JPS62105007A - Screw position detecting device for injection machine - Google Patents

Abstract

PURPOSE:To perform stable detection with high precision by presetting the contents of a reversible counting means according to reference pulses from a rotary encoder so as to make the contents of the reversible counting means correspond to a screw position after the power source is turned on. CONSTITUTION:The rotating shaft 24 of a pinion 22 rotates corresponding to the movement extent of a screw which is moved back and forth by an injection cylinder 14. Then, the rotary encoder 26 is fitted on the rotating shaft 24 to output one reference pulse at a specific rotational position on every turn of the rotating shaft and also outputs one count pulse on every fine turn. The reversible counting means 20 counts up and down the count pulses according to the moving direction of a screw 10 and supplies its counted value as the movement position of the screw 10. A detecting means 28 detects the reference pulse being a movement range determined so that one reference pulse is outputted and when the reference pulse is outputted in this state, a preset means 32 presets a preset value corresponding to the position of the screw 10 to which the reference pulse is sent in the means 20.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a screw position detection device for an injection device, and particularly to a technique for improving the detection accuracy of screw position.

(Prior Art) In the injection device of an injection molding machine, a predetermined injection operation is generally performed by moving a screw in the injection cylinder forward and backward, but in order to perform a good injection operation, it is necessary to It is necessary to control forward and backward operations according to injection conditions. For this purpose, it is necessary to always know the moving position of the screw, that is, the screw position, which changes due to forward and backward operations. Therefore, the injection device of an injection molding machine is generally equipped with a screw position detection device that detects the screw position.

The screw position detection device for this injection device is generally a rotary encoder type screw position detection device that uses a rotary encoder to detect the amount of rotation of a rotating shaft that rotates in response to the amount of movement of the screw. A rotary encoder-type screw position detection device can be constructed at a lower cost than a device using a so-called absolute type rotary encoder, which outputs a signal representing the rotating position of the rotating shaft. Many use a so-called incremental rotary encoder that outputs one counting pulse for each minute rotation. A screw position in which an incremental rotary encoder is attached to the rotating shaft, and counting pulses from the incremental rotary encoder are reversibly counted according to the direction of movement of the screw using a reversible counting means, and the counted contents are given as the screw position. That is the detection device.

By the way, in a screw position detection device using such an incremental rotary encoder, the count content of the reversible counting means that gives the screw position represents the amount of relative displacement from a certain reference position, and is erased when the power is turned off. Therefore, it is necessary to make the counted contents correspond to the screw position after the power is turned on again. Therefore, in the past, when the screw came to a predetermined specific position, it was detected using a switch means such as a limit switch or a proximity switch, and a preset value corresponding to that specific position was presented to the reversible counting means. The counting content of the means is made to correspond to the screw position.

(Problem) However, in this way, conventional methods detect when the screw comes to a predetermined specific position using a switch means such as a limit switch or a proximity switch, and preset a preset value according to the detection result. The screw position detection device has a problem in that there are large errors due to the mechanical locking of the switch and 7-inch, and errors over time due to long-term use, and the screw position detection error caused by these errors is large.

(Solution Means) Here, the present invention has been made to solve such problems, and its gist is as follows:
(a) a rotating shaft that is rotated in accordance with the amount of movement of the screw that is moved forward and backward within the injection cylinder;
(b) A rotary device that is attached to the rotating shaft and outputs one reference pulse at a specific rotational position for each rotation of the rotating shaft, and also outputs one counting pulse for each minute rotation of the rotating shaft. an encoder; (c) reversible counting means for reversibly counting the counting pulses output from the rotary encoder according to the moving direction of the screw, and providing the counted contents as the moving position of the screw; a detection means for detecting that the screw is within a predetermined specific movement range of the screw, which is set so that only one reference pulse is output from the encoder; e) When the reference pulse is output from the rotary encoder in a state where the detection means detects that the screw is within the predetermined specific movement range, the reversible counting means The present invention further includes a preset means for presetting a preset value corresponding to the screw position at which the reference pulse is generated.

(Function/Effect) According to such a screw position detection device, an incremental rotary encoder can be used as a rotary encoder for screw position detection, so the device can be constructed at low cost and is economically advantageous. Moreover, after the power is turned on again, the precent value for making the count contents of the reversible counting means correspond to the screw position is outputted accurately at a specific screw position. Therefore, the count content of the reversible counting means always accurately matches the screw position, and the screw position can always be detected with high precision and stably over a long period of time.

Note that the reference pulse generation function described above is provided in a normal incremental rotary encoder, but in a conventional screw position detection device using an incremental rotary encoder, this reference pulse is used to detect the screw position. It was not used.

