Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Feed control of material en route to shaping area
Patent
1987-11-19
1989-05-09
Woo, Jay H.
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Feed control of material en route to shaping area
264 403, 264 407, 425149, B29C 4577
Patent
active
048284734
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an injection molding machine and more particularly to an injection control apparatus for an injection-molding machine, which is adapted to perform injection/hold pressure control with a numerical control unit.
BACKGROUND ART
According to the injection/hold pressure control in an injection-molding machine, when a predetermined switching condition is satisfied, injection speed control is switched to hold pressure control and pressure holding is executed over a predetermined period of time thereafter, and then the process continues to the next measuring block. There are two systems for switching from the speed control to the hold pressure control: the first system uses a screw position as a control parameter to switch the control to the hold pressure control when a screw reaches an injection/hold pressure switching position, and the second one uses an injection time as the control parameter to perform the switching to the hold pressure control when a predetermined time elapses from the start of the injection.
Conventionally, in controlling an injection molding machine with a numerical control unit (hereinafter referred to as an NC unit), the switching to the hold pressure control has been done by the first switching system that involves the screw position. However, when a screw cannot inject resin at a set injection speed due to a large viscosity of resin or for some other reason and the screw does not, as a consequence, reach the injection/hold switching position within a predetermined time from the beginning of the injection control, the injection cycle becomes long, thus deteriorating the production efficiency. In this case, because the screw does not move as instructed by a speed command, a move command is accumulated in an error register in an NC unit and this value may exceed a given amount so that the NC unit stops a pulse distribution and the overall injection-molding machine stops functioning.
Further, in an injection-molding machine which is subjected to injection control by means of the NC unit, the following problem would occur when the injection/hold pressure control is performed based on the injection time.
When the injection speed control stage approaches its end and the amount of resin filled in a mold increases, the pressure on the resin gradually increases so that this pressure may reach an excess value corresponding to the maximum torque of a servomotor which drives the injection device before the switching to the hold pressure control is executed. In this case, excess pressure is applied on the resin, thus undesirably causing burrs or cracks in a molded article.
DISCLOSURE OF THE INVENTION
It is, therefore, an object of this invention to provide an injection control apparatus for an injection-molding machine for executing an injection operation under the control of an NC unit, which control apparatus controls the switching from the injection speed control to the hold pressure control based on both of the injection time and the pressure acting on resin, so as to improve the operational reliability of the injection-molding machine as well as produces good-quality molded articles.
To achieve the above object, there is provided an injection control apparatus for an injection-molding machine for performing injection control using a servomotor that is controlled by a numerical control unit, which apparatus comprises:
pressure detection means for detecting pressure applied on resin in a mold;
an injection high-timer for counting a predetermined time after injection starts and outputting a time-up signal upon elapse of the predetermined time;
comparison means for comparing the pressure detected by the pressure detection means with preset pressure and outputting an output signal when the detected pressure is higher than the preset pressure;
hold pressure control means for starting hold pressure control in response to the time-up signal from the injection high-timer or the output signal from the comparison means; and
follow-up means for followi
REFERENCES:
patent: 3859400 (1975-01-01), Ma
patent: 3932083 (1976-01-01), Boettner
Kobayashi Toshio
Otake Hiromasa
Fanuc Ltd.
Heitbrink Timothy W.
Woo Jay H.
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