JPS6365434B2 - - Google Patents

Description

Detailed Description of the Invention The present invention detects the welding voltage in arc welding using a non-consumable electrode, drives the welding torch in a direction where the detected value matches a reference value, and maintains the welding voltage at a constant value by controlling the arc voltage. The present invention relates to a device that performs this.

Normally, in non-consumable electrode arc welding, a pulse voltage or high-frequency voltage is supplied between the electrode and the workpiece at the start of welding to induce a spark discharge and subsequently generate a welding arc. The distance from the surface of the workpiece to be welded is set to be as small as possible. Once a welding arc is generated and a period of instability has elapsed, the electrode is gradually pulled up to a desired position where the necessary arc voltage and arc spread are obtained. Until this time, the welding torch is subjected to follow-up control with respect to a separately determined position reference signal. (Hereinafter, this control will be simply referred to as torch position control.) After the welding torch is positioned at the required position, the distance between the tip of the electrode and the surface of the workpiece will be maintained even if the surface of the workpiece is uneven. Switching to so-called arc voltage control, which uses the fact that arc voltage is approximately proportional to arc length to detect arc voltage and moves the welding torch so that it always matches the reference value. It will be done.

FIG. 1 is a connection diagram showing an example of a conventional non-consumable electrode arc welding device that performs such control.

In the apparatus shown in FIG. 1, 1 is a welding power source, 2 is a welding torch, 3 is a workpiece, 4 is a welding arc, and 5 is a drive mechanism for moving the welding torch 2 forward and backward toward the surface of a workpiece 3. It consists of an electric motor 6, a feed screw rod 7, and a nut 8 that holds the welding torch 2. 9 is a welding voltage detector that detects the voltage between the welding torch 2 and the workpiece 3; 10 is a welding voltage setting device, and a variable resistor is used to adjust the output voltage of the DC power source E1.
Partial pressure is applied at VR1. 11 is a comparator for comparing the output voltage of the welding voltage setting device 10 and the output voltage of the welding voltage detector 9 to obtain a difference output, and the output is connected to a changeover switch 16 which is closed during arc voltage control.
(a) is supplied to the amplifier 17 through the contact point (a) to rotate the electric motor 6 of the welding torch drive mechanism 5. 12 and 13 are push button switches 1 during torch position control.
Welding torch 2 by pressing 4 or 15
These are voltage signal generators for advancing and retracting the
3 and variable resistors VR2 and VR3.

In the apparatus shown in FIG. 1, before welding starts, it is necessary to bring the welding torch 2 close to the workpiece 3 to facilitate arc generation as described above, so the changeover switch 16 is moved to the (b) contact side. and press pushbutton switch 14 or 15 to turn on welding torch 2.
are set at predetermined close positions. In this state, a welding starting device (not shown) generates a welding arc 4, and after this becomes stable, the push button switch 15 is activated.
Press to raise the welding torch to the desired height required for welding. Then, turn the selector switch 16
(a) If you switch to the contact side, welding voltage setting device 1
Automatic arc voltage control is performed to keep the distance of the welding torch from the object to be welded constant so that the welding voltage becomes the welding voltage determined by 0.

In such a conventional device, the changeover switch 1
At the moment when 6 is switched from the (b) contact side to the (a) contact side, that is, from the torch position control to the arc voltage control side,
It is extremely difficult to adjust the position of the welding torch 2 or the output of the welding voltage setting device 10 so that the output of the welding voltage detector 9 and the output of the welding voltage setting device 10 match. If there is a difference between the two, the output from the comparator 11 is supplied to the amplifier 17 in steps at the moment the selector switch 16 is switched. At this time, the comparator 11 and the amplifier 17
If the welding torch 2 is highly sensitive, the welding torch 2 may vibrate. In arc welding using non-consumable electrodes, the distance between the electrode at the tip of the torch and the surface of the workpiece is usually very short, on the order of several mm, so we switched from torch position control to arc voltage control as described above. Occasionally, even the slightest vibration can cause the welding arc to flare up or cause a short circuit with the workpiece. In order to prevent such accidents, it may be possible to solve the problem by slowing down the response speed of the control system, but if the response speed is slowed down, it will not be possible to control at a sufficient speed when necessary, which makes the control system highly sensitive. It disappears. Another method is to install a display that displays the output voltage of the comparator, and then adjust the welding torch position or welding voltage setting device to confirm that the comparator output has become zero before switching the switch. However, this method is not only inefficient as it takes time and effort to switch, but also there is a risk that welding defects may occur at the switching part because the switching between the two controls is not performed smoothly.

