JPS62156084A - Spot welding machine - Google Patents

Abstract

PURPOSE:To prevent the reverse charging of an electrolytic capacitor and to prevent the deterioration of the performance of the electrolytic capacitor by incorporating two pieces of electrolytic capacitors, two pieces of gate turnoff thyristors and resistor with the specified circuit into the power source circuit of a capacitor type spot welding machine. CONSTITUTION:The charging and discharging circuit for capacitor equipping a thyristor switch 2 is formed between the DC power source 5 of a capacitor type spot welding machine and the primary line of the transformer for welding. The electrolytic capacitor 1a, 1b in the same capacity is connected in parallel by reversing the polarity via a charging resistance 6 to the DC power source 5 and the connection point at the cathode side of both capacitors is linked with the connection point of two pieces of gate turnoff thyristor 7a, 7b and connected to the negative pole side of the DC power source 5 via a resistance 8 and the thyristor 2 is connected to the primary side of a welding transformer 3 as well. Since both electrolytic capacitors 1a, 1b are not charged reversely in case of spot welding the body 4 to be welded, the performance of the capacitor is not deteriorated by the reverse charging and its use for long term is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a capacitor type spot welding machine, and more particularly to a spot welding machine designed to prevent reverse charging of an electrolytic capacitor.

[Conventional technology]

Figure 3 is an electric circuit diagram of a conventional capacitor-type spot welding machine. In the figure, (1) is an electrolytic capacitor for charging and discharging, and (2) is a back-to-back circuit that draws current from this capacitor (1) for charging and discharging. Format of Thyristasui Sochi, (
3) is a welding transformer to multiply the current, (4)
is the material to be welded to which the output of the welding transformer (3) is connected,
(5) is a DC power source for charging the charging/discharging capacitor (1), and (6) is a charging resistor for suppressing charging fat current.

A conventional spot welding machine is configured as described above, and after charging the electrolytic capacitor (sample) to a voltage of V using the DC power source (5), when the cyrisk switch (2) is turned on, the electrolytic capacitor (1) is charged. The stored charge is discharged through the low impedance welding transformer (3) and a large peak current i flows. Figure 4 (a) and (bl) are explanatory diagrams of the waveforms of the terminal voltage V and discharge current i of an electrolytic capacitor, and as a result of loss in the circuit components, both of them are oscillating waveforms that attenuate over time. The material to be welded (4
) through the welding transformer (3), a current approximately corresponding to the turns ratio i in FIG. 4(b) flows. As shown in FIG. 4, the oscillating current 1 is at the upper current point after turning off the thyrisk switch (2), that is, at time t. After that, the electrolytic capacitor (1) is charged again by the DC power supply (5) and returns to the initial state. The spot welding machine performs localized spot welding by repeatedly passing the pulsed vibration wave M flow several times.

[Problem that the invention seeks to solve]

With conventional capacitor type spot welding machines, the
As shown in the shaded areas (10a) and (10b), there is a time period in which the terminal voltage of electrolytic capacitor [1] becomes negative, so electrolytic capacitor (1) deteriorates and welding performance gradually decreases. There was a problem with that.

This invention was made to solve the above-mentioned problems, and aims to provide a spot welding machine that prevents reverse charging of an electrolytic capacitor and significantly reduces deterioration of the capacitor.

[Means for solving problems]

The spot welding machine according to the present invention includes first and second electrolytic capacitors connected in parallel to a direct current, having substantially the same capacitance and opposite polarity, and a first and second electrolytic capacitor connected in parallel to a direct current power source so that the cathode sides of each capacitor are connected directly to each other. Weld the first and second gate Kuhn-off thyristors which are connected and each anode side is connected to the positive side of each electrolytic capacitor, the switch which is connected in series to the DC power supply, and the material to be welded which is connected in series to the switch. A main circuit is constituted by a welding circuit and a resistor, one of which is commonly connected to the connection point of both electrolytic capacitors and the connection point of both gate turn-off thyristors, and the other is connected to a DC power supply. ? The present invention is configured such that the charging current of the first electrolytic capacitor flows through the welding circuit when the switch is turned on after only the first electrolytic capacitor is charged by the power source.

