market.
“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,” said Robert Katzschmann, a professor at the Soft Robotics Lab at ETH Zurich, commenting on how it’s still not powered by mobile battery technology.
But, if these limitations are worked on, artificial muscles could open the door to having real robots walking around on more uneven terrain, due to their ability to adapt and make smaller and more nuanced adjustments to movement.
This, the researchers say, is because electric motors require sensors to continuously tell what angle the robotic leg is at, while the artificial muscle adapts to find the right position through the interaction with its environment.
“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,” said Katzschmann.