JP3414987B2 - Injection speed control method for 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 a method for controlling an injection speed of an injection molding machine, and in particular, it suppresses a variation in an injection filling amount due to a variation in a measurement stop position (measured value) and always produces a good product. The present invention relates to an injection speed control method for an injection molding machine.

[0002]

2. Description of the Related Art Conventionally, in injection molding of molten resin,
For example, as shown in FIG. 6, the horizontal axis represents the position or time T of the injection screw, and the vertical axis represents the forward speed V or pressure P of the injection screw. Filling step S1 of filling molten resin into
After the molten resin is filled, the injection control is performed by the pressure holding step S2 in which the pressure P is controlled and applied in multiple stages to the resin in the mold cavity to perform molding.

Generally, in the filling step S1, the pressure control valve of the hydraulic circuit is set to a high pressure, and the flow rate is changed in a plurality of stages based on the forward position of the injection screw or the elapsed time from the start of injection. The opening of the control valve is set to change according to the injection stroke position of the injection screw or with the passage of time. Therefore, the injection speed of the piston of the injection cylinder, that is, the injection screw is controlled by adjusting the flow rate control valve, and the molten resin is filled into the cavity at such a high speed that the resin in the mold cavity does not entrap air.

After the molten resin is filled in the cavity, the flow control valve is fixed to a relatively small opening,
Next, a pressure holding step S2 of adjusting the hydraulic pressure by the pressure adjusting valve is performed. This pressure holding step S2 is performed by a pressure adjusting valve so that a predetermined pressure can be applied to the molten resin filled in the cavity with the passage of time. The opening is changing.

In this case, in the injection speed control in the filling step, the control target value of the injection speed of a plurality of stages is switched when the detected value of the injection screw position coincides with the preset injection speed position.

However, when injecting the molten resin,
The timing of the operation of the check valve provided to prevent the molten resin located in front of the injection screw from flowing back to the injection screw side, that is, the operation of closing the check ring, differs from shot to shot.

However, in the conventional injection control method, the switching position between the injection speed and the injection pressure is set in advance as a fixed position, and in the shot when the closing operation of the check ring is delayed, the injection speed and the injection are set. The actual injection stroke in each section with the pressure becomes shorter. That is, in a shot in which the check ring closes slowly, the amount of work performed by the actual injection is reduced despite the setting of the same injection time and the same injection speed, which affects the weight and quality of the product, and The variation in the closing motion of the product causes variations in the weight and quality of the product. Further, in the shot in which the check ring is closed slowly, the injection time becomes long, and the molten resin in the mold cavity is cooled in a large amount due to the increase in the injection time.
There is a problem that the flow resistance in the mold cavity becomes large, the filling amount in the cavity becomes insufficient, and a defective molded product occurs.

Therefore, in the prior art, when switching to the pressure-holding process due to a decrease in the filling speed, if the measured value fluctuates due to some cause, among the strokes divided into multiple stages, the stroke of the first stage and the stroke of the final stage Since the stroke changes and the actual pressure change also fluctuates, a stable molded product cannot be obtained.Therefore, the measured set value set in the measuring setter and the measured value during plasticization by the screw position detector are Is calculated, and the calculation result is added / subtracted to / from the weighing set value and the speed switching position setting value set in the weighing setter and the speed switching position setting device to obtain the weighing correction value and the speed switching position correction value. When the filling process is controlled by the correction value and the screw speed decreases at the final stage of the filling process, and this speed value matches the value preset in the speed switching position setter, The method of controlling an injection molding machine which is configured to switch the pressure step has been proposed (KOKOKU 4-33
No. 254).

