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6 Common Sensing Techniques for Reactive Robots
HORIZONTAL FOV coordinates, where one angle is the horizontal FOV and the other is the vertical
VERTICAL FOV FOV. The other aspect is the range, or how far the sensor can make reliable
RANGE
measurements. In spherical coordinates, this would be the values of r that
defined the depth of the operating range.
Field of view and range are obviously critical in matching a sensor to an
application. If the robot needs to be able to detect an obstacle when it’s 8 feet
away in order to safely avoid it, then a sensor with a range of 5 feet will not
be acceptable.
2. Accuracy, repeatability, and resolution. Accuracy refers to how correct
the reading from the sensor is. But if a reading for the same conditions is
accurate only 20% of the time, then the sensor has little repeatability. If the
sensor is consistently inaccurate in the same way (always 2 or 3 cm low),
then the software can apply a bias (add 2 centimeters) to compensate. If the
inaccuracy is random, then it will be difficult to model and the applications
where such a sensor can be used will be limited. If the reading is measured
RESOLUTION in increments of 1 meter, that reading has less resolution than a sensor reading
which is measured in increments of 1 cm.
3. Responsiveness in the target domain. Most sensors have particular
environments in which they function poorly. Another way of viewing this is
that the environment must allow the signal of interest to be extracted from
noise and interference (e.g., have a favorable signal-to-noise ratio). As will
be seen below, sonar is often unusable for navigating in an office foyer with
large amounts of glass because the glass reflects the sound energy in ways
almost impossible to predict. It is important to have characterized the eco-
logical niche of the robot in terms of what will provide, absorb, or deflect
energy.
4. Power consumption. Power consumption is always a concern for robots.
Since most robots operate off of batteries, the less power they consume, the
longer they run. For example, the battery life on a Nomad 200, which carries
five batteries, was improved from four hours to six by shutting off all sensors.
Power is so restricted on most mobile robots that many robot manufacturers
will swap microprocessor chips just to reduce the power drain (which was
part of the motivation for the Transmeta Crusoe chip). Sensors which require
a large amount of power are less desirable than those which do not. In gen-
eral, passive sensors have less power demands than active sensors because
they are not emitting energy into the environment.
The amount of power on a mobile robot required to support a sensor pack-
age (and any other electronics such as a microprocessor and communications
HOTEL LOAD links) is sometimes called the hotel load. The sensor suite is the “guest” of the