JP2016131998A - Spot welding power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spot welding power source capable of switching a frequency of electric power to be applied to a metal plate to a desirable frequency without using a plurality of power sources when joining metal plates by resistant spot welding.SOLUTION: Switching either of resonance capacitors 260a, 260b in which a capacitance is set such that a resonance circuit based on an inductance L of a load side circuit as a circuit containing a metal plate S which is a circuit of a load side rather than an inverter circuit 240 and either of capacitances C, Cof the resonance capacitors 260a, 260b in accordance with a frequency of AC power outputted from the inverter circuit 240 is performed during one time welding operation.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a spot welding power source, and is particularly suitable for use in resistance spot welding of overlapping portions of metal plates.

  In resistance spot welding, Joule heat is generated in the overlapping portion of the metal plate by applying pressure and energization to the overlapping portion of the metal plate such as a steel plate from above and below by a pair of electrodes. The overlapping part is dissolved and joined. There are technologies described in Patent Documents 1, 2, and 3 as technologies related to the power supply device for resistance spot welding.

  In Patent Document 1, resistance spot welding is performed with high-frequency power of low voltage and large current using an inverter circuit and a welding transformer that convert DC power into single-phase AC power of about 1 [kHz] to 10 [kHz]. It is described to do. Patent Document 1 also describes that the voltage or frequency applied to the welding transformer is changed by controlling the inverter circuit in order to modify the metal structure of the weld by performing heat treatment after resistance spot welding. Yes.

Patent Document 2 describes that only one of an inverter conversion circuit and a capacitor discharge circuit is selected according to the purpose of welding, and electric power is output from the selected circuit to a welding transformer.
Patent Document 3 discloses that power from a low-frequency power source having a frequency of 50 [Hz] is applied to the welding electrode, and then power from a high-frequency power source having a frequency of 30 [kHz] is applied to the welding electrode. Yes.

JP-A-60-255287 Japanese Patent Laid-Open No. 10-137948 International Publication No. 2011-013793 JP-A-4-75788

Here, the technique described in Patent Document 1 outputs high-frequency power with an inverter device for the purpose of reducing the weight of a welding transformer for mounting on a robot. However, since it does not have a matching circuit that resonates with the inductance of the welded part, only one high-frequency power that resonates with the inductance of the welded part can be selected. Is impossible.
Further, the techniques described in Patent Documents 2 and 3 require a plurality of power supplies. This increases the size of the device.

  The present invention has been made in view of the above problems, and when joining metal plates by resistance spot welding, the frequency of power applied to the metal plates is set to a desired frequency without using a plurality of power sources. The purpose is to enable switching.

  A spot welding power source according to the present invention is a spot welding power source that outputs power supplied to a welding electrode for resistance spot welding of an overlapped portion of metal plates, and is an inverter that converts DC power into AC power and outputs the power. A circuit, a plurality of resonant capacitors each consisting of at least one capacitor, and a selection means for selecting any one of the plurality of resonant capacitors, wherein the inverter circuit includes a series including the resistance spot welding. The frequency of the AC power to be output is changed at least once during the welding operation, and the selection means is a circuit on the load side of the inverter circuit at the frequency of the AC power output from the inverter circuit. Based on the inductance of the load side circuit that is a circuit including the metal plate and the capacitance of the resonant capacitor. As Ku resonance circuit is constituted, in accordance with a change in frequency of the AC power output from the inverter circuit, and selects either one of the resonant capacitor of the plurality of resonant capacitors.

  According to the present invention, any one of the plurality of resonance capacitors is selected according to the frequency of the AC power output from the inverter circuit so that the resonance circuit is configured at the frequency of the AC power output from the inverter circuit. Select two resonant capacitors. Therefore, when joining a metal plate by resistance spot welding, the frequency of the electric power given to a metal plate can be switched to a desired frequency, without using a some power supply.

It is a figure which shows an example of a structure of a resistance spot welder. It is a figure which shows an example of an electricity supply pattern notionally. It is a figure which shows notionally the specific example of an electricity supply pattern. It is a flowchart explaining an example of operation | movement of a control apparatus. It is a figure which shows the modification of a structure of a resistance spot welder.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an example of a configuration of a resistance spot welder.
In FIG. 1, the resistance spot welder includes a spot welding gun 100 and a spot welding power source 200.

