Design
Roomba models are designed to be low enough to fit under beds or other furniture. Most Roomba models are disc-shaped, measuring 338-353 mm in diameter and 86-94 mm in height depending on the model. The S9 series robots are semicircular rather than circular, with a flat part at the front, and are narrower at 311 mm wide. All models feature a large contact-sensing mechanical bumper on the front half, with a multi-directional infrared sensor located at the top front center. Most models also have a recessed handle located on the top.[8]
The first and second-generation Roomba models utilized the Virtual Wall, a separately sold accessory that prevents it from entering an area. It projects a pattern of infrared light,[9] which the vacuum detects and treats as a physical wall, prompting it to stop and turn around. However, third-generation and newer models have now been made compatible with the Dual Mode Virtual Wall, which, in addition to simulating a straight wall, can create a circular barrier roughly 4 ft in diameter. Some 500, 700, and 800 series models are compatible with the Virtual Wall Lighthouse.[10][11] It initially confines the vacuum to one area to be cleaned. Once the vacuum reports the area being sufficiently cleaned (based on its estimated area), it directs it to proceed to the next space to be cleaned and contains it there.[12]
A Roomba's bumper allows it to sense when it has bumped into an obstacle, after which it will reverse or change paths. Infrared "cliff sensors" on the bottom of the unit similarly prevent them from falling off ledges such as stairs. These may also trigger a false positive on dark or black-colored surfaces, such as some carpets, preventing Roombas from entering or cleaning those areas. Third-generation and newer models have additional forward-looking infrared sensors to detect obstacles. These sensors slow down the Roomba's speed when nearing obstacles to reduce its force of impact.[13] It also cleans along walls without repeatedly bumping into them. This technology can also distinguish between hard and soft obstacles.
Most second- and third-generation models, as well as all newer ones, have internal acoustic-based dirt sensors that allow them to detect and focus on particularly dirty spots. Fourth-generation and newer models have an optical sensor located in front of the vacuum bin, allowing detection of wider and smaller messes.[14]
Third-generation and newer models can reverse their brushes' rotation direction to escape entangled cords and tassels. If at any time the unit senses that it has become stuck,[15] is unable to turn its main brushes, no longer senses the floor beneath it, or decides that it has worked its way into a narrow area from which it is unable to escape, it stops and sounds an error alert to help someone find it. Early models use only flashing lights or several beeps to indicate specific problems, while later models use a synthesized voice to announce a problem and a suggested solution.[16]