The present invention provides a device that can stably switch from torch position control to highly sensitive and fast responsive arc voltage control.

FIG. 2 is a connection diagram showing an embodiment of the present invention.
In the figure, parts having the same functions as those in FIG. 1 are given the same reference numerals. 18 is a welding voltage detector 9
It is a memory circuit that stores the output of the I terminal and takes in the input signal of the I terminal while the CC terminal is open.
When the CC terminal is short-circuited, the input signal immediately before the short-circuit is stored and output to the O terminal. Although a commercially available semiconductor integrated circuit can be used as this memory circuit, it is convenient to use a sample-and-hold circuit that captures and holds input signals in response to opening and closing of external contacts, for example. 19-1 and 19-2 are changeover switches for switching between torch position control and arc voltage control, and both are interlocked.

In the device shown in Fig. 2, before welding starts, selector switches 19-1 and 19-2 are set to the (b) contact side and the first
As in the conventional example shown in the figure, the pushbutton switch 15 is pressed to rotate the electric motor 6 and move the welding torch 2 to the object to be welded.
Adjust the welding arc to a position suitable for starting the welding arc. In this state, electric power is supplied from the welding power source 1, and a high frequency voltage for arc starting is supplied from a high frequency power source (not shown) to ignite the welding arc. Push button switch 1 again after starting the welding arc.
4 and pull up the welding torch 2 until the predetermined welding voltage is reached. At this time, selector switch 19-2
Since (b) is set on the contact side, the memory circuit 18 is in a state where it can take in the output of the welding voltage detector 9 supplied to the input terminal I and store each instantaneous value of the input signal. After raising the welding torch to a predetermined position, switch the changeover switches 19-1 and 19-2 to the (a) contact side, and the memory circuit 18 will short-circuit between the CC terminals, so the I terminal at this moment Store input signal. The welding torch drive mechanism 5 is driven by the output of a comparator 11 that obtains the difference output between the output of the welding voltage detector 9 and the content stored in the memory circuit 18, and arc voltage control is started. At this time, memory circuit 1
Since the stored content of 8 is the output of the welding voltage detector 9 at the time of switching, the output of the comparator 11 is zero before and after the switching. As a result, the changeover switch 19-
1 and 19-2, even when switching from torch position control to arc voltage control, the position of the welding torch does not change suddenly and the switching operation can be performed smoothly.
Thereafter, the welding torch drive mechanism 5 operates to match the welding voltage stored at the time of switching. In FIG. 2, a combination of a feed screw rod and a nut is used for the welding torch drive mechanism 5, but it may also be a combination of a rack and pinion gear with good responsiveness. In this case, in order to prevent natural fall due to gravity during position control, use a motor with a brake or use the voltage signal generator 1.
2, 13 and pushbutton switches 14, 15, a reference signal generator that generates a continuous voltage signal and a potentiometer that detects the position of the welding torch are provided, and position servo control is used to compare both signals. is necessary.

Further, after switching to arc voltage control, depending on the shape of the object to be welded, it may be necessary to change the welding voltage from the value at the time of switching. In the embodiment shown in FIG. 2, in such a case, it is necessary to return the changeover switches 19-1 and 19-2 to the (b) contact side again and press the push button switch 14 or 15 to correct it, which is somewhat inconvenient. .

FIG. 3 is a connection diagram showing another embodiment in which the welding voltage can be corrected without changing the changeover switch. In the same figure, 1 to 6, 9, 17, 18,
19-1 and 19-2 have the same functions as in FIG. 20 is a rack, and 21 is a pinion gear, which together with the electric motor 6 constitute a welding torch drive mechanism. 22 is a position reference voltage generator consisting of a power source E4 and a variable resistor VR4, 23 is a potentiometer connected to a power source E5, and its slider is mechanically connected to the welding torch 2 to correspond to its advance and retreat. It is a welding torch position detector that generates an output.
24 is a comparator, which compares the output of the position reference voltage generator 22 and the output of the potentiometer 23;
The differential voltage is supplied to the amplifier 17 via the (b) contact of the changeover switch 19-1. This reference voltage generator 22,
potentiometer 23, power supply E5, comparator 24,
The amplifier 17 and the welding torch drive mechanism 5 constitute a position servo mechanism for controlling the torch position. 25 is a welding voltage correction circuit, which includes power supplies E6, E7, pushbutton switches PB1, PB2, resistors R1, R2 forming an integrating circuit, a capacitor C1, and an operational amplifier OP1. Here, PB1-1a, PB
2-1a shows the normally open contacts of pushbutton switches PB1 and PB2, respectively, and PB1-1b, PB1
-2b, PB2-1b, and PB2-2b each indicate a normally closed contact. 26 is an adder that adds the output of the memory circuit 18 and the output of the welding voltage correction circuit 25 to obtain a composite output; 27 is a comparator that compares the output of the adder 26 and the output of the welding voltage detector 9; , and supplies the differential output to the amplifier 17 via the changeover switch 19-1.

