JPS6244415A - Control method of changeover of dwelling of injection molding machine - Google Patents

Abstract

PURPOSE:To eliminate dispersion in dimensions and strength of a molded article, by changing over to a dwelling process from an injection process at a point of time when a detected value becomes identical with preset pressure at the first stage of dwelling by detecting a thrust to be applied directly to a screw by a sensor. CONSTITUTION:A thrust F while is varied according to each process is applied to a screw 1 during operation of an injection molding machine and a variation of the thrust of the screw is grasped as elastic deformation in the axial direction of a sensor body 21. On the one hand, a preset value signal of the thrust at the time of changeover of dwelling is being signaled from a setting device Y1 and while the thrust F of the screw 1 is being detected by a sensor 2, an injection process is kept on during a period of time when the thrust F is weaker than a preset value from the device Y1. The changeover from the injection process of the screw to a dwell process of the same is performed by applying instructions about starting of the dwell process to a motor controller Y3 at a point of time when decision is performed by a comparator Y2 that the thrust of the screw is identical with the preset value. With this construction, it is possible to reduce dispersion in dimensions and strength of a molded article by changing over the thrust of the screw at the time of the changeover of the dwelling at the preset value always without dispersion.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an injection molding machine in which a screw is driven by a motor, and the thrust of the screw is directly detected by a sensor to switch from the injection process to the pressure holding process. The invention relates to a method for controlling the amount of plastic, and is used in the plastic molding and processing industry.

[Conventional technology]

An injection molding machine that uses an electric motor to apply thrust to the screw 4 is known in the art. For example, as shown in FIG. The nut 4 is moved back and forth by motor 8 → drive gear 7 → transmission shaft 6 → drive gear 5 →
It was driven by the route of Natsu 4. In a molding machine where the screw is controlled by a motor, the thrust force of the screw changes in various ways as shown by the solid line A in the injection process region ZI from 0 to P1 on the horizontal axis (time) as shown in Figure 5A. At point P, when filling is almost completed, screw thrust force F is set by the operator using unique technology according to the molded product.

Switch to the pressure holding process, hold pressure 1st stage Zffi, hold pressure 2
The injection molding process is completed at point P3 after passing through stage 23, etc., and the screw thrust force F becomes zero. Since the screw thrust force F value is mechanically converted from the motor torque value T, the screw thrust value is calculated by converting the current-torque characteristic unique to the motor into the change in current-torque characteristic caused by coil heat generation during motor operation. For example, control was performed based on the relationship @A in FIGS. 5A and 5B, which was calculated in advance by taking into account the following.

The control for switching from the injection process of speed control to the pressure holding process of pressure control monitors the current consumption of the motor and switches to pressure holding when the value becomes equal to the current that generates pressure F1 in the first stage of holding pressure. was.

[Problem that the invention seeks to solve]

However, with conventional holding pressure switching control using current consumption,
Because the relationship between the motor's current value and the generated torque changes depending on the motor usage conditions, the pressure when switching to holding pressure varies, and this variation is a contributing factor to variations in the quality of molded products.

In other words, the current-torque characteristics unique to the motor are determined assuming changes in characteristics due to coil heat generation, but in reality, heat generation that is υ larger than the assumption in Fig. 5B 1fsA occurs and the characteristics change to @B. In the end, the actual value becomes +ΔT, or, conversely, if the heat generation is smaller than expected (if cooling is successful), the expected value shown in @C becomes -ΔT. The current-torque characteristic varies between lines B and C in the conventional injection molding machine, and the control of motor torque by current in a conventional injection molding machine varies between dotted lines B and C in FIG. 5A.

Therefore, at point PI, it was thought that the switch to holding pressure was achieved with the required thrust of the scree, F, but in reality, F was larger, but smaller.

In injection molding, the injected material solidifies from the part that is in contact with the mold (outside) and solidifies from the depths of the pattern.
Even after injection and injection of the material, the pressure holding process is important to compensate for the volume reduction due to solidification of the material, and a large pressure is required when holding the pressure at the back of the mold, and it is necessary to hold the pressure at the front of the mold. Since a small pressure is sufficient, for example, in FIG. 5A, the region z2 of the first stage of holding pressure between RPt and the region 2 of the second stage of holding pressure between p and -p. The holding pressure process is set as appropriate depending on the molded product. If the pressure in the pressure holding process, that is, the screw thrust, varies, the molded product may Dimensions and strength vary, and in extreme cases, cracks and sink marks occur, contributing to variations in molded products.

[Means for solving problems]

In an injection molding machine that drives a screw with a motor, a sensor for detecting the load is installed between the screw and a device pushing the screw, and this sensor directly detects the thrust force applied to the screw, and the detected value and the By switching from the injection process to the holding process when the set pressure of the first stage becomes equal, the motor torque, that is, the screw thrust, is controlled regardless of the motor's current consumption, thereby solving the problems of the conventional method described above. I understood.

[Effect]

By directly detecting the thrust force applied to the screw with a sensor, the actual screw thrust force can be ascertained, and while the screw thrust force has not yet reached the predetermined value, the injection process is continued until the material is sufficiently filled and the screw thrust force is increased. The pressure holding process can be started the moment the set value is reached, and the injection process → pressure holding process can always be switched at a constant screw thrust value, regardless of variations in current-torque characteristics derived from differences in motor usage. It can be achieved.

