JPH08290448A - Injection control method of injection molding machine - Google Patents

Abstract

PURPOSE: To stabilize the wt. of a molded product by performing speed feedback control from the start of primary injection to a point of time before a dwelling changeover point and changing over the same to pressure feedback control at a point of time when a pressure actually measured value reaches a predetermined pressure value. CONSTITUTION: A weighing completion position is measured at every shot to calculate a stored weighed resin amt. The pressure rise curve corresponding to the advance stroke of a screw from the weighing completion position is operated on the basis of the calculated resin amt. of the compression characteristic data of a resin to set the advance stroke of the screw coinciding with a preset filling completion pressure value in the pressure rise curve as a dwelling changeover point. Further, the pressure rise curve is set as the pressure control objective value from the midway of a primary injection process to the dwelling changeover point. Speed feedback control is performed from the start of primary injection to a point of time appropriately before the dwelling changeover point and changed over to pressure feedback control at the point of time when a pressure actually measured valve monitored during injection reaches the predetermined pressure value in the pressure rise curve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection control method for an in-line screw type injection molding machine, and more particularly to an injection molding machine for stabilizing the pressure at the completion of filling (holding pressure switching point). Regarding control method.

[0002]

2. Description of the Related Art A servo motor is used as an injection drive source,
The injection molding machine with feedback control of the injection process (primary injection process and subsequent pressure-holding process) is capable of precise speed feedback control and pressure feedback control. There is.

In an injection molding machine that performs such feedback control, normally, the velocity feedback control is performed on the primary injection process (the process from the measurement completion position (injection start position) to the filling completion position (holding pressure switching point)). The pressure holding process is controlled by pressure feedback. That is, a velocity target value is set during the primary injection stroke period, and velocity feedback control is performed so that the measured velocity value matches this, and a pressure target value is set during the pressure holding stroke period. The pressure feedback control is performed so that the measured pressure values match.

[0004]

However, as described above, in the prior art, since the velocity feedback control is performed until the end of the primary injection stroke, the resin pressure becomes large due to an unexpected situation at the end of the primary injection stroke. Even if the pressure is increased (for example, by completing the filling before the pressure switching point)
Since the speed feedback control is forcibly performed so as to maintain the speed corresponding to the speed target value, the resin pressure is further increased and sometimes the pressure is applied with the maximum torque of the machine (injection molding machine). There is a possibility that it may cause excessive overfilling (overpacking).

Further, even if the pressure feedback control is immediately switched at the time of completion of filling (holding pressure switching point), there is variation in the resin pressure value at the pressure holding switching point, and there is also a response delay of the controller system. There is also a problem that a surge occurs in the resin pressure in the early stage of the pressure stroke.

There is also a problem that if the amount of measured resin for each shot is not stable (the position at which the measurement is completed is not stable), the weight of the molded product is not stable and good product molding cannot be achieved.

A method may be considered in which the speed feedback control is switched to the pressure feedback control at a predetermined position before the completion of filling (holding pressure switching point). However, the pressure feedback control may involve a variation in the measured resin amount. Regardless of this, the same target pressure value is always set, and in this case as well, there was the problem that the weight of the molded product was not stable due to variations in the measured resin amount.

The present invention has been made in view of the above points,
The purpose is that even if the amount of measured resin for each shot is not strictly stable, the resin pressure at the completion of filling (holding pressure switching point) can always be kept constant and overfilling can be prevented. An object of the present invention is to provide an injection control method that enables good pressure application in the pressure-holding process and thus stabilizes the weight of a molded product, which greatly contributes to molding of a good product as a whole.

