JP3292622B2 - Injection control device of injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection control apparatus for an in-line screw type injection molding machine, and more particularly to an injection control apparatus for an injection molding machine which stabilizes the pressure at the time of filling completion (holding pressure switching point). It relates to a control device .

[0002]

2. Description of the Related Art A servo motor is used as an injection drive source,
An injection molding machine in which the injection process (the primary injection process and the subsequent pressure-holding process) is feedback-controlled is capable of precise speed feedback control and pressure feedback control. I have.

[0003] In an injection molding machine that performs such feedback control, usually, the speed of the primary injection stroke (the stroke from the metering completion position (injection start position) to the filling completion position (hold pressure switching point)) is controlled by speed feedback. And the pressure-holding process is controlled by pressure feedback. That is, during the primary injection stroke period, a speed target value is set, and speed feedback control is performed so that the actual speed value matches the speed target value. During the pressure-holding stroke period, a pressure target value is set. The pressure feedback control was performed so that the measured pressure values coincided with each other.

[0004]

However, as described above, in the prior art, since the speed feedback control is performed until the end of the primary injection stroke, the resin pressure at the end of the primary injection stroke becomes larger due to an unexpected situation. Even if the pressure is increased (for example, due to completion of filling before the pressure holding switching point),
Since the speed feedback control is forcibly performed so as to keep the speed corresponding to the speed target value, the resin pressure is further increased, and sometimes the pressure is added with the maximum torque of the machine (injection molding machine). And there is a problem that it may cause extreme overfilling (overpacking).

Further, even if the pressure feedback control is immediately switched to when the filling is completed (the pressure holding switching point), the resin pressure value at the pressure holding switching point varies, and the response of the controller system is delayed. There is also a problem that a surge occurs in the resin pressure at the beginning of the pressure stroke.

[0006] Further, if the amount of resin measured for each shot is not stable (the measurement completion position is not stable), there is a problem that the weight of the molded product is not stable, and it is not possible to achieve good molding.

It is to be noted that a method of switching from speed feedback control to pressure feedback control at a predetermined position before the point of time when the filling is completed (holding pressure switching point) may be considered. Regardless, since the same pressure target value is always set, there is also a problem that the weight of the molded product is not stable due to the variation in the amount of the measured resin.

[0008] The present invention has been made in view of the above points,
The purpose is to ensure that the resin pressure at the time of filling completion (holding pressure switching point) can always be kept constant even if the measured resin amount for each shot is not strictly stable, thereby preventing overfilling and Another object of the present invention is to provide an injection molding machine which can apply a good pressure in the pressure-holding process and can stabilize the weight of a molded product, which greatly contributes to good-quality molding as a whole.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to an in-line screw type injection molding machine, in which a measurement completion position is measured and stored for each shot (each shot cycle). Calculate the amount, calculate the pressure rise curve corresponding to the screw advance stroke from the metering completion position based on the measured resin amount and the compression characteristic data of the resin given in advance, and set the pressure rise curve in this pressure rise curve in advance. Screw advance stroke (screw advance position) that matches the completed filling pressure value
Is set as a pressure-holding switching point, and the pressure rise curve is set as a pressure control target value from the middle of the primary injection stroke to the pressure-holding switching point. Up to this point, the speed feedback control is performed, and the actual measured pressure value is monitored during injection by the speed feedback control, and when the measured actual pressure value reaches a predetermined pressure value in the pressure rise curve, the pressure rise curve is changed. Accordingly, the pressure feedback control is performed.

[0010]

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

The microcomputer uses the data of the pressure rise curve obtained as described above to determine the screw stroke (screw advance position) in this pressure rise curve that matches a preset filling completion pressure value in the current shot. And the pressure rise curve is set as a pressure control target value from the middle of the primary injection stroke to the pressure holding 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, the microcomputer operates from the switching point of the feedback control object to the pressure holding switching point of the current shot set as described above. In the meantime, based on the screw movement amount (distance) necessary to ensure that the speed is reduced to, for example, almost 0, the screw obtained by subtracting the above distance from the screw stroke value of the holding pressure switching point of the current shot The pressure value on the pressure rise curve at the stroke value (screw forward position) is calculated as the pressure data for the feedback control target switching timing, and is held.

