JP4240450B2 - Control method of injection molding machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling an injection molding machine, and more particularly to a method for controlling a plasticizing process.
[0002]
[Prior art]
The conventional injection molding machine's metering control method is to rotate the screw to melt and knead the molding material, supply molten resin against the back pressure to the tip of the screw, and the screw moves backward to complete the set measurement. There is one that stops the screw rotation when the position is exceeded (see, for example, Patent Document 1 and Patent Document 2).
[0003]
[Patent Document 1]
Japanese Examined Patent Publication No. 4-43775 (Claims 1 and 4)
[Patent Document 2]
Japanese Patent Publication No. 6-73883 (Claim 1 and FIG. 4)
[0004]
However, according to this control method, when the screw exceeds the set measurement completion position, the screw rotation is suddenly stopped, so the impact is great and the screw back pressure may remain, so the screw actually stops. Is a position that has passed the set weighing completion position. In addition, this excessive amount changes depending on conditions such as the screw rotation speed before the stop, the screw back pressure value, the viscosity of the molten resin, etc., so the molten resin cannot be accurately measured, and the molten resin cannot be measured. When the mold is injected and filled, the accuracy of the molded product decreases.
[0005]
In addition, there is a type in which the screw rotation is decelerated to a fine speed when a position set just before the set measurement completion position is exceeded, and the screw rotation is stopped when the set measurement completion position is exceeded (for example, Patent Document 3). ).
[0006]
[Patent Document 3]
Japanese Examined Patent Publication No. 4-6535 (Claims 1 and 3-4)
[0007]
In this control method, since the setting of the screw rotation deceleration start point and the screw rotation slow speed are affected by conditions such as the screw rotation speed, screw back pressure value, viscosity of the molten resin, etc. Have difficulty. When the optimum setting is not performed, the screw does not move backward from the position where the screw rotation is decelerated, and there is a problem that the time of the measurement process varies and the measurement does not end.
[0008]
In order to solve this problem, in the metering process of the injection molding machine, the predicted stop position is calculated from the screw position, screw speed, and stop deceleration time, and the predicted stop position is compared with the set measurement completion position. If the set weighing completion position is exceeded, the back pressure control is switched to the stop control and the screw speed is decelerated during the stop deceleration time.At the same time, the rotation control is switched to the deceleration control and the screw rotation is decelerated during the stop deceleration time. There is one that stops at the set weighing completion position (Patent Document 4).
[0009]
[Patent Document 4]
JP-A-8-276473 (Claims 1 and 3)
[0010]
However, according to this method, since the current screw speed, which is unstable depending on the plasticization state, is used as the reference for the predicted stop position, there is a problem that the stop predicted position fluctuates and the molten resin metering changes.
[0011]
[Problems to be solved by the invention]
The present invention has been proposed in order to solve the above-described problems in the prior art, and terminates the substantial plasticization at a switching position before a predetermined distance from the weighing completion position, and from the switching position to the weighing completion position. The screw rotation can be stopped smoothly based on the time constant and the screw can be positioned at the measurement completion position, so that it is possible to meet various plasticization conditions and obtain a highly accurate measurement completion position. An object is to provide a method for controlling a molding machine.
[0012]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a control method for an injection molding machine comprising an injection device for injecting a molten resin obtained by plasticizing and melting a resin material into a mold, and a control device for controlling the injection device. During the plasticizing process for melting, the control device controls the rotational speed of the screw until the screw reaches the switching position a predetermined distance before the measurement completion position from the start of plasticization, and when the screw reaches the switching position. The rotation of the screw is controlled with a predetermined time constant until it stops, and the screw is controlled in a closed loop while controlling the reverse speed at a predetermined speed for a predetermined distance from the switching position to the measurement completion position. In positioning control, the time constant is set to zero the rotational speed of the screw that is decelerated when the positioning control ends at the measurement completion position. According to the control method of the injection molding machine is set to a time constant that does not.
[001 4 ]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a partial cross-sectional view showing an outline of a main part of an injection molding machine for implementing the present invention. FIG. 2 is a graph showing changes in screw rotation speed with respect to screw position. FIG. 3 is a flowchart showing the control method of the present invention.
[001 5 ]
The injection molding machine 1 includes an injection device 2, a mold clamping device (not shown) that contacts and separates or presses the mold 3 that is filled with the molten resin 7 injected from the injection device 2, and the injection device 2 and the mold. And a control device 4 for controlling the fastening device.
