JPH02127021A - Controlling device of back pressure of injecting apparatus - Google Patents

Abstract

PURPOSE:To stabilize metering by providing a screw backward motion-detecting circuit for detecting the backward motion of a screw/of a motor and a current instruction signal limiting circuit for turning ON and OFF a current giving an instruction according to which the screw is made to operate in the direction of a forward motion. CONSTITUTION:A back pressure detection signal outputted from a load cell 7 is converted into a voltage signal ep and supplied, together with a back pressure setting signal epi, to an addition point 21a of an amplifier 21. A difference voltage between the signals ep and epi is amplified and then inputted as a current instruction signal epo to a current instruction signal circuit 23. A speed signal of a tachometer generator for detecting the number of rotations of a motor 14 for injection is inputted to a screw backward motion detecting circuit 24. The motion in the backward direction is discriminated from the polarity of the input signal in the screw backward motion detecting circuit 24, the current instruction signal epo is given limitation by an instruction based on the discrimination by the detecting circuit 24, and a signal epo' is outputted. Only when the polarity is negative, the motor 14 is driven in the direction of a forward motion of a screw.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a back pressure control device for an injection device using an electric motor as a drive source.

[Prior art] An in-line screw injection device using an electric motor as a drive source is equipped with an injection electric motor and a transmission mechanism that converts the rotational motion of the electric motor into forward and backward movement of the screw. The device for controlling the back pressure during the material metering process controls the output torque of the injection motor.

The device disclosed in Japanese Unexamined Patent Publication No. 61-31221 calculates and amplifies the difference signal between a back pressure measurement signal and a back pressure command signal obtained by measuring the molten material pressure or screw reaction force as screw back pressure. This is a back pressure control device using an electric motor that drives the electric motor based on the signal obtained by the above control so that the back pressure matches the set value by υ11[l.

On the other hand, the braking function of the electric motor is used to provide screw back pressure, and the output torque value of the electric motor (current value of the electric motor)
There is also a back pressure υjilt device that performs this by controlling the υjilt constant.

[Problems to be Solved by the Invention] In the case of the conventional device described in Japanese Unexamined Patent Publication No. 61-31221, which uses the rotational force of the electric motor, it is possible to reduce back pressure due to resistance generated by the frictional force of the electric mechanism. However, if the back pressure is lower than the set back pressure, output torque is generated in the motor in the direction that increases the back pressure, and the screw rotates as at the start of metering. When the number does not rise to a predetermined value, sufficient material is not accumulated in the heating cylinder, and no preferential screw force is generated, the screw is forcibly moved forward. Also, in the case of a control device that uses the braking action of the electric motor by keeping the output torque value of the electric motor constant (current value of the electric motor), the screw retraction force accompanying the screw rotation is 5oI11 as described above. When the torque is smaller than the output torque, the screw moves forward until the load and output are balanced.

If the screw is forced to move forward in this way, it will apply back pressure to the screw regardless of the material accumulation rate as the screw rotates, and not only will stable metering be impossible, but the screw will not advance to its forward limit. There was a risk of damage to the screws, etc.

The purpose of the present invention is to provide back pressure i using an electric motor that can control the back pressure during metering without the screw moving forward.
II control device.

[Means for Solving the Problems] The present invention according to the above object includes: a transmission mechanism that converts the forward and backward movement of the screw into a rotational movement; an electric motor that controls the forward and backward movement of the screw via the transmission mechanism; A back pressure control device for an injection device that controls back pressure during metering by controlling the electric current of the electric motor, the back pressure control device comprising: a screw backward movement detection circuit that detects backward movement of the screw; The above-mentioned conventional problem is solved by providing a current command signal limiting circuit that turns off or turns on the current that acts on the screw of the electric motor in the forward direction in response to a command.

[Function] When the screw in the metering process is rotated by the screw rotation electric motor, the material is sent to the front part of the screw by the lead of the screw and accumulated in the front part of the heating cylinder. It is so-called back pressure that applies a braking force to the screw in the direction of preventing movement, and control of back pressure is important for good plasticization of the material. When the electric motor and the motor control device apply a braking force in the backward direction to the screw, a current flows through the electric motor in the direction of moving the screw in the forward direction, and the output torque of the electric motor corresponds to the magnitude of the current command signal. The back pressure is controlled at a value that balances the loads on the screws, etc. For this reason, the conventional back pressure control device has a total of II? I! When no backward movement force is generated on the screw at the start, etc., the output torque of the electric motor for generating back pressure causes the screw to move forward.