〔Example〕

FIG. 1 shows an example of a device used to carry out the present invention, in which a screw 1 is connected to a ball screw 3 via a load sensor 2, and the ball screw 3 is driven back and forth by the rotation of a nut 4. . The nut 4 is rotated by the path of the motor 8 → drive gear 7 → transmission shaft 6 → drive gear 5 → nut 4.

YI is a setting device, and inputs the set value of the screw thrust at the time of pressure holding switching. Y2 is a comparator, and Sen? It compares the thrust signal S1 taken out from -2 with the signal S from the setting device Y1, and issues instructions on the control method to Y3.
, is a motor controller that supplies the necessary current i to the motor 8.

Figure 2 shows an example of how the sensor is installed.
7 mounting langes 21' and 21' at both ends of the screw are fixed to the shaft ends of the screw mounting shaft 12 and the ball screw 3, respectively, with 7 fixed split flange 14' and 14' and tightening bolts 15' and 15'. , the screw 1 is its fixing part 1'
is inserted into the screw mounting shaft 12 and fixed with the key 13, and its clamping part 1' is clamped with the divided seven flange 14,
Tighten the 7 langes 14 to the screw mounting shaft I2 with the bolts 15, and then tighten the screws 1 and 2. -2, each of the ball screws 3 is firmly connected like a single rigid body.

As is clear from FIG. 3, the sensor 2 consists of a sensor main body 21 having connecting flanges 21' at both ends, an inner sleeve 28 that is fitted into the main body and rotates together with the main body, and a bearing 30 on the inner sleeve. A strain gauge 22 for detecting elastic deformation in the axial direction of the sensor main body 21 is provided on the surface of the main body 90.
Four sheets are pasted at intervals of 50° to detect axial strain.

Leads from each strain gauge 22 @ 23 → Intermediate terminal block 24 →
The insulated lead wire 23' is pulled out, the lead wire 23' is passed through the inner sleeve 28, and connected to each corresponding slip ring 25 provided on the insulator 26 on the surface of the sleeve 28 via a slip ring set screw 25'. A brush 27 attached to the outer case 29 with a terminal bolt 31 is in contact with each slip ring 25, respectively.

In the figure, the number of pairs of slip rings and terminal bolts is four for strain gauges 22 and one for grounding. A lead wire (not shown) for taking out an electric signal is connected to the terminal bolt 31.

During operation of the injection molding machine, the thrust force F changes depending on each process.
is applied to the screw 1, as shown in FIG. 5A, for example, and changes in the screw thrust are detected on the basis of elastic deformation of the sensor body 21 in the axial direction. On the other hand, the set value signal of the thrust force at the time of pressure holding switching is output from the setting device Y, and while the thrust force of the screw 1 is detected by the sensor 2, the thrust force F changes to Y,
The injection process continues as long as the screw thrust is smaller than the set value, and when the comparator Y determines that the screw thrust is equal to the set value, an instruction to start the holding pressure process is sent to the motor controller Y3, and the screw thrust starts the injection process. Switching from to pressure holding process was always achieved at the set pressure value.

In addition, not only the set value signal of the screw thrust at the time of holding pressure switching is input to the setting device Y, but also a screw thruster program such as the actual MA in FIG. If the screw drive motor is controlled by constantly comparing the signal Sl and the signal from the setting device YI issued by the screw thruster program, the thrust force F in the entire injection molding process of the screw 1 will be
Regardless of changes in GT flow-torque characteristics, the set value can of course be achieved at any required point during the injection molding process, such as point P1+ in FIG. 5A, by combining the setting device Y1 program and sensor 2. It is also possible to control the screw thrust F to a set value only by points such as point P2+point P8.

〔Effect of the invention〕

There is no variation in the scree thrust when changing the holding pressure, and it can always be changed at the set value. As a result, it is possible to reduce variations in the dimensions and strength of the molded product, and it is also possible to prevent the screw thrust force when changing the holding pressure from being too large and causing cracks in the molded product, and conversely, the screw thrust force when changing the holding pressure was so small that it was possible to prevent sink marks from occurring on the molded product due to insufficient filling of the material.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of an apparatus used in the present invention. FIG. 2 is a partially cross-sectional explanatory diagram of the sensor mounting part. FIG. 3 is a partially cross-sectional explanatory diagram of the sensor. FIG. 4 is a schematic explanatory diagram of a conventional device. FIG. 5A is an explanatory diagram of changes in screw thrust force. FIG. 5B is a current-torque characteristic diagram of the motor. I-niscrew, 2: Load sensor, 3: Ball screw, 4: Nut, 5.7: Drive gear,
6: Transmission shaft, 8: Motor, Yl: Setting device, Y,: Comparator, Y3a motor controller,
SI Niscrew thrust signal, S: Thrust set value signal when switching to holding pressure. 1...Screw 2...Load sensor 3...? - Runeno 4...Nand 5.7...Drive gear 6...Transmission shaft 8...Motor 21...Sensor body 27...Brush 24...Intermediate terminal block 30...Bearing 25...Slip ring 31.
・・Terminal bolt 26 ・・・Insulator
32...Rotating stop diagram Figure 58

Claims (1)

[Claims] 1. In an injection molding machine where the screw is driven by a motor,
Screw (1) and device for pushing screw (1) (3)
A sensor (2) that detects the load is installed between the A holding pressure switching control method characterized by switching to a pressure process.