The spot welding gun 100 is a main part of a resistance spot welder that receives electric power from the spot welding power source 200 and performs resistance spot welding on the overlapping portion of the metal plates S. That is, the spot welding gun 100 generates Joule heat in the overlapping portion of the metal plate S by applying pressure and energization to the overlapping portion of the metal plate S from above and below by the pair of welding electrodes 110a and 110b. The overlapping portion of the metal plate S is melted and joined by Joule heat.
The overlapping portion of the metal plates S may be a portion where different metal plates S are overlapped, or may be a portion where the same metal plate S is overlapped (by bending). Further, the number of metal plates S to be superimposed is not limited to two and may be three or more.

  The spot welding gun 100 has a configuration (not shown) necessary for functioning as a spot welding gun in addition to the welding electrodes 110a and 110b. For example, the spot welding gun 100 includes a shank that holds the welding electrodes 110a and 110b so that the welding electrodes 110a and 110b are rotatable about the axis thereof, an electrode holder that holds the shank, and an arm that holds the electrode holder. In addition, since the structure of the spot welding gun 100 is implement | achieved by the well-known technique described, for example in patent document 4, the detailed description is abbreviate | omitted here.

(Spot welding power source 200)
The spot welding power source 200 is for supplying electric power to the spot welding gun 100 (welding electrodes 110a and 110b with the metal plate S disposed therebetween).
The spot welding power source 200 includes a three-phase AC power source 210, a three-phase rectifier circuit 220, a smoothing capacitor 230, an inverter circuit 240, a changeover switch 250, resonant capacitors 260a and 260b, a welding transformer 270, and a control device 280. And have.

The three-phase AC power supply 210 outputs three-phase AC power. The frequency of the three-phase AC power is, for example, a commercial frequency.
The three-phase rectifier circuit 220 rectifies the three-phase AC power output from the three-phase AC power source 210. Here, the case where the three-phase rectifier circuit 220 is a three-phase full-wave rectifier circuit (when the three-phase AC power output from the three-phase AC power supply 210 is full-wave rectified) will be described as an example.

The smoothing capacitor 230 is a capacitor for smoothing the power rectified by the three-phase rectifier circuit 220 (reducing ripple (voltage fluctuation)).
The inverter circuit 240 converts the power (DC power) smoothed by the smoothing capacitor 230 into AC power based on the on / off operation of the switching element. Since a known inverter circuit can be used as the inverter circuit 240, its detailed configuration is omitted.

  Here, the case where three-phase AC power is used has been described as an example, but single-phase AC power may be used instead of three-phase AC power. Although the case where full-wave rectification is performed is shown as an example here, half-wave rectification may be performed instead of full-wave rectification.

The changeover switch 250 selects one of the two resonance capacitors 260a and 260b based on a command from the control device 280 described later.
The resonant capacitors 260a and 260b have different capacitances.
The value of the capacitance of the resonance capacitors 260a and 260b is set so that a resonance circuit based on the inductance L of the load side circuit and the capacitance C ₁ or C ₂ of the resonance capacitors 260a and 260b is configured. Here, the load side circuit is a circuit on the load (output) side of the inverter circuit 240 and includes the metal plate S. An equivalent circuit of the spot welding gun 100 including the metal plate S is, for example, a circuit in which a resistor and an inductor are connected in series. In this case, the load side (output side) circuit from the inverter circuit 240 is a series resonance circuit.

  The inductance L of the load side circuit is measured before resistance spot welding of the metal plate S by using, for example, an LCR meter. At this time, the inductance L in a state where the metal plate S to be welded is set on the spot welding gun 100 (the welding electrodes 110a and 110b are in contact with the metal plate S) can be obtained. However, the inductance L in a state where a metal plate having the same material, thickness and number as that of the metal plate S to be welded (not the metal plate S itself to be welded) is set on the spot welding gun 100 is measured in advance. The inductance L may be used. In this case, for example, the relationship between the material L, the thickness and the number of the metal plates S and the inductance L is investigated in advance for each of the plurality of metal plates S having at least one different material, thickness and number, A table indicating the relationship between the material L, the thickness, the number of the metal plates S and the inductance L is stored in the control device 280, and the inductance L corresponding to the metal plate S to be welded designated by the operator is read out. May be.

