JP3619700B2 - Transistor-type AC welding power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a resistance welding power source, and more particularly to a transistor type AC welding power source.
[0002]
[Prior art]
Resistance welding is known as a pressure welding method in which heat is applied to metal members while applying pressure to each other. There are two types of resistance welding: lap resistance welding that uses heat generated by electrical resistance when currents flow through metal layers, and butt resistance welding that heats current by flowing current through the butted parts. .
[0003]
The lap resistance welding includes spot welding, parallel gap welding, and seam welding. Spot welding is a method in which a stacked metal is sandwiched between two electrodes and a current is passed in the thickness direction of the metal. In parallel gap welding, a pair of parallel electrodes are pressed parallel to one side of a metal, and a current flows in the plane direction of the metal. In seam welding, two metal plates are sandwiched between two rotating electrodes, an intermittent current is passed between both electrodes, and spot welding is performed in a continuous manner.
[0004]
4 and 5 are known as welding power sources used for the lap resistance welding. FIG. 3 is a diagram showing a comparison of waveforms of welding currents by these known methods.
[0005]
FIG. 4 is a diagram showing a circuit configuration of a transistor type welding power source. In this method, the voltage of the commercial AC power supply is reduced by the transformer 20 and full-wave rectified by the bridge circuit 32 to charge the capacitor 34. Here, the charging voltage of the capacitor 34 is controlled by controlling the ignition phase of the switching elements (thyristors) 32 a and 32 a that are part of the rectifying element of the bridge circuit 32 by the charge control circuit 36.
[0006]
The current guided from the capacitor 34 to the welding electrode 38 is amplified and controlled by the transistor 40. That is, the welding current and the welding voltage are input to the amplification multiplication circuit 42, where the current / voltage / power is obtained and fed back to the amplification control circuit 44. The amplification control circuit 44 determines the amplification degree of the transistor 40 according to the conditions set by the welding condition setting unit 46 and controls the transistor 40.
[0007]
Here, the welding conditions include, for example, setting of control modes such as constant current, constant voltage, and constant power, setting of welding current / voltage / power, and welding end conditions. FIG. 3A shows a current waveform when welding is performed in a constant current mode by this transistor type welding power source.
[0008]
In such a transistor type welding power source, since the welding current is directly controlled by the transistor 40, a fine and smooth waveform can be obtained as shown in FIG. In addition, there is an advantage that the response speed is fast. On the other hand, since it has a direct current output, a material having a large polarity effect has poor weldability and has a drawback that the electrode is reduced on one side.
[0009]
In welding between dissimilar metals, heat absorption or heat generation occurs due to the Peltier effect in the contact portion according to the direction of the current. Because the heat is absorbed at the + pole side, the welding temperature is lowered and the welding strength is weakened, and the electrode wears up. On the minus pole side, the electrode is heated, so the welding is good and the electrode is consumed little. is there.
In addition, since the energy once charged in the capacitor 34 is discharged, the energization time is short, so that there is a disadvantage that the welding energy is small.
[0010]
FIG. 5 is a diagram showing a circuit configuration of an inverter type welding power source. In this circuit, three-phase commercial alternating current is rectified by a rectifier circuit 50 including a diode bridge and the capacitor 52 is charged to a predetermined voltage. The capacitor 52 is discharged through the inverter circuit 54 and the primary side of the welding transformer 56. The secondary side of the transformer 56 is connected to the electrode 60 via a rectifier circuit 58.
[0011]
The welding current and the welding voltage are supplied via a feedback circuit 62 to PWM (Pulse
The feedback is returned to the (Width Modulation) circuit 64. The PWM circuit 64 performs PWM control of the inverter circuit 54 so that the welding conditions set by the control circuit 66 are satisfied. The curve shown in FIG. 3B shows a current waveform according to this method, and is a welding current that changes on and off at a frequency sufficiently higher than that of the commercial power source.
