JPH0681673B2 - Capacitor storage type inverter controlled welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a capacitor energy storage type inverter control type welding machine.

[Conventional technology]

A conventional condenser type spot welding machine is, for example, one shown in FIG. In the figure, an AC power supply 1 is connected to the primary winding of a transformer 11, and its secondary winding is connected to a bridge-connected rectifier 2. The rectified output of the rectifier 2 is connected to the capacitor 6 via the thyristor 30 and the resistor 300. A control pulse synchronized with the AC power supply 1 is supplied to the thyristor 30 at its gate electrode to control the charging current to the capacitor 6 to a desired value. The capacitor 6 is further fed via the thyristor 70 to the primary winding of the transformer 8. A large current multiplied by the inverse ratio of the turns ratio between the primary winding and the secondary of the transformer 8 flows from the secondary winding to the welding electrode 9. The object to be welded sandwiched between the welding electrodes 9 is welded.
In this welding machine, the charging current i1 of the capacitor 6 in which energy is accumulated follows a typical capacitor charging curve as shown in FIG. 5, and normally one charging period t1 is selected to be about 1 second. The welding current i2 flowing through the welding electrode 9 has a waveform of capacitor discharge as shown in the figure, and the current flowing period t2 and the waveform are almost fixed.

[Problems to be Solved by the Invention]

However, in the discharge control of such a conventional condenser type spot welder, the electric current is discharged as a one-way current through the welding transformer. Since the welding current i2 is unidirectional and the conduction period is about t2 = 0.1 seconds as shown in Fig. 5, the magnetic core of the welding transformer must be larger than that of a transformer of the same electric power commercial frequency. Absent.

Further, the welding current waveform is one pulse, and the thyristor 70 cannot be turned off until it becomes less than the holding current, and the portion behind the welding current waveform (wave tail) is long. In the period of this wave tail,
When the welding electrode is raised, an arc is generated between the welding electrode and the work piece, which causes spatter. In particular, when the object to be welded is a magnetic material such as casting, the wave tail is often long, and its length is 2 times longer than that of a non-magnetic material.
It can be more than doubled. Therefore, in the condenser type spot welder, it is necessary to predict and wait for this long wave tail period. However, there was a problem that spatters were generated when the welding electrode was lifted due to the variation in the length of the wave tail, and the object to be welded and the welding electrode were damaged.

On the other hand, there is an inverter welder that uses a high-frequency inverter. In that case, the welding current waveform can be set freely,
There is a problem that the input power becomes extremely large because a continuous high frequency large current is supplied.

In the present invention, while suppressing the input power to a low level in the welding machine,
The challenge is to obtain the formability of the welding current waveform, especially to prevent spatter generation by shortening the wave tail of the welding current waveform.

[Means for Solving the Problems]

In order to solve such a problem, the present invention provides a capacitor obtained by supplying energy stored in a capacitor to a primary winding of a welding transformer and connecting a welding electrode to a secondary winding of the welding transformer. In the energy-storing welder, an inverter is connected between the capacitor and the primary winding of the transformer for welding, and each switching element of this inverter is connected with a diode in anti-parallel so that the energy of one welding is almost equal to one welding. The present invention proposes a capacitor-storing inverter-controlled welding machine characterized by operating an inverter with a waveform suitable for a workpiece at a sufficiently high frequency after accumulating the energy.

[Action]

Since the present invention has such characteristics, the charging period for the capacitor is performed in 1 to several seconds, and the stored energy is supplied by the inverter between the welding electrodes in a period much shorter than the charging period. While the power is kept low, the output power is the instantaneous high power required for welding.
The welding current waveform can be formed freely because the conversion fraction of the inverter is sufficiently high.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention. First, the configuration will be described. The AC power supply 1 is connected to the primary winding of the transformer 11, and the secondary winding of the AC power source 1 is connected to the bridge-connected diodes 21 to 21.
It is connected to the rectifier 2 consisting of 24. The rectified output of the rectifier 2 is connected to the capacitor 6 via the thyristor 30. Although not shown, a control pulse synchronized with the AC power supply 1 is supplied to the gate electrode of the thyristor 30 to control the charging current to the capacitor 6 to a desired value. The capacitor 6 is further connected to an inverter 7 composed of field effect transistors 701 to 704. Field effect transistors 701-7
04 is switching-driven by the control circuit 709 at about 20 kHz and sent to the primary winding of the transformer 8. The diodes 705 to 708 connected in parallel between the drains and sources of the field effect transistors 701 to 704 function as so-called freewheeling diodes. That is, when the pair of field effect transistors 701 and 704 are turned off from the state where they are turned on, the current energy stored in the welding transformer 8 that has been flowing up to that point instantaneously passes through the diodes 707 and 706 and becomes a capacitor. It is recharged to 6.
This current causes the welding transformer 8 to smoothly transition to the next opposite period, that is, the state in which the pair of field effect transistors 702 and 703 is turned on. These diodes 705
There are both cases where the intrinsic diode is used due to the structure of the field effect transistor and cases where a diode is separately provided. (When connecting diodes separately, forward diodes are connected in series between each drain and source.) The turns ratio between the primary winding and the secondary winding of the transformer 8 is selected to be about 60: 1. A large current multiplied by this reverse ratio flows from the secondary winding to the welding electrode 9. The object to be welded sandwiched between the welding electrodes 9 is welded.

