JPH07284950A - Power source for plasma cutting - Google Patents

Abstract

PURPOSE:To prevent a nozzle from being deformed by being heated with an arc when separating a torch from a base material while continuing the arc. CONSTITUTION:A plasma cutting power source device is provided in which an alternative current power source is rectified and smoothed into a direct current, after this DC current is switched in terms of a high frequency wave by an output control means using a chopper 12, the DC current is smoothed again, and a plasma current is detected with a current detector to make the DC current a constant-current by controlling the power control means through a controller 36 which controls the output control means with use of the output of an error amplifier 61 amplifying the error between a detection signal and an output current setting signal. The device is provided with a voltage buffer circuit 62 to output a maximum load voltage setting signal when the plasma current flows, an OR circuit 74 to select the output voltage of the error amplifier and the buffer circuit, and a comparator 75 to stop the output signal of the controller when the output voltage of the buffer circuit is higher than the output voltage of the OR circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for plasma arc cutting.

[0002]

2. Description of the Related Art Generally, in a plasma cutting power supply device, an alternating current power source is transformed by a transformer, rectified and smoothed to be a direct current, and then this direct current is converted to a high frequency by a chopper circuit having switching elements such as IGBTs, MOSFETs and transistors. There is one that is switched and smoothed, and then supplied to the plasma-loaded torch and the base material after smoothing. The plasma cutting power supply device detects the output current supplied to the plasma load, and the constant current control is performed so that the output current has a constant value.

When a steel material is cut by using such a plasma cutting power supply device, the torch 22 and the base material 24 are usually disposed in the vicinity and cut as shown in FIG. 10 (a). However, as shown in FIG. 10B, when the torch 22 is separated from the base material 24, the arc 26 extends and the power source is controlled by the constant current, so that the arc continues up to the voltage of the ability to obtain the constant current control. Therefore, the nozzle 2 of the torch 22
As shown in FIG. 11 (b), the nozzle 20 is deformed toward the side closer to the base material by the arc from the normal state where 0 is the circular shape in FIG. 11 (a). When the torch of the deformed nozzle is used for cutting, the cutting performance is deteriorated, so that it is necessary to replace the nozzle.

Therefore, in Japanese Patent Application No. 5-77639, a voltage detector for detecting the output voltage of the power supply for plasma cutting is provided, and when the torch is separated from the base material, the output voltage of the power supply is made constant. It has been proposed to stop the control device and the output control means for controlling the chopper when the detection signal of the voltage detector becomes higher than the reference value.

[0005]

However, when a steel material is cut using such a plasma cutting power supply device, the output voltage increases due to constant current control when the torch is separated from the base material. At this time, there is a time delay in the rise of the output voltage due to the constant current, and the operation of the voltage detector is delayed. Due to this delay in operation, the arc may contact the nozzle of the torch and damage the nozzle.

[0006]

In order to solve the above-mentioned problems, the present invention rectifies and smoothes an AC power supply to convert it into a direct current, high-frequency switches the converted direct current to high-frequency switching, and then smoothes it again. A current error amplifier for detecting the plasma current by the current detector and amplifying the error between the detection signal and the output current setting signal, and a controller for controlling the output control means by the output of the error amplifier. A voltage buffer circuit that is applied to a plasma cutting power supply device that controls the output control means to make a constant current, and outputs a maximum load voltage setting signal when the plasma current flows, an output voltage of the error amplifier, and the voltage The OR circuit that selects the output voltage of the buffer circuit and the output signal of the control device when the output voltage of the voltage buffer circuit is higher than the output voltage of the OR circuit. The is provided with a comparator to stop.

A timer for starting the count when the maximum load voltage setting signal flows a plasma current, an analog switch for turning on by a signal from the timer from the count start of the timer until the time up, and the analog switch for turning on Formed by a maximum load voltage setting device including a peak hold circuit that holds the peak value of the voltage detection signal of the voltage detector and an adder circuit that raises and raises the output of the peak hold circuit by a predetermined ratio during the period It is a thing.

The above ratio is 15 to 50%.

The ratio of the adder circuit and the output current setting signal are unitarily adjusted.

