Note: Descriptions are shown in the official language in which they were submitted.
~ 53~C~
The presen-t invention relates to a new and improved
method of controlling the welding capacity during electrical resis-
tance welding by means of alternating-current at an electrode roll-
resistance seam welding machine having a we:ldlng trans-former, and
further rela-tes to a new and improved construction oE apparatus for
the performance oE the aEoresaid method.
~ hen forming a welding seam between two welding rolls
the welding energy delivered to each location of the welding seam
is proportional to the square of the effective (roo-t-mean-square )
value of the current intensity of the current which flows between
the welding rolls through the workpiece parts which are to be weld-
ing to one another and proportional to the length of time during
which a given location of the welding seam is disposed between the
welding rolls and exposed to the current flow. In order to produce
a qualitatively high-grade welding seam the welding energy supplied
to each location of the welding seam must be maintained within
relatively narrow limits as closely as possible to a predetermined
reference or set value. If the supplied welding energy is too small,
then there is produced an inadequate welding of the workpiece parts.
Conversely, if the supplied welding energy is too great, then there
occurs an impermissibly great heating of the material or, in fact,
a partial scorching thereof, resulting in damage to the workpiece
material.
With the aid of electronic control devices it is pos-
sible to maintain -the effective value of the welding current inten-
sity, during the welding operation, sufficiently constant, so that
the welding energy also remains practically constant. If also
the weldi~g speed, i.e., the feed of the workpiece parts between
the electrodes and which are to be welded to one another, re-
mains constant, then each point along the formed welding seam hasdelivered thereto a uniform welding energy.
~t has been proposed, during resistance welding by means of
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alternating-current,to influence the operating or welding capacity
by phase control of the half-waves of the alternating-current vol-
tage in that the ignition or firing point is shifted within the
voltage wave, resulting in a change in the effective value of the
welding current intensity. For this purpose there are available
both ignitron as well as also thyristor circuit arrangement which
can be connected at the primary current circuit of the welding trans-
former.
The inductance of the welding transformer and the
welding current circuit, as is known, brings about a phase differ-
ence a between the voltage and the current, with the current trail-
ing the voltage. ~he magnitude of the phase difference is different
for different welding machines. DuPing the phase control the cur-
rent flow always begins at the firing or ignition point i.e. with
the surge-like appearance of the voltage, whereafter the current
flows until the following null throughpass of the.current half-
wave. Due to the inductance of the current circuit there.occurs
an overshoot of the voltage.past the null point at the end of the .
cut voltage half-wave, resulting in a corresponding prolongation
of the current flow. Hence, the currentless intervals between the
successive current half-waves are shorter than would be expected :~
from the displacement angle of the firing or ignition point. Con-
sequentl~,. there is limited the output control range in contrast .
to the case of an ohmic load. The greater the phase difference ~
that much smaller becomes the control range, i.e., that much greater
must be the displacement angle of the ignition point in order to
be able to even bring about a reduction of the welding energy.
On the other hand, it has been found that independent
of the phase difference ~ the welding capacity can be reduced to
null already with an ignition point-~isplacement angle of 155.and
with an ignition point~displacement angle of 120 only amount to
about 10%. Hence, the control range wikh phase control is limited
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both towards the bottom as well as also towards the top, so that
for we]~.in~ energy control between 100~ and 10~ there
is only available a range of about 30 to 120 and 70 to 120 of
the ignitlon point-displacement angle respectively, depending upon
whether the phase dlfEerence ~ between the vol-tage and current
amounts to 30 or 70.
The described phenomena during the welding energy
o~ a welding machine by phase control is disadvanta~eous for the
following reasons:
Due to the relatively narrow adjustment range of the
ignition point~displacement angle the adjustment becomes critical
since even slight changes of the ignition or firing point cause
relatively large changes of the welding capacity. In the case of
electrode roll-resistance seam welding larger ignition point-dis- .-
placement angles result in correspondingly greater spacing between
the individual weld spots or points o the seam, which can lead to
leakiness and mechanical weakness of the welding seam. It is for
this reason that in practice there is not exceeded an ignition point-
displacement angle of about 90, which, however, stiIl further
narrows the adjustment range. In order to nontheless be able to
cover a sufficiently large welding capacity range, there is required
the use of a welding transformer with tapping at the primary side. .
