JP2018176169A - Covered arc welding system and welding power source for covered arc welding - Google Patents

Abstract

An object of the present invention is to provide a covered arc welding system that suppresses arc breakage when the polarity of an output current changes and that can reduce the size and weight of a welding power source device. In a coated arc welding system comprising a coated arc welding rod B and a welding power supply device A1 for supplying electric power to the coated arc welding rod B, the welding power supply device A1 rectifies the AC power. A DC reactor 5 that smoothes the output of the rectifier circuit 4, an inverter circuit 7 that converts the DC power output from the DC reactor 5 into AC power and outputs the AC power to the coated arc welding rod B, and the coated arc welding rod B And a voltage superimposing circuit 6 that superimposes a re-ignition voltage on the output to. The voltage superimposing circuit 6 superimposes the re-ignition voltage when the polarity of the output current of the inverter circuit 7 is switched. [Selection] Figure 1

Description

  The present invention relates to a covered arc welding system and a welding power supply for covered arc welding.

  Coated arc welding is known as welding suitable for outdoor work. In coated arc welding, an arc is generated between a coated arc welding rod and a workpiece, and welding is performed by the heat of the arc. In the case of coated arc welding, unlike carbon dioxide gas arc welding etc., there is no need to blow gas. Therefore, the welding operation can be performed with a simple device. The welding operation can also be performed outdoors where the gas is dissipated by the wind. An example of an AC output coated arc welding system is disclosed, for example, in Patent Document 1.

  FIG. 7 is a diagram showing an example of a conventional coated arc welding system. The coated arc welding system shown in FIG. 7 includes a coated arc welding rod B, a welding rod holder C for holding the coated arc welding rod B and conducting a welding current, and a coated arc welding rod via the welding rod holder C. And a welding power supply A100 for supplying electric power to B. Welding power supply device A100 includes transformer 300 for transforming AC power, inputs AC power from commercial power source D to the primary side of transformer 300, and outputs AC power after transformation from the secondary side of transformer 300. . One output terminal a of the welding power supply device A100 is connected to the workpiece W by a cable, and the other output terminal b is connected to the welding rod holder C by a cable. Welding power supply device A 100 generates an arc between the tip of coated arc welding rod B and workpiece W to supply electric power.

Unexamined-Japanese-Patent No. 06-126459

  In the coated arc welding system shown in FIG. 7, it is necessary to increase the reactance on the secondary side of the transformer 300 in order to prevent arc breakage when the polarity of the output current changes. Therefore, the size of the transformer 300 has been increased, which has been an obstacle to reducing the size and weight of the welding power supply device A100.

  The present invention has been conceived under the above-described circumstances, and provides a covered arc welding system capable of suppressing arc breakage when the polarity of output current changes and reducing the size and weight of the welding power supply. The purpose is to

  The coated arc welding system provided by the first aspect of the present invention is a coated arc welding system comprising a coated arc welding rod and a welding power source for supplying power to the coated arc welding rod, The welding power supply device converts a DC power output from the DC reactor into AC power and outputs the AC power to the coated arc welding rod, a rectifier circuit that rectifies AC power, a DC reactor that smoothes the output of the rectifier circuit, and And a voltage superimposing circuit that superimposes a re-ignition voltage on the output to the coated arc welding rod, and the voltage superimposing circuit is configured to switch the polarity of the output current of the inverter circuit. It is characterized in that the re-ignition voltage is superimposed. According to this configuration, since the re-ignition voltage is superimposed when the polarity of the output current of the inverter circuit is switched, it is possible to suppress arc breakage when the polarity is changed. Further, since the arc breakage is suppressed by the superposition of the re-ignition voltage, it is not necessary to increase the reactance to suppress the arc breakage. Therefore, the direct current reactor can be miniaturized. Thereby, the welding power source can be reduced in size and weight.

  In a preferred embodiment of the present invention, the voltage superposition circuit comprises: a reignition capacitor for charging the reignition voltage; a charging circuit for charging the reignition voltage to the reignition capacitor; And a discharge circuit for discharging the re-ignition voltage charged in the re-ignition capacitor, wherein the charge circuit is controlled in timing of start or end of charge. According to this configuration, the reignition capacitor can be charged with the reignition voltage, and the reignition voltage charged with the reignition capacitor can be discharged. Also, charging of the reignition voltage to the reignition capacitor can be controlled.

