JP3104825B2 - Control method and device for resistance welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control apparatus for a resistance welding machine for controlling the phase of a thyristor by synchronizing the power supply control of the resistance welding machine with a power supply voltage.

[0002]

2. Description of the Related Art Conventionally, in order to control the energization of a resistance welding machine by a thyristor, the firing angle of the thyristor is controlled in synchronization with the power supply voltage. The synchronization signal is in phase with the power supply voltage phase. (Or almost in-phase). The certain phase generally detects a zero cross of the power supply voltage, and uses this detection signal as the origin of the thyristor control angle.

[0003]

However, in a factory where a large number of resistance welding machines are used, the power supply may have many distortion waveforms. For this reason, the synchronization signal may be disturbed, and an excessive current may flow due to an erroneous synchronization signal, which may cause an accident such as a blast of welding or a fall of a power supply breaker. Examples of power supply equipment that gives such a distortion to the power supply voltage include a flicker prevention device, a large-capacity DC rectification power supply device (such as a plating power supply and a painting power supply), and a rectifying resistance welding machine.

The flicker device controls the energization of a large-capacity capacitor in order to prevent flicker of the power supply voltage. When controlling the energization, a distortion waveform is given to the power supply. A large-capacity DC power supply also generates a six-phase distorted voltage waveform when energization is controlled. Finally, there is a distortion waveform due to energization of the rectifier resistance welder. When the rectifier resistance welder is energized, the current rises sharply.
Due to the reactance L of the electric circuit, a steep spike-like voltage drop of v = Ldi / dt is generated. When this welding machine is divided and arranged in a three-phase circuit, and each of them is energized in an arbitrary phase, the voltage waveform e causes a spike-like drop at various points in the voltage waveform. Influence on the synchronization signal given by the above three types of power supply equipment and load (generally zero cross signal)
Is shown in FIG.

As shown in FIG. 1, the synchronization signals are P1, P2,
When output at the wrong phase like P3, P4, P5,
The ignition control of the thyristor shown in FIG. 2 is disturbed. In the case of a normal synchronizing signal pulse such as P6, P7, P8 in FIG. 2, a normal current flows like i6, i7, i8.

Here, α in FIG. 2 indicates the firing control angle from the input of the synchronizing signal to the firing of the thyristor, which is caused by a distorted power supply such as P1 before P6. When an incorrect synchronization signal pulse is input to the phase control circuit, an excessive current such as i1 flows. As a result, an accident such as poor welding or interruption of the current breaker may be caused.

According to the present invention, the aforementioned large power supply distortion waveform is
By changing the waveform to a normal waveform with the integration filter means having a large time constant, generating a synchronizing signal from this normal waveform, and using this synchronizing signal as the synchronizing signal of the thyristor that fires at the next power supply half-wave, Even so, a normal synchronization signal is generated.

[0008]

According to the present invention, a power supply voltage waveform is suppressed by a smoothing means such as a C / R integrator having a sufficient time constant to suppress a distortion waveform, and the output voltage of the distorted integration circuit is reduced. To detect the power supply synchronization signal. This synchronization signal is delayed by several tens degrees or more from the power supply voltage phase because it passes through a large filter constant of the integration circuit. Therefore, the synchronizing signal is further delayed by the delay means and used as a synchronizing signal for performing the ignition control of the next power supply half-wave.
It is important that the distortion waveform is completely removed by the filter having such a sufficiently large time constant, a synchronizing signal is generated from the clean voltage waveform, and the synchronizing signal is used for the ignition control of the next half wave. Features.

[0009]

By taking the above measures, the power supply synchronizing signal is not disturbed even in the case of an electric circuit having a distorted power supply waveform. Welding results can be obtained.

