JPH08290269A - Control device of welding equipment - Google Patents

Abstract

PURPOSE: To improve the working environment of the welding work by providing a setting means to variably set the switching frequency to achieve the pulse width modulation PWM control by a controlling means according to the load condition to reduce the noise generated by the switching frequency or the higher harmonics. CONSTITUTION: A setting instrument 10 to output the modulation frequency setting signal swfB to variably set the modulation frequency to achieve the PWM control of an inverter 4 by a PWM generating circuit 12 according to the load condition is provided. An operator of a welding machine can set the modulation frequency according to the load condition, i.e., the mechanical conditions of the welding machine, the noise can be reduced, and the working environment of the welding works can be improved thereby.

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 a welding machine, in which an AC output of an inverter is added to a primary winding of a welding transformer and an AC welding current is supplied from a secondary winding. Pulse width modulation (hereinafter, PW
A control device for a welding machine, which reduces noise generated by a switching frequency (modulation frequency) for performing control and harmonics of a current reference waveform to improve the working environment of welding work. Is.

[0002]

2. Description of the Related Art Conventionally, a controller for a welding machine has been used in which an AC output of an inverter is added to a primary winding of a welding transformer and an AC welding current is supplied from a secondary winding. FIG. 8 is a block diagram showing an example of the overall configuration of a control device for a conventional welding machine of this type.

That is, as shown in FIG. 8, a conventional welding machine control apparatus includes a rectifier circuit for exchanging AC power from an AC power source 1 into DC power, and a smoothing capacitor 3, and a rectifier circuit for this. Inverter 4 for inversely converting DC power from AC to AC, current detector 5 for detecting output current from this inverter 4, and a rectangular wave current reference of a predetermined frequency according to a current command set from the outside. A reference generating circuit 8 to be generated, a current reference I _ref of this reference generating circuit 8 and a current feedback I _FB from the current detector 5 are compared, and a comparison amplifier 9 for amplifying a deviation between the two is provided, and a constant modulation frequency. A modulation frequency generation circuit 11 for outputting
The output from the modulation frequency generation circuit 11 and the comparison amplifier 9
PW for performing PWM modulation according to the output from
A PWM generator circuit 12 for generating an M control waveform, a welding transformer (hereinafter referred to as a welding transformer) 6 connected to the output side of the inverter 4, and a secondary side of the welding transformer 6 are connected to generate a welding current. It is composed of a welding head 7 for supplying to the welding portion.

By the way, in the controller of the welding machine configured as described above, the current is controlled based on the rectangular wave-shaped current reference I _ref from the reference generation circuit 8, so that a constant (fixed) switching frequency (hereinafter, Referred to as the modulation frequency)
By this, PWM control is performed.

However, in this case, since the modulation frequency is often about several kilohertz, the noise caused by the modulation frequency is generated from the welding transformer 6 and the welding machine, which gives the welding operator discomfort and pressure. ing.

In particular, noise is often emphasized when the modulation frequency is the same as or close to the resonance point of the mechanical system of the welding machine. Further, since the waveform of the current reference I _ref from the reference generation circuit 8 is a rectangular wave, there is also a noise component due to the harmonics included in this current reference I _ref ,
Together with the above modulation frequency, it causes further noise. Therefore, from such a point of view, it is necessary to reduce noise and reduce the mental burden on the welding operator.

[0007]

As described above, in the conventional welding machine control device, noise is generated due to the switching frequency (modulation frequency) for performing PWM control and the harmonics of the current reference waveform. However, there is a problem that the work environment of the welding work is deteriorated.

The object of the present invention is to reduce the noise generated due to the switching frequency (modulation frequency) for performing PWM control and the harmonics of the current reference waveform without impairing the original control performance, and to perform the welding work. It is to provide a control device for a welding machine capable of improving the environment.