[0009]

In order to achieve the above-mentioned object, the present invention uses an in-line screw type injection molding machine to measure and store a measuring completion position for each shot (each shot cycle). The amount of resin is calculated, and based on this measured resin amount and the compression characteristic data of the resin given in advance, the pressure increase curve corresponding to the screw forward stroke from the measurement completion position is calculated, and the preset pressure increase curve is set. Forward stroke (screw forward position) corresponding to the completed filling pressure value
Is set as a holding pressure switching point, and the above-mentioned pressure rise curve is set as a pressure control target value from the middle of the primary injection stroke to the holding pressure switching point. Speed feedback control is performed up to this side, and the measured pressure value is monitored during injection by this speed feedback control, and when the measured pressure value reaches the predetermined pressure value in the above pressure increase curve, the above pressure increase curve is set. Therefore, the control is switched to the pressure feedback control.

[0010]

[Function] The microcomputer (microcomputer) that controls the entire machine obtains the information of the measurement completion position for each shot (each shot cycle) from the measurement information from the screw position detection sensor, and the accumulated measurement data is obtained. The amount of resin is first calculated. Here, the compression characteristic for each resin type is known, and the microcomputer corresponds to the screw stroke from the measurement completion position (injection start position) based on the measured and calculated measured resin amount and the resin compression characteristic data. The pressure rise curve (pressure rise characteristic curve along the screw stroke) is calculated. That is, when the resin compression characteristic data is constant (in other words,
If the amount of resin to be measured is determined, the pressure rise curve corresponding to the screw stroke from the measurement completion position (injection start position) will be the learning data acquired by a case study in advance or a predetermined calculation. It can be easily calculated from the formula.

The microcomputer uses the data of the pressure rise curve obtained as described above, and determines the screw stroke (screw forward position) in this pressure rise curve that matches the preset filling completion pressure value at this time. Is set as the filling completion position (that is, the holding pressure switching point), and the pressure increase curve is set as the pressure control target value from the middle of the primary injection stroke to the holding pressure switching point of the current shot.

Further, when the microcomputer switches from the speed feedback control to the pressure feedback control in the course of the primary injection stroke, from the switching point of this feedback control object to the holding pressure switching point of the current shot set as described above. During this period, based on the screw movement amount (distance) required to ensure that the speed is reduced to near 0, for example, the screw stroke value at the holding pressure switching point of this shot is reduced by the above distance. The pressure value on the pressure rise curve at the stroke value (screw forward position) is calculated as pressure data for the feedback control target switching timing, and this is held.

Then, the microcomputer performs speed feedback control from the start of the primary injection to an appropriate point before the holding pressure switching point, and monitors the measured pressure value during injection by this speed feedback control to measure the measured pressure value. When the pressure value for the feedback control target switching timing is reached, the pressure feedback control is switched to the pressure feedback control according to the pressure increase curve.

By performing such control, the resin pressure at the time of completion of filling (holding pressure switching point) can be kept constant even if the amount of measured resin varies from shot to shot, and overfilling can be prevented. At the same time, good pressure can be applied in the pressure-holding process after the pressure-holding switching point, the density of the molded product becomes stable, and the weight of the molded product becomes stable.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to one illustrated embodiment. FIG. 1 is a block diagram showing a main configuration of a control system in an injection molding machine according to an embodiment of the present invention. In FIG. 1, only a control system related to an injection process is shown.

In FIG. 1, reference numeral 1 is a microcomputer, which is actually an MPU, ROM, RAM,
It is composed of various I / O interfaces and the like, and executes various processes by various programs created in advance to control the entire machine (injection molding machine). For convenience of description, as described above, as the functional blocks related to the injection process, the storage unit 11 for fixed setting data for primary injection, the calculation / storage unit 12 for setting data for each shot for primary injection, and the setting data for pressure holding are provided. Injection section control section including storage section 13, speed feedback control section 14a, and pressure feedback control section 14b, clock section 15, speed calculation section 16, input processing section 1
The following description will be made on the assumption that the device has the elements 7, 18 and the like.

In FIG. 1, 2 is a stroke sensor for detecting the position of the screw, 3 is the resin pressure pressed by the screw (the pressure of the resin injected / filled into the mold).
Is a pressure sensor for detecting 4), 4 is an injection servomotor which is an injection drive source for moving the screw forward and backward, and 5 is a driver for the motor 4.