First, the operation during position control when the changeover switches 19-1 and 19-2 are on the (b) contact side will be explained. At this time, the output of the position reference voltage generator 22 and the output of the potentiometer 23 are compared by the comparator 24, and the difference voltage is amplified by the amplifier 17 via the changeover switch 19. Rotate. At this time, the electric motor 6 is set to rotate in a direction in which the differential voltage decreases. Welding torch 2 stops at the position where the output of comparator 24 becomes zero. In this state, when the welding arc 4 is generated, the selector switch 19-
When controlling the arc voltage by switching 1 and 19-2 to the (a) contact side, the welding voltage at the time of switching is stored in the memory circuit 1 in the same way as explained in the embodiment shown in FIG.
8, and the pushbutton switch PB1,
PB2 is not pressed and therefore normally closed contact PB
Since 1-1b and PB2-1b are closed, the output of operational amplifier OP1 is zero, and adder 26 transmits the output of storage circuit 18 to comparator 27 as is. As a result, the arc voltage of the welding torch 2 is thereafter controlled so as to maintain the welding voltage immediately before being switched. During such arc voltage control, if it becomes necessary to change the welding voltage, press push button switch PB1 or PB2.
This can be easily implemented without switching the changeover switches 19-1 and 19-2. Now consider the case where the welding voltage is increased. Changeover switch 19-1, 19-
2 to the (a) contact side, press push button switch PB1 during welding. At this time, normally closed contact PB of PB1
Since 1-1b is open, the voltage of power supply E6 is the same as that of resistor R1, operational amplifier OP1, and capacitor C.
The output which is integrated by the integrating circuit consisting of 1 and gradually increases is outputted to the adder 26. The adder 26 outputs the combined output of the output of the integrating circuit and the output of the memory circuit 18 to the comparator 27 as a command signal, and the comparator 27 compares this command signal with the output signal of the welding voltage detector 9. and the difference signal is amplified by the amplifier 17.
and drives the electric motor 6. At this time, power supply E6
Since the polarity of the output voltage is as shown in the figure, the polarity of the output obtained by integrating this output voltage is reversed, and the polarity becomes the same as that of the output signal of the memory circuit 18, and the value of the composite signal increases. As a result, the comparator 27 outputs a polarity difference signal in which the detected welding voltage is insufficient with respect to the reference signal, and the welding torch 2 is driven in a direction away from the workpiece. When pushbutton switch PB1 is released after the welding voltage has been corrected to the predetermined value, the CC terminal of memory circuit 18 also retains the previous input signal since normally closed contacts PB1-2b of pushbutton switch PB1 close again. do. On the other hand, the push button switch
Since the normally closed contact PB1-1b of PB1 is also closed, the input and output terminals of the above-mentioned integrating circuit are short-circuited and the output becomes zero. As a result, the input of the adder 26 is only the corrected output of the memory circuit 18, and the welding torch 2 is held at the position where the corrected welding voltage is applied. When further increasing the welding voltage, further correction can be made by pressing push button switch PB1 again. Conversely, if it is desired to lower the welding voltage, it can be easily lowered by pressing the push button switch PB2 and supplying the voltage of the power source E7 with the opposite polarity to the previous one to the integrating circuit.

In the embodiment of FIG. 3, the contents of the memory circuit 18 are changed each time a correction operation is performed, but if it is convenient to leave the contents of the memory circuit 18 as they were without performing this, , push button switch
Normally closed contacts of PB1 and PB2 PB1-1b, PB2-1
Instead of b, connect a series circuit of a reset push button switch and a discharge resistor in parallel to capacitor C1, and remove normally closed contacts PB1-2b and PB2-2b. By doing this, even if the welding voltage is modified during arc voltage control, the initial welding voltage is memorized, so to return to the original voltage, press this reset push button switch. The return is completed when the output of the integrating circuit gradually decreases and reaches zero.