  The welding transformer 270 steps down the AC voltage input from the inverter circuit 240 via the changeover switch 250 and the resonant capacitor 260a or 260b, and applies a large current suitable for resistance spot welding of the metal plate S to the spot welding gun 100 (metal plate). S is output to the welding electrodes 110a and 110b) disposed therebetween. For example, an alternating current of several thousand A to several tens of thousands of A flows from the welding transformer 270 to the spot welding gun 100 (welding electrodes 110a and 110b with the metal plate S disposed therebetween).

  As shown in FIG. 1, one ends of the resonant capacitors 260 a and 260 b are connected to each other, and the connected portion is connected to one end on the primary side of the welding transformer 270. The other end of the primary side of the welding transformer 270 is connected to one end of the output terminal of the inverter circuit 240. One end of the changeover switch 250 can be in contact with one of the other ends of the resonance capacitors 260 a and 260 b, and the other end of the changeover switch 250 is connected to the other end of the output terminal of the inverter circuit 240.

  The control device 280 controls the operation of the inverter circuit 240 and the operation of the changeover switch 250. The hardware of the control device 280 is realized by using, for example, an information processing device (personal computer or the like) having a CPU, ROM, RAM, HDD, and various interfaces, a PLC (Programmable Logic Controller), or dedicated hardware. can do.

Below, an example of the function which the control apparatus 280 has is demonstrated.
<Energization pattern storage unit 281>
The energization pattern storage unit 281 stores an energization pattern indicating a relationship between an electrode current, which is a current that is energized to the welding electrodes 110a and 110b, and time.
FIG. 2 is a diagram conceptually illustrating an example of an energization pattern.
The energization pattern shown in FIG. 2, initially, the welding electrodes 110a, 110b and to be brought into contact with the metal plate S, started resistance spot welding (energized) at time t _1, from the time t ₁ to time t _2, the frequency f _1, flow the sinusoidal alternating current effective value I ₁ welding electrode 110a, the 110b. Then, stop the current supply to the welding electrodes 110a, 110b from the time t ₂ to time t ₃ (the electrode current to 0 (zero)), from the time t ₃ to time t _4, the frequency f ₂ (<f _1), A sinusoidal alternating current having an effective value I ₂ (<I ₁ ) is passed through the welding electrodes 110a and 110b. Then, energization is terminated at time t ₄ (the electrode current is set to 0 (zero)), and a series of welding operations are terminated. Incidentally, after completion of the energization at the time t _4, after the elapse of a predetermined time, the welding electrodes 110a, and 110b away from the metal plate S, may be terminated a series of welding operations.

In the energization pattern shown in FIG. 2, the effective value I ₁ of the electrode current in the _first energization period (period from time t ₁ to time t ₂ ) is the second energization period (period from time t ₃ to time t ₄ ). Is larger than the effective value I ₂ of the electrode current. Further, the frequency f ₁ of the electrode current in the _first energization period is higher than the frequency f ₂ of the electrode current in the second energization period. With such an energization pattern, for example, the metal plate S is heated and melted in the first energization period, and the metal plate is in the non-energization period between the first energization period and the second energization period. Solidification of the molten portion of S is started, and reheating can be performed in the solidification process of the metal plate S in the two energization periods. The first energization period is appropriately set based on past results. The second energization is performed for structure control, but the energization period is appropriately set in consideration of the quality of welding.

FIG. 3 is a diagram showing a specific example of the energization pattern shown in FIG.
Time _{t 1, t 2, t 3} , t 4 shown in FIG. 3, corresponds to a time _{t 1, t 2, t 3} , t 4 shown in FIG. In the energization pattern shown in FIG. 3, the frequency f ₁ in the first energization period is 1 [kHz], and the frequency f ₂ in the second energization period is 0.1 [kHz]. As the period (deenergization period) from the time t ₂ time t _3, for example, may be employed time 0.1 [s] ~0.2 [s] . In the non-energization period, a period in which re-coagulation does not occur is appropriately set.

  The energization pattern storage unit 281 acquires and stores information indicating the energization pattern as described above. As an acquisition form of information indicating an energization pattern, for example, an operation of a user interface by an operator, transmission from an external device, and reading from a portable storage medium can be cited. The energization pattern storage unit 281 can store information indicating a plurality of types of energization patterns.

