JP2595539Y2 - Torch burnout prevention device for plasma arc machine - Google Patents

Description

[Detailed description of the invention]

[0001]

INVENTION The present invention relates to a burning prevention device of the torch for fusing <br/> to Help Razumaaku machine the object to be cut by generating a plasma arc between the electrode and the workpiece torch Things.

[0002]

2. Description of the Related Art Electrodes used for plasma arc welding and cutting are relatively intensely worn, and especially when a gas containing a large amount of air or oxygen is used as a working gas, a hardly consumable material such as hafnium is embedded. Even if an electrode is used, its life is extended for several tens of minutes to several hours. And as the consumption of the electrode progresses, not only does the parallelism of the cut surface worsen and the cutting width increases, but also the cuttable plate thickness decreases, and in the worst case, the torch body is burned. Become. However, it is difficult to observe the electrodes directly from the outside because the electrodes are hidden inside the nozzle of the torch. There is no other way than to remove the tip (nozzle part) attached to the tip of the torch and check the consumption of the internal electrodes. Even with such direct observation, considerable experience is required to predict the remaining life of an electrode in which a hard-to-wear material such as hafnium is embedded in a copper electrode. Was.

Further, even when the amount of consumption of the electrode is small and the time for replacement has not been reached yet, when a current exceeding the allowable current of the torch flows due to incorrect setting of conditions during use or occurrence of abnormality in the power supply output, When the machining voltage is higher than the normal value because the distance between the nozzle and the nozzle becomes larger than the specified value when installing the electrode, the power consumption in the electrode part becomes excessive and the torch may be burned. there were.

On the other hand, an electrical change which occurs when the life of the electrode has expired, for example, a change in an arc voltage or a current value is detected, and when the change amount becomes larger than a reference value. A device that emits an abnormal signal has also been proposed. (For example, JP-A-61-269975)

[0005]

However, in the above-mentioned conventional apparatus, although accidents due to excessive use caused by inexperience or carelessness of a worker (supervisor) can be prevented,
When the arc length changes suddenly due to the hand movement of the operator or the molten metal blows up from the workpiece, the arc voltage may fluctuate considerably. It was difficult to distinguish between them, and often they generated unnecessary abnormal signals.

Further, a voltage between the electrode and the nozzle is detected so as not to detect a voltage change due to the influence of camera shake, and when this detected value or a change in the detected value exceeds a reference value, it is determined that the electrode is excessively consumed. A device for performing this is also proposed.
(For example, Japanese Patent Application Laid-Open Nos. 1-197063 and 62-12
No. 7173)

However, such an apparatus can eliminate the effects of camera shake and sudden changes in the thickness of the workpiece, but cannot cope with abnormalities in the power supply output current due to setting errors or malfunctions, and burnout of the torch. Is mainly caused by excessive input to the electrode,
For example, even if the voltage is high, if the flowing current is small, burning will not occur, and if the flowing current is large even if the voltage is low, burning may occur.

In the present invention, not only when the electrode wears out and the voltage rises, but also when the output current from the power supply is abnormal or the voltage is abnormal due to the electrode mounting error, the torch may be burned if the use is continued. When there is, this is detected and processing is prohibited.

[0009]

In the present invention, a product of a current flowing through the electrode and a voltage between the electrode and the nozzle is employed as a signal corresponding to an input to the electrode, and the product exceeds a reference value. In such a case, it is determined that an abnormality has occurred and the machining is interrupted.

The input to the electrode (power consumed by the electrode) is the product of the current flowing through the electrode and the voltage drop generated near the electrode, and this voltage drop is detected unless a special probe is used. Impossible. In contrast, the voltage between the electrode and the workpiece can be easily measured. However, since the power supply device used for plasma arc processing has a constant current characteristic or a drooping characteristic, when the distance between the electrode tip and the workpiece, that is, the arc length changes, the change in current is small, but the voltage is low. The change is big. Therefore, if the voltage between the electrode and the workpiece is substituted for the voltage drop near the electrode, the input to the electrode does not actually change when the arc length changes due to camera shake or a change in the shape of the non-workpiece. Nevertheless, an input change is detected, and an erroneous detection signal is generated.