  In a preferred embodiment of the present invention, the battery control apparatus further comprises a current sensor that detects an instantaneous value of the output current of the inverter circuit, and the charging circuit charges based on the current instantaneous value detected by the current sensor. Start. According to this configuration, the charging time until the next discharge can be extended.

  In a preferred embodiment of the present invention, a voltage sensor for detecting a voltage across terminals of the reignition capacitor is further provided, and the charging circuit charges based on the voltage across terminals detected by the voltage sensor. Finish. According to this configuration, it is possible to suppress the reignition capacitor from being charged more than necessary.

  In a preferred embodiment of the present invention, the apparatus further includes a control circuit that outputs a drive signal to the inverter circuit, and the discharge circuit controls discharge based on the drive signal. According to this configuration, the discharge can be controlled according to the drive signal.

  In a preferred embodiment of the present invention, the apparatus further comprises a current sensor that detects an instantaneous value of the output current of the inverter circuit, and the discharge circuit discharges based on the current instantaneous value detected by the current sensor. Control. According to this configuration, discharge can be controlled according to the output current of the inverter circuit.

  In a preferred embodiment of the present invention, a waveform target setting unit for setting a control target of the output current waveform of the inverter circuit is further provided, and the discharge circuit controls the discharge based on the control target. According to this configuration, discharge can be controlled according to the control target of the output current.

  In a preferred embodiment of the present invention, the voltage superposition circuit superposes the re-ignition voltage only when the current output to the coated arc welding rod switches from negative to positive. According to this configuration, since the re-ignition voltage can be superimposed only when arc breakage is more likely to occur, generation of arc breakage can be suppressed. Furthermore, since the reignition voltage is not superimposed when arc breakage is relatively unlikely to occur, power loss can be reduced.

  In a preferred embodiment of the present invention, the inverter circuit outputs a sinusoidal alternating current. According to this configuration, since the generated arc becomes wide, the welding mark can be made wide. Moreover, the noise generated from the welding power supply can be suppressed.

  A welding power source provided by a second aspect of the present invention is a welding power source for coated arc welding, which supplies electric power to a coated arc welding rod, wherein the rectifier circuit rectifies AC power; A direct current reactor for smoothing the output of the motor, an inverter circuit for converting direct current power output from the direct current reactor into alternating current power, and outputting it to the coated arc welding rod, and reignitioning the output to the coated arc welding rod And a voltage superposition circuit for superposing a voltage, wherein the voltage superposition circuit superposes the re-ignition voltage when the polarity of the output current of the inverter circuit is switched. According to this configuration, since the re-ignition voltage is superimposed when the polarity of the output current of the inverter circuit is switched, it is possible to suppress arc breakage when the polarity is changed. Further, since the arc breakage is suppressed by the superposition of the re-ignition voltage, it is not necessary to increase the reactance to suppress the arc breakage. Therefore, the direct current reactor can be miniaturized. Thereby, the welding power source can be reduced in size and weight.

  According to the present invention, since the re-ignition voltage is superimposed when the polarity of the output current of the inverter circuit switches, it is possible to suppress arc breakage when the polarity changes. Further, since the arc breakage is suppressed by the superposition of the re-ignition voltage, it is not necessary to increase the reactance to suppress the arc breakage. Therefore, the direct current reactor can be miniaturized. Thereby, the welding power source can be reduced in size and weight.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the whole structure of the covered arc welding system which concerns on 1st Embodiment. It is a figure which shows an example of the charge circuit which concerns on 1st Embodiment, and a discharge circuit. It is a time chart which shows the waveform of each signal of the welding power supply concerning a 1st embodiment. It is a functional block diagram showing an internal configuration of a modification of a control circuit concerning a 1st embodiment. It is a time chart which shows the waveform of each signal in the modification of the discharge control part concerning a 1st embodiment. It is a figure which shows the whole structure of the covering arc welding system which concerns on 2nd Embodiment. It is a figure which shows the whole structure of the conventional covered arc welding system.

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the attached drawings.

  FIG. 1 is a view showing an entire configuration of a coated arc welding system according to a first embodiment. As shown in FIG. 1, the coated arc welding system comprises a welding power source A1, a coated arc welding rod B and a welding rod holder C. The welding rod holder C is for the operator to hold and perform welding, holds the coated arc welding rod B, and applies an alternating current input from the welding power source A1 to the coated arc welding rod B. Welding power supply device A1 converts AC power input from commercial power supply D and outputs the converted power from output terminals a and b. One output terminal a is connected to the workpiece W by a cable. The other output terminal b is connected to the welding rod holder C by a cable. The welding power supply device A1 generates an arc between the tip of the coated arc welding rod B and the workpiece W to supply power. Welding is performed by the heat of the arc.

