JPS6216771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wire breakage detection device for detecting a sudden breakage accident of a wire electrode in a wire cut electrical discharge machining apparatus.

[Conventional technology]

BACKGROUND ART Conventionally, as a device for detecting a breakage of a wire electrode during machining with a wire electric discharge machining apparatus, a device that mechanically detects a wire electrode using tension of the wire electrode has been widely used.

FIG. 1 shows an example of a wire cut electric discharge machining apparatus equipped with such a conventional wire breakage detection device. In this figure, 1 is a workpiece, 3 is a table on which the workpiece 1 is mounted, and 4 and 5 are an X-axis drive motor and a Y-axis drive motor that drive the table 3 in the X-Y direction.

2 is a wire electrode, and this wire electrode 2 is pulled out from the supply reel 6, passes through the lower wire guide 7, the wire guide 8, and the feeder 9 in order.
Take-up reel 10 while being given tension T
It is wound up.

Reference numeral 11 denotes a machining fluid that is supplied to the machining gap formed between the wire electrode 2 and the workpiece 1;
2, it is supplied from the nozzle 13 to the machining gap. 14 is a processing power supply that applies a processing voltage to the processing gap, and includes a normal DC power supply 15, a switching element 16, a charging current limiting resistor 17, a capacitor 18,
A circuit composed of a control circuit 19 for the switching element 16 and the like is used.

Reference numeral 30 denotes a control panel consisting of a copying control device, an N/C control device, a computer, etc., and the commands from this control panel 30 drive the X-axis drive motor 4 and Y-axis drive motor 5 to drive the wire electrode 2. The workpiece 1 is moved relatively, and electricity is applied while supplying the machining fluid 11 to the machining gap to electrically cut the workpiece 1 into a desired shape using a scroll saw.

Reference numeral 20 denotes a wire breakage detection device for detecting sudden breakage of the wire electrode 2 during processing, and is arranged so as to come into contact with the portion of the wire electrode 2 to which the tension T is applied. Its configuration is shown in FIG. Shown below.

In FIG. 2, reference numeral 21 denotes a contact rod whose end 21A contacts the wire electrode 2, and is rotatably held at its center by a fulcrum 22. 23 is a spring, and its repulsive force F provides a torque for rotating the contact rod 21 in the direction of arrow A in the figure.

24 is a limit switch, and this limit switch 24 is operated by the end 21B of the contact rod 21 on the opposite side from the end 21A that contacts the wire electrode 2.

Next, the operation of this wire breakage detection device 20 will be explained. When processing is progressing normally, that is, when the wire electrode 2 is not disconnected, the wire electrode 2 is in contact with the end 21A of the contact rod 21, and the tension T applied to the wire electrode 2 is As a result, a rotational torque in the direction of arrow B shown in FIG. 2 is applied to the contact rod 21, and the contact rod 21 rotates by θ in the direction of arrow B against the repulsive force F of the spring.

If the wire electrode 2 breaks during processing, the tension T of the wire electrode 2 loses its effect, and the contact rod 2
1 is rotated by θ in the direction of arrow A shown in FIG. 2 by the action of the repulsive force F of the spring 23. At this time, the contact rod 21
By operating the limit switch 24 at the end 21B of the wire electrode 2, an electrical signal indicating that the wire electrode 2 has been disconnected can be obtained.

Generally, when the wire breakage detection device 20 detects a break in the wire electrode 2, this signal is input to the control circuit 19 of the processing power source 14 to turn the switching element 16 "OFF".
It is configured to cut off the output of the processing power source 14.

[Problem that the invention seeks to solve]

However, in the conventional wire breakage detection device 20 that mechanically detects the breakage of the wire electrode 2 as described above, after the wire electrode 2 is broken, the contact rod 21 moves θ in the direction of the arrow A shown in FIG. , and operate the limit switch 23.
Since an electrical signal of a wire breakage is obtained, various conditions such as the degree of friction when the contact rod 21 rotates with respect to the fulcrum 22 and the degree of repulsive force F of the spring 23 change over time, making it difficult to detect a wire breakage. There is a risk that the characteristics may change over time, and there is also the disadvantage that it takes time and effort to stretch the wire electrode 2. Additionally, because the device is mechanically constructed, it is prone to failure.

Furthermore, several tens to hundreds of milliseconds are required before wire breakage is detected, and during this time the wire electrode 2 that has broken wire is not restrained and the machining voltage remains applied between it and the workpiece 1. left alone.

During this time, the wire electrode 2 to which this voltage was applied
is workpiece 1 or table 3 which is at the same potential as this
This conventional wire breakage detection device has drawbacks such as damage caused by discharge between the wire and the wire.

The present invention has been made in view of these points, and provides a wire breakage detection device that reduces the occurrence of failures, has little change in detection characteristics over time, and is capable of good wire breakage detection without the hassle of special setup. Its purpose is to provide.

[Summary of the invention]

In the present invention, when the wire electrode is disconnected when the feeder is provided only on one side with respect to the workpiece, the opposing area between the wire electrode and the workpiece decreases, and the resistance is equivalently reduced. By utilizing the fact that the value increases, disconnection is detected by detecting that the instantaneous value of the machining voltage at this time becomes higher than the average value of the peak values by a certain voltage or more.

