JPH0577052A - Plasma arc monitor - Google Patents

Abstract

PURPOSE:To detect the melting phenomenon of a nozzle of a plasma fusing device. CONSTITUTION:The emitted light from a plasma arc 14 is guided by a phototransmission/condensation line 31 to a inlet slit of a spectroscope 32 to form a real image of plasma. A detector 33 detects a light divided by a specstrope 32 and outputs informations of positions of line spectra and informations of strength. The information of this position and the information of the strength are read out and stored by the information of sampling hold transient memory 34 at a specified period. Spacial position informations are stored in correspondence to the absolute value of a wave length in the ROM 36. A comparator 35 compares the measurement data (position, strength) of the sampling hold transient memory 34 with the data table set (position, strength) of the ROM 36 to output a comparison output signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma arc monitoring device used in a plasma fusing device for fusing a material to be cut by injecting a high temperature plasma arc from a nozzle.

[0002]

2. Description of the Related Art A plasma fusing device is a device for fusing a material to be cut by injecting a high temperature plasma arc from a nozzle. There are two types of plasma processing by this plasma fusing device, that is, a plasma jet and a plasma arc. In the plasma jet processing, a working gas such as O ₂ is blown into a plasma torch in a swirling flow to generate an arc discharge between the Hf cathode and the inner surface of the Cu anode nozzle, so that the working gas is heated to a high temperature plasma. Turned into
It is projected on the material to be cut as a high energy beam into the atmospheric pressure. On the other hand, plasma arc machining is one in which a material to be cut is used as an anode and an arc discharge is generated between the material and the cathode, and the working gas flowing in the nozzle becomes a fluid sheath for the arc near the inner surface of the nozzle and compresses the arc. , Make its current density very large. In any case, the plasma fusing device includes a plasma torch having an electrode, a nozzle that covers the electrode, and a cap that covers the nozzle, and the working gas flows into the space between the electrode and the nozzle.

In such a plasma fusing device, each component constituting the plasma torch is a consumable component and needs to be replaced periodically. Regarding the relative life of each component forming the plasma torch, assuming that the life of the electrode is 1, the life of the nozzle is 2 to 3, and the cap is sufficiently long. If the parts are not replaced regularly, the parts will be damaged due to the explosion phenomenon of the plasma torch. Such an explosion phenomenon is called "puncture" in this technical field. If a puncture occurs, all of the electrode, nozzle, and cap will be destroyed. That is, the range of parts to be replaced is expanded. Therefore, avoiding punctures and the number of consumable parts to be replaced (range of replacement)
It is required to accurately predict the replacement of parts in order to narrow the problem. In other words, if the degree of consumption of the consumable parts being used can be accurately known, the consumable parts can be exchanged systematically, and the production line can be saved and the operating rate can be improved. it can.

However, at present, since the cause of puncture is unclear, a reliable prediction method for eliminating it has not been established. Some of the skilled workers on site are
Some people have the ability to predict abnormalities in the plasma fusing device from sound waves in the audible range emitted from the plasma arc (plasma jet). However, this prediction method is a sensory method, and standardization is extremely difficult. In addition, as another prediction method, the fact that the electrical characteristics of the plasma arc reflect the state of the plasma arc to some extent is used to measure the arc sustaining voltage, and from this measured arc sustaining voltage, an abnormality of the plasma fusing device is detected. A method of predicting is also known. However, this prediction method is not a sufficiently reliable prediction method for the following reason. That is, in the work using the plasma fusing device for this type of plasma arc processing, since the material to be cut is the arc facing electrode (+ electrode) due to the nature of plasma cutting, the cutting conditions (nozzle opening and cutting material Distance to) is constantly changing. Under such a work, the amount of change in the arc voltage due to the change in the cutting condition is so large that it cannot be ignored.

[0005]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to predict the puncture phenomenon and improve the productivity by diagnosing the operating state of the plasma arc of the plasma fusing device by a quantitative and highly reliable method. It is to provide a plasma arc monitoring device.

[0006]

A plasma arc monitoring apparatus according to the present invention monitors the state of the plasma arc in a plasma fusing apparatus for fusing a material to be cut by injecting a high temperature plasma arc from a nozzle. And a means for detecting light information emitted from the plasma arc, and a means for monitoring the abnormality of the plasma arc by processing the detected light information. ..

