JPH10128553A - Resistance welding equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a switching element and to improve the welding quality at the same time by controlling the rest time for switching the energization cycle to the required minimum length. SOLUTION: In the first energization period, only a switching element of the first set (positive pole side) in a switching means is continuously switched (Steps S2-S6) at the high frequency (10kHz) by the feedback type pulse width control. When the first energization period is completed, a control part stops the supply of the first switching control signal to the switching element of the first set (positive pole side), and also stops the take-in of the measured value of the current from a current measured value operating circuit, and takes in the current detected signal from a current sensor instead to monitor the instantaneous value of the primary side current or the welding current (Step S8). The monitor period corresponds to the first rest time, and the current falls with the time constant corresponding to the load impedance at this time. When the timing 1 that the current reaches the current monitor value is detected, the control part immediately completes the monitor period or the rest period, and the second energization period is started on the negative pole side (Steps S10, S11).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0010]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding apparatus which performs a switching operation at a high frequency and supplies a low frequency AC welding current to a workpiece to perform resistance welding.

[0020]

2. Description of the Related Art In a conventional resistance welding apparatus of this type, a primary coil of a welding transformer is connected to an output terminal of an inverter, and a secondary coil is directly connected to a pair of welding electrodes (without a rectifier circuit). Is done. The inverter includes a positive-side switching element and a negative-side switching element corresponding to the direction of energization or the polarity of an output pulse, and inputs DC power obtained by rectifying a commercial frequency from a rectifier circuit. The inverter control circuit connects the switching element on the positive electrode side and the switching element on the negative electrode side of the inverter to a half cycle TW of the cycle TW set for the secondary side AC welding current.
High frequency switching is alternately and selectively performed for each energizing period TA corresponding to / 2. That is, in the conduction period TA corresponding to the half cycle of the positive electrode of the AC welding current, only the switching element on the positive side is switched at a high frequency, for example, 10 kHz, and the conduction period T corresponding to the half cycle of the negative electrode of the AC welding current is performed.
In A, only the switching element on the negative electrode side is switched at the same high frequency (10 kHz).

As a result, as shown in FIG. 6, a high-frequency (10 kHz) pulse of which polarity is inverted from the output terminal of the inverter every conduction period TA is supplied to the primary coil of the welding transformer, and the secondary circuit of the welding transformer is supplied. In this case, an alternating welding current having a cycle TW flows through the pair of welding electrodes to the workpiece, and the welded portion of the workpiece is resistance-welded.

The inverter controlled AC type resistance welding method as described above is a stable welding method with less splash compared to a normal low frequency AC type in which AC power of a commercial frequency is supplied to a material to be welded through a welding transformer as it is. There is an advantage that can be done. Also, compared to the inverter control DC type, which converts the high frequency pulse from the inverter to DC by the rectifier circuit on the secondary side of the welding transformer and supplies it to the material to be welded, the life of the welding electrode is longer, There are advantages such as no failure, power consumption and space for the secondary rectifier.

[0050]

In the conventional inverter-controlled AC resistance welding apparatus, a constant cycle TW is set in advance for the AC welding current, and during one cycle TW, the energizing period TA on the positive electrode side and the negative electrode side is set. Are alternately switched at a constant timing.

However, more precisely, as shown in FIG.
Between the end of each energization period and the start of the next energization period, a certain pause period TH for switching the polarity is inserted. That is, even if the switching operation of the inverter is stopped once at the end of each energization period, the welding current on the secondary side does not stop immediately, but it takes some time until it cuts off (falls). A primary current similar to the welding current on the secondary side also flows on the primary side. During the fall of this current (for example, during the fall as shown by the broken line IW 'in FIG. 7), if the next energization period of the opposite polarity is started (as shown by the broken line P1' in FIG. 7), If the switching element on the polarity side is turned on), a voltage is applied to the switching element which is in a conductive state due to the inertia of the welding current due to the current application, and the switching element is immediately destroyed.

The fall time of the current at the end of such an energization period changes according to the variation and fluctuation of the load (particularly, the material to be welded). Therefore, in order to reliably prevent the switching element from being damaged as described above, it is sufficient to provide a sufficient margin to the pause time TH. However, if the pause time TH is long, as shown in FIG. 8, the cooling time TC corresponding to the pause time TH in the welding energy supplied to the workpiece is also lengthened by that much, thereby reducing the thermal efficiency of resistance welding. There is a disadvantage that welding quality is reduced. In particular, when the material to be welded is a small metal such as an electronic component, if the energization time is long, the object to be welded is easily damaged, so the energization time is set as short as possible. Therefore, a decrease in thermal efficiency greatly affects welding quality.

