JPS61266178A - Power source for arc welding - Google Patents

Abstract

PURPOSE:To stabilize a welding by providing a current variation factor detecting means and output current control means and by increasing as the time elapsing the amplification of a signal amplifier circuit as well from the time when the arc load transfer to a short circuit state, etc. CONSTITUTION:The secondary coil 9 is provided as a current variation factor detecting means on a DC reactor 8 and the voltage induced on the coil 9 is used as the signal corresponding to the variation factor of the output current I. When the output current I is increased, the ON time intervals of a switching element 5 is reduced and in the reverse case,increased to hold the control function of the current variation. Instantaneously with the arc load 12 moving to the short circuit state from the arc state or to the arc state from short circuit state the amplification is increased as the time elapses via the delay element of an operational amplifier IC2. the welding is stabilized because of the prevention from the spatter generation and arc cut being enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] 11 The present invention relates to an arc welding power source suitable for automatic arc welding using a consumable electrode, particularly for CO2 arc welding by short-circuit transfer.

[Background of the invention]

In CO2 arc welding due to short-circuit transfer, if the short-circuit condition continues for a long time due to some reason, an excessive short-circuit current will flow and large spatter will occur at the moment of arc regeneration, and if the arc condition continues for a long time, the current will decrease. This causes arc breakage and poor bead shape.

Conventionally, to reduce spatter, as shown in Fig. 3, measures have been taken to limit the peak value IP of the short-circuit current by providing means to suppress the increase in current when the output current exceeds a certain set value IH. Efforts have been made to prevent excessive current ■P' from flowing, and to prevent arc breakage, as shown in Figure 4, if the output current drops below a certain set value IL during the arc generation period, the output current is increased or Efforts have been made to prevent the current from reaching zero by providing a means to control the current to constant. These have been made possible by the realization of an inverter-controlled arc welding power source that controls the output using a high-speed switching element such as a power transistor.

However, when trying to prevent the generation of large spatter and arc breakage using the following conventional techniques, (1) current value detection means (2) TI setting means (3) current increase suppressing means (4) Tl, 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 the following problems as in the prior art:
), with a simple and inexpensive configuration,
An object of the present invention is to provide an arc welding power source that can sufficiently reduce spatter and prevent arc breakage.

[Summary of the invention]

31 The present invention provides, in a consumable electrode type arc welding power source whose output is controlled by a high-speed switching element such as a power transistor, current change rate detection means for generating a signal corresponding to the change rate of output current; output current control means for changing the on-off time ratio of the high-speed switching element so as to suppress a change in the output current by amplifying a signal corresponding to the current change rate and adding it to the output control signal; The amplifier circuit that amplifies the signal corresponding to the rate of change is configured such that the amplification degree increases with time from the time when the arc load changes from the arc state to the short circuit state and from the time from the time when the short circuit state changes to the arc state. It is characterized by being

In the first place, in CO27-k 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 the arc condition. This is when it continues for a long time.

41 The present invention focuses on this fact and strengthens the suppression of changes in output current (brings it closer to constant current propensity) when short-circuit conditions and long-term arc conditions continue. Rather than switching based on current or set time, the control circuit is simplified by making the change in 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, 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 using a high-speed switching element 5 such as a power transistor or MOSFET converts the current into high-frequency alternating current (for example, 20 kHz), steps down the voltage through the welding transformer 6, converts it back to direct current through the output rectifier 7, and connects the DC reactor. 8 is an inverter-controlled arc welding power supply that smoothes and supplies DC output to an arc load 12; 10 is a welding wire used as a consumable electrode; 11 is a wire feed 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 current change rate detection means, and the voltage induced in the secondary winding 9 is determined by the rate of change (d) of the output current supplied to the arc load 12.
i/dt, ). The output current control means amplifies the induced voltage of the next winding 9 in the - amplification circuit 14, adds it to the output control signal from the output voltage setter 16 in the 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 ■ 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, and both 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 determined by the amplifier circuit 14. Determined by the degree of amplification (gain).

