JPH0459189A - Capacitor type spot welding machine - Google Patents

Abstract

PURPOSE:To prevent the reverse voltage from being impressed on a capacitor by providing a switching element having self-extinction of arc of a transistor, etc., in parallel with a switching element having nonself-arc-extinguishing characteristics for discharge. CONSTITUTION:When the voltage on both ends of the capacitor 4 attains almost zero, since the switching element having the self-extinction of arc is turned on for a short period of time, the switching element having nonself-arc- extinguishing characteristics for discharge is made to less than a holding current and turned off. At this time, exciting energy of a transformer 6 for welding flows through a path of a resetting means and continues for a short period of time till the exciting energy is extinguished. Accordingly, the exciting energy of the transformer 6 for welding is extinguished quietly and a magnetic core can be reset and the switching element is turned off, hence the reverse voltage is not impressed at all on the capacitor 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a capacitor type spot welding machine, and particularly to a capacitor type spot welding machine that improves reverse voltage application during discharge of a capacitor.

[Prior art/problems to be solved by the invention] A capacitor type spot welding machine uses a switching element such as a thyristor to instantly discharge the energy stored in a capacitor, and then changes the winding ratio to further increase the current in a transformer. The object to be welded is welded between selected welding electrodes connected to the secondary winding of the transformer. In this case, the thyristor is a suitable switching element for instantaneously discharging a large current, but it has a non-self-extinguishing characteristic.

- Once conductive, the self-control ability cannot turn it off unless the current drops below the holding current. Furthermore, the method for resetting the excitation energy of the transformer after the thyristor is turned off is incomplete, and a reverse voltage is applied to the capacitor, which shortens its life.

To give an example, the conventional configuration is as shown in FIG. 3. That is, an AC power supply l is connected to the primary winding of the transformer 2, the secondary winding boosts the voltage to a predetermined voltage, and this voltage is controlled and rectified by a bridge circuit consisting of a thyristor 31, 32 and a diode 33, 34. death.

Electrolytic capacitor 4 is charged via resistor 36.

Next, a signal to turn on the gate of the thyristor 5 is driven by the discharge control circuit 51. The discharge current of the capacitor 4 flows through the thyristor 5 through the primary winding 61 of the transformer 6 . A welding electrode 7 is connected to the secondary winding 62 of the transformer 6, and a welded object 71 is held between the welding electrodes 7 and 71. Since a large current flows through this, high heat is generated and welding is performed.

The current and voltage waveforms of each part at this time are shown in Figure 4 (18) to (6).
Shown below. As shown in the figure (a) showing the voltage waveform of the capacitor 4, when the thyristor 5 is turned on at time 1 to, the voltage 4 gradually decreases from V4=VO.

Finally, at 11, the voltage becomes zero. During this period, the current in the thyristor 5 gradually decreases after a mountain-shaped current flows from time to, as shown in TC), but at time tl, the current increases by an amount corresponding to the excitation energy of the transformer 6. value exists. This current source reverses the polarity of the voltage v61 across the primary winding 61 of the transformer 6, resulting in a waveform as shown in (dl). This current flows through the series circuit of the diode 43 and resistor 44. Therefore, the capacitor The voltage of 4 is (as shown in al, from time t1 to t
2, it becomes a negative voltage, and its maximum value is V
It becomes r. Since this maximum value V' impairs the performance of the capacitor 4, attempts have been made to reduce it by adjusting the value of the resistor 44 in various ways.
It stays at around r=120v.

The present invention completely resets the excitation voltage of the welding transformer,
The objective is to essentially eliminate the voltage applied to the capacitor in transit.

[Means to solve the problem]

In order to solve the above problems, first, a reset means is provided in the welding transformer. Then, a switching element with self-extinguishing characteristics such as a transistor is provided in parallel with a switching element having non-self-extinguishing characteristics for discharging, and when the voltage of the capacitor becomes almost zero, this self-extinguishing characteristic is activated. This method uses a means to turn on the switching element that has the switch for a short period of time.

[Effect]

When the voltage across the capacitor becomes almost zero, the switching element has a self-extinguishing characteristic for a short time.

Since it is turned on, the switching element having a non-self-extinguishing characteristic for discharging becomes lower than the holding current and is turned off. At this time, the excitation energy of the welding transformer flows through the path of the reset means and continues for a short time until the excitation energy disappears.

