Note: Descriptions are shown in the official language in which they were submitted.
12S3~22(~
Background of the Invention
The present invention relates to a method and an
apparatus for sensing the presence of arc discharge in arc
discharging.
In order to determine the welding quality in arc
welding, there is a known method for sensing its welding current.
The method is convenient as the welding current is sensed easi1y
by providing a transformer (curr0nt transformer) in an electric
current feeding line. However, it is sometimes put in motion
erroneously by inductive noise from the outside and there also is
a case that a large electric current flows without arc discharge
because of a base material coming in contact with a work-piece
and it is erroneously sensed as arc discharge.
For the purpose of dealing with such errors, there is a
known method for sensing arc light to determine the quality of
arc discharge. It can be said that as a method for sensing the
presence of arc discharge, this method is better than the method
in which an electric current is sensed.
However, even in the method for sensing arc light, the
apparatus may be put in motion mistakingly by light in a
surrounding area or arc light of another welding operation which
goes on at close quarters. This problem can be solved by shading
light in the surrounding area, however, to structure such shading
is difficult since it affects arc discharge and is expensive.
Accordingly, the present invention aims to provide a
method and an apparatus that can sense the presence of arc
discharge easily and reliably.
Summary of the Invention
In order to achieve the object described above,
according to the present invention, there is provided a method
comprising sensing a change in electric current at the time of
discharge, and sensing light to be emmitted from a welding
positin only when the sensed electric current surpasses a
predetermined level, whereby the presence of arc discharge is
sensed. According to this method, since arc discharge is sensed
1~53'~2~3
, .
simultaneously with a change in electric current at the time
of arc discharge, the problems caused by sensing solely an
electric current is solved, and influence of light from other
sources can be eliminated as arc light is sensed in synchro-
nism with the welding current, resulting in accurate sensing
of good arc discharge.
According to a further broad aspect of the present
invention there is provided a method for sensing the presence
of arc discharge in an arc welding device wherein an arc
discharge device is connected by current feeding lines to a
workpiece and to an article to be welded thereto at a weld-
ing position. The method comprises the steps of sensing the
magnitude of electric current passing through the current
feeding lines and sensing the presence of light emitted at
the welding position only when the sensed electric current
surpasses a predetermined level, whereby the presence of a
valid arc discharge is confirmed.
For carrying out the method of the present inven-
tion as described above, the present invention provides anapparatus for sensing arc welding operation comprising means
for sensing a welding current from a welding current feeding
line of a welder to produce a predetermined voltage, photo-
receptor means disposed adjacent the welding position to be
activated by the voltage producing means, and means for
receiving a signal from said photoreceptor means to output a
good arc discharge signal. Thus, the above method is
effectively carried out with an extremely simple construction.
According to a still further broad aspect of the
invention, there is provided an apparatus for sensing arc
discharge in a welding operation wherein an arc discharge
device is connected by current feeding lines -to a workpiece
and to an article to be welded thereto at a work area. The
apparatus comprises voltage producing means for sensing elec-
tric current passing through one of the current feeding lines
to produce a predetermined voltage. The voltage producing
means is connected to a photoreceptor means disposed adjacent
the welding position for applying a voltage thereto. Signal-
ling means is provided for receiving an output from the
photoreceptor to indicate a valid arc discharge signal.
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Brief Description of the Drawing
Fig. 1 is a circuit diagram of an embodiment
apparatus for sensing arc discharge welding operation accord-
ing to the present invention; and
Fig. 2 is a circuit diagram of another embodimen-t.
Description of the Preferred Embodiments
. . . _ . . _
The present invention is described further by way
of embodiments, referring to accompanying drawings~
In Fig. 1, two welding current feeding lines 2, 2
extend from an arc discharge device 1, one of which is
connected to a base material 3 while the other is connected
to, for example, a stud 4. In one of the lines 2, 2, a
current transformer (CT: transformer~ 5 for sensing a weld-
ing current is located to take out an electric current which
flows in the line 2.