Prior to a detailed description of the structure and operation of this embodiment, referring to FIGS. 2 and 3, the measured resin amount and the pressure rise curve with respect to the screw stroke from the measured completion position (injection start position) are shown. The relationship will be described.

FIG. 2 is a schematic cross-sectional view of the main part of the heating cylinder of the injection molding machine according to this embodiment, in which the reference numeral 21 indicates the heating cylinder, and the reference numeral 22 indicates the end of the heating cylinder 21. Attached to the nozzle, 23
Is a screw provided in the heating cylinder 21 so as to be rotatable and movable back and forth.

As is well known, during the plasticizing / measuring process, the screw 23 is rotationally driven by a rotation driving motor (not shown), and the resin material supplied from the hopper (not shown) to the rear end side of the screw 23 is kneaded. -While being plasticized, it is transferred to the tip end side of the screw 23, and accordingly, the screw 23 moves backward while the back pressure is controlled by the injection servomotor 4. Then, when a predetermined amount of molten resin is stored on the tip side of the screw 23, that is,
The screw rotation is stopped when the metering completion position is reached.

The above-mentioned measurement completion position is preset to a predetermined value when the mold is replaced, and is managed by the amount of retreat of the screw 23 (retract stroke amount) based on the information from the stroke sensor 2. Has become. Figure 2
M1 indicates the reference measurement completion position, and at this time, the measurement resin amount 24 becomes the reference value. However, due to the expansion variation of the resin during the plasticizing / measuring process, the reaction force received from the molten resin measured by the screw 23 is not uniform, and strictly speaking, the measurement completion position is the standard measurement completion position. A variation occurs in the front and back with respect to the position MI,
The measurement completion position is the measurement completion position M where the amount of measurement resin is slightly large.
2 or the measurement completion position M3 where the amount of the measurement resin is slightly smaller may be set (in practice, the measurement completion position M2 is often set rather than the measurement completion position M3).

When the measurement completion position is the reference measurement completion position MI, the screw 23 causes the injection servomotor 4 to move.
Therefore, when the vehicle is driven forward by a preset forward stroke, the filling completion position is the reference filling completion position N.
The cushion amount 25 at this time becomes a reference value. On the other hand, when the measurement completion position is the measurement completion position M2 or the measurement completion position M3 described above and the screw 23 is driven forward by a preset advance stroke,
As a matter of course, the filling completion position shifts before and after the reference filling completion position N1, and the filling pressure at the filling completion position varies with respect to the preset filling completion pressure value. The pressure is not stable, and it becomes difficult to give a good holding pressure (the density of the molded product varies), which leads to the variation of the weight of the molded product.

By the way, there is a correlation between the measured resin amount and the pressure rise curve with respect to the screw stroke from the measurement completion position (injection start position). If the compression characteristic data for each resin type is determined, The pressure rise curve of can be obtained. FIG. 3 is a diagram showing an example of a pressure increase curve with respect to the screw stroke from the measurement completion position (injection start position) due to the difference in the measured resin amount.

In FIG. 3, S1 shows a pressure increase curve when the measurement completion position is the reference measurement completion position MI, and S2 is the measurement completion position M2 where the measurement resin amount is slightly large. A pressure increase curve in a certain case is shown, and S3 shows a pressure increase curve in a case where the measurement completion position is the measurement completion position M3 in which the amount of the measurement resin is slightly smaller. In each pressure rise curve S2, S1, S3,
The slope of the latter half of the stroke is different, and the slope of the pressure rise curve becomes steeper as the amount of measured resin decreases. As a result, the screw strokes from the respective measurement completion positions M2, M1, M3 until reaching the set filling pressure (preset filling completion pressure value) Pc have different values.

In the present embodiment, the operator gives the compression characteristic data of the resin to be used to the microcomputer 1 before the automatic molding operation of the machine is started, and the microcomputer 1 calculates the measured resin amount for each shot, Based on the calculated amount of measured resin and the compression characteristic data of the resin, the pressure increase curve for the screw stroke from the measurement completion position is obtained.

