JP5981735B2 - Plasma keyhole welding system and plasma keyhole welding method - Google Patents

Description

  The present invention relates to a plasma keyhole welding system and a plasma keyhole welding method.

  In the plasma keyhole welding method, for example, when welding a butt joint having an I-shaped groove as a base material, an arc generated when a tungsten electrode is generally used as a cathode, a water-cooled nozzle, a plasma gas gas flow, Restrained by. The high temperature plasma flow having good concentration is generated, and this high temperature plasma flow moves on the welding line while forming a keyhole penetrating the base material at the tip of the molten pool. This welding is directly applied until the arc heat reaches the back surface, and the back surface can be appropriately melted. The plasma keyhole welding method is described in Patent Document 1, for example.

  During steady welding where welding is performed while moving the plasma flow, the size of the keyhole may vary. When the size of the keyhole varies, there is a possibility that the width of the bead formed on the base material becomes non-uniform or that a bead is not formed on the back surface of the base material.

Japanese Patent Publication No. 02-18893

  The present invention has been conceived under the circumstances described above, and its main object is to provide a plasma keyhole welding method and a plasma keyhole welding system capable of forming a cleaner bead.

According to the first aspect of the present invention, an output circuit for passing a pulse current of a set frequency between the plasma electrode and the base material, and a keyhole size detection unit for detecting the size of the keyhole formed in the base material And a frequency calculation circuit that calculates the set frequency based on a change in the size of the keyhole detected by the keyhole size detection unit, and detects a welding voltage between the plasma electrode and the base material. The keyhole size detection unit includes a low-pass filter that allows only a low-frequency component of the welding voltage detected by the voltage detection circuit to pass, and the frequency calculation circuit includes the low-pass filter. based on the output voltage value, we calculate the set frequency, the plasma keyhole welding system is provided.

  Preferably, a reference voltage value storage unit that stores an output voltage value of the low-pass filter as a reference voltage value is further provided, and the frequency calculation circuit is configured such that the frequency difference is 0 or more when the voltage difference is positive. In addition, the set frequency is calculated, and when the voltage difference is negative, the set frequency is calculated so that the frequency difference is 0 or less, and the voltage difference is the output voltage of the low-pass filter. The reference voltage value is subtracted from the value, and the frequency difference is a value obtained by subtracting the set frequency when the output voltage value is the reference voltage value from the calculated set frequency.

  Preferably, the reference voltage value storage unit stores, as the reference voltage value, the output voltage value when the output voltage value of the low-pass filter is stabilized after the time when the keyhole penetrates.

  Preferably, the information processing apparatus further includes a confirmation auxiliary unit for obtaining auxiliary information based on the size of the keyhole, and the auxiliary information is information for assisting confirmation of a bead formed in the base material, and the confirmation auxiliary unit Includes a notification unit for reporting the auxiliary information.

  Preferably, the information processing apparatus further includes a threshold value storage unit that stores a threshold value, and the confirmation assisting unit includes a comparison circuit that compares the threshold value with a variation parameter that represents a variation in the size of the keyhole.

  Preferably, the notification unit notifies the auxiliary information when the comparison circuit determines that the fluctuation parameter has exceeded the threshold value.

  Preferably, the auxiliary information includes confirmation location information indicating a location to be confirmed in a bead formed on the base material, and the confirmation assistance portion is configured to check the confirmation location information based on a change in the size of the keyhole. The notifying unit notifies the confirmation location information obtained by the computing circuit.

  Preferably, the auxiliary information includes confirmation range information indicating a range to be confirmed in a bead formed on the base material, and the arithmetic circuit is configured to check the confirmation range information based on a change in the size of the keyhole. The notification unit notifies the confirmation range information determined by the arithmetic circuit.

  Preferably, the variation parameter is the voltage difference.

  Preferably, the notification unit notifies the auxiliary information by sound or light.

According to the second aspect of the present invention, the step of penetrating the keyhole by an arc between the plasma electrode and the base material, and the setting between the plasma electrode and the base material after the keyhole has penetrated A step of performing steady welding while flowing a pulse current of a frequency, and the step of performing steady welding includes detecting a size of a keyhole formed in the base material, and changing the size of the keyhole. the basis, see containing and a step of calculating the set frequency, further comprising the step of detecting the welding voltage between the plasma electrode and the base material, the step of detecting the size of the keyhole, by the low-pass filter Including a step of allowing only a low-frequency component of the welding voltage to pass, and in the step of calculating the set frequency, based on the output voltage value of the low-pass filter, the set frequency It calculates the number, plasma keyhole welding method is provided.

  Preferably, the method further comprises a step of storing the output voltage value of the low-pass filter as a reference voltage value in a reference voltage value storage unit, and in the step of calculating the set frequency, if the voltage difference is positive, the frequency difference The set frequency is calculated so that is equal to or greater than 0, and when the voltage difference is negative, the set frequency is calculated such that the frequency difference is equal to or less than 0. The value obtained by subtracting the reference voltage value from the output voltage value of the low-pass filter, and the frequency difference is the set frequency when the output voltage value is the reference voltage value from the calculated set frequency. Subtracted value.

  Preferably, in the step of calculating the set frequency, the output voltage value when the output voltage value of the low-pass filter is stabilized after the time when the keyhole penetrates is used as the reference voltage value.

  Preferably, the method includes a step of obtaining auxiliary information for assisting confirmation of a bead formed on the base material based on the size of the keyhole, and a step of notifying the auxiliary information.

  Preferably, in the step of obtaining the auxiliary information, a variation parameter representing a variation in the size of the keyhole is compared with a threshold value.

  Preferably, the notifying step is performed when it is determined in the comparing step that the variation parameter exceeds the threshold value.

  Preferably, the auxiliary information includes confirmation location information indicating a location to be confirmed in a bead formed on the base material, and the step of obtaining the auxiliary information is based on a change in the size of the keyhole. In the step of informing, including the step of obtaining location information, the confirmation location information is informed.

  Preferably, the auxiliary information includes confirmation range information indicating a range to be confirmed in a bead formed on the base material, and in the step of obtaining the confirmation location information, based on a change in the size of the keyhole. The confirmation range information is obtained, and in the notification step, the confirmation range information is notified.

  Preferably, the variation parameter is the voltage difference.

  Preferably, in the notification step, the auxiliary information is notified by sound or light.