Therefore, with the foregoing inmind it is a primary
object of the present invention to provide a new and improved method
- of, and apparatus for, controlling the wel.ding capacity during
electrical resistance welding by means of alternating-current, where-
in the previously discussed drawbacks do not occur and there lS
avoided the need for a phase control of the welding alternating-
current voltage.
Another and more specific object of .the present inven-
tion aims at the provision of a new and improved construction of
apparatus for controlling the welding capacity during resistance
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welding in an extremely efficient and reliable manner, which appara-
tus is relatively simple in construction and design, economical to
manufacture, extremely reliable in performance, not readily subject
to breakdown or malfunction, and requires a minimum of servicing
and maintenance.
Now in order to implement these and still further
objects of the invention which will become more readily apparent as
the description proceeds, the method aspects of the present develop-
ment contemplate controlling the effective value or root-mean-square
value of the current intensity of the welding alternating-current
by changing the amplitude of the at least approximately sinusoidal
alternating-current voltage applied to,the primary winding of the
welding transformer during each complete half-wave.
According to an advantageous constructional manifesta-
tion of the method it is possible to rectify the current supplied by
an alternating-current power distribution network and to control
its voltage, for instance by a phase controlled rectifier, and then
to transform the rectified current into an alternating-current by
means of a preferably static inverter. The alternating-current is
then used to supply the primary winding of the welding transformer.
According to a still further advantageous variant of
the method the primary winding of the weldlng transformer can be
supplied with an alternating-current produced by a separately excit-
ed generator and the amplitude of the voltage of the alternating-
current produced by the generator is controlled by altering the
excitation o~ the generator. In this regard it is advantageous to
supply the excitation winding of the generator by means of a con-
trollable rectifier from an alt~rnating-current distribution net-
work and to drive the generator by means of an electric motor which
is powered from the alternating-current distribution network.
In both instances it is possible and, if necessary,
advantageous, to impart to the welding alternating-current produced
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by means of the sta-tic inverter and the generator, respectively, a
greater frequency than that of the alternatin~-current distribution
network.
Not only is the invention concerned with the afore-
mentioned method aspects, but also deals with apparatus for the
performance thereof, which apparatus comprises means for controll-
ing the effective value (root-mean-square value) of the current
intensity of the welding alternating-current, such control means
being arranged at the primary current ci.rcuit of the welding trans-
former. Further, such control means render possible changing the
amplitude of the at least approximately sinusoidal voltage of the -
alternating-current delivered to the primary winding of the welding
transformer during each complete half-wave.
By virtue of the teachings of the present invention
it is possible to change throughout a relatively large range the
operating or welding capacity of an elec-trical resistance welding
machine by a continuous voltage change of the welding alternating-
cu~rent, so that there can be avoided the drawbacks of the previous-
ly employed phase control. Moreover, there is also possible auto-
matically maintaining constant the effective value of the weldingcurrent intensity and thus the welding capacity, so that with con-
stant feed speed of the workpiece pa~ts between the welding rolls,
and which workpiece parts are to be welded together, there is :
delivered to all of the welding points or sports of the welding
seam produced by a respective alternating-current half-wave of the
welding current, the same thermal energy. However, there are situa-
tions where the welding speed unitentionally experiences termporary
changes. Also, it is known from Swiss patent 572,375 ~ranted on
February 13, 1976, to Runtel Holding Company S.A. Glarus, to control
during the welding operation the feed speed of the workpiece parts
to be welded to one another, such that the last weld spot of the
seam which is produced by an alternating-current half-wave of the
weldin~ current is dispositioned at a predetermined distance from
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the trailing end of the parts which are to be welded to one
another. This of course requires a control of the welding
speed and results in a speed-change in the operation of the
welding machine. ~lence, in this instance it is not sufficient
to maintain the welding capacity constant, as such practice
was heretofore conventional.
Thus, it is a further object of the present invention
to also then prevent the formation of poor welding seams due
to too low or excessively supplied welding energy, if during
the welding operation the feed speed of the workpiece parts to ~`
be welded to one another changes unintentionally or intentionally.
