Page 182 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Hard Navigation vs. Fuzzy Navigation

Figure 11.12 shows another possibility for this function. In this case, we simply refuse to
grant a quality factor greater than Q1, so the navigation will never take the whole
implied correction. Furthermore, any error that is greater than E2 is considered so
suspect that it is not believed at all. If the breakpoints of this profile are stored as
blackboard variables, then the system can be trimmed during operation to product
the best results.

The referenced state
It should be obvious that the navigation scheme we are pursuing is one that requires
the robot to know roughly where it is before it can begin looking for and processing
navigation features. Very few sensor systems, other than GPS, are global in nature,
and very few features are so unique as to absolutely identify the robot’s position.
When a robot is first turned on, it is unreferenced by definition. That is, it does not
know its position. To be referenced requires the following:
1. The robot’s position estimate must be close enough to reality that the sensors
can image and process the available navigation features.

2. The robot’s uncertainty estimate must be greater than its true position error.
If our robot is turned on and receives globally unique position data from the GPS or
another sensor system, then it may need to move slightly to determine its heading
from a second position fix. Once it has accomplished this, it can automatically
become referenced.
If, however, a robot does not have global data available, then it must be told where
it is. The proper way to do this is to tell the robot what its coordinates and azimuth
are, and to also give it landmarks to check. The following incident will demonstrate
the importance of this requirement.

Flashback…
One morning I received an “incident report” in my email with a disturbing photo of a
prone robot attached. A guard had stretched out on the floor beside the robot in mock
sleep. Apparently, the robot had attempted to drive under a high shelving unit and had
struck its head (sensor pod) on the shelf and had fallen over. This was a very serious—and
thankfully extremely rare—incident.
Those who follow the popular TV cartoon series “The Simpsons” may remember the
episode in which Homer Simpson passed down to his son Bart the three lines that had

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