JPH05309712A - Dwell controlling device of injection molding machine - Google Patents

Abstract

PURPOSE:To control so as to predict a mold temperature in the following cycle based on the mold temperature in one cycle and to vary the operating quantity of a servo valve based on the predicted value. CONSTITUTION:Prediction calculating means 31,32,33 are adapted to calculate the corrected value of in-mold resin pressure in the following cycle on the basis of a mold temperature detecting signal from a mold temperature sensor in one cycle, a cooling medium temperature detecting signal from a cooling medium temperature sensor for controlling mold temperature and a resin temperature detecting signal from a cylinder resin temperature sensor. Converting means 34,35 are adapted to convert the corrected value in the calculated in-mold resin pressure into infection cylinder oil pressure on the basis of an injection cylinder oil pressure detecting signal and a resin pressure detecting signal from the in-mold resin pressure sensor. A system of an injection cylinder feedback control is provided to conduct the control of the injection cylinder oil pressure by the use of the converted injection cylinder oil pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an injection molding machine.

[0002]

2. Description of the Related Art Generally, injection molding is carried out by a process of plasticizing resin, injecting, holding pressure, and cooling. In order to make the weight, size, photoelasticity, etc. of the molded product obtained through such a process uniform, it is necessary to improve the reproducibility of the resin state transition (transition of resin specific volume, temperature, pressure). Will be needed. The specific volume is the reciprocal of the density of the molded product, and the holding pressure is the resin pressure in the mold controlled in the holding step.

By the way, it is known that the relationship between the specific volume of resin in the molten state-the temperature-the pressure is expressed by the following equation of state of Spencer.

(P + π) (v−ω) = RT where P is pressure, v is specific volume, T is temperature, and π, ω, and R are constants determined according to the material.

This relationship is expressed in the three-dimensional plane of P, v, and T as shown in FIG. 5, which is shown by the solid line in FIG. 5 in one molding cycle of plasticizing → injection → holding pressure → cooling described above. Draw a trace. It is desirable that this locus be the same even when the injection molding work is repeated.

[0006]

However, in reality, since the resin temperature and the mold temperature fluctuate from the start to the end of the molding cycle, the trajectory deviates from the locus shown by the solid line in FIG. 5 with the passage of time. And draws a locus as indicated by a broken line, and as a result, the quality of the molded product varies. Therefore, it is necessary to control the time variation of the resin state quantity (pressure, temperature, specific volume) during the flow of the resin flowing into the mold or the compression of the pressure holding process to be as uniform as possible in each cycle.

On the other hand, a method of correcting the set value of the holding pressure in the holding process is disclosed in, for example, Japanese Patent Laid-Open No. 63-3411.
No. 6 is disclosed. Briefly, this method is a method of detecting a mold temperature in a certain cycle and calculating an operation amount of the injection molding machine in the next cycle, for example, a correction value of a holding pressure based on the detected value. Therefore, in this method, as shown in FIG. 6, the control is performed such that the manipulated variable is changed based on the temperature information of the cycle immediately before, not the information of the temperature variation in the cycle in which the operation is performed. Needless to say, the temperature fluctuation in one cycle is not always reflected as it is in the temperature fluctuation in the next cycle.

Regarding the mold temperature, since the mold temperature governs the heat dissipation of the resin temperature inside the mold, the temperature fluctuation of the mold is the main cause of the temperature fluctuation of the resin inside the mold. Therefore, in order to equalize the specific volume during resin flow and compression with respect to mold temperature fluctuations, set values such as holding pressure should be systematically set in proportion to the mold temperature fluctuations. It will be necessary to correct every cycle.

From the above viewpoints, the problems of the present invention are as follows.
To provide a holding pressure control device for an injection molding machine capable of predicting a mold temperature in the next cycle based on a mold temperature in a certain cycle and changing a manipulated variable based on the predicted value. is there.

