JP3534990B2 - Control method 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 a method for controlling an in-line screw type injection molding machine, and more particularly to a method for controlling a measuring process suitable for stabilizing the resin density.

[0002]

2. Description of the Related Art In an in-line screw type injection molding machine, as is well known, by rotating and retreating a screw, the plasticized molten resin is stored in the tip side of the screw for measurement.

In the above-mentioned metering process , generally, the backward stroke of the screw to the metering completion position is set (the metering completion position is set), and when the injection drive source is a hydraulic cylinder, the screw rotation is performed. Number and back pressure are set, the screw rotation speed and back pressure are controlled according to these setting conditions, and when the injection drive source is an electric servomotor, the screw rotation speed and screw tip resin pressure are set. Set and control the screw rotation speed and the pressure that the screw receives by the resin according to these setting conditions.In any case, when the measurement completion position is reached, the screw rotation and retreat operations are stopped It was supposed to finish the process .

FIG. 3 shows one of the states of the conventional weighing process described above.
In the figure showing an example, in the figure, the horizontal axis represents the retracted position of the screw, and the vertical axis represents the screw rotation speed and the resin pressure. As shown in FIG. 3, in the conventional metering operation, the timing of completion of metering is determined by the retracted position of the screw (reverse stroke of the screw), and when the metering completed position is reached, the retracting operation of the screw is stopped. The measurement completion position is always fixed.

[0005]

As described above, in the conventional measuring operation, the timing of the completion of the measurement is defined by the backward stroke of the screw, and the measurement completion position is always constant. There is a problem that the density of the resin (molten resin) stored on the tip side of the is likely to vary. This will be described with reference to FIG.

FIG. 4 is a view showing a main mechanism of an electric drive type injection molding machine. In FIG. 4, 51 is a heating cylinder, and 52 is arranged in the heating cylinder 51 so as to be rotatable and forward / backward. Screw 53, hopper 53 for supplying the raw material resin, 54 a pulley which rotates integrally with the screw 52, 55 a servomotor for measurement which is a metering drive source for rotationally driving the pulley 54, 56 converts rotational motion into linear motion Rotation to linear motion conversion mechanism transmitted to the screw 52, 57 is an injection servomotor which is an injection drive source for rotationally driving the rotated part of the rotation to linear motion conversion mechanism 56, and 58 is a load cell for detecting the pressure applied to the screw 52. Is. Note that in the configuration shown in FIG.
The measuring servomotor 55 is configured to move forward and backward together with the screw 52.

In an injection molding machine, since it is difficult to directly detect the pressure of the resin stored on the tip side of the screw 52, a load cell 58 is attached coaxially with the screw 52 as shown in FIG. , This load cell 58
The detection output by is replaced with the resin pressure value.

By the way, the pressure detected by the load cell 58 and P _L Now, when the actual pressure of the resin was P _A, during the rotation of the screw 52 is not P _A and P _L are equal, screws rotating in the load cell 58 Since the propulsive force (pressure) P _B (P _B <P _A ) from 52 acts, the load cell 5
The detected pressure P _{L of} 8 is actually P _L = P _A + P _B.

Here, the propulsive force (pressure) P _B generated by the screw 52 is generated between the screw 52 and the resin and between the heating cylinder 5 and the heating cylinder 5.
It is liable to fluctuate due to fluctuations in the frictional force between the inner surface of No. 1 and the resin. Therefore, even if pressure feedback control is performed so that the detected pressure P _L of the load cell 58 matches the set resin pressure, propulsion by the screw 52 is performed. Power (pressure) P _B
There the variation, the actual pressure P _A of the resin will exhibit a variation. Therefore, the resin density of the molten resin that has been measured and stored fluctuates, which is an impeding factor in achieving good product molding. In the experiment by the inventors of the present application, in the conventional measuring method, the variation in the resin density is 3-4.
It was about%.

The present invention has been made in view of the above points,
The purpose is to reduce the variation in the resin density of the molten resin that is measured and stored as much as possible.

