JPS6076278A - Arc welding machine - Google Patents

Abstract

PURPOSE:To provide a titled welding machine which eliminates a semiconductor trouble owing to magnetic deviation and controls stably output in semiconductor control of arc welding with an inverter by synchronizing output power control with a pulse generating circuit and taking balance between pulses. CONSTITUTION:Output electric power is controlled 16 and the pulse width of current is modulated 17 to control semiconductors 4a-4d in arc welding 8-10 using a current rectifier 2, a semiconductor circuit 4, a voltage transformer 5 and a current rectifier 6. The output power control is synchronized with a pulse generating circuit 19a of a synchronizing circuit 19 to balance the current width between pulses. If the semiconductors 4a-4d are controlled in such a way, the burn of the semiconductors by overcurrent is eliminated and the transformer trouble owing to magnetic deviation is eliminated. Satisfactory welding is thus accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inverter-controlled arc welder whose output is controlled by a switching element such as a transistor inserted and connected to the primary side of a welding transformer.

Conventional configurations and their problems In recent years, switching elements such as power transistors and power FETs have become widespread, and their use has spread to various industrial fields. An inverter-controlled arc welding machine has been put into practical use, in which a power transistor is placed in the welding area, the switching state of which is controlled using control means such as frequency modulation or pulse width modulation, and the welding output is supplied via a welding transformer. It seems that it will become more popular in the future.

A conventional arc welding machine will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of a pulse width modulation method that modulates the pulse width to control output. In FIG. 1, 1 is an AC input terminal of a welding machine, 2 is a rectifier that rectifies the AC input, and 3 4 is a capacitor that smoothes the rectified output of the rectifier 2, and 4 is a transistor that alternately converts the power converted into DC by the rectifier 2 and capacitor 3 into high-frequency AC power (for example, 1 to 100 KHz). The circuit is composed of transistors 48 to 4d.

5 is a transformer that steps down the AC power notched by the transistor circuit 4 to a voltage suitable for welding; 6 is a rectifier that rectifies the stepped down AC power to obtain DC power; and 7 is a rectifier that adjusts arc characteristics. 8 is a consumable electrode, 9 is a base material, 10 is a welding load generated between the consumable electrode 8 and the base material 9, 11 is a current detector for detecting welding current,
12 is an electrode feeding device that feeds the consumable electrode 8 at a constant rate;
13 is a current amplification circuit that amplifies the output of the current detector 11 and outputs a voltage signal according to the welding current value; 14 is a current amplification circuit that inputs the welding voltage and outputs the short-circuited state of the welding load 10 and the current amplification circuit 13; The output signal inputs the output and the output of the welding voltage discrimination circuit 14, and generates an output signal for controlling the welding power according to the output of the welding output command device 15, welding current, and welding voltage state. A power control circuit; 17 is a pulse width modulation circuit that receives the output signal of the output power control circuit 16 and outputs a pulse width modulation signal proportional to the output signal; 18 is a pulse width modulation circuit that amplifies the pulse signal output from the pulse width modulation circuit 17; This is a transistor drive circuit that drives the transistor 4.

Regarding the conventional arc welding machine configured as above,
The operation will be explained below. AC power input to the AC input terminal 1 is rectified by a rectifier 2, smoothed by a capacitor 3, and becomes DC power. The DC power is controlled by switching by transistors 48 to 4d and converted into high frequency AC power. This situation will be explained using FIG. 2.

FIG. 2a shows the current flowing to the primary side of the transformer 5 through the primary terminals 5a, 5b of the transformer 5, which are switched by the transistors 4a to 4d.

However, in a certain period t1, transistor 4
All of a to 4d are in the OFF state, and no current flows. In the following period t2, the transistor 4a.

