JP3136987B2 - Control apparatus and method for resistance welding machine - Google Patents

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 using resistance heating, and more particularly, to a control device and method for controlling electric power supplied to a material to be welded.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional control device for a resistance welding machine. Hereinafter, description will be made based on this drawing.

A resistance welding machine 50 rectifies a three-phase alternating current of a commercial power supply 52 by a rectifier circuit 54 and converts it to a direct current. The direct current is converted into a high-frequency alternating current by an inverter circuit 56, and the high-frequency alternating current is converted by a welding transformer 58. The voltage is reduced, the low-frequency high-frequency alternating current is converted again into direct current by the rectifier circuit 60, and the direct current is converted to the welding target material 64 via the welding electrodes 62a and 62b.
a, 64b. In addition, resistance welding machine 5
0 is provided with a control device 70. Control device 70
Is a current variable unit 72 that changes the high-frequency AC current by controlling the inverter circuit 56;
a, a current detector 74 for detecting a current supplied to 64b
And a control unit 76 that controls the current variable unit 72 so that the current detected by the current detection unit 74 is constant.

When the direct current obtained from the rectifier circuit 60 is supplied to the workpieces 64a and 64b via the welding electrodes 62a and 62b, Joule heat is generated due to the resistance of the workpieces 64a and 64b themselves. As a result, the materials to be welded 64a, 64
b is melted, so that the materials to be welded 64a, 64a
b are joined together. At this time, the control unit 76 operates as follows. The current detecting unit 74 is provided with the materials to be welded 64a, 6
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 compares the difference with the current variable unit 72.
Output to The current variable unit 72 controls the ON / OFF of the inverter circuit 56 so as to eliminate the difference. The set current value is a value determined by the material, the plate thickness, and the like of the materials to be welded 64a and 64b together with the energizing time, and is input to the control unit 76 in advance.

[0005]

SUMMARY OF THE INVENTION A conventional resistance welding machine 50 is disclosed.
Then, if the welding conditions are inappropriate, the materials to be welded 64a, 6
At the time of welding of 4b, a phenomenon called "scattering" in which the molten metal is scattered occurs. This "scatter" causes the following problem (1), and it is desired to suppress the occurrence. . Since the scattered molten metal solidifies and accumulates in the surroundings, the working environment deteriorates and periodic cleaning is required. . Since molten metal is scattered toward surrounding workers and the like, it is not preferable in terms of safety. . This has an adverse effect on the joining strength of the materials to be joined.

As a conventional technique for suppressing the occurrence of the "scattering", a technique for suppressing an excessive current such as a control device 70 and a technique for suppressing an excessive voltage as disclosed in Japanese Patent Publication No. 6-77851 are known. ing. However, none of the prior arts has provided satisfactory results.

[0007]

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

[0008]

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

A control device and method according to the present invention rectify a commercial alternating current by a rectifier circuit and convert it to a direct current, convert the direct current to a high-frequency alternating current by an inverter circuit, and reduce the high-frequency alternating current to a low voltage by a welding transformer. This low-frequency high-frequency AC is used as it is or in a resistance welding machine that converts the DC into a direct current again by a rectifier circuit and supplies the DC to a workpiece through a welding electrode.

[0010] A control device according to the present invention includes a power variable unit that changes the power of the high-frequency AC by controlling the inverter circuit, a power detection unit that detects power supplied to the workpiece, electrostatic detected by the power detector
The amount of power and power change determined by the material, plate thickness, etc.
And a control unit that controls the power variable unit from the start to the end of the joining so that the power increase rate is equal to or less than a certain value.

[0011] The control method according to the present invention is characterized in that:
The supplied power is detected, and this power depends on the material, plate thickness, etc.
Power amount and power changes
From the start of joining so that the rate of increase of the power is below a certain level
Until the end, the power of the high-frequency AC is changed .

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

[0013]

FIG. 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 made based on this drawing. However, the same parts as those in FIG.

The resistance welding machine 10 is provided with a control device 12. The control device 12 controls the inverter circuit 56 to change the power of the high-frequency AC, a power variable unit 14, a power detection unit 16 for detecting the power supplied to the workpieces 64a and 64b, and a power detection unit 16 The electric power detected in the above is the electric energy and electric power determined by the material, plate thickness, etc.
And a control unit 18 for controlling the power variable unit 14 from the start to the end of the joining so that the force changes and the rate of increase of the power becomes equal to or less than a certain value. Power detector 1
Reference numeral 6 denotes an ammeter 161 for detecting a current supplied to the workpieces 64a and 64b, a voltmeter 162 for detecting a voltage applied to the workpieces 64a and 64b, And a multiplier 163 for obtaining electric power based on the voltage detected by the voltmeter 162. The ammeter 161 outputs a current signal I, the voltmeter 162 outputs a voltage signal V, and the multiplier 163 outputs a power signal P.

The rectifier circuits 54 and 60 are composed of rectifier diodes, smoothing capacitors, and the like, and convert AC to DC. The inverter circuit 56 includes, for example, a power MOSF
This is an H-type bridge constituted by a switching element such as an ET, and converts a direct current into a 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 controlling on / off of 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 made based on this drawing.