[0011]

In order to achieve the above-mentioned object, the present invention provides a metering drive source for rotatably driving a screw, which is arranged in a heating cylinder so that the screw can rotate and move forward and backward. In- line screw type injection molding equipped with an injection drive source that drives forward and backward
A method for controlling a metering process in the machine, first screw
Rotate the screw while controlling the pressure on the
Stop the screw rotation, and the screw stops rotating
Continues pressure control for the screw even after
The timing at which the axial movement of the screw stopped
Then, the pressure control for the screw is terminated.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a main configuration of an inline screw type injection molding machine according to one embodiment (hereinafter, referred to as this embodiment) of the present invention, in which a mechanism shows only measurement and control, and a control system. Shows only the measurement system.

In FIG. 1, 1 is a heating cylinder, 2 is a screw arranged in the heating cylinder 1 so as to be able to rotate and move back and forth, 3 is a servomotor for measurement as a measurement drive source, 3a is for measurement. Output pulley of servo motor 3, 4 is a timing belt for transmitting the rotation of output pulley 3a to pulley 5 coupled to the rear end of screw 2, 6 is an injection servo motor as an injection drive source, and 6a is an injection servo motor 6 is an output pulley, 7 is a timing belt for transmitting the rotation of the output pulley 6a to the pulley 8a of the rotation-> linear motion conversion mechanism 8, and 8 is a ball screw mechanism for converting the rotational motion into the linear motion and transmitting it to the screw 2. Rotation to linear motion conversion mechanism, 9 is an encoder for detecting the rotation of the measuring servomotor 3, and 10 is a pressure applied to the screw 2. Load cell which detects a, 11 is an encoder for detecting the rotation of the injection servomotor 6. In the present embodiment, the measuring servomotor 3 and the timing belt 4 move forward and backward together with the screw 2.

Reference numeral 12 is a metering condition setting storage unit embodied by a function of a microcomputer or the like, and includes a screw rotation speed setting storage unit 12a and a resin pressure condition setting storage unit 12b. Reference numeral 13 is a metering control unit that is also embodied by a function such as a microcomputer, and includes a screw rotation speed feedback control unit 13a and a pressure feedback control unit 1.
3b. Further, 14 is a servo amplifier for driving and controlling the measuring servo motor, and 15 is a servo amplifier for driving and controlling the injection servo motor 6.

The screw rotation speed setting storage unit 12a of the measurement condition setting storage unit 12 rewritably stores the control conditions of the screw rotation speed of the measuring process . In this embodiment, the screw 2 is moved from the measurement start position. The screw rotation speed (rpm) until reaching a predetermined retracted position is stored. Further, the resin pressure condition setting storage unit 12b of the measuring condition setting storage unit 12 rewritably stores the control conditions of the resin pressure of the measuring process. In the present embodiment, the movement of the screw 2 from the measuring start position is moved. The set resin pressure (kgf / cm ² ) corresponding to the position is stored in multistage settings.

The screw speed feedback control unit 13a of the metering control unit 13 monitors the actually measured screw position obtained from the output A3 of the encoder 11, and also sets the data stored in the screw speed setting storage unit 12a and the encoder 9 The measured screw rotation speed data obtained from the output A1 is compared to generate a control signal so that the section from the measurement start position to the predetermined retracted position of the screw 2 reaches the set screw rotation speed. , This is output to the servo amplifier 14, and the servomotor 3 for weighing is output.
Drive control. The rotation of the metering servomotor 3 is transmitted to the screw 2 via the output pulley 3a, the timing belt 4 and the pulley 5, so that the screw 2 is rotationally driven by feedback control so that the screw 2 has a set rotational speed. It

Further, the pressure feedback control section 13b of the metering control section 13 monitors the actually measured screw position obtained from the output A3 of the encoder 11, and sets the data stored in the resin pressure condition setting storage section 12b and the load cell 10. In comparison with the detected pressure data obtained from the output A2, a control signal is generated so that the resin pressure is set corresponding to the screw retracted position from the measurement start position, and this is output to the servo amplifier 15. Then, the injection servomotor 6 is rotationally controlled. The rotation of the injection servomotor 6 is transmitted to the pulley 8a of the rotation → linear motion conversion mechanism 8 via the output pulley 6a and the timing belt 7, and the rotation → linear motion conversion mechanism 8 converts the rotary motion into the linear motion. So that the pressure applied to the screw 2 transmitted to the screw 2 and detected by the load cell 10 becomes the set resin pressure,
The screw 2 is driven back and forth or stopped by feedback control.

