JPH01148526A - Device for controlling suck-back of injection molder - Google Patents

Abstract

PURPOSE:To contrive to prevent molten resin from drooling from a nozzle by a method wherein a piston means is retreated and stopped until the pressure of molten resin at the finish of metering lowers down to a certain value, which is set in advance. CONSTITUTION:The pressure of molten resin, which is stored at the tip part of a screw 2 through the rotation of the screw 2 during the plasticizing process, is detected with a sensor 5. The detected input value of the sensor 15, which is read through an analog-to-digital converter 22, is compared with the value, which is set with the setter 26 of metering resin pressure, in order to perform the metering process by feedback controlling the retreating speed of the screw 2 by means of an injection servo motor 6 so as to bring the difference between said values to zero. At the same time, the retreat position of the screw 2 is detected with a position sensor 17. The detected input value of the sensor 17, which is read through an analog-to-digital converter 23, is compared with the value, which is set with the setter 27 of metering end position, so as to stop the rotational driving motor 13 of the screw at the time when the difference between said values becomes zero. At the same time, the metering of the retreating operation of the screw 2 by the injection servo motor 6 is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a device for controlling a suckback operation performed after completion of a metering process in an injection molding machine.

[Background of the invention]

The purpose of the suckback operation performed after the completion of the metering process of an injection molding machine is to reduce the amount of molten resin inside the tip of the heating cylinder at the time of completion of metering, which corresponds to the back pressure applied as a resistance to the retraction of the piston means during the metering operation. This is to prevent the molten resin from drooling from the nozzle before the injection process if the pressure remains as it is. Conventionally, a stroke for retracting the piston means from the metering completion position, or a minute time for retracting the piston means from the point at which metering is completed, was set to mechanically control a constant stroke or a suckback operation for a constant period of time. .

However, with the control method described above, the molten resin pressure inside the tip of the heating cylinder after the hack-hack operation is rather variable, as shown in Figure 4, and if the molten resin pressure remains high, the Dru ring Concerns will remain.

CObject of the present invention] The present invention eliminates variations in the pressure of the molten resin inside the tip of the heating cylinder after the suckback operation as described above, and prevents the molten resin from leaving the nozzle before the start of the next injection. The purpose is to completely prevent drooling (runny nose).

[Means for solving problems]

In order to achieve the above object, the present invention provides a heating cylinder having an injection nozzle disposed at its tip, a resin supply means for supplying molten resin to the tip of the heating cylinder, and a resin supply means for supplying molten resin to the tip of the heating cylinder. A pressure sensor that directly or indirectly measures the pressure of the molten resin inside the tip of the heating cylinder in the injection molding machine equipped with piston means for injecting the molten resin into the cavity of the mold through the injection nozzle. is installed, and after completing the metering process by the resin supply means, the piston means is controlled to retreat until the molten resin pressure at the time of completion of metering falls to a preset constant value. It is.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of a motor-driven injection device. In the figure, reference numeral 1 denotes the main body of the injection molding machine, and a heating cylinder 3 is integrally provided inside the injection screw 2 so that the injection screw 2 can be rotated and slid back and forth. A hopper 4 for supplying raw resin into the container 3 is installed. 5 is a tip nozzle of the heating cylinder 3.

Reference numeral 6 denotes an injection servo motor, and a gear 7 fixed to its rotating shaft 6a is connected to a bearing 8 at the rear end of the injection screw 2.
The gear 10 is meshed with a gear 10 which is threaded onto a screw shaft 9 connected through a screw shaft 9.

A screw rotation drive gear 11 is attached to the rear end shaft portion 2a of the injection screw 2 via a slide key 12, and meshes with a gear 14 fixed to the rotation shaft of the drive motor 13.

Reference numeral 15 denotes a resin pressure measuring sensor embedded in the tip of the heating cylinder 3 in the vicinity of the injection nozzle 5, with its detection part facing inside the tip of the heating cylinder 3. It is electrically connected to the injection servo motor 6.

Reference numeral 17 denotes a position sensor for measuring the screw position, which is configured to be rotated coaxially with the pinion by a bracket 18 and a rack 19 fixed to the piston means, and a pinion 20 screwed into the rack.

