JPH09216266A - Control of injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically set a screw back pressure control condition to a proper value at the time of a weighing process. SOLUTION: At first, for example, a weighing process is performed under an initial back pressure control condition constant in back pressure to actually measure the screw retreat speed at the time of this weighing process and, when a change degree of the actually measured screw retreat speed exceeds a tolerance range, the back pressure control condition is corrected on the basis of the relation data between the screw retreat speed preliminarily obtained by a case study and back pressure so that the actually measured screw retreat speed is received within a tolerance range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for an injection molding machine, and more particularly to a control method for an in-line screw type injection molding machine, which is capable of automatically setting a screw back pressure at an appropriate value during a measuring process. It is a thing.

[0002]

2. Description of the Related Art An in-line screw type injection molding machine rotates a screw in a heating cylinder to knead and plasticize a raw material resin while sending it to the front end side of the screw, and at the same time, melted resin accumulated at the front end side of the screw. The metering stroke is performed by retracting the screw while controlling the screw back pressure by the pressure from the.

In the above measuring process, controlling the resin pressure of the molten resin accumulated on the tip side of the screw to an appropriate value is one of the important control factors for achieving good product molding. It is very important to control the back pressure applied to the screw that moves backward by the pressure from the molten resin accumulated on the tip side of the screw.

By the way, in order to accurately grasp the resin pressure of the molten resin accumulated on the tip side of the screw, it is directly provided with a pressure sensor for directly detecting the resin pressure in the nozzle attached to the tip of the heating cylinder. The most accurate method, but such a pressure sensor is very expensive and has a problem in durability. Therefore, a relatively inexpensive pressure sensor is attached to the rear part of the screw, etc., and the load pressure from the resin on the screw detected by this pressure sensor is converted into the resin pressure of the molten resin accumulated at the tip side of the screw, It is common to take the method that is regarded as resin pressure. Then, the back pressure applied to the screw is controlled by using the screw forward / backward drive source so that the load pressure from the resin applied to the screw is maintained at a predetermined value.

[0005]

However, as described above, when the method of detecting the load pressure value for the screw and substituting it for the resin pressure of the molten resin accumulated on the tip side of the screw is adopted, It was hard to say that the load pressure value for the screw and the resin pressure of the molten resin on the screw tip side always have a correct correlation. In other words, the actual resin pressure of the molten resin fluctuates even if the load pressure value on the screw is constant due to the influence of the supply torque due to the screw feeding resin forward and the influence of the resin pressure that cuts into the screw. Therefore, it is very difficult to properly control the back pressure of the screw.

[0006] The present invention has been made in view of the above points,
The purpose is to follow the method of detecting the load pressure value for the screw using an inexpensive pressure sensor, and to automatically set the screw back pressure control condition during the measurement process to an appropriate value. , It is to contribute to good product molding by appropriate screw back pressure control.

[0007]

In order to achieve the above-mentioned object, the present invention provides a method of controlling an in-line screw type injection molding machine, wherein during a test shot operation prior to continuous molding operation, (a) first, for example, back pressure Perform a metering stroke under a constant initial back pressure control condition, measure the screw retreat speed during this metering stroke, and check whether the change in the measured screw retreat speed is within the allowable range width and can be regarded as almost constant. Judgment, (b) when the change in the measured screw retreat speed exceeds the allowable range width, based on the relationship data between the screw retreat speed and the back pressure, which is acquired in advance by a case study according to the resin type, The back pressure control condition is corrected and the next measurement stroke is executed, and it is judged whether or not the measured change of the screw retreat speed is within the allowable range and can be regarded as almost constant. (C) The process of (b) above is repeated as necessary so that the change in the measured screw retreat speed falls within the allowable range width, and (d) the change in the measured screw retreat speed falls within the allowable range. The back pressure control condition when it falls within the width is automatically set as the back pressure control condition during continuous molding operation.

[0008]

Embodiments of the present invention will be described below. FIG. 1 is an explanatory diagram showing a main configuration of an injection molding machine according to an embodiment of the present invention. In FIG. 1, 1 is a heating cylinder, 2 is a screw, 3 is, for example, a servo motor that is a rotational drive source of the screw 2, 4 is an injection cylinder (hydraulic cylinder) that is a forward and backward drive source of the screw 2, and 5 is a rear side of the screw 2. A load cell (pressure sensor) 6 provided on the end side is a stroke sensor for detecting the forward / backward stroke of the screw 2. A servo motor may be used as a forward / backward drive source of the screw 2 and the rotation of the servo motor may be transmitted to the screw 2 via a rotation → linear motion conversion mechanism.

