JPH04175135A - Control method of motor-driven injection molding machine - Google Patents

Abstract

PURPOSE:To secure continuity of injection pressure at the time of a beginning of a changeover process, by a method wherein an operation signal in the beginning state of the changeover process is made identical to an injection speed setting signal directly before a changeover to the changeover process. CONSTITUTION:A changeover process is provided between an injection process and dwell process, overshoot pressure is operated by a model provided within a controller and changeover pressure becoming a changeover condition from the injection process to the changeover process is operated based on overshoot pressure. Then the changeover pressure becoming the changeover condition from the changeover process to the dwell process is set up and a gain G during the changeover process is made G=V0/l, in the changeover process. Hereupon, V0 and l represent respectively a screw speed prior to the changeover and an overshoot pressure signal.

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. 2 is a diagram showing a conventional 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 pole screw shaft 2. The ball nut 3 is integrally formed with a member 4, which is mounted along a guide bar 5.5' installed between fixed members 6.6' and 7.7' of a frame (not shown). The screw 10 is attached so as to be movable in the forward and backward directions of the screw 10, which will be described later. therefore,
As the ball screw shaft 2 rotates, the member 4 can move back and forth on the guide bar 5.degree. 5'. The forward and backward movement of the member 4 is controlled by a screw 10 via a load cell 8 and a hair ring 9.
can be conveyed to.

Further, as the screw IO moves 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, and is amplified by the load cell amplifier 13.
It is input to the controller 15.

Furthermore, a position detector (hereinafter referred to as an "encoder") 11 is attached between the member 4 and the fixed member 6 (6', 7.7') so that the amount of movement of the screw 10 can be detected. The signal output from 11 is amplified by amplifier 14 and input to controller 15. The controller 15 outputs current commands to the servo amplifier 12L according to the settings of the operator for each process.
Drives the injection servo motor.

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. Molding is performed by controlling the speed and reaction force (injection pressure), respectively.

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

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. 3.

FIG. 3 is a block diagram for implementing a conventional electric injection molding machine control method.

In the figure, when a signal from an encoder 11 (FIG. 2) 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.
) and send this deviation signal to compensator 1.
The operation signal g obtained by the compensation calculation in step 6 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 is sent to a speed feedback system (differentiator 17 → subtracter 22 → compensator 16) like the injection speed setting signal C during the injection process. This is the amount of operation to be performed.

That is, the operation signal i is a speed command signal to the speed foot bank system. On the other hand, the speed feed bank system mentioned above is a pressure feedback system (load cell amplifier 13→
It operates as a minor feed hassock 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 j 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 switching pressure setting signal a
and the injection pressure detection signal e are compared, and the injection process (the contact 2-3 side of the selection switch 18) is switched to the holding pressure process (the contact 1-3 side of the selection switch 18) depending on the condition 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 Due to the large inertia of the motor, large injection pressure is generated when the motor speed is high in the injection process to the low motor speed in the holding process, which can damage the mold or cause molding defects such as stiffness, causing machine damage. Shorten lifespan.

Furthermore, since the injection speed control system is switched to the pressure holding control system in step 2, the command to the servo amplifier that drives the servo motor changes suddenly, causing the servo motor to operate rapidly. At this time,
Since the injection pressure fluctuates significantly compared to the pressure before switching,
Continuity between the injection process and the pressure holding process is lost, control during the process becomes difficult, and reproducibility is poor, making it difficult to obtain good products.

Additionally, when switching from the injection speed control system to the holding pressure control system, overshoot may occur during switching as shown in Figure 4, or the pressure may drop from the set value (holding pressure setting signal b) after switching. or For this reason, the continuity of the injection pressure is lost at the time of 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.

In other words, the injection pressure is PL, and the injection speed immediately before switching is ■1.
, if the resin in the mold beyond the screw 10 is assumed to be a compressible spring and the spring constant is k, then the injection pressure P
L is P,=to/' VLd t+B VL 10FL・(1
) t: Current time to = Time when the resin beyond the screw 10 can be imagined to be a spring, that is, the time when the cavity is almost filled with resin B: Resin viscosity FL: Other things that can be expressed in terms of load torque can.

