Among the many reasons humans are bizarre among mammals (the dearth of body hair, the bipedalism, the fact that someone invented the turducken) is a sad shortcoming: You and I don’t have sensory whiskers. Cats, dogs, raccoons, sea lions—you name a mammal and it’s probably got special hairs sprouting out of its face. After all, whiskers are immensely useful. Rats use them to navigate the darkness, for instance, while a seal's whiskers detect the movements of fishy prey.
Whiskers are all the rage in nature, so why not give them to robots? Mechanical engineer Mitra Hartmann of Northwestern University is doing just that. In a new paper published in the journal Soft Robotics, Hartmann and her team detail how they’re one step closer to a rat-like machine that can feel an object and pinpoint it in 3-D space—meaning robots of all kinds could soon get a powerful new sense.
In animals, the whisker doesn’t have sensors running along its length—they're packed into the follicle instead. When the whisker hits an object, those sensors trip and relay information to the brain, acting as a supplement to the critter’s other senses.
If you wanted to give a robot whiskers, you could use something called a six-axis load cell. Connect a whisker to this device and it can relay lots of information when the appendage hits an object: lateral force, how much the whisker twists in the follicle, how much it pushes into the follicle, in what direction the whisker bends and how much it bends. That's a whole lot of information, and that kind of cell is bulky and expensive.
Working in a simulation, Hartmann and her team discovered that you don't actually need all of this information to pinpoint objects with a whisker. “You just need how much the whisker bent, what direction the whisker bent, and how much it got pushed into the follicle,” Hartmann says. She's currently working on two versions of a sensor that can measure those three signals. At .8 mm cubed, the first is about half the size of a macro-scale six-axis load cell. The other is 1 mm long and 0.5 mm in diameter—about the same size of a real rat's follicle.
The team also looked at the effectiveness of two different whisker designs: tapered and plain old cylindrical. Tapered is what you'd find in nature—thicker at the base and ending with a pointy tip—and the team found that they could pinpoint objects with tapered whiskers but not cylindrical ones. Why, exactly, Hartmann can't say. But she ventures a guess. "If the whisker were cylindrical, then at every point along the whisker's length the stiffness would be the same," Hartmann says. "The tapered whisker is more flexible in some regions than other regions—it's more flexible at the tip."
So, now Hartmann knows what signals and what whisker shape she needs to build a rat-like robot. The question then becomes: Why whiskers? Robots can already map their surroundings in incredible detail using lasers. Why complicate matters with funny-looking face hairs?
The idea is that whiskers aren’t a replacement for machine vision—they’re a complement. Once night falls, traditional vision is no longer an option. And when a dust storm moves in, lasers are right out. So in these trying times, the robot could feel its way around instead. Whiskers could even detect currents like a seal, making for a powerful underwater robot.
Another upside: Whiskers are a sneaky way to map your environment. “What if you wanted to avoid detection?” Hartmann asks. “You wouldn't want to go blazing light all over the place, right? You'd want to be sneakier than that.”
So does that mean one day you'll get a whiskered robot cat instead of a real one, à la Blade Runner? Maybe. If it comes without the attitude problem, count me in.
