JPS6138769Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a DC arc welding machine that increases the welding current to a set value almost simultaneously with arc start and prevents excessive current.

Generally, when TIG welding a thin plate to be welded using a DC arc welding machine, such as a DC arc welding machine that uses a non-consumable electrode, it is recommended to set the current to flow from the main circuit at the same time as the arc starts. An excessive current higher than the current, that is, a hot current flows at the start of the arc, causing welding defects such as destruction of the welded object or formation of holes due to heat.

Therefore, conventional DC arc welding machines use a high-frequency generator to apply high-frequency waves caused by spark discharge between the electrode and the workpiece to cause dielectric breakdown, and at the same time, the high-voltage, small-current generating circuit section A small current arc is generated by applying a high voltage and small current power source. Then, by detecting this high voltage and small current, the welding current is gradually increased along with the arc in the main circuit until it reaches the set current value.

That is, as shown in FIG. 1, a method generally called a cold start is used. In the figure, I ₁ is the current value supplied from the high voltage small current generation circuit, I ₂ and I ₃ are the set current values of the welding current, and t ₁ is the current supplied from the high voltage small current generation circuit. Start time, _t2 is the time to detect the supply of high voltage and small current and start the arc in the main circuit,
t ₃ and t ₄ are arc start times, and A and B are arc start characteristic curves.

For example, in a thyristor TIG welding machine,
The welding current I is detected by a current detection unit such as a current shunt, and is converted into a voltage proportional to the welding current I, and the operational amplifier unit converts this voltage and the reference voltage for determining the set current values I ₂ and I ₃ A feedback system is employed in which the error is amplified by the output signal of the operational amplifier and the phase of the thyristor in the output control section is controlled by the output signal of the operational amplifier.

The operational amplifier operates as described in Japanese Patent Publication No. 47-28491 and Japanese Patent Publication No. 55-47401, and the input on the detection side of the operational amplifier is almost equal to the input on the reference side. The output current of the current detection section is constant, and therefore the welding current proportional to the output current of the current detection section is controlled to be a constant current.

Incidentally, the feedback system includes a delay element such as a capacitor in order to improve the stability of operation.

In addition, in the phase shifter that controls the phase of the thyristor in the output control section, a voltage drop between the base and emitter of the transistor that is a component thereof, or a forward voltage drop of the diode, etc. occurs, and therefore, as shown in Fig. 2, Even when the input signal V ₁ is applied to the phase shifter, a state occurs in which the output voltage V ₂ of the output control section is zero, and this state is commonly called a dead voltage Vt period.

The time from the start of the arc to the end of the voltage period varies depending on the magnitude of the set current value, as shown in Figure 3, based on the aforementioned delay factors. The curve shown shows the characteristics when the current values of I ₂ and I ₃ in FIG. 1 are set, and the broken line shows the dead voltage Vt.
Further, the time T ₁ is the time from t ₂ to t ₃ in FIG. 1, and the time T ₂ is the time from t ₂ to t ₄ in FIG.

That is, when welding is performed by cold start, there is a problem in that the smaller the welding current value at arc start, the worse the arc start characteristics become.

This idea was made with the above points in mind, and when the set current value is small, the welding current at arc start is adjusted to the set current by using a differential signal for delay compensation in the feedback system. When the set current value is large, the reference voltage of the set current value is increased to the reference voltage of the set current value without using the differential signal to prevent overcurrent due to the differential signal. Therefore, the welding current at arc start is increased, and regardless of whether the set current value is large or small, the welding current is raised to the set current value almost simultaneously with the arc start, and the current is prevented from becoming excessive. Next, this invention will be explained in detail with reference to FIGS. 4 to 6 showing embodiments thereof.

As shown in FIG. 4, the AC input from the input terminal 1 is rectified by the output control section 2, which constitutes a rectification circuit using control elements such as thyristors.
The output is supplied to an output terminal 4 via a current detection section 3 such as a shunt. On the other hand, one end of the input side of a high voltage and small current generation circuit section 5 that flows a high voltage and small current is connected to the input terminal 1, and the other end of the output side of the generation circuit section 5 is connected to the input terminal 1 through a start current detection section 6. It is connected to output terminal 4.

