JP3808989B2 - Control method of servo mechanism at the start of pressure holding process - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, when a screw or plunger in an injection cylinder is driven in the injection direction by a servo mechanism to inject molten resin into a mold and hold pressure, the injection pressure is controlled by feedback control of the injection speed during the injection process. The present invention relates to a servo mechanism control method at the start of a pressure holding process, which is sometimes controlled by feedback control of the pressure holding pressure.
[0002]
[Prior art]
As is well known, the injection molding machine is roughly composed of a cylinder provided with an injection nozzle at the tip, and a screw or plunger provided so as to be driven in the cylinder. . In a hydraulic injection molding machine in which the screw of such an injection molding machine is driven by a hydraulic piston / cylinder unit, a servo valve is provided between the cylinder of the hydraulic piston / cylinder unit and a hydraulic pump or accumulator. Is intervening.
Therefore, when the resin material is metered at the screw tip and the hydraulic oil controlled by the servo valve is supplied to the cylinder of the hydraulic piston / cylinder unit, the metered resin material is injected into the mold at a predetermined speed, and The pressure is maintained at a predetermined pressure. Therefore, a mold can be obtained by waiting for cooling and solidification to open the mold.
[0003]
By the way, the magnitude of the injection speed when injecting the measured molten resin material to the mold also causes molding defects of the molded product, for example, insufficient filling, sink marks, etc., so set the injection speed with the setting device, It is controlled by speed feedback control so that the injection speed becomes the set speed. In addition, the pressure holding process in the second half of injection is also important, and the magnitude of the pressure holding may cause overpacking, that is, overfilling, mold release failure, sink marks on the molded product, and the like. Therefore, even during the pressure holding process, control is performed by pressure feedback control so that the pressure holding pressure becomes the pressure setting pressure. Thus, when switching from feedback control of injection speed to feedback control of holding pressure, a certain operation amount is added as the feedforward amount.
[0004]
[Problems to be solved by the invention]
As described above, even in the conventional control method, the feedforward manipulated variable is added even if the manipulated variable is constant, so that a temporary effect is recognized in terms of control operation and stability.
However, because the feed forward operation amount of the servo valve at the start of the pressure holding process is a predetermined constant operation amount, depending on the operation amount of the servo valve at the end of the injection process, immediately after switching to the pressure holding process The pressure may not follow the set value. The reason will be described in more detail. For example, when the injection speed is slow and the holding pressure setting value is low, the operation amount of the servo valve at the end of the injection process is compared with the output when switching to the holding process. The preset feed-forward operation amount of the servo valve is increased, and the servo valve operation amount immediately after switching to the pressure-holding process is increased, so the measured pressure value exceeds the pressure-holding pressure setting value. Shoot. This overshooting state is shown in FIG. 3 with time on the horizontal axis and the operation amount and pressure of the servo valve on the vertical axis.
[0005]
On the other hand, when the injection speed is fast and the holding pressure setting value is high, a preset servo valve is output when switching to the holding pressure process compared to the servo valve operation amount at the end of the injection process. The feedforward manipulated variable becomes smaller, and the measured pressure value undershoots the set pressure value. Thus, if overshooting or undershooting is performed when switching to the pressure-holding process, the quality of the molded product is degraded.
Therefore, the present invention provides a control method of the servo mechanism at the start of the pressure-holding process, in which the pressure-holding pressure becomes the set value even immediately after the pressure-holding process is started, thereby obtaining a high-quality molded product. The purpose is to do.
[0006]
[Means for Solving the Problems]
The above object of the present invention is to provide a calculated value obtained by comparing the actual injection pressure value at the end of the injection process and the holding pressure setting value or the operation amount of the servo mechanism at the end of the injection process, and the servo mechanism at the start of the pressure holding process. This is achieved by setting the feedforward manipulated variable as follows. That is, in order to achieve the above object, the present invention drives the screw or plunger in the injection cylinder in the injection direction by the servo mechanism to inject the molten resin into the mold and hold the pressure. In the method of controlling by feedback control and controlling by feedback control of holding pressure during the holding pressure process , the servo mechanism at the start of the holding pressure process is such that the actual measured injection pressure at the end of the injection process is less than the holding pressure setting value. Is lower than the operation amount of the holding pressure feedback control, the operation amount is obtained by adding the first feedforward operation amount that is the operation amount of the servo mechanism at the end of the injection process, and at the end of the injection process. when the injection pressure measurement is higher than the dwell pressure setting value, the operation amount of the holding pressure of the feedback, and the injection pressure measurement during the injection step is completed Configured to operate in a second feedforward manipulated variable manipulated variable has been added to that obtained by calculating from the pressure pressure setpoint.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example in which the embodiment of the present invention is applied to a hydraulic injection molding machine A will be described with reference to FIG. A hydraulic injection molding machine A according to an embodiment of the present invention includes an injection cylinder device 1, a mold device in which a molten resin measured by the injection cylinder device 1 is injected, and a hydraulic circuit 10 that drives the injection cylinder device 1. The controller 20 is configured to control the injection process and the pressure holding process. Note that a control device such as a hydraulic motor 6 that rotationally drives the screw during weighing is not shown in FIG.
