JP2011240347A - Power source device for arc machining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent parts such as chips from being deteriorated by application of a large voltage to a chip that forms a cutting torch, due to hand movement during the operation of cutting a workpiece.SOLUTION: This power source device for arc machining includes: a DC power source circuit which rectifies and smoothes commercial AC power supply to output a DC voltage; an inverter circuit which converts a DC voltage into a high-frequency AC voltage; a main transformer which converts the high-frequency AC voltage into an AC voltage suitable for welding; a secondary rectifying circuit which rectifies the output of the main transformer; a rectified output current detection circuit which detects the rectified output current; and a main control circuit which controls the inverter circuit based on an output current value. When the output current value is equal to or greater than a predetermined output current reference value, the main control circuit performs external characteristic control creating a maximum load voltage characteristic at which a maximum load voltage is lowered to a predetermined value.

Description

  The present invention relates to a technique for switching the maximum load voltage of an arc machining power supply device.

  With an arc machining power supply device (for example, a high-current plasma cutting machine having characteristics of an output current of 600 A and a no-load voltage of 400 V), when an operator performs a cutting operation for a long time, camera shake occurs due to fatigue. In particular, if a long handle type plasma cutting torch is used, camera shake is likely to occur. When the arc length is increased due to this camera shake, the load voltage rises and a high voltage is applied to the chips, electrodes, etc. constituting the cutting torch, causing deterioration. End up.

  FIG. 8 is an electrical connection diagram of a conventional arc machining power supply device. In the figure, a primary rectifier circuit DR1 and a smoothing capacitor C1 form a DC power supply circuit. The primary rectifier circuit DR1 rectifies an AC power supply AC to generate a rectified voltage, and the smoothing capacitor C1 is a rectifier having a pulsating current. The voltage is smoothed to generate a DC voltage.

  The first switching element TR1 to the fourth switching element TR4 form a full-bridge inverter circuit, which converts a DC voltage into a high-frequency AC voltage and outputs it. The main transformer INT converts the high-frequency AC voltage into a voltage suitable for arc machining, and the secondary rectifier circuit DR2 rectifies the output of the main transformer INT and supplies DC power via the DC reactor L.

  The changeover switch SW is a changeover switch having two contacts, contact a and contact b, and the maximum load voltage is stepped down by selecting the contact a and becomes the predetermined maximum load voltage by selecting the contact b.

  When cutting the workpiece M, there are a long handle type plasma cutting torch, a short handle type plasma cutting torch, etc. as a cutting torch to be used. Many camera shakes occur. When the arc length becomes longer due to this camera shake, the load voltage rises, and may rise to, for example, around 400V. This rise causes chip deterioration.

  As a countermeasure, when cutting using a long handle type plasma cutting torch or the like, the tap a provided on the secondary winding of the main transformer INT is subjected to secondary rectification with the changeover switch SW set to the contact a side. When connected to the circuit DR2, the maximum load voltage is stepped down to a predetermined load voltage, and the rise of the load voltage when the arc length becomes long due to camera shake is suppressed, thereby preventing chip deterioration. .

  In the power supply device for arc processing described in Patent Document 1, a thyristor element is connected to each tap provided in the secondary winding of the main transformer INT, and each thyristor is energized according to the type of torch. Each tap provided in the secondary winding of the device INT is selected.

Japanese Patent Laid-Open No. 11-58009

In plasma cutting, in order to improve the starting property of the plasma arc, a no-load voltage as high as 400 V, for example, is required as shown in FIG. At this time, the maximum load voltage at each output current value is also 400V to 370. On the other hand, the standard load voltage at each output current value is as low as 80V to 180V. As shown in FIG. 4, for example, when the output current is 300A, the difference between the maximum load voltage 390V and the standard load voltage 150V is about 240V. Become.
When a workpiece is cut using a plasma cutting machine having this external characteristic, for example, using a long handle type plasma cutting torch, the arc length is usually set to about 30 mm. However, when an operator performs a long cutting operation, it is difficult to maintain the arc length at about 30 mm and camera shake occurs. When the arc length becomes longer due to this camera shake, the load voltage rises and a high voltage is applied to the tip, electrode, etc. that form the cutting torch. Furthermore, the heat generated by the chip, the electrode, etc. increases as the load voltage increases, causing thermal damage.

