JPS5832862Y2 - spot welding machine - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a spot welding machine that charges a large-capacity capacitor with electric charge and releases it instantly when the button is pressed.

Conventionally, as a welding power source for a spot welding machine that has a large capacity capacitor and utilizes instantaneous discharge of the energy stored in this capacitor, as shown in Figure 1, a 50 Hz AC boosted through a power transformer 1 is rectified. diode 2A, 2B
and a rectifier 4 consisting of charging control thyristors 3A and 3B.
Full-wave rectification is performed by the charging control thyristor 3A,
The charging control thyristor 3A is connected to the charging circuit after the large capacity capacitor 5 is charged while being controlled by the large capacity capacitor 3B and the terminal voltage of the large capacity capacitor 5 reaches a predetermined voltage.

At the same time as giving a charging stop command signal to 3B, a discharge command signal is given to the discharge control thyristor 6 provided in the discharge circuit, and this is made conductive to instantly release the energy charged in the large capacity capacitor 5. , the welding transformer 7 converts the current into a low voltage and a large current, and the welding object 8 is welded using the Joule heat generated in the welding object due to the resulting large current (2).

The most important point in such a welding method is to stabilize the output current (2).

If the output current (2) of the welding power source is unstable, the welding of the welded object 8 will be unstable, resulting in unstable quality and failure.

Considering this point, in the above conventional configuration, the on/off command signal Sc of the charge control means iris 3A, 3B and the on/off command signal sb of the discharge control thyristor 6 have a relationship as shown in FIG. The off command signal Sc for the charging control thyristors 3A, 3B and the on command signal sb for the discharging control thyristor 6 are generated simultaneously from the charging thyristor and the discharging thyristor control circuits 9, 10. .

By the way, even after the terminal voltage of the large capacity capacitor 5 is charged to a set voltage, it naturally discharges and the voltage gradually decreases, so by supplementary charging, the terminal voltage of the capacitor 5
In order to maintain the voltage at the set voltage, charging thyristors 3A and 3B are used.
is constantly repeating on and off operations.

This operation continues until the discharge control thyristor 6 becomes conductive.

Next, when the welding command signal Sa is issued, the discharge control thyristor 6 becomes conductive, and the charge control thyristor 3A becomes conductive.
, 3B are input with an off signal Sc.

However, once the ON command signal is input, the charging control thyristors 3A and 3B remain conductive until the anode potential reaches zero. It cannot be cut.

Therefore, even if the welding command signal Sa is output during supplementary charging, there is a time period during which the charge control thyristors 3A, 3B and the discharge control thyristor 6 are simultaneously conductive, resulting in a short circuit state.

The duration of this short-circuit state is a maximum of 10 m5 in the case of a 50 Hz full-wave rectifier circuit.

In this case, the current flowing from the power supply through the charging thyristors 3A and 3B is superimposed on the discharge current due to the electrical energy stored in the capacitor, and an output larger than the set value is supplied to the welding part, causing the current flowing to the workpiece to be varied. This results in variations in welding.

The present invention was developed in view of the shortcomings of the conventional technology, and the purpose is to provide a spot welding machine that can perform stable welding and improve quality by keeping the current flowing through the welded object constant. do.

In order to achieve the above object, the present invention includes a delay circuit for delaying a discharge command signal to the discharge control means by a charge stop signal to the charge control means, and controls the discharge after completely rendering the charge control means non-conductive. It is characterized in that the means is configured to be electrically conductive.

The configuration of the spot welding machine according to the present invention will be explained below with reference to FIG.

The alternating current from the power source passes through a power transformer 11, rectifying diodes 12A and 12B, and a charging control thyristor 13A as charging control means.

connected to the input side of the full-wave rectifier circuit 14 consisting of 13B,
The output side of the full-wave rectifier circuit 14 is connected to both sides of a large-capacity capacitor 15 and a discharge control thyristor 16 as discharge control means.
and the series circuit of the welding transformer 17.

A workpiece 18 is connected to the output side of the welding transformer 17.

A movable terminal of a charging voltage setting variable resistor 19 connected in parallel to the charging circuit of the large-capacity capacitor 15 is connected to a charging control thyristor control section 21 operated by a welding command switch 20.

The output signal from the charging control thyristor 21 is connected to the control terminals of the charging control thyristors 13A and 13B.

The welding command switch 20 is further connected to a discharge control thyristor control section 23 via a delay circuit 22, and the control output of the discharge control thyristor control section 23 is connected to a control terminal of the discharge control thyristor 16. There is.

Next, the operation of the apparatus having such a configuration will be explained with reference to FIG.

In the same figure, ■ indicates the welding current flowing through the workpiece 18, and Sa, Sb, and Sc are the a r b t in Fig. 3, respectively.
In the command signal in the part C, Sa is the welding command signal,
Sb indicates a discharge command signal, and Sc indicates a charge command signal.

In this circuit, when the power switch (not shown) is turned on, the charge control thyristors 13A and 13B are made conductive, and the capacitor 15 is charged at 1, when the terminal voltage of the capacitor 15 reaches the set voltage, and the predetermined charging is completed. After that, the welding command switch 20 is turned on, and the replenishment is repeated in small steps.

Next, when the welding command switch 20 is closed and the welding command signal Sa is applied, the charging command signal Sc is immediately stopped.

After 10 to 15 m5 have elapsed, a discharge command signal sb is applied from the discharge control thyristor control section 23 to the discharge control thyristor 16 in response to a signal from the delay circuit 22, and the energy of the large capacity capacitor 15 is discharged and a large amount is applied to the workpiece 18. Apply current to weld this part.

When the capacitor 15 is sufficiently discharged, the continuous charging command signal Sc is output again, and the capacitor 14 is charged.

When charging reaches a predetermined voltage at 1, the signal is switched to an intermittent supplementary charging signal again, and in this state, the welding command signal S
When a is added, the charging command signal S
c stops and repeats the same operation.

As is clear from the above explanation, according to the spot welding machine of the present invention, charging of the capacitor is stopped before the electrical energy charged in the capacitor starts to be discharged by the welding command signal Sa. Only the energy already charged in the capacitor is discharged, and the current flowing from the power source through the charging thyristor does not overlap with the output current, making the output current constant and eliminating variations in welding.

Therefore, welding is stabilized, quality is significantly improved, and yield is also greatly improved.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of the power supply circuit of a conventional spot welding machine, Fig. 2 is a diagram showing the control signal button and welding current waveform of the conventional spot welding machine, and Fig. 3 is a spot welding according to the present invention. FIG. 4 is a block diagram showing the configuration of the power supply circuit of the machine, and FIG. 4 is a diagram showing control signals and welding current waveforms of the spot welding machine according to the present invention. 13A, 13B...Charging control thyristor, 15...
・Large capacity capacitor, 16... Thyristor for discharge control, 20... Welding command switch, 21... Thyristor leg for charge control, 22... Delay circuit, 23... Thyristor control for discharge control Part, Sa...Welding command signal,
sb...Discharge command signal, Sc...Charge command signal.

Claims (1)

[Scope of utility model registration request] 1. Spot welding including a capacitor for charging electric charge, a charging control means provided in a charging circuit to control charging of the capacitor, and a discharge control means provided in a discharging circuit to control discharging of the capacitor. 1. A spot welding machine comprising a delay circuit for delaying a discharge command signal to a discharge control means by a charge stop command signal to a charge control means. 2. The spot welding machine according to claim 1, wherein the charging control means and the discharge control means are comprised of thyristors.