JP5351307B1 - Pressure control device for injection molding machine - Google Patents

Abstract

An object of the present invention is to provide a pressure control device for an injection molding machine capable of performing high-accuracy weighing by performing accurate pressure detection that eliminates an error due to resin resistance in a preliminary injection process.
An injection process is executed (SA01), a pressure holding process is executed by pressure control based on a load cell detection value (SA02), a metering process is executed (SA03), and a nozzle pressure sensor is detected. Based on the value, the preliminary injection process is executed by pressure control (SA04), and the process is continued until the cycle is completed (SA05).
[Selection] Figure 3

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 in the heating cylinder is rotated to melt and knead the resin material, the molten resin is pumped to the tip of the heating cylinder, and the screw is moved backward while performing pressure control. When the screw reaches the set measurement point, the screw is stopped and the backward movement of the screw is stopped to measure the resin. Then, after this measurement, an injection process and a pressure holding process are performed in which the screw is advanced to fill the mold with the molten resin. In the pressure-holding step, pressure control is performed so that the resin pressure becomes a predetermined value, thereby compensating for sink marks due to shrinkage of the molded product.

  In order to stabilize the quality of the molded product, it is necessary to reduce variations in the filling amount of the molten resin filled in the mold for each molding cycle. When the screw moves back to the weighing completion position and then injects, if the measured amount of molten resin is filled into the mold by the amount determined for each molding cycle, there will be no variation in the weight of the molded product, and the quality of the molded product. Can be kept uniform. However, when the molten resin flows backward from the tip of the cylinder to the rear from the completion of metering to the start of injection, the amount of metering resin at the cylinder tip changes and the resin density changes, the screw advances during the injection process. Even if the amount is the same every molding cycle, there is a problem that the amount of molten resin varies every cycle.

  In the metering process, the molten resin generated with the rotation of the screw is supplied to the cylinder tip, and in the injection process, the molten resin at the cylinder tip does not flow backward and is injected into the mold. In addition, a valve such as a backflow prevention valve and a check ring is provided at the tip of the screw. Through this valve, when the injection is started after the completion of the measurement, the molten resin is prevented from moving between the screw front end portion and the rear end portion to change the amount of the measured resin, so that the measured resin amount is accurately injected. It is configured. However, there is a problem in that the molten resin flows backward with a delay in the operation of the backflow preventing means such as a valve for preventing the molten resin from flowing back, and an accurate amount of the molten resin cannot be injected. Various techniques for improving this point have been proposed.

For example, in Patent Document 1, after plasticizing and measuring a molten resin, a pressure lower than the injection pressure of the molten resin into the cavity is maintained for a certain period of time or while the pressure rises to a certain pressure in the pressure chamber of the injection cylinder. A technique is disclosed in which a preliminary injection is performed and a screw is rotated in a direction opposite to that during plasticization measurement during the preliminary injection to create a differential pressure due to a resin pressure before and after the backflow prevention valve to retract the backflow prevention valve.
In Patent Document 2, after the measurement main processing step is finished, the screw is moved forward in a rotational free state, the rotational state of the screw during the forward movement is monitored, and the rotation of the screw is stopped. Then, a technique of a post-weighing process that reversely rotates the screw by a predetermined rotation amount is disclosed.

In Patent Document 3, when the set measurement completion position is reached, the rotation of the screw is stopped, the injection servo motor is driven to advance the screw, and a pressure P2 higher than the back pressure P1 is applied to act as a backflow prevention valve. Is closed, and then the rotary servo motor is driven while the pressure P2 is applied to reverse the screw by a certain amount so that the pressure p1 of the molten resin in the cylinder is reduced to 0 or p2 close to 0 as much as possible. ing.
In Patent Document 4, after the screw or plunger is completely metered and after the retreating process in which the screw or plunger is retracted in the direction opposite to the injection direction and before the injection process, until a predetermined pressure is reached at a predetermined speed, or A technique is disclosed in which a screw or plunger is advanced in the injection direction until a predetermined position is reached or for a predetermined time, and then the screw is rotated at a predetermined speed in a direction opposite to the metering step.