[0012]
Such an inverter type welding power source has a configuration in which the primary power source is directly controlled by the inverter circuit 54 while being smoothed by the rectifying / smoothing circuit including the rectifier circuit 50 and the capacitor 52, and the welding current is passed. Has advantages. On the other hand, since it is PWM control by switching such as IGBT (Insulated Gate Bipolar Transistor), there is a drawback that a switching trace remains in the welding current.
[0013]
[Problems to be solved by the invention]
As described above, the conventional welding power sources have the following problems.
(1) In the case of a transistor type welding power source, since it is a direct current output, a material having a large polarity effect has poor weldability, and one side of the electrode is reduced. Further, since the energy once charged in the capacitor is discharged, the energization time is short, and therefore the welding energy is small.
(2) In the case of an inverter type welding power source, a jagged switching trace remains when the inverter circuit is switched by PWM control.
In order to solve the above-mentioned problems, the present invention has a good weldability by changing one set of transistors of an inverter circuit from a switching operation to an amplifying operation, does not reduce one side of the electrode, and does not leave a trace of switching. An object is to provide an AC welding power source.
[0014]
[Means for Solving the Problems]
The transistor type AC welding power source according to the present invention is a transistor type resistance welding power source for controlling current with a power transistor to perform welding. Voltage and current as optimum welding conditions are set as optimum values for feedback control, respectively. A welding condition setting unit that sets a switching frequency as a welding condition as a setting value for switching control, a current detector connected to the output side of the power transistor and detecting a current from the power transistor, and the current detection A welding electrode connected to the output side of the power transistor through a detector, a voltage detection unit for detecting a voltage applied to the welding electrode, a voltage from the voltage detection unit and a current from the current detector. Each feedback amplifying unit and feedback from this feedback amplifying unit The voltage and current are respectively compared with the voltage and current for feedback control set in the welding condition setting unit, and the amplification control unit for determining and controlling the amplification degree of the power transistor is set in the welding condition setting unit A switching control unit that determines and controls a switching operation of the power transistor according to a switching frequency that is set, and the power transistor operates as two pairs of amplification switching circuits each having a pair of power transistors that perform the amplification operation and the switching operation. It is characterized by this.
[0015]
According to the present invention, the current flowing through the welding electrode and the voltage applied to the welding electrode are detected and amplified, and the result is compared with the voltage and current for feedback control set in the welding condition setting unit, respectively. In addition, the amplification degree of the power transistor is determined and controlled, and the switching operation of the power transistor is determined and controlled according to the switching frequency set in the welding condition setting unit, and the power transistor performs the amplification operation and the switching operation. Since it was decided to operate as two pairs of amplification switching circuits with a power transistor as a pair, since an alternating current flows through the welding electrode, it is not affected by the polarity effect, so the weldability is good and there is no reduction on one side of the electrode, No trace of switching remains.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a circuit configuration diagram of a transistor type AC welding power source showing an embodiment of the present invention, and FIG.
[0017]
In FIG. 1, 100 is a transformer for stepping down an inputted commercial power supply voltage to a required voltage, 102 is a rectifying unit for full-wave rectification of AC composed of a bridge circuit, and 104 is a capacitor for smoothing the rectified voltage. Through these circuits, the capacitor 104 is charged with a required DC voltage to the polarity shown in FIG.
[0018]
Reference numeral 106 denotes an amplifying switching circuit configured by the power transistors 108 (108a, 108b, 108c, 108d), which performs an amplifying operation and a switching operation. The power transistors 108a, 108c perform an amplifying operation, and the power transistors 108b, 108d perform a switching operation. Do. The power transistors 108a and 108b and the power transistors 108c and 108d are paired to perform an amplification switching operation.
An amplification control unit 110 and a switching control unit 112 are provided as control units for the amplification operation and the switching operation.
The switching control unit 112 sends a switching signal whose switching frequency changes according to the conditions set by the welding condition setting unit 114 to the power transistors 108b and 108d that perform the switching operation. The switching frequency is sufficiently higher than the commercial frequency.
