JPH0481931B2 - - Google Patents

Description

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 resins and 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 screws that directly affect molding quality include the screw's most advanced position, injection speed, injection pressure, resin pressure in the mold, holding pressure, injection time, holding pressure switching time, metering time, metering stop position, and screw rotation speed. , upper and lower limit values are set for physical quantities such as resin temperature, which are monitoring ranges for molding quality.

Then, while actually measuring the physical quantity during the molding cycle, this measured value is compared with the above-mentioned upper limit value or lower limit value, and if the actual measured value is outside the above-mentioned monitor range, it is determined to be a defective product, and on the other hand, if it is within the monitor range, the product is determined to be defective. Judged as 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 check the physical quantity. (for example, the most forward position of the screw). Note that 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 position (rotation angle (controlled quantity) of a motor that determines the position relative to a physical quantity), etc. is called feedback control. This method can be used to easily and reliably control things such as molded products that have a certain range of good and defective products, or things that have a correlation but are not clear. The reality is that the operator is forced to rely on the intuition of the operator and make manual settings.

[Problem that the invention seeks to 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. For this reason, if a defective product occurs, the operation will stop at this point, and production will be halted until the operator resets the settings and restarts the operation, which will greatly affect productivity, or the molded product removal device may be activated. However, this method only eliminates defective products, resulting in 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 described below.

That is, the method for controlling an injection molding machine according to the present invention is as follows:
First, a monitoring range M for determining good products and defective products is set for physical quantities that affect molding quality (for example, the most forward position of the screw). On the other hand, an allowable range m narrower than the monitor range M is set inside the monitor range M. Then, when the actual measured value of the physical quantity deviates from the permissible range m, the control amount (for example, holding force) of the control means for varying the physical quantity is corrected in the next cycle. Note that the correction can be performed when the actual measured value deviates from the allowable range m a plurality of times in succession, and the amount of correction for one correction operation can be set in advance.

[Effect]

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, a tolerance range m narrower than the monitor range M is used to determine whether to permit or correct. 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 it so that the actual measured value falls within the allowable range m in the next cycle. Note that if the actual measurement value is within the tolerance range m, it is accepted and no correction is performed.

〔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 forward position of the screw in an injection molding machine implementing the method of the present invention, and FIG. 2 is a diagram showing the relationship between the number of advances of the screw in FIG. 1 and the most advanced position.

In general, in an in-line screw type injection molding machine, physical quantities that directly affect molding quality include the screw's most advanced position, injection speed, injection pressure, resin pressure in the mold, holding pressure, injection time, and 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 and lower limit values, it is normal (good product).
If it exceeds the upper limit or is less than the lower limit, it is treated as an abnormality (defective product).

For example, although the screw most advanced positions P1 to P5 are illustrated as typical physical quantities in the embodiment, there is a deep relationship between the screw most advanced position and molding quality or holding force. That is, in the injection process during molding, the nozzle 3 of the injection device 2 comes into contact with the clamped mold as shown in Figure 1, and is integrally connected to the injection piston by supplying pressure oil to an injection cylinder (not shown). Skrill 4 moves forward. And this Sukuriyu 4
The molten resin material measured and accumulated in the front is injected from the nozzle 3 and filled into the mold. Therefore,
The filling amount changes depending on the most advanced position P1 to P5 of the screw 4, and if it is within the monitoring range M defined by the upper limit BU and lower limit BL, it is a good product, but if it is out of this range M, for example, position P1
In the case of , insufficient filling occurs and so-called sink marks and shoots occur in the molded product, and in the case of excessive filling at position P5, overfilling occurs resulting in abnormal internal stress and burrs 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 forward position, the screw most forward position moves forward, and conversely, when it is decreased, the screw most forward position moves backward.

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

By setting the allowable range m in this manner, the following control is performed.

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

If the screw most advanced position is within the permissible range m, it is completely normal and the operation continues in that state.

On the other hand, even though the optimum molding conditions have been set, the molding environment changes such as the oil temperature rising while automatic operation continues, and the screw's most advanced position shifts.
If the upper limit (SU) is exceeded as shown in P40 in Figure 2,
Moreover, if the number of times exceeded continues three or more times in a row, a correction command is issued and the control means (hydraulic circuit, etc.)
Holding force (control amount) in the next cycle by varying
Correct to make it smaller. In this case,
The amount of correction, that is, the range by which the holding force is reduced by one correction, can be set in advance, and the correction operation can be repeated multiple times until it falls within the allowable range m, and can be configured with a relatively simple logic circuit. Also, average the outlying measured values,
Alternatively, the necessary correction amount may be predicted by calculating the size just beforehand, so that the correction can be made in one correction. This correction is performed in the same way when the lower limit value SL is not met and the number of times it is not met is three times in a row, as shown at P20 in FIG. 2, 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. However, by setting multiple times as in the embodiment, it is possible to determine whether the disturbance 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 the case where the holding force is varied as a control variable of the control means has been shown, in the present invention, since control can be performed as long as there is a certain degree of correlation, other control variables, such as the metering stop position, back pressure, etc., can be individually adjusted. Alternatively, they can be controlled simultaneously. As described above, the present invention is suitable for cases where the physical quantity and the controlled quantity are different, such as the screw most advanced position and the holding force, and the physical quantity has a width (a width corresponding to quality).

On the other hand, the upper limit value as shown in P41 and P42 in Fig. 2
If the molded product deviates from the SU or lower limit value SL once or twice and is within the monitoring range M, the molded product is within the good product range, and no correction is made and operation continues as it is. Further, when the molded product is out of the monitoring range M, such as P50 and P10, 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. Furthermore, by detecting the filling time and correcting the filling pressure, it is generally possible to detect any physical quantity that affects molding quality, and to correct the controlled quantity of the arbitrary control means that varies this physical quantity. These physical quantities, correction widths, etc. can be appropriately selected depending on the molded product, mold, etc. Furthermore, since the present invention assumes a certain degree of correlation, a plurality of physical quantities may be detected at the same time and a plurality of control quantities may be corrected, thereby making it possible to perform correction with higher accuracy. Other details can be arbitrarily changed without departing from the spirit of the 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 range for physical quantities that affect molding quality.
Since the correction is made when the deviation falls outside of this permissible range, the following significant effects are obtained.

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

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.

If the correction amount for one correction operation is set in advance according to the optimal embodiment, complicated arithmetic processing or the like is not necessary, and it 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 drawing, M: monitor range, m: tolerance range.

Claims (1)

[Claims] 1. Setting a monitoring range for determining good products and defective products for physical quantities that affect molding quality,
A tolerance range narrower than the monitor range is set inside this monitor range, and when the actual measured value of the physical quantity deviates from the tolerance range, the control amount of the control means for varying the physical quantity is corrected in the next cycle. A method for controlling an injection molding machine, characterized in that: 2. The method of 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 amount of correction for one correction operation is set in advance.