  According to such a configuration, the keyhole size can be adjusted by adjusting the frequency of the pulse current. Thereby, a cleaner bead can be formed.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

It is a figure which shows the structure of the plasma keyhole welding system concerning 1st Embodiment of this invention. It is a partial expanded sectional view which shows the welding torch shown in FIG. It is a graph which shows the relationship between a voltage difference and a frequency difference for the frequency calculation circuit of FIG. 1 to calculate a setting frequency. It is a timing chart which shows an example of the plasma keyhole welding method concerning 1st Embodiment of this invention. It is a figure which shows an example of the waveform of a welding current in detail. It is a figure which shows an example of the waveform of a welding current in detail. It is a figure which shows an example of the waveform of a welding current in detail. It is sectional drawing which shows the state of the base material in the plasma keyhole welding method of 1st Embodiment of this invention. It is a figure which shows the welding state desired when performing plasma keyhole welding. It is a figure which shows the structure of the plasma keyhole welding system concerning 2nd Embodiment of this invention. It is a timing chart which shows the change state of a signal etc. when the size of a keyhole changes in the middle of welding. It is a figure which shows the structure of the plasma keyhole welding system concerning 3rd Embodiment of this invention. It is the figure which showed an example of the auxiliary information, the confirmation location information, and the confirmation range information which were displayed on the display part of the teach pendant.

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

<First Embodiment>
FIG. 1 is a diagram showing a configuration of a plasma keyhole welding system according to a first embodiment of the present invention.

  A plasma keyhole welding system A1 shown in FIG. 1 includes a welding robot 1, a robot control device 2, a welding power supply device 3, and a gas supply device 4.

  The welding robot 1 includes a welding torch 11 and a manipulator 12.

  As shown in FIG. 2, the welding torch 11 has a nozzle 111 and a plasma electrode 112. The nozzle 111 is a cylindrical member made of a metal such as copper. The nozzle 111 has a water cooling structure as appropriate. The plasma electrode 112 is a non-consumable electrode. The plasma electrode 112 is a metal rod made of tungsten, for example. The plasma electrode 112 is an electrode for applying a welding voltage Vw to the base material W. The plasma gas PG is ejected from the nozzle 111 so as to surround the plasma electrode 112. The plasma gas PG is, for example, Ar. When a welding voltage Vw is applied between the plasma electrode 112 and the base material W, an arc a1 is generated using the plasma gas PG as a medium. When the arc a <b> 1 is generated, a welding current Iw flows between the plasma electrode 112 and the base material W. The manipulator 12 holds the welding torch 11. The manipulator 12 is, for example, an articulated robot. The base material W is made of, for example, aluminum, an aluminum alloy, or stainless steel.

  The gas supply device 4 is for supplying a plasma gas PG to be ejected toward the base material W. The amount of plasma gas PG supplied by the gas supply device 4 (that is, the amount of plasma gas PG ejected from the nozzle 111) is determined by a gas flow rate setting signal (not shown).

  The robot control device 2 includes an operation control circuit 21 and a teach pendant 23. The robot control device 2 is for controlling the operation of the welding robot 1.

  The teach pendant 23 is connected to the operation control circuit 21. The teach pendant 23 is for the user of the plasma keyhole welding system A1 to set various operations. When the teach pendant 23 receives an instruction to start welding from the user of the plasma keyhole welding system A1, it sends a welding start signal St.

  The operation control circuit 21 has a microcomputer and a memory (not shown). The memory stores a work program in which various operations of the welding robot 1 are set. Further, the operation control circuit 21 controls the moving speed VR of the plasma electrode 112. The moving speed VR is the speed of the plasma electrode 112 with respect to the base material W in the welding progress direction Dr along the base material W. The operation control circuit 21 sends an operation control signal Ms to the welding robot 1 based on the work program, the coordinate information from the encoder, the moving speed VR, and the like. The welding robot 1 receives the operation control signal Ms and rotates a motor (not shown). As a result, the welding torch 11 moves to a predetermined welding start position on the base material W or moves along the in-plane direction of the base material W.

  The welding power supply device 3 is a device for applying a welding voltage Vw and causing a welding current Iw to flow between the plasma electrode 112 and the base material W. Welding power supply device 3 includes an output circuit 31, a voltage detection circuit 32, a steady welding start determination circuit 33, a frequency calculation circuit 38, and a reference voltage value storage unit 39.

  The output circuit 31 is for causing the welding current Iw to flow at a value instructed between the plasma electrode 112 and the base material W. The welding current Iw is a pulse current. The output circuit 31 includes a power supply circuit 311 and a frequency control circuit 312.

  The power supply circuit 311 receives, for example, a commercial power supply such as three-phase 200 V, performs output control such as inverter control and thyristor phase control according to a current error signal (not shown), and outputs a welding voltage Vw and a welding current Iw. The power supply circuit 311 receives the welding start signal St from the operation control circuit 21.

  The frequency control circuit 312 controls the frequency Ff of the welding current Iw that is a pulse current. The frequency control circuit 312 sends a frequency setting signal Ffs for allowing a welding current Iw to flow at a setting frequency Ffr described later to the power supply circuit 311.

  The voltage detection circuit 32 is for detecting the value of the welding voltage Vw between the plasma electrode 112 and the base material W. The voltage detection circuit 32 sends a voltage detection signal Vd corresponding to the value of the welding voltage Vw.

  The steady welding start determination circuit 33 receives the voltage detection signal Vd from the voltage detection circuit 32. The steady welding start determination circuit 33 determines whether to start steady welding based on the voltage detection signal Vd. When the steady welding start determination circuit 33 determines that steady welding should be started, it sends a steady welding start instruction signal Cm3 to the operation control circuit 21.

  In the present embodiment, the steady welding start determination circuit 33 includes a keyhole penetration detection circuit 331 and a comparison circuit 332. When the keyhole penetration detection circuit 331 detects that the keyhole 889 has penetrated the base material W, the keyhole penetration detection circuit 331 generates a keyhole penetration detection signal Cm2 and sends it to the comparison circuit 332.

  Specifically, the keyhole penetration detection circuit 331 includes an absolute value calculation circuit 341, a low-pass filter 342, and a voltage fluctuation detection circuit 343.

  The absolute value calculation circuit 341 receives the voltage detection signal Vd. The absolute value calculation circuit 341 calculates the absolute value of the input voltage detection signal Vd. Then, the absolute value calculation circuit 341 outputs the result of the calculation as a voltage absolute value signal Va. The low-pass filter 342 receives the voltage absolute value signal Va. The low-pass filter 342 performs an operation for removing the high frequency component of the input voltage absolute value signal Va and passing only the low frequency component. The low-pass filter 342 outputs the result of the calculation as a shaped voltage signal Vf. The absolute value calculation circuit 341 is not necessary when the voltage absolute value signal Va is a direct current instead of an alternating current.

