Roomba® robot vacuum cleaners
by Chris Woodford. Last updated: December 17, 2018.
We're learning to love our machines—or, at least, that's how it's starting to seem! Things have come an awfully long way since the early 19th-century, when an infamous band of textile workers called the Luddites smashed up the machines they feared were stealing their jobs. What would they make of life 200 years later, when most products come from highly automated factories and many of us are now inviting robots into our homes? It's still very early days for household robots, but a popular little machine called the Roomba could be the shape of things to come. It's a small, computerized cleaner that nips round your house automatically brushing and vacuuming the carpets, rugs, and floors. How does it work? Is it any good? Should you buy one? Let's take a closer look!
Photo: When Roomba finishes the housework, it docks itself in this recharging station and charges up its batteries, ready for next time. The CLEAN button flashes orange while it's charging; once Roomba is fully charged, the button turns green, as shown here. The whole thing is extremely simple to use. You simply press the CLEAN button to start it off—and that's all you have to do. If you want it to clean while you're out, you can program in a complete daily or weekly cleaning schedule. This is one of the popular Roomba 560s dating from around 2010.
What is Roomba?
Roomba is a compact, computerized vacuum cleaner that automatically guides itself around your home. Like a conventional cleaner, it picks up dirt with spinning brushes and a vacuum. There's a side-mounted, flailing brush that pushes dirt underneath the machine and, once there, two more counter-rotating brushes (turning in opposite directions) pick up the dirt and direct it toward the powerful vacuum, which sucks it away into a little storage bin. Unlike a normal cleaner, Roomba moves itself around your room with two large tractor-style wheels, each one independently driven by a separate electric motor. The wheels can turn in opposite directions, which means Roomba can literally "spin on a dime" and clean almost any space it can drive into. Power comes from an onboard NiMH rechargeable battery pack. That might be a drawback, but virtually all of Roomba's features have been designed to use as little power as possible so it can work for quite a long time (maybe 90 minutes if you're lucky) between charges. Roomba has numerous onboard sensors to detect dirt, dodge obstacles, and steer clear of things like tassels on rugs and telephone cords that could cause it problems. When it's finished, it nips back into its "docking" station and recharges itself for next time. You could almost say it has a mind of its own!
How does Roomba work?
Roomba's makers, iRobot Corporation, describe their creation as a "vacuum cleaning robot"—and that's a fair and accurate description. Just like the industrial robots that weld cars in factories, it follows a series of preprogrammed instructions, but it also uses a certain amount of built-in "intelligence" to work out what it needs to do and how it needs to do it.
Photo: Turn your Roomba over and this is what you'll see underneath. The dirt bin, filter, and brushes are very easy to remove for cleaning.
Watch Roomba for a short time (it's hard not to) and you might think it's following a completely random pattern. Most of the time it is! According to one of iRobot's original patents for the Roomba, the optimum way for a robot to clean a room is to use a combination of two main patterns: "wall following" (where it moves around the walls of your room, using its side-mounted, flailing brush to clean right into corners) and "random bounce" (where it cleans until it hits an obstacle, then moves off again in a random direction). The original Roombas (like the model 560 pictured here) seem to use several different cleaning modes, including sweeping across a room at speed to clean large areas, spiraling outward to cover larger spaces, and repeatedly retracing over areas that are particularly dirty (there's a flash of Roomba's bright blue "dirt detect" light to let you know when this happens).
Photo: Turn Roomba upside down and you'll see the infrared "cliff" sensors underneath the sturdy plastic case, which prevent Roomba from tumbling down stairs. It cleans right to the edge of stairs but never falls over! The white blob you can see on the right is the pivoting front wheel. The black curved edge at the bottom of the picture is the touch-sensitive front bumper.
Just as humans use our five senses to interact with the world, so Roomba has various onboard sensors to help it figure out what it can about your room. Mounted on top of Roomba, at the very front, there's a prominent infrared beam and photocell sensor. Immediately underneath, there's a plastic front bumper with a built-in touch sensor. The infrared beam detects walls and obstacles so Roomba slows down when it gets near them. The touch-sensitive bumper stops Roomba when it actually hits things. There are also infrared sensors mounted underneath, pointing straight downward, so Roomba can detect what it calls "cliffs" (stairs and steep drops). If it feels its brushes might tangle up on tassels or cables, it stops them rotating straight away and drives itself to safety.
How does Roomba know when it hits a particularly dirty patch? According to iRobot's patents, it uses a piezoelectric sensor (essentially a crystal that generates electrical impulses when things strike it). When bits of dirt hit the sensor, they generate tiny electric impulses and, presumably, an excessive number of these impulses triggers "dirt detect," causing the robot to retrace its steps, cleaning a little bit more slowly and thoroughly second time around. (Roomba's designers considered using an optical sensor to measure the dirt being sucked through the machine, but decided that would clog up too quickly and prove less reliable.)
Some Roomba models come with little standalone beacons called Virtual Wall® Lighthouses™, which are like flashlights that send out invisible, infrared beams. Use them in lighthouse mode and they help Roomba understand where one room ends and another begins, so it can clean one room properly before moving to the next; use them in "virtual wall" mode and you can set up barriers the robot isn't allowed to cross. Frankly, it's easier just to close doors and put down books or brushes to pen your Roomba into certain areas—but possibly not as much fun!
The original Roombas (like the 560) cleaned almost entirely randomly: contrary to what you might think, they didn't build "mental maps" of your rooms or your home. That's why cleaning took so long and was a bit haphazard. Newer versions (like the Roomba 980) have moved away from random cleaning to a much more intelligent approach called VSLAM (Vision Simultaneous Localization and Mapping). They use onboard infrared cameras to take snapshots of your room, gradually building up a picture so they know where they're going and where they've been. That means they can clean more quickly (one study by Roomba's engineers found map-building cut cleaning time by about 20 percent) and thoroughly—and, unlike original Roombas, move in more confident straight lines (like a human cleaner would vacuum). It also means they can stop vacuuming when the battery is low, nip to the charger for a few hours, and then pick up where they left off when they've refilled with juice! One of the latest Roombas, the i7+, has persistent mapping: it not only maps your home but remembers the layout of your rooms from one cleaning session to the next, so future sessions can be planned even more efficiently.
The latest Roombas also offer handy Wi-Fi connectivity, which means you can program them from your smartphone or tablet with a simple app—even when you're away from home.