JP3128752B2 - Spot 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 spot welding machine for performing welding by discharging a charging voltage to a capacitor.

[0002]

2. Description of the Related Art In a capacitor-type spot welding machine that performs welding by discharging a charging voltage to a capacitor, charging control of the capacitor is performed by a rectifier and a rectifier provided before the capacitor.
The voltage is controlled by a voltage control circuit, and the discharge control from the capacitor is performed by a discharge control circuit provided at a stage subsequent to the capacitor.
A conventional spot welder is generally configured using a function as a switching element of a thyristor.

FIG. 10 is a diagram showing a rectifier / voltage control circuit in a spot welding machine using a thyristor. In the figure, the rectifier / voltage control circuit uses thyristors SCR1, SCR2, and SCR3 as switching elements.
A step-down transformer T2 is used for synchronizing the three-phase ignition circuit K1.
Is used. When a charge command is issued, the three-phase ignition circuit K1
Uses the thyristor SCR to output the ignition gate signal synchronized with each phase.
1, SCR2 and SCR3. When the thyristors SCR1, SCR2, and SCR33 are turned on by the ignition signal, the charging current Ic flows through the capacitor C through the current limiting resistor R. The charging voltage of the capacitor C gradually increases as shown in FIG. 11, and when the charging voltage detected through a voltage detection circuit (not shown) reaches the set voltage Vo, the charging command is turned off. Thus, the thyristors SCR1, SCR2, and SCR3 are turned off, and a series of charging steps is completed.

FIG. 12 is a diagram showing a discharge control circuit in a spot welding machine using a thyristor. Thyristor SCR4, SCR as switching element in discharge control circuit
5, SCR6 and SCR7 are used. The voltage charged in the capacitor C in the above charging step is applied to the welding transformer T3.
When discharging to the ignition control circuit K2, a first discharge command is issued to the ignition control circuit K2. By this first discharge command, thyristor SCR4
The SCR 5 is turned on, and the discharge current I1 flows to the primary side of the welding transformer T3 through the route shown in the figure.

When the discharge from the capacitor C is completed, the thyristors SCR4 and SCR5 are turned off, and the above-described charging step is performed again to charge the capacitor C with a voltage. When charging is completed, the ignition control circuit K2
Issue a second discharge command. By the second discharge command, the thyristors SCR6 and SCR7 are turned on, and the discharge current I
2 flows to the primary side of the welding transformer T3 through the route shown in the figure. At this time, the discharge currents I1 and I2 have opposite polarities as shown in FIG. By repeating the above operation, the operation as a spot welding machine is performed.

[0006]

However, once the thyristor is turned on, even if the firing command is turned off, the thyristor does not turn off unless the current flowing through the thyristor becomes zero. Therefore, immediately after the discharge command is turned off, charging is stopped. It was not possible to start and it took time to start charging.

That is, thyristors SCR4, SCR5
As shown in FIG. 14, the discharge current I1 flowing through continues to flow during the time to even though the firing command based on the first discharge command is turned off. If charging is started when the time tp has elapsed from the firing command, the thyristor S
Since CR4 and SCR5 are not turned off, current flows to the welding transformer T3 through the thyristors SCR4 and SCR5, and the capacitor C is not charged. In order to avoid this phenomenon, generally, after the ignition command is turned off (after the first and second discharge commands are turned off), a charge command is issued with a delay of time tq. For this reason, charging requires time, which has been a factor of deteriorating the work efficiency of spot welding. The present invention has been proposed in view of the above, and it is an object of the present invention to provide a spot welding machine that can start charging immediately after a discharge command is turned off and can increase a tact time of a spot welding operation.

[0008]

To achieve the above object, according to the Invention The, the inventions are welded Trang the charging voltage to the capacitor
A spot welding machine that performs welding by discharging to a primary side of a rectifier, a rectifier and a voltage controller that performs full-wave rectification of an input voltage and charges the capacitor with the voltage of the full-wave rectified waveform;
Discharge from the above capacitor is insulated gate bipolar
It includes a discharge control unit for controlling at off the transistor, and the rectifier and the voltage control unit, the charging, the full wave
Insulated gate bipolar transistor with rectified waveform voltage
The setting is performed by the pulse wave formed by the on / off control of
If the difference between the voltage and the charging voltage of the capacitor is large,
When the difference is small, the pulse wave is short
Control the pulse wave so that
Are four insulated gate bipolar transistors according to the first discharge command.
Turn on two of the transistors, and in the first route
A discharge current is applied to the primary side of the welding transformer and the
1 The discharge current is instantly turned off by turning off the discharge command.
And four insulated gate type bipolar
And turn on another two of the
With a polarity opposite to that of the first route on the primary side of the welding transformer.
When the discharge current flows and the second discharge command is turned off,
And instantaneously turn off the discharge current.
I have.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of the spot welding machine. In the figure, the spot welding machine uses a commercial AC 200 V three-phase AC power supply as a power supply.
The voltage is increased to 400 V AC by using the power supply 1 to increase the capacity, and then sent to the rectification and voltage control unit 10. The voltage stepped up by the step-up transformer T1 is applied to the rectification and voltage control unit 10
After that, the capacitor (capacitor group) C is charged via the current limiting resistor R. The charging voltage V of the capacitor C is detected by the voltage detection circuit 31 and the charging voltage V
Reaches a set voltage Vo, a charge stop command is output from the charge voltage control circuit 32, and charging is stopped. Thus, a series of charging steps is completed. And the discharge control unit 2
0 discharges the voltage charged in the capacitor C in the charging step to the welding transformer T3.

