JPH09300410A - Back pressure control method for electric injection molding machine - Google Patents

Abstract

(57) Abstract: In an injection device using an electric motor of an electric injection molding machine as a drive source, the screw does not move forward during the process of measuring the molding material, the feedback control constant is not adjusted, and a stable spin is achieved. A back pressure control method that enables easy pressure control. In an injection device using an electric motor of an electric injection molding machine as a drive source, when a back pressure of a molten molding material in a measuring step exceeds a set value, a screw 2 is retracted a minute distance,
The retreat of the screw 2 is repeated.

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 back pressure of an injection device using an electric motor as a drive source in an electric injection molding machine.

[0002]

2. Description of the Related Art Generally, in an electric injection molding machine, in an in-line screw type injection device using an electric motor as a drive source,
In order to control the back pressure during the measuring process of the molding material due to the rotation of the screw by the plasticizing electric motor, the output torque of the injection electric motor that is connected to the screw is controlled via the transmission mechanism that converts the rotational movement into forward and backward movement. This has been done conventionally.

In the back pressure control method disclosed in Japanese Patent Laid-Open No. 61-321221, an electric motor for back pressure control is provided at the end of the screw, and the pressure of the molten molding material or the reaction force of the screw is applied to the screw back pressure. As a result, the back pressure control electric motor is driven based on the signal obtained by calculating and amplifying the difference signal between the obtained back pressure measurement signal and the back pressure command signal so that the back pressure matches the set value. The output torque is feedback controlled.

Alternatively, the back pressure control is performed by utilizing the braking action of the electric motor to control the output torque value (current value of the electric motor) of the electric motor to a constant value to give back pressure to the screw.

[0005]

Since the conventional back pressure control method for the injection device using the electric motor as a drive source in the electric injection molding machine is configured as described above, the following problems exist. ing. That is, when the back pressure is controlled by controlling the output torque (rotational force) of the electric motor, it is possible to control the back pressure lower than the back pressure due to the resistance generated by the frictional force of the transmission mechanism. Is lower than the set back pressure, the output torque is generated in the direction in which the back pressure increases. Therefore, at the time when the screw rotation speed has not yet risen to the predetermined value, the amount of material stored in the cylinder is insufficient, and the screw retracting force is not generated, as in the case of the start of measurement, the screw is forcibly advanced. . Similarly, when the back pressure is controlled by controlling the output torque value of the electric motor to be constant, if the screw retreating force is smaller than the output torque of the electric motor, the screw retreating force and the output torque of the electric motor are balanced until the screw retreating force is equal to the output torque of the electric motor. Moves forward. As a result, the screw is given a back pressure irrespective of the material storage speed accompanying the rotation of the screw, and stable weighing cannot be performed. Also, the screw may advance to the forward limit and be damaged.

Further, the optimum value of the feedback control constant of the control device in the feedback control differs when the type of molding material changes or the molding conditions change.
Furthermore, stable back pressure control cannot be performed because the control gain does not change appropriately due to the inertial force of the transmission mechanism, the non-linear control system, and the like. Therefore, adjusting the feedback control constant is complicated and difficult.

The present invention has been made to solve the above problems, and in an injection device using an electric motor of an electric injection molding machine as a drive source, the screw does not move forward during the step of measuring the molding material. An object of the present invention is to provide a back pressure control method that easily enables stable back pressure control without adjusting the feedback control constant.

[0008]

In order to achieve the above object, a back pressure control method according to the present invention in an injection device using an electric motor of an electric injection molding machine as a drive source is configured as follows. ing. That is, in the injection device using the electric motor of the electric injection molding machine as a drive source, when the back pressure of the molten molding material in the measuring step exceeds the set value, the screw is retracted by a minute distance, and the screw is repeatedly retracted.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a back pressure control method in an injection device using an electric motor of an electric injection molding machine as a drive source according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a configuration diagram of an injection device using a motor as a drive source to which the back pressure control method of the present invention is applied. In FIG. 1, a reference numeral 1 is a cylinder, and a screw 2 is rotatably driven in the cylinder 1. A plasticizing electric motor 3 is connected to the rear end of the screw 2 via a first timing belt 4. Further, the screw 2 is connected to a moving plate 7 in the axial direction of the rear end via a thrust bearing 5 and a load cell 6. A ball nut 8b of a ball screw 8 is provided on the moving plate 7 in parallel with the screw 2. A ball screw shaft 8a is screwed into the ball nut 8b, and the injection motor 9 is attached to the second timing belt 10 at one end of the ball screw shaft 8a.
Are connected via

Control device 2 for controlling the operation of the injection device
1 outputs a speed command signal 21B to the plasticizing electric motor 3 via the first servo motor amplifier 22, and outputs a position command signal 21A to the injection electric motor 9 via the second servo motor amplifier 23. Further, the back pressure measurement value signal of the load cell 6 is input to the control device 21 via the amplifier 24. In the first servo motor amplifier 22, a measured value signal 3aA of the rotation speed of the plasticizing electric motor 3 is output from an encoder 3a provided in the plasticizing electric motor 3.
Is input, and the measurement value signal 9aA of the position of the injection motor 9 is input to the second servo motor amplifier 23 from the encoder 9a provided in the injection motor 9.

In the injection device constructed as described above, the operation of the measuring process is performed as follows. FIG. 2 is a flow chart showing a control example of the weighing process, and FIG. 3 is a diagram showing a first form of control timing. That is, in a state in which the screw 2 is fully inserted into the cylinder 1, first, the speed command signal is output from the control device 21 to the plasticizing electric motor 3 via the first servo motor amplifier 22 together with the start signal, and the metering is performed. The operation is started (first
Step 100). As a result, the plasticizing electric motor 3 is started, controlled to rotate at a predetermined rotational speed, and rotated, and the screw 2 is rotationally driven via the first timing belt 4. On the other hand, a position command signal is output from the control device 21 to the injection electric motor 9 via the second servo motor amplifier 23. As a result, the injection motor 9 is servo-locked at the current position (second step 101), and the moving plate 7 is fixed at the current position.

