JPH02207981A - Method and circuit for controlling inverter type direct current resistance welding machine - Google Patents

Abstract

PURPOSE:To restrict an overcurrent by magnetic deflection and to proceed to steady operation in a short time by detecting a signal inputted to an inverter to obtain a differential pulse and detecting a magnetic-deflected state of a welding transformer to restrict pulse width of base driving signals. CONSTITUTION:A current detector 13 outputs the detected signal (i) to a welding timer 26 and outputs it to a differentiation circuit 22. The circuit 22 outputs the signal (i) which is the derivative pulse on a derivation value of the detected signal (i) to a magnetic deflection detection circuit 24. The circuit 24 outputs a base driving pulse width restriction signal Cs to a base driving pulse width restriction circuit 28. Further, the circuit 28 outputs a base control signal Ct to a base driving circuit 30 based on the signal Cs from the circuit 24. The circuit 30 outputs the base driving signals Sa-Sd to a base B of switching transistors 12a-12d of an inverter circuit part 12 based on the signal Ct and controls a current inputted to the inverter circuit part and converts the inputted current into Ac.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control method and circuit for an inverter-type DC resistance welding machine. The present invention relates to a control method and circuit for an inverter-type DC resistance welding machine that can limit overcurrent due to biased magnetism at the time of starting energization of the DC resistance welding machine by performing signal processing.

- [Background of the Invention] Recently, with the commercialization of high-voltage, large-current transistors, resistance welding machines using a transistor-inverter control system that enables high-speed, precise control have come into widespread use. A secondary rectifier type DC resistance welding machine (hereinafter referred to as an inverter type DC resistance welding machine) based on this transistor/inverter control method converts commercial three-phase AC into DC current using a rectifier, and then converts this into AC current using a transistor/inverter. It is then converted into a welding transformer built into the welding gun that straddles the welding machine. The output of this transformer is a low voltage, high current alternating current, which is rectified again and supplied as a direct current welding current from the electrodes to the workpiece for welding.

By the way, when power is applied to operate such an inverter-type DC resistance welding machine, an overcurrent flows in the circuit due to magnetic saturation of the welding transformer, a so-called biased magnetism phenomenon, etc., in the initial stage of energization. The constituent transistors may be destroyed. Therefore, in order to prevent this inconvenience, conventionally, the pulse width of the pulsed alternating current output from the inverter section is set in advance to a narrow width immediately after the start of energization, and the pulse width is gradually widened to the pulse width during normal operation. It is known how to control (
(See Japanese Patent Application Laid-Open No. 63-154274). However, when changing the rating of a welding transformer or replacing it with another welding transformer, the pulse width of the pulsed AC current output from the inverter section must be reset immediately after energization starts. -This is inevitably a nuisance. In addition, in order to prevent excessive current from flowing through the transistors that make up the inverter and destroying the transistors due to DC bias in the welding transformer of the DC resistance welding machine, when an abnormal current is detected by detecting the current, A technique for immediately stopping the switching operation of a transistor has been disclosed (see Japanese Patent Laid-Open No. 62-107867).

However, although the abnormal current is detected at a dark level and the switching operation of the inverter section is thereby stopped, the stopping operation is not quickly achieved due to the presence of a time delay in the detection circuit. Therefore, when the dark value level is set to a value corresponding to the rated value of the transistor, there is a risk that a current exceeding the rated value will flow through the transistor and destroy the transistor due to the existence of the time delay. Therefore, it is necessary to take this into account and set the dark value level of the abnormal current to a small value, but if this measure is adopted, the welding current that can be passed through the transistor during normal conditions will be restricted and will have to be made small. Moreover, these conventional techniques do not eliminate the biased magnetization of the welding transformer when it is first energized, and even if an abnormal current is detected during energization, the operation of the inverter is simply stopped, and the biased magnetization is not eliminated. It is difficult to suppress it effectively.

[Object of the Invention] The present invention has been made to overcome the above-mentioned disadvantages, and is an inverter-type DC resistance welding machine that detects a signal input to an inverter and generates a differential pulse based on a differential value of the detected signal. The biased magnetization state of the welding transformer is detected from the positive/negative polarity and the number of pulses of the differential pulse, and by limiting the pulse width of the base drive signal, overcurrent due to biased magnetization is limited. It is an object of the present invention to provide a control method and circuit for an inverter-type DC resistance welding machine that enables the inverter type DC resistance welding machine to reach a predetermined steady state of operation in an extremely short period of time.