  Welding power supply device A1 includes rectifying and smoothing circuit 1, inverter circuit 2, transformer 3, rectifier circuit 4, DC reactor 5, voltage superposition circuit 6, inverter circuit 7, control circuit 8, current sensor 91 and voltage sensor 92. .

  The rectifying and smoothing circuit 1 converts AC power input from a commercial power source D into DC power and outputs the DC power. The rectifying and smoothing circuit 1 includes a rectifying circuit that rectifies an alternating current, and a smoothing capacitor that smoothes.

  The inverter circuit 2 is, for example, a single phase full bridge type PWM control inverter, and includes four switching elements. The inverter circuit 2 switches the switching element according to the drive signal input from the control circuit 8 to convert the DC power input from the rectifying and smoothing circuit 1 into high frequency power and output it. In addition, the inverter circuit 2 should just convert direct-current power into alternating current power, for example, may be a half bridge type, and may be an inverter circuit of another structure.

  The transformer 3 transforms the high frequency voltage output from the inverter circuit 2 and outputs it to the rectifier circuit 4. Since the transformer 3 is a high frequency transformer, it is smaller and lighter than a commercial frequency transformer.

  The rectifier circuit 4 is, for example, a full wave rectifier circuit, and rectifies high frequency power input from the transformer 3 and outputs the rectified high frequency power to the inverter circuit 7. The rectifier circuit 4 may be any one that rectifies high frequency power, and may be, for example, a half wave rectifier circuit. The direct current reactor 5 smoothes the direct current output from the rectifier circuit 4 to the inverter circuit 7.

  The inverter circuit 7 is, for example, a single-phase full bridge type PWM control inverter, and includes four switching elements. The inverter circuit 7 converts the DC power input from the rectifier circuit 4 into AC power and outputs the AC power by switching the switching element according to the switching drive signal input from the control circuit 8. The inverter circuit 7 may be of any type as long as it converts direct current power into alternating current power, and may be, for example, a half bridge type or may be an inverter circuit of another configuration. The inverter circuit 7 corresponds to the "inverter circuit" of the present invention, and the switching drive signal corresponds to the "drive signal" of the present invention.

  The voltage superposition circuit 6 is disposed between the rectifier circuit 4 and the inverter circuit 7, and when the polarity of the output current of the inverter circuit 7 is switched, a high voltage is applied between the output terminals a and b of the welding power supply A1. Superimpose. The said high voltage is for improving the re-ignitability at the time of polarity switching, and it may describe it as "re-ignition voltage" below. The voltage superposition circuit 6 includes a diode 61, a re-ignition capacitor 62, a charging circuit 63 and a discharging circuit 64.

  The re-ignition capacitor 62 is a capacitor having a predetermined capacitance or more, and is charged with a high voltage (re-ignition voltage) to be superimposed on the output of the welding power supply device A1. The reignition capacitor 62 is connected in parallel to the rectifier circuit 4. The reignition capacitor 62 is charged by the charging circuit 63 and discharged by the discharging circuit 64.

  The charging circuit 63 is a circuit for charging the reignition capacitor 62 with the reignition voltage, and is connected in parallel to the reignition capacitor 62. FIG. 2A shows an example of the charging circuit 63. As shown in FIG. As shown in FIG. 2A, in the present embodiment, the charging circuit 63 includes an isolated forward converter. The charging circuit 63 also includes a drive circuit 63a for driving the isolated forward converter. The drive circuit 63a outputs a pulse signal for driving the switching element 63b based on a charge circuit drive signal input from a charge control unit 86 described later. The drive circuit 63a outputs a predetermined pulse signal to the switching element 63b while the charge circuit drive signal is on (for example, a high level signal). Thereby, the reignition capacitor 62 is charged. On the other hand, the drive circuit 63a does not output a pulse signal while the charge circuit drive signal is off (for example, a low level signal). Thus, charging of the reignition capacitor 62 is stopped. That is, the charging circuit 63 switches between the state in which the re-igniting capacitor 62 is charged and the state in which it is not charged, based on the charging circuit drive signal. Note that the charge control unit 86 may directly input a pulse signal to the switching element 63b as a charge circuit drive signal without providing the drive circuit 63a. Further, the configuration of the charging circuit 63 is not limited.

