JPS59220285A - Control device for welding current of arc welding machine - Google Patents

Abstract

PURPOSE:To reduce the weight of the transformer of a titled device which controls welding current by feeding the same back to a set value by supplying the pulse voltage obtd. by rectifying a three-phase line input and convertng the same to DC then converting the DC to a high frequency with an inverter for the input to said transformer. CONSTITUTION:A three-phase line input 1 is rectified with the 1st rectifier circuit 2 and is converted to a high frequency AC voltage by an inverter 13. The voltage is converted to a prescribed low voltage by a high frequency transformer 14 and is rectified by the 2nd rectifier cirucuit 15 to a welding voltage v0 to supply a pulse voltage. This device has a feedback control circuit 19. A pulse width modifying circuit 22 sets the pulse width with the output signal v1 from a basic pulse determining circuit 21 and outputs a signal v2. The comparator 10 of a detected signal deciding circuit 20 outputs a signal v5. An inverter control circuit 23 adjusts the starting time Tx (when the pulse train of the voltage v0 is generated) and the stopping time Ty in accordance with the signals v2, v5 and controls the same so as to repeat alternately said time and at the same time said circuit controls the ration between the time Tx and Ty. The welding current is thus maintained at the set value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding current control device for an arc welding machine, and particularly to one that maintains a constant welding current by feedback control.

In general, DC arc welding machines are widely used because they have better arc stability than AC arc welding machines. Conventionally, a rectifier type device shown in FIG. 1 is known as a current control device for this DC arc welding machine.

In the same figure, <la), (lb), (Ic>
is the input terminal of the 3-phase line input (1) of 50 or 6011z, (2) is the Y-Δ type 3-phase transformer, (3) is the first rectifier circuit formed by bridge-connecting diodes, for example,
(4) is a switching power transistor (hereinafter S, P
, TR), (5) is a filter reactor, (6)
is the electrode, (7) is the base material, and (8) is the above S, P, TR (4
) is a flywheel diode that continuously passes current to the filter reactor (5) when it is off, (9) is a current detector such as a shunt that detects a signal Va corresponding to the welding current,
(10) is a comparator that controls on/off the above s, p, and TR (4), and (12) is a smoothing capacitor.

The output of the comparator (10) becomes 1 when the detection signal va is higher than the set value ρf and when O1 is lower.

The operation of the current control device for the arc welding machine having such a configuration will be explained below. The three-phase line input (1) is converted to a low voltage by the three-phase transformer (2), and then converted to direct current by the first rectifier circuit (3) and the smoothing capacitor (12).The converted direct current is , above S, P, TR (4)
The filter reactor (5) supplies a DC output to a load consisting of an electrode (6) and a base material (7). The output of the comparator (10) that determines whether the S, P, and TR (4) are on or off is determined by the detection signal va from the current detector (9) set to 14. If it is higher than Z, it becomes 0, turns off S, P, and TR, and the detection signal Va becomes the set value V.
pr (if it is lower than 1, it becomes 1 and turns on S, P, and TR. Therefore, by providing 1U with hysteresis in the comparator (10), the cold welding consisting of the electrode (6) and the base material (7) A DC welding current with a certain ripple can be supplied to the load, and this welding current can be maintained at the set value.

However, as mentioned above, the conventional device has the disadvantage that the input frequency of the three-phase transformer (2) is low at 50 or 6011z, and the weight of the three-phase transformer (2) is considerably large. Ta.

The present invention was made in order to eliminate such conventional drawbacks.The present invention was made to rectify the three-phase line input as the input of the transformer, convert it to direct current, and then supply pulse voltage converted to high frequency by an inverter. This is intended to reduce the weight of the transformer. Moreover, by matching the number of positive and negative pulses of the pulse voltage input to the transformer, biased magnetization can be prevented, and by changing the pulse width of the output voltage depending on the load, it is possible to generate a low-ripple welding current. The present invention provides a current control device for an arc welding machine, and the present invention will be described in detail below using examples.

FIG. 2 is a circuit diagram showing an embodiment of the welding current control device for an arc welding machine according to the present invention, and in the same figure (13a
), (13b), (13c).

(13d) is a bridge-connected S, P, TR1 which constitutes a full bridge inverter (14) is a high frequency transformer that converts the output pulse voltage of the inverter (13) into a low voltage, (15) is a diode ( 15a), (1
5b), a second rectifier circuit that rectifies the output of the high frequency transformer (]4), (16a), (16b),
(16c), (16d) are the above S, P, TR (
13a), (13b).

