JPH0253217B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a kneading control method for an injection molding machine that performs injection and kneading using a servo motor.

Conventional technology Conventional injection molding machines perform injection by moving the screw in the axial direction using hydraulic pressure. During metering and kneading, a certain amount of hydraulic pressure is applied to the injection mechanism to rotate the screw while applying back pressure. Let it knead.
Perform weighing. That is, the molding material is plasticized and molten by the rotation of the screw, and is stored at the tip of the heating cylinder, thereby generating pressure. This pressure overcomes the back pressure due to the hydraulic pressure applied to the injection mechanism and causes the screw to retreat.The amount of retreat is detected by a limit switch, etc., and when a certain position is reached, the rotation of the screw is stopped, and the metering and
Finish the kneading process. The above process was performed, but when a servo motor is used as the drive source for the screw rotation mechanism and the injection mechanism that moves the screw in the axial direction and performs injection, it is necessary to use the above hydraulic pressure to maintain back pressure. In addition, conventional kneading methods that involve kneading cannot be employed.

Problems to be Solved by the Invention The present invention provides an injection molding machine that uses a servo motor as a drive source for a screw rotation mechanism and an injection mechanism, which enables uniform kneading and shortens the kneading and metering time. The purpose of the present invention is to provide a kneading control method that can be used.

Means for Solving the Problems The present invention provides an injection molding machine that uses a servo motor as a drive source for an injection mechanism that moves a screw in the axial direction to perform injection, and a drive source for a screw rotation mechanism that rotates the screw. A torque limiting means for limiting the torque command value to a set value or less is provided in the servo circuit of the servo motor that drives the mechanism, and during kneading, the torque corresponding to the set back pressure value is set in the torque limiting means as the limiting value. ,
The difference between the torque limit value and the actual output torque of the servo motor of the injection mechanism is detected, and the rotational speed of the screw is varied based on the difference, so that the actual output torque of the servo motor of the injection mechanism is adjusted to the setting speed. The above problem was solved by controlling the torque to correspond to the pressure value.

Effect If there is a difference between the torque limit value corresponding to the set back pressure and the output torque of the servo motor of the injection mechanism,
The servo motor of the screw rotation mechanism rotates at high speed according to the difference, rotating the screw at high speed, which promotes plasticization of the molding material, increases melt pressure, and increases the force pushing the screw backwards. However, when the torque exceeds the torque limit value corresponding to the set back pressure, the screw moves backward against the output torque (limited torque) of the servo motor of the injection mechanism. Then, if a difference occurs, the above-mentioned operation is repeated, and the resin is automatically controlled so that a constant torque, that is, a set back pressure is always applied to the resin by the output torque of the servo motor of the injection mechanism. .

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention.
SB1 is a servo circuit for servo motor M1 to move the screw in the axial direction, and SB2 is a servo circuit for servo motor M2 to rotate the screw. SB1 and SB2 are conventionally known servo circuits. And servo circuit SB1
and SB2 have almost the same circuit configuration, and the difference is that a torque limiting means is added to the servo circuit SB1, and the outputs of the subtracter 8 and code converter 9 are added to the input to the compensator 12 of the servo circuit SB2. They differ in that they are In this example, DC motors are shown as the servo motors M1 and M2, but AC motors are also used, and pulse encoders are used as the detectors P1 and P2, but resolvers of other detectors may be used. , a speed generator, etc. may be used.

Conventionally known servo circuits SB1 and SB2 when the above-mentioned subtracter 8 and code converter 9 are not provided.
To outline the operation of the servo motor M1,
When a position command composed of a pulse train is input as a drive command for M2 as a movement amount per unit time, this position command and a detector P1 such as a pulse encoder, etc.
The difference between the amount of movement of the servo motors M1 and M2 detected at P2 is converted to a digital-to-analog converter (hereinafter referred to as D/
(referred to as A converter) 1, 10 converts it into an analog quantity voltage as a speed command value. That is, the position command and the servo motor M1 from the detectors P1 and P2,
If there is a large difference in the amount of movement of M2, a large speed command value is output. If the difference is small and the position command and the movement amount are close, a small speed command value is output. In order to improve responsiveness, this servo circuit performs speed feedback, which converts the signals from detectors P1 and P2 into voltages using F/V converters 2 and 11, and provides the actual speed of the servo motor. Subtract the voltage corresponding to the above speed command value, and calculate the difference,
That is, the error between the command speed and the actual speed v is compensated for by the compensators 3 and 12.
is amplified and output as a torque command. Note that the servo circuit SB1 of the servo motor M1 of the injection shaft is provided with a torque limiting means 4 to control the back pressure, and the torque limiter 4 saturates the torque exceeding a certain value, and limits the output so as not to output more than a certain value. It is restricted.
The torque command output in this way is output as a voltage corresponding to the current value flowing through the armatures of the servo motors M1 and M2.In order to further improve responsiveness to this torque command, the servo motor M
The voltage corresponding to the armature current from the current detectors 7 and 15 that detect the armature current of 1 and M2 is fed back, and the difference between the torque command and the feedback signal of the armature current is compensated for. The power amplifiers 5 and 13 amplify the signal, and the power amplifiers 6 and 14 drive and control the servo motors M1 and M2.

