JPH08155654A - Inverter resistance welding controller - Google Patents

Abstract

PURPOSE: To improve welding quality by rising electric current in high speed without generating overshoot phenomenon at initial stage of energizing and executing stable welding. CONSTITUTION: The inverter resistance welding controller is provided with an electric current detecting part 40, limiter control part 42, PWM control part 44, sequence control part 46 and inverter drive part 48. The electric current detecting part 40 consists of a hall CT50 mounted to a primary conductor. The limiter control part 42 is constituted of a comparator 52, limiter level generating part 54, latch circuit (D type flip/flop) 56, AND gates 58, 60 and clock circuit 62. The PWM control part 44 is constituted of an electric current effective value operating part 68, electric current setting part 70, PWM control pulse generating part 72, pulse width measuring part 74 and clock circuit 62. The sequence control part 46 is provided with the energizing control switching function by which the control means for an inverter circuit 18 is switched to either the limiter control part 42 or PWM control part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for controlling welding energization in an inverter type resistance welding machine.

[0002]

2. Description of the Related Art FIG. 5 shows a main circuit configuration of a conventional inverter type resistance welding machine. The inverter circuit 100 has a G
It incorporates a switching element composed of TR, IGBT, power FET, or the like, and outputs a high-frequency AC pulse by chopping the DC input voltage E by high-frequency switching in accordance with the control pulse CP from the inverter control unit 116. The AC pulse output from the inverter circuit 100 is supplied to the primary side coil of the welding transformer 102, and an AC pulse similar to the primary side is obtained on the secondary side thereof. The secondary side AC pulse is a pair of diodes 104.
It is converted into direct current by the rectifying circuit 106 composed of a and 104b. Then, this direct current IW is applied to the welding electrode 10
It is supplied to the materials 112, 114 to be welded via 8, 110.

Also in the inverter type resistance welding machine, constant current control is most often used in which feedback is performed so that a constant current is passed through the material to be welded during welding.
The main reasons are that the electric current is the three major welding conditions of resistance welding together with the pressing force and the energization time, and the current can be easily and accurately measured by the toroidal coil or the current transformer, so that the feedback loop can be easily constructed. There are such things. The constant in constant current control means that the effective current value that regulates resistance heating (Joule heat) is constant.

In FIG. 5, the inverter control unit 116 is shown.
Is an input of a current detection signal DI from a current sensor (toroidal coil) 118 provided in the secondary side circuit to obtain an effective value of the welding current IW, and the effective current value [IW] is set as a current set value IS. A comparison error is generated by comparison, and a control pulse CP having a variable pulse width that makes the comparison error zero is supplied to the inverter circuit 100. Each switching element of the inverter circuit 100 is turned on for a time corresponding to the pulse width of the control pulse CP.

As a result, when the actual current effective value [IW] is smaller than the current setting value IS, the pulse width of the control pulse CP gradually increases, so that the pulse width of the AC pulse output from the inverter circuit 100 is increased. PWM in which the pulse width of the control pulse CP gradually decreases when [IW] is larger than IS, and therefore the pulse width of the AC pulse output from the inverter circuit 100 gradually decreases. (Pulse width modulation) type constant current control is performed.

[0006]

According to the constant current control of the PWM method as described above, the primary current I1 and the welding current IW gradually rise with a waveform as shown in FIG. 6 immediately after the start of energization. However, from the viewpoint of weldability, it is desirable that the current reaches the set value as soon as possible. For this reason, adjustments are made to increase the gain of the pulse width variable control in the feedback loop.

However, this adjustment is difficult, and if the start-up is attempted to be quick, the current greatly exceeds the set value, that is, an overshoot phenomenon easily occurs, as shown by the alternate long and short dash line in FIG. PWM constant current control
This is predictive control that calculates the controlled variable (pulse width of the control pulse) from the comparison error between the measured value and the set value. At the beginning of energization, the current rises from a zero value to the set value with a steep gradient (rate of change). When increasing the current, it is difficult to stop the momentum immediately when the current reaches the set value, and inevitably overshoot occurs. Such a current overshoot phenomenon causes a splash and is undesirable.

The present invention has been made in view of the above problems. In the initial stage of energization, the current is quickly started without causing an overshoot phenomenon, and the resistance welding is stabilized during the energization time after the start. It is an object of the present invention to provide an inverter-type resistance welding control device that improves welding quality.