As shown in equation (1) above, the injection pressure PL before switching
is the integral value of the injection speed ■, that is, the screw 100
A component proportional to the stroke (first term), a component proportional to the speed of the screw IO (second term), and other components (third term)
section) is included. Among these, the component proportional to the stroke of the screw lO does not become zero even if the injection speed VL becomes zero. On the other hand, the component proportional to the speed of the screw 10 becomes zero when the injection speed vL becomes zero. This causes the injection pressure P to fluctuate at the time of switching.

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 manually input to the speed feed hack 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 pt.

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, or if the switching position is not properly adjusted during operation. It becomes difficult to choose.

The present invention solves the problems of the conventional electric injection molding machine control method described above, secures the continuity of injection pressure when switching from the injection process to the pressure holding process, protects the mold, and protects the mold. 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 such problems and obtain a good molded product, extend the life of the injection molding machine, and improve the precision of the molded product. purpose.

(Means for Solving the Problems) For this purpose, in the control method for an electric injection molding machine of 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, the holding pressure The control system is provided with a minor feed hack for the injection speed, which is shared with the speed feed bank system of the injection speed control system, and a switching process is provided between the injection process and the holding pressure r period.

Then, the overshoot pressure is calculated using a model installed inside the controller, and based on the overshoot pressure, the switching pressure that is the switching condition from the injection process to the switching process is calculated, and the switching process from the switching process to the holding pressure process is calculated. Set the switching pressure as the condition. In the above switching process, the gain G during the switching process is G-V. /f ■o: Screw speed before switching! The two overshoot pressure signals are as follows.

(Function) According to the present invention, as described above, a minor feed hassock for injection speed is provided in the pressure holding control system, and this is shared with the speed feed bank system of the injection speed control system, and between the injection process and the pressure holding process. A switching process is provided, and a first switching pressure, which is a switching condition from the injection process to the switching process, is calculated based on the overshoot pressure estimated by the model, and a switching process from the switching process to the holding pressure process is calculated. A second switching pressure is set.

Therefore, when the injection pressure increases and reaches the first switching pressure, the injection process is switched to the switching process, and when the injection pressure increases further and reaches the second switching pressure, the switching process is switched to the pressure holding process.

At this time, the gain G during the switching process is G-V. /P, so the operation signal in the initial state of the switching process is equal to the injection speed setting signal immediately before switching to the switching process.

Further, in the state where the switching process is completed, the operation signal becomes almost zero, and the change from the injection speed command signal immediately after switching to the pressure holding process is small.

(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.

At the time, when the signal from the encoder 11 (see FIG. 2) is input to the controller 15 through the amplifier 14, the signal is differentiated by the differentiator 17 to provide the 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.
) and send this deviation signal to compensator 1.
The operation signal g obtained by the compensation calculation in step 6 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 subtracted (feedhacked) to become a deviation signal, which is subjected to compensation calculation in compensation n19 to obtain the operation signal i.

At this time, the operation signal 1 is not a direct operation signal to the servo amplifier 12, but is sent to a speed feedback system (differentiator 17 → subtracter 22 → compensator 16) like the injection speed setting signal C during the injection process. This is the amount of operation to be performed.

That is, the operation signal 1 is a speed command signal to the speed feedback system. On the other hand, the speed feedback system C, the 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 or operation signal i is to be used as the operation amount to the speed feed bank system during the injection process and the pressure holding process. 23 are provided. This selection switch 23 is provided as a condition for switching from the injection process to the pressure holding process. Then, the switching pressure setting signal and the injection pressure detection signal e are compared, and the injection process is switched to the pressure holding process depending on the condition of e≧h.

By the way, as described above, when switching from the injection process to the pressure holding process, a short switching process is interposed, and continuity of the injection pressure is ensured.

For this purpose, a compensator 2 for the switching process is provided in parallel with the compensator 19.
4 is provided and connected to the selection switch 23. Therefore, the selection switch 23 has terminals 1 to 3 and terminal 4.
It is designed to be selectively connected to.

The compensator 24 also compensates for the deviation of the injection pressure detection signal e based on the holding pressure setting signal and outputs it to the speed feed bank system (differentiator I7 - subtractor 22 -> compensator 16).

Further, the comparator 25 compares the injection pressure detection signal e with the switching pressure setting signal, which is a condition for each switching from injection process to switching process to pressure holding process, and outputs a switching signal to the selection switch 23. . The selection switch 23 receives the switching signal from the comparator 25, selects one signal from the injection speed setting signal C1, the operation signal j of the compensator 24, and the operation signal j of the compensator 19, and outputs it to the speed feedback system. .