In this embodiment, the injection shaft servo motor M
The output from the current detector 7 that detects the armature current of 1, that is, the output torque of the servo motor M1, is subtracted by the subtractor 8 from the torque limit value S input to the torque limiting means 4, and the output of this difference is converted into a sign. The value is converted into a positive value by the device 9 and added to the speed command to the servo motor M2 of the screw rotation axis. That is,
The code converter 9 is connected to the output from the D/A converter 10.
I am trying to add the outputs of .

Next, the operation of this embodiment will be explained.

First, the back pressure during injection is controlled by the servo motor M of the injection shaft.
The torque limit value S is set as 1, and the servo motor M2 is driven. The servo motor M2 of the rotating shaft is similarly driven as described above, and rotates the screw. On the other hand, the output from the current detector 7 indicating the output torque of the servo motor M1 of the servo circuit SB1 of the injection shaft is input to a subtracter 8, and the output of the current detector 8 is subtracted from the torque limit value S. Output the difference. That is, the subtracter 8 outputs the difference between the set torque value S corresponding to the set back pressure and the actual torque value, and the sign converter 9 outputs the difference between the set torque value S and the actual torque value. Speed command (D/A converter 10)
is added to the output of Therefore, if the actual output torque value of the servo motor M1 is smaller than the set torque value S, a voltage corresponding to the difference will be added to the speed command (output of the D/A converter 10) of the servo motor M2 that rotates the screw. Since the servo motor M2 is outputted as a speed command, the servo motor M2 rotates faster. Therefore, the molding material is plasticized more quickly, the melt pressure increases, and the output torque of the servo motor M1 of the injection shaft increases and becomes equal to the set torque value S. Then, as the plasticization progresses further and the melt pressure increases and becomes larger than the torque limit value S, the servo motor M1 begins to rotate in the reverse direction, causing the screw to retreat. As a result of the screw retracting, the melting pressure applied to the servo motor M1 decreases, and as a result, the output torque of the servo motor M1 becomes smaller than the torque limit value S. As mentioned above, the difference is calculated by the subtractor 8 and the sign converter. 9 is added as a speed command, the rotation of the servo motor M2 that rotates the screw becomes faster, and the molding material is plasticized more quickly.

In this way, in this example, the speed command to the servo motor that rotates the screw is automatically varied so that a constant back pressure (torque limit value S) is always applied to the molding material during kneading. Since the speed is automatically controlled, uniform kneading can be achieved with constant back pressure. Second
The figure shows the speed command to be added from the subtracter 8 and code converter 9 by subtracting the current speed from the F/V converter 11 from the speed command from the D/A converter 10 in FIG. OP1 is an operation amplifier, and R1 to R
4 is a resistor, and this compensator 12 itself constitutes an adder, and the speed command signal from the D/A converter 10 is input with a positive sign, and the torque limit value (set back pressure) S and the actual Since the torque limit value S is always larger or equal to the signal from the subtracter 8 and the sign converter 9, which is the difference between the output torques, the signal is input as a positive sign. Since the output of the F/V converter 11 is input as a minus sign, as a result, the voltage corresponding to the speed command of the D/A converter 10 corresponds to the difference between the torque limit value S and the actual output torque. F/V converter 1
The compensator 12 outputs a new torque command by subtracting the voltage corresponding to the actual speed from 1. output).