The present invention has been made in view of the above-mentioned problems of the prior art, and controls the downtime for switching the energization period to a minimum necessary length to protect the switching element and improve the welding quality. It is an object of the present invention to provide a resistance welding device and a resistance welding control device that simultaneously improve the resistance welding device and the resistance welding device.

[0090]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a rectifying circuit for converting an alternating current of a commercial frequency into a direct current, and a direct current from the rectifying circuit. Bidirectional current-type switching means for converting the output of the welding means into a high-frequency pulse, a welding transformer for inputting an output of the switching means to a primary coil, and outputting a voltage of a high-frequency pulse from a secondary coil, and a secondary of the welding transformer. A pair of welding electrodes respectively connected to both ends of the side coil and pressed into contact with the material to be welded at positions separated from each other, and an odd number in a plurality of energizing periods constituting an energizing time for one resistance welding In the third energizing period, the switching means is continuously switched at one predetermined polarity at a predetermined high frequency, and in the even-numbered energizing period, the switching means is continuously switched at the other polarity. Switching control means for switching at the predetermined high frequency, current detection means for detecting a current on the primary or secondary side of the welding transformer and outputting a current detection signal, and immediately after the end of each energizing period. A current monitoring unit that monitors the current based on a current detection signal from the current detection unit and detects a timing at which the current reaches a predetermined monitoring value, and according to the timing detected by the current monitoring unit. And an energization start control means for starting the next energization period.

According to a second aspect of the present invention, in the configuration of the resistance welding apparatus according to the first aspect, the switching control means controls the current based on a current detection signal from the current detection means every switching cycle. Current measurement means for obtaining a current measurement value representing an effective value or an average value of the current measurement value, and a current measurement value from the current measurement means is compared with a desired set current value. And pulse width control means for obtaining the pulse width of the output pulse of the switching means.

According to a third aspect of the present invention, a commercial frequency alternating current is converted into a direct current by a rectifier circuit, the direct current from the rectifier circuit is converted into a high frequency pulse, and the high frequency pulse is supplied to a primary coil of a welding transformer. In a resistance welding control device for performing welding by supplying a welding current to a material to be welded via a welding electrode in a secondary circuit of the welding transformer, the direct current from the rectifier circuit is converted into the high-frequency pulse. Bi-directional energizing type switching means and a plurality of energizing periods constituting an energizing time for one resistance welding, the odd numbered energizing periods continuously switch the switching means with one polarity at a predetermined high frequency. Switching control means for switching the switching means continuously at the predetermined high frequency with the other polarity in the even-numbered energization period, Current detecting means for detecting the current on the primary side or the secondary side of the welding transformer and outputting a current detection signal, and detecting the current based on the current detection signal from the current detection means immediately after the end of each energizing period. Current monitoring means for monitoring and detecting a timing at which the current has reached a predetermined monitoring value; and energization start control means for starting the next energization period in accordance with the timing detected by the current monitoring means. It is characterized by doing.

[0120]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a circuit configuration of a resistance welding apparatus according to one embodiment of the present invention. The switching means 14 in the resistance welding apparatus is composed of four transistor switching elements 16, 18, 20, 20 each formed of a GTR (Shift Transistor) or an IGBT (Insulated Gate High Wheel Transistor).
22.

These four switching elements 16 to 22
Of the switching elements 16, 2 of the first set (positive electrode side)
0 is the first switching control signal F from the drive circuit 42
a, the switching elements 18 and 22 of the second pair (negative electrode side) are simultaneously controlled by the second switching control signal Fb from the drive circuit 42 at the predetermined high frequency (for example, 10 kHz). On / off control is performed at a frequency (10 kHz).

The input terminals (La,
Lb) is connected to the output terminal of the rectifier circuit 12, and the output terminals (Ma, Mb) are connected to both ends of the primary coil of the welding transformer 24, respectively. Welding transformer 24
A pair of welding electrodes 26 and 28 are directly connected to both ends of the secondary coil (ie, not through a rectifier circuit). The two welding electrodes 26 and 28 are in contact with the workpieces 30 and 32 apart from each other (for example, facing each other), and are brought into pressure contact with a pressing force from a pressure mechanism (not shown).