[001 6 ]
The injection device 2 includes a heating cylinder 5 that is attached to the housing 9 and contacts and presses against the mold 3, a screw 6 that is rotatably inserted into a central inner hole of the heating cylinder 5, and an extension shaft of the screw 6. A movable plate 10 that holds the ball nut 14 in a rotatable manner, a screw rotating servo motor 12 that is attached to the non-heating cylinder side of the movable plate 10 to rotate the screw 6, and is attached to both ends of the housing. The ball screw 13 is screwed to the ball nut 14 and the injection servo motor 11 is fixed to both ends of the housing on the side where the heating cylinder 5 is attached and drives the ball screw 13 to move the screw 6 back and forth.
[001 7 ]
The control device 4 includes sequence control of the mold clamping device and the injection device 2 in the injection molding machine 1, speed control, force control, or positioning control of actuators such as an injection servo motor 11 and a screw rotation servo motor 12, heating, and the like. Temperature control of a band heater or the like for heating the cylinder 5 is executed. This control device 4 has a known configuration based on a microprocessor, and includes a display unit composed of a liquid crystal display, a setting unit composed of a touch panel provided on the surface of the display unit, and a RAM / ROM for setting values and control programs. A storage unit for storing, an input unit for inputting signals from various sensors such as the encoder 15, and an output unit for outputting signals to the actuator are included. The encoder 15 is connected to the rotation shaft of the injection servomotor 11 and detects the rotation angle of the injection servomotor 11, so that the position of the screw 6 can be detected, but the screw is detected by a position sensor separately attached to the movable platen 10. The position of 6 may be detected.
[001 8 ]
The plasticizing process in the injection device 2 will be described. The resin material supplied from the upper surface of the housing 9 into the heating cylinder 5 through the through-hole is transferred forward with the rotation of the screw 6 by a screw-like flight engraved on the outer periphery of the screw 6. The resin material transferred through the heating cylinder 5 is plasticized and melted by the amount of heat of the heating cylinder 5 adjusted by a heater and is kneaded by the screw 6 while being melted into the inner hole of the heating cylinder 5 in the heating cylinder 5. Accumulated as.
[00 19 ]
The heating cylinder 5 is brought into contact with and pressed against the mold 3, and the cavity 8 of the mold 3 is filled with the molten resin 7 injected and cooled in the previous molding cycle, so that it is accumulated in front of the screw 6. The pressure of the molten resin 7 during plasticization rises, and a screw back pressure is generated that pushes the screw 6 backward as a screw back pressure. The screw back pressure is controlled to a predetermined value by the servo motor 11 for injection. In this control process, as shown in FIG. 2, the screw 6 moves backward while rotating, and moves back to the measurement completion position P2 where the molten resin 7 corresponding to the volume of the cavity 8 that is a molded product is accumulated. And stop. The molten resin 7 weighed in this manner is transferred to the cavity 8 by the forward movement of the screw 6 by the injection servo motor 11 in the next molding cycle after the mold 3 is opened and the molded product in the cavity 8 is taken out. The injection process is executed.
[002 0 ]
Next, based on FIG. 2 and FIG. 3, the control method of this invention is demonstrated in detail. The control device 4 starts the plasticizing process after the injection process (S1). The screw 6 is rotationally driven by a screw rotation servomotor 12 whose speed is controlled based on a predetermined set value, and starts to retreat from the cushion position P0, which is a position where the molten resin 7 remains at the end of the injection stroke (S2). . The control device 4 compares and calculates whether or not the position of the screw 6 has reached the switching position P1 that is a predetermined distance B before the measurement completion position P2 (S3), and continues to rotate the screw 6 in S2 until it reaches P1. . When the position of the screw 6 reaches the switching position P1 before the predetermined distance B from the measurement completion position P2, the control device 4 stops the screw rotation with a predetermined time constant (S4).
[002 1 ]
The predetermined distance B is calculated in advance by the control device 4 and stored in the storage unit according to the following equation.
B = (r / R) × A
Here, r is a set value (rpm) of the screw rotation speed, and is appropriately set and input by the setting unit according to the type of the molding material and the molded product as the plasticizing condition. R is a set value (rpm) of the maximum screw rotation speed that can be set, and is fixedly stored in the storage unit in advance as a value unique to the injection molding machine. A is a coefficient (mm), and when the maximum screw rotation speed is set, the setting unit appropriately inputs the time constant together with the time required for the screw 6 to retract and stop during the rotation stop process. .
