JPH0357618A - Screw thrust control method for injection molding machine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a screw thrust control method for an injection molding machine in which a screw is driven by a motor, and more specifically, to a method for controlling the screw thrust of an injection molding machine in which a screw is driven by a motor. The present invention relates to a suitable screw thrust control method.

(Prior art) In injection molding, in which a molded product is manufactured by injecting a resin material such as plastic into a mold, conventionally,
Hydraulic injection molding machines have been used, but in recent years, electric injection molding machines have been developed.

In this electric injection molding machine, the screw is rotationally driven by a motor, and the thrust applied to the screw is controlled by setting the motor torque based on the relationship between the motor current and torque determined in advance. This was done by passing a current corresponding to the current through the motor.

(Problem to be solved by the invention) However, since the relationship between current and torque constantly changes depending on the usage status of the motor, the above control method causes a difference between the desired set screw thrust force and the actual screw thrust force. The problem is that it is not possible to accurately control the thrust force and the thrust force varies, resulting in variations in dimensions, strength, etc. of the molded product during the injection and holding processes, making it difficult to mass-produce homogeneous molded products. was there.

A method proposed to solve these problems is disclosed in Japanese Patent Laid-Open No. 62-444-17.

To explain this with reference to FIG. 7, a screw 71 is connected to a ball screw 73 via a load sensor 72, and the ball screw 73 is driven back and forth by the rotation of a nut 74, which is driven by a motor 78 and a drive gear 77. , transmission shaft 7
6. It is configured to rotate along the path of the drive gear 75 and nut 74, and the thrust signal Sl taken out from the load sensor 72 is
The comparator Y2 compares the predetermined screw thrust setting value signal S2 output from the setting device Y, and inputs an instruction S according to the result to the motor controller Y3. A driving current i is supplied to make the motor torque, that is, the screw thrust, accurately follow the set value.

In this way, the sensor that detects the screw load from the start of injection to the holding pressure detects the actual screw thrust, and the current value of the motor is controlled so that the thrust always matches the set value. In this method, a homogeneous molded product with no variation in dimensions, strength, etc. is obtained, and in the plasticizing process, back pressure can be accurately controlled.

By the way, in the above-mentioned injection molding machine, in order to densely fill the molding material into the cavity, it is necessary to inject at a constant injection rate from the start of injection to the pressure holding stroke.

In particular, when manufacturing thin molded products, the injected molding resin is difficult to reach the corners of the mold, and the injection ends with gaps remaining in the mold, resulting in the resulting molded products having whiskers and shape defects. The problem arises that this occurs. In order to avoid such inconveniences, it is important to ensure a constant injection rate during the injection stroke, and for this purpose the speed of the screw must be controlled. However, with the screw thrust control method described above, in which the actual screw thrust is detected by a sensor that detects the screw load from the start of injection to the holding pressure so that the thrust always matches the set value, the screw speed is It becomes unclear and it is not possible to obtain a constant injection rate.

The present invention was developed to solve these problems, and it achieves a desired screw thrust in the pressure holding process and maintains a constant injection rate by controlling the screw speed in the injection process. , an injection molding machine that is designed to tightly fill the molding resin into the cavity without leaving any voids, even when molding particularly thin molded products, to obtain molded products without whiskers or shape defects. The purpose is to provide a screw thrust control method.

(Means for Solving the Problems) In order to solve the above problems, the screw thrust control method for an injection molding machine of the present invention provides an electric injection device in which a motor drives a screw housed in a heating cylinder. , comprising a pressure detection means for detecting the injection pressure of the screw and a means for detecting the stroke of the screw,
Speed control is performed from the start of injection until the filling rate of the preformed material in the cavity reaches a set value immediately before the pressure holding stroke, and subsequent injection and pressure holding control are performed by the output of the pressure detection means. shall be.

(Function) In the above configuration, if the volume of resin in the cylinder required to fill the cavity is measured in advance, the filling rate of the molding material in the cavity can be obtained by detecting the stroke of the screw. In this way, a predetermined filling rate is set just before the pressure holding stroke, and by controlling the speed of the screw from the start of injection until the set filling rate is reached, injection is performed at a constant injection rate. The injection and pressure holding control can perform desired screw thrust control based on the output of the pressure detection means that detects the injection pressure of the screw.