~ n apparatus for sensing welding operation accord-
ing to the present invention comprises the aforementioned
current transformer 5, a regulator 6 lor rectifying the
electric current received from the current transformer 5 to
produce a predetermined voltage, a photoreceptor (photo-
transistor 7 in the
l;~S322C~
-
embodiment shown in the drawing) for sensing arc light at the
time fo arc discharge, and an output portion 8 which outputs a
good arc discharge signal in response to a signal received from
the photoreceptor, or the phototransistor 7. In the above-
described construction, the current transformer 5 and the
regulator 6 compose means for sensing a welding current and
producing a voltage while the output portion 8 functions to
electrically treat and snape the signal from the phototransistor
7. Basically, the phototransistor 7 alone can serve as signal
output means.
The regulator 6 receives an electric current output from
the current transformer 5 to rectify it with a rectifier 12
through a resistor 11, and smoothes it with a diode (Zener diode)
13 and a capacitor 14 to produce a predetermined voltage.
The phototransistor 7 as the photoreceptor is attach to
the tip of a welding gun (not shown in the drawing) at such a
position that receives arc light at the time of welding. The
phototransistor 7 is supplied with the voltage from the regulator
6 to very an amount of output electric current in response to the
impedance which changes in accordance with the intensity of light
received. As long as the phototransistor 7 is not fed with the
predetermined voltage from the regulator 6, the phototransistor 7
is in an inoperative condition (i.e., not activated).
As mentioned above, the output portion 8 is basically a
supplement, however, it is preferred because a signal from the
phototransistor 7 includes noise and is dim. In the output
portion 8, a resistor 16 is provided in an input portion to
preferably suppress excessive signal current, and then a diode 17
and a capacitor 18 delete harmful noise. The signal from which
noise has been removed is supplied to a light emitting element 20
of a photocoupler 19, and its light output is received by a light
receiving element 21. An output from the light receiving element
21 toutput form a collector and an emitter) is forwarded to
terminals 22, 23. Thus, the output has been electrically
isolated by the photocoupler 19, and problems such as interaction
are not caused even if another electric circuit is connected to
the output.
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i~S~ZO
In operation, when a large electric current at a
predetermined level passes through the welding current feeding
lines, a predetermined voltage is produced by the current
transformer 5 and the regulator 6 to activate the phototransistor
7 as the photoreceptor. When arc light is produced between the
stud 4 and the base material 3 at that time, the phototransistor
7 senses the light to activate the light emitting element 20 of
the photocoupler 19 of the output portion 8 to output a short
circuit signal (ON) to the terminals 22, 23. Unless a large
electric current corresponding to the welding current passes
through the lines 2, the regulator 6 does not produce the
predetermined voltage, nor does the phototransistor 7 change the
impedance even if it receives light from the outside. The
phototransistor 7 is activated by inductive noise or a large
electric current which is supplied to the line by contact between
the stud 4 and the base material 3. However, the impedance of
the phototransistor 7 does not undergo any change because no arc
light is emitted and hence, no output. That is to say, a signal
is outputted only ~hen an actual welding current flows and arc
light is emitted. Thus, good arc discharge can be confirmed very
accurately.
Fig. 2 shows another embodiment according to the present
invention.
In this embodiment, significant difference from the
embodiment of Fig. 1 is found in an output portion 8~. The rest
remains unchanged except a regulator 6- which is slightly
changed. In the regulator 6 , a resistor 11 is connected
parallel to the current transformer 5. The rectifier 12
rectifies the electric current and the capacitor 14 smoothes it.
The phototransistor 7 is activated by a voltage from the
regulator 6 and changes its output electric current upon receipt
of arc light. The output unit 8 converts an electric current
output from the phototransistor 7 into a voltage by a resistor,
and outputs voltage amplified by an operational amplifier 26 to
the terminals 22, 23. It is advantageous that in the embodiment
of Fig. 7, an amount of the output signal is proportional to the
intensity of light received by the phototransistor 7 (i.e., the
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intensity of light emit-ted at the time of welding). Since this
embodiment operates in the same way as the embodiment of Fig. 1,
the explanation is omitted.
According to the present invention, since a good arc
discharge is sensed by double sensing of the presence of a
welding current and of arc light in the presence of the welding
current, the confirmation is extremely accurate. Because of the
sensing of an electric current synchronized with emission of arc
light, false acknowledgement due to erroneous actin can be
avoided. Furthermore, -the apparatus is of very simple
construction and its manufactwring cost can be held at a
remarkably low level.
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