Here, the inductance L at 1 [kHz] and 0.1 [KHz] of the load side circuit (the circuit on the load side (output side) than the inverter circuit 240 and including the metal plate S) is 130 respectively. It is assumed that [μH] and 140 [μH]. In this case, the capacitance C when 1 [kHz] and 0.1 [KHz] become the series resonance frequency f ₀ is 195 [μF] and 18111 [μF], respectively, from f ₀ = 1 / (2π√LC). become. As described above, in the energization pattern shown in FIG. 3, the frequency f ₁ in the first energization period is 1 [kHz], and the frequency f ₂ in the second energization period is 0.1 [kHz]. Therefore, in the example shown in FIG. 1, 195 [μF] and 18111 [μF] are selected as the capacitances C ₁ and C ₂ of the resonant capacitors 260a and 260b. Hereinafter, a specific example will be described on the assumption that 195 [μF] is selected as the capacitance C ₁ of the resonance capacitor 260 a and 18111 [μF] is selected as the capacitance C ₂ of the resonance capacitor 260 b.

<Control unit 282>
The control unit 282 reads one piece of information indicating the energization pattern stored in the energization pattern storage unit 281 based on, for example, an operation of the user interface by the operator, and based on the information indicating the read energization pattern, the inverter circuit 240. And an operation command is output to the changeover switch 250.
The control unit 282 includes an inverter control unit 282 a that controls the operation of the inverter circuit 240 and a changeover switch control unit 282 b that controls the operation of the changeover switch 250.

[Inverter control unit 282a]
The inverter control unit 282a determines a switching pattern (timing for turning on / off each switching element) of the switching element included in the inverter circuit 240 from the information indicating the read energization pattern. Then, the inverter control unit 282a outputs an operation command to the switching element of the inverter circuit 240 based on the determined switching pattern. Thereby, each switching element of the inverter circuit 240 operates so that the electrode current indicated by the energization pattern flows through the welding electrodes 110a and 110b.

In the energization pattern shown in FIG. 2 and FIG. 3, when the time t ₁ that is the start timing of the _first energization period is reached, the inverter control unit 282 a switches each switching element of the inverter circuit 240 according to the switching pattern in the first energization period. The operation command to operate is output. The switching pattern in the first energization period is a switching pattern for causing a sinusoidal alternating current having a frequency f ₁ (= 1 [kHz]) and an effective value I ₁ to flow through the welding electrodes 110a and 110b.
Thereafter, when the first time t ₂ is the timing of the end of the conduction period of the inverter control unit 282a outputs an operation command to turn off all the switching elements of the inverter circuit 240. Thereby, welding electrode 110a, 110b will be in a non-energized state.

Thereafter, when the second is a timing of the start of the energizing period time t _3, the inverter control unit 282a outputs an operation command for operating the respective switching elements of the inverter circuit 240 according to the switching pattern in the conduction period of second. The switching pattern in the second energization period is a switching pattern for causing a sinusoidal alternating current having a frequency f ₂ (= 0.1 [kHz]) and an effective value I ₂ to flow through the welding electrodes 110a and 110b. In the example shown in FIGS. 2 and 3, for example, the frequency and effective value of the alternating current / alternating voltage output from the inverter circuit 240 are made smaller than those in the first energization period.
Thereafter, at time t ₄ , which is the end timing of the second energization period, the inverter control unit 282 a outputs an operation command for turning off all the switching elements of the inverter circuit 240. Thereby, welding electrode 110a, 110b will be in a non-energized state.

[Changeover switch controller 282b]
The changeover switch control unit 282b configures the resonance capacitor in which the above-described resonance circuit is configured at the frequency of the electrode current in the first energization period of the resonance capacitors 260a and 260b before the start timing of the first energization period. An operation command instructing selection of 260 a or 260 b is output to the changeover switch 250. Thereby, the changeover switch 250 is connected to the resonance capacitor 260a or 260b indicated in the operation command.

As described above, in the energization pattern shown in FIG. 3, the frequency f ₁ in the first energization period is 1 [kHz]. Further, the capacitance C when 1 [kHz] becomes the series resonance frequency f ₀ is 195 [μF], and the capacitance C ₁ of the resonance capacitor 260a is 195 [μF]. Therefore, the changeover switch controller 282b is before the first time is a timing of the start of the energizing period time t _1, and outputs an operation command for instructing to select the resonance capacitor 260a to the changeover switch 250.

