Closed Loop Control for Injection Molding Processes

Abstract

Systems and approaches for controlling an injection molding machine having a mold forming a mold cavity and being controlled according to an injection cycle include extruding a molten polymer according to an extrusion profile and measuring at least one variable during the extrusion profile with a first sensor. At least one extrusion operational parameter is adjusted based on the measured variable. The extrusion profile is terminated upon the molten polymer exceeding a first threshold, and the molten polymer is injected into the mold cavity according to an injection profile via a screw that moves from a first position to a second position. Upon completion of the injection profile, a recovery profile commences in which the screw is moved to the first position.

What is claimed is: 
     
         1 . An injection molding machine comprising:
 an injection unit having a mold forming a mold cavity and a screw that moves from a first position to a second position, the injection unit adapted to receive and inject a molten plastic material into the mold cavity via the screw to form a molded part;   a controller adapted to control operation of the injection molding machine according to an injection cycle;   a first sensor coupled to the injection molding machine and the controller, the first sensor adapted to measure at least one variable during an extrusion profile;   wherein the controller is adapted to:
 adjust, during the extrusion profile, at least one extrusion operational parameter of the injection molding machine based on the at least one measured variable measured from the first sensor, 
 terminate the extrusion profile upon the molten polymer exceeding a first threshold, 
 inject the molten polymer into the mold cavity according to an injection profile using a screw that moves from a first position to a second position, and 
 upon completion of the injection profile, commence a recovery profile in which the screw is moved to the first position. 
   
     
     
         2 . The injection molding machine of  claim 1 , further comprising a second sensor coupled to the injection molding machine and the controller, the second sensor adapted to measure at least one additional variable during the recovery profile, wherein the controller is further configured to adjust at least one injection operational parameter of the injection molding machine based on the at least one additional measured variable measured from the second sensor during the recovery profile. 
     
     
         3 . The injection molding machine of  claim 1 , wherein during the extrusion profile, the screw is maintained at the first position. 
     
     
         4 . The injection molding machine of  claim 1 , wherein the at least one extrusion operational parameter comprises at least one of a back pressure set point, a screw rotational speed value, or a measured plastic flow front position. 
     
     
         5 . The injection molding machine of  claim 1 , wherein the at least one variable comprises a pressure value of molten polymer being urged towards a nozzle of the screw. 
     
     
         6 . The injection molding machine of  claim 1 , wherein the first sensor is located at a leading end of the screw near the nozzle. 
     
     
         7 . The injection molding machine of  claim 1 , wherein the first sensor is located at a position ahead of a check ring of the screw. 
     
     
         8 . The injection molding machine of  claim 1 , wherein the at least one variable comprises a nozzle pressure, and wherein the at least one extrusion operational parameter is in the form of an adjustable back pressure having a plurality of discrete set points, the back pressure being adjusted according to the sensed nozzle pressure. 
     
     
         9 . The injection molding machine of  claim 1 , wherein the at least one variable comprises a nozzle pressure, and wherein the at least one extrusion operational parameter comprises a continuously variable back pressure, the variable back pressure being adjusted according to the sensed nozzle pressure. 
     
     
         10 . The injection molding machine of  claim 1 , wherein the first threshold comprises a melt flow front position. 
     
     
         11 . The injection molding machine of  claim 10 , wherein the position of the melt flow front is determined by at least one of a sensor or an algorithm. 
     
     
         12 . The injection molding machine of  claim 1 , wherein the injection profile commences after termination of the extrusion profile. 
     
     
         13 . The injection molding machine of  claim 1 , wherein the injection profile commences during the extrusion profile.