(Example) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment device according to the present invention, FIG. 2(a) is a schematic sectional view of an electric injection device according to the present embodiment, and FIG. ),
Figure 2 (C) is a cross-sectional view taken along III-III in Figure 2 (a), Figure 3 is a perspective view of the rotation mechanism, linear mechanism, back pressure mechanism, clutch and electric motor in Figure 2, and Figure 4. (a) to (e) are explanatory diagrams of the operation of this embodiment, FIG. 5 is a flowchart of injection molding by the apparatus of this embodiment, and FIG. 6 is a diagram showing the relationship between speed control and pressure control of the electric motor. .

In FIG. 1, a ball screw 6 is provided behind a screw 2 housed in a heating cylinder l via a pressure sensor 50 that detects the injection pressure of the screw, and the ball screw 6 is driven back and forth by rotation of a pole nut 9. be done.

The pole nut is for motor Mo. The screw 2 is rotationally driven by the motor M0 via a linear movement mechanism 54 that converts the rotational movement of the motor M0 into linear movement of the screw 2, and a pole nut 9. Molds 51, 51 each having a cavity 52 are pressed into contact with the tip of the cylinder 1.

The pressure value PI preset in the pressure setting means Y is sent to the pressure comparison means 55, where it is compared with the screw injection pressure P2 detected by the pressure sensor 50, and an instruction SP is given to the motor according to the result of this comparison. It is input to control device C.

On the other hand, the speed V set in advance in the speed setting means Yv
．． is sent to the speed comparison means 56, and the motor rotation speed V2 detected by the tacho generator M is sent to the speed comparison means 56 and compared, and an instruction Sv is sent to the motor control device C according to the comparison result. is input.

A movement stroke detection signal S of the screw 2 is detected by a screw stroke detection sensor 28 provided on the side of the ball screw, and this signal is sent to the motor control device C. The molding material in front of the screw 2 is the motor M.

The cavity 52 is filled by moving the screw 2 forward by the drive of the screw 2, but during the injection operation of the screw, the movement stroke detection signal S3 of the screw 2 is
is input to control device C. Then, the signal S. Based on the state of , it is determined in this motor control device C whether the control in the motor control device C should be based on the signal from the speed comparison means 56 or the signal from the pressure comparison means 55, and based on the result, the controlled current i is motor Ambient M
A is sent to the motor M0.

The filling rate can be set based on the relationship between the movement stroke S0 of the screw 2 required to fill the cavity 52 measured in advance and the actual movement stroke S of the screw 2. For example, to detect the point of 90% filling, the movement stroke S of the screw 2 is measured in advance. 90% stroke (S, = 0.9xSo)
The position of the sensor 28 is set so that the screw stroke detection sensor 28 emits the signal S0 when the screw 2 moves during injection. This detection signal S. from,
The time point when the filling rate into the cavity 52 reaches 90% from the start of injection is determined. In the injection process, first the speed comparison means 5
Based on the instruction Sv from 6, the voltage value V sent from the motor control device C to the motor 19 is controlled so that the motor rotation speed 1 always matches the set speed V. Then, the sensor 28 receives a detection signal S. The motor control is switched from speed control to pressure control when the filling rate reaches 90%, and thereafter the injection pressure P2 is made to always match the set pressure P1 based on the instruction SP from the pressure comparison means 55. The current value i sent from the motor control device C to the motor 19 is controlled, and the remaining filling and pressure holding are performed.

With such motor control, injection is performed at a constant injection rate by speed control from the start of injection until the filling rate into the cavity 52 reaches the set value, so even if the cavity is formed thin, the molding material can be kept in the cavity. It becomes possible to fill the molded product densely, and it is possible to mold a molded product without sink marks or shape defects. The subsequent injection and holding pressure are carried out at a desired holding force by pressure planning, making it possible to mold a homogeneous molded product with no variations in size, strength, etc.

Furthermore, by adjusting the movement of the sensor 28 in accordance with desired injection conditions, it is possible to change the setting at what percentage of the filling rate to switch from speed control to pressure control.

Hereinafter, a specific example of an electric injection device using the screw thrust control means of an injection molding machine as described above will be described with reference to FIGS. 2 and 3.

Note that the same reference numerals are used for parts corresponding to the configuration shown in FIG.