Note that the generation circuit section 5 has a current-voltage conversion function and forms high-voltage, small-current DC power from AC input.

The output current of the output control section 2 is detected by the current detection section 3, and is converted by the current detection section 3 into a voltage proportional to the output current of the output control section 2, and this converted voltage is applied to the operational amplifier section 7. is applied to one input terminal of

Furthermore, the other input terminal of the operational amplifier 7 is
The reference voltage of the reference power source 9 for setting the welding current, which is input to the first diode 8a of the OR circuit 8 via the first switch 6a which is turned on by the energization of the start current detector 6, or the voltage of the differential signal for delay compensation of the differential signal generating circuit 10, which is input to the second diode 8b of the OR circuit 8 via the second switch 6b which is turned on in conjunction with the first switch 6a, is applied. The current detector 6 is, for example, a current relay, and in this case, the switches 6a and 6b are formed by two contact switches of the relay. The OR circuit 88 forms the selection output means.

Then, the operational amplifier section 7 amplifies the error between the voltage at one input terminal and the voltage at the other input terminal, and the output voltage of the operational amplifier section 7 is applied to the phase shifter 11 which fires the thyristor of the output control section 2. is applied, and the phase of the thyristor is controlled by the phase shifter 11.

Next, the operation shown in FIG. 4 will be explained with reference to FIGS. 5 and 6.

Now, suppose that an AC input from an AC power source is input to the input terminal 1. At this time, the thyristor of the output control section 2 is turned off, and the output control section 2 stops outputting.

Then, the AC input of the input terminal 1 is input to the generation circuit section 5.
For example, at time t ₁ in FIG. 1, the current value I ₁ in FIG. A high voltage, low current power is supplied as shown, and the power generates a low current arc between the electrode and the workpiece.

Further, the current detection unit 6 detects the conduction of high voltage and small current and controls the first and second switches 6a and 6b to turn on. At this time, due to the inherent detection delay of the detection unit 6, both switches 6a , 6b are turned on, for example, at time _t2 in FIG.

Further, the current detection unit 6 includes a first switch 6 and a second switch 6
The generator 10 is activated at the same time as the switches a and 6b are turned on, and based on the activation, the generator 10, which is a known differentiating circuit, differentiates the step signal, for example.
As shown by the solid line c in FIG. 6, a differential signal with a steeply rising waveform that rises at the same time as the first and second switches 6a and 6b are turned on, for example at _t2 , is sent to the second diode via the second switch 6b. Output to 8b.

On the other hand, the reference power source 9 outputs the reference voltage set by the operation, and when the first switch 6a is turned on at time _t2 , the reference voltage of the reference power source 9 is changed to the reference voltage of the reference power source 9.
The signal is input to the first diode 8a via.

Then, the OR circuit 8 selects the larger voltage between the voltage of the differential signal and the reference voltage and outputs it to the operational amplifier section 7.

In addition, if the voltages for setting the welding current value to the small current value I ₂ in Fig. 5 and the large current value I ₃ of the maximum rated current are respectively set to the voltage values V ₂ and V ₃ in Fig. 6, the differential signal of The peak value is set to a voltage value between voltage values _V2 and _V3 . In addition, the time it takes for the differential signal to fall from the peak voltage value to the voltage value V ₂ was experimentally determined so that the time when the welding current value is set to the small current value I ₂ is the time when the operation is most stable. is set.

When the AC power input starts, the output of the output control section is 0, so the output of the current detection section is also 0, and the output of the operational amplifier section 7 is the maximum output. The maximum output is applied to the phase shifter 11, and the phase shifter 11 applies a gate pulse to the thyristor of the output control section 2, causing the thyristor to fire.

Furthermore, due to the ignition of the thyristor, input terminal 1
The alternating current is controlled and rectified by the output control section 2, and the welding current I is supplied to the output terminal 4, and this current is detected by the current detection section 3 and applied to one input terminal of the comparison amplifier section 7. .

Further, the output signal of the current detection section 3 and the output signal selected by the OR circuit 8 are error-amplified by the operational amplifier section 7, and this operationally amplified signal is passed through the phase shifter 11 to the output control section 2. is controlled and a feedback system is constructed.