The rectifier circuit 10 is composed of, for example, a three-phase rectifier circuit in which six diodes are connected in a three-phase bridge.
A three-phase AC voltage of a commercial frequency from a three-phase AC power supply terminal (U, V, W) is converted into a DC voltage. The DC voltage output from the rectifier circuit 10 is supplied to the switching means 14 via the smoothing capacitor 12.

A current sensor 34 composed of, for example, a current transformer is mounted on a conductor between the output terminal of the switching means 14 and the primary coil of the welding transformer 24. During welding power supply, the current sensor 34 outputs a current detection signal <I1> representing the instantaneous value of the primary current I1 having a waveform similar to the secondary welding current IW. The current detection signal <I1> from the current sensor 34 is supplied to the control unit 40 and also to the current measurement value calculation circuit 36.

The current measurement value calculation circuit 36 detects the current detection signal from the current sensor 34 for each switching cycle <
Based on I1>, the effective or average value of the primary current I1 is obtained as a current measurement value [I1], and the obtained current measurement value [I1] is given to the control unit 40.

The control unit 40 comprises a microcomputer, and includes a CPU, a ROM (program memory), a RAM
(Data memory), a clock circuit, an interface circuit, and the like. All controls in the apparatus, such as current control and sequence control in welding current application, setting input and registration management related to set values of various welding conditions, and Output control such as a measured value and a judgment value is performed. In the current control, constant current control is performed by feedback pulse width control (PWM) as described later. In the sequence control, current monitoring control and energization start control according to the present embodiment, which will be described later, are performed.

The input unit 38 comprises a pointing device such as a keyboard or a mouse, and is used to input various welding conditions. The main welding conditions set and input in this embodiment are the welding current IW or the primary current I1, the conduction time TG, the conduction period TA, the current monitoring value IK, the initial pulse width value D0, and the like.

Of these welding conditions, “Electrification time TG
"Is the total energization time from the start to the end of the energization of the welding, and may be set as an integral multiple or an even multiple of the half of the" energization period TA ". The “energization period TA” is one independent energization period in which the switching means 14 performs a continuous or continuous switching operation on the positive electrode side or the negative electrode side. The “current monitoring value IK” is a welding condition set in place of the “pause period TH” in this embodiment, and is usually selected to be a value near 0 A (ampere). "Pulse width initial value P0" is an initial value that defines the first energizing pulse width (switching on time) in each energizing period TA. The control unit 40 is also connected to other peripheral devices such as a display device and a printing device.

FIG. 2 shows the processing operation of the control unit 40 (particularly the CPU) for energizing welding according to the present embodiment. In FIG.
The timing of welding current supply in this embodiment is shown.

The welding electrode 2 is applied at a predetermined pressure from the pressing mechanism.
When a start signal ST is sent from an external device (not shown) such as a welding robot in a state where the workpieces 6 and 28 are in pressure contact with the workpieces 30 and 32, the control is performed in response thereto. Part 4
0 starts welding current supply. At this time, the start signal ST not only indicates the start of welding energization, but also the current welding energization condition No. Or schedule No. May be specified.

First, the control unit 40 determines the energization time TG, energization period TA, and primary current set value IS related to the current energization of welding.
The various set value data, such as the current monitor value IK and the initial pulse width value D0, are read out from the memory and set in predetermined storage addresses or registers, timers or counters, respectively (step S1).

Next, the control unit 40 controls the switching means 1
A first switching control signal Fa having an initial pulse width D0 is supplied to the first set (positive side) of the switching elements 16 and 20 through the drive circuit 42, and the switching elements 16 and 20 are turned on. (Step S2). The first energization period TA from this time point tS1 starts on the positive electrode side.

When the welding current Iw and the primary current I1 flow in the secondary and primary circuits of the welding transformer 24 in the first switching cycle, the current sensor 34 outputs a current detection signal representing the instantaneous value of the primary current I1. <I1>
Is output, and the measured current value (effective value or average value) [I1] of the primary current I1 in this switching cycle is obtained from the measured current value calculation circuit 36.

The control section 40 fetches the measured current value [I1] from the measured current value calculation circuit 36 (step S3).
The current measured value [I1] is compared with the current set value [IS], and the pulse width (switching on time) D1 in the next switching cycle is determined based on the comparison error (step S4).

