Page 336 - Concise Encyclopedia of Robotics

Triangulation
TRIANGULATION
Robots can navigate in various ways. One good method is like the
scheme that ship and aircraft captains have used for decades. It is called
triangulation.
In triangulation, the robot has a direction indicator such as a compass.
It also has a laser scanner that revolves in a horizontal plane. There must
be at least two targets, at known, but different, places in the work envi-
ronment, which reflect the laser beam back to the robot. The robot also has
a sensor that detects the returning beams. Finally, it has a microcomputer
that takes the data from the sensors and the direction indicator, and
processes it to get its exact position in the work environment.
The direction sensor (compass) can be replaced by a third target. Then
there are three incoming laser beams; the robot controller can determine
its position according to the relative angles between these beams.
For optical triangulation to work, it is important that the laser beams
not be blocked. Some environments contain numerous obstructions, such
as stacked boxes, which interfere with the laser beams and make triangu-
lation impractical. If a magnetic compass is used, it must not be fooled by
stray magnetism; also, Earth’s magnetic field must not be obstructed by
metallic walls or ceilings.
The principle of triangulation, using a direction sensor and two reflec-
tive targets, is shown in the illustration. The laser beams (dashed lines)
arrive from different directions, depending on where the robot is located
with respect to the targets. The targets are tricorner reflectors that send all
light rays back along the path from which they arrive.
Tricorner
reflector Tricorner
reflector

Laser beams

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Robot
Triangulation

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