JPH05318547A - Apparatus for controlling filling pressure of injection molding machine - Google Patents

Abstract

PURPOSE:To prevent the damage of a mold by preventing the generation of the warpage, bending and strain of a molded product by suppressing the generation of surge pressure to the min. CONSTITUTION:A filling speed is detected and the operation quantity (a) of a speed control system is calculated on the basis of the speed set value V set by a speed setting device 31 and the detected filling speed. Further, filling pressure is detected and a pressure set value P is set by a pressure setting device 35 and the value obtained by subtracting imaginary surge pressure kV<2> from the pressure set value is set as an initial corrected pressure set value P'. When the filling pressure reaches the initial corrected pressure set value P', the corrected pressure set value P' is allowed to gradually approach the pressure set value P. The operation quantity (b) of a pressure control system is calculated on the basis of the filling pressure and the corrected pressure set value P'. The operation quantities (a), (b) of the speed control system and the pressure control system are compared and the control system lower in the operation quantities (a), (b) is selected and the operation quantities (a), (b) of the selected control system are outputted to an actuator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filling pressure controller for an injection molding machine.

[0002]

2. Description of the Related Art Conventionally, a molding material, such as a resin, which has been heated and fluidized in a heating cylinder is injected into a mold at high pressure,
In an injection molding machine that is cooled and solidified or hardened therein and then a mold is opened to take out a molded product, there is a screw type in which a screw in the heating cylinder is moved forward and backward to perform injection molding.

In the screw type injection molding machine,
A screw is rotatably and rotatably supported inside the heating cylinder, is connected to a drive system including an injection cylinder and a hydraulic motor, and is rotated and moved forward and backward by the drive system. The injection molding of the injection molding machine includes a measuring process, a filling process, and a pressure maintaining process. In the measuring process, the screw is driven by the hydraulic motor to rotate, and at this time, the resin supplied from the material supply port. Is melted in the heating cylinder while moving forward by the rotation of the screw, and is stored in the front end portion of the screw. The pressure of the resin in the heating cylinder, which is generated by the melting, becomes a reaction force to the screw, and the reaction force causes the screw to retract to a preset position.

Thus, the resin stored in the front end portion of the screw is injected from the injection nozzle by subsequently pushing the screw forward by the injection cylinder, and is filled in the cavity of the mold. When the filling process is completed, in order to compensate for the amount of resin in the cavity that cools and shrinks, a constant hydraulic pressure is applied to the screw to hold the pressure. When the pressure holding process is completed, the screw is rotated again and weighing is performed. Done.

Here, speed (flow rate) control is performed in the filling step, and pressure control is performed in the pressure holding step. Therefore, a speed control system and a pressure control system are provided for one actuator, a control system with a small operation amount is selected, and the operation amount of the control system is output. FIG. 2 is a block diagram of a conventional filling pressure control device for an injection molding machine.

In the figure, 11 is an injection molding machine, 12 is a variable pump connected to an injection cylinder for reciprocating a screw, and supplies oil to the injection cylinder. Thirteen
Is a speed setter, and sets a speed set value V for speed control. Reference numeral 14 denotes a subtractor, which is the speed setter 1
The flow rate detection value detected by the injection molding machine 11, that is, the filling speed, is subtracted from the speed setting value V of 3 to obtain the deviation, and the deviation is output to the filling speed control compensator 15.

The filling speed control compensator 15 calculates and outputs an operation amount a of the variable pump 12 based on the deviation.
On the other hand, 21 is a pressure setting device, which sets a pressure set value P for performing pressure control. Reference numeral 22 denotes a subtracter, which subtracts the pressure detection value detected by the injection molding machine 11, that is, the filling pressure from the pressure setting value P of the pressure setting device 21, to obtain the deviation, and to the filling pressure control compensator 23. Output.

The filling pressure control compensator 23 calculates and outputs the operation amount b of the variable pump 12 based on the deviation.
Reference numeral 25 is a comparator for determining whether the control target is the filling speed or the filling pressure. The comparator 25 receives the operation amounts a and b and compares them, and the command c is sent to the control switching device 26. Output to. The control switching device 26 is the comparator 25.
It switches in response to the command c from and outputs the manipulated variables a and b to the variable pump 12. The variable pump 12
Controls with the manipulated variables a and b selected by the control switching device 26.

