JPH0654469U - Torch burnout prevention device for plasma arc machine - Google Patents

Abstract

(57) [Summary] [Purpose] The objective is to prevent malfunctions due to voltage changes due to camera shake of the operator, and to sufficiently protect the torch from burnout against abnormal output from the machining power supply circuit. A product Vn · Ia of a current Ia flowing through an electrode of a plasma arc processing torch and a voltage Vn between the electrode of the torch and a nozzle is compared with a reference value sr, and Vn · Ia ≧ s.
A torch burnout prevention device for a plasma arc machine, which judges that there is an abnormality when r, outputs an alarm signal, and prohibits machining work.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a burnout prevention device for a torch for an ECE plasma arc machine, which generates a plasma arc between an electrode of the torch and a workpiece to melt the workpiece.

[0002]

[Prior art]

 Electrodes used for plasma arc welding / cutting, etc. are relatively heavily consumed.Especially when air or a gas with a large oxygen content is used as the working gas, even electrodes with difficult-to-wear materials such as hafnium are used. The service life is extended to tens of minutes to hours. Then, as the consumption of the electrode progresses, not only the parallelism of the cut surface deteriorates, the cut width increases, but also the thickness of the cuttable plate decreases, and in the worst case, the torch body is burned. It will also happen. However, since the electrode is hidden inside the torch nozzle, it is difficult to observe it directly from the outside. In addition to removing the tip (nozzle part) attached to the tip of the torch and examining the wear state of the internal electrode, In addition, even if such direct observation is performed, it is necessary to have some experience to predict how long the remaining life will be in the electrode in which the copper electrode is embedded with a non-consumable material such as hafnium. Was needed.

Further, even when the amount of consumption of the electrodes is small and the time for replacement has not yet come, when a current that exceeds the allowable current of the torch flows due to erroneous setting of conditions during use, an abnormality in the power supply output, etc., When the machining voltage becomes higher than the normal value due to the gap between the nozzle and the nozzle becoming larger than the specified value by mistake when installing the electrode, the power consumption at the electrode part becomes excessive and the torch may burn out. there were.

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

[0005]

[Problems to be solved by the device]

 However, with the above-mentioned conventional device, although accidents due to overuse caused by lack of experience of the worker (monitor) or carelessness can be prevented, sudden changes in the arc length due to camera shake of the worker and the workpiece If the molten metal blows up, the arc voltage may fluctuate considerably, and it is difficult to distinguish these from fluctuations due to electrode wear. Was sometimes emitted.

Further, the voltage between the electrode and the nozzle is detected so as not to detect the voltage change due to the influence of camera shake, and when the detected value or the change in the detected value exceeds the reference value, the electrode is excessively consumed. A determination device has also been proposed. (For example, Japanese Patent Laid-Open Nos. 1-197063 and 62-127173)

However, in such an apparatus, although the influence of camera shake or a sudden change in the thickness of the workpiece can be eliminated, it is not possible to deal with an abnormality in the power supply output current due to a setting error or a malfunction, and the torch burns out. Is mainly caused by an excessive input to the electrodes, so for example, even if the voltage is high, if the flowing current is small, it will not burn out.On the contrary, even if the voltage is low, if the flowing current is large, it may burn out. It is a thing.

According to the present invention, the torch is burned out if the electrode is worn out and the voltage rises, but also when the output current from the power source is abnormal or the voltage is abnormal due to an electrode mounting error if the electrode is used continuously. When there is a possibility, this is detected and processing is prohibited.

[0009]

[Means for Solving the Problems]

 In the present invention, the product of the current flowing through the electrode and the voltage between the electrode and the nozzle is adopted as the signal corresponding to the input to the electrode, and when this product exceeds the reference value, it is judged as abnormal. The processing 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, but this voltage drop does not use a special probe. As long as it is undetectable. On the other hand, the voltage between the electrode and the work piece can be easily measured. However, since the power supply device used for plasma arc processing has constant current characteristics or drooping characteristics, the distance between the electrode tip and the work piece, that is, the arc length changes, the change in current is small but the voltage changes. The changes are big. Therefore, if the voltage between the electrode and the work piece 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 the shape change of the non-work piece. Nevertheless, the input change will be detected, and a false detection signal will be emitted.

