JPH032049B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present description relates to injection molding machines, and particularly to injection speed control and pressure control of injection molding machines.

(Prior Art) When molding a resin molded product using an injection molding machine, control is performed in the following order: injection of molten resin, filling, holding pressure, and cooling. The injection speed is controlled in the stage from injection to filling, while the filling pressure is controlled in the stage from holding pressure to cooling.

Here, we will discuss the fifth example of a conventional injection molding machine.
This will be explained with reference to the figures.

The injection molding machine is equipped with an injection cylinder 2 having a popper 1 and a melt screw 3. This melting screw 3 can move back and forth while rotating within the cylinder 2. The rear end of the melting screw 3 passes through a pressurizing actuator 4 and is held within a piston 5 coaxially with the piston and rotatably. The melting screw 3 is connected to and driven by a hydraulic motor 6. A plate member 7 is attached to the final end of the melting screw 3 so as not to interfere with the rotation of the melting screw 3 and to be movable along the melting screw axis along the melting screw 3. The plate member 7 is connected via a piston rod 8 to a speed detector 9. Displacement detector 1 for detecting the position of the melting screw
0 is equipped with a rack 11, which moves integrally with the plate member 7, and also has a gear 11a.
rotates according to the movement of the rack 11. On the other hand, the hydraulic motor 6 is equipped with a screw rotation speed detector 1.
2 are connected.

The speed detector 9 is electrically connected to the injection speed regulator 13. The injection speed regulator 13 is electrically connected to the servo bubble 15 via a switching device 14 . Chamber 4 of pressure actuator 4
a is connected to the servo valve 15 via a hydraulic flow path 15a. The displacement detector 10 is electrically connected to a program setter 16, which outputs a predetermined setting value corresponding to the position of the melting screw 3. The program setting device 16 is electrically connected to an injection speed regulator 13, a holding pressure regulator 17, a screw back pressure regulator 18, and a screw rotation regulator 19 as shown. Holding pressure regulator 17 and screw back pressure regulator 18 are electrically connected to servo valve 15 via switching device 14 . Further, the holding pressure regulator 17 and the screw back pressure regulator 18 are electrically connected to a pressure detector 21 that senses the pressure within the chamber 4a of the pressurizing actuator. On the other hand, a screw rotation speed detector 12 is electrically connected to the screw rotation speed regulator 19 , and this screw rotation speed regulator is electrically connected to the servo valve 20 . The hydraulic motor 6 is connected to the servo valve 20 by the hydraulic flow path 20a.
and is driven by the servo valve 20.

Next, injection and filling of molten resin into an injection molding cavity (not shown) will be explained.

Contact 14a and contact 14b of switching device 14 are connected. The driving pressure from the servo valve 15 is sent to the cylinder chamber 4a, and the injection piston 5, that is, the screw 3 moves forward in the left direction in the axial direction in FIG. As mentioned above, the program setting device 1
6 instructs the injection speed regulator 13 to set the speed. The injection speed regulator 13 compares the actual value from the speed detector 9 with the above speed setting value, and the thermovalve 15 is controlled based on this result. Then, the piston 5 continues to operate due to the pressure appropriately controlled via the hydraulic flow path 15a, and the screw 3
advances toward the injection port 2a of the cylinder 2, filling the injection molding cavity with molten resin.

By the way, the pressure inside the mold reaches its maximum value just before filling with molten plastic ends. In addition, the pressure required for holding pressure is higher than the normal filling pressure (injection pressure), but the maximum value (peak value) of the pressure at the end of filling mentioned above
known to be smaller. Therefore, when the screw advances a predetermined distance and the pressure in the injection process (filling) becomes larger than the set pressure value in the pressure holding process, the contacts 14a and 14c of the switching device 14 are connected, and the pressure holding process starts. to move to. The holding pressure regulator 17 compares the pressure setting value from the program setting device 16 with the actual value measured by the pressure setting device 21, and controls the servo valve based on the result to apply a predetermined pressure and hold the pressure.

(Problems to be Solved by the Invention) By the way, in the case of the conventional injection molding machine described above, only speed control is performed during injection and pressure control is performed during pressure holding, so there is a transition from the filling stage to the pressure holding stage. edge,
In other words, when switching from speed control to pressure control, the sixth
As shown in Figures a to d, a large difference occurs between the speed setting value and the detected speed. That is, a surge occurs in which the detection speed changes in a negative direction. Furthermore, a large overshoot occurs in the detected pressure in response to the above-mentioned surge in the detected speed. That is, there is a large difference between the pressure setting value and the detected pressure.