In the second switching cycle, the first switching control signal Fa having the pulse width D1 is supplied to the first set (positive side) of the switching elements 16 and 20 of the switching means 14, and their switching is performed. The elements 16 and 20 are turned on (steps S6 and S2).
).

As described above, during the first energizing period TA1, the switching element 14 of the first set (the positive electrode side) of the switching means 14 is controlled by the feedback pulse width control.
Only the switches 6 and 20 are continuously switched at a high frequency (10 kHz) (steps S2 to S6). During this time, the switching elements 18 and 22 of the second pair (negative electrode side) are maintained in the off state. As a result, the welding current IW, which is controlled by the constant current so as to substantially coincide with the set current value [IW], flows in the secondary circuit of the welding transformer 24 in the positive electrode direction.

When the first energizing period TA1 ends, the control unit 40 sets the first set (positive side) of the switching elements 16,
The supply of the first switching control signal Fa to the current sensor 20 is stopped, and the reading of the current measurement value [I1] from the current measurement value calculation circuit 36 is stopped.
4 to monitor the instantaneous values of the primary current I1 and the welding current IW (step S8). This monitoring period corresponds to the first pause period TH1, and the current I1 (IW) falls with a time constant corresponding to the load impedance at this time.

When detecting the timing tE1 at which the current I1 (IW) reaches the current monitoring value [IK], the control unit 40 immediately ends the monitoring period or the quiescent period TH1, and switches the second energizing period TA2 to the negative polarity. Let the side start. That is, the pulse width initial value Do is set (step S1).
0), the second switching control signal Fb having the initial pulse width D0 is supplied to the switching elements 18 and 22 of the second pair (negative electrode side) of the switching means 14 via the drive circuit 42 at time ts2 immediately after the detection timing tE1. To turn on the switching elements 18 and 22 (steps S11 and S2).

Thereafter, only the switching elements 18 and 22 of the second set (negative electrode side) of the switching means 14 are driven at a high frequency (10 kHz) by feedback pulse width control.
(Steps S2 to S6).
During this time, the first set (the positive electrode side) of the switching elements 16 and 2
0 is kept off. As a result, the welding current IW, which is controlled by the constant current so as to substantially match the set current value [IW], flows in the secondary circuit of the welding transformer 24 in the negative direction.

When the second energization period TA2 ends, the control unit 40 sets the switching elements 18 of the second set (negative side),
The supply of the second switching control signal Fb to the current measurement value calculating circuit 36 is stopped, and the current measurement value [I1] from the current measurement value calculation circuit 36 is stopped.
4 to monitor the instantaneous values of the primary current I1 and the welding current IW (step S8). This monitoring period corresponds to the second pause period TH2, and the current I1 (IW) falls with a time constant corresponding to the load impedance at this time.

When detecting the timing tE2 at which the current I1 (IW) reaches the current monitoring value [IK], the control unit 40 immediately ends the monitoring period or the quiescent period TH2, and switches the third energizing period TA3 to the positive polarity. Let the side start. That is, the pulse width initial value Do is set (step S1).
0) At time ts3, a first switching control signal Fa having an initial pulse width D0 is supplied to the first pair of switching elements 16 and 20 of the switching means 14 (positive electrode side) via the drive circuit 42, and their switching is performed. Element 18, 2
2 is turned on (step S2). In the third energizing period TA3, the switching elements 1 of the second set (negative electrode side)
8, 22 are maintained in the off state.

Thereafter, the same energization period as described above is alternately repeated on the positive electrode side and the negative electrode side. When the end time of the energization time TG is reached, the energization control operation ends (step S7). In this embodiment, the energization time TG is set with an even number of cycles of the energization period TA, so that the welding energization ends when the energization time setting counter counts the set value.

As described above, in the resistance welding apparatus of the present embodiment, the switching element 16 on the positive electrode side of the switching means 14 during the odd-numbered energizing periods TA1, TA3, TA5,.
20 is subjected to high frequency switching by PWM control, and the current I
1 (IW) flows in the positive direction, and the even-numbered energization period TA
During the period between 2, TA4, TA6,..., Only the switching elements 18 and 22 on the negative side of the switching means 14 are switched at high frequency, and the current I1 (IW) flows in the negative direction. And
When switching from each energization period TAi to the next energization period TA (i + 1), the switching means 14
Is stopped, the instantaneous value of the current I1 (IW) is monitored, the timing tEi at which the current I1 (IW) reaches the predetermined monitoring value [IK] is detected, and immediately after this timing tEi, the next energizing period is detected. Start TA (i + 1).