[0010]

According to the present invention, an injection cylinder hydraulic pressure feedback control system for controlling the injection cylinder hydraulic pressure in a pressure holding process based on an injection cylinder hydraulic pressure detection signal from an injection cylinder hydraulic pressure sensor and a holding pressure set value. In a controller of an injection molding machine equipped with, a mold temperature detection signal from a mold temperature sensor in a certain cycle, a cooling medium temperature detection signal from a cooling medium temperature sensor for controlling the mold temperature, and a cylinder resin temperature sensor Prediction calculating means for calculating the correction value of the resin pressure in the mold in the next cycle based on the resin temperature detection signal, and the calculated correction value of the resin pressure in the mold are used as the injection cylinder oil pressure detection signal and the metal value. The injection cylinder is provided with a conversion means for converting into an injection cylinder hydraulic pressure based on a resin pressure detection signal from the in-mold resin pressure sensor. Hydraulic feedback control system is characterized in that for controlling the injection cylinder hydraulic pressure with the converted injection cylinder hydraulic pressure.

Further, according to the present invention, the predictive calculation means calculates the predicted value of the mold temperature in the next cycle from the mold temperature detection signal, the cooling medium temperature detection signal and the resin temperature detection signal in a certain cycle. A mold temperature predicting unit for calculating, and a mold resin temperature predicting unit for calculating a predicted value of the resin temperature in the mold from the calculated predicted value of the mold temperature,
And an in-mold pressure correction value calculation unit for calculating a correction value of the in-mold resin pressure from the calculated predicted value of the in-mold resin temperature, wherein the converting means includes the injection cylinder hydraulic pressure detection signal and the injection cylinder hydraulic pressure detection signal. A pressure dynamic characteristic estimation unit that estimates the dynamic characteristic of the injection cylinder hydraulic pressure from the resin pressure detection signal, and the in-mold resin from the in-mold pressure correction value calculation unit based on the inverse characteristic of the estimated dynamic characteristic. A pressure holding control device for an injection molding machine, which includes a pressure conversion unit that converts a corrected value of pressure into an injection cylinder hydraulic pressure is obtained.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, an injection molding machine comprises an injection molding machine main body 10, a molding machine control device 20 for controlling an operation amount thereof, for example, an injection cylinder hydraulic pressure, and a holding pressure set value and a correction value for the molding machine control device. And a main controller 30 for providing

The sensors installed in the injection molding machine body 10 include an injection cylinder oil pressure sensor 11 installed in an injection cylinder, a cylinder resin temperature sensor 12 installed in a reservoir of a heating cylinder, and a mold installed in a mold. There are a temperature sensor 13, a resin pressure sensor in the mold 14, and a cooling water temperature sensor 16 arranged in the cooling water pipe of the mold temperature controller 15 for cooling the mold to detect the temperature of the cooling water. The resin temperature detection signal from the cylinder resin temperature sensor 12, the mold temperature detection signal from the mold temperature sensor 13, and the cooling water temperature detection signal from the cooling water temperature sensor 16 pass through sensor amplifiers 12A, 13A, 16A, respectively. It is then input to the main controller 30.

The molding machine controller 20 will be described with reference to FIG. 2 only in terms of the functions required for the present invention. The operation amount of the servo valve (control valve for controlling the hydraulic system for driving the screw) in the pressure holding process. It includes a calculator 21 and a pre-compensator 22. The main controller 30 is for controlling the resin state quantity, and includes a next cycle mold temperature predictor 31, a next cycle mold in-mold resin temperature predictor 3.
2, die pressure correction value calculator 33, pressure dynamic characteristic estimator 3
4, resin pressure in the mold-injection cylinder hydraulic pressure converter 35, 1
A cycle memory 36 is included. Since the main controller 30 is realized by a microcomputer or the like, the actual hardware configuration is, as shown in FIG. 1, a processor CPU, signal converters SIO, PIO, A / D converter A / D, and display C.
It comprises an RT, a keyboard KB, a storage device FD, and the like.

