JPS6261407B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method and apparatus for an injection molding machine, and particularly to a control method and apparatus for controlling an injection molding machine, and particularly to a method for making the injection time of an injection process coincide with a set injection time.

The injection process of an injection molding machine is an important process that almost determines the appearance of the molded product, and it is necessary to perform the injection process at a predetermined injection speed, that is, at a predetermined injection time. However, when starting molding,
When starting after a stop due to a failure or the like, or when there are fluctuations in temperature conditions due to the use of a hot runner, defective products such as short shots may occur depending on the molded product. In such cases, molding is currently carried out while adjusting the injection pressure and injection speed. That is, since the injection time is different from the normal time, a good product can be obtained by adjusting the injection pressure and injection speed to the normal injection time.

The following factors can be considered to cause the injection time to fluctuate.

(1) Screen and cylinder of the injection machine at the start of molding,
Changes in resin viscosity due to deviation from the temperature during steady molding using hot runners, etc.

(2) Changes in the volumetric efficiency of the hydraulic pump due to oil temperature deviations.

(3) Changes in resin flow resistance due to changes in mold temperature, etc.

(4) Changes in resin viscosity due to changes in resin temperature and differences in resin rod.

Conventionally, the injection pressure and injection speed are usually set in an open loop for these, but it is possible to set the injection pressure and injection speed in a closed loop by relatively easily installing a pressure detector. can. However, there is no practical method for determining the flow rate that is accurate and responsive in the injection process, and the flow rate is an open loop. Also, if a servo valve is used, the second factor, changes in oil amount due to changes in oil temperature, can be improved to some extent, but there is no guarantee against the other factors 1, 3, and 4. . Therefore, in order to solve these problems, the speed at which the injection cylinder moves during injection is measured with a speed detector, this speed is compared with the set value, and the deviation is fed back to the injection pressure and injection flow rate to set the set injection speed. However, in this case, a speed detector is required to control the injection speed, making the mechanism complicated. Furthermore, when there is a large difference in temperature, etc. from normal conditions, such as at the start of molding, the injection pressure and injection flow rate may reach their maximum, which may cause unreasonable conditions depending on the mold.

Taking these points into consideration, the present invention measures the injection time of the injection molding machine, compares it with the set injection time,
A control signal proportional to the difference is fed back to the injection pressure and flow rate of the next shot, and the injection time is made to match the set value.By keeping the injection time constant, the need for molded products is minimized as much as possible. The aim is to improve the stability of molding.

The present invention will be explained with reference to FIG. 1, which is a simplified configuration diagram of one embodiment. In the figure, 1 is the injection cylinder and piston 1
The movement of a is taken out, detected by the position detector 12, and input into the injection time measuring device 8. Also, pressure oil from the hydraulic pump 11 is injected into the injection cylinder 1, but during this time the pressure control valve 5 and the flow rate control valve 2 are injected into the injection cylinder 1.
The pressure and flow rate of the pressure oil applied to the injection cylinder 1 are controlled. On the other hand, 10 is a comparison/judgment device, which receives the actual injection time measurement output from the injection time measuring device 8 and the set output from the injection time setting device 9, and adjusts the set value according to the difference between the set value and the actual measurement value. In order to achieve convergence, the output of the comparison/judgment device 10 is given to the pressure setting device 7 and the flow rate setting device 4 to perform a feedback action. Other amplifiers 3 and 6 amplify the setting signal outputs of the flow rate setting device 4 and the pressure setting device 7, respectively, and apply the amplified signals to the flow rate control valve 2 and pressure control valve 5, thereby controlling the flow rate and pressure with respect to the hydraulic pressure.

Next, the operation according to the block configuration shown in the figure will be explained. First, the actual injection time is measured by the injection time measuring device 8 using a signal given by the position detector 12 according to the movement of the piston 1a of the injection cylinder 1.
The injection time set from the injection time setting device 9 is compared with the injection time set by the comparison/judgment device 10, and a control signal proportional to the deviation from the injection time is given to the flow rate setting device 4 and the pressure setting device 7 to determine the injection pressure or pressure for the next injection. This feeds back the injection flow rate to follow fluctuation factors.

It is normal for temperature changes to occur gradually and slowly, regardless of variations in resin lots.
It is unlikely that there will be sudden and extreme changes during molding.

Therefore, if the previous injection time is measured and fed back to the next shot as in the present invention, abnormalities can be alleviated, and if the injection machine is controlled by a computer, it can be done by simply changing the software. This is easy to do and eliminates the need for a speed detector.