As described above, the screw rotation speed command is varied according to the difference between the torque limit value S and the actual output torque, that is, the difference between the set back pressure and the actual back pressure, and the screw rotation speed is varied to reduce the back pressure. Although the back pressure is always set to the set value, here is a method to keep the back pressure constant by varying the position command instead of varying the speed command according to the above difference.
This will be explained with reference to FIG.

In FIG. 3, SB3 is exactly the same as a conventional servo circuit having a position control loop, and the position command input to the servo circuit SB3 is output via an acceleration/deceleration control section 21 and a time constant circuit 22. These acceleration/deceleration control section 21 and time constant circuit 22
is also publicly known, and in the present invention, this acceleration/deceleration control section 21
Similar to the first embodiment, the difference between the torque limit value S and the actual output torque of the injection servo motor M1 is added to the difference.

That is, when a movement amount is input as a drive command to the servo motor M2 for rotating the screw, infinite speed and infinite torque are required to drive the servo motor M2 by this command movement amount. Therefore, the acceleration/deceleration control section 21 outputs the movement amount per unit time as a pulse train per unit time while sequentially adding and subtracting the amount of movement per unit time at the rise and fall of the movement command. A sudden change is alleviated, and the position command is input to the servo circuit SB3 as a position command composed of a pulse train representing the amount of movement per unit time.

Therefore, as described above, the present invention subtracts the difference between the torque limit value S of the injection shaft, that is, the set back pressure, and the actual output of the servo motor M1 that advances the screw using the subtractor 9, and converts the V/F. The difference is converted into a frequency by the converter 20 and inputted to the acceleration/deceleration control section 21, and the output of the V/F converter 20 is converted into a pulse train as the amount of movement per unit time which is the output of the acceleration/deceleration control section 21. The configuration is such that the number of pulses corresponding to the amount of movement per unit time is changed by adding the pulses. As a result, when the output of the subtractor 8 is large, that is, when the output torque of the servo motor M1 has not reached the set back pressure, the number of pulse trains per unit time from the acceleration/deceleration control section 21 increases, and the number of pulse trains per unit time increases by the amount of the increase. Only servo motor M2 rotates at high speed,
This will prompt the plasticization of the molding material and automatically control it to reach the set back pressure.

In this second embodiment, the subtracter 8 is replaced with a comparator, and when a difference occurs between the torque limit value S and the output torque, a certain number of pulses are added to the output pulses of the acceleration/deceleration control section 21 and output. You may also do so.

Effects of the Invention As described above, the present invention automatically detects the difference between the set back pressure and the actual back pressure during kneading and measuring, and changes the rotational speed of the screw based on the difference. Since the back pressure is controlled to be the set back pressure, the back pressure is always kept constant, uniform kneading can be obtained, and kneading can be carried out efficiently and promptly.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is an explanatory diagram of a main part of the same embodiment, and FIG. 3 is a block diagram of a main part of a second embodiment of the present invention. be. SB1 to SB3... Servo circuit, M1... Servo motor of injection axis, M2... Servo motor of screw rotation axis, P1, P2... Detector, 8... Subtractor, 9... Sign converter, OP1... ...Operation amplifier.

Claims (1)

[Scope of Claims] 1. In an injection molding machine that uses a servo motor as a drive source for an injection mechanism that moves the screw in the axial direction to perform injection and a drive source for a screw rotation mechanism that rotates the screw, the injection mechanism is driven. A torque limiting means for limiting the torque command value to a set value or less is provided in the servo circuit of the servo motor, and during kneading, the torque corresponding to the set back pressure value is set in the torque limiting means as a limiting value, and the torque is limited. The difference between the value and the actual output torque of the servo motor of the injection mechanism is detected, and the rotational speed of the screw is varied based on the difference, so that the actual output torque of the servo motor of the injection mechanism reaches the set back pressure value. A kneading control method for an injection molding machine that controls the corresponding torque. 2 The difference between the torque limit value corresponding to the set back pressure value and the actual output torque of the servo motor of the injection mechanism is added to the speed command to the servo motor of the screw rotation mechanism to automatically adjust the screw rotation speed. A method for controlling kneading in an injection molding machine according to claim 1. 3. By varying the frequency of the position command to the servo motor of the screw rotation mechanism according to the difference between the torque limit value corresponding to the set back pressure value and the actual output torque of the servo motor of the injection mechanism. A kneading method for an injection molding machine according to claim 1, wherein the screw rotation speed is varied.