Therefore, in the present invention, the voltage between the electrode and the nozzle, which does not change depending on the change in the arc length, is adopted as the one corresponding to the voltage drop near the electrode.
Based on the product of the voltage and the current, a signal proportional to the power consumption at the tip of the electrode is obtained to determine the occurrence of abnormality.

[0012]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an AC power supply, which is usually a commercial frequency single-phase or three-phase power supply. Reference numeral 2 denotes a power supply circuit for processing, a first rectifier circuit for rectifying an input from the AC power supply 1, and an inverter circuit for converting a DC output of the first rectifier circuit into a high-frequency AC with an output corresponding to an output current setting signal. A transformer for converting the output of the inverter circuit to a voltage suitable for plasma arc machining, and a second for rectifying the output of the transformer again to convert the output to DC.
A well-known power supply circuit such as an inverter-type power supply circuit including a rectifier circuit described above, or a power supply circuit of a type in which input from the AC power supply 1 is appropriately transformed and output is controlled and rectified by a switching element such as a thyristor is used. Numeral 3 denotes a torch for plasma arc processing, which schematically shows only an electrode 3a and a nozzle 3b provided in a shape surrounding the electrode 3a.

Reference numeral 4 denotes a workpiece, and a plasma arc 5 is formed between the electrode 3a and the workpiece 4 by the working gas flow confined by the nozzle 3b and the output from the power supply circuit 2. The nozzle 3b of the torch 3 is connected to a pilot arc current output terminal (b) of the power supply circuit 2.
Reference numeral 6 denotes a current detector, and reference numeral 7 denotes a voltage detector that detects a voltage between the electrode 3a and the nozzle 3b. 8 is an output current setting device,
9 an error amplifier for outputting a detection signal comparison difference signal and Ia [Delta] I = Ir-Ia setting signal Ir and the current detector 6 in the output current setter 8, 10 are analog Gusuitchi.

Reference numeral 11 designates a detection signal Ia of the current detector 6 and a detection signal Vn of the voltage detector 7 as inputs, and a product V of the two signals.
a multiplier for calculating n · Ia, 12 a reference value setting device for setting a reference value sr corresponding to the allowable power loss of the torch 3, 21 an integration circuit, a capacitor C1 and a resistor R
1, R2, switching transistor Q1 and IN
It consists of a barta INV. Reference numeral 13 compares the output sr of the reference value setting unit 12 with the output sp of the integration circuit 21, and determines that sp ≧ sr
(Or a comparator that outputs a high-level signal (hereinafter referred to as H) when sp> sr), and 14 is a comparator 1
A flip-flop circuit which is set when the output of 3 becomes H and is reset when the reset button 17 is pressed, 15 is a start signal generating circuit for a plasma arc machining command, 16 is an AND circuit, and 18 is a flip-flop circuit 1
This alarm is activated by the non-inverted output S2 when 4 is set, and uses a lamp, a buzzer, or the like.

Reference numeral 19 denotes a high-frequency generation circuit for generating a high-frequency high voltage from when the output of the start signal generation circuit 15 rises to the time when the plasma processing current flows, and 20 denotes the output of the high-frequency generation circuit 19 to the output of the power supply circuit 2. And a coupling coil to be supplied to the torch 3 while being superimposed on the torch 3.