[0009]

In order to achieve the above object, the first inverter resistance welding control apparatus of the present invention rectifies commercial alternating current into direct current, and converts this direct current into an alternating current of a predetermined frequency by an inverter. In an inverter type resistance welding machine, which converts the AC pulse into a pulse, passes the AC pulse through a welding transformer, then converts it into a direct current, and supplies this direct current to a workpiece through a welding electrode, First inverter control means for controlling the inverter so that a current having a peak value equal to or lower than a predetermined limiter level flows through the material; and a first inverter control means for controlling the inverter so that a current having a predetermined effective value flows through the material to be welded The second inverter control means and the inverter control by the first inverter control means turn on the power supply, and the second inverter is activated at a predetermined timing. It has a configuration comprising a current control switching means for switching the energization of the inverter control by the over motor control means.

A second inverter type resistance welding control device of the present invention is the first inverter type resistance welding control device, wherein the first inverter control means has a primary side circuit or a secondary side of the welding transformer. Current detection means for detecting a current flowing through the circuit and outputting a current detection signal representing the current waveform, limiter level generation means for giving the limiter level, the current detection signal from the current detection means and the limiter level generation Comparing means for comparing the limiter level from the means and outputting a comparison result signal having a logical value indicating the magnitude relationship between the two, and a frequency equal to the frequency of the AC pulse and having a constant pulse width. A clock circuit for generating a clock pulse, the clock pulse from the clock circuit and the comparison result from the comparison means. And a control pulse which rises in response to the rising of the clock pulse and which falls in response to a change in the logical value of the comparison result signal or the falling of the clock pulse in order to control the inverter. The inverter control pulse generating means for generating is included.

According to a third inverter resistance welding control apparatus of the present invention, in the above-mentioned second inverter resistance welding control apparatus, the limiter level generating means increases the limiter level stepwise every predetermined time. It has a different structure.

According to a fourth inverter resistance welding control apparatus of the present invention, in the first inverter resistance welding control apparatus, the second inverter control means has a primary side circuit or a secondary side of the welding transformer. Current detection means for detecting a current flowing through the circuit and outputting a current detection signal representing the current waveform or a current differential waveform, and a current effective for obtaining an effective value of the current based on the current detection signal from the current detection signal Value calculating means, current value setting means for giving a desired current setting value, and comparing the current effective value from the current effective value calculating means with the current setting value from the current setting value generating means, And a pulse width control means for variably controlling the pulse width of the control pulse for the inverter so as to make the comparison error zero.

A fifth inverter type resistance welding control apparatus according to the present invention is the fourth inverter type resistance welding control apparatus, further comprising pulse width measuring means for measuring a pulse width of the control pulse. The means starts the variable control of the pulse width based on the output signal from the pulse width measuring means representing the pulse width of the control pulse immediately before the switching by the energization control switching means.

According to a sixth inverter resistance welding control apparatus of the present invention, in the first inverter resistance welding control apparatus, the energization control switching means starts energization of a clock pulse having a frequency equal to the predetermined frequency. The second value is counted when the count value reaches a predetermined value.
Inverter control means is switched to energization for inverter control.

[0015]

In the inverter type resistance welding control device of the present invention,
Immediately after the start of energization, the first inverter control means operates, and inverter control is performed so that a welding current having a peak value equal to or lower than a predetermined limiter level flows through the material to be welded. By this limiter control, the current rapidly rises up to the set current value without overshooting while limiting its peak value to the limiter level. Then, after the current rises, the second inverter control means operates, and inverter control is performed so that a current having a predetermined effective value flows through the material to be welded. This inverter control is preferably performed by PWM control of a feedback loop. As a result, the effective value of the current is maintained at a predetermined value even if there is a power supply voltage fluctuation or a load fluctuation, and resistance welding is stabilized.

[0016]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 shows a circuit configuration of an inverter type resistance welding control apparatus according to an embodiment of the present invention. In an inverter-type resistance welding machine to which this control device is applied, four bridge-connected large capacity transistors (GTR) 10
˜16 form an inverter circuit 18. Welding transformer 2 connected to the output side of this inverter circuit 18
The circuit of 0, the diodes 22a and 22b, the welding electrodes 24 and 26, and the materials to be welded 28 and 30 is the same as the conventional circuit (FIG. 5).
Similar to that of). The three-phase rectifier circuit 32 connected to the input side of the inverter circuit 18 converts commercial three-phase AC into DC of a predetermined voltage and supplies the DC to the inverter circuit 18. A smoothing capacitor 34 is connected between the three-phase rectifier circuit 32 and the inverter circuit 18.