Now this objective is solved by a further ~anifestation
of the inventive method in that there is produced an electrical
welding current-correction signal which is analogous to the
welding speed and by means of this analogous electrical welding
current-correction signal there is controlled the welding
alternating~current in such a manner that each change in the
welding speed causes a corresponding change in the same sense of
the electrical output of the welding current, and thus~ the
welding energy delivered to the workpieces to be welded at
each section of the formed weldlng seam remains at least approxim-
ately constant. Advantageously, there can be superimposed upon
the welding current-correction signal which is analogous to
the welding speed a welding current-reference value signal which
is delivered by a reference value transmitter, and which auto- :`
matically controls the welding current intensity.
According to the present invention, a method of
controlling the welding energy during electrical resistance
welding o~ workpieces by means of an electrode roll-resistance
seam welding machine, in which the effective value of the welding
current is controlled in response to an electrical control
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signal, at least a component of which is a welding current-
correction signal substantially analogous to the welding
speed in order to provide a substantially constant welding
energy supplied to the workpieces at each section along the
formed welding seam at any welding speed, the said welding`
current-correction signal being produced by means of a program-
med control device which simultaneously delivers an electrical
rotational speed-reference value signal to a rotational speed
regulator for controlling and regulating the welding speed.
~ The invention will be better understood and objects
other than those set foxth above will become apparent when
consideration is given to the following detailed description
thereof. Such description makes reference to the annexed
drawings wherein:
Figure 1 is a diagram showing the previously proposed
phase control, illustrating the course as a function of time
of the voltage curve and current curve of the welding alternating-
current appearing at the primary side of the welding transformeri :
Figure 2 is a diagram on an enlarged scale of an analo-
20 ~ gous illustration of the voltage curve and current curve with
greater phase difference ~ between the voltage and current,
Figure 3 is a diagram showing the functional correlation
between the ignition point-displacement angle a and the resultant
welding capacity for different phase differences ~ between the ::
voltage and current;
Figure 4 is`a block circuit diagram of a first circuit
arrangement for use in the preferred embodiment of the invention
as illustrated in Figure 7;
Figure 5 illustrates graphs portraying the course as a
function of time oE the voltage curves and current curves of the
welding alternating-current at the primary side of the welding
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transformer for different welding energies controlled by means
of the apparatus shown in Figure 4;
Figure 6 is a block circuit diagram of a second
circuit arrangement for use in the preferred embodiment as
illustrated in Figure 7; and
Figure 7 is a block circuit diagram of the preferred
embodiment of the invention, wherein the welding speed is
controlled as a func~ion of a program control device or a
computer and the welding energy is thereby maintained constant.
Turning now to the drawings, based upon the showing
of Figures 1 to 3 there initially will again be considered the
reasons why the previously conventional phase control was , '
relatively unsuitable for controlling the welding energy. At
the upper portion of the diagram of Figure 1 there is shown a
curve portraying the course as a function of time of the
alternating-current voltage U which prevails across the primary ' '
winding of a welding transformer at an ignition point-displacement -
angle ~ of about 70. There will be recognized that always
at the ignition or firing point there increases in a surge-
like or sudden manner the instantaneous voltage and that during
the next null throughpass of the voltage curve the voltage over-
shoots to the opposite polarity. This is a consequence of the
inductance of the primary winding of the transformer., In the
lower part of the diagram of Figure~l there is shown a curve of
the correspondlng course as a function of`time of the current I -'
flowing in the primary winding of the transformer. It wlll be
seen that the current gradually appears (due to the inductance) '
always at the firing or ignition point and lasts through the null
throughpass of the voltage curve until the null throughpass of
the current curve. The current intervals between the successive
currenthalf-waves of opposite polarity are thus smaller than
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the ignition point displacement.
The operations have been shown even more clearly
in Figure 2 relating to a transformer winding with large
inductance, wherein, however, the ignition point-delay angle
~, like in Figure l, amounts to about 70~. At the time al there
suddenly appears the instantaneous voltage U. It overshoots
the ne~t null throughpass of the voltage curve until reaching-
the point bl, and then rapidly breaks to null. The corresponding
half-wave of the current I begins at the firing or ingition
point al and first ends at the point bl relatively shortly
prior to ignition of the next voltage half-wave at the ignition
point a2. At the firing or ignition point a2 there however
already begins the next current half-wave of the opposite polarity,
so that only relatively short current pauses or intervals are
present between the successive half~waves. Thus, the resultant
effective or root-mean-square value of the welding current Is
is only relatively slightly less than that which would be
present without phase control. Consequently, also the resultant
welding energy PWs = Is R, wherein R designates the resistance
2G of the current circuit, is not located below, to the desired
degree, the complete welding energy without phase control.
