Control systems for injection molding machines

A control system of an injection molding machine for molding a molten resin and including a heating cylinder connected to a metal mold defining therein a mold cavity, a screw coaxially contained in said heating cylinder for kneading and injecting said molten resin into said metal mold cavity through a first end of said heating cylinder, an injection cylinder connected to said screw on a second end of said heating cylinder for reciprocating said screw in said heating cylinder, and means connected to said injection cylinder for rotating said screw, said control system comprising:

• means (12) for detecting a position of said screw during an injection stroke thereof;
• a plurality of position setters (13-16) located along said injection stroke and respectively set with predetermined positions along said injection stroke;
• a plurality of comparators (17-20), each comparator inputted with an output signal of said position detecting means (12) and an output signal of a corresponding position setter for producing a coincident signal when said output signal of said position detecting means and a signal from a corresponding position setter coincide with each other;
• means (25) responsive to the coincident signal of any one of said comparators;
• a plurality of setters (21-24) each connected to receive an output signal from a corresponding comparator (17-20) for setting an injection speed or a number of revolutions of said screw;
• a transfer switch (28) responsive to any one of the output signals received by said setters (21-24) for selectively controlling said injection cylinder and said screw rotating means and electromagnetic flow control valves (26)(27) controlled by said transfer switch for controlling the injection speed of said screw or the number of revolutions of said screw;
• and
• means for continuing rotation of said screw during advancement caused by said injection cylinder;
• and
• wherein said position detecting means (12), said plurality of position setters (13-16), said plurality of comparators (17-20), said means responsive to the coincident signal (25), said plurality of setters (21-24), said transfer switch (28) and said means for continuing rotation of said control system are connected to perform multistage program control of the injection speed or the number of revolutions of the screw.