JPS59224324A - Control of injection process in electric molding machine - Google Patents

Abstract

PURPOSE:To remove the effect of inertia energy in an injection process in an electric molding machine with an electric servomotor by a method wherein the speed control section is placed under a closed loop control and a speed reduction section is provided just before injection changes from a speed control region to an injecton force control region. CONSTITUTION:In an injection molding process in which an electric servomotor 9 is used as the drive source, rotary speed values V and torque values F are set to the drive source during a charging process while the rotary speed of the drive source controlled by a servo-amplifier 25 is performed under a closed loop control so that it makes a suitable injection speed value. Then, when charging ends, the set value of the speed V is changed by the operation of a concentrated control unit 24 through a signal switch 27 into such a low value that the inertia energy of an injection screw, etc. can be nearly neglected. After the speed reduction section is provided in a closed loop and the injection speed arrives near the set value, the torque value F and the rotary speed value V of the drive source are changed into the set value and shifted from the speed control to the injection force control.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new injection process control method for an electric injection molding machine using a servo motor as a drive source.

Among the various steps in an injection molding machine, the injection step of filling the mold with molten resin is an extremely important step that affects the quality of the molded product.

The injection process consists of a filling process from the start of injection until the mold is almost filled with resin, a compression stage to compress the resin filled in the mold, and a refilling process to compensate for the shrinkage of the compressed and filled molten resin due to cooling. This can be divided into pressure holding processes, such as for compressing the oil, recompressing it, or stopping the backflow of fat to the nozzle side of the machine. However, it is extremely difficult to find the dividing point. In conventional injection process control methods, dividing points are predetermined for convenience in control. For example, the filling process is performed by controlling the speed of the injection screw or plunger, and the compression process and pressure holding process are performed by controlling the injection screw or plunger speed. The forward force (rotational torque of the drive motor in the case of an electric molding machine), that is, the force control has been used to control the compression process, or the compression process has been carried out as part of the final stage of the filling process.

In any case, when switching from speed 1 control to force control, conventional injection process control relies on indirect control based on the balance between the force on the drive side and the load on the molten resin-9. Since the control state was included, it was difficult to achieve stable control, making it difficult to produce molded products of constant quality. In addition, in the case of an electric molding machine, switching from the speed control state to the direct force control state in the filling process will not only affect the injection screw at the filling completion point, but also the rotor of the electric motor, drive gear, shaft, etc. Since the unique inertia energy of a mechanical molding machine is separated, the actual injection force acting on the resin during the compression process is much lower than that of a hydraulic molding machine compared to the set injection force. Therefore, the resin may be overfilled in the mold, and even if the setting value of the injection force immediately after the filling process is lowered, the influence of the above-mentioned inertial energy cannot be eliminated. It had some serious drawbacks.

Originally, it is desirable to directly control the compression process as well, but in order to control the injection speed or injection force with good repeatability for each formation cycle, it is necessary to control the influence of the inertial energy mentioned above. It is effective to reduce the injection speed until it becomes negligible and then shift to injection force control, which allows stable molding, and also makes it easier to set molding conditions and rationalize the work.

This invention has been developed in view of the above, and its purpose is to provide an improved control method for an electric molding machine and to directly control the speed or force of all sections of the injection process. The object of the present invention is to provide a new injection process control method that can

”-One feature of this invention for the purpose of writing is that: 1.
During H, the rotation speed value and torque value of the drive source are set, and the speed is controlled by closed loop control so that the rotation speed of the drive source matches the injection speed, and the speed is adjusted at the filling completion point. When switching to a preset zero or injection force control, the inertial energy of the injection screw, etc. is almost negligible. After the injection speed has almost reached the set value, change the settings of the torque value and rotational speed value of the driving source to the values set in advance, and then change the injection speed from the speed control f wholesaler to the injection force. The injection process is controlled by a method for controlling the injection process.

Another feature of the present invention is that during the filling process, the rotational speed and torque values of the drive source are set, and the speed is controlled by closed loop control so that the rotational speed of the drive source matches the injection speed. At the filling completion point, the speed setting value is changed to a preset zero or to a value so low that the inertial energy of the injection screw, etc. can be almost ignored when switching to injection force control, and the deceleration section is used to decelerate in a closed loop. The injection process control method includes changing the rate of decrease in the injection speed in the deceleration section by changing the setting of the torque value of the drive source in the deceleration section after the completion point of the filling process.

Hereinafter, the present invention will be described in detail using illustrated examples and supplementary explanations of conventional examples.

FIG. 1 schematically shows, as an example, the main structure of an injection mechanism of an electric injection molding machine using an electric servo motor as a drive source.