[Means for Achieving the Object] In order to achieve the above object, the present invention includes an inverter circuit section in which a current detection means is attached to the DC input section, a welding gun incorporating a welding transformer, and an inverter control circuit section. including,
In the method for controlling an inverter type DC resistance welding machine, the control method for an inverter-type DC resistance welding machine includes controlling the magnitude of alternating current output from the inverter circuit unit by controlling the pulse width of the drive signal output from the inverter control circuit unit, wherein the DC input of the inverter circuit unit After obtaining a detection signal by detecting the current input to the inverter by the current detection means, the inverter control circuit generates a differential pulse according to the differential value of the detection signal, and determines the state of change of the differential pulse within a predetermined time. and a control signal that detects biased magnetization from the number of pulses, generates a predetermined control signal based on the biased magnetization state, and controls the pulse width of the drive signal supplied to the inverter circuit section in accordance with this control signal. The current is generated and output to the inverter circuit section to control the current input to the inverter circuit section, the input current is converted to alternating current, and the alternating current is supplied to the welding gun to perform welding. do.

The present invention also provides an inverter circuit section that converts direct current introduced into the direct current input section into alternating current based on a drive signal that is a repetitive square wave pulse signal, and an inverter circuit section that detects the current input to the direct current input section and outputs the detection signal. a detection means for outputting, and a differentiation means for generating a differential pulse according to a differential value of the detection signal;
an inverter control comprising a comparison means for detecting biased magnetism from a polarity change state and pulse number of the differential pulse within a predetermined time and outputting a control signal for limiting the pulse width of the drive signal supplied to the inverter circuit section; It is characterized by comprising a circuit section.

[Embodiments] Next, the method for controlling an inverter type DC resistance welding machine according to the present invention will be described in detail below with reference to the accompanying drawings, citing preferred embodiments in relation to a circuit for implementing the method.

In FIG. 1, reference numeral 10 indicates an inverter type DC resistance welding machine incorporating a control circuit for implementing the control method for an inverter type DC resistance welding machine according to the present embodiment.

The inverter type DC resistance welding machine IO includes an inverter circuit section 12, a welding gun 14 incorporating a welding transformer, and an inverter control circuit section 15. The inverter circuit section 12 achieves the function of inversely converting direct current into pulsed alternating current, and includes switching transistors 12a to 1.
Consists of 2d. The switching transistor 1
The emitter E of 2H and the collector C of the switching transistor 12d are connected, and the emitter E of the switching transistor 12C and the switching transistor 1
The collector C of 2b is connected. A converter section (not shown) including a rectifier circuit and a smoothing circuit that converts commercial alternating current into direct current is connected to the collectors C of the switching transistors 12a and 12C and the emitters E of the switching transistors 12d and 12b.

From the converter section to the switching transistor 1
A current detector 13 as a detection means for detecting the current input to the DC input section of the inverter circuit section 12 is provided on the connection line leading to the collector C of 2a and 12G, and the output signal of the current detector 13 is The inverter control circuit section 1
Connected to 5. That is, the current detector 13 is attached to the DC input section side of the inverter circuit section 12 that corresponds to the pulsed alternating current output from the inverter circuit section 12 to the welding gun 14, and detects the current input to the inverter circuit section 12. is detected and outputs a detection signal i to the inverter control circuit section 15.

A connection point between the emitter E of the switching transistor 12a and a collector C of the switching transistor 12d, and a connection point between the emitter E of the switching transistor 12c and the collector C of the switching transistor 12b are connected to the welding gun 14.

In this case, the welding gun 14 is connected to the welding transformer 16 and the rectifier 18.
a, 18b and an electrode 20. The welding transformer 16 transforms the pulsed alternating current supplied from the inverter circuit section 12 to the rectifiers 18a and 18.
Output to b. The rectifiers 18a and 18b convert the transformed pulsed alternating current into direct current and supply it to the electrode 20. The electrode 20 is composed of a pair of electrodes, and a workpiece W to be welded is held under pressure between the two sets of electrodes, and a large current is applied to the contact portion of the workpiece W to bring the workpiece W into contact. Welding is performed using Joule heat based on resistance.

On the other hand, the inverter control circuit section 15
A detection signal l related to an input current is introduced from the input current, and drive signals S1, Sl, and Sc, which are repetitive pulse signals, are supplied to the bases B of switching transistors 12a to 12d forming the inverter circuit section 12 based on this detection signal i.
and Sd (hereinafter referred to as the base drive signal), and constitutes a part of the first comparing means and a differentiating circuit 22 as a differentiating means that generates a differential pulse corresponding to the differential value of the detection signal. a timer 26, a biased magnetism detection circuit 24 constituting a second comparing means, and the base drive signal S.
. A circuit 28 incorporating a limiting circuit (hereinafter referred to as a base drive pulse width limiting circuit) that limits the pulse width of the base drive signal S in accordance with a control signal to be described later;
. The base drive circuit 30 outputs signals Sa to Sa'.

