JPH0253220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an injection control device for an injection molding machine that drives an injection mechanism by an electric motor.

[Prior Art] This type of injection control device is disclosed in Japanese Patent Application Laid-open No. 174625/1983. This conventional device will be explained with reference to FIG. 4. Reference numeral 1 denotes an injection device, in which an injection screw 4 is housed inside a heating cylinder 3 whose nozzle is connected to a mold 2 so that it can move forward and backward. A screw rotating electric motor is connected to the rear of the injection screw 4 via a gear mechanism 5.

Further, the rear end of the injection screw 4 is directly connected to a transmission mechanism 7 that drives the injection screw forward and backward through a rotating means and a screw member, and an injection electric motor 8 is connected to the transmission mechanism 7 through a coupling 9. It is installed.

The driving force of the electric motor 8 is transmitted to the injection screw 4 via the transmission mechanism 7, and by driving and controlling the electric motor 8, the injection speed, injection pressure (holding pressure), or back pressure can be controlled.

In order to measure the injection pressure (injection force) by detecting the amount of deformation of the portion of the injection screw 4 that receives the forward force or the reaction force due to the load, a pressure sensor 10 consisting of a strain gauge is connected to the receiving member 11 of the transmission mechanism 7. is attached to.

A tachometer generator 12 as a speed detector and a rotation angle detector 13 for detecting the position of the injection screw 4 by detecting the rotational position of the electric motor 8 are directly connected to the electric motor 8.

In the injection device 1, the central controller 31, which controls the sequence control of the injection control device, issues a power converter operation command signal to put the power converter 26 into operation, and the power converter 26 is turned on to start injection. do.

The speed command signal e _v from the speed command circuit 15 is passed through the command switching means 19 by the changeover switch, and is converted into the speed command signal e _v ′ (e _v = e _v ′), and the speed detected by the tachometer generator 12. The signal is converted into an injection speed detection signal e _o by the conversion circuit 27 and supplied to the addition point 20 . As a result, the difference signal e _v ′−e _o =Δe _o is output from the summing point 20, and the difference signal Δe _o is amplified by the speed control amplifier 21 and sent to the summing point 22 as the speed control signal Δe _op . Supplied.

Further, the motor current that determines the output torque of the motor 8 is detected by the current detector 24, and the current detection signal is converted by the conversion circuit 25 into a current detection signal e _i consisting of a voltage signal, and is supplied to the addition point 22. be done.

As a result, the difference signal Δe _op −e _i =Δe _i is output from the summing point 22, and the difference signal Δe _i is amplified to Δe _ip by the current control amplifier 23 and then supplied to the power converter 26. be done. The above power converter 21
is constituted by an ignition control circuit using a thyristor or a pulse width control circuit using a transistor, and based on the signal Δe _ip , the motor 8
The motor 8 is configured to be driven by passing a predetermined current through the motor 8.

As described above, injection speed control is performed by feedback control of rotational speed. Injection filling is continued by injection speed control, and the rotation angle detector 13
The signal is converted into an injection screw position signal by the conversion circuit 28, and based on this position signal and a command from the central controller 31, a screw position setting value is set for setting the injection screw position for switching from injection speed control to injection pressure control. The set value signal from the signal generator 30 is compared by the comparator 29, and if the signals match, a switching command is issued from the central controller 31 to the command switching means 1.
9, and the injection speed control shifts to the injection pressure control.

From the pressure command circuit 16 to the central controller 3
1 command, the injection pressure command signal e _pi has an addition point of 1
7. Further, the injection pressure detection value of the pressure sensor 10 is converted by the conversion circuit 14 into an injection pressure signal e _p consisting of a voltage signal, and is supplied to the addition point 17 .

As a result, the summing point 17 outputs a difference signal e _pi −e _p =Δe _p , and this difference signal is transmitted to the pressure control amplifier 1
8, the injection pressure control signal Δe _pp is amplified, and the signal is passed through the command switching means 19 to the speed command signal.
e _v ′ (Δe _pp = e _v ′).

In the same way as described above, the motor 8 is driven and controlled by the speed command signal e _v ', and the injection pressure is controlled by feedback control of the rotational speed so that the injection pressure matches the injection pressure command value.

When the set injection time has elapsed, the central controller 31 issues an injection end signal, and the pressure command circuit 16 issues a back pressure command signal.
e _pi (for convenience of explanation, the command value is different, but it is called with the same symbol as the pressure command signal explained above) is issued.
The electric motor 8 is driven and controlled by the back pressure command signal e _pi in the same manner as during the injection pressure control, and the injection control process shifts to the so-called back pressure control process.

