JPS62279918A - Control of injection molding machine - Google Patents

Abstract

PURPOSE:To improve productivity, molding quality and reliability by automating stably control corresponding to mold quality, by correcting a controlled variable discriminating non-defective articles from defective articles through a monitoring range and making a physical quantity variable through an allowable range whose width is narrower than that of the monitoring range. CONSTITUTION:A monitoring range is provided to a physical quantity affecting directly to molding quality. When a measured value is between the upper limit value and lower limit value it is treated as normal and on the other hand, when the same exceeds the upper limit value or less than the lower limit value it is treated as abnormal. An allowable range(m) whose width is narrower than that of a monitoring range M is provided on the inside of the monitoring range M further. When the most advanced position of a screw is changed also by changing molding surroundings such as raising of an oil temperature while automatic operation is continued, the value exceeds the upper limit value SU as per P40 of a drawing and that the number of times of the excesses last continuously more than two times, correction is performed so as to make dwell force (controlled variable) in the next cycle small by issuing corrective instructions and making a control device (hydraulic circuit) variable. The correction is performed similarly also when the value does not arrive at the lower limit value SL and the number of times of unarrivals are continued three times.

Description

Detailed Description of the Invention 2. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method of controlling an injection molding machine used for molding synthetic resin or the like.

[Conventional technology]

Conventionally, a method of controlling an injection molding machine, particularly a method of correcting a control amount based on information related to the molding quality of a molded product, is performed as follows.

First, the most advanced screw position, injection speed, injection pressure, total resin pressure in the mold, holding pressure, injection time, holding pressure switching time, metering time, total I stop position, which directly affects molding quality,
Upper and lower limit values are set for physical quantities such as screw rotation speed and resin temperature, which are monitoring ranges for molding quality.

Then, while actually measuring the physical quantity during the molding cycle, this actual measurement value is compared with the previous S upper limit value or lower limit value, and if the actual measurement value is outside the monitor range, it is determined to be a defective product, and if the other value is within the monitor range. If so, it is determined to be a good product. As a result, in the case of a defective product, the operation is stopped and an alarm is issued, or a molded product removal device is activated.After this, if the defective product is caused by a disturbance that changes over time, the operator can remove the physical The control amount (for example, holding force) that changes the @ (for example, the most forward position of the screw) is reset. In addition,
The reason for adopting such a method depends on the correlation between the physical quantity and the controlled quantity. In other words, in general, there is a nearly 100% correlation between a physical quantity and a controlled quantity that changes this physical quantity, such as the rotation angle (control ■) of a motor that determines the position (physical quantity), etc. Easily controlled by control system, sequence control system, etc.
However, this type of control cannot be used for molded products that have a certain range of good and defective products, or for products that are not clearly correlated or not, and require operator control. The reality is that we have no choice but to rely on intuition and manually set the operations.

[M points while trying to invent or solve]

As described above, the conventional control method described above ultimately only determines the quality of the molded product from the detection of defective conditions, and does not go beyond this. Therefore, the control itself must be performed manually as described above, which is extremely inefficient. This f
, -f If a defective product occurs, the operation will stop at this point, and production will be stopped until the operator resets the settings and restarts the operation, which will greatly affect productivity, or the molded product removal device will be activated. However, if the system only eliminates defective products, it may cause a problem where operation continues in an abnormal state. In addition, the control amount varies, which adversely affects the uniformity of molding quality, which has been a major obstacle for injection molding machines that require a high degree of automation and high quality.

[Means for solving problems]

The present invention aims to provide a control method for an injection molding machine that solves the problems existing in the prior art described above, and is achieved by the method shown below.

That is, in the method for controlling an injection molding machine according to the present invention, first, a monitoring range (M) for determining good products and defective products is set for a physical quantity that affects molding quality (for example, the most advanced position of a screw). On the other hand, inside this monitor range (M), a tolerance range (m) is set that is smaller than the monitor range ('d). Then, either the actual measured value of the above physical quantity or the permissible range (
m), the control amount (for example, holding force) of the control means for varying the upper S physical quantity is corrected in the next cycle. In addition, the above actual measured value is within the allowable range (m) for correction.
It is possible to perform the correction when the correction operation is deviated a plurality of times in succession, and to preset the amount of correction by the negative correction operation.

