Servo - January 2014

Figure 1 shows the original iRobot Roomba introduced in

2002. Back then, there was only one company that made robot vacuum cleaners and there was only one model. I’m going to review two of the most prominent robot vacuum cleaners on the market, but more from a technical aspect.

Issues to Consider Regarding the Designs of a Robot Vacuum Cleaner

One might think that changing a basic upright vacuum cleaner’s design by adding batteries and battery-powered motors for the wheels and impeller with some sort of simple navigation system might turn it into a robot vacuum cleaner. Not really. The fact that it must use batteries presents the greatest design hurdle.

A cheap ‘standard’ vacuum can use a relatively powerful AC motor and probably suck up just as much dust and dirt as a model twice as expensive. AC motors are comparatively inexpensive but basic vacuum cleaners are notoriously power-hungry beasts, drawing up to 10 amps at 120 volts. That is 1,200 watts — far more than any battery can supply. Therefore, inventive designers have to create systems for robot vacuums that can operate efficiently from a greatly diminished power source that will require regular replenishment at a charging base.

Improved impeller and cavity designs allow less powerful systems to closely match full-sized AC models. Simple suction alone does not pick up dirt and debris from a carpet. Sufficient air flow is required around each twisted strand of carpet to reach below the surface and cause the particles to rise to the top to join a larger flow of air into the vacuum cleaner’s dust collector. One or more rotating brushes can assist in this task.

The required length of time over any part of a carpet determines the robot’s speed. Faster means less time to clean an area but hastens the job’s completion, whereas a slower movement means better cleaning at the expense of a longer overall process. A designer must be cognizant that a robot vacuum cleaner will not have a human behind it, holding onto a handle and directing it to all the places that need cleaning. A robot vacuum must not ding walls, suck up drapes, cats, wires, or rug fringes, or dive down the stairs. It must cover all carpet areas only once — something that a human can easily see by marks on the carpet.

Everyone loves a rousing conversation about whose team, product, political party, or even robot vacuum cleaner is best.

Usually in these conversations, both sides finally stop touting their opinions and quietly step to the side, holding to their particular views or convictions. However, manufacturers never stop trying to convince potential buyers of their product's worthiness. "We've been in business longer than our competitors." "Our product uses this unique technology that surpasses that of the other manufacturers." "We've sold more units than those other companies." All these and many more are typical of the hype used to convince customers that they are buying or have bought the best product.