On the other hand, after a predetermined period of time has elapsed since the end of the injection control process, the central controller 31 gives a screw rotation command to the screw rotation electric motor drive device 32. The screw rotation electric motor 6 starts rotating, the injection screw 4 is rotated, and the generally-called metering is performed by the above-mentioned back pressure control. Injection screw position signal and screw position set value signal generator 3
The comparator 29 compares the metering limit setting position signal emitted from 0, and when the injection screw position reaches the set metering setting position, the central controller 31, the power converter 26, the screw rotation electric motor drive device 32, The command to the command switching means 19 is cut off, the metering process is completed, and the system waits for the next injection process.

As mentioned above, the prior art consists of controlling the injection process divided into two processes: the injection signal control process and the injection pressure control process, and the motor drive control controls the injection speed by feedbacking the speed detection signal from the speed detector. When controlling the injection pressure, the injection pressure control signal Δe is obtained by operationally amplifying the difference signal Δe _p between the injection pressure detection signal e _p obtained by detecting the injection pressure with a pressure sensor and the injection pressure command signal e _pi . The configuration is such that the motor is driven and controlled using _pp as a speed command signal e _v ', and injection pressure is controlled.

[Problems to be Solved by the Invention] In such a conventional injection control device, the following problems occurred during pressure control.

To explain this with reference to FIGS. 5B and 5C, which are examples of characteristic curve diagrams showing the relationship between pressure and speed settings and measured values in the injection process, the speed command signal e _v is
e _A value, injection pressure command signal e _pi is set to e _c value, and the measured pressure when switching to injection pressure control is
e _B , and e _B < e _C.

When the amplification degree of the pressure control amplifier 35 is α, the speed command signal e _v ′ (e _v ′=
For Δe _pp ), the relationship e _v ′=(e _C −e _B )×α holds true.

The actual injection speed when switching to pressure control is e _A , which is equal to the speed command signal. If e _A < (e _C − e _B ) × α and the difference is large, the speed command signal value will change from e _A to (e _C
-e _B )×α, and a phenomenon occurs in which the injection speed is instantaneously amplified as shown in FIG. 5B. For the set injection pressure command signal e _C value,
The actual value becomes a constant value e _C after exceeding β. This causes the resin pressure within the mold to rise rapidly and more than necessary, resulting in a molded product with so-called overpacking and internal distortion. Or, in extreme cases, flashing occurs in the molded product.

On the other hand, if the conditions are such that e _A > (e _C - e _B ) x α, the speed command signal at the time of switching to injection pressure control becomes smaller in steps, so that If the injection speed slows down too much, an undershoot occurs in which the actual pressure drops once and then rises.
If the pressure drop is large, contrary to the above phenomenon, the mold will be insufficiently filled with resin, resulting in sink marks in the molded product.

In this way, the pressure characteristics during injection pressure control include the actual injection speed when switching to injection pressure control, the measured pressure when switching to injection control, the injection pressure command signal (pressure setting), and the amplification of the injection pressure control amplifier 18. Since the molding conditions are mutually influenced by the degree α value, the molding conditions can vary widely as shown in the examples shown in FIG. 5B and C, and in either case, it is impossible to produce a good product. Therefore, in order to determine the injection speed, switching point to injection pressure control, injection pressure, and other set values for molding a good product, a large number of trial shots were required, resulting in poor operability.

[Means for Solving the Problems] The present invention was conceived in view of the above circumstances, and its purpose is to control each of injection speed and injection pressure in an injection control device using an electric motor as a drive source. High accuracy is achieved by controlling the rotational speed using a speed detector and pressure sensor (a sensor for detecting injection force or a sensor for detecting resin pressure in a heated cylinder), and molding conditions (setting values) can be easily determined. An object of the present invention is to provide an injection control device.

The features of the present invention according to the above object include an adder that compares and calculates a speed command signal from a speed command circuit and a speed detection signal from a speed detector, and a speed control signal that amplifies the difference signal of the adder and uses it as a speed control signal. A control amplifier, an injection screw or plunger that is driven by a motor that performs speed control based on a speed command signal and can move forward and backward through a rotating member and a screw member, an injection pressure detector, and an injection pressure detector that amplifies the detected value of the injection pressure. an amplifier that outputs an injection pressure detection signal as an injection pressure detection signal; an adder that compares and calculates the injection pressure command signal and the injection pressure detection signal from the injection command circuit; and a pressure signal that amplifies the difference signal from the adder and outputs it as an injection pressure control signal. When switching between control amplifier, injection speed control and injection pressure control,
In an injection control device comprising a command switching means for inputting an injection pressure control signal in place of the speed command signal, the command switching means performs injection pressure control using the injection pressure control signal as a speed command signal, the injection control device comprising: the pressure control amplifier; A speed command signal control circuit for limiting the magnitude of the speed command signal during injection pressure control is provided between the command switching means.

