JPS6332544B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a constant voltage power supply device used in an arc welding machine.

In a constant voltage power supply for an arc welding machine, for example, in a DC constant voltage power supply in which the output voltage rectifier circuit is a double star rectifier circuit using a phase-controlled thyristor,
If the firing angle of the thyristor is the same, the no-load voltage will be about 1.2 to 3 times the load voltage. Therefore, when performing constant voltage control by feedbacking the welding voltage, a method is used to detect no-load and reduce the amount of feedback compared to when under load, so that the no-load voltage is not directly fed back. was. However, since the ratio of no-load voltage to load voltage is extremely wide, 1.2 to 3 times, reducing the amount of feedback at a fixed ratio makes it possible to control a specific welding voltage range, but it is possible to control a specific welding voltage range; I couldn't control it. Therefore, for arc welders that use consumable electrodes, where arc interruptions occur periodically or irregularly during welding and which tend to generate no-load voltage, it is difficult to maintain stability even when no-load voltage occurs. It was difficult to control the output so as to obtain a desired output. This will be explained in detail below.
FIG. 1 is a schematic diagram of the main circuitry of an arc welder using consumable electrodes. 1 is star-connected 2
The main transformer consists of two welding transformers, and 2 is an interphase reactor connected between the neutral points of the two welding transformers.

Each of the six windings of the main transformer 1 has a main thyristor 3
are connected to each other, and their cathodes are connected to a common welding wire 7. In the figure, only one thyristor circuit is shown, and the other five thyristor circuits are shown.
The thyristor circuits are not shown. 4 is a gate signal control circuit for the main thyristor 3, and one input terminal 4
Reference numeral ₂ denotes an input terminal connected to the base material 8 via an output terminal 10' for feeding back the welding voltage. The output terminal ₄₃ is connected to the gate of the thyristor 3, and the feedback input of the welding voltage inputted from the input terminal ₄₂ is compared with a set voltage (not shown), and the ignition is controlled in phase according to the difference voltage. Output a signal. 7 is a welding wire, 8 is a base metal, and a welding load, that is, a welding arc 9 is generated between these welding wire 7 and the base metal 8. 5 is a DC reactor inserted between the intermediate tap of the interphase reactor 2 and the base material 8. Next, the operation is as shown in the waveform diagram shown in FIG. That is, a is the starting signal of the device, b is the firing bias of the main thyristor 3, c is the welding voltage, the broken line part (ⓓ) shows the no-load voltage, and the bar part (-) shows the load voltage. d is the output current and e is the welding wire feeding speed. Also,
The horizontal axis is the time axis, and time points A to H each indicate the break point of the welding operation. Start signal turns ON at time A
However, arc 9 is generated at B, the arc is interrupted at C, and the arc is re-ignited at D. Furthermore, time E
A welding stop signal is issued. At F, the arc breaks and welding stops, and at G, the welding voltage is turned off. After that, the start signal turns ON at time H, and the start signal turns ON at time A.
The welding operation will be repeated in the same condition as in . The no-load voltage is output during the welding procedure from when the start signal is turned ON at time A until time B when the welding wire 7 is fed and hits the workpiece 8. After the wire 7 is fed toward the base material by inertia between C-D and E, where arc breakage occurs, it burns out at time F.
This is until the welding voltage is turned off at time G.
Since this no-load voltage is about 1.2 to 3 times as large as the load voltage, the feedback circuit rapidly pushes down the firing bias b so as to delay the firing angle of the main thyristor. Therefore, at the time of arc start at time B or when re-ignition immediately after no-load voltage occurs as at time D, the ignition bias b is low, so the ignition phase of the thyristor is delayed and the welding voltage is low. It will be an arc start. Therefore, sufficient voltage for restriking the arc could not be obtained, making it difficult to start the arc and making the arc unstable.

The present invention eliminates the above-mentioned conventional drawbacks, feeds back the welding voltage controlled by the output control element connected to the main transformer, compares it with the set voltage, and controls the input of the output control element according to the deviation voltage. This is a welding power supply device that switches the deviation signal to zero voltage when the welding arc stops.

