Where am I? Sensors and Methods for Mobile Robot Positioning

Chapter 4: Sensors for Map-Based Positioning 119
4.2.4 TRC Light Direction and Ranging System
Transitions Research Corporation (TRC), Danbury, CT, offers a low-cost lidar system (see Figure
4.23) for detecting obstacles in the vicinity of a robot and/or estimating position from local
landmarks, based on the previously discussed Acuity Research AccuRange 3000 unit. TRC adds a
2-DOF scanning mechanism employing a gold front-surfaced mirror specially mounted on a vertical
pan axis that rotates between 200 and 900 rpm. The tilt axis of the scanner is mechanically
o
synchronized to nod one complete cycle (down 45 and
back to horizontal) per 10 horizontal scans, effectively
creating a protective spiral of detection coverage around
the robot [TRC, 1994] (see Fig. 4.29). The tilt axis can be
mechanically disabled if so desired for 360-degree
azimuthal scanning at a fixed elevation angle.
A 68HC11 microprocessor automatically compensates
for variations in ambient lighting and sensor temperature,
and reports range, bearing, and elevation data via an
Ethernet or RS-232 interface. Power requirements are
500 mA at 12 VDC and 100 mA at 5 VDC. Typical
operating parameters are listed in Table 4.12.
Table 4.12: Selected specifications for the TRC Light
Direction and Ranging System. (Courtesy of
Transitions Research Corp.)
Parameter Value Units
Maximum range 12 m
39 ft
Minimum range
0 m
Laser output
6 mW
Wavelength
780 nm
Beam divergence
0.5 mrad
Modulation frequency
2 MHz
Accuracy (range) 25 mm
1 in
Resolution (range) 5 mm
0.2 in
(azimuth) 0.18 (
Sample rate
25 kHz
Scan rate
200-900 rpm
Size (scanner) 13×13×35 cm
5×5×13.7 in
(electronics) 30×26×5 cm
12×10×2 in
Weight
4.4 lb
Power
12 and 5 VDC
500 and mA
100
Figure 4.28: The TRC Light Direction and
Ranging System incorporates a two-axis
scanner to provide full-volume coverage
o
o
sweeping 360 in azimuth and 45 in
elevation. (Courtesy of Transitions Research
Corp.)