In Fig. 3 above, the welding voltage correction circuit is configured with an integral circuit, but since the correction operation can be performed smoothly if the output voltage is a circuit in which the output voltage increases or decreases continuously from zero, other circuits such as single-shot circuits can be used. It may also be an oscillator that generates a triangular wave.

In the embodiments shown in FIGS. 2 and 3, the welding power source 1 is a power source that outputs direct current or alternating current with substantially constant current characteristics. However, in non-consumable electrode arc welding, Depending on the welding process, welding may be performed by switching to a plurality of different current values, such as when pulsed high current is periodically superimposed on the DC current, or when the welding current is switched between large and small values. In such a case,
Since the voltage and current characteristics of the arc are positive, even if there is no change in the actual arc length at that time, when the welding current becomes small, the welding voltage also decreases, and conversely, when the welding current becomes large, the welding voltage decreases. will also rise. For this reason, in a device that stores a single welding voltage as in the examples shown in Figures 2 and 3, only the welding voltage at the moment of switching from torch position control to arc voltage control is stored. If the welding voltage changes to another value, the welding voltage will change even though there is no change in the actual arc length, and the drive device 5 will operate to return this to the previously stored value. The arc voltage control would induce completely unnecessary operations.

FIG. 4 is a connection diagram showing an embodiment in which measures are taken to prevent the above-mentioned problems from occurring even when using a welding power source that outputs a welding current by switching it between two values, high and low. In the figure, reference numeral 1 designates a welding power source capable of switching output current, which outputs a high current when a contact 30-1a of an output relay of a welding current switching command circuit (not shown) is closed, and outputs a low current when it is opened. 19-1, 19-2, and 19-3 are changeover switches that operate in conjunction with each other.
As in the figure, torch position control is performed on the (b) contact side, and arc voltage control is performed on the contact side (a). 28 and 29 are memory circuits, which, like the embodiments shown in FIGS. 2 and 3, take in the input from the I terminal while the CC terminal is open, and when the CC terminal is closed, they receive the input from the I terminal. It holds and stores the instantaneous I terminal input signal. The changeover switch 19-2 and the normally closed contact 30-1b of the output relay for the welding current switching command are connected in parallel to the CC terminal of the memory circuit 28, and the CC terminal of the memory circuit 29 is connected in parallel. The changeover switch 19-3 and the normally open contact 30-2a of the output relay for the welding current switching command are connected in parallel.

In the device shown in FIG. 4, after starting welding in the same way as the device shown in FIG. The welding arc 4 is moved back and forth to a position where the welding arc 4 has a predetermined length. During this time, the welding current is switched between high and low levels according to the opening and closing of the contact 30-1a. In addition, the CC terminals of the memory circuits 28 and 29 are connected to the switches 19-2 and 1.
Since 9-3 is on the (b) contact side, the contacts 30-1b and 30 interlock with the welding current switching command contact 30-1a.
-2a opens and closes, the input signal of the I terminal is taken in, or the value of this input signal at the moment when the CC terminal closes is held and stored. That is, the memory circuit 28 stores the welding voltage value at high current when the contact 30-1b is open, and the memory circuit 29 stores the welding voltage value when the contact 30-1b is open.
Store the welding voltage at low current when a is open.
In this way, switch 19-1, 19-2, 19-
While 3 is on the (b) contact side, the above operation is repeated every time the welding current is switched, and the memory circuit 2
8 and 29 always store the latest welding voltage for each current. When the changeover switches 19-1, 19-2, and 19-3 are switched to the (a) contact side in this state, the welding current changes in height according to the opening and closing of the output contact 30-1a of the current switching command circuit. At the same time, the contact 30-3a or 30-2b closes, and in synchronization with this, the memory contents of the memory circuit 28 or 29 are read out and output to the comparator 11, and compared with the output of the welding voltage detector 9, respectively. Ru. As a result, the distance between the welding torch and the workpiece is always kept constant even when the welding current changes, so the arc length does not change and unnecessary operations are not induced.

