31.01.2014 Views

Sensors and Methods for Mobile Robot Positioning

Sensors and Methods for Mobile Robot Positioning

Sensors and Methods for Mobile Robot Positioning

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Chapter 2: Heading <strong>Sensors</strong> 43<br />

6 = rotational velocity<br />

= freespace wavelength of laser<br />

n = refractive index of the fiber.<br />

Like the IFOG, the all-solid-state RFOG is attractive from the st<strong>and</strong>point of high reliability, long<br />

life, quick start-up, <strong>and</strong> light weight. The principle advantage of the RFOG, however, is that it<br />

requires significantly less fiber (from 10 to 100 times less) in the sensing coil than the IFOG<br />

configuration, while achieving the same shot-noise-limited per<strong>for</strong>mance [S<strong>and</strong>ers, 1992]. S<strong>and</strong>ers<br />

attributes this to the fact that light traverses the sensing loop multiple times, as opposed to once in<br />

the IFOG counterpart. On the down side are the requirements <strong>for</strong> a highly coherent source <strong>and</strong><br />

extremely low-loss fiber components [Adrian, 1991].<br />

2.3.6 Commercially Available Optical Gyroscopes<br />

Only recently have optical fiber gyros become commercially available at a price that is suitable <strong>for</strong><br />

mobile robot applications. In this section we introduce two such systems.<br />

2.3.6.1 The Andrew “Autogyro"<br />

Andrew Corp. [ANDREW] offers the low-cost Autogyro, shown in Figure 2.11, <strong>for</strong> terrestrial<br />

navigation. It is a single-axis interferometric fiber-optic gyroscope (see Sec. 2.1.2.3) based on<br />

polarization-maintaining fiber <strong>and</strong> precision<br />

fiber-optic gyroscope technology. Model<br />

3ARG-A ($950) comes with an analog<br />

output, while model 3ARG-D ($1,100) has<br />

an RS-232 output <strong>for</strong> connection to a computer.<br />

Technical specifications <strong>for</strong> the<br />

3ARG-D are given in Table 2.1. Specifications<br />

<strong>for</strong> the 3ARG-A are similar. A more<br />

detailed discussion of the Autogyro is given<br />

Table 2.1: Selected specifications <strong>for</strong> the Andrew<br />

Autogyro Model 3ARG-D. (Courtesy of [Andrew<br />

Corp].)<br />

Parameter Value Units<br />

Input rotation rate ±100 (/s<br />

Minimum detectable<br />

rotation rate<br />

±0.05<br />

±180<br />

(/s<br />

(/hr<br />

Rate b<strong>and</strong>width 100 Hz<br />

Bias drift (at stabilized<br />

temperature) — RMS<br />

Size<br />

(excluding connector)<br />

0.005<br />

18<br />

77 dia × 88<br />

3.0 dia × 3.5<br />

Weight (total) 0.63<br />

1.38<br />

Power 9 to 18<br />

630<br />

(/s rms<br />

(/hr rms<br />

mm<br />

in<br />

kg<br />

lb<br />

VDC<br />

mA<br />

Figure 2.11: The Andrew Autogyro Model 3ARG.<br />

(Courtesy of [Andrew Corp].)

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!