Page 220 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Instilling Pain, Fear and Confidence

current lateral uncertainty. Likewise, during normal navigation the robot should not
be allowed to continue moving if its uncertainty is greater in magnitude than the path
limits. The smaller of the lateral path limits then makes an acceptable parameter
against which to compare lateral uncertainty in calculating inherent confidence.

Obstacle

Danger levels
Lateral Uncertainty

Robot path
Obstacle

Figure 13.4. Deriving confidence from uncertainty in a force field system

Again, there is an equivalent way of deriving a position confidence factor when using
force field routing. A reasonable approximation of the danger posed by position un-
certainty is shown in Figure 13.4. In this case, we are simplifying the calculation by
assuming that the lateral uncertainty is the most critical element. Since paths usually
follow valleys in the force field, this is usually the case. In a few cases there may ac-
tually be a higher field level under the footprint of the robot’s whole uncertainty, but
the benefit for finding it is minimal. Again, we are dealing with nondeterministic
values that need only elicit a generally appropriate response.

By simply calculating the floor level at a distance equal to the lateral uncertainty to
the left and right, we find the danger (strength of the field) if we are out of position
by the full magnitude of the uncertainty. The worst (highest) of these two values is
used to determine the position confidence.

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