[0019]
The high-voltage AC voltage from the amplification switching circuit 106 is guided to the welding electrodes 120a and 120b. As a result, a changing welding current flows as shown in FIG. A workpiece (not shown) is welded by these electrodes 120a and 120b.
[0020]
The current flowing through these electrodes 120a and 120b is detected by a current detector 118 such as a Hall element current detector. The voltage is detected by the voltage detector 122. Signals indicating these currents and voltages are input to a feedback amplifier 116 serving as a feedback circuit, where they are amplified, and these results are fed back to the amplification controller 110.
[0021]
The welding condition setting unit 114 sets the constant voltage mode welding, and the set values such as the welding voltage, the frequency of the switching signal and the welding end condition are input, and these are sent to the amplification control unit 110 and the switching control unit 112. When a start switch (not shown) is pressed, the switching control unit 112 sends a switching signal to the power transistors 108b and 108d at the set frequency.
The power transistors 108b and 108d are alternately turned on / off by this switching signal. Therefore, when the power transistor 108b is turned on, a current flows in the direction of the arrow indicated by the solid line in FIG. Conversely, when the power transistor 108d is turned on, a current flows in the direction of the arrow indicated by the broken line.
[0022]
This welding current flows through the welding electrodes 120a and 120b, and welding is performed. At this time, the voltage between the welding electrodes 120a and 120b is detected by the voltage detector 122, amplified by the feedback amplifier 116 as described above, fed back to the amplification controller 110, and compared with the welding voltage set here. The amplification power transistors 108a and 108c are controlled so as to obtain a predetermined welding voltage. In this way, welding in the constant voltage mode is performed.
[0023]
【The invention's effect】
According to the present invention, as described above, since the commercial input power supply is controlled as it is by the amplification switching circuit while being smoothed, the energization time can be increased, so that the welding energy can be increased.
In addition, since the amplification switching circuit is configured by dividing the four power transistors into two pairs for performing the amplification operation and the switching operation, the welding current becomes an alternating current and is not affected by the polarity effect. Uniform welding is possible even with the material, and in addition, one side of the electrode does not decrease.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram of a transistor type AC welding power source according to an embodiment of the present invention.
FIG. 2 is a diagram showing a waveform of a welding current of the welding power source of FIG.
FIG. 3 is a diagram showing a waveform of a welding current of a conventional apparatus.
FIG. 4 is a block diagram of a conventional apparatus (transistor welding power source).
FIG. 5 is a block diagram of a conventional device (inverter welding power source).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 Transformer 102 Rectification part 104 Capacitor 106 Amplification switching circuit 108 Power transistor 110 Amplification control part 112 Switching control part 114 Welding condition setting part 116 Feedback amplification part 118 Current detector 120a, 120b Welding electrode 122 Voltage detection part

Claims (1)

In a transistor type resistance welding power source that controls the current with a power transistor and welds it,
A welding condition setting unit for setting voltage and current as optimum welding conditions as set values for feedback control, and setting a switching frequency as optimum welding conditions as setting values for switching control;
A current detector connected to the output side of the power transistor for detecting a current from the power transistor;
A welding electrode connected to the output side of the power transistor via the current detector;
A voltage detector for detecting a voltage applied to the welding electrode;
A feedback amplifier for amplifying the voltage from the voltage detector and the current from the current detector,
An amplification control unit that compares the feedback voltage and current from the feedback amplification unit with the feedback control voltage and current set in the welding condition setting unit, respectively, and determines and controls the amplification degree of the power transistor; ,
A switching control unit that determines and controls the switching operation of the power transistor according to the switching frequency set in the welding condition setting unit, and the power transistor includes two pairs of power transistors that perform the amplification operation and the switching operation. Transistor-type AC welding power supply, characterized by operating as an amplification switching circuit.

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