As a result, the idle period THi between each energization period TAi and the next energization period TA (i + 1) is not always a fixed period, but an indefinite period depending on the current fall characteristic at that time. However, the next energization period TA (i + 1) is started earliest while preventing short-circuit destruction of the switching elements 16 to 22, and the actual elapsed time of the energization time TG is minimized. Therefore, it is a necessary minimum rest period.
Thereby, the materials to be welded 30, 3
In this way, it is possible to minimize the necessary decrease in welding energy or Joule heat generated at the weld portion 2 temporarily, and to improve welding quality in this type of AC resistance welding method.

The resistance welding apparatus according to this embodiment can be applied to various resistance welding methods, but a remarkable effect can be obtained particularly in resistance welding of small metals such as electronic parts.

FIGS. 4 and 5 show the operation when the resistance welding apparatus according to the present embodiment is applied to series welding. In this series welding, the energizing period TA on the positive electrode side and the energizing period TA on the negative electrode side are alternately performed once each so that the total energizing time T
G.

In the first energizing period TA1 on the positive electrode side, a positive output pulse is supplied from the switching means 14 to the primary coil of the welding transformer 24, and the positive circuit having a substantially trapezoidal current waveform in the secondary circuit. The welding current I2 flows. In this case, as shown in FIG.
W flows along the path of the first welding electrode 26 → the workpiece 30 → the first welding location Pa → the workpiece 32 → the second welding location Pb → the workpiece 30 → the second welding electrode 28. That is,
At the first welding point Pa, the material 3 to be welded is
The welding current IW flows to the second side, and the welding current IW flows from the workpiece 32 to the workpiece 30 at the second welding point Pa. Thus, for example, a Peltier effect of absorbing heat occurs at the first welding point Pa, while a Peltier effect of generating heat occurs at the second welding point Pb. Thus, in the first energization period TA1 on the positive electrode side, the second welded portion Pb is more than the nugget Na at the first welded portion Pa.
The nugget Nb grows larger.

However, in the second energization period TA2 on the negative electrode side, a negative output pulse is supplied from the switching means 14 to the primary coil of the welding transformer 24, and the secondary circuit has a substantially trapezoidal current waveform. Negative welding current I
2 flows. In this case, as shown in FIG.
The welding current IW is the second welding electrode 28 → the workpiece 30 → the second welding location Pb → the workpiece 32 → the first welding location Pa.
→ The material to be welded 30 → flows through the first welding electrode 26.
That is, at the first welding point Pa, the welding current IW flows from the material to be welded 32 to the material to be welded 30, and at the second welding point Pa, the welding current IW flows from the material to be welded 30 to the material to be welded 32. Flows. Thereby, this time, the first welding point P
While the Peltier effect of generating heat occurs at a, the Peltier effect of absorbing heat occurs at the second welding point Pb. Therefore, in the second negative electrode-side energizing period TA2, the nugget Na at the first welding point Pa grows larger than the nugget Nb at the second welding point Pb.

As a result, when the entire energizing time TG has ended, the nugget Na at the first welding point Pa and the second
Has grown to almost the same size as the nugget Nb at the welding point Pb. Therefore, substantially uniform welding strength can be obtained at the first welding point Pa and the second welding point Pb.

Also in this series welding, it is possible to switch from the end of the first positive-side energizing period TA1 to the second negative-side energizing period TA2 with the minimum necessary rest period TH1 interposed therebetween, for example, as short as about 10 ms. The required welding strength can be obtained by increasing the heat generation efficiency during the energization time TG.

In the above-described embodiment, among the plurality of energizing periods constituting the energizing time, the odd-numbered ones are on the positive side and the even-numbered ones are on the negative side. It is also possible to use Further, the energizing time can be set not only by an integral multiple of the energizing period but also by a time (second). If necessary, a predetermined (for example, last) energizing period can be stopped halfway, It is also possible to set the length to a different length or to variably control the length.

In the above embodiment, the three-phase alternating current of the commercial frequency is converted to direct current and supplied to the switching means 14. However, the single-phase alternating current of the commercial frequency may be converted to direct current. The circuit configuration of the switching means 14 is also an example, and various modifications are possible. In the above embodiment, the current sensor 34
Is provided in the primary circuit, but may be provided in the secondary circuit.