(Example) Hereinafter, in order to clarify the present invention more specifically,
One embodiment thereof will be described in detail based on the drawings.

In FIG. 1, 10 is a heating cylinder 12 of the injection device.
The screw is inserted into the interior and is moved forward and backward by the injection cylinder 14 and rotated by the servo motor 16, and its forward, backward, and rotational operations cause the front end of the heating cylinder 12 to move forward and backward. A predetermined injection material is injected from the nozzle 18 in the section.

Screw 10. A rack 20 is fixed parallel to the axial center of the screw 10 and immovably in the axial direction, and a pinion 22 is always engaged with the rack 20. Then, one reference pulse is outputted to the rotating shaft 24 of the pinion 22 at a specific rotational position of the rotating shaft 24 for each rotation of the rotating shaft 24, and for each minute rotation of the rotating shaft 24. , an incremental rotary encoder 26 that outputs one count pulse each of leading pulses and lagging pulses with a predetermined phase difference.

Here, the diameter of the pinion 22 is set to an accuracy that satisfies the screw position by taking into account the resolution of the rotary encoder 26, usually 0.01 to 0.11.
It is determined to be a size that can be detected with a certain degree of accuracy, and a circumferential length of at least a predetermined length, usually about 25 syllables or more. Further, the rotary encoder 26 is connected to the screw 1
0 is about 2011 degrees closer to the backward limit position from the forward limit position (hereinafter, this position will be referred to as A, and the distance from the forward limit position of the screw 10 to this position A will be referred to as B). It is attached to the rotating shaft 24 so as to output the first reference pulse at position A when the screw 10 moves backward from its forward limit position.

The heating cylinder 12 also includes a limit switch 2.
8 is provided in a fixed position. This limit switch 28 is actuated by the rank 20 when the screw 10 advances close to its forward limit position, and as shown in FIG. An activation signal is output when the distance C is within a distance C from the distance C. In this embodiment, as shown in FIG. 2, this distance C is longer than the distance B from the forward limit position of the screw 10 to the position, and the distance The limit switch 28 is fixedly attached to the heating cylinder 10 so as to be shorter than the distance E including the length.

That is, in this embodiment, while the limit switch 28 is outputting the actuation signal, the rotary encoder 26 outputs the reference pulse only in the position.

Each pulse output from the rotary encoder 26 and the actuation signal output from the limit switch 28 are supplied to two signal processing circuits. The leading pulse is supplied to a reversible counter 30 as a reversible counting means, and the actuation signal output from the limit switch 28 is supplied to a recent circuit 32 as a presetting means. Incidentally, the leading pulse and the delayed pulse output from the rotary encoder 26 are supplied to a direction determining circuit (not shown), and this direction determining circuit determines the rotation based on the phase difference between the leading pulse and the delayed pulse. The direction of rotation of the shaft 24, that is, the direction of movement of the screw 10 is determined.

A setter 34 for setting a preset value is connected to the precent circuit 32, and the precent circuit 32 maintains the preset value set by the setter 34 while the actuation signal from the limit switch 28 is supplied. The value is output to a reversible counter 30. On the other hand, the reversible counter 30 is connected to the preset circuit 32.
The preset value is preset only when the reference pulse from the rotary encoder 26 is input while the preset value is being output from the rotary encoder 26. Depending on the direction of movement, the preset value is added or subtracted. and,
In this embodiment, the preset value set by the setting device 34 is a value corresponding to the path if B, that is, the preset value is output from the rotary encoder 26 while the screw 10 is moving from its forward limit position to the position A. The number of advance pulses is set to the number of advance pulses, and the advance pulse is added to and counted from the preset value when the screw 10 moves backward, and subtracted from the preset value when the screw 10 moves forward.

Thereby, the count content of the reversible counter 30 always corresponds to the moving position of the screw 10, and this count content is supplied to the screw position display 36 to display the screw position, and the process supplied to the controller 38 to control the operation of the screw 10;
Furthermore, it has come to be used for process control of the entire injection molding machine. Note that the reversible counter 30
The preset operation is performed each time the screw 10 passes through position A. Furthermore, as is clear from the above description, in this embodiment, the limit switch 28
constitutes a detection means for specifying the reference signal from the rotary encoder 26.

