JPH03243321A - Controlling method of motor-operated injection molder - Google Patents

Abstract

PURPOSE:To ensure the continuity of injection pressure and consequently protect mold, prevent burrs and the like from developing and improve the accuracy of molded item by a method wherein the operating signal of the minor feedback of the injection speed of dwell controlling system in injection process is compared with injection speed setting signal so as to adopt either smaller one of both the signals as speed command signal. CONSTITUTION:Operating signal (g), which is obtained by compensatingly calculating the value obtained by subtracting screw speed detection signal (d) from injection speed setting signal (c) with a subtracter 22, with a compensator 16, is sent to a servo amplifier 12. Further, operating signal (i) obtained by compensatingly calculating the value, which is obtained by subtracting injection pressure detection signal (e) inputted from a load cell amplifier 13 into a controller 15 from dwell setting signal (b) with a subtracter 21, with a compensator 19 and becomes the speed command signal to speed feedback system and acts as minor feedback, which stabilizes the internal state of dwell feedback system. A comparator 23 compares the operating signal (i) and the injection speed setting signal (c) with each other. When the signal (i) is larger than the signal (c), a selective switch 18 is brought into 2-3 connection so as to carry out injection process, while, when the signal (i) is equal to or smaller than the signal (c), the selective switch 18 is brought into 1-3 connection so as to be changed-over to dwell process.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of controlling an electric injection molding machine using a servo motor as a drive source for injection and pressure holding.

(Conventional technology) Conventionally, in injection molding machines that use servo motors as drive sources for injection and pressure holding, when transitioning from the injection process to the pressure holding process, the screw position, resin pressure, etc. are detected and matched with the set value. The switch is made based on whether or not the

FIG. 4 is a diagram showing a conventional electric injection molding machine.

In the figure, reference numeral 1 denotes an injection servo motor, and the rotation of the injection servo motor 1 is transmitted to a ball screw nut 3 via a ball screw shaft 2. The ball nut 3 is integrally formed with a member 4, which extends along a guide bar 55' installed between fixed members 6.6' and 7.7' of a frame (not shown). It is attached so as to be movable in the forward and backward movement direction of the screw 10, which will be described later. Therefore, as the ball screw shaft 2 rotates, the member 4 moves toward the guide bar 5°5.
'You can move forward and backward on the top. The forward and backward movement of the member 4 is transmitted to the screw IO via the load cell 8 and hair ring 9.

Furthermore, by moving the screw 10 back and forth in an injection cylinder (not shown), the stored molten resin is forced into the mold and injection molding is performed. At this time, the force pushing the resin is detected as a reaction force by the load cell 8, amplified by the load cell amplifier 13, and manually applied to the controller 15.

In addition, a position detector (hereinafter referred to as "
Encoder. ) 11 is attached, and the signal output from the encoder 11 is amplified by an amplifier 14 and input to a controller 15. The controller 15 outputs a current command corresponding to each process to the servo amplifier 12 according to the operator's settings, and drives the injection servo motor 1.

With the above configuration, the screw speed is fed back in the injection process in which the molten resin is pushed into the mold, and the reaction force applied to the load cell 8 is fed back in the pressure holding process in which a constant pressure is applied to the molten resin pushed into the mold. , the bottom shape is performed by controlling the speed and reaction force (injection pressure), respectively.

Here, in the conventional control method, when switching from the injection process to the pressure holding process, the injection pressure detected as the screw position or load cell load is compared with the set value,
It was switched when the two matched.

Next, an example of switching from the injection process to the pressure holding process based on the injection pressure in the conventional electric injection molding machine will be described with reference to FIG. 5.

FIG. 5 is a block diagram for implementing a conventional electric injection molding machine control method.

In the figure, when a signal from an encoder 11 is input to a controller 15 via an amplifier 14, the signal is differentiated by a differentiator 17 to provide a screw speed detection signal d.

C is an injection speed setting signal during the injection process, and the screw speed detection signal d is subtracted from this injection speed setting signal C by a subtractor 22.
(feedback constantly) This deviation signal is sent to the compensator 16.
The operation signal g subjected to the compensation calculation is sent to the servo amplifier 12.