There is a problem in that the quality of the molded product (appearance, internal orientation of the resin) deteriorates due to speed surges and excessive pressure that occur when switching from speed control to pressure control.

(Means for Solving the Problems) The present invention includes an injection cylinder that stores molten resin and a screw section that is arranged to move forward and backward within the injection cylinder, and injects the molten resin by moving the screw section forward. In an injection molding machine that performs injection molding into a cavity, there is a speed comparison means for determining a speed deviation between a preset injection speed and an actual injection speed from an injection cylinder, and a speed comparison means that calculates a speed deviation between a preset resin pressure and an actual resin pressure from an injection cylinder. a pressure comparison means for determining the pressure deviation between the two; and a pressure comparison means for determining the speed operation amount based on the speed deviation and the pressure operation amount based on the pressure deviation; and calculation means for calculating a corrected speed operation amount and a corrected pressure operation amount by correcting with the set speed parameter and pressure parameter, and drive control of the screw part based on the corrected speed operation amount and the correction pressure operation amount. It is characterized by what it did.

(Example) The present invention will be explained below with reference to Examples.

First, with reference to FIG. 1, an overview of speed/pressure control of an injection molding machine according to the present invention will be explained.

The speed deviation between the speed setting value and the speed detection value of the controlled object (screw) 27 is determined by the servo speed controller 2.
3, one pressure set value and servo valve 2
The pressure deviation between the pressure (hydraulic pressure) and the detected pressure value according to No. 6 is input to the servo pressure controller 24.
The servo speed controller 23 determines the opening of the servo valve (hereinafter referred to as speed servo command (U _{v )) based on the above speed deviation, and the servo pressure controller 24 determines the opening of the servo valve (hereinafter referred to as speed servo command (U v} )) based on the above pressure deviation. (hereinafter referred to as pressure servo command (U _p ))
Determine. These speed and pressure servo commands are input to the weighting function generator 25. A speed weighting parameter α and a pressure weighting parameter β are input in advance to the weighting function generator 25, and these speed weighting parameter α and pressure weighting parameter β change depending on the position of the controlled object (screw) as shown in FIG. do. That is, α and β vary in the range from 0 to 1. The weighting function generator 25 performs the calculation shown in the following equation (1) to determine the opening degree of the servo valve (hereinafter referred to as the overall servo command (U)). The opening degree of the servo valve is controlled by this comprehensive servo command.

U=α×U _v +β×U _p (1) (0α1, 0β1, α+β=1) Here, the injection molding machine according to the present description will be described in detail with reference to FIG. Note that the same reference numerals are given to parts having the same configuration as those of the conventional example, and explanations thereof will be omitted.

The program setting device 28 is connected to an α, β pattern input device 29 for inputting the aforementioned speed weighting parameter α and pressure weighting parameter β.
The screw back pressure regulator 18 is connected to the servo valve 15 via a switch 30, and the injection speed regulator 1
3 and the holding pressure regulator 17 are connected to the servo valve 15 via a weighting calculation device 31. On the other hand, the outputs of the speed detector 9 and the pressure detector 21 are input to a monitor device 32.

The driving pressure from the servo valve 15 is sent to the cylinder chamber 4a, and the injection piston 5, that is, the screw 3 moves forward in the left direction in the axial direction in FIG.
Corresponding to the screw position input from the displacement detector 10, a speed weighting parameter α and a pressure weighting parameter β are inputted from the program setting device 28 to the weighting calculation device 31. On the other hand, the program setting device 28 inputs a speed setting value and a pressure setting value to the injection speed regulator 13 and the holding pressure regulator 17, respectively, in accordance with the screw position. Injection speed regulator 13
calculates the speed deviation between the actual measured speed of the screw (speed detection value) and the speed setting value, and calculates the speed servo command (U _v ).
is input to the weighting calculation device 31 as follows. The holding pressure regulator 17 calculates the deviation value between the measured pressure (pressure detector) of the cylinder chamber 4a and the pressure setting value, and sends it to the weighting calculation device 31 as a pressure servo command (U _p ).
Enter. The weighting calculation device 31 performs the above-mentioned
A comprehensive servo command (U) is obtained using equation (1), and the opening degree of the servo valve is controlled by this comprehensive servo command.

