Robot Vacuum Cleaners and Lawn Mowers
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NOW Then and ROBOT VACUUM CLEANERS AND LAWN MOWERS by Tom Carroll t’s Saturday morning and you’ve mounted to a mobile robot base. These tiful machine may not have been able to Islept in. The bed is soft and cozy early machines were more of an snake its way under a low coffee table, when you are awakened to the whir of experiment in functionality than actual but it was one of the most stunningly- a motor off in the distance. You look at usefulness. It did not take experi- built robots that I had ever seen. your alarm clock and see the blue menters long to discover that a vacuum Today’s robot vacuum cleaner “8:00” shining back at you. Oh, yeah, cleaner’s cleaning power was not just a designers have been “backed into a it’s time for my robot vacuum cleaner result of the vacuum level attained in corner” of sorts as they soon realized to begin its daily ritual. Then, suddenly, ”inches of water,” but also the volume that greater cleaning ability required a you hear a louder whirring noise of air moved in cubic feet per minute at larger motor. A larger motor required a outside your window as your robot that lowered pressure. We’ve all seen larger battery. Longer operating time lawn mower begins it weekly chore. the TV ad where the hand-held vacuum also required a larger battery. A small- “Dang,” you mutter to yourself, “I’ve cleaner is attached to a large funnel er, practical size was certainly more got to re-program those things to start and the spokesperson sucks a bowling desirable for a typical homemaker. All later on Saturday; I need my sleep.” ball onto the funnel and lifts it up. This of these requirements were hard to Ahh, the ubiquitous labor-saving in no way demonstrates the cleaning meet in a mobile robot. What was the tools of the modern age! These two ability of a vacuum cleaner as we could designer to do? appliances are the epitome of a robot easily do the same thing sucking with The first step was to reduce the experimenter’s goal. Every homeowner our mouth. If the funnel had an effec- motor’s power requirements, thus would like a lawnmower that can tive area of only 20 square inches reducing the battery size and, there- decide when the grass needs to be touching the 16-pound ball, less than fore, the overall machine’s size and mowed, have it exit from its storage one pound per square inch (or two area, and mow the lawn completely inches of mercury) of vacuum (out of Figure 1. This is Frank Jenkins’ without a person’s involvement. It 14.7 PSI) suction with your mouth home-built robot. must safely perform this task effective- could allow you to lift the ball. Vacuum ly in the midst of people, obstacles, cleaner design is a bit more complex children’s toys, and pets. Today’s than just raw suction. homemaker wants the same thing in a Figure 1 shows an early home-built vacuum cleaner for carpets and floors, robot vacuum cleaner that was a work but operating within the ever-changing of art, though a bit tall to clean under environment of a home. Tall orders? most furniture. Frank Jenkins of the Possibly — several decades ago. Robotics Society of California demon- strated his home vac for our group 15 Robot Vacuum years ago. At 23 inches high and 44 pounds, HomeR was a bit larger than Cleaners Design today’s machines, but contained over Dilemma 80 sensors. It used an Ampro 386SX board computer with four megabytes of The first experimenter-built robot memory. It also had a Black and Decker vacuum cleaners that I remember all hand vacuum system built in for the used a “Dust Buster” type of battery- sweeping function and could find its operated, hand-held vacuum cleaner way back to a charging dock. This beau- SERVO 11.2006 79 weight. Now, with less effective suc- other design issues. a ‘cool’ factor; he wanted as machine tion and “cleaning power,” the design- that would do a job well. Jones — the er was left with slowing the robot vac- The iRobot Roomba lead designer for the Roomba — uum’s speed down to have the nozzle designed it with an undercarriage over a given area for a longer period of There is no doubt to all of us that containing the dirt collection pan and time, or, devising an overall better the iRobot Roomba is the run-away the revolving brushes that rise or lower nozzle arrangement augmented with best selling “home robot” ever, with according to the floor type. You may rotating brushes or similar devices. over two million sold and counting, remember him as the co-author of the The designers of the best-selling