JPH0246370B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an injection molding machine, and particularly to a control mechanism for injection conditions such as injection speed and/or filling pressure during molding.

[Background of the invention]

Particularly in the case of precision molding among injection molding, it is necessary to accurately control injection conditions such as injection speed and filling pressure of synthetic resin during molding.

Methods for controlling the injection speed and filling pressure include relay control and control methods using a microcomputer. In addition, in order to improve the dimensional accuracy of molded products and prevent the occurrence of cracks, the injection speed is switched to multiple stages during the filling process, and the filling pressure (holding pressure) is also adjusted in the holding pressure process after filling.
Switching to multiple stages.

By the way, when switching the injection speed and filling pressure in this way, the above-mentioned relay control may cause variations in the on/off operation of the relay contacts.
The switching timing varies. Also,
In the case of microcomputer control, the movement state of the injection cylinder during the injection process (consisting of the filling process and pressure holding process) is detected by a sensor, and the injection speed and filling pressure are switched based on the data. However, the timing of switching varies depending on the sampling timing of the sensor.

Figures 9 and 10 are explanatory diagrams showing variations in injection speed. Figure 9 is the state before the response delay of the hydraulic system is added, and Figure 10 is the state after the response delay of the hydraulic system is added. are shown respectively.

In these figures, the arrow on the horizontal axis indicates the direction of movement of the injection cylinder, and in this example, from the start point (Po) of the injection cylinder to the holding pressure switching point (P ₄ )
In the filling process up to, an example is shown in which the injection speed is switched to four stages. That is, the first switching point (P ₁ ) and the second switching point correspond to the progress state of the injection cylinder.
The injection speed is switched at the switching point (P ₂ ) and the third switching point (P ₃ ), and the injection cylinder is at the first speed position from the start point (P ₀ ) until it reaches the first switching point (P ₁ ). Then, the injection speed is at the first speed (V ₁ ), and at the second speed position from the first switching point (P ₁ ) to the second switching point (P ₂ ), the injection speed is at the second speed (V ₂ ).
At the third speed position from the second switching point (P ₂ ) to the third switching point (P ₃ ), the injection speed is at the third speed (V ₃ ).
Furthermore, in the fourth speed position from the third switching point (P ₃ ) to the holding pressure switching point (P ₄ ), the injection speed is changed so that the molten resin is filled into the mold at the injection speed of the fourth speed (V ₄ ). The switch is now being made.

In these figures, the shaded areas near each switching time point (P ₁ to _{P 3} ) indicate the range of variation in actual switching timing. In other words, in the case of the above-mentioned relay control, if there is no delay in the ON/OFF operation of the relay contacts, for example, the first speed (V ₁ ) is switched from the second speed (V ₂ ) at the first switching point (P ₁ ). Although it changes,
Since relays are mechanical switching means using elastic contacts, there is inevitably a delay in on/off operation.
For example, after passing the first switching point (P ₁ ), the first speed (V ₁ ) is switched to the second speed (V ₂ ) with a delay.
This delay time (Δt ₁ , Δt ₂ , Δt _{3 ,} etc. in FIG. 9) varies depending on the relay used.

Furthermore, in the case of microcomputer control, the timing of sensor sampling is determined by a program. Therefore, while controlling each part of the injection molding machine according to a predetermined programmed routine, for example, if the sampling timing of the injection speed happens to coincide with the first switching point (P ₁ ), the 1st gear (V ₁ ) at the time
The engine switches to second speed (V ₂ ). However, in the control routine, if the first switching point (P ₁ ) comes after the step of sampling the injection speed, the conventional first switching point will continue until the next sampling step.
Injection is performed at the same speed (V ₁ ), and the injection speed is not sampled until the next sampling step, at which time the first speed (V ₁ ) is switched to the second speed (V ₂ ). In this case as well, a delay occurs in the switching operation. Therefore, the delay times (Δt ₁ , Δt ₂ , Δt _{3 ,} etc. in FIG. 9) vary depending on the correspondence between the sensor sampling timing in the program and the actual switching time.

The control section of the injection molding machine outputs a step output as shown in Figure 9, but the actual output to the injection cylinder is delayed due to the response delay of the hydraulic system.
Although the output pattern is as shown in the figure, the aforementioned delay times (Δt ₁ , Δt ₂ , Δt _{3 ,} etc.) appear as they are.

