A high-density cold storage distribution center reported that a Crown TSP 6500 VNA turret truck would randomly lose wire-guidance control mid-aisle. When the guidance dropped out, the truck drifted laterally toward the racking, and on two occasions the operator had to make a hard manual steering correction to prevent a rack strike. Additionally, the truck frequently "bumped" the end-of-aisle guard rail before transitioning into the cross-aisle.
The technician first inspected the "Wire-Guidance Antenna Coil" mounted beneath the truck's front chassis. The antenna coil is a flat, rectangular electromagnetic sensor that detects the alternating current flowing through the guide wire embedded in the floor. He connected an oscilloscope to the antenna's output. In a healthy system, the antenna produces a steady 6.25 kHz sinusoidal signal with amplitude proportional to the truck's lateral offset from the wire. The oscilloscope showed the signal was intermittent-dropping to near-zero for 200-millisecond intervals every few seconds, and the amplitude fluctuated by 40 percent, indicating a partially failing coil.
Further inspection of the antenna coil revealed the protective housing had cracked from repeated floor impact, allowing condensation to enter the coil windings. The moisture had corroded the fine copper wire, creating an intermittent open circuit. He also inspected the floor guide wire. At the cross-aisle transition point, the wire had a factory-designed "splice loop" that shifts the electromagnetic field to alert the truck it is approaching the aisle end. Using a wire-tracer tool, he found the splice loop had been damaged by a floor-scrubbing machine and was emitting a weak signal. The weak splice signal was the reason the truck was not detecting the aisle-end transition early enough to slow down (causing the guard-rail bump).
The repair involved replacing the wire-guidance antenna coil assembly with a new unit and resealing the protective housing against moisture. The floor guide wire splice loop at the cross-aisle transition was repaired by cutting out the damaged section, installing a new splice kit, and re-verifying the electromagnetic field strength with the wire tracer. The truck's wire-guidance controller was recalibrated, and the operator's steering-offset zero point was re-centered. After reassembly, the turret truck traveled the full aisle length with rock-steady wire guidance, no dropouts, and clean transitions at the cross-aisle without contact with the end-of-aisle guard rail.
