Where am I? Sensors and Methods for Mobile Robot Positioning

104 Part I Sensors for Mobile Robot Positioning
Figure 4.9: The SEO TreeSense. (Courtesy of
Schwartz Electro-Optics, Inc.)
Figure 4.10: Scanning pattern of the SEO TreeSense
system. (Courtesy of Schwartz Electro-Optics, Inc.)
SEO AutoSense
The AutoSense I system was developed by SEO under a Department of Transportation Small
Business Innovative Research (SBIR) effort as a replacement for buried inductive loops for traffic
signal control. (Inductive loops don’t always sense motorcyclists and some of the smaller cars with
fiberglass or plastic body panels, and replacement or maintenance can be expensive as well as
disruptive to traffic flow.) The system is configured to look down at about a 30-degree angle on
moving vehicles in a traffic lane as illustrated in Figure 4.12.
AutoSense I uses a PIN photo-diode detector and a pulsed (8 ns) InGaAs near-infrared laser-diode
source with peak power of 50 W. The laser output is directed by a beam splitter into a pair of
cylindrical lenses to generate two fan-shaped beams 10 degrees apart in elevation for improved
target detection. (The original prototype projected
only a single spot of light, but ran into problems
due to target absorption and specular reflection.)
As an added benefit, the use of two separate beams
makes it possible to calculate the speed of moving
vehicles to an accuracy of 1.6 km/h (1 mph). In
addition, a two-dimensional image (i.e., length and
Figure 4.11: Color-coded range image created by
the SEO TreeSense system. (Courtesy of
Schwartz Electro-Optics, Inc.)
Table 4.6: Selected specifications for the
TreeSense system. (Courtesy of Schwartz Electro-
Optics, Inc.)
Parameter Value Units
Maximum range 9
30
Accuracy
(in % of measured range)
Wavelength
Pulse repetition frequency
Scan rate
Length 229
9
Width 229
9
Height 115
4.5
Weight
Power 12
12
m
ft
1 %
902 nm
15 KHz
29.3 rps
mm
in
mm
in
mm
in
5 lbs
V
W