Page 233 - Introduction to AI Robotics

216
6 Common Sensing Techniques for Reactive Robots

Figure 6.9 The ring of IR sensors on a Khepera robot. Each black square mounted
on three posts is an emitter and receiver.

by looking at the sonar returns, which often suggest specular reflection or
crosstalk. One team in a robot competition attached a voltmeter next to the
emergency stop button on their robot to ensure that this problem would not
go undetected.
One method of eliminating spurious readings, regardless of cause, is to
take the average of three readings (current plus the last two) from each sen-
sor. This method is fairly common on purely reactive robots, but is ad hoc.
As will be seen in later chapters, other approaches treat the reading as be-
ing uncertain and apply formal evidential reasoning techniques to refine the
reading. These uncertainty techniques are employed by architectures oper-
ating under the Hybrid Paradigm, and will be covered in Ch. 11.

6.5.2 Infrared (IR)

Infrared sensors are another type of active proximity sensor. They emit near-
infrared energy and measure whether any significant amount of the IR light
is returned. If so, there is an obstacle present, giving a binary signal. IR
sensors have a range of inches to several feet, depending on what frequency
of light is used and the sensitivity of the receiver. The simplest IR proximity
sensors can be constructed from LEDs, which emit light into the environment
and have a range of 3-5 inches. Fig. 6.9 shows the IR emitters and receivers
placed side by side in a single rectangular package on a Khepera robot. These
often fail in practice because the light emitted is often “washed out” by bright