Next, the operation of the weighing process of this embodiment will be described with reference to FIG. FIG. 2 is a weighing machine according to this embodiment.
Is a diagram showing an example of a degree of a state, in the figure, the abscissa indicates the retracted position of the screw (mm), the vertical axis represents a screw rotational speed (rpm) and resin pressure (kgf / cm ²⁾
Is shown.

In the example shown in FIG. 2, the screw rotation speed corresponds to a predetermined retracted position of the screw 2 from the measurement start position (the timing at which one shot of molten resin is substantially completely accumulated at the tip end side of the screw 2). Is set to 400 rpm in the section up to the position where
Further, the resin pressure is set in four stages here according to the retracted position of the screw 2 from the measurement start position, and is 150 kgf / cm ² in the first section and 10 in the second section.
To 0 kgf / cm ^2, the third section 50 kgf / cm ²
In the fourth section, it is set to 20 kgf / cm ² . Here, in this example, the start of the third section of the resin pressure control is set to the timing immediately before the rotation of the screw 2 is stopped, but the start of the third section of the resin pressure control is set to the rotation of the screw 2. You may make it set to the timing to stop.

In the state where the control conditions for the above-described measuring process are set and stored in the screw rotation speed setting storage unit 12a and the resin pressure condition setting storage unit 12b, when the measurement start timing is reached, the screw rotation speed feedback control unit 13a. The measuring servomotor 3 starts to rotate in response to a command from the. As a result, the screw 2 is rotationally driven from the metering start position, the feeding of the molten resin to the tip end side of the screw 2 is started, and the set rotational speed rises up to 400 rpm. Further, when the molten resin starts to be fed to the tip side of the screw 2 due to the rotation of the screw 2, the resin pressure value applied to the screw detected by the load cell 10 starts to increase. In the first section of the resin pressure control, when the pressure value applied to the screw detected by the load cell 10 reaches the set value of 150 kgf / cm2, the injection servomotor 6 is rotationally driven and controlled by the command from the pressure feedback control unit 13b. Then, this rotation is converted into a movement in the axial direction of the screw by the rotation → linear motion conversion mechanism 8 to start the backward movement of the screw 2, and thereafter, the pressure value applied to the screw detected by the load cell 10 is the set value of 150 kgf. / Cm
2 so that the pressure feedback control unit 13b matches
The resin pressure is controlled by controlling the injection servomotor 6 in accordance with the command from the forward / reverse rotation drive control or stop control and by driving the screw 2 forward or backward or stopping.

Next, when the second section of the resin pressure control is entered, the detected resin pressure value is the set value 100 in the second section of the resin pressure control.
The resin pressure acting on the screw 2 is feedback-controlled so as to match kgf / cm ^2, and when the screw 2 reaches a predetermined retracted position at the end of the second section of the resin pressure control, the rotation of the screw 2 starts from 400 rpm. It begins to decelerate to stop rotation. And screw 2
When the resin reaches the screw retreat position just before the rotation stops (a state close to the rotation stop), that is, when the molten resin for one shot is almost completely accumulated at the tip side of the screw 2, the resin pressure control is performed. Of the screw 2 so that the detected resin pressure value matches the set value 50 kgf / cm ² of the resin pressure control in the third section.
The resin pressure acting on is controlled. As described above, the transition timing of the resin pressure control to the third section is the screw retracted position where the screw 2 stops rotating (this is also the case where one shot of molten resin is almost at the tip side of the screw 2). It is a screw retreat position corresponding to the timing of complete storage).