In the welding machine configured as described above, the charging current i1 of the capacitor 6 in which energy is accumulated is as shown in FIG.
According to a typical capacitor charging curve, one charging period t1 is usually selected to be about 1 second. The current i2 flowing through the welding electrode through the inverter 7 and the welding transformer 8 has a waveform as shown in FIG. The current flow period t2 and the waveform can be freely obtained depending on the characteristics of the control circuit 709. For example, during the discharge, the discharge of the capacitor 6 can be stopped to wasteful energy consumption and prevent the spatter of the workpiece.

FIG. 3 shows another embodiment of the present invention. This embodiment is the first
In the embodiment shown in the figure, the circuit for charging the capacitor 6 is performed via the converter 3 operating at high frequency, and an inverter (7, 7) for supplying energy from the capacitor 6 is used.
2) and a transformer for welding (8, 82) are configured in two systems. To explain the configuration, the AC power supply 1 is rectified by the rectifier 2 including the diodes 21 to 24, and the capacitors 31 and 32 are charged to the same potential. Field-effect transistors 33, 34 connected in series to both ends of the capacitors 31, 32
Are connected. A capacitor 38 and an inductor 37 are connected in series between the junction of the capacitors 31 and 32 and the junction of the field effect transistors 33 and 34. And capacitor
The primary winding of the transformer 4 is connected to both ends of 38, and the secondary winding thereof is connected to the rectifier 5 composed of the diodes 51 to 54. The field effect transistors 33 and 34 are driven on and off at a high frequency by the control circuit 39 to form the converter 3. That is, the waveform of the AC power supply 1 at 50 to 90 Hz is exchanged to a frequency of several hundred to 1,000 times higher than that, and the capacitor 6 is controlled and charged.

In this embodiment, the inputs are connected in parallel and the outputs are connected in series. According to the equal ampere-turn rule, the welding transformer 8,
The current in the 82 secondary winding is forced to be equal, which is convenient. By utilizing this property and preparing a plurality of inverters having the same standard capacity, the intended large capacity welding machine can be manufactured with the standard inverter having a limited capacity. These multiple inverters
The operating frequencies and phases of the 7 and 72 are basically selected to be equal to each other, but other operating modes may be used depending on the purpose.

Although not shown, the embodiment of FIG. 3 can be expanded to provide an arbitrary number of n inverters and the secondary side of the welding transformer can be connected in series. It is also possible to provide an arbitrary number and n converters and connect them to an arbitrary number and n inverters, respectively, and connect the secondary side of the welding transformer in series.
In that case, each control circuit shall be controlled individually or in cooperation.

Furthermore, by inserting and connecting a rectifier in series with the secondary winding of the welding transformer, it is possible to apply a unidirectional polarity current to the work piece.

〔The invention's effect〕

Since the present invention has the characteristics as described above, it is possible to freely control the welding current waveform while suppressing the input power to a low level, so that it is possible to adapt it to the characteristics of the welded object and the tail of the welding current. Can be shortened to prevent the generation of spatter. In particular, it is suitable when a magnetic substance such as iron is used as the welded object. Alternatively, it can handle special welding objects and conditions. Further, the energy utilization rate is improved by making the welding current waveform most suitable for the object to be welded. In addition, the efficiency of the welding transformer and the higher frequency have the effect of making it compact and economical.

[Brief description of drawings]

FIG. 1 shows an embodiment of a capacitor energy storage type inverter control type welding machine according to the present invention, and FIG. 2 shows a waveform for explaining its characteristics. FIG. 3 shows another embodiment of the capacitor storage type inverter control type welding machine according to the present invention. FIG. 4 shows an example of a conventional condenser type spot welder, and FIG. 5 shows a waveform for explaining its characteristics. 1 …… AC power supply, 11 …… Transformer, 2 …… Rectifier, 21,22,23,24 …… Diode, 3 …… Converter, 30 …… Thyristor, 300 …… Resistor 31,32 …… Capacitor, 33,34 …… Field effect transistor,
35,36 …… Diode 37 …… Inductor, 38 …… Capacitor, 39 …… Control circuit, 4 …… Transformer, 5 …… Rectifier, 51,52,53,
54 …… Diode 6 …… Capacitor 7,72 …… Inverter 701,702,703,704 …… Field effect transistor 705,706,707,708 …… Diode 721,702,723,724 …… Field effect transistor 725,726,727,728 …… Diode 709,729 …… Control circuit 8,82 …… Welding transformer, 9 ...... Welding electrode

Claims (1)

[Claims] Claim: What is claimed is: 1. A capacitor storage type welding machine comprising: the energy stored in a capacitor is supplied to a primary winding of a welding transformer; and a welding electrode is connected to a secondary winding of the welding transformer. An inverter is connected between the capacitor and the primary winding of the welding transformer, and a diode is connected in antiparallel to each switching element of the inverter, and after the energy for one welding is stored in the capacitor, A capacitor-accumulation type inverter-controlled welding machine, characterized in that the inverter is operated at a sufficiently high frequency with a waveform suitable for the workpiece.