Page 261 - Concise Encyclopedia of Robotics

Proximity Sensing
In theory, either type of displacement transducer can function in any
application,but one type is usually easier to work with,in a given situation,
than the other.
Capacitance and inductance
The presence of nearby objects can cause mutual capacitance or mutual in-
ductance effects. These effects can be sensed and the signals transmitted to
the robot controller. Capacitive proximity sensors operate using electrostatic
effects, while inductive proximity sensors employ ferromagnetic coupling.
Ladar
An infrared (IR) or visible laser beam can be bounced off anything that
will reflect or scatter the energy. The return-signal delay can be measured,
and the distance to the object determined by the robot controller. This is
called ladar (short for laser detection and ranging).
Ladar will not work for objects that do not reflect IR or visible energy.
A white painted wall will reflect such energy well; the same wall painted
dull black will not. Ladar works better at relatively long distances than at
short distances, over which sonar or interferometry provide superior results.
Radar and sonar
Proximity sensing can be done using radar or sonar. Radar works with
ultra-high-frequency (UHF) or microwave radio signals. Sonar uses
acoustic waves. Pulses are transmitted and picked up after they reflect
from objects. The delay time is measured, and the results sent to the
robot controller. The principle is basically like that of a laser-ranging
proximity sensor.
Radar will not work for objects that do not reflect UHF or microwave
energy. Metallic objects reflect this energy well; salt water is fair; and trees
and houses are poor. Radar, like ladar, works better at long distances than
close up. Sonar can function well at small distances, because the speed of
sound in much slower than the speed of electromagnetic (EM) waves in
free space.

For further information
Related definitions, besides those already mentioned here, include
ACOUSTIC PROXIMITY SENSOR, ARTIFICIAL STIMULUS, CAPACITIVE PROXIMITY SENSOR, COMPUTER
MAP, DISTANCE MEASUREMENT, GUIDANCE SYSTEMS, INDUCTIVE PROXIMITY SENSOR, LADAR, PAR-
ALLAX, PHOTOELECTRIC PROXIMITY SENSOR, PRESENCE SENSING, RADAR, RANGE SENSING AND
PLOTTING, SONAR, and VISION SYSTEM.

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