JP5702878B2 - Pressure control device for injection molding machine - Google Patents

Description

  The present invention relates to a pressure control device for an injection molding machine.

  In an in-line screw type injection molding machine, the screw is moved backward while rotating the screw in the heating cylinder, and the metering process in which the molten resin is pumped to the tip of the heating cylinder, and then the screw is advanced into the mold. An injection process for filling the molten resin and a pressure holding process are performed.

  In the injection process, the mold is filled with the molten resin in the heating cylinder by advancing the screw based on a preset injection stroke and injection speed. Then, when moving forward to the injection / holding pressure switching position, the injection process is switched to the pressure holding process. In the pressure-holding step, pressure control is performed based on a preset pressure-holding pressure and pressure-holding time, so that the molten resin is fully filled in the mold, and further, sink marks of the molded product due to resin shrinkage are compensated.

  In Patent Literature 1, the screw is advanced to start filling the resin into the mold cavity, and the screw position of the screw is maintained before the resin is filled in the cavity. A technique for shifting to a pressure holding process after filling is disclosed (see FIG. 5).

  In Patent Document 2, the pack pressure control timer starts to be counted from the point in time when the injection pressure reaches the preset switching pressure, and the pack pressure is applied. A technique for switching to control is disclosed. In Patent Document 3, filling is performed by speed control until the detected value of the filling pressure reaches the first set pressure value, and the detected value of the filling pressure becomes equal to or higher than the first set pressure value. Then, the control is switched from the speed control to the pressure control controlled by the first set pressure value, and the second set pressure is reached when the filling speed becomes lower than the set speed in the state where the filling is performed by the pressure control. A technique for switching to holding pressure control that is controlled by a value is disclosed (see FIG. 6).

JP 2008-74114 A JP-A-2-274522 JP 2010-721 A

  In order to fully fill the resin when the resin flow path in the mold is narrow or in the case of thin-wall molding, a large peak pressure may be required in the injection / pressure holding process. However, if the peak pressure is excessive, the heating cylinder or mold may be damaged, or burrs may occur in the molded product, so the mold is fully filled with resin without generating excessive peak pressure. Technology is required.

  Here, the filling performance of the resin into the mold cavity per injection pressure is referred to as filling efficiency. The higher the filling efficiency, the more resin can be fully filled in the mold with a lower injection pressure. In order to obtain high filling efficiency, pressure control that maintains high pressure within the range that does not become excessive until filling completion or just before filling completion, that is, peak pressure holding control, is followed by a pressure holding process that compensates for sink marks in the molded product. It is desirable to switch.

  Accordingly, an object of the present invention is a pressure control device for an injection molding machine, comprising a pressure control unit that controls an injection pressure in a pressure-holding step, a peak pressure detection unit, and a peak pressure holding control unit, wherein the peak pressure The detection unit detects a peak pressure generation time and a peak pressure value of the injection pressure, and the peak pressure holding control unit is configured to detect a peak pressure holding control completion condition from when the peak pressure is generated in the pressure holding process. In the meantime, the present invention is to provide a pressure control device for an injection molding machine that performs pressure control so that the injection pressure maintains the detected peak pressure value.

  The invention according to claim 1 of the present application includes an injection screw driving unit that drives an injection screw, an injection pressure detection unit that detects an injection pressure, a screw speed control unit that controls a moving speed of the injection screw in an injection process, A pressure control unit that controls the injection pressure in the pressure-holding process, an injection pressure-holding switching unit that switches from the injection process to the pressure-holding process, and a peak pressure detection unit that detects the peak pressure generation point and the peak pressure value of the injection pressure. In the pressure holding process, the peak is controlled so that the injection pressure holds the detected peak pressure value from the time when the peak pressure is generated to the time when the peak pressure holding control completion condition is satisfied. A pressure holding control unit, and the pressure control unit is based on a set pressure of the pressure holding process from the time when the peak pressure holding control is completed to the time when the pressure holding process is completed. A pressure control device for an injection molding machine and performs pressure control.

