JP3907971B2 - Control method of injection molding machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control method for safely driving one actuator in an injection molding machine with a plurality of servo motors.
[0002]
[Prior art]
As a control method for driving an actuator of an injection molding machine with a plurality of servo motors, for example, as disclosed in JP-A-1-247128, one servo motor of a plurality of servo motors (electric motors) is used as a reference. Some servomotors are electrically controlled so as to be equal to the rotational speed of the servo motor as a reference while maintaining the set rotational speed. However, in such control, while the types of control devices increase and become complicated, other servo motors are controlled following the reference servo motor. The control is delayed by time, and it is substantially difficult to simultaneously rotate all the servomotors at the same speed.
[0003]
By the way, in the mold clamping device in the injection molding machine, in the process of aligning the mold by bringing the movable plate close to the fixed plate, it is necessary to limit the mold matching force of the mold low in order to protect the mold from foreign matter. is there. Similarly, when the mold is opened, the mold opening force may be limited to protect the mold or the molded product. Further, in an ejector apparatus that protrudes a molded product from a mold or cuts out a gate, the protruding force may still need to be limited in order to protrude or damage the molded product without damaging the molded product. Furthermore, in an injection apparatus that melts a resin material and injects and fills the molten resin into a mold, when the screw is forcibly retracted, the retracting force must be limited due to insufficient strength due to its mechanical factors. Limiting the driving force of the actuator in the mold clamping device, ejector device, and injection device is executed by limiting the output torque of the servo motor.
[0004]
However, when the actuator is driven by a plurality of torque-limited servo motors, the servo motor whose rotational speed has decreased due to load bias or equipment failure due to some cause is used to maintain the target speed. The amplifier tries to increase the current, but the torque limit, i.e. the current limit, is acting so that it cannot supply the servo motor with a larger current to reach the target rotational speed. For this reason, the servo motors whose rotational speed has decreased cannot return to the target rotational speed, and the synchronization between the servo motors is lost.
[0005]
[Problems to be solved by the invention]
As described above, when controlling one actuator with a plurality of servo motors, particularly by limiting the output torque of the servo motor, this problem is solved in order to solve the problem that the synchronization between the servo motors is lost and the drive mechanism section is damaged. Invented, the drive of each servo motor does not depend on the rotational speed of the other servo motors, but achieves synchronous operation by strictly closed-loop control independently based on one command, The allowable deviation distance of each axis of the servomotor of the actuator based on the deviation of the rotation angle between the servomotors was monitored as the difference between the rotation angles of the servomotors, and the operation of the servomotor was stopped when it became abnormal. .
[0006]
[Means for Solving the Problems]
That is, according to the first aspect of the present invention, in the control of an injection molding machine that drives one actuator by a plurality of servo motors with limited torque, the plurality of servo motors are individually closed-loop controlled based on one command, The rotation angle signals of the encoders attached to the servo motors are compared and calculated to detect the difference in rotation angle between the servo motors, and the rotation angle difference is selected according to the torque limit amount. monitors whether or not exceeded, according to the control method of the injection molding machine to drive the servo motor Ru is stopped when the difference of the rotational angle exceeds a predetermined value.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the interrelationship among a control device, a servo amplifier, a servo motor, and an actuator that execute the control method of the present invention shown in the flowchart of FIG.
[0009]
Reference numeral 1 denotes an actuator, which corresponds to a movable plate of a mold clamping device in an injection molding machine, an ejector bar of an ejector device, a screw mounting plate of an injection device, and the like. Ball nuts 2, 3 are fixed to the actuator 1, and the ball nuts 2, 3 are screwed with ball screws 4, 5 connected to the rotors of the servo motors 6, 7 to rotate the servo motors 6, 7. Thus, a drive mechanism that allows the actuator 1 to reciprocate linearly is configured.
[0010]
Servo motors 6 and 7 are driven by current supplied from servo amplifiers 10 and 11 via switches 17 and 18. The servo amplifiers 10 and 11 are publicly known, and servo control the servo motors 6 and 7 according to a control signal output from the control device 19. Reference numerals 8 and 9 denote encoders connected to the rotors of the servo motors 6 and 7, which detect the rotation angles of the servo motors 6 and 7, respectively. The angle signals of the encoders 8 and 9 are transmitted to the servo amplifiers 10 and 11, the feedback calculation units 12 and 13, and the comparison calculation unit 16. FIG. 1 shows an example in which two servo motors drive one actuator, but the present invention is not limited to this, and one actuator is driven by three or more servo motors. It may be.
[0011]
The control device 19 sets and controls the speed, position, and force of all the actuators of the injection molding machine, and also performs sequence control of the actuators and temperature control of the heating cylinder of the injection device. A rotation command 14 which is a speed setting of the actuator 1 is transmitted in parallel to feedback calculation units 12 and 13 provided corresponding to the servomotors 6 and 7. The feedback calculation units 12 and 13 match the rotation command 14 with the angle signals 20 and 21 and output the control signals 22 and 23 to the servo amplifiers 10 and 11 so that the angle signals 20 and 21 coincide with the rotation command 14. .
