JPH0360586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transformerless capacitor discharge type welding device for welding studs such as nail-shaped pins onto a base material such as a metal plate.

[Conventional technology]

Conventionally, various types of transformer-less capacitor discharge type welding apparatuses have been known as so-called stud welding machines. As an example, in a transformerless capacitor discharge type welding device as shown in FIG. 2, input terminals 1a and 1b to which AC is supplied from an AC power source (not shown) are Further, a welding capacitor 4 is connected through a bridge rectifier circuit 3 consisting of a rectifying diode, and a welding gun 6 and a base material 5 on which studs are to be welded are connected in parallel to this welding capacitor 4. is connected.

Here, a switching element 7 for controlling the charging voltage of the welding capacitor 4 is inserted on one side between the bridge rectifier circuit 3 and the welding capacitor 4, and this switching element 7 is operated so that the charging voltage control circuit 8 charges the welding capacitor 4 to a constant voltage, and thereafter does not perform charging. Furthermore, switching elements 9 and 9' having the polarity matched to the switching element 7 are connected in series to both sides of the base material 5 and the welding gun 6, respectively, and the switching elements 9 are connected to a discharge control circuit. When turned on by 9a, the switching element 9' discharges the electric charge charged in the welding capacitor 4, and when the charging is completed, the switching element 9'
This prevents a backflow of the positive voltage induced in the welding gun 6 connected to the negative output of the welding gun 6.

In the transformerless capacitor discharge type welding apparatus configured as described above, when the power switch 2 is turned on, the input terminal 1 is connected to the AC power source (not shown).
Electric power is supplied via a and 1b, and the input alternating current is rectified by a bridge rectifier circuit 3 and then charged into a welding capacitor 4. At this time, the switching element 7 is controlled by the charging voltage control circuit 8, so that the welding capacitor 4 is charged to a predetermined voltage, and when charging is completed, the switching element 7 is turned off and charging is stopped. Ru. Subsequently, the backflow prevention switching element 9' of the discharge control switching element 9 is connected to the discharge control circuit 9a.
The welding capacitor 4 is turned on and the electric charge charged in the welding capacitor 4 is discharged, and an arc is generated between the base material 5 and the welding gun 6, so that studs are welded onto the base material 5. That will happen.

[Problem that the invention seeks to solve]

However, in the transformerless capacitor discharge type welding apparatus configured as above, the base material 5 may be connected to the earth ground E as shown by the dotted line in the drawing, but in such a case, When the switching elements 9 and 9' are turned on during discharge, electricity flows from the earth ground E through the base material 5, the welding gun 6, the switching element 9', and through the rectifier diode 3a or 3b of the bridge rectifier circuit 3. Short circuit current flows in the direction of the arrow. Further, the charging voltage control circuit 8 includes a switching element 7
When controlling the switching element 7, the switching element 7 cannot be turned on during the half-cycle portion corresponding to the rising edge of the input AC, so if the welding capacitor 4 reaches a predetermined voltage at the timing of this portion, will be further charged before the switching element 7 is turned off, and the charging voltage of the welding capacitor 4 will become higher than the predetermined voltage, causing a so-called overshoot, which will prevent stud welding. It becomes stable.

In view of the above points, the present invention prevents short-circuit current from flowing during discharge even when the base material is connected to the earth ground, and prevents the stud from flowing by overshooting the charging voltage of the welding capacitor. The object of the present invention is to provide a transformerless capacitor discharge type welding device that does not cause unstable welding.

