"Intra-Hug Gestures," and 11 Commandments, Prove Key to Building an Enjoyable Hugging Robot

A team of roboticists from the Max Planck Institute for Intelligent Systems, ETH Zurich, and the University of Copenhagen have built a third-generation hugging-robot capable of autonomous operation — using "intra-hug gestures" to improve enjoyability.

"We investigated robot responses to four human intra-hug gestures: Holding, rubbing, patting, and squeezing," the team explains in the abstract to the resulting paper, brought to our attention by IEEE Spectrum. "Thirty-two users each exchanged and rated sixteen hugs with an experimenter-controlled HuggieBot 2.0.

"The robot’s inflated torso's microphone and pressure sensor collected data of the subjects' demonstrations that were used to develop a perceptual algorithm that classifies user actions with 88% accuracy."

Built using two six-degrees-of-freedom (6DoF) robot arms with added padding, the HuggieBot robot designed by the team boasts inflatable chambers filled with warmed air that can be inflated and deflated at will — and which double as pressure sensors. Initially, the team controlled the robot remotely — having a human control each hug — but only to gather data for a fully-autonomous variant.

"From average user ratings, we created a probabilistic behavior algorithm that chooses robot responses in real time," the team explains. "We implemented improvements to the robot platform to create HuggieBot 3.0 and then validated its gesture perception system and behavior algorithm with sixteen users.

"The robot's responses and proactive gestures were greatly enjoyed. Users found the robot more natural, enjoyable, and intelligent in the last phase of the experiment than in the first. After the study, they felt more understood by the robot and thought robots were nicer to hug."

The final HuggieBot 3.0 design includes a custom 3D-printed head hiding a desktop computer running Ubuntu 14.04 and ROS Kinetic, an Intel RealSense depth-sensing camera, a display on which the robot projects an animated face, a small speaker, and what the team describes as "many cables."

Key to the success of the project: A list of 11 "commandments" that, the roboticists say, all hugging robots should follow. A full version of the list has been published by IEEE Spectrum, and includes such requirements as being soft and warm as well as offering a size roughly similar to an adult human. Hugging robots should also, the team suggests, offer hugs whenever someone walks past by opening its arms — but wait for them to step forward before beginning.

The team's work has been published in the ACM Transactions on Human-Robot Interaction, as a closed-access paper; a preprint PDF is available under open-access terms.