In the device shown in FIG.
Before the output of the machining command signal (H signal) from the output signal 5, the output of the AND circuit 16 is at a low level (hereinafter denoted by L), the analog switch 10 is shut off, and no signal is sent to the power supply circuit 2 for processing. The power supply circuit 2 does not generate an output. At this time, since the output current and the output voltage are both zero, the output of the multiplier 11 is naturally zero.
Is low due to sr> sp , the flip-flop circuit 14 is reset, and its inverted output S1 is high. The output of the current detector 6 is zero.
Therefore, the input of the inverter circuit INV of the integration circuit 21 is L
Therefore, the output becomes H and the switching transistor
The star Q1 conducts and the electric charge of the capacitor C1 is
Discharged through R2. Therefore, the processing stop time
If it is long enough, the integration circuit 21 is completely reset
The output voltage is zero. In this state, when the output of the start signal generation circuit 15 becomes H, the output signal of the AND circuit 16 becomes H because both input signals become H, the analog switch 10 becomes conductive, and the output signal ΔI of the error amplifier 9 is supplied to the power supply circuit. 2 (At this time, ΔI = Ir because the output current Ia = 0.) The power supply circuit 2 is activated by this signal, and an output voltage is generated at the terminals (a) to (c).

On the other hand, when the output of the starting signal generating circuit 15 becomes H, the starting high frequency generating circuit 19 generates a high frequency high voltage, and this high frequency high voltage is superimposed on the output of the power supply circuit 2 by the coupling coil 20. As a result, the insulation of the gap between the electrode 3a of the torch 3 and the nozzle 3b is broken, and a spark discharge occurs, and this spark discharge and the voltage output between the output terminals (a) and (b) of the power supply circuit 2 are reduced. This causes an arc discharge. This arc discharge becomes a pilot arc limited to a small current by a current suppressing element including a resistor provided inside the terminal (b).
Further, at this time, air, oxygen,
A plasma arc working gas such as an inert gas is supplied, and is ejected from a narrow opening at the tip of the nozzle 3b.
This gas is ionized by the pilot arc generated between the electrode 3a and the nozzle 3b. When the nozzle 3b of the torch 3 in this state is brought close to the workpiece 4, the gas is ionized by the ionized gas flow. An arc is induced between the workpiece and the workpiece 4. This arc increases rapidly because it does not pass through the current suppression element . This current is detected by the current detector 6 to become a detection signal Ia, which is compared with the set value Ir of the output current setting unit 8 by the error amplifier 9 to obtain the difference signal Δ
I = Ir−Ia. As a result, the output current Ia is controlled to be equal to the output set value Ir.

[0018]

[0019]

[0020]

[0021]

[0022]

The output Ia of the current detector 6 is also
It is also supplied to one of the input terminals of the inverter circuit INV and the multiplier 11. When the signal Ia rises from zero, the output of the inverter circuit INV is inverted from H to L, and the switching transistor Q1 of the integration circuit 21 is cut off to stop discharging the capacitor C1.

At the same time, the detection voltage Vn and the detection current Ia between the electrode 3a of the torch 3 and the nozzle 3b are converted into a signal Vn.Ia corresponding to the product of the two by the multiplier 11 and become the integration circuit 2
The capacitor C1 starts to be charged through the first resistor R1. By this charging, the terminal voltage sp of the capacitor C1 is increased toward the signal Vn.Ia by the time constant r1.c1 (r1 is the resistance value of the resistor R1, and c1 is the capacitance of the capacitor C1).

This terminal voltage sp is compared with the set value sr of the reference value setter 12 by the comparator 13. The product Vn · Ia of the detection voltage Vn and the detection current Ia is obtained by dividing the product Vn · Ia by the integration circuit 21.
Is smaller than the reference value sr,
Alternatively, even if Vn · Ia is large, while the integrated value sp is smaller than the reference value sr, the output of the comparator 13 is L, so that the flip-flop circuit 14 remains reset,
Since the inverted terminal output S1 is H, the processing is not prohibited.

However, the signal sp ≧ sr (or sp> s
r), the output of the comparator 13 becomes H, the inverted output s1 of the flip-flop circuit 14 becomes L, and the AND circuit 1
The output of 6 is inverted from H to L, the analog switch 10 is shut off, and the power supply circuit 2 stops outputting. (Processing prohibited).

At the same time, the non-inverted output s2 of the flip-flop circuit 14 becomes H and activates the alarm 18 to notify the operator of the abnormality.