Now, in FIG. 2, the transistor 11 is removed, one terminal of the reference voltage setting variable resistor 13 is directly connected to the DC power supply +Vcc, the diode 25 is removed and the resistor 16 is directly connected to one input terminal of the amplifier 26, and the diode 24, consider the prior art equivalent of removing transistor 12. The voltage between the welding wire 7 and the base metal 8 (welding voltage) is applied to the input terminal 4 as a detection voltage (negative voltage).
₂ is input. This voltage is divided by resistors 20 and 22 and an adder circuit (resistors 14, 15, 16, 1
7 and amplifier 26),
When this is added to the voltage (target value) set by the variable resistor 13, the set voltage is positive and the voltage at input terminal ₄₂ is negative, so it is essentially subtracted, and as a result, the target value is The difference between the value and the welding voltage will be output to the output terminal of the amplifier 26.
That is, this output indicates the deviation between the actual value (feedback signal) and the target value (set value), and based on this deviation signal, a corrective operation is performed at a later stage to bring the actual value closer to the target value. Therefore,
When the target value and the actual value match, this deviation signal becomes zero and no corrective action is performed.

Generally, a feedback system includes a delay element (integrator circuit) for stabilization, and the deviation signal is input to this integrator circuit. Since the integrating circuit integrates the changing input voltage, if the input voltage becomes zero, the output value of the integrating circuit will continue to take the same value as the previous output voltage. (Actually, it changes very slowly toward the offset level of the integrating circuit due to other factors such as the resistor 21.) The present invention utilizes this principle when a no-load voltage appears in the welding load. Forcibly sets the deviation signal between the set voltage and the feedback signal to zero, and maintains the output of the thyristor gate signal control circuit 4 at the level before no-load when no-load voltage occurs due to short-term arc breakage. Or, I tried to make it move towards the offset level very gently. As a result, welding becomes stable by ensuring that the output of the feedback system hardly changes during short-time no-load voltages caused by arc breakage or the like.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 is a circuit diagram of the main part (ignition control circuit 4) of an embodiment of the welding power supply device according to the present invention. In this figure, the same reference numerals as in FIG. 1 indicate the same parts. +Vcc and -Vcc are each +15 (V) -15
(V) DC power supply line. 11 and 12 are transistor switches (first switch 11 and second switch 12) forming a switching circuit, respectively.
The base of each is the current detection circuit 3, which will be described later.
0 and 31.

Current detection circuits 30 and 31 detect current signals generated when welding current flows either when the torch switch is turned on at the start of welding or when there is a torch signal output from a holding circuit in a sequence circuit (not shown). Outputs transistor 1
Turn on 1 and 12. Although current detection circuits 30 and 31 detect the same welding current, their output signals have opposite characteristics. That is, since transistor 11 is a PNP type transistor and transistor 12 is an NPN type transistor,
Turn both transistors 11 and 12 on or off at the same time
In order to do this, the output from the current detection circuit 30 is
The output from the welding current detection circuit 31 is always set to a high level voltage and is set to a low level voltage when detecting a welding current, and the output from the welding current detection circuit 31 is set to a constantly low level voltage and set to a high level voltage when detecting a welding current.

13 is a variable resistor connected to the collector side of the transistor 11, and its movable terminal is connected via the resistor 14 to the side terminal of the amplifier 26, the anode of the diode 25, and one end of the resistor 17, and outputs a voltage. It is now possible to adjust the Amplifier 2
The side input of 6 is grounded via a resistor 15, and the output end is connected to the other end of a resistor 17 and one end of a resistor 18.

The cathode of the diode 25 is connected to the cathode of the diode 24, and the resistors 16 and 2
2 to terminal ₄₂ . 27 is an amplifier whose side input terminal is connected to the other end of the resistor 18, one end of the resistor 21, and one end of the capacitor 28, and since the resistor 21 and the capacitor 28 are connected in parallel, the other ends are connected in common. It is connected to the output end of the amplifier 27. Further, the side input terminal of the amplifier 27 is grounded via a resistor 19. 2
Reference numeral 9 denotes a phase control circuit for the thyristor gate signal, and its input terminal is connected to the output terminal of the amplifier 27 via a resistor 23, and its output is connected to the terminal ₄₃ , which is connected to the DC bias switch of the output of the integrating circuit in the previous stage. The phase of the pulse that fires the thyristor 3 is changed accordingly.