That is, the present invention is characterized in that the resin pressure control is continued even after the control is ended in the conventional measurement control method, and the screw 2 is in the rotation stop state or a state close to the rotation stop state. Measurement
The pressure control for the screw 2 is continued even at the end of the process .

Even after the rotation of the screw 2 is completely stopped after entering the third section of the resin pressure control, the pressure feedback control is continued so that the detected resin pressure value matches the set value of 50 kgf / cm ^2. Since the propulsive force (pressure) P _B accompanying the rotation of the screw 2 does not act on the load cell 10 at all, the detected pressure P _L of the load cell 10 and the actual pressure P _{A of the} resin become equal to each other. (P _L = P _A ). Therefore, when the set value in the third section of the resin pressure control is equal to the set value in the second section of the resin pressure control, the propulsive force (pressure) P _{B of the} screw 2
The screw 2 advances so as to compensate for the pressure difference corresponding to the loss of pressure, but the driving force (pressure) P _B of the screw 2 is a fraction of the actual resin pressure P _A at maximum.
Since the setting value of the third section of the resin pressure control is half of the setting value of the second section of the resin pressure control, it is set even after the rotation of the screw 2 is completely stopped. When the pressure feedback control with the value of 50 kgf / cm ² is executed, the screw 2 will further retract.

When the screw 2 is further retracted and the retracted position enters the fourth section of the resin pressure control, it shifts to the fourth section of the resin pressure control, and the detected screw pressure value is the fourth section of the resin pressure control. The resin pressure acting on the screw 2 is controlled so as to match the set value of 20 kgf / cm ² . As a result, the screw 2 is further retracted, and when it is detected that the axial movement of the screw 2 has come to a stop or a state close to a stop (this is obtained by appropriately converting the output A3 of the encoder 11). , Which is known from the axial movement speed information of the screw 2),
The pressure feedback control by the pressure feedback control unit 13b is stopped.

The metering operation is completed by the above operation, and the screw 2 is stopped at the metering completion position further retracted from the position where the screw rotation is stopped. As shown in FIG. 2, this measurement completion position is S1, S depending on the variation in the propulsive force (pressure) P _B of the screw 2 described above.
, S3, ..., but on the contrary, the measured and stored pressure of the molten resin is not affected by the dispersion of the propulsive force (pressure) P _B of the screw 2 at all times and is always It will show a stable and constant value. Therefore, the resin density of the measured and stored molten resin was extremely stable, and according to the experiments by the inventors of the present application, it was confirmed that the variation in the resin density can be suppressed to less than 1%. It was also confirmed that the time taken from the position where the screw rotation was stopped to the position where the measurement was completed was as short as 0.2 to 0.3 seconds.

By the way, in the present embodiment, as described above, the measurement completion position varies in each cycle. Therefore, in the present embodiment, the position of the screw 2 at the time when the measurement is completed is used as a reference point for stroke control of suck back and injection processes in each cycle. That is, for example, when the suck back is not performed, the injection process is performed for each cycle with the position of the screw 2 at the time when the measurement is completed as a starting point (reference point).
An injection operation (primary injection operation) is performed by advancing the screw 2 by a preset constant stroke. In this primary injection process , the injection speed and the injection pressure are set in multiple stages according to the forward stroke position of the screw 2, and the injection speed and the injection pressure are feedback-controlled in accordance with the set data. . Therefore, in the injection process , the absolute position of the screw 2 changes each time, but the capacity of the resin filled in the mold is stable, and the resin density is stable as described above. Will contribute to.

It should be noted that in the present embodiment, the above-mentioned screw 2 is in a state where the screw 2 stops rotating or is in a state close to rotating stop.
Pressure control that continues at the end of the process (pressure control in the third and fourth sections of the resin pressure control described above) is controlled by pressure control before that (pressure control in the second section of the resin pressure control described above). Although the pressure value is smaller than the value, this is because the screw 2 is always retracted by the pressure control which is continued at the end of the metering process when the screw 2 stops rotating or is close to stopping rotation, and the injection is performed. This is to prevent the forward stroke of the screw 2 from becoming insufficient during the process . Therefore, when the forward stroke of the screw 2 during the injection process can be sufficiently ensured, or when it is desired to obtain high-pressure resin, the screw 2 is stopped at the end of the measuring process when the screw 2 stops rotating or is close to rotating stop. There is no problem even if the screw 2 is advanced from the screw rotation stop position by performing the pressure control at a pressure value equal to or higher than the pressure control before that.