[0009]

In order to achieve the above object, first, in the invention corresponding to claim 1, an inverter for converting a DC voltage into an AC voltage by pulse width modulation (PWM), and an inverter. And a welding transformer having a primary winding to which an AC voltage is applied and having a secondary winding that supplies an AC welding current to the welding head, and a rectangular-wave current reference of a predetermined frequency is generated, and the current reference In the controller of the welding machine, which is provided with a control means for PWM-controlling the inverter based on the switching frequency so that the deviation between the two is zero by comparing with the output current of the inverter, the control means performs the PWM control. Setting means for variably setting the switching frequency according to the load condition is provided.

Further, in the invention corresponding to claim 2, in the control device of the welding machine of the invention according to claim 1,
Limiting means for limiting the upper limit value of the current reference is added according to the switching frequency set by the setting means.

Further, in the invention according to claim 3, in the control device for a welding machine according to the invention according to claim 1, the switching frequency for performing the PWM control by the control means is frequency-modulated at a low frequency. Modulation means is added.

On the other hand, in the invention corresponding to claim 4, in the control device of the welding machine of the invention according to claim 1,
The current reference waveform is a sine wave with a predetermined frequency.

Further, in the invention corresponding to claim 5, in the control device of the welding machine of the invention according to claim 4,
A harmonic superimposing means for superimposing an appropriate harmonic component is added to a sinusoidal current reference having a predetermined frequency.

Further, in the invention corresponding to claim 6, in the control device for a welding machine of the invention according to claim 4, limiting means for limiting the peak value of the sinusoidal current reference of a predetermined frequency is added. Become.

On the other hand, in the invention corresponding to claim 7, in the control device of the welding machine of the invention according to claim 1,
A means for changing the switching frequency for performing the PWM control by the control means in accordance with the change of the energization time is added.

Further, in the invention corresponding to claim 8, the control device for a welding machine according to claim 1 is further provided with a frequency modulating means for frequency-modulating the basic frequency of the current reference at a low frequency. .

[0017]

Therefore, first, the control device for a welding machine according to the first aspect of the present invention is provided with the setting means for variably setting the switching frequency for performing the PWM control by the control means according to the load condition. Thus, the user of the welding machine can set the switching frequency according to the load condition, that is, the mechanical condition of the welding machine.

Thus, the switching frequency can be set so as to avoid the mechanical resonance frequency of the welding machine, and noise can be reduced. Further, in the control device for a welding machine of the invention according to claim 2, the limiting means for limiting the upper limit value of the current reference is provided in accordance with the switching frequency set by the setting means. In addition to the same effect as the control device for the welding machine of the corresponding invention is obtained, the upper limit value of the welding current is automatically set according to the set switching frequency.

As a result, the loss of the main circuit element can be suppressed, and the noise can be reduced and the reliability of the device can be secured. Further, in the control device for a welding machine of the invention corresponding to claim 3, the control means includes a modulation means for frequency-modulating a switching frequency for performing PWM control at a low frequency, whereby the above-mentioned claim 1 is provided.
In addition to the same effect as that of the control device for a welding machine according to the invention, the set modulation frequency is further frequency-modulated at a low frequency.

As a result, the noise becomes white noise, and the intimidating feeling of the noise can be reduced. On the other hand, in the control device for a welding machine of the invention according to claim 4, the current reference waveform is a sine wave having a predetermined frequency, so that a sine wave current reference according to a current command from the outside is output. It

As a result, it is possible to reduce the noise caused by the harmonics contained in the trapezoidal wave current. Further, in the control device for a welding machine of the invention corresponding to claim 5, the harmonic superimposing means for superimposing an appropriate harmonic component on the sinusoidal current reference having a predetermined frequency is provided. In addition to the same effect as that of the control device for a welding machine according to the corresponding invention, a harmonic is superimposed on a sinusoidal current reference waveform.