According to a second aspect of the present invention, the peak pressure holding control completion condition is that a predetermined time elapses from the peak pressure generation time, a screw is advanced by a predetermined screw advance amount from the peak pressure generation time, or a screw advance speed. The pressure control device for an injection molding machine according to claim 1, wherein the pressure control device is at least one of decreasing to a predetermined speed.
According to a third aspect of the present invention, the peak pressure detection unit detects a point in time when the pressure change amount per unit time becomes a predetermined change amount or less, or a time point when the screw speed becomes a predetermined speed or less as the peak pressure generation time 3. The pressure control device for an injection molding machine according to claim 1, wherein the injection pressure at the time when the peak pressure is generated is detected as a peak pressure value.

The invention according to claim 4 is characterized in that the pressure control unit performs pressure control based on the set pressure in the pressure holding process from the injection holding pressure switching time to the peak pressure generation time. 4. The pressure control device for an injection molding machine according to any one of 3 above.
The invention according to claim 5 is characterized in that the pressure control unit controls the screw speed to be equal to or lower than the pressure holding limit speed from the injection holding pressure switching time to the peak pressure generation time. It is a pressure control apparatus of the injection molding machine as described in any one of -3.

  According to the pressure control device for an injection molding machine according to the present invention, by maintaining the peak pressure value from the time when the peak pressure is detected, a high filling efficiency can be obtained while suppressing the pressure value to be lower than the occurrence of burrs. Further, according to the present invention, after the peak pressure holding control completion condition is satisfied, the pressure is controlled to compensate for the sink of the molded product. Can be prevented.

It is a schematic block diagram of the injection molding machine and the control apparatus which controls this injection molding machine. It is a block diagram showing one embodiment of a pressure control device concerning the present invention. It is a graph for demonstrating temporal transition between one molding cycle of the injection pressure at the time of shape | molding with the injection molding machine which has the pressure control apparatus which concerns on this invention, and a screw position. It is a figure explaining the flow of the process of the pressure control which the pressure control apparatus which concerns on this invention performs. It is a graph for demonstrating temporal transition between one molding cycle of the injection pressure at the time of shape | molding with the injection molding method which concerns on a prior art (patent document 1), and a screw position. It is a graph for demonstrating temporal transition between one molding cycle of the injection pressure at the time of shape | molding with the injection molding method which concerns on a prior art (patent documents 2, 3), and a screw position.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an injection molding machine and a control device that controls the injection molding machine. A nozzle 2 is attached to the tip of the cylinder 1 in which the screw 3 is inserted, and a hopper 4 for supplying resin pellets to the cylinder 1 is attached to the side of the rear end of the cylinder 1. The screw 3 is driven in the axial direction by an injection servo motor M1 as a driving means for driving the screw 3 in the axial direction, a transmission mechanism, and a conversion mechanism 7 that converts a rotary motion of a ball screw / nut or the like into a linear motion. And back pressure control. The screw 3 is rotationally driven by a servo motor M2 as a rotational driving means for rotating the screw 3 and a transmission mechanism 6 including a belt, a pulley, and the like.

  A position / speed detector Penc1 and a position / speed detector Penc2 for detecting the rotation position / speed are attached to the injection servomotor M1 and the screw rotation servomotor M2, respectively. These position / speed detectors Penc1 and Penc2 can detect the position of the screw 3 (position in the screw axis direction), the moving speed (injection speed), and the rotational speed of the screw 3. In addition, a pressure sensor 5 such as a load cell that detects the pressure in the axial direction of the screw from the molten resin applied to the screw 3 is provided.

  Connected to the PMCCPU 17 are a ROM 18 storing a sequence program for controlling the sequence operation of the injection molding machine and a RAM 19 used for temporary storage of calculation data. Connected to the CNC CPU 20 are a ROM 21 that stores an automatic operation program and the like for overall control of the injection molding machine, and a RAM 22 that is used for temporary storage of calculation data.

  The servo CPU 15 is connected to a ROM 13 that stores a control program dedicated to servo control that performs processing of a position loop, a speed loop, and a current loop, and a RAM 14 that is used for temporary storage of data. Furthermore, the servo CPU 15 is connected to a servo amplifier 12 that drives a screw rotation servomotor M2 and a servo amplifier 11 that drives an injection servomotor M1 based on a command from the servo CPU15.

  As described above, the position / speed detectors Penc1 and Penc2 are attached to the servomotors M1 and M2, respectively. Outputs from these position / velocity detectors Penc 1 and Penc 2 are fed back to the servo CPU 15. The servo CPU 15 receives a movement command to each axis (injection servo motor M1 or screw rotation servo motor M2) commanded by the CNC CPU 20, and detection fed back from the position / speed detector Penc1 and position / speed detector Penc2. Based on the position and detection speed, position and speed feedback control is performed, and current feedback control is also executed to drive-control the servo amplifiers 11 and 12.

