JPH0330468B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention maintains the welding current at a predetermined value by setting a reference voltage to determine the output voltage of the welding power source, and by maintaining the feeding speed of the consumable electrode wire at the reference value. The present invention relates to an arc welding machine control device that determines welding conditions based on the following conditions.

In arc welding using a consumable electrode wire, a power source with approximately constant voltage characteristics is used as the welding power source,
A method is used in which the welding current is determined by feeding a consumable electrode wire at a substantially constant speed. In this case, the purpose of controlling the welding current is mostly achieved by controlling the wire feeding speed to a constant value, since the welding current is uniquely determined to a value that provides a melting rate that matches the wire feeding speed. , and even if the distance between the workpiece and the welding torch suddenly changes, the arc length changes, and the apparent wire feeding speed changes, the welding current will change depending on the output voltage of the power supply.
The arc length is recovered by making use of the so-called self-control of the welding power source, in which the amount of melt changes and the arc length recovers by changing according to the current characteristics.

However, the welding voltage varies, not only in welding power sources that do not feed back the output voltage, but also in those that do feed back and follow the reference value, due to errors in the feedback control system, as shown in Figure 1. It is unavoidable that the output voltage tends to decrease as the voltage increases.
Figure 1 shows the output voltage Ea of the welding power source on the vertical axis, the output current Iw on the horizontal axis, and the output voltage reference signal e _r as a parameter (e _r1 < e _r2 <
e _r3 ). As can be seen from the figure, the fluctuation rate of the output voltage with respect to the change in the output current varies depending on the output voltage reference signal, and generally increases as the output voltage is set to a higher value. Therefore, even if the welding current Iw is set to the same value, the output voltage difference △V from the reference signal is different, and the output voltage moves on each voltage/current characteristic curve as the welding current changes. , the output voltage deviates from the planned value at each instant during welding. For this reason, the output voltage is usually reset at the same time as the welding current setting value is changed. For example, in Figure 1, the current is changed from I ₁ to I ₂ (I ₁ <
I ₂ ), change the output voltage reference value from e _r1 to
It is necessary to change the output voltage to e _r ′ ₁ (e _r1 < e _r ′ ₁ ) to obtain the original output voltage e _0. In this case, measure the output voltage and check if this measured value is the desired value. It is necessary to turn the output voltage setting dial until it returns. In this way, there is a correlation between the output voltage Ea and the output current Iw based on the characteristics of the power supply, and if they are arbitrarily set independently, the output obtained will be different depending on the setting values of both. becomes.

The above phenomenon also occurs when the rotational speed of the electric motor, which determines the wire feeding speed, is controlled to a substantially constant speed based on the output current setting value.
In other words, even when controlling the rotational speed of the wire feeding motor to a speed corresponding to the current setting value, a speed error always occurs when performing normal feedback control, and this speed error increases as the set speed increases. That is, the larger the set value of the output current becomes, the larger the output current becomes, and the fluctuation rate of this rotational speed directly appears as the fluctuation rate of the output current. However, because the control system itself operates based on the difference between the set value and the motor rotation speed due to its operating principle, it is not possible to compensate for this change in the output current.

The present invention detects the actual output current Iw with respect to the set value Ir of the output current, obtains the difference (Ir - Iw), and changes the rotation speed of the wire feeding motor in the direction in which this difference signal decreases. The speed is controlled according to the output signal of the setting device to compensate for errors in the output current when feedback control of the rotation speed is normally performed, and the output voltage/current characteristic curve of the power supply is adjusted to each output voltage setting value. When each value of output voltage and output current is input, the characteristics corresponding to each value are read out and the reference signal is corrected by these values, so that a predetermined output voltage can be set as desired. It was designed so that it could be obtained.

FIG. 2 is a connection diagram showing an embodiment of the present invention.
In the figure, reference numeral 1 denotes a welding power source that outputs a voltage corresponding to a reference voltage supplied to a terminal S, and supplies welding power to a welding torch 2 and a workpiece 3. Reference numeral 4 denotes a consumable electrode wire, which is fed by a feed roll 6 driven by an electric motor 5 to the workpiece 3 via the welding torch 2. 7 is an output current setting device that outputs a welding current setting signal as a digital signal, 8 is a D/A converter for converting the output of the output current setting device 7 into an analog signal, and 9 is an output current setting device that outputs the output current of the welding power source 1. Current detector to detect, 10
is a comparator that compares the output of the D/A converter 8 and the output of the current setter 9. 11 is an output voltage setting device that outputs an output voltage setting signal as a digital signal; 12 is a memory circuit that stores the output voltage/current characteristics of the welding power source 1 in correspondence with each combination of output voltage and current; This is an arithmetic circuit that receives each output of the output current setter 7 and the output voltage setter 11, reads out the stored contents of the storage circuit 12 corresponding to each set value, and corrects the output signal of the output voltage setter 11. When the output voltage/current characteristics of the welding power source 1 show a linear change expressed by a simple linear equation as shown in FIG. circuit 1
2 is a correction amount setter for setting the maximum correction amount, and the arithmetic circuit 13 multiplies the output signal of this correction amount setter by a coefficient corresponding to the combination of each output of the output voltage setting device 11 and the output current setting device 7. An addition counter that adds the output signal of the output voltage setter 11 can be used. When the output voltage/current characteristics of the welding power source 1 show complex curved changes, the memory circuit 1
2, a semiconductor memory circuit is used as the arithmetic circuit 13, and the memory location of the memory circuit 12 is specified and read out according to the output of the output voltage setter 11 and the output of the output current setter 7, and the output voltage setter 11
A microprocessor programmed to correct and output the output signal may be used.
14 is a D/A converter for converting the digital output of the arithmetic circuit 13 into an analog signal and supplying it to the S terminal of the welding power source 1 as an output voltage command signal.

