JP2005041236A - Method for controlling injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling an injection molding machine by which correction control can be performed so as to maintain the same flight posture of a screw at the time of the start of metering. <P>SOLUTION: In this method, a reference angle position is previously set at the rotating angle position of a screw and the angle correction operation for correcting the rotating angle position of the screw so as to make the former agree with the reference angle position, is performed at an arbitrary shot interval correspondingly with a pressure relief operation before the start of a metering process from the end of a dwelling process. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for controlling an injection molding machine.

  With reference to FIG. 2, an electric injection molding machine will be described focusing on the injection device. The injection device performs filling of the molten resin by converting the rotary motion of the servo motor into a linear motion using a ball screw and a nut. In FIG. 2, the rotation of the injection servo motor 10 is transmitted to the ball screw 11. A nut 12 that moves forward and backward by the rotation of the ball screw 11 is fixed to a pressure plate 13, and the pressure plate 13 is movably attached on a plurality of guide bars 14 fixed to a frame (not shown). The forward / backward movement of the pressure plate 13 is transmitted to the screw 20 via the load cell 15, the bearing 16, and the drive shaft 17. The drive shaft 17 is also rotationally driven via a timing belt 18 by a servo motor 19 for rotationally driving the screw.

  When the screw 20 is driven to rotate in the heating cylinder 21 by the drive of the servo motor 19 for rotating the screw, the molten resin is stored at the tip of the heating cylinder 21. Then, the molten resin stored by advancing the screw 20 by driving the servomotor 10 for injection is filled in the mold and pressed to perform molding. At this time, the force pushing the resin is detected as a reaction force by the load cell 15, amplified by the load cell amplifier 22, and input to the controller 23. A position detector 24 for detecting the amount of movement of the screw 20 is attached to the pressure plate 13, and this detection signal is amplified by an amplifier 25 and input to the controller 23. The controller 23 outputs a current (torque) command corresponding to each process to the servo amplifiers 26 and 27 according to the setting of the operator, and the servo amplifiers 26 and 27 control the drive current of the servo motors 10 and 19 to control the servo. The output torque of the motors 10 and 19 is controlled.

  Next, the screw 20 will be described in detail with reference to FIG. In Fig.3 (a), the screw 20 is divided into the supply part 20-1, the compression part 20-2, the measurement part 20-3, and the head part 20-4. The supply unit 20-1 is a part for feeding the resin supplied from the hopper in a solid state or by melting only a part thereof, and the resin is warmed to near the melting point during this period. For this reason, in the supply part 20-1, the diameter of the rod-shaped body which forms the spiral body (usually called a flight) shown by FIG.3 (b) is normally substantially constant.

  The compression unit 20-2 has a gap between the particles of the resin supplied from the supply unit 20-1, and the volume of the compression unit 20-2 is reduced to about half when the resin is melted. In order to compensate for this volume reduction, the space through which the resin can pass is reduced. This is realized by providing a taper on the rod-like body forming the spiral body in the compression section 20-2 to make the groove of the spiral body shallow. This compresses the molten resin, increases the heat generation effect due to friction, raises the resin pressure, and pushes back moisture, volatile gas, etc. contained in the air / resin to the hopper side. As is clear from this, the resin pressure in the heating cylinder is highest in the compression section 20-2.

  The metering unit 20-3 is the shallowest part of the spiral groove, and during this time, the resin is subjected to a large shearing force and raised to a homogeneous temperature with self-heating. Then, a certain amount of resin is sent out to the nozzle side.

  Note that the molten resin is fed from the measuring unit 20-3 to the nozzle side through the backflow prevention ring 20-5 in the head unit 20-4. The backflow prevention ring 20-5 is in a position on the left side in the drawing in the measuring step, and in this state, the molten resin can be sent out from the measuring unit 20-3 to the nozzle side. When the measuring process is completed, the backflow prevention ring 20-5 moves to a position on the right side in the figure due to the pressure difference. As a result, the return of the resin from the nozzle side to the measuring unit 20-3 side is prevented. Normally, the head portion 20-4 is configured by cutting a screw on the base side and screwing it into the tip of a rod-shaped body of the screw body. For this reason, the diameter of the base side of the head part 20-4 is smaller than the diameter of the rod-shaped body of the screw body.

  By the way, the variation of the screw flight position (screw angle) at the start of measurement is an unstable factor given to measurement. This is mainly because the posture of the screw flight at the hopper port for supplying the resin is not the same for each shot. The current metering system that performs pressure control has a mechanism in which variation factors occur in the pressure control during metering because a fluctuation factor is inherent in the biting pressure of the resin pellets.

  This will be described with reference to FIG. In FIG. 4, the resin pellets before melting are in the hopper. This function that is supplied to the front end side of the heating cylinder 21 by the rotation of the screw 20 is called a metering operation. This metering operation detects the reaction force obtained by rotating the screw 20 and feeding the resin forward, and controls the reverse speed of the screw 20 so as to make it constant. Therefore, all the pressure fluctuations generated by factors other than the resin being fed forward become disturbance factors.

  Here, the major factor of the disturbance is contact between the resin pellets at the hopper port 21-1 and the flight of the screw 20. Although this contact cannot be eliminated when the resin is supplied, the disturbance factor can be reduced if the disturbance is steadily applied between shots.

  When the hopper port 21-1 is viewed from above, the flight state of the screw 20 is as shown in FIG. At this time, even if the position of the screw 20 does not change, if the screw 20 rotates, the position of the flight moves forward or backward by one pitch. Conventionally, this movement for one pitch remains as a disturbance factor.