By the rotation of the screw 2, the molten molding material is stored at the tip of the cylinder 1, and the screw 2 is pulled backward by the pressure of the molten molding material with respect to the cylinder 1 fixed to a frame (not shown). Trying to retreat. The load cell 6 is distorted due to the backward movement of the screw 2, that is, the back pressure, and the generated strain data is input from the load cell 6 to the control device 21 via the amplifier 24 as the back pressure measurement value signal 21a.

Next, in the control device 21, a minute predetermined time Δ from the time when the current position of the injection motor 9 is servo-locked.
Every time t (for example, 10 milliseconds) elapses (third step 102)
In addition, the back pressure measurement value signal 2 constantly input from the load cell 6
4a is compared with the back pressure set value input to the control device 21 in advance (fourth step 103). When the back pressure measurement value is equal to or less than the back pressure setting value, the servo lock state of the injection motor 9 is maintained. When the back pressure measurement value signal 21a exceeds the back pressure setting value, the injection motor 9 is moved so as to retract the moving plate 7 by a minute axial distance Δpos (for example, 0.1 mm) (fifth step 104). The position command signal 21A is output to. The injection motor 9 is driven by the position command signal 21A.
Rotates a predetermined number of revolutions, and the moving plate 7 moves backward by a distance Δpos via the ball screw 8.

The strain generated in the load cell 6 due to the retreat of the moving plate 7 is eliminated or becomes a minute amount less than the back pressure set value.
The screw 2 also retreats within the distance Δpos. When the screw 2 is retracted, the plasticizing motor 3 is integrally retracted by a frame (not shown). The back pressure of the molten molding material fluctuates within a minute range around the back pressure setting value by retracting the moving plate 7 by a minute axial distance Δpos every time a minute predetermined time Δt elapses. Can be regarded as being controlled to a constant value of.

As described above, the comparison between the back pressure measurement value and the back pressure set value and the retraction of the distance Δpos are repeated every time the time Δt elapses, and the screw 2 is also retracted a minute distance, and the screw 2 is weighed. When the completion position is reached (sixth step 105), the injection electric motor 9 is servo-locked (seventh step 1
06), and the rotation of the plasticizing electric motor 3 is stopped (eighth step 107).

FIG. 4 is a diagram showing a second form of control timing. In the first form shown in FIG. 3, the retreat distance of the moving plate 7 is always constant Δpos, but in the second form shown in FIG. 4, first, it is moved backward by 2Δpos and then moved forward by Δpos. The distance is Δpos. As described above, the position command signal to the injection motor 9 may be set in various forms depending on the weighing process.

In the above embodiment, the signal output from the control device 21 to the injection motor 9 may be a time command signal instead of the position command signal. That is, when the injection motor 9 rotates for a minute predetermined time Δt1, the moving plate 7 retracts a minute axial distance Δpos1. Further, the back pressure measurement value may be obtained directly from the molten molding material stored in the tip portion (not shown) of the cylinder 1 instead of the load cell 6.

[0018]

The back pressure control method for an electric injection molding machine according to the present invention is configured as described above, so that the following effects can be obtained. That is, in an injection device that uses an electric motor of an electric injection molding machine as a drive source, when the back pressure of the molten molding material in the measuring step exceeds a set value, the screw is retracted a minute distance, and the screw is repeatedly retracted to control the back pressure. As a result, the screw does not move forward during the measuring process of the molding material, and basically the feedback control constant is not adjusted but the feedback control constant is not adjusted. This makes it possible to easily control the back pressure.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an injection device to which a back pressure control method according to the present invention is applied.

FIG. 2 is a flow chart showing a control example of a weighing process in the back pressure control method according to the present invention.

FIG. 3 is a diagram showing a first embodiment of control timing in the back pressure control method according to the present invention.

FIG. 4 is a diagram showing a second embodiment of the control timing in the back pressure control method according to the present invention.

[Explanation of symbols]

 1 ··· Cylinder 2 ··· Screw 3 ··· Plasticizing motor 6 ··· Load cell 7 ··· Moving plate 8 ··・ Ball screw 9 ・ ・ ・ ・ Injection electric motor 21 ・ ・ ・ ・ Control device 22 ・ ・ ・ ・ ・ ・ First servo motor amplifier 23 ・ ・ ・ ・ ・ ・ ・ ・ Second servo motor amplifier 24 ・ ・ ・··amplifier

Claims (3)

[Claims] 1. In an injection device using an electric motor (9) of an electric injection molding machine as a drive source, when the back pressure of the molten molding material in a measuring step exceeds a set value, the screw (2) is retracted by a minute distance, and the screw (2) is retracted. A back pressure control method for an electric injection molding machine, characterized in that (2) is repeated for a minute distance. 2. An injection device using an electric motor (9) of an electric injection molding machine as a drive source, wherein a back pressure of a molten molding material in a measuring step is measured, and the back pressure measurement value and the back pressure set value are minutely measured. When the back pressure measurement value exceeds the back pressure setting value, the screw (2) is retracted by a small axial distance (Δpos, Δpos), and is compared with each other after a predetermined time (Δt) elapses. Minute axial distance of screw (2) (△ pos, △ po
s) A back pressure control method for an electric injection molding machine, which is characterized by repeating retreat. 3. A load cell (6) in which the back pressure of the molten molding material is axially connected to the rear end of the screw (2).
The back pressure control method for an electric injection molding machine according to claim 1 or 2, wherein