A feedback diode (18) returns the electromagnetic energy of the leakage inductance (17) of the high frequency transformer (14) to the smoothing content (12) when all of (13c) and (13d) are off.

P, TR (13a), (13b), (13c)
.

(13d) is a base circuit that drives the circuit, and (19) is a feedback control circuit. The feedback control circuit (19) includes a comparator (10
) and a basic pulse width determining circuit (21), a pulse width modulating circuit (22) that sets the pulse width based on the output signal V1 from the basic pulse width determining circuit (21). , the time T x of the welding pulse voltage Vo, which will be described later, based on the output signal V5 from the comparator (10).

'Fy and the input voltage v9 of the transformer (14)
an inverter control circuit (23) that controls the inverter (13) to match the number of positive pulses and negative pulses;
It consists of

First, the basic operation of the welding current control device for an arc welder according to the present invention will be explained using the time chart shown in FIG.

In the present invention, the welding voltage V. Then, a pulse voltage as shown in Fig. 3 time) Ty are provided alternately. According to such a pulse voltage Vo, the welding current i. As shown in FIG. 3 (bl), the pulse voltage V rises at the pulse train generation time Tx and falls at the pulse train removal time ry. By changing the ratio between time Tx and time Ty in By controlling the inverter (13) based on the output signal V5 of the comparator (10), the control circuit (23) generates a pulse voltage V9 consisting of a positive pole and a negative pole as shown in FIG. is supplied to the negative side of the high-frequency transformer (14).Specifically, the pulse of the voltage v9 is controlled to control the pulse of the voltage v9 for the above-mentioned time Tx.

The average current 1o is adjusted by controlling 1゛y. Furthermore, in the present invention, a high frequency transformer (
14) In order to prevent biased magnetization, the inverter control circuit (
23) operates to match the positive and negative voltage time dimensions of the voltage v9 applied to the negative side of the high frequency transformer (15). That is, as shown in FIG. 3 tc+, the numbers of positive and negative pulses of the pulse voltage v9 are made equal.

The inverter control circuit (23) includes, for example, as shown in FIG. 25) and the pulses of signals v6 and v7 are output alternately, and the base circuit (18) not shown in FIG.
and an output circuit (26) that drives the.

The driving time control circuit (24) is a flip-flop (2
7) an AND circuit in which the gate is opened when the output signal Vf5 of the output terminal Q is 1, and outputs the pulse signal V2 from the pulse width modulation circuit (22), and the gate is closed when the signal output terminal Q is 0; (28), an AND circuit (31) that ANDs the output signal v5 from the comparator (10), and a trigger pulse signal obtained by differentiating the pulse signal V2 with a differentiating circuit (30); The flip-flop circuit (2) is set by the output signal s of the circuit (31) and reset by the output signal ≠ from the AND circuit (32).
7) and is reset by the inverted output signal V4I of this flip-flop (27), and the signal v5 is sent to the inverting circuit (33).
) and then differentiated by a differentiating circuit (34) to set the trigger pulse signal V to A and supply the output signal VD to the AND circuit V & (32), and the output set by signal v6,
The output signal V7 is inverted by the inverting circuit (36), and the differentiating circuit (
The above-mentioned pulse number control circuit (25) is composed of a flip-flop (38) which is reset by a trigger pulse signal 1ht obtained by differentiating with 37).
The flip-flop ( 41). Note that the signal 'lhI of the output element 1 Q of this flip-flop (41) is supplied to one input side of the AND circuit (42) of the output circuit (26), and the signal 'lhI of the output terminal 6 is supplied to the AND circuit ( (Jj) is supplied to one input side of the AND circuit (43). The output signal Vchit of the AND circuit (28) is supplied to the other input side of the AND circuit (42) and (43).

Note that the output signal 76 from the output circuit (26) is supplied to the drive circuits (18a) and (18b) forming the base circuit (18) as shown in FIG. From (18b), the signal 'Ihb, 1
/lc- is output, S, P of impark (13)
, TR(13b), and (13c) are turned on, and the ii pulse of either the positive electrode or the negative electrode is obtained. In addition, the output signal V is the drive circuit (18c,), (18d
), at this time the drive circuit (18C), (1
8(1) J'ri signal %A-? 'y+1 is output and the inverter (13) S, P, TR (13a), (13
d) is turned on and a pulse opposite to the above pulse is obtained. In this way, positive and negative pulses are generated from the inverter (13) at each of the signals p, 116 and v7, as shown in FIG. 3 tc+.