[0007]

In the plasma fusing device, when the parts constituting the plasma torch are new, the plasma arc is stable and puncture is unlikely to occur. Therefore, the melting of the nozzle and the damage of the electrode are not so serious. The plasma arc becomes unstable for some reason as the operating time of the plasma fusing device elapses, the distance between the plasma arc and the nozzle becomes narrow, the nozzle opening melts, and the arc extension of the plasma arc becomes insufficient. As a result, the arc current that should reach the material to be cut flows partially in the space where the nozzle and the electrode are close to each other (double arc phenomenon), and as a result, melting also occurs in that space portion. During this time, the constituent elements of the nozzle are vaporized and mixed into the plasma arc. When the element (copper) that is the main component of the nozzle evaporates and enters the plasma arc, the following process occurs. 1. Excitation of atoms by absorption of photons and electron collisions 1. Ionization of atoms by electron collision 3. Luminescence of excited atoms 4. Ion-excited luminescence In the plasma arc, the elements 1-4 other than copper also undergo the above-mentioned steps 1-4, so that strong luminescence is accompanied. Among them, neutral atoms of copper emit strongly when they are excited to a metastable state by electron collision and return to the stable state. The emission spectrum line and intensity of the plasma arc emitted at that time are as follows. Atomic emission: 3273.96 (3000R), 3247.54 (5000R), 2824.37
(1000) There is strong light emission in Angstrom. Ion emission: 4674.76 (200), 3602.03 (50), 4555.92 (2),
There is light emission at 4506.00 (1) angstrom. Here, the numbers in parentheses indicate relative values of intensity, and the larger the number, the brighter the image. R indicates that the light is too strong and atomic absorption occurs, causing a measurement reversal in the direction of the line of sight and appearing dark. In the present invention, focusing on the fact that the emission phenomenon from neutral atoms of copper is extremely strong as described above, the spectral line of copper from the plasma arc is detected, and the melting phenomenon of the copper nozzle is detected. .. In the present invention, light emission from ions can be used according to the same principle. However, since the emission intensity of ions is weaker than that of atoms, the utility is low. The important thing to note here is
As described above, since elements other than copper are also present in the plasma arc in this measurement, it is likely that light emission by these elements interferes with the measurement of the copper spectral line. Of particular concern here are the iron spectral lines. However, from the measurement results of the spectral line intensities of copper and iron, the spectral line intensity of copper far exceeds that of iron, so there is no problem. That is, in the practice of the present invention, by attaching a suitable dimming element to the spectroscope, or by narrowing the input slit of the spectroscope to diminish the light, the amount of light in the spectrum of obstructive elements such as iron is weakened, and the spectrum of iron Since the spectrum of copper still has a sufficient amount of light even when the is less than the detection sensitivity, there is no difficulty in measurement due to the spectrum of the obstacle element.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 3 shows the configuration of a plasma fusing device to which a plasma arc monitoring device according to an embodiment of the present invention is applied. The illustrated plasma fusing device has an electrode 11 which is a cathode.
And a plasma torch having a copper nozzle 12 for covering the electrode 11 and a cap (described later) for covering the nozzle 12. The material 13 to be cut is an anode, and an arc 14 as shown in the figure is generated between the material 13 to be cut and the electrode 11. The plasma fusing device includes an electrode 11
A high frequency generator 16 is connected between the nozzle 12 and the nozzle 12 via a start switch 15. A pilot arc current adjusting resistor 17 is connected between the high frequency generator 16 and the material 13 to be cut. The material to be cut 13 is connected to the anode of the plasma arc power supply 18, and the negative electrode of the plasma arc power supply 18 is connected to the electrode 11 via the switch 19. The switch 19 includes a control input terminal 19a to which an open / close control signal described later is supplied.