The molding machine control device 20 will be briefly described. In the arithmetic unit 21, the operator operates the keyboard KB.
The deviation between the holding pressure set value set through the above and the injection cylinder oil pressure detected by the injection cylinder oil pressure sensor 11 is calculated.
The predistorter 22 performs a control calculation based on this deviation to determine the operation amount of the servo valve.

In the main controller 30 for controlling the state quantity of resin in the mold, the resin temperature from the cylinder resin temperature sensor 12, the mold temperature from the mold temperature sensor 13 and the cooling water temperature from the cooling water temperature sensor 16 are used. Correction of the in-mold resin pressure of the next cycle by the method described later by the next-cycle mold temperature predictor 31, the next-cycle in-mold resin temperature predictor 32, and the in-mold pressure correction value calculator 33. Calculate the value. Therefore, the components 31 to 33 form a prediction calculation unit. The in-mold resin pressure-injection cylinder oil pressure converter 35 converts the correction value of the in-mold resin pressure in the next cycle into a correction value of the injection cylinder oil pressure based on the output of the pressure dynamic characteristic estimator 34. Therefore, the components 34 and 35 form a pressure conversion unit. The corrected value of the injection cylinder hydraulic pressure is temporarily stored in the one-cycle memory 36 in preparation for the pressure holding process of the next cycle.

In the next cycle, the molding machine controller 20 determines the operation amount of the servo valve based on the correction value of the injection cylinder hydraulic pressure, the holding pressure setting value, and the injection cylinder hydraulic pressure from the 1-cycle memory 36.

By the way, as is clear from the above description,
In the main controller 30, it is necessary to perform the prediction calculation and the correction value calculation based on each detection signal, and when the correction value is calculated, the cycle in which the temperature fluctuation has occurred is completed. However, as shown in FIG. 3, main controller 30 in the present invention predicts the injection cylinder hydraulic pressure in the next cycle, so that the delay in the operation timing can be compensated.

Next, the arithmetic operation in main controller 30 will be described. When the injection operation starts in a certain cycle i, the mold temperature, the cooling water temperature, and the cylinder resin temperature are measured until the pressure holding is completed. After the measurement is completed, the next cycle mold temperature predictor 31 calculates the time average of the above three types of measurement results, and based on the time average of the three types of quantities, the recursive least squares method (Yasuto Takahashi, "System And control ”on page 430 of the second volume)
Predict the mold temperature in the next cycle (i + 1) by. Next, the resin temperature predictor 32 for the next cycle mold
Is based on the predicted mold temperature for the next cycle (i +
Predict the resin temperature in the mold in 1).

In the mold pressure correction value calculator 33, the predicted mold temperature T _m and the detected cylinder resin temperature T
The two values of _r (t) (t represents the injection start time) are compared with the mold temperatures θ _m and θ _r (t) as the ideal values obtained in advance during the test molding, and the holding pressure is compared. The correction value Δp _f is calculated as the correction pressure by, for example, the following formula 1.

[0021]

[Equation 1]

In Expression 1, the expression in {} shows the calculation in the resin temperature predictor 32 in the next cycle mold.

Using the correction value Δp _f , the in-mold pressure correction value calculator 33 further determines a time function g _(t) depending on the holding pressure pattern (time change of the holding pressure set value ₎ , and Δp _{(t )} = G
Calculate the time waveform of the corrected pressure as _(t) · Δp _f . In order to determine the time function g _(t) , molding can be performed at two different mold temperatures prior to molding, and g _(t) can be determined from the difference between the mold internal pressures.

Conversion between the resin pressure in the mold and the oil pressure in the injection cylinder is performed by the following procedure. First, in the pressure dynamic characteristic estimator 34, the injection cylinder hydraulic pressure in the pressure holding process of each cycle,
The pressure dynamic characteristics are determined by the above-mentioned successive least squares method using the resin pressure in the mold. In the in-mold resin pressure-injection cylinder oil pressure converter 35, the corrected value from the in-mold pressure correction value calculator 33 is passed through the inverse characteristic of the dynamic characteristic calculated by the pressure dynamic characteristic estimator 34 to the corrected value of the injection cylinder hydraulic pressure. Convert to.

