Sensors and Methods for Mobile Robot Positioning

Chapter 6: Active Beacon Navigation Systems 167
interfering structures block the view. Additional
NOADS are typically employed to
increase fault tolerance and minimize ambiguities
when two or more robots are operating
in close proximity. The optimal set of
three NOADS is dynamically selected by the
host PC, based on the current location of the
robot and any predefined visual barriers. The
selected NOADS are individually addressed
over the network in accordance with assigned
codes (set into DIP switches on the
back of each device at time of installation).
An interesting and unconventional aspect
TM
of CONAC is that no fall-back dead-reckoning
capability is incorporated into the
system [MacLeod and Chiarella, 1993]. The
3,000 rpm angular rotation speed of the laser
STROAB facilitates rapid position updates at
a 25 Hz rate, which MTI claims is sufficient
Figure 6.20: Stationary NOADs are located at known
for safe automated transit at highway speeds,
positions; at least two NOADs are networked and
provided line-of-sight contact is preserved
connected to a PC. (Courtesy of MTI Research, Inc.)
with at least three fixed NOADS. To minimize
chances of occlusion, the lightweight
(less than 250 g — 9 oz) STROAB is generally mounted as high as possible on a supporting mast.
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The ability of the CONAC system was demonstrated in an intriguing experiment with a small,
radio-controlled race car called Scooter. During this experiment, the Scooter achieved speeds greater
than 6.1 m/s (20 ft/s) as shown by the Scooters mid-air acrobatics in Figure 6.22. The small vehicle
was equipped with a STROAB and programmed to race along the race course shown in Figure 6.23.
The small boxes in Figure 6.23 represent the desired path, while the continuous line represents the
Stationary
NOADs
3000+ rpm
α 2
α 1
α 3
Cable link
radio link to
host PC
Laser line
projection
Mobile
STROAB
Optional
heading data
link
TM
Figure 6.21: The Computerized Opto-electronic Navigation and Control (CONAC )
system employs an onboard, rapidly rotating and vertically spread laser beam, which
sequentially contacts the networked detectors. (Courtesy of MTI Research, Inc.)