Plastic article or earthenware shaping or treating: apparatus – Control means responsive to or actuated by means sensing or... – Molding pressure control means responsive to pressure at...
Patent
1991-03-25
1992-10-13
Heitbrink, Tim
Plastic article or earthenware shaping or treating: apparatus
Control means responsive to or actuated by means sensing or...
Molding pressure control means responsive to pressure at...
264 403, 425170, B29C 4577
Patent
active
051549352
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an injection pressure control apparatus for an electrically-operated injection molding machine, and more particularly, to an injection pressure control apparatus which permits the production of high-quality molded articles without the need of using an expensive internal mold pressure sensor.
BACKGROUND ART
Conventionally, a hydraulically-operated injection molding machine is known, which is so designed as to maintain the maximum internal mold pressure at a predetermined target value during a period for the filling of a mold with a molten resin, thereby preventing excessive or short filling. In the injection molding machine of this type, the internal mold pressure is subjected to closed-loop control by means of a hydraulic mechanism in accordance with a feedback signal indicative of the internal mold pressure and supplied from a pressure sensor disposed in a resin passage of the mold (Japanese Patent Publication No. 58-52486). However, the internal mold pressure sensor, which is arranged to be embedded in the resin passage, is high in cost. Moreover, since the internal mold pressure sensor is exposed to molten resin, it is liable to be lower in performance and have a shorter life. These drawbacks are particularly noticeable when the pressure sensor is embedded in a hot-runner mold. Furthermore, it is difficult to dispose the internal mold pressure sensor in the hot-runner mold which provides only a small embedding space for the sensor.
Also known is an electrically-operated injection molding machine which is so designed as to control the injection speed in an injection process to a target value which can be variably set in accordance with the axial moved position of an injection screw, control the hold pressure in a hold process to a target value in accordance with a detection output supplied from pressure detecting means, formed of an internal mold pressure sensor or a strain gauge, and optimize the timing for the switching from the injection process to the hold process (Japanese Provisional Patent Publication No. 62-218118). In the injection molding machine of this type, however, the injection pressure sometimes becomes improper. In this case, the quality of molded articles is degraded.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an injection pressure control apparatus for an electrically-operated injection molding machine, which permits the production of high-quality molded articles without the need of using an expensive internal mold pressure sensor.
In order to achieve the above object, according to the present invention, there is provided an injection pressure control apparatus mounted to an electrically-operated injection molding machine in which an injection screw is driven in an axial direction thereof by means of a servomotor, to thereby apply an injection pressure to molten resin through the injection screw. The injection pressure control apparatus comprises: a pressure sensor mounted on the injection screw for generating an output indicative of a pressure applied to the injection screw by the molten resin and corresponding to an actual injection pressure; setting means for setting a target injection pressure beforehand; and control means for controlling the actual injection pressure to the target injection pressure in a closed-loop in accordance with the pressure sensor output and the target injection pressure.
Preferably, the apparatus of the present invention is operable to control a hold pressure in a like manner, and the setting means is operable to variably set the target injection pressure in accordance with a time period elapsed from an instant at which injection starts, and the control means is operable to control an output torque of the servomotor, thereby controlling the actual injection pressure to the target injection pressure.
According to the present invention, as described above, the actual injection pressure is controlled to the target injection pressure in a closed-loop in accordance with t
REFERENCES:
patent: 4828473 (1989-05-01), Otake et al.
patent: 4968462 (1990-11-01), Hara
patent: 4970447 (1990-11-01), Kamiguchi et al.
patent: 5023028 (1991-06-01), Kamiguchi et al.
Kamiguchi Masao
Neko Noriaki
Fanuc Limited
Heitbrink Tim
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