Page 297 - Concise Encyclopedia of Robotics

Sentry Robot
two or more redundant sensors to minimize the number of false negatives
and false positives.
Whenever a single sensor is used to detect a phenomenon or occur-
rence in the environment, there is a chance for error. If the output of the
sensor is a simple “yes/no”(logic 1 or logic 0), the output will occasionally
be 1 when it should be 0 (false positive) or vice versa (false negative). If a
sensor detects a range of values such as visible-light intensity, the measure-
ment is always subject to some error.
Suppose two binary-output (1 or 0) sensors are used to detect or
measure the same phenomenon. The output of the combination can be
considered 1 if and only if both sensors output 1; the output of the com-
bination can be considered 0 if and only if both sensors output 0. Usually
the two sensors will agree, but occasionally they will not. In cases where
the two sensors disagree, the robot controller can instruct the sensors to
take another sampling. In the case of analog sensors, such as those used
to measure visible-light intensity, the outputs can be averaged to get a
more accurate reading than either sensor produces alone.
Numerous competing sensors can be used to obtain much greater
accuracy than is possible with a single sensor. In general, the larger the
number of competing sensors, the less frequent will be the errors in a
binary digital system, and the smaller will be the error in an analog sys-
tem. There are various ways in which the sensor outputs can be com-
bined to obtain a result of the desired accuracy, while maintaining
reasonable system speed.
SENSOR FUSION
The term sensor fusion refers to the use of two or more different types of
sensors simultaneously to analyze an object. Examples of characteristics
that can be measured include mass (or weight), volume, shape, light reflec-
tivity, light transmittivity, color, temperature, and texture.
Sensor fusion is used by smart robots to identify objects. The robot con-
troller can store a large database of objects and their unique characteristics.
When an object is encountered, the sensors provide input and compare
the characteristics of the object with the information in the database.
Compare SENSOR COMPETITION.
See also BACK PRESSURE SENSOR, COLOR SENSING, EYE-IN-HAND SYSTEM, FEEDBACK, JOINT-
FORCE SENSING, OBJECT RECOGNITION, TACTILE SENSING, TEMPERATURE SENSING, TEXTURE SENS-
ING, and WRIST-FORCE SENSING.

SENTRY ROBOT
A sentry robot is a specialized type of security robot that alerts people to
abnormal conditions. Such a robot can be designed to detect smoke, fires,

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