JPS5855175A - Electric power source device for welding machine - Google Patents

Abstract

PURPOSE:To maintain output current constant against fluctuations in input voltage and to improve the accuracy of controlling by correcting the patterns for setting the output voltage of a thyristor according to the detected value of a load power factor. CONSTITUTION:The data of patterns for setting voltage according to the capacity and welding current conditions of a load welding machine are inputted in the form of per cent from a data inputting device 20. The inputted data are stored via a microprocessor 17 into a memory element 19. A load power factor is determined from the conduction angle of a thyristor when the thyristor is fired at a prescribed firing angle at the 1st cycle of conduction of electricity by the command for starting. The patterns for setting the output voltage of the thyristor are corrected according to the detected value of the load power factor.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply device for a welding machine, and more particularly to a power supply device for a spot welding machine using a multi-transformer.

FIG. 1 is a block diagram showing an example of a power supply device for a welding machine that includes a microcomputer control circuit and performs constant voltage control.

When the secondary side of the welding transformer 6 is used in such a way that the secondary side of the welding transformer 6 is energized simultaneously in two circuits as shown in the figure, it is preferable to use constant voltage control rather than constant current control in the power supply device that controls the primary side of the welding transformer. The reason for this is that when one circuit of the secondary cable of a welding transformer breaks, which is often experienced with spot welding machines, the constant current control method theoretically allows twice as much current to flow through a healthy circuit. This is because it may cause problems such as holes forming in the parts. In the case of a constant voltage control system, the above-mentioned trouble does not occur because the current value of a healthy circuit hardly changes even when one circuit is disconnected.

The detection transformer 4 in the figure is for detecting the zero point of the input voltage and determining the reference phase for determining the entire firing angle of the thyristor. Further, the output voltage detection transformer 5, the waveform shaping circuit 1o, and the analog/digital converter 12 constitute an output voltage value feedback circuit.

In the conventional constant voltage control method, the output voltage normal value is sampled during each half cycle after thyristor firing via a detection transformer 5, a waveform shaping circuit 10, and an analog-to-digital converter 12, and the output voltage is sent to a microcomputer. After the data is input, the thyristor firing angle for the next cycle is calculated and determined by comparing it with a voltage setting pattern that has been input in advance and canceling out the error.

At this time, the conventional method is to use the values on the horizontal axis of the curve shown in FIG. 2 as they are as the voltage setting pattern for data input. In other words, the setting is 100% when the rated input voltage is directly transmitted to the output side, and 80% when it is desired to control the effective value of the output voltage to 80% of the rated input voltage by changing the ignition phase. be. As shown in Figure 2 of this method, as the load power factor decreases, the percentage of output current becomes smaller relative to the percentage of output voltage, and the percentage setting value entered in the data and the actual output current flowing There was a problem where the values were not proportional.

Furthermore, as can be seen from the solid line in Figure 3, the input voltage is ±20
When considering a power supply system for a welding machine that fluctuates by about 10%, if constant voltage control is performed to keep the output voltage at a constant value, for example 80% of the rated voltage, the load power factor will be as low as about 0.4. There is also the problem that the output current fluctuates significantly by about ±15% under certain conditions, making it impossible to obtain a constant current. This problem arises from the fact that it is the welding current, not the voltage, that essentially affects the welding quality etc. on the load side.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a constant voltage control power supply device for a welding machine that can obtain constant current characteristics when there is no change in load impedance.

The gist of the present invention is to control the output current to a constant level when the load impedance does not change by adding corrections corresponding to the load power factor and input voltage value to the voltage setting pattern data input in advance.

FIG. 4 shows a block diagram of an embodiment of the present invention.

The difference from Fig. 1 is that the detection transformer 4 not only detects the reference phase for determining the firing angle but also captures the input voltage value, and also serves as the transformer 5 for detecting the output voltage shown in Fig. 1. That is what we are doing. Also, the transformer 5 in this embodiment
0 is a detection transformer for determining the period during which current is flowing (conduction angle) after the thyristor firing pulse is output by checking the voltage across the thyristor.