  Thereafter, the changeover switch control unit 282b determines the electrode current in the second energization period of the resonance capacitors 260a and 260b from the end timing of the first energization period to the start timing of the second energization period. An operation command instructing selection of the resonance capacitor 260a or 260b that constitutes the above-described resonance circuit at the frequency is output to the changeover switch 250. Thereby, the changeover switch 250 is connected to the resonance capacitor 260a or 260b indicated in the operation command.

As described above, in the energization pattern shown in FIG. 3, the frequency f ₂ in the second energization period is 0.1 [kHz]. The capacitance C when 0.1 [kHz] is the series resonance frequency f ₀ is 18111 [μF], and the capacitance C ₂ of the resonance capacitor 260b is 18111 [μF]. Therefore, the changeover switch controller 282b is between the first time t ₂ is the timing of the end of the conduction period until the timing of the start of the time of the second conduction period t _3, by selecting the resonance capacitor 260b Is output to the changeover switch 250.

(Operation flowchart)
Next, an example of the operation of the control device 280 will be described with reference to the flowchart of FIG. Here, the description will be made assuming that information indicating a desired energization pattern is already stored in the energization pattern storage unit 281.
First, in step S401, the control unit 282 stands by until an energization pattern read instruction is issued based on an operation of a user interface by an operator or the like. When information indicating a plurality of types of energization patterns is stored in the energization pattern storage unit 281, information for specifying an energization pattern to be read is included in the energization pattern read instruction.

If there is an instruction to read the energization pattern, the process proceeds to step S402. In step S <b> 402, the control unit 282 reads information indicating the energization pattern for which a read instruction has been issued from the energization pattern storage unit 281.
Next, in step S403, the inverter control unit 282a determines a switching pattern (timing for turning on / off each switching element) of the switching element included in the inverter circuit 240 from the information indicating the energization pattern read in step S402. To do.

Next, in step S404, the control unit 282 sets “1” to a variable n that identifies the number of energization periods.
Next, in step S405, the changeover switch control unit 282b outputs to the changeover switch 250 an operation command that instructs to select the resonance capacitor 260a or 260b corresponding to the n-th energization period among the resonance capacitors 260a and 260b. To do. That is, the changeover switch control unit 282b instructs the selection of the resonance capacitor 260a or 260b that constitutes the resonance circuit described above at the frequency of the electrode current in the n-th energization period among the resonance capacitors 260a and 260b. Is output to the changeover switch 250.

Next, in step S406, the inverter control unit 282a outputs an operation command to operate each switching element of the inverter circuit 240 according to the switching pattern in the n-th energization period.
Next, in step S407, the control unit 282 waits until the n-th energization period ends.

When the n-th energization period ends, the process proceeds to step S408. In step S408, the inverter control unit 282a outputs an operation command for turning off all the switching elements of the inverter circuit 240. Thereby, welding electrode 110a, 110b will be in a non-energized state.
Next, in step S409, the control unit 282 determines whether or not the variable n that identifies the number of energization periods is the number N of energization periods included in the energization pattern read in step S402. In the energization pattern shown in FIGS. 2 and 3, the number N of energization periods included in the energization pattern is “2”.

As a result of the determination, if the variable n for identifying the number of energization periods is not the number N of energization periods included in the energization pattern read out in step S402, the process proceeds to step S410.
In step S410, the control unit 282 adds “1” to the variable n that identifies the number of energization periods. Then, the process returns to step S405, and the operation in the n-th energization period after the update is performed as described above.

  As described above, the operation in all the energization periods included in the energization pattern read out in step S402 is completed. In step S409, the variable n for identifying the number of energization periods is included in the energization pattern read out in step S402. If it is determined that the number N of energization periods is determined, the process according to the flowchart of FIG. 4 is terminated.

