JPH02207982A - Method and circuit for controlling inverter type direct current resistance welding machine - Google Patents

Abstract

PURPOSE:To prevent a switching element from being broken down by detecting a current inputted to an inverter circuit part, obtaining a derivation value of a detected signal and detecting magnetic deflection in a prescribed time from a changing state of polarity of the derivation value and the number of pulses. CONSTITUTION:A magnetic deflection detection circuit 24 outputs a base driving pulse width restriction signal Cs to a base driving pulse width restriction circuit 28 based on a differential signal (i) from a differentiation circuit 22 and a base driving source signal Ct0 outputted from a welding timer 26. In addition, the welding timer 26 outputs the base driving source signal Ct0 to the base driving pulse width restriction circuit 28. Further, the base driving pulse width restriction circuit 28 outputs a base control signal Ct to a base driving circuit 30 based on the base driving source signal Ct0 from the welding timer 26 and the base driving pulse width restriction signal Cs from the magnetic deflection detection circuit 24. By this method, an abnormal current flowing to transistors is restricted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control method window and circuit for an inverter-type DC resistance welding machine. An inverter-type DC resistance welding machine that detects biased magnetism in the welding transformer of the DC resistance welding machine by performing predetermined signal processing on the DC resistance welding machine and limits overcurrent caused by biased magnetization flowing to the inverter circuit. The present invention relates to a control method and circuit.

[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 using a rectifier, and then converts this into AC using a transistor/inverter. It is converted and fed to the welding transformer built into the welding machine or welding gun. The output of this transformer is a low-voltage, high-current alternating current that is rectified again and supplied as a direct current welding current to the workpiece through electrodes for welding.

By the way, when power is applied to operate such an inverter type DC resistance welding machine, an overcurrent is generated in the circuit due to magnetic saturation of the welding transformer in the initial stage of energization, a so-called biased magnetism phenomenon due to current imbalance during energization, etc. flows, which may destroy the transistors that make up the inverter section.

Conventionally, in order to prevent this inconvenience, 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. The pulse width is controlled accordingly (see Jikai Sho No. 63-154274). In addition, in order to prevent excessive current from flowing through the transistors that make up the inverter due to DC bias in the welding transformer of the DC resistance welding machine, the transistors are destroyed.
There is also a technique for detecting current and immediately stopping the switching operation of a transistor when an abnormal current is detected (see Jikai Sho No. 62-107867). However, in these conventional technologies, abnormal current is detected at a threshold level and the switching operation of the inverter section is thereby stopped. not achieved. When the threshold 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 abnormal current threshold level low, but if this measure is adopted, the welding current that can be passed through the switching transistors in the inverter section during normal conditions will also be restricted and must be set low. It disappears. Moreover, even with these conventional techniques, the biased magnetism of the welding transformer when energized is not eliminated;
Even if an abnormal current is detected during energization, the operation of the inverter is simply stopped, and it is difficult to effectively suppress magnetic bias.

[Purpose of the Invention] The present invention has been made to overcome the above-mentioned disadvantages. In an inverter-type DC resistance welding machine, the output current of the inverter is detected, the differential value of the detected current is determined, and the differential value is calculated. By detecting the current caused by biased magnetization from the positive/negative polarity and number of pulses of the inverter and the timing of the drive signal supplied to the transistor pace of the inverter, and limiting the pulse width of the drive signal supplied to the base. An object of the present invention is to provide a control method and circuit for an inverter-type DC resistance welding machine that makes it possible to limit abnormal current flowing through a transistor.

[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. A control method for an inverter type DC resistance welding machine comprising: supplying a drive signal from the inverter control circuit section to the inverter circuit section; and detecting a current input to the inverter circuit section using the current detection means. A first controller that obtains a signal and introduces it into the inverter control circuit section, and then compares the detection signal with a preset value in the inverter control circuit section to control a drive signal supplied to the inverter circuit section. Outputting a control signal, generating a differential pulse according to the differential value of the detection signal, detecting biased magnetism of the welding transformer from the state of change of the differential pulse and the number of pulses within a predetermined time, and supplying the detected bias to the inverter circuit section. controlling the current input to the inverter circuit section by sending out a second control signal that controls the drive signal to be input, converting the current input to the inverter circuit section into alternating current, and transmitting this alternating current to the welding gun. It is characterized by supplying and welding.