after its September 2002 debut. Back great book Mobile Robots — robot vacuum cleaners actually took then, everyone was talking about Dean Inspiration to Implementation. many more design aspects into consider- Kamen’s Segway Transporter, as this When Roomba encounters friction- ation such as height above the carpet or other small New England company causing surfaces such as carpet, the floor, number and location of “nozzles;” quietly designed and produced what torque derived from the friction on the shape of the air flow channels; shape, many say is the first truly useful brushes causes the assembly to rise a speed, and location of brushes; number consumer robot. This amazing product bit, thus lessening the load torque. of passes over an area, and many more that people have called a ‘low-flying fly- When the load lessens — such as on a aspects. Then comes the navigation and ing saucer,’ a “Frisbee on steroids,’ and hard floor — the brush assembly low- steering of the robot cleaner. Do you even a ‘bathroom scale that walks’ is in ers. This seemingly complex action is just allow the machine to bump into millions of homes around the world. created by a simple string and friction walls, reverse, and then go off in anoth- The overall design and basic shape clutch arrangement to keep the cost er direction like a sheep randomly eating and size were not iRobot’s biggest down. A single motor is used for the grass in a meadow? Eventually, the hurdle; their problem was how to make brush assembly and the lifting/lower- machine finally covers the entire carpet the robot vacuum affordable to be able ing system. Roomba utilizes a spinning in a given room — or does it? to be sold through major retail chains. side brush to push dirt from edges into Does it keep bumping into the There were already some capable — but the path of the main cleaning head same chair and table legs, only to miss very expensive — robot vacuum clean- (see Figures 2 and 3). many areas of the carpet? Does the ers on the market. In the beginning, The next generation of Roombas designer need to add optical or they decided that they needed a simple uses the C programming language and ultrasonic sensors to allow the robot to eight-bit processor and a small number is compiled with commercially available travel parallel to a wall without touch- of parts that could be easily machined software. A 16-bit Freescale ing it? Does one need to add a higher- or molded, much like toy manufacturers Semiconductor MC9S12 processor level processor to bit-map a room? Do who create amazing devices for using only 2K bytes of RAM executes you need to add sensors to detect child-sized budgets. Uniquely enough, the algorithms. Several years ago, they what parts of the carpet the machine iRobot did have experience with toy came out with the Roomba Pro and Pro has covered by detecting carpet fibers manufacturing — their disastrous My Elite. The Roomba Pro Elite model brushed in a specific direction? How Real Baby, a robot doll that failed included a remote control that allowed does the robot regain its original path miserably in the toy market. users to navigate the robot vacuum once it detects an obstacle and goes around a room, set cleaning options, around it? Detecting a full dirt bin, Roomba Design and turn the Pro Elite on or off with the orientation, low batteries, dangerous Constraints touch of a button. The Roomba Pro overhangs, and getting permanently Elite also featured a “MAX” cleaning stuck were other designer problem iRobot wanted the Roomba to be mode for multi-room cleaning or high- areas. Today’s robot vacuum manufac- effective on both carpeted and hard traffic areas. The software featured turers have solved these and many floors. Designer Joe Jones wasn’t after one or two virtual walls and a “cliff- avoidance” detector that prevented the Figure 2. The inside of the Roomba. Figure 3. The bottom of the Roomba. robot from falling down stairs. “These newer generations are able to deter- mine how large the room is and plot the most effective cleaning tactic based on the room’s layout,” says Colin Angle, iRobot’s CEO. The current cheapest model — Roomba Red — costs $150, though I’ve seen it on closeout sales for less than $75. The Roomba Sage model has a longer-lasting battery that charges faster, for an additional $50. Roomba Discovery goes for $250, has auto 80 SERVO 11.2006 charging ability, and a larger trash bin, Scooba actually sucks up the dirty blade (and engine) when the handle is or, for $50 more, it can charge while water from the first cycles and deposits released.