[Means and actions for solving problems]

According to the present invention, two input terminals to be connected to an AC power supply, a capacitor for welding connected between the two input terminals via a bridge rectifier circuit, and a capacitor for welding A base material and a welding gun connected in parallel to the capacitor, a first switching element for controlling discharge, and a second switching element for preventing backflow, connected in series on both sides of the base material and the welding gun, respectively. and a discharge control circuit that turns on the first and second switching elements during discharge, a transformerless capacitor discharge type welding device for welding studs on a base material, comprising two input terminals and a bridge rectifier. Two third switching elements for charging control are inserted between the input side of the circuit, and a current limiting resistor for discharging and a fourth switching element for discharging are connected in parallel to the welding capacitor. Furthermore, a charging voltage control circuit for controlling the third and fourth switching elements is provided, and the charging voltage control circuit controls the third switching element only when charging the welding capacitor. If the charging voltage of the welding capacitor is higher than the predetermined voltage and an overshoot occurs, the fourth switching element is turned on and the welding capacitor is discharged to reach the predetermined charging voltage. This is achieved by making the control action take place.

According to this invention, a third switching element for charge control is inserted between the two input terminals and the input side of the bridge rectifier circuit, and the third switching element is used only when charging the welding capacitor. Since the input side of the bridge rectifier circuit is cut off from the AC power supply when the welding capacitor is discharged, even if the base material is connected to the earth ground, there is no connection from the earth ground. No short-circuit current would flow through the base material, the welding gun, or the rectifier diodes of the bridge rectifier circuit, and the charging voltage of the welding capacitor would become higher than the specified voltage, causing a so-called overshoot. In some cases, the charging control circuit turns on the discharging switching element and discharges through the current limiting resistor until a predetermined voltage is reached, so the overshoot can cause the stud melt of this device to occur. The planting action will not become unstable.

〔Example〕

The present invention will be further described below based on embodiments shown in the drawings.

FIG. 1 shows an embodiment of a transformerless capacitor discharge type welding device according to the present invention, and the transformerless capacitor discharge type welding device 10 has an input terminal 1 to which AC is supplied from an AC power source (not shown).
For 1 and 12, double pole double throw power switch 1
A welding capacitor 16 is connected on one side of the welding capacitor 16 via a fuse 14 and a bridge rectifier circuit 15 consisting of a rectifying diode, and a stud is to be welded in parallel to this welding capacitor 16. The base material 17 and the welding gun 18 are connected.

Here, on the input side of the bridge rectifier circuit 15,
Charging control switching elements 19 and 20 for controlling charging of the welding capacitor 16 are inserted on both sides thereof. Further, a discharge current limiting resistor 21 and a discharge switching element 22 are connected in parallel to the welding capacitor 16. These switching elements 19, 20, and 22 are controlled by a charging voltage control circuit 23 as described later. That is, charging voltage control circuit 2
3 turns on the switching elements 19 and 20 only when charging the welding capacitor 16, and turns on the switching element 22 when the charging voltage of the welding capacitor 16 is higher than a predetermined voltage and overshoot occurs. is turned on to discharge the welding capacitor 16 via the current limiting resistor 21 until the charging voltage of the welding capacitor 16 reaches a predetermined voltage.

Further, on both sides of the base material 17 and the welding gun 18, switching elements 24 and 25 are installed in series with the base material 17 and the welding gun 18.
are connected to each other, and the switching elements 24
When turned on by the discharge control circuit 26, the charge charged in the welding capacitor 16 is discharged, and the switching element 25
prevents the backflow of the positive voltage induced in the welding gun 18 connected to the negative output of the bridge rectifier circuit upon completion of charging.

The transformerless capacitor discharge type welding device according to the present invention is constructed as described above, and when the power switch 13 is first turned on, power is supplied from an AC power source (not shown) through the input terminals 11 and 12, and the input signal is input. Since the switching elements 19 and 20 are turned on by the charging voltage control circuit 23 when charging the welding capacitor 16, the alternating current is rectified by the bridge rectifier circuit 15 and then used for welding. The capacitor 16 is charged.

