JPH0349803Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> This invention relates to a power supply circuit for an arc welding machine that includes a feedback system to perform constant current control of welding current.

<Prior Art> In general, the power supply circuit of an arc welding machine having a feedback system, as shown in FIG. I is detected by a detector 3, and the detected signal is compared with a reference signal of a reference signal generation circuit 4 for setting the welding current I by an error amplifier 5, the error is amplified, and the output of this error amplifier 5 is The welding current main control circuit is configured to feed back to the welding current main control circuit. FIG. 5 is a specific circuit diagram of the conventional reference signal generation circuit 4 and error amplifier 5. In FIG. In Fig. 5, the output signal (reference signal) V1 of the variable resistor Rv that sets the welding current I, the detection signal V2 detected by the detector 3, and the operational amplifier IC
The feedback signal V ₀ is input to the operational amplifier IC through resistors R1, R2 and R3, respectively, and
The output signal V ₀ is input to the welding current main control circuit 6 to control the welding current I so that ≈V2. The variable resistor Rv has B-type characteristics, and a constant DC voltage E is applied to one of its fixed terminals. A variable divided voltage obtained by sliding the sliding terminal is a reference signal V1 for setting the welding current I.

For example, the variable resistor Rv of a TIG welder rated at 300A
The scale is shown in FIG. 6, and the relationship between the rotation angle θ (sliding angle) of the variable resistor Rv and the reference voltage V1 is shown in FIG. In FIG. 7, the α and β sections are so-called play areas at the beginning and end of rotation of the variable resistor Rv, but in other ranges, the value of the reference signal V1 changes linearly with respect to the value of the rotation angle θ.

Generally, TIG welding machines with a rating of 200 or 300A are most commonly used, but in actual welding work,
There is a high frequency of thin plate welding work where welding is performed with the welding current set to 150A or less. For this reason, in a variable resistor with an equal division scale as shown in Figure 6, both the frequently used small current region and the less frequently used large current region have the same linear characteristics. However, there was a problem in that it was difficult to set the welding current in the small current range.

<Purpose of the invention> This invention was made in view of the above-mentioned circumstances.
In the variable resistor adjustment range, the rate of current change with respect to the variable resistor operation amount in the frequently used small current area is made finer, and the current change rate with respect to the variable resistor operation amount in the less frequently used large current area is made coarser. It is an object of the present invention to provide a power supply circuit for an arc welding machine that allows easy setting of welding current.

<Configuration of the invention> To summarize, this invention includes a detector that detects welding current and generates a detection signal, a reference signal generation circuit that generates a reference signal, and a difference component between the detection signal and the reference signal. In a power supply circuit for an arc welding machine, the power supply circuit includes an error amplifier for amplification, and a welding current main control circuit for inputting the output of the error amplifier to make the welding current constant, wherein the reference signal generation circuit divides a constant voltage. It is characterized by comprising a variable resistor and a resistor connected between the sliding terminal of the variable resistor and ground.

With the above configuration, the rate of change of welding current with respect to the manipulated variable of the variable resistor becomes fine in the small current region of the variable resistor's adjustment range, and the change rate of welding current with respect to the manipulated variable of the variable resistor in the large current region. The ratio becomes coarser. As a result, it becomes easier to preferentially set the welding current in the frequently used small current range.

<Embodiment> FIG. 2 is a circuit diagram of a portion for setting the welding current in the power supply circuit of an arc welding machine which is an embodiment of this invention. This circuit differs in configuration from the circuit shown in FIG. 5 in that a resistor R4 is connected between the sliding terminal of the variable resistor Rv and the ground. When the resistor R4 is connected, the reference signal V3 becomes the voltage divided by the series-parallel circuit of the resistors Rv1, Rv2 of the variable resistor Rv divided by the sliding terminal and the resistor R4, and V3=E×〓〓〓〓〓〓/〓 〓〓〓〓〓＋Rv2 ＝Rv1／Rv1＋〓〓・(R4＋Rv1)・E……(1). In the circuit of FIG. 5 in which the resistor R4 is not connected, the reference signal V1 becomes V1=Rv1/Rv1+Rv2·E (2). Comparing equations (1) and (2), the denominator of equation (1) is larger than the denominator of equation (2), so the relationship V1>V3 holds true. Therefore, regarding the magnitude of the reference signal V3 with respect to the rotation angle θ of the variable resistor Rv, as shown in FIG. In the range where the rotation angle θ increases, the reference signal V3 exhibits an exponential characteristic in which the rate of increase increases. For this reason, with a TIG welding machine rated at 300A, the scale arrangement of the variable resistor Rv that sets the welding current I is such that the frequently used small current region up to 150A is wide, and the less frequently used small current region is wider, as shown in Figure 4. The high current region of 150-300A becomes rough. Therefore, it becomes easy to set the welding current in the frequently used small current range, and the welding work is expedited.

Note that in the embodiment shown above, the resistor R4 connected between the sliding terminal of the variable resistor and the ground is a single fixed resistor, but this resistor R4 can be connected to a plurality of fixed resistors and a variable resistor. It may also be configured with series-parallel circuits.

<Effects of the invention> As described above, according to this invention, the rate of change of welding current with respect to the variable resistor operation amount in the small current region of the variable resistor adjustment range is fine, and the welding current with respect to the variable resistor operation amount in the large current region is Since the rate of change of the current becomes rough, it becomes easier to set the welding current in the frequently used small current range, improving work efficiency.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the power supply circuit of an arc welding machine that is the premise of this invention, Figure 2 is a circuit diagram of the welding current setting section in the power supply circuit of an arc welding machine that is an embodiment of this invention, and Figure 3 is FIG. 2 is a diagram showing the relationship between the reference signal V3 and the rotation angle θ of the variable resistor, and FIG. 4 is a diagram showing the scale arrangement of the variable resistor. Figure 5 is a circuit diagram of the welding current setting section in the power supply circuit of a conventional arc welding machine, Figure 6 is a diagram showing the scale arrangement of a conventional variable resistor, and Figure 7 is a diagram showing the conventional reference signal V1 and variable resistor. FIG. 2 is a diagram showing the relationship between rotation angle θ and 1... Welding electrode, 2... Base material, 3... Detector,
Rv...variable resistor.

Claims (1)

[Claims for Utility Model Registration] A detector that detects welding current and generates a detection signal, a reference signal generation circuit that generates a reference signal, and an error amplifier that amplifies the difference component between the detection signal and the reference signal. In the power supply circuit for an arc welding machine, which is composed of a welding current main control circuit that inputs the output of this error amplifier and makes the welding current a constant current, the reference signal generation circuit is configured with a variable resistor that divides a constant voltage. , a power supply circuit for an arc welding machine, comprising a resistor connected between the sliding terminal of the variable resistor and ground.