The microcomputer performs the speed feedback control from the start of the primary injection to a point shortly before the holding pressure switching point, and monitors the measured pressure value during the injection by the speed feedback control. When the pressure reaches the pressure value for the feedback control target switching timing, the pressure is switched to the pressure feedback control according to the pressure rise curve.

By performing such control, the resin pressure at the time of completion of filling (holding pressure switching point) can always be kept constant even if the amount of resin measured for each shot varies, 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, and the density of the molded product is stabilized, and thus the weight of the molded product is stabilized.

[0015]

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

In FIG. 1, reference numeral 1 denotes a microcomputer, which is actually an MPU, ROM, RAM,
It is configured with various I / O interfaces and the like, executes various processes by various programs created in advance, and controls the overall control of the machine (injection molding machine). For the sake of convenience, as described above, as the functional blocks related to the injection stroke, the storage unit 11 for the fixed setting data for the primary injection, the calculation / storage unit 12 for the shot-specific setting data for the primary injection, the setting data for the pressure holding Storage unit 13, an injection stroke control unit including a speed feedback control unit 14a and a pressure feedback control unit 14b, a clock unit 15, a speed calculation unit 16, an input processing unit 1.
The following description will be given assuming that the device includes 7, 18, and the like.

In FIG. 1, reference numeral 2 denotes a stroke sensor for detecting the position of the screw, and 3 denotes a resin pressure pressed by the screw (pressure of the resin injected and filled into the mold).
Is an injection servomotor as an injection drive source for moving the screw back and forth, and 5 is a driver of the motor 4.

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

FIG. 2 is a schematic sectional view of a main part of a heating cylinder in the injection molding machine according to the present embodiment, in which 21 is a heating cylinder, and 22 is a tip of the heating cylinder 21. Nozzle mounted on 23
Is a screw provided in the heating cylinder 21 so as to be able to rotate and move forward and backward.

As is well known, during the plasticizing and metering process, the screw 23 is driven to rotate by a rotation driving motor (not shown), and the resin material supplied to the rear end of the screw 23 from a hopper (not shown) is kneaded. -While being plasticized, it is transferred to the tip side of the screw 23, and the screw 23 retreats while controlling the back pressure by the injection servomotor 4 with this. Then, when a predetermined amount of molten resin is stored at the tip side of the screw 23, that is,
The screw rotation is stopped when the weighing is completed.

The above-mentioned weighing completion position is set in advance to a predetermined value when the mold is replaced, and is controlled by the retreat amount (retreat stroke amount) of the screw 23 based on the information from the stroke sensor 2. Has become. FIG.
Represents the reference weighing completion position, and at this time, the measured resin amount 24 becomes the reference value. However, the reaction force received from the measured molten resin by the screw 23 is not uniform due to variations in the expansion of the resin during the plasticization / measurement process. Variations occur before and after the position MI,
The weighing completion position is the weighing completion position M where the amount of weighing resin is slightly larger.
2, or may take a weighing completed position M3 where the amount of weighed resin is slightly smaller (in practice, the weighing completed position M2 is often taken more than the weighing completed position M3).

When the measurement completion position is the reference measurement completion position MI, the screw 23
Is driven forward by a predetermined forward stroke, the filling completion position becomes the reference filling completion position N
1 and the cushion amount 25 at this time becomes a reference value. On the other hand, when the screw 23 is driven forward by a preset forward stroke when the measurement completion position is the measurement completion position M2 or the measurement completion position M3 described above,
Naturally, the filling completion position is shifted 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 apply a good holding pressure (the density of the molded product varies), which leads to the variation in 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 metering completion position (injection start position). If the compression characteristic data for each resin type is determined, the measured resin amount is calculated as follows. Can be obtained. FIG. 3 is a diagram illustrating an example of a pressure rise curve with respect to a screw stroke from a metering completion position (injection start position) due to a difference in a metering resin amount.

In FIG. 3, S1 shows a pressure rise curve when the weighing completion position is the reference weighing completion position MI, and S2 is a weighing completion position M2 where the weighing resin amount is slightly larger. A pressure rise curve in a certain case is shown, and S3 shows a pressure rise curve in a case where the measurement completion position is a measurement completion position M3 where 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 metering resin amount becomes smaller. As a result, the screw strokes from the weighing completion positions M2, M1 and M3 to the set filling pressure (preset filling completion pressure value) Pc have different values.

In this 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 measured resin amount and the compression characteristic data of the resin, a pressure rise curve with respect to the screw stroke from the metering completion position is obtained.