The current detector 13 outputs the detection signal i to the welding timer 26 and also to the differentiating circuit 22.

The differentiating circuit 22 outputs a signal i/(hereinafter referred to as a differential signal i') which is a differential pulse related to the differential value of the detection signal i to the bias detection circuit 24. The biased magnetism detection circuit 24 sends a second pulse width to the base drive pulse width limiting circuit 28 based on the differential signal 1' from the differentiation circuit 22 and the base drive original signal C0° which is the first control signal output from the welding timer 26. A base drive pulse width limit signal C5, which is a control signal of the base drive pulse width limit signal C5, is output. Further, the welding timer 26 has a preset current value (11).
is set, takes in the detection signal i from the current detector 13 as a feedback signal, and outputs the base drive original signal C3° as a first control signal to the base drive pulse width limiting circuit 28.

Further, the base drive pulse width limiting circuit 28 generates a base control signal C2, which is a third control signal, based on the base drive original signal C1O from the welding timer 26 and the base drive pulse width limiting signal C8 from the biased magnetic detection circuit 24. is output to the base drive circuit 30. The base drive circuit 3
0 is the inverter circuit section 1 based on the base control signal Ct.
Base drive signals Sl to S are output to the bases B of the two switching transistors 12a to 12d.

The control circuit of the inverter type DC resistance welding machine according to this embodiment is basically configured as described above, and its operation and effects will be explained in detail below with reference to the accompanying drawings. In addition, FIG. 2 and FIG. 3 are a flowchart and a time chart explaining the control method of the said inverter type DC resistance welding machine.

First, by turning on the start switch (not shown) of the inverter-type DC resistance welding machine 10, direct current flows from the converter section (not shown) to the collectors C of the switching transistors 12a, 12c and the emitters of the switching transistors 12b, 12d of the inverter circuit section 12. E (see Figure 1). Next, the inverter control circuit section 15
The welding start signal C8 is supplied to the welding timer 26, and the base drive original signal C4° is outputted from the welding timer 26 to the base drive pulse width limiting circuit 28 (second
(see Figures, STP 1 and Figure 3C).

Then, a base control signal CL (see FIG. 3) having a predetermined pulse width is supplied from the base drive pulse width limiting circuit 28 to the base drive circuit 30, and a base drive signal S is generated in accordance with this base control signal C0.

Sa to Sa (see FIG. 3C) are the inverter circuit section 12
is supplied to the bases B of switching transistors 12a to 12d. In this case, a base drive signal S at a predetermined timing is applied to the bases B of the switching transistors 12a and 12b from the aSb side of the base drive circuit 30.
, , S are supplied, and base drive signals Sc and Sd at different timings are supplied from the output terminals c and d of the base drive circuit 30 to the switching transistor 12c.
112d is supplied to base B. Then, the switching transistors 12a and 12b are simultaneously turned on or off by these base drive signals S6 to Sd, and the switching transistor 12C11 is turned on or off at the same time.
2d are simultaneously turned on or off (STP
2). Therefore, a pulsed alternating current is introduced from the inverter circuit section 12 into the primary coil of the welding transformer 16 constituting the welding gun 14 in response to the base drive signals S6 to Sd shown in FIG. 3C.

In this case, the input current corresponding to the magnitude of the pulsed alternating current output from the inverter circuit section 12 is detected by the current detector 1.
3 (STP3), and a detection signal i (see FIG. 3C) corresponding to this magnitude is supplied to the differentiating circuit 22. Further, the detection signal i is supplied to the welding timer 26, compared with a set current value ImaK (STP4), and fed back to change the pulse width of the base drive original signal CLo (STP5). That is, when the detection signal 1 corresponding to the magnitude of the current input to the inverter circuit section 12 exceeds the set current value ■yoa8, the pulse width of the base drive original signal C5° is limited and the base drive original signal CtO A base control signal Ct is output to the base drive circuit 30 based on.

Next, the base drive circuit 30 generates a base drive signal S having a limited pulse width based on the base control signal C4.
By supplying the switching transistors 6 to Sd to the switching transistors 12a to 12d of the inverter circuit section 12, the current flowing through the switching transistors 12a to 12d is suppressed.

