Method And Apparatus For Moving Material

Abstract

An apparatus and method for providing ground fault protection to a lifting device utilizing an electromagnet and powered by a generator. The apparatus and method rectifies an AC voltage emanating from the generator source and monitors unsafe operating conditions of the generator's circuit wherein operation of the lifting device is ceased when predetermined electrical operating parameters are exceeded.

What is claimed is: 
     
         1 . A method for interrupting operation of an open-loop system for controlling an electromagnetic lifting device powered by a generator source, the method comprising the steps of:
 aligning a bi-polar DC voltage emanating from the generator source into a DC voltage;   providing a predetermined safe current level;   monitoring electrical leakage current associated with the generator; and,   generating an indicator in response to the monitored electrical leakage current exceeding the predetermined safe current level.   
     
     
         2 . The method of  claim 1  further comprising the step of:
 generating an interrupt signal in response to the generation of the indicator. 
 
     
     
         3 . A safety circuit for an electromagnetic lifting device configured in a closed-loop system and powered by a generator voltage source, the safety circuit comprising:
 a programmable logic controller providing an output control signal relative to a circuit ground;   a bi-directional driver including an input operatively coupled to the output control signal of the programmable logic controller;   the bi-directional driver providing an output control signal relative to the circuit ground,   wherein fluctuations in the voltage level of the circuit ground are reflected in the bi-directional output control signal to the field windings of the generator.   
     
     
         4 . A method of adjusting operating conditions of a closed-loop control system for an electromagnetic lifting device powered by a generator source, the method comprising the steps, of:
 generating an output control signal relative to a circuit ground;   transmitting the output control signal to field windings of the generator source;   monitoring the circuit ground; and,   altering the output control signal in response to fluctuations in the circuit ground.