JPH08197260A - Inverter control ac resistance welding equipment and its resistance welding method - Google Patents

Abstract

PURPOSE: To obtain an inverter control AC resistance welding equipment capable of effectively utilizing thermal efficiency and improving welding speed by setting the oscillating frequency of a switching element in the prescribed range and lowering the frequency of trapezoidal wave AC of secondary side output of welding transformer lower than that of commercial power unit. CONSTITUTION: An oscillating frequency of the switching elements Q1 -Q4 , to which DC power from a rectifier circuit and smoothing circuit is supplied, is switched under 2-5KHz. At first, high frequency is made oscillate to left side for fixed interval and after oscillation of positive side it is oscillated in high frequency to negative side for fixed interval, trapezoidal wave AC is outputted to the secondary side N2 of welding transformer. A frequency of the trapezoidal wave AC is controlled lower than that of commercial power unit. To the tip of secondary side conducting bodies 5, 6 as the secondary winding N2 of welding transformer 4, electrodes 7, 8 are arranged. By placing electrodes 7, 8, at both side of a base material 9, resistance welding is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter-controlled AC resistance welding apparatus using an inverter circuit and a resistance welding method thereof.

[0002]

2. Description of the Related Art FIG. 14 shows a block circuit diagram of a conventional inverter type resistance welding apparatus, and FIG. 15 shows voltage and current waveforms of respective portions of FIG. The power source may be a single-phase alternating current, but in the illustrated example, a three-phase alternating current (50/60
Hz) is shown (see FIG. 15 (a)). 1 is a rectifier circuit consisting of a three-phase diode bridge circuit,
The rectifier circuit 1 rectifies (converts to DC) a three-phase alternating current as shown in FIG. The rectified output from the rectifying circuit 1 is smoothed by the smoothing circuit 2 including the smoothing capacitor C _0, and the inverter circuit 3 is supplied with DC power as a power source.

The inverter circuit 3 is composed of, for example, a full-bridge circuit composed of four switching elements, and the switching elements of each arm are alternately switched by a control circuit (not shown), as shown in FIG. A high frequency alternating current as shown in is output.
This high-frequency alternating current is applied to the primary winding N ₁ of the welding transformer 4 and is stepped down to a desired voltage, so that the welding transformer 4 has 2
It is output to the next winding N ₂ . Secondary winding N of welding transformer 4
₂ is a center composed of rectifying diodes D ₁ and D _2.
A tap type single-phase full-wave rectifier circuit is provided.

Secondary side conductors 5 and 6 are connected to the cathode side of the diodes D ₁ and D ₂ and the center tap of the secondary winding N ₂ , and a pair of secondary side conductors 5 and 6 are provided at the tips of the secondary side conductors 5 and 6. Electrodes 7 and 8 are provided. Then, the base material (for example, two plates) 9 is pressed by the electrodes 7 and 8 to switch the switching element of the inverter circuit 3 for several cycles of the commercial frequency to output the output of the welding transformer 4 to the diode D ₁ ,
And rectified by D ₂ performs resistance welding by flowing a period of time the base material 9 a direct current (welding current) as shown in FIG. 15 (d).

By the way, the above-mentioned inverter DC type and single-phase AC type already exist in the resistance welding apparatus, and they are appropriately used. The single-phase AC type eliminates the need for a rectifier on the secondary side of the welding transformer, and can be downsized accordingly.
Further, the greatest feature of the single-phase AC type is that the price of the entire apparatus is low because there is only an inexpensive thyristor, which is a switching element that also serves as output adjustment, on the primary side of the welding transformer. Therefore, the single-phase AC type resistance welding device is widely used. Further, as shown in FIG. 4, the AC type has a feature that the electrode life is long. FIG. 4 shows the relationship between the number of hitting points and the nugget diameter. The details will be described in the embodiment part.
800 times and constant voltage control inverter DC type 2900
The single-phase AC type has a longer electrode life of 3100 times compared to the number of times.

However, in the case of the inverter direct current type, the welding current range for forming the nugget is about 2 to 4 times that in the case of the single phase alternating current type, and the welding portion is splashed.
Stable welding with less heat generation is possible. Further, the welding current required to obtain a predetermined nugget diameter (4√t: t is the plate thickness) is, for example, from about 8700A in the single-phase AC system, and from about 5600A in the inverter DC system. Inverter DC type enables welding with lower welding current than single-phase AC type.

Therefore, the inverter DC type is often used from the viewpoint of welding in a stable current range and welding with a low welding current even though the cost of the apparatus is low. Especially, in terms of construction difficulty and welding quality, direct current without zero cross is advantageous for aluminum alloys with good heat conduction (wide welding current stable range).
The same is true when dislike of scatter.

[0008]

However, not only the inverter DC type having various advantages as described above, but also the single-phase or three-phase rectification type DC type electrodes 7 and 8 for supplying welding current are provided. Since the polarity of is fixed to plus and minus, there are many problems as shown below that do not appear in the AC type. The deformation of the tip of the electrode in contact with the object to be welded is biased to the anode and the contact area is expanded, so the current density is reduced, and therefore the electrode life is shorter than that of the AC type. The voltage drop in the rectifier results in power loss and consumes more power than the AC type. The price of the rectifier and the cooling plate for cooling this rectifier is high. Welding transformers can be made smaller and lighter, but since a rectifier and a cooling plate are required, the expected size and weight reduction cannot be achieved overall. The object to be welded may be magnetized and residual magnetism may result in poor quality. With an aluminum alloy or the like, the nugget may be biased in the plate thickness direction, resulting in poor quality or difficult welding. Depending on the type of plated steel sheet, welding may be difficult unless the polarities are reversed. As a phenomenon similar to the above, particularly in the case of series energization, surface states such as dents, dents, and burns may differ depending on the polarity, resulting in poor quality and difficult welding.

Therefore, in order to solve the above-mentioned problems, the applicant of the present invention has an inverter control AC resistance welding apparatus and an inverter control AC resistance welding apparatus having both advantages of an inverter DC resistance welding apparatus and an AC resistance welding apparatus. I have already applied for the resistance welding method. However, even in the inverter-controlled AC type, a new problem arises in that the rising of the welding current is poor and the heat loss is large. Also, when the rising and falling of the welding current is made steep, the current change there is large and the vibration noise caused by energization becomes unpleasant noise for the worker and its surroundings, deteriorating the work environment and shortening the life of the welding equipment. There was a problem that it had an adverse effect. Further, in the conventional seam welding in the single-phase AC type, the energization time and the dwell time depend on the frequency of the commercial power source, and there is a problem that the welding speed cannot be improved.