Then, due to the feedback system, the voltage at one input terminal of the operational amplifier section 7 (voltage on the detection side) is
The welding current I is controlled to a current determined by the output voltage of the OR circuit 8 so as to be equal to the voltage of the other input terminal (voltage on the reference power supply side).
If the output voltage is a constant voltage, the welding current is controlled to be a current determined by the constant voltage.

By the way, since the feedback system includes a delay element such as a capacitor for stabilizing operation, at time _t2 , for example, switches 6a and 6b are turned on and control based on the voltage selected by OR circuit 8 is started. Also, the output current of the output control section 2 has a characteristic based on the output voltage of the OR circuit 8, for example, the third
The current value increases to approximately the current value I ₁ with a delay of the dead voltage period corresponding to T ₁ and T ₂ in the figure, and the current value increases from the current value I ₁ to the set current value I ₂ or I ₃ , and at this time the output control unit The time it takes for the output current of No. 2 to rise to the set current value becomes longer as the output voltage of the OR circuit 8 becomes lower.

In Fig. 4, the welding current value is set to a small current value I ₂
When set to , the welding current is approximately B in Figure 1.
The differential signal is used to compensate for the delay, and for example, T ₂ in FIG. 3 is shortened to T ₁ so that the characteristic increases with the characteristic when the large current value I ₃ is set.

Now, if the set value of the welding current I in the reference power source 9 is set to a small current value _I2 as shown in _FIG. Since the reference voltage V ₂ of the reference power supply 9 is lower than the rising voltage of the differential signal of the differential signal generator 10, the voltage of the differential signal is selected by the OR circuit 8 and input to the operational amplifier 7, and the voltage of the differential signal is selected by the OR circuit 8 and input to the operational amplifier 7. At step 7, the voltage signal from the current detection section 3 and the error are amplified and input to the phase shifter 11.

Then, the rising voltage of the differential signal is the reference voltage V ₂
Therefore, the welding current rises more steeply than when feedback control is performed based on the reference voltage _V2 , and for example, the welding current rises to a small current value _I2 at time t3 in Fig. ₁ with the characteristic of rising to the current value _I1 . do.

Furthermore, after the welding current rises to a small current value I ₂ ,
When the differential signal converges and the voltage gradually decreases and becomes smaller than the reference voltage V ₂ of the reference power source 9, the OR circuit 8 selects the reference voltage V ₂ and inputs it to the operational amplifier, and the welding current changes to a small current value. Constant current is controlled by I ₂ .

Therefore, the welding current has a characteristic as shown by the curve A' in Figure 5, and at arc start, the delay of the capacitor for stabilizing the operation of the feedback system is compensated for based on the voltage of the differential signal. The current increases sharply in the same way as when the large current value I ₃ was set, and furthermore, as the differential signal converges, after reaching the set current value I ₂ , the current does not become excessive and the small current increases. Constant current is controlled to the value _I2 .

On the other hand, when the setting value of the welding current I in the reference power source 9 is set to the large current value _I3 of the maximum rated current as shown in FIG. Even if 6a and 6b are turned on, since the reference voltage V ₃ of the reference power supply 9 is higher than the voltage of the differential signal, the operational amplifier 7 amplifies the error between the reference voltage V ₃ and the voltage signal of the current detection unit 3. , the welding current has a characteristic as shown by the curve B' in Fig. 5, that is, almost the same characteristic as the characteristic curve B in Fig. 1,
At this time, since the reference voltage V ₃ is large, the welding current is controlled at a constant current to a large current value I ₃ with _a steep characteristic that increases to the current value I 1 at time t ₃ .

When the set current value is a small current value _I2 , the welding current is sharply increased and controlled to the set current value by using a differential signal larger than the reference voltage _V2 at the time of arc start; When the set current value is a large current value _I3 , the welding current I at arc start is controlled to the set current value by the reference voltage _V3 of the set current value without using a differential signal. Differences between voltage groups due to differences in value are eliminated, overcurrent can be prevented, and arc starting characteristics can be significantly improved.