The actual correlation between the attainable welding
energy PWs and the ignition point-dispalcement angle ~ has been ~ -
graphically illustrated in Figure 3 for different phase angles
between the vGltage and current in the primary current circuit
of the welding transformer. From the graphs of Figure 3 there
will be apparent, for instance, that with a phase angle q~ of
60 and an ignition point-displacement angle ~ of 70 there only
results a reduction in the welding energy PWs to 82%. Since in
consideration of the quality of the welding seam which is to be
formed it is not practically possible to exceed an ignition
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point-displacement angle of 90, there is available for the
control of the welding energy PWs only a relatively small
region within which there can be adjusted the ignition point-
displacement angel ~, and the welding energy only can be altered
within a range of 100~ down to about 40~ (atC~=~0~) and 55~
(at~ =70 ) respectively. This narrow control range for the
welding energy is oftentimes inadequate in practice. What is
also disadvantageous is that the adjustment of the ignition
point-displacement angel ~ is relatively critical, because a
relatively small change in the ignition point setting or ad-
justment has an appreciable effect upon the resultant welding
energy.
In order to overcome the discussed drawbacks it is
proposed to change the effective or root-mean-square value of
the welding current by amplitude change at the complete voltage
half-waves, instead of by phase control. This can be accomplish-
ed, for instance, by means of the control circuits shown by way
- of example in Figures 4 and 6. These control circuits are
intended for use with the preferred embodiment of the invention ~ -
which will be more fully described in connection with Figure 7. -
In Figure 4 reference numeral 20 designates a welding
transformer having a primary winding 21 carrying, for instance,
a voltage of 380 vol~s and a secondary winding 22 for a low
voltage of a few ~olts, but a high current intensity of several
lO00 amperes. The low voltage-secondary wlnding 22 of the
welding transformer 20 is electrically connected in conventional
manner with a lower roller electrode 23 and an upper roller
electrode 24. Passing between there electrodes 23 and 24 are
the workpiece parts 26 and 27 which are to be welded to one
another. In order to accomplish the feed of the workpiece parts
26 and 27 between the electrodes 23 and 24 during the welding
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operation, the electrodes are driven in a manner which will be
described in greater details with reference to the preferred
embodiment of Fig. 7. There is conventionally arranged in the
primary current circuit of the transformer 20 an electronic
switch 25, Eor instance a thyristor or ignitron switch or
circuit arrangement, which merely serves the purpose of closing
the current circuit when a welding operation i5 to be started
and to interrupt such current circuit when the welding operation
is terminated.. The switching-in and switching-off to the
current circuit is advantageously synchronized in e~ch instance
with a null throughpass of the supply alternating-current
voltage.
The control circuit 30 provided for controlling the
welding enerqy of the welder possesses a controllable rectifier `~
or rectifier arrangement 32, powered by means of the connection
terminals 31 from an alternating-current distribution network,
generally indicated by reference character 31aO The rectifier
32 may be, Eor instance, a three-phase-semi-controlled bridge
circuit arrangement of conventional construction employing
thyristors an,d diodes. The rectifier 32 delivers a direct-
current voltag:e to two conductors or lines 33 and 34, this~
direct-current voltage being smoothed by a choke or reactance
coil 35. The amplitude of the produced direct-current voltage
between the conductors or lines 33 and 34 can be controlled
with the aid of a circuit arrangement 36 functioning as a voltage
regulator, which delivers to the rectifier 32 ignition or firing
pulses synchronized with the power supply network and rendering
it possible to change the firing or ignition point of the
thyristors within each power network alternating-current voltage
hal~~wave as a function of a controlling direct-current. The
aforementioned controlling direct-current is composed of two
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control components. The one control current component serves
as a reference or set value signal and is supplied by an
adjustable reference value transmitter 37, which, for instance,
comprises a potentiometer connected with a constant direct-
current vol.tage source. The other component of the control
current serves as an actual value signal and is produced with
the aid of a voltage div.ider formed by two resistors 38 and 39
connected across the conductors or lines 33 and 34. The
reference value signal is delivered by means of a line or
conductor 41 and the actual value signal by means of a return
or feedback line 42 to inputs 43a and 43b respectively of a
summation amplifier 43, where both of the control current
components are algebraically added and then conjointly
delivered by means of an output or connection 44 to the voltage .
