JPS633730B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a control method for an injection molding machine.

In injection control of an injection molding machine, speed and pressure cannot be controlled simultaneously. In particular, in closed-loop control, the injection process is divided into a speed control area and a pressure control area, and the timing of the transition from speed control to pressure control depends on the screw position, the injection cylinder hydraulic pressure, or the resin in the mold. Generally, this is when the pressure, etc. reaches a set value.

However, with such timing settings, the following problems arise in closed loop control.

(b) In order to prevent burrs from forming on the molded product due to the size of the molded product, the mold structure, and the mold closing force of the machine, or to prevent mold damage, it is necessary to It is often necessary to regulate the maximum value of pressure. For this purpose, it is necessary to appropriately switch from the speed control region to the pressure control region, and also to appropriately set the pressure in the pressure region. Further, when switching from the speed region to the pressure region is performed by the position of the screw, it is particularly necessary to appropriately set the position of the screw. In this case, if the material is weighed too much or the screw position setting for switching to the pressure region is inappropriate, the mold will remain in the velocity region even after it is almost filled with material, resulting in a closed The loop control feature controls the actual speed to approach the set speed, and the speed control valve operates in the direction of increasing speed, ie, increasing pressure. For this reason, the injection pressure may reach a pressure that causes burrs, or even damage to the mold.

(b) Valves used for closed-loop control are required to have high performance such as good response, so they are generally susceptible to dirty hydraulic fluid due to their structure, and are not compatible with other valves. In comparison, malfunctions or failures due to foreign objects in the hydraulic fluid are more likely to occur. In such a case, even if an electrical control signal is generated, the valve body cannot be controlled, speed or pressure cannot be controlled, and if the injection process continues, the injection process will continue after the material is filled into the mold. , the injection pressure increases, which eventually causes burrs to occur and, in some cases, to breakage of the mold.

(c) In devices where the timing for switching from speed control to pressure control is determined by the screw position, or in devices that change the injection speed in multiple stages, after the screw position reaches the set value and the hydraulic pressure of the cylinder reaches the set value, the speed control is switched off. In equipment that switches to pressure control, if a multi-cavity mold is used and the gate is clogged, material will no longer be injected into the cavity where the gate is clogged.
Even if other cavities are filled with material before the screw reaches the screw position where it switches to pressure control (i.e. in the speed control region), speed control will continue as it is, and excessive injection pressure will cause these cavities to fill with material. This may cause burrs to form or damage to the mold due to excessive injection pressure.

This invention was made to solve the above problems, and when the difference between the set speed (or pressure) and the actual speed (or pressure) exceeds a certain range and continues for a certain period of time, injection An object of the present invention is to provide a method for controlling an injection molding machine that can prevent the occurrence of burrs and damage to a mold by interrupting the process.

The present invention will be explained in detail below based on illustrated embodiments.

FIG. 1 shows one embodiment of this invention.
is the injection nozzle, 2 is the cylinder, 3 is the hopper,
4 is a screw, 5 is a hydraulic cylinder, 6 is a piston, 7 is an oil motor, and 8 is a position/speed detector for detecting the position and speed of the screw 4, such as a potentiometer. 9 is a pressure detector; 10 is an injection pressure/speed control valve (hereinafter referred to as a control valve); 11 is an injection on/off valve; and 12 is a hydraulic pump;
and the hydraulic cylinder 5 via the control valve 10.
It is connected to the. A servo valve is used as the control valve 10, and speed and pressure are controlled by one valve.

Reference numeral 13 denotes a sequence control unit that controls and controls sequence operations by exchanging signals with the machine and with each detector and controller. Reference numeral 14 denotes a signal switch that selects the control target (speed and pressure) of the control valve 10 based on the signal from the sequence control section 13. 15 is a pressure setting device; 16 is a pressure control amplifier; the pressure detector 9 and the pressure setting device 15;
Take the output of as input. 17 is a speed setting device, and 18 is a speed control amplifier, which receives the outputs of the position/speed detector 8 and the speed setting device 17 as inputs. 19 is a pressure difference setting device, 20 is a speed difference setting device, 21 and 22
is a comparator, and in one of the comparators 21, the output of the pressure control amplifier 16 and the pressure difference setting device 1 are connected.
In the other comparator 22, the output of the speed control amplifier 18 and the output of the speed difference setting device 20 are compared. 23 is a timer unit to which the outputs of both the comparators 21 and 22 are added as a driving signal.