The present invention has been provided in view of the above points, and solves the problem in the inverter control DC type,
It is designed to have the characteristics of the single-phase alternating current type as well, in particular to improve the welding speed in seam welding, and
Provided is an inverter-controlled AC resistance welding device and its resistance welding method, in which the rising of the welding current is made steep to minimize the thermal loss, and furthermore, the vibration noise generated at the rising and the falling of the welding current is eliminated. The purpose is to do.

[0011]

Therefore, the first aspect of the present invention is described.
In the described inverter-controlled AC resistance welding device, a rectifier circuit 1 for rectifying a commercial power source, a smoothing circuit 2 for smoothing the output of the rectifier circuit 1, and a DC power source DC-converted by the smoothing circuit 2 are used as power sources. Supplied switching element Q ₁ ~
An inverter circuit 3 composed of Q ₄ and a welding transformer 4 to which the output of the inverter circuit 3 is applied to the primary winding N _1.
And a pair of electrodes 7 and 8 provided on both ends of the secondary side conductors 5 and 6 of the welding transformer 4 for resistance welding the base material 9 and the oscillation frequencies of the switching elements Q _{1 to} Q ₄ of the inverter circuit 3. The trapezoidal wave AC is output to the secondary side of the welding transformer 4 by switching at 2 to 5 KHz to oscillate on the positive side for a certain period of high frequency and after oscillating on the positive side for a certain period of high frequency oscillating. It is characterized by including an inverter control device 10 for controlling the frequency of the wave alternating current to be lower than the frequency of the commercial power source.

Further, in the inverter-controlled AC resistance welding method according to the second aspect, the rectifying circuit 1 for rectifying the commercial power source.
A smoothing circuit 2 for smoothing the output of the rectifying circuit 1, an inverter circuit 3 including switching elements Q _{1 to} Q ₄ to which a direct-current power source converted into a direct current by the smoothing circuit 2 is supplied as a power source, and the inverter circuit The output of 3 is the primary winding N ₁
Applied to the welding transformer 4, a pair of electrodes 7 and 8 provided on both ends of the secondary side conductors 5 and 6 of the welding transformer 4 for resistance welding the base material 9, and the switching element Q _{1 of the} inverter circuit 3. And an inverter control device 10 for switching Q ₄ at an oscillation frequency of ₂ to 5 KHz,
The above-mentioned inverter control device 10 causes the switching elements Q ₁ and Q ₂ of the inverter circuit 3 to oscillate on the positive side at a high frequency for a certain period of time, and then the switching element Q of the inverter circuit 3 is oscillated.
₃ , Q ₄ is oscillated on the negative side for a certain period of high frequency, and a trapezoidal wave alternating current having a frequency lower than the frequency of the commercial power source is output to the secondary side of the welding transformer 4 to resistance-weld the base material 9. Is characterized by.

Further, in the inverter-controlled AC resistance welding device according to the third aspect, the rectifying circuit 1 for rectifying the commercial power source.
A smoothing circuit 2 for smoothing the output of the rectifying circuit 1, an inverter circuit 3 including switching elements Q _{1 to} Q ₄ to which a direct-current power source converted into a direct current by the smoothing circuit 2 is supplied as a power source, and the inverter circuit The output of 3 is the primary winding N ₁
Applied to the welding transformer 4, a pair of electrodes 7 and 8 provided on both ends of the secondary side conductors 5 and 6 of the welding transformer 4 for resistance welding the base material 9, and the switching element Q _{1 of the} inverter circuit 3. ˜Q ₄ is switched by PWM control to oscillate on the positive side for a certain period of high frequency, and after oscillating on the positive side, oscillates for a certain period of high frequency on the negative side to output a trapezoidal wave AC to the secondary side of the welding transformer 4. The inverter control device 10 is provided, and the ON period width of the first pulse or a plurality of pulses from the first pulse at the start of each half cycle of the trapezoidal wave AC is widened.

The inverter-controlled AC resistance welding device according to the present invention is characterized in that the ON period width of the pulse after the trapezoidal wave AC rises is narrowed.

In the inverter-controlled AC resistance welding device according to the fifth aspect, a rectifying circuit 1 for rectifying a commercial power source, a smoothing circuit 2 for smoothing the output of the rectifying circuit 1, and a DC for the smoothing circuit 2. DC power is supplied as a power supply inverter circuit 3 consisting of the switching elements Q ₁ to Q ₄
And a welding transformer 4 to which the output of the inverter circuit 3 is applied to the primary winding N ₁ and a pair of resistance welding of the base material 9 provided at both ends of the secondary side conductors 5 and 6 of the welding transformer 4. The electrodes 7 and 8 and the switching elements Q _{1 to} Q ₄ of the inverter circuit 3 are switched by PWM control to oscillate on the positive side for a certain period of high frequency, and after oscillating on the positive side for a certain period of high frequency oscillating. An inverter control device 10 for outputting a trapezoidal wave alternating current is provided on the secondary side of the welding transformer 4, and at least one of the first part or a plurality of parts from the first falling part of each half cycle of the trapezoidal wave alternating current is provided. The feature is that the ON period width of the pulse is narrowed.

[0016]

SUMMARY OF According to the inverter control AC resistance welding apparatus according to claim 1, the oscillation frequency of the switching elements Q ₁ to Q ₄ is switched 2-5 kHz, also, the welding current of the secondary side output of the welding transformer 4 By making the frequency of the trapezoidal wave alternating current that is lower than the frequency of the commercial power source, the thermal efficiency can be effectively utilized. Furthermore, in the case of seam welding, compared to the conventional single-phase AC type, the energizing time and the dwell time can be set arbitrarily without depending on the frequency of the commercial power source, so the optimum frequency for welding can be selected. Can be improved by about 50% from the conventional one.