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, and the product of this voltage and the current is used. It is obtained as a signal proportional to the power consumption at the electrode tip to determine the occurrence of an abnormality.

[0012]

【Example】

 FIG. 1 shows an embodiment of the present invention. In the figure, reference numeral 1 is an AC power supply, and usually a commercial frequency single-phase or three-phase power supply is used. Reference numeral 2 denotes a processing power supply circuit, which is a first rectifier circuit that rectifies the input from the AC power supply 1, and an inverter that converts the DC output of the first rectifier circuit into high-frequency AC with an output according to the output current setting signal. From the AC power supply 1 and the inverter type power supply circuit that includes a transformer that converts the output of the circuit and inverter circuit into a voltage suitable for plasma arc machining, and a second rectifier circuit that rectifies the output of the transformer again into DC. A publicly known power supply circuit such as a power supply circuit of a system in which an input of is properly transformed and an output is controlled and rectified by a switching element such as a thyristor is used. Reference numeral 3 is a torch for plasma arc processing, and schematically shows only an electrode 3a and a nozzle 3b provided around the electrode 3a.

Reference numeral 4 is a workpiece, and a plasma arc 5 is formed between the electrode 3 a and the workpiece 4 by the working gas flow narrowed by the nozzle 3 b and the output from the power supply circuit 2. The nozzle 3b of the torch 3 is connected to the pilot arc current output terminal (b) of the power supply circuit 2. 6 is a current detector, and 7 is a voltage detector for detecting the voltage between the electrode 3a and the nozzle 3b. 8 is an output current setting device, 9 is an error amplifier that compares the setting signal Ir of the output current setting device 8 with the detection signal Ia of the current detector 6 and outputs a difference signal ΔI = Ir-I a, and 10 is an ILOG switch. is there.

Further, 11 is a multiplier for calculating the product Vn · Ia of both signals by inputting the detection signal Ia of the current detector 6 and the detection signal Vn of the voltage detector 7, and 12 is the allowable power loss of the torch 3. A reference value setter for setting a corresponding reference value sr, 13 compares the output sr of the reference value setter 12 with the output Vn · Ia of the multiplier 11 to obtain Vn · Ia ≧ sr (or Vn · Ir). When Ia> sr), a comparator that outputs a high level signal (hereinafter referred to as H), 14 is set when the output of the comparator 13 becomes H, and when the reset button 7 is pressed. A flip-flop circuit to be reset, 15 a plasma arc machining command start signal generating circuit, 16 an AND circuit, and 18 an alarm device which operates by its non-inverted output s2 when the flip-flop circuit 14 is set. , Such as a lamp or a buzzer is used.

Further, 19 is a high-frequency generation circuit for generating a high-frequency high voltage from the rise of the output of the start-up signal generation circuit 15 to the start of the plasma processing current, and 20 is the output of the high-frequency generation circuit 19 of the power supply circuit 2. This is a coupling coil for superimposing on the output and supplying it to the torch 3.

In the device shown in FIG. 1, before the machining command signal (H signal) is output from the start signal generation circuit 15, the output of the AND circuit 16 is at a low level (hereinafter indicated by L), and the analog switch 10 Is cut off and no signal is transmitted to the processing power supply circuit 2, and therefore 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, the output of the comparator 13 is L because sr> Vn · Ia, and the flip-flop circuit 14 is reset. Its inverted output s1 is H. In this state, when the output of the start signal generation circuit 15 becomes H, the AND circuit 16 outputs both signals because the 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. Transfer to circuit 2. (At this time, since the output current Ia = 0, ΔI = Ir.) The power supply circuit 2 is activated by this signal, and the output voltage is generated at the terminals (a) to (c).