The AC power supply is rectified / smoothed into a direct current, and the direct current converted into the direct current is subjected to high frequency switching by an output control means such as a chopper or an inverter, then smoothed or rectified / smoothed again, and a plasma current is detected by a current detector. A constant current is controlled by controlling the output control means through a current error amplifier for detecting and amplifying an error between the detection signal and the output current setting signal and a control device for controlling the output control means by the output of the error amplifier. Applied to the optimized power supply for plasma cutting, voltage error that detects the output voltage and voltage error that amplifies the error between the voltage detection signal of the voltage detector and the maximum load voltage setting signal when the plasma current flows The output voltage of the amplifier, the OR circuit that selects the output voltage of both the error amplifiers, and the output voltage of the voltage error amplifier are higher than the output voltage of the OR circuit. When, is provided with a comparator for stopping the output signal of the control device.

The current detection signal of the current detector is input to the voltage error amplifier.

A timer for starting counting when the maximum load voltage setting signal flows a plasma current, an analog switch for turning on with a signal from the timer from the start of counting of the timer to the time up, and the analog switch for turning on Formed by a maximum load voltage setting device including a peak hold circuit that holds the peak value of the voltage detection signal of the voltage detector and an adder circuit that raises and raises the output of the peak hold circuit by a predetermined ratio during the period It is a thing.

[0013]

When the output is output from the constant-current plasma power supply device and the plasma current flows, the maximum load voltage setting signal for setting the maximum load voltage is output to the output of the voltage buffer circuit. On the other hand, the current detection signal detected by the current detector and the output current setting signal are error-amplified by the error amplifier, and the output signal of the voltage buffer circuit and the error-amplified signal are selected by the OR circuit. When the voltage buffer circuit is selected, the output signal of the voltage buffer circuit controls the output control means through the control device to perform the constant phase control. When the output voltage of the voltage buffer circuit becomes higher than the output voltage of the OR circuit, the comparator stops the output signal of the control device.

When a plasma current flows, the timer starts counting, the timer is turned on to turn on the analog switch, and the timer is turned off to turn off the analog switch. The peak hold circuit causes the peak value of the output voltage of the power supply device to be held by the output signal of the timer during the ON period of the analog switch. An output signal of the peak hold circuit and a signal having a predetermined ratio of this output signal are added by an adder circuit, and the output signal of the adder circuit is switched from constant current control to constant phase control.

The output signal of the peak hold circuit is set to 1
The constant current control can be switched from the optimum constant current control to the constant phase control by increasing the rate at a rate of 5 to 50%.

Further, by adjusting the ratio of the adder circuit and the output current setting signal in a unified manner, the ratio can be reduced when the plasma current is rated and can be increased when the low current region is used. It is possible to switch from constant current control to constant phase control.

Further, when the plasma current output from the plasma power supply device which has been made constant current flows, the error between the voltage detection signal of the voltage detector and the maximum load voltage setting signal is amplified by the voltage error amplifier, and the voltage error signal is amplified. The output signal of the error amplifier and the output signal of the current error amplifier are selected by the OR circuit. When the voltage error amplifier is selected, the output signal of the voltage error amplifier controls the output control means via the control device to perform constant voltage control. When the output voltage of the voltage error amplifier becomes higher than the output voltage of the OR circuit, the comparator stops the output signal of the control device.

When the current detection signal of the current detector is input to the input of the voltage error amplifier, the current detection signal is added to the voltage detection signal, and the error between the added signal and the maximum load voltage setting signal is added. Is amplified by the voltage error amplifier. When the output signal of the voltage error amplifier is selected by the OR circuit, the output signal of the voltage error amplifier controls the output control means via the control device to perform slope control.

When the plasma current flows, the timer starts counting, the timer counts to turn on the analog switch, and the timer switches up to turn off the analog switch. During the ON period of the analog switch, the peak hold circuit holds the peak value of the output voltage of the power supply display by the output signal of the timer. An output signal of the peak hold circuit and a signal having a predetermined ratio of this output signal are added by an adder circuit, and the output signal of the adder circuit is switched from constant current control to constant voltage control as an input signal of the voltage error amplifier.

