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4 The Reactive Paradigm

Figure 4.12 Example of an obstacle exerting a repulsive potential field over the ra-
dius of 1 meter.

One way of thinking about potential fields is to imagine a force field acting
on the robot. Another way is to think of them as a potential energy surface
in three dimensions (gravity is often represented this way) and the robot as
a marble. In that case, the vector indicates the direction the robot would
“roll” on the surface. Hills in the surface cause the robot to roll away or
around (vectors would be pointing away from the “peak” of the hill), and
valleys would cause the robot to roll downward (vectors pointing toward
the bottom).
FIVE PRIMITIVE FIELDS There are five basic potential fields, or primitives, which can be combined
to build more complex fields: uniform, perpendicular, attractive, repulsive, and
UNIFORM FIELD tangential. Fig. 4.13 shows a uniform field. In a uniform field, the robot would
feel the same force no matter where it was. No matter where it got set down
and at what orientation, it would feel a need to turn to align itself to the
direction the arrow points and to move in that direction at a velocity propor-