Further, 11 is a microcomputer (hereinafter referred to as a microcomputer) which controls the operation and display control of the entire machine (injection molding machine), and 12 is composed of a large number of sensors arranged in each part of the machine. The load cell 5 and the stroke sensor 6 are included in the sensor group. 13
Is a driver group composed of a large number of driver circuits for driving and controlling a large number of driving sources arranged in various parts of the machine, and controls the motor driver 13a for driving and controlling the servo motor 3 and the injection cylinder 4. The valve driver 13b that drives and controls the valve is also included in this. Reference numeral 14 is a key input device provided on the front surface of the machine, and 15 is a display device provided adjacent to the key input device, for example, a color CRT display, a color LCD or the like.

The microcomputer 11 controls the entire molding process such as measuring operation (kneading / plasticizing / measuring operation), injection operation (primary injection operation and pressure holding operation), mold opening / closing operation, ejecting operation, and actual measurement data. Various processing such as calculation / storing processing, non-defective / defective determination processing, abnormality determination processing, display control processing of the output image of the display device 15 and the like are executed. This microcomputer 11 is actually various I
/ O interface, ROM, RAM, MPU and the like, various processing is executed by various programs created in advance, in this example, the input data processing unit 21, the molding condition setting storage unit 22, The following description will be made assuming that the molding process control unit 23, the measured value storage unit 24, the display processing unit 25, and the like are provided.

In the molding condition setting storage unit 22, reference numeral 22a denotes a back pressure control condition setting storage unit for the measuring process, and 2a.
2b is an automatic change processing unit of the back pressure control condition at the time of the test shot. In the actual measurement value storage unit 24, 24a is a screw retreat speed storage unit and 24b is a load cell output storage unit.

The input data processing section 21 appropriately converts externally input information such as various measurement information sent from the sensor group 12 and various information input by the key input device 14 as necessary. Then, it is supplied to each part in the microcomputer 11. The measurement information (pressure measurement information) sent from the load cell 5 is converted into pressure data applied to the screw 2. The measurement information (screw position measurement information) sent from the stroke sensor 6 is used as screw stroke (screw position) data from the reference position, and the screw stroke information and a clock from a clock means (not shown) are used. Depending on the information, the screw 2
Is converted into the speed data of.

The molding condition setting storage unit 22 stores various operating condition values input by the key input device 14 or the like in a rewritable form. The operating condition values (operating condition setting data) include, for example, measurement control conditions, injection (primary injection and holding pressure) control conditions, mold closing (mold clamping) control conditions, mold opening control conditions, eject control conditions, products. The control conditions of the automatic take-out machine, the band heater temperature of each part, the cooling temperature of each part, etc. can be mentioned. Further, in the present example, as the above-mentioned measurement control conditions, the screw rotation speed corresponding to the screw position during the measurement stroke, the screw retreat speed corresponding to the screw position, the back pressure corresponding to the screw position, the limit of the servomotor 3 The torque value (allowable upper limit torque value) is set,
This back pressure control condition (back pressure setting data) is stored in the back pressure control condition storage unit 22a. Also, in this example,
At the time of a test shot prior to continuous automatic operation, the back pressure control condition automatic conversion processing unit 22b causes the measured value storage unit 24 to operate.
The back pressure control condition (back pressure setting data) is newly calculated and generated as needed by referring to the data from 1), and this is rewritten and stored in the back pressure control condition storage unit 22a.

The molding process control unit 23 is provided in each unit of the machine based on a molding process control program created in advance and operating condition values (operating condition setting data) stored in the molding condition setting storage unit 24. The sensor group 12 (position sensor, pressure sensor, rotation speed detection sensor,
The driver group 13 (motor driver, electromagnetic hydraulic pressure control) while referring to the actual measurement data from the actual measurement value storage unit 24 in which the measurement information from the temperature sensor and the like) and the clock information from the clock means (not shown) are referred to. A corresponding drive source is driven and controlled via a valve driver, a heater driver, etc.) to execute a series of control steps.

