JPH06656A - Welding transformer for inverter type dc resistance welding equipment - Google Patents

Abstract

PURPOSE:To provide the miniature and lightweight welding transformer for the inverter type DC resistance welding equipment capable of obtaining the efficient welding transformer by designing the welding transformer based on the correlation between the ratio of the number of windings of the welding transformer and the current variation in rising and falling of a primary current. CONSTITUTION:The relation between the current variation DELTAI1/DELTAt in the rise time Tr and the fall time Tf of the primary current I1 and the ratio N of the number of windings is made to (DELTAI1/DELTAt)=V1/(kN<2>) and based on this expression, a value of the current variation >=I1/DELTAt is set from the ratio N of the number of windings, by which the maximum frequency fmax which can be taken by the primary current I1 can be obtained. The transformer weight can be easily obtained from the maximum frequency fmax which can be taken by the primary current I1 obtained in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding transformer of an inverter type direct current resistance welding apparatus, and more particularly to a welding transformer of an inverter type direct current resistance welding apparatus which can be reduced in size and weight.

[0002]

2. Description of the Related Art In the industrial field, an inverter type DC resistance welding apparatus is widely used for welding various works. However, this type of welding apparatus is used to reduce the cost and space of the apparatus. There is a demand for smaller and lighter welding transformers.

The inverter type DC resistance welding apparatus is usually provided with a converter circuit, an inverter circuit, a welding transformer circuit, a welding gun section, a control circuit, etc., and a control signal of welding current is output from the control circuit to the inverter circuit. However, by increasing the frequency of this control signal and the frequency of the primary current supplied to the welding transformer, it is known that the cross-sectional area of the core of the welding transformer can be reduced and the welding transformer can be miniaturized. (See FIG. 6).

A technical idea for downsizing a welding transformer by varying the frequency of a control signal output to the inverter circuit according to the type of work is disclosed in Japanese Patent Laid-Open No. 63-273575 entitled "Inverter DC Resistance". Welder ".

[0005]

However, in the method for reducing the size of the welding transformer by increasing the frequency of the control signal in the above-mentioned conventional technique, the leakage inductance of the welding transformer and the resistance value on the primary side cause the leakage. Depending on the rise time and fall time of the primary current generated by the transient phenomenon, as shown in FIG.
For example, there is an inconvenience that the output voltage V _O drops significantly at 1 kHz or higher.

For this reason, there is a problem that a desired output cannot be obtained even if an attempt is made to reduce the size of the welding transformer by simply increasing only the frequency.

The present invention has been made in order to solve such a conventional problem, and pays attention to the fact that the turns ratio of the welding transformer and the current change amount at the rise and fall of the primary current have a correlation. However, an object of the present invention is to provide a welding transformer of an inverter type DC resistance welding device which is small and lightweight and which can obtain an efficient welding transformer by designing a welding transformer based on the correlation. To do.

[0008]

In order to achieve the above object, the present invention provides a welding transformer of an inverter type DC resistance welding apparatus for generating a welding current to be applied to a work by a pulse-shaped primary current. The frequency of the primary current supplied to the welding transformer is set based on the turns ratio of the welding transformer and the amount of change in current per unit time at the rise and fall of the pulsed primary current. To do.

[0009]

In the welding transformer of the inverter type DC resistance welding apparatus according to the present invention, the primary current is determined from the relationship between the turn ratio of the welding transformer and the amount of change in current per unit time at the rise and fall of the pulse-shaped primary current. It becomes easy to obtain the maximum value of the possible frequencies and the volume of the welding transformer from the maximum value of the frequency.

[0010]

EXAMPLES Next, preferred examples of the welding transformer of the inverter type DC resistance welding apparatus according to the present invention will be described.
The following is a detailed description with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the overall construction of an inverter type DC resistance welding apparatus 20 embodying the present invention.