Various techniques for performing feedback control by detecting the resin pressure in the nozzle have been proposed.
In Patent Document 5, the injection speed feedback control is performed during the injection process, the resin pressure in the nozzle is detected at the time of transition from the injection process to the pressure holding process, and the speed control is performed from the speed control based on the detected resin pressure in the nozzle. A technique is disclosed that switches to internal resin pressure control, detects the resin pressure in the nozzle during the pressure holding process and the metering process, and performs feedback control of the detected resin pressure in the nozzle.
In Patent Document 6, when the metering is completed, the resin pressure inside the valve is detected with the nozzle opening / closing valve closed, the injection cylinder is controlled to apply a preload, and then the nozzle opening / closing valve is opened for injection. In addition, a technique for holding pressure is disclosed.

JP 60-76321 A JP 2006-327127 A JP 2007-253388 A JP 2007-253606 A Japanese Patent Laid-Open No. 2-12921 JP-A-4-336222

  In general, in the pressure holding process and the preliminary injection process after the completion of measurement, the force received by the screw from the compressed molten resin in the cylinder is detected using force detection means such as a load cell, and the detected force and the cross-sectional area of the screw are calculated. A method is known in which the resin pressure is calculated based on the pressure and pressure control is performed so that the calculated resin pressure becomes a predetermined value.

  By the way, the force received by the screw includes not only the reaction force received from the compressed molten resin in front of the screw but also the resistance due to the semi-molten resin at the screw base. Therefore, the pressure (load cell detection value) detected using the load cell includes an error due to the resistance of the resin. On the other hand, the pressure detector (nozzle pressure sensor) provided in the nozzle portion can eliminate errors due to the resistance of the semi-molten resin at the screw base. For this reason, the pressure (load cell detection value) detected using the load cell may not exactly match the actual resin pressure (nozzle pressure sensor detection value) (see FIG. 1). In particular, in the preliminary injection process after the completion of measurement, it is necessary to make the resin density uniform by accurately controlling the resin pressure, so it is important to accurately detect the resin pressure.

  Therefore, in view of the above-described problems, the present invention provides a pressure control device for an injection molding machine capable of performing high-precision weighing by performing accurate pressure detection that eliminates errors due to resin resistance in the preliminary injection process. The purpose is to provide.

The present invention includes a resin pressure detector that detects the resin pressure in front of the screw, performs pressure control based on the resin pressure detected by the resin pressure detection unit in the preliminary injection process, and further receives the screw in the axial direction. A force detector for detecting force is provided, and in the pressure holding step, pressure control is performed based on a force detection value detected using the force detector.
In the metering step, pressure control may be performed based on the resin pressure detected by the resin pressure detection unit, or pressure control may be performed based on the force detection value detected using the force detector. Good.

  The invention according to claim 1 of the present application is directed to a force detection unit that detects a force that the screw receives in the axial direction, a resin pressure detection unit that detects a resin pressure in front of the screw, and a screw forward and backward drive for moving the screw back and forth. And a screw rotation drive unit for rotating the screw, a pressure holding unit that performs pressure control by moving the screw back and forth between the start of injection and the start of measurement, and a screw in the forward direction during measurement. Injection molding having a measuring unit that rotates the screw back to a predetermined measurement completion position while rotating, and a preliminary injection unit that controls the pressure by moving the screw in the axial direction between the end of measurement and the start of injection In the pressure control device of the machine, the pressure holding unit performs pressure control based on the force detected by the force detection unit, and the preliminary injection unit is detected by the resin pressure detection unit. A pressure control device for an injection molding machine and performing pressure control based on the resin pressure.

The invention according to claim 2 is the pressure control device for an injection molding machine according to claim 1, wherein the force detection unit is a load cell.
The invention according to claim 3 is characterized in that the screw forward / reverse drive unit is a hydraulic drive system, and the force detection unit detects a force that the screw receives in the axial direction based on a pressure value of the hydraulic drive system. The pressure control device for an injection molding machine according to claim 1.
The invention according to claim 4 is the pressure control device for an injection molding machine according to claim 1, wherein the resin pressure detection unit is a nozzle pressure sensor.