The switching pressure setting signal is given by a model of an injection molding machine provided inside the controller 15.

FIG. 5 is a layout diagram of a model of an injection molding machine, and FIG. 6 is a diagram showing a gain calculation compensator.

In the figure, 26 is a model that receives the injection speed setting signal C and outputs the output signal β, and 27 is the output signal f of the model 26.
This is an adder that adds the injection pressure detection signal e, and the signal p1
Output. 29 is a selection switch for selecting the signal PI and a signal P2 set higher than the signal PI;
Select P2 to set the switching pressure setting signal.

Here, the model 26 is a model before and after the electric injection molding machine switches from the injection process to the pressure holding process. Before and after switching from the injection process to the pressure holding process, overshoot occurs as described above. In other words, if the injection speed is not zero before the above switching, the speed command will be zero (stop command).
It does not respond instantaneously even when the speed is reached, and a deceleration stroke is required. This deceleration stroke is S, and the screw speed before switching is ■.

given that S=2A...(1) A: Maximum acceleration when decelerating injection speed It is expressed as

Further, assuming that the filling is almost completed before switching, the resin pressure is approximated by a spring curve with respect to the screw stroke. Therefore, if this spring constant is set as K, the overshoot pressure Δp at the time of the above switching becomes Δp=Ks (2).

From equations (1) and (2), ■02 ΔT)=□ ...(3) A, and here the constant M of the above model 26 is set as M=□
...(4) If A is defined, equation (3) is expressed as Δp=MVot (5). That is, the overshoot pressure at the time of the switching can be determined based on the screw speed V0 before the switching and the constant M of the model 26. Therefore, when the value of the injection pressure detection signal at the time of switching is e, the screw speed is V. When screw 0 is decelerated and stopped, the model 26 can estimate how the injection pressure will change due to pressure overshoot. It is sufficient to start deceleration by the switching process when the output signal l, that is, the output signal P1 obtained by adding the overshoot pressure Δp, becomes the first-stage holding pressure setting signal of the holding pressure process.

Here, the gain G of the compensator 24 is calculated using the gain calculation compensator 28 so that the screw speed is continuous during the injection process, the switching process, and the pressure holding process.

G-■. /! (6) FIG. 7 is an operational flowchart of the method for controlling an electric injection molding machine of the present invention.

Step (2) First, at the start of the injection process, the injection speed setting signal C is output, the connection state of the selection switch 23 is set to the L4 connection, the connection state of the selection switch 29 is set to the 1-3 connection, and control based on the injection speed is started.

Step ■ During the injection process, the output signal l (Δp) is calculated by the model 26, and by adding it to the injection pressure detection signal e, the switching pressure setting signal, which is the switching condition from the injection process to the switching process, is set as the signal P1. Output.

Step ■■ Execute control using the normal injection speed until the injection pressure detection signal e exceeds the switching pressure setting signal.

Step■ When it comes to hoe, set the selection switch 23 to 2-4.
connection, and the selection switch 29 is set to 2→3 connection to start the switching process. As a result, a switching pressure setting signal serving as a switching condition from the switching process to the pressure holding process is output as signal P2. Also, at this time, calculate the gain G, and calculate the gain G.
performs compensation calculation during the switching process.

Step ■■ The switching process is executed until the injection pressure detection signal e becomes larger than this switching pressure setting signal.

Step ■■ If h≦e is satisfied, select switch 2
3 to 3-4 connection and perform the normal pressure holding process.

Here, in the above switching step, the same pressure control is performed except that the compensation content of the compensator 24 is different. This is shown in the next 2.

j-GX(b e) ... (7) At this time,
G is the gain, which is set as Equation 1% at the start of the switching process. Combining the above equations (6) and (7), we get C2 as shown in the following equation.

■.

J = lX (b - e)... (8) Above formula (4
), the initial state of the switching process is r+e, so 2.

J--X (1+e e)#Vo -(9)! becomes. This is the injection speed V just before switching to the switching process.
. This shows that the operation signals j immediately after switching to the switching process are equal, that is, they are continuous.