In the filling pressure control device of the injection molding machine having the above-mentioned structure, one actuator, that is, the variable pump 1
2, a speed control system and a pressure control system are provided so that the manipulated variables a and b are calculated in advance, and the comparator 25 compares them to output the smaller manipulated variables a and b to the variable pump 12. It has become.

[0010]

However, in the filling pressure control device for the conventional injection molding machine, the variable pump 12 is operated within the operating speed limit in the switching condition between the speed control system and the pressure control system. It is set in a static state, and the respective manipulated variables a and b are calculated based on the switching conditions.
Then, the switching condition is set by values near the speed setting value V and the pressure setting value P.

Therefore, when the pressure rises sharply, such as when the resin is in the packed state immediately before entering the pressure-holding step from the fluid state, inertia due to kinetic energy or operation exceeding the operating speed limit causes the variable pump to operate. Due to the operation delay caused by the requirement of No. 12, a large surge pressure is generated. That is, when the control target is switched from the filling speed to the filling pressure, the control target of the pressure control system is the pressure set value P.
Equal to, the inertia of the kinetic energy produces a surge pressure. If a value obtained by subtracting the surge pressure from the pressure setting value P is set as the control target and the pressure setting value P is switched to when the control target is reached, the surge due to the deviation between the control target and the pressure setting value P is set. Pressure is generated.

Due to the surge pressure, a pressure higher than the pressure set value P is locally generated and transmitted in the cavity, which damages a weak part of the mold in manufacturing, warps the molded product, bends, or strains ( It will cause blemishes and the like.
The present invention solves the problems of the conventional filling pressure control device for an injection molding machine and minimizes the occurrence of surge pressure, thereby preventing warpage, bending, and distortion of a molded product. It is also an object of the present invention to provide a filling pressure control device for an injection molding machine, which can prevent the mold from being damaged.

[0013]

Therefore, in the filling pressure control device of the injection molding machine of the present invention, an actuator for moving the screw, a means for detecting the filling speed and the filling pressure, and a speed setting value for the filling speed. And a filling speed control compensator for calculating the manipulated variable of the speed control system based on the filling speed and the speed set value.

Further, a pressure setter for setting a pressure setting value of the filling pressure, a means for setting a value obtained by subtracting a virtual surge pressure amount from the pressure setting value as an initial correction pressure setting value, and the filling pressure is the initial value. It has means for gradually approaching the corrected pressure set value to the pressure set value when the corrected pressure set value is reached, and a filling pressure control compensator for calculating the manipulated variable of the pressure control system based on the filling pressure and the corrected pressure set value.

Then, the operation amounts of the speed control system and the pressure control system are compared, the control system with the smaller operation amount is selected, and the operation amount of the selected control system is output to the actuator.

[0016]

According to the present invention, the actuator for moving the screw is provided as described above, and the actuator moves the screw according to the input operation amount,
The molding material is filled in the cavity of the mold. The filling speed is detected, and the manipulated variable of the speed control system is calculated based on the speed setting value set by the speed setter and the detected filling speed.

Further, the filling pressure is detected, on the other hand, the pressure setting value is set by the pressure setting device, and the value obtained by subtracting the virtual surge pressure from the pressure setting value is set as the initial correction pressure setting value. Then, when the filling pressure reaches the initial correction pressure setting value, the correction pressure setting value is gradually brought close to the pressure setting value. Then, the operation amount of the pressure control system is calculated from the filling pressure and the corrected pressure set value.

The manipulated variables of the speed control system and the pressure control system are compared, the control system with the smaller manipulated variable is selected, and the manipulated variable of the selected control system is output to the actuator.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 is a block diagram of a filling pressure controller for an injection molding machine showing an embodiment of the present invention, and FIG. 3 is a time chart of the injection molding machine showing an embodiment of the present invention.
In the drawing, 11 is an injection molding machine, 12 is a variable pump connected to an injection cylinder as an actuator for reciprocating a screw, and supplies oil to the injection cylinder.
A speed setter 31 sets a speed set value V for speed control. Reference numeral 14 denotes a subtracter, which subtracts the flow rate detection value detected by the injection molding machine 11, that is, the filling speed from the speed setting value V of the speed setting device 13 to obtain a deviation, and to the filling speed control compensator 15. Output.