When the processing is stopped due to the detection of an abnormality or the output of the start signal generating circuit 15 having become L due to a command from the operator, the outputs of the current detector 6 and the voltage detector 7 become zero. Output Vn · Ia of multiplier 11
Is also zero. When Ia = 0 due to the stop of the processing, the output of the inverter circuit INV of the integration circuit 21 is inverted from L to H, and the switching transistor Q1 is turned on. Due to the conduction of the switching transistor Q1, the charge of the capacitor C1 starts discharging through the switching transistor Q1 and the resistor R2, whereby the terminal voltage sp of the capacitor C1 becomes a time constant c1 · r2.
(However, r2 decreases in accordance with the resistance value of the discharge circuit including the switching transistor Q1 and the resistor R2).

As described above, the terminal voltage sp of the capacitor C1 is
Rises in accordance with the time constant c1 · r1 during machining, and discharges in accordance with the time constant c1 · r2 after machining is stopped. Therefore, these time constants are generally referred to as a time constant when the temperature of the torch 3 is increased and a time constant when cooled. Let it match. By setting in this way, it is possible to use even if Vn · Ia is large as long as the heat capacity of the torch is within the allowable range of the heat capacity of the torch for a short-time overload.
Can be used if is within the allowable value.

The integrating circuit 21 used in the embodiment shown in FIG. 1 may be constituted by using an operational amplifier.

FIG . 2 is a connection diagram showing an example in which an integrating circuit is configured using an operational amplifier, and shows only the integrating circuit.

In the figure, OP1 is an operational amplifier, R
3, R4 is a resistor, C2 is a capacitor, AN1 is an analog switch, and INV is an inverter circuit. In the case of the integrating circuit shown in the figure, the integration time constant during the plasma arc machining is c2 · r3, and the discharge time constant when the machining is stopped is c2 · r4. (However, c2 is the capacitor C
The capacitance of 2, the resistance r3 indicates the resistance of the resistor R3, and the resistance r4 indicates the resistance of the discharge circuit including the resistor R4 and the analog switch AN1. )

It should be noted that the relationship between H and L of each signal described in each of the above embodiments and the logic circuit to be used are not limited to those shown in each of the embodiments, and the same operations as those described in each of the embodiments. And the logical configuration is arbitrary.

[0034]

According to the present invention, the voltage between the electrode and the nozzle corresponding to the power actually consumed in the torch is different from that of the conventional device which simply detects a change in the electrode voltage or current to determine an abnormality. Since the risk of torch burnout is estimated based on the product of Vn and the machining current Ia, there is no malfunction due to voltage change due to camera shake of the operator, and sufficient output from the machining power supply circuit can be avoided. In addition, the torch can be protected from burning.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention.

FIG. 2 is a connection diagram showing another embodiment of the integration circuit used in the present invention.
Continued figure.

Claims (2)

(57) [Scope of request for utility model registration] An apparatus for preventing heat loss of a torch used in a plasma arc machine for generating a plasma arc confined by a nozzle and a working gas between an electrode of a torch and a workpiece and fusing or welding the workpiece. A current detector that detects a current flowing through the electrode of the torch, a nozzle voltage detector that detects a voltage between the electrode of the torch and a nozzle, an output Ia of the current detector, and the nozzle voltage detector and the output Vn and multiplier for obtaining the product Vn · Ia of the front
An integrating circuit for integrating the output of the multiplier with a predetermined time constant;
Discharge the output of the integration circuit with a predetermined time constant when machining is stopped
Discharging circuit, a reference value setting device, and an output of the integrating circuit
sp is compared with the set value sr of the reference value setting device, and sp ≧
A torch heat loss prevention device for a plasma arc processing machine, comprising: a comparator that determines an abnormality when sr is detected and outputs a warning signal; and a protection circuit that prohibits a processing operation by the output signal of the comparator. 2. An operator is alerted by an output signal of the pre-comparator.
The torch heat loss prevention device for a plasma arc processing machine according to claim 1, further comprising an alarm circuit for issuing an alarm .