Page 333 - Concise Encyclopedia of Robotics

Track-Drive Locomotion
shifting can save expensive on-line time to write long programs or compose
long messages at an active terminal. Compare REAL TIME.
TOPOLOGICAL PATH PLANNING
Topological path planning, also called topological navigation, is a scheme
in which a robot can be programmed to negotiate its work environment.
The method makes use of specific points called landmarks and gateways,
along with periodic instructions for action.
Topological path planning is used by people in everyday life. Suppose
you are in an unfamiliar town, and you need to find the library. You ask
someone at a small corner grocery how to get to the library. The person
says, while pointing in a certain direction,“Go down this street here until
you get to the sugar mill. Turn left at the sugar mill. You will pass three
traffic lights and then the road will bear left. Keep going around the curve
to the left. Just as the curve ends, turn right and follow the bumpy street
until you get to a red brick building with white window trim. The building
will be on the right side of the road. That is the library. If you get to a large
shopping mall on the left, you have gone too far; turn around and go
back. The library will then, of course, be on the left-hand side of the road.”
Topological path planning is a qualitative scheme.Note that in the above
set of directions, specific distances are not indicated. If you follow the
directions, however, you will reach the library, and a computer-controlled
robot would find it as well. The instructions, although they do not contain
information about specific distances and compass directions, nevertheless
provide sufficient information to allow you (or the robot) to find the
intended destination.
Topological path planning does not always work. In complex environ-
ments,or in environments that change geometry often,more sophisticated
navigational schemes are required. Compare GRAPHICAL PATH PLANNING and METRIC
PATH PLANNING.
See also COMPUTER MAP, GATEWAY, LANDMARK, and RELATIONAL GRAPH.
TRACK-DRIVE LOCOMOTION
When neither wheels nor legs effectively propel a robot over a surface,
track-drive locomotion sometimes works. Track drive is used in military
tanks, and in some construction vehicles.
A track drive has several wheels and a pair of belts or tracks, as shown
in the illustration. (This drawing shows only one side of the track drive.
An identical wheel-and-belt set exists on the other side, out of sight in
this perspective.) The track can be rubber if the vehicle is small; metal is
better for large, heavy machines. The track can have ridges or a tread on
the outside; this helps it grip dirt or sand.

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