According to the inverter control AC resistance welding method of the second aspect, the switching elements Q _{1 to} Q _{4 are connected.}
Of the trapezoidal wave alternating current that becomes the welding current of the secondary side output of the welding transformer 4 is made lower than the frequency of the commercial power source, thereby effectively utilizing the thermal efficiency. be able to. Furthermore, in the case of seam welding, compared to the conventional single-phase AC type, the energizing time and the dwell time can be set arbitrarily without depending on the frequency of the commercial power source, so the optimum frequency for welding can be selected. Can be improved by about 50% from the conventional one.

Further, according to the inverter control AC resistance welding apparatus of the third aspect, the ON period width of the first pulse or a plurality of pulses from the first pulse at the start of each half cycle of the trapezoidal wave AC is widened. Therefore, the rising of the welding current can be made steep. As a result, the thermal loss at the rising and falling of the welding current can be minimized.

According to the inverter-controlled AC resistance welding device of the fourth aspect, the ON period width of the pulse is narrowed after the welding current sharply rises, thereby suppressing an increase in the welding current in the flat portion 23. be able to. As a result, thermal vibration can be prevented and the stable range of welding can be prevented from becoming narrow.

According to another aspect of the inverter-controlled AC resistance welding apparatus of the present invention, at least one pulse before the trailing edge of each trapezoidal AC half cycle or a plurality of pulses from the first pulse is turned on. Since the period width is narrowed, the trapezoidal wave alternating current can be rounded at least at the falling portion from the flat portion 23. Therefore, the change in the current at the falling portion of the welding current becomes relatively smooth, and as a result, the magnetic change also becomes smooth and the vibration noise can be reduced. Therefore, no unpleasant noise is given to the worker and the surroundings thereof, the working environment is not deteriorated, and the life of the welding equipment is not shortened.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. First, the overall configuration and welding method of the present invention will be described in detail.

FIG. 1 shows a block circuit diagram of the present invention, in which the welding transformer 4, the inverter circuit 3 and the like have the same construction as the conventional one, and 10 is an inverter control device for controlling the inverter circuit 3. Further, unlike the conventional configuration shown in FIG. 14, no rectifier (diodes D ₁ and D ₂ ) is used. The configuration for supplying power to the inverter circuit 3 is similar to that of the conventional example shown in FIG.
The smoothing circuit 2 is not shown.

The inverter circuit 3 is composed of a full bridge circuit of _four switching elements Q _{1 to} Q ₄ .
The switching elements Q _{1 to} Q ₄ are, for example, IGBTs (Ins
It is composed of semiconductor switching devices such as ulated gate bipolar transistor) and transistors. The primary winding N ₁ of the welding transformer 4 is interposed between the connection points of the switching elements Q ₁ and Q ₄ and Q ₃ and Q ₂ , and the secondary side of the welding transformer 4 as the secondary winding N ₂ Electrodes 7 and 8 are provided at the tips of the conductors 5 and 6, respectively. And the base material 9
The electrodes 7 and 8 are arranged on both sides of, and resistance welding is performed as is well known.

As shown in FIG. 1, the inverter control device 10 includes a basic timing generation circuit 11, a PWM circuit 12, a driver 13, a waveform shaping circuit 14, a bias magnetic prevention circuit 15,
It is composed of an A / D converter 16, a correction circuit 17, a command circuit 18, and the like. In addition, the correction circuit 17 and the command circuit 1
8 is actually performed by software.
The output of the driver 13 is the switching element Q ₁ ~
It is input to the base of Q ₄ respectively, and driver 1
The switching signals Q _{1 to} Q ₄ are switching-controlled by the output signal of 3. Further, a current transformer 21 is provided on the primary winding N ₁ side of the welding transformer 4, that is, the output side of the inverter circuit 3, and the output thereof is input to the waveform shaping circuit 14.

The basic timing generating circuit 11 is a circuit for outputting a frequency within a predetermined range so as to oscillate the switching elements Q _{1 to} Q ₄ of the inverter circuit 3 at a high frequency. It is possible to oscillate. The PWM circuit 12 controls the ON period width of the switching elements Q _{1 to} Q ₄ so that a predetermined voltage value or a predetermined current value is obtained during welding, and the switching elements Q _{1 to} Q ₄ are Q ₁ and Q ₂ ,
Q ₃ and Q ₄ have a function of controlling on / off, respectively, and the output from the PWM circuit 12 alternately turns on the switching elements Q ₁ and Q ₂ and Q ₃ and Q ₄ via the driver 13. The drive is controlled to turn off.

Switching element Q _{1 of the} inverter circuit 3
Output current of the welding transformer 4 by the switching operation of the to Q ₄ is a trapezoidal wave alternating current, as described below, illustrating the overall operation of the block circuit diagram shown in FIG. 1 in front. First, the operator presets the switching frequencies of the switching elements Q _{1 to} Q _{4 and} the frequency of the trapezoidal wave AC, and a signal corresponding to the set values is input to the PWM circuit 12 via the correction circuit 17 and the command circuit 18. , The PWM circuit 12 via the driver 13 the switching elements Q ₁ , Q ₂ (or Q ₃
, Q ₄ ) is switched. When the inverter circuit 3 is subjected to constant current control, the secondary output of the current transformer 21 is input to the A / D converter 16 via the waveform shaping circuit 14, and the detected value is input to the correction circuit 17. Then, the correction circuit 17 compares the set value with the detected value and controls the PWM circuit 12 via the command circuit 18 so that the current becomes a constant current, thereby controlling the ON period width of the switching elements Q _{1 to} Q ₄ . In this case, the current value set on the primary side of the welding transformer 4 is controlled. Of course, the current value can be set arbitrarily.

On the other hand, the output from the waveform shaping circuit 14 is also input to the magnetic bias prevention circuit 15 in order to prevent the magnetic bias phenomenon of the welding transformer 4, and the magnetic bias prevention circuit when the welding transformer 4 is about to reach magnetic saturation. PWM circuit 12 at the output of 15
The thereby preventing the excessive current from flowing to the switching element Q ₁ to Q ₄ is controlled so that the ON period width of the switching element Q ₁ to Q ₄ is small, the switching elements Q ₁ to Q
Preventing ₄ from destroying. Further, in the case of constant voltage control, a pulse transformer is connected in parallel with the primary winding N ₁ of the welding transformer 4, the output voltage on the secondary side of the pulse transformer is detected, and the detected output is corrected circuit 17 side. To perform constant voltage control.