Further, b is a holding pressure setting signal during the holding pressure process.

The holding pressure setting signal is sent to the load cell amplifier 1 by the subtracter 21.
Injection pressure detection signal e manually input from 3 to controller 15
is subtracted (feedback) and becomes a deviation signal, which is subjected to compensation calculation in the compensator 19 to obtain the operation signal i.

At this time, the operation signal i is not directly an operation signal to the servo amplifier 12, but is sent to the speed feedback system (differentiator 17 → subtracter 22 → compensator 16) in the same way as the injection speed setting signal during the injection process. The amount of operation is

In other words, the operation signal i is a speed command signal to the speed feedback system. On the other hand, the speed feedback system described above is a holding pressure feedback system (load cell amplifier 13→
It operates as a minor feed hunk to stabilize the internal state of the subtracter 21→compensator 19>.

In the above control system, a selection switch is provided so that it is possible to select which of the injection speed setting signal C and the operation signal i is to be used as the operation amount to the speed feedback system during the injection process and the pressure holding process. One day is set. This selection switch 18 is provided as a condition for switching from the injection process to the pressure holding process. Then, the switching pressure setting signal a
and the injection pressure detection signal e are compared, and the injection process (on the contact 2-3 side of the selection switch 18) is switched to the holding pressure process (on the contact 1-3 side of the selection switch 18) under the condition of e≧a. ing.

(Problem to be Solved by the Invention) However, in the control method for the electric injection molding machine with the above configuration, in the case of a control system that detects resin pressure and switches from the injection process to the pressure holding process, the servo motor itself and the drive transmission system Because of the large inertia of the motor, a large injection pressure is generated when moving from the injection process with a high motor speed to the holding process with a low motor speed, which can damage the mold or cause molding defects such as burrs, resulting in machine damage. Shorten lifespan.

Furthermore, since the injection speed control system is suddenly switched to the pressure holding control system, the command to the servo amplifier that drives the servo motor changes suddenly, causing the servo motor to operate suddenly. At this time, the injection pressure fluctuates significantly compared to the pressure before switching, so the continuity between the injection process and the pressure holding process is lost, control during that time becomes difficult, and the reproducibility is poor, making it difficult to obtain good products. Become.

Also, when switching from the injection speed control system to the holding pressure control system,
As shown in FIG. 6, overshoot may occur during switching, or the pressure may drop from the set value (holding pressure setting signal b) after switching. For this reason, the continuity of the injection pressure is lost during switching, making it difficult to obtain a good molding state. This drop in pressure is caused by the components that make up the injection pressure immediately before switching.

That is, the injection pressure is PL, the injection speed immediately before switching is VL,
If the resin in the mold beyond the screw lO is assumed to be a compressible spring and the spring constant is k, then the injection pressure P
L is: t: Current time to: When the resin beyond the screw 10 can be imagined as a splash, that is, the time when the cavity is almost filled with resin B - Resin viscosity F, - Other load torques can be expressed.

As shown in equation (1) above, the injection pressure PL before switching includes an integral value of the injection speed ■1, that is, a component proportional to the screw stroke (first term), a component proportional to the screw speed ( 2) and other ingredients (3rd term). Among these, the component proportional to the stroke of the screw does not become zero even if the injection speed becomes zero. On the other hand,
The component proportional to the screw speed becomes zero when the injection speed becomes zero. From this, the injection pressure P at the time of switching
L will fluctuate.

Furthermore, in the control system having the above configuration, when the speed control system is switched to the pressure control system, the speed command signal input to the speed feedback system suddenly changes from the injection speed setting signal C to the operation signal i. For example, the switching pressure setting signal a
If the holding pressure setting signal and the holding pressure setting signal are set to the same size,
The switching condition at the time of switching is a=e, and the switching pressure setting signal a and the injection pressure detection signal e are equal. At this time, b=e, the injection pressure detection signal e becomes equal to the holding pressure setting signal, and the pressure deviation in the pressure control system immediately after switching becomes zero.