[Function] In the present invention, during injection pressure control, the injection pressure is controlled by controlling the rotational speed under the action of the speed command signal limiting circuit that limits the magnitude of the speed command signal. Limits the upper limit value of the speed command signal during control in a transient state, such as when switching to control, where the difference between the injection pressure command signal and the injection pressure detection signal is large, and the injection pressure command signal is larger than the injection pressure detection signal. and can be controlled to prevent overspeeding.
It is possible to eliminate the occurrence of injection pressure overshoot that occurs in conventional devices, and the amplification degree of the injection pressure control amplifier can be made higher than that in conventional devices, so the injection pressure command signal when switching to injection pressure control can be reduced. When the injection pressure detection signal is small, the magnitude of the speed command signal is larger than that of the conventional device, and the degree of undershoot can be reduced.
Furthermore, since the amplification degree of the pressure control amplifier is high, even when there is a slight difference between the injection pressure set value and the measured value, the speed command signal can be made larger than before, and injection pressure control can be performed with high precision.

[Example] The present invention will be described below based on FIGS. 1 to 3.

In addition, in the figure, the same parts as those of the above-mentioned conventional device are given the same reference numerals, and the description thereof will be omitted.

The speed command circuit 15 receives a signal from the central controller 31 to set a speed command signal during injection speed control, a speed command signal limit value during injection pressure control, or a speed command signal limit value during back pressure control. , free speed reference signal as needed
This is a signal generator that can generate e _v . In this embodiment, during the injection control process, the speed command circuit 15 is controlled so that the command signal e _v continues to be output without changing its magnitude. Further, during back pressure control, a speed command signal e _v is generated which is set in advance so that a predetermined injection screw retraction speed value can be obtained.

A characteristic feature of the present invention is that a speed command signal limiting circuit 33 is used to limit the magnitude of the injection pressure control signal as a speed command signal during injection pressure control.
This is provided between the pressure control amplifier 18 and the command switching means 19.

The speed command signal limiting circuit 33 is composed of a combination of operational amplifiers, as shown in _FIG . Since the speed command signal e _v is input, the injection pressure control signal Δe _PO
It is possible to output a signal Δe _PO ' with a limited upper or lower limit value.

FIG. 3 shows that the input signal Δe _PO of the speed command signal limiting circuit 33 is changed to the output signal Δe _PO ′ by the speed command signal e _v .
FIG. As shown in the figure, the output signal Δe _PO ′ depends on the magnitude of the injection pressure control signal Δe _PO.When Δe _PO ≦e _v ″, Δe _PO ′=e _v ″ When e _v ″<Δe _PO <e _v When Δe _PO ′=Δe _PO e _v ≦Δe _PO , Δe _PO ′=e _v , and the upper limit is limited to the e _v value, and the lower limit is set by the operational amplifier 34 in the speed command signal limiting circuit 33.
The value e _v ″ is reduced in magnitude and has a different polarity than the speed command signal e _v .

In this way, the injection pressure control signal Δe _PO during injection pressure control is limited by the speed command signal e _v by the speed command signal limiting circuit 33, so when switching to injection pressure control, the injection pressure command signal The speed command signal is replaced by the injection pressure control signal, no matter how much greater it is than the pressure detection signal.
e _v ′ is the speed command signal when switching to injection pressure control
The upper limit is limited to e _v .

Therefore, when the injection pressure command signal is considerably larger than the injection pressure detection signal, the pressure response characteristics to the load are improved as shown in FIG. 5A compared to FIG. 5B. That is, the actual pressure increases and reaches the pressure command value without the occurrence of pressure overshoot.

In addition, since the upper limit of the speed command signal e _v ′, which replaces the injection pressure control signal during injection pressure control, is limited, the occurrence of pressure overshoot can be suppressed, and therefore the pressure control amplifier 18 The degree of amplification can be increased. As a result, even when the difference between the injection pressure command value and the injection pressure detection signal is small, the speed command signal is lower than that of the conventional device.
Since the magnitude of e _v ' becomes large, the pressure response characteristics are improved as shown in FIG. 5A compared to FIG. 5C, and the magnitude of pressure undershoot is reduced compared to the conventional device be able to.