Next, the operation will be explained using FIG. 4. In this figure, as in FIG. 3, the horizontal axis indicates the time axis, and symbols A and 9 indicate the breakpoints of the welding operation. The vertical axis shows the signals of each part of the device, where a is the starting signal, and b is the firing bias of the main thyristor 3 and the phase control circuit 29.
c is the output voltage, d is the output current, and e is the welding wire feeding speed.

When the feedback control according to the present invention is performed,
The reference voltage signal is set by the volume controller 13, is input to the amplifier 26 through R14, and is outputted by the transistor 12 only when there is a load.
Also, the feedback signal is connected to the resistor 2 from the output terminal ₄₂ .
2. Feedback is carried out through 16 during load.
The transistor 12 is turned on and turned off when there is no load, so that feedback is provided only when there is a load. In this case, the delay of the system is determined by capacitor 28 and resistor 18. When the welding arc 9 is extinguished and a no-load voltage is output, the deviation signal between the set voltage and the feedback signal is forced to zero in the amplifier 26, so the output of the amplifier 26 becomes zero. Therefore, the output of the integrating circuit constituted by amplifier 27, resistor 18, and capacitor 28 substantially maintains its previous value. Therefore, the firing bias of the main thyristor 3 continues to maintain its initial level during the time period A-B as shown in b.

That is, when the operator operates the torch switch and the start signal a of the device is turned on, the welding wire 7 is fed and contacts the base material 8 at point B.

During A-B, the output voltage C is a high no-load voltage, and the firing bias b of the thyristor 3 is such that the transistors 11 and 12 are OFF because there is no output from the current detection circuits 30 and 31, and the amplifiers 26 and 27 are turned off. Since the output maintains the 0 state, it hardly changes.
Since the welding current flows at point B, the current detection circuit 3
Low level voltage and high level voltage are output from transistors 0 and 31, respectively, and transistors 11 and 12
It becomes ON state. The reference voltage set by the volume controller 13 and the feedback voltage input from the terminal ₄₂ are compared to perform normal feedback control. Bias b is offset level L
to the active state bias level. Furthermore, in the section between points C and D, the arc is interrupted and a high no-load voltage is fed back from the terminal ₄₂ , but at this point the arc bias is also maintained at its previous value, so the welding arc 9 is stabilized. It can be re-ignited. Furthermore, even when the arc is started again at time G after welding is once completed at time F, a stable arc start can be performed because a sufficient load voltage can be obtained in the same manner as described above.

As described above, the present invention provides feedback for controlling the welding voltage controlled by the output control element connected to the main transformer, comparing it with the set voltage, and controlling the input of the output control element according to the deviation voltage. Since this is a welding power supply device that switches the signal to zero when the welding arc stops, even if no-load voltage occurs due to arc breakage for a short time, the output at arc start will decrease due to the high no-load voltage. Since it does not change, arc starting can be performed stably.

[Brief explanation of the drawing]

FIG. 1 shows a circuit diagram of the main parts of a semi-automatic arc welding machine using consumable electrodes. FIG. 2 shows a specific embodiment of the present invention. FIG. 3 is an explanatory diagram of the operation when conventional feedback control is performed. FIG. 4 is an explanatory diagram of the operation when feedback control according to the present invention is performed. 1...Main transformer, 2...Interphase reactor, 3...
...Output control element (thyristor), 4...Thyristor gate signal control circuit, 7...Welding wire, 8...
... Base material, 30, 31 ... Current detection circuit, 11, 1
2...Transistor, 13 to 23...Resistor, 2
4, 25...Diode, 26, 27...Amplifier, 28...Diode, 29...Phase control circuit.

Claims (1)

[Claims] 1 A main transformer, an output control element and a welding load connected to the main transformer, a reference power source that generates a set voltage to be compared with the welding voltage applied to the welding load, and a reference power source that generates a set voltage to be compared with the welding voltage applied to the welding load, ) and the set voltage; a current detection circuit that detects the presence or absence of a welding current supplied to the welding load; 1. A welding power source apparatus comprising: a switch that zeros a signal input to the integrating circuit when the detection circuit detects that no welding current is flowing.