  The discharge circuit 64 discharges the reignition voltage charged in the reignition capacitor 62, and is connected in series to the reignition capacitor 62. FIG. 2B shows an example of the discharge circuit 64. As shown in FIG. The discharge circuit 64 includes a switching element 64a and a current limiting resistor 64b. In the present embodiment, the switching element 64a is an IGBT (Insulated Gate Bipolar Transistor). The switching element 64a may be a bipolar transistor, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), or the like. The switching element 64 a and the current limiting resistor 64 b are connected in series and connected in series to the reignition capacitor 62. The emitter terminal of the switching element 64a is connected to the terminal on the positive electrode side of the rectifying circuit 4, and the collector terminal of the switching element 64a is connected to one terminal of the current limiting resistor 64b. The current limiting resistor 64b may be connected to the emitter terminal side of the switching element 64a. A discharge circuit drive signal is input to the gate terminal of the switching element 64a from a discharge control unit 85 described later. The switching element 64a is turned on while the discharge circuit drive signal is on (for example, a high level signal). As a result, the reignition voltage charged in the reignition capacitor 62 is discharged and superimposed on the output voltage of the rectifier circuit 4 through the current limiting resistor 64b. On the other hand, the switching element 64a is in the off state while the discharge circuit drive signal is off (for example, low level signal). Thereby, the discharge of the reignition voltage is stopped. That is, the discharge circuit 64 switches between the state in which the reignition capacitor 62 is discharged and the state in which it is not discharged based on the discharge circuit drive signal. The configuration of the discharge circuit 64 is not limited.

  The diode 61 is connected in parallel to the discharge circuit 64, the anode terminal is connected to the terminal on the positive electrode side of the input of the inverter circuit 7, and the cathode terminal is connected to the reignition capacitor 62. The diode 61 causes the reignition capacitor 62 to absorb the transient voltage of the input voltage of the inverter circuit 7.

  The current sensor 91 detects the output current of the welding power supply device A1, and in the present embodiment, is arranged on a connection line connecting one output terminal of the inverter circuit 7 and the output terminal a. The current sensor 91 detects an instantaneous value of the output current and inputs it to the control circuit 8. In the present embodiment, the case where the current flows from the inverter circuit 7 toward the output terminal a is positive, and the case where the current flows from the output terminal a toward the inverter circuit 7 is negative.

  The voltage sensor 92 detects the voltage between the terminals of the reignition capacitor 62. The voltage sensor 92 detects the voltage between the terminals and inputs it to the control circuit 8.

  The control circuit 8 is a circuit for controlling the welding power supply A1, and is realized by, for example, a microcomputer. The control circuit 8 receives an instantaneous value of the output current from the current sensor 91 and receives an inter-terminal voltage of the reignition capacitor 62 from the voltage sensor 92. Then, drive signals are output to the inverter circuit 7, the charging circuit 63 and the discharging circuit 64, respectively. The control circuit 8 includes a current control unit 81, a current target setting unit 82, a polarity switching control unit 83, a waveform target setting unit 84, a discharge control unit 85, and a charge control unit 86.

  The current control unit 81 controls the inverter circuit 2. The current control unit 81 calculates an effective value from the instantaneous value of the output current input from the current sensor 91, and the inverter circuit 2 is calculated based on the effective value and the effective value target value input from the current target setting unit 82. And generates a drive signal for controlling the switching element of FIG.

  The polarity switching control unit 83 controls the inverter circuit 7. The polarity switching control unit 83 controls switching of the switching elements of the inverter circuit 7 based on the instantaneous value of the output current input from the current sensor 91 and the current waveform target value input from the waveform target setting unit 84. The drive signal is generated and output to the inverter circuit 7. The current waveform target value corresponds to the "control target" of the present invention.

  The discharge control unit 85 controls the discharge circuit 64. Discharge control unit 85 generates a discharge circuit drive signal for controlling discharge circuit 64 based on the instantaneous value of the output current input from current sensor 91 and the switching drive signal input from polarity switching control unit 83. It is generated and output to the discharge circuit 64.