[0008]
As is well known in the art, the injection cylinder device 1 includes an injection cylinder 2 provided with an injection nozzle at its tip. A material hopper 3 is attached to the rear side of the injection cylinder 2 and a driving device 5 is provided at the rear end thereof. As is well known, the drive device 5 is composed of a hydraulic motor 6 and a hydraulic piston / cylinder unit, and an output shaft of the hydraulic motor 6 is provided inside the injection cylinder 2 so as to be able to be driven in the rotational direction and the axial direction. The screw 4 is mechanically connected to the rear end of the screw 4 in a known manner. Therefore, the screw 4 can be rotationally driven by the hydraulic motor 6 to measure the resin material. The hydraulic cylinder 7 of the hydraulic piston / cylinder unit is provided with an injection piston 8, which is also mechanically connected to the screw 4. Therefore, when hydraulic oil is supplied to the cylinder head side of the hydraulic cylinder 7, the screw 4 is driven in the axial direction, and the molten resin is injected into the mold. In the injection cylinder apparatus 1 configured as described above, an injection speed detector S is associated with the screw 4 in order to detect the injection speed of the molten resin, for example, to detect the axial speed of the screw 4. Is provided. Further, a pressure sensor P for detecting the pressure of hydraulic oil, that is, the injection pressure, is provided on the cylinder head side of the hydraulic cylinder 7. The injection pressure is indirectly measured by the pressure sensor P.
[0009]
Although not shown in FIG. 1, the mold apparatus is composed of a fixed mold attached to the fixed platen, a movable mold attached to the movable platen, and the like as is well known in the art. These molds are provided with cavities for molding a molded product.
[0010]
The hydraulic circuit 10 includes a hydraulic pump 11. A check valve 13, an accumulator 14, a servo valve 15, and the like are interposed in the discharge pipe 12 of the hydraulic pump 11 and connected to the cylinder head side of the hydraulic cylinder 7 . As will be described later, the servo valve 15 adds the calculated operation amount or the operation amount at the end of the injection process as the feedforward operation amount to the operation amount obtained by feedback control of the holding pressure, as will be described later. It is operated with the operated amount.
[0011]
As shown in FIG. 1, the control device 20 that controls the injection process or the pressure holding process includes a speed controller 21, a first joining point 22, an adjustment operation device 28, a comparator 24, a computing unit 25, 2 joining points 30, a storage device 31, a first switch 32, an operation signal switch 33, and the like. The control device 20 is also provided with a pressure setting device 34, an operation amount switching device 35, a holding pressure switching setting device 36, and the like. The speed controller 21 is composed of a feedback control device that uses the injection speed measured by the injection speed detector S as a main feedback amount. However, the speed controller 21 is a speed setting unit for controlling the injection speed feedback. Since the merging point, the adjusting operation unit, and the like are conventionally known, in FIG. 1, the speed controller 21 is simply connected to the injection speed detector S through the signal line a.
[0012]
The pressure sensor P is connected to one input terminal of the first joining point 22 by a signal line b. This signal line b is branched and further connected to a comparator 24 and an arithmetic unit 25. Therefore, the injection pressure measured by the pressure sensor P is input to the comparator 24 and the calculator 25 in addition to the first joining point 22. The pressure setter 34 is connected to the other input terminal of the first joining point 22 and the comparator 24 by a signal line c, and is connected to the calculator 25 by a signal line d. The arithmetic unit 25 and the multiplier 26 are connected to the signal line e, one input terminal “0” of the multiplier 26 and the operation signal switch 33 is connected to the signal line f, and the coefficient setting unit 27 and the multiplier 26 are connected to the signal line e. Each is connected by a line g.
[0013]
The output terminal of the first joining point 22 is connected to the adjusting operator 28 via the second switch 23 by the signal line h, and one input terminal of the adjusting operator 28 and the second joining point 30 is connected to the signal line. i are connected by i. The output terminal of the second joining point 30 is connected to the other input terminal “0” of the operation amount switch 35 by the signal line j. The operation signal switch 33 is connected to the first switch 32 by a signal line k, the first switch 32 and the storage device 31 are connected by a signal line k ′, and the storage device 31 and a second joining point. The other input terminal 30 is connected by a signal line m.
