JPH059256B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling an injection molding machine, and particularly to a method for controlling a screw in an injection process.

[Conventional technology]

Conventional in-line screw injection molding machines generally include a heating cylinder with a hopper disposed at the rear for supplying molding material, and a screw whose advancement/retraction and rotation are controlled is inserted into the heating cylinder. In the metering step, the screw is rotated to accumulate molten resin material in front of the screw, and in the injection step, the screw is moved forward to inject and fill the mold. Therefore, in this type of injection molding machine, accurate control of injection speed, injection pressure (holding pressure), etc. is extremely important to ensure high precision, high quality, and stable molded products. Become.

[Problem to be solved by the invention]

However, such conventional in-line screw type injection molding machines have the following problems to be solved.

First, there is a problem caused by the molding material. As shown in FIG. 6, a heating cylinder 6 into which a screw 61 is inserted
2 is supplied with molding material from a material supply path (hopper) 63 formed in a direction perpendicular to the axial direction of the screw 61. In this case, a solid material (pellet) W with particularly high hardness, such as acrylic resin, polycarbonate resin, glass-filled resin, etc., is used as the molding material, and the groove 6 of the screw 61 is used as the molding material.
If the depth of 1d is shallow compared to the size of the solid material W, when the screw 61 moves forward (in the direction of arrow A)
At this time, the solid material W present in the groove portion 61d is sheared by the lower edge 64 of the material supply path 63 and the peak portion 61h of the screw 61. The shearing force at this time varies depending on the diameter of the screw 61, but is 100 to 500 kg.
In a small aircraft with an ejection force of several tons, this will create quite a large amount of resistance.

In addition, since the rotational direction position of the screw 61 at the post-measurement stop position in the metering process, that is, the injection start position, differs for each molding cycle, the arrangement state of the solid material W, the density,
This causes a difference in quantity, etc., and the mechanical resistance to the screw 61 varies from shot to shot.

On the other hand, it would be ideal if the pressure of the resin material inside the mold cavity could be directly detected, but in reality this is technically difficult, so a pressure sensor is usually provided on the drive section side. For example, in the case of a hydraulic injection molding machine, the oil pressure in the injection cylinder is detected by a pressure sensor such as a hydraulic pressure sensor, and in the case of an electric injection molding machine, the reaction force of the screw is detected by a load cell (strain gauge). ), etc., and is disclosed in, for example, Japanese Unexamined Patent Publication No. 174625/1983 (Japanese Patent Publication). Then, the detection signal (detection value) from the pressure sensor and the injection pressure (holding pressure)
Closed-loop control is performed to ensure that the set values match.

However, in this type of pressure detection, the screw 61
In addition to the pressure of the molten resin material existing in front of the molten resin material, the mechanical resistance based on the solid material W near the material supply path 63 mentioned above is also detected. In the end, the variation in resistance directly affects the detection value of the pressure sensor, and despite closed-loop control, the pressure of the molten resin that should be detected cannot be accurately detected, resulting in high quality, high precision, and stable However, it was not possible to obtain a molded product.

An object of the present invention is to provide a method for controlling an injection molding machine that eliminates the problems existing in the conventional technology.

[Means to solve the problem]

The present invention includes a screw 2 that rotates or moves forward and backward;
When carrying out a method for controlling an in-line screw type injection molding machine equipped with a heating cylinder 4 in which a screw 2 is inserted and a hopper 3 for supplying molding material is arranged,
During molding of the solid material W, a predetermined speed r, that is, r≈Vs/L (rotation/
sec) (where, Vs: Screw advance speed (mm/
sec), L: Screw pitch (mm)) The screw 2 is rotated in the opposite direction to the rotation direction during measurement, and as the screw 2 moves forward, the heating cylinder 4 is rotated at a prescribed speed r. Control is performed so that the apparent position of the ridge 2h of the screw 2 remains almost immobile (including immobility or slight movement to the extent that it is recognized as an error in the forward and backward directions that can achieve the purpose of the present invention). Features.

[Effect]

Next, the operation of the present invention will be explained.