The inverter type DC resistance welding device 20 includes a converter circuit 22 for full-wave rectifying the alternating current output from the alternating current power source 21, an inverter circuit 24 for converting the full-wave rectified direct current into a high frequency alternating current, and the high frequency alternating current. A welding transformer circuit 26 for rectifying and rectifying, a welding gun portion 28 for sandwiching the work W, and a control circuit 30 for controlling a welding current supplied to the work W are provided.

Further, an inverter type DC resistance welding device 2
Reference numeral 0 denotes a primary side current detector 32 formed of a toroidal coil for detecting a current (hereinafter, referred to as a primary current) I ₁ applied to a primary coil of the welding transformer circuit 26, and a secondary side of the welding transformer circuit 26. Current induced in the coil (hereinafter 2
Secondary current detector 34 for detecting I _{2 (referred} to as secondary current)
And a keyboard 36 for inputting welding conditions and the like to the control circuit 30, and a CRT 38 which is a display device as a display means.

The welding gun section 28 has movable gun arms 40 and 41 for holding the work W, and the movable gun arm 4
Electrode tips 42 and 43 fixed to 0 and 41, and a cylinder 44 that drives the movable gun arms 40 and 41 to open and close freely. An air pressure source 48 is connected to the cylinder 44 via an electromagnetic switching valve 46. To be done. The switching operation of the electromagnetic switching valve 46 is controlled by a control signal output from the control circuit 30.

The welding transformer circuit 26 comprises a welding transformer 50 and diodes 52, 54 as rectifying elements, and the inverter circuit 24 has transistors 56, 58, 60, 62 as switching elements.

The operation of welding the work W in the inverter type DC resistance welding apparatus 20 configured as described above will be described with reference to the configuration block diagram of FIG. 1 and the timing chart of FIG.

The electromagnetic switching valve 46 is energized by the switching signal output from the control circuit 30, and the compressed air from the air pressure source 48 is introduced into the cylinder 44. The cylinder 44 slides under the action of this compressed air to close the movable gun arms 40 and 41, and the work W is held by the electrode tips 42 and 43 arranged on the movable gun arms 40 and 41.

Next, by the pulse-shaped drive signals I _a and I _b output from the control circuit 30 (see FIG. 2A), the transistor 56 forming the inverter circuit 24.
The bases 62 to 62 are sequentially energized, and the primary current I ₁ is supplied from the converter circuit 22 to the primary side coil of the welding transformer 50 (see FIG. 2B). This primary current I
_A pulse-shaped secondary voltage V ₂ (see FIG. 2C) is induced in the secondary coil of the welding transformer 50 by ₁ and the secondary current I ₂ is rectified by the diodes 52 and 54 and the welding current I ₃ Then, the work W is energized via the movable gun arms 40 and 41 and the electrode tips 42 and 43.

At this time, as shown in FIG. 2B, the rise time T _r is caused by the transient phenomenon caused by the leakage inductance L of the welding transformer 50 and the primary side resistance R1 in the pulsed primary current I _1. And a fall time T _f occurs.
The rising time T _r and the falling time T _f are always constant because they are circuit constants based on the time constant composed of the leakage inductance L and the primary side resistance R1, and therefore the drive signal output from the control circuit 30. When the frequencies of I _a and I _b are increased (see FIG. 3A), the upper limit of the frequency that the primary current I ₁ can take is the time of the sum of the rise time _Tr and the fall time T _f (hereinafter , Dead time T _D ) (see FIG. 3B).

Therefore, as a result of earnest studies, the inventor of the present application found that the amount of change in current ΔI ₁ / Δt per unit time at the rising time T _r and the falling time T _f of the primary current I ₁ which is the dead time T _D is as follows. , And found that there is a close relationship with the winding ratio N of the welding transformer 50.