In the above example, the switching pattern of the injection speed was explained, but when switching the filling pressure, there is a delay in switching as well, and the delay time varies.

In this way, during the injection process, if there is a delay in switching the injection speed and filling pressure, and if the delay time varies, the amount of cushion in the injection molding will not be constant, resulting in residual strain in the molded product and deterioration in quality.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an injection molding machine that eliminates the above-mentioned drawbacks of the prior art and can produce molded products of stable quality.

[Summary of the invention]

In order to achieve the above object, the present invention detects injection conditions such as injection speed and/or filling pressure during molding at a predetermined sampling period, and compares the detected value with a preset target value. In an injection molding machine that is controlled to match the injection conditions with a target value by a control signal output based on the comparison result, for example, the first speed of the injection speed related to the injection conditions. a first target set value such as, for example, a second speed of injection speed, and a second target set value such as, for example, a first switching point at which the first target set value switches to a second target set value. the switching point, and the first switching point from that switching point.
a set value switching pattern in which the inclination angle changes linearly over time toward a second target set value from the target set value of A setting means such as a dial type or numeric keypad type setting device that can arbitrarily set the injection conditions, and a potentiometer for detecting the injection cylinder position or a filling device that detects the injection conditions at a predetermined sampling period according to a control program. A detection means such as a pressure gauge for detecting resin pressure is used to compare the detected value from the detection means with a target value preset by the setting means, and the injection conditions are set based on the comparison result. and a control section, such as a microcomputer, which outputs a control signal so that the value matches the target value set by the setting means.

The controller is configured to control the injection conditions so as to follow a preset setting value switching pattern when the switching point set by the setting means arrives. This is a characteristic feature.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram of a control device in an in-line screw injection molding machine according to this embodiment.

A pellet-like synthetic resin material 1 supplied from a hopper (not shown) is injected and filled into a mold (not shown) while being kneaded and plasticized by the rotation and advancement of a screw 2. This screw 2 is connected to an actuator 4 in a hydraulic cylinder 3, and oil in an oil tank 5 is pumped into the cylinder 3 by a hydraulic pump 6.
By being supplied to the rear chamber of the screw 2, the screw 2 moves forward. In this hydraulic circuit, there is a proportional solenoid valve 7 for speed control and a proportional solenoid valve 8 for pressure control.
Both electromagnetic valves 7 and 8 are connected to a central processing unit (CPU) 11 via an output port 10 of a control section 9.

A rack gear 13 is attached to the actuator 4 via a connecting bar 12, and a pion that meshes with the rack gear 13 is provided. An optical encoder 15 that rotates in synchronization with the pinion is installed, and the output thereof is input to the central processing unit 11 via an input port 16. Therefore, the rack gear 13, pinion 14, and encoder 15 constitute a detector for detecting the stop position of the tip of the screw 2 during the injection process, and a position signal from the encoder 15 is input to the control section 9. It's summery.

Although the encoder 15 is used in this embodiment, a potentiometer may be used instead.

Also connected to the input port 16 is a setting device 17, such as a dial type or numeric keypad type, for setting injection conditions such as injection speed, filling pressure, and cushion amount. 18 in the figure is a digital switch 19 which is connected to the central processing unit 11 via the input port 16, and the central processing unit 11 is adapted to send and receive signals to and from the memory 20.

FIG. 2 is a pattern diagram of the injection speed in the filling process. In this figure, the arrow on the horizontal axis indicates the advancing direction of the screw 2, and in this example, the screw 2 starts from the start point _P0 to the holding pressure switching point _P4.
In the filling process up to, an example is shown in which the injection speed is switched to four stages.

That is, the first switching time P ₁ , the second switching time P ₂ , and the third switching time are determined depending on the progress state of the screw 2.
The injection speed is set to be switched at _P3 . Then, in the first speed position until the tip of the screw 2 reaches the first switching point P1 from the start point _P0 , the injection speed is the first speed _V1 , and the injection speed is at the first speed _V1 .
In the second speed position from the switching point P ₁ to the second switching point P ₂ , the injection speed is the second speed V ₂ and the second switching point P ₂
In the third gear position from to the third switching point P ₃ , the third
At an injection speed of V ₃ , and at the 4th speed position from the 3rd switching point P ₃ to the holding pressure switching point P ₄ , the 4th speed V ₄
Each injection speed is set as a target value so that the synthetic resin is filled into the mold at an injection speed of .

