JP4091488B2 - Screw control method for injection molding machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a screw control method for an injection molding machine, and in particular, in the process of advancing a screw in a heating barrel and filling molten resin into a mold, when shifting from a filling process to a pressure holding process, The present invention relates to a screw control method for suppressing the generation of surge pressure.
[0002]
[Prior art]
The injection molding machine uses a heated barrel with a screw inside, rotates the screw to introduce resin into the heated barrel and simultaneously melts the resin (referred to as the “metering process”), and then melts the resin into the heated barrel. Is stored, the screw is advanced at a predetermined speed to fill the mold with molten resin (referred to as “filling step”), and the screw is set in a preset position (referred to as “pressure holding start position”). Then, the screw is decelerated, and then the position of the screw is controlled so that the pressure of the resin in the mold is maintained at a predetermined value (referred to as “pressure-holding step”).
[0003]
Such conventional screw control methods have the following problems. That is, when it is necessary to fill the resin at a high speed, the conventional control method cannot sufficiently suppress the inertia force in the forward direction of the screw, so that a large surge pressure is generated when the pressure holding process is switched. When surge pressure is generated, the pressure of the resin in the mold after switching to the pressure holding process becomes unstable. As a result, the quality of the injection-molded product is not stable, and the yield is adversely affected. In addition, the mold may be damaged.
[0004]
In addition, in JP 2000-167892 A (Patent Document 1), in the case of manufacturing a thin molded product, a screw is inserted immediately before the transition from the filling process to the pressure holding process for the purpose of preventing the occurrence of burrs and the like. It is described to retract to a predetermined position, thereby reducing the pressure on the molded product (claim 1, paragraph [0006], FIGS. 1 to 3).
[0005]
Japanese Patent Laid-Open No. 2001-277322 (Patent Document 2) discloses that the screw is retracted to a predetermined position when shifting from the filling process to the pressure holding process, thereby performing pressure relief to create a necessary pressure waveform. (Claim 1, FIGS. 2 to 4).
[0006]
Japanese Patent Laid-Open No. 2002-028960 (Patent Document 3) provides a position commanded by a position retracted by a predetermined correction amount when the screw reaches the holding pressure start position in the filling process, thereby decelerating the screw. Then, it is described that the process proceeds to the pressure holding step (Claim 1, FIG. 2).
[0007]
In the methods described in Patent Documents 1 and 2, there is a problem that the resin does not catch up with the speed at which the screw actually moves back, and air is entrained. Further, the methods described in Patent Documents 2 and 3 have a problem in that the effect of surge pressure relief is not good because the screw is retracted or decelerated when the screw actually reaches the pressure holding start position.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-167892
[Patent Document 2]
Japanese Patent Laid-Open No. 2001-277322
[Patent Document 3]
Japanese Patent Laid-Open No. 2002-028960 (FIG. 2)
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of the problems of the conventional screw control method in the injection molding machine as described above, and the object of the present invention is to change from a filling process to a pressure holding process during injection. An object of the present invention is to provide a screw control method capable of suppressing the generation of surge pressure and thereby stabilizing the quality of an injection molded product even when resin is filled at high speed.
[0012]
[Means for Solving the Problems]
The screw control method of the injection molding machine of the present invention,
A weighing process in which resin is introduced into a heated barrel equipped with a screw, melted and stored;
By controlling the position of the screw in accordance with the position command, the filling step of advancing the screw in the heating barrel and filling the resin into the mold,
A pressure holding step for maintaining the pressure of the resin in the mold at a predetermined value by controlling the position of the screw according to the position command;
In a screw control method of an injection molding machine equipped with
The value of the position command is monitored, and when the value reaches the preset pressure holding start position, the filling process is shifted to the pressure holding process. At this time, the position command is set in advance from the position command immediately before that. The forward speed of the screw is decelerated by giving the position retracted by the correction amount as a position command only once.
[0013]
According to the screw control method for an injection molding machine of the present invention, in the filling process, when the position command value reaches the pressure holding start position, the position commanded by the correction amount is indicated as the screw position command. Thus, the screw can be quickly decelerated. As a result, the generation of surge pressure can be suppressed.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The screw control method based on this invention is demonstrated using drawing.