Therefore, when the compensator 19 performs only proportional operation, the operation signal i will also be zero, so the signal given to the subtractor 22 will suddenly change from the injection speed setting signal C to zero due to switching. This also impairs the continuity of the injection pressure PL.

In addition, even in the case of a control system that switches between the injection process and the pressure holding process based on the screw position, problems may occur due to the sudden switch from the injection speed control system to the pressure holding control system, and it is difficult to select the switching position appropriately for operational reasons. becomes difficult.

The present invention solves the problems of the conventional electric injection molding machine control method described above, ensures continuity of injection pressure when switching from the injection process to the pressure holding process, protects the mold, and reduces firmness. It is an object of the present invention to provide a control method for an electric injection molding machine that can prevent the occurrence of molding and obtain a good molded product, extend the life of the electric injection molding machine, and improve the precision of the molded product. purpose.

(Means for Solving the Problems) To this end, in the control method for an electric injection molding machine of the present invention, the pressure holding control system is A minor feed hack for the injection speed is provided in , which is shared with the speed feedback system of the injection speed control system, and is used to send operation signals to the minor feed hack for the injection speed of the holding pressure control system and injection speed setting signals during the injection process. The smaller one of both signals is selected and used as the speed command signal.

(Function) According to the present invention, when switching between the injection process and the pressure holding process of an injection device using a servo motor as a drive source as described above, minor feedback of the injection speed is provided in the pressure holding control system, and this is applied to the injection speed. It is shared with the speed feedback system of the speed control system, and compares the operation signal for minor feed deviation of the injection speed of the holding pressure control system during the injection process with the injection speed setting signal, and selects the smaller of both signals. Since it is selected as the speed command signal, the injection pressure detection signal is subtracted from the holding pressure setting signal during the injection process to obtain the operation signal, and the operation signal and the injection speed setting signal are compared.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram for carrying out the method of controlling an electric injection molding machine of the present invention.

In the figure, when a signal from an encoder 11 is input to a controller 15 through an amplifier 14, the signal is differentiated by a differentiator 17 to provide a screw speed detection signal d.

C is an injection speed setting signal during the injection process, and the screw speed detection signal d is subtracted from this injection speed setting signal C by a subtractor 22.
(feedback constantly) This deviation signal is sent to the compensator 16.
The operation signal g obtained by compensation calculation is sent to the servo amplifier 12.

Further, b is a holding pressure setting signal during the holding pressure process.

The holding pressure setting signal is sent to the load cell amplifier 1 by the subtracter 21.
Injection pressure detection signal e input from 3 to controller 15
is eliminated (feedback), becomes a deviation signal, and is subjected to compensation calculation in the compensator 19 to obtain the operation signal i.

At this time, the operation signal i is not a direct operation signal to the servo amplifier 12, but a speed feed hack system (differentiator 17 → subtracter 22 → compensator 16) like the injection speed setting signal during the injection process described above. This is the amount of operation to be performed.

In other words, the operation signal i is a speed command signal to the speed feedback system. On the other hand, the speed feedback system described above is a holding pressure feedback system (load cell amplifier 13→
It operates as a minor feed hanok to stabilize the internal state of the subtracter 21→compensator 19).

In the above control system, a selection switch is provided so that it is possible to select which of the injection speed setting signal C and the operation signal i is to be used as the operation amount to the speed feedback system during the injection process and the pressure holding process. 18 are provided. This selection switch 18 is provided as a condition for switching from the injection process to the pressure holding process. Then, the operation signal i is output from the pressure feedback system to the speed feedback system.
and the injection speed setting signal C, and the injection process is switched to the pressure holding process based on the condition of i≦C.

For this purpose, a comparator 23 to which the operation signal i and the injection speed setting signal C are manually input is provided, and the selection switch 18 is configured such that terminals 1 and 2 are selectively connected to terminal 3. There is.

The comparator 23 compares the operation signal i, which is a condition for switching between the injection process and the pressure holding process, with the injection speed setting signal C, and outputs a switching signal to the selection switch 1. That is, when i>c, the selection switch 18 is connected to 2-3 and the injection process is performed, and when i≦C, the selection switch 18 is connected to 1-3 and the injection process is performed.

