JPH082569B2 - Control method of injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control method for an in-line screw type injection molding machine, and more particularly, to a hydraulic injection cylinder as a main drive source and a small power as an auxiliary drive source. The present invention relates to a speed or pressure control method in a configuration in which the electric servo motor is combined.

[Prior Art] In an inline screw type injection molding machine, when the hydraulic drive control of the injection cylinder (hydraulic cylinder) is performed by open control, the primary injection process, which is the screw forward process from the measurement end point to the holding pressure switching point. The injection speed at
There is a drawback that stable molding cannot be performed because it changes due to load fluctuations and disturbances. Figure 2 shows this situation,
In contrast to the set value shown by the broken line in the figure, the actual measurement value shown by the solid line fluctuates due to load fluctuations and disturbances.

Therefore, when the injection drive source is an injection cylinder (hydraulic cylinder), feedback control is performed using a hydraulic servo valve to correct the deviation of the injection speed from the set value, and the injection speed due to load fluctuations or external disturbances is corrected. I was trying to deal with fluctuations.

[Problems to be Solved by the Invention] However, in the feedback control of the injection speed by the hydraulic servo valve described above, there is a problem that the gain cannot be increased (the response cannot be sharpened) because it is via oil. there were.

On the other hand, it has also been attempted to perform feedback control using an electric servomotor as an injection drive source. Feedback control of injection speed by this electric servomotor can provide relatively responsive and relatively satisfactory control. A power (large-capacity) servomotor is required, which causes a problem of cost increase. Also,
When an electric servomotor is used as the injection drive source, the pressure (holding pressure) during the holding pressure stroke that follows the primary injection stroke
The feedback control accuracy of is inferior to the feedback control accuracy of pressure by the hydraulic servo valve (however, when using an electric servo motor, a load cell, which is inferior in measurement reliability to the hydraulic pressure sensor, must be used as a pressure sensor. However, there is a problem that a defective molded product may be caused due to insufficient pressure accuracy during holding pressure.

The present invention has been made in view of the above points, and an object of the present invention is to provide an injection molding machine capable of excellent feedback control of both the injection speed during the primary injection stroke and the holding pressure during the pressure holding stroke. It is to provide a control method.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a method for controlling an in-line screw type injection molding machine in which molten resin is injected / filled in a mold by advancing a screw in a heating cylinder. , A relatively small power (small capacity) electric servomotor is connected to a piston rod of a hydraulic injection cylinder connected to move forward and backward integrally with the screw through a rotation-linear conversion mechanism, and opens according to a predetermined sequence. When the measured drive value of the hydraulic injection cylinder to be controlled deviates from the set target value, the electric servomotor is auxiliary driven to perform feedback control so that the measured drive value matches the set target value. To be done.

[Operation] The microcomputer that controls the entire injection molding machine (hereinafter referred to as the microcomputer) uses the position detection information from the rotary position detector attached to the electric servomotor and the timing information from the clock built into itself. By measuring the forward speed (injection speed) of the screw, and by highly accurate pressure detection information from the hydraulic pressure sensor attached to the hydraulic line system of the hydraulic injection cylinder (hereinafter simply referred to as the injection cylinder), The hydraulic pressure is actually measured.

Then, the microcomputer drives and controls the injection cylinder by open control according to a predetermined sequence based on the predetermined operating condition data, whereby the injection / filling process (primary injection process and pressure holding process) is mainly (basically) performed. ) It is executed by the driving force of the injection cylinder. At this time, in the primary injection process, the measured injection speed value and the set injection speed value are compared, and if there is a difference between the two, the set injection speed value and the measured injection speed value are matched so that the measured injection speed value matches the set injection speed value. The electric servomotor is driven to perform feedback control of injection speed. Further, in the pressure-holding process following the primary injection process, the measured pressure value and the set pressure value are compared, and if there is a difference between the two, the set pressure value and the measured pressure value match so that The electric servomotor is driven to perform feedback control of the holding pressure.

By adopting such a control method, when the injection speed of the hydraulic drive source (injection cylinder) that is open-controlled deviates from the set target value due to load fluctuation or disturbance, this deviation amount can be controlled with good responsiveness. Since it is corrected immediately by the servo motor, highly accurate injection speed control can be achieved. In addition, if the holding pressure (that is, the hydraulic pressure corresponding to this) by the hydraulic drive source (injection cylinder) that is similarly open-controlled deviates from the set target value due to load fluctuations or disturbance, highly accurate measured pressure The shift amount is calculated based on the value, and the shift amount is immediately corrected by the electric servomotor, so that highly accurate control of the holding pressure can be achieved. Since the electric servomotor for speed and pressure feedback control is driven auxiliary to correct the deviation from the set target value, a small motor with small power (small capacity) may be used. It is inexpensive and consumes less power.

