JPH01200928A - Speed/pressure control system of injection molding machine - Google Patents

Abstract

PURPOSE:To efficiently control the injection speed and follow-up pressure of an injection molding machine, by correcting the deviation between the predetermined injection speed or pressure order value of a molding resin and an actual detection value by a specific correction means. CONSTITUTION:When an injection molding cycle is started, a screw position detector 10 counts a screw position X. The injection speed order value Vr preliminarily stored in a memory apparatus 20 is read corresponding to the screw position X to calculate injection deviation Ve. Operation quantity UV1 is calculated according to the program for a speed control system servo stored in the memory apparatus 20 on the basis of the injection speed deviation Ve and subsequently added to the corrected operation quantity UV2 stored in the memory apparatus 20 to set operation quantity U which is, in turn, sent to a servo amplifier 13 through a D/A converter 23. In a follow-up pressure process, the operation quantity UV1 is added to operation quantity UP2 to set the operation quantity U which is, in turn, sent out to the servo amplifier 13 through the D/A converter 23.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an injection molding machine, and more particularly to a speed/pressure control system for an injection molding machine.

[Conventional technology] The injection molding process of the injection molding machine is injection, filling.

It is divided into four stages: pressure holding and cooling. The injection stage is a speed control in which the molten resin is poured into the mold at a set speed, whereas the stage from filling to pressure holding is
This is pressure control that applies pressure to the resin in the mold in order to make the density of the molded product and its internal pressure distribution uniform.

Here, an example of a conventional injection molding machine will be explained with reference to FIG.

The injection molding machine is equipped with a heating cylinder 2 having a hopper 1 and a screw 3. This screw 3 can move back and forth while rotating within the cylinder 2. The rear end of the screw 3 passes through a pressure actuator 4, and is held and driven within a piston 5 coaxially and rotatably with the piston. The screw 3 is connected to and driven by a hydraulic motor 6. A plate member 7 is provided at the final end of the screw 3 so as not to hinder the rotation of the screw 3 and to be freely displaceable along the screw axis. The plate member 7 is connected to a speed detector 9 via a piston rod 8. A screw position detector 10 for detecting the position of the screw includes a rack 11, which is integrally interlocked with the plate member 7, and a gear lla rotates as the rack 11 moves forward and backward. Further, a pressure detector 12 is attached to the pressurizing actuator 4 to sense the internal pressure thereof. The detection outputs of the speed detector 9, screw position detector 10, and cylinder resin pressure detector 12 are input to a speed/pressure control device 100'.

Next, a conventional speed/pressure control device 100' will be explained with reference to FIG. t1.

The screw position X detected by the screw position detector 10 is input to the input terminal of the injection speed command value generator 110, the control input terminal of the cylinder resin pressure command (FI generator 120', and the control input terminal of the switching device 130). The injection speed command value generator 110 generates a predetermined injection speed command value V according to the screw position X.The cylinder resin pressure command Vi generator 120' has a timer (not shown). , when the screw position K reaches the predetermined position, the timer operates,
A predetermined in-cylinder resin pressure command ff1P,' is generated according to the timer value of the timer.

The injection speed command 1iiVr output from the injection speed command value generator 110 and the injection speed detection value V detected by the speed detector 9 are input to the difference circuit 140, where the difference (V, -V) is calculated and the injection speed is It is output as the speed difference v0. On the other hand, the cylinder resin pressure command values P,' output from the cylinder resin pressure command value generator 120 and the cylinder resin pressure detection value P' detected by the cylinder resin pressure detector 12'
is input to the difference circuit 150, where the difference (P, ′−P′
) is calculated and output as an in-cylinder resin pressure deviation of 20°. The injection distance plane difference V0 is input to the speed control system PID sleeve compensator 160', where the manipulated variable U'9 is determined and input to one input terminal of the switching device 130. On the other hand, the in-cylinder resin pressure difference P0' is input to the pressure control system PID compensator 170', where the operation nU'P is determined and input to one input terminal of the switching device 130. The switching device 130 selects and outputs either operation iu' or U'P as the chestnut harvesting amount U according to the screw position X.
3 to the servo valve 14. The servo valve 14 adjusts the flow rate and pressure of oil from the oil source 15 to the pressurizing actuator 4, so that the detected injection speed value V and the detected resin pressure inside the cylinder value P' are respectively the injection speed command value ■ and the inside cylinder pressure. Control is performed to follow the resin pressure command values P,'.

