JPS597546B2 - Transformerless capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in capacitor discharge type welding equipment.

Conventionally, charge is accumulated in a capacitor from an AC power source through a power transformer and a rectifier, and the charge is discharged directly or through a welding transformer to the stud weld, and SCR is used to control the charging voltage of the capacitor and turn on and off the discharge circuit. Various devices have been proposed that are configured to perform welding operations.

This type of welding device is required to be small and lightweight, requires little control power, has a long life, and is easy to maintain.

However, with conventional capacitor discharge type welding equipment,
It is equipped with a power transformer and in some cases a welding transformer, and these transformers weigh about 10 mm and have a large weight per volume, making the supporting parts heavy. Furthermore, since the weight of the capacitor itself is considerable, the demand for small size and light weight is not fully met in practice.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a so-called transformerless capacitor discharge type welding device in which a power transformer is removed in order to satisfy the demand for reduction in size and weight. By the way, if you simply remove the power transformer, when you turn on the power switch,
Voltage is induced in the welding gun terminal of the welded part connected to the negative power terminal, creating a risk of electric shock to the operator. That is, according to experiments, for example, the terminal voltage of a capacitor is 156V.
If -56V (this value is measured between the terminal of the welding gun and the zero volt earth) is induced at the welding gun terminal of the welding section connected to the negative power supply terminal, and this induced voltage It was observed that the magnitude of , increases and decreases in proportion to the magnitude of the terminal voltage of the capacitor. Furthermore, it was observed that the induced voltage was not only a negative value but also a positive value. Therefore, from the viewpoint of preventing the danger of electric shock due to such induced voltage, in order to achieve the above object, the transformerless capacitor discharge type welding device according to the present invention uses a welding gun to weld studs into the base material. A capacitor is connected in parallel between the welding section and the power supply terminal, and a control circuit is provided that controls the charging/discharging circuit of the capacitor to be turned on or off using a trigger signal from the welding gun in response to the state of charge of the capacitor. The present invention is characterized in that a backflow prevention element is connected between the connection point between the capacitor and the negative power supply terminal and the welded part.

The backflow blocking element serves to prevent voltage induction in the welding gun as described above, thereby preventing any electrical shock hazard to the operator.

That is, in the above-mentioned experimental example, when no backflow blocking element was provided, a voltage of -56V (when the capacitor terminal voltage was 156V) was induced at the terminal of the welding gun, but by providing such a backflow blocking element, Therefore, the voltage applied to the welding gun terminal (relative to zero volts ground) is -0.
It became 05V. In the above measurement example, it was found that the same voltage value was obtained no matter how many times the measurement was performed under the same conditions. This backflow blocking element is preferably a silicon rectifier (S
It consists of a semiconductor rectifier such as a silicon controlled rectifier (SCR) or a silicon controlled rectifier (SCR); other switching elements can also be used. Hereinafter, the present invention will be described by way of example with reference to the accompanying drawings.

The drawing shows an embodiment of the present invention, in which 1 and 2 are AC power input terminals, 3 is a power switch, 4 to 7 are diodes constituting a rectifier bridge, and 8 is a switching element of a charging circuit for a welding capacitor 9. A silicon controlled rectifier comprising: 1
0 is a silicon-controlled rectifier forming a switching element of the discharging circuit of the welding capacitor 9; 11 is the base material; 12 is the welding gun; 13 is a charging voltage control circuit for the welding capacitor 9;
Reference numeral 4 denotes a control circuit for controlling on/off of the discharge circuit of the welding capacitor 9.

A welding capacitor 9 is connected between the output terminals of a rectifier bridge consisting of diodes 4 to 7 via a silicon-controlled rectifier 8, and one plate of this welding capacitor 9 and a stud are welded together. A switching element 10 of a discharge circuit for the capacitor 9 is connected to the base material 11. Charging voltage control circuit 13 and discharging circuit control circuit 14
For example, the configuration proposed in Japanese Patent Application No. 49-31009 is advantageously used, and a detailed explanation of these circuits will be omitted here. In the circuit arrangement shown in the drawing in which the power transformer is removed, a positive voltage is applied to the terminal of the welding gun 12 of the welding section connected to the negative output terminal of the rectifier bridge when the power switch 3 is closed. induced.