The inverter type resistance welding control apparatus of this embodiment has a current detection section 40, a limiter control section 42, a PWM control section 44, a sequence control section 46 and an inverter drive section 48.

The current detector 40 is composed of a current sensor, for example, a Hall CT50, mounted on the primary conductor between the capacitor 34 and the inverter circuit 18. While the inverter circuit 18 is operating, the Hall CT 50 has a waveform in which the AC pulse current I1 ′ flowing in the primary coil of the welding transformer 20 is made into an absolute value, that is, the pulse of the positive polarity is the negative polarity as it is. A DC pulse current I1 having a waveform in which the polarity of the pulse is inverted to the positive side flows. Hall C
T50 outputs an analog current detection signal HI representing the waveform of this primary current I1.

The limiter control section 42 includes a comparator 5
2, a limiter level generator 54, a latch circuit (D-type flip-flop) 56, AND gates 58 and 60, and a clock circuit 62. Comparator 52
One of the input terminals (non-inverting input terminal) is supplied with the current detection signal HI from the Hall CT 50 of the current detecting section 40, and the other input terminal (inverting input terminal) of the comparator 52 is provided with the limiter level generating section 54. A signal representing the limiter level LM is supplied.

The output terminal of the comparator 52 is connected to the terminal of the H-level power supply voltage Vcc through the pull-up resistor 64, and is also connected to the input terminal CK of the latch circuit 56. HI <LM on the input side of the comparator 52
At that time, an L level output voltage is obtained at the output terminal,
When HI ≧ LM, an H level output voltage is obtained at the output terminal.

In the present embodiment, the limiter level generator 54
Is a two-phase clock pulse φA, φB from the clock circuit 62
The limiter level LM is raised stepwise every half cycle of the clock frequency.

[0023] The inverted output terminal Q of the latch circuit 56 _- is AN
The D gates 58 and 60 are connected to the respective first input terminals. Two-phase clock pulses φA and φB from the clock circuit 62 are ORed to the reset terminal R of the latch circuit 56.
It is given through the gate 66. These two-phase clock pulses φA and φB have a frequency (for example, 1 KHz) that defines the switching frequency of the inverter circuit 18, and are also supplied to the third input terminals of the AND gates 58 and 60, respectively. The output terminals of the AND gates 58, 60 are connected to the input terminals of four drive circuits 80, 82, 84, 86 of the inverter drive unit 48 described later in a predetermined correspondence relationship.

The PWM control section 44 includes a current effective value calculation section 6
8, a current setting unit 70, a PWM control pulse generating unit 72, a pulse width measuring unit 74, and a clock circuit 62. The current effective value calculation unit 68 is the current detection unit 40.
The current detection signal HI from the Hall CT50 is input, and the effective value of the primary current I1 is calculated based on the current detection signal HI for a fixed time, for example, every half cycle of the clock frequency. The current setting unit 70 is a current setting value signal [KI] representing a desired current setting value (effective value) KI in constant current control.
Is output.

The PWM control pulse generator 72 includes a current effective value [HI] from the current effective value calculator 68 and a current setting unit 7.
An error generator that compares the current set value signal [KI] from 0 to obtain a comparison error between the two, and a comparison error obtained from this error generator and the immediately preceding PWM control pulse PA (i-1) or A pulse width determination unit that determines the pulse width of the next PWM control pulse PA (i) or PB (i) from the value of the pulse width of PB (i-1), and the next control pulse PA (i) or PB. It has a built-in pulse output unit that outputs (i) in synchronization with clock pulse φA or φB. Of the two-phase PWM control pulses PA and PB obtained at the output terminal of the PWM control pulse generator 72, PA is supplied to the second input terminal of the AND gate 58 and PB is supplied to the second input terminal of the AND gate 60. To be done.

The pulse width measuring section 74 includes an AND gate 5
Control pulses CA and CB respectively output from 8 and 60 are input and their pulse widths W (CA) and W (CB) are measured, and respective pulse width measurement values [W (CA)], [W (CB )] Is held at least until the next control pulse is input. The pulse width measurement values [W (CA)], [W
(CB)] is the control pulse immediately before when the limiter control unit 42 is switched to the constant current control unit 44 as described later, that is, when the PWM control pulse generation unit 72 generates the first PWM control pulse. Used as a pulse width value.