Incidentally, the transfer function a'GV(S) of the speed control system PID compensator 160' and the transfer function a'op(s) of the pressure control system PID compensator 170' are expressed by the following equations, respectively.Equation % is a constant.

[Problems to be Solved by the Invention] By the way, when such an injection molding machine is used to mold a molded product that requires precision, such as a compact disc, it is necessary to perform precise control.

For example, if precise removal is not performed, appearance defects such as scum burn 201, weld lines 202, air marks 203, liquid flow marks 204, and jetting 205 will appear on the molded product as shown in FIG. These defective areas are represented by the indicated ranges of screw position and injection speed, as shown in FIG. 7, for example. Therefore,
To obtain a good product, it is necessary to program the injection speed according to the screw position so as not to overlap the defective area.

Generally, during the injection stage and pressure holding stage of an injection molding machine, the flow characteristics of the resin change over time depending on the temperature of the resin, the pressure it receives, the shape of the gold, and other factors. As a result, the load characteristics seen from the actuator of the injection molding machine change. However, conventional speed/pressure control devices use either a compensator that calculates the manipulated variable from the deviation, or a so-called untimely variable system that does not have constant control parameters and consists of a transfer function. This causes steady-state deviation, etc. Therefore, it is difficult for conventional speed/pressure control devices to mold products such as compact discs that have a narrow range of good quality products.

Therefore, a technical object of the present invention is to provide a speed/pressure control system for an injection molding machine that can be accurately controlled even when load characteristics change.

[Means for Solving the Problems] The present invention is based on a predetermined command value for the resin pressure in the mold or the resin pressure in the mold and the injection speed, and the resin pressure in the mold or the resin pressure in the mold and the injection speed. A system for controlling the injection speed and holding pressure of an injection molding machine by means of a compensating means that outputs a manipulated variable in response to a deviation from a detected value, the compensating means being a time-variable system. A speed/pressure control method for the molding machine can be obtained.

[Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing the configuration of an injection molding machine to which the present invention is applied, and the same components as in FIG. 5 are designated by the same reference numerals. The difference from FIG. 5 is that a control parameter input device 17 such as a digitizer is included.

Next, referring also to FIG. 1, a speed/pressure control device 100 according to the present invention will be described. Components having the same functions as those in FIG. 4 are given the same reference numerals. The difference from FIG. 4 is that instead of the speed control system PID compensator 160', a speed control system servo controller 161, a speed control system learning: r Citrolla 162, and a sum circuit 163 are used, and the pressure control system PID control system Instead of the PID compensator 170', mold-like resin pressure control system servo controller 1 to roller 171, mold-like resin pressure control system learning controller L-roller 17
2 and sum circuit 173 are used.

The speed control system servo controller 161 inputs the injection speed surface difference V0 and the screw position X, and outputs the operation ff1Uv. Here, the speed control system servo controller 16
1 transfer function G. c[S) is expressed by the following formula.