This electric injection device consists of a screw 2 housed in a heating cylinder 1, a spline shaft 3 fixed to the screw 2 by a pin 4, and a stopper connected to the upper end of the spline shaft 3 by a bolt (not shown). The hollow ball screw guide shaft 5 to which the plate 7 is fixed, the hollow ball screw 6 slidably fitted to the ball screw guide shaft 5, and the stopper plate 7 of the guide shaft 5 provided above the guide shaft 5 are thrust bearings. The cylinder rod 33 and the cylinder rod 33 that come into contact with each other through the cylinder rod 35 are arranged in the same straight line in the vertical direction.

A mold 51.51 having a cavity 52 is brought into contact with the nozzle tip of the heating cylinder 1.
A hopper 29 is connected above the heating cylinder 1 for supplying molding material into the heating cylinder 1 via a vibrator 29a.

The motor 19 (corresponding to M0 in FIG. 1) is mounted on the injection unit base 2l that fixedly holds the heating cylinder 1 so as to be arranged parallel to the above-mentioned components, and the motor control device 30 (corresponding to C in FIG. (equivalent to). A human power shaft 18 is connected to this electric motor 19 via a joint sleeve 20. The input shaft l8 has two clutches 16 and 17 (clutch l
6 is referred to as a metering/mixing clutch, and clutch 17 is referred to as an injection clutch) are fixed. The metering/interference clutch 16 can be connected to the input timing boolean 14,
This booster is connected via a timing belt 12 to an output-side timing booster 10 that is fixed to the outer periphery of the spline nut 8 fitted to the spline shaft 3. Therefore, when the clutch 16 is connected to the pulley l4, the spline shaft 3 is rotated by the rotational drive of the electric motor l9 via the pulley 14, the timing belt l2, the timing pulley 10, and the spline nut 8, which causes the screw 2 to rotate. do. The clutch 17 is connectable to an input timing pulley l5, and the pulley 15 is connected to an output timing pulley 1l fixed to a pole nut 6 via a timing belt 13. Therefore, clutch 1
7 is connected to the pulley l5, the electric motor 19 rotates the pole nut 9 via the pulley l5, the timing belt 13, and the timing pulley 11, and the hollow ball screw 6 moves up and down accordingly. The hollow ball screw 6 is provided with a projection piece 31 whose cross section is shown in FIG. ) By fitting the guide rod 32, the hollow ball screw 6 does not rotate as the pole nut 9 rotates, and can only move linearly relative to the guide shaft 5.

The hollow ball screw 6 is slidably fitted onto the guide shaft 5 as described above, and a ring-shaped pressure sensor 50 is fixed to the lower end of the hollow ball screw 6, and the detection results of the pressure sensor 50 are sent to the motor control device. Sent to 30.

A stop collar plate 7 having a larger diameter than the hollow ball screw 6 is fixed to the upper end of the guide shaft 5, and the lower end of the guide shaft 5 is fixed to the spline shaft 3, which also has a larger diameter than the hollow ball screw 6. When it moves, the pressure sensor 50 at the lower end of the hollow ball screw 6 abuts against the stopper plate 7 at the top and the spline shaft 3 at the bottom. Therefore, the stopper plate 7, the guide shaft 5, the spline shaft 3
Since the screws 2 and 2 are integrally fixed to each other as described above, the hollow ball screw 6 moves up and down as the pole nut 9 rotates in conjunction with the rotational drive of the electric motor 19, and the upper stopper plate 7 or the spline By pushing out the shaft 3, the screw 2 is inserted into the heating cylinder l.
When the screw 2 descends, the molten molding material inside the heating cylinder 1 is injected into the cavity 52. Also, during this downward movement, the pressure sensor 50 comes into pressure contact with the spline shaft 3, so that the injection pressure of the screw 2 changes from the detection result from the pressure sensor 50 (P2
) is sent to the motor control device 30.