Next, the operation of the inverter control circuit (23) shown in FIG. 4 will be explained below using FIG.

The A1' circuit (28) of the drive time control circuit (24) is
Since the gate is opened when the output signal l; 8vP of the flip-flop (27) is 1, the pulse signal v2 outputted from the pulse width modulation circuit (22) as shown in FIG. 28).

On the other hand, when the output signal 7flr of the flip-flop (27) is 00, case 1 is closed, so the AND circuit (28)
From then on, the pulse signal V2 is no longer output. Therefore, the output signal vyi of the un(- circuit (28) is
As shown in FIG. 2, the signal consists of a portion in which a pulse train is formed over time Tx when signal k is 1, and a portion where the pulse train is removed over time Ty when signal 1kr is 1.

Note that the output signal Ver of the flip-flop (27) becomes 1 when the rising edge of the signal v2 and the 1 of the signal V5 overlap. That is, the signal V2 rises from O to 1, and the signal V5 becomes 1, so that the output signal V0 of the AND circuit (31) becomes 1, the flip-flop (27) is set, and a signal output of 1 is output from its output terminal Q. 5 is output. Further, the signal 1kr becomes 0 at the first fall of the signal "V7 after the signal V5 becomes 0. In other words, the signal 1kr becomes 0 at the first fall of the signal "V7.
, becomes 0, the signal v4z becomes 1, the flip-flop (35) is set, and its output signal 1kj becomes 1. On the other hand, at the falling edge of the signal V7, an output signal of 1 is output from the differentiating circuit (37), which resets the flip-flop (38), and this flip-flop (3
A signal Vrr of 1 is output from the output terminal d of 8). Therefore, the output signal of the AND circuit (32)? 7n becomes 1, the flip-flop (27) is reset, and the output signal Vg of its output 11Q becomes 0. In addition, Frisozov 1! Since the knob (38) is turned on at the rising edge of the signal V6, its output terminal Q becomes 0. The even number IAI of the signal 11y6 at the time Tx when the above signal 7kr becomes 1
The pulse is generated as a signal V6 by the operation of the output circuit (26), which will be described later.
and V7 are alternately output, so that the inverter (13) outputs the pulse voltage V9 shown in FIG. 3 by the operation of the base circuit (18) described above. That is, at time 7 x, the inverter (13) is driven and outputs positive and negative pulse voltages, and at time 'ry when the signal becomes O of 5, it stops and does not generate a pulse voltage (fss
(see C1), the welding voltage V of the waveform shown in FIG. The time when
Since 7'x is set, the ratio between time Tx and Ty is adjusted based on the output signal v5.

Regarding the pulse number control circuit (25), if the output signal 1kt of the flip-flop (41) is 1 and the output signal strength δ is O in the initial settings, then the AND circuit (43)
The gate of is opened and the signal ? from the AND circuit (43). 7+
One pulse of 6 is output, resulting in an output signal v6. Note that the gate of the AND circuit (42) is closed. At this time, - at the falling edge of the above one pulse, the differentiating circuit (
Pulse signal from 40)? h is output, the flip-flop (41) is inverted, and the output signal h7 becomes the O1 output signal 1/
``42 is inverted to 1, the gate of the AND circuit (43) is closed, and the gate of the AND circuit (42) is opened, so
The next pulse of signal V46 is output from the AND circuit (42) and becomes output signal r7.

In this way, the pulse number control circuit (25) operates in the AND circuit 17&
It operates to alternately distribute the pulses of the output signal V4& of (2B) to the AND circuits (43) and (42). Therefore, the output signal V6. v7 is shown in Figure 6 (h).

(As shown in 11, it starts with the pulse of the signal "rJ"6 and ends with the pulse of the signal 'V7, resulting in equal number of pulses that are output alternately. In the above embodiment, the signal V=
The number of pulses of the signal v6 and the signal V7 that are output when ts is 1 is controlled to match, but in order to match the overall number of positive and negative pulses with arbitrary synchronization, the signal V
6 and signal r7 may be output alternately in any case.