The injection mechanism 1 includes an injection screw 2 and a hopper 4.
The housing 5 has an injection heating cylinder 6 and a housing 5 which also serves to hold the injection heating cylinder 6. Inside the housing 5,
A rotating shaft 16 having a threaded shaft 17 is mounted on a 4jl frame, and a movable member 18 is screwed onto the threaded shaft 17. Further, at the rear end of the screw 2, there is an extension shaft 15 integrally connected to the screw 2, the tip of which is supported by the movable member 18. In addition, the rotation axis 16 and extension'! Qll 15 is extended with gear 19 for screw advancement in a position where they do not interfere with each other! PlI
Freely movable in 11 directions via 115 splines
It has a gear 14 for rotating the screw which is attached at the end of the rotation 11qil 16.
There are several back pressure control devices 22 that control the hysteresis pressure fixed to the inner device.

A transmission shaft 21 parallel to the rotation shaft 16 and the extension shaft 15 is provided in the lower part of the housing 5 and extends through the housing 5 . Power can also be transmitted to the mold clamping mechanism via the transmission shaft 21 and a clutch mechanism (not shown).

Transmission gears 12.13 meshing with the gears 14.19 are rotatably connected to the transmission shaft 21, and the transmission gears 12.13 and 12.13 mesh with the gears 14.19, respectively.
This is provided so that it can be connected to or released from 11I21. The electromagnetic clutch 11 is energized during the injection process, and the electromagnetic clutch 20 is energized during the needle wheel process.

Furthermore, the shaft portion of the transmission shaft 21 projecting outward from the housing wall 5a is connected to an electric servo motor 9 fixed to the housing wall 5a, and the servo motor 9 is equipped with a tachometer generator 10. 6 is an injection switching position detector, 7 is a screw rotation speed slowdown position detector, 8 is a metering limit position detector, and 7'L is composed of a limit switch, a proximity switch, etc. Note that 26 is a machine stand.

FIG. 2 shows an example of the control device, in which the central control device 24
and the servo motor side leg amplifier 25 connected to the servo motor 9 and tachometer generator 10, the speed setting devices v1 to v6 and the torque setting device (maximum current value setting device)
F1 to F4 signal switch 26.27 and servo motor switch 9
The normal rotation/reverse rotation command circuit 28 is connected to the normal rotation/reverse rotation command circuit 28. The servo motor 9 in this example is a DC servo motor.

The servo motor control amplifier 25 has a function of controlling forward/reverse rotation, rotation speed, current (torque), etc. of the servo motor 9 according to commands from the central control device 24, and feeds back signals from the tachometer generator 1°. ,
The closed loop 1frlJ (71+) of the number of revolutions (speed) is performed.In addition, the central control +i11+ device 24 is a machine,
Has the function of controlling Makoto, Sufu IJ Yu rotation (H amount)
, back pressure, etc. (not shown), and the concentration side (It device 24 includes the above-mentioned position detectors 6 to 8, time setters T1 and T2, an electromagnetic clutch 11 for injection, and an electromagnetic clutch 20 for screw rotation). etc. are connected.

Next, a conventional injection control method will be explained.

FIG. 6 is an explanatory diagram of an example of a conventional injection control method, showing the rotational speed # of the servo motor 9 in the injection process (C,
In the control relationship diagram of injection speed) and torque, set value V+,
Fi (i=112.3), actual values Va and Fa are vertically Ii
+1 represents the screw position and time on the horizontal axis.

Due to the characteristics of a DC servo motor, current and torque are in a proportional relationship. Based on the command from the central control device 24, as shown in the figure, the speed setting value V1 is set by the speed setting device 1, and the torque setting value (current limit setting value) F+ to F3 is set by each of the torque setting devices F1 to FB. be done. In response to the input, the servo motor 9 is accelerated between a and b, as shown by the execution value Va, and rotates almost linearly at increased speed up to the set value V1 of vl. At this time, in order to accelerate the servo motor 9, a starting current is set using the setting device P'1 ic J:F1.
However, after point b when the execution speed reaches vl, the large torque is no longer needed, so the current value decreases.
1 meter As a result of closed loop control of the speed of the feedback signal of the generator 10 by the servo amplifier 25, the speed execution value Va between b and c becomes equal to vl. The amount of resin filled into the mold increases ((Accordingly, the effective current value (torque) increases again, and when the screw reaches the operating position of the injection switching position detector B, which is the filling completion point, the signal The central control device 24 operates, and the signal switch 27 switches the torque setting device F2.
is selected, the current value drops instantaneously to F2, and control shifts from speed control area I to force control area ■. On the other hand, the effective injection speed Va is driven by the inertial energy of the screw, etc. at the 0 point and the motor rotation torque value, because the current value (drive source) / torque value) is F2, even though the speed setting value is Vl. The speed decreases depending on the relationship between the force on the side and the load on the resin side, and the speed becomes almost 0 at point d, where the forces are balanced. Interval c, -d
The resin is compressed between the two.