[0460]

As described above, according to the resistance welding apparatus or the resistance welding control apparatus of the present invention, the welding transformer is provided immediately after the end of each of the energization periods in which the polarity is alternately reversed at a predetermined cycle during the energization time. By monitoring the fall of the current on the primary side or the secondary side to detect the timing at which the current has reached a predetermined monitoring value, and starting the next energizing period according to the timing, the energizing period is switched. Is controlled to the minimum necessary length, so that the switching element can be protected, and at the same time, a decrease in thermal efficiency during the pause can be minimized to improve welding quality.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of a resistance welding apparatus according to one embodiment of the present invention.

FIG. 2 is a flowchart showing a processing operation of a control unit for energizing welding in the resistance welding apparatus according to the embodiment.

FIG. 3 is a diagram showing the timing of welding energization in the resistance welding apparatus according to the embodiment.

FIG. 4 is an enlarged partial sectional view showing a main part when the resistance welding apparatus according to the embodiment is applied to series welding.

FIG. 5 is a diagram showing the timing of welding current when the resistance welding apparatus of the embodiment is applied to series welding.

FIG. 6 is a diagram showing the timing of welding energization in a conventional inverter-controlled AC resistance welding apparatus.

FIG. 7 is a diagram showing a timing at the time of switching of an energization period in a conventional inverter-controlled AC resistance welding apparatus.

FIG. 8 is a diagram schematically showing the timing (waveform) of welding energy supplied to a workpiece in a conventional inverter-controlled AC resistance welding apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Rectifier circuit 14 Inverter 16,18,20,22 Switching element 24 Welding transformer 26,28 Welding electrode 30,32 Material to be welded 34 Current sensor 36 Current measurement value calculation circuit 38 Input unit 40 Control unit 42 Drive circuit

Claims (3)

[Claims] A rectifier circuit for converting an alternating current of a commercial frequency into a direct current; a bidirectional current-type switching means for converting a direct current from the rectifier circuit into a high-frequency pulse; an output of the switching means being input to a primary coil. And
A welding transformer that outputs a high-frequency pulse voltage from the secondary coil; and a pair of welding electrodes that are connected to both ends of the secondary coil of the welding transformer, respectively, and that press-contact the material to be welded at a distance from each other In a plurality of energizing periods forming an energizing time for one resistance welding, in the odd-numbered energizing periods, the switching means is continuously switched at one polarity at a predetermined high frequency, and the even-numbered energizing periods are switched. In the period, switching control means for continuously switching the switching means with the other polarity at the predetermined high frequency, and current detection for detecting a current on the primary or secondary side of the welding transformer and outputting a current detection signal Means for monitoring the current based on a current detection signal from the current detection means immediately after the end of each energization period, wherein the current is a predetermined monitoring value A resistance welding apparatus, comprising: a current monitoring unit that detects a timing at which a current has reached, and an energization start control unit that starts the next energization period in accordance with the timing detected by the current monitoring unit. 2. A current measuring means for obtaining a current measurement value representing an effective value or an average value of the current based on a current detection signal from the current detection means for each switching cycle; And a pulse width control means for comparing a measured current value from the measuring means with a desired set current value and obtaining a pulse width of an output pulse of the switching means in a next switching cycle according to the comparison error. The resistance welding apparatus according to claim 1, wherein 3. A commercial frequency alternating current is converted into a direct current by a rectifier circuit, a direct current from the rectifier circuit is converted into a high frequency pulse, and the high frequency pulse is supplied to a primary coil of a welding transformer. In a resistance welding control device for supplying a welding current to a material to be welded via a welding electrode in a secondary circuit and performing resistance welding, bidirectional current-type switching for converting a direct current from the rectifier circuit to the high-frequency pulse Means, for a plurality of energizing periods constituting an energizing time for one resistance welding, in the odd-numbered energizing periods, the switching means is continuously switched at one polarity at a predetermined high frequency, and the even-numbered A switching control means for continuously switching the switching means with the other polarity at the predetermined high frequency during an energization period; Current detection means for detecting a current on the side or the secondary side and outputting a current detection signal; immediately after the end of each energization period, monitoring the current based on a current detection signal from the current detection means, A current monitoring means for detecting a timing at which a predetermined monitoring value is reached, and an energization start control means for starting a next energization period in accordance with the timing detected by the current monitoring means. Resistance welding control device.