FIG. 5 shows waveforms of each part of the embodiment shown in FIG. 4 immediately after the thyristor starts firing.

The general operation of the embodiment of the present invention will be explained using FIGS. 4 and 5.

Before applying current to the load welding machine, first, a voltage setting pattern corresponding to the capacity of the load welding machine and welding current conditions is input in the form of a percentage from the data input device 20 shown in FIG. In addition to the above, the types of data to be input include the number of energization cycles, the number of electrode pressurization cycles, and the like. The input data is stored in the data storage memory element 19 via the microprocessor 17.

After the data input is completed, when a start command is input, the power supply device starts energizing after a delay in electrode pressurization. Fifth
The figure shows the waveforms of various parts from the start of energization. First, the microphone 9 processor 17 sets the counter 15 to determine the thyristor firing phase of 120° at the beginning of the period (3), and the input voltage reaches the peak value. The input voltage instantaneous (1n) is taken in and stored in the microprocessor 17 via the analog-to-digital converter 12 at a phase of 90° as shown.The microprocessor 17 then receives the output signal of the counter at a firing angle of 120°. This outputs an ignition signal to the cyrisk gate.

The firing angle of 120° in the first cycle was decided because we were going to conduct a test run with a small current to check the load conditions and find the load impedance and load power factor, and the firing angle was 120° in particular. There's no need.

It is also possible to adopt values such as 90° and 100'.

After firing at 120°, the period ■ continues while the voltage across the thyristor ■ is at 0 level, and the output voltage (
One method is to obtain the effective value of the output voltage by inputting the output voltage (the shaded area in Figure 5) to the microprocessor 17 via an analog-to-digital converter at regular intervals;
When the value of changes to rubel and the period of ■ ends, θ,
The time corresponding to microprocessor 1 is calculated from the counter value.
Another processing content is to obtain the load power factor by taking in the load power factor.

During the period of ■, it is not necessary to control the thyristor, etc., but during this period, the data is first manually entered and corrected to the memorized output voltage setting pattern based on the input voltage value and load force taken in during this period. Perform the process of adding . Details of how to apply the correction will be described later. After the above processing is completed, the output voltage value actually measured during the period (2) is compared with the pattern value after the completion of the correction, and the firing phase α2 that makes the error between the two zero is determined by calculation. (2) starts 180° after the start of (2), and the main processing contents include firing the thyristor and setting the firing phase α2 for the second cycle.

From the second cycle onward, the actual measured output voltage values during each half-cycle period indicated by ■, ■, and ■ are successively compared with the pattern values obtained during the period ■ after completion of correction, and the error is set to zero in the next cycle. The process of determining the ignition phase will continue.

The above operation makes it possible to keep the current flowing through the load constant despite input voltage fluctuations and load power factor fluctuations for each welding point.

The method for correcting the output voltage setting pattern is described in Part 2.
．． This will be explained with reference to Figures 3, 6, and 7.8.

Figure 2 shows the percentage value of the output current effective value (100% indicates the current flowing when the output voltage is 100%) relative to the percentage value of the output voltage effective value (100% indicates the case where the input voltage becomes the output voltage as it is). ), and shows the relationship between the two using the load power factor as a parameter. For example, if the output voltage setting pattern is 80% as shown in the figure, the output current will be 80% due to the power factor.
% to about 66%, the method of correction is to find the voltage setting pattern value at each power factor to keep the current constant at 80% and then apply the correction. In the case of the figure, when the power factor pf is 20 or 8, the corrected setting value V
, (O,S) is 87.5% pf=0.4 is 89.5%
It will have to be done. If the ratio of the corrected voltage setting pattern vp('p') to the voltage pattern V of pf=1.0 (1,0) is 1, then If we take the setting pattern of V, (1,0) as the horizontal axis, and draw a curve of 1 on this as pff and the parameter, we get something like FIG. 6. If the curve shown in Fig. 6 is stored as a table in the memory element, the set pattern can be created based on the percentage value of the input data set in advance and the load power factor taken in from the detection circuit at the first cycle of energization. Correction becomes possible.