4d is in the ON state, transistors 4b and 4c are in the FF state, and the primary current l flows through the transformer 50. 1 at this time
The direction of the secondary current 1 is from the primary terminal 5a of the transformer 60 to the 91st secondary terminal 5b. During the period <t3, all the transistors 4a to 4d are turned off again, and no current flows. In the following period t4, transistors 4b and 4c are O.
In the N state, the transistors 4a+4d are in the OFF state, and the primary current -1 of the transformer 60 flows. The direction of the primary current -1 at this time is a direction opposite to the direction of the primary current 1, and is a direction from the primary terminal 5b of the transformer to the primary terminal 6a. In the power supply device of the input/output control type, the switching states t4 to t4 of the transistors 48 to 4d as described above are defined as one cycle T, and this cycle is repeated to transfer the DC power charged in the capacitor 3 to the first cycle. Figure 2a
It is converted into high-frequency AC power as shown in the figure below.

In such a Varne width modulation method, the output is controlled by changing the ratio of the ON time (t2+t4) of the transistor (hereinafter referred to as switching duty) that occupies the period T. The high frequency AC power obtained by the above switching is stepped down to a voltage suitable for welding by a transformer 6, rectified by a rectifier 6,
The DC power becomes as shown in FIG. 2, and is supplied to the welding load 1o via the reactor 7. The consumable electrode 8 is fed to the base material 9 at a constant speed by the electrode feeding device 12, and welding is performed between the consumable electrode 8 and the base material 9.

The waveform of the welding current during welding is shown in Fig. 2C, and the waveform of the welding voltage is shown in Fig. 2D. During welding, the consumable electrode 8 is short-circuited to the base metal 9, and the short-circuit period Y during which the short-circuit current flows and the arc This is a short-circuit transition type welding in which periods X and Z, in which this occurs, are alternately and continuously repeated.

The welding current is detected by a current detector 11 and amplified by a current amplification circuit 13 to a voltage signal corresponding to the welding current value,
It is input to the output power control circuit 16.

The welding voltage is determined by a welding voltage determination circuit 14 as to whether it is in a short circuit state or an arc state, and the determination output is inputted to an output power control circuit 16. The output power control circuit 16 controls the output of the welding output command device 15 and the current amplification circuit 1.
3 and the discrimination output of the welding voltage discrimination circuit 14 are respectively input, and the output power is controlled to perform welding satisfactorily according to each state of the inputs.

The output of the output power control circuit 16 is output from the pulse width adjustment circuit 17.
and is converted into a pulse width signal that obtains a switching duty proportional to the output signal of the output power control circuit 16. The transistor drive circuit 18 amplifies the pulse width signal output and outputs an output for driving the transistor circuit 4'fr.

The welding power control operation of a conventional arc welding machine will be explained with reference to FIG. When the welding load 10 is in a normal arc state as shown by X in FIG.

Next, when the welding load 10 becomes short-circuited as shown in Y, the welding voltage discrimination circuit 14 detects the short-circuited state, and the output power control circuit 16 pulses a signal ■ lower than the command output ■ of the welding output commander 15. Spatter generated during welding is output to the width modulation circuit 17, and the switching dates of the transistors 48 to 4d are set low to reduce the welding power and suppress the rising slope and peak value of the current at the time of a short circuit. This reduces the occurrence of When the welding load 10 is in an arc state, as shown by Z, when the welding current drops significantly, the output power control circuit 16 receives the output of the current amplifier circuit 1 and detects the drop in the welding current. Welding output command device 15
The command output ■signal higher than the machine■2 is sent to the pulse width modulation circuit 1
7 and increases the switching duty of the transistors 4a to 4d to increase the welding power and prevent the welding current from further decreasing to prevent the welding arc from breaking. Changes in the output of the output power control circuit 16 in each of the above operating states are shown in FIG. Further, FIG. 3C shows each of the above-mentioned operations. It shows the primary current of the transformer 5, which is pulse width modulated in proportion to the output signal of the output power control circuit 16.

T1 to T8 shown in FIG. 3C are transistors 4, respectively.
The switching period is from a to 4d.

By the way, in the arc welding machine having such a conventional configuration, there is no temporal relationship between the output signal of the output power control circuit 16 and the switching period T of the transistors 4a to 4d. The output signal of 16 changes even during the switching period.