[0020]

FIG. 2 shows an embodiment of a plasma cutting power supply device according to the present invention. The plasma cutting power supply device 1 receives an AC power supply at an input terminal 2, and a non-consumable electrode 18 and a nozzle 2
Direct current is supplied to the plasma load constituted by the torch 22 having 0 and the base material 24. Now, AC power is received by the input terminal 2 and input to the transformer 6 via the input switch 4. The voltage transformed by the transformer 6 is rectified by the rectifier 8 and smoothed by the capacitor 10. The smoothed current is high-frequency switched by a chopper circuit 12 having switching elements such as IGBT, MOSFET, power transistor, etc., and smoothed by a reactor 14 and a flywheel diode 16. The smoothed DC voltage applies the negative electrode to the electrode 18 and the positive electrode to the base material 24. Further, a pilot arc opening / closing means 28, a current limiting resistor 30, and a high frequency generator 32 for generating high voltage high frequency.
It is applied to the nozzle 20 and the electrode 18 via.

On the other hand, the output current is detected by the current detector 34, and the detected signal is input to the chopper control device 36 for controlling the chopper circuit 12 to amplify the error from the built-in reference signal, thereby forming a feedback system. The output current is constant.

Numeral 38 is a relay or an electronic switchgear, which inputs the output signal of the current detector 34 and which is connected to the electrode 18
When a current flows through the base material 24, an output signal is output to the chopper control device 36.

Next, a concrete block diagram of the chopper control device 36 is shown in FIG. 61 is an error amplifier for current, 6
2 is a voltage buffer circuit. The detection signal of the current detector 34 and the output current setting signal of the output current setting power supply 67 are input to one input terminal of the error amplifier 61, and the reference value is input to the other, and the error between both signals is amplified. . The output signal of the maximum load voltage setting device 71, which inputs the bias power supply 69, is input to the voltage buffer circuit 62, and the maximum load voltage setting device 71 receives the output signal of the switchgear device 38 and outputs the maximum load voltage setting device 71 of A normally-closed opening / closing means 38b such as a normally-closed contact or a normally-closed analog switch for short-circuiting the input and output is connected. Diodes 63 and 64 are connected to the outputs of the error amplifier 61 and the voltage buffer circuit 62, respectively, and the diodes 63 and 64 form an OR circuit 74. A comparator 75 compares the output signal of the OR circuit 74 with the output signal of the voltage buffer 62. Reference numeral 76 is a PWM control device that performs PWM control of the chopper circuit 12 by the output signal of the OR circuit 74, and stops the PWM control signal by the output signal of the comparator 75. The output of the comparator 75 is connected to a normally open switch 38a such as a normally open switch of the switch 38 or a normally open analog switch. Incidentally, 65, 66, 68, 70, 72 and 73 are resistors.

