Developing robots that can walk more naturally

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Walking on two legs isn’t as easy as it seems. Especially for robots, where a natural stride is a major challenge. Researchers at EPFL’s Biorobotics Laboratory are testing novel systems to improve humanoids’ ability to walk and interact.

For humans, it comes perfectly naturally. But walking on two legs is actually a complicated task, requiring several muscles to perform delicate balancing acts. That’s why humanoid robots still walk so awkwardly despite years of major technological advancements in the field. Engineers at EPFL’s Biorobotics Laboratory are experimenting with new walking systems on a robot called COMAN, short for COmpliant HuMANoid Platform. This 95-cm-tall humanoid is designed specifically for studying walking - which is why it has no head.

COMAN was developed under the EU AMARSi project and is being used by several research teams. The EPFL team is looking specifically at the "brains" of the machine. "We developed algorithms that can improve the robot’s balance while it’s walking," says Hamed Razavi, an engineer at the Biorobotics Lab.

In harmony with symmetries

One of COMAN’s distinguishing features is its joints, which are made from elastic elements that give it greater flexibility in movement. The EPFL team came up with a revolutionary type of control system for the robot, based on operational symmetries involving the structure of the robot’s movements as well as the mathematical equations defining them. "You could say we’re working in harmony with these symmetries rather than against them. That gives us a steadier gait," says Razavi.

The control system uses sophisticated computer programs to carefully analyze COMAN’s movements - in terms of speed, position, the angles of its joints, etc. - and send the data to its motors in real-time, telling the motors what action to take to maintain the robot’s balance. "If someone pushes COMAN, for example, our algorithms will calculate exactly where its foot should land and what strength to use to counter the force," says Razavi.

Climbing stairs and opening doors

The algorithms are geared towards three types of robot applications. The first is carrying out rescue efforts at disaster sites. "At sites designed by and for humans - like a nuclear power plant with stairs to climb and doors to open - humanoid robots can get around more efficiently than those on wheels," says Razavi. The second is helping with tasks like carrying heavy boxes or moving objects (see box). And the third is creating exoskeletons for the disabled.

"Making the robots more stable is just the tip of the iceberg," says Razavi. The next step is refining the algorithms so that the humanoids have a wider range of movement and can overcome obstacles and walk on irregular or sloped surfaces.

Humanoids helping humans

As part of this project, Jessica Lanini and Hamed Razavi studied how two people carrying an object together are able to walk, turn and speed up in a coordinated manner - without communicating with each other. Their findings, recently published in PLOS ONE , indicate that the two people automatically synchronize their steps, like a quadruped. Now the researchers plan to apply their results to humanoid robots.

"Whether for manufacturing or natural disasters, we need robots that can interact with humans and help us carry heavy objects," says Lanini. "But such robots don’t exist. That’s because, in order to operate safely and effectively, the robots would need to be able to make decisions and respond to unexpected circumstances."

The researchers decided to observe humans, who do things better and more naturally than robots. They analyzed the way humans move and found that some factors like speed, force and hand position play a pivotal role in understanding "commands" like speeding up or stopping. The next step is modeling these observations in order to program the robots. "What is it exactly that makes us slow down or turn? The applied force? A combination of force and speed? The boundary is not yet clear," says Razavi.