[0012]
The torque limit command 15 is set by an input unit including a display and a keyboard provided in the control device 19 and stored in the storage unit of the control device 19. The torque limit command 15 is transmitted to the servo amplifiers 10 and 11 and the comparison calculation unit 16. The servo amplifiers 10 and 11 output the current converted according to the control signals 22 and 23 to the servo motors 6 and 7, but the current is limited based on the torque limit command 15. Accordingly, the output torque of the servo motors 6 and 7 is not output more than the value set by the torque limit command 15.
[0013]
The comparison calculation unit 16 reads the rotation angle signals 20 and 21 of the servo motors 6 and 7 transmitted from the encoders 8 and 9, always calculates the rotation angle difference between the two, and the difference is preset in the comparison calculation unit 16. When a predetermined value selected from a plurality of predetermined values is exceeded (FIG. 2, S2), the synchronization abnormality signal 24 is output to the feedback arithmetic units 12, 13 and the switches 17, 18 (FIG. 2, S3). ), The control signals 22 and 23 and the current to the servo motors 6 and 7 are cut off, and the servo motors 6 and 7 are stopped.
[0014]
Here, the process in step S1 of FIG. 2 will be described in detail. A plurality of predetermined values are stored according to the number of operating modes of the actuator 1, that is, the number of torque limit commands 15, and are not limited to those illustrated in FIG. 2. Next, a specific method for setting the predetermined value will be described. First, when the actuator 1 is a movable platen, when the mold is not attached, or when the actuator 1 is a screw attachment plate, the actuator 1 is brought into an unloaded state as when the raw material resin is not present in the screw. Then, without supplying current to the servo motors 6 and 7, one ball screw is rotated by hand to move the actuator 1 by a minute distance. At this time, it is determined that the rotation angle of the rotation of one ball screw before the other ball screw starts rotating is the maximum allowable deviation between the plurality of servo motors. Incidentally, the actual measurement allowable deviation distance obtained by converting the shift in the mold clamping device having a mold clamping force of 1200 kN into the inclination of the movable platen is 100 μm. The rotation angle between the servomotors corresponding to this deviation is the maximum value of the predetermined value when the torque limit command is applied, and all other predetermined values are smaller than this value according to the torque limit amount.
[0015]
The predetermined value thus obtained is stored in the storage device. Each time the comparison calculation unit 16 takes in the torque limit command 15 that changes according to the command from the sequencer corresponding to the operation mode of the actuator 1, as shown in step S <b> 1, the minimum necessary value corresponding to the torque limit command 15 is obtained. The predetermined predetermined value is selected and set as the allowable value of the rotation angle difference. For example, when the actuator 1 is a movable platen, the torque is not limited (torque limit command 100%). During high-speed mold closing control, the predetermined value 1 is within 10% of the maximum predetermined value obtained above, and the mold is closed at low speed. If the torque is limited to 30% during the control, the predetermined value 2 is set to 70% of the maximum predetermined value. If the torque is limited to 60% during the mold opening low speed control, the predetermined value 3 is set to 30% of the maximum predetermined value. To do.
[0016]
As described above, the predetermined value is manually input at the judgment of the molding engineer with reference to the maximum predetermined value and the torque limit value, but may be automatically calculated as described below.
Predetermined value = (10 / A) × B × C
A: Torque limit (%)
B: Maximum predetermined value (number of encoder pulses)
C: Correction count However, even if the predetermined value exceeds the maximum predetermined value as a result of the calculation, the maximum predetermined value is set.
Note that even if the predetermined value is increased when the torque of the servo motor is limited, the energization current to the servo motor is limited, so excessive force is not applied to the actuator drive mechanism including the ball screw and ball nut. The drive mechanism is not damaged.
[0018]
【The invention's effect】
Since the present invention controls the injection molding machine as described above, even when controlling one actuator by limiting the output torque of the servo motor by using a plurality of servo motors, it is safe without damaging the drive mechanism. Make controllable.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the interrelationship among a control device, a servo amplifier, a servo motor, and an actuator that execute a control method of the present invention.
FIG. 2 is a flowchart showing a control method of the present invention.
[Explanation of symbols]
1 ……… Actuators 2, 3 ……… Ball nuts 4, 5 ……… Ball screws 6, 7 ……… Servo motors 8, 9 ……… Encoders 10, 11 ……… Servo amplifiers 12, 13 ……… Feedback Calculation unit 14 ...... Rotation command 15 ...... Torque limit command 16 ...... Comparison calculation unit 17, 18 ...... Switch 19 ...... Control devices 20, 21 ...... Rotation angle signals 22, 23 ...... Control signal 24 ...... Synchronization error signal

Claims (1)

In the control of an injection molding machine that drives one actuator by a plurality of servo motors with limited torque, the plurality of servo motors are individually closed-loop controlled based on one command, and the rotation angle of an encoder attached to each servo motor Detecting a difference in rotation angle between the servomotors by comparing the signals, and monitoring whether the difference in rotation angle exceeds a predetermined value selected according to the torque limit , the method of controlling an injection molding machine, characterized in Rukoto the driving of the servo motor is stopped when the difference in rotational angle exceeds a predetermined value.

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