[0014]
The speed controller 21 is connected to the other input terminal “1” of the operation amount switch 35 via a signal line n. This signal line n is also connected to the other input terminal “1” of the operation signal switch 33 and the calculator 25. The holding pressure switching setting unit 36 is connected to the operation amount switching unit 35 and the first and second switches 32 and 23 through a switching signal line p. When a pressure holding process start signal is output from the pressure holding switching setting device 36, the operation amount switching device 35 is switched to the "0" side, that is, the pressure holding side, as shown in FIG. It is turned off and the second switch 23 is turned on. The comparator 24 and the operation signal switch 33 are connected by a switch signal line r. When output from the comparator 24, that is, when the injection pressure measured by the pressure sensor P is higher than the holding pressure setting pressure set by the pressure setting device 34, the operation signal switching device 33 is shown in FIG. One input terminal "0" shown is switched to the side.
[0015]
Next, an example in which a molded product is molded by the hydraulic injection molding machine A will be described. The screw 4 is rotationally driven by the hydraulic motor 6 to supply the resin material from the material hopper 3. Thereby, the resin material is weighed as conventionally known. The holding pressure is set by the pressure setting device 34, and the holding pressure start time, for example, the position of the screw 4 is set by the holding pressure switching setting device 36. Then, the injection is started.
[0016]
During the injection process, since the signal from the holding pressure switching setting device 36 is not applied to the operation amount switching device 35, the operation amount switching device 35 is switched to the “1” side. Therefore, the servo valve 15 is operated by the servo valve operation amount (e ₁ ) output from the speed controller 21, hydraulic oil is supplied from the accumulator 14 to the piston head side of the hydraulic cylinder 7, and the screw 4 is moved in the injection direction. Driven. As a result, the measured molten resin material is injected into the mold cavity at a set speed. The servo valve operation amount (e ₁ ) during the injection process is sent to the operation signal switch 33 by the signal line n as the first feedforward operation amount (e ₁ ) at the start of the pressure holding process, and to the calculator 25. Is output as the number of operations.
[0017]
The calculator 25 is supplied with the injection pressure measured by the pressure sensor P, the holding pressure setting pressure set by the pressure setter 34, and the servo valve operation amount output from the speed controller 21. In 25, the operation amount is calculated by the following equation.
{(Holding pressure set value) / (actual injection pressure value)} × servo valve operation amount As will be described in detail later, the actual injection pressure value and the servo valve operation amount are values at the end of the injection process.
The operation amount calculated by the above equation is multiplied by the coefficient set by the coefficient setting unit 27 in the multiplier 26, and the operation signal switching unit 33 receives the second feedforward operation amount (e ₂ ) during the pressure holding process. It is output.
[0018]
On the other hand, the comparator 24 compares the injection pressure measured by the pressure sensor P with the holding pressure setting pressure set by the pressure setting device 34. Now, when the injection pressure measured by the pressure sensor P is higher than the holding pressure setting pressure set by the pressure setting device 34, a switching signal is applied from the comparator 24 to the operation signal switching device 33 by the switching signal line r. The operation signal switch 33 is switched to the “0” side. Accordingly, at this time, the calculated value calculated as described above by the calculator 25 and the multiplier 26 via the first switch 32 is stored in the storage device 31 as the second feedforward manipulated variable (e _2). ) Will be stored. The second feedforward manipulated variable (e ₂ ) changes every moment because the injection pressure measured by the pressure sensor P and the servo valve manipulated variable output from the speed controller 21 change with the progress of the injection process. It will be. Therefore, the latest second feedforward manipulated variable (e ₂ ) is always calculated in the storage device 31 and updated.
[0019]
On the other hand, when the injection pressure measured by the pressure sensor P is lower than the holding pressure setting pressure set by the pressure setting device 34, the operation signal switching device 33 is switched to the “1” side. Accordingly, at this time, the servo valve operation amount (e ₁ ) output from the speed controller 21 via the first switch 32 is stored in the storage device 31 as the first feedforward operation amount (e ₁ ). Is done. At this time as well, the latest first feedforward manipulated variable (e ₁ ) is always stored and updated. Thus, either the first or second feedforward manipulated variable (e ₁ , e ₂ ) is stored in the storage device 31, but these feedforward manipulated variables (e ₁ , e ₂ ) are Since the pressure holding process start signal is output from the pressure holding switch setting device 36 to the first switch 32 and is the operation amount when the first switch 32 is turned off, the injection process ends or the pressure holding process starts. This is the amount of operation.