regulator 36. The one input 43a of the summation amplifier
43 additionally is connected by a conductor or. line 100 with a :
connection terminal 101, the significance oE which will be .
described more fully hereinafter in conjunction with Figure 7. `
The two lines or conductors 33 and 34 are connected
with the inputs 45a of a.static direct-current/alternating-
current.inverter 45 of known construction, the~outputs 45b of
: which supply by means of the lines 46 and 47 and the switch 25
the primary winding 21 of the welding transformer 20 with an -
at least:approximately sinusoidal alternating-current voltage
and deliver the necessary welding a1ternatlng-current. The
amplitude of the alternating-current voltage produced by the
inverter 45 is proportional to the amplitude of the direct-
current voltage between the lines 33 and 34. The frequency
of the welding alternating-current produced by means of the
inverter 45 can advantageously be higher than the frequency of
the alternating-current distribution network 31a at which there
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- are connected the connection terminals 31.
~ he ~se and mode oE operation of the described circuit
arrangement and the method for controlling the welding energy
which can be caLried out thereby are as follows:
With the aid of the reference or set value transmitter -
37 there is produced a reference or set value signal which, in
: the form of a first control current component, is delivered
via the summation amplifier 43 to the voltage regulator 36.
In accordance with this reference value signal there is set
the ignition or firing point of the thyristors in the rectifier -
or rectifier arrangement 32 within each voltage half-wave
of the network alternating-current delivered to such rectifier
32, so that the rectified voltage appeàring at the lines 33 and
34 assumes a value which is analogous to the reference value
signal. The inverter 45 delivers to the lines or conductors
46 and 47 and thus to the primary winding 21 of the welding
transformer 20 an at least approximately sinusoidal alternating-
current vol~age, the amplitude of which is proportional to the
amplitude of the rectified voltage at the llnes 33 and 34O
Hence, the amplitude of the alternating-current voltage at the -~
primary winding 21 of the welding transformer 20 corresponds :
to the reference value signal which has been set by means of
the reference transmitter 37. By changing this reference value
signal it is possible to continuously alter the amplitude of
the aforementioned alternating-current voltage, also resulting
in a corresponding change in the effective value of the practical~
ly sinusoidal welding alternating-current and thus also in a
continuous change of the welding energy~ -
With the aid of the voltage divider 33, 39 there is
also produced an actual value signal which is proportionaJl to
the amplitude of the rectified voltage, this actual value signal
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being supplied by means o~ the return or feedback line 42 to
the sl~mmation amplifier 43. In the summation amplifier 43 there
are combined the reEerence value signal delivered by the
reference value transmitter 3~ and the actual value signal in
a manner such that each deviation of the actual value of the
rectified voltage from the reference value results in such
a change in ~he control direct-current appearing at the line
or conductor 44 that by means oE the voltage regulator 36 there
occurs a corresponding change in the ignition point of the .
thyristors in the rectifier circuit or arrangement 32, with the
result that the occurring deviation of the rectified voltage
from the desired reference value can be at least approximately
compensated. In this way there is automatically maintained
constant the rectified voltage at the set reference value. This
has the result that also the amplitude of the.:alternating-
current voltage which is produced by the inverter 45 and theeffective value of the welding alternating-current as well as
also the resultant welding energy remain practically constant.
The reference value set at the reference value transmitter 37
is thus.automatically maintained if, for instance, the voltage
.of the alternating-current network or the load at the output
; side of the inverter 45 fluctuates.
. Now in Figure 5 there is illustrated ~he course as a -~ ~.
: function of time of the voltage at the primary winding 21 of
the welding.transformer 20 as well as the current flowing through
the primary winding for dif~erent weldin~ capacities or outputs.