Next, the operations of the basic pulse width determining circuit (21) and the pulse width modulating circuit (22) will be described. - As described above, if the number of pulses of the signal V6 and the signal v7 are made equal, biased magnetization will not occur. However, as shown in FIG. 7 (al), even if the detection signal νa (proportional to the welding current io) exceeds the set voltage .l, the detection signal νa increases by the time sum, resulting in time wastage. In FIG. 7 1bl, when the pulse 'l1gh is generated, even if the detection signal Fa exceeds the set voltage f/pel at time 1o, the comparator (
Suppose that the output '7/''5 of the pulse number control circuit (25) becomes 0 as shown in Fig. 3 fcl.
), the pulse 97 opposite to the pulse 1/''4a is always output, so the detection signal Va, that is, the welding current i.

continues to rise, and finally begins to fall after 7M has elapsed. Here, this amount of overshoot, that is ('fSV diagram (
To reduce the rise ■ shown in al, the basic pulse v2
Either increase the frequency of the welding current, or decrease the slope of the welding current rise characteristic curve A as shown in FIG. It is effective to reduce the slope of the characteristic curve A.In order to reduce the slope of this characteristic curve A, the second
The inductance of the filter reactor (5) shown in the figure may be increased, or the average value of the voltage "V"0 at the pulse train generation time Tx shown in FIG. 3(a) may be reduced. The former has the disadvantage that the weight of the fill acrylic 1-1 (5) increases. FIG. 3 (voltage F during a period of time Tx in al).

In order to lower the average value of , the ratio of the pulse generation period T and the pulse width T.N shown in FIG. 3 (al) may be changed.

This is realized by the basic pulse width determining circuit (21) specifically shown in FIG. In FIG. 8, the set value V/le (is amplified by an amplifier (21a), and a predetermined value v5
An adder (2lb) adds the output voltage 171 to generate the output voltage 171. The pulse width modulation circuit (22) uses this output voltage V1
Since a pulse with a pulse width corresponding to the magnitude number is output as the signal V2, the voltage V shown in FIG. Time T6. can be adjusted. Note that the magnitude of the welding arc voltage can be predicted if the welding arc current io is known.
The voltage V falling during the Tx period shown in FIG. 3 fa). If the amplifier (218) and the predetermined value Vset are set in advance so that the difference between the average value of The ripple of the welding arc current io can be reduced as follows.The effect of the basic pulse width determining circuit (21) is specifically shown in FIG. 9(a).

(b) and Fig. 10 (al, (bl). Fig. 9 shows Fig. 3 (Fig.
Figure 10 shows the operating characteristics when the time T6N shown in 1) is always constant. This is the operating characteristic when the length is shortened. By reducing the area of the welding current rise characteristic curve in this way, the welding voltage V can be increased. Since the pulse widths T and N of the pulse widths T and N become smaller and their average value becomes smaller, the above-mentioned wasteful increase VL can be reduced.

In the above embodiment, a full bridge type inverter is used, but a half bridge type, center tap type, or other type inverter may be used. Further, although transistors are used as switching elements constituting the inverter in the first embodiment, GTOs, FETs, SITs, etc. may also be used.

Further, the pulse number control circuit is not limited to the circuit shown in FIG. 4, but any circuit may be used as long as it is a circuit that matches the positive and negative numbers of voltage pulses of voltage v9 shown in FIG. 3(e). . In addition, instead of making the positive and negative numbers of voltage pulses of the voltage v9 match during the time Tx shown in FIG. 3 (81), as a whole as shown in FIG. Even if the circuit matches the positive and negative numbers of the voltage pulses of the voltage V9, as shown in FIG.
As shown in 1, the detection signal Va, that is, the welding current i (1) can be maintained at the set value, and biased magnetization can be prevented.