The filling speed control compensator 15 calculates and outputs the operation amount a of the variable pump 12 based on the deviation.
On the other hand, 35 is a pressure setter, which sets a pressure set value P for performing pressure control. A subtractor 36 corrects the pressure set value P in the subtractor 36 and sets the corrected pressure set value P ′ as a control target.

That is, the speed set value V set by the speed setter 31 is output to the calculator 37, and the virtual surge pressure kV ² (k is a constant) is calculated in the calculator 37. In the present embodiment, the surge pressure kV ² is calculated by the speed setting value V, but it may be calculated by the filling speed detected by the injection molding machine 11. The surge pressure kV ² is generated by the switch 38 and the primary delay pattern generator 3
The correction value ΔP is sent to the subtractor 36 via 9. In the subtractor 36, the correction value ΔP is subtracted from the speed setting value V to obtain the correction pressure setting value P ′ as the control target.

Reference numeral 40 denotes a comparator which compares the corrected pressure set value P'with the pressure detection value detected by the injection molding machine 11, that is, the filling pressure, and when the corrected pressure set value P'is higher than the filling pressure. Then, the switch 38 is turned on to set the corrected pressure set value P ′ lower than the pressure set value P by the surge pressure kV ² as a control target, and when the filling pressure reaches the corrected pressure set value P ′, the switch 38 is turned off and the correction is performed. The pressure set value P ', that is, the control target is gradually brought close to the pressure set value P.

The corrected pressure set value P'obtained in this way is input to the filling pressure control compensator 23. The filling pressure control compensator 23 calculates and outputs the operation amount b of the variable pump 12 based on the corrected pressure set value P '. Reference numeral 25 is a comparator for determining whether the control target is the filling speed or the filling pressure. The comparator 25 is the operation amount a, b.
In response to the received command, the command c is output to the control switching device 26. The control switching device 26 receives the command c from the comparator 25 and switches to output the manipulated variables a and b to the variable pump 12. The variable pump 12 is controlled by the manipulated variables a and b selected by the control switching device 26.

In the filling pressure control device of the injection molding machine 11 having the above structure, both the filling speed and the filling pressure at the start of filling are 0, and at this time, the control switching device 26 selects the speed control system. .. In the filling step, the flow rate detection value, that is, the filling speed is detected by the injection molding machine 11, the filling speed is subtracted from the speed setting value V of the speed setting device 31, and the deviation is obtained, and the filling speed control compensator is obtained. It is output to 15.

The filling speed control compensator 15 calculates and outputs an operation amount a of the variable pump 12 based on the deviation.
As the filling process progresses, the filling speed increases and reaches the speed set value V. Here, when the speed control system is switched to the pressure control system, the pressure set value P set by the pressure setter 35 is set.
If the feedback control is attempted by the surge pressure kV ² , surge pressure kV ² is generated due to the operation delay of the variable pump 12 and the inertia caused by the kinetic energy of the transmission mechanism.

Therefore, a value obtained by subtracting the surge pressure kV ² from the original pressure set value P set by the pressure setter 35 is set as a corrected pressure set value P ', which is set as a control target of the pressure control system. Therefore, the calculator 37 calculates the surge pressure kV ² by the speed setting value V set by the speed setter 31, and the surge pressure kV ² is passed through the primary delay pattern generator 39 to obtain the correction value ΔP. Then, the correction pressure setting value P ′ is obtained by subtracting the correction value ΔP from the pressure setting value P of the pressure setting device 35, and the correction pressure setting value P ′ is set as the control target.

When the filling process further progresses and the filling pressure reaches the corrected pressure set value P ', the comparator 25 causes the control switching device 2 to operate.
A command c is given to 6 to select the pressure control system. At the same time, since the comparator 40 turns off the switch 38, the input to the first-order delay pattern generator 39 becomes 0, the correction value ΔP gradually approaches 0 due to the first-order delay, and finally the correction pressure set value P ′ and The pressure set value P is P '= P. In addition to the first-order lag pattern generator 39, a ramp input or the like can be used to gradually bring the corrected pressure set value P ′ close to the pressure set value P.