Next, the operation will be explained. When an injection signal is input from the machine to the sequence control section 13, an electric signal is issued from the sequence control section 13 to operate the injection on/off valve 11, and at the same time, the speed setting device 17 and signal switch 14 are operated. And the position
The speed control amplifier 18 is operated by the speed signal from the speed detector 8 and the setting signal from the speed setter 17, a speed command signal is transmitted to the control valve 10, and injection is started.

In the speed region, the speed setting signal and the speed signal detected by the detector 8 are compared by the speed control amplifier 18, and the control valve 10 is controlled so that the respective signals match, and the setting by the speed setter 17 is performed. Injection continues at the same speed.

When a pressure control start signal is sent from the sequence control unit 13 to the signal switch 14 and the pressure setting device 15, the signal switching device 14 switches to the pressure control side, and the pressure setting device 15 is activated to change the setting signal to the pressure It is added to the control amplifier 16. As a result, amplifier 16
The output of the control valve 10 is transmitted to the control valve 10 to shift from the speed region to the pressure region.

In the pressure region, the pressure setting signal and the pressure signal from the pressure detector 9 are input to the pressure control amplifier 16, and the operation of the amplifier 16 causes the control valve 10 to match the pressure setting value and the actual value. The injection process is then continued at the pressure set by the pressure setting device 15.

When the sequence control unit 13 issues an injection end signal, the injection on/off valve 11 is turned off, and the pressure setting device 15 is also turned off, thereby completing the injection process.

By the way, during injection speed control, if there is a failure, incorrect setting, or gate clogging of the control valve 10, a difference will occur between the actual speed and the set value. This difference appears as the output of the speed control amplifier 18, which is compared with the output of the speed difference setter 20 in the comparator 22, and if the difference signal is greater than the set value of the speed difference setter 20, the comparator 22 The output is applied to timer unit 23 as a timer drive signal. This drive signal is continuously input to the timer unit 23.
When the set time is reached, an abnormality occurrence signal is sent to the sequence control section 13. As a result, an injection interruption signal is sent from the sequence control unit 13 to the injection on/off valve 11, the injection on/off valve 11 is turned off, and the injection process is interrupted.

On the other hand, if the control valve 10 becomes uncontrollable due to foreign matter or the like during injection pressure control, a difference will occur between the set pressure and the actual pressure. In this case as well, the same operation as when a problem occurs in the speed range described above is performed.
When the pressure difference exceeds a certain value and continues for a certain period of time, an abnormality occurrence signal is sent from the timer unit 23 to the sequence control section 13, and the injection process is interrupted.

Note that the set values of the speed difference setter 20 and the pressure difference setter 19 are preferably set to values that are as small as possible and exceed the error range of the closed loop system including the speed setter 17 and the pressure setter 15. . Further, it is preferable that the set time of the timer unit 23 is set to a value that exceeds the response time of the closed loop system including the valve and is as small as possible. Furthermore, although the position/velocity detector 8 and the control valve 10 have functions of position, velocity, and velocity and pressure, they may each be devices having independent functions.

FIG. 2 shows another embodiment of this invention,
As a closed-loop control valve, an electrical signal is input only when a difference occurs between the set value and the actual value, and the control operation is performed to bring the set value and the actual value closer together (for example, the injection valve manufactured by Hunker Corporation in the United States) This is a case where a hydro control valve for controlling the molding machine is used. In this case, if the voltage or current value input to the control valve 10 exceeds a certain value and continues for a certain period of time or more, it is determined that there is an abnormality.