  The voltage fluctuation detection circuit 343 is a circuit for detecting fluctuations in the shaped voltage signal Vf. The voltage fluctuation detection circuit 343 is provided for detecting the fluctuation of the shaping voltage signal Vf and detecting the time when the keyhole 889 penetrates. The voltage fluctuation detection circuit 343 includes a differentiation circuit BV, a comparison circuit CM1, a keyhole formation start reference voltage setting circuit VS, and a comparison circuit CM2.

  A shaping voltage signal Vf is input to the differentiation circuit BV. The differentiating circuit BV calculates a time differential value of the input shaped voltage signal Vf and outputs a voltage differential signal Bv. The voltage differentiation signal Bv is input to the comparison circuit CM1. The comparison circuit CM1 determines that the formation of the keyhole 889 has started when the voltage differential signal Bv becomes equal to or less than a predetermined reference value Bth1. At this time, the comparison circuit CM1 outputs a keyhole formation start signal Cm1 that becomes High level for a short time.

  The keyhole formation start reference voltage setting circuit VS receives a keyhole formation start signal Cm1 and a shaping voltage signal Vf. The keyhole formation start reference voltage setting circuit VS sets the shaping voltage signal Vf when the keyhole formation start signal Cm1 is input as the keyhole formation start reference voltage signal Vs. The keyhole formation start reference voltage setting circuit VS outputs a keyhole formation start reference voltage signal Vs.

  The comparison circuit CM2 receives the keyhole formation start reference voltage signal Vs and the shaping voltage signal Vf. When the difference between the keyhole formation start reference voltage signal Vs and the shaping voltage signal Vf is equal to or greater than a reference value Bth2 determined in advance by the type of the plasma gas PG, the comparison circuit CM2 penetrates the keyhole 889. Judge. At this time, the comparison circuit CM2 outputs a keyhole penetration detection signal Cm2 that becomes High level for a short time.

  Comparison circuit 332 receives keyhole penetration detection signal Cm2 and voltage differential signal Bv. When the voltage differential signal Bv reaches a predetermined reference value Bth3 or less after receiving the keyhole penetration detection signal Cm2, the comparison circuit 332 appropriately forms the weld back bead and the keyhole 889 has an appropriate size. Judging that it has come. At this time, the comparison circuit 332 determines that steady welding should be started, and sends a steady welding start instruction signal Cm3 that is at a high level for a short time. The steady welding start instruction signal Cm3 is sent to the frequency calculation circuit 38, the reference voltage value storage unit 39, and the operation control circuit 21.

  In addition, the steady welding start judgment circuit 33 demonstrated above also bears the function of a keyhole size detection part. That is, the steady welding start determination circuit 33 detects the size of the keyhole 889 formed in the base material W. In this embodiment, calculating the value of the shaping voltage signal Vf corresponds to detecting the size of the keyhole 889. In the present embodiment, the size of the keyhole 889 refers to the diameter of the opening of the keyhole 889 formed on the back side of the base material W.

  The reference voltage value storage unit 39 receives the shaping voltage signal Vf. The reference voltage value storage unit 39 stores the value of the shaping voltage signal Vf received at a certain time (the output voltage value of the low-pass filter 342) as the reference voltage value Vf1. Preferably, the reference voltage value storage unit 39 stores the output voltage value when the output voltage value of the low-pass filter 342 is stabilized after the time when the keyhole 889 penetrates the base material W as the reference voltage value Vf1. In the present embodiment, the reference voltage value storage unit 39 receives a steady welding start instruction signal Cm3. Upon receiving the steady welding start instruction signal Cm3, the reference voltage value storage unit 39 stores the output voltage value of the low pass filter 342 as the reference voltage value Vf1.

  The frequency calculation circuit 38 calculates a set frequency Ffr. The set frequency Ffr is a value for indicating the frequency Ff of the welding current Iw. The frequency calculation circuit 38 sends the calculated set frequency Ffr to the frequency control circuit 312. In the present embodiment, the frequency calculation circuit 38 receives the shaped voltage signal Vf from the low pass filter 342. The frequency calculation circuit 38 calculates the set frequency Ffr based on the value of the shaped voltage signal Vf (the output voltage value of the low pass filter 342). Details will be described later. Note that the frequency calculation circuit 38 also receives a steady welding start instruction signal Cm3.

  Next, an example of a plasma keyhole welding method using the plasma keyhole welding system A1 will be described with reference to FIG.

  4A shows the time change of the voltage detection signal Vd, FIG. 3B shows the time change of the voltage absolute value signal Va, and FIG. 3C shows the time of the shaped voltage signal Vf (output voltage value of the low-pass filter 342). (D) shows the time change of the keyhole formation start signal Cm1, (e) shows the time change of the keyhole penetration detection signal Cm2, and (f) shows the time change of the steady welding start instruction signal Cm3. (G) shows the time change of the moving speed VR of the plasma electrode 112, (h) shows the time change of the welding start signal St, (i) shows the time change of the frequency Ff of the pulse of the welding current Iw. Show.

  8 (s-1), (s-2), and (s-3) are the states of the arc a1 and the base material W in FIGS. 4 (s-1), (s-2), and (s-3), respectively. Corresponding to

  A voltage detection signal Vd shown in FIG. 4A represents an AC pulse waveform voltage signal having a peak value and a base value.

<Time t1 to Time t2>
When the welding start signal St from the outside is input to the operation control circuit 21 via the teach pendant 23 at time t1, the operation control circuit 21 outputs the welding start signal St to the output circuit 31 (specifically, To the power supply circuit 311). Then, the power supply circuit 311 applies the welding voltage Vw between the plasma electrode 112 and the base material W, and the arc a1 is ignited. Then, energization of the welding current Iw is started.

  As shown in FIG. 4 (i), the welding current Iw starts to flow at a predetermined frequency Ff from time t1.

  Here, the waveform of the pulse current will be described with reference to FIG. FIG. 5 is a graph showing approximately two pulse periods of the welding current Iw. Note that the time scale in FIG. 5 is extremely smaller than the time scale in FIG.

  In FIG. 5, the vertical axis indicating the welding current Iw is positive for the current that flows when the plasma electrode 112 becomes the anode. As can be understood from this figure, the welding current Iw is an alternating current that takes the electrode positive polarity current Iep and the electrode negative polarity current Ien once in the period Te. The electrode positive polarity current Iep is a current that flows when the plasma electrode 112 is an anode and the base material W is a cathode. The electrode negative polarity current Ien is a current that flows when the plasma electrode 112 is a cathode and the base material W is an anode.

  The electrode negative polarity current Ien is a pulse current having a period Te2. The period Te2 is shorter than the electrode negative polarity period Ten. During this period Te2, the electrode negative polarity current Ien takes the electrode negative polarity peak current Inp and the electrode negative polarity base current Inb once.