In the method for controlling an injection molding machine according to the present invention, especially when the screw 2 moves forward in the injection process, the screw 2 simultaneously rotates in the opposite direction to the rotation direction during metering. The apparent position of the mountain portion 2h remains substantially unchanged. Therefore, the adverse effect of the solid material W being sheared as the screw 2 advances is eliminated or significantly reduced, and the resistance due to the solid material W is significantly smaller than before and has no variation, so it is possible to The pressure detection signal value from the installed pressure sensor such as a load cell substantially matches the actual molten resin pressure, and accurate injection pressure (holding pressure) is detected.

〔Example〕

Below, preferred embodiments according to the present invention are listed,
This will be explained in detail based on the drawings.

First, in order to facilitate understanding of the present invention, a schematic configuration of the injection device 1 in an in-line screw type injection molding machine will be described with reference to FIG. 3.

Reference numeral 4 denotes a heating cylinder, which is equipped with an injection nozzle 12 at its front end, and a hopper 3 at its rear upper end for supplying the molding material (solid material W) into the heating cylinder 4, into which the screw 2 is inserted. Further, the rear end of the heating cylinder 4 is supported by a support plate 14, and the support plate 14 is further provided with a plurality of tie bars 15 extending horizontally toward the rear. The tie bars 15... are provided with a sliding member 16 that can freely slide in the front and back direction, and a rotation regulating member 16a that is allowed to move forward and backward and is restricted in the rotational direction is inserted into the sliding member 16.
A rotatable coupling member 17 is provided in the rotation regulating member 16a. A ring-shaped load cell 18 is interposed between the rear end surface of the coupling member 17 and the sliding member 16. On the other hand, a screw 2 is provided at the front end of the coupling member 17.
The rear ends of the connecting member 17 are connected to each other, and an inner shaft member 19 extending rearward is connected to the rear end of the connecting member 17. Inner shaft member 19
A cylindrical outer shaft member 20 that is coaxially rotatable is inserted into the outer shaft member 20, and the outer circumference of the outer shaft member 20 and the sliding member 1
An injection ball screw mechanism 21 is interposed between the holes 6 and 6. Further, a driven gear 22 is provided at the rear end of the outer shaft member 20.
This driven gear 22 is connected via a timing belt 23 to a drive gear 25 attached to an injection servo motor 24. On the other hand, the driven gear 2 is connected to the rear end of the inner shaft member 19 via a spline mechanism 26.
7, and this driven gear 27 meshes with a drive gear 29 attached to a servo motor 28 for rotating the screw.

The injection device 1 having the above configuration functions as follows.

First, due to the forward rotation of the servo motor 28, the rotational force of the motor 28 is transferred from the driving gear 29 to the driven gear 2.
7→spline mechanism 26→inner shaft member 19→coupling member 17→screw 2. Therefore, the screw 2 rotates forward and the molten resin material can be measured. Note that by rotating the motor 28 in the reverse direction, the screw 2 can be rotated in the reverse direction along the same route.

On the other hand, due to the forward rotation of the servo motor 24, the rotational force of the motor 24 is transferred from the driving gear 25 to the driven gear 2.
2→outer shaft member 20→ball screw mechanism 21→sliding member 16→coupling member 17. Therefore, the screw 2 moves forward, and the measured amount of molten resin material can be injected and filled into the mold. Note that by rotating the motor 24 in the opposite direction, the screw 2 can be moved backward along the same route.

Next, a method for controlling an injection molding machine according to the present invention will be explained with reference to FIGS. 1 and 2.

First, the central control unit 32 in the metering process provides a measurement command signal and a measurement value signal based on a set value set by a measurement value setter (not shown) to the motor control unit 33 that controls the servo motor 28 .
As a result, the motor 28 (indicated by the same reference numerals in FIG. 3) rotates in the forward direction to perform weighing. This state is shown in FIG. 1b.

On the other hand, when the metering process is completed, the process moves to the injection process. In the injection process, when the mold (not shown) closes, the central control unit 32 sends an injection command signal and an injection speed command signal based on the setting value set by the injection speed setting device 34 to the servo motor 24. It is given to the motor control unit 36 that controls it. As a result, the motor 24 rotates to advance the screw 2, and at the same time, a detection signal from a tachometer generator 38 that detects the speed of the motor connected to the motor 24 is given to the motor control unit 36, which is used as an injection speed command signal. Perform closed-loop control to ensure consistency.