If the high frequency generator 32 is not operated even if a start switch (not shown) is turned on, the electrode 18
Since no pilot arc is generated between the nozzle 20 and the nozzle 20, no output current flows in the power supply device 1. This allows
The detection signal of the current detector 34 is 0, the switchgear 38 does not operate, the switchgear 38b is closed, and the switchgear 38a is open. Since the detection signal of the current detector 34 is 0, the output of the error amplifier 61 outputs the maximum value, the input of the maximum load voltage setter 71 is short-circuited, and the bias current 69 is input to the input of the voltage buffer circuit 62. Is input, and the buffer circuit 62 outputs the maximum value. Therefore, the maximum value is input to the PWM control device 76, and the chopper circuit 12 is driven by the drive signal of the chopper control device 36. As a result, the direct current rectified by the rectifier 8 is applied to the chopper circuit 1
2 is subjected to high frequency switching and smoothed by the reactor 14 and the flywheel diode 16 so that the electrode 18
An unloaded DC voltage indicated by the point X in FIG. 3 is applied to the base material 24, the electrode 18, and the nozzle 20. Here, when the high frequency generator 32 is operated, a high voltage high frequency is applied between the electrode 18 and the nozzle 20, and a pilot arc is generated between the electrode 18 and the nozzle 20. Then, a pilot current flows through the rectifier 8, the chopper circuit 12, the current detector 34, the opening / closing means 28, the current limiting resistance 30, the high frequency generator 32, the nozzle 20, the electrode 18, the reactor 14, and the rectifier 8. Then, the output current is detected by the current detector 34. However, since the main current does not flow between the base material 24 and the electrode 18, the switchgear 38 continues the initial state. Here, when the torch 22 is brought close to the base material 24, the plasma flow excited by the pilot arc moves to the electrode 18 and the base material 24,
The plasma arc 26 is generated, and the cutting of the base material 24 is started. Then, although the output voltage of the current error amplifier 61 becomes low, the output of the current error amplifier 61 is the PWM control signal 76 because the error between the detection signal and the output setting signal is large.
Input into the plasma arc. When a plasma arc is generated, the main current due to the plasma arc is detected by the current detector 34, the switchgear 38 is operated, the normally open switchgear 38a is closed, and the normally closed switchgear 38b is opened.
As a result, the output voltage of the voltage buffer circuit 62 outputs the voltage set by the maximum load voltage setting unit 71.
On the other hand, the detection signal of the current detector 34 is compared with the output setting signal of the output current setting power supply 67, and the error is amplified.
Due to the arc load characteristic, the output voltage of the error amplifier 61 is lower than the output voltage of the buffer circuit 62, the diode 63 is turned on, and the PWM controller 7 is turned on by the signal of the error amplifier 61.
6 is controlled, and further, the chopper circuit 12 is controlled,
The output current of the chopper circuit 12 becomes a constant current as shown in FIG. When a plasma arc is generated, the high frequency generation circuit 32 is cut off, the opening / closing means 28 is cut off, and the pilot arc is also stopped.

When the torch 22 is near the base metal 24 as shown in FIG.
Is short, and the output voltage of the power supply device 1 is at a point lower than the maximum load voltage as indicated by point A in FIG. Since the output voltage of the buffer circuit 62 is higher than the output voltage of the error amplifier 61, the comparator 75 does not output, and the PWM control device 76 is controlled without being turned off to control the chopper circuit 12,
The base material 24 is stably cut.

However, as shown in FIG. 10 (b), when the torch 22 is separated from the base material 24, the power supply device 1 is under constant current control, so the output voltage of the power supply device 1 is from point A shown in FIG. The voltage rises to point B, the output voltage of the error amplifier 61 becomes higher, and finally becomes higher than the output voltage of the voltage buffer circuit 62, the diode 64 on the buffer circuit 62 side is turned on, and the PWM control device 76 causes the voltage buffer circuit 62 to turn on. Is controlled by the output signal of the maximum load voltage setting unit 71 in the chopper circuit 12,
Move to the straight line C in FIG. Further, the input voltage of the comparator 75 is such that the output voltage of the voltage buffer circuit 62 becomes lower than the output voltage of the diode 63 on the output side of the error amplifier 61, and the comparator 7
5 outputs an output, and PWM is output via the normally-opening / closing means 38a.
Input to the control device 76, the chopper control device 36 stops the output of the drive signal, and turns off the chopper circuit 12.

As a result, when the maximum load indicated by point B in FIG. 3 is reached, constant phase control is performed by the output of the voltage buffer circuit 63, and the chopper circuit 12 is controlled without receiving a feedback system by constant current control. By stopping the drive signal of the control device 36, it is possible to reliably prevent the maximum power from being input to the torch 22,
It is possible to prevent the nozzle 20 of the torch 22 from being damaged.

FIG. 4 shows a power supply device for plasma cutting according to another embodiment. 2 that are the same as those in FIG. 2 have the same functions. In the power supply device of FIG. 4, the AC power supply is rectified by the rectifier 44 and smoothed by the capacitor 46 in order to reduce the size and weight. Inverter 4 incorporating this smoothed direct current into a switching element such as an IGBT, MOSFET or power transistor
8 obtains high frequency alternating current, and this high frequency alternating current
Is transformed by the rectifier 52 on the output side, rectified again by the rectifier 52 on the output side, and smoothed by the reactor 54. And
A current is detected by the current detector 34, the detection signal is input to the inverter control device 58 that controls the inverter 48, the error with the built-in reference signal is amplified to form a feedback system, and the output current is made constant. ing. Further, the specific circuit of the inverter control device 58 may be configured by converting the chopper PWM control device 76 of the chopper control device 36 of FIG. 1 into an inverter PWM control device 88. The operation of this power supply device is basically the same as that of the plasma cutting power supply device of FIG. As a result, the power supply device can be downsized.