T3 shown in FIG. T5. The period T8 is such an example; since the output signal of the output power control circuit 16 changes during the switching period of the transistors 4a to 4d, the pulse width changes at this time and The next current is 1
The pulse width of the current in one direction during the cycle (the current flowing from the primary terminal 5a of the transformer 5 toward the primary terminal 5b) and the pulse width of the current in the -i force direction (the current flowing from the primary terminal 6b of the transformer 5 to the primary terminal 5b) The current flowing in the direction of the terminal 5a) is changing.

This change in the primary current of the transformer 5 during one cycle does not cause imbalance in the magnetization state of the transformer 6, especially when the degree of change during one cycle is rapid.
The transformer 5 becomes unbalanced, and the value of the primary current with the wider pulse width increases rapidly, which may destroy the transistor circuit 4.

In this way, the output of the output power control circuit 16 during one period of the transistors 4a to 4d, that is, the output of the transistors 48 to 4
In conventional arc welding machines, the output signal of the output power control circuit 16 cannot be changed abruptly, and sufficient welding power cannot be applied. Since the control speed cannot be obtained, it is not possible to obtain good welding performance, and there are also problems with the reliability of the equipment, such as destruction of the transistors 4a to 4d due to biased magnetism.

Purpose of the Invention The present invention has been made in view of the above-mentioned drawbacks, and provides a highly reliable arc welding machine that can control welding power at high speed and obtain good welding properties without causing damage to transistors. The purpose is to provide the following.

Structure of the Invention In order to achieve this object, the DC arc welding machine of the present invention has a switching output control element such as a transistor arranged on the primary side of a transformer, and a switching output control element such as a transistor, and a switching output control element such as a transistor. A main circuit that supplies DC power to an arc welding load, an output power control circuit that controls the output power of this main circuit, and a switch of the output control element starting from an arbitrary time during the OFF period of the output control element. - A synchronous circuit that repeats the operation of inputting and holding the output signal of the output power control circuit at the starting point of the switching period and outputting this held value during one cycle in each period, and the output signal of this synchronous circuit is controlled by a pulse width. a modulation circuit that performs modulation or frequency modulation and converts it into a switching signal for the output control element and outputs the signal,
The switching date for output control is changed in synchronization with the switching period T of the output control element.

With this configuration, welding power can be controlled at high speed, good welding performance can be obtained, and moreover, it is possible to prevent destruction of the transistor and ensure high reliability.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 4 to 7.

In Figure 4, 1.2, 3, 4, 5, 6, 7° 8.9,
10, 11, 12, 13, 14, 16゜16.1 completed, 1
8 is the same as the conventional AC input terminal, rectifier, capacitor, transistor circuit, transformer, rectifier, reactor, consumable electrode, base material, welding load, current detector, electrode feeding motor, and feeding device. These are a current amplification circuit, a welding voltage discrimination circuit, a welding output command, an output power control circuit, a pulse width modulation circuit, and a transistor drive circuit. 19
is a periodic circuit composed of a pulse generation circuit 19a, a reading circuit 19b, and a sample hold circuit 19c, which is disposed between the output power control circuit 16 and the pulse width modulation circuit 17, and is configured to receive the output signal of the output power control circuit 16. This circuit converts the signal into a signal synchronized with the switching period T of the transistor circuit 4 and outputs it to the pulse width modulation circuit 17.

The operation of the DC arc welding machine configured as described above will be explained below. AC power input to the AC input terminal 1 is rectified by a rectifier 2, smoothed by a capacitor 3, and becomes DC power. The DC-converted electric power IrJ,,l-transistor circuit 4 generates a current of 1.
It is converted into high-frequency AC power, stepped down to a voltage suitable for welding by a transformer 5, and rectified by a rectifier 6 to become DC power and supplied to a welding load 10 via a reactor 7. The consumable electrode 8 is fed to the base material 9 at a constant speed by the electrode feeding device 12, and welding is performed between the consumable electrode 8 and the base material 9.

It is detected by a welding current detector 11 as shown in FIG.

The welding voltage is determined by the welding voltage discrimination circuit 14 to indicate a short circuit state.
The arc state is determined and its output is input to the output power control circuit 16.