Further, in the present embodiment, the pressure control which is continued at the end of the metering process in which the screw 2 stops rotating or close to rotation is the multi-stage pressure control. There is no problem in controlling the pressure.

In this embodiment, as described above, the rotation stop timing of the screw 2 is set at the screw retracted position. However, the rotation stop timing of the screw 2 is set as follows. Two
May be performed by the cumulative screw rotation amount after the start of rotation.

In the present embodiment, the electric injection molding machine is shown in which the metering drive source and the injection drive source are electric servomotors. However, the metering drive source is a hydraulic motor and the injection drive source is a hydraulic cylinder. It goes without saying that the present invention can be applied to the above hydraulic injection molding machine.

In the present embodiment, the pressure feedback control is stopped by detecting that the axial movement of the screw 2 has stopped or has reached a state close to the stop. You may make it the timing which completes | finishes with the timer after screw rotation stop.

[0032]

As described above, according to the present invention, it is possible to reduce the variation in the resin density of the molten resin that is measured and stored as much as possible, and this kind of in-line screw type injection molding machine is provided. Therefore, its value is enormous.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing an example of a state of a weighing process according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an example of a state of a weighing process according to a conventional technique.

FIG. 4 is an explanatory diagram showing a main part configuration of a general electric injection molding machine.

[Explanation of symbols]

1 heating cylinder 2 screws 3 Servomotor for weighing (driving source for weighing) 3a Output pulley 4 Timing belt 5 pulleys 6 Injection servo motor (injection drive source) 6a Output pulley 7 Timing belt 8 rotation → linear motion conversion mechanism 8a pulley 9 encoder 10 load cell 11 encoder 12 Measurement condition setting storage section 12a Screw rotation speed setting storage section 12b Resin pressure condition setting storage section 13 Measurement controller 13a Screw rotation speed feedback control unit 13b Pressure feedback control unit 14 Servo amplifier 15 Servo amplifier

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B29C 45/46-45/63 B29C 45/70-45/84

Claims (8)

(57) [Claims] 1. A heating cylinder is provided with a screw rotatably and forward / backward, and a metering drive source for rotationally driving the screw and an injection drive source for forward / backward driving of the screw are provided . a method of controlling a metering process in inline screw type injection molding machine, first the disk while the pressure control on the screw
Rotate the Liu and then stop the screw rotation.
So, that the above screw continues to pressure control for the screw noted above after stopping rotation, at a timing that led to stop axial movement of the screw is stopped, and so as to terminate the pressure control to the above-mentioned screw A method for controlling an injection molding machine, the method comprising: 2. The method of claim 1, wherein the axial movement of the screw position of the screw in a state that resulted in stop and a suck-back or injection process as a reference point for stroke control A method for controlling an injection molding machine, the method comprising: 3. The method for controlling an injection molding machine according to claim 1, wherein the pressure control which is continued even after the rotation of the screw is stopped is multistage pressure control. 4. The pressure control according to claim 1, wherein the pressure control that is continued even after the rotation of the screw is stopped is performed at a pressure value smaller than the pressure value obtained by the pressure control performed before that. Control method of injection molding machine. 5. The control method for an injection molding machine according to claim 1, wherein the injection drive source is an electric servomotor, and the pressure control for the screw is performed by feedback control. 6. The method of controlling an injection molding machine according to claim 1, wherein the timing of stopping the rotation of the screw is set at a screw retracted position. 7. The control of an injection molding machine according to claim 1, wherein the rotation stop timing of the screw is set by the cumulative screw rotation amount after the screw starts rotating. Method. 8. The method for controlling an injection molding machine according to claim 1, wherein the timing for ending the pressure control is performed by a timer after the screw rotation is stopped.