In the back pressure v control device of the present invention, the backward movement of the screw is detected by the screw backward movement detection circuit that detects the backward movement of the screw, and the detection signal is used to turn on the current that acts on the screw of the electric motor in the forward direction. Turn off the current command signal limit circuit (so that no limit is given)
,,Control the motor so that the current flows in accordance with the current command signal. When the screw is moving backwards, it is a good time to generate braking force, and the motor screw is in a state where it can flow a current that acts in the forward direction.

When the screw is not moving backwards, the current command signal limiting circuit is turned on, so even if a current command signal in the direction in which the screw moves forward is input, that signal is limited by the current command signal limiting circuit. Since it acts to prevent current from flowing, the screw is not moved forward by the electric motor. In other words, the backward movement of the screw is detected by the screw backward movement detection circuit and the current command limit circuit, and while the screw is moving backward, the 1111 machine can generate output torque in both the forward and reverse directions, and when the screw is not moving backward. Since the screw forward force is controlled so as not to be generated, the screw does not move forward during the metering process.

[Embodiment] Fig. 1 shows an example of an in-line injection device using an electric motor as a drive source, and the injection electric motor is also used for back pressure control.

The screw 1 inside the heating cylinder 2 of this injection device has a tie bar 3
．． It is connected to a rotating member 5 within a movable body 4 that is slidably supported by a rotary member 3 . The rotating member 5 is supported within the movable body with a thrust bearing 6, and a load cell 7 is interposed between the rear end and a receiving edge within the movable body as a sensor for detecting back pressure. Further, the rotating member 5 is connected to a rotary transmission shaft 11 that is rotatably inserted into a hollow screw shaft 10 that meshes with a screw cylinder 8 at the rear end of the movable body through a number of balls 9. When rotated by the screw rotating electric motor 13 via the gear 12, the screw rotates together with the screw 1.

In addition, the injection motor 14 allows the injection to be carried out via the transmission belt 15.
When the screw shaft 10 rotates, the screw cylinder 8 moves together with the movable body 4, and at the same time, the rotating body 5 also moves together with the screw 1.

FIG. 2 is a block diagram of the back pressure control device of the present invention in the injection device of FIG. 1.

The back pressure detection signal output from the load cell 7 is converted by the conversion circuit 20 into a back pressure detection signal e0 consisting of a voltage signal, and is supplied to the addition point 21a of the pressure control amplifier 21. Also, at the addition point 21a, a back pressure setting signal e p consisting of a voltage signal according to the back pressure setting value is sent from the back pressure setting device 22.
1 is supplied. The voltage difference between the signal e p H and the signal ep is the high current command signal @ amplified by the pressure control amplifier 21.
e po and is input to the current command signal limiting circuit 23. The speed signal of the tachometer generator for detecting the rotational speed (speed) of the injection motor 14 is sent to the screw backward movement detection circuit 2.
4 is entered.

The screw backward movement detection circuit 24 detects that the screw has moved in the backward direction by determining the polarity of the input signal, and issues a command to the current command signal limiting circuit 23.

The current command signal limiting circuit 23 limits the current command signal epo, which is an input signal, according to the command from the screw backward movement detection circuit 24, and outputs a signal e-.

When the polarity of O e - is negative, the injection motor 14 is driven in the direction of advancing the screw.

FIG. 3 shows an example of the current command signal v1 limiting circuit 23. When the screw backward movement detection circuit 24 does not detect the screw backward movement, the command of the analog switch 23a becomes [0g], and the analog switch CH23a is ON
bawl. When the polarity of the current command signal e is negative, a current flows from the ground point O which is at O potential through the diode 23b, and o=e - in e =:e. When the polarity of is positive, po
p.

Because of the diode 23b, the current Wi does not flow to the ground point, so it is output as e - e -.

po p.