While the constant phase control is performed in FIG. 1,
In FIG. 4, the torch 22 is the base material 24 as shown by the broken line.
While the constant phase control shown in FIG. 1 is performed when it is separated from the control unit, it is provided for the purpose of constant voltage control so as not to be affected by fluctuations in the power supply. The figure is shown in FIG. That is, the torch 22
The output voltage due to the relationship between the base material 24 and the base material 24 is detected by the voltage detector 56, and the detection signal is input to the inverter control device 58. A voltage error amplifier 81 receives a voltage detection signal and a maximum load voltage setting signal from a maximum load voltage setting power supply 86 at one input terminal, and a reference value at the other input terminal. Is amplified. Further, the input part of the voltage detection signal is provided with a normally open opening / closing means 38c of the opening / closing device 38.
Is provided. Incidentally, 84, 85 and 87 are resistors.

At the time of start-up, the detection signal of the current detector 34 is 0, so the output of the error amplifier 61 for current outputs the maximum value. On the other hand, since the opening / closing means 38c of the switching device 38 is opened, the output of the voltage error amplifier 81 also outputs the maximum value, the maximum value is input to the PWM control device 88, and the inverter 48 of the inverter control device 58. Operated by drive signal. As a result, the inverter 48 outputs the maximum value, and the voltage applied to the torch 22 and the base material 24 via the transformer 50, the rectifier 52, and the reactor 54 is the maximum no-load voltage. Then, as in the apparatus shown in FIG. 1, the high frequency generator 32 is operated to generate a pilot arc between the electrode 18 and the nozzle 20, and the torch 22 and the base material 24.
The plasma arc 2 on the electrode 18 and the base metal 24
6 occurs and the cutting of the base material 24 is started. In addition, the normally open / close means 36c is short-circuited due to the generation of the plasma arc,
Although the error between the voltage detection signal and the maximum load voltage setting signal is amplified, the output voltage of the error amplifier 61 becomes lower than the output voltage of the error amplifier 81 due to the arc load characteristic, and A of FIG.
Constant current control is performed as indicated by the dots.

Then, as shown in FIG. 10B, when the torch 22 separates from the base material 24, the output voltage of the power supply device 1 rises from point A to point B shown in FIG. 6, and the output of the error amplifier 61. The voltage becomes higher and finally becomes higher than the output voltage of the error amplifier 81, and the diode 64 on the error amplifier 81 side
Is turned on, the PWM control device 88 is subjected to constant voltage control to a voltage determined by the setting signal of the maximum load voltage setting power supply 86 of the error amplifier 81, and moves from the point B to the straight line D. Further, the input voltage of the comparator 75 is such that the output voltage of the error amplifier 81 becomes lower than the output voltage of the output diode 63 of the error amplifier 61, and the comparator 75 outputs it to the PWM control device 88 via the normally open / close means 38a. Input and stop the output signal to stop the inverter 48. It is desirable that the setting signal of the maximum load voltage setting device 86 is set to a voltage slightly lower than the output setting signal having the constant phase shown in FIG.

As a result, since the constant voltage is controlled at the maximum load, the maximum power input to the torch can be reduced, and by stopping the drive signal of the inverter controller 58, the torch can be reliably input. The maximum power can be reduced and damage to the nozzle 20 of the torch 22 can be prevented.

Further, another concrete block diagram of the inverter control device 58 is shown in FIG. The difference from FIG. 5 is that the detection signal detected by the current detector 34 is output to the error amplifier 81.
It is adapted to be input via the resistor 91.