The sequence control unit 46 controls the sequence of welding energization in this resistance welding machine.
Particularly, in the present embodiment, the energization time control function of generating the energization enable signal EN which defines the welding energization time in response to the activation signal ST from the outside, and the control means for the inverter circuit 18 are the limiter control unit 42 or the PWM control unit 44.
And a power supply control switching function for switching to any of the above.

In the energization time control function, the sequence controller 46 sends the energization enable signal EN to the AND gate 5.
It is applied to the fourth input terminal of 8,60. In the energization control switching function, the sequence control unit 46 causes the limiter control unit 42 to control the inverter circuit 18 at the start-up immediately after the start of energization, and keeps the PWM control unit 44 substantially inoperative. Then, the clock pulses φA and φB are counted from the start of energization, and when the count value reaches the set value, the operation of the limiter control unit 42 is stopped,
Instead, the PWM control unit 44 is caused to control the inverter circuit 18.

The inverter drive section 48 is composed of four drive circuits 80, 82, 84 and 86. First
AND to the input terminals of the fourth drive circuits 80 and 86
The output terminal of the gate 58 is connected, and the output terminal of the AND gate 60 is connected to the input terminals of the second and third drive circuits 82 and 84. The output terminals of the first to fourth drive circuits 80, 82, 84, 86 are connected to the base terminals of the first to fourth GTRs 10, 12, 14, 16 of the inverter circuit 18, respectively.

When the H-level control pulse CA is output from the AND gate 58, the control pulse CA causes the first and fourth GTRs 10 and 16 of the inverter circuit 18 to simultaneously pass through the first and fourth drive circuits 80 and 86. The primary current I1 'in the forward direction flows to the output side of the inverter circuit 18 by turning it on. At this time, the primary current I1 having the same polarity and waveform as the primary current I1 'on the output side flows through the Hall CT50 on the input side of the inverter circuit 18.

When the H-level control pulse CB is output from the AND gate 60, the control pulse CB is transmitted through the second and third drive circuits 82 and 84 to the second and third GTRs 12 and 12 of the inverter circuit 18. 14 are turned on at the same time, whereby a negative primary current I1 'flows to the output side of the inverter circuit 18. At this time, in the Hall CT 50 on the input side of the inverter circuit 18, a primary current I1 having the same waveform as the primary current I1 'on the output side but having the opposite polarity (positive polarity) flows. Thus, the primary current I1 flowing through the Hall CT50 is a DC pulse current having a waveform in which the AC pulse current I1 'flowing at the output side of the inverter circuit 18 is made into an absolute value.

Next, the operation of the inverter type resistance welding control apparatus of this embodiment will be described with reference to the signal waveform diagram of FIG.

When the activation signal ST is input from the outside, the sequence control unit 46 responds to this by generating the H level energization enable signal EN, and supplies this signal EN to the AND gates 58 and 60. Then, the limiter level generator 54 is set to the operation mode and the PWM control pulse generator 72 is set to the non-operation mode.

PWM control pulse generator 7 in non-operation mode
2 outputs PWM control pulses PA and PB having the same phase and pulse width as the clock pulses φA and φB. This allows
Both AND gates 58 and 60 output output signals (control pulses) CA and CB depending on the logic level of the output signal obtained at the inverting output terminal Q ₋ of the latch circuit 56 during the pulse periods of the clock pulses φA and φB, respectively. Will be done.

In the operation mode, the limiter level generator 54
Generates the lowest value of the first limiter level LM (1) in response to the rising edge of the first input clock pulse φA ((A) and (F) in FIG. 2). At this point, Hall CT5
The level of the current detection signal HI from 0 is still lower than the first limiter level LM (1), and the output voltage of the inverting output terminal Q ₋ of the latch circuit 56 is at the H level. Therefore, AND is performed in response to the rising edge of the clock pulse φA.
The output voltage (control pulse CA) of the gate 58 rises to the H level ((G) in FIG. 2).