Further, at this time, according to the control method according to the present invention, a setting signal preset by the screw reverse rotation speed setting device 39 is applied to the motor control section 33, and the servo motor 28 starts reverse rotation. At the same time, a detection signal from the tachometer generator 40 coupled to the motor 28 is applied to the motor control section 33, and closed-loop control is performed so as to match the reverse rotation speed setting value. In other words, Figure 1b
As shown in the figure, the screw 2 rotates in the opposite direction to the rotation direction during measurement in the measurement process. In this way, the screw 2 in the injection process moves forward at the set speed and at the same time rotates backward at the set predetermined speed r. The predetermined speed r is set so that the apparent position of the peak portion 2h of the screw 2 at a predetermined position of the heating cylinder 4 remains substantially fixed when the screw 2 moves forward.

In this example, the reverse rotation speed of the screw 2 is set in advance by the screw reverse rotation speed setting device 39, but a microprocessor is used in the central control section 32, and the reverse rotation speed of the screw 2 is set in advance from the setting value of the injection speed setting device 34. The rotation speed may be automatically calculated.
That is, the pitch of the screw 2 is L (mm), and the pitch of the screw 2 is
The injection (forward) speed is Vs (mm/sec), screw 2
When the reverse rotation speed of is set to r (rotations/sec), calculation processing may be performed so as to satisfy the relational expression r≈Vs/L (including r=Vs/L). As a result, even if the screw 2 moves forward, the apparent position of the peak 2h of the screw 2 at the predetermined position of the heating cylinder 4 remains almost constant (immobile, or to the extent that it can be recognized as a forward/backward error that can achieve the purpose of the present invention). ).

Further, a position sensor 50, for example, is installed to detect the apparent position of the peak 2h of the screw 2 in the axial direction, and a predetermined speed r of reverse rotation is controlled by feedback so that the position is approximately constant during injection. It's okay.

The range in which the screw 2 is reversely rotated is preferably the entire stroke in which the screw 2 moves forward during the injection process. Further, it may be a part of the stroke if necessary. Furthermore, as shown by the virtual line Vm in FIG. 1, when controlling the injection speed (injection motor speed) to be changed in multiple stages during the injection process, the screw rotates in reverse at a predetermined speed corresponding to the control. It is sufficient to variably control r in multiple stages.
Although the injection process has been exemplified above, the present invention is not limited to this, and can be similarly applied to cases in which the screw 2 is advanced in other processes.

On the other hand, in the injection process, as the screw 2 moves forward, the screw 2 connected to the servo motor 24
The detection signal of the pulse generator 35 is input to the central processing section 32. When the screw 2 moves to the setting value set by the holding pressure switching position setter 41, the central control unit 32 applies a holding pressure control signal to the servo motor 24, and the motor 24 changes from the speed control state to the setting value set by the holding pressure switching position setter 41. While entering the pressure control (injection pressure control) state, at the same time, a reverse rotation stop signal is given to the motor control unit 33 to stop the rotation of the servo motor 28. Note that the above-mentioned holding force control signal is set in advance by the holding force setting device 43. In the holding force control state, the detection signal of the load cell 18 that performs pressure detection is input to the central control unit 32 via the amplifier 44, and closed-loop control is performed so as to match the holding force control signal. When the injection timer (not shown) times up and a predetermined injection time has elapsed, each control signal for the servo motors 24 and 28 is turned OFF and the entire injection process is completed.

FIG. 4 shows a diagram of actually measured injection pressure P and injection speed V when controlled by the method of the present invention. Figure a shows actually measured recorded data of the injection pressure (load cell output) P, and Figure b shows actually measured recorded data of the injection speed V. In both cases, 100 shots are overwritten with the horizontal axis as the time axis. The molded product used was a small acrylic lens with a weight of about 0.2 (g) and a total weight of about 5.6 (g) including four pieces and a spool and runner.

On the other hand, FIG. 5 shows an actual measurement diagram similar to FIG. 4 when controlled by the conventional method. That is, when the screw 2 is not rotated during injection,
Figure 5a shows actual measurement record data of injection pressure P, Figure 5b
is actually measured recorded data of the injection speed V. In each case, 30 shots are overwritten with the horizontal axis as the time axis.