Conversely, the condition for completing the switching process is h=P2≦e, so immediately before the switching process ends, P2'=e. At this time, if the signal P2 and the holding pressure setting signal S are set to very close values, then P2-b becomes b-P2LiO.

Therefore 3 ,　　　V　　　　　　　　　　　, 　　　V　

J = -X (b-P2) =: ~i x (P
2 ' 2 ) ''. This means that the injection speed is zero at the end of the switching process, that is, just before switching to the holding pressure process, and if P2 is applied, the pressure deviation will also be close to zero. Indicates that there is a

Even if you switch to the pressure holding process in this state, b#P2''=re
Therefore, since the pressure deviation value is close to zero, the operation signal i from the pressure holding control system is also close to zero in the initial stage, making it possible to switch continuously.

Also, during this switching process, the pressure foot system is executed by the gain G and the target holding pressure setting signal, so the switching pressure setting signal of the switching pressure changes from the initial state signal P1 to the final state signal P2. Continuously controlled up to As a result, while controlling the pressure, the operation signal it J, which is the operation amount to the speed feedback system, and the injection speed setting signal C are continuously controlled.

Here, the switching conditions from the switching process to the holding pressure process are b''=,
P2 is bf-P2. This is because many control systems do not cause overrun or have a residual deviation, and the pressure control system during the switching process may not permanently satisfy the condition of P2≦e.

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 of the electric injection molding machine of the present invention, the injection speed minor feed is provided in the pressure holding control system, and this is used as the speed feed bank of the injection speed control system. A switching process is provided between the injection process and the pressure holding process, which is shared with the system, and the first switching pressure, which is the switching condition from the injection process to the switching process, is calculated based on the overshoot pressure estimated by the model. At the same time, a second switching pressure is set, which is a condition for switching from the switching process to the pressure holding process.

Therefore, when the injection pressure increases and reaches the first switching pressure, the injection process is switched to the switching process -1, and when it increases further and reaches the second switching pressure, the switching process is switched to the pressure holding process.

At this time, the gain G during the switching process is CV. /r■. = Screw speed before switching! : Since the OHA chute pressure signal is the same, the operation signal in the initial state of the switching process is equal to the injection speed setting signal immediately before switching to the switching process, ensuring continuity of the injection pressure at the start of the switching process. can.

In addition, at the end of the switching process, the operation signal is almost zero, and the change from the injection speed setting signal immediately after switching to the holding pressure process is small (to ensure continuity of injection pressure at the end of the switching process). can do.

In other words, it ensures the continuity of injection pressure when switching from the injection process to the pressure holding process, protects the mold, prevents the occurrence of bulges, etc., and makes it possible to obtain a good molded product. It becomes possible to extend the life of the machine and improve the precision of molded products.

Furthermore, the switching conditions when switching from the injection process to the pressure holding process can be automatically set, improving operability. Furthermore, since the optimal conditions are selected depending on the model, highly accurate switching can be performed at all times.

[Brief explanation of the drawing]

Fig. 1 is a block diagram for implementing the control method for an electric injection molding machine of the present invention, Fig. 2 is a diagram showing a conventional injection molding machine, and Fig. 3 is a block diagram for implementing the control method for a conventional electric injection molding machine. Figure 4 is a speed/pressure state diagram in the conventional electric injection molding machine control method, Figure 5 is the arrangement circle of the injection molding machine model, and Figure 6 is the gain calculation compensator. 7 are operational flowcharts of the method for controlling an electric injection molding machine of the present invention. DESCRIPTION OF SYMBOLS 1... Servo motor for injection, 12... Servo amplifier, 13... Load cell amplifier, 15... Controller, 16°19, 24... Compensator, 17... Differentiator, 25...・Comparator, 26...model. Figure 3 Figure 4 Water injection term: Plate pressure distance vJ screw nine Figure 5 / /28 Figure 7

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) provide a switching process between the injection process and the pressure holding process; (c) calculate the overshoot pressure using a model installed inside the controller; d) Calculate the switching pressure that is the switching condition from the injection process to the switching process based on the above overshoot pressure, (e) Set the switching pressure that is the switching condition from the switching process to the pressure holding process, (f) In the above switching process, the gain G during the switching process is
A method for controlling an electric injection molding machine, characterized in that G=V_0/l V_0: screw speed before switching l: overshoot pressure signal.