The measured value storage section 24 stores all measured data of preset monitor items in continuous automatic operation over a predetermined number of consecutive shots. The monitor items to be captured include a time monitor item, a position monitor item, a rotation speed monitor item, a speed monitor item, a pressure monitor item, a temperature monitor item, a power monitor item, and the like, and the important items of the molding operation condition setting items described above. Is almost included. In this example, the measured screw retreat speed of the measuring stroke is stored in the screw retreat speed storage unit 24a.
The actually measured load pressure on the screw 2 obtained by converting the output of the load cell 6 in the measuring process is fetched and stored in the load cell output storage section 24b.

The display processing unit 25 displays the designated display mode on the basis of a display image creation / control program created in advance in response to an instruction from the key input device 14 to call the display screen in the mode desired by the operator. Create screen data and output it on the display device 15.
Display.

Next, an automatic correction / setting method of the back pressure control condition of the metering stroke at the time of the test shot based on the above-mentioned configuration will be described with reference to FIG. 1 and FIGS.

FIG. 2 shows the load pressure 31 to the screw 2 obtained from the output of the load cell 5 and the retreat of the screw 2 when the metering stroke is executed under the initial back pressure control condition where the back pressure is constant during the trial shot. It is a figure which shows the relationship with the speed 32. The initial back pressure control conditions such as constant back pressure are
It is set in the back pressure control condition storage section 22a by the operator.

As shown in FIG. 2, since the initial back pressure control condition is constant back pressure, the load pressure 31 on the screw 2 obtained from the output of the load cell 5 is stable. However, the measured screw retreat speed 32 drops in the middle thereof. In such a case, it was confirmed by experiments by the inventor of the present application that the pressure of the molten resin accumulated on the tip end side of the screw 2 tends to be unstable, depending on the type of resin. Reference numeral 33 in FIG. 2 indicates a measured value of the resin pressure of the molten resin on the tip side of the screw 2, and the heating cylinder 1
Sensor 7 that directly detects the resin pressure in the nozzle at the tip of the
It is the data measured by (indicated by the broken line in FIG. 1), and the measured value 33 of the resin pressure here is an unstable value that falls in the middle part thereof, which becomes a factor that hinders a good weighing operation. . On the other hand, it was confirmed by experiments by the inventor of the present application that the actual resin pressure in the nozzle is substantially constant and stable if the change in the measured screw retreat speed is small and falls within a predetermined allowable range.

The machine of this example (injection molding machine) is
The pressure sensor 7 for directly detecting the resin pressure in the nozzle is not provided, and the pressure sensor 7 is attached to the test machine to measure the measured value 33 of the resin pressure in the nozzle in advance.

The automatic change processing unit 22b of the back pressure control condition at the time of the test shot of the machine of this example has a relationship between the screw retreat speed and the resin pressure in the nozzle, which is obtained by performing a case study in advance for each resin type. The data and the relational data between the screw retreat speed and the back pressure corresponding to the output of the load cell 5 are stored. Then, the back pressure control condition automatic change processing unit 22b is configured to operate the screw retreat speed storage unit 24b.
Import the measured screw retreat speed data from a,
It is determined whether or not the back pressure control condition needs to be changed. If the back pressure control condition needs to be changed, the back pressure control condition is automatically changed according to a pre-created automatic change processing program.

That is, in the back pressure control condition automatic change processing unit 22b, the actually measured screw retreat speed in the metering process under the initial back pressure control condition with a constant back pressure is within the allowable range width (this allowable range width differs depending on the resin type). If the measured screw retreat speed can be regarded as being substantially constant (actually, if it can be regarded as being substantially constant over a plurality of consecutive shots),
The initial back pressure control condition is established as the back pressure control condition during continuous molding operation.

Further, when the measured screw retreat speed in the measuring stroke under the initial back pressure control condition of constant back pressure deviates from the permissible range width, the automatic back pressure control condition changing unit 22b causes It is determined that the actual resin pressure is unstable, and based on the relationship data between the screw retreat speed and the back pressure corresponding to the output of the load cell 5 that was previously case-studied, the screw retreat speed is set within the allowable range width. The back pressure control condition is corrected, set in the back pressure control condition storage unit 22a, and the next measurement process is executed. And the measured screw retreat speed in the next metering stroke is
It is judged whether or not it can be regarded as being substantially constant within the allowable range width, and this processing process is repeated as necessary, and finally, the actually measured screw retreat speed is set within the allowable range width. Back pressure control condition automatic change processing unit 22b
Defines the back pressure control condition when the measured screw retreat speed falls within the allowable range width as the back pressure control condition during continuous molding operation (actually, the measured screw retreat speed falls within the allowable range width). The average value of the back pressure control conditions of continuous multiple shots set in is set as the back pressure control condition during continuous molding operation).