In the figure, 10 is a control valve, 31 is a servo amplifier, 3
2 is a setter for setting a voltage or current value; 33 is a comparator for comparing the voltage or current value input to the control valve 10 with the set value; the output thereof becomes a drive signal for the timer unit 23;

During control, the input signal of the control valve 10 and the setting device 3
The comparator 33 compares the input signal with the second setting signal, and when the input signal is greater than the set value, the comparator output is sent to the timer unit 23 as a drive signal. When the drive signal is generated continuously for a period longer than the set time of the timer unit 23, an abnormality occurrence signal is sent from the timer unit 23 to the sequence control section 13, thereby interrupting the injection.

FIG. 3 shows another embodiment of the present invention, in which an abnormality is detected when the speed and pressure control signals are sent to the control valve as a fully closed or fully open signal. In the figure, 10 is a control valve, 23
is a timer unit, 31 is a servo amplifier, 41
is a detector which detects whether the input signal of the control valve 10 is a fully closed or fully open signal, and its output becomes the input of the timer unit 23. Reference numeral 42 denotes an AND circuit which receives the output of the timer unit 23 and the injection signal, and its output is sent to the sequence control section as an abnormality occurrence signal.

In such a configuration, when the input signal of the control valve 10 is detected by the detector 41 as a valve fully closed or fully open signal, the output of the detector 41 is sent as a drive signal to the timer unit 23. join. When this drive signal continues to be generated for a period longer than the set time of the timer unit 23, an output is generated from the timer unit 23 and is applied to the AND circuit 42. At this time, if a signal indicating that injection control is in progress is applied to the AND circuit 42, the AND condition is satisfied and the AND output is sent to the sequence control section 13 as an abnormality occurrence signal, and the injection is interrupted.

The method for controlling an injection molding machine according to the present invention described above has advantages such as preventing the occurrence of burrs and damage to the mold even if there is a setting error, valve malfunction or breakdown, or gate clogging. , it also has the following features:

(b) Speed control limits can be detected.

The maximum injection speed is determined by the balance between the flow resistance when the material flows from the nozzle of the molding machine to the spool in the mold, the runner gate, and the product section, and the force transmitted to the material by the hydraulic pressure acting on the injection piston. Since the speed is determined, even if the machine's pump discharge amount is sufficient and the maximum speed capability under light load is high, if the injection force is insufficient, the injection speed may not be as set. It comes out. This means that the control limit has been exceeded,
The injection speed becomes unstable, which adversely affects the quality of the molded product, but if the control limit can be detected, this problem can be avoided.

(b) Since the speed limit field can be detected, it can be used as is for many types of machines.

Set the unit of the speed setting device to an absolute value (e.g. mm/
sec.) and used in common among many types of machines, the maximum controllable speed capability of each machine is generally different, so the maximum speed of the machine is different from the maximum value of the setting device. Although it may be difficult to match or cause practical inconvenience,
Operation reliability is improved because control limits can be automatically detected.

(c) Good automatic operation is possible by installing a circuit that issues an injection interruption alarm when an abnormality is detected.

(d) Once adjusted, there is no need to readjust each molded product.

(E) In addition to detecting control valve failures, injection ON/OFF
Failure of the off valve can also be detected.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of a control device for an injection molding machine according to the present invention, and FIGS. 2 and 3 are block diagrams showing other embodiments of the invention. 8...Position/speed detector, 9...Pressure detector,
10... Injection pressure/speed control valve, 11... Injection on/off valve, 13... Sequence control section, 14...
...Signal switcher, 15...Pressure setting device, 16...Pressure control amplifier, 17...Speed setting device, 18...
Speed control amplifier, 19...Pressure difference setting device, 20
... Speed difference setter, 21, 22 ... Comparator, 23
...Timer unit, 32...Setting device, 33...
... Comparator, 41 ... Detector, 42 ... AND circuit.

Claims (1)

[Claims] 1 In an injection molding machine that controls the injection speed or pressure in a closed loop, a command signal to the injection speed or pressure control means is detected, and the value exceeds a preset tolerance range and continues for a certain period of time or more. A method for controlling an injection molding machine, characterized in that the injection process is sometimes interrupted.