Even with all their limitations, IR and/or ultrasonic
ranging sensors can provide reasonably accurate (within 1/2
inch or so) and reliable information, especially in a
controlled or known environment. This — plus the fact that
rangers cost only slightly more than digital sensors — makes
them an excellent choice for many hobbyists. Sometimes
though, better accuracy, greater distances, and more
reliability are needed.
Laser ranging sensors are significantly more expensive
than IR or ultrasonic, but they solve many problems. Lasers
generally have no trouble detecting dark or soft objects,
and — perhaps even more important — they easily detect
angled surfaces that can confuse IR and ultrasonic sensors.
Furthermore, their detection range can be 50 times greater
than IR and ultrasonic rangers.
The accuracy of a laser sensor (typically around 1 cm) is
not significantly better than other types of rangers, but
that’s not the entire story. The readings from IR and
ultrasonic sensors often bounce or jitter around the actual
value. The distance to a stationary object might, for
example, be reported as 10 inches, then 9, then 11, then
10, etc. Such individual readings are obviously not truly
accurate, but an accurate reading can often be obtained by
averaging the readings over time. The readings from laser
rangers — by comparison — are far more stable and
repeatable than other types.
For many applications, a laser’s capabilities are worth
the higher price. The extended range of a laser, for
example, can greatly enhance a robot’s navigational
behaviors because it can map its environment and more
precisely determine its location by accurately measuring the
distance to known objects and distant walls.
Lasers don’t just improve the standard mobile robotic
behaviors we are all familiar with. They also make it simpler
to deal with new technologies. For example, the extended
range of a laser sensor can make it easy to determine
the altitude of a drone, and the speed and accuracy of
the measurements can enhance the ability to land
autonomously.
Interfacing with many laser rangers can be
difficult, but Parallax has made it easy with its new
line of laser-based sensors. Figure 6 shows a typical
model in their SF10 series which can measure
distances up to 100 meters. Figure 7 shows the SF02
which has a maximum range of 50 meters. Both of
these lasers were designed to be used as altimeters
for small aircraft, but they also make excellent
perimeter sensors for mobile robots.
No matter which model you choose, a major
advantage of the Parallax lasers is their variety of
interfaces which allows them to connect with almost
any processor. The interfaces include USB, analog,
CMOS serial, and I2C. Another advantage of these
lasers is that they can be configured to meet your
specific needs. Let’s look at an example to illustrate
this point.
I felt my Arlo robot (see the series, The Robot
62 SERVO 11.2015
Figure 6.
Figure 7.
Figure 8.