The present invention also provides an inverter circuit section that converts direct current to alternating current based on a drive signal, current detection means for detecting a current input to the inverter circuit section after being converted to alternating current to obtain a detection signal, and a first comparing means for comparing the signal with a preset value and outputting a first control signal for controlling the drive signal supplied to the inverter circuit section; and differentiating the detection signal to generate a differential pulse. and a differentiating means for detecting biased magnetization of the welding transformer by receiving the differentiated pulse and detecting the state of change and the number of pulses of the differentiated pulse within a predetermined time, and outputting a drive signal to be supplied to the inverter circuit section. The present invention is characterized by comprising an inverter control circuit section having a second comparison means for sending out a second control signal for control.

[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 10 includes an inverter circuit section 12, a welding gun 14 incorporating a welding transformer, and an inverter control direction 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 the switching transistor 12a is connected to the collector C of the switching transistor 12d, and the emitter E of the switching transistor 12c is connected to the collector C of the switching transistor 12d.
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 collector C of the switching transistor 12aS12c and the emitter E of the switching transistors 12d and 12b.

From the converter section to the switching transistor 1
A current detector 13 as a current detection means is provided on the connection line leading to the collector C of 2a and 12c, and the output signal of the current detector 13 is transmitted to the inverter control circuit section 15.
connected to. That is, the current detector 13 is installed on the DC input side of the inverter circuit section 12, detects the current input to the inverter circuit section 12, 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 substantially composed of a welding transformer 16, rectifiers 18a and 18b, and an electrode 20.

The welding transformer 16 transforms the pulsed alternating current supplied from the inverter circuit section 12 to the rectifier 18a,
18b. 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 set of electrodes, and a workpiece W to be welded is held under pressure between these sets of electrodes, and a large current is applied to the contact portion of the workpiece W to bring the workpiece W into contact with the workpiece W. Welding is performed using Joule heat based on resistance.

On the other hand, the inverter control circuit section 15
A detection signal i related to the current inputted to the inverter circuit section 12 is introduced from the switching transistor 12 that constitutes the inverter circuit section 12 based on this detection signal i.
Drive signals S1 and S supplied to bases a to 12d
5, a differentiation circuit 22 that outputs So and Sd (hereinafter referred to as base drive signal) and serves as a differentiator that generates a differentiated pulse by differentiating a detection signal corresponding to the current input to the inverter circuit section 12; A welding timer 26 constituting a part of the first comparison means, a biased magnetism detection circuit 24 constituting the second comparison means, and the base drive signal S. ~S
, and a base drive circuit 30 that outputs the base drive signals Sa to Sd. be done.

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 receives the differential signal i' from the differentiating circuit 22 and the base drive original signal C which is the first control signal output from the welding timer 26.
1°, a base drive pulse width limit signal Cs, which is a second control signal, is output to the base drive pulse width limit circuit 28. Further, the welding timer 26 has a preset current value of 11.
1 mAN is set, the detection signal i from the current detector 13 is taken in as a feedback signal, and the base drive original signal C1O is output 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 CtO from the welding timer 26 and the base drive pulse width limiting signal C8 from the biased magnetism detection circuit 24. is output to the base drive circuit 30. The base drive circuit 30 drives the inverter and inverter circuit section 12 based on the base control signal C4.
A base drive signal S is applied to the bases B of the switching transistors 12a to 12d. Outputs Sd to Sd.

The control circuit for implementing the control method for the inverter-type DC resistance welding machine according to this embodiment is basically configured as described above. This will be explained in detail below. 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 IO, direct current is applied 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
Welding start signal C8 is supplied to welding timer 26 of
(See Figure 5TP1 and Figure 3C).