Furthermore, the occurrence of defective products due to the above-mentioned fluctuation factors is prevented, contributing to improved productivity.

Next, using characteristic diagrams to explain the cases in which no feedback is performed and cases in which feedback is performed in the embodiments shown in FIGS. It will look like Figure 2.

In Figure 2, curve A shows the relationship between the injection time (seconds) and the number of shots, B shows the relationship between the mold temperature (°C) and the number of shots, and C shows the relationship between the resin temperature (°C) and the number of shots. At the start of molding, the mold temperature and resin temperature are considerably lower than in the steady state, so the injection time is also lower than the steady state (the state in which the mold temperature and resin temperature become constant over a certain cycle time), and the resin flows into the mold. It is longer because the resistance is greater. In the example shown in FIG. 2, the molding is performed up to 5 shots, and the parts with large sink marks are defective. In this case, since the resin flow resistance into the mold is large, the resin does not completely enter the end portion of the mold, resulting in a short shot, and the resin pressure is not applied sufficiently, resulting in sink marks. To solve this problem, the injection oil pressure or injection speed may be increased to overcome the resin flow resistance within the mold.

In the above example, the injection oil pressure is constant at 130Kg/ ^cm2 and the injection speed is constant at 60% (opening of the flow rate control valve), but the injection oil pressure is adjusted by trial and error so that the injection speed is constant at 60% and the injection time is 4.6 seconds. The result is as shown in Figure 3, and from the first shot there were no defective products such as shot shots or sink marks.

If this is done in the present invention, the injection time of the first shot is determined by measuring the time taken by the position detector 12 from the start of injection to the completion of injection using the injection time measuring device 8,
It will be 5.4 seconds. Injection time that allows good products to be obtained under steady state conditions
Set a time of 4.6 seconds on the injection time setting device 9. In this case, the comparator 10 calculates a time difference of 0.8 seconds (actual value - set value). Then, the comparator 10 sends a signal to the pressure setting device 7 to increase the injection oil pressure to correspond to the injection time difference of 0.8 seconds.
The pressure setting device 7 is set to 130Kg/cm ² , but this is mapped to 4Kg/cm ² to 134Kg/cm 2 and amplified by the amplifier 6, and the injection oil pressure of the pressure control valve 5 is set to 134Kg/cm ² .
Readjust to Kg/cm ² and inject next time.

In this case, if P control is adopted for the output of the comparator 10 and the target injection time is achieved with a short number of shots, a better product can be obtained from the second shot even if the first shot is unnecessary. It becomes.

[Brief explanation of the drawing]

FIG. 1 is a simplified configuration diagram showing one embodiment of the present invention;
FIGS. 2 and 3 are diagrams for explaining actual examples of injection molding. In the figure, 1 is an injection cylinder, 1a is a piston, 2 is a flow control valve, 4 is a flow rate setting device, 5 is a pressure control valve,
7 is a pressure setting device, 8 is an injection time measuring device, 9 is an injection time setting device, 10 is a comparison/judgment device, 11 is a hydraulic pump, and 12 is a position detector.

Claims (1)

[Scope of Claims] 1. A first step of measuring the actual injection time via a position detector provided in conjunction with a piston of an injection cylinder in an injection process of an injection molding machine; and the first step. a second step in which the actual injection time obtained from the injection time measuring device and the injection time preset by the injection time setting device are compared by a comparative judgment device, and the deviation from the comparison judgment device is compared; a third step of applying a proportional control signal to a pressure control valve and a flow rate control valve connected to the injection cylinder, and controlling the injection pressure and injection flow rate of the shot from next time onwards using the control signal; A method for controlling an injection molding machine, characterized in that subsequent injection times are made to match the preset injection time. 2. An injection cylinder, a position detector that detects the movement of the injection piston in the injection cylinder, an injection time measuring device that uses the output of the position detector as input to measure the actual injection time, and an injection cylinder that injects pressure oil into the injection cylinder. a pressure control valve and a flow rate control valve that respectively control the pressure and flow rate of the pressure oil from the hydraulic pump; an injection time setting device that sets the injection time; and an injection time setting device that sets the injection time; A comparison/judgment device that compares the set output with the actual injection time output from the injection time measuring device, and a deviation output from the comparison/judgment device to provide feedback to the next injection pressure and injection flow rate to track fluctuation factors. A control device for an injection molding machine, comprising a pressure setting device and a flow rate setting device that control the pressure control valve and the flow rate control valve, respectively, in order to perform the injection molding machine.