JPH04241918A - Control method for injection molding machine - Google Patents

Abstract

PURPOSE:To stabilize the charging volume in the case of setting the dwell pressure high and charging pressure low by using an electric servo motor as an injection driving source. CONSTITUTION:Immediately after the completion of dwelling process, an injection motor 7 is rotated and driven in the direction reverse to the direction of injection to force a screw 3 to move back, and the screw is further moved back forcibly and the loading pressure to the screw is confirmed to be the given value or lower by a pressure sensor 13 for sensing the loading pressure applied to the screw.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling an in-line screw type injection molding machine using an electric servo motor as an injection drive source.

0002

[Prior Art] Injection molding machines that use electric servo motors as the driving source for various operations, such as the injection driving source, do not require hydraulic maintenance because they do not have hydraulic equipment or hydraulic piping, and the equipment can also be made lighter. be. Furthermore, feedback control using an electric servo motor has the advantage of better responsiveness than a hydraulic circuit.

By the way, in injection molding machines, molding conditions often occur that require the holding pressure to be set high and the charging pressure to be set low. However, when such a setting is made, in this type of injection molding machine that uses an electric servo motor as the injection drive source, when moving to the charging stroke after the pressure holding stroke, the drive source itself (unlike hydraulic equipment) Because the load was light, a phenomenon occurred in which the screw rebounded in the backward direction.

0004

[Problems to be Solved by the Invention] As mentioned above, in an injection molding machine using an electric servo motor according to the prior art, when the holding pressure is set high and the charging pressure is set low, (
For example, when the holding pressure is about 2000 kgf/cm2 and the charging pressure is about 50 kgf/cm2), the screw rebounds in the backward direction after the holding pressure is completed, and this causes the actual cushion position to vary and the charge amount (metering resin There was a big problem that the quantity) varied. Also,
If the charging amount is set too low, the above-mentioned rebound will cause the screw to move back beyond the metering completion position (charging completion position), so in this case the machine will apparently assume that charging is complete. A fatal problem arose.

[0005] In order to prevent the screw from rebounding when transitioning from the holding stroke to the charging stroke, the holding pressure during the holding stroke is set in multiple stages, and the holding pressure at the end of the holding stroke is adjusted so that rebound does not occur. However, this is often not possible due to constraints on the molding conditions required for molding a good product. Further, if the operator forgets to set the holding pressure at the end of the holding pressure stroke to a value that does not cause rebound, the above-mentioned problem still occurs.

Therefore, the technical problem to be solved by the present invention is to solve the above-mentioned problems of the prior art.
The purpose of this is to reliably prevent screw rebound and stabilize the charge amount even when the holding pressure is set high and the charging pressure is set low in injection molding machines that use electric servo motors as the injection drive source. An object of the present invention is to provide a method for controlling an injection molding machine.

[0007]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a method for controlling an injection molding machine in which the forward and backward movement of a screw disposed in a heating cylinder is performed by an electric servo motor. After completion of the injection stroke including the above, the electric servo motor forcibly retracts the screw by a predetermined amount, after which the charge stroke begins.

[0008]

[Operation] Immediately after the pressure holding stroke is completed, the electric servo motor for injection (hereinafter referred to as the injection motor) is driven to rotate in the opposite direction to the injection direction, and the screw begins to be forcibly retracted, and the load pressure is applied to the screw. The screw is forcibly retracted until it is confirmed by the pressure sensor that the load pressure on the screw is below a predetermined value, and then the rotation of the injection motor in the above-mentioned reverse direction is stopped. And after this, the electric servo motor for charging (
The charging motor (hereinafter referred to as a charging motor) is driven to rotate, and a charging process is started. By doing this, the screw position at the start of charging is always kept constant, which eliminates variations in the amount of charge (metered amount of resin).
Stable molding becomes possible.

[0009]

[Embodiment] The present invention will be explained below using an embodiment shown in FIGS. 1 to 3. FIG. 1 is an explanatory diagram showing a simplified configuration of the main parts of an injection molding machine according to this embodiment, FIG. 2 is an explanatory diagram of operation,
FIG. 3 is an explanatory diagram showing the processing flow executed by the microcomputer during the forced backward stroke of the screw.

In FIG. 1, reference numeral 1 denotes a heating cylinder, the rear part of which is attached and held by a known headstock (not shown). A nozzle 2 is screwed onto the tip of the heating cylinder 1, and a known band heater (not shown) is wrapped around the outer periphery of the nozzle 2. Reference numeral 3 denotes a screw, which is disposed within the heating cylinder 1 so as to be able to move forward and backward as well as rotate, and a shaft member 3a integrated with the rear end thereof extends outside the heating cylinder 1. Reference numeral 4 denotes a hopper for supplying resin material, from which the resin material falls and is supplied into the heating cylinder 1.

The shaft member 3a integrated with the screw 3 is
The spline shaft is coupled to a rotating body 6 that is rotationally driven by a charging motor (electric servo motor for charging) 5, and the screw 3 is rotated by the rotation of the charging motor 5.
is designed to be rotationally driven. In addition, the shaft member 3a
is a nut-screw connection (specifically, a ball screw connection) to a rotating body 8 which is rotationally driven by an injection motor (injection electric servo motor) 7, and the rotation of the injection motor 7 causes the screw 3 to move in the axial direction. It is designed to be driven by

The charging motor 5 and the injection motor 7 are operated by a microcomputer (hereinafter referred to as microcomputer) 9.
The drive is controlled by the driver circuits 10 and 11. This microcomputer 9 controls the operation of the entire machine (injection molding machine), and controls the entire molding process such as charging operation, injection operation (primary injection and holding pressure operation), mold opening/closing operation, and ejecting operation, as well as actual measurement. Executes data calculations, storage processing, etc. In other words, the microcomputer 9 actually handles various I/
The machine is equipped with an O interface, ROM, RAM, CPU, etc., and is equipped with a large number of sensors (position sensors, pressure sensors, The driver circuit 10 described above,
Each of the corresponding drive sources is driven and controlled through a group of drivers including 11 to execute a series of molding processes.

