Patent ID: 7408317

Claim:
A method of controlling a vertical reciprocating conveyor having a motor, lifting apparatus, and path in which the lifting apparatus moves in response to a mechanical power produced by the motor, the method comprising: loading material into the lifting apparatus; determining if the motor has been started to move the vertical reciprocating conveyor and the material; reading an initial amount of current drawn by the motor required for the vertical reciprocating conveyor to move the material; determining a statistical value of the initial amount of current drawn by the motor; deriving a fixed steady state limit of the operating parameter from the statistical value and the initial amount of current drawn by the motor, wherein the fixed steady state limit remains fixed while the motor continues to drive the vertical reciprocating conveyor and the material, and wherein the limit remains independent of how far the vertical reciprocating conveyor has moved; moving the vertical reciprocating conveyor with the material after the fixed steady state limit has been derived; reading a subsequent amount of current drawn by the motor after the vertical reciprocating conveyor has started to move the material; comparing the subsequent amount and the fixed steady state limit; and stopping the motor when the subsequent amount is above the fixed steady state limit for a period of time.