Servo - May 2012

Then

and

NOW

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Sensors For Mobile Robots by Tom Carroll

That is exactly the title of Bart Everett’s great sensor book from 1995, shown in Figure 1. Well, it’s no coincidence because Bart’s book has literally been a ‘bible’ for me in robot writing and consulting, as well as for thousands of other experimental robot builders. Bart is a friend of mine and works in one of the most enviable positions for a robotics enthusiast at the Navy’s SPAWAR Systems Center in San Diego, CA. I have visited the site on several occasions and have seen some of the most amazing robot creations you could imagine.

In his book, Bart starts out discussing robots that he built as a kid, starting with Walter back in 1965. Bart’s teleoperated anthropomorphic robot met its untimely demise when the household cleaning lady went into young Bart’s bedroom (he was a sophomore in high school at the time) and turned on an old vacuum cleaner that emitted so much electromagnetic static that the five foot tall radio-controlled robot went berserk. When he came home and saw his decapitated robot on the floor, the dented vacuum cleaner on its side still running, and the front screen door off its hinges, it was obvious that the maid had ‘killed it’

FIGURE 1. Sensors for Mobile Robots by Bart Everett.

with one mighty swing of the vacuum and left in such a hurry as to never be seen again.

Walter had no onboard sensors for perceiving its physical surroundings. Its successor was Crawler I — a small tracked robot equipped with tactile feelers made from looped guitar strings, and barely enough onboard intelligence to support a very primitive bump-and-recover mobility behavior. Non-contact sensing had to wait for Everett’s first computer-controlled robot — ROBART I — which was his thesis project at the Naval Postgraduate School in the early 1980s. This robot utilized two types of sensors. One was an active ranging system based on the National Semiconductor LM-1812 monolithic sonar transceiver chip used in underwater fish finders and the other was a modified near-infrared proximity sensor from surplus circuit boards used on toys. ROBART I also had considerable collision detection capability in the form of an extensive array of tactile sensors, along with over-current sensing for its tandem drive motors.

The big sensing breakthrough on ROBART II came in 1982 with the introduction of Polaroid’s ultrasonic ranging system which employed a novel electrostatic transducer specifically designed for operation in air; the original application, of course, being automatic camera focusing. The LM-1812 compatible transducers were designed for underwater use and had trouble achieving an effective impedance match with air. Thanks to the high-volume camera application, the Polaroid system was both small and inexpensive which allowed a total of 36 of these sensors to ultimately be incorporated on ROBART II (Figure 2). These