  Therefore, in the prior art, in order to prevent the deterioration of the chip due to the application of a high voltage, a changeover switch SW for selecting a tap provided on the secondary side winding of the main transformer INT is provided, and a long handle type in which camera shake is likely to occur. When cutting a workpiece using a plasma cutting torch, the tap with a low output voltage of the main transformer INT is selected with a changeover switch to lower the maximum load voltage to a predetermined load voltage, and the arc length increases due to camera shake. The rise in the load voltage that occurred when

  However, in the prior art, it is possible to prevent chip deterioration by lowering the maximum load voltage according to the type of cutting torch used. However, the arc start performance is deteriorated by reducing the maximum load voltage. Furthermore, a tap is separately required for the secondary winding of the main transformer INT, and a changeover switch and a thyristor element for selecting the tap are required.

  Therefore, the present invention provides a power supply device for arc machining that has good arc startability and can suppress an increase in load voltage without providing a tap and a changeover switch on the secondary winding of the main transformer INT. For the purpose.

In order to solve the above-described problem, the invention of claim 1 includes a DC power supply circuit that outputs a DC voltage by rectifying and smoothing a commercial AC power supply, an inverter circuit that converts the DC voltage into a high-frequency AC voltage, and A main transformer for converting a high-frequency AC voltage into an AC voltage suitable for welding, a secondary rectifier circuit for rectifying the output of the main transformer, an output current detection circuit for detecting the rectified output current, and the output A main control circuit for controlling the inverter circuit based on a current value, and an arc machining power supply device comprising:
The main control circuit performs external characteristic control for forming a maximum load voltage characteristic in which the maximum load voltage is stepped down to a predetermined value when the output current value is equal to or greater than a predetermined output current reference value. It is a power supply device for arc processing.

  The invention according to claim 2 is the power supply device for arc machining according to claim 1, wherein the external characteristic control is performed by reducing the maximum ON / Duty of the inverter circuit.

  The invention of claim 3 is provided with an output voltage detection circuit that detects the rectified output voltage, and performs the external voltage control when the output voltage value is equal to or higher than a predetermined output voltage reference value. The arc machining power supply device according to claim 1, wherein:

  The invention according to claim 4 is the power supply device for arc machining according to claim 3, wherein the output voltage reference value is set based on an output current set value.

  According to the first and second aspects of the present invention, when the output current value exceeds the output current reference value, the maximum load voltage of the inverter circuit is decreased and the maximum load voltage is stepped down to a predetermined load voltage. The increase in the applied voltage between the electrode and the chip that occurs as the length increases can be suppressed at a predetermined value, so that the deterioration of the chip and the electrode can be prevented, and the no-load voltage at the time of the arc is not reduced, so the arc start property Will not get worse. And since it is not necessary to provide another component in order to perform the above, a circuit structure can be simplified.

  According to the third and fourth aspects of the present invention, in addition to the above effect, when the output voltage value becomes larger than the output voltage reference value set based on the output current set value, the constant current control is changed to the constant voltage control. Since switching is performed, an increase in output power supplied to the chip and the electrode can be suppressed, and heat generated by the suppression of the increase in output power can be suppressed to an optimum value, and the chip, the electrode, and the like can be prevented from being damaged by heat.