The output power control circuit 16 inputs the output of the welding output command device 15, the output of the current amplification circuit 13, and the discrimination output of the welding voltage discrimination circuit 14, and controls the output power to improve welding according to each state of the inputs. , like the conventional arc welding machine, the fifth
The output signal shown in the figure is output. The synchronization circuit 19 is synchronized with the switching period of the transistor circuit 4, and includes a pulse generation circuit 19a that outputs a pulse as shown in FIG. Read the output signal of circuit 16. It consists of a reading circuit 19b and a sample hold circuit 19C that holds the read signal during one switching cycle of the transistor circuit 4 and updates the held value with the read signal every cycle, as shown in FIG. 5d. The output of the sample hold circuit 19C is used as the output signal of the synchronization circuit 19. The output signal of the synchronization circuit 19 is input to a pulse width modulation circuit 17, and is converted into a pulse width signal that obtains a switching duty proportional to the output signal of the synchronization circuit 19.

Thus, in the embodiment of the present invention, transistors 48 to 4
The output signal of the output power control circuit 16, which has no synchronous relationship with the switching period of d, is synchronized with the switching period of the transistors 48 to 4d by the synchronization circuit 19, and the switching duty of the transistors 4d to 4d is changed by the synchronized signal. Therefore, the primary current of the transformer 5 shown in Fig. 5 θ is balanced during one cycle in any cycle from T1 to T9, and is stable without causing biased magnetism. Control is possible.

Note that when the output signal of the output power control circuit 16 changes continuously as shown in FIG. 6a, the output of the synchronization circuit 19 is synchronized as shown in FIG. 7a, the output of the synchronizing circuit 19 is synchronized as shown in FIG.
The output of can be synchronized with the switching period of transistors 4a to 4d. In this embodiment, the pulse width modulation method has been described, but the principle is the same for the frequency modulation method.

Effects of the Invention As described above, in the present invention, even if the welding output power is rapidly controlled, biased magnetization of the transformer does not occur, and good welding performance can be obtained by performing high-speed welding power control. It is possible to provide a highly reliable arc welding machine in which there is no possibility of destruction of the output control element.

[Brief explanation of the drawing]

Figure 1 (is a circuit diagram of a conventional arc welding machine, Figure 2 a, b)
, c, d are signal waveform diagrams of the main parts of a conventional arc welding machine, Fig. 3 a, )), c are signal waveform diagrams for explaining output power control by a conventional arc welding machine, and Fig. 4 is a signal waveform diagram of the main parts of a conventional arc welding machine. A circuit diagram of an arc welding machine according to an embodiment of the present invention, FIGS. 6a and 6b,
Figures a, d, and 6 are signal waveform diagrams for explaining the operating principle of the arc welding machine, and Figure 6 is a signal waveform diagram for explaining the operating principle of another embodiment of the present invention. FIG. 7 is a signal waveform diagram for explaining the operating principle in still another embodiment of the present invention. 4... Transistor circuit, 4a, 4b, 4c. 4d...Transistor, 5...Transformer, 8...
...consumable electrode, 9...base material, 16-...
Output power control circuit, 17-... Modulation circuit, 19...
Synchronous circuit, 19a...Pulse generation circuit, 19b...
・Reading circuit, 19c... Sample hold circuit. Name of agent: Patent attorney Toshi Nakao and 1 other person No. 1
Figure 2: Closing 6 Figure 3 × Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] A switching output control element such as a transistor is placed on the primary side of the transformer to control the main circuit that supplies power to the arc welding load generated between the electrode and the base metal, and the output power of this main circuit. inputting and holding an output signal of the output power control circuit at a starting point of a switching period of the output control element starting from an arbitrary time during the OFF period of the output power control circuit; It has a synchronous circuit that repeats the operation of outputting a value during one period in each period, and a modulation circuit that performs pulse width modulation or frequency modulation on the output signal of this synchronous circuit and converts it into a switching signal of the output control element and outputs the signal. . An arc welding machine configured to change a b switching duty for output control in synchronization with each switching period of the output control element.