Therefore, the excitation energy of the welding transformer quietly disappears,
Since the magnetic core can be reset and the switching element is turned off, no reverse voltage is applied to the capacitor.

〔Example〕

FIG. 1 shows an embodiment of the invention. In the figure, an AC power source 1 is connected to the primary winding of a transformer 2 and boosted to a predetermined voltage by the secondary winding. This voltage is controlled and rectified by a bridge circuit consisting of a thyristor 31 , 32 and a diode 33 , 34 and charges the electrolytic capacitor 4 via a resistor 36 . Thyristors 31 and 32 are controlled by a charging control circuit 35.

Next, a signal to turn on the gate of the thyristor 5 is driven by the discharge control circuit 51. Current flows through the thyristor 5 through the primary winding 61 of the transformer 6 .

A welding electrode 7 is connected to the secondary winding 62 of the transformer 6, and a welded object 71 is held between the welding electrodes 7 and 71. Since a large current flows through this, high heat is generated and welding is performed.

The current and voltage waveforms of each part at this time are shown in Figure 2 (a) ~ (Company)
Shown below. As shown in the figure (a) showing the voltage waveform of the capacitor 4, when the thyristor 5 is turned on at time 1 to, the voltage v4 gradually decreases from V4=VO.

Finally, the voltage becomes zero at tl. During this period, the current in the thyristor 5 gradually decreases after a mountain-shaped current flows from time to as shown in FIG. exists. At this time, the voltage detector 41 connected to both ends of the capacitor 4 causes the discharge control circuit 51 to apply a drive signal to the transistor 52 from its terminals J and H.
As shown in FIG. 2(C), the transistor 52 is turned on for a short time from 1=11 to 1=111. This time requires several μs to several tens of μs until the thyristor 5 turns off. The current +52 flowing through the transistor 52 is (C
), the value is small compared to the maximum current of the thyristor 5, and since the maximum applied voltage of the capacitor 4 is required only for the withstand voltage, a transistor with a relatively small capacity can be used. t
= After tll, the transistor 52 connected in parallel with the thyristor 5 is turned off, so the voltage v4 of the capacitor 4
continues to be zero. On the other hand, due to the excitation energy of the transformer 6, the polarity of the voltage V61 of the negative winding 61 is reversed and the same (d
The waveform will be as shown in l. This current flows through diode 63
and resistor 64 in series circuit.

As described above, the transformer 6 is reset and the capacitor 4 is reset.
reverse voltage prevention is achieved.

In addition, as a means for resetting the welding transformer 6.

Although the method shown in this embodiment is simple, it is also possible to provide a separate winding and connect it to a series circuit of a resistor and a diode. It is also possible to feed back to the capacitor 4 via a diode in a separate winding.

Transistor 52 may also be replaced by other types of self-extinguishing switching elements, such as field effect transistors.

〔Effect of the invention〕

The present invention has the above-mentioned features and can completely prevent reverse voltage from being applied to the capacitor in order to ensure the reset of the welding transformer. Therefore, the life of the capacitor can be extended.

Conventionally, in this type of capacitor type spot welding machine, it was inevitable that a reverse voltage was applied to the capacitor, so the capacitor had to be large in size to accommodate the withstand voltage. Therefore, according to the present invention, a capacitor can be made smaller and have a longer life.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of a capacitor type spot welding machine according to the present invention, and FIG. 2 shows waveforms for explaining its operation. Figure 3 shows an example of a conventional capacitor type spot welding machine, and Figure 4 (shows waveforms to explain other operations.・
Thyristor 33, 34--Diode, 35--Charging control circuit 4--Capacitor, 41--Voltage detector 5
...Thyristor, 51...Discharge control circuit 6-...
Transformer, 63...-Diode, 64-...Resistor 7.
...Welding electrode, 71-...Welded object patent applicant Origin Electric Co., Ltd. ± 1 Figure Figure Ogoju

Claims (1)

[Claims] A transformer having a capacitor charged by a charging circuit, a primary winding, and a secondary winding, and having an electrode connected to the secondary winding by welding, and the primary winding of the transformer. and the capacitor; a reset means connected to the transformer; a self-extinguishing switching element connected in parallel to the non-self-extinguishing switching element; and the capacitor. and a control circuit that turns on the self-extinguishing switching element for a short time when the voltage across it is approximately zero.