According to such a screw position detection device, since the rotary encoder 26 can be an inexpensive incremental type, the entire device can be constructed at low cost, which is economically advantageous. Furthermore, after the power is turned on again, the preset throat value for making the count contents of the reversible counter 30 correspond to the screw position is determined to be accurate when the screw 10 is at the position A.
Since the reversible counter 30 is preset in response to the reference pulse from the rotary encoder 26 that is output when the screw reaches the position, the counted contents of the reversible counter 30 and the screw position always match exactly. Positions can always be detected with high precision and stably over long periods of time. Furthermore, in this embodiment, since the preset operation of the reversible counter 30 is performed each time the screw 10 passes through position A, as described above, a counting error may occur in the reversible counter 30 due to noise. Even in such cases, there is an advantage that the error can be corrected immediately and automatically.

Note that if the output position A of the reference pulse for precenting the reversible counter 30 is brought closer to the forward limit position of the screw 10 and the distance #B from the forward limit position of the screw 10 to the position A is too small, the normal During the injection operation, the screw 10 does not advance to the position A, and the opportunity to correct the counting error of the reversible counter 30 due to noise is lost, so the distance B from the advance limit position of the position A is, as described above, Normally, it is desirable to set it within a range of about 20 degrees or more.

Although one embodiment of the present invention has been described above, this is a literal illustration, and it goes without saying that the present invention should not be interpreted as being limited to this specific example.

For example, in the embodiment, one end of the movement range of the screw 10 specified by the limit switch 28 is set as the forward limit position of the screw 10, and the reference pulse for presetting the reversible counter 30 is used as the reference pulse closest to the forward limit position of the screw 10. However, the reference pulse that performs the brisk operation of the reversible counter 30 is not limited to this, and the reference pulse output at an arbitrary position can be selected by the reversible counter. It is possible to select as a reference pulse to perform 30 precent operations. However, even in this case,
As in the previous embodiment, it is desirable to select a reference pulse that is output within the movement range in which the screw 10 is moved forward and backward during normal injection operations, and to ensure that the reference pulse is output in each injection cycle. It is desirable to do this in order to eliminate detection errors caused by noise at any time. Note that the reference pulse for presetting the reversible counter 30 can be easily specified by specifying the operating position of the limit switch notch 28.

Further, in the above embodiment, the limit switch 28 was used as a detection means for specifying the reference pulse for presetting the reversible counter 30, but the detection means is not limited to this, and the detection means may be a proximity switch, etc. It is also possible to use other switching means.

Furthermore, in the embodiment described above, the reversible counter 30 counts the leading pulses among the counting pulses output from the rotary encoder 26, but the reversible counter 30
may be designed to count delayed pulses.

Further, in the above embodiment, when the screw 10 is operated backward, the reversible counter 30 performs an addition count, and when the screw 10 is operated forward, it performs a subtraction count. It is also possible that the reversible counter 30 performs subtraction counting at times and addition counting during forward operation.

Further, in the above embodiment, an example was described in which the present invention was applied to an injection device of a type in which the forward and backward operations of the screw 10 are performed by the injection cylinder 14. However, in the present invention, the forward and backward operations of the screw 10 are It is also possible to apply the present invention to an injection device operated by an electric servo motor. In this case, an incremental rotary encoder attached to the electric servo motor can be used to detect the screw position.

In addition, various changes may be made to the diameter of the pinion 22, the configuration of the signal processing circuit 29, etc., although these are not listed, without departing from the spirit of the present invention.

It goes without saying that the present invention can be implemented with modifications, improvements, etc.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the screw position detection device according to the present invention, and FIG. 2 shows the generation timing of the limit switch activation signal and the generation timing of the reference pulse of the rotary encoder 26 in the device of FIG. FIG. 3 is a waveform chart showing the relationship between the two and the moving position of the screw. 10: Screw 20 Rotary encoder 22: Pinion 24: Rotary shaft 26 2 Rotary encoder 28: Limit switch (detection means) 29: Signal processing circuit 30: Reversible counter (reversible counting means) 32 Nib reset circuit (presetting means) 34: Setting device

Claims (2)

[Claims] (1) A rotating shaft that is rotated in accordance with the amount of movement of the screw that is operated forward and backward in the injection cylinder; In addition to outputting two reference pulses,
a rotary encoder that outputs one counting pulse for each minute rotation of the rotary shaft; and a rotary encoder that reversibly counts the counting pulses output from the rotary encoder according to the moving direction of the screw, and records the counting contents of the screw. a reversible counting means for providing the movement position as a movement position; a detection means for detecting that the screw is within the predetermined specific movement range, and when the reference pulse is output from the rotary encoder in a state where the detection means detects that the screw is within the predetermined specific movement range A screw position detection device for an injection device, comprising: a preset means for presetting the reversible counting means to a preset value corresponding to the screw position at which the reference pulse is emitted. (2) The screw position detection device according to claim 1, wherein the predetermined specific movement range is set with the forward limit position of the screw as one end.