[Embodiment] Hereinafter, the present invention will be described with reference to one embodiment shown in FIG.

FIG. 1 is an explanatory diagram showing a configuration of a main part of an injection molding machine. In the figure, 1 is a heating cylinder, 2 is a hopper for supplying a raw material resin to the rear portion of the heating cylinder 1, and a screw 3 is arranged in the heating cylinder 1 so as to be rotatable and forward and backward. . Reference numeral 4 denotes a driven body which is spline shaft-coupled to the rear end portion of the screw 3 (combined so as to be integrally rotatable but slidable in the axial direction), and is rotatable only to an appropriate supporting member (not shown). And is driven to rotate by the hydraulic motor 5.

Reference numeral 6 denotes an injection cylinder (hydraulic cylinder). In the present embodiment, a piston rod 6b is integrally projectingly provided in front of and behind the piston body 6a therein.
The rear end of the screw 3 is integrally connected to the front side of 6b. A ball screw 7 is integrally connected to the rear side of the piston rod 6b through an appropriate connecting means 8. Reference numeral 9 denotes a nut body screwed with the ball screw 7, which is rotatably held by a supporting member (not shown) via a bearing 10 and a gear 11 is integrally fixed. Reference numeral 12 is an electric servomotor of small power (small capacity), which is attached to an appropriate supporting member (not shown), and a pinion 13 fixed to its output shaft meshes with the gear 11.

Therefore, as is apparent from the above-mentioned configuration, when the piston rod 6b of the injection cylinder 6 is moved forward and backward, the screw 3 and the ball screw 7 are also moved forward and backward together, and with the forward and backward movement of the ball screw 7 at this time, , The nut body 9,
The electric servomotor 12 is synchronously rotated via the gear 11 and the pinion 13. When the electric servomotor 12 is driven and rotated, the ball screw 7 is moved back and forth by an amount commensurate with the drive rotation amount of the motor 12 via the pinion 13, the gear 11 and the nut body 9, and accordingly, the piston rod 6b. And the screw 3 are also moved forward and backward together.

Reference numeral 14 is a rotational position detector including an optical pulse encoder attached to the electric servomotor 12, and a detection signal S1 of the rotational position detector 14 is sent to a microcomputer 30 described later. In addition, the electric servomotor 12 is a microcomputer 30
Drive control is performed by the servo driver circuit 15 based on the control signal from the.

The lower left portion of the drawing in FIG. 1 shows a hydraulic circuit system for the injection cylinder 6, and in the illustrated portion, 16
Is a pump that pumps up the oil pumped up from the tank and discharges it at a predetermined pressure, 17 is a variable relief valve for pressure control (proportional electromagnetic pressure control valve), 18 is a variable flow control valve for speed control (proportional electromagnetic flow control) Valve), 19 is a 4-port 3-position switching type directional control valve (electromagnetic directional control valve), 20 is a relief valve for back pressure control, which is connected to the R port connected to the ABR at the neutral position of the directional control valve 19. Is. The variable relief valve 17, the variable flow control valve 18, and the directional control valve 19 are drive-controlled via a driver group 21 based on a control signal from a microcomputer 30 described later, and in the illustrated example, a drive signal D1 of the driver group 21. Drives the variable relief valve 17 and drives the drive signal D2.
Drives and controls the variable flow control valve 18, and drive signals D3 and D4 drive and control the directional control valve 19. 22
Is a hydraulic pressure sensor arranged in the forward drive hydraulic line of the injection cylinder 6, and a detection signal S2 of the hydraulic pressure sensor 22 is sent to a microcomputer 30 described later.

Reference numeral 30 denotes a microcomputer that controls the operation of the entire injection molding machine, and executes various types of processing and control such as control of the entire molding operation process such as mold opening / closing operation, charging operation, and injection operation, and calculation processing of measurement data. The microcomputer 30 is actually various
It is equipped with an I / O interface, a ROM that stores main control programs and various fixed data, a RAM that reads and writes various flags and measurement data, and a CPU (Central Processor Unit) that controls the entire system. Various processes are executed according to various programs,
In the present embodiment, for convenience of explanation, the molding condition setting storage unit
The following description will be given on the assumption that functional units such as 31, a molding sequence control unit 32, an actual measurement data processing unit 33, and a feedback control unit 34 are provided.

In the molding condition setting storage unit 31, various molding condition values input by a key input means (not shown) or the like are stored in a rewritable form after being arithmetically processed as necessary. The molding conditions include, for example, charge conditions, primary injection speed conditions that are subdivided from the injection start position to the holding pressure switching point (position), and subdivisions from the holding pressure switching time to the pressure holding end time. Next injection pressure (holding pressure) conditions, mold closing stroke and speed, mold clamping force, mold opening stroke and speed, eject control conditions, temperature of each part and the like can be mentioned.