FIG. 2 is a diagram showing a circuit configuration of the rectification and voltage control unit. The rectification and voltage control unit 10 of the spot welder developed this time includes diodes D1, D2, D3, D4,
D5 and D6 form a full-wave rectifier circuit 11, and an insulated gate bipolar transistor (Insulated Gate Bipola Transistor) is provided between the full-wave rectifier circuit 11 and the current limiting resistor R.
Hereinafter, it is referred to as “IGBT”).
Is controlled by a charge command via the control circuit 12 to perform charge control.

The above-mentioned IGBT has the advantages of both a MOS FET and a bipolar transistor in which the high-speed switching characteristics and voltage driving characteristics of a MOS FET and the low on-voltage characteristics of a bipolar transistor are formed on a single chip. A self-erasing element that is turned on when a voltage is applied to the gate and turned off when the gate voltage is reduced to zero because it is a power element and a voltage driving element.

The input voltage (AC 400 V, FIG. 3)
3A is full-wave rectified through the full-wave rectifier circuit 11, and becomes a full-wave rectified waveform of FIG. 3B, that is, a waveform as shown in FIG. The voltage of this full-wave rectified waveform is converted to a current limiting resistor R
To charge the capacitor C. At that time, IGBT0
Has the role of a switch. The charge control is performed by the control circuit 12 based on the charge command. When the charge voltage V reaches the set voltage Vo, the charge command is turned off, and the charging is stopped by switching the IGBT0. When the charge command is turned off, the IGBT 0 is turned off instantly as a characteristic of the element, so that charging is also stopped instantaneously.

FIG. 4 is a diagram showing a circuit configuration of the discharge control unit. The discharge control unit 20 includes four IGBTs 1 and IGBTs.
2, IGBT3 and IGBT4 are used as switching elements. When discharging the voltage charged in the capacitor C in the charging step to the welding transformer T3, a first discharge command is issued to the control circuit 13. By this first discharge command, IGBT1 and IGBT4 are turned on, and discharge current I1 flows to the primary side of welding transformer T3 through the route shown in the figure.

When the discharge from the capacitor C is completed, the IGBT 1 and the IGBT 4 are turned off, and the above charging step is performed again to charge the capacitor C with a voltage. When the charging is completed, the control circuit 13
Issue a discharge command. This second discharge command causes the IGBT
2 and the IGBT 3 are turned on, and a discharge current I2 having a polarity opposite to the discharge current I1 flows to the primary side of the welding transformer T3 through the route shown in the figure. By repeating the above operation, the operation as a spot welding machine is performed.

FIG. 5 is a diagram showing a current curve of a discharge current. When IGBT1 to IGBT4 are used for the discharge control unit 20, when the discharge command is turned off, the IGBT is turned off instantaneously, and the discharge current is also turned off. Therefore, it is not necessary to secure the delay time tq as in the case of using a thyristor. , Charging can be started immediately. For this reason, the time from discharge to the start of charging can be shortened, and the tact time of spot welding work can be increased.

By the way, in the conventional spot welding machine, the charging of the capacitor C is performed by the rectification waveform from the rectification / voltage control circuit using the thyristor shown in FIG. 10, and the rectification waveform at that time is shown in FIG. The waveform is as shown in FIG. On the other hand, in this embodiment, charging of the capacitor C is
As described above, the charging is performed with the full-wave rectified waveform as shown in FIG. 6B, so that the charging can be efficiently performed in a shorter time than in the conventional case.

As described above, when quick charging is performed with a full-wave rectified waveform, the charging voltage V may exceed the setting voltage Vo even if the charging is turned off when the charging reaches the setting voltage Vo. This is because there is a time delay from the detection by the voltage detection circuit 31 until the IGBT 0 is actually turned off, so that rapid charging cannot be performed.

Therefore, in this embodiment, a pulse charging method has been developed in order to avoid such a phenomenon. This means that the IGBT 0 is turned on / off at several hundred Hz and the set voltage V
When the difference between o and the charging voltage V is large, the pulse width is increased as shown in FIG. 7, and when the difference is small, the pulse width is shortened as shown in FIG. This controls the charge of the battery.

As a result, the operation of the IGBT 0 is as shown in FIG. 9. When the difference between the set voltage Vo and the charging voltage V is large, the amount of charge per unit time increases, and the charging is rapidly performed. When the charging voltage V approaches the set voltage Vo, the amount of charge per unit time is reduced, and charging is performed slowly, and the set voltage Vo is accurately determined.
Can charge up to.