When the control pulse CA from the AND gate 58 rises to the H level, the first and fourth GTRs 10 and 16 of the inverter circuit 18 are turned on at the same time, and the primary side and secondary side circuits of the resistance welding machine are set to 1 respectively. The primary current I1 (I1 ') for the pulse and the welding current IW start to flow.
As a result, the level of the current detection signal HI output from the Hall CT 50 rises and reaches the first limiter level LM (1) before the clock pulse φA falls ((F) in FIG. 2). Then, the output terminal of the comparator 52 becomes H level, whereby the inverted output terminal Q of the latch circuit 56 _- the output voltage becomes L level, the output voltage (control pulse CA) of the AND gate 58 also falls to the L level ((G) in Figure 2). Immediately thereafter, the clock pulse φA falls, the latch circuit 56 is reset, and the output voltage of its inverting output terminal Q ₋ returns to the H level.

Next, when the clock pulse .phi.B is output from the clock circuit 62, the limiter level generator 54 responds to the rise of the clock pulse .phi.B and the first limiter level LM.
The second limiter level LM (2) which is one step higher than (1) is given to the comparator 52 ((B) and (F) in FIG. 2). in this case,
The control pulse CB is output from the AND gate 60, and the second and third GTRs 12 and 14 of the inverter circuit 18 are turned on at the same time. Then, when the level of the current detection signal HI from the Hall CT 50 reaches the second limiter level LM (2) ((F) of FIG. 2), the output terminal of the comparator 52 becomes H.
The level, the output voltage of the inverting output terminal Q ₋ of the latch circuit 56 becomes the L level, and the output voltage of the AND gate 60 (control pulse CB) falls to the L level ((H) in FIG. 2). Immediately thereafter, the clock pulse φB falls, the latch circuit 56 is reset, and the output voltage of its inverting output terminal Q ₋ returns to H level.

In this way, immediately after the start of energization, the inverter circuit 18 is controlled by the control pulses CA and CB obtained by the limiter control in which the limiter level LM is raised stepwise every half cycle, and the current of the resistance welding machine is changed. Can be launched. In this case, the pulse widths of the control pulses CA and CB are when the level of the current detection signal HI reaches or does not reach the limiter level LM (n) of each step from the rising edge of the clock pulses φA and φB. Lasts until the falling edges of clock pulses φA and φB.
As a result, the primary current I1 (I1 ') and the welding current IW
Flows at full pulse width (duration) while the peak value is limited to a constant value every half cycle of the clock frequency,
Rise at the highest speed (gradient) possible.

The sequence controller 46 counts clock pulses φA and φB from the start of energization. Then, when the count value reaches the set value, the limiter control unit 42
In order to stop the above operation, the limiter level generator 54 releases the limiter level. In the present embodiment, when the limiter level generator 54 receives an instruction from the sequence controller 46, the limiter level is raised to a level FM that is significantly higher than the primary current peak value corresponding to the current set value KI. As a result, the output voltage of the comparator 52 becomes H
It does not go to level and the inverting output terminal Q ₋ of the latch circuit 56 is held at H level.

The limiter level LM (n) immediately before the operation of the limiter control unit 42 is stopped is preferably set to a value near the primary current peak value corresponding to the current setting value KI. By doing so, it is possible to smoothly shift to the control by the PWM control unit 44 described later.

On the other hand, the sequence control section 46 operates the PWM control section 44, and therefore the PWM control pulse generating section 7
2 is given a predetermined control signal. Then, the PWM control pulse generation unit 72 knows the pulse width of the control pulse CA or CB output immediately before this switching, and therefore the pulse width measurement value from the pulse width measurement unit 74 (in the example of FIG. 2, [W ( Read CB)]). Further, at this point, the PWM control pulse generator 72 has the current effective value [HI] from the current effective value calculator 68 immediately before this switching and the current setting unit 7.
The comparison error with the current setting value [KI] from 0 is obtained. Therefore, the PWM control pulse generator 72 obtains the first pulse width W (PA) from the comparison error immediately before the switching and the pulse width measurement value [W (CB)], and determines the obtained pulse width W (PA). The PWM control pulse PA that it has is output in synchronism with the clock pulse .phi.A (the respective rising edges are substantially matched).

Sequence voltage is held at H level, to be supplied to the respective fourth input terminals _- [0042] In the AND gate 58 and 60, the inverted output terminal Q of the latch circuit 56 is supplied to each of the first input terminal The energization enable signal EN from the control unit 46 is also held at the H level.
Therefore, the AND gates 58 and 60 output the output signals (depending on the logic level of the PWM control pulses PA and PB given to the third input terminal from the PWM control pulse generator 72 during the pulse periods of the clock pulses φA and φB, respectively). Control pulses) CA and CB will be output.