In the above embodiment, even after the welding current I reaches the set current value I ₂ or I ₃ at the time of arc start, the current is not allowed to flow through the series circuit of the high voltage small current generating circuit section 5 and the starting current detecting section 6. However, this series circuit may be opened after the set current value I ₂ or I ₃ is reached. In that case, the same effect can be obtained if the first switch 6a is kept on by itself.

As described above, this invention rectifies the AC input using an output control section configured using a thyristor.
A welding current is supplied to the load, the welding current is detected by a current detection section, and a comparison amplification section compares and amplifies the voltage of the current detection section and the reference voltage of the reference power source for setting the welding current, and also performs a phase shift. In a DC arc welding machine in which the phase of the thyristor of the output control section is controlled through a device to configure a feedback system so that the output characteristic is a constant current characteristic, a high voltage and small current generating circuit section that flows a high voltage and small current; A series circuit of a start current detection section through which a high voltage and small current flows is provided between the input terminal of the AC input and the output terminal of the welding current, and the peak value is the reference that makes the welding current a small current. a differential signal generator that generates a differential signal for delay compensation in the feedback system, which is set to a value larger than the voltage and smaller than the reference voltage, and which is set to a large current larger than the voltage; , a first device that operates in conjunction with the energization of the current detection section;
a second switch, a selection output means for selecting and outputting a larger voltage out of the reference voltage and the signal voltage of the differential signal generator via the both switches, and an output voltage of the selection output means and the current detection section. and an operational amplifier section that outputs an error amplified signal with respect to the voltage to the phase shifter.

Therefore, according to this invention, when the welding current is set to a small current, the welding current is increased to the set current value by the signal voltage of the differential signal generator almost at the same time as when the welding current is set to a large current, and then the welding current is set. current, and on the other hand, when the welding current is set to a large current, the reference voltage allows the welding current to rise to the set current value almost simultaneously with the arc start without causing an overcurrent, preventing an overcurrent. The arc starting characteristics can be significantly improved regardless of whether the set current is large or small.

Especially when applied to DC arc welding machines using non-consumable electrodes, when set to high current,
Since the signal voltage of the differential signal generator is lower than the reference voltage and has no relation to the feedback system, the current density at the tip of the electrode does not increase, which has the advantage of preventing electrode wear.

[Brief explanation of the drawing]

Figure 1 is a cold start characteristic curve diagram of a conventional DC arc welding machine, Figure 2 is a diagram of the relationship between the output control unit output voltage and the phase shifter input signal, and Figure 3 is the phase shifter input from the arc start point. Figure 4 is a block diagram of one embodiment of the DC arc welding machine of this invention, and Figures 5 and 6 are characteristic curve diagrams of the arc start welding current and signal voltage shown in Figure 4. be. DESCRIPTION OF SYMBOLS 1...Input terminal, 2...Output control section, 3...Current detection section, 4...Output terminal, 5...High voltage and small current generation circuit section, 6...Start current detection section, 6a...
...First switch, 6b...Second switch, 7...
Operational amplifier section, 9... Reference power source, 10... Differential signal generator, 11... Phase shifter.

Claims (1)

[Scope of utility model registration request] The AC input is controlled and rectified by an output control section configured using a thyristor, a welding current is supplied to the load, the welding current is detected by a current detection section, and a comparison amplifier section calculates the voltage of the current detection section and the welding current. A DC arc welding machine that compares and amplifies the reference voltage of a reference power source for setting, controls the phase of the thyristor of the output control section via a phase shifter, and configures a feedback system to make the output characteristics constant current characteristics. , a series circuit of a high-voltage, small-current generation circuit that flows a high-voltage, small current and a start current detection unit, through which the high-voltage, small-current flows, is connected between the input terminal of the AC input and the output terminal of the welding current. and generating a differential signal for compensating for a delay in a feedback system, the peak value of which is set to a value larger than the reference voltage that makes the welding current a small current and smaller than the reference voltage that makes the welding current a large current. a first and second switch connected to the respective output terminals of the reference power supply and the generator, and operated in conjunction with the energization of the current detection section; and the reference voltage via the two switches. selection output means for selecting and outputting a larger voltage among the signal voltages of the differential signal generator; and outputting an error amplification signal between the output voltage of the selection output means and the voltage of the current detection section to the phase shifter. A DC arc welding machine equipped with an operational amplifier.