JPH0482098B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a control device for an injection molding machine, and more particularly to a control device capable of switching between injection process control and pressure holding process control.

(Prior Art) Conventionally, in the injection molding process of an injection molding machine, when transitioning from the injection process to the pressure holding process, that is, when switching the control system from the injection speed control loop to the pressure control loop, the screw stroke When any one of the injection time, the oil pressure of the hydraulic cylinder, and the resin pressure in the mold exceeds a preset value, the control system is switched from the injection speed control loop to the pressure control loop.

(Problem to be solved by the invention) However, conventionally, when the amount exceeds a preset value, the control system is switched, so the amount of operation to the servo valve, etc. for operating the screw of the injection molding machine is becomes discontinuous, and as a result, when entering the pressure holding process, a sudden change in resin pressure within the mold (pressure drop or pressure overshoot) occurs as shown in FIG. Therefore, there is a problem that backflow of resin or overfilling of resin occurs, resulting in defective molded products.

SUMMARY OF THE INVENTION An object of the present invention is to provide a speed-pressure switching device that can smoothly switch control systems and produce good molded products.

(Means for Solving the Problems) According to the present invention, there is provided a speed detector for detecting the injection speed of molten resin, a position detector for detecting the screw position, and a pressure detector for detecting resin pressure or hydraulic cylinder pressure. When the detected injection stroke exceeds the preset injection stroke and the absolute value of the difference between the manipulated variable for injection speed control and the manipulated variable for pressure control becomes less than or equal to the preset value, the injection process control A speed-pressure switching control device is obtained, characterized in that it has a control means for switching control to pressure process control.

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

First, referring to FIG. 1, there is a screw 31 in the heating cylinder 31b equipped with the hopper 31a.
c is arranged so that it can move back and forth and also rotate. A piston member 31d is attached to the rear end of the screw 31c, and this piston member 31d is arranged within the hydraulic cylinder 31e. A hydraulic pump (not shown) is connected to this hydraulic cylinder 31e via a servo valve. Furthermore, an electric motor 31f for rotating the screw 31c is provided at the rear end of the screw 31c. Note that a mold (not shown) is provided on the left side of the heating cylinder 31b.

Now, when the screw 31c is rotated by the electric motor 31f, the material resin is supplied from the hopper 31a into the heating cylinder 31b, and the cylinder 31
It is melted in b. As the material resin is supplied, the screw 31c gradually moves backward, and the screw 31
When the motor 31e reaches a predetermined reverse position, the electric motor 31e is stopped and the metering process is completed. After that, the servo valve is controlled as described later, and the hydraulic cylinder 31
Send hydraulic pressure to e to advance the screw 31c,
Inject molten resin into the mold.

Here, the control device will be explained with reference also to FIG.

The control device includes a position detector 24 that detects the screw position, a speed detector 25 that detects the injection speed,
A pressure detector 26 that detects the resin pressure inside the mold, a servo valve 28 that controls the amount of hydraulic pressure to the hydraulic cylinder,
and an injection speed/pressure control device 30.

The injection speed-pressure control device 30 includes a central processing unit (CPU) 18, an interface 19, and a memory 2.
0, PG counter 21, A/D converters 22 and 2
2' and a D/A converter 23, and a control parameter input device 29 is connected to the CPU 18 via an interface 19. On the other hand, the above-mentioned position detector 24, speed detector 25, and pressure detector 26 are connected to the CPU via the PG counter 21, A/D converter 22, and A/D converter 22', respectively, and the servo valve 28 is connected to the CPU 18 via a servo amplifier 27 and a D/A converter 23.

Here, regarding injection speed-pressure switching control,
This will be explained with reference to FIG. 3 as well.

As shown in FIG. 3, the CPU 18 includes a speed control compensation section 7, a pressure control compensation section 8, a switching system determination section 9, and a control loop switching section 10.

First, the operator calculates in advance the screw stroke Zset[1] when the mold cavity is filled with molten resin based on the cavity volume, screw diameter, etc. Furthermore, Uset[17], which allows the manipulated variable U[14] to be considered continuous when switching from the injection process to the pressure holding process, is determined in advance. These setting amounts Zset[1] and Uset[17] are stored from the control parameter input device 29 to the memory 20.

As mentioned above, when the injection operation is started, the screw speed detection value 5 (Z) becomes the screw speed command value 2.
(Zr), the deviation (speed deviation) is compensated by the speed control compensator 7, and inputted as the manipulated variable 15 (Uz) to the servo amplifier 11 (27) via the control loop switching unit 10. This operation amount is input to the injection molding machine 12 (ie, the servo valve 28) via the servo amplifier 11, and the injection speed of the injection molding machine 12 is controlled to the speed command value 2 (Zr). Also,
The output of the speed control compensator 7 is input to the switching condition determiner 9.

On the other hand, the pressure detection value 6 (P) of the pressure detector 25 is compared with the pressure command value 3 (Pr) preset in the memory 20, the pressure deviation is compensated by the pressure control compensator 8, and the pressure operation amount 16 (Up) is input to the switching condition determining section 9. Furthermore, the position detector 24
The detected screw position value 4(z) from 4(z) is directly input to the switching condition determining section 9.

The switching condition determination unit 9 compares the detected screw position value 4(z) and the set screw stroke Zset[1], and also determines the absolute value of the difference between the manipulated variable 15 (Uz) and the pressure manipulated variable 16 (Up). , that is, 1 | Uz
Find −Up| Then, screw position detection value 4 (z) ≧ setting screw stroke Zset [1],
When |Uz−Up|≦Uset(17), the switching condition determining unit 9 sends a switching signal to the control loop switching unit to switch from contact A to contact B. That is, the connection relationship is switched from (A-C) to (B-C). As a result, the pressure operation amount 16 (Up) is input to the servo amplifier 11, and the injection molding machine 12 (ie, the servo valve 28) is controlled by the pressure operation amount 16 (Up). That is, the speed control loop is continuously switched to the holding pressure (pressure) control loop.

In the above-described embodiment, the resin pressure inside the mold is detected, but the pressure inside the hydraulic cylinder may be used for control.

(Effects of the Invention) As explained above, according to the present invention, after the molten resin is filled into the mold, the injection speed control loop sends the pressure to the injection speed control loop while maintaining continuity between the speed control amount and the pressure control amount. The control system can be switched to the control loop, so good molded products can always be obtained.

[Brief explanation of the drawing]

Figure 1 shows the injection device of the injection molding machine, Figure 2 shows the injection device of the injection molding machine.
The figure shows an embodiment of a control device using a microcomputer, FIG. 3 is a block diagram for explaining speed-pressure switching control according to the present invention, and FIG.
The figure is a diagram for explaining conventional discontinuity. 7...Speed control compensation section, 8...Pressure control compensation section, 9...Switching condition determination section, 10...Control loop switching section, 11...Servo amplifier, 12...Injection molding machine, 24...Position detection 25... Temperature detector, 26... Pressure detector, 27... Servo amplifier, 28... Servo valve, 29... Speed-pressure switching control device, 30... Control parameter input device.

Claims (1)

[Claims] 1. A control device that controls the injection process and pressure holding process of an injection molding machine includes a speed detector that detects the injection speed of molten resin, a position detector that detects the screw position, and detects resin pressure or hydraulic cylinder pressure. The injection stroke detected by the pressure detector and the position detector is a preset injection stroke, and the absolute value of the difference between the manipulated variable of the injection speed control and the manipulated variable of the pressure control is less than or equal to the preset value. Then, a speed-pressure switching control device for an injection molding machine, comprising a control means for switching from the injection process control to the pressure holding process control.