JPS595395B2 - Capacitors - Google Patents

Description

[Detailed Description of the Invention] This invention provides a switching element in the discharge circuit of a capacitor that stores energy for welding the stud j into the base material using a welding gun, and a switching element is provided in the discharge circuit of the capacitor that stores energy for welding the stud j into the base material using a welding gun, and the switching element is configured to respond to the state of charge of the capacitor. This invention relates to a capacitor discharge type spot welding machine in which the charging/discharging circuit of the capacitor is controlled to be turned on or off by a trigger signal from a welding gun.

In this type of capacitor discharge type stud welding machine,
The discharge circuit of the capacitor cannot be operated until the capacitor is charged to a predetermined value, and the charging circuit of the capacitor is cut off when the capacitor is discharged, that is, when the stud is welded.

Furthermore, semiconductor controlled rectifiers such as SCRs are widely used as switching elements for turning on and off capacitor charging and discharging circuits. However, during operation of the welding machine, if the switching element inserted into the discharge circuit of the capacitor is damaged in a conductive state, for example, the voltage of the capacitor will be applied to the output terminal of the discharge circuit of the capacitor, and the voltage of the capacitor will be applied to the output terminal of the discharge circuit of the capacitor. Not only will the power supply be short-circuited and a large current will flow, damaging the power supply, but it can also cause shock to the worker.
Very dangerous. Therefore, an object of the present invention is to provide an electric shock prevention device that short-circuits the capacitor's discharge circuit to cut off the capacitor's power supply circuit or charging circuit when the capacitor's discharge circuit is damaged. An object of the present invention is to provide a capacitor discharge type stud welding machine.

That is, according to the present invention, a short circuit operating through a delay circuit is connected to the discharging circuit of the capacitor, and the power source or the charging circuit of the capacitor is cut off in response to the operation of the short circuit.

The short circuit preferably comprises a switching element such as an SCR. Further, the capacitor charging circuit is disconnected by disconnecting the switching element of the capacitor charging circuit by means of a relay device which operates in response to conduction of the short circuit. Hereinafter, the present invention will be further described with reference to the accompanying drawings.

In FIGS. 1 to 3, the same components will be described with the same reference numerals.

Fig. 1 shows an embodiment of the present invention, where A and B are power supply terminals, F is a fuse, T is a power transformer, D1 to D4 & diodes forming a rectifier bridge, Cl and C2 are capacitors, SCRl, SCR2 is a silicon controlled rectifier, R
1 to R3 are resistors, D5 is a diode, and X and Y are output terminals.

As shown, the primary side of power transformer T is connected to power terminals A and B via fuse F, and the secondary side of power transformer T is connected to rectifier bridges D1-D4. A capacitor C1 for storing charge for welding is connected between the output terminals of the rectifier bridges D1 to D4, and a silicon-controlled rectifier serving as a switching element of the discharge circuit of the capacitor C1 is connected between this capacitor C1 and one of the output terminals x. SCRl is connected. As shown in the figure, the discharge circuit of capacitor C1 includes a large capacity low resistance R3 and a silicon controlled rectifier SCR2.
A short circuit is provided consisting of a silicon controlled rectifier S
The gate electrode of CR2 is a small capacitance high resistance Rl, R2 for voltage division.
and a capacitor C2 via a diode D5. In the illustrated embodiment, a control circuit for controlling ON/OFF of the switching element SCRl of the discharge circuit according to the charging state of the capacitor C1 is omitted. The operation of the apparatus of the embodiment shown in FIG. 1 constructed in this manner will be described below.

In normal operation, the switching element SC of the discharge circuit
If Rl is damaged in a conductive state, the voltage of the capacitor C1 is applied to the output terminals X and Y.

On the other hand, capacitor C2 is charged with the voltage divided by resistors Rl and R2. The charging voltage of this capacitor C2 causes a gate current to flow through the diode D5 to the gate electrode of the short-circuited silicon-controlled rectifier SCR2, so that this silicon-controlled rectifier SCR2 becomes conductive. As a result, current flows in a short circuit through resistor R3 and silicon controlled rectifier SCR2, and the charge on capacitor C1 is discharged. As a result of this discharge, fuse F is blown by a current determined by the impedance of power transformer T. Therefore, no current flows through the capacitor C1, so the voltage becomes almost zero. FIG. 2 shows another embodiment of the invention.

In this embodiment, the power supply transformer consists of a magnetic leakage voltage generator LT, a keep relay LR is connected between the terminals of a short circuit resistor R1 via a constant voltage diode ZD, and a normally closed contact LR-C of this relay LR is connected between the terminals of a short circuit resistor R1. is connected to the gate electrode of the switching element SCR3 inserted into the charging circuit of the capacitor C1. Further, this gate electrode is connected to a circuit (X) not shown. To explain the operation of the embodiment of FIG. 2 constructed in this way, as in the case of FIG. The voltage of capacitor C1 is applied. On the other hand, capacitor C2 is charged with a voltage divided by resistors Rl and R2. When capacitor C2 is charged, a gate current flows through diode D5 to silicon controlled rectifier SCR2, making it conductive. As a result, the charge on capacitor C1 is discharged through resistor R3 and silicon controlled rectifier SCR2. The current flowing through this short circuit generates a voltage between the terminals of resistor R3, and this voltage operates keep relay LR. The contact LR-C is thereby opened and the gate current of the switching element SCR3 of the charging circuit of the capacitor C1 is cut off. Therefore, no charging current flows to the capacitor C1, and the voltage becomes almost zero. FIG. 3 shows a modification of the embodiment of FIG. 2, in which a no-fuse breaker NFB is connected between the input terminal and the power transformer LT, and in this embodiment, the keep relay LR of FIG. 2 is replaced. It is configured to directly break the no-fuse breaker NFB.

As explained above, according to the present invention, in a capacitor discharge type stud welding machine, a short-circuit discharge circuit for preventing electric shock is provided in the discharge circuit of the capacitor that stores charge for stud welding, and the charging of the capacitor is prevented. Even if the switching element of the capacitor's discharging circuit were to fail in the conductive state, the capacitor's charge would be discharged through the short circuit and the charging current to the capacitor would be interrupted, thus interrupting the power supply. Excellent effects such as protecting equipment and preventing shock to workers are brought about.

[Brief explanation of the drawing]

1, 2 and 3 are circuit diagrams showing three embodiments of a capacitor discharge type stud welding machine equipped with an electric shock prevention device according to the present invention. In the diagram, F is a fuse, NFB is a no-fuse breaker,
C1 is a capacitor, SCR1 to SCR3 are silicon controlled rectifiers, R1 to R3 are resistors, C2 is a capacitor (delay circuit), and LR is a keep relay.

Claims (1)

[Claims] 1. A switching element is inserted into the discharge circuit of a capacitor that stores energy for welding a stud into a base material using a welding gun, and in response to the state of charge of the capacitor, a trigger signal from the welding gun activates the capacitor. A short circuit that operates via a delay circuit is inserted into the discharge circuit of the capacitor, and depending on the operation of this short circuit, the power supply or the charging circuit of the capacitor is turned on and off. A capacitor discharge type stud welding machine equipped with an electric shock prevention device.