  As shown in FIG. 3, the output current (see FIG. 3 (b)) of the welding power supply A1 changes in accordance with the switching drive signal (see FIG. 3 (a)). In the switching drive signal shown in FIG. 3A, the output terminal a (workpiece W) is positive when it is on, the output terminal b (coated arc welding rod B) is negative, and the output terminal a (when it is off) The workpiece W) is negative, and the output terminal b (coated arc welding rod B) is positive. The output current of welding power supply A1 decreases from when the switching drive signal is switched from on to off (time t1 in FIG. 3), and after zero (time t2 in FIG. 3), the minimum current value (Time t3 in FIG. 3). In addition, the output current of welding power supply device A1 increases from when the switching drive signal is switched from off to on (time t5 in FIG. 3) and passes zero after passing the polarity (time t6 in FIG. 3). It becomes a current value (time t7 in FIG. 3). The discharge control unit 85 generates a discharge circuit drive signal so as to be turned on when the polarity of the output current of the welding power supply device A1 changes. Specifically, discharge control unit 85 is switched on when the switching drive signal is switched (at time t1 and time t5 in FIG. 3), and when the instantaneous value of the output current becomes the maximum current value or the minimum current value. A pulse signal that is switched off at time t3 and time t7 in FIG. 3 is generated and output as a discharge circuit drive signal (see FIG. 3C). In fact, since the current instantaneous value input from the current sensor 91 fluctuates minutely, the discharge control unit 85 determines that the maximum current value has been reached when the current instantaneous value becomes equal to or greater than a predetermined first threshold value, When the current instantaneous value becomes equal to or less than a predetermined second threshold value, it is determined that the minimum current value is reached.

  The charge control unit 86 controls the charging circuit 63. The charge control unit 86 charges the charge circuit 63 based on the instantaneous value of the output current input from the current sensor 91 and the voltage across the re-ignition capacitor 62 input from the voltage sensor 92. A circuit drive signal is generated and output to the charging circuit 63.

  As shown in FIG. 3, the voltage across the terminals of the reignition capacitor 62 (see FIG. 3 (e)) turns on the discharge circuit drive signal (see FIG. 3 (c)) (time t1 in FIG. 3). When the polarity of the output current (see FIG. 3 (b)) changes (at time t2 in FIG. 3), the reignition capacitor 62 drops due to discharge. It is necessary to charge the re-ignition capacitor 62 with the re-ignition voltage by the timing of the next discharge (time t6 in FIG. 3). In addition, when the reignition capacitor 62 is charged to a predetermined voltage, it is not necessary to further charge it. The charge control unit 86 generates a charge circuit drive signal so that the re-ignition capacitor 62 is turned on until the predetermined voltage is reached after the re-ignition capacitor 62 is discharged. Specifically, when the discharge circuit drive signal is switched off (at time t3 and t7 in FIG. 3), that is, the instantaneous value of the output current becomes the maximum current value or the minimum current value. Generates a pulse signal that is switched on when the voltage across the terminals of the re-ignition capacitor 62 becomes a predetermined voltage (at times t4 and t8 in FIG. 3), and is output as a charging circuit drive signal (See FIG. 3 (d)).

  Next, the operation and effects of the coated arc welding system according to the present embodiment will be described.

  According to the present embodiment, the coated arc welding rod B can generate an arc between its tip and the workpiece W by the AC power output from the welding power supply device A1, and arc welding can be performed. The discharge control unit 85 of the welding power supply device A1 generates a discharge circuit drive signal that is turned on when the polarity of the output current of the welding power supply device A1 changes. The discharge circuit 64 receives the discharge circuit drive signal input from the discharge control unit 85. Thus, the discharge circuit 64 can superimpose the re-ignition voltage charged in the re-ignition capacitor 62 on the output voltage of the rectifier circuit 4 when the polarity of the output current of the welding power supply device A1 changes. Therefore, it is possible to suppress arc breakage when the polarity of the output current of welding power supply device A1 changes. Further, since the arc breakage is suppressed by the superposition of the re-ignition voltage, it is not necessary to increase the reactance to suppress the arc breakage. Therefore, the direct current reactor 5 can be miniaturized. Further, since the transformer 3 is a high frequency transformer, it is smaller and lighter than a commercial frequency transformer. As a result, the size and weight of the welding power source A1 can be reduced as compared with the case of the conventional coated arc welding system.