Here, FIG. 2A shows the output voltage of the inverter circuit 3, and FIG. 2B shows the output current of the welding transformer 4. During the period from time t ₁ to time t ₂ shown in FIG. 2, the switching elements Q ₁ and Q _{2 of the} inverter circuit 3 are turned on and off at the switching frequency of 10 KHz, and the switching elements Q ₃ and Q ₄ of the other arm are turned off. There is. Next, during the period from time t ₂ to time t ₃ , the switching elements Q ₁ and Q ₂ are off, and the switching element Q 1
₃ and Q ₄ are turned on and off at a switching frequency of 10 KHz. Then, this switching operation is repeated for a predetermined number of cycles of the commercial power source to weld the base material 9. That is, the polarity output current at time t ₁ ~ time t ₂ the welding transformer 4 in FIG. 2 is a positive polarity (positive side DC current) and the output current at time t ₂ ~ time t ₃ the welding transformer 4 is negative (DC current on the negative side). Therefore, the output current of the welding transformer 4 as a whole becomes a trapezoidal wave alternating current as shown in FIG.
Resistance welding.

The output current of the welding transformer 4, that is, the frequency of the trapezoidal wave AC, is 100 to 100 times, which is 2 to 5 times the frequency of the commercial power source so that the cycle control of the commercial power source conventionally used conventionally can be performed. It is set to 300 Hz. In the case shown in FIG. 2, the frequency of the trapezoidal wave AC is doubled to 100
Since it is set to Hz (or 120 Hz), 100 Hz
In the case of, one cycle is 10 msec, and in the case of 120 Hz, it is 8.3 msec. Therefore, since the cycle control of the commercial power source can be performed, the operator does not feel any discomfort like the conventional apparatus.

As described above, the frequency of the trapezoidal wave alternating current is intended to eliminate the discomfort for the user's operation by inheriting the cycle control of the commercial power source which is the time setting unit of the conventional control device. Technically, it is not limited to this. Therefore, the frequency of the trapezoidal wave alternating current of the secondary output of the welding transformer 4 may be variably controlled in units of 1 Hz as long as it is between 100 Hz and 300 Hz within the range of 2 to 5 times that of the commercial power source. is there. Further there as can be set to any frequency within the switching frequency of the switching elements Q ₁ to Q ₄ of the inverter circuit 3 also show 10～30KHz. This switching frequency is 10
-30 KHz is set so that a large number of pulses are provided in each of the positive side and negative side of the trapezoidal wave AC, and when the magnetic saturation occurs in the welding transformer 4, the output current is changed by the first plurality of pulses. The main reason is to control in the direction of squeezing and enable constant current or constant voltage control with the remaining pulses. Thus it becomes easy to control the magnetic deviation phenomena of the welding transformer 4, it is possible to prevent destruction of the switching elements Q ₁ to Q _4.

Here, FIG. 3 shows the time required to reach the nugget forming temperature of the base material 9 for each welding method.
In the so-called capacitor type, the time to reach the nugget formation temperature is P ₁ which is the earliest, because the discharge is performed all at once. The second fastest is the conventional inverter-controlled DC type, which is P ₂ .
However, this DC type inverter control has many problems as described in the conventional example. Although the inexpensive single-phase AC type does not have the problem in the inverter-controlled DC type, it is P ₃ which takes the slowest time to reach the nugget formation temperature. Further, the single-phase AC type also has a problem that a high welding current is required and the range of stable welding current is narrow as described in the conventional example. Therefore, the time P ₄ to reach the nugget formation temperature in the trapezoidal-wave AC system according to the present invention has a characteristic that is substantially similar to that in the case of the inverter control DC system, but is slightly slower, but is relatively early when compared to the case of the single-phase AC system. Reach the nugget formation temperature.

FIG. 4 shows the relationship between the number of spots and the nugget diameter in the galvannealed steel sheet. The electrode life is 1800 times in the conventional constant current type inverter control DC type and 2900 in the constant voltage type inverter control DC type. Times, 3100 times in the conventional alternating current method. However, in the trapezoidal wave AC type of the present invention, the life is greatly extended to 3900 times. This is because the trapezoidal wave AC type does not bias the polarity of the electrodes and enables welding with a lower welding current compared to the AC type.

Further, in the trapezoidal wave AC type, since a DC welding current flows alternately in positive and negative directions, compared to the case of the single-phase AC type, welding is performed in a DC type for a fixed period, so that a low welding current is used. Welding becomes possible, and compared to the single-phase AC type, stable welding with less dispersion of the welded portion is possible over a wider range of welding current. Further, in the trapezoidal wave AC type, unlike the conventional case, the rectifier on the secondary side of the welding transformer 4 is not required, the power loss due to the voltage drop in the rectifier is eliminated, and the welding current can be lower than that of the AC type. Therefore, the power consumption can be significantly reduced. Further, in the trapezoidal wave AC type of the present invention, the rectifier and the cooling plate for cooling the rectifier are not required, so that the size and weight can be reduced.

In the conventional inverter-controlled direct current type, since the polarity of the electrodes is fixed, the object to be welded may be magnetized, resulting in poor quality due to residual magnetism. Since welding can be performed with a welding current lower than that of the conventional AC type, the residual magnetism can be made equal to or less than the AC type, and quality defects due to the residual magnetism can be prevented.

Further, conventionally, in the inverter-controlled direct current type, in the case of aluminum alloy or the like, the nugget was unevenly distributed in the plate thickness direction and the quality was poor, and welding was difficult in some cases. Similarly to, the nugget can be welded without being biased in the plate thickness direction, the occurrence of defects can be prevented, and the welding can be easily performed. Further, in the conventional inverter-controlled direct current type, welding may be difficult unless the polarities are reversed depending on the type of plated steel sheet.However, in the trapezoidal wave alternating current type of the present invention, the polarity is constant at a fixed period because it is trapezoidal wave alternating current. Since it is reversed, welding can be easily performed regardless of the type of plated steel sheet. Especially when the series is energized,
Since the polarities are reversed at regular intervals, the surface states such as dents, dents, and burns do not differ, and the occurrence of defects is prevented and welding becomes easy.