The description will be continued with reference to FIG. The stroke sensor 2 detects the position information of the screw 23, and after this 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 calculating section 16 calculates the actual measured value of the speed of the screw 23 in real time based on the position data from the input processing section 17 and the clock signal from the clock section 15, and sends it to the injection stroke control section 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.

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

The calculation and storage unit 12 of the shot-specific setting data for the primary injection stores the screw 23 input from the stroke sensor 2 via the input processing unit 17 at the end of the plasticizing and measuring process of each shot cycle. The metering completion position is recognized based on the position information (1), and the stored metering resin amount is calculated from the acquired measurement completion position data based on the injection system mechanical dimension information and the calculation formula given in advance. Next,
The storage unit 12 uses learning data obtained through a case study in advance based on the calculated measured resin amount and compression characteristic data of the resin given in advance, or from a predetermined calculation formula,
A pressure rise curve corresponding to the screw stroke from the above-mentioned metering completion position is calculated, and this is set as a pressure set value along the screw stroke (screw position) for pressure feedback control at the end of the primary injection region of the current shot. (Target pressure control value) is set and stored.

The calculation / storage section 12 stores a preset filling completion pressure value (set filling pressure) Pc in the storage section 11.
, The screw advance stroke (screw advance position) that matches the filling completion pressure value (set filling pressure) Pc in the obtained pressure rise curve is set and stored as the pressure holding switching point of the current shot.

Further, in the primary injection region, the operation / storage unit 12 controls the speed, for example, from the time when the speed feedback control is switched to the pressure feedback control to the time when the pressure holding switching point of the current shot is reached. A screw stroke value (screw forward position) obtained by subtracting the distance L1 from the screw stroke value of the pressure-holding switching point of the current shot based on the screw movement amount (distance L1) necessary to guarantee that the speed is reduced to almost zero. ) Is calculated as pressure data for switching timing from the speed feedback control to the pressure feedback control and held. Note that the distance L1 is constant if the speed value when switching from speed feedback control to pressure feedback control is constant.
The value is the same for each shot, and can be easily obtained by performing a case study or the like. In addition, the speed at the time when the pressure-holding switching point is reached is not always required to be near 0, and depending on the control condition of the molded product, the maximum speed is several tens of times.
In some cases, a value of about% may be acceptable, and the point is that the speed at the time when the pressure holding switching point is reached does not affect the pressure holding control condition.

The injection stroke control unit 14 controls the screw position information from the stroke sensor 2 on the basis of the control condition data of the primary injection stroke and the pressure-holding stroke stored in each of the storage units 11, 12, and 13. The speed feedback control unit 14a and the pressure feedback control unit 14b drive and control the injection servomotor 4 via the driver 5 with reference to the resin pressure information from the pressure sensor 3 and the clock information from the clock unit 15. I 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, and performs the pressure holding switching point (primary injection) from the end of the primary injection region. Until the end), the pressure feedback control along the screw stroke is performed, and the pressure holding area performs the pressure feedback control along the time axis.

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

When the measured weighing completion position is the reference weighing completion position M1, the pressure rise curve obtained therefrom is the above-mentioned pressure rise curve S1, and the set filling completion pressure value is the set filling completion pressure value. Pressure Pc
The microcomputer 1 sets a screw stroke (screw forward position) at a point corresponding to the set charging pressure Pc on the pressure rise curve S1 in FIG. 4 as the pressure-holding switching point Xa1, and primary injection of the pressure rise curve S1. Set as the pressure control target value at the end of the stroke. Also, microcomputer 1
States that the speed is reduced to, for example, almost 0 in the primary injection region from the time when the speed feedback control is switched to the pressure feedback control to the time when the pressure holding switching point Xa1 of the current shot is reached. A pressure value on the pressure rise curve S1 at a 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.

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

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

When the operation at the end of the primary injection by the pressure feedback control proceeds and the screw stroke reaches the pressure-holding switching point Xa1, the microcomputer 1 starts to control the pressure-holding stroke, and according to the pressure-holding setting condition, Perform pressure feedback control along the time axis. When the pressure-holding switching point Xa1 is reached, the measured pressure value is equal to the set charging pressure Pc, and the measured speed value is almost 0, so that the pressure can be satisfactorily applied in the pressure-holding region thereafter without variation. In addition, the density of the molded product is stabilized, and the weight of the molded product is stabilized.

