Page 277 - Concise Encyclopedia of Robotics

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ever; a specific procedure must be followed to reinitialize such devices.
See CONTROLLER.

RELATIONAL GRAPH
A relational graph is a representation of a robotic work environment as
points, called nodes, and lines connecting those points, called edges. A
relational graph is generated on the basis of a computer map.
Consider a simple floor plan, such as that shown in the illustration. A
basic relational graph can be generated by locating the center points of all
the rooms, and the center points of all the doorways, and defining each
such point as a node. If there is a turn in the hallway, a point midway
from the protruding corner to the opposite wall, subtending an angle of
135° with either wall at the corner, is defined as a node. These nodes are
then connected with straight-line edges.
Relational graphs provide a means of robot navigation in environments
that do not change geometrically, and in which no new obstructions are
placed. However, this type of graph does not generally represent the most
efficient navigation method, and it can be inadequate for large robots or
for fleets of robots in a limited space.
See also COMPUTER MAP, GATEWAY, LANDMARK, and TOPOLOGICAL PATH PLANNING.
RELIABILITY
Reliability is an expression of how well, and for how long, machines keep
working. It is the proportion of units that still work after they have been
used for a certain length of time.
Suppose that 1,000,000 units are placed in operation on January 1,
2010. If 920,000 units are operating properly on January 1, 2011, then the
reliability is 0.92, or 92 percent, per year. On January 1, 2012, you can

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