Actual measurement results show that even when 30 shots were molded using the conventional control method, the weight variation was about 10 to 16 (mg) relative to the total weight of 5.6 (g), resulting in two defective products. On the other hand, in the method of the present invention, even though 100 shots were molded, the weight variation was as small as 4.3 (mg) compared to the total weight of 5.6 (g), and all were good products.

In addition, as is clear from the comparison between Figures 4a and 5a, the variation in injection pressure during injection speed control is reduced to about 1/6 of the conventional method by the method of the present invention, and compared to the rated injection pressure. This results in a variation of approximately 0.4 (%). Therefore, the method of the present invention is more effective when used in an injection molding machine in which the holding pressure is switched after the injection pressure reaches a constant value. In addition, according to the method of the present invention, it can be expected that the viscosity resistance due to the resin material inside the heating cylinder can be further reduced, and that the ring valve (check valve) provided at the front of the screw will be easier to close during injection.

Although the embodiments have been described in detail above, the present invention is not limited to such embodiments, and the present invention is not limited to such embodiments, but includes the following in terms of configuration, shape, method, numerical value, quantity, etc.
Any changes can be made without departing from the spirit of the invention. In particular, in the examples, the case of an electric injection molding machine is shown, but this does not preclude application to a hydraulic injection molding machine.

〔Effect of the invention〕

As described above, in the injection molding machine control method according to the present invention, in the injection process of molding a solid material, the screw is rotated in the opposite direction to the rotation direction at the time of measurement, and the screw crest at a predetermined position of the heating cylinder is adjusted. Since the apparent position of is controlled so as to be substantially immobile, the following effects are achieved.

It is possible to eliminate the problem of solid material being pinched and sheared between the screw and the material supply path, and it is possible to significantly reduce variations in pressure from shot to shot. As a result, injection control and holding pressure control can be stabilized, and a molded product of high quality and high precision can be obtained.

The mechanical resistance between the solid material-based screw and the inner wall of the heating cylinder is reduced, and the variation in mechanical resistance from molding cycle to molding cycle is also reduced. Accurate pressure detection that substantially matches the internal resin material pressure can be performed.

Since the mechanical resistance between the screw and the heating cylinder can be reduced, power loss based on this can be reduced.

[Brief explanation of the drawing]

Fig. 1: A schematic diagram of the operation of each motor in the metering process and injection process according to the control method according to the present invention, Fig. 2: A block circuit diagram showing only the main parts of the control device that implements the control method, Fig. 3: A vertical cross-sectional view of an injection device in an injection molding machine implementing the same control method,
Figure 4: Actual measurement diagram of injection pressure and injection speed when controlled by the method of the present invention, Figure 5: Actual measurement diagram of injection pressure and injection speed when controlled by the conventional method, Figure 6 : A vertical cross-sectional view of the vicinity of the hopper in the injection device to explain the problems of the background art. In the drawings, 2...Scrill, 2h...Scroll peak, 3...Hotsupa, 4...Heating tube, W...Solid material.

Claims (1)

[Scope of Claims] 1. A method for controlling an in-line screw injection molding machine comprising a screw 2 that rotates or moves back and forth, and a heating cylinder 4 equipped with a hopper 3 into which the screw 2 is inserted and which supplies molding material. , during molding of the solid material W, in all or part of the stroke range of the injection process in which the screw 2 is advanced in the axial direction,
The screw 2 is rotated in the opposite direction to the rotation direction during measurement at a predetermined speed r set by the following formula, and the apparent position of the peak 2h of the screw 2 at a predetermined position of the heating cylinder 4 remains almost constant. A method for controlling an injection molding machine, the method comprising: controlling an injection molding machine so that Predetermined speed r≒Vs/L (rotations/sec) where Vs: Screw forward speed (mm/sec) L: Screw pitch (mm) 2 The predetermined speed r is characterized by being variable in accordance with the forward speed of screw 2. A method for controlling an injection molding machine according to claim 1 or 2. 3 detecting the apparent position of the peak 2h of the screw 2 in the axial direction at a predetermined position of the heating cylinder 4;
2. The method of controlling an injection molding machine according to claim 1, wherein feedback control is performed based on the detection result so that the apparent position of the peak portion 2h at the predetermined position remains substantially fixed.