FIG. 3 is an electrical connection diagram of the arc machining power supply device according to the first embodiment. FIG. 2 is a detailed diagram of a main control circuit shown in FIG. 1. FIG. 4 is a timing chart for explaining the operation of the first embodiment. It is an external characteristic view of the power supply device for arc processing shown in FIG. FIG. 5 is an electrical connection diagram of a power supply device for arc machining according to a second embodiment. FIG. 6 is a detailed diagram of the main control circuit shown in FIG. 5. FIG. 6 is an external characteristic diagram of the power supply device for arc machining shown in FIG. 5. It is an electrical connection figure of the power supply apparatus for arc processing of a prior art.

  FIG. 1 is an electrical connection diagram of the arc machining power supply device according to the first embodiment. In the figure, components having the same reference numerals as those in the electrical connection diagram of the arc machining power supply device of the prior art shown in FIG. 8 perform the same operations, and thus description thereof will be omitted. Only components having different reference numerals will be described.

  FIG. 2 is a detailed diagram of the main control circuit SCA according to the first embodiment. The first comparison circuit CP1, the first dead time reference circuit DT1, the second dead time reference circuit DT2, the pulse width modulation circuit PWM, the triangular wave The generation circuit OSC, the current error amplifier circuit EI, the first diode D1 and the second diode D2 are formed, and the first comparison circuit CP1 generates a value of the output current detection signal Id and a predetermined output current reference signal Iref. When the value of the output current detection signal Id is larger than the value of the output current reference signal Iref, the first comparison signal Cp1 is set to High level and output.

  The first dead time reference generation circuit DT1 outputs a first dead time reference signal Dt1 having a predetermined value, and the second dead time reference generation circuit DT2 outputs when the first comparison signal Cp1 is at a high level. Then, a predetermined second dead time reference signal Dt2 larger than the value of the first dead time reference signal Dt1 is output.

  The current error amplification circuit EI compares and calculates the value of the output current setting signal Ir and the value of the output current detection signal Id and outputs the result as a current error amplification signal Ei.

  The pulse width modulation circuit PWM shown in FIG. 2 performs control to modulate the pulse width with a constant pulse frequency, and the first output control signal Sc1 and the second output control signal Sc1 according to the values of the triangular wave signal Osc and the current error amplification signal Ei. The pulse width of the output control signal Sc2 is controlled and output.

  The inverter drive circuit DK shown in FIG. 1 outputs a first inverter drive signal Dk1 and a fourth inverter drive signal Dk4 in response to the first output control signal Sc1, and the second output control signal Sc2 in response to the second output control signal Sc2. The inverter drive signal Dk2 and the third inverter drive signal Dk3 are output to control the output current of the inverter circuit.

FIG. 3 is a timing chart for explaining the operation of the first embodiment.
3A shows the start signal Ts, FIG. 3B shows the output current detection signal Id, FIG. 3C shows the first comparison signal Cp1, and FIG. (D) shows the dead time reference signal Dt, (E) shows the triangular wave generation signal Osc, and (F) shows the maximum ON / Duty signal.

Next, the operation of Embodiment 1 of the present invention will be described with reference to FIGS.
When the activation signal Ts becomes High level at time t = t1 shown in FIG. 3, the pulse width modulation circuit PWM of the main control circuit SCA starts operation, and the first comparison circuit CP1 determines the value of the output current detection signal Id. And the value of the output current reference signal Iref (for example, 50 A), and since the value of the output current detection signal Id is smaller than the value of the output current reference signal Iref, the first comparison signal Cp1 shown in FIG. Becomes Low level.

  The second dead time reference generation circuit DT2 shown in FIG. 2 stops the output of the second dead time reference signal Dt2 when the first comparison signal Cp1 is at the low level, and the first diode D1 and the second diode The OR circuit formed at D2 selects the first dead time reference signal Dt1 output from the first dead time reference generation circuit DT1 and inputs it to the pulse width modulation circuit PWM. The pulse width modulation circuit PWM The inverter circuit is driven at the maximum ON · Duty shown in FIG. 3F to generate an arc. At this time, a no-load voltage of 400 V shown in FIG. 4 is applied between the cutting torch ES and the workpiece M, and an arc is generated at time t = t2.

