JPH0439410B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a metering control method for keeping the retraction speed of a screw constant during metering in an injection molding machine.

Conventional technology An injection molding machine that rotates a screw to knead the molding material, melt it, store the molten material at the tip of a heating cylinder, and retract the screw to a certain position against back pressure to determine the injection amount. In the conventional injection molding machine, the back pressure applied to the screw and the rotation speed of the screw were controlled by a program in the measuring process. That is, the kneading and measuring processes were performed by controlling the magnitude of back pressure and the rotational speed of the screw in a program based on the backward position of the screw.

Problems to be Solved by the Invention When kneading is carried out by controlling back pressure and screw rotation using the conventional measuring method as described above, the retraction speed of the screw is not constant, and as a result, the amount of plasticization per unit time is There is a drawback that a uniform melted state cannot be obtained. Further, the setting of the kneading time, that is, the measuring time cannot be uniformly determined. This measuring time is also the period for cooling the molded product, so by setting this measuring (kneading) time according to the time required to cool the molded product, the injection molding cycle of the injection molding machine can be made more efficient. The present invention improves the problems of the prior art.

Means for Solving the Problems The present invention detects the screw retraction speed with a screw retraction speed detection means, and controls the screw rotational speed so that the detected screw retraction speed becomes a predetermined screw retraction speed, or The back pressure was controlled to keep the screw retraction speed constant.

Function The screw retraction speed is detected by the screw retraction speed detection means during metering and kneading of the injection molding machine,
If the detected speed is lower than the predetermined retraction speed, the rotational speed of the screw is increased or the screw back pressure is decreased to increase the retraction speed of the screw. In addition, if the detected screw retraction speed is faster than the predetermined retraction speed, the screw rotation is slowed down or the back pressure is increased to slow down the screw retraction speed, and finally the screw retraction speed is set to the predetermined retraction speed. Match the backward speed and keep it constant.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention, in which 1 is a screw of an injection molding machine, 2 is a heating cylinder,
3 is a hopper, and 4 is a screw shaft of the screw, and the screw shaft 4 is rotated by a servo motor M2 via a transmission mechanism 5. Further, the screw shaft 4 is driven by a servo motor M1 via a transmission mechanism 6.
Injection is performed by moving in the axial direction. Reference numeral 11 denotes a servo drive circuit for driving and controlling the servo motor M2, which controls the speed of the servo motor M2 based on a speed command issued from the output circuit 18 of the NC control device 15 and a feedback signal from the speed detector 9. . Further, 12 is a servo drive circuit for the servo motor M1, which drives and controls the servo motor M1 based on a command issued from the output circuit 18 of the NC control device 15. 7 is a speed detector of the servo motor M1, and the output of the speed detector 7 is converted into a digital signal by an A/D converter 10.
It is input to the input circuit 19 of the NC control device 15.
Reference numeral 8 denotes a position detector which generates pulses by rotation of the servo motor M1, which are counted by a counter 20 to detect the position of the screw. In addition, the servo drive circuit 1
A drive current detector 13 for detecting a drive current for driving the servo motor M1 is connected to servo motor M1, and the detected drive current value is input to an input circuit 19 via an A/D converter 14. 15 is an NC control device, 16 is a central processing unit (hereinafter referred to as CPU), 17 is a memory composed of ROM for storing the entire control program of the injection molding machine, RAM for arithmetic processing, etc., and 18 is an output circuit. , 19 is an input circuit, 21 is a manual input device for manually inputting various setting values and commands, and 22 is a bus.

Next, the operation of this embodiment having the above configuration will be described in a second manner.
This will be explained with reference to the operation flow shown in FIGS.

The flow shown in Figure 2 is based on the back pressure of screw 1.
This relates to the first embodiment in which the rotation of the screw 1 is controlled while Pb is kept constant, and the backward speed Vb of the screw 1 is controlled to be constant.

First, from the manual input device 21, the screw 1
At the initial rotational speed So, screw 1 is driven forward (to the left in Figure 1) and a constant back pressure is applied to screw 1.
A drive current value Io for driving the servo motor M1 is set to give Pb. Furthermore, the measured value, that is, the screw retraction speed Vb is set in consideration of the screw retraction position L and the cooling time. Then, when metering and kneading is started, the CPU 16 stores the set screw rotation speed So in the register S (step S1), and drives the servo motor M1 with the drive current Io set above to apply a constant back pressure to the screw 1. (Step S2). And servo motor M
The screw is driven to rotate with the value 2 stored in the register S (step S3). When the servo motor M2 is driven and the screw 1 rotates, the molding material is kneaded and becomes molten, and the screw 1 is pressed against the back pressure.
It moves backward (to the right in Figure 1) against Pb.
As the screw 1 moves rearward, the position detector 8 generates pulses which are counted by the counter 20. And this counter 20
The CPU 16 determines whether or not the value has reached the set value L, which is the kneading end point (step S4).
The detected speed from the speed detector 7, that is, the backward speed V of the screw 1 is read through the D converter 10 and compared with the set speed Vb (step S5). If the backward speed V detected by the speed detector 7 and the set speed Vb match, the value of the register S will not change, and the value stored in the register S will control the servo motor M.
2 to rotate the screw 1. If the backward speed V is greater than the set speed Vb, the value stored in the register S is decreased by .DELTA.S (step S6), and the servo motor M2 is rotated by that value to rotate the screw 1 (step S3). As the rotation of the screw 1 decreases, the melting pressure of the molding material also decreases, so the retraction speed V of the screw 1 also decreases and becomes close to or coincides with the set speed Vb. Also, when the backward speed V becomes smaller than the set speed Vb (step S5), the value of the register S is increased by ΔS (step S7), and the servo motor M2 and screw 1 are rotated according to the value stored in this register S. (step)
S3). As the rotation of the screw 1 becomes faster, the melting pressure also increases and the retraction speed V of the screw 1 also increases and becomes equal to or close to the set speed Vb. In this way, the backward speed V of the screw 1 is set at the set speed Vb.
is controlled to be equal to In this way, kneading is performed at the set speed Vb, and when the value on the counter 20 reaches the screw retraction set position L, that is, the metering and kneading end point (step S4), the servo motors M1 and M
2 is stopped, and the metering and kneading operation is completed.

