JPH09254206A - Method and device for controlling back pressure of motor-driven injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for controlling back pressure of a motor-driven injection molding machine by which back pressure in a weighing process is controlled in a constant range by simple constitution. SOLUTION: In the weighing process of a motor-driven injection molding machine, when back pressure reaches the upper limit command value by rotation of a motor 8 for rotating a screw, the motor 8 is stopped and also lock of a motor 7 for injection is released and a screw 2 is retreated in prescribed torque to lower back pressure. When back pressure reaches the lower limit command value, the motor 7 for injection is locked and also the motor 8 for rotating the screw is rotated to raise back pressure. Back pressure is controlled in a range of the upper limit command value and the lower limit command value by repeating this operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling back pressure during a measuring process of an electric injection molding machine.

[0002]

2. Description of the Related Art Conventionally, as a back pressure control method and device for an electric injection molding machine of this type, for example, Japanese Patent Publication No. 4-71 is used.
There is one disclosed in Japanese Patent No. 697, which will be described with reference to FIG.

In the figure, the hopper 101 during the weighing process.
Molten resin pressure or screw 10 accompanying material supply from
The back pressure detected by the reaction force of 2 is detected by the back pressure sensor 103.
It is performed by The signal detected by the back pressure sensor 103 is amplified by the amplifier 104 and becomes a back pressure detection signal, which is input to the control device 105. In the control device 105, the back pressure detection signal and the back pressure command signal set by the back pressure setting device 106 are compared and calculated, and an injection motor control signal is output. This control signal becomes a signal limited by the speed limiter device 109 so that, for example, a positive voltage is not output, and the injection motor speed control device 1
10 is input. Injection motor speed controller 110
Controls the rotation speed of the injection motor 107 according to the magnitude of 0 or a negative voltage of the injection motor control signal. When the control signal is negative, the screw 102 is moved backward (measurement direction). Let it work.

In the above-described method and apparatus for controlling the back pressure of the electric injection molding machine, the speed limiter device 109 provided next to the control device 105 causes the screw 102 when the back pressure detection signal value is smaller than the back pressure command value. Is controlled so as to stop, and when it is large, the screw 102 is controlled so as to move in the backward direction (measurement direction), and feedback control is performed so that the back pressure detection signal value and the back pressure command value match. Therefore, the screw 102 does not move forward during the measuring process, and it is possible to prevent a large fluctuation of the back pressure during the measuring process and perform stable measuring.

[0005]

In the conventional method and apparatus for controlling the back pressure of the electric injection molding machine described above, the error between the back pressure detection signal and the back pressure command signal is calculated, and the injection motor control signal is output. are doing. This is a feedback control for obtaining the target moving position of the screw such that the back pressure becomes the set back pressure value by using PI (proportional integral) calculation from the error amount, and therefore the following problems can be considered. (A) When a stick or slip occurs due to mechanical friction in the mechanical mechanism, the target moving position of the screw determined by PI control does not match the actual retreat amount of the screw, and the back pressure during the measuring process is not stable . (B) Since the mechanical friction coefficient of the mechanical mechanism changes over time, P
It is difficult to determine the I coefficient. (C) The back pressure sensor has a filter for removing noise, which causes a signal delay and deteriorates the control response due to the integral calculation.

In view of the above-mentioned problems of the prior art, the present invention provides a back pressure control of an electric injection molding machine capable of performing a back pressure control that is equal to or more than that in the PI calculation with a simpler control configuration. It is an object to provide a method and a device.

[0007]

Means for Solving the Problems The above-mentioned problems have been solved by the present invention as follows. That is, in the measuring process of the electric injection molding machine, when the back pressure reaches the upper limit command value due to the rotation of the screw rotation motor, the screw rotation motor is stopped and the injection motor is unlocked, When the back pressure is lowered by retracting the screw under a predetermined torque and the back pressure reaches the lower limit command value, the injection motor is locked and the screw rotation motor is rotated to increase the back pressure. By repeating the operation, the back pressure is controlled within the range between the upper limit command value and the lower limit command value.

According to another aspect of the invention, in the measuring process of the electric injection molding machine, when the back pressure reaches a command value due to the rotation of the screw rotation motor, the injection motor is unlocked to a predetermined torque. The screw is retracted under to reduce the back pressure, and after a certain period of time, the injection motor is locked to increase the back pressure. By repeating this operation, the back pressure is controlled near the command value.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described based on examples with reference to the drawings. FIG. 1 is a block diagram showing a back pressure control device for an electric injection molding machine according to the present invention.