The description will be continued again with reference to FIG. The stroke sensor 2 detects the position information of the screw 23, and after the detection information is appropriately converted by the input processing unit 17, the calculation / storage unit 12 for the shot-specific setting data for the primary injection and the It is sent to the speed calculation unit 16 and the injection stroke control unit 14. The speed calculation unit 16 calculates the speed actual measurement value of the screw 23 in real time from the position data from the input processing unit 17 and the clock signal from the clock unit 15, and sends this to the injection stroke control unit 14. The pressure sensor 3 detects the resin pressure, and this detection information is appropriately converted by the input processing unit 18 and then sent to the injection stroke control unit 14.

The fixed setting data storage section 11 for the primary injection is stored in the storage section 11 for the speed setting value along with the screw stroke (screw position) for controlling the predetermined area of the primary injection area by the speed feedback control. The completed pressure value (set filling pressure) Pc and the like are stored. Further, the storage portion 13 of the setting data for holding pressure stores a pressure set value along the time axis for controlling the holding pressure region by pressure feedback control.

The calculation / storing unit 12 for the shot-by-shot setting data for the primary injection is input to the screw 23 from the stroke sensor 2 via the input processing unit 17 at the end of the plasticizing / measuring process of each shot cycle. The position where the measurement is completed is recognized, and the amount of the measured resin stored is calculated from the acquired position data of the measurement based on the mechanical dimension information of the injection system and the calculation formula given in advance. Next, calculate
The storage unit 12 uses learning data acquired by performing a case study in advance or a predetermined calculation formula based on the calculated measured resin amount and the compression characteristic data of the resin given in advance.
The pressure rise curve corresponding to the screw stroke from the above-mentioned measurement completion position is calculated, and this is used as the pressure set value along the screw stroke (screw position) for pressure feedback control at the end of the primary injection region of this shot. Set and store as (pressure control target value).

The calculating / storing unit 12 stores the preset filling completion pressure value (set filling pressure) Pc in the storing unit 11.
With reference to, the screw forward stroke (screw forward position) that matches the filling completion pressure value (set filling pressure) Pc in the obtained pressure increase curve is set and stored as the holding pressure switching point for the current shot.

Further, in the primary injection area, the calculating / storing unit 12 determines that the speed is, for example, from the time when the speed feedback control is switched to the pressure feedback control to the holding pressure switching point of the current shot. Based on the screw travel distance (distance L1) required to ensure that the speed is reduced to near 0, the screw stroke value (screw forward position) obtained by subtracting the distance L1 from the screw stroke value at the holding pressure switching point of this shot. ), The pressure value on the pressure rise curve is calculated as the pressure data for the switching timing from the speed feedback control to the pressure feedback control, and this is held. In addition, if the speed value at the time of switching from the speed feedback control to the pressure feedback control is constant, the distance L1 is
The value is the same for each shot, and can be easily obtained by conducting a case study or the like. In addition, the speed at which the holding pressure switching point is reached does not necessarily have to be close to 0.
There may be a case where the value is about%, and the point is that the speed at the time when the holding pressure switching point is reached does not affect the holding pressure control condition.

The injection stroke control section 14 determines the screw position information from the stroke sensor 2 based on the control condition data of the primary injection stroke and the pressure-holding stroke stored in each of the storage sections 11, 12, and 13. While referring to the resin pressure information from the pressure sensor 3 and the clock information from the clock unit 15, the speed feedback control unit 14a and the pressure feedback control unit 14b drive and control the injection servomotor 4 via the driver 5. To do. That is, the injection stroke control unit 14 performs speed feedback control along the screw stroke from the start of injection to the middle (end) of the primary injection region, from the end of the primary injection region to the holding pressure switching point (of primary injection). Until the end), pressure feedback control is performed along the screw stroke, and the pressure holding region is pressure feedback control along the time axis.

