Patent ID: 7791856

Claim:
A method for controlling a lifting device for moving magnetic material, the lifting device including an electromagnet coupled to a voltage generator, the method comprising the steps of: providing a predetermined voltage reference to a controller for releasing magnetic material from an electromagnet; receiving a release material signal from an operator interface; transmitting a first control signal to the generator; monitoring the voltage at the generator armature output; terminating transmission of the first control signal in response to the monitored voltage at the generator armature output being substantially equal to the provided voltage reference; measuring the length of time elapsed between transmitting and terminating the first control signal; utilizing the elapsed length of time of the first control signal to calculate a forward thrust set-point voltage; transmitting a second control signal to the generator; and, terminating transmission of the second control signal in response to the monitored voltage at the generator armature output being substantially equal to the forward thrust set-point voltage.