Further, when the screw backward movement detection circuit 24 detects the screw backward movement, contrary to the above, the analog switch command is
H, the analog switch 23a turns OFF,
Since the diode 23b is disconnected from the ground point, the current command signal eo is generated. becomes e − regardless of polarity. Note 2
3c is a resistance.

O That is, when the screen 1 is not moving backward, the current command signal limiting circuit 23 outputs a current limiting signal e. is subject to restrictions, el. When the polarity is negative, the output signal @e
-=O.

O Command signal e - is the addition point 25 of the power 11 control amplifier 25
all: The current detected by the current detector 26 is inputted by the conversion circuit 27 together with the feedback type current signal e consisting of voltage, and the difference voltage is amplified by the power control amplifier 25 and becomes the signal @eio and the power A converter 28 is provided. The power converter 28 is configured with an ignition control circuit using a thyristor or a pulse wide control circuit using a transistor, and receives the input signal ei.
The injection motor 14 is configured to flow a current corresponding to o to the injection motor 14. The driving force of this injection motor 14 is transmitted to the screw 1 via the transmission mechanism shown in FIG. 1 and the load cell 7, and is fed back pressure! 1Ill is done.

As is clear from the above description, since the driving force of the electric motor in the forward direction of the screw is allowed and controlled only when the screw is moving backward, the injection electric motor 14 does not move the screw forward.

The screw backward movement detection circuit of the above embodiment is a device that compares the magnitude of the rotational speed detection signal of the electric motor using a comparator and detects the backward movement of the screw. The rotational position change detection circuit (description with figures is omitted) can also be used to detect backward movement of the screw.

Also, if the back pressure command signal e p (from the back pressure setting device) is made a negative signal and it is directly controlled as the current command signal e po without using the back pressure feedback circuit shown in Fig. 2, back pressure can also be controlled by the oven loop. It can also be done easily.

Furthermore, it goes without saying that the same method can be applied to a back pressure control device using a speed control device for an electric motor.

[Effects of the Invention] As described above, the present invention controls and measures the current of an electric motor.
In the back pressure control device of the injection device that controls the back pressure during
A screw backward detection circuit detects the backward movement of the screw, and a command from the screw backward detection circuit turns OFF or ON the current that acts on the screw of the electric motor in the forward direction.
Since a current command signal limiting circuit is provided, no material is accumulated during metering, and the screw is not forced to move forward by the electric motor even when no force is generated in the backward direction of the screw. Therefore, the following effects are achieved.

(1) At the start of measurement, the screw is advanced to its forward limit and there is no risk of damaging the screw, etc. In order to maintain good plasticization or increase measurement accuracy, etc.
When changing the screw rotation speed or back pressure in multiple stages, the force generated as the screw rotates in the backward direction of the screw varies greatly. At this time, there is no forced advance of the screw, so stable metering can be performed.

■ The rate of accumulation of material as the screw rotates varies greatly depending on the condition of the material, the temperature of the heating cylinder or the screw, etc. There is no increase in back pressure due to the forced advance of the screw by the electric motor, and a stable measurement ω can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic longitudinal sectional view of an in-line injection device using an electric motor as a drive source. FIG. 2 is a block diagram of the back pressure control device of the present invention. FIG. 3 is an explanatory diagram of a current command signal limiting circuit used in the back pressure control device of the present invention. 1... Screw 7...
・Load cell 14...Injection motor 2
0...Conversion circuit 21...Pressure control amplifier 22...Back pressure setting device 23...N flow command signal restriction circuit 24...
・Screw backward detection circuit 25... Power control amplifier 26... Current detector 27... Conversion circuit 28... Power converter

Claims (1)

[Claims] A transmission mechanism that converts the forward and backward movement of the screw into rotational movement, an electric motor that controls the forward and backward movement of the screw via the transmission mechanism, and a control device for the electric motor, and controls the electric current of the electric motor to control the measurement time. In the back pressure control device of the injection device, a screw backward movement detection circuit detects the backward movement of the screw, and a command from the screw backward movement detection circuit turns off or turns on the current that acts on the screw of the electric motor in the forward direction. 1. A back pressure control device for an injection device, characterized in that a current command signal limiting circuit is provided.