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6 Common Sensing Techniques for Reactive Robots
A better solution would be to detect a person using vision. Notice that
detection is not the same thing as recognition. Detection means that the robot
is able to identify a face, which is reactive. Recognition would label the face
and be able to recognize it at a later time, which is a deliberative function, not
reactive. Is there a simple visual affordance of a face? Actually, to a vision
system human skin is remarkably similar in color, regardless of ethnicity.
Once the robot had found a colored region about the size and shape of a
head, it could then more reliably find the VIP badges.
The other opportunity for an affordance was Puffer Fish’s navigation to
Borg Shark. Although Puffer Fish would receive Borg Shark’s coordinates,
it was unlikely that Puffer Fish could reliably navigate to Borg Shark using
only dead reckoning. The coordinates were likely to be incorrect from Borg
Shark’s own drift over time. Then Puffer Fish would accumulate dead reck-
oning error, more so if it had to stop and start and avoid people. Therefore,
it was decided that Puffer Fish should look for Borg Shark. Borg Shark’s
head piece was deliberately made large and a distinctive blue color to afford
visibility over the crowd and reduce the likelihood of fixating on someone’s
shirt.

Step 4-7: Design, test, and refine behaviors. The choice of sensors for other
behaviors, such as treat removal, was influenced by the physical location of
the sensors. For example, the SICK laser for Borg Shark came mounted on the
research platform as shown in Fig. 6.30b. The research platform, nominally
the top of the robot, was at hand height, making it a logical place to attach a
tray for holding food. It was obvious that the laser could be used to monitor
the food tray area. Other teams tried various approaches such as having a
colored tray and counting the amount of that color visible (more color means
fewer treats on the tray, covering the color). Another approach was to build
a scale and monitor the change in weight.
An interesting aspect of the robots that impacted the sensor suite indi-
rectly were the costumes. As part of giving the robots personality, each robot
had a costume. The Puffer Fish had an inflatable skirt that puffed out when
the robot was crowded or annoyed. The team had to empirically test and
modify the skirt to make sure it would not interfere with the sonar readings.
Fig. 6.30c shows the profile of the skirt.
As seen in the behavior table below, the only behavior using any form of
sensor fusion was move-to-goal in Puffer Fish, which had two competing
instances of the goal making it sensor fission.