The back pressure cylinder 22 is attached to the injection unit base 21 (not shown), is arranged on the same straight line as the stopper plate 7, the guide shaft 5, the spline shaft 3, and the screw 2 as described above, and moves the cylinder rod 33 up and down. Make it move. Thereby, the cylinder rod 33 can be lowered to press the stopper plate 7 and apply back pressure to the screw 2. In addition, 23 is a pressure regulator of the back pressure cylinder, and the back pressure cylinder 22 is connected via a tube 34.
It is connected to a compressed fluid (air, etc.) supply source (not shown). Pressure control of the back pressure cylinder 22 is performed by controlling the pressure of compressed fluid using a pressure regulator 23. With the back pressure mechanism configured as described above, it is possible to apply thrust to the screw 2 against the pressure generated in the molten molding material that gradually accumulates in front of the screw due to the metering and mixing of the molding material, thereby reducing the back pressure. It is possible to prevent the generation of bubbles, etc. that would otherwise occur in the molten molding material.

The thrust bearing 35, which is provided at the lower end of the cylinder rod 33 and comes into contact with the stopper plate 7, has two angular bearings 36 and 37 stacked symmetrically, as shown in FIG. 2(C). .37 inner race is fixed with a nut 38 screwed onto the stepped part of the cylinder rod 33 and the tip of the cylinder rod 33,
Further, the outer race is sandwiched and fixed between a cylindrical member 40 having a shoulder portion 39 and a cylindrical member 42 having a protruding portion 4l.
When the cylinder rod 33 comes into contact with the stopper plate 7, the cylindrical member 40.42 rotates, and the cylinder rod 33 does not rotate because of the interposition of the bearings 36.37.

24, 25, 26, 27, and 28 are sensors for detecting the stroke of the screw 2 or the hollow ball screw 6, 24 is a sack pack completion detection sensor, 25 is a metering completion detection sensor, and 26 is a screw overrun detection sensor. The sensor 27 is a hollow ball screw standby position sensor, and 28 is a screw movement stroke detection sensor for detecting the movement stroke of the screw 2. Each sensor is connected to a motor control device 30, and each detection result is input to this motor control device 30.

In this embodiment, the pressure setting means Y is based on the configuration shown in FIG.
,, the pressure comparison means 55, the speed setting means Yv, the speed comparison means 56, the tacho generator M, the motor amplifier Ma, etc. are similarly provided in the apparatus shown in FIG. ．． Sv and the screw movement detection value are sent to the motor control device 30, and the current value i or voltage value V controlled by this control device 30 is sent to the motor 19 via the motor amplifier MA.

In this embodiment, it is assumed that a pressure-holding tie and a cooling timer are installed in the motor control device 30 in order to measure the pressure-holding time and cooling time of the molded product in the mold cavity. .

Next, regarding the operation of the electric injection device configured as described above, the operation diagrams shown in FIGS. 4(a) to (e), the flowchart shown in FIG. 5, and the speed control and pressure control of the motor shown in FIG. This will be explained with reference to a diagram showing the relationship.

Note that the symbol S in parentheses indicates a step in the flowchart shown in FIG.

FIG. 4(a) shows the state during metering and crosstalk.

The back pressure cylinder 22 and metering clutch 16 are in the ON state (Sl). At this time, motor l9 rotates clockwise (CW).
; clockwise) (S2). screw 2
is rotated via the timing belt 12, spline nut 8, and spline shaft 3, and the molding material supplied into the heating cylinder 1 is kneaded and molten.

As this molten molding material accumulates in front of the screw within the heating cylinder 1, the screw 2 retreats upward within the heating cylinder 1. At the same time, back pressure is applied to the screw 2 by the back pressure cylinder 22 via the stopper plate 7, the guide shaft 5, and the spline shaft 3.

Next, the screw 2 rises to the state shown in FIG. 4(b), and the measurement completion detection sensor 25 receives an ON signal (S
3) Then, the motor 19 is stopped (S4). After the weighing and resting are completed, the weighing clutch and back pressure cylinder are turned off.
F is performed (S5).

While the molding material is being measured and kneaded in the cylinder 1 as described above, the molding material that was measured and kneaded in the previous step and injected into the mold cavity (not shown) is simultaneously cooled. It is being done. At this time, when the mold is opened to take out the molded product in the next step, sack packing is performed to prevent the molten molding material measured in this step from leaking from the injection port of the cylinder 1. Therefore,
Metering/mixing clutch l6 and back pressure cylinder 22 are OF
After F, the injection clutch 17 is turned on (S6). Motor l9 is rotated clockwise (CW) (S7). As a result, as shown in FIG. 4(C), the hollow ball screw 6 is connected via the timing belt l3 and the pole nut 9.
When the stopper plate 7 is raised by an amount a, the hollow ball screw 6 activates the suckback completion detection sensor 24.
When the detection sensor 24 is turned on, the motor 19 is stopped (S9) and the suckback is completed.

