Robotics: "HuggieBot is like a friendly stranger".

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HuggieBot spreads his arms and says in a gentle voice: "I am ready for a hug." Those who accept the invitation, spread their arms in turn and hug the creature in the light gray hoodie, purple skirt and fluffy gloves experience something unexpected: The broad robot chest is warm and soft, and the hug feels surprisingly real. The pressure and height of the robot arms are just right. And when I inevitably start to stroke and pat the robot on the back, I get a reaction: The HuggieBot pats back.

It is probably the first haptically intelligent hugging robot ever - because the test subjects demanded this intelligence. "People take it personally when they pat it on the back during the hug and it doesn't respond," says Alexis Block, who developed the robot as part of her doctoral research at Stuttgart's Max Planck Institute for Intelligent Systems (MPI-IS) and ETH Zurich. The experience is so pleasant that you don't want to leave the hug - and apparently neither does the robot.

What should a hug be like?

At the beginning, there was the question of how a robot hug should be designed so that it feels comfortable for humans. It quickly became clear that both softness and body warmth were important, reports Block. The question of the appropriate length of a hug was particularly tricky, he says. "People don't like it when the robot lets go of them too quickly," Block says. Others thought it held them too long. However, both are highly individual: "It not only varies from person to person, but it changes for the same person depending on the situation."

The robot tested is already version 3.0 - sensors measure pressure and noise in the robot's rear, air-filled torso. With this data, the team has trained a machine learning system to recognize people's desires.

And that works. I end the embrace slowly - as if I wanted to break free from the embrace of a human being - and notice: The robot obviously senses that I have had enough now and opens its arms as well.

Block has conducted several series of studies with test subjects and was initially surprised herself at the positive reactions. "Some even came back later and wanted to hug him again," she recalls.

"We compare HuggieBot to a friendly stranger."

She could understand that well. During the pandemic, she was separated from her family for a longer period of time and longed for physical closeness. It is not so much a matter of completely replacing a human embrace. The feeling of a hug is not the same as the feeling you get when you hug a good friend or your own partner, Block points out: "We compare HuggieBot to a friendly stranger."

The researchers also measured people's physical responses, such as heart rate variability and levels of oxytocin and cortisol in saliva. The results are still being published, says MIP-IS Director Katherine Kuchenbecker. "But we clearly see that the robot hugs lower stress levels." In each study, she adds, there were also people who said they even preferred hugging the robot to hugging humans. "You're not judged socially in the process, so that makes it easier for some people to ask for a hug." HuggieBot hugs unconditionally, wondering about nothing and not asking why.

(jle)