Since the detection signal of the startup current detector 34 is 0, the error amplifier 61 outputs the maximum value. On the other hand, the opening / closing means 38c of the opening / closing device 38 is opened, the input of the error amplifier 81 is 0 for both the current detection signal and the voltage detection signal, the output of the error amplifier 81 also outputs the maximum value, and the PWM control device 88 has the maximum output. A value is input and the inverter 48 operates. As a result, the inverter 48 outputs the maximum value, and the transformer 50, the rectifier 52, and the reactor 54
Is applied to the torch 22 and the base material 24 via the, and the applied voltage is the maximum no-load voltage. Then, the high frequency generator 32 is operated to generate a pilot arc between the electrode 18 and the nozzle 20, bring the torch 22 close to the base material 24, and generate a plasma arc 26 to cut the base material. Normally-opening / closing means 38c due to generation of plasma arc
Are short-circuited, the output voltage of the error amplifier 61 becomes lower due to the output voltage of the error amplifier 81 due to the arc load characteristic, and constant current control is performed as indicated by point A in FIG.

When the torch 22 moves away from the base material 24 as shown in FIG. 10B, the output voltage of the power supply device 1 rises from point A to point B shown in FIG. Becomes higher than the output voltage of the error amplifier 81, the diode 64 on the error amplifier 81 side is turned on, and the PWM control device 88 outputs the setting signal of the maximum load voltage setting power supply 86 of the error amplifier 81, the voltage detection signal, and the current detection signal. The slope characteristic corresponds to the added signal, and the line moves to the straight line E shown in FIG.

The input of the comparator 75 is the error amplifier 81.
Becomes lower than the output voltage of the output diode 63 of the error amplifier 61, and the comparator 75 outputs it and inputs it to the PWM control device 88 via the normally open switching means 38a to stop the output signal and turn on the inverter 48. Stop.

As a result, since the slope characteristic is controlled at the maximum load, the maximum power input to the torch can be reduced, and by stopping the drive signal of the inverter control device 58, the torch can be surely input. The maximum power required for the torch 22 can be reduced.
0 damage can be prevented.

In the above embodiment, the maximum load voltage is set when the output current is set. However, if the plate thickness of the object to be cut changes during cutting, or if the cutting speed changes from a straight line cutting to a slow cutting line or vice versa, the output voltage changes and the constant current region changes. There is a problem that it is impossible to make the most of the cutting ability by shifting to constant phase, constant voltage and slope characteristics. Therefore, in order to solve this problem, the maximum load voltage setting device 1 shown in FIG.
An inverter control circuit or a chopper control circuit having 00 is proposed. That is, the maximum load voltage setting device 10
0 is an analog switch 101 that inputs the detected voltage detected by the voltage detector 56, a timer 103 that starts counting by the normally open switching means 38f of the switchgear 38 and turns on the analog switch 101 until the time is up, and an analog A peak hold circuit 102 that holds the maximum value of the voltage detection signal while the switch 101 is on,
Operational amplifier 107 and resistors 104, 105, 106, 10
8 and an adder circuit 109 having an output signal of the peak hold circuit 102 and an input signal circuit for inputting a signal for outputting a predetermined ratio of this output signal; and an adder circuit 1
It is constituted by a normally-open opening / closing means 38e of the opening / closing device 38 having an output of 09.

Since the detection signal of the startup current detector 34 is 0, the output of the error amplifier 61 outputs the maximum value. on the other hand,
The opening / closing means 38b of the opening / closing device 38 is short-circuited, 38e is opened, the output of the voltage buffer circuit 62 also outputs the maximum value, the maximum value is input to the PWM control device 88, and the output of the inverter 48 is the maximum value. Output torch 22 and base material 2
The maximum no-load voltage is applied to No. 4. Then, the high frequency generator 32 is operated to generate a pilot arc between the electrode 18 and the nozzle 20, bring the torch 22 close to the base material 24, and generate a plasma arc 26 to cut the base material. Due to the generation of the plasma arc, the normally open / close means 38b is opened and the normally open / close means 38e, 38f are short-circuited.

The timer 103 starts counting by the normally-opening / closing means 38f, and the analog switch 101
Input the ON signal to. The analog switch 101 is turned on, and the voltage detection signal of the voltage detector 56 is input to the peak hold circuit 102 via the analog switch 101.
Then, the period until the timer 103 times out,
The analog switch 101 continues to be turned on, and the peak value of the voltage detection signal is held. Peak hold circuit 10
The signal for which 2 is held is input to the operational amplifier 107 via the resistor 104 and the ratio adjusting resistor 105.
The signal divided by is passed through the resistor 106 to the operational amplifier 10
7, and the signal obtained by raising the voltage detection signal by a predetermined ratio is input to the voltage buffer circuit 62 via the normally-open switching device 38e. However, due to the arc load characteristic, the output voltage of the error amplifier 61 becomes lower than the output voltage of the voltage buffer circuit 62, and constant current control is performed.