Further, a general inverter-controlled DC type requires a controller and a dedicated welding transformer, but in the trapezoidal wave AC type, the welding transformer for the conventional AC type can be used, so that the range of application is limited. It is possible to reduce the equipment cost widely. For example, in the case where the AC welding machine currently used is a trapezoidal wave AC type of the present invention to improve weldability, the control device is a conventional trapezoidal wave AC type (the inverter control device of the present invention). ). Therefore, the cost of the welding transformer alone and the cost of exchanging the welding transformer are unnecessary, the construction period is shortened, and the economic effect is extremely large.

FIG. 5 shows another embodiment of the inverter circuit 3, which is constructed by a half bridge. That is,
An inverter circuit is composed of the switching elements Q ₁ and Q ₂ and the capacitors C ₁ and C ₂ . The configuration of the inverter circuit 3 used in the present invention may be either the full bridge shown in FIG. 1 or the half bridge shown in FIG. 5. For example, a large capacity machine (200 V system, 15 kVA, 4
The 00V system may be used as a full bridge at about 30 kVA) and as a half bridge below this.

As the operation of the switching elements Q _{1 to} Q ₄ of the inverter circuit 3 shown in FIG. 1, the switching elements Q ₁ and Q ₂ or Q ₃ and Q ₄ are simultaneously switched. The element Q ₁ is turned on, and the switching element Q _{2 is set} to a high frequency (10
KHz) may be used for switching.

Further, the present invention can be applied to the commercial power source of the present welding apparatus, whether it is single-phase alternating current or three-phase alternating current. In the case of three-phase alternating current, the power supply equipment can be constructed inexpensively. The reason for this is as follows. In other words, the equipment and parts used for power supply facilities with a relatively large capacity, because the load is mainly a three-phase AC machine,
Three-phase specifications are standard, and single-phase specifications are special and expensive. The wiring in a general production factory is three-phase, and if a single-phase load is connected to this three-phase equipment, the voltage drop will increase, and there is a high possibility that other equipment will be adversely affected. In order to avoid this, a single-phase equipment different from the above three-phase equipment is required. If the welding machine has a three-phase input, additional work is not required if the capacity is large, and if the capacity is insufficient, it is sufficient to reinforce only the insufficient part, so that the overall cost is low.
Furthermore, if the impedance of the line of the electric power company is large, there is a risk of voltage flicker, and the magnitude of the three-phase line current is 1 / √3 of single phase, and the margin for voltage flicker becomes large.

(Embodiment 2) As described above, the characteristics of the above-mentioned inverter control AC type, that is, trapezoidal wave AC, have the disadvantages of the DC type due to the high speed precision control and smooth welding current which are the characteristics of the inverter type. It is a welding machine that has the advantages of an AC type by eliminating it. The ideal shape of a smooth welding current in the AC type is a rectangular wave, but due to the resistance component R and the reactance component L of the welding circuit, the welding current has rise time and fall time. Although not all of these times,
It is not preferable because the heat generation at the welding point is reduced. Therefore, if the oscillation frequency of the trapezoidal wave AC is lowered, the number of times is reduced and the thermal efficiency is improved as a result, but in this case, the iron core of the welding transformer must be increased.

By the way, FIG. 6 shows a welding current in seam welding in a single-phase AC system and a nugget 22 formed by the welding current. As shown in FIG. 6A, the normal seam welding is performed with the energization time set to two cycles of the commercial power supply and the rest time (cooling time) set to one cycle of the commercial power supply. Here, one nugget 22 is formed in one energization time,
The downtime is necessary to prevent shunting to the prefabricated nugget 22. Nugget 22
In the case of seam welding, the electrodes are continuously formed without being removed because the electrode is a disk and a welding current flows not only directly below but also directly below and before and after it.

The seam welding described above is a method of repeatedly energizing and pausing while moving the welding position. In seam welding in the conventional single-phase AC type, the timing of energizing and pausing depends on the frequency of the commercial power source. I have to do it.
That is, the energization time and the dwell time in the AC seam welding are determined by the half cycle of the frequency of the commercial power source or the number of cycles, and the energization time and the dwell time cannot be arbitrarily set. Therefore, the energization cycle must be a half cycle, one cycle, or several continuous cycles of the frequency of the commercial power source (50 Hz or 60 Hz). The welding conditions of seam welding include welding time in addition to energization time in spot welding, welding current and welding pressure.There is a close relationship between the timing depending on this frequency and the welding speed, which hinders speedup. ing.

Therefore, in this embodiment, the energization time and the rest time in seam welding can be set arbitrarily,
It is designed to increase the welding speed. First, the oscillation frequency of the switching elements Q _{1 to} Q ₄ of the inverter circuit 3 controlled by the command circuit 18 and the PPM circuit 12 shown in FIG. The frequency is the frequency of the commercial power source (50
Hz or 60 Hz). Note that these control and the oscillating frequency of the switching elements Q ₁ to Q _4, control of the output frequency of the trapezoidal wave alternating is performed by inverter control device 10.

In FIG. 7, the frequency of the trapezoidal wave AC itself is, for example, 25 Hz (40 msec) or 30 Hz (33.3).
msec). The energization time in seam welding is set to one cycle of trapezoidal wave AC, and the rest time is set to an arbitrary time (for example, one cycle same as trapezoidal wave AC). The dwell time that is all the switching elements Q ₁ to Q ₄ of the inverter circuit 3 off, it is possible to set an arbitrary time. The unit of the energization time of the inverter control alternating current is the time during which the on-off of the switching elements Q ₁ to Q ₄ by varying, can be arbitrarily set. In particular, the oscillation frequency of the switching elements Q _{1 to} Q ₄ is set lower than that of the previous embodiment, and the frequency lower than the frequency of the commercial power source (25 Hz or 30 H in this example).
By adopting z), the number of transitions from the positive side to the negative side and from the negative side to the positive side is reduced as compared with the case where the frequency is higher than the frequency of the commercial power supply, and the heat efficiency can be more effectively utilized. .

