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6 Common Sensing Techniques for Reactive Robots
been used for range, ignoring the placement of the shark teeth and the com-
putational complexity. There was also a large amount of logical redundancy,
which was exploited through the use of behavioral sensor fusion.

6.9 Summary

The success of a reactive system depends on the suitability of the robot’s sen-
sor suite. It is often more useful to think of sensing in terms of perceptual
schemas or logical sensors needed to accomplish a task, rather than focus on
the characteristics of a particular transducer or modality. Reactive percep-
tion may appear limited since it uses only behavior-specific representations
and does not involve recognition. However, it supports a diversity of forms
of perception, including behavioral sensor fusion. Advances in electronics
have led to a plethora of range sensors and algorithms. Many of these are
logically equivalent and can be used interchangeably; for example, with ob-
stacle avoidance behaviors.
The design of a perceptual schema or a sensor suite requires a careful anal-
ysis. Each individual sensor should fit the task, power, and processing con-
straints. Likewise, the entire sensor suite should provide complete coverage
of all perceptual processing required by the robot.
Almost all mobile robots have some form of proprioception, most likely
shaft or wheel encoders used to estimate the distance traveled based on the
number of times the motor has turned. Outdoor robots may carry GPS, and
this trend is expected to increase as the cost of receivers goes down and in-
expensive DGPS systems emerge.
Reactive navigation requires exteroception, whereby the robot observes
the environment. Proprioception can guide a robot on a path, but exterocep-
tion can prevent it from hitting an unmodeled obstacle or falling off a cliff.
The most common exteroceptive sensor on reactive robots is an ultrasonic
transducer or sonar. An ultrasonic transducer is an active sensor which re-
turns a single range reading based on the time-of-flight of an acoustic wave.
Some of the difficulties associated with ultrasonics include erroneous read-
ings due to specular reflection, crosstalk, and foreshortening. Other popular
proximity sensors are IR and laser rangers.
Due to the low price and availability of consumer electronics, computer
vision is becoming more common in robotic systems. Computer vision pro-
cessing operates on images, regardless of the modality which generated it.
Color coordinate systems tend to divide an image into 3 planes. The two