METHOD AND APPARATUS FOR CONTROLLING A LIFTING MAGNET OF A MATERIALS HANDLING MACHINE

摘要

A magnetic controller (26) controls a lifting magnet (12) of a materials handling machine (10) to eliminate arcing between contacts (70-80) as well as voltage spikes. The magnetic controller (26) excites shunt field windings (66, 68) of a direct current generator (22). The magnitude and direction of current passing through the shunt field windings (66, 68) are varied by the controller (26) to control the magnitude and polarity of the voltage at the generator output (23). The generator (22) is driven by a hydraulic motor. The controller (26) includes a programmable logic controller (40). The programmable logic controller (40) is connected to indicator lamps (L1-L5) within the operator's cab (14) to provide an operator information regarding the magnet control system (27). A drop time adjustment control (81) is positioned in the operator's cab (14) and operable to vary the drop time of the magnetic controller (26).