Next, the operation of the microcomputer 1 of this embodiment will be described with reference to FIG.
Will be explained. Every shot (every shot cycle)
After completion of the plasticization / measurement process for each of the above, the microcomputer 1 obtains the measurement completion position information from the measurement information from the stroke sensor 2 and calculates the stored amount of measured resin. Then, as described above, the pressure increase curve for the screw stroke from the measurement completion position (injection start position) is obtained based on the calculated measurement resin amount and the resin compression characteristic data.

When the measured measurement completion position is the reference measurement completion position M1, the pressure increase curve obtained from this is the above-described pressure increase curve S1, and the set filling completion pressure value is the set filling pressure. Since the pressure is Pc,
The microcomputer 1 sets the screw stroke (screw forward position) at the point on the pressure increase curve S1 in FIG. 4 that matches the set filling pressure Pc as the holding pressure switching point Xa1, and also performs the primary injection of the pressure increase curve S1. Set as the pressure control target value at the end of the stroke. Also, microcomputer 1
In the primary injection region, the speed is reduced to, for example, about 0 in the period from the time of switching from the speed feedback control to the pressure feedback control to the holding pressure switching point Xa1 of the current shot. The pressure value on the pressure increase curve S1 at the screw stroke value (screw forward position) obtained by subtracting the distance L1 from the screw stroke value at the pressure holding switching point Xa1 based on the screw movement amount (distance L1) necessary for guaranteeing. Vb1
Is calculated and set as pressure data for switching timing from speed feedback control to pressure feedback control.

After that, when the injection start timing is reached, the microcomputer 1 starts the injection control operation to drive the screw 23 forward from the measurement completion position (injection start position) by speed feedback control along the stroke. Begin to inject and fill the measured molten resin into the mold (not shown). During the injection operation by the speed feedback control, the measured speed value is measured in addition to the measured speed value for speed feedback control, and the measured pressure value is the pressure calculated and set as described above. It is monitored whether or not the value Vb1 has been reached.

With the progress of injection / filling by the speed feedback control, the measured pressure value is the pressure increase curve S1.
Rises almost in accordance with
reach b1. At the time when the measured pressure value matches the pressure value Vb1, the microcomputer 1 switches the control of the primary injection from the speed feedback control to the pressure feedback control, and the primary injection region after the screw forward position Xb1 at the pressure value Vb1 is Pressure feedback control along the screw stroke is performed so as to match the pressure increase curve S1.

When the operation at the final stage of the primary injection by the pressure feedback control progresses and the screw stroke reaches the pressure holding switching point Xa1, the microcomputer 1 enters the pressure holding stroke control, and according to the pressure holding setting condition, Performs pressure feedback control along the time axis. When the holding pressure switching point Xa1 is reached, the measured pressure value is equal to the set filling pressure Pc, and the measured speed value is almost 0. Therefore, the pressure application in the holding pressure region thereafter can be satisfactorily performed without variation. , The density of the molded product is stable, and the weight of the molded product is stable.

On the other hand, when the measured measurement completion position is the measurement completion position M2 in the case where the number of measurements is slightly large, the pressure increase curve to be obtained is the above-mentioned pressure increase curve S2. At this time, the microcomputer 1 causes the screw stroke (screw advance position) of the point on the pressure increase curve S2 in FIG. 4 that matches the set filling pressure Pc.
Is set as the holding pressure switching point Xa2, and the pressure increase curve S2 is set as the pressure control target value at the end of the primary injection stroke. Further, the microcomputer 1 decelerates the speed to, for example, near 0 in the primary injection region from the time of switching from the speed feedback control to the pressure feedback control to the holding pressure switching point Xa2 of the current shot. On the pressure increase curve S2 at the screw stroke value (screw forward position) obtained by subtracting the distance L1 from the screw stroke value at the holding pressure switching point Xa2 based on the screw movement amount (distance L1) required to ensure that Pressure value Vb2 is calculated and set as pressure data for switching timing from speed feedback control to pressure feedback control.