On the other hand, when the output of the activation signal generation circuit 15 becomes H, the activation high frequency generation circuit 14 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 in the gap between the electrode 3a of the torch 3 and the nozzle 3b is destroyed and a spark discharge is generated, and this spark discharge and the voltage output between the output terminals (a) and (b) of the power supply circuit 2 are Causes an arc discharge. This arc discharge becomes a pilot arc limited to a small current by the current suppressing element 2a made of a resistor provided inside the terminal (b). Further, at this time, a plasma arc working gas such as air, oxygen, or an inert gas is supplied between the electrode 3a of the torch 3 and the nozzle 3b by a working gas supply means (not shown), and the tip of the nozzle 3b is Gush out from a narrow opening. 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. Arc is induced between the electrode 3a and the workpiece 4. Since this arc does not pass through the current suppressing element 2a, it rapidly increases. This current is detected by the current detector 6 and becomes the detection signal Ia, which is compared with the set value Ir of the output current setter 8 by the error amplifier 9 to give the difference signal ΔI = Ir-Ia. As a result, the output current Ia is controlled to be equal to the output set value Ir.

At this time, the detection signal Ia of the output current detector 6 is also supplied to the multiplier 11 and the product Ia · Vn with the output Vn of the voltage detector 7 is calculated. The multiplication value Ia · Vn is compared with the set value sr of the reference value setting unit 12 in the comparator 13. The comparator 13 compares the both input signals and outputs an L signal while sr> Vn · Ia (or sr ≧ Vn · Ia), and outputs H when sr ≦ Vn · Ia (or sr <Vn · Ia). Output a signal. While the output of the comparator 13 is L, the inverted output s1 of the flip-flop circuit 14 is H, so the output of the AND circuit 16 remains H and the starting state is not released, but the output of the comparator 13 becomes H. Then, since the inverted output s1 of the flip-flop circuit 14 becomes L, the output signal of the AND circuit 16 becomes L regardless of the output of the start signal generating circuit 15, the analog switch 10 is cut off, and at the same time, the non-operation of the flip-flop circuit 14 is turned off. The inverted output s2 becomes H and the alarm device 18 operates to notify the operator of the abnormality. Here, the flip-flop circuit 14, the AND circuit 16, and the analog switch 10 constitute a protection circuit that prohibits the machining work when the output of the multiplier 11 is excessive, and the flip-flop circuit 14, the alarm device 18, and the reset button 17 alarm. It constitutes a circuit.

In the apparatus of FIG. 1, the set value sr of the reference value setter 12 may be set to a value slightly lower than the value of the multiplication value Ia · Va which has a risk of burning the torch. That is, the reference value sr is set based on a value corresponding to safe power consumption with respect to the capacity of the torch 3, and the distance between the electrode 3a and the nozzle 3b becomes long due to electrode consumption, so that the detection voltage is increased. The product Vn · Ia of the current Ia and the voltage Vn is excessive when Vn becomes abnormally high, or when a large current exceeding the allowable current of the torch 3 flows due to an incorrect current setting or an abnormality in the power supply circuit 2. When Vn · Ia ≧ sr, the output of the comparator 13 becomes H, the inverted output s 1 of the flip-flop circuit 14 becomes L, and the output of the AND circuit 16 becomes L, and the analog switch 10 becomes It shuts off and stops the output of the processing power supply circuit 2. Since the flip-flop circuit 14 maintains the set state until the operator pushes the reset button 17, the output of the machining power supply circuit 2 is cut off and both the output voltage and the current become zero, and the product Ia · Vn becomes less than the reference value sr. Even if it becomes smaller, the output prohibition state is maintained. On the other hand, when the output voltage Vn · Ia of the multiplier 11 does not exceed the reference value sr, as in the case where the detected voltage Vn is high, the current Ia is small, and conversely, when the detected current Va is large, the voltage Vn is low, the power source is not supplied. The output of circuit 2 is not prohibited and processing continues.