  According to the present embodiment, the discharge circuit 64 controls the discharge based on the discharge circuit drive signal input from the discharge control unit 85. The discharge circuit drive signal (see FIG. 3 (c)) is switched on when the switching drive signal (see FIG. 3 (a)) is switched, and the output current (see FIG. 3 (b)) is the maximum current value or It switches off when the minimum current value is reached. Therefore, when the polarity of the output current of welding power supply device A1 changes, the discharge circuit drive signal is always on, and discharge circuit 64 can appropriately overlap the re-ignition voltage.

  According to the present embodiment, the charging circuit 63 controls charging based on the charging circuit drive signal input from the charging control unit 86. The charge circuit drive signal (see FIG. 3D) is switched on when the discharge circuit drive signal (see FIG. 3C) is switched off. Therefore, charging circuit 63 can start charging immediately after discharging. Thereby, the charge time until the next discharge can be extended. Also, the charging circuit drive signal is switched off when the voltage across the terminals of the reignition capacitor 62 (see FIG. 3E) reaches a predetermined voltage. As a result, the charging circuit 63 can suppress the reignition capacitor 62 from being charged more than necessary.

  In the present embodiment, although the case where the charge control unit 86 generates the charge circuit drive signal based on the instantaneous value of the output current and the voltage between the terminals of the reignition capacitor 62 has been described, the present invention is limited thereto. Absent. If the re-ignition capacitor 62 can be charged with the re-ignition voltage by the timing of the next discharge, the timing of start and end of charging is not limited. In addition, the charging circuit 63 may be constantly charged. In this case, the charge control unit 86 is unnecessary, and the drive circuit 63a may keep outputting a pulse signal for driving the switching element 63b.

  In the present embodiment, the discharge control unit 85 generates the discharge circuit drive signal based on the instantaneous value of the output current and the switching drive signal. However, the present invention is not limited to this. The discharge circuit drive signal may be turned on before the polarity changes and may be turned off after the polarity changes, as long as the re-ignition voltage can be superimposed when the polarity of the output current of the welding power source A1 changes. For example, when the instantaneous value of the output current becomes zero and a predetermined time has elapsed, the discharge circuit drive signal may be switched off.

  Further, as shown in FIG. 4A, instead of the switching control signal being input from the polarity switching control unit 83, the discharge control unit 85 receives a current waveform target value from the waveform target setting unit 84, and the current waveform is When the target value is switched, the discharge circuit drive signal may be switched on. Also in this case, the waveform of the discharge circuit drive signal is similar to the case of switching based on the switching drive signal.

  Furthermore, as shown in FIG. 4B, when the discharge control unit 85 receives only the instantaneous value of the output current from the current sensor 91 and the instantaneous value of the output current decreases from the maximum current value, or the minimum current The discharge circuit drive signal may be switched on when rising from the value. Also in this case, the waveform of the discharge circuit drive signal is similar to the case of switching based on the switching drive signal. Further, a first threshold value smaller than the maximum current value and larger than zero, and a second threshold value larger than the minimum current value and smaller than zero are set, and the discharge circuit drive signal is set to an instantaneous value of the output current being the first threshold value and the second threshold value. It may be switched on when entering the range between and and switched off when out of the range. Also in this case, the discharge circuit drive signal is turned on before the polarity changes, and turned off after the polarity changes.

  Moreover, in this embodiment, although the case where the waveform of an output current is a substantially rectangular wave (refer FIG.3 (b)) was demonstrated, it is not restricted to this. The waveform of the output current may be a sine wave. The waveform target setting unit 84 outputs a sine wave signal as the current waveform target value, and the polarity switching control unit 83 outputs the instantaneous value of the output current input from the current sensor 91 and the current waveform target value input from the waveform target setting unit 84 If the switching drive signal is generated on the basis of the above, the waveform of the output current can be made to be a sine wave. If the waveform of the output current is a sine wave, the discharge circuit drive signal may be generated based on the instantaneous value of the output current detected by the current sensor 91. For example, a first threshold value smaller than the maximum current value and larger than zero and a second threshold value larger than the minimum current value and smaller than zero are set, and the discharge circuit drive signal Switch on when entering the range between and, and switch off when out of the range. Assuming that the waveform of the output current is a sine wave, the generated arc becomes wider, so the welding mark can be made wider. Moreover, the noise generated from the welding power supply device A1 can be suppressed.