With this, without increasing noise,
It is possible to perform welding with less noise and less fluctuation in heat generation at the welded portion. Further, the control device for a welding machine according to the invention according to claim 6 is provided with a limiting means for limiting the peak value of the sinusoidal current reference of a predetermined frequency, whereby the welding machine according to the invention according to claim 4 is provided. In addition to the same effect as that of the control device described above, the output peak value of the sinusoidal current reference waveform is limited equally on both the positive side and the negative side.

As a result, it becomes possible to easily superimpose higher harmonics, and it is possible to perform welding with little fluctuation in the amount of heat generated at the welded portion without increasing noise. on the other hand,
According to a seventh aspect of the present invention, there is provided a control device for a welding machine according to the first aspect of the present invention, which is provided with a unit that changes a switching frequency for performing PWM control by the control unit according to a change in energization time. In addition to the same effect as that of the control device for a welding machine according to the invention described above, the modulation frequency increases at a predetermined rate according to the energization time.

As a result, the intimidating feeling of noise can be reduced as compared with the case where the switching frequency is constant.
Further, in the control device for a welding machine of the invention according to claim 8, the invention corresponding to claim 1 is provided by including frequency modulation means for modulating the basic frequency of the current reference at a low frequency. The operation similar to that of the welding machine control device is obtained, and the fundamental frequency itself of the current reference is frequency-modulated at a lower frequency. As a result, the noise of the fundamental frequency is converted into white noise, so that the audible noise can be reduced.

[0025]

Embodiments of the present invention will now be described in detail with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing an example of the overall configuration of a control device for a welding machine according to the invention corresponding to claim 1. The same elements as those in FIG. Is omitted and only different parts will be described here.

That is, as shown in FIG. 1, the controller of the welding machine of this embodiment changes the modulation frequency in the modulation frequency generating circuit 11 according to the load condition, that is, the mechanical condition of the welding machine. The setting device 10 that outputs the modulation frequency setting signal swfB for setting is added to FIG.

Next, in the controller of the welding machine of the present embodiment configured as described above, the modulation frequency for performing the PWM control of the inverter 4 by the PWM generating circuit 12 is variably set according to the load condition. By providing the setting device 10 for outputting the modulation frequency setting signal swfB, the welding machine user can set the modulation frequency according to the load condition, that is, the mechanical condition of the welding machine. Is possible.

As a result, the modulation frequency can be set so as to avoid the mechanical resonance frequency of the welding machine, noise can be reduced, and the working environment of welding work can be improved.

As described above, in the control device for a welding machine of this embodiment, the modulation frequency in the modulation frequency generating circuit 11 is variably set according to the load condition, that is, the mechanical condition of the welding machine. Since the setting device 10 that outputs the frequency setting signal swfB is provided, it is possible to avoid the mechanical resonance point of the welding machine, and suppress noise due to the modulation frequency being at the mechanical resonance point. It will be possible.

Further, even if there is a frequency at which noise is easily generated mechanically, the noise can be reduced by changing the modulation frequency. (Second Embodiment) FIG. 2 is a block diagram showing an example of the overall configuration of a control device for a welding machine according to the invention corresponding to claim 2. The same elements as those in FIG. Is omitted and only different parts will be described here.

That is, as shown in FIG. 2, the controller of the welding machine according to the present embodiment has a structure in which the upper limit value limiting circuit 13 is added to the stage before the reference generating circuit 8 in FIG.
Here, the upper limit value limiting circuit 13 uses a current command from the outside and a modulation frequency setting signal swfB from the setting device 10.
Is input and the upper limit value of the current command is limited according to the value of the modulation frequency setting signal swfB and is output as I _refB .

The characteristic of the upper limit value limiting circuit 13 is as follows.
It is set so that the loss of the main circuit element does not exceed the specified value of the element. For this reason, as in the characteristic diagram shown in FIG. 2, no limitation is made in a region where the modulation frequency is low, and an upper limit value to the lower right is imposed in a region where the modulation frequency is high.