FIG. 2 is a connection diagram showing another embodiment of the present invention. In the embodiment shown in the figure, the output Vn · Ia of the multiplier 11 is continuously integrated during plasma arc machining, and when the integrated value exceeds a reference value, it is judged as abnormal and machining is prohibited. is there. For this purpose, an integrating circuit consisting of a capacitor C1, resistors R1 and R2, a switching transistor Q1 and an inverter INV is connected between the output of the multiplier 11 and the comparator 13 as shown in the same figure. I have inserted it. The other parts of the figure have the same functions as those of the embodiment shown in FIG.

In the embodiment shown in FIG. 2, before the machining is started, the output of the current detector 6 is zero, so that the input of the inverter circuit INV of the integrating circuit 21 is L, so that the output thereof becomes H 2, and switching occurs. The transistor Q1 for conduction is turned on, and the charge stored in the capacitor C1 is discharged through the resistor R2. Therefore, when the machining stop time is sufficiently long, the integrating circuit 21 is completely reset and the output voltage becomes zero.

When the output signal of the starting signal generating circuit 15 becomes H and plasma arc machining is started in the same manner as described in the apparatus of FIG. 1, the machining current is detected by the current detector 6. The output signal Ia is compared with the set value Ir of the output current setter 8 by the error amplifier 9, and the difference signal ΔI = Ir-Ia is supplied to the power supply circuit 2 so that the output current becomes equal to the set value Ir. Controlled by.

The output Ia of the current detector 6 or the inverter circuit INV of the integrating circuit 21 and one input terminal of the multiplier 11 are also supplied. When the signal Ia rises from zero, the output of the inverter circuit INV is inverted from H to L, the switching transistor Q1 of the integrating circuit 21 is cut off, and the discharge of the capacitor C1 is stopped.

At the same time, the detection voltage Vn and the detection current Ia between the electrode 3 a of the torch 3 and the nozzle 3 b become a signal Vn · Ia corresponding to the product of the two in the multiplier 11, and the resistor R 1 of the integrating circuit 21. The capacitor C1 begins to be charged through. Due to this charging, the terminal voltage sp of the capacitor C1 increases 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).

The terminal voltage sp is compared with the set value sr of the reference value setter 12 by the comparator 13. When the product Vn · Ia of the detected voltage Vn and the detected current Ia is smaller than the reference value sr (Vn · Ia <sr or Vn · Ia ≦ sr) or the integrated value sp is the reference value even if Vn · Ia is large. While the value is smaller than sr, the output of the comparator 13 is L, the flip-flop circuit 14 remains reset, and the inverting terminal output s1 is H, so that the processing is not prohibited.

However, when the signal sp ≧ sr (or sp> sr), the output of the comparator 13 becomes H and the inverted output s1 of the flip-flop circuit 14 becomes L, and the output of the AND circuit 16 is inverted from H to L. The analog switch 10 is cut off and the power supply circuit 2 stops the output. (No processing allowed).

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

When the machining is stopped due to the output of the start signal generating circuit 15 becoming L due to an abnormality detection or a command from the operator, each output of the current detector 6 and the voltage detector 7 becomes zero. The output Vn · Ia of the multiplier 11 also becomes zero. Further, when the processing is stopped and Ia = 0, the output of the inverter circuit INV of the integrating circuit 21 is inverted from L to H, and the switching transistor Q1 is made conductive. When the switching transistor Q1 is turned on, the charge stored in the capacitor C1 starts to discharge through the switching transistor Q1 and the resistor R2, which causes the terminal voltage sp of the capacitor C1 to have a time constant c1 · r2 (where r2 is for switching). It gradually decreases according to the resistance value of the discharge circuit composed of the transistor Q 1 and the resistor R 2.

As described above, since the terminal voltage sp of the capacitor C1 rises according to the time constant c1.r1 during machining and discharges according to the time constant c1.r2 after machining is stopped, these time constants are set to those of the torch 3. Approximately match the time constant when the temperature rises and the time constant when cooling. By setting in this way, even if Vn · Ia is large, it is possible to use for a short time overload as long as it is within the allowable range of the heat capacity of the torch. -If Ia is within the allowable value, it can be used.