The first switching pattern Q ₁ for decreasing from the first speed V ₁ to the second speed V ₂ at the first switching point P ₁ is
2nd speed V ₂ to 3rd speed V ₃ at the second switching point P ₂
The second switching pattern Q ₂ for lowering to V 3 further changes from the third speed V ₃ to the fourth speed V ₄ at the third switching point P ₃ .
A third switching pattern _Q3 is set for each of the above. Each of these switching patterns Q ₁ to _{Q 3}
is set to change linearly over time, and the inclination angles Θ of the switching patterns Q ₁ to _{Q 3} are all set to be the same.

3 to 5 are rough flowcharts showing part of the control program for an injection molding machine according to an embodiment of the present invention, with FIG. 3 showing the main routine, and FIGS. 4 and 5 respectively. This shows the subroutine.

First, the main routine will be explained with reference to FIG.

By turning on the power, the step (hereinafter S)
In step 1 (abbreviated as ), the initial live subroutine is called and the initial state is returned. Next, in S2, it is determined whether it is normal or abnormal, and if it is abnormal, a subroutine of the abnormality processing program is called in S3. If normal, proceed to S4,
A determination is made as to whether or not it is in the driving mode. If the driving mode is automatic driving or manual driving is determined in S5. If automatic driving, a subroutine of the automatic driving program is called in S6, and if manual driving is the automatic driving program. At S7, a subroutine of the manual operation program is called.

If it is determined in the above-mentioned S4 that the mode is not the exercise mode, the process proceeds to S8, where it is determined whether the mode is the mold thickness adjustment mode, and if YES, the subroutine of the mold thickness adjustment program is called in S9. If it is determined in S8 that the mode is not the mold thickness adjustment mode, the process proceeds to S10, where it is determined whether or not the screw removal mode is in effect.If yes, the subroutine of the screw removal program is called in S11, and if the screw removal mode is not in the screw removal mode, the next step is executed. It is programmed to proceed to step S2, and ultimately return to the previous stage of S2.

FIG. 4 shows the subroutine of the automatic driving program called in S6 mentioned above.

First, it is determined in S21 whether or not the cycle timer has timed up, and if yes, the cycle timer has timed up and is displayed in S22. If the cycle timer has not timed up, the process proceeds to the next step, and it is determined in S23 whether or not the step flag has been set. If the flag has not been set, it is determined in S24 whether mold clamping has been completed. As a result of the judgment, if mold clamping is not completed, a mold clamping preparation flag is set in S25, and if mold clamping is complete, a nozzle touch flag is set in S26.

If the above-mentioned S23 is determined to be YES, it is determined in S24 whether or not the mold clamping preparation flag has been set.
If YES, the mold clamping preparation program subroutine is called in S25. Next, it is determined in S26 whether the mold clamping flag has been set, and if YES, the subroutine of the mold clamping program is called in S27. Next, in S28, it is determined whether or not the nozzle touch flag has been set, and if YES, S28 is performed.
At step 29, the subroutine of the nozzle touch program is called. Next, it is determined in S30 whether or not the injection flag has been set, and if YES, a subroutine of the injection program is called in S31.
Next, it is determined in S32 whether the charge flag has been set, and if YES, the subroutine of the charge program is called in S33.

FIG. 5 shows the subroutine of the injection program called in S31 described above.

First, in S41, it is determined whether or not the heating tube temperature has been raised. If the temperature has been raised, the process proceeds to S42, and it is determined whether or not the nozzle touch has been completed. If it has been completed, the process advances to the next step. After other judgments and executions (not shown) are made, it is determined in S50 whether the position of the tip of the screw is in the first speed position, and if so, in S51 the position is in the first speed position.
At V ₁ , the mold is filled with synthetic resin. When it is determined in S52 that the position of the tip of the screw has reached the second speed position as the screw advances, the synthetic resin is filled in the second speed _V2 in S53. When it is determined in S54 that the tip position has reached the third speed position, S5
4, filling with synthetic resin takes place in third speed _V3 . During these filling steps, the first filling pressure is maintained in S56, a check is made in S57 as to whether or not the filling step has been completed, and when the filling step is completed, an indication that the filling step has been completed is displayed in S58.

When it is determined in S59 that the position of the tip of the screw has reached the fourth speed position, the injection speed is switched to the fourth speed in S60, and the filling pressure is also switched to the second filling pressure in S61. If the answer is NO in S59, the process advances to S62 and a charge flag is set.