[0010]

FIG. 3 is a block diagram of the first embodiment.
FIG. 4 shows operation waveforms of FIG. The configuration is as follows. Reference numeral 1 denotes a welding power source having a distortion waveform. Reference numeral 2 denotes a step-down transformer for stepping down the power supply. Reference numeral 3 denotes a CR integrating circuit having a long time constant for removing a power source distortion of the welding power source 2. Reference numeral 4 denotes a power supply synchronization signal detection circuit (means) for detecting a power supply synchronization signal using the output of the C / R integration circuit 3. Reference numeral 5 denotes a delay circuit (means).
This is a delay circuit for controlling the firing of the synchronizing signal S1, which is the output of the synchronizing signal detecting means, by the next half-wave of the power supply. Reference numeral 6 denotes a power supply start circuit, 7 denotes a power supply control circuit, 8 denotes a phase control circuit, 9 denotes a thyristor firing circuit, 10 denotes a thyristor, and 11 denotes a resistance welding machine. Reference numerals 6 to 11 denote control circuits of the resistance welding machine, which are generally well known and will not be described in detail.

The voltage of the welding power source 1 is stepped down by a step-down transformer 2, and the output is passed to a CR integrating circuit 3. The C / R integration circuit 3 has a long time constant capable of sufficiently smoothing the distortion voltage. In the case of the first embodiment shown in FIG. 3, the time constant is as high as 60 milliseconds. The output of the integration circuit 3 is used to generate a synchronization signal S1 by a power supply synchronization signal detection circuit 4. The synchronizing signal S1 is delayed by the integrating circuit 3 by more than 80 degrees with respect to the power supply voltage zero cross. The delayed synchronizing signal S1 is led to a delay circuit 5 for further delaying, and the delayed output signal S2 is used as a synchronizing signal for firing control of a thyristor for firing at the next power supply half-wave. The power supply synchronizing signal S2 is output to the conduction control circuit 7.

It is to be noted that the present invention is a control method which is more improved than that of Japanese Unexamined Patent Publication No. Hei 5-31587 "AC resistance welding control or measuring device" which has already been proposed as a new technology of the power supply synchronous circuit.

That is, in the above technique, the PLL circuit (P
According to the present invention, the detected synchronization signal is improved and the thyristor is only used for the thyristor that is energized by the current power supply half-wave, whereas the present invention provides a further improved control. It is. That is, as described above, the synchronization signal detected by the current half-wave is used as the synchronization signal of the thyristor to be fired by the next power supply half-wave.

As represented by Japanese Patent Publication No. 54-37057, invented in the past by the same inventor as the present application, the present invention uses a synchronization signal detected 180 degrees or more before the firing angle of the thyristor to be fired. To fire (ie, detect the synchronization signal of the previous half-wave and use it as the synchronization signal of the thyristor of the next half-wave). This provides an excellent control method that also has a function of preventing imbalance of the primary welding current caused by the phase shift of the synchronization signal caused by the welding machine energization.

Next, a second embodiment will be described with reference to FIGS. In FIG. 3, circuits or means having the same functions as those of the first embodiment described above are denoted by the same numbers as those described in the first embodiment. The second embodiment uses a second integration circuit 12 instead of the delay circuit 5 of the first embodiment. The synchronization signal S2 is detected from the output of the second integration circuit.

The operation of the second embodiment will be described. As shown in FIG. 3 of the first embodiment, the output of the first integration circuit 3 is delayed by about 90 degrees from the power supply voltage. This output is given to the second integration circuit 12. Since the second integration circuit forms an integrator using an operational amplifier, the second integration circuit is delayed by 90 degrees from the first integration circuit 3 and has a sufficient output voltage value. Note that the 90-degree delay is not limited to 90 degrees, and can be changed in magnitude by a subsequent control method.

A synchronization signal S2 is generated from the output of the second integration circuit 12 through the power supply synchronization detection circuit 4. That is, in the second embodiment, as shown in FIG.
The power supply distortion is sufficiently removed by the integration circuit, and is approximately 90
Output a delayed voltage.
It is further delayed about 90 degrees by the integration circuit. By passing through these two integrating circuits, an AC voltage detection signal S3 having a phase difference of about 180 degrees with a power supply having no distortion waveform is generated. Then, a synchronization signal S2 is generated from the voltage of the voltage detection signal S3. Thus, it is considered that the first integrating circuit 3 detects and integrates the voltage of the previous half-wave, and the second integrating circuit 13 performs a delay operation to generate a synchronization signal for the next half-wave. You can also.