Reference numeral 12 denotes an injection stroke detection sensor consisting of an encoder, etc., and 13 an injection pressure detection sensor consisting of a load cell, etc. Based on the measurement information of these sensors 12 and 13, the microcomputer 9 determines the position of the screw 3 and the position of the screw 3. It is designed to recognize the load pressure in the forward direction.

In the above configuration, during the charging process, the charging motor 5 is rotated in a predetermined direction, and the resin material introduced from the hopper 4 into the rear part of the heating cylinder 1 is kneaded and plasticized by the rotation of the screw 3. At the same time, it is transferred to the front side of the heating cylinder 1 by the screw feeding action of the screw 3. As the molten resin is stored in the front side of the heating cylinder 1 (the front side of the head of the screw 3), the screw 3 moves backward while the back pressure is controlled by the injection motor 7, and moves toward the front side of the heating cylinder 1. At the time when it is confirmed by the measurement information of the injection stroke detection sensor 12 that the molten resin equivalent to one shot has been stored (when the screw 3 has retreated to the metering completion position), the screw rotation is stopped. Then, when the injection start timing is reached after an appropriate period of time, the injection motor 7
is rotationally driven in a predetermined direction, thereby causing the screw 3 to rotate in a predetermined direction.
is driven forward, and the nozzle 2 at the front end of the heating cylinder 1
The molten resin is injected and filled into the cavity of a clamped mold (not shown) (primary injection process). After the primary injection stroke ends, the injection motor 7 maintains the preset holding pressure condition under the control of the microcomputer 9 that refers to the measurement information from the injection pressure detection sensor 13. As a result, pressure is applied to the molten resin in the mold for a predetermined period of time (pressure holding stroke).

[0015] The end of the above-mentioned pressure holding stroke is determined by the microcomputer 9 using its own clock function. In this embodiment, unlike the previous example, the charging stroke does not proceed immediately after the pressure holding stroke, but in other words, for example, 2000 kgf/cm
Instead of immediately shifting from a state where a holding pressure (load pressure in the forward direction) of about 50 kgf/cm2 is applied to a charge setting pressure of about 50 kgf/cm2, a forced backward stroke of the screw 3 is performed after the holding pressure stroke is completed. It is arranged to move to the charging process later. That is, when the microcomputer 9 determines that the pressure holding stroke is completed, it rotates the injection motor 7 in the opposite direction to that during the injection stroke to forcibly retreat the screw 3, and the injection pressure detection sensor 13 causes the injection pressure detection sensor 13 to This forced retraction of the screw is executed until it is confirmed that the load pressure in the forward direction has decreased to a preset pressure value.

FIG. 2 is an explanatory diagram showing this situation, and the screw 3, which is at the position shown by the solid line at the time of completion of pressure holding, is first forcibly retreated to the position shown by the dashed line in the figure after the completion of pressure holding. For example, the holding pressure setting value is 2000 kgf/cm
2, when the charge pressure setting value is 50 kgf/cm2, the screw 3 at the forced retreat position indicated by the dashed line
The load pressure is set to be about 300 kgf/cm2, and the amount of forced retraction corresponds to about 5 mm or less, although it depends on the model. When such forced screw retraction control is performed, the screw does not bounce an indefinite length in the retraction direction after the end of the pressure holding stroke as in the conventional case, and the screw position at the start of charging is always stable. and,
The screw 3 is driven to rotate as described above from the one-dot chain line position and shifts to the charging stroke, and when the screw 3 retreats to the charging completion position shown by the two-dot chain line in the figure, the screw rotation is stopped. Therefore, the amount of charge is always kept constant.

FIG. 3 shows a processing flow executed by the microcomputer 9 during the above-mentioned forced backward stroke of the screw 3. In step S1, it is asked whether the pressure holding stroke has been completed, and if YES, the process advances to step S2. If NO, return to step S1. In step S2, forced retraction of the screw 3 is executed, and the process proceeds to step S3. In step S3, it is asked whether the forward direction load pressure on the screw 3 has become below a predetermined value. If NO, the process returns to step S2, and if YES, the forced retreat execution process ends (exits to another process).

[0018]

[Effects of the Invention] As described above, according to the present invention, in an injection molding machine that uses an electric servo motor as an injection drive source, the rebound of the screw can be reliably prevented even when the holding pressure is set high and the charging pressure is set low. It is possible to provide a control method for an injection molding machine that can prevent this problem and stabilize the amount of charge, and its value is great.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a simplified configuration of main parts of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram showing a forced retraction operation of the screw according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a processing flow executed by a microcomputer during a forced retraction operation of a screw according to an embodiment of the present invention.

[Explanation of symbols]

1 Heating cylinder 2 Nozzle 3 Screw 5 Electric servo motor for charging (charging motor) 7 Electric servo motor for injection (injection motor) 9
Microcomputer 12 Injection stroke detection sensor 13 Injection pressure detection sensor

Claims (2)

[Claims] 1. A method for controlling an injection molding machine in which a screw disposed in a heating cylinder is moved back and forth by an electric servo motor, wherein after the completion of an injection stroke including a pressure holding stroke, the electric servo motor moves the screw 1. A method for controlling an injection molding machine, comprising forcibly retracting the injection molding machine by a predetermined amount, and then transitioning to a charging process. 2. The method of controlling an injection molding machine according to claim 1, wherein the forcible retraction of the screw is performed until the load pressure applied to the screw in the forward direction becomes equal to or less than a predetermined value.