On the other hand, when the injection switching position detector 6 is activated, the time setting device'
■゛1 is activated. At the 0 point at which the time setter 'j1' times out, it switches to the torque setter F6.

In this way, the pressure holding process after the compression process is executed, and the injection process is completed by a command from the central control device 24. As mentioned above, even if the servo motor is operated in the torque control state I measurement, the injection force that actually acts on the resin is the set F2 due to the inertial energy of the screw etc. held at the 0 point. It becomes excessive. In other words, this is an unstable and transient control section in which the execution value is determined by the relationship between the load and the set value.

Next, the present invention will be explained using examples shown in FIGS. 1, 2, and 4.

FIG. 4 is an explanatory diagram of an example of the injection control method of the present invention, and shows a control relation diagram between the rotational speed (injection speed) and torque (current value) of the servo motor 9 in the injection process, and shows the set value V
i (i = 1.2.3), Fi (i - 1, 2, 3) -
The execution values Va and Fa are plotted on the vertical axis, and the screw position and time are plotted on the horizontal axis. Based on the command from the central control device 240, as shown in the figure, the speed set values ■1 to V3 are set by the speed setters ■1 to ■6, and each torque setter F1 to
Torque setting value (current limit setting value) by F3
F5 is set. When the injection process is started, the electromagnetic clutch 11 is energized based on the command from the central control device 24, and the Surf J5 motor 9 generates g as shown in the execution value Va.
It is accelerated between -h and rotates to the setting value ■1 of setting 29V1. At this time, the starting current for accelerating the servo motor 9 is set and the current is generated up to the Pa1 value, but after the 11th point, the large torque is no longer needed, so the current value decreases.
As a result of closed loop control of the speed by the servo amplifier 25 based on the foot check signal of the tachometer generator 100, the speed execution value Va between 11-4 coincides with Vl. As the amount of resin filled in the mold increases, the effective current value (torque) increases again.

When the injection screw reaches the activated layer of the injection switching position detector B, which is the filling completion point, the central control device i is activated by the signal.
#24 is activated, and the speed setter v2 is selected by the signal switch 26, and its set value v2 is set to 0 or 1 to a value so low that the inertial energy of the injection screw, etc. can be almost ignored when switching to force control. Therefore, the area between I and No becomes a deceleration region, and the speed used for the braking action of the servo motor decreases almost linearly at the value of Since the value has been changed to 0 or a small value, a negative current flows through the motor 12 up to the set value F1 of the current setting device (torque setting device) Fl by closed loop control of the speed, as shown in the figure, and regenerative braking is applied to the motor. This is because it occurs.

On the other hand, the time setters T+ and T2 operate from the filling completion point I. The time setter T1 in this example is used to set the completion point of the deceleration section between 1 and 3, and is usually used as a substitute for confirming that the speed IW has reached 2. . This is done in time using a time setting device that can be set in units of seconds or less. The reason for this is that the period between 1 and 3 is a deceleration section by closed loop control, so the reproducibility of the operation is good, so the time is not a problem, and the operability is good.
This is due to the fact that it is an inexpensive device.

Note that the detection of the j point may be performed by detecting the speed depending on the case, or by using a screw position detector, a screw movement amount detector, or a detection device for detecting the resin pressure within the entire mold.

When the time t1 set by the time setting device 'F1 has elapsed, the time-up signal causes the control device 24 to
is activated, and the speed setter V3 and current setter F2 are selected at point j. After the resin is compressed between 1 and 3, the injection force becomes F2 at 3 points ((switching from speed control area 2 to force control (injection force control) area IV f).The speed setting value v3 is set. It is used to speed up the response of current (torque) by setting a larger value than v2.Time setting device T2
When the set time t2 has elapsed, the current setting device F6 is selected, and the injection force becomes the set value of 1, and the pressure holding process is continued.

By the injection process end command from the central control device 24,
The motor stops operating, the electromagnetic clutch 11 is released, and the injection process is completed. The electromagnetic clutch 2o is excited by the command Q of the central control device 24, and the back pressure: fjlJ control device 2
2 is energized, the motor starts, the screw starts rotating at a preset speed, and the weighing process begins.
The screw moves backward as the resin is transferred, and when the screw rotation speed slowdown position detector 7 is activated, the speed is changed to a preset low speed, and after reaching the low speed rotation, the screw limit position indicator 8 is activated. The signal causes the motor to stop operating, and then the electromagnetic clutch 20 is released to complete the metering process. The backpressure control device 22 is appropriately released by command of the control device slave 24. The screw rotation speed is controlled in a closed loop similar to the injection speed (figures such as operation diagrams are omitted).