The molding sequence control unit 32, based on the molding sequence control program created in advance and the setting condition values stored in the molding condition setting storage unit 31, the measurement information from the sensor group arranged in each part of the machine and the microcomputer 30. While referring to the data of the actual measurement data processing unit 33 that processes and stores the time information from the clock built in, the corresponding drive source is drive-controlled via the driver group 21 and a series of molding process is opened in the machine. Let it run under control.

The actual measurement data processing unit 33 is, as described above, the measurement information and the microcomputer from the machine group arranged in each unit of the machine.
It is possible to recalculate various position data, various speed data, various pressure data, time data, etc. by appropriately calculating the time information from the clock built into the 30 and rewriting it for at least the latest one shot cycle. Hold on. Here, the description of the data processing not directly related to this embodiment will be omitted, but the measured data processing unit 33
Detects the position of the screw 3 (piston rod 6b of the injection cylinder 6) by adding / subtracting the detection signal S1 of the rotational position detector 14 described above, and detects the detection signal (position information) S1 and clock information. Based on the above, the speed (screw forward / backward speed) is calculated in real time at a predetermined sampling cycle, and the calculated (measured) speed value is stored in a predetermined storage area in association with the position information at that time. Also,
The actual measurement data processing unit 33 detects the hydraulic pressure value (or the resin pressure value converted from the hydraulic pressure value) by the detection signal S2 of the hydraulic pressure sensor 22. The actual measurement pressure data is associated with time or a screw position to determine a predetermined value. Stored in the storage area.

The feedback control unit 34 sets the latest measured speed value obtained by the measured data processing unit 33 and the screw position stored at this time in the molding condition storage setting unit 31 at the time of the primary injection stroke described later. When the corresponding set speed value is compared, and there is a difference between the two, a drive control signal is sent to the servo driver circuit in order to rotate the electric servomotor 12 by an amount that matches the set speed value with the measured speed value. 15
Send to. Further, the feedback control unit 34 also sets the latest measured pressure value obtained by the actual measurement data processing unit 33 and the setting corresponding to this time stored in the molding condition storage setting unit 31 at the time of the pressure holding process which will be described later. The pressure value is compared, and if there is a difference between the two, a drive control signal is sent to the servo driver circuit 15 in order to rotate the electric servomotor 12 by an amount that matches the measured pressure value with the set pressure value. .

Next, the operation of this embodiment having the above configuration will be described.

When the charge stroke start timing is reached in a state where the screw 3 is at the most forward position, the microcomputer 30
The molding sequence control unit 32 controls the hydraulic motor system control valve (not shown) via the driver group 21 to start the hydraulic motor 5 in a predetermined direction at a predetermined rotation speed, and prior to this, the driver group 21. Through the directional control valve
The drive signal D4 is sent to 19 to switch the directional control valve 19 to the neutral position. When the screw 3 starts to rotate, the raw material resin supplied from the hopper 2 is kneaded and plasticized as the screw rotates, is melted while being transferred to the tip side of the screw 3, and the molten resin is stored at the tip side of the screw 3. As the screw 3 is moved, the screw 3 moves backward. On this occasion,
The hydraulic pressure in the injection cylinder 6 is set to a pressure value (back pressure value) determined by the relief valve 20 for back pressure control described above. The rotation position detector 14 measures that the screw 3 moves backward while controlling the back pressure, and reaches a position where one shot of molten resin is stored on the tip side of the screw 3 (measurement completion point). When the information confirms, the molding sequence control unit 32 stops the rotation of the screw 3 (rotation of the hydraulic motor 5).

Thereafter, when the injection start timing after a predetermined time has passed, the molding sequence control unit 32 causes the directional control valve 19
To the variable relief valve 17 while sending a drive signal D3 to the directional control valve 19 to the right side switching position in the figure, and sending a drive signal D1 to the variable relief valve 17 to set a hydraulic pressure value during the primary injection stroke (set primary pressure). Injection pressure value) to raise the pressure, the piston rod
Begin advancing 6b (ie screw 3). At this time, the molding sequence control unit 32 sends the drive signal D2 to the variable flow rate control valve 18 while referring to the position of the screw 3 so that the injection speed is set to the set speed corresponding to the forward position of the screw 3. Open control. By the forward movement of the screw 3, the molten resin stored on the tip end side of the screw 3 is injected and filled into the cavity of a mold (not shown) that is clamped.

