JPS62261419A - Control device for injection holding pressure - Google Patents

Abstract

PURPOSE:To enlarge the applying range of molding condition determining method without any limit by a method wherein pressure control is divided into the first period of holding pressure, in which mold internal pressure control is suitable, and the latter period of holding pressure, in which cylinder internal hydraulic pressure control is suitable, while the pressure control is continued. CONSTITUTION:A CPU 1 reads a hydraulic pressure in an injection cylinder after (HT) hours of holding pressure control zone through a hydraulic pressure sensor 2 and an I/F 3 and memorized it into a memory 12. Simultaneously, the CPU 1 indicates this hydraulic pressure in a measured value indicator 7 through another I/F 6. The CPU 1 outputs a switching command from mold internal pressure control to hydraulic pressure control to a control amplifier 5 through the I/F 4 while the CPU 1 sends the pressure value of injection hydraulic pressure control, which maintains the injection cylinder hydraulic pressure memorized after (HT) time, to the control amplifier 5 through the I/F 4 during TB1 zone. Accordingly, the maintaining control of the injection cylinder internal hydraulic pressure is continued without any relation to the value of PL1 during the TB1 operation zone when this control mode is selected. Thereafter, the control of the hydraulic pressure in the injection cylinder is effected in accordance with the set values of PL2 and PL3 during TB2 and TB3 operation zones.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an injection holding pressure control device for an injection molding machine that can be used for closed loop control or adaptive control.

(Prior Art) Conventional injection holding pressure control includes waveform control of mold internal pressure as a method of controlling resin pressure within a mold to a constant level. In the control system diagram shown in Fig. 4, the resin pressure during the injection process is measured by a pressure detector 31 installed at a fixed point inside the mold, and the resin pressure inside the mold is set in advance in the control device 35. The control device 35 controls the hydraulic pressure, which is the pressure driving source, using a servo valve or a proportional valve 32 so that the resin pressure is controlled in a closed loop to a constant value, so that the molded product in the mold By measuring and evaluating the weight of each of the 34 pieces, it is possible to produce molded products with little variation.

(Problem to be solved by the invention) In the conventional injection holding pressure control method, pressure control during the injection process is performed in a closed loop such that the mold internal pressure is detected and the pressure falls to the target value of the mold internal pressure. I was in control. However, the pressure detected by the pressure detector is (1) the pressure on the surface of the molded product molded with the mold.

(2) The resin filling status of thick-walled molded products or complex-shaped molded products whose pressure distribution tends to be uneven in time and location can be detected at a single point.

Therefore, as shown in Fig. 1, there is no problem in controlling the injection holding pressure in the early process because the pressure difference between the pressure detector part and the pressure application part is small, but the resin volume shrinks due to the progress of cooling. In the latter stage of the holding pressure process, where there is a large difference between the pressure detector part and the pressure application part, excessive pressure is locally applied to the pressure detector part of the molded product, creating an abnormal pressure distribution. This results in the creation of a molded product with non-uniform density.

The present invention is an attempt to solve the problems of the earlier conventional methods, and the control mode of the injection holding pressure is divided into the earlier process and the latter process. It is an object of the present invention to provide an injection holding pressure control device which has a function of switching the control object to pressure control and continuing pressure control.

(Means for Solving the Problems) Therefore, the present invention provides a means for controlling the injection holding pressure of an injection molding machine in a closed loop, a waveform control means using the mold internal pressure, a pressure control means using the injection cylinder internal hydraulic pressure, and a pressure control means using the injection cylinder pressure during the injection process. It has a control means for switching the control object from mold internal pressure control to injection cylinder internal oil pressure control and a switch that can select the same means, and also has a control means for switching the control object from mold internal pressure control to injection cylinder internal oil pressure control in the injection process. In order to prevent an inflection point from occurring in the pressure control during switching, the system has an arithmetic control means that can replace the injection cylinder oil pressure at the end of the mold internal pressure control with the pressure command value for the next process. The transition to hydraulic control is continuous and automatic, and it is equipped with a digital display that can display the injection hydraulic pressure command value at the time of transition from mold internal pressure control to injection cylinder internal hydraulic control. is used as a means to solve problems.

(Function) In the waveform control of the mold internal pressure, correction control is performed so that the measured value of the mold internal pressure matches the command value, so the injection cylinder hydraulic pressure, which is the main factor that generates the mold internal pressure, is a secondary factor. Determined. Therefore, the control transition from mold internal pressure control to injection cylinder internal hydraulic pressure control uses the injection cylinder internal hydraulic pressure at the time of transition to injection cylinder internal hydraulic pressure control as a set value, thereby creating an inflection point in control. You can make a smooth transition without any problems.