If the detection signal i is within the set current value I□6X, the base drive original signal C2° limited to a predetermined pulse width is output to the base drive circuit 30, The drive signals S6 to S are applied to the switching transistors 12a to 12 of the inverter circuit section 12.
d.

By repeating this operation, the direct current introduced from the converter section to the inverter circuit section 12 is output as an alternating current having a predetermined pulse width Tll (see FIG. 3C).

By the way, if current imbalance occurs immediately after energizing the DC resistance welding machine 10 or during operation (Fig. 3, time to), as shown in Fig. 3 d, the AC current with a predetermined pulse width TR is The pulse width 'L, T2, T3 (TI
<T2 <T3 <T11) input terminals flow into the inverter circuit section 12, and the current values Pl to P3 rapidly increase. This current having a steep rise portion (hereinafter referred to as spike current P1 to P3) may cause destruction of the switching transistors 12a to 12d of the inverter circuit section 12. Therefore, when the differential value of the detection signal i is determined in the differentiating circuit 22 (STP6), as shown in FIG. 3e, the spike currents PI, P2, Pl
Pulses Pl', P2', and P3' of differential signals are generated. These pulses P1' to P,' are the input current detection signal i in the pulse of the differential signal i' of the input current detection signal l.
Rising part q. This pulse has the same polarity (in this case, positive polarity) as the pulse of the differential signal qn/ (n=L 2.3...) corresponding to (n=1.2.3...). Therefore, the differential signal i' output from the differentiating circuit 22 is introduced into the bias detection circuit 24, and among the pulses related to the differential signal i' of the detection signal l, the second pulse of the same polarity is recognized as an abnormal current. 5TPT), base drive original signal c,. A base drive pulse width limitation signal C8 (see FIG. 3C) is output to the base drive pulse width limitation circuit 28 (SrF2) to limit the pulse width of the base drive pulse width. Next, the base drive pulse width limiting circuit 28 limits the pulse width of the base drive original signal C5° from the welding timer 26 at the timing of the base drive pulse width limiting signal Cs, and outputs the base control signal C to the base drive circuit 30.
5 (see Figure 3). The base drive circuit 30 generates a base drive signal S whose pulse width is limited based on this control signal C4. Abnormal current can be limited by limiting the time that the switching transistors 12a to 12d of Sa to Sa (see FIG. 3C) are in the on state.

When an abnormal current is not detected and an alternating current with a predetermined pulse width is output from the inverter circuit unit 12, the control circuit of the inverter type DC resistance welding machine 10 enters a steady operating state.

Then, an alternating current with a predetermined pulse width is supplied to the welding transformer 16 of the welding gun 14, converted into a direct current in the rectifiers 18a and 18b, and supplied between the electrodes 20 to
Welding is performed on (SrF9).

As described above, according to this embodiment, the base drive signals S1 to S for outputting the pulsed alternating current set from the start of energization are transmitted from the inverter control circuit section 15 to the switching transistors 12a to 12a of the inverter circuit section 12. 12d, and outputs a pulsed alternating current. Next, the detection signal 1 of the input terminal corresponding to this pulsed alternating current is set to a preset current value l. Set current value compared to X! □. , the base drive signal S. ~S,
In addition, the polarity at which the differential value of the detection signal i appears during the operation of the control circuit of the inverter type DC resistance welding machine 10 is detected, and by detecting the second pulse of the same polarity, the abnormal current is detected. , detects the biased magnetism of the welding transformer 16 and outputs the base drive pulse width limiting signal C5, limits the pulse width of the base drive original signal CLO, and outputs the base drive pulse width limiting signal C5.
Base drive signals S6 to S with limited pulse widths are supplied to the switching transistors 12a to 12d. This can prevent overcurrent from flowing through the switching transistors 12a to 12d constituting the inverter circuit section 12 due to biased magnetism.