In the embodiment shown in FIG. 4, the welding current is switched using the relay contact 30-1a, but it may also be switched using a voltage signal, or it may be switched using a sequence built into the welding power source 1. It may be something that occurs. Also, the memory circuits 28 and 2
The write command signal to terminal C-C terminal 9 does not need to be a relay contact, and may be a logic signal synchronized with the output current switching of the welding power source.Also, an output current detector is provided separately, and the output signal of this detector is may be converted into a logic signal indicating high current and low current, and this may be used as a write command signal for memory circuits 28 and 29. Furthermore, even if the welding power source 1 outputs two or more different currents, the present invention can be implemented by providing a memory circuit corresponding to the number of changes in the output current. Moreover, one memory circuit can be used as long as the memory circuit can store a plurality of contents. in this case,
The present invention can also be applied to arbitrary waveform welding currents by using a device with a relatively large storage capacity.

FIG. 5 is a connection diagram showing an example of application to an arbitrary waveform welding current in this manner.
This figure shows an example in which a rack pinion is used for the torch drive mechanism, similar to the embodiment shown in FIG.
In the figure, 1 is a welding power source as in the previous example, but it is a power source that outputs a welding current with a waveform determined at a constant cycle, and a synchronous pulse signal is sent to the S terminal in synchronization with the cycle of the current change. Output. 31
is a storage circuit that stores a plurality of contents, and stores input signals over one cycle over time by a synchronization pulse signal to the S terminal. Memory circuit 31
The C-C terminal is the read command terminal, and this C-C terminal is the read command terminal.
- While the C terminal is open, the input signal of the I terminal is stored over one cycle over time in synchronization with the cycle of the S terminal input. Conversely, when the CC terminal is closed, the memory circuit 31 repeats and outputs the stored contents every cycle in synchronization with the S terminal input. 32 to 34 are analog switches that transmit the input signal to the next stage while the external command signal is arriving, and 35 is a command circuit for opening and closing these analog switches 32 to 34. For example, the welding power source 1 The input is the synchronous pulse signal from the S terminal of the switch 19, and the contact input (a) of the switch 19 that switches between position control and arc voltage control.
AND gate 351 and this AND gate 351
The flip-flop circuit 352 is set by the output of the flip-flop circuit 352 and reset by the changeover switch becoming the contact point (b). The Q output of this flip-flop circuit is the analog switch 3.
3 and 34 to close them, and the output is supplied to analog switch 32 to close them.

In the apparatus shown in FIG. 5, when controlling the torch position, the changeover switch 19 is set to the (b) contact side. At this time, the analog switch 32 is closed upon receiving the output signal from the flip-flop Q, and the welding torch 2 is moved in response to the setting value of the variable resistor VR4, which is the torch position setting device, in the same way as explained in FIG. The position is determined. In this state, adjust the variable resistor VR4 to obtain the desired arc length. During this time, the analog switch 34 is open because no output appears at the Q terminal of the flip-flop circuit 352.
Therefore, the CC terminal of the memory circuit 31 remains open, and the input signal of the I terminal is synchronized with the synchronization pulse to the S terminal, and changes in the arc voltage are stored over time every cycle. When the changeover switch 19 is switched to the (a) contact side from this state, the flip-flop circuit 352
is set, the output at the terminal disappears, and an output appears at the Q terminal. Therefore, the analog switch 32
is open and analog switches 33 and 34 are closed. As a result, the storage circuit 31 sequentially reads out the previously stored arc voltage signals, and the read arc voltage signal is compared with the output voltage of the arc voltage detector 9 in the comparator 11, and the difference voltage is output to the analog switch. 33 to the amplifier 17, and arc voltage control is started. At this time, the welding current changes periodically according to the output characteristics of the welding power source 1,
The arc voltage also fluctuates in accordance with this, but since this fluctuation corresponds to the change in the arc voltage previously stored in the memory circuit 31, the welding torch 2 changes the welding current as long as there is no fluctuation in the true arc length. Always maintain a constant position and never make unnecessary movements. Furthermore, when switching from torch position control to arc voltage control, the state of torch position control is maintained until the first synchronous pulse is generated, so changes in arc voltage during the last cycle of current change are reliably memorized. This allows for extremely stable operation.