  According to the present invention, in the preliminary injection step, pressure control is performed based on the nozzle pressure detection value detected using the pressure detector provided in the nozzle portion, so that accurate pressure detection that eliminates errors due to resin resistance is performed. Thus, it is possible to provide a pressure control device for an injection molding machine capable of performing high-precision weighing.

  By the way, the pressure detector provided in the nozzle part can eliminate the error due to the resistance of the semi-molten resin at the screw base, but generally has a problem that the response speed of the signal detection is slower than the load cell provided in the rear part of the screw. . In particular, in the injection / holding process, it is necessary to control the pressure with high responsiveness, such as reducing the pressure increased by the injection in the pressure holding process, so it is important that the response speed of signal detection is fast. According to the present invention, in the injection / holding step, pressure control is performed based on the load cell pressure detection value detected using the load cell, so that the problem that the response speed of signal detection is slow is solved, and the response is high. Pressure control can be performed.

It is a figure explaining the error factor of pressure detection. It is a schematic block diagram of the injection molding machine and the control apparatus which controls this injection molding machine. It is a figure explaining the flow of the process performed in the control apparatus of an injection molding machine.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic configuration diagram of an injection molding machine and a control device that controls the injection molding machine. An injection molding machine generally includes an injection device and a mold clamping device on a machine base. FIG. 2 shows a schematic configuration of the injection apparatus. The control device 30 is a device that controls the entire injection molding machine. A nozzle 2 is attached to the tip of the cylinder 1 into which the screw 3 is inserted, and a hopper 4 for supplying resin pellets to the cylinder 1 is attached to the rear end of the cylinder 1. The screw 3 is driven in the axial direction by a conversion mechanism 8 that converts a rotary motion of the injection servomotor M1, a transmission mechanism 7, and a ball screw / nut, etc., as a drive means for driving the screw 3 in the axial direction thereof, into a linear motion, Injection and back pressure control are performed. 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. Further, a force detector 5 such as a load cell for detecting the force received in the axial direction of the screw from the molten resin applied to the screw 3 is provided.

  A nozzle pressure sensor 9 is attached to the nozzle attachment member of the injection cylinder 1. The detection signal of the resin pressure in front of the screw detected by the nozzle pressure sensor 9 is A / D converted by the A / D converter 10 and then input to the servo CPU 15.

  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 from 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 the detection signal from the force detector 5 into a digital signal by the A / D converter 16.

  An input device 25 with a display device having a display device composed of a liquid crystal display device or the like is connected to a bus 26 via a 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. The servo CPU 15 detects the movement command distributed to each axis (the injection servo motor M1 and the screw rotation servo motor M2) and the position / speed detectors Penc1 and Penc2. Based on the position and velocity feedback signals and the like, servo control of position loop control, velocity loop control, and current loop control is performed in the same manner as in the past, and so-called digital servo processing is executed.

  The molding operation process in the injection molding machine is roughly divided into a mold closing process in which the mold is closed and clamped in the mold clamping apparatus, and an injection in which the molten resin is injected into the mold and filled by advancing the screw in the injection apparatus. After the molten resin is filled in the mold, the pressure holding process for controlling the pressure of the resin in the mold, the cooling process for cooling the resin in the mold, and the resin by rotating while applying back pressure to the screw A measurement process for measuring the molten resin, a preliminary injection process for controlling the pressure by moving the screw 3 in the axial direction between the end of measurement and the start of injection, and opening the mold in the mold clamping device There exist a process, the protrusion process (eject process) etc. which ejects a molded product from the inside of a metal mold | die. In general, as a method for controlling the injection holding pressure of the injection molding machine, the screw position / speed control is performed from the start of injection until the predetermined screw position is reached, and the predetermined screw position (injection holding pressure switching position) is reached. After that, a control method of switching to pressure control and holding pressure is widely adopted.

  According to the present invention, in the injection / holding step, pressure control is performed based on the force detection value detected using the force detector 5, so that a high response can be achieved without causing a delay in the signal detection response speed. Pressure control can be performed. In the preliminary injection process, since pressure control is performed based on the detected value of the nozzle pressure sensor detected by using the nozzle pressure sensor 9 provided in the nozzle portion, errors due to the resistance of the semi-molten resin at the screw base are eliminated. Since the resin pressure can be accurately detected, the resin pressure can be accurately controlled and the resin density can be made uniform.

