Then
and
NOW
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Sensors For Mobile Robots — Part 2
Location and Object Recognition
by Tom Carroll
Last month, I began by referencing Bart Everett’s sensor book from 1995,
Sensors for Mobile Robots — a book that, in my opinion, should be on every
robot experimenter’s bookshelf. Everett’s book emphasizes just how critical the
need and use of sensors is for successful robot designs. His book not only
describes how they work, but which ones to use and how to use them. Though
it was published 17 years ago, almost all of the types and technology involved
are still appropriate for today’s robot designs.
In May’s article, I highlighted Bart’s Robart I and Robart II as examples of some pretty sophisticated robots. His
Robart III — begun in 1992 and a work-in-progress at the
time his book was published — is shown in Figure 1. Bart’s
third-generation robot sported some unique ‘military
appendages’ such as a pneumatically powered six-barrel
FIGURE 1. Robart III.
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Gatling-style gun as its right arm shown in the figure. It
fires simulated tranquilizer darts or rubber bullets, strictly
for demonstration purposes. Down at the base, you can see
the blue SICK LIDAR ranging system that replaced some of
the original Polaroid ultrasonic distance ranging sensors,
though nine remain on the lower base, the lower waist,
and the arms. Robart III — like its predecessors — is strictly a
laboratory prototype and certainly could not be used on a
modern battlefield or even outdoors, though the A-BEC
unlockable hub electric wheelchair motor-wheel units are
the very best for large mobile robots. Also note the
‘necklace’ of security system PIR sensors around Robart’s
neck which are useful for detecting people moving around
the robot.
Passive Infrared Sensors
Last month, I concentrated on basic object detection,
tactile, active IR, ultrasonic sensors, and a simple laser
range finder. I specifically did not mention passive IR
sensors since those are object-specific; they only sense
objects that emit IR radiation at human body temperatures,
and the object or the robot must be moving. A lot of
people seem to feel that PIR (passive infrared) sensors
detect people when, in fact, they can only detect
temperature changes that a moving person causes.
Therefore, they are people motion detectors. PIR sensors
have a crystal of pyroelectric (heat changing electrical
characteristics) material such as lithium tantalate (Li TaO3),
gallium nitride (GaN), cesium nitrate (CsNO3), and other
materials that react to a change of charge status when the