Reference numeral 22 denotes a subtracter, which subtracts the pressure detection value detected by the injection molding machine 11, that is, the filling pressure from the corrected pressure setting value P'to obtain the deviation, and supplies it to the filling pressure control compensator 23. Output. The filling pressure control compensator 23 determines the operation amount b of the variable pump 12 based on the deviation.
Is calculated and output.

In the case of the filling pressure control device of the injection molding machine 11 of the present invention, the filling speed and the filling pressure change as shown in FIG. That is, in the pressure control system, as shown by the broken line h, the corrected pressure set value P ', which is lower than the pressure set value P by the surge pressure kV ² is set as the control target, and the correction is made when the filling pressure on the solid line k reaches the control target. The pressure setting value P'changes as shown by the broken line i. At this time, the filling speed is reduced as indicated by the solid line n. Therefore, the surge pressure kV ² is not generated, and the control target does not change suddenly. When the pressure set value P is used as the control target instead of the corrected pressure set value P ', the filling speed changes as shown by the broken line p, and the surge pressure k is caused by the overrun of this portion.
V ² is generated.

The present invention is not limited to the above-mentioned embodiments, but various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0031]

As described above in detail, according to the present invention, the filling speed is detected, and the speed set value set by the speed setting device and the operation amount of the speed control system are detected by the detected filling speed. Is calculated. Also, the filling pressure is detected, while the pressure setting value is set by the pressure setting device,
A value obtained by subtracting the virtual surge pressure from the pressure setting value is set as the initial correction pressure setting value. Then, when the filling pressure reaches the initial correction pressure setting value, the correction pressure setting value is gradually brought close to the pressure setting value. And
The operation amount of the pressure control system is calculated based on the filling pressure and the corrected pressure set value.

The operation amounts of the speed control system and the pressure control system are compared, the control system with the smaller operation amount is selected, and the operation amount of the selected control system is output to the actuator. Therefore, when switching from the speed control system to the pressure control system, the control target gradually approaches the pressure setting value from the value obtained by subtracting the virtual surge pressure from the pressure setting value, so surge pressure does not occur. It is possible to prevent warpage, bending, distortion, etc. of the molded product. Further, it is possible to prevent breakage of a weak portion due to the structure of the mold.

[Brief description of drawings]

FIG. 1 is a block diagram of a filling pressure control device of an injection molding machine showing an embodiment of the present invention.

FIG. 2 is a block diagram of a filling pressure control device of a conventional injection molding machine.

FIG. 3 is a time chart of the injection molding machine showing the embodiment of the present invention.

[Explanation of symbols]

 11 injection molding machine 12 variable pump 15 filling speed control compensator 23 filling pressure control compensator 25, 40 comparator 26 control switching device 31 speed setting device 35 pressure setting device 37 calculator 38 switch 39 primary delay pattern generator a, b Operation amount V Speed set value P Pressure set value P'Corrected pressure set value

Claims (1)

[Claims] 1. (a) an actuator for moving a screw; (b) means for detecting a filling speed and a filling pressure; (c) a speed setter for setting a speed setting value of the filling speed; and (d) the above. A filling speed control compensator that calculates the manipulated variable of the speed control system based on the filling speed and the speed setting value, (e) a pressure setting device that sets the pressure setting value of the filling pressure, and (f) surge pressure from the pressure setting value. Means for setting the value obtained by subtracting the minutes as the initial corrected pressure set value, and (g) means for gradually approaching the corrected pressure set value to the pressure set value when the filling pressure reaches the initial corrected pressure set value, h) The filling pressure control compensator that calculates the manipulated variable of the pressure control system based on the filling pressure and the corrected pressure set value, and (i) the manipulated variables of the speed control system and the pressure control system are compared, and the one with the smaller manipulated variable Means for selecting a control system of (j) A filling pressure control device for an injection molding machine, comprising means for outputting an operation amount of a selected control system to an actuator.