[002 2 ]
The time constant starts to act when the position of the screw 6 reaches the switching position P1, and the control device 4 decelerates the screw rotating servo motor 12 according to the change in the number of rotations per time according to the predetermined time constant. The value of the time constant normally used is 0.05 to 0.5 seconds.
[002 3 ]
The coefficient A and the time constant can be set to arbitrary values. However, the number of screw speed deceleration control patterns from the switching position P1 to the measurement completion position P2 obtained as a result of the combination of the coefficient A and the time constant is extremely diverse, and although the degree of freedom of setting increases, setting is extremely difficult. It becomes. Therefore, about 10 types of control patterns that can be set for various resin materials and screw back pressure settings are prepared in advance and stored in the storage unit, and one of them is selected according to the actual plasticizing conditions, and control is thereby performed. The device 4 controls the deceleration to stop the screw rotation. If a control pattern is selected so that the screw rotation speed is zero at the measurement completion position P2, the back pressure is most preferably zero at the measurement completion position P2. If a control pattern having a relatively large time constant with respect to the coefficient A is selected, the plasticizing process may be completed while the screw rotation speed does not become zero and the back pressure remains slightly at the measurement completion position P2. This may stabilize the state of the molten resin.
[002 4 ]
When the screw 6 has reached the switching position P1, the control device 4 performs positioning control of the backward position of the screw 6 within a predetermined distance B from the switching position P1 to the measurement completion position P2 as S5 together with the processing of S4. This positioning control is performed by closed loop control of the injection servo motor 11. The retreating speed of the screw 6 at this time is the retreating speed by plasticization before the screw 6 reaches the switching position P1, and the control device 4 stores the retreating speed in the storage unit during the plasticization, and the average value thereof. Etc. are set as values to control the reverse speed of the screw 6.
[002 5 ]
Positioning control is continued until the screw position coincides with the measurement completion position P2 (S6), and when the screw position coincides with the measurement completion position P2, plasticization ends (S7) and the screw position is maintained.
[002 6 ]
The present invention is not limited to the embodiments shown and described above, and can be implemented with various modifications without departing from the spirit of the invention. For example, the screw back pressure and the screw positioning control are described as being executed by the injection servo motor, but may be executed by a hydraulic device such as a servo valve. The screw rotation servomotor can also be replaced with an induction motor or hydraulic motor using an inverter.
[002 7 ]
【The invention's effect】
The present invention ends substantial plasticization at a switching position a predetermined distance before the measurement completion position, smoothly stops the screw rotation from the switching position to the measurement completion position based on the time constant, and completes the screw measurement. Since positioning is performed at a position, a highly accurate measurement completion position can be obtained without being affected by the residual screw back pressure and screw rotation speed, and a highly accurate and stable molded product can be produced. Furthermore, since the control from the switching position to the measurement completion position can be selected from a plurality of patterns, it is possible to cope with various conditions of plasticization by easy setting.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing an outline of essential parts of an injection molding machine for carrying out the present invention.
FIG. 2 is a graph showing a change in screw rotation speed with respect to a screw position.
FIG. 3 is a flowchart showing a control method of the present invention.
[Explanation of symbols]
1 ……… Injection molding machine 2 ……… Injection device 3 ……… Mold 4 ……… Control device 5 ……… Heating cylinder 6 ……… Screw 7 ……… Molten resin 8 ……… Cavity 9… ... Housing 10 ... Movable platen 11 ... Servo motor for injection 12 ... Servo motor for screw rotation 13 ... Ball screw 14 ... Ball nut 15 ... Encoder B ... ... Predetermined distance P0 ... Cushion position P1 ... Switching Position P2 ... Measurement completion position

Claims (1)

In a control method of an injection molding machine provided with an injection device for injecting molten resin obtained by plasticizing and melting a resin material into a mold and a control device for controlling the injection device,
During the plasticizing process of plasticizing and melting the resin material, the control device controls the rotational speed of the screw until the screw reaches a switching position before a predetermined distance from the measurement completion position from the start of plasticization, and the screw is controls decelerated when reaching the changeover position to the stop with a time constant rotation of predetermined said screw, for a predetermined distance of the screw from the switching position to the metering completion position, the retracting speed at a predetermined speed When performing positioning control in a closed loop while controlling, the time constant is set to a time constant that does not make the rotation speed of the screw controlled to be decelerated when the positioning control ends at the measurement completion position. A method for controlling an injection molding machine.

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