That is, as shown in FIG. 7, the apparatus for carrying out the control method of the injection molding machine according to the above-mentioned proposal has a barrel 1
0, screw 12, injection cylinder 14, injection plunger 16, in the initial state, the filling stroke S, that is, the set value of the weighing setter 18 is set to a plurality by the speed switching position setters 20a, 20b, ... 20n. It is divided. During molding, the measured value is S +
When it changes to Δε, the deviation calculator 24 calculates the deviation between the output of the screw position detector 22 and the set value of the measurement setting device 18, and this deviation Δε is calculated by the deviation setting device 18 and the speed switching position setting devices 20a, 20b. 20n is added / subtracted to each set value and given to the weighing compensator 26 and the speed switching position compensators 28a, 28b, ... 28n. As a result, the stroke of each stage is maintained constant, each corrected value is sent to the sequencer 30 during the injection process, and the amplifiers 31, 33 are provided.
The filling step is performed while controlling the flow rate adjusting valve 32 and the pressure adjusting valve 34 via the.

As the stroke of the final stage is reached and the mold cavity becomes full, the screw speed decreases, and the speed signal from the converter 36 and the holding pressure switching speed setter 3 are set.
The set value of 8 is compared by the comparator 40, and when both are in agreement, a signal is output to the sequencer 30 to switch to the pressure maintaining process, and the flow rate adjusting valve 32 and the pressure adjusting valve 34 are controlled to hold the pressure. The process is controlled for a predetermined time to finish the injection process.

According to the control method of the injection molding machine having such a structure, even if the measured value changes due to plasticization, each of the multiple strokes of the filling stroke does not change during the injection process, and each injection does not change. It is characterized in that the speed and pressure can be reproduced in the same state in the process.

Further, the screw should be stopped at the same time as the end signal of plasticization and metering, but it is slightly rotated due to the moment of inertia of the screw rotating body, and the amount of molten resin measured in this case is melted. From the viewpoint that it is difficult to keep constant due to instability of resin viscosity, instability of mechanical loss of rotating body, etc., the screw position detector detects the actual screw position immediately before the start of injection. , The detected value and the value of the memory that stores the screw position immediately before the start of injection at the previous shot are compared by the comparison calculator, the deviation is calculated, and the deviation is calculated by the addition / subtraction calculator. The stroke from the screw position immediately before the start of injection to each filling speed and holding pressure switching position is always added to or subtracted from the setting value set in the filling speed and holding pressure switching position setter. A method of controlling the injection process of an injection molding machine is proposed in which the correction is performed so that the correction value becomes constant, and when the corrected value and the detection value from the screw position detector match, switching control is performed. (Tokuhei 4-7097
No. 1).

That is, an apparatus for carrying out the injection process control method of the injection molding machine according to the above-mentioned proposal, as shown in FIG.
When the screw 12 in the cylinder 10 is driven by the hydraulic oil of the injection ram 14 and the position of the screw 12 is detected by the screw position detector 22 and the injection start signal 42 is issued. Is detected by the comparator 44 via the amplifier 44a.
The detected value obtained through the amplifier 44a is stored in the memory 4
It is stored in 8a as the screw position immediately before the start of injection of the latest shot. Further, the comparison calculator 46 is provided with the screw position immediately before the start of injection of the previous shot stored in the memory 48b. Then, the comparison calculator 46
Thus, the detected value of the screw position immediately before the start of injection of the main shot executed at that time is compared with the stored value of the screw position immediately before the start of injection of the previous shot, and the deviation Δs is output to the addition / subtraction calculator 50. To do. This adder / subtractor 50
Is to add or subtract the deviation Δs to the switching speed setting value of each filling speed and the holding pressure switching position setting device 52 to correct the setting value and replace the setting value with the correction value.
Use the set value for the next shot.

Further, since the actual position of the screw 12 is detected by the screw position detector 22 and the detected value is directly given to the adder / subtractor calculator 50 through the amplifier 44a, the detected value and the correction are corrected. When the set value matches the set value, a control signal is sent from the addition / subtraction calculator 48 to the pressure control valve 34 or the flow rate control valve 32 via the amplifier 44b.
Performs filling speed and holding pressure switching control. Then, the screw position immediately before injection of the latest shot stored in the storage device 48a is transferred to the storage device 48b by the pressure holding completion signal 54.