Here, the frequency of the trapezoidal wave AC is set lower than the frequency of the commercial power source from the viewpoint of effectively utilizing the thermal efficiency, but from the frequency where the frequency is lowered and the disadvantage of the inverter DC system does not occur. , Just before the frequency of the commercial power supply (50 Hz or 60 Hz). Within the range of the frequency, it can be set every 1 Hz, and trapezoidal wave alternating current of any frequency can be used. When decreasing the frequency of the trapezoidal wave AC, it is necessary to increase the cross-sectional area of the iron core of the welding transformer 4. Further, it is possible to set an arbitrary time separately from the energization time and the rest time shown in FIG. 7 (b).

In this way, in this embodiment, the oscillation frequency of the switching elements Q _{1 to} Q ₄ of the inverter circuit 3 is set to 2 to 5 KHz, which is lower than that in the previous embodiment, and the frequency of the trapezoidal wave AC is set to be higher than that of the commercial power source. By making it low, the thermal efficiency at the time of welding can be utilized more effectively. Further, in the inverter control AC type, the energization time and the rest time can be arbitrarily set, so that the optimum frequency for welding can be selected and the welding speed in seam welding can be increased. In the experimental example, the welding speed could be increased by about 50% as compared with the case of the conventional single-phase AC type.

(Embodiment 3) The on / off control of the switching elements Q _{1 to} Q ₄ of the inverter circuit 3 shown in FIG. 1 is PWM-controlled by the PPM circuit 12, and the on period of the switching elements Q _{1 to} Q ₄ is on. The width is the same for each pulse. This state is shown in FIG. The switching elements Q ₁ , Q ₂ or Q ₃ , Q ₄ are on / off controlled by pulses p _{1 to pn} on the positive side or the negative side, respectively, and these pulses p _{1 to pn} are the same as shown in the figure. The pulse has an ON period width and the frequency is the same.
Therefore, as shown in FIG. 8, the rising of the welding current is slow and the thermal loss here is large.

As shown in FIG. 8A, the pulses p _{1 to} p
_Since all _n have the same on period width, the first pulse p ₁
The welding current did not rise sharply, and the following pulse p ₂ ,
p ₃ ... As a result,
As shown in, the welding current has a long rise. As described above, in the normal PWM control, the fundamental oscillation frequency is preset, so even if the pulse width is widened to the maximum, there is an off period between the pulses, but there is an off period so that the current rises. There is a problem of making it longer.

Therefore, in this embodiment, as shown in FIG.
The frequency of the first pulse p ₁ or the first pulse p ₁ and the second pulse p ₂ is lowered, and the ON period width of the pulse is widened so that the rise of the current is made steep. In other words, in order to shorten the rise time and fall time of the welding current, the basic oscillation frequency of the inverter control should be different until the welding current rises to the set value at the start of each half cycle of trapezoidal wave AC (from the basic oscillation frequency (Lower) to make the pulse width suitable for the set current and load. In FIG. 9A, the ON period width of the _first pulse p ₁ and the second pulse p ₂ is made wider than the subsequent pulses p ₃ ... It is designed to rise sharply to the set value.

[0050] Of course it stand up to the welding current in one second pulse p ₁ is steep, a pulse with at ON period width may only pulse p _1. Further, the ON period width of three or more pulses may be widened until a desired rising edge is obtained.

Here, in order to obtain a steep rising characteristic of the welding current, the pulse p ₁ or the pulse p is used in this embodiment.
_The frequency is controlled to be low in order to make the ON period width of ₁ and p ₂ wider than the ON period width of other pulses p ₃ ...
It has control. Incidentally, as long afford the desired rise characteristic of the welding current, a constant frequency pulse p ₁ ~p _n, the pulse p ₁ or pulse p ₁ by PWM control,
The ON period width of p ₂ may be widened.

As described above, in this embodiment, the rising of the welding current can be made steep by widening the ON period width of the pulse at the start of each half cycle of the trapezoidal wave AC. As a result, the thermal loss at the rising and falling of the welding current can be minimized. Since the steepness of the trapezoidal wave AC is steep without any particular control, the steep rise of the trapezoidal wave AC minimizes the thermal loss at the rise and the fall of the trapezoidal AC. it can.

Further, in FIG. 9A, the ON period width of the pulse p _n before the falling edge is set to the other pulse p ₃ ,
Although p ₄ illustrates narrower than ..., 1 the measured example where the pulse p ₃ ~ pulse p _n all same ON period width
It is shown in 0 (a). Since the ON period width of the pulse p ₃ ~ pulse p _n after rises welding current trapezoidal wave alternating current is the same, is gradually increased to the flat portion 23 falling portion of the welding current. The welding current in the flat portion 23 of the trapezoidal wave increases due to the accumulation of magnetic energy in the welding circuit in the constant current control. The increase in the welding current in the flat portion 23 of the trapezoidal wave causes thermal vibration and narrows the welding stable range.

Therefore, in order to prevent the welding current from increasing in the flat portion 23 of the trapezoidal wave, the ON period width of the pulse after the rising of the welding current is narrowed as shown in FIG. 9A.
By narrowing the ON period width of the pulse p ₄ subsequent pulse p ₅ ~ pulse p _n in the illustrated example, is prevented an increase of the welding current of the flat portion 23 of the trapezoidal wave. FIG. 10B shows the waveform (measurement example) of the trapezoidal wave welding current (output current) in this state.
The control of the ON period width of these pulses may be PWM control or the above-mentioned FM modulation control. As described above, in this embodiment, the increase of the welding current in the flat portion 23 of the trapezoidal wave is suppressed, so that the thermal vibration is prevented and the stable range of welding is prevented from being narrowed.

(Embodiment 4) Unlike the inverter control AC type (trapezoidal wave AC type) of the present invention, in the conventional or general single-phase AC type, phase control is performed by a thyristor on the primary side of the welding transformer. However, since the waveform of the welding current is a continuous or intermittent sine wave, the current change is relatively smooth. As a result, the magnetic changes are smooth and the vibration noise is relatively low. However, when the rising and falling edges of the welding current are made steep as in the third embodiment, or in the case of the normal trapezoidal wave AC shown in FIG. 11, the rising and falling edges are relatively steep. Therefore, the current change at the rising and falling parts of the welding current is large,
A vibrating sound is generated due to energization, and the vibrating sound becomes unpleasant noise for the worker and its surroundings, deteriorating the working environment and adversely affecting the life of the welding equipment. That is, the above-mentioned vibration causes loosening and fatigue around the welding transformer, the secondary conductor for passing the welding current, and the surroundings of the machine body, and causes the mechanical life to be shortened.

