Patent ID: 6865924

Claim:
A drift detection method for detecting drift in a pressure detection value output from a pressure detector used in a control apparatus for controlling an injection molding machine, the method comprising the steps of: detecting, by use of the pressure detector, a first pressure at a preset detection point in a pressure-uncontrolled region in an arbitrary molding cycle; setting the detected pressure as a reference pressure; detecting, by use of the pressure detector, a second pressure at the preset detection point in the pressure-uncontrolled region in a subsequent molding cycle; obtaining a deviation of the detected pressure from the reference pressure; and performing correction processing for eliminating drift when the deviation is greater than a preset value, wherein the correction processing comprises the steps of: rotating a screw by one turn; obtaining a middle value between a minimum value and a maximum value of a pressure detection value output from the pressure detector during the one-turn rotation, the pressure detection value representing an error caused by ripples produced with rotation of the screw; rotating the screw further and stopping the screw when the pressure detection value output from the pressure detector becomes equal to the middle value; and correcting the pressure detection value after stoppage of the screw.