JPH0453619B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an arc welding power source suitable for automatic arc welding using consumable electrodes, in particular for CO ₂ arc welding with short-circuit transfer.

[Background of the invention]

In CO ₂ arc welding due to short-circuit transition, if the short-circuit condition continues for a long time for some reason, the short-circuited electrode will flow excessively and large spatter will occur at the moment of arc regeneration, and if the arc condition continues for a long time,
The decrease in current causes arc breakage, resulting in poor bead shape.

Conventionally, as a countermeasure to reduce spatter, as shown in Figure 3, when the output current exceeds a certain set value I _H , a means is provided to suppress the increase in current, thereby limiting the peak value I _P of the short circuit current. and excessive current
Efforts have been made to prevent I _P ' from flowing, and to prevent arc breakage, as shown in Figure 4, when the output current drops below a certain set value I _L during the arc generation period, the output current is increased or fixed. Efforts were made to prevent the current from reaching zero by providing a means to control the current. These have been made possible by the realization of an inverter-controlled arc welding power source whose output is controlled using advanced switching elements such as power transistors.

However, when trying to prevent the generation of large spatters and arc breakage using the above conventional technology, (1) current value detection means (2) I _H setting means (3) current increase suppressing means (4) I _L setting means (5) Current reduction suppressing means is required, making the control circuit complicated and expensive.

[Purpose of the invention]

The purpose of the present invention is to solve (1) to (5) as in the prior art described above.
It is an object of the present invention to provide an arc welding power source that can sufficiently reduce spatter and prevent arc breakage with a simple and inexpensive configuration without using the above means.

[Summary of the invention]

The present invention includes current change rate detection means for controlling an output current by a high-speed switching element and generating a signal corresponding to the rate of change of the output current, and output current output means for changing the on-off time ratio of the high-speed switching element. In the arc welding power supply device, the output from the current change rate detection means is input to operational amplifier IC ₁ , the output is input to the negative terminal of operational amplifier IC ₂ via a resistor, and the output of operational amplifier IC ₂ is connected to the negative terminal. A delay element consisting of a resistor R ₃ connected in parallel between the terminals, a capacitor C ₁ in parallel with the resistor R ₃ , and a resistor R ₂ , and the positive terminal of the operational amplifier IC ₂ are configured to be grounded via a resistor R ₄ . and an adder circuit that adds the amplification degree of the amplifier circuit to the output control signal. This is an arc welding power supply device characterized in that the amplification degree increases with the passage of time.

In the first place, in CO ₂ arc welding due to short-circuit transition, large spatters due to excessive current occur when the short-circuit condition continues for a long time, and arc breakage due to decrease in current occurs due to changes in arc length. This is when it continues for a long time.

The present invention has focused on this fact, and is designed to strengthen the suppression of changes in output current (approximate to constant current tendency) when a long-term short-circuit condition or long-term arc condition continues. Rather than switching at a set time, the control circuit is simplified by making the change in the output current gradual, almost exponentially, over time as shown in FIG.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG.

In this embodiment, the input from a commercial AC power supply 1 is converted into DC by a rectifier circuit 2, smoothed by a smoothing capacitor 3, and then
The inverter circuit 4 uses high-speed switching elements 5 such as MOSFETs to generate high-frequency alternating current (for example, 20k
Hz), the voltage is stepped down by a welding transformer 6, and then converted to DC again by an output rectifier 7, smoothed by a DC reactor 8, and supplied to an arc load 12 with an inverter-controlled arc welding power source. 10 is a welding wire used as a consumable electrode, 11 is a wire feeding roller, and 13 is a base material.

The DC reactor 8 is small enough to smooth the high-frequency AC component, and its function as an inductance, which is necessary for welding characteristics, is achieved by current change rate detection means and output current control means, which will be described below.

In this embodiment, a secondary winding 9 is provided in the DC reactor 8 as a current change rate detection means.
The voltage induced in the arc load 12 is used as a signal corresponding to the rate of change (di/dt) of the output current I supplied to the arc load 12. The output current control means amplifies the induced voltage of the secondary winding 9 with an amplifier circuit 14, adds it with an output control signal from an output voltage setter 16 in an adder circuit 15, applies it to the drive circuit 17, and adjusts the pulse width. By driving the high-speed switching element 5 of the inverter circuit 4 with a modulated signal, when the output current I is about to increase, the on-time width of the switching element is narrowed, and when the output current I is about to decrease, conversely. has the function of suppressing current changes by widening the on-time width of the switching element,
The current increase rate during the short-circuit period of the arc load 12 and the current decrease rate during the arc generation period are both determined by the amplification degree (gain) of the amplifier circuit 14.

The amplifier circuit 14 is connected to the secondary winding 9 of the DC reactor 8.
The voltage from the amplifier IC ₁ is amplified by the operational amplifier IC 1, and its output is applied to the (-) input terminal of the operational amplifier IC ₂ through the resistor R ₁ , and is further amplified and output to the adder circuit ₁₅ . is the feedback resistance
R ₃ and a capacitor C ₁ in parallel with this feedback resistor,
It has a delay element consisting of resistor _R2 , and the (+) input terminal is grounded through resistor _R4 .

The amplification degree of the operational amplifier IC ₂ in the amplifier circuit 14 is determined by R ₃ /R ₁ in DC terms, but by appropriately selecting the values of the capacitor C ₁ and the resistors R ₁ to R ₃ , the arc load 12 The amplification degree of operational amplifier IC ₂ is reduced to approximately (R ₂・ R ₃ / R ₂ + R ₃ ) / R ₁ at the moment when the voltage changes from an arc state to a short circuit state and from a short circuit state to an arc state, and The amplification degree can be increased exponentially to R ₃ /R ₁ as time progresses.