U v+= G ovfs) ・V o (S) Here, the control parameters that change depending on the screw position are Kv (X), R1 (X), R2 (X), Q
+(x) and Q2(X) are input in advance from the control parameter input device 17 shown in FIG. In addition, the speed control system learning controller 162 has a memory, stores the injection speed deviation (■) for each injection cycle, calculates the correction operation amount uv2 for ejecting this stored injection speed surface difference (2), and calculates the correction operation amount uv2 for the next injection. The corrected operation amount Uv□ is output at the injection stage of the injection cycle. The sum circuit 163 is the speed control system servo controller 16
The switching device 130 adds the operation Jiuvl output from 1 and the corrected operation amount Uv2 output from the speed control system learning controller 162, and uses this addition result as the operation amount Uv.
input to one of the input terminals. The calculation algorithm executed by the speed control system learning controller 162 is a transfer function Guv (■
, -Gi/Uv). However, if this is difficult to achieve, Gc! Using a function G skin close to, Uv2=G′ L, v■.

Therefore, the correction operation JIUv2 may be calculated.

On the other hand, the resin pressure control system servo controller 171 in the mold
has a timer (not shown), and when the screw position ix reaches a predetermined position, the timer operates and outputs the manipulated variable U p+. Here, the transfer function G, , (S) of the in-mold resin pressure control system servo controller 171 is expressed by the following equation.

Up+=Gop(S)・P.

Here, the control parameters that change depending on the timer value are: (t), R, (t), R, (t)
.

Q3ft) and Q4(t) are also input in advance from the control parameter input device 17 shown in FIG. Also, like the speed control system learning controller 162, the in-mold resin pressure control system learning controller 172 has a memory, and stores the mold resin pressure 1 deviation P for each injection cycle. A correction operation fi U p 2 is calculated to cancel the difference P of resin pressure in the mold, and a correction operation amount UP2 is output at the pressure holding stage of the next injection cycle. Sum circuit 173 Operation ffk U p + output from in-mold resin pressure control system servo controller 171 and correction operation JIUP□ output from in-mold resin pressure control system learning controller 172
Similarly to the speed control system learning controller 162, the in-mold resin pressure control system learning controller 172, which adds this addition result as an operation MU and inputs it to the other input terminal of the switching device 130, performs U P? = G ′upP − (4) The corrected operation amount Upi is calculated. This transfer function G
'up is the resin pressure deviation P in the mold from the operation amount U, ノ\
The inverse function G' of the transfer function Gup (P--GupUp) of
, J! is an approximation function of

In other words, note that the injection molding operation is a repeated operation with the four processes of injection, filling, holding pressure, and cooling as one cycle, and using the deviation information of m1 cycles, This reduces the difference in surface area.

Finally, a case will be described in which the speed/pressure control device 100 described above is configured as an electronic computer system.

Referring to FIG. 3, the operator first inputs appropriate constant control parameters from the control parameter input device 17.The central processing unit (CPU) 18
The control parameters input via 9 are stored in a storage device (memory) 20.

The memory 20 includes the servo controller 161 .
A servo program for executing 171 operations,
The learning controllers 162 and 172 are pre-recorded with a learning program for executing Soichi's operations.
Hidden. The injection molding machine is tested without the learning program being operated, and the operator determines the change pattern of the control parameters.

The operator thus sets the control parameter KV (X) according to the determined screw position X.

R1(X), R2fx), Q+fx), and Q2(X), and the control parameters according to time t,
(t).

R3(H, R1(j), Qs(i) and Q4(t
) is input from the control parameter input device 17. This input control parameter is determined by the cpu i s.
It is stored in the memory 20 in correspondence with the screw position X or time via one interface.

Next, run the learning program as well.

When an injection molding cycle is started by the injection molding machine, the screw position X detected by the screw position detector 10 is
It is counted by the program counter (PG counter) 21, and the CPU 18 reads out the injection speed command value Vr stored in the memory 20 in advance in correspondence with the screw position D converter 22
Input via . The injection surface difference V is determined from the injection speed detection value ■. Based on this determined injection differential velocity surface difference (2), the speed control system servo program stored in the memory 20 calculates the manipulated variable UVt from equation (1), and sets this as the manipulated variable U to the D/A. It is sent to the servo amplifier 13 via the converter 23. At the same time, the injection speed surface difference ■,
is temporarily stored in the memory 20, and the corrected operation amount Uv□ for the injection process of the next injection molding cycle is calculated using equation (2) and stored in the memory 20.