Next, in the controller of the welding machine of the present embodiment configured as described above, the modulation frequency setting signal is inputted with the current command from the outside and the modulation frequency setting signal swfB from the setting device 10 as input. By including the upper limit value limiting circuit 13 which limits the upper limit value of the current command according to the value of _swfB and outputs it as I _refB , the upper limit value of the welding current is set according to the modulation frequency set by the setter 10. Is automatically set.

As a result, the loss of the main circuit element can be suppressed, and the noise can be reduced and the reliability of the device can be secured. As described above, in the control device for a welding machine according to the present embodiment, the current command from the outside and the modulation frequency setting signal swfB from the setting device 10 are input, and the current command is generated according to the value of the modulation frequency setting signal swfB. Since the upper limit value limiting circuit 13 for limiting the upper limit value of I _refB and outputting it is provided, the switching loss of the main circuit element is increased by setting the modulation frequency high in the case of the first embodiment. However, in this embodiment, since the upper limit value of the current is limited according to the modulation frequency, the switching loss of the main circuit element is suppressed within the specified value of the element.

As a result, even if the welding operator arbitrarily sets the modulation frequency, the upper limit value of the welding current is automatically suppressed within the capacity of the apparatus, noise is reduced, and the reliability of the apparatus is ensured. It will be possible.

(Third Embodiment) FIG. 3 is a block diagram showing an example of the essential structure of a control device for a welding machine according to the invention corresponding to claim 3. The same elements as those in FIG. The description thereof will be omitted, and only different parts will be described here.

That is, as shown in FIG. 3, the controller of the welding machine of this embodiment comprises an adder 14 and a low frequency generating circuit 15 between the setting device 10 and the modulation frequency generating circuit 11. The modulation means is added to FIG.

Here, the low frequency generation circuit 15 generates the frequency signal swfm in the low frequency region. The adder 14 receives the modulation frequency setting signal swfB from the setting unit 10 and the frequency signal swfm from the low frequency generating circuit 15 as an input, and uses the modulation frequency setting signal swfB from the setting unit 10 as a low frequency generating circuit. The frequency signal swfm from 15 is added and output as swf, and the modulation frequency setting signal swfB is frequency-modulated as a result by giving a low frequency fluctuation to the modulation frequency setting signal swfB.

The level of the signal added as the frequency signal swfm can be arbitrarily adjusted according to the condition of the welding machine. Next, in the control device for a welding machine of the present embodiment configured as described above, the low frequency generating circuit 15 for generating the frequency signal swfm in the low frequency region, and the modulation frequency setting signal swfB from the setting device 10 and the low frequency. The frequency signal swfm from the frequency generation circuit 15 is input,
The frequency signal swfm from the low frequency generation circuit 15 is added to the modulation frequency setting signal swfB from the setting device 10 to obtain s.
By outputting as wf, the modulation frequency setting signal s
Since the modulation means including the adder 14 that frequency-modulates wfB is provided, the modulation frequency setting signal swfB that has been set is subjected to frequency modulation at a lower frequency.

As a result, the noise becomes white noise, and the intimidating feeling of the noise can be reduced. As described above, in the control device for a welding machine according to the present embodiment, the low frequency generation circuit 15 that generates the frequency signal swfm in the low frequency region,
Also, the modulation frequency setting signal swfB from the setting device 10 and the frequency signal swfm from the low frequency generating circuit 15 are input, and the modulation frequency setting signal swfB from the setting device 10 is input.
In addition, since the frequency means swfm from the low frequency generation circuit 15 is added and output as swf, the modulation means including the adder 14 for frequency modulating the modulation frequency setting signal swfB is provided. As described above, when the modulation frequency is constant, the generated noise is also a constant frequency, and thus it is felt to be intimidating. However, in the present embodiment, since the modulation frequency can be continuously changed at a low frequency, the noise Frequency distribution spreads (white noise is generated),
It is possible to reduce the intimidating feeling of hearing.