Then, as shown in FIG. 10B, when the torch 22 is separated from the base material 24, the output voltage of the power supply device 1 rises, and the output voltage of the error amplifier 61 becomes lower than the output voltage of the voltage buffer circuit 62. Voltage buffer circuit 62
The diode 64 on the side is turned on, and the PWM control device 88 moves to a curve of a constant phase corresponding to the signal voltage raised by a predetermined ratio to the voltage detection signal during the period when the analog switch 101 is on.

The input voltage of the comparator 75 is the output voltage of the voltage buffer circuit 62 and the output diode 6 of the error amplifier 61.
The output voltage becomes lower than the output voltage of No. 3, and the comparator 75 outputs it and inputs it to the PWM control device 88 through the normally-opening / closing means 38a to stop the output signal and stop the inverter 48.

As a result, the power supply device can be controlled in a constant phase without receiving a feedback system by the constant current control.
At this time, the value that shifts from constant current control to constant phase control is determined by the function of the power supply device output voltage determined by the arc load characteristics under constant current control. The optimum transition point is also determined by the change of, and the cutting ability can be maximized.

The ratio of raising the voltage detection signal is 15 to 50%, 15 to 20% near the rated current of the power supply device, and 30 to 5 in the low current region where the thin plate is cut.
Selected as 0%. In addition, as shown by the one-dot chain line in FIG.
If the output current setting power supply 67 and the ratio adjusting resistor 105 are adjusted by one adjuster 111, workability is improved.

In FIG. 9, the case of the constant phase has been described, but the case of shifting from the constant current control to the constant voltage control as shown in FIG. 5 and the constant current control to the slope control as shown in FIG. Can also be applied to the transition of. In this case, the normally-open opening / closing means 38c and the resistors 84 and 8 shown in FIGS.
5 and the maximum load voltage setting power supply 86 may be replaced with the maximum load voltage setting device 100.

In the above embodiment, the diodes 63 and 64 forming the OR circuit 74 are connected in the direction of pulling in the error amplifier, but they may be connected in the direction of outputting positive from the error amplifier.

[0047]

As described above, according to the power supply device for plasma cutting of the present invention, the output voltage rises when the torch is separated from the base material. This increased output voltage performs constant phase control, constant voltage control or slope control for the maximum load, and further stops the control device, so that maximum power can be prevented from being input to the torch, and the nozzle Can be prevented and the life of the nozzle can be extended. Further, even if the thickness of the object to be cut changes in the cutting width or the cutting speed changes, the optimum maximum load voltage can be obtained and the cutting ability can be maximized.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a control device used in a plasma cutting power supply device of the present invention in the form of a partial block.

FIG. 2 is a circuit diagram showing an embodiment of a plasma cutting power supply device of the present invention in the form of a partial block.

FIG. 3 is a characteristic diagram of output current and output voltage of FIG.

FIG. 4 is a circuit diagram showing another embodiment of the plasma cutting power supply device of the present invention in the form of a partial block.

FIG. 5 is a circuit diagram showing another embodiment of the control device used in the plasma cutting power supply device of the present invention in the form of a part of a block.

6 is a characteristic diagram of the output current and output voltage of FIG.

FIG. 7 is a circuit diagram showing another embodiment of the control device used for the plasma cutting power supply device of the present invention in the form of a part of a block.

8 is a characteristic diagram of output current / output voltage of FIG. 7. FIG.

FIG. 9 is a circuit diagram showing another embodiment of the control device used in the power supply device for plasma cutting of the present invention in the form of a part of a block.

FIG. 10 is an explanatory diagram illustrating the relationship between the torch and the base material in the form of a partial cross-sectional view.

FIG. 11 is a bottom view of the nozzle seen from the base material side.

