Section 8.Theory of Operation

Functional Operation

calculate the position of the truck relative to the guide wire. The TM is constantly being updated as to the position of the drive unit relative to home position as well as travel speed and direction that it in turn communicates to the GM. When the CM detects that S4 is opened (Auto position), it advises the TM that S4 is open. The TM determines that the truck is ready for wire guided operation and informs the GM.

The GM then tells the TM to put the truck into Seeking Mode and try to acquire the wire. Travel speed is limited to 1 mph (1.6 km/h) in the forks-first direction and limited to the Acquire speed set in Configure Mode for tractorfirst travel. If the Sense Creep Speed (SensCreep) option is enabled in the Configure Mode menu, truck speed is limited to 1 mph (1.6 km/h) whenever S4 is detected closed (Manual position) and the GM reports that a guide wire is detected. During Seeking Mode, an audible tone is generated and the green LED triangles of the wire guidance icon blink. Steering at this time is still in manual control because the truck has not acquired the wire. The operator must steer the truck toward the guide wire location to help the truck acquire the wire.

As either the tractor or load end center pair of sensor coils (Near Wire coils) approach the guide wire, they begin to detect the magnetic field around the guide wire. If the Near Wire coils do not detect this magnetic field for any reason, the truck does not acquire the wire, even if the outer coils (Guidance coils) detect the magnetic field. The magnetic field around the guide wire causes an AC voltage to be induced into the sensor coils that is sent to the Filter Card (GM) for conditioning. The Filter Card removes any noise that is picked up by the antenna coils and also converts this AC voltage into a DC voltage to be used by the Guidance Card. As either the tractor end or the load end Near Wire coils get closer to the wire, the value of the DC voltage to the Guidance Card increases. When the Near Wire coils get close enough (to the wire), and the voltage is high enough, the Guidance Card tells the TM to release full control of issuing the steering commands to the Guidance Card.