  Further, a current position register for obtaining the forward position (axial position) of the screw 3 by a position feedback signal from the position / speed detector Penc1 is provided, and the screw position can be detected by the current position register. ing. Further, the servo CPU 15 receives a resin pressure (resin pressure applied to the screw) obtained by converting a detection signal (analog signal) from the pressure sensor 5 into a digital signal by the A / D converter 16.

  An LCD / MDI (manual input device with a liquid crystal display device) 25 is connected to a bus 26 via an LCD display circuit 24. Further, a molding data storage RAM 23 composed of a nonvolatile memory is also connected to the bus 26. The molding data storage RAM 23 stores molding conditions relating to injection molding work, various set values, parameters, macro variables, and the like.

  With the above configuration, the PMC CPU 17 controls the sequence operation of the entire injection molding machine, and the CNC CPU 20 controls the servo motors M1 and M2 for each axis based on the operating conditions stored in the ROM 21 and the molding conditions stored in the molding data storage RAM 23. To distribute the movement command. Further, the servo CPU 15 sends a movement command distributed to each axis (injection servo motor M1 and screw rotation servo motor M2), and position and speed feedback signals detected by the position / speed detectors Penc1 and Penc2. Based on the above, servo control of position loop control, speed loop control, and current loop control is performed in the same manner as in the past, and so-called digital servo processing is executed.

Next, an embodiment of a pressure control device for an injection molding machine according to the present invention will be described with reference to the block diagram of FIG.
The pressure control device of the injection molding machine includes an injection screw drive unit 30 that drives the screw 3, an injection pressure detection unit 40 that detects the injection pressure, a screw speed control unit 31 that controls the moving speed of the screw 3 in the injection process, and The pressure control unit 32 that controls the injection pressure in the pressure holding step, the injection pressure holding switching unit 50 that switches from the injection step to the pressure holding step, and the peak pressure detection that detects the peak pressure generation point and the peak pressure value of the injection pressure Unit 41 and a peak pressure holding control unit 42.

The screw speed control unit 31 receives a speed command from either the peak pressure holding control unit 42 (contact point B) or the pressure control unit 32 (contact point A), and sends a torque command to the injection screw drive unit 30 (servo amplifiers 11 and 12). To drive the injection servo motor M1.
The peak pressure detector 41 detects the peak pressure generation time and the peak pressure from the value of the injection pressure detected by the injection pressure detector 40. The peak pressure detected by the peak pressure detection unit 41 is output to the peak pressure holding control unit 42.

  In the pressure holding process, the peak pressure holding control unit 42 gives a speed command to the screw speed control unit 31 via the switching contact B from the time when the peak pressure is generated until the time when the peak pressure holding control completion condition is satisfied. The pressure control is performed so that the injection pressure maintains the peak pressure value detected by the peak pressure detection unit 41.

  On the other hand, the pressure control unit 32 receives the injection pressure from the injection pressure detection unit 40, holds the pressure from the injection holding pressure switching time by the injection holding pressure switching unit 50 to the peak pressure generation time, and from the time when the peak pressure holding control is completed. Until the completion of the process, the speed control is performed based on the set pressure of the pressure holding process by giving a speed command to the screw speed control unit 31 via the switching contact A.

Next, the injection pressure control executed by the pressure control device of the injection molding machine according to the present invention will be described with reference to FIG.
In order to reduce the excessive peak pressure during filling and to obtain high filling efficiency within the prescribed injection pressure, as described above, the peak pressure generated during injection holding pressure switching should be slightly before filling completion or filling completion. It is desirable to perform pressure control (that is, peak pressure holding control) that maintains the pressure until the pressure is maintained, and then switch to a pressure holding process that compensates for sink marks in the molded product.

  FIG. 3 is a graph for explaining the temporal transition of the injection pressure and screw position during one molding cycle when molding is performed by an injection molding machine having the pressure control device according to the present invention. In the pressure control by the pressure control device of the present invention, as shown in FIG. 3, the speed control in the injection process is switched to the pressure control in the pressure holding process, and the peak pressure holding control completion condition is satisfied when the injection pressure reaches the peak value. 1 is held, and the pressure control is performed by the control device 10 shown in FIG. 1 based on the set pressure in the pressure holding process from the time when the peak pressure holding control is completed to the time when the pressure holding process is completed. .