Here, the force detector that detects the force that the screw 3 receives in the axial direction, the resin pressure detector that detects the resin pressure in front of the screw 3, and the pressure controller will be described supplementarily.
<About the force detection part that detects the force that the screw receives in the axial direction>
The force detection unit may be a load cell. In addition, a strain gauge may be installed on a member that transmits the driving force of the screw forward / reverse drive unit to the screw, and the force that the screw receives in the axial direction may be detected. The screw forward / reverse drive unit may be a hydraulic drive system, and the force detection unit may detect a force that the screw receives in the axial direction based on a pressure value of the hydraulic drive system. The screw forward / reverse drive unit may be a servo motor, and the force detection unit may detect the force that the screw receives in the axial direction based on the driving force of the servo motor or the force received by the servo motor.

<About the resin pressure detector that detects the resin pressure in front of the screw>
The resin pressure detection unit may be a nozzle pressure sensor. Moreover, a pressure sensor may be provided in the front part of the injection cylinder or the nozzle mounting member to detect the resin pressure in front of the screw. The nozzle pressure sensor may be a sensor that directly detects the resin pressure in contact with the resin in the nozzle, or a sensor that indirectly detects the resin pressure using a strain gauge attached to the nozzle member.

<About pressure control unit>
The pressure control unit may move the screw back and forth so that the detected pressure matches a predetermined value. Alternatively, the screw may be moved forward or backward until the detected pressure matches a predetermined value, and the screw may be stopped when the detected pressure matches the predetermined value. The pressure control method in the pressure holding process and the pressure control method in the preliminary injection process may be the same or different.

FIG. 3 is a diagram for explaining the flow of processing in the embodiment of the present invention. Hereinafter, it demonstrates according to each step. In addition, the process relevant to the mold clamping apparatus of an injection molding machine is not described here.
[Step SA01] The injection process is executed.
[Step SA02] A pressure holding process is executed. In the pressure holding step, pressure control is performed based on the load cell detection value.
[Step SA03] The weighing process is executed.
[Step SA04] A preliminary injection process is executed. In the preliminary injection process, pressure control is performed based on the detected value of the nozzle pressure sensor.
[Step SA05] It is determined whether or not the cycle is finished. If the cycle is not finished, the process returns to Step SA01, and if the cycle is finished, the process is finished.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Nozzle 3 Screw 4 Hopper 5 Force detector 6, 7 Power transmission mechanism 8 Conversion mechanism 9 Nozzle pressure sensor 10 A / D converter 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 Display Circuit 25 Input Device with Display Device 26 Bus

30 Control device

Penc1 Position / Speed Detector Penc2 Position / Speed Detector M1 Injection Servo Motor M2 Screw Rotation Servo Motor

Claims (4)

A force detection unit that detects the axial force applied to the screw, a resin pressure detection unit that detects the resin pressure in front of the screw, a screw forward / reverse drive unit for moving the screw back and forth, and a screw for rotating the screw A rotation drive unit,
A pressure holding part that controls the pressure by moving the screw back and forth between the start of injection and the start of measurement, and a meter that moves the screw back to a preset measurement completion position while rotating the screw in the forward direction during measurement. In a pressure control device of an injection molding machine having a portion and a preliminary injection unit that performs pressure control by moving the screw in the axial direction between the end of measurement and the start of injection,
The pressure holding unit performs pressure control based on the force detected by the force detection unit, and the preliminary injection unit performs pressure control based on the resin pressure detected by the resin pressure detection unit. Pressure control device for injection molding machines.   The pressure control apparatus for an injection molding machine according to claim 1, wherein the force detection unit is a load cell.   The screw forward / reverse drive unit is a hydraulic drive system, and the force detection unit detects a force that the screw receives in an axial direction based on a pressure value of the hydraulic drive system. Pressure control device for injection molding machines.   The pressure control apparatus for an injection molding machine according to claim 1, wherein the resin pressure detection unit is a nozzle pressure sensor.

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