As described above, according to the welding current control device for an arc welder according to the present invention, the primary frequency of the insulation transformer is increased by an inverter, so the size and weight of the insulation transformer can be significantly reduced. By setting the positive and negative numbers of the pulse voltage input to the transformer to be the same, it is possible to prevent biased magnetization of the transformer, and by controlling the pulse width of the welding voltage, it is possible to minimize welding current ripple. effective.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a conventional welding current control device for an arc welding machine, Fig. 2 is a circuit diagram showing an embodiment of a welding current control device for an arc welding machine according to the present invention, and Fig. 3 +
a) to (C1 is a time chart for explaining the operating principle of current control of the present invention, FIG. 4 is a circuit diagram showing in detail an example of the pulse control circuit shown in FIG. 2, and FIG. 5 is a circuit diagram shown in FIG. 2. 6 is a time chart for explaining the operation of the pulse control circuit shown in FIG. 4, and FIG. 7 is a circuit diagram showing the details of the base circuit shown in FIG. Figure 8 is a diagram showing a specific example of the basic pulse width determining circuit shown in Figure 2. Figures 9 and 10 are diagrams showing the basic pulse width determination circuit shown in Figure 2. Figure 11 (a) is a voltage waveform diagram showing the difference between the case without and the case with the pulse width determining circuit, (bl is the voltage at each part when the pulse control circuit shown in Figure 2 is implemented using another method) It is a diagram for showing the state. (1)...3-phase line input, (3)...first rectifier circuit, (5)...filter reactor, (6)...
Electrode, (7)...Base material, (8)...Flywheel diode, (9)...Current detector, (10)...
Comparator, VPef... Voltage setting value, (12)...
Smoothing capacitor, (13)...Inverter, (14)
... High frequency transformer, (15) ... Second rectifier circuit, (18) ... Base circuit, (19) ... Inverter control circuit, (2o) ... Detection signal judgment circuit, (
21) Basic pulse width determination circuit, (22) Pulse width variation circuit, (23) Pulse control circuit, (2
4)... Pulse train control circuit, (25)... Pulse switching circuit, (26)... Output circuit. The same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa (2 others) Commissioner of the Japan Patent Office 1. Indication of the case: Japanese Patent Application No. 58-962492, title of invention: Welding current control device for arc welding machine; 3. Relationship with the case of the person making the amendment To the representative of the patent applicant, Kata Yuhito, Part 4, Agent (ren::'+5'+:・su(,゛犀1・','11++
:i'' 1 copy) 5, Column 6 for detailed description of the invention subject to amendment, Contents of amendment + 11 In the specification, page 4, line 15, the phrase "at high times" is amended to read "at high times."that's all

Claims (3)

[Claims] (1) In a welding current control device for an arc welding plate that compares the welding current with a set value and performs feedback control so that the welding current is maintained at the set value, the first controller rectifies the AC input.
a rectifier circuit, an inverter that converts the rectified DC voltage into a high-frequency AC voltage, a high-frequency transformer that converts the high-frequency AC voltage output from the inverter into a predetermined low voltage, and a high-frequency transformer that converts the voltage output from the high-frequency transformer into a predetermined low voltage. It consists of a second rectifier circuit that performs rectification, and a feedback control circuit that controls the inverter. The inverter is driven for a period of time Ty to generate a high-frequency AC voltage from the inverter, the inverter is stopped for a time Ty, and the inverter is controlled to alternately repeat such driving and stopping, and A welding current control device for arc welding plates, comprising: a drive time control circuit that controls the ratio of the dependent time Tx and the fUto time Ty of the inverter based on an output signal from the inverter. . (2) In a welding current control device for an arc welding plate that compares the welding current with a set value and controls the welding current so that the welding current is maintained at the set value, the first rectifier that rectifies the AC input a circuit, an inverter that converts the rectified DC voltage into a high-frequency AC voltage, and a high-frequency transformer that converts the high-frequency AC voltage output from the inverter into a predetermined low voltage, and the high-frequency voltage output from the lance. The feedback control circuit includes a second rectifier circuit that rectifies the voltage, and a feedback control circuit that controls the inverter. The inverter is driven to generate positive and negative pulse voltages from the inverter, the inverter is stopped for a time Ty, and the inverter is controlled so as to alternately repeat such driving and stopping, and based on the output signal from the determination circuit. A drive time control circuit that controls the ratio between the drive time 1x and the stop time Ty of the inverter, and a drive time control circuit that controls the generation timing of the positive and negative pulse voltages output from the inverter to control the positive pulse voltage and negative pulse voltage. A welding current control device for an arc welding machine, comprising a pulse number control circuit that matches the number of pulse voltages. (3) The feedback control circuit controls the inverter so that the high-frequency AC voltage output from the inverter becomes a positive and negative pulse voltage, and also controls the pulse width of the pulse voltage to adjust the rise characteristics of the welding current. A welding current control device for an arc welding machine according to claim 2, which includes a width determining circuit.