[0015]
FIG. 1 shows an example of the configuration of an apparatus and a control system when the control method of the present invention is applied to an electric injection molding machine. In the figure, 1 is a heating barrel, 2 is a screw, 3 is a hopper, 5 is a metering drive motor, 6 is an injection drive motor, and 20 is a control system.
[0016]
A screw 2 is incorporated in the heating barrel 1. A hopper 3 is connected to a side surface in the vicinity of the rear end portion (right side in the drawing) of the heating barrel 1. The front end portion (left side in the figure) of the heating barrel 1 is connected to the back surface of a mold (not shown). The resin 9 as a molding material is a pellet processed into a granular shape, and is introduced into the heating barrel 1 from the hopper 3.
[0017]
A metering drive motor 5 and an injection drive motor 6 are connected to the rear end of the screw 2. The metering drive motor 5 rotates the screw 2 in the heating barrel 1 during metering. Thereby, the resin 9 is introduced from the hopper 3 into the heating barrel 1. The introduced resin 9 is heated, melted and kneaded, sent to the front end side of the screw 2, and stored on the front end side of the heating barrel 1. Along with this, the screw 2 is retracted by the pressure of the resin in the front end of the heating barrel 1, and an amount of molten resin corresponding to the retreat amount is generally stored on the front end side of the heating barrel 1. The injection drive motor 6 advances the screw 2 in the heating barrel 1 during injection and fills the mold with molten resin.
[0018]
A screw rotation speed detector 11 that detects the rotation speed of the screw 2 is attached to the shaft of the metering drive motor 5. A screw position detector 12 that detects the axial position of the screw 2 is attached to the shaft of the injection drive motor 6. An injection pressure detector 13 is attached to the rear end of the screw 2. The injection pressure detector 13 detects the injection pressure applied to the resin 9 (molten resin) stored on the front end side of the heating barrel 1 by the screw 2 from the reaction force acting on the rear end portion of the screw 2.
[0019]
As shown in FIG. 1, a control system 20 for this electric injection molding machine includes a metering drive amplifier 21, an injection drive amplifier 22, a sensor input unit 23, a calculation unit 24, and an MMI / F (man machine). Interface 25 and a control output unit 26
[0020]
The metering drive amplifier 21 takes in the data of the number of revolutions of the screw 2 detected by the screw revolution number detector 11, controls the movement of the metering drive motor 5, and supplies the current supplied to the metering drive motor 5 to the sensor input unit. Send to 23. The injection drive amplifier 22 controls the movement of the injection drive motor 6 and sends the axial position data of the screw 2 detected by the screw position detector 12 to the sensor input unit 23. The sensor input unit 23 includes an injection pressure of the screw 2 detected by the injection pressure detector 13, a supply current to the metering drive motor 5 sent from the metering drive amplifier 21, and a screw sent from the injection drive amplifier 22. Each data of the two axial positions is sent to the calculation unit 24.
[0021]
The calculation unit 24 determines the drive condition of the screw 2 based on an instruction input from the operator via the man-machine interface 25 and sends a command to the control output unit 26. The control output unit 26 sends control signals to the metering drive amplifier 21 and the injection drive amplifier 22, respectively, and controls the movements of the metering drive motor 5 and the injection drive motor 6.
[0022]
Next, the control method of the screw 2 in an injection process is demonstrated using the flowchart shown in FIG.
[0023]
In the flowchart, “position” means the position of the screw (2: FIG. 1) in the heating barrel (1: FIG. 1), the forward limit (measurement start position) of the screw is 0 mm, and the backward direction is the normal. (+). The measurement of the resin (9: FIG. 1) is started from the position where the screw is at the previous injection completion position (advance limit), and as described above, the screw gradually moves backward while feeding the resin forward. When a predetermined amount of resin (melted resin) is stored in the heating barrel, the screw retreat is stopped. This stop position is referred to as a “measurement completion position”. Next, the process proceeds to the injection process, and the screw is advanced to fill the mold with the molten resin. In this example, the measurement completion position is 100 mm.
[0024]
“Position command” means a reference input signal on the feedback loop regarding the position of the screw in the filling process and the pressure holding process.
[0025]
The “distribution position” (ΔP) is a screw movement command speed (V) determined from the relationship between the set speed of the screw and the pressure (for example, the injection pressure detected by the injection pressure detector 13) in the filling process and the pressure holding process. ) And the time interval (Δt) for updating the screw position command on the feedback loop.