The control unit 18 includes a V / F converter 20, a differentiator 22, a deviation counter 24, a D / A converter 26, adders / subtractors 28 and 30, amplifiers 32 and 34, a triangular wave generator 36, a comparator 38 and the like. It is constituted by. V / F converter 20
Converts the power signal P (analog voltage), the pulse signal P ₀ having a frequency corresponding to the voltage value. The deviation counter 24 is an up / down counter, and inputs a pulse command P ₁ to an UP terminal and inputs an output signal P ₂ of the V / F converter 20 to a DOWN terminal. Pulse command P ₁ is,
The number of pulses indicates the amount of power, and the pulse frequency indicates the rate of power increase. The power increases sharply as the pulse frequency increases. The output signal P ₀ of the deviation counter 24 gradually increases by _first inputting the pulse command P _1, and becomes almost constant by inputting the output signal P ₂ with a delay,
Gradually decreases by the output of the pulse command P ₁ is completed, and finally becomes zero. The D / A converter 26 outputs the output signal P ₀
To 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 the result 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 the result to the amplifier 34. Set current value I ₁ is for suppressing the excessive current.
The comparator 38 inputs the output signal c of the amplifier 34 to the + terminal, inputs the output signal d of the triangular wave generator 36 to the − terminal,
A pulse signal e including a pulse width corresponding to the output signal c and a frequency of the output signal d is output to the power variable unit 14 (FIG. 1). The output signal c is an analog voltage, and the pulse width of the pulse signal e increases as the output signal c increases.

Next, the operation of the resistance welding machine 10 and the control device 12 will be described with reference to FIGS.

First, the pulse command P ₁ is supplied to the deviation counter 2
4, the output signal P of the deviation counter 24 starts.
₀ starts to increase gradually. Then, the pulse signal e is output from the comparator 38, and the power variable unit 14 starts PWM control of the inverter circuit 56. Thus, the DC output from the rectifier circuit 60 is supplied to the workpieces 64a and 64b via the welding electrodes 62a and 62b. On the other hand, the current and power supplied to the workpieces 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. When the 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, the output of the pulse command P ₁ is completed, the output signal P ₀ of the deviation counter 24 becomes zero substantially eventually begins to gradually decrease from the constant. Then, the pulse signal e is not output from the comparator 38, and the power varying unit 14
6 is stopped. By this series of operations, parts of the materials to be welded 64a and 64b are melted, and the materials to be welded 64a and 64b are joined to each other.

During welding, the power signal P
Rapidly increases, the power increase rate signal dP / dt output from the differentiator 22 also rapidly 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 is reduced. Accordingly, an increase in the power of the high-frequency AC output from the inverter circuit 56 is suppressed, so that the occurrence of “scattering” is also suppressed.

The higher the frequency of the high-frequency alternating current, that is, the frequency df of the output signal d of the triangular wave generator 36, the easier it is to follow the occurrence of "scattering", while increasing the power loss in the inverter circuit 56. Therefore, the frequency df
Is preferably 1 kHz to 50 kHz, and 10 kHz to 30 kHz.
More preferably, it is 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 and an integral operation may be added as necessary. Further, the present invention can be applied to a resistance welding machine in which a low-frequency high-frequency alternating current is supplied as it is to the workpieces 64a and 64b via the welding electrodes 62a and 62b without providing the rectifier circuit 60. .

[0023]

According to the control device and method according to the present invention, the power supplied to the material to be welded is detected, and this power is used for the material.
The amount of power and power changes determined by the quality, plate thickness, etc.
So that the rate of increase of the power is below a certain level
By changing the power of the high-frequency AC from the start to the end of the joining , rapid heat generation can be suppressed,
The occurrence of "scatter" can be sufficiently suppressed. As a result, the joining strength of the materials to be joined can be improved.

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

[Brief description of the drawings]

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

FIG. 2 is a block diagram illustrating 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]

 DESCRIPTION OF SYMBOLS 10 Resistance welding machine 12 Control device 14 Power variable part 16 Power detection part 18 Control part 52 Commercial power supply 54, 60 Rectification circuit 56 Inverter 58 Welding transformer 62a, 62b Welding electrode 64a, 64b Material to be welded

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-101083 (JP, A) JP-A-61-49792 (JP, A) JP-A-9-29454 (JP, A) JP-A-6-29454 269955 (JP, A) JP-A-6-344155 (JP, A) JP-A-63-180384 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 11/24-11 /twenty five

Claims (4)

(57) [Claims] 1. A commercial AC is rectified by a rectifier circuit and converted into DC, the DC is converted into a high-frequency AC by an inverter circuit, and the high-frequency AC is reduced in voltage by a welding transformer. Is used for a resistance welding machine that supplies DC to the workpiece as it is via a rectifier circuit as it is or through a rectifier circuit, and controls the inverter circuit to change the power of the high-frequency AC. When electrodeposition wherein a power detection unit for detecting the power supplied to the workpieces, the power detected by the power detection unit is determined material, the thickness, etc.
A control device for a resistance welding machine, comprising: a control unit that controls the power variable unit from the start to the end of joining so that the power and the power change and the rate of increase of the power is equal to or less than a certain value. 2. A commercial AC is rectified by a rectifier circuit and converted into DC, the DC is converted into a high frequency AC by an inverter circuit, and the high frequency AC is reduced in voltage by a welding transformer. Is used as it is or in a rectifier circuit to convert it again to direct current, and is used for a resistance welding machine that supplies a material to be welded via a welding electrode.
The amount of power and power changes determined by the quality, plate thickness, etc.
So that the rate of increase of the power is below a certain level
A method for controlling a resistance welding machine, wherein the power of the high-frequency alternating current is changed from the start to the end of joining . 3. The frequency of the high frequency alternating current is 1 kHz to 50 kHz.
The control device for a resistance welding machine according to claim 1, wherein z is z. (4) The frequency of the high-frequency alternating current is 1 kHz to 50 kHz.
The control method for a resistance welding machine according to claim 2, wherein z is z.