According to the injection process control method of the injection molding machine having the above-mentioned structure, after the measurement completion signal is issued,
Even if the screw position fluctuates just before the start of injection, the resin filling amount filled in the mold between each filling speed and holding pressure switching position is constant for each shot regardless of this fluctuation amount, and stable molding is always performed. It is characterized by being able to obtain goods.

[0016]

However, the conventional injection molding machine has the following problems due to its structure. That is, it is sufficient if the measured molten resin can be simply filled by advancing the screw, but in reality, it leaks to the rear part due to the closed state of the check valve for preventing backflow incorporated in the tip part of the screw. As a measure against this point, for example, in the initial stage of injection start, it is proposed to check and control the position where the check ring as a check valve is closed and the preset pressure is reached, as the formal injection filling process start position. .

That is, a check valve closing determination pressure for preventing backflow of molten resin is set at an arbitrary point in the filling process, and the injection screw position when the injection pressure reaches this determination pressure after the start of filling, According to the speed control method configured to perform arithmetic storage of the difference in the injection screw position at the judgment pressure in the preset reference shot and to switch the speed of the injection molding machine, the closing characteristic of the check valve at the time of injection Although it is possible to suppress the adverse effect of the variation, there are drawbacks such as not only a complicated structure but also an increase in manufacturing cost, which is not satisfactory.

Therefore, as a result of intensive studies, the present inventors calculated the deviation between the measurement stop position (measurement value) set in the reference measurement position setter and the screw position immediately before the injection filling process, and obtained the result. The specified deviation value is converted into a gradient change amount by a preset algorithm, and this is set as an initial rising gradient value of the injection speed to control the injection speed, and at the same time, it is configured to control the closing speed of the check ring. Therefore, the variation of the injection filling amount due to the variation of the measurement stop position, that is, the variation of the measured value, the initial rising gradient value of the injection speed is set, the closing speed of the check ring is controlled, and the amount of the molten resin flowing back is controlled. We have found that it can be controlled properly.

Therefore, an object of the present invention is to control the injection speed by calculating and setting the initial rising gradient value of the injection speed in order to suppress the dispersion of the injection filling amount due to the dispersion of the measured value in the injection molding machine. An object of the present invention is to provide an injection speed control method for an injection molding machine that can always achieve stable and good molding by controlling the closing speed of the check ring.

[0020]

In order to achieve the above object, an injection speed control method for an injection molding machine according to the present invention comprises a screw position detector for detecting an injection stroke position of an injection screw, and has a plurality of injection steps. In an injection molding machine configured to set different injection speeds and to control the injection speed based on the preset injection stroke position of the injection screw, a measuring stop position set in a reference measuring position setter and , The deviation from the screw position immediately before the injection filling process detected by the screw position detector is calculated, and the calculated deviation value is converted into a gradient change amount of the initial injection speed by a predetermined algorithm. Configured to set the amount as the initial rising slope value of the injection speed and control the injection speed, and also to control the closing speed of the check ring And wherein the Rukoto.

In this case, when the screw position detected by the screw position detector due to the metering stop is larger than the metering stop position set in the reference metering position setter, the initial rising gradient value of the injection speed is set relatively low. It is preferable to make the gradient small and set so as to delay the closing of the check ring.

Further, when the screw position detected by the screw position detector due to the metering stop is smaller than the metering stop position set in the reference metering position setter, the initial rising gradient value of the injection speed is relatively large. It is preferable to set the gradient so that the check ring closes faster.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of an injection speed control method for an injection molding machine according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an example of the configuration of a control device for carrying out the injection speed control method for an injection molding machine according to the present invention. Therefore, in FIG. 1, reference numeral 10 is a heating barrel, 12 is a screw, 14 is an injection cylinder, and a screw position detector 22 is provided for the screw 12.

