JPH09271960A - Device and method for controlling resistance welding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently suppress generation of surface flash at the time of welding. SOLUTION: A resistance welding machine 10 is equipped with a controller 12. The controller 12 is provided with a variable power part 14 for varying a high frequency AC power by controlling an inverter circuit 56, power detector 16 for detecting power supplied to a material 64a, 64b to be welded, and a controller 18 for controlling the variable power part 14 so that the rate of increase of the power detected in the detector 16 may be at a fixed level or below.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding machine for joining materials to be welded by using resistance heating, and more particularly to a control device and method for controlling electric power supplied to the materials to be welded.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional controller for a resistance welding machine. Hereinafter, description will be given with reference to this drawing.

The resistance welding machine 50 rectifies the three-phase alternating current of the commercial power source 52 by a rectifying circuit 54 and converts it into a direct current, converts this direct current into a high frequency alternating current by an inverter circuit 56, and converts this high frequency alternating current by a welding transformer 58. The voltage is lowered, and the high-frequency alternating current having the lowered voltage is converted into direct current again by the rectifier circuit 60, and this direct current is welded through the welding electrodes 62a and 62b to the welded material 64.
It is supplied to a and 64b. Also, resistance welding machine 5
A controller 70 is attached to 0. Control device 70
Is a current variable portion 72 that changes the high-frequency alternating current by controlling the inverter circuit 56, and the material to be welded 64.
current detector 74 for detecting the current supplied to a and 64b
And a control unit 76 for controlling the current varying unit 72 so that the current detected by the current detecting unit 74 becomes constant.

When the direct current obtained from the rectifying circuit 60 is supplied to the materials to be welded 64a and 64b via the welding electrodes 62a and 62b, Joule heat is generated due to the resistance value of the materials to be welded 64a and 64b. As a result, the materials to be welded 64a, 64
By melting a part of b, the materials to be welded 64a, 64
b is joined. At this time, the control unit 76 operates as follows. The current detection unit 74 includes the materials to be welded 64a, 6
The current supplied to 4b is detected, and the detected current value (effective value) is output to the control unit 76. The control unit 76 compares the detected current value with the set current value and determines the difference between them.
Output to The current variable unit 72 controls the on / off of the inverter circuit 56 so that the difference is eliminated. The set current value is a value that is determined by the material, plate thickness, and the like of the materials to be welded 64a and 64b together with the energization time, and is input in advance to the control unit 76.

[0005]

Conventional resistance welding machine 50
Then, if the welding conditions are inappropriate, the materials to be welded 64a, 6
A phenomenon called "scattering" occurs in which molten metal scatters during welding of 4b. Since this "scattering" causes the following problems (1) to (3), it is desired to suppress the occurrence thereof. . Since the scattered molten metal solidifies and accumulates in the surroundings, the working environment deteriorates and periodic cleaning is required. . Molten metal is scattered toward surrounding workers, which is not preferable for safety. . It adversely affects the bonding strength of the materials to be bonded.

As a conventional technique for suppressing the occurrence of this "scattering", there are known a controller 70 for suppressing an excessive current and a controller for suppressing an excessive voltage as disclosed in Japanese Patent Publication No. 6-77851. ing. However, none of the conventional techniques have obtained sufficient results.

[0007]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a control apparatus and method for a resistance welding machine which can sufficiently suppress the occurrence of "scattering".

[0008]

The inventor of the present invention first conducted experiments and studies on the cause of "scattering" by using a high-speed video camera or the like. As a result, the occurrence of "scatter"
We have found that it is due to the increase rate [W / s] of the electric power supplied to the material to be welded, not the excessive current or voltage supplied to the material to be welded. In other words, if the electric power supplied to the material to be welded suddenly increases for some reason, the amount of heat generated sharply increases, far exceeding the amount of heat radiation, so that part of the material to be welded melts and scatters. In addition, the present inventor
It was also found that occurs in a short time of about 1 [ms]. The present invention has been made based on these findings.

The control device and method according to the present invention rectify commercial alternating current by a rectifying circuit and convert it into direct current, convert this direct current into high frequency alternating current by an inverter circuit, and lower this high frequency alternating current with a welding transformer, It is used for a resistance welding machine in which the low-frequency high-frequency alternating current is converted into direct current as it is or by a rectifier circuit again and is supplied to the material to be welded via the welding electrode.

A control device according to the present invention comprises a power variable part for changing the power of the high frequency alternating current by controlling the inverter circuit, and a power detecting part for detecting the power supplied to the material to be welded. And a control unit that controls the power variable unit so that the rate of increase of the power detected by the power detection unit is below a certain level.