〔Example〕

Hereinafter, one embodiment of the disconnection detection device according to the present invention will be described based on the circuit diagram shown in FIG. Third
In the figure, 40 is a first detection circuit that detects the average value of the peak value of the machining voltage applied to the machining gap, and a series body of a backflow prevention diode 41, a charging resistor 42, and a peak voltage holding capacitor 43 is connected to the machining gap. Further, a discharge resistor 44 is connected in parallel to the peak voltage holding capacitor 43.

In this first detection circuit 40, the backflow prevention diode 4 is activated by the machining voltage applied to the machining gap.
1 and the charging resistor 42, the peak voltage holding capacitor 43 is charged, but this capacitor 43 is discharged only through the discharging resistor 44.
Since the backflow prevention diode 41 prevents discharge from being discharged into the machining gap, the average value Vp of the peak values of the machining voltage is maintained between the poles of the capacitor 43.

50 is a differential amplifier circuit, which is connected to the first detection circuit 40
The average value Vp of the peak value of the machining voltage that is the output of
and the value Vg that is directly detected from the instantaneous value of the above machining voltage.
is input. 51 is a high speed, high slew rate operational amplifier, 52 and 53 are both resistance values R ₃
The resistors 54 and 55 are both resistors having a resistance value of R ₄ , and a differential amplifier circuit 50 is constituted by these elements.

When the average value Vp and the instantaneous value Vg of the peak values of the machining voltage are input to the differential amplifier circuit 50, the output Vo is expressed by the following equation.

Vo = R ₄ /R ₃ (Vp - Vg) ...... (1) 56 is a comparator that compares the output Vo of this differential amplifier circuit 50 with a preset reference voltage Vr, and calculates the instantaneous value of the processing voltage. When Vg becomes higher than the average value Vp of the peak values by a predetermined value (R ₃ /R ₄ ·Vr) or more, a detection signal e ₀ is output. This detection signal is input to the control circuit 19 of the switching element 16 in the machining power supply 14, and when the detection signal _e0 is output from the comparator 56, the switching element 16 is turned OFF and the output of the machining power supply 14 is cut off. is configured to do so.

Next, the operation of the detection circuit configured as above will be explained. In the wire-cut electric discharge machining apparatus shown in FIG. 3, a machining liquid 11 having conductivity is present in the machining gap formed between the wire electrode 2 and the workpiece 1, so that the machining current due to the electric discharge is It is considered that a leakage current flows through the resistor r shown in the figure and is equivalent to the resistor r shown in the figure being connected to the machining gap.

When machining is performed normally with this device, the instantaneous value is higher than the average value Vp of the peak value of the machining voltage.
Vg never appears. That is, the instantaneous value Vg never becomes higher than the average value Vp of the peak values by more than a preset constant value R ₃ /R ₄ ·Vr, and the detection signal e ₀ of the comparator 56 is not output.

Next, if the wire electrode 2 is disconnected in the machining gap formed between it and the workpiece 1 during machining, since the feeder 9 is provided only on one side of the workpiece 1, the machining gap The area in which the wire electrode 2 and the workpiece 1 face each other decreases, and the leakage current flowing therebetween decreases, resulting in an increase in the equivalent resistance.

As a result, the capacitor 18 in the machining power supply 14 is rapidly charged, and the voltage between the wire electrode 2 and the workpiece 1, that is, Vg, rises and becomes considerably higher than the average value Vp of the above-mentioned peak values, and the above-mentioned comparator The input Vo of the regulator 56 becomes higher than the constant voltage Vr,
A detection signal _e0 is output.

That is, when the wire electrode 2 is disconnected during machining, the detection signal e ₀ is immediately output to detect the wire disconnection, and the control circuit 19 shuts off the output of the machining power source 14.

〔Effect of the invention〕

As explained above, according to the wire breakage detection device according to the present invention, wire breakage of the wire electrode is detected electrically, so the occurrence of failures is reduced, and there is little change in detection characteristics over time, and the wire electrode breakage is electrically detected. This has the effect that disconnection can be detected well without requiring any special effort during tensioning.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of a wire cut electrical discharge machining apparatus equipped with a conventional wire breakage detection device, FIG. 2 is a perspective view showing the configuration of a conventional wire breakage detection device, and FIG. FIG. 2 is a circuit diagram showing an example. The same symbols in the figures indicate the same or corresponding parts, 1
1 is a workpiece, 2 is a wire electrode, 11 is a processing liquid, 1
4 is a processing power source, 20 is a wire breakage detection device, 21
is the contact rod, 24 is the limit switch, and 40 is the first
In the detection circuit, 41 is a reverse current prevention diode, 43 is a peak voltage holding capacitor, 50 is a differential amplifier, 51 is an operational amplifier, and 56 is a comparator.

Claims (1)

[Claims] 1. A machining liquid is interposed in the machining gap formed between the wire electrode and the workpiece, and a machining voltage is applied to the machining gap from either side via a power supply while sandwiching the workpiece. In a wire breakage detection device for a wire cut electric discharge machining device that electrically cuts a workpiece and shuts off the power supply when the wire electrode is cut, a first detection means;
A second detection means for detecting the instantaneous value of the machining voltage is compared with the detection values of the first and second detection means, and the instantaneous value is higher than the average value of the peak values by a predetermined value or more. A disconnection detection device characterized by comprising: a comparison means that outputs a signal for cutting off the power supply when the power source is cut off.