Therefore, in the present invention, in order to prevent this voltage induction, a backflow prevention element (in the illustrated embodiment, a silicon rectifier) is provided between the welding gun 12 and the connection point P1 between the welding capacitor 9 and the negative output terminal of the rectifier bridge. )15 is inserted. The operation of the apparatus according to the present invention constructed as described above will be briefly described.

Initially, it is assumed that the power switch 3 is closed and the welding capacitor 9 is in a discharged state, that is, in a state of zero voltage.

In this state, when the trigger switch (not shown) of the welding gun included in the control circuit 14 of the discharge circuit is opened, the relay coil in the control circuit 14 is demagnetized. Via the normally closed contacts of the relay in the charging voltage control circuit 13, the oscillating circuit of this circuit oscillates, which supplies an ignition signal to the gate terminal of the switching element 8 of the charging circuit of the welding capacitor 9, so that the switching Element 8 is conducting. As a result, the welding capacitor 9 starts to be charged via the switching element 8, and when the welding capacitor 9 is charged to a predetermined value, the oscillation circuit in the charging voltage control circuit 13 stops. As a result, the switching element 8 is disconnected and the charging of the welding capacitor 9 is therefore stopped. In this state, when the welding gun is triggered, that is, when the trigger switch in the control circuit 14 is closed, the relay coil is energized, the normally open contacts in this control circuit are closed, and the discharge circuit is connected from this control circuit 14. An ignition signal is sent to the gate terminal of the switching element 10, which causes the switching element 10 to conduct. As a result, the implantation capacitor 9 discharges through the switching element 10. In this way, the studs are welded into the base material. On the other hand, when the trigger switch is closed, that is, the relay coil is energized, the normally closed contacts in the control circuit 13 are opened, and the charging circuit for the welding capacitor 9 is opened when the switching element 8 is disconnected. Further, the conduction time of the switching element 10 in the discharge circuit is set longer than the discharge time of the welding capacitor 9. In this way, one welding operation is performed and the initial state is returned. Furthermore, the charging circuit of the welding capacitor 9 is immediately released when the switching element 8 is disconnected. Further, the conduction time of the switching element 10 in the discharge circuit is set longer than the discharge time of the welding capacitor 9. In this way, one welding operation is performed and the initial state is returned. Furthermore, the control circuits 13 and 14 of the charging/discharging circuit of the welding capacitor 9 prevent the capacitor from discharging even if the trigger switch of the welding gun is closed before the charge of the welding capacitor reaches a predetermined value. It also works to reliably prevent further charging of the capacitor. As explained above, according to the present invention, a small, lightweight, and relatively inexpensive S
By using R, SCR, etc., the main body of the device can be made smaller and lighter, the cost of the device can be lowered, maintenance can be made easier, and many other effects can be brought about.

As a result, handling of the welding device main body becomes easier, and work efficiency can be further improved. However, it is clear that the present invention may be modified in various ways within the scope of the present invention in the illustrated circuit arrangement, and may also be applied to other conventional capacitor discharge type welding devices.

[Brief explanation of drawings]

The accompanying drawings are circuit diagrams showing one embodiment of the present invention. In the circuit, 8 and 10 are switching elements, 9 is a welding capacitor, 11 is a base material, 12 is a welding gun, 13 and 14 are control circuits, and 15 is a backflow prevention element.

Claims (1)

[Claims] 1. A capacitor is connected in parallel between the welding part where studs are welded into the base material using a welding gun and the power terminal, and in response to the state of charge of this capacitor, a trigger signal from the welding gun is used to activate the capacitor. A transformerless capacitor discharge type, characterized in that a control circuit for controlling on and off of the charge/discharge circuit is provided, and a backflow prevention element is connected between the connection point between the capacitor and the negative power terminal and the welded part. Welding equipment.