Reference numeral 60 indicates a reference measuring position setting device. In the reference measuring position setting device 60, a backward limit position where the screw 12 is moved backward by the measurement is set. Further, the reference measurement position setting device 60 is used to determine the position after completion of screw measurement or the Japanese Patent Publication No. 2-175 by the applicant.
Set the backward limit position of the screw 12 during the molding cycle such as the suck back completion position as described in Japanese Patent Publication, and screw rotation or suck back to a preset screw position by a command from the sequencer described later. The screw retreating operation such as
Will stop.

However, due to the inertia of the rotation of the screw 12 and the action of the molten resin pressure, the actual screw stop position differs from the value set in the reference measuring position setter 60.

Therefore, the screw position detector 22 detects and sets the screw position immediately before the injection step of the next molding cycle, and the value of the detected actual position of the screw 12 and the reference measuring position setter 60. The deviation calculator 62 is configured to calculate the deviation from the value set in the above.

The deviation value obtained by the deviation calculator 62 is converted into a gradient change amount in the initial injection velocity gradient calculator 64 based on a required algorithm. The calculated value thus obtained is set as the initial rising gradient value of the injection speed, and is supplied to the control amplifier 68 of the flow control valve 70 provided in the hydraulic control circuit of the injection cylinder 14 via the sequencer 66. It is configured to send an opening degree command, control the flow rate of the hydraulic oil supplied from the hydraulic pressure source 72, and control the injection speed.

The control operation of the injection speed control device of the injection molding machine according to the above-described embodiment will be described with reference to FIGS.

As described above, in the present invention, the measurement stop position (measurement value) set in the reference measurement position setter 60 and the screw position immediately before the injection filling process detected by the screw position detector 22 are set. The deviation is calculated by the deviation calculator 62. Therefore, as shown in FIG. 2A, when the screw position detected by the screw position detector 22 accompanying the stop of the measurement is close to the measurement stop position set in the reference measurement position setter 60, The initial rising velocity gradient value of the injection velocity calculated by the initial injection velocity gradient calculator 64 becomes a medium gradient as shown in (b) of FIG. 2, an appropriate check ring is closed, and the melt flows backward from the check ring. The amount of resin is also properly maintained.

On the other hand, as shown in FIG. 3A, when the screw position detected by the screw position detector 22 due to the stop of the measurement is larger than the measurement stop position set in the reference measurement position setter 60, Initial injection velocity gradient calculator 64
The initial rising gradient value of the injection speed calculated by is a small gradient as shown in FIG. 3B, delays the closing of the check ring, and increases the amount of molten resin flowing back from the check ring. .

Further, as shown in FIG. 4A, when the screw position detected by the screw position detector 22 due to the stop of the measurement is smaller than the measurement stop position set in the reference measurement position setter 60, Initial injection velocity gradient calculator 64
The initial rising gradient value of the injection speed calculated by is a large gradient as shown in FIG. 4 (b), so that the check ring is closed faster and the amount of molten resin flowing back from the check ring is reduced. To do.

That is, as shown in FIG. 5, the screw position detected by the screw position detector 22 accompanying the stop of the measurement is set to the measurement stop position S set in the reference measurement position setter 60 as shown in FIG. In case of approximation, the acceleration coefficient k preset in the initial injection velocity gradient calculator 64
From × C (k is a constant, C is a coefficient set based on the deviation value obtained by the deviation calculator 62),
The following equation calculates the initial injection speed = k × C × acceleration × time with C = 1. In FIG. 3B, C <
1 and (b) of FIG. 4, C> 1 is set, and conversion calculation is performed into a gradient change amount based on a similar algorithm. Needless to say, C and k are appropriately set depending on molding conditions and resin.

By performing the control in this manner, it is possible to correct the variation in the injection filling amount due to the variation in the screw measurement stop position, and always achieve stable and good molding.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and many design changes can be made without departing from the spirit thereof.