As shown in FIG. 1, the back pressure control device according to the present invention rotates the screw 2 during the weighing process to rotate the hopper 1a.
This is for plasticizing the resin supplied from the cylinder 1 to the cylinder 1 and controlling the molten resin pressure generated as the plasticized molten resin accumulates on the tip side of the screw 2 within a certain range. Load cell 3 as a back pressure sensor that measures the back pressure by detecting the reaction force of the screw 2 generated by the resin pressure, and the back pressure setting that presets the upper limit command value and the lower limit command value of the back pressure or the upper limit command value. And a control device 5 to which a back pressure detection signal from the load cell 3 is input via an amplifier 4a and a back pressure command signal from the back pressure setting device 6 is input. The injection motor 7 and the screw rotation motor 8 are controlled by control signals output via the amplifiers 4b and 4c.

As the back pressure sensor 3, there is one that detects the molten resin pressure, the current value of the injection motor 7 and the like to measure the back pressure. (Embodiment 1) FIG. 2 is an operation diagram showing back pressure control of an electric injection molding machine according to an embodiment of the present invention. As shown in the figure, the back pressure control method of the electric injection molding machine according to the present invention is
In the measuring process, the rotation of the screw rotation motor 8 (O
When the back pressure (output of the load cell) reaches the upper limit command value H due to N), the screw rotation motor 8 is stopped and the injection motor 7 is unlocked (ON) to a predetermined torque (A). When the screw 2 is retracted below and the back pressure reaches the lower limit command value L, the injection motor 7 is locked and the operation of rotating (turning on) the screw rotation motor is repeated to control the back pressure. It is a thing. The unlocking (ON) of the injection motor 7 means unlocking the position lock and applying the torque (A), and the forward force of the screw 2 by the torque (A) is the lower limit command value (L). ) It is considered to be a smaller value.

Next, the above-mentioned back pressure control method will be described more specifically with reference to the flowchart of FIG.

At the start of weighing in the weighing process, the injection motor 7 is first locked (step S1), and the screw rotation motor 8 is rotated (ON) (step S2). Then, the output of the load cell 3, which is the back pressure due to the molten resin pressure, increases with the rotation of the screw 2. Next, it is determined whether the output of the load cell 3 has reached the upper limit command value H (step S3). When the upper limit command value H is reached, the control device 5
Stops the screw rotation motor 8 (step S4),
The lock of the injection motor 7 is released (ON) (step 5). Then, since the screw 2 retracts, the molten resin pressure (output of the load cell) decreases. Next, it is determined whether the output of the load cell 3 has reached the lower limit command value L (step S6). When the lower limit command value L is reached, it is further determined whether or not the position of the screw 2 has reached the measurement completion position (step S7). When the measurement completion position has not been reached, the process returns to step S1 and the operations of steps S1 to S7 are repeated. During this time, the output of the load cell 3 is between the upper limit command value H and the lower limit command value L. Such a process is repeated until the position of the screw 2 reaches the measurement completion position, and at that time, the injection motor 7 is locked (step S
8) The measurement process is completed. (Embodiment 2) FIG. 4 is an operation diagram showing back pressure control of an electric injection molding machine according to another embodiment of the present invention. As shown in the figure, in the back pressure control method of the present invention,
When the back pressure (output of the load cell) reaches the command value (N) due to the rotation (ON) of the screw rotation motor 8, the injection motor 7 is unlocked (ON) and the predetermined torque (A) is reduced. The back pressure is controlled by retracting the screw 2 and repeating the operation of locking the injection motor 7 after a lapse of a predetermined time (T). Note that unlocking (ON) the injection motor 7 means unlocking the position lock and applying torque (A), and the forward force of the screw 2 due to the torque (A) is a command value (N). It is set to a smaller value.

Next, the back pressure control method described above will be described more specifically with reference to the flow chart of FIG.

At the start of weighing in the weighing process, first, the screw rotation motor 8 is rotated (ON) (step S1), and the injection motor 7 is locked (step S2). Then, the output of the load cell 3, which is the back pressure due to the molten resin pressure, increases with the rotation of the screw 2. Next, it is determined whether or not the output of the load cell 3 has reached the command value N (step S
3). When the command value N is reached, the injection motor 7 is unlocked (ON) (step 4). Then, since the screw 2 retracts, the molten resin pressure (output of the load cell) decreases. After the elapse of a certain time (T) (step 5), it is determined whether or not the position of the screw 2 has reached the measurement completion position (step S6). When the measurement completion position has not been reached, the process returns to step S2, and steps S2 to S are performed again.
Repeat the operations up to 6. During this time, the molten resin pressure (output of the load cell) is near the command value N. This process is repeated until the position of the screw 2 reaches the target measurement completion position, at which point the injection motor 7 is locked (step S7) and the screw rotation motor is stopped (step S8). The process is completed.