Here, when the charging voltage of the welding capacitor 16 reaches a predetermined voltage, the charging voltage control circuit 23 turns off the switching elements 19 and 20, thereby completing the charging of the welding capacitor 16. In this case, in the half cycle portion corresponding to the falling edge of the input AC, the switching elements 19 and 20
Since it is not possible to turn off the welding capacitor 1
When the charging voltage of the welding capacitor 16 becomes higher than a predetermined voltage and a so-called overshoot occurs, the charging voltage control circuit 23 turns on the switching element 22 until the charging voltage of the welding capacitor 16 reaches the predetermined voltage. Discharge through the current limiting resistor 21,
When the charging voltage reaches a predetermined voltage, the switching element 22 is turned off. In this way, the welding capacitor 16 is charged.

Subsequently, the discharge control circuit 26 is activated, and the switching elements 24 and 25 are both turned on, thereby discharging the electric charge stored in the welding capacitor 16 and discharging the charge between the base material 17 and the welding gun 18. The studs are welded onto the base material 17 by the generation of an arc during this time. At this time, base material 1
7 is the earth ground E as shown by the dotted line in Figure 1.
When connected to the switching element 19,
20 is turned off, no short circuit current will flow from the ground E through the base material 17 and the welding gun 18.

〔Effect of the invention〕

As described above, according to the present invention, a third switching element for charging control is inserted between the two input terminals and the input side of the bridge rectifier circuit, and the switching element Since it is turned on only when charging the capacitor, the input side of the bridge rectifier circuit is cut off from the AC power supply when discharging the welding capacitor.
Even if the base material is connected to earth ground,
A short-circuit current will not flow from the earth ground through the base metal, the welding gun, and each rectifier diode of the bridge rectifier circuit, and the charging voltage of the welding capacitor will become higher than the specified voltage, resulting in so-called overshield. When an overshoot occurs, the charging control circuit turns on the discharging switching element and discharges through the current limiting resistor until a predetermined voltage is reached. The stud welding operation of the device will not become unstable.

Therefore, according to the present invention, no short circuit current flows even when the base material is connected to the earth ground, and the welding capacitor is always charged to a constant charging voltage, so that stable stud melting is always achieved. It is possible to provide a transformerless capacitor discharge type welding device in which welding can be performed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of a transformerless capacitor discharge type welding device according to the present invention. Second
The figure is a circuit diagram of an example of a conventional transformerless capacitor discharge type welding device. 10...Transformerless capacitor discharge type welding device; 11, 12...Input terminal; 13...Power switch; 14...Fuse; 15...Bridge rectifier circuit;
16... Capacitor for welding; 17... Base material; 18... Welding gun; 19, 20... Switching element for controlling charging voltage; 21... Current limiting resistor for discharging; 22... Switching element for discharging; 23... Charging voltage control circuit ;
24...Switching element for discharge control; 25...Switching element for backflow prevention; 26...Discharge control circuit;
E...Earth ground.

Claims (1)

[Claims] 1. Two input terminals to be connected to an AC power source, a welding capacitor connected between the two input terminals via a bridge rectifier circuit, and a welding capacitor connected in parallel to the welding capacitor. a base material and a welding gun connected to the base material, a first switching element for controlling discharge and a second switching element for preventing backflow connected in series on both sides of the base material and the welding gun, and the above-mentioned A transformerless capacitor discharge type welding apparatus for welding studs in a base material, comprising a discharge control circuit that turns on first and second switching elements during discharge, two input terminals and an input of a bridge rectifier circuit. Two third switching elements for charging control are inserted between the two sides, and a current limiting resistor for discharging and a fourth switching element for discharging are connected in parallel to the welding capacitor, and further A charging voltage control circuit is provided for controlling the third and fourth switching elements, and the charging voltage control circuit turns on the third switching element only when charging the welding capacitor, In addition, if the charging voltage of the welding capacitor is higher than a predetermined voltage and an overshoot occurs, a control operation is performed to turn on the fourth switching element and discharge the welding capacitor to reach the predetermined charging voltage. A transformerless capacitor discharge type welding device that performs the following.