(Fourth Embodiment) That is, the controller of the welding machine according to the present embodiment has exactly the same configuration as the controller of the welder according to the first embodiment. The reference generation circuit 8 outputs a current reference I _ref having a rectangular wave shape having a predetermined frequency in the first embodiment as an output with respect to a current command from the outside as a sine wave current reference I _refB having a predetermined frequency. It is configured.

Next, in the controller for a welding machine of the present embodiment configured as described above, the reference generation circuit 8 _serves as a sine wave current reference I _refB of a predetermined frequency in response to a current command from the outside. By providing the reference generating circuit 8 for outputting, the sine wave current reference I _refB corresponding to the current command is output.

This makes it possible to reduce the noise due to the harmonics contained in the trapezoidal wave current. As mentioned above,
In the control device for a welding machine according to the present embodiment, as the reference generation circuit 8, the reference generation circuit 8 that outputs the sine-wave current reference I _refB of a predetermined frequency in response to a current command from the outside is provided. In the case of the first embodiment, since the energized current has a trapezoidal wave shape, the harmonic component contained in the trapezoidal wave current is felt as noise, but in the present embodiment, the current reference is a sine wave shape. Therefore, it is possible to reduce the noise due to the harmonic current component of the trapezoidal waveform and improve the working environment.

(Fifth Embodiment) FIG. 4 is a block diagram showing an example of the essential structure of a control device for a welding machine according to the invention corresponding to claim 5. The same elements as those in FIG. The description thereof will be omitted, and only different parts will be described here.

That is, the control apparatus for a welding machine according to the present embodiment is provided with the reference generation circuit 8 which outputs the current reference I _{refB in the form} of a sine wave having a predetermined frequency in response to a current command from the outside. In the controller of the welding machine of the example, as shown in FIG. 4, a harmonic wave superposing means including an adder 14 and a harmonic wave generation circuit 16 is added between the reference generation circuit 8 and the comparison amplifier 9. There is.

Here, the harmonic generation circuit 16 synchronizes with the sinusoidal current reference I _refB waveform of the reference generation circuit 8 to generate harmonics (third-order, 5th-order) in the frequency range that do not affect the noise characteristics.
Next, ...) I _refHn is generated.

Further, the adder 14, a sine-wave current reference I _refB from reference generating circuit 8, by outputting as I _ref by adding the harmonics I _RefHn from harmonic generation circuit 16, the result As a _result , the harmonic wave I _refHn is superimposed on the sinusoidal current reference I _refB .

Next, in the controller of the welding machine of the present embodiment configured as described above, the frequency that does not affect the noise characteristics is synchronized with the sinusoidal current reference I _refB waveform of the reference generation circuit 8. A harmonic generation circuit 16 for generating a _higher harmonic I _{refHn of a} region, a sinusoidal current reference I _refB from the reference generation circuit 8, and a higher harmonic I from the _higher harmonic generation circuit 16.
_By adding _refHn and outputting as I _ref ,
As a result, the sinusoidal current reference I _refB and the harmonics I
_{Since the} harmonic superimposing means including the adder 14 for superimposing _refHn is provided, the harmonic I _refHn is superposed on the sinusoidal current reference I _refB waveform.

As described above, in the welding machine controller of this embodiment, the sinusoidal current reference I _refB of the reference generation circuit 8 is _used.
A harmonic generation circuit 16 that generates a harmonic I _refHn in a frequency range that does not affect noise characteristics in synchronization with the waveform, and a sinusoidal current reference I _refB from the reference generation circuit 8,
By outputting the I _ref by adding the harmonics I _RefHn from harmonic generation circuit 16, as a result, harmonics superimposed an adder 14 for superimposing harmonics I _RefHn sinusoidal current reference I _refB Because I have set up a means,
In the fourth embodiment, when the control based on the sinusoidal current reference is performed, the noise is reduced, but the heat generation fluctuation of the welded portion is large, which may affect the welding quality. Since the harmonics (third, fifth, ...) of several hundred hertz or less, which have low ear sensitivity, are superimposed on the sinusoidal current reference, the flat portion of the welding current increases and the fluctuation of heat generation is minimized. can do. Further, since the fluctuation of the heat generation amount is reduced, it is possible to improve the welding quality while reducing the noise.