The state of each signal at this time will be explained with reference to FIG. 2.

Fig. 2 is a time/pressure/speed relation diagram in the control method of the electric injection molding machine of the present invention, Fig. 2 (A) is a diagram showing the transition of the injection pressure detection signal, and Fig. 2 (B) is a diagram showing the transition of the injection pressure detection signal. FIG. 3 is a diagram showing the transition of a selected signal.

The solid lines in FIG. 2(A) indicate the injection pressure detection signal e and the holding pressure setting signal i. Both signals e and b are subjected to subtraction processing in the subtracter 21, and compensation and calculation are performed in the compensator 19, resulting in an operation signal as shown by the broken line in FIG. 2(B)! is obtained.

On the other hand, the injection speed setting signal C is indicated by a dashed line in FIG. 2(B). Then, the operation signal i and the injection speed setting signal C
is selected by the selection switch 18, and a selection signal as shown by the solid line in FIG. 2(B) is obtained. After switching from injection speed control to pressure holding control, the pressure is smoothly decelerated by the time constant of the pressure holding control system, and the pressure approaches the holding pressure set value.

FIG. 3 is an operational flowchart of the method for controlling an electric injection molding machine according to the present invention.

First, at the start of the injection process, the injection speed setting signal C and the holding pressure setting signal S are output, and the injection process is started.

Step ■■ Holding pressure setting signal Skara Injection speed setting signal C
is subtracted and compensated and calculated in one compensator (FIG. 1) to obtain the operation signal i. Then, the operation signal i is compared with the injection speed setting signal C, and control at the normal injection speed is executed until the operation signal 1 exceeds the injection speed setting signal C. During this time, the selection switch 18 is placed in the 2-3 connection state.

Step (2) When 1≦C, the selection switch 23 is set to 13 and the pressure holding control process is executed.

Note that the present invention is not limited to the above embodiments,
Various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

(Effects of the Invention) As explained in detail above, in the control method for an electric injection molding machine of the present invention, the injection speed minor feed hunk is provided in the pressure holding control system, and this is connected to the speed feedback system of the injection speed control system. The operation signal for the injection speed minor feedback of the pressure holding control system during the injection process is compared with the injection speed setting signal, and the smaller of both signals is selected as the speed command signal. An electric injection molding machine that ensures continuity of injection pressure when switching from the injection process to the pressure holding process, protects the mold, prevents the occurrence of cracks, etc., and makes it possible to obtain good molded products. This makes it possible to extend the life of the molded product and improve the precision of the molded product.

[Brief explanation of drawings]

FIG. 1 is a block diagram for carrying out the method of controlling an electric injection molding machine of the present invention, FIG. 2 is a time/pressure/speed relationship diagram in the method of controlling an electric injection molding machine of the present invention, and FIG.
) is a diagram showing the transition of the injection pressure detection signal, FIG. 2(B) is a diagram showing the transition of the signal selected by the selection switch, FIG. 3 is an operation flowchart of the control method for the electric injection molding machine of the present invention, Fig. 4 is a diagram showing a conventional electric injection molding machine, Fig. 5 is a block diagram for implementing a conventional electric injection molding machine control method, and Fig. 6 is a switch in the conventional electric injection molding machine control method. FIG. 3 is a time/pressure/velocity relationship diagram. l... Injection servo motor, 12... Servo amplifier, 13... Load cell amplifier, 15... Controller, 16° 19... Compensator, 17... Differentiator, 18
...Selection switch, 23...Comparator.

Claims (1)

[Scope of Claims] A control method for an electric injection molding machine for switching between an injection process and a pressure holding process in an injection device using a servo motor as a drive source, comprising: (a) providing minor feedback of injection speed to a pressure holding control system; (b) compare the operation signal to the injection speed minor feedback of the pressure holding control system during the injection process with the injection speed setting signal; (c) A method for controlling an electric injection molding machine, characterized in that the smaller of the two signals is selected as the speed command signal.