  As shown in FIG. 3, in the pressure control device of the injection molding machine of the present invention, by holding the peak pressure value from the time when the peak pressure is detected, high filling while suppressing the pressure value lower than the occurrence of burrs. Efficiency is obtained. After the peak pressure hold control completion condition is satisfied, pressure control is performed based on the set pressure of the pressure holding process that compensates for sink marks in the molded product, so that the molded product is distorted by holding the peak pressure for a long time. Can be prevented.

<Peak pressure detector>
The injection pressure may be acquired by detecting the force that the screw receives in the axial direction by using a force detector such as a load cell, or by detecting the resin pressure in the injection cylinder using a resin pressure sensor. It may be acquired by detecting the driving torque of the injection screw drive unit 30, or when the injection screw is driven by hydraulic pressure, it may be acquired by detecting the pressure of the hydraulic pressure.

  The peak pressure detection unit 41 that detects the peak value of the injection pressure detects the amount of pressure change per unit time, and the time when the amount of pressure change per unit time starts to increase (decreases when the maximum value occurs) is the peak pressure. It can be detected as the time of occurrence. At this time, since the time point when the peak pressure generation is detected is the time point when the amount of pressure change per unit time has started to decrease, the time point when the peak pressure generation is detected is one sampling time after the actual peak pressure generation time point. The pressure value at the time of detecting the peak pressure is smaller than the actual peak pressure. However, since the time difference between the actual peak pressure generation time and the detection time of the peak pressure is small, and the difference between the actual peak pressure value and the pressure value at the peak pressure detection time is also small, the detected peak pressure value is In holding, the pressure value at the time when the generation of the peak pressure is detected may be held.

  Alternatively, the peak pressure detection unit 41 may detect a point in time when the pressure change amount per unit time near the peak pressure generation is equal to or less than a predetermined change amount as the peak pressure generation point. When the predetermined change amount is a positive value, the peak pressure detection unit 41 detects a time point slightly before the time when the maximum value of the pressure is generated as the peak pressure generation time point. On the other hand, when the predetermined change amount is a negative value, Detects a time point slightly later than the time point when the maximum value of pressure is generated as the time point when peak pressure is generated.

  Alternatively, the peak pressure detection unit 41 may detect a time point when the screw speed is equal to or lower than a predetermined speed as a peak pressure generation time point. This is because the resin flow into the cavity decreases near the completion of resin filling, and the amount of increase in the injection pressure per unit time becomes almost proportional to the screw speed. It uses the fact that it almost coincides with the time when the speed becomes zero.

  At this time, depending on the type of resin and the shape of the molded product, the screw speed corresponding to the peak pressure generation time changes, so the predetermined speed may be determined in advance by the type of resin and the shape of the molded product, It may be set by an operator.

<Peak pressure holding control unit>
The peak pressure holding control unit 42 may perform pressure control by operating the screw speed so that the injection pressure maintains the peak pressure, or may perform pressure control by operating the driving torque of the injection screw driving unit 30. May be. Further, during the peak pressure holding control, the screw may not stop completely in the axial direction but may advance to hold the pressure. The advance speed at this time varies depending on the type of resin, the shape of the molded product, or the state of resin filling into the mold. It should be noted that during the period from when the injection holding pressure is switched to when the peak pressure is generated, pressure control may be performed based on the set pressure in the holding pressure process, the screw may be controlled to stop, or the screw speed may be May be controlled to be a predetermined speed.

  As a condition for completing the peak pressure holding control, a predetermined time may elapse from the time when the peak pressure is generated (the control device 10 shown in FIG. 1 includes a time measuring means) or a predetermined time from the time when the peak pressure is generated. The screw may advance by the amount of advancement of the screw. The advance amount of the screw 3 can be measured using a position detection signal fed back to the servo CPU 15 from the position / speed detector Penc1 attached to the injection servomotor M1.

