Method for controlling injection molding machine and injection molding machine

1. 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.

2. The method for controlling an injection molding machine according to claim 1 ,

wherein the other actuator is a mold clamping cylinder,

, and

the operation start confirming position of the mold clamping cylinder is corrected during a period of any molding cycle at the time of the continuous molding.

3. An injection molding machine for transmitting 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 for thereafter clamping molds by a mold clamping mechanism, wherein the ball screw and molds are configured to thermally expand during a continuous molding, the injection molding machine comprising:

a rotary encoder additionally provided on the mold opening/closing servo motor and capable of detecting a position of the movable platen;

another actuator that performs an operation of the injection molding machine, the operation being of other than the mold opening/closing servo motor; and

a control device programmable to enable the other actuator to operate only when it is confirmed that the movable platen has reached an operation start confirming position of the other actuator, detects a position of the movable platen at a time of the continuous molding, and performs

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;

wherein the mold opening/closing servo motor is disposed on a bed or the stationary platen, and the ball screw nut is disposed on the movable platen.

4. The injection molding machine of claim 3 , further comprising:

the ball screw to which a driving force of the mold opening/closing servo motor is transmitted;

a ball screw nut disposed on the movable platen and into which the ball screw is inserted;

a mold clamping cylinder of the mold clamping mechanism disposed on the stationary platen, the mold clamping cylinder including a rod that serves as a tie bar having a plurality of locking portions thereon; and

a half nut including locking teeth which is configured to engage with the plurality of locking portions.

5. The injection molding machine of claim 4 , wherein

the control device is programmable to cause the half nut to engage with the plurality of locking portions of the tie bar to enable the mold clamping cylinder to operate when it is confirmed that the movable platen has reached the operation start confirming position of the half nut or the mold clamping cylinder, detects by the rotary encoder additionally provided on the servo motor, the position of the movable platen at the time of a mold closing completion position or a time when it is detected that a pressure of the mold clamping cylinder is increased to a preset pressure during continuous molding, and performs

the comparative arithmetic operation between the position detected by the rotary encoder and a previously stored position,

to correct the operation start confirming position, thereby preventing the rotary encoder from being unable to detect that the movable platen has reached the operation start confirming position of the mold clamping cylinder due to thermal expansion of the ball screw and the molds during the continuous molding.