Almost all human-robot interaction (HRI) approaches today rely on three senses: hearing, sight, and touch. Your robot vacuum might beep at you, or play recorded or synthesized speech. An LED on its enclosure might blink to red to signify a problem. And cutting-edge humanoid robots may even shake your hand. But what about the other senses? Taste seems like a step too far, so researchers at KAIST experimented with “Olfactory Puppetry” to test smell’s suitability for HRI communication.

This concept seems pretty obvious, but there is very little formal research on the topic. What if a robot could communicate with humans by emitting scents?

Imagine if a factory worker suddenly began smelling burning rubber. That could effectively communicate the idea that a nearby robot is malfunctioning, without relying on auditory or visual cues. Or a personal assistant robot could give off the smell of sizzling bacon to tell its owner that it is time to wake up.

The researchers wanted to test these ideas and chose to do so using puppets instead of actual robots. By using puppets — paper cutouts on popsicle sticks — test subjects could act out scenarios. They could then incorporate scent and observe the results.

For that to work, they needed a way to produce specific smells on-demand. They achieved that with a device built using an Arduino Nano R3 board that controls four atomizers. Those emit rose, citrus, vanilla, and musk scents, respectively. Another device performs a similar function, but with solid fragrances melted by heating elements.

This research was very open-ended, but the team was able to determine that people prefer subtle scents, don’t want those to happen too frequently, and want them to mesh well with what their other senses are telling them. That knowledge could be helpful for scent-based HRI experiments in the future.