The amplifier circuit 14 amplifies the voltage from the secondary winding 9 of the DC reactor 8 with an operational amplifier TC1, applies the output to the (-) input terminal of the operational amplifier TC2 through a resistor R, and further amplifies it to the adder circuit 15. It is designed to output
The operational amplifier ■C2 has a delay element consisting of a feedback resistor R8, a capacitor C□ in parallel with the feedback resistor, and a resistor R2, and its (+) input terminal is grounded through the resistor R4.

-1- The amplification degree of the operational amplifier C2 in the amplifier circuit 14 is determined by R3/R in DC terms, but by appropriately selecting the values of the capacitor C2 and the resistors R□ to R3, the arc load 12 The amplification degree of operational amplifier TC2 is approximately (R2・Ra/R2+R3
)/R□, and the amplification degree can be increased exponentially to R3/R1 over time.

FIG. 2 shows the output current waveform and each part signal waveform.

That is, as time passes from the time when the arc load 12 changes from the arc state to the short circuit state, the operational amplifier C2
As the degree of amplification increases, the temporal change in the output signal becomes gradual as shown in Figure 2 a → b, which acts to strengthen the suppression of the increase in the output current ■, and also causes the transition from the short circuit state to the arc state. The same is true when the time elapses from this point on, as the amplification degree of operational amplifier ■C2 increases, the temporal change in the output signal becomes gradual as shown in Figure 2 c-+d, and the output current ■ increases. It works to strengthen the control against decline.

Figure 5 is a diagram showing how the output current ■ is controlled. At the beginning of the short-circuit period and the arc generation period, the current changes rapidly to obtain an appropriate short-circuit period (number of short-circuits per unit time) under normal welding conditions. It is possible to prevent the generation of large spatter due to excessive current ■P' by keeping the current peak value IP low when the short-circuit condition continues for a long time while ensuring that the current peak value IP when the short-circuit condition continues for a long time. arc breakage can be prevented by suppressing the decrease in

~8- Although one embodiment of the present invention has been described above, the present invention is not limited to the configuration of the embodiment described in "-". For example, as a current change rate detection means, it may be Instead of providing a secondary winding 9 in the DC reactor 8, a current detector is used to convert the output current ■ into a voltage, and this voltage is applied to a differentiator circuit to obtain a signal corresponding to the rate of change of the output current. Good too.

Furthermore, as a means for increasing the degree of amplification over time, there is not only a method using a delay element as in the above embodiment;
A variable gain amplifier circuit (gain control TC) whose amplification degree is changed by an external control signal is used in the amplifier circuit 14, and the output voltage and current are determined 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. The degree of amplification may be increased over time by using an integral signal or the like that is reset using changes in as an external control signal.

〔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 at the time 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 change over time 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 decreases below the set value, and the 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 each part signal waveform in this embodiment, and FIG. 3 is a current waveform for explaining the conventional technology related to spatter reduction. 4 are current waveform diagrams for explaining the prior art related to prevention of arc breakage, and FIG. 5 is a current waveform diagram for explaining the present invention in detail. -10= 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)

Claims (1)

[Claims] A consumable electrode type arc welding power source whose output is controlled by a high-speed switching element such as a power transistor includes a current change rate detection means that generates a signal corresponding to the rate of change of the output current, and a current change rate detection means that generates a signal corresponding to the rate of change of the current. output current control means for changing the on/off time ratio of the high-speed switching element so as to suppress changes in the output current by amplifying and adding the amplified signal to the output control signal, and amplifying the signal corresponding to the current change rate. The amplifier circuit is characterized in that it is configured such that the degree of amplification increases with time from the time when the arc load changes from the arc state to the short circuit state and from the time when the arc load changes from the short circuit state to the arc state. Power source for welding.