[0020]
When the pressure holding process start time set by the pressure holding switch setting device 36 is reached, the operation amount switching device 35 is switched to the “0” side by a signal from the pressure holding switch setting device 36. Further, the first switch 32 is turned off. Furthermore, the second switch 23 is turned on. Thereby, the pressure holding process is started. That is, at the first joining point 22, the deviation signal obtained from the main feedback amount measured by the pressure sensor P and the holding pressure setting pressure set by the pressure setting unit 34 is operated by the adjustment operating unit 28 with the operation amount (e ) As adjusted. Then, the first or second feedforward operation amount (e ₁ , e ₂ ), that is, the operation amount indicated by (e ₀ ) in FIG. 1 is added at the second joining point 30, and the servo valve 15 is operated. Is done. As a result, hydraulic oil at a predetermined pressure is supplied from the accumulator 14 to the piston head side of the hydraulic cylinder 7 and is held at a predetermined pressure.
[0021]
More specifically, when the injection pressure measured by the pressure sensor P at the end of the injection process is lower than the holding pressure setting pressure set by the pressure setter 34, the storage device 31 stores the first feedforward manipulated variable ( Since e ₁ ) is stored, the servo valve 15 is operated by an operation amount obtained by adding the first feedforward operation amount (e ₁ ) to the operation amount (e) output from the adjustment operation device 28. On the other hand, when the injection pressure measured by the pressure sensor P at the end of the injection process is higher than the holding pressure setting pressure set by the pressure setter 34, the storage device 31 stores the second feedforward manipulated variable ( Since e ₂ ) is stored, the servo valve 15 is operated by the operation amount to which the second feedforward operation amount (e ₂ ) is added. Thereby, overshoot at the time of holding pressure switching is prevented. This state is shown in FIG. 2 in contrast to the conventional FIG.
[0022]
It should be noted that the present invention is not limited to the in-line screw injection molding machine of the hydraulic injection molding machine A, and it is obvious that the present invention can be similarly applied to a hydraulic pre-plastic injection molding machine. Furthermore, for example, it is also apparent that the present invention can be similarly implemented in an electric injection molding machine by controlling the torque of the electric motor that drives the screw 4 in the injection direction as described above.
[0023]
【The invention's effect】
As described above, according to the present invention, at the time of the injection process is controlled by a feedback control of the injection speed, the method at the time of pressure holding process is controlled by the feedback control of the pressure-holding pressure, the servo mechanism at the start of the pressure holding process, an injection process When the actual injection pressure value at the end is lower than the holding pressure setting value , the first feedforward operation amount, which is the operation amount of the servo mechanism at the end of the injection process , is added to the operation amount of the holding pressure feedback control. operated by the operation amount plus, when injection pressure measurement during the injection step is completed is higher than the dwell pressure setting value, the operation amount of the holding pressure of the feedback, the injection process at the end of the injection pressure measurement because operating in the holding pressure setting value and the second feedforward manipulated variable manipulated variable has been added to that obtained by calculation from the overshoot and immediately after the start of the pressure holding process Undershoot is prevented, holding pressure reaches the set value Street. Therefore, an effect peculiar to the present invention that a high-quality molded product can be obtained is obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically showing an embodiment of the present invention.
FIG. 2 is a diagram showing a relationship between holding pressure and time when controlled by the control method according to the embodiment of the present invention.
FIG. 3 is a diagram showing a relationship between holding pressure and time when controlled by a conventional control method.
[Explanation of symbols]
2 Injection cylinder 4 Screw 15 Servo mechanism (servo valve)
20 Control device 21 Speed controller 22 First joining point 28 Adjustment operator

Claims (1)

When the screw (4) or plunger in the injection cylinder (2) is driven in the injection direction by the servo mechanism (15) to inject molten resin into the mold and hold the pressure, it is controlled by feedback control of the injection speed during the injection process In the method of controlling by the feedback control of the holding pressure during the holding process,
The servomechanism (15) at the start of the pressure-holding process has an operation amount (e) for feedback control of the pressure-holding pressure when the actual injection pressure value at the end of the injection process is lower than the pressure-holding pressure set value. , operating at an injection step manipulated variable at the end of the servo mechanism (e ₁₎ a first feed-forward manipulated variable is (e ₁₎ the operation amount obtained by adding,
When the actual injection pressure value at the end of the injection process is higher than the holding pressure setting value, the actual operation pressure and the holding pressure setting value at the end of the injection process are added to the operation amount (e) of feedback of the holding pressure. The servo mechanism control method at the start of the pressure-holding process, characterized in that the operation is performed with an operation amount obtained by adding a _second feedforward operation amount (e ₂ ) obtained by calculating from the above .

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