In the next cycle, the calculator 21 adds the holding pressure set value, the measured injection cylinder oil pressure, and the predicted injection cylinder oil pressure, and based on the result of addition, the predistorter 22 makes the next cycle of the next cycle. Determine the operation amount of the servo valve.

As described above, the present control device predicts the injection cylinder hydraulic pressure in the next cycle (i + 1) based on the mold temperature, the cylinder resin temperature, and the cooling water temperature detected in a certain cycle i, and this prediction is made. The servo valve operation amount during the pressure holding process in cycle (i + 1) is determined by the value and the pressure holding setting value.

[0027]

EFFECTS OF THE INVENTION According to the present invention, when the weight change of a molded product is used as an index, the following effects can be obtained, as is clear from the characteristic diagram shown in FIG.

The time until the weight becomes stable (or the number of shots) is reduced.

Weight fluctuation can be suppressed over a long period of time.

It is possible to reduce the weight fluctuation range for each cycle.

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention.

FIG. 2 is a configuration diagram of a molding machine control device and a main control device shown in FIG.

FIG. 3 is a diagram for explaining the transition of arithmetic operation according to the present invention.

FIG. 4 is a characteristic diagram for explaining the effect of the present invention.

FIG. 5 is a diagram showing a locus of state transition of molten resin in a molding cycle of an injection molding machine.

FIG. 6 is a diagram for explaining the transition of arithmetic operation according to the conventional method.

[Explanation of symbols]

 10 Injection Molding Machine Body 11 Injection Cylinder Oil Pressure Sensor 12 Cylinder Resin Temperature Sensor 13 Mold Temperature Sensor 14 Mold Resin Pressure Sensor 16 Cooling Water Temperature Sensor

Claims (2)

[Claims] 1. Control of an injection molding machine having an injection cylinder hydraulic pressure feedback control system for controlling the injection cylinder hydraulic pressure in a pressure holding process based on an injection cylinder hydraulic pressure detection signal from an injection cylinder hydraulic pressure sensor and a holding pressure set value. In the device, based on a mold temperature detection signal from a mold temperature sensor in a certain cycle, a cooling medium temperature detection signal from a cooling medium temperature sensor for controlling the mold temperature, and a resin temperature detection signal from a cylinder resin temperature sensor. Prediction calculating means for calculating the correction value of the resin pressure in the mold in the next cycle, and the calculated correction value of the resin pressure in the mold are used as the injection cylinder oil pressure detection signal and the resin from the resin pressure sensor in the mold. The injection cylinder hydraulic pressure feedback control system, which includes a conversion means for converting into an injection cylinder hydraulic pressure based on a pressure detection signal. Is a pressure control device for an injection molding machine, which controls the injection cylinder hydraulic pressure by using the converted injection cylinder hydraulic pressure. 2. The holding pressure control device according to claim 1,
The prediction calculation unit, a mold temperature prediction unit that calculates a predicted value of the mold temperature in the next cycle from the mold temperature detection signal in a certain cycle, the cooling medium temperature detection signal and the resin temperature detection signal, A resin temperature predicting unit in the mold for calculating the predicted value of the resin temperature in the mold from the calculated predicted value of the mold temperature, and the resin pressure in the mold from the predicted value of the resin temperature in the mold calculated And an in-mold pressure correction value calculation unit for calculating a correction value of the injection cylinder pressure, and the conversion means estimates a pressure dynamic characteristic for estimating a dynamic characteristic of the injection cylinder hydraulic pressure from the injection cylinder hydraulic pressure detection signal and the resin pressure detection signal. Department,
And a pressure conversion unit for converting the correction value of the resin pressure inside the mold from the correction value inside the mold pressure value into the injection cylinder hydraulic pressure based on the inverse characteristic of the estimated dynamic characteristic. Pressure control device for injection molding machine.