On the other hand, during the above-described primary injection stroke, the feedback control unit 34 of the microcomputer 30 compares the latest measured speed value with the corresponding set speed value as described above, and if there is a difference between them, A drive control signal is sent to the servo driver circuit 15 so that the measured speed value matches the set speed value, and the electric servomotor 12 is driven. That is, when the measured speed value is smaller than the set speed value, the electric servomotor
Rotate the screw 12 by a predetermined amount in the forward direction of the screw 3 to increase the speed. On the contrary, if the measured speed value is larger than the set speed value, rotate the electric servo motor 12 by a predetermined amount to rotate the speed. And the feedback control of the injection speed is performed so that the measured speed value always matches the set speed value.
Therefore, when the injection speed of the open-controlled injection cylinder 6 deviates from the set target value due to load fluctuation or disturbance, this deviation amount is immediately corrected by the electric servomotor 12 having good responsiveness. High injection speed control can be achieved.

When the above-mentioned primary injection stroke ends (when the screw 3 advances to the pressure holding switching point), the sequence control unit
32 acknowledges this, and after this point, the set hydraulic pressure value (holding pressure value) that is set in correspondence with the specified time segment
As described above, the drive signal D1 is sent to the variable relief valve 17 to perform the pressure-holding step of applying the pressure-holding pressure to the molten resin filled in the cavity by the open control.

Further, during the pressure-holding process, the feedback control unit 34 compares the latest measured pressure value with the corresponding set pressure value as described above, and if there is a difference between the two, the set pressure value is measured. A drive control signal is sent to the servo driver circuit 15 to drive the electric servomotor 12 so that the pressure values match. That is, when the measured pressure value is smaller than the set pressure value, the electric servomotor 12 is rotated by a predetermined amount in the direction in which the screw 3 moves forward to increase the pressure, and conversely, the measured pressure value is set to the set pressure value. If it is larger than the above, the electric servomotor 12 is reversely rotated by a predetermined amount to reduce the pressure,
Feedback control of the holding pressure is performed so that the measured pressure value always matches the set pressure value. This pressure feedback control is performed by the highly accurate measured pressure measurement information (compared to the load cell) by the hydraulic pressure sensor 22 described above, so that highly accurate feedback control of the holding pressure can be achieved.

Further, as described above, the electric servomotor 12 used for the feedback control of the speed and the pressure is an auxiliary drive for correcting the deviation from the set target value, and therefore has a small power (small capacity). It requires a small motor, is relatively inexpensive, and consumes less power.

[Effects of the Invention] As described above, according to the present invention, by combining the hydraulic injection cylinder, which is the main drive source that is open-controlled, and the electric servomotor of small power, the injection speed and the holding speed during the primary injection stroke are maintained. It is possible to provide a control method for an injection molding machine that is capable of excellent feedback control of the holding pressure during the pressure stroke, and its industrial value is great.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a main part of an injection molding machine according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing how the measured injection speed fluctuates by conventional open control. 1 ... Heating cylinder, 2 ... Hopper, 3 ... Screw, 4
...... Driven object, 5 ...... hydraulic motor, 6 ...... injection cylinder (hydraulic cylinder), 6b ...... piston rod, 7 ...... ball screw, 8 ...... connecting means, 9 ...... nut body, 10 ...... bearing, 11 …… Gear, 12 …… Electric servomotor, 13 ……
Pinion, 14 …… Rotary position detector, 15 …… Servo driver circuit, 16 …… Pump, 17 …… Variable relief valve, 18 ……
Variable flow control valve, 19 …… Direction control valve, 20 …… Relief valve, 21 …… Driver group, 22 …… Hydraulic pressure sensor, 30 ……
Microcomputer (microcomputer) 31, molding condition setting storage unit 32, molding sequence control unit 33, actual measurement data processing unit 34, feedback control unit 34.

Claims (3)

[Claims] 1. An in-line screw type injection molding machine for injecting and filling a molten resin into a mold by advancing a screw in a heating cylinder, comprising: a hydraulic injection cylinder connected to the screw so as to move forward and backward. An electric servomotor of relatively small power is connected to the piston rod via a rotation-linear conversion mechanism, and when the actual drive value of the hydraulic injection cylinder that is open-controlled according to a predetermined sequence deviates from a set target value, A control method for an injection molding machine, characterized in that the electric servomotor is auxiliary driven to perform feedback control so that the actual drive value matches the set target value. 2. The injection speed is calculated and measured on the basis of detection information from a rotational position detector installed in the electric servomotor according to claim 1, and the measured injection speed value and the set injection speed value are used during the primary injection stroke. The control method for the injection molding machine is characterized in that the electric servomotor is caused to perform feedback control of the injection speed. 3. The pressure according to claim 1, wherein the pressure is detected by detection information of a hydraulic pressure sensor for measuring the hydraulic pressure of the hydraulic injection cylinder, and the measured pressure value and the set pressure value are compared with each other during a holding pressure stroke. A method for controlling an injection molding machine, characterized in that the electric servomotor is made to perform feedback control of a holding pressure.