Patent ID: 6371748
Filing Date: 2002-04-16
Classification: B29C

Abstract:
A back pressure control apparatus for controlling back pressure in an injection molding machine including an injection device having a heating cylinder for heating resin powder therein to melt the resin powder into molten resin, a screw disposed in said heating cylinder for feeding the molten resin in said heating cylinder forward to meter the molten resin, and an injection actuator operatively coupled to said screw for driving said screw along an axial direction to inject the molten resin metered in said heating cylinder forward, said injection device being provided with a back pressure detector for detecting back pressure of the molten resin in said heating cylinder that is metered ahead of said screw to produce a pressure detected signal indicative of a back pressure detected value of the back pressure and with a screw position detector for detecting a retreat position of said screw to produce a screw position detected signal indicative of the retreat position of said screw, said back pressure control apparatus comprising:level selecting means for selecting a back pressure control level and for outputting a level signal indicative of the selected back pressure control level; determining means, connected to said level selecting means, for determining, on the basis of the selected back pressure control level indicated by the level signal, a back pressure pattern having a variable back pressure command value which continuously changes with respect to a retreat position of said screw at least at a maximum back pressure command value, said determining means producing a pattern signal indicative of the back pressure pattern; and a controller, connected to said determining means, said back pressure detector, and said screw position detector, and operatively coupled to said injection actuator, for controlling, in response to the pressure detected signal and the screw position detected signal, said back pressure in accordance with the back pressure pattern by means of said injection actuator.