JP3651181B2 - Plasma arc machining power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma arc machining power supply device for cutting or welding a workpiece.
[0002]
[Prior art]
Conventionally, in a plasma arc machining power supply device having a pilot arc current circuit, a no-load output voltage is output through a resistor as a pilot arc current, and the pilot arc current is induced to shift to the plasma arc current. Performed constant output current control and output stable plasma arc current to perform plasma welding or cutting. For example, FIG. 4 shows a circuit configuration of a conventional plasma arc machining power supply apparatus of an inverter control system. In FIG. 4, reference numeral 1 denotes an AC power source, which uses a three-phase or single-phase AC power source. Reference numeral 2 denotes a first rectifier circuit that rectifies the AC power supply 1 and converts it to DC, and 3 is an output voltage or output current adjustment circuit, which is composed of an inverter circuit. 4 is an insulation transformer, 5 is a second rectifier circuit for rectifying the output of the insulation transformer 4, 6 is a pilot arc current suppression resistor, 7 is a current detector for detecting plasma arc current, and 8 is a main of a plasma processing torch. Electrode, 9 is a tip of a plasma processing torch, 10 is a workpiece, 11 is an output current setter, 12 is a signal for comparing and amplifying the signal of the output current setter 11 and the signal of the current detector 7 to perform constant output current control. The comparison amplifier 13 is a drive circuit for the output adjustment circuit 3 that performs constant output current control by the output current control signal of the comparison amplifier 12. A is a known output current setting circuit comprising a current detector 7, an output current setting unit 11, and a comparison amplifier 12.
[0003]
In the above conventional configuration, the pilot arc current is generated by outputting the output voltage of the plasma arc machining power source between the main electrode 8 and the tip 9 via the pilot arc current suppression resistor 6 to generate a pilot arc. When this pilot arc is brought into contact with the workpiece 10, a plasma arc current is generated between the main electrode 8 and the workpiece 10 by induction of the pilot arc current. Here, the plasma arc current is detected by the current detector 7, is compared and amplified by the comparison amplifier 12 with the output current setting signal of the output current setting device 11, and is output to the drive circuit 13 as an output current control signal, so that constant output current control of the plasma arc current is performed. Is to do. Here, when no current flows through the current detector 7, the comparison amplifier 12 receives the signal from the output current setting device 11 only, the output signal of the comparison amplifier 12 becomes the maximum value, and the output of the plasma arc machining power source is the maximum no-load voltage ( The maximum no-load voltage that can be output by the device occurs. That is, the pilot arc current flows as a pilot arc current between the main electrode 8 and the tip 9 of the cutting torch via the pilot arc current suppression resistor 6 through the maximum no-load voltage.
[0004]
[Problems to be solved by the invention]
The pilot arc current of the above-described conventional configuration is such that the maximum no-load voltage of the plasma arc machining power source is output via the pilot current suppression resistor 6, and therefore the maximum no-load voltage value of the plasma machining power source and the value of the pilot current suppression resistor 6 Depends on. The load voltage required for plasma processing varies depending on the processing current value, and the no-load voltage of each device varies depending on the rated output current value in order to obtain the load voltage. Therefore, it is necessary to select the pilot current suppression resistor 6 for each plasma processing power source having a different rated current. Further, since the maximum no-load voltage of the plasma processing power supply varies according to the input power supply voltage, the pilot current also varies accordingly, and when the input power supply voltage rises greatly, the pilot current suppression resistor 6 may burn out. When the input power supply voltage drops greatly, there is a problem that the pilot arc current is insufficient and the transition to the plasma arc current is hindered. The present invention aims to solve these conventional problems.
[0005]
[Means for Solving the Problems]
In order to achieve this object, the present invention provides an output current setting circuit that controls a plasma arc current and an output voltage setting circuit that has an output voltage setting device that controls an output voltage when a pilot arc is generated. Is equipped with an output command signal selector that selects either the pilot arc load or plasma arc load according to the output load state, and can stably output a stable pilot arc current and plasma arc machining current. It is.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
With the above configuration, when a pilot arc is generated by alternative selection of the output command signal selector, a stable pilot arc current is obtained according to the state of the pilot arc load, and when the plasma arc load is shifted, a stable plasma is obtained. It has an effect of controlling so as to obtain an arc machining current.
[0007]
(Embodiment 1)
Embodiment 1 of the present invention will be described below with reference to FIG.
[0008]
The schematic configuration of the first embodiment is the same as that shown in the conventional example (FIG. 4), and the description of the overlapping symbols is omitted.
[0009]
In FIG. 1, 14 is an output voltage setter for setting an output voltage when no plasma arc load current is flowing through the current detector 7, and 15 is an output command signal selector composed of an analog switch or the like. 7, when the plasma arc load current is detected, the output command signal of the comparison amplifier 12 is selected in the output current setting circuit, and when the pilot arc load does not detect the plasma load current, the output voltage is set. The output signal of the circuit output voltage setter 14 is selected.
[0010]
