Where am I? Sensors and Methods for Mobile Robot Positioning

Chapter 4: Sensors for Map-Based Positioning 99
4.1.1.2 Polaroid Ultrasonic Ranging Modules
Figure 4.4: The Polaroid OEM kit included the transducer and a small
electronics interface board.
The Polaroid ranging module is
an active TOF device developed
for automatic camera focusing,
which determines the range to
target by measuring elapsed
time between the transmission
of an ultrasonic waveform and
the detected echo [Biber et al.,
1987, POLAROID]. This system
is the most widely found in
mobile robotics literature
[Koenigsburg, 1982; Moravec
and Elfes, 1985; Everett, 1985;
Kim, 1986; Moravec, 1988;
Elfes, 1989; Arkin, 1989;
Borenstein and Koren, 1990;
1991a; 1991b; 1995; Borenstein
et al., 1995], and is representative
of the general characteristics
of such ranging devices. The most basic configuration consists of two fundamental components:
1) the ultrasonic transducer, and 2) the ranging module electronics. Polaroid offers OEM kits with
two transducers and two ranging module circuit boards for less than $100 (see Figure 4.4).
A choice of transducer types is now available. In the original instrument-grade electrostatic
version, a very thin metal diaphragm mounted on a machined backplate formed a capacitive
transducer as illustrated in Figure 4.5 [POLAROID, 1991]. The system operates in the monostatic
transceiver mode so that only a single transducer is necessary to acquire range data. A smaller
diameter electrostatic transducer
(7000-series) has also
been made available, developed
for the Polaroid Spectra camera
[POLAROID, 1987]. A more
rugged piezoelectric (9000-series)
environmental transducer
for applications in severe environmental
conditions including
vibration is able to meet or exceed
the SAE J1455 January
1988 specification for heavyduty
trucks. Table 4.2 lists the
technical specifications for the
different Polaroid transducers.
The original Polaroid ranging
module functioned by transmitting
a chirp of four discrete fre-
Figure 4.5: The Polaroid instrument grade electrostatic transducer
consists of a gold-plated plastic foil stretched across a machined
backplate. (Reproduced with permission from Polaroid [1991].)