[For production]

Next, the operation of the present invention will be explained.

The control method according to the present invention discriminates between non-defective products and defective products based on the monitor range (M). On the other hand, this monitor range (M)
It is determined whether to allow or correct it based on the width tolerance range (m). Then, when the actual measured value of the physical quantity deviates from the allowable range (m), correction is performed. This correction increases or decreases the control amount that changes the physical quantity, and corrects the actual measured value so that it falls within the allowable range in the next cycle.

Note that if the actual measurement value is within the allowable range (ffl), it is accepted and no correction is made.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is a diagram showing the most advanced position of the screw in an injection molding machine that implements the method of the present invention, and Fig.
It is a figure which shows the relationship between the prefectural number of times of a screw, and the most advanced position in a figure.

In general, in an in-line screw injection molding machine, physical quantities that directly affect molding quality include the screw's most forward position, injection speed, injection pressure, total resin pressure in the mold, holding pressure, injection time, holding pressure switching time, Measurement time, measurement stop position, screw rotation speed, resin temperature, etc. Normally, actual measured values for these physical quantities are obtained using a predetermined sensor, etc., and if the actual measured value falls between the preset monitoring range, that is, the upper limit value and lower limit value, it is normal (good product). If it exceeds the value or is less than the lower limit value, it is treated as an abnormality (defective product).

For example, in the examples, screw most advanced positions (Pl) to (P5) are illustrated as representative physical quantities, but there is a deep relationship between this screw most advanced position and molding quality or holding force. In other words, in the injection process during molding, the nozzle (3) of the injection device (2) as shown in Figure 1 comes into contact with the clamped mold, and is integrated into the injection piston by supplying pressure oil to the injection cylinder (not shown). The screw (4) connected to moves forward.

Then, the molten resin material measured and accumulated in front of the screw (4) is injected from the nozzle (3) and filled into the mold. Therefore, the highest position of the screw (4) (
The filling amount changes depending on PI) to (P5), and the upper limit (B
If it is within the monitoring range (M) defined by U) and the lower limit value (BL), it will be a good product, but if it is outside this range (M), for example in the hand moe position (Pl), it will be defective due to insufficient filling. , so-called sink marks and short circuits occur in the molded product, and if the molded product is located at an excessive position (P5), overfilling becomes defective, and abnormal internal stress or flaking occurs in the molded product. In this case, when the holding force (control amount) of the screw (4) is increased by the control means for varying the screw most advanced position, the screw most advanced position shifts to the front, and conversely, when it is decreased, the screw most advanced position shifts to the rear.

In the present invention, inside the monitor range (M), a permissible range (m) that is smaller than the width of the monitor range (M) is further set. Upper limit value (SU) that regulates the width of this tolerance range (1)
and the lower limit value (SL), and the position of the entire tolerance range (m) (
(not limited to the center of the monitor range) can be set arbitrarily depending on the type of molded product, etc. Note that the narrower the width of the tolerance range (m), the more uniform the molded product can be obtained, and the more frequently the correction described below will be performed.

In this way, by setting the tolerance range (m),
It is controlled as follows.

In FIG. 2, the black dots are plotted at the most advanced position of the screw, and are actual measured values of the screw position detected by a position sensor such as a potentiometer.

If the screw most forward position is within the permissible range (1), it is completely normal and the operation continues in that state.