  In FIG. 5, the absolute value of the electrode negative polarity current Ien is indicated by a broken line. Furthermore, the figure shows the time average value Ia of the welding current Iw.

The relationship between the frequency Ff and the period Te is as follows.
Ff = 1 / Te

Further, the EN ratio is defined by the following equation using the period Te, the electrode negative polarity period Ten, or the electrode positive polarity period Tep.
EN ratio (%) = Ten / Te × 100
= Ten / (Ten + Tep) × 100

  In order to change the frequency Ff, for example, both the electrode negative polarity period Ten and the electrode positive polarity period Tep are changed without changing the EN ratio and the time average value Ia. However, changing the frequency Ff is not limited to this, and the frequency Ff may be adjusted while changing the EN ratio. In order to change the time average value Ia, for example, the maximum absolute value Iepp of the welding current Iw, the maximum absolute value Ienp of the welding current Iw, or the like is changed without changing the EN ratio.

  The waveform of the welding current Iw is not limited to that shown in FIG. 5, and may be that shown in FIG. 6 or FIG.

  As shown in FIG. 4G, the moving speed VR is 0 and the plasma electrode 112 is stopped with respect to the base material W from time t1 to time t4.

  The absolute value calculation circuit 341 calculates the absolute value of the voltage detection signal Vd corresponding to the welding voltage Vw, and sends a voltage absolute value signal Va shown in FIG. The low-pass filter 342 removes the high frequency component of the voltage absolute value signal Va and outputs a shaped voltage signal Vf shown in FIG. The low pass filter 342 removes a high frequency component that is, for example, 10 times or more the frequency Ff of the welding current Iw. As shown in FIG. 8 (s-1), after time t 1, the arc a 1 forms a molten pool 881 on the surface of the base material W. When the molten pool 881 starts to be formed, the arc a1 is unstable. Therefore, the shaping voltage signal Vf is likely to fluctuate.

<Time t2 to t3 (Keyhole formation period)>
As shown in FIG. 4C, when the forming voltage signal Vf rises and reaches time t2, the arc a1 is stabilized. Therefore, after time t2, the rate of increase of the shaped voltage signal Vf becomes small. When the voltage differential signal Bv obtained by time-differentiating the shaped voltage signal Vf becomes equal to or less than a predetermined reference value Bth1, the comparison circuit CM1 starts digging the keyhole 889 in the base material W, and the keyhole 889 is formed. Is determined to have started. When it is determined that the formation of the keyhole 889 is started, the comparison circuit CM1 outputs a keyhole formation start signal Cm1 that becomes High level for a short time as shown in FIG. When the keyhole formation start reference voltage setting circuit VS receives the keyhole formation start signal Cm1, the keyhole formation start reference voltage signal Vs (see FIG. c) See). As shown in FIG. 8 (s-2), after the time t2, the formation of the keyhole 889 is continued, and the surface 882 of the molten pool 881 gradually decreases. Note that the period from the time when the formation of the keyhole 889 is started (time t2) to the time when the keyhole 889 penetrates (time t3 described later) is a keyhole formation period.

<Time t3 to t4>
At time t3, the keyhole 889 penetrates through the base material W as shown in FIG. When the keyhole 889 penetrates, at time t3, as shown in FIG. 4C, the difference between the shaping voltage signal Vf and the keyhole formation start reference voltage signal Vs becomes larger than a predetermined reference value Bth2. In this case, the comparison circuit CM2 determines that the keyhole 889 has penetrated. Then, the comparison circuit CM2 sends a keyhole penetration detection signal Cm2 to the comparison circuit 332 as shown in FIG. Immediately after the keyhole 889 penetrates, the molding voltage signal Vf is unstable due to the penetration of the keyhole 889. After a while from the time t3 when the keyhole 889 penetrates, the shaping voltage signal Vf becomes stable after the shaping voltage signal Vf decreases, and the reduction rate of the shaping voltage signal Vf becomes small.

<After time t4>
At time t4, when the voltage differential signal Bv reaches a predetermined reference value Bth3 or less, the comparison circuit 332 determines that the weld back bead is properly formed and the keyhole 889 has an appropriate size. At this time, as shown in FIG. 4 (f), the comparison circuit 332 determines that the steady welding should be started, and sends a steady welding start instruction signal Cm3 that becomes a high level for only a short time.

  At time t4, when the operation control circuit 21 receives the steady welding start instruction signal Cm3, as shown in FIG. 4G, the operation control circuit Ms welds an operation control signal Ms for setting the moving speed VR to a predetermined speed. Send to robot 1. Thereby, the movement with respect to the base material W of the plasma electrode 112 in the welding advancing direction Dr is started.

  As described above, the process of performing steady welding is started from time t4, and welding to the base material W is performed. As a result, as shown in FIG. 9, a weld surface bead is formed on the surface of the base material W along the welding progress direction Dr, and a weld back bead is formed on the back surface of the base material W along the welding progress direction Dr.

  At time t4, when the reference voltage value storage unit 39 receives the steady welding start instruction signal Cm3, the value of the forming voltage signal Vf (the output voltage value of the low-pass filter 342) is set to the reference voltage value Vf1 (see FIGS. 1 and 4). ). That is, the reference voltage value storage unit 39 stores, as the reference voltage value Vf1, the output voltage value of the low-pass filter 342 when the output voltage value of the low-pass filter 342 is stabilized after the time when the keyhole 889 penetrates (time t3). To do. The reference voltage value Vf1 is 20.5V, for example. Unlike the present embodiment, the reference voltage value storage unit 39 may store the output voltage value of the low-pass filter 342 after a time of several seconds from the time t4 as the reference voltage value Vf1. Also by this, the reference voltage value storage unit 39 can store the output voltage value of the low-pass filter 342 when the output voltage value of the low-pass filter 342 is stabilized as the reference voltage value Vf1.

  In the process of performing steady welding after time t4, the size of the keyhole 889 may vary. The variation in the size of the keyhole 889 is caused by the variation in the balance of heat input from the arc a1 to the base material W, the change in the temperature of the base material W, or the like. Alternatively, the change in size of the keyhole 889 is caused by a change in the thickness of the base material W. As an example of the change in the thickness of the base material W, there is a case where the thickness of the base material W changes from 6 mm or 10 mm to 15 mm. The size of the keyhole 889 has a positive correlation with the value of the shaping voltage signal Vf (that is, the output voltage value of the low-pass filter 342). In other words, the output voltage value of the low-pass filter 342 increases as the size of the keyhole 889 increases, while the output voltage value of the low-pass filter 342 decreases as the size of the keyhole 889 decreases.

