Injection molding same cycle control

An injection molding machine including a hydraulically driven reciprocating ram for injecting plasticized material from an injection barrel into a mold cavity and a control system therefore comprising;

• hydraulic pressure fluid circuit means for advancing said ram;
• electrically responsive valve means for controlling said hydraulic pressure fluid circuit means;
• a sensor responsive to the fluid pressure of material within said mold cavity;
• sensing means connected to said sensor to read said mold cavity pressure at uniformly spaced time intervals;
• first accumulating and averaging means for averaging a first series of cavity pressure readings beginning from a first event and terminating at a second event to generate a first sensed average pressure value;
• second accumulating and averaging means for averaging a second series of cavity pressure readings beginning at a third event and terminating at a fourth event to generate a second sensed average pressure value;
• means to produce a first reference pressure value;
• first compare means for comparing said first sensed average pressure value to said first reference pressure value to produce a first error signal;
• first modification means connected to said electrically responsive valve means for varying the hydraulic system pressure driving said ram during the same cycle of machine operation by an increment which is a function of the sign and magnitude of said first error signal;
• means to produce a setpoint reference pressure value;
• second compare means for comparing said second sensed average pressure value to said setpoint reference value to produce a second error signal;
• and
• second modification means connected to said electrically responsive valve means for varying the hydraulic system pressure driving said ram during a subsequent cycle of machine operation by an increment which is a function of the sign and magnitude of said second error signal.