Control systems for injection molding machines

摘要

Products having a relatively large thickness such as optical lenses for various industrial applications are molded by an injection molding machine by advancing the screw by operating an injection cylinder for filling metered quantity of a molten resin into a metal mold. The screw is rotated while it is being advanced. A plurality of position setters are provided along the stroke of the screw and their outputs are respectively compared with the output of a screw position detector by using comparators. The outputs of the comparators are used to effect a program control of screw rotation in multistages. According to a modified embodiment, during the filling step effected by screw rotation, the injection speed is varied stepwisely. The injection speed is reduced to zero for a short interval and then increased again. The number of revolutions of the screw, however, is maintained at a constant value until the injection speed is increased again.