In this configuration, the pilot arc current is applied between the main electrode 8 and the tip 9 of the plasma processing torch through the pilot arc current suppression resistor 6 as a no-load voltage of the plasma arc machining power supply device. Since it does not pass through the detector 7, the output command signal selector 15 selects the signal voltage of the output voltage setter 14. Therefore, the output voltage is set to an arbitrary value below the maximum no-load voltage by the output voltage setter 14. And even if the maximum no-load voltage value of the plasma arc machining power source changes, an arbitrary pilot arc current can be output by setting the output voltage at the time of pilot arc current output by the output voltage setting unit 14 to an arbitrary value. . After shifting to the plasma arc load state by the induction of the pilot arc current, the plasma arc machining current flows between the main electrode 8 and the workpiece 10, the current is detected by the current detector 7, and the output command signal selector 15 selects the output command signal of the comparison amplifier 12, that is, the output command signal of the output current setting circuit. At this time, the comparison amplifier 12 compares and amplifies the feedback signal of the current detector 7 and the signal of the output current setting device 11 so as to keep the output current, that is, the plasma arc current constant.
[0011]
(Embodiment 2)
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 shows a plasma arc machining power supply apparatus corresponding to a plurality of input voltages. In FIG. 2, reference numerals 14a and 14b denote output voltage setters for setting the output voltage of the plasma processing power source when the pilot arc current is generated at the same input voltage to each other. The switch 16 is switched according to each input voltage. In addition, an output voltage setting circuit is configured. For example, in the case of a plasma arc machining power supply apparatus corresponding to an input voltage of 200V / 220V, switching is performed according to each input voltage. That is, according to the configuration of FIG. 2, even if the input power supply voltage is different, if the output voltage setting value of the output voltage setting device 14a or 14b is selected corresponding to each input power supply voltage, the plasma arc machining power supply apparatus The output voltage can be kept the same, and the pilot arc current value can also be set to an arbitrary value.
[0012]
(Embodiment 3)
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 3 includes an output voltage detector 17 connected to an output circuit, and the input voltage fluctuates due to the comparison amplifier 18 comparing and amplifying the detection signal and the setting signal of the output voltage setting device 14 to fluctuate the output voltage. Even in this case, the output voltage when the pilot arc current of the plasma arc machining power source is generated is controlled so as to be always constant. In FIG. 3, the output setting circuit includes an output voltage setting device 14, an output voltage detector 17, and a comparison amplifier 18. As a result, a stable pilot arc current can be obtained regardless of fluctuations in the input power supply voltage or the output voltage.
[0013]
In the third embodiment, the inverter-controlled plasma arc machining power supply device has been described. However, in the plasma arc machining power supply of the thyristor phase control method and the transistor chopper control method that are controlled and rectified by the secondary circuit of the insulation transformer. The same control can be performed.
[0014]
【The invention's effect】
According to the first means of the present invention, the output voltage when the pilot arc current is generated is controlled by the output voltage setting device even in the plasma arc machining power supply device in which the maximum (rated) output current is different and therefore the output voltage (maximum no-load voltage) is different. It is possible to set the same and use the same pilot arc current suppression resistor and obtain a stable pilot arc current.
[0015]
According to the second means of the present invention, when the power circuit configuration of the plasma arc power supply device is the same, the output voltage is set so as to correspond to the input power supply voltage to be connected when the plurality of input power supply voltages are supported. By switching the setting device, the output voltage when the pilot arc current is generated can be set the same even if the input power supply voltage is different and the maximum no-load voltage is changed. Even if the same pilot arc current suppression resistor is used, A stable pilot arc current can be obtained.
[0016]
According to the third means of the present invention, when the input power supply voltage fluctuates during plasma arc machining, the output voltage at the time of the pilot arc generation is feedback-controlled and kept constant so that it is not affected by the fluctuation of the input power supply voltage. A stable pilot arc current can always be obtained.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram of a plasma arc machining power supply apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block configuration diagram of a plasma arc machining power supply apparatus according to Embodiment 2. FIG. Block diagram of the plasma arc machining power supply unit [Fig. 4] Block diagram showing a conventional example [Explanation of symbols]
14, 14a, 14b Output voltage setter 15 Output command signal selector 16 Switch 17 Output voltage detector 18 Comparison amplifier

Claims (3)

A plasma arc machining power supply device having a pilot arc current circuit, comprising: an output voltage setting circuit having an output voltage setting device for setting an output voltage when a pilot arc is generated; and an output current setting circuit for setting a plasma arc current; Equipped with an output command signal selector that selects either of the output command signals according to the output load status of either pilot arc load or plasma arc load. When pilot arc load is selected, select the output command signal of the output voltage setting circuit And a plasma arc machining power supply apparatus that selectively controls the plasma arc machining power supply output by selecting an output command signal of the output current setting circuit during plasma arc load. The plasma arc machining power supply device according to claim 1, further comprising a plurality of output voltage setting devices and their switches so as to switch the output voltage command signal of the output voltage setting circuit in accordance with the input power supply voltage. An output voltage detector that detects the output voltage to the pilot arc load or plasma arc load is provided, the signals of this output voltage detector and the output voltage setter are compared and amplified, and feedback control of the output voltage value is performed, and the pilot arc load The plasma arc machining power supply device according to claim 1, wherein the output voltage value at the time is kept constant.

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