Sensors and Methods for Mobile Robot Positioning

44 Part I Sensors for Mobile Robot Positioning
Table 2.1: Selected specifications for the Andrew
Autogyro Navigator (Courtesy of [Andrew Corp].)
Parameter Value Units
Input rotation rate ±100 (/s
Instantaneous
bandwidth
100 Hz
Bias drift (at stabilized
temperature) — RMS
Size
(excluding connector)
0.005
18
115×90×41
4.5×3.5×1.6
Weight (total) 0.25
0.55
Power Analog
Power Digital
< 2
< 3
(/s rms
(/hr rms
mm
in
kg
lb
W
W
in [Allen et al., 1994; Bennett and Emge,
1994].
In fall 1995 Andrew Corporation announced
a newer model, called the AUTO-
GYRO Navigator. This laser gyro, shown in
Fig. 2.12, is only one third the weight, consume
only half the power, and cost 15% less
than its predecessor, the AUTOGYRO.
Figure 2.12: The Andrew AUTOGYRO Navigator.
(Courtesy of [Andrew Corp].)
2.3.6.2 Hitachi Cable Ltd. OFG-3
Hitachi Cable Ltd. markets an optical fiber gyroscope called OFG-3 (see Figure 2.13). Komoriya and
Oyama [1994] tested that sensor and found its drift rate to be quite linear with 0.00317(/s (11.4(/hr).
This result is close to the advertised specification of 10(/hr. This low drift rate is substantially better
than that provided by conventional (mechanical) gyros. Table 2.2 shows technical specifications of
the OFG-3 gyro, as reported by Komoriya and Oyama [1994].
One point to keep in mind when considering the use of fiber optic gyros in mobile robot
applications is the minimum detectable rotation rate. This rate happens to be the same for both the
Andrew 3ARG-A and the Hitachi OFG-3 gyros: 0.05(/s. If either gyro was installed on a robot with
a systematic error (e.g., due to unequal wheel diameters; see Sec. 5.1 for more details) of 1 degree
per 10 meter linear travel, then neither gyro would detect this systematic error at speeds lower than
0.5 m/s.