Furthermore, when switching from injection speed control to injection pressure control, if the injection pressure command signal is set to be smaller than the injection pressure detection signal to the injection pressure control, the polarity of the speed command signal e _v ′ will change in the above case. This is temporarily reversed, and a force is generated in the electric motor in the opposite direction to that during forward injection, and the injection pressure detection signal decreases to become the injection pressure command signal.

Pressurized resin acts on the front part of the injection screw as a screw retraction force, which is assisted by the driving force of the motor, so when lowering the injection pressure detection signal (back pressure) to the back pressure command signal, the above The driving force (reverse rotational force) of the motor may be smaller than that in the case where the back pressure is increased.

Therefore, when the polarity of the speed command signal e _v ′ is negative, it is preferable to limit the lower limit value using a signal e _v ″ whose absolute value is smaller than that of the speed command signal limiting circuit e _v . Pressure undershoot can be reduced by the opposite effect to the above case.

In this example, the speed command signal limit value during injection pressure control is controlled to be the same as the speed command signal value during injection speed control. In special cases where you want to increase the packing speed, you can selectively activate the setting device of the speed command signal limiter circuit during injection pressure control to make the speed command limit value as much larger than the injection speed setting value. good. Further, as means for detecting the injection pressure, a resin pressure sensor may be attached to the heating cylinder or the nozzle, and a detection signal from a rotation angle detector may be used as the speed detection signal.

In addition, switching from injection speed control to injection pressure control is performed by detecting the injection screw position, but the mold cavity resin pressure value, injection pressure value,
The filling amount of the resin may be detected by detecting the current value of the electric motor or the like.

If necessary depending on the molded product, one or both of the injection speed and speed pressure may be controlled in multiple stages depending on the injection screw position or time using a timer.

It goes without saying that the present invention can also be implemented in a so-called pre-plastic injection device or a plunger-type injection device equipped with a pre-plasticizing device.

[Effects of the Invention] As explained above, the present invention is configured to limit the magnitude of the speed command signal replaced by the injection pressure control signal when controlling the injection pressure using the injection pressure sensor. Therefore, the speed command signal can be increased by increasing the amplification of the pressure control amplifier without overshooting of the injection pressure, and injection pressure control that is less likely to cause undershoot of the injection pressure is possible, improving operability. It is possible to perform highly accurate injection control.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing a specific configuration example of the speed command signal limiting circuit in Fig. 1, and Fig. 3 is an example of characteristics of the speed command signal limiting circuit. Fig. 4 is a block diagram showing an example of a conventional injection control device, Fig. 5 is a characteristic curve diagram showing a comparison of examples of the relationship between set values and measured values of pressure and speed in the injection process. In the curve diagram, A shows the case of the present invention, and B and C show the case of the conventional example. 4... Injection screw, 6... Electric motor for rotating the screw, 8... Electric motor, 10... Pressure sensor, 12
... Tachometer generator, 13 ... Rotation angle detector, 15 ... Speed command circuit, 16 ... Pressure command circuit, 18 ... Pressure control amplifier, 19 ... Command switching means, 21 ... Speed control amplifier, 23...
Current control amplifier, 24...Current detector, 26...
Power converter, 29... Comparator, 30... Screw position set value signal generator, 31... Central controller, 32... Screw rotation motor drive device, 33... Speed command signal limiting circuit.

Claims (1)

[Claims] 1. An adder 20 that compares and calculates the speed command signal from the speed command circuit 15 and the speed detection signal from the speed detector 12, and amplifies the difference signal from the adder 20 to generate a speed control signal. a speed control amplifier 21 which controls the speed according to a speed command signal; an injection screw or plunger which is driven forward and backward by a rotating member and a screw member and whose driving source is an electric motor 8 that performs speed control using a speed command signal;
An injection pressure detector 10, an amplifier 14 that amplifies the detected injection pressure value to produce an injection pressure detection signal, an adder 17 that compares and calculates the injection pressure command signal from the injection command circuit 16 and the injection pressure detection signal, and the addition a pressure control amplifier 18 that amplifies the difference signal from the device 17 to produce an injection pressure control signal; and a command switching means that inputs the injection pressure control signal in place of the speed command signal when switching between injection speed control and injection pressure control. 19, in which the command switching means 19 performs injection pressure control using an injection pressure control signal as a speed command signal, between the pressure control amplifier 18 and the command switching means 19, the speed An injection control device for an injection molding machine, comprising a speed command signal control circuit 33 that limits the magnitude of a command signal.