Then, a base control signal Ct of a predetermined pulse width is sent from the base drive pulse width limiting circuit 28 (see FIG. 3).
is supplied to the base drive circuit 30, and a base drive signal S is supplied in response to the base control signal C5. S to S (see FIG. 3C) are supplied to the bases B of switching transistors 12a to 12d of the inverter circuit section 12. In this case, the base B of the switching transistors 12a, 12b
Base drive signals S, , Sb at predetermined timings are supplied from the a and b sides of the base drive circuit 30 to the output terminals of the base drive circuit 30, and base drive signals Sc and Sa at different timings are supplied to the output terminals of the base drive circuit 30. It is supplied from the c and d sides of the switching transistors 12c and 12d to the bases B of the switching transistors 12c and 12d. These base drive signals S1 to S,
The switching transistors 12a, 12b
are simultaneously turned on or off, and switching transistors 12c and 12d are simultaneously turned on or off (SrF2). 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 S shown in FIG. 3C.

In this case, the current input to the inverter circuit section 12 is detected by the current detector 13 (SrF3), and a detection signal l (see FIG. 3d) corresponding to this magnitude is sent to the differentiating circuit 22.
is supplied to Further, the detection signal i is supplied to the welding timer 26 and compared with the set current value IIlaM (SrF2
), which is fed back to change the pulse width of the base drive original signal C5° (SrF2). That is, when the detection signal i corresponding to the magnitude of the current input to the inverter circuit section 12 exceeds the set current value IllaM, the pulse width of the base drive original signal C5° is limited and the base drive original signal C5° Base drive circuit 30 based on
A base control signal Ct is output to the base control signal Ct. Next, the base drive circuit 30 generates a base drive signal S whose pulse width is limited based on the base control signal C5. By supplying Sd 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. Also,
If the detection signal 1 is within the set current value Iwax, the base drive original signal Cto controlled to have a predetermined pulse width is output to the base drive circuit 30, and the base drive signal S is limited to a predetermined pulse width. S to S are supplied to switching transistors 12a to 12d of the inverter circuit section 12. By repeating this operation, the current introduced from the converter section to the inverter circuit section 12 is output as an alternating current having a predetermined pulse width Tl (see FIG. 3d).

By the way, if current imbalance occurs immediately after energization of the inverter-type DC resistance welding machine 10 or during operation (Fig. 3, time t).

point), the predetermined pulse width Ti is not achieved, but the pulse width T
I, T2, Ts (TI < T2 < T3 < TR)
The input terminal of flows into the inverter circuit section 12, and the current value rapidly increases (reference symbols Pl to P3 in the figure). At this time, there is a possibility that this current having a steep rise portion (hereinafter referred to as spike current P1 to P) may cause destruction of the switching transistors 12a to 12d of the inverter circuit section 12.

Therefore, when the differentiation circuit 22 calculates the differential value of the current detection signal l input to the inverter circuit section 12, (
SrF2), as shown in FIG. 3e, the pulses p, / , p, / , of the differential signals of the spike currents Pt to P3
p,' is generated.

These pulses Pl' to P,' are the detection signal i and the differential signal j
The rising portion q of the current detection signal i input to the inverter circuit section 12 during the pulse .

Differential signal q corresponding to (n=1.2.3...).

This is a pulse of the same polarity (in this case, positive polarity) as the pulse of (n=1.2.3...). Therefore, the differentiating circuit 22
In order to recognize the second pulse of the same polarity as the pulse of the differential signal i' of the detection signal i as an abnormal current by introducing the differential signal 1' output from the detection signal i into the bias detection circuit 24, the base drive original signal CtO base i[tJ
J Outputs the Hals width limit signal CS (see FIG. 3C) to the base drive pulse width cutoff circuit 28 (SrF8).

Next, the base drive pulse width limiting circuit 2B limits the pulse width of the base drive original signal Cto from the welding timer 26 at the timing of the base drive pulse width limiting signal C3, and supplies the base drive circuit 30 with the base control signal C4 (third (see figure).