As described above, in this embodiment, since the IGBT1 to IGBT4 are used for the discharge control unit 20, the IGBT is turned off instantly when the discharge command is turned off, and the delay time tq as in the case of using a thyristor is used. It is not necessary to secure the battery and charging can be started immediately. For this reason, the time from discharge to the start of charging can be shortened, and the tact time of spot welding work can be increased.

Also, since the capacitor C is charged with a full-wave rectified waveform, quick charging can be performed, the charging time can be reduced, and from this point, the tact time of spot welding work can be increased. can do.

At the time of quick charging by the full-wave rectified waveform,
The full-wave rectified waveform is pulsed using IGBT0, and when the difference between the set voltage Vo and the charging voltage V is large, the pulse width is increased to increase the amount of charge per unit time.
When the charging is performed rapidly and the charging voltage V approaches the set voltage Vo, the pulse width is reduced to reduce the amount of charge per unit time, so that the charging is performed slowly. Can charge up to.

[0023]

As described above, according to the spot welding machine of the present invention, the discharge from the capacitor is controlled by turning on / off the power element having a high switching speed. In addition, the power element is also turned off, and it is not necessary to secure a delay time as in the case of using a thyristor, and charging can be started immediately. For this reason, the time from discharge to the start of charging can be shortened, and the tact time of spot welding work can be increased.

Further, since the charging of the capacitor is performed with the full-wave rectified waveform, rapid charging can be performed, the charging time can be reduced, and in this respect, the tact time of the spot welding operation can be increased. be able to.

At the time of quick charging by the full-wave rectified waveform,
The full-wave rectified waveform is pulsed using a power element with a high switching speed, and when the difference between the set voltage and the charging voltage is large, the pulse width is increased to increase the amount of charge per unit time, thereby rapidly When charging is performed and the charging voltage approaches the set voltage, the pulse width is reduced to reduce the amount of charge per unit time, so that charging is performed slowly. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a spot welding machine.

FIG. 2 is a diagram illustrating a circuit configuration of a rectification and voltage control unit.

FIG. 3 is a diagram showing waveforms of an input voltage and an output voltage to a full-wave rectifier circuit.

FIG. 4 is a diagram illustrating a circuit configuration of a discharge control unit.

FIG. 5 is a diagram showing a current curve of a discharge current.

FIG. 6 is a diagram for explaining a comparison between a waveform of a charging voltage to a capacitor and a conventional waveform.

FIG. 7 is an explanatory diagram of pulse width control when a full-wave rectified waveform is pulsed.

FIG. 8 is an explanatory diagram of pulse width control when a full-wave rectified waveform is pulsed.

FIG. 9 is an explanatory diagram of pulse width control when a full-wave rectified waveform is pulsed.

FIG. 10 is a diagram showing a rectification / voltage control circuit in a conventional spot welding machine using a thyristor.

FIG. 11 is a diagram showing a lapse of time of a charging voltage.

FIG. 12 is a diagram showing a discharge control circuit in a conventional spot welding machine using a thyristor.

FIG. 13 is a diagram showing a waveform of a discharge current.

FIG. 14 is a diagram showing a waveform of a discharge current flowing through thyristors SCR4 and SCR5.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 rectification and voltage control unit 11 full-wave rectification circuit 12 control circuit 13 control circuit 20 discharge control unit 31 voltage control circuit 32 charging voltage control circuit C capacitor IGBT0-4 insulated gate bipolar transistor I1, I2 discharge current T1 step-up transformer T3 welding Trance

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-24877 (JP, A) JP-A-5-237657 (JP, A) JP-A-7-266060 (JP, A) JP-A-1- 234063 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 11/26 H02J 1/00 H02M 9/00

Claims (1)

(57) [Claims] 1. A welding transformer for charging voltage to a capacitor.
A spot welding machine that performs welding by discharging to the primary side of a rectifier and a voltage controller that performs full-wave rectification of an input voltage and charges the capacitor with the voltage of the full-wave rectified waveform; Discharge insulated gate type bipolar
It includes a discharge control unit for controlling at off the transistor, and the rectifier and the voltage control unit, the charging, the full-wave rectifier
The waveform voltage is controlled by the insulated gate bipolar transistor
The setting voltage is controlled by the pulse wave generated by the on / off control.
Pulse wave when the difference between
When the difference is small, the pulse wave becomes
The discharge control unit performs pulse wave control in such a manner that the four insulating gates are controlled by the first discharge command.
Turn on two of the bipolar transistors
Passing discharge current to the primary side of the welding transformer in the first route
At the same time as the first discharge command is turned off.
The current is turned off and four insulated gate bipolars are turned on by the second discharge command.
Turn on another two of the ranistas and on the second route
Discharge of polarity opposite to the first route on the primary side of the welding transformer
When current flows and the second discharge command turns off,
A spot welding machine characterized in that the discharge current is sometimes turned off .