FIG. 3 shows the output of the load cell 5 during the continuous molding operation after the automatic change processing of the back pressure control condition from the initial back pressure control condition of constant back pressure shown in FIG. 2 by the above-mentioned method. It is a figure which shows the relationship between the load pressure 31 'to the obtained screw 2 and the retreat speed 32' of the screw 2. As shown in FIG. 3, the measured screw retreat speed 32 'is within the allowable range width described above, and can be regarded as substantially constant. On the other hand, the load pressure 31 ′ to the screw 2 obtained from the output of the load cell 5 has a swelling in the middle part, and is a curve that is almost similar to the curve of this actually measured load pressure 31 ′, and the back pressure control condition is set. ing. That is, in this case, the back pressure control condition is not constant (uniform), but is a multi-stage or inclined back pressure control condition corresponding to the screw stroke. When the resin pressure in the nozzle at this time is directly measured, it becomes a measured value 33 'of the resin pressure, which is stable and constant. Therefore, a good metering operation can be achieved with a good back pressure control condition.

In the above description, the initial back pressure control condition is constant back pressure, but the initial back pressure control condition can be set in any form.

[0026]

As described above, according to the present invention, the screw back pressure control condition at the time of the measuring process is automatically set to an appropriate value while following the method of detecting the load pressure value for the screw by using the inexpensive pressure sensor. It can be set, and its value is enormous in this type of in-line screw type injection molding machine.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a main configuration of an injection molding machine according to an embodiment of the present invention.

FIG. 2 shows the load pressure on the screw obtained from the output of the load cell and the screw when the metering stroke is executed under the initial back pressure control condition in which the back pressure is constant during the test shot in the embodiment of the present invention. FIG. 6 is an explanatory diagram showing the relationship with the reverse speed of

FIG. 3 shows the load pressure on the screw obtained from the output of the load cell during the continuous molding operation and the backward speed of the screw after the back pressure control condition is automatically changed in the embodiment of the present invention. It is explanatory drawing which shows the relationship with.

[Explanation of symbols]

 1 Heating Cylinder 2 Screw 3 Servo Motor (Screw Rotational Drive Source) 4 Injection Cylinder (Screw Forward / Backward Drive Source) 5 Load Cell (Pressure Sensor) 6 Stroke Sensor 11 Microcomputer (Microcomputer) 12 Sensor Group 13 Driver Group 13a Motor Driver 13b Valve driver 14 Key input device 15 Display device 21 Input data processing unit 22 Molding condition setting storage unit 22a Back pressure control condition setting storage unit 22b Automatic change processing unit of back pressure control condition at trial shot 23 Molding process control unit 24 Measured Value storage unit 24a Screw backward speed storage unit 24b Load cell output storage unit 25 Display processing unit

Claims (3)

[Claims] 1. By rotating a screw in a heating cylinder, the raw material resin is kneaded and plasticized and sent to the tip side of the screw, and the screw generates back pressure by the pressure from the molten resin accumulated at the tip side of the screw. In an in-line screw type injection molding machine that retreats while being controlled, during a test shot operation that precedes the continuous molding operation, (a) First, the metering stroke under the initial back pressure control condition is executed, and the screw retreat speed during this metering stroke is set. Actually measured,
It is judged whether or not the measured change of the screw retreat speed is within the allowable range width and can be regarded as substantially constant. (B) If the measured change of the screw reverse speed exceeds the allowable range width, the resin type Based on the relationship data between the screw retreat speed and back pressure, which was obtained in advance by a case study, the back pressure control conditions are corrected and the next measurement stroke is executed, and the measured screw retreat speed changes within the allowable range. It is judged whether or not it can be considered to be almost constant within the width, and (c) the processing process of (b) above is repeated as necessary so that the change in the measured screw retreat speed falls within the allowable range width. A method for controlling an injection molding machine, comprising: 2. The back pressure control condition according to claim 1, wherein the back pressure control condition when the change in the measured screw retreat speed falls within the allowable range width is automatically set as the back pressure control condition during the continuous molding operation. A method for controlling an injection molding machine, characterized in that. 3. The method for controlling an injection molding machine according to claim 1, wherein the initial back pressure control condition is a constant back pressure control condition.