It will be apparent from this graphic illustration that the
alternating-current voltag.e for fu.ll slnusoidal half-waves is
variable in amplitude so that for instance there are formed the
voltage curves ul, u2, U3, which, in turn, result in the cor-
responding current curves il, i2, i3, with full half-waves at
a phase angle ~
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In the arrangement shown in Figure 6 the primary
winding 21 of the welding transformer 20 is supplied by a
synchronous generator 5U by means of the lines or conductors
46 and 47, at one of which lines there is connected the elec-
tronic switch 25. The rotor of the synchronous generator 50 is
connected by means of a shaft Sl with the rotor of an electric
motor 42, which, by means of the connection terminals 53, is
powered from an alternating-current distribution network,
generally indicated by reference character 53a. Generator 50
comprises an excitation winding 55 which is supplied by a control
circuit 60 which will be described more fully hereinafter.
The control circuit 60 contains a controllable rectifier
62, the input side or inputs 62a of which are connected via the
lines 61 with the alternating-current distribution network 53a
and the output side or output 62b of which are connected via ;
- the lines 63 and 64 directly with the excitation winding 55 of the
generator 50. The rectifier 62 preferably contains thyristors,
the firing of which can be controlled within each half-wave of
~ the alternating-current voltage. In order to control the firing
or ignition point there are provided two integration ci~rcuit
arrangements 65-and 66 which are connected in series. The
input or input means 65a of the first integration circuit
arrangement 65 lS connected ùy a line or conductor 68 with a
reference value transmitter 37 which serves to produce an
adjustable reference value signal in the form of a direct-current.
Further, the input side 65a of the same integration circuit
arrangement 65 is supplied by means of the line or conductor 70
with an actual value signal in thé form of a direct-current
which is derived from the actual value of the alternating-
current voltage between the conductors 46 and 47. For this pur-
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pose the primary winding 71a of a measuring tranformer 71 is con-
nected wi-th the lines or conductors 46 and 47, and the secondary
winding 71b of such measuring transformer 71 is connected by means
of a rectifler 75 with the aforesaid line or conductor 70. Further-
more, a measuring current converter 80 is connected with the line
or conductor ~7. whose measuring winding, generally designated by
reference character 80a, delivers by means of a rectifier 82 a
further actual value signal in the form of a direct-current which
is supplied by the line 83 to the input side or input means 66a of
the second integration circuit arrangement 66.
The use and mode of operation of the apparatus portrayed
in Figure 6 and the method for controlling the welding capacity
which is rendered possible with the use thereof, are as follows:
By means of the reference value transmitter 37 there is
adjusted or set a reference value signal. In accordance with this
reference value signal there is controlled within each alternating- .
current voltage half-wave and by means of the integration circuit
arrangements 65 and 66 the firing points of the thyristors of the ~:'
rectifier 62, so that the direct-current flowlng through the ex-
citation winding 55 of the generator 50 assumes a predetermined
current intensity, resulting in a predestined amplitude of-the
alternating-current voltage between the lines 46 and 47 and which
is produced by the generator 50. When the reference vaIue singal
is changed, then there is also changed the excitation of the gene-
rator 50 and the amplitude of the alternating-current voltage
produced by such generator, and the alternatiny-current voltage
half-waves always remain intact, as such has been illustrated in
Figure 5. With the amplitude change of the alternating-current
voltage between the lines or conductors 46 and 47 and accomplish-
ed in the aforedescribed manner, there is also changed theeffective or root-mean-square value of the alternating-current
flowing through the primary winding 21 of the welding transformer
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20, and as likewise shown in Figure 5. The change in the current
intensity results in a corresponding change of the resultant welding
en~r~y. ~ccordingly, it is possible to select ancl sec the current
intensity o~ the welding alternating-current and the weldiny energy
respectively, by m~ans oE tlle reE~rence valu~ tr~nsmitter 37.
The first actual value signal which is produced by means
of the measuring transformer 71 and the rectifier circuit 75, is
proportional to the amplitude of the alternating-current voltage
produced by the generator 50, whereas the second actual value signal
which is produced by means of the current converter 80 and the rec-
tifier 82, is proportional to the intensity of the welding current
flowing in the primary current circuit of the welding transformer
20. If the amplitude of the alternating~current voltage between
the lines 46 and 47 deviates from the reference value set by means -
of the reference value transmitter 37, then the first actual value
signal automatically ensures for such a shift of the firing or igni-
tion point of the thyristors in the rectifier circuit 62 that the
voltage deviation is compensated. If the current intensity in the
primary current circuit of the welding transformer 20 changes, for
instance due to load fluctuations at the secondary side of the weld-
ing transformer, then the second actual value signal automatically
ensures for a shift or displacement of the flring point of the thy-
ristors in such a manner that the excitation of the generator 50
correspondingly changes, in order to again compensate for the
current intensity changes which have arisen. Changes ln the current
intensity at the primary current circuit of the w lding transformer
20 of course also result in corresponding changes in the voltage
amplitude, and for which reason the regulation accomplished with
the aid of the first actual value signal proportional to the voltage
amplitude would be sufficient for achleving the desired constancy.