By the way, when the welding current changes periodically, for example when the welding current makes a steep change such as when a rectangular waveform changes into a sawtooth shape, the power output and arc voltage change before and after this steep change. may become unstable. Therefore, it is advantageous in terms of stability to suspend arc voltage control for a certain period before and after the sudden change in the unstable current, and to fix the position of the welding torch during that period. FIG. 6 is a connection diagram showing an embodiment that is effective in the case where such an unstable period occurs in the arc voltage. In this figure, parts having the same functions as those in FIGS. 1 to 5 are given the same reference numerals. 36 is a synchronizing signal generating circuit for temporarily interrupting arc voltage control and obtaining timing for fixing the welding torch during that time, and is composed of two mono-multivibrators 361 and 362. Further, 37 is an analog switch similar to 32 to 34, and is closed by the output of the synchronizing signal generating circuit 36. Regarding the operation of the device shown in the same figure, other parts can be easily understood from the above-mentioned FIGS. 4 and 5.
The function for interrupting the arc voltage control realized by the analog switch 37 will be mainly explained with reference to the waveform diagram in FIG. Assume now that the output current Ia of the welding power source 1 changes in a sawtooth pattern at a constant period t ₀ as shown in FIG. 7a. At this time, if the arc length is kept constant, the arc voltage Va will also change in the same way as the welding current a. A synchronizing pulse S is output from the S terminal of the welding power source 1 at the starting point of each cycle of the output current a as shown in FIG. If the multivibrators 361 and 362 of the synchronization signal generation circuit 36 are configured to output a pulse with a fixed time width to the Q terminal at the rising edge of the input signal, the output of the Q terminal of the multivibrator 361 receiving the synchronization pulse S is as shown in the figure c. like width t ₁
Therefore, the output from this terminal becomes as shown in the figure d. The Q terminal output of the multivibrator 362 which receives this as an input, that is, the output of the synchronizing signal generating circuit 36, becomes a pulse with a width t ₂ as shown in FIG. 7e. As shown in the figure, the output pulse width _{t 1 of} the multivibrator 361 and the output pulse width t ₂ of the multivibrator 362 are set so that t ₀ > t ₁ + t ₂ with respect to the period t 0 in which the welding current changes. Pulse width t ₁
and t ₂ are selected, the analog switch 37 closes t ₁ hour after the current abruptly changes, and {t ₀ − (t ₁ + t ₂ )} will open earlier. Therefore, arc voltage control is executed only during the period _t2 when the analog switch 37 is closed, and during the period indicated by diagonal lines as partially shown in FIG. 2 is mechanically held in position by a feed screw rod 7 and a nut 8. Therefore, by appropriately selecting the values of these pulse widths _t1 and _t2 , it is possible to efficiently eliminate the period in which the current suddenly changes and the arc voltage itself becomes unstable, resulting in more stable control. It becomes possible. Note that the synchronizing signal generating circuit 36 is not limited to the structure shown in FIG. 6, and may be provided with a similar function by combining other known circuits such as a timer and a differential circuit. In addition, if there are multiple parts where the welding current changes rapidly in one cycle, obtain the corresponding input signal and use the same configuration to temporarily interrupt arc voltage control before and after each point where the current changes suddenly. be able to.

In FIGS. 5 and 6, the storage circuit 31 stores input signals over time from when an external synchronization signal is input until when the next synchronization signal is input, and in response to a read command, Any system may be used as long as the stored content is read out repeatedly in response to the same external synchronization signal as when it was stored. A specific example of this memory circuit is shown in FIG. 8 and FIG. 9. In Figures 8 and 9, terminals I, S, O, and CC are connected to Figures 5 and 6, respectively.
These terminals correspond to terminals I, S, O, and CC of the storage circuit 31 in the figure, respectively.