Referring to FIG. 4, the plasma torch has a hollow electrode 11, a nozzle 12 that covers the electrode 11, and a cap 20 that covers the nozzle 12. Electrode 11
Is cooled by flowing cooling water as shown by the broken line arrow in FIG.
The space between the nozzle 12 and the cap 20 is cooled by the flowing cooling water, as indicated by the dashed arrow in FIG. A working gas (also referred to as a working gas) flows into a space between the electrode 11 and the nozzle 12 as indicated by a solid arrow in the drawing. As shown in FIG. 4, through the opening of the nozzle 12, the arc 14, that is, the plasma arc, is transferred to the electrode 11.
Flows between the tip of the and the material to be cut 13. Since the nozzle 12 is cooled, this plasma arc has a large temperature rise due to the thermal pinch effect. Due to this high temperature and a high-speed plasma gas flow due to the working gas, the material to be cut 13
Is blown out.

The operation of the plasma fusing device will be described with reference to FIGS. 3 and 4. First, in order to ignite plasma, the working gas is adjusted to an appropriate pressure and flow rate, the start switch 15 and the switch 19 are closed, and the high frequency generator 1
A high frequency voltage is applied between the electrode 11 and the nozzle 12 from No. 6. As a result, the high frequency auxiliary plasma is generated in the portion indicated by in FIG. 4, that is, in the opening of the nozzle 12. Since the current from the plasma arc power source 18 flows through the resistor 17 into the plasma torch, the plasma cannot grow in the arc 14. At the stage where the high frequency auxiliary plasma could be generated,
The start switch 15 is opened, and the plasma current is commutated between the material 13 to be cut and the electrode 11. At this stage, the plasma current grows and moves to the arc 14 to start the cutting operation. In order to stop the plasma, the voltage of the plasma arc power supply 18 can be lowered so as to be below the sustain voltage of the arc discharge 14 to extinguish the arc.

Referring to FIG. 1, a plasma arc monitoring apparatus according to an embodiment of the present invention is an apparatus for monitoring the state of the arc (plasma arc) 14 of the plasma fusing apparatus shown in FIG. The plasma arc monitoring device of this embodiment has an optical emission analyzer. The emission analysis device has an optical transmission / focusing system 31, a spectroscope 32, and a detector 33. The spectroscope 32 has an entrance slit (not shown), a concave mirror (not shown), and a diffraction grating (not shown). Arc 1
The light emitted from the spectroscope 4 is emitted from the spectroscope 3 by the optical transmission / focus system 31.
It is guided to the entrance slit of 2 and forms a real image of plasma.
The real image of this plasma is dispersed by the concave mirror and the diffraction grating. This dispersed emission is imaged on the detector 33, forming a line spectrum. As the detector 33, a one-dimensional CCD or a one-dimensional phototransistor array is adopted. In this embodiment, a one-dimensional CCD is used as the detector 33. The spectral lines imaged on the detector 33 provide position and intensity information. The position information represents the wavelength of the spectrum line, and in this embodiment, the wavelength of the spectrum line of the copper atom. The intensity information represents the number of copper atom particles. As described above, in this embodiment, the nozzle 12
Since copper or a copper alloy is used in the above, the information detected by the detector 33 is the wavelength of the emission spectrum line of copper originating from the copper or the copper alloy. The wavelengths obtained in this case are 3247.54 Å and 3
273.96 Angstroms. However,
Hafnium or a hafnium alloy may be used as the nozzle 12. In this case, the wavelength obtained as the detection information also includes wavelengths originating from hafnium or a hafnium alloy, that is, 5040.82 angstroms and 5311.60 angstroms.

The plasma arc monitor further includes a sampling and holding transient memory 34, a comparator 35, and a ROM 36. The information on the position of the spectral line and the information on the intensity detected by the detector 33 are read out by the sampling hold transient memory 34 in a predetermined cycle and stored. The ROM 36 stores in advance data of spectrum lines of atoms whose spatial arrangement is determined by the dispersion characteristics of the spectroscope 32. In other words, the ROM 36 stores the spatial position information in association with the absolute value of the wavelength. The comparator 35 compares the measurement data (position, intensity) of the sampling hold transient memory 34 with the data table set (position, intensity) of the ROM 36. As is well known, the emission spectrum line from an element is a universal physical constant. Therefore, in this measurement, the emission spectrum line is used as a ruler of the detector 33. The comparator 35 outputs a comparison output signal. When the intensity of the measured spectrum line is weaker than the intensity of the spectrum line stored in the ROM 36, that is, when the amount of evaporation of copper from the nozzle 12 is small, the comparator 35 outputs, for example, a negative voltage as a comparison output signal. Generates an abnormal signal. On the contrary, when the intensity of the measured spectrum line is stronger than the intensity of the spectrum line stored in the ROM 36, that is, when the evaporation amount of copper from the nozzle 12 is large, the comparator 35 outputs the comparison output signal as, for example, Generates a signal indicating an abnormal positive voltage.