That is, when the primary current I ₁ is applied to the primary coil L ₁ of the welding transformer 50, the primary coil L _1
The electromotive force E generated at ₁ is obtained by the following equation, where Φ is the magnetic flux. E = N (ΔΦ / Δt) = N {Δ (kNI ₁ ) / Δt} = kN ² (ΔI ₁ / Δt) (1) Here, the electromotive force E is defined as the voltage V ₁ across the primary coil L _1. Then, from the equation (1), (ΔI ₁ / Δt) = V ₁ / (kN ² ) ... (2), and the current change amount ΔI at the rising time T _r and the falling time T _f of the primary current I ₁ becomes. ₁ / Δt and the turns ratio N have the relation of the above equation (2), and the constant k and the primary coil L ₁
It becomes possible to obtain the current change amount ΔI ₁ / Δt with respect to the winding number ratio N by the calculation with the voltage V ₁ between the both ends being constant. This is the actual measurement value (Fig.
When compared with (B)), a very good correlation is obtained, and it can be confirmed that the equation (2) is a practical equation.

Based on the equation (2), the relationship between the turn ratio N and the current change amount ΔI ₁ / Δt becomes clear, and the maximum frequency f _max that the primary current I ₁ can take can be obtained.

In this way, the transformer weight can be easily obtained from the maximum frequency f _max that the obtained primary current I ₁ can take.

Output of welding transformer 50, eg 140
When kVA, the turns ratio N_O~ N ₈Maximum frequency at
Number f_maxAnd the relationship of the weight of the welding transformer 50 is shown in FIG.
Show. As is apparent from FIG. 5, the winding ratio N is set to the value N._FourSet up
Maximum frequency f_maxIs about 3.8 (kHz)
At this time, the weight of the welding transformer 50 is about 5 times that of the conventional one.
It will be 5%.

As described above, according to this embodiment,
Since the value of the current change amount ΔI ₁ / Δt of the primary current I ₁ can be determined by the winding ratio N of the welding transformer 50, it is possible to limit the design of the welding transformer 50 in terms of downsizing.

[0026]

With the welding transformer of the inverter type DC resistance welding apparatus according to the present invention, it is possible to obtain a welding transformer having a minimum volume that satisfies the output and can operate at the maximum frequency.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an inverter type DC resistance welding apparatus for carrying out the present invention.

2 is a timing chart showing the relationship between the welding current control signal and the welding current in the embodiment shown in FIG. 1. FIG.

FIG. 3 is a timing chart showing the relationship between the welding current control signal and the welding current when the frequency of the welding current control signal is increased in the timing chart shown in FIG. 2;

FIG. 4 is a graph illustrating the relationship between the turns ratio of the welding transformer and the amount of change in the primary current in the embodiment shown in FIG.

5 is a graph for explaining the relationship between each winding ratio of the welding transformer, the maximum frequency, and the weight of the welding transformer in the embodiment shown in FIG.

FIG. 6 is a graph illustrating the relationship between the frequency of the control signal output to the inverter circuit and the cross-sectional area of the core of the welding transformer in the related art.

FIG. 7 is a graph illustrating the relationship between the frequency of a control signal and the output voltage in the related art.

[Explanation of Codes] 20 ... Inverter type DC resistance welding device 24 ... Inverter circuit 26 ... Welding transformer circuit 28 ... Welding gun section 30 ... Control circuit 40, 41 ... Movable gun arm 50 ... Welding transformer 56, 58, 60, 62 ... Transistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Miyanaga 1-10-1 Shin-Sayama, Sayama-shi, Saitama Prefecture Honda Engineering Co., Ltd. (72) Gen Moto Tsujii 1-10-1 Shin-sayama, Sayama-shi, Saitama Prefecture Engineering Co., Ltd.

Claims (1)

[Claims] 1. A pulse-shaped welding current applied to a workpiece is used.
What is claimed is: 1. A welding transformer of an inverter type DC resistance welding device which is generated by a secondary current, wherein the welding transformer is obtained from the winding ratio of the welding transformer and the amount of change in current per unit time at the rising and falling of the pulsed primary current. A welding transformer of an inverter type DC resistance welding device, wherein a frequency of a primary current applied to the device is set.