  Alternatively, the peak pressure holding control completion condition may be that the screw forward speed is reduced to a predetermined speed. The forward speed of the screw 3 can be measured using a speed detection signal fed back to the servo CPU 15 from a position / speed detector Penc1 attached to the injection servomotor M1. This is because the resin flows into the mold cavity when the filling is not completed, and the screw speed for maintaining the peak pressure is large. The fact that the screw speed for maintaining the pressure is small is utilized. By completing the peak pressure holding control after the screw forward speed has dropped to the specified speed, the peak pressure is maintained until the completion of filling, and then the pressure is based on the set pressure in the pressure-holding process to compensate for sink marks in the molded product. Take control.

FIG. 4 is a diagram for explaining a flow of pressure control processing executed by the pressure control apparatus according to the present invention. Hereinafter, it demonstrates according to each step.
[Step SA01] The injection process is executed.
[Step SA02] Injection holding pressure process switching is executed.
[Step SA03] Pressure control is performed so that the set pressure is reached.
[Step SA04] It is determined whether or not a peak pressure has occurred. If it has occurred (YES), the process proceeds to Step SA05. If not (NO), the process returns to Step SA03.
[Step SA05] Control is executed so as to maintain the peak pressure.
[Step SA06] It is determined whether or not a predetermined time has elapsed from the peak occurrence point. If the predetermined time has elapsed (YES), the process proceeds to Step SA07, and if the predetermined time has not elapsed (NO). Returns to step SA05.
[Step SA07] The pressure control is executed so that the set pressure is reached.
[Step SA08] It is determined whether or not the pressure holding process is completed. When the pressure holding process is completed (YES), the process proceeds to Step SA09, and when the pressure holding process is not completed (NO), the step Return to SA07.
[Step SA09] The measurement process and the decompression process are executed, and the process is terminated.

1 cylinder 2 nozzle 3 screw 4 hopper 5 pressure sensor 6 transmission mechanism 7 conversion mechanism

10 Controller 11 Servo amplifier 12 Servo amplifier 13 ROM
14 RAM
15 Servo CPU
16 A / D converter 17 PMCCPU
18 ROM
19 RAM
20 CNCCPU
21 ROM
22 RAM
23 Molding data storage RAM
24 LCD display circuit 25 LCD / MDI
26 Bus

30 Injection screw drive unit 31 Screw speed control unit 32 Pressure control unit

40 Injection pressure detection unit 41 Peak pressure detection unit 42 Peak pressure holding control unit

50 Injection holding pressure switching part

M1 Servo motor for injection Penc1 Position / speed detector

M2 Servomotor for screw rotation Penc2 Position / speed detector

Claims (5)

An injection screw driving unit that drives the injection screw, an injection pressure detection unit that detects the injection pressure, a screw speed control unit that controls the moving speed of the injection screw in the injection process, and a pressure that controls the injection pressure in the pressure holding process A control unit, an injection / holding pressure switching unit that switches from the injection step to the pressure-holding step, and a peak pressure detection unit that detects a peak pressure generation time point and a peak pressure value of the injection pressure,
In the pressure holding process, the peak pressure holding is performed so that the injection pressure holds the detected peak pressure value from the time when the peak pressure is generated to the time when the peak pressure holding control completion condition is met. Having a control unit,
The pressure control device for an injection molding machine, wherein the pressure control unit performs pressure control based on a set pressure in the pressure holding process from the time when the peak pressure holding control is completed to the time when the pressure holding process is completed.   The peak pressure holding control completion condition is that a predetermined time elapses from the peak pressure generation time, the screw advances by a predetermined screw advance amount from the peak pressure generation time, or the screw advance speed decreases to a predetermined speed. The pressure control device for an injection molding machine according to claim 1, wherein the pressure control device is at least one of them.   The peak pressure detection unit detects when a pressure change amount per unit time is equal to or less than a predetermined change amount or when a screw speed is equal to or less than a predetermined speed as a peak pressure generation time. 3. The pressure control device for an injection molding machine according to claim 1, wherein the injection pressure is detected as a peak pressure value.   4. The pressure control unit according to claim 1, wherein the pressure control unit performs pressure control based on a set pressure in a pressure holding process from an injection holding pressure switching time to a peak pressure generation time. Pressure control device for injection molding machine.   4. The pressure control unit according to claim 1, wherein the screw speed is controlled so as to be equal to or lower than a pressure holding limit speed from an injection holding pressure switching time to a peak pressure generation time. 5. The pressure control apparatus of the injection molding machine as described.