To view an on-demand seminar featuring the Roomba Discovery robotic vacuum, click here.
The flying-saucer-shaped Roomba Discovery robotic vacuum, at the upper end of a range of Roomba devices from iRobot, features autoreturn to a home charger base when the unit is finished or low on juice. A wireless remote control included in the Discovery package allows operation from up to 20 feet away.
Cleaning aspects of the Discovery rely on a primary beater bar and brush design along with a perimeter whiplike brush to get out to the edges of the floor boundary. A bagless dirt bin collects all debris. Though lacking the high suction of a conventional upright, the Discovery did a decent job of collecting grime in our very limited test run.
Figure 1: Inside look at the Roomba (click on image to enlarge).
For mobility, two drive-wheel mechanisms combine with a third idler wheel. All three have basic spring suspensions (likely used to deal with automatic height adjustment). The drive-wheel assemblies provide locomotion and are based on simple dc motors, but wheel control is a bit more sophisticated than a simple on or off. An optical chopper within the wheel assembly housing detects rotation, monitoring wheel speed by way of counting the interruptions a wheel vane makes in an emitter/detector optical circuit.
Along with providing the feedback needed to control steering (by spinning one wheel faster than the other), the monitoring may form the basis for creating an internal "map" showing which areas of a room have been cleaned and which still require attention. By tracking its effort, the Discovery could ensure that autonomous vacuuming is not just a random walk.
Much of the science in making a usable robotic vacuum rests in knowing the surroundings. An edge-detection "bumper" and switches on the wheels flag when the Roomba is up against an obstruction and sitting on a surface, respectively. Perhaps more important, the device uses a set of four IR emitter/detector pairs around the perimeter to detect when the Roomba might be hanging out over a "cliff," thus enabling it to avoid a damaging tumble down a flight of stairs. When the unit is on solid footing on a floor, light from the emitters will bounce back up to the detectors. If an open space appears below one of the emitters, however, no light will bounce back to the detectors, signifying potential trouble and letting the Roomba back up or stop to save itself. Simple, cheap and clever.
Also clever is a "dirt detect" feature. Because some areas of flooring are inevitably dirtier than others, the Roomba tries to spend most of its time where the most dirt exists. Once dirt is adequately removed from a specific location, the detect feature lets the Roomba know it can move on.