FIG. 2 is a diagram showing the output current waveform and each part signal waveform in FIG. 1.

Figure a shows changes in the output current I.

Figure b shows changes in the output voltage of the operational amplifier _IC1 .

The output of operational amplifier IC ₁ is inverted and amplified.
The output voltage of operational amplifier IC ₂ is as shown in .

Next, the set voltage V ₁₆ from the output voltage setter 16 is added to the output of the operational amplifier IC ₂ in the adder circuit 15, and an output signal as shown in d in the figure is sent to the drive circuit 1.
7 is input.

Subsequently, the drive circuit 17 obtains an output signal shown in FIG. The drive circuit 17 includes an adder circuit 15
This circuit outputs narrow pulses when the signal level of the signal output from is low, and outputs wide pulses when the signal level is high.

Furthermore, the inverter circuit outputs an output signal shown in FIG.

As is clear from FIG. 2e, the ON time of the output signal of the drive circuit 17 increases as the input voltage changes between a and b, and the ON time increases as the input voltage changes between c and d. Becomes shorter. However, the (ON+OFF) time is always constant.

In other words, the amplification degree of the operational amplifier IC ₂ increases as time passes from the time when the arc load 12 changes from the arc state to the short circuit state, so that the output signal changes slowly over time as shown in Fig. 2 a → b. This works to strengthen the suppression of the increase in the output current I, and the same is true when moving from a short-circuit state to an arc state, and the amplification degree of the operational amplifier IC ₂ increases as time passes from this point on. The temporal change in the output signal becomes gradual as shown in FIG. 2 from c to d, which acts to strengthen the suppression of the decrease in the output current I.

FIG. 5 is a diagram showing how the output current I is controlled.
At the beginning of the short-circuit time and arc generation period, the current changes rapidly to ensure an appropriate short-circuit cycle (number of short-circuits per unit time) under normal welding conditions, but when the short-circuit condition continues for a long time, the current peak By keeping the value I _P low, it is possible to prevent the generation of large spatters due to excessive current I _P ', and it is also possible to prevent arc breakage by suppressing the decrease in current when the arc condition continues for a long time.

Although one embodiment of the present invention has been described above,
The present invention is not limited to the configuration of the above embodiment, and for example, instead of providing the secondary winding 9 in the DC reactor 8 as in the above embodiment, a current detector may be used as the current change rate detection means. Alternatively, the output current I may be converted into a voltage, and this voltage may be applied to a differentiating circuit to obtain a signal corresponding to the rate of change of the output current.

In addition, as a means for increasing the amplification degree over time, there is not only a method using a delay element as in the above embodiment, but also a variable gain amplifier circuit (gain control IC) in which the amplification degree is changed by an external control signal in the amplifier circuit 14. The amplification degree is controlled over time using an external control signal such as an integral signal that is reset using changes in the output voltage and current at the time of transition from the arc state to the short circuit state and the time of transition from the short circuit state to the arc state. It may also be made larger over time.

〔Effect of the invention〕

According to the present invention, the amplification degree of the amplifier circuit that amplifies a signal corresponding to the rate of change of the output current and adds it to the output control signal is adjusted when the arc load changes from the arc state to the short circuit state and from the short circuit state to the arc state. By increasing the current as time passes from the point when the current changes, the suppression of current changes is strengthened. There is no need to separately provide a means to suppress the decrease in current when the current drops below the set value, and a simpler and cheaper circuit configuration prevents the generation of large spatters due to excessive current, and prevents arcing due to decrease in current. The effect of preventing cuts can be fully exhibited.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
Fig. 2 is a diagram showing the output current waveform and various signal waveforms in this embodiment, Fig. 3 is a current waveform diagram for explaining a conventional technique for reducing spatter, and Fig. 4 is a diagram for explaining a conventional technique for preventing arc breakage. FIG. 5 is a current waveform diagram for explaining the effects of the present invention. 5... High-speed switching element, 9... Current change rate detection means (secondary winding of DC reactor), 10...
...Consumable electrode (welding wire), 12... Arc load, 14, 15... Output current control means (14...
amplifier circuit, 15...addition circuit), _C1 , _R2 ...delay element that changes the degree of amplification.

Claims (1)

[Scope of Claims] 1. Current change rate detection means for controlling an output current by a high-speed switching element and generating a signal corresponding to the rate of change of the output current, and an output current for changing the on-off time ratio of the high-speed switching element. In an arc welding power supply device having an output means, the output from the current change rate detection means is input to an operational amplifier IC ₁ , the output is inputted to a negative terminal of an operational amplifier IC ₂ via a resistor, and the output is connected between the negative terminal and the operational amplifier. A delay element consisting of a resistor R ₃ connected in parallel between the output terminals of IC ₂ , a capacitor C ₁ and a resistor R ₂ in parallel with the resistor R ₃ , and an operational amplifier.
An amplifier circuit configured to ground the positive terminal of IC ₂ via a resistor R ₄ , and an adder circuit that adds the amplification degree of the amplifier circuit to the output control signal. A power supply device for arc welding, characterized in that the power supply device for arc welding is configured such that the degree of amplification increases with the passage of time from the time of transition to a short circuit state and the time of transition from a short circuit state to an arc state.