In addition, by measuring and displaying the absolute value (actual oil pressure) of the oil pressure in the injection cylinder at this time, it is possible to provide repeatability during control switching transitions, and to change operation data. Make it easier.

(Example) The present invention will be described below with reference to the embodiments shown in the drawings. FIG. 1 is a control state diagram during an injection process showing an embodiment of the present invention. FIG. 2 is an example of a data setting display panel for implementing the present invention. Now, the functions added according to the present invention are (11) provision of a select switch 9a that automatically switches control from mold internal pressure control to injection cylinder oil pressure control; (2) display that measures and displays the injection cylinder oil pressure at the time of switching; This is because a select switch 9b is provided.

FIG. 3 is a control block diagram illustrating the control method of the present invention. To explain in relation to the control state shown in FIG. 1, the waveform control section (rsTJ) and the holding pressure control section (rHTJ
) is SP (mold internal pressure control target set value) after the mold internal pressure reaches the SSP value (mold internal pressure control start set pressure) as per conventional control.
Control the waveform toward The CPU 1 reads the oil pressure in the injection cylinder after the HT time via the oil pressure sensor 2 and I/F (interface) 3, and stores it in the memory 12.

At the same time, this oil pressure is displayed on the measured value display 7 via the I/F 6. In addition, the CPU is connected to the control amplifier 5 via I/F4.
In addition to issuing a command to switch from mold internal pressure control to hydraulic pressure control, during the TBI (holding pressure 1 setting time) period, input the injection hydraulic pressure control pressure value to I/F4 to maintain the memorized injection cylinder hydraulic pressure after the HT time. The signal is sent to the control amplifier 5 via the control amplifier 5.

Therefore, when this control mode is selected, regardless of the value of PLI (holding pressure 1 control set pressure) during the TBI operation period,
Maintenance control of the oil pressure inside the injection cylinder continues. Thereafter, in the operation periods TB2 (holding pressure 2 setting time) and TB3 (holding pressure 3 setting time), the injection cylinder internal oil pressure is controlled according to the set values of PL2 and PL3.

The select switch 9a for mold internal pressure/injection oil pressure is added to select whether to use the additional functions of the present invention or to control as before, and the pressure display "holding pressure" select switch 9b is also TBI This was added so that the control command pressure during the section can be displayed. Also, a data setting device, a data display device 8, a molding machine sequence control device 11
and memory 12, molding machine sequence control device 11 and C
The I/FIO etc. with the PU 1 may be completely the same as in the past, and the functions of the present invention are realized by adding a program that operates the CPU.

(Effects of the Invention) Since the present invention is configured as explained in detail above,
Conventionally, waveform control of mold internal pressure has been limited to molded products that are thin, molded products that are symmetrical from the gate position, resin flow lengths that are the same, and that require only a short holding pressure. According to the present invention, the scope of application is divided into the first stage of holding pressure, which is suitable for mold internal pressure control, and the second stage, which is suitable for cylinder internal hydraulic pressure control. ! Since this has been made possible, the range of application can be expanded without limit even if conventional methods for determining molding conditions are used.

[Brief explanation of drawings]

Fig. 1 is a control state diagram during the injection process in an embodiment of the present invention, Fig. 2 is an explanatory diagram showing a data setting display panel in an embodiment of the present invention, and Fig. 3 is a control method in an embodiment of the present invention. FIG. 4 is a control block diagram of a conventional injection molding machine. Explanation of main parts of the diagram 1-CPU 2--Oil pressure sensor 3--1/F (interface) 4--I/
F 5...Control amplifier 6...I/F 7-Measurement value display 8-Data setting display 9a, 9b-Select switch 10-1/F 11-Molding machine sequence control device 12- ··memory

Claims (1)

[Claims] A means for controlling injection holding pressure of an injection molding machine in a closed loop;
It has a waveform control based on the mold internal pressure and a pressure control means based on the injection cylinder internal hydraulic pressure, a control means for switching the control object from the mold internal pressure control to the injection cylinder internal hydraulic pressure control during the injection process, and a switch that can select the means, Even if the control target is switched from mold internal pressure control to injection cylinder internal hydraulic pressure control in the injection process, in order to prevent an inflection point from occurring in the pressure control at the time of switching, the injection cylinder internal hydraulic pressure at the end of mold internal pressure control is changed to the pressure in the next process. It has an arithmetic control means that can be replaced with a command value, and the transition from mold internal pressure control to injection cylinder internal hydraulic pressure control is performed continuously and automatically, and when transitioning from mold internal pressure control to injection cylinder internal hydraulic control An injection holding pressure control device comprising a digital display capable of displaying an injection hydraulic pressure command value.