[0026]
In this example,
V = 10 [mm / sec]
Δt = 1 [msec]
ΔP = V · Δt = 0.01 [mm]
It is.
[0027]
Note that the symbol “=” in the flowchart means that the position command is updated every time interval (Δt). Specifically, the value on the left side of “=” is sequentially changed to the value on the right side. It is meant to be replaced.
[0028]
As shown in the flowchart, the current position (specifically, the measurement completion position) is set in the position command at the start of the filling process. After starting the filling step, the screw is advanced at a predetermined set speed corresponding to the filling step while updating the position command at each time interval (Δt). At this time, the actual screw position is monitored, and feedback control of the injection drive motor (6: FIG. 1) for driving the screw is performed. At the same time, it is also monitored whether or not the position command has reached the pressure holding start position (position where switching from the filling process to the pressure holding process is performed). In this example, the pressure holding start position is 4 mm.
[0029]
When the position command reaches the pressure holding start position, the next position command is added with a correction amount ("pressure holding start correction amount" in the figure, 1 mm in this example) set in advance from the position command at that time. Switch to value. That is, the position command is set at a position that is retracted by the correction amount from the position command at that time. As a result, the screw is quickly decelerated. Next, the process immediately shifts from the filling process to the pressure holding process.
[0030]
After shifting to the pressure-holding step, the screw is advanced again at a predetermined set speed corresponding to the pressure-holding step while updating the position command every time interval (Δt). Also at this time, the actual screw position is monitored and feedback control of the injection drive motor is performed. At the same time, a predetermined elapsed time (injection time, for example, 60 seconds) measured from the start of the preset injection process or a predetermined elapsed time (pressure holding time, for example, 20) measured from the start of the pressure holding process. (Seconds) has been reached (whether the timer has timed out) and whether the screw has reached the forward limit.
[0031]
When the injection time or pressure holding time is reached, or when the screw reaches the forward limit, the screw is stopped and the injection process is terminated.
[0032]
FIG. 3 shows an example of the relationship between the screw position, speed, and injection pressure when the control method of the present invention is employed. According to the control method of the present invention, the speed is quickly reduced immediately before the screw reaches the holding pressure start position, so that almost no surge pressure is generated.
[0033]
FIG. 4 shows an example of the relationship between the screw position, speed, and injection pressure when a conventional control method is employed. According to the conventional control method, a large surge pressure is generated as a result of delaying the screw deceleration.
[0034]
【The invention's effect】
According to the screw control method of the injection molding machine of the present invention, the screw can be quickly decelerated when shifting from the filling process to the pressure holding process. This suppresses generation of surge pressure. As a result, the phenomenon that the pressure of the resin in the mold becomes unstable after shifting to the pressure holding process is prevented, so that the quality of the injection molded product can be stabilized and the yield can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an electric injection molding machine to which a screw control method according to the present invention is applied.
FIG. 2 is a flowchart showing a screw control method according to the present invention.
FIG. 3 is a diagram for explaining a relationship between a screw position, a speed, and an injection pressure when a control method according to the present invention is employed.
FIG. 4 is a diagram for explaining the relationship between screw position, speed, and injection pressure when a conventional control method is employed.
[Explanation of symbols]
1 ... heated barrel,
2 ... screw,
3 ... Hopper,
5 ... Metering drive motor,
6 ... Injection drive motor,
9 ... resin,
11 ... Screw rotation number detector,
12 ... Screw position detector,
13 ... Injection pressure detector,
20 ... control system,
21 ... Metering drive amplifier,
22 ... Injection drive amplifier,
23 ... Sensor input section,
24 ... arithmetic unit,
25 ... Man-machine interface,
26: Control output unit.

Claims (1)

A weighing process in which resin is introduced into a heated barrel equipped with a screw, melted and stored;
By controlling the position of the screw in accordance with the position command, the filling step of advancing the screw in the heating barrel and filling the resin into the mold,
A pressure holding step for maintaining the pressure of the resin in the mold at a predetermined value by controlling the position of the screw according to the position command;
In a screw control method of an injection molding machine equipped with
The value of the position command is monitored, and when the value reaches the preset pressure holding start position, the filling process is shifted to the pressure holding process. At this time, the position command is set in advance from the position command immediately before that. A screw control method for an injection molding machine, wherein the screw is decelerated by giving a position retracted by a correction amount as a position command only once.

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