[0016]

Since the present invention is configured as described above, the following effects can be obtained. That is, in the conventional technique, the backward movement position of the screw capable of maintaining the set back pressure value is calculated by PI control, but in the present invention, such calculation is not necessary, and the command value is set only in the backward direction. Since no output is made, the back pressure during the measuring process can be controlled within a certain range with a simpler configuration.

[Brief description of drawings]

FIG. 1 is a block diagram showing a back pressure control device of an electric injection molding machine.

FIG. 2 is an operation diagram showing back pressure control according to the first embodiment.

FIG. 3 is a flowchart according to the first embodiment.

FIG. 4 is an operation diagram showing back pressure control according to the second embodiment.

FIG. 5 is a flowchart according to the second embodiment.

FIG. 6 is a block diagram showing a back pressure control device of a conventional electric injection molding machine.

[Explanation of symbols]

 1 cylinder 1a hopper 2 screw 3 load cell (back pressure sensor) 4a, 4b, 4c amplifier 5 controller 6 back pressure setting device 7 injection motor 8 screw rotation motor

Claims (7)

[Claims] 1. In a weighing process of an electric injection molding machine,
When the back pressure reaches the upper limit command value (H) due to the rotation of the screw rotation motor (8), the screw rotation motor (8) is stopped and the injection motor (7) is unlocked (ON). Then, the screw (2) is retracted under a predetermined torque (A), and when the back pressure reaches the lower limit command value (L), the injection motor (7) is locked and the screw rotation motor (8) is A back pressure control method for an electric injection molding machine, characterized in that the back pressure is controlled by rotating. 2. In the weighing process of the electric injection molding machine,
Locking the injection motor (7) and rotating the screw rotation motor (8), and determining whether the output of the back pressure sensor (3) has reached a preset upper limit command value (H). When the upper limit command value (H) is reached, the screw rotation motor (8) is stopped and the injection motor (7) is unlocked (ON) to give a predetermined torque (A).
The step of retracting the screw (2) below, the step of determining whether the output of the back pressure sensor (3) has reached a preset lower limit command value (L), the lower limit command value (L) When the position of the screw (2) has reached the measurement completion position, the step of determining whether the position of the screw (2) has reached the measurement completion position. A method for controlling back pressure of an electric injection molding machine, comprising the steps of performing until reaching and locking the injection motor (7) at the time of reaching. 3. In the measuring process of the electric injection molding machine,
When the back pressure reaches the command value (N) due to the rotation of the screw rotation motor (8), the injection motor (7) is unlocked (ON) and the screw () is operated under a predetermined torque (A). 2. A back pressure control method for an electric injection molding machine, characterized in that the injection motor (7) is locked and the back pressure is controlled after a lapse of a predetermined time (T) after the step 2) is retracted. 4. In the weighing process of the electric injection molding machine,
A step of rotating the screw rotation motor (8) to lock the injection motor (7), a step of determining whether or not the output of the back pressure sensor (3) has reached a preset command value (N), When the command value (N) is reached, the injection motor (7) is unlocked (ON) and a predetermined torque (A) is reached.
Step of retracting the screw (2) below, fixed time (T)
After the lapse of time, a step of determining whether or not the position of the screw (2) has reached the measurement completion position, and when the measurement completion position has not been reached, the above steps are performed while the screw rotation motor (8) is being rotated. An electric method characterized by including the steps of performing until the position of the screw (2) reaches the measurement completion position, locking the injection motor (7) at that time, and stopping the screw rotation motor (8). Back pressure control method for injection molding machine. 5. A back pressure control device for an electric injection molding machine, wherein a back pressure sensor (3) for measuring a back pressure and an upper limit command value (H) and a lower limit command value (L) of the back pressure are preset. From the back pressure setting device (6) and the control device (5) to which the back pressure detection signal from the back pressure sensor (3) and the back pressure command signal from the back pressure setting device (6) are input. When the back pressure reaches a preset upper limit command value (H) by the control signal of the control device (5), the screw rotation motor (8) is stopped and the injection motor (7) is stopped. ) Is released and the back pressure reaches the lower limit command value (L), the injection motor (7) is locked and
A back pressure control device for an electric injection molding machine, comprising controlling a back pressure by rotating a screw rotation motor (8). 6. A back pressure control device for an electric injection molding machine, comprising a back pressure sensor (3) for measuring back pressure, and a back pressure setting device (6) for presetting a back pressure command value (N). A control device (5) to which a back pressure detection signal from the back pressure sensor (3) and a back pressure command signal from the back pressure setting device (6) are input. When the back pressure reaches the preset command value (N) by the control signal of (1), the lock of the injection motor (7) is released for a fixed time (T) to control the back pressure. A back pressure control device for electric injection molding machines. 7. The back pressure control device for an electric injection molding machine according to claim 5, wherein the back pressure sensor is a load cell (3).