[Effect]

In this invention, there is a resistor, one of which is commonly connected to the connection point of the first and second electrolytic capacitors and the connection point of the first and second gate turn-off thyristors, and the other of which is connected to the DC power supply. Therefore, the first
Only electrolytic capacitors are charged. In addition, after the switch is turned on after charging only the first electrolytic capacitor,
By alternately operating the first and second gate turn-off thyristors, which are connected in parallel to the DC power source and whose cathodes are connected in series, the first and second gate turn-off thyristors, which are connected in parallel to the DC power source and whose cathodes are connected in series, are connected in parallel to the DC power source, and which have substantially the same capacity and opposite polarity. The first and second electrolytic capacitors are operated only in a time domain in which the terminal voltages thereof are positive, and both electrolytic capacitors are not charged in the opposite direction.

〔Example〕

FIG. 1 is an electrical circuit diagram showing one embodiment of the present invention.

In the figure, (la) is an electrolytic capacitor for charging and discharging,
(1b) is a second electrolytic capacitor for charging and discharging, (2) is a back-to-back type silice switch, (3) is a welding transformer, (4) is the material to be welded, (5) is a DC power supply, (
6) is a charging resistor, (7a) is a first gate turn-off thyristor, (7b) is a second gate turn-off thyristor,
(8) is resistance. The spot welding machine of this embodiment is connected in parallel to the above-mentioned DC power source (5) via a charging resistor (6), and has first and second electrolytic capacitors (LA) connected in series with approximately the same capacitance and opposite polarity. ), (lb)
and first and second gates 1- which are connected in parallel to the DC power supply (5), have their cathodes connected in series, and have their respective anodes connected to the positive sides of the respective electrolytic capacitors (Ia) and (lb). Turnoff Sirisk (7a),
(7b), a thyristor switch (2) connected in series to the DC power source (5), a welding transformer (3) for welding the material to be welded (4) connected in series to the switch (2), and one of the above The connection point of both electrolytic capacitors (la), (lb) and the above-mentioned both gate turn-off thyristors (7a),
(7b), the other is connected to the negative side of the DC power supply (5), and the main circuit is constituted by the t resistor (8).

In the spot welding machine configured as described above, first, the first electrolytic capacitor (1a) is charged by the DC power supply (5) to a voltage of ■, and then the thyristor switch (2) is turned on. The charge stored in 1a) is discharged through the low impedance welding transformer (3) and a current i with a large peak value flows. At this time,
In order to prevent the terminal voltage of the first electrolytic capacitor (1a) from becoming negative, the first and second gate turn-off thyristors (7a) and (7b) are operated as shown in FIG. 2(C).

Figures 2 (a) and (b) show the first and second electrolytic capacitors (
The terminal voltages V, , V2 of Ia), (Ib) and the first and second gate Kuhn-off slopes (7a), (7
It is a figure which shows the operating state of b) and the waveform of the discharge current i.

Based on FIG. 2, the first and second electrolytic capacitors and the first
and t ) ton of the second gate turn-off thyristor
The operation at each time will be explained.

First, while the first electrolytic capacitor (1a) charged by the DC power source (5) is discharging, the first gate turn-off thyristor (hereinafter referred to as "first thyristor") (7a) is off, and the second gate turn-off thyristor (hereinafter referred to as "first thyristor") (hereinafter referred to as "first thyristor") is off. "Second
(7b) is turned on and the first
A closed circuit of electrolytic capacitor (1a) - welding transformer (3) - second cylisk (7b) - first electrolytic capacitor (1&) is formed, and a gradually increasing discharge current 1 flows.

Next, when the discharge current l begins to decrease, the first thyristor (7a) is turned on, the second thyristor (7a) is turned off, and the second electric folding capacitor (1b) - welding transformer (
3) - First cyrisk (7a) - Second electrolytic capacitor (
When the closed circuit 1b) is formed and the discharge current i starts to decrease, a back electromotive force is generated in the welding transformer (3), and the terminal voltage of the welding transformer (3) becomes the opposite polarity to the above-mentioned voltage. 2
Charge the electrolytic capacitor (1b) with the correct polarity.

When charging of the second electrolytic capacitor (1b) is completed, discharging begins, and a gradually increasing discharge current i flows.

During this discharge, the first thyristor (7a) is still on and the second thyristor (7b) is still off.

Furthermore, when the discharge current i starts to decrease again, the first
Thyristor (7a) is off, second thyristor (7b)
is turned on, forming a closed circuit of the first electrolytic capacitor (la) - the second cylisk (7b) - the welding transformer (3) - the first electrolytic capacitor (1a), and when the discharge current i begins to decrease, the circuit is turned on again. A back electromotive force is generated in the welding transformer (3), and the terminal voltage of the welding transformer (3) becomes reverse polarity, charging the first capacitor (1a) with the correct polarity, and then charging the first capacitor (1a) as described at the beginning. Discharging of the electrolytic capacitor (1a) begins.