As described above, the PWM control pulse generator 72
When the PWM control pulse PA having the pulse width W (PA) is output, the PWM control pulse PA remains unchanged from AN.
As a control pulse CA passing through the D gate 58, the first and fourth GTRs 10 and 16 of the inverter circuit 18 are simultaneously turned on. As a result, similarly to the limiter control, the primary current I1 (I1 ') and the welding current IW for half a cycle start to flow in the primary side circuit and the secondary side circuit of the resistance welding machine, respectively. However, control pulse C in PWM control
The pulse width W (CA) of A is a control amount in the feedback loop for matching the current effective value at that time with the set current value.

In this way, when the current I1 (I1 '), IW for half a cycle flows in this resistance welding machine, the DC primary current I1 is detected by the Hall CT50 and the Hall CT50.
Further, the current detection signal HI representing the current waveform is given to the effective current value calculator 68. The current effective value calculation unit 68 calculates the effective value of the current detection signal HI for the half cycle, and supplies the calculated current effective value [HI] to the PWM control pulse generation unit 72. The PWM control pulse generation unit 72 compares the effective current value [HI] with the current setting value [KI] from the current setting unit 70 to obtain a comparison error between the two, and the comparison error and the previous pulse width W ( PA) and the pulse width W (PB) for the next half cycle is determined, and the determined pulse width W
PWM control pulse PB having (PB) is clock pulse φ
Output in synchronization with B.

This PWM control pulse PB is the same as AN.
The second and third GTRs 12 and 14 of the inverter circuit 18 are simultaneously turned on as a control pulse CB through the D gate 60. As a result, in the primary side and secondary side circuits of this resistance welding machine, the primary current I1 for half a cycle each
(I1 '), welding current IW begins to flow.

In this way, after the energization is started, the PWM control is performed by the feedback loop so that the primary resistance circuit and the secondary side circuit of the resistance welding machine have substantially constant effective values. Primary current I1 having
(I1 '), welding current IW flows. This ensures good welding quality, in particular by keeping the effective value of the welding current IW substantially constant.

In this respect, when the limiter control is continued even after the energization is started, the current peak value can be kept constant (aligned), but as shown in FIG. If the current pulse width W fluctuates due to fluctuations in load or load, the effective current value fluctuates,
There is a problem that resistance heating and eventually weldability become unstable. If the inverter is controlled by PWM control by a feedback loop after the start of energization as in the present embodiment, the effective value of the welding current is maintained substantially constant even if there is a power supply voltage fluctuation or load fluctuation, and resistance heating occurs. It is possible to stabilize the weldability.

FIG. 4 shows the waveform of the welding current IW obtained by the inverter type resistance welding control apparatus of this embodiment.
As described above, the inverter is controlled by the limiter control immediately after the start of energization, so that the welding current IW is started up from the value of zero to the current setting value KIW as quickly as possible (in a short time) without overshooting. be able to. After reaching the current set value KIW, the inverter is controlled by the PWM control of the feedback loop so that the welding current IW can be maintained even if the power supply voltage or the load fluctuates.
The effective value of can be maintained at a predetermined current setting value and stable resistance welding can be performed.

In the embodiment described above, the DC primary current I1 in the resistance welding machine is detected by the Hall CT50, but the AC primary current I1 'on the output side of the inverter 18 is detected by the Hall C.
Alternatively, the welding current IW on the secondary side may be detected by a toroidal coil or the like.

In the above-described embodiment, the limiter level is raised stepwise every half cycle immediately after the start of energization. However, at first, the limiter level is raised by the control pulse having the pulse width of the clock pulse, and halfway from the middle. Alternatively, the limiter control may be applied in the latter half of startup. Further, the current setting value in the PWM control may be variably controlled as necessary, and the effective current value may be made to follow it. The condition or timing for switching between the limiter control and the PWM control can be set arbitrarily, and the both controls may be switched in a scene other than the start-up as needed.

In the above embodiment, the limiter control and the PWM control each use a half cycle of the clock frequency as the basic cycle, but it is also possible to use one cycle or more of the clock frequency as the basic cycle.