Similarly, after this, when the injection start timing is reached, the microcomputer 1 starts the injection control operation, and drives the screw 23 forward from the measurement completion position (injection start position) by speed feedback control along the stroke. , Start injection and filling of the measured molten resin into a mold (not shown). With the progress of injection / filling by the speed feedback control, the measured pressure value is the pressure increase curve S2.
Rises almost in accordance with
reach b2. At the time when the measured pressure value matches the pressure value Vb2, the microcomputer 1 switches the control of the primary injection from the speed feedback control to the pressure feedback control, and the primary injection region after the screw forward position Xb2 at the pressure value Vb2 is Pressure feedback control along the screw stroke is performed so as to match the pressure increase curve S2.

When the operation at the final stage of primary injection by the pressure feedback control progresses and the screw stroke reaches the pressure holding switching point Xa2, the microcomputer 1 enters the pressure holding stroke control, and according to the pressure holding setting condition, Performs pressure feedback control along the time axis. At the time when the holding pressure switching point Xa2 is reached, the measured pressure value is equal to the set filling pressure Pc and the measured speed value is almost 0, as before.
The subsequent application of pressure in the pressure holding region can be performed satisfactorily without variation, the density of the molded product is stable, and the weight of the molded product is stable.

Although not shown in FIG. 4, similar control is performed also when the weighing completion position is the above-described weighing completion position M3.

[0041]

As described above, according to the present invention, even if the measured resin amount for each shot is not strictly stable, the resin pressure at the completion of filling (holding pressure switching point) is not always constant. Get
Overfilling can be prevented and good pressure can be applied in the pressure-holding process, so that the weight of the molded product can be stabilized.
As a whole, an injection control method that greatly contributes to good product molding can be provided, and its value is enormous.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of an essential part schematically showing the front end side portion of the heating cylinder in the injection molding machine according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an example of a pressure increase curve with respect to a screw stroke from a measurement completion position (injection start position) due to a difference in measurement resin amount.

FIG. 4 is an explanatory diagram showing an injection control method according to an embodiment of the present invention.

[Explanation of symbols]

1 microcomputer (microcomputer) 2 stroke sensor 3 pressure sensor 4 injection servo motor 5 driver 11 storage unit for fixed setting data for primary injection 12 arithmetic / storage unit for shot setting data for primary injection 13 for holding pressure Setting data storage unit 14 Injection stroke control unit 14a Speed feedback control unit 14b Pressure feedback control unit 15 Clock unit 16 Speed calculation unit 17,18 Input processing unit 21 Heating cylinder 22 Nozzle 23 Screw 24 Weighing resin amount 25 Cushion amount

Claims (2)

[Claims] 1. A screw in a heating cylinder is rotated to transfer the resin material to the tip side of the screw while kneading and plasticizing the resin material, storing the measured molten resin at the tip side of the screw, and advancing the screw to move the metal. In an injection molding machine that injects and fills the molten resin into the mold, the metering completion position is measured for each shot, and the stored measured resin amount is calculated, and this measured resin amount and the compression characteristic data of the resin given in advance. Based on the, the pressure increase curve corresponding to the screw forward stroke from the metering completion position is calculated, and the screw forward stroke (screw forward position) that matches the preset filling completion pressure value in this pressure increase curve, The pressure rising curve is set from the middle of the primary injection stroke to the holding pressure switching point (of the primary injection stroke). Set as the pressure control target value up to the end point), speed feedback control is performed from the start of the primary injection to the point immediately before the holding pressure switching point, and the measured pressure value is monitored during injection by this speed feedback control. Then, when the measured pressure value reaches a predetermined pressure value in the pressure increase curve, the pressure feedback control is switched to the pressure feedback control according to the pressure increase curve. 2. The position according to claim 1, wherein the position for switching to the pressure feedback control is a position for ensuring that the speed at the time when the pressure holding switching point is reached is reduced to a sufficiently low speed. Control method for injection molding machine.