  As an example of the size of the keyhole 889 and the output voltage value of the low pass filter 342, the size of the keyhole 889 (the diameter of the opening of the keyhole 889 formed on the back surface side of the base material W) is 2.0 mm. When the output voltage value of the low-pass filter 342 is 22.0 V and the size of the keyhole 889 (the diameter of the opening of the keyhole 889 formed on the back surface side of the base material W) is 5.0 mm, The output voltage value of the filter 342 is 25.0V. In the process of performing steady welding after time t4, when the size of the keyhole 889 varies within the range of 1.5 to 2.5 mm, the output voltage value of the low-pass filter 342 is, for example, 21.5 to 22.5 V It fluctuates within the range.

  In this embodiment, in order to maintain the same size of the keyhole 889, control is performed so that the output voltage value of the low-pass filter 342 can be maintained the same. Specifically, the frequency calculation circuit 38 calculates the set frequency Ffr so that the voltage difference ΔV and the frequency difference ΔFf have a relationship shown in, for example, any one of FIGS. . The voltage difference ΔV shown in the figure is a value obtained by subtracting the reference voltage value Vf1 from the output voltage value of the low-pass filter 342. The frequency difference ΔFf is a value obtained by subtracting the set frequency Ffr when the output voltage value of the low-pass filter 342 is the reference voltage value Vf1 (time t4) from the calculated set frequency Ffr. 3A to 3F, when the voltage difference ΔV is positive, the frequency difference ΔFf is 0 or more, and when the voltage difference ΔV is negative, the frequency difference ΔFf is 0. It is as follows.

  When the voltage difference ΔV is positive, the size of the keyhole 889 is larger than the size at time t4. The frequency calculation circuit 38 calculates the set frequency Ffr so that the frequency difference ΔFf is 0 or more when the voltage difference ΔV is positive. Thereby, when the frequency Ff of the welding current Iw becomes larger than that at the time t4, the arc pressure becomes smaller. As a result, the base material W does not melt so much and the size of the keyhole 889 is reduced.

  On the other hand, when the voltage difference ΔV is negative, the size of the keyhole 889 is smaller than the size at time t4. The frequency calculation circuit 38 calculates the set frequency Ffr so that the frequency difference ΔFf is 0 or less when the voltage difference ΔV is negative. Thereby, when the frequency Ff of the welding current Iw becomes smaller than that at the time t4, the arc pressure increases. As a result, the base material W is melted well, and the size of the keyhole 889 is increased.

  As described above, the set frequency Ffr is calculated by the frequency calculation circuit 38, and the voltage difference ΔV is controlled to be zero. As a result, the output voltage value of the low-pass filter 342 is controlled so as to coincide with the reference voltage value Vf1 at time t4. That is, the size of the keyhole 889 is controlled to be the same as the size at time t4.

  Next, the effect of this embodiment is demonstrated.

  In the present embodiment, the plasma keyhole welding system A1 includes a frequency calculation circuit 38. The frequency calculation circuit 38 calculates a set frequency Ffr based on a change in the size of the keyhole 889 detected by the keyhole size detection unit (in this embodiment, the steady welding start determination circuit 33). With such a configuration, since the frequency Ff of the welding current Iw is determined by the set frequency Ffr, the frequency Ff can be adjusted based on a change in the size of the keyhole 889. If the frequency Ff can be adjusted, the arc pressure can be adjusted and the size of the keyhole 889 can be adjusted. Therefore, according to the present embodiment, the size of the keyhole 889 itself can be adjusted according to the change in the size of the keyhole 889. Thereby, a cleaner bead can be formed.

  In addition to adjusting the frequency Ff, the time average value Ia of the absolute value of the welding current Iw may be adjusted, the gas flow rate of the plasma gas PG may be adjusted, and the moving speed VR may be adjusted. May be. On the other hand, when adjusting the frequency Ff, the time average value Ia of the absolute value of the welding current Iw may not be changed. In this case, there is an advantage that it is not necessary to change the amount of heat input to the base material W. Further, when adjusting the frequency Ff, the gas flow rate of the plasma gas PG may not be changed. In this case, the possibility that the arc a1 cannot be shielded by the plasma gas PG can be avoided. Further, when adjusting the frequency Ff, the moving speed VR may not be changed. In this case, the time required for welding can be prevented from becoming longer than the desired time.

  In the present embodiment, the plasma keyhole welding system A1 includes a voltage detection circuit 32 that detects the welding voltage Vw. The keyhole size detection unit (steady welding start determination circuit 33 in the present embodiment) includes a low-pass filter 342 that allows only a low-frequency component of the welding voltage Vw detected by the voltage detection circuit 32 to pass therethrough. The frequency calculation circuit 38 calculates a set frequency Ffr based on the output voltage value of the low pass filter 342. As described above, the size of the keyhole 889 and the output voltage value of the low-pass filter 342 have a positive correlation. Therefore, according to the configuration of the present embodiment, the size of the keyhole 889 can be detected by a circuit in the plasma keyhole welding system A1. Therefore, according to the present embodiment, a device capable of detecting the size of the keyhole 889 can be obtained more easily.

  In the present embodiment, the plasma keyhole welding system A1 includes a reference voltage value storage unit 39 that stores the output voltage value of the low-pass filter 342 as the reference voltage value Vf1. As described with reference to FIGS. 3A to 3F, the frequency calculation circuit 38 sets the set frequency Ffr so that the frequency difference ΔFf is 0 or more when the voltage difference ΔV is positive. Is calculated. On the other hand, the frequency calculation circuit 38 calculates the set frequency Ffr so that the frequency difference ΔFf is 0 or less when the voltage difference ΔV is negative. According to such a configuration, as described above, the set frequency Ffr can be calculated so that ΔV becomes zero. Therefore, the output voltage value of the low-pass filter 342 can be maintained at the reference voltage value Vf1. That is, the size of the keyhole 889 can be maintained uniformly.

  In the present embodiment, the reference voltage value storage unit 39 obtains the output voltage value of the low-pass filter 342 when the output voltage value of the low-pass filter 342 is stabilized after the time (time t3) when the keyhole 889 penetrates, as the reference voltage. Store as value Vf1. When the output voltage value of the low-pass filter 342 is stabilized after the time when the keyhole 889 penetrates (time t3), the keyhole 889 has an appropriate size. Therefore, the configuration of this embodiment is suitable for maintaining the size of the keyhole 889 uniformly while maintaining an appropriate size.

Second Embodiment
FIG. 10 is a diagram showing a configuration of a plasma keyhole welding system according to the second embodiment of the present invention.