  In the present embodiment, although the case where the re-ignition voltage is superimposed when the polarity of the output current of the welding power supply device A1 changes is described, the present invention is not limited thereto. Generally, since the output terminal a (the workpiece W) is positive and the output terminal b (the coated arc welding rod B) is negative, the output terminal a (the workpiece W) is negative and the output terminal b (the workpiece W) is negative. It is known that arc breakage is likely to occur when the coated arc welding rod B) switches to the reverse polarity which is positive. Therefore, the re-ignition voltage may be superimposed only when switching from the positive polarity to the reverse polarity, and may not be superimposed when switching from the negative polarity to the positive polarity. A modification in this case will be described with reference to FIG. In the modification, only the method of generating the discharge circuit drive signal by the discharge control unit 85 changes.

  FIG. 5 is a time chart showing waveforms of respective signals in the modification. FIG. 5A shows a switching drive signal generated by the polarity switching control unit 83, which is the same as that shown in FIG. FIG. 5 (b) shows the output current of the welding power source device A1, which is the same as that shown in FIG. 3 (b). FIG. 5C shows the discharge circuit drive signal generated by the discharge control unit 85. FIG. 5D shows the charge circuit drive signal generated by the charge control unit 86. FIG. 5E shows the voltage between the terminals of the reignition capacitor 62.

  Discharge control unit 85 generates a discharge circuit drive signal such that it turns on when the polarity of the output current of welding power supply device A1 changes from the positive polarity to the reverse polarity. Specifically, when the switching drive signal (see FIG. 5A) is switched from on to off (time t1 in FIG. 5), the discharge control unit 85 is switched on and the output current of the welding power supply device A1 A pulse signal that is switched off when (see FIG. 5B) reaches the minimum current value (time t3 in FIG. 5) is generated and output as a discharge circuit drive signal (see FIG. 5C). When the switching control signal is switched from off to on (time t5 in FIG. 5), and when the output current of welding power supply device A1 reaches the maximum current value (time t7 in FIG. 5) Does not switch the discharge circuit drive signal.

  Since the discharge circuit drive signal (see FIG. 5C) generated by the discharge control unit 85 is different from the discharge drive signal shown in FIG. 3C, the charge circuit drive signal generated by the charge control unit 86 (see FIG. And the voltage across terminals of the re-ignition capacitor 62 (see FIG. 5 (e)) have waveforms different from those shown in FIG. 3 (d) and FIG. 3 (e), respectively.

  In this modification, since the reignition voltage is superimposed when switching from the positive polarity to the reverse polarity is more likely to cause arc breakage, it is possible to suppress the occurrence of arc breakage. In addition, since the re-ignition voltage is not superimposed when switching from reverse polarity to positive polarity that arc breakage is relatively unlikely to occur, the re-ignition voltage is also superimposed when switching from reverse polarity to positive polarity. In comparison, the loss in the current limiting resistor 64b can be reduced. In addition, since it takes a long time to charge the re-ignition voltage since it takes a long time to discharge the re-ignition voltage until the next discharge, which is particularly effective.

  When the re-ignition voltage is superimposed only when switching from the positive polarity to the reverse polarity as in the above modification, the voltage superposition circuit 6 may be disposed on the output side of the inverter circuit 7. This case will be described below as a second embodiment.

  FIG. 6 is a view showing an entire configuration of a covered arc welding system according to a second embodiment. In FIG. 6, the same or similar elements as or to those of the covered arc welding system (see FIG. 1) according to the first embodiment are denoted by the same reference numerals. In FIG. 6, the control circuit 8 is shown in a simplified manner. As shown in FIG. 6, welding power supply device A2 differs from welding power supply device A1 according to the first embodiment in that voltage superposition circuit 6 is disposed on the output side of inverter circuit 7.

  The voltage superposition circuit 6 is disposed on the output side of the inverter circuit 7 and superposes the re-ignition voltage between the output terminals a and b so as to raise the potential of the output terminal b (coated arc welding rod B). It is configured. The discharge circuit 64 is conductive when the switching drive signal (see FIG. 5A) is switched from on to off (at time t1 in FIG. 5), and the polarity of the output current (see FIG. 5B) Is changed (time t2 in FIG. 5), the reignition capacitor 62 is discharged, and the reignition voltage is superimposed between the output terminals a and b.