[0036]

As is apparent from the above-described embodiments, the injection speed control method for an injection molding machine according to the present invention is equipped with a screw position detector for detecting the injection stroke position of the injection screw, and has a plurality of injection steps. In the injection molding machine configured to switch control based on the injection stroke position of the preset injection screw while setting different injection speeds, the measurement stop position set in the reference measurement position setter, Calculate the deviation from the screw position immediately before the injection and filling process detected by the screw position detector,
The calculated deviation value is converted into a gradient change amount of the initial injection speed by a predetermined algorithm, the gradient change amount is set as the initial rising slope value of the injection speed, and the injection speed control is performed. By controlling the closing speed, the injection speed control is performed by calculating and setting the initial rising gradient value of the injection speed in order to suppress the dispersion of the injection filling amount due to the dispersion of the measurement stop position (measurement value). At the same time, the closing speed of the check ring can be controlled to always achieve stable molding of a good product.

[Brief description of drawings]

FIG. 1 is a schematic configuration showing a configuration example of an injection control device of an injection molding machine that implements an injection speed control method according to the present invention and a control system diagram thereof.

FIG. 2 shows speed control characteristics by the injection speed control method according to the present invention, (a) is a general metering speed characteristic diagram, and (b) corresponds to the characteristics of (a). It is an injection velocity characteristic diagram which has an initial start-up characteristic of a medium gradient.

3A and 3B show speed control characteristics by the injection speed control method according to the present invention, FIG. 3A is a metering speed characteristic diagram when the metering stop position is relatively long, and FIG. It is an injection velocity characteristic diagram which has the initial starting characteristic of comparatively small gradient corresponding to the characteristic of (a).

4A and 4B show speed control characteristics by the injection speed control method according to the present invention, in which FIG. 4A is a metering speed characteristic diagram when the metering stop position is relatively short, and FIG. It is an injection velocity characteristic diagram which has the initial startup characteristic of comparatively large gradient corresponding to the characteristic of (a).

FIG. 5 is a characteristic diagram showing initial velocity characteristics of the injection molding machine calculated by an initial injection velocity gradient calculator based on a screw position detected by a screw position detector.

FIG. 6 is a characteristic diagram showing speed control characteristics and pressure control characteristics in a filling step and a pressure holding step in conventional injection control.

FIG. 7 is a system diagram showing a configuration example of an apparatus that implements a conventional injection molding machine control method.

FIG. 8 is a system diagram showing another configuration example of an apparatus for carrying out the process control method of the conventional injection molding machine.

[Explanation of symbols]

10 heating barrel 12 screws 14 injection cylinder 60 Standard weighing position setter 62 Deviation calculator 64 Initial injection velocity gradient calculator 66 Sequencer 68 Flow control valve amplifier 70 Flow control valve 72 Hydraulic source

Claims (3)

(57) [Claims] 1. A screw position detector for detecting an injection stroke position of an injection screw is provided, wherein an injection process is set to different injection speeds of a plurality of stages, and the injection speed is preset based on the injection stroke position of the injection screw. In an injection molding machine configured to switch control, calculate the deviation between the metering stop position set in the reference metering position setter and the screw position detected by the screw position detector immediately before the injection and filling process. The calculated deviation value is converted into a gradient change amount of the initial injection speed by a predetermined algorithm, and this gradient change amount is set as the initial rising slope value of the injection speed to control the injection speed and the closing speed of the check ring. Controlling the injection speed of the injection molding machine. 2. When the screw position detected by the screw position detector due to the metering stop is larger than the metering stop position set in the reference metering position setter, the initial rising gradient value of the injection speed is relatively small. The injection speed control method for an injection molding machine according to claim 1, wherein the gradient is set so that the check ring is closed more slowly. 3. When the screw position detected by the screw position detector due to the metering stop is smaller than the metering stop position set in the reference metering position setter, the initial rising gradient value of the injection speed is relatively large. The injection speed control method for an injection molding machine according to claim 1, wherein the gradient is set so that the check ring is closed earlier.