  A plasma keyhole welding system A2 shown in FIG. 1 includes a welding robot 1, a robot control device 2, a welding power source device 3, and a gas supply device 4.

  Since the welding robot 1 and the gas supply device 4 in the plasma keyhole welding system A2 are the same as the configuration in the plasma keyhole welding system A1, description thereof will be omitted.

  The welding power supply device 3 is the same as that of the first embodiment except that the welding power supply device 3 further includes a comparison circuit 361, a threshold value storage unit 362, and a notification unit 364.

  In the present embodiment, the comparison circuit 361 and the notification unit 364 constitute a confirmation auxiliary unit of the present invention. The confirmation auxiliary unit obtains auxiliary information Inf1 based on the size of the keyhole 889. The auxiliary information Inf1 is information for assisting confirmation of the beads formed on the base material W. The auxiliary information Inf1 will be described later.

  The threshold value storage unit 362 stores a threshold value Vth. The comparison circuit 361 receives the shaped voltage signal Vf from the low pass filter 342. Further, the comparison circuit 361 receives the reference voltage value Vf <b> 1 from the reference voltage value storage unit 39. The comparison circuit 361 compares the variation parameter indicating the variation in the size of the keyhole 889 with the threshold value stored in the threshold value storage unit 362. In the present embodiment, the comparison circuit 361 uses the voltage difference ΔV (a value obtained by subtracting the reference voltage value Vf1 from the output voltage value of the low-pass filter 342) as the variation parameter. When the comparison circuit 361 determines that the voltage difference ΔV exceeds the threshold value Vth, the comparison circuit 361 determines that the size of the keyhole 889 has changed, and generates the keyhole size change detection signal Sc. The comparison circuit 361 sends the generated keyhole size variation detection signal Sc to the notification unit 364.

  The notification unit 364 is for reporting the auxiliary information Inf1. When the comparison circuit 361 determines that the variation parameter has exceeded the threshold value, the notification unit 364 notifies the auxiliary information Inf1. In the present embodiment, when the comparison circuit 361 determines that the voltage difference ΔV as the variation parameter has exceeded the threshold value Vth, the auxiliary information Inf1 is notified. Specifically, when receiving the keyhole size variation detection signal Sc, the notification unit 364 notifies the auxiliary information Inf1. The notification unit 364 is, for example, a buzzer, a warning light, or a display device. The notification unit 364 notifies the auxiliary information Inf1 by sound or light. The auxiliary information Inf1 is an indication that the size of the buzzer sound, light, or keyhole has changed, for example.

  Next, the effect of this embodiment is demonstrated.

  FIG. 11 is a timing chart showing a change state of a signal or the like when the keyhole size fluctuates during welding. The size of the keyhole 889 and the signal change state in the plasma keyhole welding system A2 when the size of the keyhole 889 changes (when it increases in FIG. 11) will be described with reference to FIG. . FIG. 6A shows the size of the keyhole 889, FIG. 5B shows the change in the shaped voltage signal Vf, and FIG.

  As shown in FIG. 5A, the size of the keyhole 889 increases from time t21. As described above, the size of the keyhole 889 has a positive correlation with the shaped voltage signal Vf (that is, the output voltage value of the low-pass filter 342). Therefore, as shown in FIG. 5B, the value of the shaping voltage signal Vf also increases from time t21. At a certain time between time t21 and time t22, the frequency calculation circuit 38 calculates a set frequency Ffr for returning the size of the keyhole 889 to the size before time t21 based on the change in the size of the keyhole 889. And as shown in the figure (c), the frequency Ff of the welding current Iw increases at the time t22. As the frequency Ff of the welding current Iw increases, the arc pressure decreases. As a result, the base material W does not melt much. Then, between time t22 and time t23, the size of the keyhole 889 gradually decreases, and at time t23, the size of the keyhole 889 returns to the size before time t21.

  As described above, when the size of the keyhole 889 changes (when it increases in FIG. 11), at a time t23 when a certain period has elapsed from the time t21 when the size change of the keyhole 889 started, the keyhole 889 The size will be appropriate. That is, the size of the keyhole 889 in the period from time t21 to time t23 is not the same as the size before time t21. Therefore, the bead formed at time t21 to time t23 may have a defect such as having a different width from other parts or not formed on the back surface of the base material W. The process of adjusting the frequency Ff from time t21 to time t23 is automatically performed in the plasma keyhole welding system A2. In the arc welding system A1 according to the first embodiment, this adjusting process is not notified to the user of the arc welding system A1. Therefore, the user cannot know whether or not the size of the keyhole 889 has changed, and cannot know whether or not there is a possibility that the bead is defective.

  Although the case where the size of the keyhole 889 increases from time t21 is described in FIG. 11, the size of the keyhole 889 similarly changes even when the size of the keyhole 889 decreases from time t21. After a certain period from the time, the size of the keyhole 889 becomes appropriate. The period from time t21 to time t23 is, for example, about 1 to several seconds.

  In the present embodiment, in the plasma keyhole welding system A2, the notification unit 364 notifies auxiliary information Inf1 for assisting in confirming a bead formed on the base material W. According to such a configuration, the user of the plasma keyhole welding system A2 can know that the bead formed in the base material W may be defective as the auxiliary information Inf1. Therefore, the user of the plasma keyhole welding system A2 can easily perform the bead confirmation work.

  In the present embodiment, when the comparison circuit 361 determines that the voltage difference ΔV, which is a variation parameter, exceeds the threshold value Vth, the notification unit 364 notifies the auxiliary information Inf1. According to such a configuration, auxiliary information Inf1 can be notified during welding rather than after welding. Thereby, the user of plasma keyhole welding system A2 can know that the bead may have a defect during welding. Thereby, the confirmation work of a bead can be performed immediately after welding is completed.

  Although the comparison circuit 361 detects the fluctuation of the keyhole 889 using the voltage difference ΔV, the present invention is not limited to this. For example, the comparison circuit 361 may detect that the keyhole 889 has changed based on a change in the set frequency Ffr calculated by the frequency calculation circuit 38.

<Third Embodiment>
FIG. 12 is a diagram showing a configuration of a plasma keyhole welding system according to the third embodiment of the present invention.

  A plasma keyhole welding system A3 shown in FIG. 1 includes a welding robot 1, a robot control device 2, a welding power source device 3, and a gas supply device 4.

  Since the welding robot 1 and the gas supply device 4 in the plasma keyhole welding system A3 are the same as the configurations in the plasma keyhole welding systems A1 and A2, description thereof will be omitted.