The additional regulation by means of the second actual value signal
proportional to the current intensity, however, produces an accel~-
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ation of the correction by a leadint regulàtion of the excitation
of the generator 50. The frequency of the welding alternating- -
current produced by means of the generator 50 can be chose to
be greater than the networ~ Erequency iE such appears advantageous
as concerns the quality of the welds or the welding speed during
electrode roll-resistance seam welding. It should be clear that
by changing the rotational speed of the drive motor 52 it is
easily possible to change the frequency of the welding altern-
ating-current.
10Both of the described arrangements of Figures 4 and 6
enable a continuous re~ulation or control of the welding energy
between a maximum value and practically null and each time at
complete half-waves of the welding alternating-current voltage
and the welding alternating-current. ThereEore, it is not
necessary to use a welding transformer having taps. Since in the
practice of electrode roll-resistance seam welding it is often-
times necessary anyway to work with a higher frequency of the
welding current than that of the alternating-current distribution
network, it was necessary in these sltuations to already
previously use a static inverter or a rotating inverter for
frequency increase. The described arrangement for controlling
the welding energy by amplitude change of the welding altern-
ating-current~voltage, instead of phase control, therefore does
not require practically anu increased costly equipement expend-
iture, rather can be realized with relatively modest additional
means, which moreover are commercially available.
Apparatus in accordance with a preferred embodiment -
of the invention will now be described in connection with Figure
7~ The control circuit 30 serving for controlling the welding
energy has been shown in Figure 7 only in the form of a block,
since the components thereof are as described with reference
to Figure 4~
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In orcler to bring about the feed of the workpiece
parts 2~ and 27 between the welding or electrode rolls 23 and
24 d~lring the welding operation, the emhodiment of Figure 7 has
the upper electrode 24 sècured to a shaft 2a which can be driven
by an e]ectric motor 29 at the desired rotational speed.
Advantageously, a not particularly illustrated conventional
reduction gearing or transmission is provided between the rotor
of the motor 29 and the shaft 28. rrhe rotor of the motor 29
is coupled by a shaft 140 with a tachometer generator 141, at
the output 142 of which there appears a direct-current voltage
proportional to the actual value of the rotational speed
of the motor 29.
Instead of the tachometer generator 141 it is equally
possible to use in place thereof a tachopulse transmitter
which, during each revolution of the shafts 2~ and 140 produces
a given number of electrical pulses, and the pulse repetition
frequency serves as the actual value signal for the welding
speed.
A program control device or computer 150 is provided
for controlling the rotational speed of the motor 29 as a
function of certain criter1a which are not here of further
interest. The device 150 has two outputs 151 and 152, there
appearing at the one output 151 a digital or analogue rotational
speed-reference value signal ~or the control of the motor 29.
With the aforementioned output 151 there is connect~d an 1nput
153 of an electronic rotational speed regulator 154 of known
construction, the output 155 of which is connected with the
motor 29. The rotational speed regulator 154 has a second
input 156 which is connected with the butput 142 of the tacho-
meter generator or tachopulse transmitter 141. Thus, therotational speed regulator 154 has delivered thereto by means of
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its one input 153 a rotational speed-reference value signal
and by means of its other input 156 a rotational speed-actual
value signal. The rotational speed regulator 154 automatically
.
ensures that the rotational speed of the motor 29 corresponds
to the infed re~erence value signal and that possible arising
deviations of the actual value of the rotational speed from
the reference or set value will be automatically corrected.
