JP2001047480A - Control of pressure of resin in injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the effect of extraneous noise in low pressure control. SOLUTION: The pressure of a molten resin in an injection process is controlled by adjusting the pressure of a hydraulic cylinder 10 according to a control program 12a by a servo valve 11. At this time, when the detected A/D value of a risen pressure sensor 17 is a constant level or less, an averaging filter 12b acts to perform the averaging processing of the feedback control of the resin pressure sensor 17 at a predetermined time interval. By this constitution, the effect of extraneous noise is reduced. When the feedback signal of the resin pressure sensor 17 is larger than the constant level, the averaging filter 12b due to software does not act. Therefore, the averaging filter 12b due to the software exerts no effect on high pressure control larger than the constant level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a resin pressure in an injection molding machine for performing feedback control of a resin pressure in a heating cylinder pressurized by a pressurizing means.

[0002]

2. Description of the Related Art In an injection molding machine, a pressure sensor detects the pressure of an injection resin in a heating cylinder which is pressurized by a pressurizing means.
The control device controls the pressurizing pressure of the pressurizing means based on the feedback signal. External noise often occurs in the above-mentioned feedback signal line for some reason, causing the feedback signal to fluctuate slightly. As a result, the detection accuracy of the feedback signal decreases, and the pressure control is adversely affected. This point is more damaging because the response with higher response is more sensitive to external noise.

By the way, during high-voltage control with a high signal level, the fluctuation of the feedback signal due to external noise with respect to the signal level is small, so that the control stability is not significantly affected. However, in the control in which the signal level is low, the ratio of the fluctuation width of the feedback signal to the signal level becomes large, so that the control stability is greatly impaired.

Therefore, conventionally, a filter, which is a hard component, is provided to stabilize the level of the feedback signal, thereby preventing the adverse effects due to external noise.

[0005]

However, the hard filter has a problem that it adversely affects the high-voltage control unit, impairs control stability, and complicates the structure.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a resin molding apparatus for an injection molding machine capable of reducing the adverse effects of external noise of low pressure control without affecting high pressure control. The purpose of the present invention is to provide a control method. Another object of the present invention is to provide a method for controlling resin pressure in an injection molding machine, which can avoid a complicated structure.

[0007]

In order to achieve at least one of the above objects, the invention according to claim 1 is characterized in that the pressure of the pressurizing means for pressurizing the resin of the heating cylinder is reduced by the resin pressure of the heating cylinder. In the injection molding machine controlled by the control device based on the feedback signal of the resin pressure sensor for detecting the pressure of the resin pressure sensor, when the pressure of the pressure means is equal to or less than a predetermined level, a predetermined time of the resin pressure sensor The feedback signal is averaged by an averaging filter by software, and the pressurizing pressure of the pressurizing means is controlled based on the processing result.

In the above means, the feedback signal for a predetermined time of the resin pressure sensor is averaged by the software averaging filter when the pressurizing pressure of the pressurizing means is equal to or lower than a predetermined fixed level. Even if external noise is generated, the noise is substantially removed, and the influence of the external noise on the pressure control of the resin is reduced, thereby improving the control stability. The averaging filter has no effect on the high pressure control since it does not participate in any high pressure control above a certain level. Further, since the averaging filter is made of software and is not a hard component, the structure is not complicated.

[0009]

Embodiments of the present invention will be described with reference to the accompanying drawings. In FIG. 1, reference symbol S denotes an injection molding machine (injection unit). The injection molding machine S includes a plasticizing heating cylinder 1 and a screw 2 constituting a plasticizing device, a filling heating cylinder 3 and a filling plunger 4 constituting a filling device,
A heating and depressurizing heating cylinder 5 and a pushing plunger 6 which constitute a molten resin pressurizing and depressurizing device are provided. The molten plastic is supplied from a hopper (not shown) to the plasticizing heating cylinder 1 and plasticized by rotation of the screw 2 The resin can be injected into the molding cavity of the mold from the nozzle 3a by the operation of the filling plunger 4 of the filling heating cylinder 3 by appropriately controlling the pressure with the pushing plunger 6 of the heating cylinder 5 for pressurizing and depressurizing. I have. In addition,
This injection molding machine S has been developed by the applicant of the present invention (Japanese Patent Application No. 9-330704).

The screw 2 is rotated by a motor 8, and both plungers 4, 6 are moved forward and backward by hydraulic cylinders 9, 10, respectively. The hydraulic cylinder 10 constitutes a pressurizing means, and an electromagnetic hydraulic servo valve 11 is provided in a hydraulic circuit thereof. Servo valve 11
A D / A conversion unit 14
And a servo valve driver 15. A resin pressure sensor 17 is provided in the resin reservoir 3b of the filling heating cylinder 3, and the A / D conversion unit 1
8 are connected.

The control device 12 transmits a control program 12a for operating the servo valve 11 and a feedback signal for a predetermined time of the resin pressure sensor 17 when the pressurizing pressure of the hydraulic cylinder 10 is below a predetermined level. An averaging filter 12 b is formed by software for averaging processing, and the pressurizing pressure of the hydraulic cylinder 10 is controlled via the servo valve 11 based on a feedback signal of the resin pressure sensor 17.

