JP4427663B2 - Pressure control device for injection molding machine and injection molding machine using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pressure control device for an injection molding machine and an injection molding machine including the same, and more particularly to an improvement in injection holding pressure and back pressure control device.
[0002]
[Prior art]
FIG. 3 is a schematic configuration diagram showing an outline of an injection molding machine.
As shown in FIG. 3, the structure around the injection device of the injection molding machine includes a bed 3, a cylinder 1 and an injection motor 2 fixed to the bed 3, and an injection movable portion 6 having a screw 4 and a metering motor 5. The injection movable unit 6 is configured to move forward and backward as the ball screw 7 connected to the injection motor 2 rotates.
[0003]
Next, the operation of the above configuration will be described. By rotating the metering motor 5, the screw 4 connected to the metering motor 5 rotates, and the resin material in the hopper 8 is fed into the cylinder 1. As the material accumulates inside the cylinder 1, the injection movable part 6 moves backward, but at this time, a torque is applied to the injection motor 2 so that the resin inside the cylinder 1 becomes uniform and the inside of the cylinder 1 becomes a constant pressure. Measure to the specified position with. This control is called “back pressure control”.
[0004]
When the metering is completed, the injection motor 2 is rotated, the injection movable unit 6 is advanced, and the resin inside the cylinder 1 is injected into a mold (not shown) at high speed. When the injection is finished, the torque of the injection motor 2 is controlled so that the inside of the cylinder 1 is at a constant pressure for a certain time until the resin in the mold cools. This control is called “injection holding pressure control”.
[0005]
Conventionally, in order to perform these “back pressure control” and “injection holding pressure control”, pressure control is performed with a configuration as shown in FIG. That is, the pressure inside the cylinder 1 is detected by a load cell sensor 9 mounted on the injection movable unit 6, the voltage signal is amplified by an amplifier 10, and converted into a digital signal by an A / D converter 11. Capture to device 12. The control arithmetic unit 12 outputs a motor rotation command to the motor amplifier 13 so that the pressure instructed from the value is obtained, and the injection motor 14 is operated by the output of the motor amplifier 13. The back pressure control and injection hold pressure control of the injection molding machine described above are performed by an electric motor. However, the configuration of the present invention to be described later is not limited to the electric motor.
[0006]
[Problems to be solved by the invention]
In general, the back pressure is very small with respect to the injection holding pressure. When the injection holding pressure is 100%, the back pressure is often around 10%. For example, when a 10-bit (1024 digit) A / D converter 11 is used in the prior art, the full scale at the back pressure must be controlled with a resolution of 1/10 of 102 digits. The accuracy for performing sufficient control cannot be obtained. On the other hand, in the conventional technology, when a resolution request of 1000 digits at the time of back pressure is made in order to obtain sufficient control for back pressure control, an A / D converter of 13 bits to 14 bits (8192 to 16384 digits) is required. There was a problem of high costs.
[0007]
The present invention has been made to solve such conventional problems, and has a pressure control device for an injection molding machine in which the resolution (measurement accuracy) with respect to full scale is substantially constant and the cost is not increased, and It aims at providing the injection molding machine provided with it.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention measures the injection holding pressure and back pressure of an injection molding machine, and controls the pressure of the injection molding machine based on the measured pressure. a control device, for converting the injection and hold pressure and back pressure of the injection molding machine and a load cell for detecting as an analog signal, the analog signal detected by the load cell to a frequency signal whose frequency increases in accordance with their size The V / F converter and the frequency of the frequency signal converted by the V / F converter are measured by counting clocks having a period smaller than the period of the frequency signal, and the injection holding pressure and the back pressure are measured. And a period counter for measuring .
[0010]
In addition, according to this invention, the injection molding machine provided with the pressure control apparatus of the injection molding machine in this invention can also be provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a control device that performs injection holding pressure and back pressure control according to the present invention, and FIG. 2 is a table showing a voltage signal with respect to pressure, a frequency and period of a pulse signal, and a ratio with respect to a predetermined period.
[0012]
As the injection molding machine according to the embodiment of the present invention, for example, the one shown in FIG. 3 is applied. However, the movable part is not limited to an electric motor, and may be, for example, hydraulic.
[0013]
The control device shown in FIG. 1 includes a load cell 9 that detects pressure by strain, an amplifier 10 that amplifies the output of the load cell 9, a V / F converter 20 that converts an amplified voltage signal of the amplifier 10 into a frequency signal, From a cycle counter 21 that measures the period of a pulse signal that is an output of the V / F converter 20, a control arithmetic device 12A that inputs a digital signal from the cycle counter 21 and outputs a motor rotation command, and a control arithmetic device 12A Are provided with a motor amplifier 13 to which a motor rotation command is input, and an injection motor 14 which is operated by the output of the motor amplifier 13 and maintains the back pressure and the injection holding pressure at predetermined values.
[0014]
The operation of the embodiment will be described below.