  When the value of the output current detection signal Id shown in FIG. 3 becomes larger than the value of the output current reference signal Iref at time t = t3 after the occurrence of the arc, the first comparison circuit CP1 sets the first comparison signal Cp1 to the high level. Output. At this time, the second dead time reference generation circuit DT2 outputs a predetermined second dead time reference signal Dt2 that is larger than the value of the first dead time reference signal Dt1. The OR circuit formed by the first diode D1 and the second diode D2 selects the second dead time reference signal Dt2 and inputs it to the pulse width modulation circuit PWM.

  At this time, the maximum ON · Duty shown in FIG. 3 (F) decreases according to the value of the second dead time reference signal Dt2, and the maximum load voltage of 300A shown in FIG. 4 is changed from 390V to 290V, for example. Step down. Due to this step-down, the operator is shaken due to fatigue, and even if the arc length is increased due to the shake, the increase in applied voltage to the tip, electrode, etc. can be suppressed to 290 V, so that deterioration of the tip, electrode, etc. can be prevented. Further, since the no-load voltage at the time of arc generation is not stepped down as shown in FIG. 4, the arc startability is not deteriorated.

FIG. 5 is an electrical connection diagram of the arc machining power supply device of the second embodiment.
In the figure, components having the same reference numerals as those in the electrical connection diagrams of the arc machining power supply apparatus shown in FIGS. 1 and 10 perform the same operations, and thus description thereof will be omitted. Only components having different reference numerals will be described.

  The output voltage detection circuit VD shown in FIG. 5 detects the load voltage and outputs it as an output voltage detection signal Vd. The output current setting circuit IR sets a predetermined output current setting value Ir.

  FIG. 6 is a detailed diagram of the main control circuit SCV of the second embodiment. The main control circuit SCV shown in FIG. 6 includes a second comparison circuit CP2, an output voltage reference signal setting circuit VREF, and an output current reference signal setting circuit IREF. The first dead time reference circuit DT1, the pulse width modulation circuit PWM, the triangular wave generation circuit OSC, the current error amplifier circuit EI, the voltage error amplifier circuit EV, and the diodes D3 and D4.

  The output voltage reference setting circuit VREF sets the value of the output voltage reference signal Vref based on the output current setting value Ir. The second comparison circuit CP2 compares the value of the output current detection signal Id with a predetermined value (for example, 50 A) of the output current voltage reference signal Iref, and the value of the output current detection signal Id is the output current reference signal Iref. The second comparison signal Cp2 is set to a high level and output when the value is larger than the value of.

  The voltage error amplification circuit EV operates when the second comparison signal Cp2 becomes High level, compares the value of the output voltage reference signal Vref and the value of the output voltage detection signal Vd, and outputs the result as a voltage error amplification signal Ev.

Next, the operation of the second embodiment will be described with reference to FIGS.
In the main control circuit SCV shown in FIG. 6, the pulse width modulation circuit PWM operates when the activation signal Ts becomes High level, and an arc is generated by applying the no-load voltage 400V shown in FIG. Then, when the value of the output current detection signal Id becomes larger than the value of the output current reference signal Iref (for example, 50 A) after the arc is generated, the second comparison circuit CP2 sets the second comparison signal Cp2 to High level and outputs it.

  When the second comparison signal Cp2 becomes High level, the voltage error amplifier circuit EV compares the value of the output voltage reference signal Vref and the value of the output voltage detection signal Vd, and outputs it as a voltage error amplification signal Ev.

  After the arc is generated, for example, when the cutting operation is performed with an output current of 300 A and an arc length of about 30 mm, the load voltage becomes about 150 V from FIG. 7, and at this time, the value of the current error amplification signal Ei is The value of the current error amplification signal Ei is selected by the OR circuit formed by the third diode D3 and the fourth diode D4, and becomes larger than the value of the voltage error amplification signal Ev, so that the pulse width modulation circuit PWM has a current error. Constant current control is performed according to the value of the amplified signal Ei. Subsequently, during the cutting operation, the operator shakes due to fatigue, and when the arc length becomes longer due to the shake, the value of the output voltage detection signal Vd increases, and the value of the voltage error amplification signal Ev also increases according to this increase. To increase.