In the control method according to the present invention, commercial AC is rectified by a rectifier circuit and converted into DC, this DC is converted into high frequency AC by an inverter circuit, and this high frequency AC is reduced in voltage by a welding transformer. The voltage-converted high-frequency alternating current is converted into a direct current as it is or by a rectifier circuit and supplied to the material to be welded via the welding electrode.

The frequency of the high-frequency alternating current is 1 kHz to 50 kHz so that it can sufficiently follow the occurrence of "scattering".
It is preferable that

[0013]

1 is a block diagram showing an embodiment of a control device for a resistance welding machine according to the present invention. Hereinafter, description will be given with reference to this drawing. However, the same parts as those in FIG.

A control device 12 is attached to the resistance welding machine 10. The control device 12 controls the inverter circuit 56 to change the power of the high-frequency alternating current, the power variable unit 14, the power detection unit 16 that detects the power supplied to the materials to be welded 64a and 64b, and the power detection unit 16. So that the rate of increase of the power detected by
And a control unit 18 for controlling the. The power detection unit 16 includes an ammeter 161 that detects a current supplied to the welded materials 64a and 64b, a voltmeter 162 that detects a voltage applied to the welded materials 64a and 64b, and an ammeter 161.
And a multiplier 163 that obtains electric power based on the current detected in step 1 and the voltage detected in the voltmeter 162. The ammeter 161 outputs the current signal I, and the voltmeter 162
Outputs a voltage signal V, and the multiplier 163 outputs a power signal P.

The rectifying circuits 54 and 60 are composed of rectifying diodes, smoothing capacitors, etc., and convert alternating current into direct current. The inverter circuit 56 is, for example, a power MOSF.
It is an H-shaped bridge composed of switching elements such as ET, and converts direct current into high-frequency alternating current composed of rectangular pulses. The power variable unit 14 is a drive circuit of the inverter circuit 56, and changes the pulse width of the high-frequency AC by turning on / off the switching element of the inverter circuit 56 based on the pulse signal e output from the control unit 18. (PWM control).

FIG. 2 shows a control unit 18 in the control device 12.
FIG. 4 is a block diagram showing an example of the above. Hereinafter, description will be given with reference to this drawing.

The control unit 18 includes a V / F converter 20, a differentiator 22, a deviation counter 24, a D / A converter 26, adder / subtractors 28 and 30, amplifiers 32 and 34, a triangular wave generator 36, a comparator 38 and the like. It is composed by. V / F converter 20
Converts the power signal P (analog voltage) into a pulse signal P ₀ having a frequency corresponding to the voltage value. The deviation counter 24 is an up / down counter, and inputs the pulse command P ₁ to the UP terminal and the output signal P ₂ of the V / F converter 20 to the DOWN terminal. The pulse command P ₁ is
It is a value determined by the material of the materials to be welded 64a, 64b, the plate thickness, etc., the number of pulses indicates the amount of power, and the pulse frequency indicates the rate of power increase. The higher the pulse frequency, the more rapidly the power increases. The output signal P ₀ of the deviation counter 24 is gradually increased by _first inputting the pulse command P _1, and is made almost constant by inputting the output signal P ₂ with a delay.
When the output of the pulse command P ₁ ends, the output gradually decreases and finally becomes zero. The D / A converter 26 outputs the output signal P _0.
Is converted into an analog signal a. The differentiator 22 differentiates the power signal P and outputs a power increase rate signal dP / dt. The adder / subtractor 28 subtracts the power increase rate signal dP / dt from the analog signal a output from the D / A converter 26, and outputs it to the amplifier 32. The adder / subtractor 30 subtracts the detected current signal I from the sum of the output signal b of the amplifier 32 and the set current value I _1, and outputs it to the amplifier 34. The set current value I ₁ is for suppressing an excessive current.
The comparator 38 inputs the output signal c of the amplifier 34 to the + terminal and the output signal d of the triangular wave generator 36 to the-terminal,
The pulse signal e having the pulse width corresponding to the output signal c and the frequency of the output signal d is output to the power varying unit 14 (FIG. 1). The output signal c is an analog voltage, and the larger the output signal c, the larger the pulse width of the pulse signal e.

Next, the operation of the resistance welding machine 10 and the controller 12 will be described with reference to FIGS. 1 and 2.