On the other hand, when the measured weighing completion position is the weighing completion position M2 in the case where the weighing is slightly more, the obtained pressure rise curve is the above-described pressure rise curve S2. At this time, the microcomputer 1 determines the screw stroke (screw forward position) at the point that matches the set charging pressure Pc on the pressure rise curve S2 in FIG.
Is set as the pressure holding switching point Xa2, and the pressure rise curve S2 is set as the pressure control target value at the end of the primary injection stroke. Further, the microcomputer 1 reduces the speed to, for example, almost near 0 in the primary injection region from the time when the speed feedback control is switched to the pressure feedback control until the pressure holding switching point Xa2 of the current shot is reached. On the pressure rise curve S2 at a screw stroke value (screw forward position) obtained by subtracting the distance L1 from the screw stroke value at the pressure-holding switching point Xa2 based on the screw movement amount (distance L1) necessary to ensure that the screw movement is performed. Is calculated and set as pressure data for switching timing from speed feedback control to pressure feedback control.

Thereafter, similarly, 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 the speed feedback control along the stroke. Then, injection and filling of the measured molten resin into a mold (not shown) are started. With the progress of injection / filling by this speed feedback control, the actual measured pressure value becomes the pressure rise curve S2.
Rises almost in accordance with
reaches b2. When the measured pressure value matches the pressure value Vb2, the microcomputer 1 switches the primary injection control from the speed feedback control to the pressure feedback control, and the primary injection area after the screw advance position Xb2 at the pressure value Vb2 is Pressure feedback control is performed along the screw stroke so as to match the pressure rise curve S2.

When the operation at the end of the primary injection by the pressure feedback control proceeds and the screw stroke reaches the pressure-holding switching point Xa2, the microcomputer 1 starts to control the pressure-holding stroke, and according to the pressure-holding setting condition, Perform pressure feedback control along the time axis. When the pressure-holding switching point Xa2 is reached, the measured pressure value is equal to the set charging pressure Pc and the measured speed value is almost 0, as described above.
The subsequent application of pressure in the pressure holding region can be performed satisfactorily without variation, the density of the molded product is stabilized, and the weight of the molded product is stabilized.

Although not shown in FIG. 4, the same control is performed when the measurement completion position is the measurement completion position M3 described above.

[0041]

As described above, according to the present invention, the resin pressure at the time of completion of filling (holding pressure switching point) is not always kept constant even if the amount of resin measured for each shot is not strictly stable. Get
While being able to prevent overfilling, it is possible to apply a good pressure during the pressure-holding process, thereby stabilizing the weight of the molded product.
In general, an injection molding machine that greatly contributes to good-quality molding can be provided, and its value is enormous.

[Brief description of the drawings]

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

FIG. 2 is a schematic cross-sectional view of a main part of a tip end portion of a heating cylinder in an injection molding machine according to one embodiment of the present invention.

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

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Microcomputer (microcomputer) 2 Stroke sensor 3 Pressure sensor 4 Servo motor for injection 5 Driver 11 Storage part of fixed setting data for primary injection 12 Calculation / storage part of shot setting data for primary injection 13 Storage 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 Measured resin amount 25 Cushion amount

Claims (2)

(57) [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, store the measured molten resin at the tip end of the screw, and advance the screw by moving the screw. In an injection molding machine that injects and fills the molten resin into the mold, the metering completion position is measured for each shot, the amount of the metered resin stored is calculated, and the measured resin amount and the compression characteristic data of the resin given in advance are calculated. Based on the above, a pressure rise curve corresponding to the screw advance stroke from the metering completion position is calculated, and a screw advance stroke (screw advance position) corresponding to a preset filling completion pressure value in this pressure rise curve is calculated as follows: The pressure rising curve is set as the pressure holding switching point, and the pressure rise curve is set from the middle of the primary injection stroke. Pressure control target value up to the end point), speed feedback control is performed from the start of the primary injection to a point shortly before the holding pressure switching point, and the measured pressure value is monitored during injection by the speed feedback control. An injection control device for an injection molding machine, wherein when the measured pressure value reaches a predetermined pressure value in the pressure rise curve, the control is switched to pressure feedback control according to the pressure rise curve. 2. The method 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 sufficiently reduced to a low speed. Control device of injection molding machine.