When the CPU 18 detects that the count value of the PG counter 21 has reached a predetermined value, the CPU 18 determines that the pressure holding process has started, and sets the in-mold resin pressure command stored in advance in the memory 20 corresponding to time t. f! iPr is read out, and the in-mold resin pressure surface difference P is calculated from the read out in-mold resin pressure command value P7 and the in-mold resin pressure detection value P input via the A/D converter 24. demand. Based on this determined 10 difference P of resin pressure in the mold, the operation amount UPI is calculated from equation (3) using the pressure control system servo groderam stored in the Momeri 20, and this is operated tt! D/as ff1U
At the same time as sending it to the servo amplifier 13 via the A converter 23, the in-mold resin pressure difference P is temporarily stored in the memory 20, and according to equation (4), it is calculated for the pressure holding process of the next injection molding cycle. The corrected operation amount UP2 is calculated and recorded in the memory 20.

In the next injection molding cycle, the injection process (
1) The sum of the operation muv calculated by the formula and the corrected operation amount Uv2 stored in the memory 20 is sent as the operation amount U to the servo amplifier 13 via the D/A converter 23, and the result is In the pressure process, the D/A converter 2 uses the sum of the manipulated variable U p calculated by equation (3) and the corrected manipulated variable UP2 stored in the memory 20 as the manipulated variable U.
3 to the servo amplifier 13.

This injection molding cycle is then repeated.

[Effects of the Invention] As is clear from the above explanation, according to the present invention, the manipulated variable can be calculated from the difference between the command value and the detected value of the resin pressure in the mold or the resin pressure in the mold and the injection speed. Since the compensating means required is a time variable system rather than a time variable system, it is possible to reduce overshoot, delay, steady state deviation, etc. of the controlled variable even if the load characteristics change. Therefore, precision is required for compact discs and the like. It became possible to form molded products. In addition, with the hydraulic method, the resin pressure can only be controlled indirectly, and because there is pressure loss due to intervening hydraulic cylinders, reservoirs, gates, etc., it is not possible to control the actual resin pressure in the entire mold. When performing T control, etc., it is necessary for humans to consider the set value while keeping in mind the transmission characteristics of hydraulic pressure to mold internal pressure. Therefore, in the mold in-mold pressure control according to the present invention, the pressure can be controlled more directly.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of a control device that realizes the speed/pressure control method for an injection molding machine according to the present invention, and FIG. 2 shows an example of the configuration of an injection molding machine to which the present invention is applied. 3 is a diagram showing the control device shown in FIG. 1 as an electronic computer system, and FIG. 4 is a diagram of the control device that realizes the speed/pressure control method of a conventional injection molding machine A cross-sectional view and a block diagram showing the configuration of a conventional injection molding machine; FIG. 5 is a cross-sectional view and a block diagram showing the configuration of a conventional injection molding machine;
FIG. 6 is a diagram showing an example of a defective appearance, and FIG. 7 is a diagram showing an example of a defective region of injection speed. DESCRIPTION OF SYMBOLS 12... Resin pressure force detector in all molds, 110... Injection speed command value generator, 120... Resin pressure force command value generator in all molds, 130... Switching device, 140, 150. ...Difference circuit, 161...Speed control system servo controller, 1
62...Speed control system learning controller, 163...
Sum circuit, 171... Resin pressure control system servo controller in mold, 172... Servo controller for resin pressure control system in mold, 173... Sum circuit.

Claims (1)

[Claims] 1. The operation is performed based on the deviation between the predetermined command value of resin pressure in the mold or resin pressure in the mold and injection speed and the detected value of resin pressure in the mold or resin pressure in the mold and injection speed. A system for controlling the injection speed and holding pressure of an injection molding machine by means of a compensating means that outputs a quantity, the compensating means being a time variable system.
Pressure control method.