The above correction by 1 has the effect of making the data input percentage value directly proportional to the output current.

Note that FIG. 7 shows a curve for determining the load power factor from the conduction angle θ1 of the first cycle of energization. Figure 7 shows ignition phase 1
The value of the load power factor with respect to the conduction angle θ1 when the sirisk is fully fired at 20° is plotted as a curve. If this curve is stored in a memory device as a data conversion table, the load power factor can be determined from θ.

Next, a correction method when the input voltage fluctuates will be explained with reference to FIGS. 3 and 8.

Figure 3 is a curve drawn for the case where the relationship between output voltage and output current is 1pf = 0.4 when the input voltage fluctuates within a range of ±20%, and the output is the same as in Figure 2. It can be seen that it is possible to make the current percentage constant (for example, 80%) by adding correction to the voltage setting value. Voltage pattern Vp+ when input voltage is 100%
If the ratio of the voltage pattern Vp+(Vmu) when the input voltage to (i, o) fluctuates is set to 2, the relationship between the two will be as shown in FIG. FIG. 8 shows a curve when the pf is 2064 and the set input cover turn value is 80%.

If the above-mentioned curve is stored in a memory device as a data conversion table or a linear approximation formula, the setting pattern can be corrected based on the actual measured value of the input voltage and the actual measured value of the load power factor.

According to this embodiment, although constant voltage control is performed, the data input setting pattern is made proportional to the output current regardless of the value of the load power factor. Furthermore, the output current can be controlled to be constant even when the input voltage fluctuates. In addition, control accuracy can be further improved by applying the input voltage not only in the first cycle of the energization cycle but also in every cycle.

As described above, according to the present invention, the power supply device for a welding machine with constant voltage control has the effect of constant current control against input voltage fluctuations.
It also has the effect of making the setting pattern proportional to the current.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an example of a welding machine power supply device that performs constant voltage control, Figure 2 is a diagram showing the relationship between output voltage and output current using load power factor as a parameter, and Figure 3 is input voltage. Figure 4 is a block diagram of an embodiment of the present invention, Figure 5 is a diagram showing waveforms of each part of Figure 4, and Figure 6 is a diagram showing the relationship between output voltage and output current using parameters. FIG. 7 is a diagram showing the relationship between pattern correction coefficient and output voltage percentage using load power factor as a parameter, and FIG. 7 is a diagram showing the relationship between conduction angle θ and load power factor when α=120° firing. FIG. 8 is a diagram showing the relationship between the output voltage pattern correction coefficient 2 and the input voltage percentage. 1... Switch, 2, 3... Thyristor, 4, 5...
- Detection transformer, 6... Welding transformer, 7... Welding machine, 8... Microcomputer control circuit, 9. IO
...Waveform shaping circuit, 11...Pulse amplification circuit, 12
...Analog-digital converter, 13.21...
Three-state buffer, 14...Latch circuit, 15
. . . Counter, 16 . . . OR circuit, 17 . . . Microprocessor, 18 . S Riden IE/? -St. 〃Electron f-l West St. Wa 1 person〃Electron 6. ．． '-1: Sweat

Claims (1)

[Claims] 1. For a welding machine that performs constant voltage control and includes a control circuit that includes thyristors connected in antiparallel, a transformer for detecting the output voltage of the thyristors, a load power factor detector, and a microprocessor. A power supply device for a welding machine, wherein the output voltage setting pattern of the thyristor is corrected according to the detected value of the load power factor. 2. The power supply device for a welding machine according to claim 1, wherein the load power factor is determined from the conduction angle of the thyristor when the thyristor is fired at a predetermined firing angle in the first cycle of energization. A power supply device for welding machines. 3. In the power supply device for a welding machine according to claim 1, the voltage setting pattern after being corrected according to the load power factor is further corrected according to the input voltage detected for each welding point. A power supply device for a welding machine characterized by: