JP3601871B2 - Back pressure control method and apparatus for electric injection molding machine - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method and an apparatus for controlling a back pressure of an electric injection molding machine.
[0002]
[Prior art]
Conventionally, as an example of a back pressure control method of this type of an electric injection molding machine, there is a method disclosed in Japanese Patent Publication No. 4-71697.
[0003]
FIG. 3 is a diagram for explaining an outline of a conventional back pressure control method for an electric injection molding machine disclosed in Japanese Patent Publication No. 4-71697.
[0004]
In the conventional electric injection molding machine shown in FIG. 3, the back pressure sensor 103 detects the molten resin pressure accompanying the material supply from the hopper 101 during the weighing process or the back pressure such as the reaction force of the screw 102. . The signal detected by the back pressure sensor 103 is amplified by an amplifier 104 to become a back pressure detection signal, which is input to a back pressure feedback control circuit 105. The back pressure feedback control circuit 105 compares the back pressure detection signal with the back pressure command signal set by the back pressure setting device 106, and outputs a screw forward / reverse motor control signal. The control signal is a signal limited by the speed limiter circuit 107 so as not to output a positive voltage, for example, and is input to the screw forward / reverse motor speed controller 108. The screw forward / reverse motor speed control device 108 controls the rotational speed of the screw forward / backward motor 109 according to the magnitude of 0 or a negative voltage of the screw forward / backward motor control signal, and the control signal is negative. In this case, the screw is operated in the backward direction (measuring direction).
[0005]
In the back pressure control method for an electric injection molding machine as described above, when the back pressure detection signal value is smaller than the back pressure command value, the speed limiter circuit 107 provided next to the back pressure feedback control circuit 105 controls the screw. The feedback control is performed so that the movement stops or, if it is large, the screw moves in the backward direction (metering direction), and the back pressure detection signal value matches the back pressure command value. In addition, the screw does not advance during the weighing process, and it is possible to prevent a large fluctuation of the back pressure during the weighing process and perform stable weighing.
[0006]
In addition to the above-described method of controlling the back pressure at the time of plasticizing the electric injection molding machine, there is a method of using torque control by detecting the current of the motor.
[0007]
[Problems to be solved by the invention]
However, the above-described conventional back pressure control method of an electric injection molding machine calculates and amplifies an error between a back pressure detection signal and a back pressure command signal, and outputs a screw forward / backward motor control signal. Generally, this is feedback control for obtaining the target movement position of the screw such that the set back pressure value is obtained by using PI (proportional integration) calculation from the error, so that PI control of the back pressure is performed as follows. Difficult points are conceivable.
(1) When stick or slip occurs due to mechanical friction in the mechanical mechanism, the target movement position of the screw determined by PI control does not match the actual amount of backward movement of the screw, and the back pressure during the weighing process is not stabilized. .
(2) Since the mechanical friction coefficient of the mechanical mechanism changes over time, it is difficult to determine the PI coefficient.
(3) In the back pressure sensor, there is a filter for removing noise, which causes a signal delay and deteriorates control responsiveness due to integration calculation.
[0008]
Further, in the method using the torque control by detecting the current of the motor, if the temperature of the motor changes, the relationship between the current and the torque changes, so that there is a problem that it is difficult to control the back pressure to be constant.
[0009]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the related art, and provides a back pressure control method and apparatus for an electric injection molding machine capable of performing back pressure control equal to or greater than that by PI calculation with a simpler control configuration. With the goal.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention plasticizes a resin material with rotation of a screw, measures a back pressure generated as the plasticized molten resin accumulates in a cylinder, and measures the measured back pressure. In a back pressure control method of an electric injection molding machine that performs feedback control of an electric motor that moves a screw forward and backward based on a pressure value,
A first step of measuring the back pressure by rotating the screw at a constant speed;
The measured back pressure value in the first step is compared with a preset back pressure value. If the measured back pressure value is larger in the comparison result, the screw position is moved backward by a small fixed amount, and the measured back pressure value is measured. Is smaller, a second step of performing the first step again,
In the case where the measured back pressure value is larger in the second step and the position of the screw which has been moved backward by the minute fixed amount has reached the target weighing position, the rotation of the screw is stopped to complete the weighing, and the target weighing is completed. A third step of performing the first step and the second step again when the position has not been reached;
It is characterized by comprising.
[0011]
In addition, the resin material is plasticized with the rotation of the screw, and the back pressure generated as the plasticized molten resin accumulates in the cylinder is measured. Based on the measured back pressure value, the position of the screw is moved back and forth. In a back pressure control device of an electric injection molding machine that performs feedback control of a motor to be advanced,
A back pressure sensor for measuring the back pressure,
A control device that performs feedback control of the electric motor based on a measurement signal from the back pressure sensor,
The control device measures the back pressure by rotating the screw at a constant speed, and if the measured back pressure value at this time exceeds the set back pressure value, the screw position is reduced by a small fixed amount so that the screw position is the target measurement. It is characterized by repeating until it reaches a position.
[0012]
[Action]
In the present invention configured as described above, first, the screw is rotated at a constant speed, and the back pressure at that time is measured. When the measured back pressure value exceeds the set back pressure value, the position of the screw is moved backward by a small fixed amount. By repeating such an operation until the screw position reaches the target measuring position, the back pressure during the measuring step is controlled to be constant.
[0013]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 is a schematic configuration diagram showing one embodiment of a back pressure control method for an electric injection molding machine according to the present invention, and FIG. 2 is a flowchart of back pressure control in one embodiment of the present invention.
[0015]
The back pressure control device of the electric injection molding machine shown in FIG. 1 plasticizes the material in the hopper 1 with the rotation of the screw 2 by the screw rotation motor 6, and the plasticized molten resin accumulates in the cylinder. The back pressure, such as the retraction force of the screw 2 or the pressure of the molten resin near the nozzle, generated by the back pressure sensor 3 is measured by the back pressure sensor 3, and a back pressure signal measured by the back pressure sensor 3 is input to the control device 4, and the back and forth of the screw The driving motor 5 and the screw rotating motor 6 are configured to be controlled.
[0016]
Further, the control device 4 has a comparing means (not shown) for comparing and calculating a measured back pressure signal from the back pressure sensor 3 and a preset back pressure value. The screw rotating motor 6 keeps the screw 2 constant. If the measured back pressure signal is larger than the set back pressure value by the comparison means, the screw 2 is moved by a predetermined amount in the direction in which the screw 2 moves backward (measuring direction) by the screw forward / reverse motor 5.
[0017]
Next, a back pressure control method according to the present embodiment will be described with reference to the flowchart of FIG.
[0018]
In the plasticizing step, the screw 2 is first rotated by the screw rotating motor 6 at a constant speed (step S1), and a signal from the back pressure sensor 3 is measured (step S2).
[0019]
Then, the measured back pressure signal is compared with the set back pressure value (step S3). At this time, if the measured back pressure signal is equal to or less than the set back pressure value, the process returns to step S1. On the other hand, if the measured back pressure signal exceeds the set back pressure value, the screw forward / reverse motor 5 is operated to move the screw 2 backward in the measuring direction by a minute fixed amount (for example, 0.1 mm) (step S4).
[0020]
When the reverse movement of the minute fixed amount is stopped, it is determined whether or not the position of the screw 2 is the target measuring position (step S5). At this time, if the position of the screw 2 has not reached the target weighing position, the process returns to step S1, and the processes of steps S1 to S4 are performed again.
[0021]
Such a process is performed until the position of the screw 2 reaches the target measuring position, at which time the rotation of the screw 2 is stopped (step S6), and the measurement is completed.
[0022]
As described above, the present embodiment controls the screw position by calculating the reverse target position of the screw by PI calculation based on the difference between the measured back pressure value and the set back pressure value so that the back pressure becomes constant during the weighing process. Instead of the conventional method, the screw is rotated by a fixed amount, and when the measured back pressure signal exceeds the set back pressure signal, the screw position is moved backward by a very small fixed amount to repeat the feedback control to the target weighing position Since the method is adopted, the influence of mechanical friction of the mechanical mechanism and the bad influence of the integral calculation generated due to the delay of the signal by the filter of the back pressure sensor are not affected, and the PI calculation with a simpler control configuration The back pressure control is equal to or greater than that of the above case.
[0023]
【The invention's effect】
As described above, the present invention plasticizes the resin material with the rotation of the screw, measures the back pressure generated as the plasticized molten resin accumulates in the cylinder, and measures the measured back pressure value. When the screw position exceeds the set back pressure value, the screw position is moved backward by a small fixed amount until the screw position reaches the target weighing position. It is not necessary to calculate the backward movement position of the screw that can maintain the pressure value, and it does not need a speed limiter because it outputs a command value only in the backward direction, so the back pressure during the weighing process can be reduced with a simpler control configuration. Can be controlled constantly. Also, the back pressure can be controlled to be constant regardless of the temperature of the motor.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of a back pressure control method for an electric injection molding machine according to the present invention.
FIG. 2 is a flowchart of back pressure control in one embodiment of the present invention.
FIG. 3 is a diagram for explaining an outline of a conventional back pressure control method for an electric injection molding machine disclosed in Japanese Patent Publication No. 4-71697.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 hopper 2 screw 3 back pressure sensor 4 controller 5 screw forward / reverse motor 6 screw rotation motor

Claims (2)

The resin material is plasticized with the rotation of the screw, the back pressure generated as the plasticized molten resin accumulates in the cylinder is measured, and the screw is moved forward and backward based on the measured back pressure value. In a back pressure control method of an electric injection molding machine that performs feedback control of an electric motor,
A first step of measuring the back pressure by rotating the screw at a constant speed;
The measured back pressure value in the first step is compared with a preset back pressure value. If the measured back pressure value is larger in the comparison result, the screw position is moved backward by a small fixed amount, and the measured back pressure value is measured. Is smaller, a second step of performing the first step again,
In the case where the measured back pressure value is larger in the second step and the position of the screw which has been moved backward by the minute fixed amount has reached the target weighing position, the rotation of the screw is stopped to complete the weighing, and the target weighing is completed. A third step of performing the first step and the second step again when the position has not been reached;
Back pressure control method for an electric injection molding machine comprising: The resin material is plasticized with the rotation of the screw, the back pressure generated as the plasticized molten resin accumulates in the cylinder is measured, and the screw is moved forward and backward based on the measured back pressure value. In a back pressure control device of an electric injection molding machine that performs feedback control of an electric motor,
A back pressure sensor for measuring the back pressure,
A control device that performs feedback control of the electric motor based on a measurement signal from the back pressure sensor,
The control device measures the back pressure by rotating the screw at a constant speed, and if the measured back pressure value at this time exceeds the set back pressure value, the screw position is reduced by a small fixed amount so that the screw position is the target measurement. A back pressure control device for an electric injection molding machine, wherein the control is repeated until a position is reached.

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