  When the value of the voltage error amplification signal Ev becomes larger than the value of the current error amplification signal Ei, the value of the voltage error amplification signal Ev is selected by the OR circuit formed by the third diode D3 and the fourth diode D4. Then, the pulse width modulation circuit PWM switches from constant current control to constant voltage control according to the value of the voltage error amplification signal Ev.

  As described above, an operator causes fatigue during hand cutting using a long handle type plasma cutting torch, the arc length becomes longer due to the hand shaking, and the output voltage value becomes larger than an output voltage reference value (for example, 300 V). Sometimes, by switching from constant current control to constant voltage control and setting the maximum load voltage to 300 V, in addition to suppressing the increase in applied voltage to the chip, electrode, etc., it is possible to suppress the increase in power supplied to the chip, electrode. Since the heat generated by suppressing the increase in power is suppressed to an optimum value, the chip, electrode, etc. can be prevented from being damaged by heat.

C1 smoothing capacitor CP1 first comparison circuit Cp1 first comparison signal CP2 second comparison circuit Cp2 second comparison signal D1 first diode D2 second diode D3 third diode D4 fourth diode DK inverter drive Circuit Dk1 First inverter drive signal Dk2 Second inverter drive signal Dk3 Third inverter drive signal Dk4 Fourth inverter drive signal DCL DC reactor DR1 Primary rectifier circuit DR2 Secondary rectifier circuit DT1 First dead time reference generation Circuit Dt1 First dead time reference signal (first dead time reference value)
DT2 Second dead time reference generation circuit Dt2 Second dead time reference signal (second dead time reference value)
EI current error amplifier circuit
Ei Current error amplification signal EV Voltage error amplification circuit
Ev Voltage error amplification signal ES Cutting torch ID Output current detection circuit Id Output current detection signal INT Main transformer IR Output current setting circuit Ir Output current setting signal (output current setting value)
IREF Output current reference circuit Iref Output current reference circuit M Workpiece OSC Triangle wave generation circuit Osc Triangle wave generation signal PWM Pulse width modulation circuit SC Main control circuit Sc1 First output control signal Sc2 Second output control signal SCA Main control circuit SCV Main control circuit SW selector switch TR1 1st switching element TR2 2nd switching element TR3 3rd switching element TR4 4th switching element VD Output voltage detection circuit Vd Output voltage detection signal VREF Output voltage reference circuit Vref Output voltage reference signal (Output voltage reference value)

Claims (4)

A DC power supply circuit that outputs a DC voltage by rectifying and smoothing a commercial AC power supply, an inverter circuit that converts the DC voltage into a high-frequency AC voltage, and a main transformer that converts the high-frequency AC voltage into an AC voltage suitable for welding A secondary rectifier circuit that rectifies the output of the main transformer, an output current detection circuit that detects the rectified output current, and a main control circuit that controls the inverter circuit based on the output current value; In an arc machining power supply device comprising:
The main control circuit performs external characteristic control for forming a maximum load voltage characteristic in which the maximum load voltage is stepped down to a predetermined value when the output current value is equal to or greater than a predetermined output current reference value. Power supply device for arc machining.   2. The arc machining power supply device according to claim 1, wherein the external characteristic control is performed by reducing a maximum ON / Duty of the inverter circuit.   An output voltage detection circuit for detecting the rectified output voltage is provided, and the external characteristic control is performed by constant voltage control when the output voltage value is equal to or higher than a predetermined output voltage reference value. 1. The arc machining power supply device according to 1.   4. The arc machining power supply device according to claim 3, wherein the output voltage reference value is set based on an output current set value.

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