(Summary)
As described above, in the present embodiment, any _one of the inductance L of the load side circuit that is a circuit on the load side of the inverter circuit 240 and includes the metal plate S and the capacitances C ₁ and C ₂ of the resonance capacitors 260a and 260b. Switching one of the resonance capacitors 260a and 260b, the capacitance of which is set so that a resonance circuit based on the heel, is configured in accordance with the frequency of the AC power output from the inverter circuit 240 during one welding operation. Do. Accordingly, the capacitances C ₁ and C ₂ of the resonant capacitors 260a and 260b are set so as to resonate at a desired frequency, thereby allowing one power source (inverter circuit 240 in the example shown in FIG. 1) in one welding operation. Thereby, the frequency of the electric power given to the metal plate S can be switched to a desired frequency.

In this embodiment, a non-energization period is set, and the resonance capacitors 260a and 260b are switched during the non-energization period. Therefore, for example, the resonance capacitors 260a and 260b can be switched using a period in which the molten portion of the metal plate S is solidified. Therefore, it is possible to safely switch the resonance capacitors 260a and 260b without degrading the quality of the welded portion.
In the present embodiment, the effective value of the electrode current is changed when the frequency of the AC power output from the inverter circuit 240 is changed. Therefore, more variations of energization patterns can be configured according to the quality required for the welded portion.

(Modification)
<Modification 1>
In this embodiment, the case where the resonant capacitors 260a and 260b are arranged so as to be connected in series with the primary winding of the welding transformer 270 has been described as an example. However, as long as the above-described resonance circuit is configured on the load side (output side) with respect to the inverter circuit 240, the place where the resonance capacitors 260a and 260b are arranged is not limited to the place shown in FIG.
FIG. 5 is a diagram showing a modification of the configuration of the resistance spot welder. The resistance spot welder shown in FIG. 5 is different from the resistance spot welder shown in FIG. 1 in that the resonant capacitor and the changeover switch 510 in the spot welding power source 500 are arranged. Therefore, in FIG. 5, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

In FIG. 5, the resonant capacitors 260c and 260d play the same role as the resonant capacitors 260a and 260b shown in FIG. That is, the resonant capacitors 260c and 260d have the capacitances of the resonant capacitors 260c and 260d so that a resonant circuit based on the inductance L of the load side circuit and the capacitances C ₃ and C ₄ of the resonant capacitors 260c and 260d is configured. Value is set. Here, the load side circuit is a circuit on the load side (output side) with respect to the inverter circuit 240 and includes the metal plate S.
The changeover switch 510 selects one of the two resonance capacitors 260c and 260d based on a command from the control device 280 described later.

As shown in FIG. 5, one ends of the resonance capacitors 260 c and 260 d are connected to each other, and the connected portion is connected to one end on the secondary side of the welding transformer 270. One end of the changeover switch 510 can be in contact with either one of the other ends of the resonance capacitors 260 c and 260 d, and the other end of the changeover switch 510 is connected to the other end on the secondary side of the welding transformer 270.
In this way, the resonance capacitors 260c and 260d may be arranged so as to be connected in parallel to the secondary winding of the welding transformer 270.

  In addition, a resonance capacitor may be arranged so as to be connected in parallel to the primary winding of the welding transformer 270, or the resonance capacitor may be connected in series to the secondary winding of the welding transformer 270. May be arranged.

<Modification 2>
In the present embodiment, the case where there are two frequencies (at the time of energization) of the electrode current (1 [kHz] and 0.1 [kHz] in the example shown in FIG. 3) included in one energization pattern is taken as an example. I gave it as an explanation. However, the number of frequencies (at the time of energization) of the electrode current included in one energization pattern may be any number as long as it is two or more. Considering a series of working time of normal resistance spot welding, the number of frequencies (when energized) of the electrode current can be made three. In this case, three capacitors are used so that the above-described resonant circuit is configured at these three frequencies. In the example shown in FIG. 1, one resonance capacitor is added in parallel with the resonance capacitors 260a and 260b. Further, if necessary, the number of electrode current frequencies (at the time of energization) included in one energization pattern may be four or more.

  As described above, when the number of frequencies of the electrode current (when energized) included in one energization pattern is three or more, the frequency of the electrode current (when energized) included in one energization pattern. The number of changes will be 2 or more. When the frequency of changing the frequency of the electrode current (during energization) is set to 2 times or more, the energization period is 3 times or more. Even in this case, a non-energization period is provided between the energization periods as described with reference to FIGS.