In the embodiment shown in the figure, the rotational speed of the electric motor 5 is controlled by the difference between the output of the output current setting device 7 and the output of the current detector 9, and the feeding speed of the wire 4 is set to a desired value. Output current can be obtained. At this time, if a normal differential amplifier is used as the comparator 10, a slight error will occur between the input and output, so if the comparator uses an integrating circuit that integrates the difference between both input signals, the difference between the input and output will always be Since it is corrected until it reaches zero and then stabilizes, extremely accurate control of the output current becomes possible. On the other hand, the output e _r of the output voltage setting device 11
In the arithmetic circuit 13, △e _r corresponding to the output voltage fluctuation shown in FIG _. e _r ) and the D/A converter 14
After being converted into an analog signal, it is supplied to the welding power source 1 as an output voltage command signal.
As a result, the welding power source 1 receives a command signal that corrects voltage fluctuations that vary depending on the output current value, so the output voltage is apparently maintained at the desired value regardless of the output current value. It turns out.

As a result, the output current and the output voltage can be set completely independently of each other, and a control device that is extremely easy to adjust and accurate without being influenced by the other can be obtained.

In the embodiment shown in FIG. 2, the arithmetic circuit 13
The D/A converter 14 converts the output of No utensils are required. Furthermore, it goes without saying that the entire device can be configured as an analog signal system. Additionally, there are those that feed back the output voltage of the welding power source 1, and those that use the output of the current detector 9 instead of the output of the output current setting device 7 as the output current signal to the arithmetic circuit 13 (however, the arithmetic circuit 13 handles digital signals). signal conversion is required),
Various modifications are possible, such as replacing the comparator 10 with the D/A converter 8 by using a digital signal comparator. In particular, when the output signal of the current detector 9 is used as the output current signal to the arithmetic circuit 13, the output voltage is corrected in accordance with the actual output current, so it is not only used when changing the output current setting value. This is convenient because the output voltage command signal is corrected for changes in the output current when the arc length fluctuates due to hand shake of the operator operating the welding torch or changes in the surface shape of the workpiece. .

As described above, in the present invention, the wire feeding speed is controlled so that the difference between the output current and the output current setting value becomes zero, and the output current is maintained at a predetermined value. The output voltage and current characteristics of the welding power source stored in advance corresponding to the combination are read out, and the output voltage setting signal is corrected according to the stored contents to obtain the output voltage command signal for the welding power source. It is possible to determine the output current and the output current completely independently, and moreover, it is possible to control the welding conditions with extremely accurate welding conditions.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of output voltage/current characteristics of a welding power source, and FIG. 2 is a connection diagram showing an embodiment of the present invention. 1... Welding power source, 5... Electric motor, 7... Current setting device, 9... Current detector, 10... Comparator, 11
... Voltage setting device, 12 ... Memory circuit, 13 ... Arithmetic circuit.

Claims (1)

[Claims] 1. An output voltage setting device, an output current setting device, a welding power source that outputs a voltage according to a command signal, and a signal that directly detects the output signal and output current of the output current setting device. a wire feeding speed control circuit that determines the wire feeding speed using a signal obtained by integrating the difference signal;
a memory circuit that stores output voltage and current characteristics of the welding power source according to an output voltage setting signal; and an output of the output voltage setter and an output current signal that are inputted and stored in the memory circuit according to a combination of both signals. an arithmetic circuit that reads out the output voltage/current characteristics of the welding power source, converts the output of the output voltage setting device into a value corrected for an output voltage change that occurs according to the output current, and supplies the corrected value as an output voltage command signal of the welding power source; Arc welding machine control device equipped with 2. The arc welding machine control device according to claim 1, wherein the output current signal is an output signal of the output current setting device. 3. The arc welding machine control device according to claim 1, wherein the output current signal is a signal obtained by detecting the output current of the welding power source.