Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to means for powering a 1ash lamp.
This application is a division of our Canadian Patent Application
Serial No. 196,947 filed April 5, 1974.
Producing sufficient light to excite a laser source used in welding
and drilling applications has long been a problem. Initial attemp~s included
those where large energy storage devices such as capacitors and inductors
were charged for periods o time long in comparison to typical AC line fre-
quencies then, when full~ charged, were switched across the flash lamp. These
energy storage devices tended to be both bulky and expensive and moreover
the maximum rate at which the laser could be fired was low in that the time
required to bring them to their peak storage capabilities erom a rectlfied
power line source is long compared with desirable weld:Lng pu14c rates. Later
attempts inclu~ed couplLng tho flash lamp to an AC lino source through con~
trolled rectifiors. Theso later attemp~s roquirecl large, expensivo, con-
trolled rectifiers to implement any scheme in which enough power was trans-
ferred from the power line to the flash lamp. The prior art has not shown
methods o coupling a flash lamp to an AC power source through simple uncon-
trolled rectifier means.
rt is thus an object of the present invention to power a flash
lamp ~ithout the use of large energy storage devices.
rt ~s also an object of the present invention to fire a flash
lamp from an AC power source without the use of controll~d rectifiers.
Furthermore, it is an object of the present invention to fire a
flash lamp from an AC power source at an arbitrary phase angle of the power
source without the use of controlled rectifiers in the high current carrying
portions o~ the circuitry.
Moreover, it is an object of the present invention to fire a flash
lamp from an AC power source for a longer period of time than a single half
cycle of the AC power source.
3Q According to the broadest aspect of the invention there is provided,
4 rtcor~tfolled
in combination: means for producing light by ionization of a gas:~recti~ying
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means coupling said ligh~ producing means to a source of power, said source
of power having a plurality of phases, and said ioni~ation being continuously
sustained for a period of time longer than the ~ime period for a half-cycle
of any phase of said plurality of phases of said source of power,
means for initiating said ionization at a predetermined time com-
prising means for producing a high voltage pulse which is coupled to a trigger-
ing electrode of said light producing means and to the same electrodes of said
light producing means to which said source of power is coupled, and
means for applying a predetermined number of said pulses to said
light producing means.
Pigure 1 is a simplified circuit diagram showing therein a ~lash
lamp excited ~rom an AC power line~ in accordance with tho present :Lnvent:ion;
Figure 2 is a slmpli~ied c:ircuit diagram showin~ an ~lternat:Lvo
method of exciting th0 1ash lamp in accordance wlth the present invention;
Figure 3 is a circuit showing a flash lamp being excited from two
phases of a three-phase Y-connected alternating current source;
Figure 4 is a circuit diagram o the trigger circuitry shown in
the circuit of Figure 3;
~ Figures 5A through 5E are a series of waveforms useful in explain-
: 20 ing the operation of the present invention as described in the embodiment
of Figure 3;
Figure 6 is a circuit showing a flash lamp being excited from a
three-phase delta-connected alternating power source;
Figure 7 is a waveform showing the rectified voltage in Figure 6;
and
Figure 8 on the same sheet as Figure ~, shows a laser welding
system in which the present invention is used to advantage.
In the circuit of Figure 1 the anode 107 of the flash lamp 106,
whlch is preferably a xenon flash lamp, is coupled to one terminal of the
single phase AC power line lO0 through diode lOl. The frequency of the AC
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line may be the conventional 50 or 60 cycles per second. The cathode 108 of
the flash lamp 106 is coupled directly to the other terminal of the AC power
line 100. With this connection, the flash lamp, once excited, will emit
light and conduct only during the positive half cycles of the single phase
AC power source. During the negative half cycles, no light will be emitted
and no current will exist in the lamp. The input of the trigger circuit 102
is connected to the same AC power source 100 so that the circuit may sense
the phase of the source. The trigger circuit 102, one embodiment of which
will be discussed in conjunction with Figure 41 provides a triggering pulse
to the flash lamp 106 at a predetermined phase angle of the AC power source
100 which thereby triggers the 1ash tube 106 through an external trigger
electrode 111. Since the trigger electrode 111 is controllably switched
rather than the power input to khe cathodo an~ anode, it bccomcs unnocos~ary
to use controlled rcctifier means in the high power carrying anode and cath-
ode leads of the flash lamp 106. The output trigger pulse from the trigger
circuit 102 is coupled on lines 110 to the primary 10~ of triggering trans-
former 103. The secondary 105 of this transformer is connected between the
cathode 108 and the trigger electrode 111. The transformer 103 is used to
increase the triggering pulse voltage to a sufficient level so as to initiate
the gas breakdown in the flash lamp 106 between the anode 107 and cathode 108.
After the triggering pulse has been applied, while the voltage applied between
the cathode 108 and anode 107 from the power line 100 through diode 101 is
sufficiently high, the gas breakdown and light output will continue without
the presence of the triggering pulse. The light output will be extinguished
when the voltage applied between anode 107 and cathode 108 falls below that
voltage need to sustain the gas breakdown~ O~ coursel light output will not
be produced during the negative half cycle of the AC power source 100.