FIG. 3 shows an operation flow when controlling the retraction speed V of the screw 1 to the set speed Vb by keeping the rotational speed S of the screw 1 constant and changing the back pressure.

In this case as well, the rotation speed So of the screw 1, the backward speed Vb of the screw,
Screw retraction position L and back pressure Pb at measurement end point
Therefore, the initial drive current value given to servo motor M1
After setting Io and starting the metering and kneading operation,
CPU16 is the initial drive current value Io of servo motor 1
is stored in register I (step S11), servo motor M2 is rotated at the set speed So (step S12), servo motor M1 is driven according to the drive current value stored in register I, and a constant back pressure is applied. Add (Step S13). Next, it is determined whether the value of the counter 20 has reached the set retreat position L, which is the end point of metering and kneading (step S14).
It is read through the A/D converter and input circuit 19, and compared with the set backward speed Vb (step S15). If they match, the servo motor M1 is driven without changing the drive current value, and the backward speed is started. Speed V is set speed Vb
If it is larger, the value of register I is increased by ΔI (step S16), and this increased register I is
The servo motor M1 is driven using the value of as the drive current for the servo motor M1 (step S13). As a result, the back pressure increases, so the backward speed V of the screw 1 decreases, and steps S13, S14, S15, and S16 are repeated to make the backward speed V of the screw 1 match the established speed Vb. Furthermore, when the backward speed V becomes smaller than the set speed Vb, the value of the register I is decreased by ΔI (step S17), and the servo motor M1 is driven with the decreased drive current (step S17).
From S13), the back pressure decreases and the screw retraction speed V increases. In this way, steps S13, S14,
By repeating S15 and S17, the backward speed V of the screw is made to match the set speed Vb. As described above, through the processing of steps S13 to S17, the backward speed V of the screw 1 is maintained at a constant set speed.
It will be held at Vb.

Effects of the Invention As described above, the present invention makes it possible to keep the retraction speed of the screw constant during the metering and kneading process of an injection molding machine, so the metering and kneading time becomes constant.
It is only necessary to determine the metering kneading time in accordance with the cooling period of the molded product, and setting the retraction speed so that the metering and kneading is completed within the metering and kneading time, and the molding cycle of the injection molding machine can be operated efficiently. The operating efficiency of the injection molding machine can be increased.

Furthermore, since the screw retraction speed is constant, the amount of plasticization per unit time is constant and uniform plasticization can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of an injection molding machine implementing an embodiment of the present invention, FIG. 2 is an operational processing flow of the first embodiment of the present invention, and FIG. 3 is an operational processing flow of an embodiment of the present invention. 1... Screw, M1, M2... Servo motor, 15... NC control device.

Claims (1)

[Claims] 1. In a metering control method for an injection molding machine,
A metering control method for an injection molding machine, characterized in that during metering, a screw retract speed is detected by a screw retract speed detection means, and the screw rotation speed is controlled so that the detected screw retract speed becomes a predetermined screw retract speed. 2. The metering control method for an injection molding machine according to claim 1, wherein the predetermined screw retraction speed is determined so that metering is completed within a metering time corresponding to a cooling period of the molded product. 3 The predetermined screw retraction speed is set by the setting means, the predetermined screw retraction speed set by the setting means and the screw retraction speed detected by the retraction speed detection means are compared by the comparison means, and the detected screw retraction speed is determined as the set retraction speed. Claim 1, wherein the rotational speed of the screw is controlled so as to match the rotational speed of the screw.
3. The method for controlling the injection molding machine according to item 1 or 2. 4. In the metering control method for an injection molding machine,
A metering control method for an injection molding machine, comprising: detecting a screw retraction speed with a screw retraction speed detection means during metering, and controlling the back pressure of the screw so that the detected screw retraction speed becomes a predetermined screw retraction speed. 5. The metering control method for an injection molding machine according to claim 4, wherein the predetermined screw retraction speed is determined so that metering is completed within a metering time corresponding to a cooling period of the molded product. 6 The predetermined screw retraction speed is set by the setting means, the predetermined screw retraction speed set by the setting means and the screw retraction speed detected by the retraction speed detection means are compared by the comparison means, and the detected screw retraction speed is determined as the set retraction speed. 6. A metering control method for an injection molding machine according to claim 4 or 5, wherein the back pressure of the screw is controlled so as to match the .