Method and apparatus for controlling injection molding machine capable of reducing variations in weight of molded products

A method for controlling an injection molding machine by executing a feedback control by the use of a measured pressure value detected by a second pressure sensor and an injection and dwell pressure preset value, the method comprising:

• measuring a resin pressure by a mold internal pressure sensor, as a measured mold internal pressure value, for measuring within a metal mold cavity or within a resin flow passage extending to the cavity;
• calculating a difference between a mold internal pressure preset value and the measured mold internal pressure value;
• and
• executing the feedback control to produce an instruction value for injection and dwell pressure by adjusting the injection and dwell pressure preset value in accordance with the difference;
• wherein, with respect to the injection and dwell pressure preset value, the measured pressure value fed from the second pressure sensor is fed back so as to set operation conditions, a measured pattern of the mold internal pressure sensor, obtained when a molded product of a good quality was produced, being stored as the mold internal pressure preset values in a memory.

An apparatus for controlling an injection molding machine, comprising:

• a mold internal pressure sensor for measuring a resin pressure within a metal mold cavity or within a resin flow passage extending to the cavity;
• a second pressure sensor for measuring an injection and dwell pressure;
• an injection and dwell pressure setting section;
• and
• a mold internal pressure setting section,
• wherein:
• the mold internal pressure setting section includes a memory;
• the injection and dwell pressure setting section includes means for feeding back an injection and dwell pressure preset value and a measured value from the second pressure sensor so as to set operation conditions;
• the mold internal pressure setting section also including means for storing, as mold internal pressure preset values in the memory, a measured pattern of the mold internal pressure sensor, obtained when a molded product of a good quality was produced;
• the mold internal pressure setting section also including means for feeding back a difference between a mold internal pressure preset value, stored in the memory, and a measured value from the mold internal pressure sensor;
• the injection and dwell pressure setting section also including means for adjusting the injection and dwell pressure preset value so that an injection and dwell pressure feedback loop is used to perform mold internal pressure feedback, thereby regulating an instruction value for injection and dwell pressure.