On the other hand, even though the optimal molding conditions have been set, the molding environment changes such as the oil temperature rising while automatic operation continues, and the screw most advanced position shifts, resulting in (P2O in Figure 2)
When the upper limit (SU) is exceeded, and this exceedance continues three or more times in a row, a correction command is issued, and the control means (hydraulic circuit, etc.) is varied to adjust the holding pressure (control) in the next cycle. amount). In this case, the correction amount, that is, the range by which the holding force is reduced by - times of correction, can be set in advance, and the correction operation can be repeated multiple times until it falls within the allowable range (m), which can be done using a relatively simple logic circuit. Can be configured. Alternatively, the necessary correction amount may be predicted by averaging the actual measurement values that deviate from each other, or by calculating the previous magnitude, so that the correction can be made by -times of correction. This correction is also performed when the lower limit (SL) is not reached and the number of times or three times in a row that the lower limit value (SL) is not reached as shown in Fig. 2 (P2O), and in this case, it acts in the direction of increasing the holding force. . Note that the correction is performed when the actual measurement value falls outside the allowable range three times in a row, but of course it may be performed once or any other number of times. but,
By setting it multiple times as in the embodiment, it is possible to determine whether it is a sudden disturbance that does not require correction or a change over time in the molding environment that requires correction, and accurate correction can be performed. In addition, although we have shown the case where the holding force is varied as a control variable of the control means, in the present invention, control can be performed as long as there is a certain degree of correlation, so other control variables, such as metering stop position, back pressure, etc. Alternatively, they can be controlled simultaneously. in this way,
The present invention is suitable for cases where the physical quantity and the controlled quantity are different, such as the most advanced position of the screw and the holding force, and the physical quantity has a width (width corresponding to quality).

On the other hand, when the value deviates from the upper limit (SU) or lower limit (SL) once or twice, as shown in (P41) and (P42) in Figure 2, and it is within the written monitor range (M). In this case, the molded product is in the f1 range of good products, and the operation continues without any correction. Furthermore, when the values are outside the monitoring range (M), such as (P2O) and (PIO), the molded product is treated as a defective product.

Although the embodiments have been described in detail above, the present invention is not limited to these embodiments.

For example, when correcting the holding force, the most advanced position of the screw is detected, but the mold internal pressure may also be detected. moreover,
In general, it is possible to detect any physical quantity that affects molding quality, such as by detecting the filling time and correcting the filling pressure, and to correct the control amount of the EE control means that varies this physical quantity. These physical quantities, correction widths, etc. can be appropriately selected depending on the molded product, mold, etc. In addition, since the present invention assumes a certain degree of correlation, multiple physical quantities are detected simultaneously,
A plurality of control variables may be corrected, and thereby more accurate correction can be performed. Other details may be arbitrarily modified without departing from the spirit of the present invention.

〔Effect of the invention〕

In this way, the injection molding machine control method according to the present invention creates a new tolerance range in addition to the conventional monitoring section for physical quantities that affect molding quality, and makes corrections when the physical quantities deviate from this tolerance range. By doing so, we obtain the following effects:

■ Even if the actual measured value falls outside of the allowable range during long periods of unattended operation, it is automatically corrected, preventing the molding machine from stopping and continuing molding of defective products, and supports molding quality that was not possible with feedback control in the past. can also be stably automated and improve productivity.

■Since the molding quality can always be maintained within the allowable range, it is possible to improve the uniformity of the molding quality, and it is also possible to easily set the degree of freedom in the molding quality, that is, whether to make the quality strict or lenient.

(2) If the correction amount for one correction operation is set in advance according to the optimal embodiment, complicated arithmetic processing and the like are not necessary, and the correction can be implemented using a simple logic circuit or the like. Therefore, it is possible to construct a highly reliable system that does not cause failures, and furthermore, an inexpensive system that does not increase costs.

[Brief explanation of drawings]

FIG. 1: A diagram showing the most advanced position of the screw in an injection molding machine implementing the method of the present invention. FIG. 2: A diagram showing the relationship between the number of advances of the screw and the most advanced position in FIG. In the drawings, (M): Monitoring range (m): Permissible range Patent applicant Nissei Jushi Kogyo Co., Ltd., agent Patent attorney 1) and Figure 1 P5 P4 P3 P2 P1 Screw position Figure 2 Number of screw advances

Claims (1)

[Claims] [1] A monitor range is set for determining good products and defective products for physical quantities that affect molding quality, and a tolerance range is set inside this monitor range that is wider than the monitor range. A method for controlling an injection molding machine, comprising: correcting a control amount of a control means for varying the physical quantity in the next cycle when the measured value of the physical quantity deviates from the allowable range. [2] The method for controlling an injection molding machine according to claim 1, wherein the correction is performed when the measured value deviates from the allowable range a plurality of times in succession. [3] The method for controlling an injection molding machine according to claim 1, wherein the correction amount for one correction operation is set in advance.