Based on the base control signal C2, the base drive circuit 30 operates the switching transistors 12a to 1 of the base drive signals S1 to Sd (see FIG. 3C) whose pulse widths are limited.
By limiting the time in the on state of 2d, abnormal current can be limited. When no abnormal current is 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,
The rectifiers 18a and 18b convert the direct current into direct current, which is supplied to the electrode 20 to weld the welded material W (STP
9).

As described above, according to this embodiment, the base drive signals S6 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,
At that time, the differential value of the input terminal corresponding to the pulsed alternating current is determined, the polarity of the differential value is detected, and by detecting the second pulse of the same polarity, it is determined to be an abnormal current, and the welding transformer 16 is polarized. is detected and outputs a base limit signal. This can prevent overcurrent from flowing through the switching transistors 12a to 12d constituting the inverter circuit section 12 due to biased magnetization.

[Effects of the Invention] As described above, according to the present invention, in the control method and circuit for an inverter-type DC resistance welding machine, a current input to the inverter circuit section is detected to obtain a detection signal, and the detection signal is set. In addition to detecting whether or not the value is within the range, the differential value of the detection signal is determined, biased magnetism is detected from the change 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 current flowing through the switching elements constituting the inverter circuit section of the DC resistance welding machine, and it is possible to suitably prevent these elements from being destroyed.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments.
For example, after detecting the alternating current output from the inverter circuit and shaping the waveform into an alternating current consisting of a pulse train of the same polarity as the alternating current, it is also possible to detect biased magnetism by comparing it with a set value and finding the differential value. It goes without saying that various improvements and changes in design can be made without departing from the gist of the present invention.

[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 signal, and FIG. Figure 3 d is a diagram showing the waveform of the drive signal; Figure 3 d is a diagram showing the waveform of the detection signal related to the current input to the inverter circuit at the start of energization and during steady operation shown in Figure 1; Figure 3f shows the waveform of the differential signal of the detection signal related to the current input to the inverter circuit section shown in Figure 3, and Figure 3f shows the waveform of the second control signal output to the base drive circuit in the control circuit shown in Figure 1. It is a figure which shows a waveform. 12... Inverter circuit section 12a to 12d... Switching transistor 13.
...Current detector 14...Welding gun 15...
・Inverter control circuit section

Claims (2)

[Claims] (1) A method for controlling an inverter-type DC resistance welding machine, which includes an inverter circuit unit in which a current detection means is installed in the DC input unit, a welding gun incorporating a welding transformer, and an inverter control circuit unit, the inverter control circuit A drive signal is supplied from the unit to the inverter circuit unit, and the current detecting unit detects the current input to the inverter circuit unit to obtain a detection signal and introduces the detected signal into the inverter control circuit unit, and then the inverter control circuit The unit compares the detection signal with a preset value and outputs a first control signal for controlling a drive signal supplied to the inverter circuit unit, and generates a differential pulse according to a differential value of the detection signal. detecting biased magnetization of the welding transformer from the state of change of the differential pulse and the number of pulses within a predetermined period of time, and transmitting a second control signal for controlling the drive signal supplied to the inverter circuit section. An inverter-type DC resistance welding machine characterized by controlling the current input to the inverter circuit section, converting the current input to the inverter circuit section into alternating current, and supplying the alternating current to the welding gun to perform welding. Control method. (2) an inverter circuit unit that converts direct current to alternating current based on a drive signal; a current detection means that detects a current input to the inverter circuit unit after being converted to alternating current to obtain a detection signal; a first comparing means for outputting a first control signal for controlling a drive signal supplied to the inverter circuit unit by comparing the value with a preset value; and a differentiator for differentiating the detection signal to generate a differential pulse. means for receiving the differential pulse and detecting the state of change of the differential pulse and the number of pulses within a predetermined period of time to detect biased magnetization of the welding transformer and controlling the drive signal supplied 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 second comparison means for sending out a second control signal.