Therefore, in the present embodiment, as shown in FIG. 12A, the pulse width at the end of each half cycle of the trapezoidal wave AC or at the end thereof is made narrower than the other pulses to flatten the rising of the trapezoidal wave. The part reaching the part 23 and the part falling from the flat part 23 are rounded. Here, the number of pulses for rounding the falling of the welding current is not particularly limited, and by narrowing the width of an appropriate number of pulses, the rounding of the welding current is rounded. Therefore, it is good if vibration does not occur.

It should be noted that the portion from the actual rising of the welding current to the flat portion 23 has a rounded shape as shown in FIG. 10, and the portion that actually needs countermeasures is the portion from the flat portion 23 to the falling portion. is there. Therefore, in this embodiment, FIG.
As shown in FIG. 2 (a), the width is narrowed by the pulse corresponding to the falling portion of the trapezoidal wave. Of course, if the trapezoidal wave has a steep rising edge, the rising portion should be rounded to some extent in consideration of the steep rising edge and the occurrence of vibration. The control of the ON period width of these pulses may be PWM control or the above-mentioned FM modulation control.

By thus rounding the portion from the rising of the welding current to the flat portion 23 and the portion from the flat portion 23 to the falling of the welding current, the current change becomes relatively smooth, resulting in a magnetic change. Also makes it possible to reduce the vibration noise. Therefore, no unpleasant noise is given to the worker and the surroundings thereof, the working environment is not deteriorated, and the life of the welding equipment is not shortened. It should be noted that since the rising and falling portions of the welding current are slightly rounded, they have a slight influence on the stable range of welding, but since the influence is about 5 to 10%, there is no particular problem.

FIG. 13 shows the input characteristics when electrodes are short-circuited in various power supply systems. The same welding machine is used, and the power supply system is a single-phase AC system, an inverter DC system, an inverter control AC system of the present invention (trapezoidal wave). The input power (kVA) and power consumption (kW) are measured for the case of the AC type.
The short-circuit current can be up to 20 kA in the single-phase AC system, but can be up to 24 kA in the trapezoidal AC system. It is up to 21kA in the inverter DC type. The input kVA of the trapezoidal wave AC type is also smaller than that of the single-phase AC type. Further, the power consumption (kW) of the trapezoidal wave AC type is about 20 kW lower than that of the inverter DC type.

The switching control of the switching elements Q _{1 to} Q ₄ in each of the above-described embodiments is performed by the inverter control device 10 respectively. Further, in each of the above Examples 1 to 4, each has been described as a preferred example, but
Two or more embodiments may be combined.

[0061]

According to the inverter-controlled AC resistance welding apparatus of the first aspect, the trapezoidal wave that causes the switching element to switch the oscillation frequency at 2 to 5 KHz and serves as the welding current of the secondary side output of the welding transformer. By making the frequency of the alternating current lower than the frequency of the commercial power source, the thermal efficiency can be effectively utilized. Furthermore, in the case of seam welding, compared to the conventional single-phase AC type, the energizing time and the dwell time can be set arbitrarily without depending on the frequency of the commercial power source, so the optimum frequency for welding can be selected. Can be improved by about 50% from the conventional one.

Further, according to the inverter control AC resistance welding method of the second aspect, the trapezoidal wave which causes the oscillation frequency of the switching element to be switched at 2 to 5 KHz and serves as the welding current of the secondary side output of the welding transformer. By making the frequency of the alternating current lower than the frequency of the commercial power source, the thermal efficiency can be effectively utilized. Furthermore, in the case of seam welding, compared to the conventional single-phase AC type, the energizing time and the dwell time can be set arbitrarily without depending on the frequency of the commercial power source, so the optimum frequency for welding can be selected. Can be improved by about 50% from the conventional one.

Further, according to the inverter control AC resistance welding apparatus of the third aspect, the ON period width of the first pulse or a plurality of pulses from the first pulse at the start of each half cycle of the trapezoidal wave AC is widened. Therefore, the rising of the welding current can be made steep. As a result, the thermal loss at the rising and falling of the welding current can be minimized.

According to the inverter-controlled AC resistance welding device of the fourth aspect, the ON period width of the pulse is narrowed after the welding current sharply rises, thereby suppressing an increase in the welding current at the flat portion. You can As a result, thermal vibration can be prevented and the stable range of welding can be prevented from becoming narrow.

According to the inverter control AC resistance welding apparatus of the fifth aspect of the present invention, at least the first pulse before the trailing edge of each half cycle of the trapezoidal wave AC or the plurality of pulses from the first pulse are turned on. Since the period width is narrowed, at least the flat portion of the trapezoidal wave alternating current can be rounded from the flat portion. Therefore, the change in the current at the falling portion of the welding current becomes relatively smooth, and as a result, the magnetic change also becomes smooth and the vibration noise can be reduced. Therefore, no unpleasant noise is given to the worker and the surroundings thereof, the working environment is not deteriorated, and the life of the welding equipment is not shortened.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a welding apparatus according to an embodiment of the present invention.

FIG. 2A is a waveform diagram of the output voltage of the inverter circuit according to the embodiment of the present invention. (B) is a waveform diagram of the output current of the welding transformer of the embodiment of the present invention.

FIG. 3 is a diagram showing an energization time in each welding method until reaching a nugget formation temperature.

FIG. 4 is a diagram showing an electrode life in each welding method.

FIG. 5 is a circuit diagram showing another embodiment of the inverter circuit of the present invention.

FIG. 6 (a) is a waveform diagram when seam welding is performed with a single-phase AC type. (B) is a figure which shows the nugget at the time of performing seam welding by a single phase alternating current system.

FIG. 7A is a waveform diagram of the output voltage of the inverter circuit according to the second embodiment of the present invention. (B) is a waveform diagram of the output current of the welding transformer of the second embodiment of the present invention.

FIG. 8A is a waveform diagram of the output voltage of the inverter circuit for explaining the problem in the third embodiment of the present invention.
(B) is a waveform diagram of the output current of the welding transformer for explaining the problem in the third embodiment of the present invention.