(Sixth Embodiment) FIG. 5 is a block diagram showing an example of the essential configuration of a control device for a welding machine according to the invention corresponding to claim 6. The same elements as those in FIG. The description thereof will be omitted, and only different parts will be described here.

That is, the control apparatus for a welding machine of this embodiment is provided with the reference generating circuit 8 which outputs a sinusoidal current reference I _refB having a predetermined frequency in response to an external current command. In the welding machine controller of the example, as shown in FIG. 5, a peak value limit circuit 17 is added between the reference generation circuit 8 and the comparison amplifier 9.

Here, the peak value limiting circuit 17 limits the peak value of the sinusoidal current reference I _refB from the reference generating circuit 8 at a constant ratio and outputs it as I _ref .

Next, in the controller of the welding machine of the present embodiment configured as described above, the peak value of the sinusoidal current reference I _refB from the reference generation circuit 8 is limited to a certain ratio. _{By including} the peak value limit circuit 17 that outputs as _ref , the output peak value of the sinusoidal current reference I _refB waveform is limited equally on both the positive side and the negative side, and the current reference I _refB becomes trapezoidal. To be done.

As described above, in the welding machine controller of this embodiment, the sinusoidal current reference I from the reference generating circuit 8 is generated.
_Since the peak value limit circuit 17 for limiting the peak value of _refB at a constant rate and outputting it as I _ref is provided, in the case of the fifth embodiment, the peak value limit circuit 17 is provided separately from the sinusoidal current reference I _refB. , A circuit for generating a dedicated harmonic is required, but in the present embodiment, the peak value limit circuit 17 causes a waveform close to a waveform obtained by adding the 3rd and 5th harmonics to the sinusoidal current reference I _refB waveform. Therefore, a dedicated harmonic generation circuit is not required, and it is possible to easily optimize the fluctuation of the heat generation amount of the welded portion and perform welding with less noise.

(Seventh Embodiment) FIG. 6 is a block diagram showing an example of the essential configuration of a control device for a welding machine according to the invention corresponding to claim 7. The same elements as those in FIG. 1 are designated by the same reference numerals. The description thereof will be omitted, and only different parts will be described here.

That is, as shown in FIG. 6, the controller of the welding machine of this embodiment includes an adder 14 and a Δf generating circuit (frequency shift circuit) between the setting unit 10 and the modulation frequency generating circuit 11. ) 18 is added to FIG.

Here, the Δf generation circuit 18 generates a voltage signal that linearly rises with the passage of energization time, as shown in FIG. The adder 14 adds the modulation frequency setting signal swfB from the setting device 10 and the voltage signal from the Δf generating circuit 18 and outputs the result as swf.

Next, in the controller of the welding machine of the present embodiment configured as described above, the Δf generation circuit 18, which generates a voltage signal that linearly increases with the passage of the energization time,
And the modulation frequency setting signal swfB from the setter 10.
And the voltage signal from the Δf generation circuit 18 are added, and sw is added.
By including the means including the adder 14 that outputs as f, the modulation frequency increases at a predetermined rate according to the energization time.

As described above, in the controller of the welding machine of this embodiment, the Δf generating circuit 18 for generating the voltage signal that linearly rises with the passage of the energizing time, and the setter 10.
Modulation frequency setting signal swfB from Δf generating circuit 1
Since the means consisting of the adder 14 for adding the voltage signal from 8 and outputting as swf is provided, since the modulation frequency rises with welding time, the frequency distribution of noise is dispersed on the time axis, As compared to the case where the modulation frequency is constant as in the conventional case described above, it is possible to reduce the intimidating feeling in hearing.