Here, the control voltage of the servo valve driver 15, the detected pressure and output voltage of the resin pressure sensor 17, and the pressurizing pressure (resin pressure) of the hydraulic cylinder 10 at which the averaging filter 12b starts the averaging process of the feedback signal. Pool 3b
The following is a specific description of an example of the resin pressure) and the averaging time. Control voltage of the servo valve driver 15; 0 to 10 V Detection pressure of the resin pressure sensor 17; 0 to 400.0 MPa Output voltage of the resin pressure sensor 17; 0 to 10 V Pressurizing pressure of the hydraulic cylinder 10 on which the averaging filter 12b operates; 4.0 MPa Averaging time (Δt); 5 msec

Next, a method for controlling the resin pressure in the injection molding machine of the present invention will be described with reference to FIG. In the injection step, the pressure of the molten resin injected from the nozzle 3a into the molding cavity of the mold is controlled by adjusting the pressurizing pressure of the hydraulic cylinder 10 with the servo valve 11 according to the control program 12a. At this time, the resin pressure sensor 17 detects the pressing pressure of the pushing plunger 6 by the hydraulic cylinder 10, that is,
The resin pressure in the resin reservoir 3b is detected and a detection signal (A / D
Is output (step S1).

In the next step S2, the resin pressure sensor 17
The magnitude relationship between the detection signal (feedback signal) of the above and a predetermined constant level (4.0 MPa) is determined,
If the A / D value of the resin pressure sensor 17 is equal to or less than 4.0 MPa (YES), the averaging filter 12b operates to change the feedback signal of the resin pressure sensor 17 to Δt seconds (5 mse
An averaging process is performed for each c) (step S3).

For this reason, if the detection pressure of the resin pressure sensor 17 is 4.0 MPa, the output voltage is a low voltage which is easily affected by external noise (the voltage at this time is 0.1 V = 10 V × 4
/ 400), and even if external noise occurs,
The influence of extraneous noise is reduced by the averaging process. The averaging-processed feedback signal is output to the control program 1
2a (step S4), the control device 12 controls the pressurizing pressure of the hydraulic cylinder 10 based on the feedback signal.

If it is determined in step S2 that the feedback signal from the resin pressure sensor 17 is greater than 4.0 MPa (No), the process proceeds to step S4, where the resin pressure sensor 1
The feedback signal 7 is input to the control program 12a without being averaged by the averaging filter 12b by software. Therefore, 4.0 MPa
The higher pressure control is not affected by the software averaging filter 12b.

The above-described averaging process by the averaging filter 12b is the simplest averaging at the Δt time interval. Δ
The reason for setting t to 5 msec is that the time interval of averaging is 3 msec and 4 msec, which are too short to obtain a sufficient averaging effect, and
At 25 msec, it is based on the experimental result that the same good averaging effect was obtained.

The averaging processing method is not limited to the above-described averaging, and may be any method. For example, a method of sequentially wrapping a plurality of time intervals and further averaging the feedback signal averaged at each time interval may be used. Can also be adopted. In any case, the constant level of the averaging process and the averaging process method are determined in consideration of the magnitude of the external noise, the generation interval, and the like.

The present invention is not limited to the injection molding machine S shown in the figure having three heating cylinders 1, 3, and 5, but can be applied to pressure control of well-known pre-plastic type injection molding machines and in-line screw type injection molding machines. Can also be applied. In the case of the injection molding machine of the pre-plastic type, the hydraulic cylinder 9 for driving the filling plunger 4 shown in the figure serves as a pressurizing means, and the pressurizing pressure is controlled by the control device 12. In the case of an in-line screw type injection molding machine, the pressurizing pressure of a pressurizing means (not shown) for moving the screw 2 forward and backward is controlled. Although the injection molding machine shown is of a hydraulic type, the present invention can be applied to an electric injection molding machine.

The resin pressure sensor 17 shown in FIG.
The resin pressure sensor is provided in the resin reservoir 3b and directly detects the pressure of the injected resin. However, the resin pressure sensor may be a load cell or the like that indirectly detects the resin pressure of the heating cylinder.

[0021]

As described above, according to the present invention,
The adverse effect of the external noise of the low pressure control can be reduced without affecting the high pressure control. Also, since no additional hardware components are required, the structure is not complicated.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of an injection molding machine that implements a method for controlling a resin pressure in the injection molding machine according to the present invention.

FIG. 2 is a flowchart showing an embodiment of a method for controlling a resin pressure in an injection molding machine according to the present invention.

[Explanation of symbols]

S Injection molding machine 3 Heating cylinder for filling 3a Nozzle 5 Heating cylinder for pressurization and decompression 10 Hydraulic cylinder (pressurizing means) 11 Servo valve 12 Controller (CPU) 12b Averaging filter by software 17 Resin pressure sensor

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Yoshizawa 1300, Okayama, Niigata, Niigata Niigata Technica Co., Ltd. (72) Norio Igarashi 1300, Okayama, Niigata, Niigata Niigata Technica F Term (reference) 4F206 AP021 AQ03 AR021 JA07 JM04 JP13

Claims (1)

[Claims] An injection molding machine in which a control device controls a pressurizing pressure of a pressurizing means for pressurizing a resin of a heating cylinder with a control device based on a feedback signal of a resin pressure sensor for detecting a resin pressure of the heating cylinder. When the pressure of the pressure means is equal to or less than a predetermined level, the feedback signal of the resin pressure sensor for a predetermined time is averaged by an averaging filter by software. A method for controlling a resin pressure in an injection molding machine, comprising controlling a pressurizing pressure of a resin.