As explained above, the injection screw is decelerated by closed-loop control of the speed using the braking action of the motor during the period 1-'', so the reproducibility is good and the deceleration can be achieved in a short time. The screw speeds at the three points that switch to force (injection force) control are very slow, and since the switch is made to force control from a state where there is almost no inertial energy, the set value of torque (current) and the actual injection output are It's almost a match. As is clear from the above explanation, the current setting device F4 is set so that the current setting value between l-1 can be changed, and the setting value is changed by selectively controlling and using the central controller 24. If F4 is increased, the braking force of the motor will be increased, and if F4 is decreased, the braking force will be decreased, so it is also possible to change the speed reduction rate in the deceleration section of 'JI: fJ.

Changing the speed reduction rate can be expected to have an effect on molding by changing the compression speed of the resin. For example, in molded products where residual stress is a problem when molding various lenses, the compression speed can be slowed down. As a result, overfilling can be prevented and the reproducibility is good due to the control characteristics, making it even more effective for stable molding of good products.

In this example, the filling process completion point is determined by the screw position, but when the entire resin pressure in the mold reaches a preset pressure, or when the time set by the timer from the injection start point etc. has elapsed. The current value of the servo motor may reach a predetermined value.

Further, depending on the molded product, more effects can be expected by combined use of program control of the injection speed in which various injection speeds are programmed during the filling process.

This invention id As mentioned above, the speed control area ■ is performed with the closed loop side leg (C, and d: deceleration 1-gin is provided immediately before switching from the speed fljlJ 1jll to the force control area ■.
A state where there is almost no influence of inertia force (C force)
Injection force'): li! Since it is possible to switch to region 1 (It4), it is possible to eliminate the influence of inertial energy peculiar to hydraulic molding such as drive gears, which is a drawback of electric molding machines.

Furthermore, the following effects are also achieved.

(1) Speed (-) Since the speed is controlled in a closed loop, it has excellent reproducibility and stability, allowing stable molding.

'2) The force, velocity, or force during the entire injection process.
Since ljlJ control is performed and there is no transient control section due to load balance as in conventional methods, stable molding can be achieved unlike in the past.

(3) The feature of (2) is that it can be easily controlled by an electric motor-driven machine using a servo motor, and is extremely difficult to control with a hydraulic machine.

Also, the injection capacity is 10. Small molding machines of F or less can be implemented particularly inexpensively.

(4) Since the speed control area and the force control area are clearly separated and controlled, operability is improved and molding work is streamlined.

(5) 1 with almost no influence of inertial energy
Since llJ can be controlled, it becomes easy to produce molded products without overfilling.

(6) The speed reduction rate in the deceleration section can be changed easily and inexpensively.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of an electric molding machine that can implement the injection process control method according to the present invention, FIG. 2 is a block diagram of a control device for the electric molding machine, and FIG. 6 is a conventional method ( FIG. 4 is a diagram showing the control relationship between the speed and torque of the drive source in the injection process control force method of the present invention.-1. Injection mechanism 2.・Injection screw 6・
Injection switching position detector 9... Servo motor 10... Tachometer generator 24... Central control device 25, Servo motor control amplifiers 26, 27... Signal switch ε3, Reverse command circuit

Claims (2)

[Claims] (1) In the injection process of an electric molding machine that uses an electric servo motor as the drive source of the injection mechanism, during the filling process, the rotation speed value and torque value of the drive source are set, and the rotation speed of the drive source is The speed is controlled by closed-loop control to maintain the injection speed value, and at the point when filling is completed, the speed setting value is set in advance or the inertia of the injection screw is changed to the injection force control. The energy is changed to a low value that is almost negligible, a deceleration section is created in which the deceleration is performed in a closed loop, and after the injection speed has almost reached the set value, the torque value and rotation speed value of the driving source are set beforehand. Change the injection force from speed control to the set value? i! II
A method for controlling an injection process, the special feature of which is to control the injection process. (2) In the injection process of an electric molding machine that uses an electric servo motor as the drive source of the injection mechanism, during the filling process, the rotation speed value and torque value of the drive source are set, and the rotation speed of the drive source is The speed is controlled by closed-loop control so that the injection speed value is the same, and the speed setting value is set in advance at the filling completion point.When switching to injection force control, the injection screw etc. By changing the inertia energy to a low value that is almost negligible, providing a deceleration section in which deceleration is performed in a closed loop, and changing the setting of the torque value of one driving source in the deceleration section after the filling process completion point, deceleration 14 is achieved. Injection process of an electric molding machine characterized by changing the rate of decrease in injection speed between 1 and 1
Method.