Apparatus for operating an injection compression molding machine

In apparatus for operating an injection compression molding machine comprising a stationary metal mold, a movable metal mold, an oil pressure actuator for advancing said movable metal mold toward said stationary metal mold to form a mold cavity therebetween with a predetermined compression clearance .delta. left between said movable and stationary metal molds, a heating cylinder engaging said stationary metal mold, means for supplying a thermoplastic resin into said heating cylinder, a screw contained in said heating cylinder for injecting molten resin into said mold cavity, means for rotating said screw, and means for reciprocating said screw in said heating cylinder, the improvement comprising:

• a screw position detector for detecting an axial position of said screw;
• a plurality of screw position setters respectively setting predetermined screw positions along which said screw is moved;
• a plurality of comparators respectively comparing outputs of said screw position setters with an output signal of said screw position detector;
• a plurality of mold clamping force setters connected to receive output signals of said respective comparators;
• a transfer switch for selecting one of outputs of said mold clamping force setters;
• and
• an electromagnetic transfer valve energized by an output of said transfer switch through a control device for actuating said oil pressure actuator.