(Eighth Embodiment) FIG. 7 is a block diagram showing an example of the essential configuration of a control device for a welding machine according to the invention corresponding to claim 8. The same elements as those in FIG. The description thereof will be omitted, and only different parts will be described here.

That is, as shown in FIG. 7, the control device for the welding machine of this embodiment comprises a low frequency generation circuit 15 and a frequency modulation circuit 19 between the reference generation circuit 8 and the comparison amplifier 9. The frequency modulation means is added to that of FIG.

Here, the low frequency generation circuit 15 generates a frequency signal in the low frequency region. Further, the frequency modulation circuit 19 uses the current reference I _refB from the reference generation circuit 8.
_Is frequency-modulated with a low-frequency signal from the low-frequency generation circuit 15 and is output as I _ref .

Next, in the control device for a welding machine of the present embodiment configured as described above, the low frequency generation circuit 15 for generating the frequency signal in the low frequency region and the reference generation circuit 8 are provided.
The current reference I _refB from the current reference I _refB is frequency-modulated by the low-frequency frequency signal from the low-frequency generation circuit 15 and is output as I _ref. The fundamental frequency of _refB itself is frequency-modulated at a lower frequency.

As described above, in the welding machine controller of this embodiment, the current reference I from the low frequency generation circuit 15 for generating the frequency signal in the low frequency region and the reference generation circuit 8 is generated.
_{Since the} frequency modulation means including the frequency modulation circuit 19 that frequency- _{modifies refB} with the low-frequency frequency signal from the low-frequency generation circuit 15 and outputs it as I _ref is provided, the noise that the trapezoidal wave current waveform itself has Since the frequencies are distributed, white noise is generated, and it is possible to reduce audible noise.

[0065]

As described above, first, according to the invention corresponding to claim 1, the DC voltage is pulse width modulated (PW).
M) and has an inverter for converting to an AC voltage and a primary winding to which the AC voltage from the inverter is applied,
A welding transformer having a secondary winding that supplies an alternating welding current to the welding head and a rectangular wave current reference of a predetermined frequency are generated, and the current reference and the output current of the inverter are compared and the deviation between the two is found. In a control device for a welding machine, which is provided with a control means for PWM-controlling an inverter based on the switching frequency so as to be zero, a switching frequency for performing the PWM control by the control means is variably set according to a load condition. Since I set up a setting means to
It is possible to provide a control device for a welding machine in which the modulation frequency can be set so as to avoid the mechanical resonance frequency, noise can be reduced, and the work environment of welding work can be improved.

According to the invention corresponding to claim 2,
In the control device for a welding machine according to the first aspect of the present invention, the limiting means for limiting the upper limit value of the current reference is added according to the switching frequency set by the setting means. It is possible to provide a control device for a welding machine, which can suppress loss, reduce noise, and ensure reliability of the device.

Further, according to the invention corresponding to claim 3, in the control device for a welding machine according to the invention according to claim 1, the switching frequency for performing the PWM control by the control means is a low frequency. Since the modulating means for modulating is added, it is possible to provide the control device for the welding machine, which can make the noise white noise and reduce the intimidating feeling of the noise.

On the other hand, according to the invention corresponding to claim 4,
In the control device for a welding machine according to the first aspect of the present invention, since the current reference waveform is a sine wave having a predetermined frequency, it is possible to reduce noise due to harmonics contained in the trapezoidal current. A welding machine control device can be provided.

According to the invention corresponding to claim 5,
In the control device for a welding machine of the invention according to claim 4, since the harmonic wave superimposing means for superimposing an appropriate harmonic wave component is added to the sinusoidal current reference of the predetermined frequency, noise is increased. It is possible to provide a control device for a welding machine that can perform welding with less fluctuation in the amount of heat generated at the welded portion and without noise.