In the description of the embodiment, the power supply synchronizing signal S2
Has been described in accordance with the generally adopted zero-cross point of the power supply voltage, but this is not limited to the zero-cross point. It may be a synchronization signal output in synchronization with a certain phase of the voltage waveform. The phase may be before or after the zero crossing of the power supply voltage for the sake of control. Although the embodiment of FIG. 3 embodies the present invention by a hardware circuit, the embodiments 4 and 5 of FIG. 3 can also be realized by software of a microcomputer. This synchronization signal is also used as a synchronization signal for sequence control such as the energization time.

[0019]

As described above, the synchronizing signal of the thyristor that the distortion waveform of the power supply voltage is sufficiently smoothed by the integrating means with respect to the distortion power supply waveform, and is fired in the next half wave using a clean power supply voltage. According to the method of the present invention, a synchronizing signal that does not malfunction even with a distorted power supply waveform is generated, and the current supply control of the welding machine becomes stable, thereby eliminating the serious problem of poor welding.

In recent years, the improvement of fuel efficiency of automobiles has been avoided, and chassis of aluminum material has been adopted to reduce the weight of the vehicle body. Since a large current is required for aluminum spot welding, the welding machine must be large in capacity. In order to reduce the capacity (KVA), a rectifying resistance welding machine is frequently used. In any case, the large power supply distortion as described above is applied to the electric circuit. Therefore, in such a situation, if the control device of the present invention is used, a stable control of the welding current even with a distorted voltage waveform can be realized with a simple circuit configuration. It can greatly contribute to ensuring stable welding quality.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a malfunction of a conventional three-type distortion voltage waveform and a zero-cross detection signal.

FIG. 2 is a current waveform diagram showing a relationship between a conventional synchronization signal and thyristor firing control.

FIG. 3 is an electric block diagram showing a control device of a first embodiment for implementing the method of the present invention.

FIG. 4 is a voltage waveform diagram showing a timing relationship of a synchronization signal according to the first embodiment of the method of the present invention.

FIG. 5 is an electric block diagram showing a control device of a second embodiment for carrying out the method of the present invention.

FIG. 6 is a voltage waveform diagram showing a timing relationship of a synchronization signal according to a second embodiment of the method of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 welding power supply 2 step-down transformer 3 integration circuit (first integration circuit) 4 power supply synchronization signal detection circuit 5 delay circuit 6 energization start circuit 7 energization control circuit 8 phase control circuit 9 thyristor firing circuit 10 thyristor 11 resistance welder 12 second Integrator circuit

Claims (3)

(57) [Claims] 1. A power supply synchronization method for a control device of a welding machine connected to an electric circuit for supplying power to a resistance welding machine, wherein a power supply voltage of the electric circuit of the welding machine is detected, and the detected output is integrated and smoothed. A power supply synchronizing signal S1 is generated from the smoothed output, the synchronizing signal S1 is delayed to a predetermined power supply voltage phase, and the synchronizing signal for thyristor firing control for firing the delayed synchronizing signal S2 at the next power supply half wave. A method for controlling a resistance welding machine, characterized in that: 2. A step-down transformer for stepping down a power supply voltage, an integration circuit for integrating and smoothing a distortion waveform of an output of the transformer, and a power supply synchronization signal detection circuit for detecting a power supply synchronization signal using an output of the integration circuit. A control device for a resistance welding machine provided with a delay circuit for using an output signal of the detection circuit as a power supply synchronization signal of the next half wave. 3. A step-down transformer for stepping down a power supply voltage, a first integration circuit for integrating and smoothing a distortion waveform of an output of the transformer, and an AC output voltage of the first integration circuit for further integrating the first integration circuit. A resistance welding machine provided with a second integration circuit for generating an AC voltage output S3 delayed by a predetermined angle from the output signal, and a power supply synchronization signal detection circuit for generating a synchronization signal S2 from the AC voltage output S3 of the second integration circuit. Control device.