In Figure 2 there is illustrated an alternative method for trig-
gering the flash lanlp. This circuit is similar to Figure 1 except that
it utilizes series injection triggering through transformer 203 to initiate
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ionization of the flash lamp 207. As in the previous circuit a diode 201
couples the anode 208 of the flash lamp 207 to one terminal of the AC power
source on lines 200. Here the discharge or gas breakdown is initia~ed by
impressing a high voltage trigger pulse as an addition to the power line
voltage rather than by coupling the pulse through a separate triggering
electrode as was shown in l~igure 1. In this case the gas breakdown path
initiated by the triggering pulse lies directly between anode 208 and cathode
209 rather than through the intermedia~e triggering electrode 111 as in
Figure 1. The lamp triggering pulse produced by a triggering circuit 206 is
coupled through lines 210 to the primary 205 of transormer 203. At the
secondary 20~ of the transformer 203 the trans:Eormer stepped-up trigger
voltage is added to the AC line voltage. When the sum o the two rcachcs
the breakdown voltage o:E the :~lash lamp 207, the gas d:ischa:rgo and .l:i~ht out-
put will be initlated. Once thc cli.scharge bog.ins, :Lt will bc susta:Lned in
the absence o the trigger pulse once t~e rectiied AC line voltage is suf-
ficiently high. This sustaining AC line voltage is less than the voltage
necessary to initiate the discharge. The input o:f the triggering circuit
206 is coupled to the AC power source 200 so that it may sense the phase of
the source and produce the triggering pulse at the desired phase angle.
2Q In Figure 3 there is shown the circuit diagram of a flash lamp
circuit operating from a three-phase Y-connected AC power source in accord-
ance with. the teachings of the present invention using a half-wave rectifier.
This figure will be discussed in conjunction with the waveforms shown in
Figures 5A-5E. In Figure 5A two of the phases of the three-phase AC power
source are shown by curves 501 and 502, I~lhich represent ~A and (jB respectively.
In the circuit of Fig~lre 3 curve 501 ~A is tho voltage wavc;~`orm betwecn
points 302 and 301 while the curve 502, ~B, is the waveorm between points
303 and 301 ~C not shown, lags ~pB by 120. Point 301 is the neutral or
ground o th.e power source. Po;.nts 3()2 and 303 are coupled throug]l d:iode 305
3U and 325 to conunon point 320. The voltage l~aveorm between points 320 and
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ground as it would appear with no load is sho~n as the heavy black line in
Figure 5~. The voltage at point 320 is coupled through smoothing choke 30~
to the anode 314 o the flash lamp 313. The center troughs of the rect;fied
and summed portions of the waveform at point 320 are sufficiently higll aEter
illg smoothed by clloke 307 that the gas breakdown in the flash lamp 313
will not be ceased when the waveform passes through these po:ints of low vol-
tage. The neutral point 301 is coupled directly to the cathode 315 of the
flash lamp 313. This method of using two of the three phases of the AC power
source permits lengthening of the flash lamp pulses over that possible with
a single phase system thereby proclucing a more desirable lcngtllened laser
pulso waveform for laser weldlng appl:icat:ions. I~urthermore, since the ro-
covery time oE most elasll lalllps, partic~llarly xonon flash lmlps, is typlcally
no more tllan several hun~lrccllllicrosoS~ollds~ tllo tLIne botween puLsos using
either a 50 or 60 cycle sinuso:idal three-pllase source will be more than suf-
ficlent for complete lamp recovery between firings.
Included in the circuit shown in Figure 3 are the prepulse cap-
acitor 308, aging capacitor 327 and the capacitor charger 309. While the
flash lamp is in the recovery period~ shown at 512 in Figure 5A the cap-
acitors are charged to a DC voltage preferably in the range of 1.2 to 2.4
kilovolts from the capacitor charger 309. Charge will flow during this time
into the capacitors 308 and 326 rather than the flash lamp 313 or power
source 300 since the flash lamp 313 is at a high impedance when it is not be-
ing fired and the 1.2 to 2.4 kilovolts back biases diodes 305 and 325. When
the flash lamp 313 is initially fired the charge on the prepulse capacitor
308 and aging capacitor 327 will adcl to the initial current surge throucrll tlle
flash lamp 313 ancl will produce a higil narrow curr~nt peak at the begimling
of the firing of the lamp. Tlle current flow from the prepulse capacitor 30
primarily initiates the arc inside the elash lnnlp 313 while aging capacitor
327 is primarily responsible for ~he spread:ing or "aging" oE the arc througll-
out the flash lamp 313. ~lese peaks 51~ in ~:igure 5D appear at tlle leacling
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edges of the current pulses 505 which represent the current through the flash
l~mp 313, ensuring that there is an initial high peak of light out of the
flash lamp 313 and into the laser. This high initial peak is desirable to
ensure a fast rise time of the laser light output and that the lamp ~ires
dependably. If this fast rise time of the laser light output were not pre-
sent, the laser light would tend to be reflected of:E the surface being weld-
ed ~uring the initial portions o~ the laser light pulses thereby reducing
the eiciency o the welding operation. A fast rise time on the laser light
output ensures that the sureace of the material being welded will be initial-
ly broken by the laser and that the remainder o the pulse will be used toeffectuate the weld rather than being reflected o~ the surEace. ~n the
preferred embodiment, the capacitor charger 309 is constructed Usillg a tran5-
former with a rocti~ying diode ln thc trans~ormor socondary xcsistlvcly
coupled to the capacitor 308.