[0052]

As described above, according to the inverter type resistance welding control apparatus of the present invention, the current is changed from the value of zero to the current by the control for limiting the peak value of the current to the predetermined limiter level or less immediately after the start of energization. Since the resistance welding is stabilized by the control that keeps the effective value of the current at the current setting value during the energization time after the startup, the resistance welding is stabilized as much as possible without overshooting to near the setting value. Good welding results can be obtained.

[Brief description of drawings]

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

FIG. 2 is a signal waveform diagram showing the signal waveform of each part for explaining the operation of the inverter type resistance welding control device of the embodiment.

FIG. 3 is a current waveform diagram showing a problem of limiter control in constant current control.

FIG. 4 is a current waveform diagram showing a welding current waveform obtained by the inverter type resistance welding control device of the embodiment.

FIG. 5 is a circuit diagram showing a circuit configuration of an inverter type resistance welding machine to which a conventional inverter type resistance welding control device is applied.

FIG. 6 is a current waveform diagram showing rising characteristics of a primary current and a welding current obtained by a conventional inverter type resistance welding control device.

7 is a current waveform diagram showing an overshoot phenomenon at the time of rising of a welding current in the inverter resistance welding machine of FIG.

[Explanation of symbols]

 10-16 GTR (Large-capacity transistor) 18 Inverter circuit 20 Welding transformer 22a, 22b Rectifying diode 24, 26 Welding electrode 28, 30 Welding material 32 Three-phase rectifier 42 Limiter control section 44 PWM control section 46 Sequence control section 48 Inverter Drive part

Claims (6)

[Claims] 1. A commercial alternating current is rectified into a direct current, and this direct current is converted into an alternating current pulse having a predetermined frequency by an inverter,
In the inverter resistance welding machine in which the alternating current pulse is passed through the welding transformer and then passed through the rectifier to be converted into direct current, and the direct current is supplied to the work piece through the welding electrode, a predetermined limiter is applied to the work piece. A first controlling the inverter so that a current having a peak value below a level flows
Inverter control means, second inverter control means for controlling the inverter so that a current having a predetermined effective value flows in the material to be welded, and energization is started by inverter control by the first inverter control means. An inverter-type resistance welding control device comprising: an energization control switching unit that switches to energization for inverter control by the second inverter control unit at a predetermined timing. 2. The first inverter control means includes a current detection means that detects a current flowing through a primary side circuit or a secondary side circuit of the welding transformer and outputs a current detection signal representing the current waveform. A limiter level generating means for giving the limiter level, the current detection signal from the current detecting means and the limiter level from the limiter level generating means are compared, and a comparison result having a logical value indicating a magnitude relationship between the two. Comparing means for outputting a signal, a clock circuit for generating a clock pulse having a frequency equal to the frequency of the alternating current pulse and having a constant pulse width, the clock pulse from the clock circuit and the comparing means In order to control the inverter by inputting the comparison result signal, it rises in response to the rising of the clock pulse. Inverter control pulse generating means for generating a control pulse that rises and falls in response to a change in the logical value of the comparison result signal or a fall of the clock pulse is included. Inverter resistance welding control device. 3. The inverter type resistance welding control apparatus according to claim 2, wherein the limiter level generating means is configured to raise the limiter level stepwise at predetermined time intervals. 4. The second inverter control means detects a current flowing through a primary side circuit or a secondary side circuit of the welding transformer and outputs a current detection signal representing a current waveform or a current differential waveform of the welding transformer. Detection means, current effective value calculation means for obtaining the effective value of the current based on the current detection signal from the current detection signal, current value setting means for giving a desired current set value, and current effective value calculation means From the current effective value and the current setting value from the current value setting means are compared to obtain a comparison error between the two, and the pulse width of the control pulse for the inverter is changed so that the comparison error becomes zero. The pulse resistance control means for controlling is included, The inverter type resistance welding control apparatus of Claim 1 characterized by the above-mentioned. 5. A pulse width measurement means for measuring the pulse width of the control pulse is provided, and the pulse width control means measures the pulse width of the control pulse immediately before switching by the energization control switching means. 5. The inverter type resistance welding control device according to claim 4, wherein the variable control of the pulse width is started based on an output signal from the means. 6. The energization control switching means counts a clock pulse having a frequency equal to the frequency of the AC pulse from the start of energization, and when the count value reaches a predetermined value, the second inverter control means operates. The inverter type resistance welding control apparatus according to claim 1, wherein the inverter type resistance welding control apparatus is configured to switch to an inverter-controlled energization.