In this way, speed control and pressure control are each weighted, and the weighting coefficients are changed depending on the screw position as shown in Figure 2, so when transitioning from resin filling to pressure holding. It is possible to prevent speed surges and excessive pressure from occurring.

Note that the speed weighting parameter α and the pressure weighting parameter β can be changed depending on the type of molded product (for example, case A and case B in FIG. 2). Further, the operator inputs the outline of the α and β patterns in advance according to the type of molded product, and adjusts the α and β patterns according to the molding quality and the speed and pressure actually measured on the monitor device.

Finally, a case where the above-mentioned pressure/velocity control is configured by an electronic computer system will be explained.

Referring to Figure 4, central processing unit (CPU) 3
3 is a storage device (memory) 35 in which the α and β patterns inputted from the α and β pattern input device 29 via the interface 34 are made to correspond to the screw positions.
to be memorized. When the injection molding machine starts injection, the CPU 33 calculates a speed deviation from a preset speed setting value and a speed detection value inputted via the A/D converter 36. Similarly, the pressure deviation is determined from the pressure set value and the detected pressure value. Then, a speed servo command (U _v ) and a pressure servo command (U _p ) are calculated based on these speed deviation and pressure deviation, respectively. On the other hand, CPU33 changes the position of the screw to PG.
It is detected by the counter 37, the α and β parameters for this screw position are read out from the storage device 35, and the overall servo command (U) is determined by the first equation. This comprehensive servo command is sent to the servo valve 15 via the D/A converter 38 and servo amplifier 39. Also, CPU33 has interface 4.
A monitoring device 32 is connected via 0, by means of which the actual speed and the actual pressure can be displayed.

(Effects of the Invention) As explained above, in the present invention, speed control and pressure control are weighted, and the weighting coefficients are changed in accordance with the screw position. The speed surge and excessive pressure that occurred during the transition to the next step are eliminated, and a good molded product can be obtained.

[Brief explanation of drawings]

FIG. 1 is a control diagram for explaining the outline of speed/pressure control of an injection molding machine according to the present invention, FIG. 2 is a diagram showing an example of the pattern of the speed weighting parameter α and the pressure weighting parameter β, and FIG. A sectional view and a block diagram schematically showing an injection molding machine according to the present invention and its control circuit, FIG. 4 is a diagram showing the speed and pressure control of the injection molding machine according to the present invention configured by an electronic computer system, and FIG. 5 is a conventional A cross-sectional view and a block diagram schematically showing an injection molding machine and its control circuit, and FIGS. 6a to 6d show the speed setting value, speed detection value, pressure setting value, and pressure detection value, respectively, in a conventional injection molding machine. FIG. 1... Hopper, 2... Injection cylinder, 3... Melting screw, 4... Processing actuator, 5...
Piston, 6... Hydraulic motor, 7... Plate member, 8
...Piston rod, 9...Speed detector, 10...
...Displacement detector, 12... Rotation speed detector, 13...
Injection speed regulator, 14... switching device, 15... servo valve, 16... program setting device, 17...
... Holding pressure regulator, 18... Screw back pressure regulator, 1
9... Screw rotation speed regulator, 20... Servo valve, 21... Pressure detector, 28... Program setting device, 29... α, β pattern input device, 30
...Switch, 31...Weighting calculation device, 32
...Monitor device.

Claims (1)

[Claims] 1. It has an injection cylinder in which molten resin is stored, a screw part disposed in the injection cylinder so as to be able to move forward and backward, and a hydraulic cylinder for driving the screw part, and the screw part is moved forward to release the molten resin. In an injection molding machine that molds a molded product by injecting into an injection cavity, a screw forward speed setting value is set in advance according to the forward position of the screw portion, and a forward speed detected according to the forward position. a speed comparison means for calculating a speed deviation from the detected value; and a pressure between the oil pressure setting value in the hydraulic cylinder preset according to the forward position and the detected oil pressure value in the hydraulic cylinder detected according to the forward position. a pressure comparison means for determining a deviation; a pressure comparison means for determining a speed operation amount based on the speed deviation and a pressure operation amount based on the pressure deviation; calculation means for calculating a corrected speed operation amount and a correction pressure operation amount by correcting the speed parameter set to change from 0 to 0 and the pressure parameter set to change from 0 to 1 according to the forward position; An injection molding machine characterized in that the screw portion is driven by controlling the hydraulic pressure supplied to the hydraulic cylinder according to the corrected speed operation amount and the corrected pressure operation amount.