<Modification 3>
Further, the same frequency may be selected when the frequency of changing the frequency of the electrode current (during energization) included in one energization pattern is set to two times or more. For example, the frequency of electrode current (at the time of energization) included in one energization pattern is two, and the frequency of frequency change (at the time of energization) of the electrode current is two (the number of energization periods is three). ). In this case, the frequency in the _first energization period is f ₁ (1 [kHz] in the example shown in FIG. 3), and the frequency in the _second energization period is f ₂ (0.1 [kHz] in the example shown in FIG. 3). The frequency in the third energization period can be set to f ₁ (1 [kHz] in the example shown in FIG. 3). Furthermore, the frequencies in two or more consecutive energization periods may be the same. For example, the frequency in the first and second energization periods is f ₁ (1 [kHz] in the example shown in FIG. 3), and the frequency in the third energization period is f ₂ (0.1 [kHz in the example shown in FIG. 3). ]).

<Modification 4>
In the example shown in FIGS. 2 and 3, the effective value I ₁ of the electrode current in the first energization period is equal to the effective value I of the electrode current in the second energization period (period from time t ₂ to time t ₃ ). _The case where it is larger than ₂ has been described as an example. However, this is not always necessary, and the effective value of the electrode current in the first energization period may be smaller than the effective value of the electrode current in the second energization period. Further, the effective value of the electrode current may be the same in at least two energization periods.

<Modification 5>
Further, in the example shown in FIGS. 2 and 3, the case where the frequency f ₁ of the electrode current in the _first energization period is higher than the frequency f ₂ of the electrode current in the second energization period has been described as an example. However, this is not always necessary, and the frequency of the electrode current in the first energization period may be lower than the frequency of the electrode current in the second energization period.
As shown in Modifications 3 to 5 above, the magnitude relationship between the magnitude of the electrode current and the frequency during each energization period can be appropriately determined according to the quality required for the welded portion.

<Modification 6>
In the present embodiment, the case where the resonance capacitor is composed of one capacitor has been described as an example. However, when it is necessary to combine a plurality of capacitors (at least one of a series connection and a parallel connection) in order to obtain the capacitance for configuring the above-described resonant circuit, one capacitor is used to A resonance capacitor may be configured, and the plurality of capacitors may be selected by the changeover switches 250 and 510.

<Other variations>
Of the embodiments of the present invention described above, the processing performed by the control device 280 can be realized by a computer executing a program. Further, a computer-readable recording medium in which the program is recorded and a computer program product such as the program can also be applied as an embodiment of the present invention. As the recording medium, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.
In addition, the embodiments of the present invention described above are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. Is. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

  100: spot welding gun, 110a to 110b: welding electrode, 200: spot welding power source, 210: three-phase AC power source, 220: three-phase rectifier circuit, 230: smoothing capacitor, 240: inverter circuit, 250: changeover switch, 260a- 260d: resonance capacitor, 270: welding transformer, 280: control device, 281: energization pattern storage unit, 282: control unit, 282a: inverter control unit, 282b: changeover switch control unit, 500: spot welding power source, 510: changeover switch

Claims (3)

A spot welding power source that outputs electric power supplied to a welding electrode for resistance spot welding of an overlapped portion of metal plates,
An inverter circuit that converts DC power into AC power and outputs the power;
A plurality of resonant capacitors each consisting of at least one capacitor;
Selecting means for selecting any one of the plurality of resonant capacitors;
The inverter circuit changes the frequency of the AC power to be output at least once during a series of welding operations including the resistance spot welding,
The selection means includes an inductance of a load side circuit that is a circuit on the load side of the inverter circuit and includes the metal plate, and a capacitance of the resonance capacitor at a frequency of the AC power output from the inverter circuit. And selecting one of the plurality of resonance capacitors in accordance with a change in the frequency of the AC power output from the inverter circuit, so that a resonance circuit based on the above is configured. Spot welding power supply. The inverter circuit stops the output of the AC power for a preset period before changing the frequency of the AC power to be output,
The selection means is configured to resonate any one of the plurality of resonance capacitors so that the resonance circuit is configured at a changed frequency during a period in which the output of the AC power is stopped by the inverter circuit. The spot welding power source according to claim 1, wherein a capacitor is selected.   The inverter circuit is configured to change an effective value of an alternating current supplied to the welding electrode based on the alternating current power when changing a frequency of the alternating current power to be output. The spot welding power source according to 1 or 2.

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