As shown in FIG. 2, the control device 16 mainly includes a microcomputer 21, an analog-to-digital (A/D) converter 22 for inputting the resin pressure detection sensor 15, and a position sensor 17 for measuring the screw position. Input analog →
a digital (A/D) converter [23], an amplifier 24 for driving the injection servo motor 6, and a digital-to-analog (D/A) converter 25 for issuing commands to the amplifier;
A metering resin pressure setting device 26 for setting the resin pressure at the time of metering, a metering completion position setting device 27 for setting the measurement completion position, and a suckback completion resin pressure setting device 28 for setting the resin pressure at the time of sackback completion are connected. It is what it is.

29 and 30 are movable and fixed molds, and the molten resin injected through the nozzle 5 is filled into the cavity 31 formed between the molds.

In this embodiment configured as described above, when the screw rotation drive motor 13 is driven to rotate, the injection screw 2 is rotated via the gears II and 14, and the raw resin put into the hopper 4 is heated by the heater due to the rotation of the screw 2. It becomes molten in the heating cylinder 3, which is heated, and is sent to the tip part A, where it accumulates in the core part A and performs the measuring process. The collected molten resin is rotated by the injection servo motor 6 to rotate the gear 10 to advance the screw 2 through the screw shaft 9, and the molten resin is transferred from the tip nozzle 8 to the cavity 31 between the molds 29 and 30. An injection process is performed to press fit into the interior.

In the above-mentioned measuring process, the sensor 15 detects the pressure (back pressure) of the molten resin accumulated at the tip of the plasticizing process due to the rotation of the screw 2, and the value read by the A/D converter 22 is measured. The injection servo motor 6 is compared with the value set by the resin pressure setting device 26, and the injection servo motor 6 is adjusted so that the difference becomes 0.
The metering process is performed by feedback controlling the retraction speed of the screw 2.

At the same time, the position sensor 17 measures the retracted position of the screw 2, and the input is read by the A/D converter 23.
It is compared with the value set by the metering completion position setter 27, and when the difference becomes 0, the screw rotation drive motor 13 is stopped, and at the same time, the backward operation metering of the screw 2 by the injection servo motor 6 is stopped.

Immediately thereafter, the injection servo motor 6 performs a suck-back operation to retract the screw 2, but at this time, the molten resin at the tip of the screw begins to drop below the pressure at the end of metering. The molten resin pressure is detected again by the sensor 15, and the value read by the A/D converter 22 is compared with the value set by the suckback completion resin pressure setting device 28, until the difference becomes O. After performing a suckback operation for retracting the piston means, the piston means is stopped.

The table below provides example data from a test machine incorporating the present invention.

The suckback operation control device of the present invention can be applied in exactly the same manner to a hydraulically driven injection molding machine, only that the piston back and forth movement means is hydraulically driven.

〔Effect of the invention〕

As described above, the present invention is controlled so that the piston means is moved back and stopped until the molten resin pressure at the time of completion of metering falls to a preset constant value. It is possible to eliminate variations in the pressure of the molten resin inside the tip of the heating cylinder after the completion of the back operation, and it is possible to completely prevent the molten resin from drooling from the nozzle.

Furthermore, during the entire weighing and suck-back process, the molten resin pressure inside the tip of the heating cylinder is constantly measured and feedback control is performed, and finally, after the suck-back is completed, the molten resin pressure is ensured at a constant level. The amount of resin stored inside the tip of the cylinder is also uniform every shot, ensuring a stable injection amount and therefore a stable product weight, making it possible to achieve ultra-precision molding.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a longitudinal sectional view of the device, FIG. 2 is a block diagram of the suckback control device, and FIG. 3 is an explanatory diagram showing the effect of the control of the present invention. Fourth
The figure is a diagram illustrating variations in the molten resin pressure inside the tip of the heating cylinder in the case of the conventional suckback control all (a system in which the suckback stroke is set constant). 2...Injection screw, 3...Heating cylinder, 6...Injection servo motor (piston means), I3...Motor (resin supply means), 1
5...Resin pressure detection sensor, 16...Control device, 21...Microcomputer, 26...Resin pressure setting device during measurement, 28 ...
...Resin pressure setting device when suckback is completed, A...
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Claims (1)

[Claims] a heating cylinder having an injection nozzle disposed at its tip; a resin supply means for supplying molten resin to the tip of the heating cylinder; In an injection molding machine equipped with a piston means for injecting into the mold cavity, a pressure sensor is installed to measure the pressure of the molten resin inside the tip of the heating cylinder, and after the measuring process by the resin supply means is completed, the measurement is completed. 1. A suction control device for an injection molding machine, characterized in that the piston means is controlled to retreat until the molten resin pressure drops to a preset constant value.