The integrating circuit 21 used in the embodiment of FIG. 2 may be configured by using an operational amplifier.

FIG. 3 is a connection diagram showing an example in which an integrating circuit is configured by using operational amplifiers, and only the integrating circuit is shown.

In the figure, OP1 is an operational amplifier, R3 and R4 are resistors, C2 is a capacitor, AN1 is an analog switch, and INV is an inverter circuit. In the case of the integrating circuit in the figure, the integration time constant during plasma arc machining is c2.r3, and the discharge time constant when machining is stopped is c2.r4. (However, c2 is the capacitance of the capacitor C2, r3 is the resistance value of the resistor R3, and r4 is the resistance value of the discharge circuit composed of the resistor R4 and the analog switch AN1.)

The relationship between the H and L of each signal and the logic circuit to be used described in each of the above-described embodiments are not limited to those shown in each of the embodiments, and are similar to those described in each of the embodiments. Any logical operation can be performed as long as the operation is performed.

[0034]

[Effect of device]

 The present invention is different from the conventional device that simply detects a change in electrode voltage or current to judge an abnormality, and the voltage Vn between the electrode and the nozzle corresponding to the electric power actually consumed in the torch and the machining. Since the risk of torch burnout is estimated by the product of the current Ia, there is no malfunction due to voltage changes due to camera shake by the operator, and there is sufficient protection against abnormal output from the machining power circuit. It can protect the torch from burnout.

[Brief description of 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 present invention.

FIG. 3 is a connection diagram showing another embodiment of the integrating circuit used in the present invention.

[Explanation of symbols]

 2 Processing power supply circuit 3 Torch 3a Electrode 3b Nozzle 6 Current detector 7 Voltage detector 8 Output current setting device 9 Error amplifier 10, AN1 Analog switch 11 Multiplier 12 Reference value setting device 13 Comparator 14 Flip-flop circuit 15 Start signal Generator circuit 17 Reset button 18 Alarm device 21 Integrator circuit

Claims (3)

[Scope of utility model registration request] 1. A torch burnout prevention device for use in a plasma arc processing machine, wherein a plasma arc narrowed by a nozzle and a working gas is generated between an electrode of a torch and a workpiece to melt or weld the workpiece. A current detector for detecting a current flowing through the electrode of the torch, a nozzle voltage detector for detecting a voltage between the electrode of the torch and a nozzle, an output Ia of the current detector and a nozzle voltage detector. A multiplier for obtaining the product Vn · Ia of the output Vn, a reference value setting device, the output Vn · Ia of the multiplier and the setting value sr of the reference value setting device are compared, and Vn · Ia ≧ sr. Sometimes a comparator that judges an abnormality and outputs an alarm signal,
A torch burnout prevention device for a plasma arc processing machine, which is provided with a protection circuit for prohibiting a processing operation according to an output signal of the comparator. 2. A torch burnout prevention device for use in a plasma arc processing machine, wherein a plasma arc constricted by a nozzle and a working gas is generated between an electrode of a torch and a work piece to melt or weld the work piece. A current detector for detecting a current flowing through the electrode of the torch, a nozzle voltage detector for detecting a voltage between the electrode of the torch and a nozzle, an output Ia of the current detector and a nozzle voltage detector. A multiplier for obtaining a product Vn · Ia of the output Vn; an integrating circuit for integrating the output of the multiplier with a predetermined time constant;
A discharge circuit for discharging the output of the integrator circuit with a predetermined time constant when machining is stopped, a reference value setter, an output sp of the integrator circuit and a set value sr of the reference value setter are compared, and sp ≥
A torch burnout prevention device for a plasma arc machine equipped with a comparator that judges an abnormality when sr is output and outputs an alarm signal, and a protection circuit that prohibits machining work by the output signal of the comparator. 3. The alarm circuit according to claim 1, further comprising an alarm circuit for issuing an alarm to an operator according to an output signal of the comparator.
A torch burnout prevention device for a plasma arc processing machine according to any one of 1.