Thus, the first and second electrolytic capacitors (Ia).

(1b) operates only in the time domain where each terminal voltage is positive, and at other times the first and second sirisks (7a
) and (7b), so the entire capacitor operates as one electrolytic capacitor. Therefore, the current waveform of the discharge current l has the same oscillatory waveform as shown in FIG. 4(b), as shown in FIG. 2(d).

Is the discharge current l jof? After the first electrolytic capacitor (1a) is cut off, the first electrolytic capacitor (1a) is charged by the DC power source (5).

Spot welding can be performed by repeating this sequence. Further, the resistor (8) is provided to prevent the second electrolytic capacitor (1b) from being charged by the DC power supply (5) when the first electrolytic capacitor (1a) is charged.

In the above embodiment, a Cyrisk switch (2) is used as the switch, but an Ibunatron or a discharge trigger gap may be used.

In addition, in the above embodiment, a method of supplying a large current to the workpiece (4) through the welding transformer (3) was explained, but if an electrolytic capacitor with a sufficiently large capacity is used, the welding transformer (3) can be omitted. The output can be directly connected to the material to be welded (4).

〔Effect of the invention〕

As explained above, the invention of Party B is based on the first circuit connected in parallel to a DC power source, with approximately the same capacity and opposite polarity.
and a second electrolytic capacitor, connected in parallel to the DC power supply,
First and second gate turn-off thyristors whose cathodes are connected in series, a switch connected in series to a DC power source, a welding circuit connected in series to the switch, and one connecting point between both electrolytic capacitors and both gate turn-off thyristors. The main circuit consists of a resistor connected in common to the contact point of the thyristor, and the other connected to the DC power supply.
By alternately operating the first and second gate turn-off thyristors after the switch is turned on after only the electrolytic capacitor is charged, the first and second gate turn-off thyristors are operated only in the time range in which the respective terminal voltages of the first and second electrolytic capacitors are positive. Since we have prevented these from charging in the opposite direction,
The lifespan of the electrolytic capacitor is increased, the reliability is high, and the spot welding machine can be maintained with less maintenance of the power supply.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention, FIG. 2(a) is a diagram showing the waveform of the terminal voltage of the first electrolytic capacitor, and FIG. 2(b) is a diagram showing the terminal voltage of the second electrolytic capacitor. Figure 2(e) is a diagram showing the operation of the first and second gate turn-off thyristors, Figure 2(d) is a diagram showing the waveform of the discharge current, and Figure 3 is a diagram showing the waveform of the conventional spot welding. FIG. 4(b) is a diagram showing the waveform of the terminal voltage of the electrolytic capacitor, and FIG. 4(b) is a diagram showing the waveform of the discharge current. In the figure, (la) is the first electrolytic capacitor, (1b)
is the second electrolytic capacitor, (2) is the thyristor switch,
(3) is the welding transformer (welding circuit), (41 is the material to be welded, (7) is the first gate turn-off thyristor, (7a
) is a second gate turn-off thyristor, and (8) is a resistor. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Patent Attorney Tadashi Sato Figure 3 Figure 4 Procedural Amendment (Method) % Formula % 1. Indication of the case Japanese Patent Application No. 1988-205214 2. Name of the invention Spot welding machine 3. Case of the person making the amendment Relationship with Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Moriya Shiki 4, agent address 8-6 Toranomon 5-chome, Minato-ku, Tokyo Amitavir 5, date of amendment order January 7, 1988 (dispatch date January 27, 1988) 6, "Brief explanation of drawings" column 7 of the specification subject to amendment, contents of amendment

Claims (1)

[Claims] First and second electrolytic capacitors are connected in parallel to a DC power source and are connected in series with substantially the same capacitance and opposite polarity; The first and second gate turn-off thyristors connected to the positive side of the electrolytic capacitor, the switch connected in series to the DC power supply, and the welding circuit for welding the workpiece connected in series to the switch, one of which is connected to both of the above. After only the first electrolytic capacitor is charged by the DC power supply, the main circuit is configured with a resistor that is commonly connected to the connection point of the electrolytic capacitor and the connection point of both gate turn-off thyristors, and the other side is connected to the DC power supply. A spot welding machine characterized in that the charging current of the first electrolytic capacitor is caused to flow through the welding circuit when the switch is turned on.