FIG. 2 shows the construction of a condition judging device for making a condition judgment in response to a comparison output signal from the comparator 35. The condition judging device sends an opening / closing control signal to the control input terminal 19a of the switch 19 of the plasma fusing device of FIG. 3 according to the following two judging conditions, namely, judging condition 1 and judging condition 2. Judgment condition 1: Decrease in productivity due to puncture during the machining process, and operate the switch 19 to "close" after advancing the number of man-hours to the machining process that does not minimize the productivity, and extinguish the plasma. .. Judgment condition 2: Prioritizing the prevention of productivity deterioration caused by puncture, the switch 19 is operated on the spot to extinguish the plasma. The purpose of this determination is to: That is, as is well known,
This is so-called "one-stroke writing". For this reason, the progress of the cutting work can be sequentially determined by conditionally determining which stage of the current machining process is a single stroke (for example, the start point or the middle of the machining process) to maintain high productivity. Can be done.

For this judgment, the condition judging device includes a receiver 41, a judging device 42, a condition judging device 43, and a ROM 4.
4 and an output circuit 45. The receiver 41 receives production process management information from a production management computer (not shown) that manages the production process. Based on the output from the receiver 41, the condition determiner 43 always grasps the progress of the machining process. On the other hand, the comparison output signal from the comparator 35 is discriminated by the discriminator 42 as positive or negative. The determination condition 1 and the determination condition 2 (process pattern information) described above are stored in the ROM 44 in advance. The condition determiner 43 is configured to detect the process pattern information stored in the ROM 44 and the receiver 41.
And the output of the discriminator 42 are searched for a work that does not minimize the productivity, and the condition determination result is sent to the output circuit 45.
The output circuit 45 issues an opening / closing control signal for controlling opening / closing of the switch 19 (FIG. 3) of the plasma fusing device to its control input terminal 19a. When the switching control signal instructing "close" is received, the switch 19 is closed, whereby the plasma generated in the plasma torch (FIG. 4) is extinguished.

[0015]

As described above, according to the present invention, the optical information generated from the plasma arc of the plasma fusing device is detected, and the detected optical information is processed to monitor the abnormality of the plasma arc. It is possible to quantitatively and reliably diagnose the operating state of the plasma arc.
This has the effect of predicting the puncture phenomenon and improving productivity.

[Brief description of drawings]

FIG. 1 is a block diagram showing a plasma arc monitoring device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a condition determination device that performs a condition determination based on an output from the plasma arc monitoring device of FIG.

FIG. 3 is a block diagram showing a plasma fusing device to which a plasma arc monitoring device according to the present invention is applied.

4 is a cross-sectional view showing in detail a portion of a plasma torch in the plasma fusing apparatus of FIG. 3 together with a material to be cut.

[Explanation of symbols]

 31 Optical Transmission / Condensing System 32 Spectroscope 33 Detector 34 Sampling Hold Transient Memory 35 Comparator 36 ROM

Claims (3)

[Claims] 1. A plasma arc monitoring device for monitoring the state of the plasma arc in a plasma fusing device for fusing a material to be cut by injecting a high temperature plasma arc from a nozzle. A plasma arc monitoring device comprising: a means for detecting emitted light information; and a means for processing the detected light information to monitor the abnormality of the plasma arc. 2. A plasma arc monitoring device for monitoring the state of the plasma arc in a plasma fusing device for fusing a material to be cut by injecting a high temperature plasma arc from a nozzle. A plasma arc monitoring device comprising: means for detecting optical information originating from emitted copper or copper alloy; and means for monitoring the abnormality of the plasma arc by processing the detected optical information. .. 3. A plasma arc monitoring device for monitoring the state of the plasma arc in a plasma fusing device for fusing a material to be cut by injecting a high temperature plasma arc from a nozzle. Plasma comprising: means for detecting optical information originating from emitted hafnium (Hf) or a hafnium alloy; and means for processing the detected optical information to monitor for abnormalities in the plasma arc. Arc monitoring device.