[Explanation of symbols]

 6,50 Transformer 8,44,52 Rectifier 12 Chopper circuit 14,54 Reactor 16 Flywheel diode 18 Electrode 20 Nozzle 22 Torch 24 Base metal 26 Plasma arc 32 High frequency generator 34 Current detector 36 Chopper controller 38 Switchgear 38a Normally open / close means 38b normally closed open / close means 38c normally open / close means 38e normally open / close means 38f normally open / close means 48 inverter 56 voltage detector 58 inverter controller 61 (for current) error amplifier 62 voltage buffer circuit 63, 64 diode 67 Output current setting power supply 69 Bias power supply 71 Maximum load voltage setting device 74 OR circuit 75 Comparator 76 PWM control device 81 (for voltage) error amplifier 86 Maximum load voltage setting power supply 100 Maximum load voltage setting device 101 Analog switch 102 Kuhorudo circuit 103 timer 105 (for ratio adjustment) resistor 107 operational amplifier 109 summing circuit 111 adjuster

Front page continuation (72) Inventor Atsushi Kinoshita 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City, Osaka Prefecture Sansha Electric Manufacturing Co., Ltd. (72) Inventor Haruo Moriguchi 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City, Osaka Prefecture Sansan Electric Co., Ltd.

Claims (7)

[Claims] 1. An AC power supply is rectified / smoothed into a direct current, and the converted direct current is subjected to high-frequency switching by an output control means such as a chopper or an inverter, then smoothed or rectified / smoothed again, and a plasma is detected by a current detector. The output control means is controlled through a current error amplifier that detects a current and amplifies the error between the detection signal and the output current setting signal, and a control device that controls the output control means by the output of the error amplifier. In a power supply device for plasma disconnection that makes constant current, a voltage buffer circuit that outputs a maximum load voltage setting signal when the plasma current flows, an output voltage of the current error amplifier, and an output voltage of the voltage buffer circuit are selected. The output signal of the control device when the output voltage of the OR circuit and the voltage buffer circuit is higher than the output voltage of the OR circuit. A power supply device for plasma cutting, which is provided with a comparator for stopping the operation. 2. A timer that starts counting when the maximum load voltage setting signal flows a plasma current, an analog switch that is turned on by a signal from the timer from the start of counting of the timer to the time up, and the analog switch. Is on, the maximum load voltage setting device configured by a peak hold circuit that holds the peak value of the voltage detection signal of the voltage detector and an adder circuit that raises the output of the peak hold circuit by a predetermined ratio The power supply device for plasma cutting according to claim 1, which is formed. 3. The power supply device for plasma cutting according to claim 2, wherein the ratio is 15 to 50%. 4. The power supply device for plasma cutting according to claim 2, wherein the ratio of the adder circuit and the output current setting signal are adjusted in a unified manner. 5. An AC power supply is rectified / smoothed into a direct current, and the converted direct current is subjected to high frequency switching by an output control means such as a chopper or an inverter, then smoothed or rectified / smoothed again, and a plasma is detected by a current detector. The output control means is controlled through a current error amplifier that detects a current and amplifies the error between the detection signal and the output current setting signal, and a control device that controls the output control means by the output of the error amplifier. In a plasma cutting power supply device with a constant current, a voltage detector for detecting an output voltage, and a voltage detector for amplifying an error between the voltage detection signal of the voltage detector and the maximum load voltage setting signal when the plasma current flows. The error amplifier, the OR circuit that selects the output voltage of both the error amplifiers, and the output voltage of the voltage error amplifier is greater than the output voltage of the OR circuit. A power supply device for plasma cutting, comprising: a comparator for stopping the output signal of the control device when it is high. 6. The power supply device for plasma cutting according to claim 5, wherein the current detection signal of the current detector is input to the input of the voltage error amplifier. 7. A timer that starts counting when the maximum load voltage setting signal flows a plasma current, an analog switch that is turned on by a signal from the timer from the start of counting of the timer to the time up, and the analog switch. Is on, the maximum load voltage setting device configured by a peak hold circuit that holds the peak value of the voltage detection signal of the voltage detector and an adder circuit that raises the output of the peak hold circuit by a predetermined ratio The power supply device for plasma cutting according to claim 5, which is formed.