Page 470 - The Mechatronics Handbook

0066_frame_C19 Page 92 Wednesday, January 9, 2002 5:32 PM

FIGURE 19.64 From left to right: (1) the original instrument grade electrostatic transducer, (2) 9000-Series envi-
ronmental transducer, and (3) 7000 Series electrostatic transducer (courtesy Polaroid Corp.).

INIT
16 Pulses
TRANSMIT (INT)
BLNK
BINH
BLANKING (INT)
ECHO

FIGURE 19.65 Timing diagrams for the 6500-Series Sonar Ranging Module executing a multiple-echo-mode cycle
with blanking input (courtesy Polaroid Corp.).

• Returning echoes that exceed a fixed-threshold value are recorded and the associated distances
calculated from elapsed time.

In the single-echo mode of operation for the 6500-series module, the blank (BLNK) and blank-inhibit
(BINH) lines are held low as the initiate (INIT) line goes high to trigger the outgoing pulse train. The
internal blanking (BLANKING) signal automatically goes high for 2.38 ms to prevent transducer ringing
from being misinterpreted as a returned echo. Once a valid return is received, the echo (ECHO) output
will latch high until reset by a high-to-low transition on INIT. For multiple-echo processing, the blank
(BLNK) input must be toggled high for at least 0.44 ms after detection of the first return signal to reset
the echo output for the next return, as shown in Fig. 19.65 (Polaroid, 1990).
Laser-Based TOF Systems
Laser-based TOF ranging systems, also known as laser radar or lidar, first appeared in work performed
at the Jet Propulsion Laboratory, Pasadena, CA, in the 1970s (Lewis & Johnson, 1977). Laser energy is
emitted in a rapid sequence of short bursts aimed directly at the object being ranged. The TOF of a given
pulse reflecting off the object is used to calculate distance to the target based on the speed of light.
Accuracies for early sensors of this type could approach a few centimeters over the range of 1–5 m (NASA,
1977; Depkovich & Wolfe, 1984).
Schwartz Electro-Optics, Inc. (SEO), Orlando, FL, produces a number of laser TOF rangefinding
systems employing an innovative time-to-amplitude-conversion scheme to overcome the sub-nanosecond
timing requirements necessitated by the speed of light. As the laser fires, a precision film capacitor begins
discharging from a known set point at a constant rate, with the amount of discharge being proportional