After that, the cooling timer counts up (SIO
) and the above cooling is completed, the mold is unclamped (Sll
) The mold was opened (S12) and the molded product was taken out (S12).
13), the mold is closed again (S14), and the mold is clamped (S15).
) is carried out.

Next, in order to inject the kneaded molding material into the mold that has been clamped as described above, the motor 19 rotates counterclockwise (CC
W. Counter Clock Quiz) is rotated (S1
6). At this time, since the injection clutch l7 is still in the ON state, when the motor 19 is rotated counterclockwise, a downward thrust is applied to the hollow ball screw 6. On this occasion,
The hollow ball screw 6 is first fed blankly, and then as shown in Fig. 4 (
As shown in d), the pressure sensor 50 at the lower end of the hollow ball screw 6 hits the upper end 3a of the spline shaft, pushing the screw 2 downward and injecting it into the mold.

At the same time, the detected value P2 from this sensor is sent to the pressure comparison means 55. Note that the back pressure cylinder 22 is OF
F, so the cylinder rod 33 is as shown in Figure 4(c).
It will remain in position.

The speed control (Sl7) of the motor during this injection is such that the speed VI is set in the speed setting means Yv in FIG. The rotation speed V2 of the motor 19 detected by the MT is input to the speed comparison means 56, and the motor rotation speed v2 is determined to be the set speed V. based on the instruction Sv based on the comparison results. This is done by determining the voltage value V to be supplied from the motor control device C to the motor 19 so that it always coincides with . As described above, the detection signal S. When is issued, that is, the screw stroke detection sensor is ON.
(S18), the filling rate is changed to the set filling rate (for example, 90
%) (indicated by SP in FIG. 6), the control of the motor 19 is changed from the speed control described above to the pressure control ia.
[Switch to (S19). This pressure control is performed using a pressure value P1 preset in the pressure setting means Y in FIG.
and the injection pressure P of the screw 2 detected by the pressure sensor 50 are sent to the pressure comparison means 55, and the motor controller C controls the injection pressure P2 to always match the set pressure P1 based on the instruction Sp based on the comparison results. from motor 1
This is done by determining the current value i to be fed to 9. In this way, injection is performed to fill the remaining amount (for example, 10%), and when the pressure setting value P1 is reached (Sl9°), the holding pressure timer starts counting (S19'').This completes the injection. Subsequently, the motor moves to a pressure holding state where a constant pressure is applied to the blank material under pressure control.Assuming that the injection is completed as shown in Fig. 4(d), C is the hollow ball screw movement stroke, and d is the injection stroke. be.

Note that 26 is a screw overrun detection sensor, and in normal operation, the hollow ball screw 6 is connected to the sensor 26.
Injection is completed at a position above.

Further, 28 is the screw stroke detection sensor 2 mentioned above.
It is ONL just before reaching this state at 8 (for example, at the 90% stroke point of injection - not shown).

Next, when the pressure holding timer counts up (S20
), the motor 19 is stopped to complete pressure holding, and the cooling timer starts counting (S21).

When the pressure holding is completed as described above, in order to prepare for the next metering and crosstalk, the motor 19 is rotated in the CW direction while keeping the injection clutch 17 in the ON state (S22), and the hollow ball screw 6 is moved to the hollow ball screw standby position. Pull up until the sensor 27 turns ON, and then remove the hollow ball screw standby position sensor 27.
When the motor 19 is turned on (323), the motor 19 stops (
S24), the hollow ball screw 6 is made to stand by at that position as shown in FIG. 4(e). Also, at this time, the injection clutch 17 is turned off (S25).

In addition, in FIG. 4(e), e is the hollow ball screw movement stroke.

After going through the steps above, turn on the metering clutch l6 again.
and back pressure cylinder ONL (S L). By repeating the above steps, mixing, measuring, backpressing, sack-packing, and injection of the molding material can be performed.

Here, speed control and pressure control of the motor 19 will be explained with reference to FIG. 6.