Figures 6 and 7 show the first switching pattern.
FIG. 3 is a diagram showing the relationship between Q ₁ and the sampling period of injection speed.

As mentioned above, the injection speed changes from the first speed V1 to the second speed _V1 .
A linear first switching pattern Q ₁ that changes linearly over time when switching to speed V ₂ is set in advance.

In the case of FIG. 6, an example is shown in which the first switching point _P1 and the sampling period of the injection speed exactly match. In other words, even if the injection speed is detected at the first switching point _P1 , it is the first speed _V1 at that time.
Until the next sampling of the injection speed, S is filled at the first speed. Then, during the next sampling, the injection speed V _1-1 on the first switching pattern Q ₁
The injection speed is lowered _to
Switched to V ₂ .

The case in FIG. 7 shows an example in which the injection speed was sampled a little before the first switching point _P1 . In this case as well, the set first switching pattern Q ₁
Accordingly, the injection speed changes gradually in steps such as V _1-1 , V _1-2 , and V _1-3 , and is finally switched to the second speed V ₂ .

Figure 8 shows the inclination angle Θ of the switching pattern Q, the oil pressure,
FIG. 2 is a diagram showing a relationship between an actuation delay A of an actuator that operates an injection cylinder (screw, etc.) by air pressure or a motor, and an inclination angle ΘA. As shown in the figure, the inclination angle Θ of the switching pattern Q
If is set to be larger than the inclination angle ΘA of the actuation delay A of the actuator, the actuation delay A can be absorbed by the switching pattern Q.

In the above embodiment, switching of the injection speed has been described, but switching of the filling pressure is also carried out in the same manner.

〔Effect of the invention〕

Since the present invention is configured as described above,
The output pattern when changing injection conditions such as injection speed and (and) filling pressure is almost constant in all cases, with no variation, and the delay in the actuator that operates the injection cylinder can be absorbed, resulting in stable quality. This enables precise molding.

[Brief explanation of the drawing]

1 to 8 are for explaining an embodiment of the present invention. FIG. 1 is a functional block diagram of a control device in an injection molding machine, FIG. 2 is a pattern diagram of injection speed in the filling process, and FIG. Figure 3 is a partial flowchart of the main routine, Figure 4 is a partial flowchart of the automatic operation program, Figure 5 is a partial flowchart of the injection program, and Figures 6 and 7 are a flowchart of switching patterns and sampling. FIG. 8 is an explanatory diagram showing the relationship between the inclination angle of the switching pattern and the inclination angle of actuator activation delay. FIGS. 9 and 10 are explanatory diagrams showing the variation in injection speed in the conventional method. It is a diagram. 2... Screw, 3... Hydraulic cylinder, 7...
...Proportional solenoid valve for speed control, 8...Proportional solenoid valve for pressure control, 9...Control unit, 11...Central processing unit, 13...Rack gear, 14...Pinion, 15...Encoder, 16... input port,
17... Setting device, P ₀ to P ₃ ... Switching point, V ₁ to _{V 4}
...Injection speed, Q ₁ ~ Q ₃ ...Switching pattern, Θ...
...Inclination angle of switching pattern, A...Actuator delay, ΘA...Inclination angle of action delay.

Claims (1)

[Claims] 1. Injection conditions such as injection speed and/or filling pressure during molding are detected at a predetermined sampling period, and the detected value and a preset target value are compared and calculated. , in an injection molding machine that is controlled so that the injection conditions match a target value by a control signal output based on the comparison result, a first target setting value related to the injection condition;
a second target set value, a switching point at which the first target set value switches to the second target set value, and a change from the first target set value toward the second target set value from the switching point; a setting means that can arbitrarily set a setting value switching pattern that changes linearly over time and sets an inclination angle of a pattern that is larger than the inclination angle of the operation delay of the actuator that operates the injection cylinder; a detection means for detecting the condition at a predetermined sampling period; and a comparison operation with a target value set in advance by the detection means, and the setting means sets the injection condition based on the comparison result. a control unit that outputs a control signal to match a set target value, and when the switching point set by the setting means is reached, the injection condition is changed to a set value switching pattern that deviates from the preset value. An injection molding machine, characterized in that the injection molding machine is configured to be controlled by the control section so as to follow the directions of the injection molding machine.