It will be recalled that it was mentioned the device
150 has a second:output 152. At this second output 152 there
appears a direct-current voltage corresponding to the reference.
value signal for the rotational speed, the direct-current
voltage being supplied to a potentiometer 143. Connected with
.a tap of the potentiometer 143 is the input 144 of an amplifier
145, the output 146 of which is connected with the connection
terminal 101 of the control arrangement or control means 30
(see also Figure 4). Hence, the output 146 of amplifier 145
delivers to the summation amplifier 43 of the control'circ.uit
30 ~Fi~ure 4) a welding current-correction signal in the form
of a direct-current of variable intensity, this weIding current-
correction signal being analogous to the rotational speed ofthe motor 29,and thus the welding speed.
In the summation amplifier 43 there are combined with
one another the reerence value signal set by means of the
reference value transmitter 37 and the correction value signal
for the weldin~ current intensity delivered by the amplifier
145, so that by means of the circuit arrangement 36 and the
controlled rectifier 32 the effective value of the welding
alternating-current does not depend solely upon the setting
or adjustment of the reference value transmitter 37, rather
additionally also upon the momentary actual value of the
rotational speed of the motor 29 and thus the welding speed.
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If the rotational speed of the motor 29 increases, then there
correspondingly also increases the welding current-correction
signal at the input 436 oE the summation amplifier 43, causing
a corresponding increase of the effective value of the welding
cu~rent intensity. Conversely, a reduction in the rotational
speed of the motor 29 brings about a corresponding reduction
of the welding current intensity. By means of the potentiometer
143 it is possible to adjust the influence of the changes in
the rotational speed upon the intensity of the welding current
such that the workpiece parts 26, 27 which are to be welded
to one another have delivered thereto at each point along the
formed welding seam the same welding energy, independent of the
momentary welding speed.
If the control de~ice or unit 150 delivers an altered
rotational speed-reference value signal to the input 153 of the ~ :.
rotational speed regulator 154 in the form of a command that the
rotational speed of the motor must be correspondin~ly changed,
then the control device 150 simultaneously also causes a
correspondin change in the welding current intensity so taht
noweithstanding the change of the welding speed the.same welding
energy is delivered to each point along the formed welding seam.
As mentioned, the control device 150 can be a:computer,
and specifically as employed in a n apparatus for controlling
the start of welding and the termination of welding during continuous ~esis-
tanceweldingastaughtinsaidSwisspatent572;375~ mentioned herein~efore.
The means for generating a welding current-correction
signal, described in accordance with the preferred embodiment
of Figure 7 and which welding current-correction signal i5
dependent upon the feed speed of the workpice parts 26 and 27
to be welded to one another, can of course also be combined
with the control circuit shown in Figure 6, by connecting the
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output 146 of amplifer 145 with the connecting terminal 101 of
the control circuit 60 (Figure 6).
The apparatus particularly described controls the
welding energy during resistance welding in an extremely
efficient and reliable manner. The apparatus is relatively
simple in construction and design, economical to manufacture,
extremely reliable in performance, not readily subject to
breakdown or malfunction, and requires a minimum of servicing
and maintenance.
With the apparatus described lt is possible to change
throughout a relatively large range the welding energy of an
electrical resistance welding machine by a continuous voltage
change of the welding alternating-current, so that there can
be avoided the drawbacks of the previously proposed phase
control. Moreover, it is also possible to automatically
maintain conStaht the effective value of the welding current
intensity and thus the welding energy, so that with constant
feed speed of the workpiece parts between the welding rolls, and
which workpiece parts are to be welded together, there is
delivered to all of the welding points or spots of the welding
seam produced by a respective alternating-current half-wave o~
the welding current, the same thermal energy. However, there
are situations where the welding speed unintentionally experiences
temporary changes. Also, as described in British PatentSpecifi-
cation~o.l,509,416issuedonSep~.8,197~toFaelS.A.~thefeedspeedofthe
w3rkpiece parts to be welde~ to one another can be controlled during
welding such that the last weld spot of the seam which is
produced by an alternating-current half-wave of the welding
current is dispositioned at a predetermined distance from the
trailing end of the parts which are to be welded to one another.
This of course required a control of the welding speed and
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ll~Z~i39~ -
results in a speed-change in the operation of the welding
machine.
The apparatus described prevents the formation of
poor we:Lding seams due to too low or excessively supplied
welding energy, if during the welding operation the feed speed
of the workpiece parts to be welded to one another changes
unintentionally or intentionally.
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