The steps on the horizontal axis correspond to the operations shown in the flowchart above. In the figure, the metering clutch is turned off during the metering and crosstalk process.
N, and the motor 19 rotates clockwise (CW) at a constant speed to perform metering and crosstalk (St to S3).
). Also, at this time, the back pressure cylinder 22 is turned on, and a constant back pressure is applied to the screw 2, which is retreating upward due to metering. The measurement completion detection sensor 25 is turned on (
S3) and the motor 19 is stopped (S4). Metering clutch l6 and back pressure cylinder 22 are turned off. Then,
The injection clutch 17 is turned on and the motor 19 rotates clockwise (C
A sack pack is performed by rotating it to W). Then, the sack pack completion detection sensor 24 is turned on (S8). After the motor 19 is stopped and the mold is opened and closed (810-S16), the motor 19 is rotated counterclockwise (CCW) (S16). This injection process (
In S L 6 to S19), the motor 19 is operated until the filling rate of the molding material into the mold cavity reaches, for example, about 90%.
The injection speed is controlled at a constant injection speed setting value V1 by speed control, and the subsequent filling and holding pressure of the molding material is controlled by the injection force setting value P.
This is done by pressure control in step 1. In the figure, SP indicates the timing of switching from speed control to pressure control of motor 19. Next, after the pressure holding timer counts up (S20), the motor 19 is turned off (S2 1). Next, the motor 19 is switched clockwise (CW), and when the standby position sensor 27 is turned on (S23), the motor 19 is stopped (S24).
, turn off the injection clutch l7 and move on to the next cross-talk process. (Effects of the Invention) As explained above, in the screw thrust control method of the injection molding machine of the present invention, the filling rate of the molding material in the cavity is set immediately before the holding stroke, and the filling rate of the molding material in the cavity is set from the start of injection. Injection is performed at a constant injection rate by controlling the speed of the screw until the filling rate is reached, and the remaining injection and pressure holding control is performed by controlling the desired screw thrust using a pressure detection means that detects the injection pressure of the screw. Therefore, it is possible to obtain the desired screw thrust in the pressure holding process and to obtain a constant injection rate by controlling the speed of the screw in the injection process.
In particular, even when molding a thin molded product, by filling the cavity with a certain resin tightly without leaving any voids, it is possible to obtain a molded product without whiskers or shape defects.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the method of the present invention, and FIG.
FIG. 2(a) is a schematic sectional view of the embodiment device according to the present invention, FIG. 2(b) is a sectional view taken along line nn in FIG.
Figure (c) is an In-III sectional view in Figure 2 (a), Figure 3 is a perspective view of the rotation mechanism, linear mechanism, back pressure mechanism, clutch and electric motor in Figure 2, and Figure 4 (
a) to (e) are explanatory diagrams of the operation of the embodiment device, FIG. 5 is a flowchart of injection molding in the embodiment device, FIG. 6 is a diagram showing the relationship between motor rotational speed control and pressure control, and FIG.
The figure is a structural diagram showing screw thrust force control of a conventional injection molding machine. 1... Heating cylinder 2... Screw 3... Spline shaft 3a... Spline shaft shoulder 5... Hollow ball screw guide shaft 6... Hollow ball screw 7... Stopper plate 8... Spline Nut 9...Pole nut 10.11...Output side swimming boley 12.13
...Timing belt 14.15...Manual side timing booley 16...
Metering clutch 17...Injection clutch 8...Input shaft 9, M. ...Motor l...Injection unit base 2...Back pressure cylinder 3...Pressure regulator 4...Suckback completion detection sensor 5...Measuring completion detection sensor 6...Screw overrun Detection sensor 7...
Hollow ball screw standby position sensor 8...Screw movement stroke detection sensor 0. Mo... Motor control device 3... Cylinder rod O... Pressure sensor 1... Mold 2... Cavity 5... Pressure comparison means 6... Speed comparison means

Claims (1)

[Claims] (1) An electric injection device that uses a motor to drive a screw housed in a heating cylinder, which includes pressure detection means for detecting the injection pressure of the screw and means for detecting the stroke of the screw, The injection molding machine is characterized in that the speed is controlled until the filling rate of the molding material in the mold reaches a set value immediately before the pressure holding stroke, and subsequent injection and pressure holding control are performed by the output of the pressure detection means. screw thrust control method.