Further, according to the invention according to claim 6, in the control device for a welding machine according to the invention according to claim 4, limiting means for limiting the peak value of the sinusoidal current reference of a predetermined frequency is added. Therefore, it is possible to provide a welding machine control device capable of superimposing harmonics easily and performing welding with little fluctuation in the heat generation amount of the welded portion without increasing noise.

On the other hand, according to the invention corresponding to claim 7,
In the controller for a welding machine according to the first aspect of the present invention, the switching frequency for performing the PWM control by the control means is changed according to the change of the energization time. It is possible to provide a control device for a welding machine that can reduce the intimidating feeling of noise as compared with the case of a fixed case.

According to the invention corresponding to claim 8,
In the control device for a welding machine according to claim 1, since the frequency modulation means for frequency-modulating the basic frequency of the current reference at a low frequency is added, the noise of the basic frequency of the current reference is white noise. It is possible to provide a control device for a welding machine that can reduce the noise on the sense of hearing.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a control device for a welding machine according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the control device for the welding machine according to the present invention.

FIG. 3 is a block diagram showing a third embodiment of the control device for the welding machine according to the present invention.

FIG. 4 is a block diagram showing a fifth embodiment of the control device for the welding machine according to the present invention.

FIG. 5 is a block diagram showing a sixth embodiment of the control device for the welding machine according to the present invention.

FIG. 6 is a block diagram showing a seventh embodiment of the control device for the welding machine according to the present invention.

FIG. 7 is a block diagram showing an eighth embodiment of the control device for the welding machine according to the present invention.

FIG. 8 is a block diagram showing a configuration example of a conventional welding machine control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... AC power supply, 2 ... Rectifier, 3 ... Smoothing capacitor, 4 ... Inverter, 5 ... Current detector, 6 ... Welding transformer, 7 ... Welding head, 8 ... Reference generating circuit, 9 ... Comparison amplifier, 10 ... Setting device, 11 ... Modulation frequency generating circuit, 12 ... PWM generating circuit, 13 ... Upper limit value limiting circuit, 14 ... Adder, 15 ... Low frequency generating circuit, 16 ... High frequency generating circuit, 17 ... Peak value limiting circuit, 18 ... Δf generating circuit , 19 ... Frequency modulation circuit.

Claims (8)

[Claims] 1. An inverter for converting a DC voltage into an AC voltage by pulse width modulation (PWM), and a primary winding to which the AC voltage from the inverter is applied, and an AC welding current is supplied to a welding head. A welding transformer having a secondary winding and a rectangular-wave-shaped current reference of a predetermined frequency are generated, the current reference is compared with the output current of the inverter, and the switching frequency is adjusted so that the deviation between the two becomes zero. A control device for a welding machine, comprising: a control means for PWM-controlling the inverter based on the setting means for variably setting a switching frequency for PWM control by the control means in accordance with a load condition. A welding machine control device characterized by the above. 2. The control device for a welding machine according to claim 1, further comprising a limiting unit for limiting an upper limit value of the current reference according to the switching frequency set by the setting unit. Characteristic welding machine control device. 3. The control device for a welding machine according to claim 1, further comprising a modulation means for frequency-modulating a switching frequency for performing PWM control by the control means at a low frequency. Welder controller. 4. The control device for a welding machine according to claim 1, wherein the current reference waveform is a sine wave having a predetermined frequency. 5. The control device for a welding machine according to claim 4, further comprising a harmonic wave superposing means for superposing an appropriate harmonic wave component on the sinusoidal current reference having the predetermined frequency. Welder control device 6. The control of the welding machine according to claim 4, further comprising limiting means for limiting the peak value of the sinusoidal current reference of the predetermined frequency. apparatus. 7. The control device for a welding machine according to claim 1, further comprising means for changing a switching frequency for performing PWM control by the control means in accordance with a change in energization time. Characteristic welding machine control device. 8. The welding machine control apparatus according to claim 1, further comprising frequency modulation means for frequency-modulating the fundamental frequency of the current reference at a low frequency. Control device.