  Accordingly, an object of the present invention is to provide a control method for an injection molding machine capable of executing correction control so that the posture of a screw flight becomes the same at the start of weighing.

  According to the present invention, the reference angle position is set in advance to the rotation angle position of the screw, and the rotation angle position of the screw is set to the reference angle position in accordance with the pressure release operation from the end of the pressure holding process to the start of the weighing process. There is provided a control method for an injection molding machine, wherein an angle correction operation for correction so as to fit is executed at an arbitrary shot interval.

  In this control method, it is preferable that the angle correction operation is executed immediately before or immediately after the screw retraction operation performed immediately before the measuring step.

  In this control method, the angle correction operation is performed either in the forward rotation or the reverse rotation of the screw.

  In this control method, the angle correction operation may be performed for each shot so that the flight position of the screw at the start of measurement becomes constant.

  According to the present invention, the quality of the molded product, particularly the weight, can be stabilized by executing the correction control so that the posture of the screw flight becomes the same at the start of measurement.

  Embodiments of the present invention will be described below.

  In this embodiment, the reference angle position is set in advance to the rotation angle position of the screw, and the rotation angle position of the screw is matched with the reference angle position corresponding to the pressure release operation from the end of the pressure holding process to the start of the weighing process. An angle correction operation is performed for each shot.

  In order to execute such an angle correction operation, a deviation between the reference angular position and the current angular position of the screw is required. For this purpose, a detection signal of a rotary encoder installed in a screw rotation servomotor (19 in FIG. 2) is used. That is, since the detection signal corresponding to the rotation angle of the screw is obtained from the rotary encoder, the controller (23 in FIG. 2) can obtain the deviation between the reference angular position of the screw and the current angular position.

  When executing the angle correction operation, the controller rotates the screw in either the forward or reverse direction so that the above-described deviation becomes zero. Specifically, since the rotational speed of the screw is set in advance, the time to be rotated to make the deviation zero is calculated from the rotational speed and the deviation of the rotational angle up to the reference angular position. You just need to rotate the screw. Of course, the angle correction operation is performed by either forward rotation or reverse rotation of the screw. That is, if the angle deviation is negative, that is, if the difference is in the backward direction of the screw, correction by forward rotation (screw advance) is performed, and if the angle deviation is positive, that is, if the difference is in the forward direction of the screw, reverse rotation (screw backward) Correction is performed.

  Note that the injection molding is performed by repeating the operations of retreating before injection / holding pressure one metering, retreating after metering and one metering-injection / holding pressure. The above angle correction operation is performed at any timing immediately before or immediately after the pre-measurement backward, or immediately before or after the post-measurement backward. The pre-measurement retreat is an operation that is performed to perform pressure release after the pressure holding process is completed, and the post-measurement retreat is performed to perform pressure release after the measurement process is completed. Is the action. Here, for example, when the amount of resin filled in the mold is small (the weight of the molded product is small), the amount of movement of the screw is small. In such a case, if the angle correction operation is executed at the timing immediately before or after the retraction after weighing, the movement of the screw accompanying the angle correction may affect the resin density, and thus may adversely affect the molding quality. Therefore, the angle correction operation is preferably performed immediately before or immediately after the pre-measurement retreat.

  As described above, the screw flight position at the start of measurement is made constant by performing a correction operation for each shot so that the rotation angle position of the screw matches the reference angle position with the reference angle position set in advance as a reference. To do.

  In the electric injection molding machine, during the screw retraction operation during metering, the controller actively controls the retraction speed while monitoring the pressure value detected by the load cell (15 in FIG. 2). For this reason, if there is a variation in the rising characteristic of the pressure, as shown in FIG. 1 (a), a variation occurs in the retreat start position of the screw. On the other hand, by fixing the screw rotation angle position to the reference angle position by the angle correction operation, the above-described variation is improved as shown in FIG.

  And since the flight position of the screw at the start of measurement becomes constant, the state of resin biting at the hopper mouth is made uniform between shots. As a result, the resin density distribution on the front end side of the heating cylinder is improved in a uniform direction, and the quality of the molded product is stabilized.

  In the above embodiment, the angle correction operation is performed for each shot, but may be performed at an arbitrary shot interval.

It is a characteristic figure of the time-screw position for demonstrating the difference between the case where the angle correction operation by this invention is performed (b), and the case where it does not perform (a). It is the figure which showed the structure of the electric injection molding machine centering on the injection device. It is a figure for demonstrating an example of the screw of an injection molding machine. It is a schematic diagram for demonstrating the relationship between the screw position in the hopper mouth of a heating cylinder, and resin.

Explanation of symbols

11 Ball screw 12 Nut 13 Pressure plate 14 Guide bar 15 Load cell 16 Bearing 17 Drive shaft 18 Timing belt 20 Screw 21 Heating cylinder 24 Position detector

Claims (4)

Set the reference angular position in advance to the rotational angle position of the screw,
Corresponding to the pressure release operation from the end of the pressure holding process to before the start of the weighing process, an angle correction operation for correcting the rotation angle position of the screw to match the reference angle position is executed at an arbitrary shot interval. Control method for injection molding machine.   2. The control method for an injection molding machine according to claim 1, wherein the angle correction operation is executed immediately before or immediately after the screw retraction operation performed immediately before the measuring step.   3. The control method according to claim 1, wherein the angle correction operation is performed in either a forward rotation or a reverse rotation of the screw. 4. The injection molding machine according to claim 1, wherein the angle correction operation is performed for each shot so that the flight position of the screw at the start of measurement is constant. Control method.

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