  The welding power supply device 3 is the same as that of 2nd Embodiment except the point which does not have the alerting | reporting part 364. In the present embodiment, the comparison circuit 361 sends the generated keyhole size variation detection signal Sc to the operation control circuit 21. In addition, unlike what was shown in FIG. 12, the welding power supply device 3 may have the alerting | reporting part 364 described in 2nd Embodiment.

  The robot control device 2 includes an operation control circuit 21 and a teach pendant 23. In the present embodiment, the operation control circuit 21 is the same as that of the first embodiment except that the operation control circuit 21 includes an arithmetic circuit 211.

  The arithmetic circuit 211 receives the keyhole size variation detection signal Sc from the comparison circuit 361. The arithmetic circuit 211 obtains auxiliary information Inf1 based on a change in the size of the keyhole 889. In the present embodiment, the auxiliary information Inf1 includes confirmation location information Inf2 and confirmation range information Inf3 (see also FIG. 13). Then, the arithmetic circuit 211 obtains confirmation location information Inf2 and confirmation range information Inf3 based on a change in the size of the keyhole 889.

  The confirmation part information Inf2 is information indicating a part to be confirmed among the beads formed on the base material W (a part of the bead formed during a period from time t21 to time t23 in FIG. 11). As shown in FIG. 13, the confirmation location information Inf <b> 2 is, for example, a position based on the bead start point or a time from the start of welding. In the present embodiment, the arithmetic circuit 211 obtains confirmation location information Inf2 based on the reception of the keyhole size variation detection signal Sc. That is, the bead portion formed when the keyhole size variation detection signal Sc is received is determined as a portion to be confirmed.

  The confirmation range information Inf3 is information indicating a range to be confirmed in the beads formed on the base material W. As shown in FIG. 13, the confirmation range information Inf <b> 3 includes a display indicating a region formed between time t <b> 21 to time t <b> 23 in FIG. 11 in the bead formed on the base material W, and a length in the welding progress direction Dr. And so on.

  The teach pendant 23 has a display unit 231. The display unit 231 corresponds to an example of the notification unit of the present invention. The display unit 231 of the teach pendant 23 notifies (displays) the auxiliary information Inf1. Specifically, as shown in FIG. 13, the display unit 231 of the teach pendant 23 notifies (displays) confirmation location information Inf2 and confirmation range information Inf3 as auxiliary information Inf1.

  In the present embodiment, the comparison circuit 361, the arithmetic circuit 211, and the teach pendant 23 constitute a confirmation auxiliary unit of the present invention.

  Next, the effect of this embodiment is demonstrated.

  In the present embodiment, the auxiliary information Inf1 includes confirmation location information Inf2 indicating a location to be confirmed in the bead formed on the base material W. The arithmetic circuit 211 obtains confirmation location information Inf2 based on the change in the size of the keyhole 889. The display unit 231 of the teach pendant 23 notifies (displays) the confirmation location information Inf2 obtained by the arithmetic circuit 211. According to such a configuration, the user of the plasma keyhole welding system A3 can know the location to be confirmed among the beads formed on the base material W. Accordingly, the user of the plasma keyhole welding system A3 can more easily perform the bead confirmation work.

  In the present embodiment, the auxiliary information Inf1 includes confirmation range information Inf3 that indicates a range to be confirmed in the bead formed on the base material W. The arithmetic circuit 211 obtains confirmation range information Inf3 based on the change in the size of the keyhole 889. The display unit 231 of the teach pendant 23 notifies (displays) the confirmation range information Inf3 obtained by the arithmetic circuit 211. According to such a configuration, the user of the plasma keyhole welding system A3 can know the range to be confirmed in the beads formed on the base material W. Thereby, the user of plasma keyhole welding system A3 can perform the confirmation work of a bead further easily.

  In addition, although the display part 231 of the teach pendant 23 showed the example which alert | reports both the confirmation location information Inf2 and the confirmation range information Inf3 as auxiliary information Inf1, the present invention is not limited to this. The display unit 231 of the teach pendant 23 may notify (display) only one of the confirmation location information Inf2 and the confirmation range information Inf3 as the auxiliary information Inf1.

  In the present embodiment, an example in which the arithmetic circuit has the configuration of the operation control circuit 21 has been described. However, the configuration is not limited thereto, and the configuration of the welding power supply device 3 may be used.

  The change amount of the set frequency Ffr may be displayed on the display unit 231 of the teach pendant 23 as the auxiliary information Inf1.

  The present invention is not limited to the embodiment described above. The specific configuration of each part of the present invention can be changed in various ways.

  The steady welding start determination circuit 33 does not necessarily include the comparison circuit 332. The steady welding start determination circuit 33 may determine that steady welding should be started when a predetermined time has elapsed since the keyhole penetration detection signal Cm2 was generated. Alternatively, the steady welding start determination circuit 33 may determine that steady welding should be started when a predetermined time has elapsed since the output by the output circuit 31 started.

  Unlike the above-described embodiment, the comparison circuit CM2 determines that the keyhole 889 has penetrated when the amount of change in the formed voltage signal Vf exceeds a certain value after time t2, and outputs the keyhole penetration detection signal Cm2. May be.

  In the above embodiment, the frequency calculation circuit 38 calculates the set frequency Ffr based on the voltage difference ΔV, but the present invention is not limited to this. For example, the frequency calculation circuit 38 may calculate the set frequency Ffr based on the time differential value of the output voltage value of the low-pass filter 342.

  The keyhole size detection unit may detect the size of the keyhole 889 by image processing.

A1, A2, A3 Plasma keyhole welding system 1 Welding robot 11 Welding torch 111 Nozzle 112 Plasma electrode 12 Manipulator 2 Robot control device 21 Operation control circuit 211 Arithmetic circuit 23 Teach pendant 231 Display unit 3 Welding power supply device 31 Output circuit 311 Power supply circuit 312 Frequency control circuit 32 Voltage detection circuit 33 Steady welding start determination circuit 331 Keyhole penetration detection circuit 341 Absolute value calculation circuit 342 Low-pass filter 343 Voltage fluctuation detection circuit 332 Comparison circuit 361 Comparison circuit 362 Threshold storage unit 364 Notification unit 38 Frequency Calculation circuit 39 Reference voltage value storage unit 4 Gas supply device 881 Molten pool 882 Surface 889 Keyhole a1 Arc Bth1 Reference value Bth2 Reference value BV Differentiation circuit Bv Voltage differentiation signal Bth3 Reference value CM1 Comparison circuit m1 Keyhole formation start signal CM2 Comparison circuit Cm2 Keyhole penetration detection signal Cm3 Steady welding start instruction signal Dr Welding direction Ff Frequency Ffs Frequency setting signal Ffr Setting frequency Ia Time average value Iep Electrode plus polarity current Ien Electrode negative polarity current Iepp Maximum Absolute value Ienp Maximum absolute value Inf1 Auxiliary information Inf2 Confirmation location information Inf3 Confirmation range information Inp Electrode minus polarity peak current Inb Electrode minus polarity base current Iw Welding current Ms Operation control signal St Welding start signal Sc Keyhole size variation detection signal t1, t2 , T3, t4, t21, t22, t23 Time Te2 Period Te Period Ten Electrode negative polarity period Tep Electrode positive polarity period PG Plasma gas Va Voltage absolute value signal Vd Voltage detection signal Vf Molding voltage signal Vf1 Voltage VS keyhole formation start reference voltage setting circuit Vs keyhole formation start reference voltage signal Vth threshold Vw welding voltage W matrix