In FIG. 8, 38 is a clock pulse oscillator which determines the sampling period for storing the input signal to the input terminal I. 39 is a counter, which is reset by a synchronization signal sent to the S terminal. 40 is a random access memory whose address is determined by the count output of the counter 39, which stores the input signal to the input terminal I at the address specified by the count position of the counter 39 for each pulse of the clock pulse oscillator 38; When terminals CC are short-circuited, the contents stored at each address designated by the counter 39 are sequentially output to the O terminal. In the memory circuit shown in FIG. 8, the sampling period of the input signal is determined by the oscillation period of the clock pulse oscillator 38. Therefore, the number of samples in one cycle of the input signal changes with the length of the cycle of the input signal. Therefore, the reproduction accuracy when reading changes depending on the period of the input signal. FIG. 9 shows an example in which the number of samplings is always kept constant to make the reproduction precision approximately equal. In the same figure, 40 is the 8th
Like the example in the figure, it is a random access memory. 41 is a phase comparator, and the input signal f of the S terminal is
and the feedback signal f', and if there is a phase difference, a DC voltage proportional to this is generated.
42 is a voltage controlled oscillator that oscillates a signal f ₁ with a frequency proportional to the output voltage of the phase comparator 41;
3 is a programmable counter, and the number of stages N thereof is assumed to be N≈f ₁ /f. This programmable counter 4
Since the count-up output f' of 3 is ₁ /N of the input f1, it is approximately equal to the input f of the S terminal, and is fed back to the phase comparator 41. These phase comparator 41, voltage controlled oscillator 42, and programmable counter 43 constitute a so-called phase locked loop, and its operation is well known. It is controlled so that the frequencies are fixed where they match. Phases like this
A locked loop is a commercially available semiconductor integrated circuit, such as the phase comparator MC4044, MC4344, and voltage controlled oscillator manufactured by Motorola in the United States.
This can be achieved by combining the MC4024, MC4324 and programmable counters MC4016, MC4018, etc. Normally, the phase locked loop uses the output of the voltage controlled oscillator 42 as its output, but in FIG. The configuration is such that sampling is performed by dividing one period of 2 into N equal parts. As a result, the input signal of the I terminal is sampled at a period that accurately divides one period of the synchronization pulse into N equal parts, and the number of samplings is always the same even if the period of the input synchronization pulse changes. The signal reproduction accuracy is always approximately constant. Further, since this sampling number can be easily changed by setting the programmable counter 43, it can be appropriately selected depending on the shape in which the welding current changes.

As described above, in the device of the present invention, the welding voltage when controlling the position of the welding torch is memorized,
Since arc voltage control is performed based on this memorized voltage, the welding torch position command does not change even when switching from torch position control to arc voltage control, and the switching is performed smoothly, resulting in extremely stable operation. It will be done.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an example of a conventional device that switches between torch position control and arc voltage control;
2 to 6 are connection diagrams showing embodiments of the device of the present invention, FIG. 7 is a waveform diagram for explaining the operation of the device in FIG. 6, and FIGS. Memory circuit 3 that can be used in the device shown in Figures and Figure 6
1 is a specific configuration diagram of FIG. DESCRIPTION OF SYMBOLS 1... Welding power source, 2... Welding torch, 3... Work to be welded, 5... Welding torch drive device, 9... Welding voltage detector, 11, 27... Comparator, 18, 28, 29, 3
1...Memory circuit, 19, 19-1, 19-2, 19
-3...Selector switch, 32, 33, 34, 37...
Analog switch, 35...analog switch opening/closing command circuit, 36...synchronous signal generation circuit.

Claims (1)

[Claims] 1. Arc voltage control to maintain the welding voltage at the reference value by detecting the welding voltage and driving the welding torch forward and backward toward the workpiece in a direction in which the detected value matches the reference value; A non-consumable electrode arc welding device that selectively performs torch position control to maintain the torch position at a predetermined position by driving the torch forward and backward toward the workpiece, the welding voltage detector; and a storage circuit that stores the output of the welding voltage detector during the torch position control according to a command from the switching means, and outputs the stored content as a reference value during the arc voltage control during the arc voltage control. Equipped with non-consumable electrode arc welding equipment. 2. As a welding power source that supplies power to the welding torch and the workpiece, a welding power source that switches and outputs a plurality of welding currents having relatively different current values is used, and the memory circuit is configured to control the welding power when controlling the torch position. A patent claim that is a circuit having a plurality of memory functions that separately stores welding voltages for each output current of a power source, and selects and reads out stored contents in synchronization with switching of the output current of the welding power source during arc voltage control. The non-consumable electrode arc welding device according to item 1. 3. As a welding power source that supplies power to the welding torch and the workpiece, a power source that outputs a current with a waveform that changes over time at a predetermined period is used, and the memory circuit is configured to control the welding power when controlling the torch position. Changes in the welding voltage due to changes in the output current of the power source are stored for one period in response to the passage of time, and during arc voltage control, the stored contents are sequentially stored in synchronization with the period in which the output current waveform of the welding power source changes. The non-consumable electrode arc welding device according to claim 1, which is a repetitive readout circuit.