Mobile robots often utilize perimeter sensing in order to perform tasks such as avoiding obstacles, hugging walls, and navigating cluttered environments. Some perimeter sensors
— such as the Sharp GP2Y0D810Z0F shown in Figure 1 —
are limited in that they merely provide a true/false
indication of the presence of a detected object. These
sensors are often referred to as digital sensors because their
output is zero or one. In this case, objects can only be
detected when they are within a 2 to 10 cm range.
Ranging sensors, on the other hand, are devices that
can provide a distance measurement to objects that have
been detected. Such sensors generally utilize infrared or
ultrasonic waves to measure the distance to objects. The
measured distance supplied by these sensors can take many
forms. It might, for example, be a voltage whose amplitude
is related to the distance measured. The data might also be
provided using some form of a serial transmission (USB, I2C,
etc.). Even though serial transmissions are digital, ranging
sensors are often referred to as analog sensors because the
output from them is not a true/false condition.
Figure 2 shows an IR-based Sharp analog sensor
(GP2Y0A21YK0F) capable of measuring distances up to 80
cm. The output from this sensor is a voltage as indicated in
Mobile robots need perimeter sensing.
There are many options, including digital
and analog, IR and ultrasonic — even a
laser could be in your future.
Understanding the limitations and
advantages of various choices can help
you improve the functionality of your
By John Blankenship
60 SERVO 11.2015
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