Method for controlling injection molding machine and injection molding machine

A method for controlling an injection molding machine that transmits driving force of a mold opening/closing servo motor to a movable platen via a ball screw to move the movable platen with respect to a stationary platen, and thereafter clamps molds by a mold clamping mechanism, wherein the mold opening/closing servo motor is disposed on a bed or the stationary platen, and a ball screw nut is disposed on the movable platen, wherein the ball screw and molds are configured to thermally expand during a continuous molding, the method comprising:

• detecting by a rotary encoder additionally provided on the mold opening/closing servo motor a position of the movable platen;
• performing by another actuator an operation of the injection molding machine, the operation being of other than the mold opening/closing servo motor;
• controlling the other actuator via a control device only when it is confirmed that the movable platen has reached an operation start confirming position of the other actuator, the position being detected at a time of continuous molding by a rotary encoder additionally provided on the mold opening/closing servo motor, and
• performing by the control device a comparative arithmetic operation between a mold clamping completion position detected by the rotary encoder and a stored mold clamping completion position, or a comparative arithmetic operation between a mold closing completion position detected by the rotary encoder and a stored mold closing completion position, to correct the operation start confirming position to compensate for the thermal expansion of the ball screw and the molds.