Claims (20)

An output circuit for passing a pulse current of a set frequency between the plasma electrode and the base material;
A keyhole size detector for detecting the size of the keyhole formed in the base material;
A frequency calculation circuit that calculates the set frequency based on a change in the size of the keyhole detected by the keyhole size detection unit ;
A voltage detection circuit for detecting a welding voltage between the plasma electrode and the base material;
The keyhole size detection unit includes a low-pass filter that passes only a low frequency component of the welding voltage detected by the voltage detection circuit,
The frequency calculation circuit based on the output voltage value of the low-pass filter, it calculates the set frequency, the plasma keyhole welding system. A reference voltage value storage unit for storing the output voltage value of the low-pass filter as a reference voltage value;
The frequency calculation circuit calculates the set frequency so that the frequency difference is 0 or more when the voltage difference is positive, and the frequency difference is 0 or less when the voltage difference is negative. The above set frequency is calculated so that
The voltage difference is a value obtained by subtracting the reference voltage value from the output voltage value of the low-pass filter.
The plasma keyhole welding system according to claim 1 , wherein the frequency difference is a value obtained by subtracting the set frequency when the output voltage value is the reference voltage value from the calculated set frequency. The plasma according to claim 2 , wherein the reference voltage value storage unit stores the output voltage value when the output voltage value of the low-pass filter is stabilized after the time when the keyhole penetrates as the reference voltage value. Keyhole welding system. Based on the size of the keyhole, further comprising a confirmation assisting unit for obtaining supplementary information, the supplementary information is information for assisting confirmation of beads formed in the base material,
The plasma keyhole welding system according to claim 2 or 3 , wherein the confirmation assisting unit includes a notifying unit for notifying the assisting information. A threshold storage unit for storing the threshold;
5. The plasma keyhole welding system according to claim 4 , wherein the confirmation assisting unit includes a comparison circuit that compares a variation parameter representing a variation in the size of the keyhole with the threshold value. The plasma keyhole welding system according to claim 5 , wherein when the comparison circuit determines that the variation parameter exceeds the threshold value, the notification unit notifies the auxiliary information. The auxiliary information has confirmation location information indicating a location to be confirmed in the bead formed on the base material,
The confirmation assisting unit includes an arithmetic circuit for obtaining the confirmation location information based on a change in the size of the keyhole,
The said notification part is a plasma keyhole welding system of Claim 4 or Claim 5 which alert | reports the said confirmation location information calculated | required by the said arithmetic circuit. The auxiliary information has confirmation range information indicating a range to be confirmed in the bead formed on the base material,
The arithmetic circuit obtains the confirmation range information based on a change in the size of the keyhole,
The plasma keyhole welding system according to claim 7 , wherein the notification unit notifies the confirmation range information obtained by the arithmetic circuit. The plasma keyhole welding system according to any one of claims 5 to 8 , wherein the variation parameter is the voltage difference. The plasma keyhole welding system according to any one of claims 4 to 9 , wherein the notification unit notifies the auxiliary information by sound or light. A step of penetrating the keyhole by an arc between the plasma electrode and the base material;
A step of performing steady welding while passing a pulse current of a set frequency between the plasma electrode and the base material after the keyhole has penetrated,
The process of performing the above-mentioned steady welding includes
Detecting the size of the keyhole formed in the base material;
Based on the change in the size of the keyhole, I saw including a the step of calculating the set frequency,
A step of detecting a welding voltage between the plasma electrode and the base material;
The step of detecting the size of the keyhole includes a step of allowing only a low frequency component of the welding voltage to pass through a low-pass filter,
The plasma keyhole welding method, wherein in the step of calculating the set frequency, the set frequency is calculated based on an output voltage value of the low-pass filter . Storing the output voltage value of the low-pass filter in the reference voltage value storage unit as a reference voltage value;
In the step of calculating the set frequency, the set frequency is calculated so that the frequency difference is 0 or more when the voltage difference is positive, and the frequency is set when the voltage difference is negative. Calculate the above set frequency so that the difference is 0 or less,
The voltage difference is a value obtained by subtracting the reference voltage value from the output voltage value of the low-pass filter.
The plasma keyhole welding method according to claim 11 , wherein the frequency difference is a value obtained by subtracting the set frequency when the output voltage value is the reference voltage value from the calculated set frequency. In the step of calculating the set frequency, the output voltage value when the output voltage value of the low-pass filter after the time that the key hole is penetrated is stabilized, is used as the reference voltage value, according to claim 12 Plasma keyhole welding method. Obtaining auxiliary information for assisting in confirming a bead formed on the base material based on the size of the keyhole;
The plasma keyhole welding method according to claim 12 or 13 , further comprising a step of notifying the auxiliary information. The plasma keyhole welding method according to claim 14 , wherein, in the step of obtaining the auxiliary information, a variation parameter representing a variation in the size of the keyhole is compared with a threshold value. The plasma keyhole welding method according to claim 15 , wherein the notifying step is performed when it is determined in the comparing step that the variation parameter exceeds the threshold value. The auxiliary information has confirmation location information indicating a location to be confirmed in the bead formed on the base material,
The step of obtaining the auxiliary information includes a step of obtaining the confirmation location information based on a change in the size of the keyhole,
The plasma keyhole welding method according to claim 14 or 15 , wherein in the step of informing, the confirmation location information is informed. The auxiliary information has confirmation range information indicating a range to be confirmed in the bead formed on the base material,
In the step of obtaining the confirmation location information, the confirmation range information is obtained based on the change in the size of the keyhole,
The plasma keyhole welding method according to claim 17 , wherein in the notifying step, the confirmation range information is notified. The fluctuation parameter is the voltage difference, the plasma keyhole welding method according to any one of claims 15 to claim 18. The plasma keyhole welding method according to any one of claims 14 to 19 , wherein in the informing step, the auxiliary information is informed by sound or light.

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