First, the pulse command P ₁ is set to the deviation counter 2
4 is output, the output signal P of the deviation counter 24
₀ starts to increase. Then, the pulse signal e is output from the comparator 38, and the power varying unit 14 starts PWM control of the inverter circuit 56. As a result, the direct current output from the rectifier circuit 60 is supplied to the materials to be welded 64a and 64b via the welding electrodes 62a and 62b. On the other hand, the current and power supplied to the materials to be welded 64a and 64b are sequentially detected by the power detection unit 16 and output to the control unit 18 as a current signal I and a power signal P. Power signal P is V
When output to the / F converter 20, the output signal P ₀ of the deviation counter 24 changes from gradually increasing to almost constant. Then, when the output of the pulse command P ₁ is finished, the output signal P ₀ of the deviation counter 24 starts to gradually decrease from a substantially constant _value and finally becomes zero. Then, the pulse signal e is not output from the comparator 38, and the power varying unit 14 causes the inverter circuit 5 to operate.
The PWM control for 6 is stopped. By this series of operations, a part of the materials to be welded 64a and 64b are melted and the materials to be welded 64a and 64b are joined together.

During welding, for some reason, the power signal P
A sharp increase, the power increase rate signal dP / dt output from the differentiator 22 also sharply increases. Since the power increase rate signal dP / dt is negatively fed back to the adder / subtractor 28, the pulse width of the pulse signal e output from the comparator 38 becomes small. As a result, the increase in the high-frequency AC power output from the inverter circuit 56 is suppressed, so that the occurrence of “dispersion” is also suppressed.

As the frequency of the high frequency alternating current, that is, the frequency df of the output signal d of the triangular wave generator 36 becomes higher, it becomes easier to follow the occurrence of "dispersion", while the power loss in the inverter circuit 56 increases. Therefore, the frequency df
Is preferably 1kHz to 50kHz, 10kHz to 30kHz
It is more preferable to set to kHz.

It is needless to say that the present invention is not limited to the above embodiment. For example, the differentiator 22
In addition to the differential operation, a proportional operation or an integral operation may be added to the. Further, the present invention can also be applied to a resistance welding machine in which a high-frequency alternating current having a reduced voltage is directly supplied to the materials to be welded 64a and 64b via the welding electrodes 62a and 62b without providing the rectifying circuit 60. .

[0023]

According to the control device and method of the present invention, the electric power supplied to the material to be welded is detected, and the electric power of the high frequency alternating current is changed so that the rate of increase of this electric power is below a certain level. As a result, rapid heat generation can be suppressed, and the occurrence of "scattering" can be sufficiently suppressed. As a result, the bonding strength of the materials to be bonded can be improved.

The frequency of the high frequency alternating current is 1 kHz to 50 kH.
By setting z, it is possible to easily follow the occurrence of "dispersion" while suppressing the power loss in the inverter circuit.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an example of a control unit in the control device of FIG.

FIG. 3 is a block diagram showing a control device of a conventional resistance welding machine.

[Explanation of symbols]

 10 Resistance Welding Machine 12 Control Device 14 Power Variable Section 16 Power Detection Section 18 Control Section 52 Commercial Power Supply 54, 60 Rectifier Circuit 56 Inverter 58 Welding Transformer 62a, 62b Welding Electrode 64a, 64b Welding Material

Claims (3)

[Claims] 1. A commercial AC is rectified by a rectifier circuit and converted into DC, this DC is converted into a high frequency AC by an inverter circuit, this high frequency AC is reduced in voltage by a welding transformer, and this low voltage high frequency AC is converted. Is used for a resistance welding machine that converts the current into direct current by a rectifier circuit or supplies it to a material to be welded through a welding electrode, and a power variable unit that changes the power of the high frequency alternating current by controlling the inverter circuit. And a power detection unit that detects the power supplied to the material to be welded, and a control unit that controls the power variable unit so that the rate of increase in the power detected by the power detection unit is below a certain level. Control device for resistance welding machine. 2. The commercial alternating current is rectified by a rectifier circuit and converted into direct current, this direct current is converted into a high frequency alternating current by an inverter circuit, this high frequency alternating current is reduced in voltage by a welding transformer, and this high frequency alternating current is lowered. Is used for a resistance welding machine that supplies the material to be welded through the welding electrode by converting it into direct current as it is or with a rectifying circuit, and detects the power supplied to the material to be welded, and the rate of increase of this power is A method for controlling a resistance welding machine, which comprises changing the power of the high-frequency alternating current so as to be a certain value or less. 3. The frequency of the high frequency alternating current is 1 kHz to 50 kH.
The resistance welding machine control device according to claim 1 or the resistance welding machine control method according to claim 2, wherein z is z.