[Effects of the Invention] As described above, according to the present invention, the input current corresponding to the output current of the inverter circuit section is detected to obtain a detection signal, and it is detected whether or not the detection signal is within a set value. , the differential value of the detection signal is determined, biased magnetism is detected from the changing state of the polarity of the differential value and the number of pulses, and the pulse width of the base drive signal is limited. Therefore, it is possible to limit the overcurrent caused by biased magnetism flowing through the switching elements constituting the inverter circuit section of the DC resistance welding machine, and it is possible to prevent these elements from being destroyed. In addition, in order to supply a predetermined drive signal to the inverter-type DC resistance welding machine from the start of energization, the pulse width of the current output from the inverter circuit section at the start of energization is increased regardless of the rating of the welding transformer. It is possible to obtain an extremely versatile control circuit for an inverter type DC resistance welding machine that eliminates the need to change the cycle.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments.
For example, it is possible to directly detect the current output from the inverter circuit, compare it with a set value, and determine the differential value to detect biased magnetism. Various improvements can be made without departing from the gist of the present invention. Of course, the design can also be changed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a control circuit applied to the control method for an inverter-type DC resistance welding machine according to the present invention, Fig. 2 is a flowchart explaining the operation of the control circuit shown in Fig. 1, and Fig. 3a is a FIG. 3 is a diagram showing the waveform of the base drive original signal as the first control signal output from the control circuit shown in FIG. 1; FIG. 3 is a diagram showing the base drive signal supplied from the control circuit shown in FIG. FIG. 3C is a diagram showing the waveform of the third control signal that controls the original signal, and is supplied to the switching transistor of the inverter circuit section in response to the base drive original signal output from the control circuit shown in FIG. A diagram showing the waveform of the base drive signal. Figure 3d shows the waveform of the detection signal related to the input terminal corresponding to the pulsed AC current output from the inverter circuit shown in Figure 1 at the start of energization and during steady operation. Figure 3e shows the waveform of the differential signal of the detection signal related to the input current corresponding to the pulsed alternating current shown in Figure 3d, and Figure 3f shows the waveform of the differential signal output from the control circuit shown in Figure 1. FIG. 3 is a diagram showing a waveform of a second control signal. 12... Inverter circuit section 12a to 12d... Switching transistor 13.
...Current detector 14...Welding gun 15...
- Inverter control circuit section 16... Welding transformer 18a, 18b...
Rectifier 22... Differential circuit 24... Unbalanced magnetic detection circuit 26... Welding timer 28... Base drive pulse width limiting circuit 30... Base drive circuit (1 other person)

Claims (4)

[Claims] (1) The DC input section includes an inverter circuit section equipped with a current detection means, a welding gun incorporating a welding transformer, and an inverter control circuit section, which controls the pulse width of the drive signal output from the inverter control circuit section. In the control method for an inverter-type DC resistance welding machine, which controls the magnitude of the alternating current output from the inverter circuit section by After that, a differential pulse according to the differential value of the detection signal is generated in the inverter control circuit section, biased magnetism is detected from the state of change of the differential pulse and the number of pulses within a predetermined time, and a magnetic field is detected based on the biased magnetization state. the inverter circuit section by generating a predetermined control signal, and generating a control signal for controlling the pulse width of the drive signal supplied to the inverter circuit section according to the control signal, and outputting the control signal to the inverter circuit section. 1. A method for controlling an inverter-type DC resistance welding machine, comprising: controlling a current input to the welding machine; converting the input current into alternating current; and supplying the alternating current to a welding gun to perform welding. (2) In the control method according to claim 1, when starting energization of the inverter type DC resistance welding machine, the inverter control circuit compares the detection signal with a preset value, and determines the magnitude of the detection signal. A method for controlling an inverter-type DC resistance welding machine, characterized in that when the pulse width exceeds a preset value, the pulse width of the drive signal supplied to the inverter circuit section is controlled. (3) An inverter circuit unit that converts the DC input to the DC input unit into AC based on a drive signal that is a repetitive square wave pulse signal, and an inverter circuit unit that detects the current input to the DC input unit and outputs a detection signal thereof. a detecting means, a differentiating means for generating a differential pulse according to a differential value of the detection signal, and detecting biased magnetism from a polarity change state and the number of pulses of the differential pulse within a predetermined time and supplying the detected magnetization to the inverter circuit section. 1. A control circuit for an inverter-type DC resistance welding machine, comprising an inverter control circuit section having a comparison means for outputting a control signal that limits the pulse width of a drive signal. (4) The control circuit according to claim 3, further comprising: an inverter circuit section that converts direct current introduced into the direct current input section into alternating current based on a drive signal that is a repetitive square wave pulse signal; and a current input to the direct current input section. a detection means for detecting and outputting a detection signal; a differentiating means for generating a differential pulse according to a differential value of the detection signal; and a differentiation means for comparing the detection signal with a preset value and supplying the detection signal to the inverter circuit section. a first comparison means for outputting a first control signal for controlling the pulse width of the drive signal; and a first comparison means for detecting biased magnetism from the state of change in polarity and the number of pulses within a predetermined time of the differential pulse, and 1. A control circuit for an inverter type DC resistance welding machine, comprising: an inverter control circuit section having a second comparison means for outputting a second control signal for controlling the pulse width of a drive signal supplied to the inverter type DC resistance welding machine.