  In the second embodiment, since the reignition voltage can be superimposed when switching from the positive polarity to the reverse polarity, which is more likely to cause arc breakage, the occurrence of arc breakage can be suppressed. Further, as in the first embodiment, the size and weight of the welding power supply A2 can be reduced. Furthermore, in the present embodiment, since the re-ignition voltage is not superimposed when switching from the reverse polarity to the positive polarity, where arc breakage is relatively unlikely to occur, compared to the first embodiment, the current limiting resistance 64b can be used. Loss can be reduced. In addition, since it takes a long time to charge the re-ignition voltage since it takes a long time to discharge the re-ignition voltage until the next discharge, which is particularly effective.

  The coated arc welding system and the welding power source for the coated arc welding according to the present invention are not limited to the above-described embodiment. The specific configuration of each part of the coated arc welding system and the welding power supply for the coated arc welding according to the present invention can be varied in design in various ways.

A1 and A2: welding power supply device 1: rectifying and smoothing circuit 2: inverter circuit 3: transformer 4: rectifying circuit 5: DC reactor 6: voltage superposition circuit 61: diode 62: reignition capacitor 63: charging circuit 63a: drive circuit 63b : Switching element 64: Discharge circuit 64a: Switching element 64b: Current limiting resistance 7: Inverter circuit 8: Control circuit 81: Current control unit 82: Current target setting unit 83: Polarity switching control unit 84: Waveform target setting unit 85: Discharge Control part 86: Charge control part 91: Current sensor 92: Voltage sensor a: Output terminal b: Output terminal B: Coated arc welding rod C: Welding rod holder D: Commercial power supply W: Workpiece

Claims (10)

A coated arc welding system comprising: a coated arc welding rod; and a welding power supply for supplying power to the coated arc welding rod,
The welding power supply is
A rectifier circuit that rectifies AC power;
A direct current reactor for smoothing the output of the rectifier circuit;
An inverter circuit that converts DC power output from the DC reactor into AC power and outputs the AC power to the coated arc welding rod;
A voltage superposition circuit which superimposes re-ignition voltage on the output to the coated arc welding rod,
Equipped with
The voltage superposition circuit superposes the re-ignition voltage when the polarity of the output current of the inverter circuit is switched,
Coated arc welding system characterized in that. The voltage superposition circuit is
A reignition capacitor charged with the reignition voltage;
A charging circuit for charging the re-ignition voltage to the re-ignition capacitor;
A discharge circuit for discharging the re-ignition voltage charged in the re-ignition capacitor;
Equipped with
The charging circuit is controlled in timing of start or end of charging.
A coated arc welding system according to claim 1. It further comprises a current sensor for detecting an instantaneous value of the output current of the inverter circuit,
The charging circuit starts charging based on the current instantaneous value detected by the current sensor.
A coated arc welding system according to claim 2. It further comprises a voltage sensor for detecting a voltage across terminals of the re-ignition capacitor,
The charging circuit ends charging based on the voltage between the terminals detected by the voltage sensor.
A coated arc welding system according to claim 2 or 3. It further comprises a control circuit for outputting a drive signal to the inverter circuit,
The discharge circuit controls discharge based on the drive signal.
The coated arc welding system according to any one of claims 2 to 4. It further comprises a current sensor for detecting an instantaneous value of the output current of the inverter circuit,
The discharge circuit controls discharge based on the current instantaneous value detected by the current sensor.
The coated arc welding system according to any one of claims 2 to 4. And a waveform target setting unit that sets a control target of the output current waveform of the inverter circuit.
The discharge circuit controls discharge based on the control target.
The coated arc welding system according to any one of claims 2 to 4. The voltage superposition circuit superimposes the re-ignition voltage only when the current output to the coated arc welding rod switches from negative to positive.
A coated arc welding system according to any of the preceding claims. The inverter circuit outputs a sine wave alternating current.
A coated arc welding system according to any of the preceding claims. A welding power source for coated arc welding, which supplies power to a coated arc welding rod, comprising:
A rectifier circuit that rectifies AC power;
A direct current reactor for smoothing the output of the rectifier circuit;
An inverter circuit that converts DC power output from the DC reactor into AC power and outputs the AC power to the coated arc welding rod;
A voltage superposition circuit which superimposes re-ignition voltage on the output to the coated arc welding rod,
Equipped with
The voltage superposition circuit superposes the re-ignition voltage when the polarity of the output current of the inverter circuit is switched,
Welding power supply device for coated arc welding characterized in that.

Images