1, the voltage signal of the amplifier 10 of the load cell 9 is converted into a frequency signal that is directly proportional to the voltage by the V / F converter 20, and the period of the pulse signal is measured by the period counter 21. That is, the time from the rising edge of the pulse signal to the next rising edge is measured by the period counter 21 and input to the control arithmetic unit 12A as a digital signal.
[0015]
According to such a configuration, a signal in which the reciprocal of the pressure value is digitized is input to the control arithmetic device. This means that when the pressure is low, it is digitized in fine steps, and when the pressure is high, it is digitized in coarse steps. Therefore, the pressure is measured with sufficient resolution even at a low pressure, and sufficient control performance can be obtained for both the back pressure control and the injection pressure holding control.
[0016]
This will be described more specifically with reference to FIG. FIG. 2 is a table of numerical values of each part when the control system is actually designed. The output voltage signal V of the amplifier 10 is output in proportion to the pressure. When the pressure detected by the load cell changes from 0% to 100%, V = 3v to 8v is designed. The V / F converter 20 is designed to output a pulse signal having a frequency of f = 0 Hz to 5 kHz in proportion to an input of 0 v to 12 v. T is the reciprocal of f and is the period of the V / F converter output pulse signal.
[0017]
At this time, if the clock of the cycle counter 21 is 64 MHz, the clock cycle Tc = 0.015625 μS, and the count value input to the control arithmetic unit at each pressure is T / Tc.
[0018]
In these count values, looking at the count values at 0% to 10% at the time of back pressure control, 5120-4389, the input full-scale resolution at the time of back pressure control is 5120-4389 = 731 digits.
[0019]
Next, attention is paid to the portion where the pressure during injection holding pressure is high. The count value at 90% to 100% is 2048-1920. The input full-scale resolution converted on the assumption that this resolution is the same from 0% to 90% is (2048-1920) × 10 = 1280 digits. Since the input resolution necessary for pressure control only needs to be about 1000 digits, both back pressure control and injection control can be controlled with high accuracy by this method.
[0020]
【The invention's effect】
As described above in detail, the present invention measures the injection holding pressure and back pressure of the injection molding machine, and controls the pressure of the injection molding machine based on the measured pressure. A control device that detects the injection holding pressure and back pressure of the injection molding machine as analog signals, and converts the analog signal detected by the load cell into a frequency signal that increases in frequency according to the magnitude. The V / F converter and the frequency of the frequency signal converted by the V / F converter are measured by counting clocks having a period smaller than the period of the frequency signal, and the injection holding pressure and the back pressure are measured. by providing a period counter for measuring, because you have to measure the pressure of injection and hold pressure and back pressure, if the pressure is low are digitally valued at fine steps, if the pressure is high It is possible to obtain a numerical value (measured value) which has been digitally valued at a coarse step. Therefore, it is possible to perform pressure measurement with substantially constant accuracy in both injection holding pressure control and back pressure control, and it is possible to perform control at a low cost and with substantially constant accuracy.
[0021]
In addition, according to the configuration of the present invention, there is an advantage that it is more resistant to noise than the prior art as a secondary effect. Since the sensor such as the load cell and the control arithmetic unit are arranged at positions separated from each other, it is necessary to connect them with a cable having a certain length. Further, it is advantageous in terms of cost to reduce the number of signal lines of the cable. For this reason, in the prior art, the cable between the amplifier and the A / D converter (point A in FIG. 4) is lengthened. However, this portion of the signal is an analog voltage signal and thus has a drawback of being weak against noise. According to the present invention, the cable between the V / F converter and the period counter (point B in FIG. 1) is lengthened. Since this portion is a pulse signal, no malfunction occurs at a noise level below the HL (high, low) voltage threshold. In addition, by inputting a pulse signal to the counter through a filter that does not pass a pulse having a frequency higher than the maximum frequency, an effect of avoiding malfunction due to harmonic noise can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a pressure control device of an injection molding machine according to the present invention.
FIG. 2 is a diagram illustrating numerical values of the embodiment.
FIG. 3 is a schematic configuration diagram showing an injection molding machine.
FIG. 4 is a block diagram showing a pressure control device of a conventional injection molding machine.
[Explanation of symbols]
1 cylinder, 2 injection motor, 4 screw, 5 metering motor, 6 injection movable part, 9 load cell, 10 amplifier, 12A control arithmetic device, 13 motor amplifier, 14 injection motor, 20 V / F converter, 21 period counter.

Claims (2)

An injection molding machine pressure control device that measures injection holding pressure and back pressure of an injection molding machine and performs pressure control of the injection molding machine based on the measured pressure,
A load cell that detects the injection holding pressure and back pressure of the injection molding machine as analog signals;
A V / F converter that converts an analog signal detected by the load cell into a frequency signal whose frequency increases according to the magnitude of the analog signal;
A period counter for measuring the injection holding pressure and the back pressure by measuring the period of the frequency signal converted by the V / F converter by counting a clock having a period smaller than the period of the frequency signal ; ,
A pressure control device for an injection molding machine. An injection molding machine comprising the pressure control device for an injection molding machine according to claim 1 .

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