FIG. 9A is a waveform diagram of the output voltage of the inverter circuit according to the third embodiment of the present invention. (B) is a waveform diagram of the output current of the welding transformer of the third embodiment of the present invention.

FIG. 10A is a waveform diagram of the output current of the welding transformer according to the third embodiment of the present invention. (B) is a waveform diagram of the output current of the welding transformer when the increase of the welding current in the flat part of Example 3 of the present invention is prevented.

FIG. 11 is a waveform diagram of a normal trapezoidal wave AC according to the embodiment of this invention.

FIG. 12A is a waveform diagram of the output voltage of the inverter circuit according to the fourth embodiment of the present invention. (B) is Embodiment 4 of the present invention
FIG. 6 is a waveform diagram of the output current of the welding transformer of FIG.

FIG. 13 is a characteristic diagram showing input characteristics in a power supply short circuit of various power supply systems according to an embodiment of the present invention.

FIG. 14 is a block circuit diagram of a conventional welding device.

15 (a) to 15 (d) are diagrams showing waveforms of respective portions shown in FIG. 14 of a conventional example.

[Explanation of symbols]

1 Rectifier Circuit 2 Smoothing Circuit 3 Inverter Circuit 4 Welding Transformer 5 Secondary Side Conductor 6 Secondary Side Conductor 7 Electrode 8 Electrode 9 Base Material 10 Inverter Controller 23 Flat Part Q _{1 to} Q ₄ Switching Element

Claims (5)

[Claims] 1. A rectifier circuit (1) for rectifying a commercial power supply,
Smoothing circuit (2) for smoothing the output of this rectifier circuit (1)
And the DC power source converted to DC by the smoothing circuit (2) is supplied as a power source to the switching elements (Q ₁ ) to (Q ₄ ).
An inverter circuit (3), a welding transformer (4) to which the output of the inverter circuit (3) is applied to the primary winding (N ₁ ), and a secondary side conductor (5) of the welding transformer (4). ) A pair of electrodes (7) and (8) provided at both ends of (6) for resistance welding the base material (9) and the oscillation frequencies of the switching elements (Q ₁ ) to (Q ₄ ) of the inverter circuit (3). 2 to 5 KHz of the welding transformer (4) by performing high-frequency oscillation on the positive side for a certain period of time by switching at a frequency of 2 to 5 KHz, and oscillating on the negative side for a certain period of time after oscillation of the positive side.
An inverter control AC resistance welding apparatus, comprising: an inverter control device (10) for outputting a trapezoidal wave AC to the next side and controlling the frequency of the trapezoidal wave AC to be lower than the frequency of a commercial power source. 2. A rectifying circuit (1) for rectifying a commercial power source,
Smoothing circuit (2) for smoothing the output of this rectifier circuit (1)
And the DC power source converted to DC by the smoothing circuit (2) is supplied as a power source to the switching elements (Q ₁ ) to (Q ₄ ).
An inverter circuit (3), a welding transformer (4) to which the output of the inverter circuit (3) is applied to the primary winding (N ₁ ), and a secondary side conductor (5) of the welding transformer (4). ) A pair of electrodes (7) and (8) provided at both ends of (6) for resistance welding the base material (9) and the switching elements (Q ₁ ) to (Q ₄ ) of the inverter circuit (3) are 2 to 5
An inverter control device (10) for switching at an oscillation frequency of KHz, and the inverter control device (10) causes the switching elements (Q ₁ ) (Q ₂ ) of the inverter circuit (3) to oscillate at a high frequency for a certain period of time. Let
After that, the switching element (Q
₃ ) (Q ₄ ) is oscillated on the negative side for a certain period of high frequency, and a trapezoidal alternating current with a frequency lower than the frequency of the commercial power source is output to the secondary side of the welding transformer (4) to resist the base material (9). An inverter-controlled AC resistance welding method characterized by welding. 3. A rectifier circuit (1) for rectifying a commercial power source,
Smoothing circuit (2) for smoothing the output of this rectifier circuit (1)
And the DC power source converted to DC by the smoothing circuit (2) is supplied as a power source to the switching elements (Q ₁ ) to (Q ₄ ).
An inverter circuit (3), a welding transformer (4) to which the output of the inverter circuit (3) is applied to the primary winding (N ₁ ), and a secondary side conductor (5) of the welding transformer (4). ) A pair of electrodes (7) and (8) provided at both ends of (6) for resistance welding the base material (9) and the switching elements (Q ₁ ) to (Q ₄ ) of the inverter circuit (3) are PWM.
An inverter control device for switching by control to cause high-frequency oscillation on the positive side for a certain period and for high-frequency oscillation on the negative side for a certain period after the oscillation on the positive side to output trapezoidal wave AC to the secondary side of the welding transformer (4). And (10), wherein the ON period width of the first pulse or a plurality of pulses from the first pulse at the start of each half cycle of the trapezoidal wave AC is widened. apparatus. 4. The inverter control AC resistance welding apparatus according to claim 3, wherein the ON period width of the pulse after the trapezoidal wave AC rises is narrowed. 5. A rectifier circuit (1) for rectifying a commercial power source,
Smoothing circuit (2) for smoothing the output of this rectifier circuit (1)
And the DC power source converted to DC by the smoothing circuit (2) is supplied as a power source to the switching elements (Q ₁ ) to (Q ₄ ).
An inverter circuit (3), a welding transformer (4) to which the output of the inverter circuit (3) is applied to the primary winding (N ₁ ), and a secondary side conductor (5) of the welding transformer (4). ) A pair of electrodes (7) and (8) provided at both ends of (6) for resistance welding the base material (9) and the switching elements (Q ₁ ) to (Q ₄ ) of the inverter circuit (3) are PWM.
An inverter control device for switching by control to cause high-frequency oscillation on the positive side for a certain period and for high-frequency oscillation on the negative side for a certain period after the oscillation on the positive side to output trapezoidal wave AC to the secondary side of the welding transformer (4). And (10), wherein the ON period width of a plurality of pulses is narrowed from the first one before the at least falling portion of each half cycle of the trapezoidal wave alternating current or the first one. AC resistance welding equipment.