| inertial | laser | wire |
 Wire guidance, once the
most widely used method of AGV guidance, has slipped to second with
the advent of today's Laser
systems. But it was the leader for a long time prior to that,
and for good reason. Wire has been around since the advent of the
AGV technology.
It features high accuracy, dependability, and a simple initial setup.
Wire guidance in an AGV is possible because an electrical conductor
through which an AC current is flowing will create an electromagnetic
field around itself. This field is stronger close to the conductor
and is reduced with increased distance from the conductor. An electromagnetic
field which passes through a coil will induce an electric voltage
across the coil ends. This voltage can be detected across the termination
of the coil, and is proportional to the strength of the field. |
| |
 A guide antenna contains
two coils positioned on each side of the wire which is embedded in
the floor. The difference in electric voltage between the two coils
will, after amplification, create the steering signal to the steering
motor of the AGV. When the antenna is centered over the wire, the
voltage in the coils will be the same and the steering is equal to
zero. If the antenna is positioned to either side of the guide wire,
the voltage will be increased in one coil and reduced in the other.
This voltage difference will generate a steering which will control
the rotation direction of the steering motor.
Floor installation is made very easy today as there are several
companies specializing in this technique. Special floor cutting machines
are available which cut the floor without excessive noise, concrete
dust or water spillage and leaves a clean slot ready for installation
of the wires. With the improvements in programming capabilities, it
is no longer necessary to cut radiuses for vehicle turns. The vehicle
is also able to leave the guide path for several feet and return with
no interruption in operation.
However, wire guidance is best suited for applications
where path flexibility is not critical or where there are no forseeable
plans to alter the vehicle path layout. |