rhe Elash tube triggering circuit 310 also may be used for the
triggering circuits shown in ~igures l and 2. 'rhe trigger logic 311 senses
the alternating ~A voltage between points 302 and 301 and produces a re-
latively low voltage narrow pulse, for example, 12 volts with a width of one
microsecond, at the desired phase angle. The lamp trigger circuit 312 con-
verts the relatively low voltage input pulse from line ~20 to a relativelyhigh voltage pulse, such as two kilovolts, on lines 326 which is coupled to
the primary 317 o triggering transformer 316. The secondary 318 of trig-
gering transformer 316 is connected to the cathode 315 and triggering ele-
ctrode 319~ The trigger logic 311 also contains binary logic pulse counting
circui~ry which counts out the desired number Oe pulses firing the flash
lamp with each pulse, then counts Ollt a pause bet~cen bursts o;E pulses. ~n
this particular illustration, the flash lamp 313 is ired at the beginning
o the cycle of ~A although any other point of any phase could be used as
~Yell. I-lere, tllree pulses are counted out each burst. Tllen~ aEter counting
out a pause, the same burst of three pulses will be repeated.
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In the circuitry shown in Figure 4, the trigger logic 311 employs
a full wave diode bridge 415, ~he inputs ~16 and 417 of which are connected
to ~A on points 302 and 301 respectively, as in Figure 3. The output of the
full wave bridge 415 on point 421 is connected to the input o~ monostable
multivibrator 414. This multivibrator 414 produces a pulse on line ~18 at
the phase angle of each cycle o ~A selected by the firing angle adjustmcnt.
'~ose pulses on line 418 are shown as pulses 503 in Figure 5B. The pulses
on line ~18 are coupled both to the input of digital counter 413 and to the
input of gate circuit 412. The number of pulses in the bursts of pulses is
set on lines 425 from external switches. The digital counter 413 produces
a logical 0 state output on line ~19 whenever tho desired number of pulses
has been counted out by the counter ~13. l'he gate circuit ~12 compriscs a
blnary logic ~ND gate which produces an output only wllen both o~ its Lnputs
are :in tho logical 1 stato. Since tho peaks 503 reprosont tho logical 1
state~ the puIses will be allo~ed to pass through the AND gate ~12 only when
the output from digital counter 413 on line 419 is in the logical 1 state,
indicating that the end of the count has not been reached. The pulses on
line 42Q, which will be of the form as shown as pulses 504 in Figure 5C, are
coupled to the primary 411 of pulse transformer 410. The secondary winding
2Q 408 of transformer 410 is connected between the gate 409 and the cathode of
the silicon controlled rectifier 404 which causes the rectifier to assume
the ON state whenever pulses from lin,e 42Q are present. A potential of 200
VDC is connected through resistor 401 to the anode of silicon controlled
rectifier 404 and one terminal of capacitor 403. When silicon controlled
rectifier 4Q4 is switched on~ the capacitor 403 is coupled on lines 326 across
the primary 317 of transformer 316 of Figure 3. The current througll that
loop will be a half sine wave pulse since the capacitor 403 and transformer
inductance form a resonant circuit and the current cannot reverse through
the silicon controlled rectifiers 404. The pulse is then coupled tllrougll
trigLtoring trans~ormer 316 to the triggering electrode of the flash lamp 313.
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Figure 6 shows a circuit similar to the circuit of Figure 3 wllere a delta-
connected three-phase power source, shown generally at 700, is used to excite
the flasll lamp. With the diodes 707-710 connected as shown in Figure 6, the
voltage between point 701 and ground is shown by the heavy lines in the
waveform shown in Figure 7. The dotted lines are used for clarity to indicate
partially the individual phases of the three-phase source 700. The ripple
in each pulse 720 is less than for the circuit shown in Figure 3 since three
overlapping half-sine waves contribute to the pulse rather than two, thus
smoothing the center troughs of the pulses. The remainder of the circuit is
the same as in Figure 3.
~i;gure 8 illustrates the use of tho present invention ln a laser
welding application. Ilcre, the flash lamp 605 and laser rocl 606 are loca~ed
each at one o the two foci o~ the cavLty 603 which Is olliptical in cross
section. Tho inside surfaco 60~ Oe cabity 603 is nnirrorccl so that all li~ht
emanating rom the flash lamp 605 will be focussed onto laser rod 606. The
trigger circuit 602 is coupled on line 609 to the cavity 603 wh~ch also serves
as the external triggering electrode since it is a conducting surface. ~le
power supply 601, the input of which is furnished from the three-phase AC
source, is coupled to the cathode of flash tube 605 on line 611 and to the
anode on line 610. The pulsed laser beam 612 is focussed through lens 613
onto the material to be welded 614. Many other arrangements could be used
for the flash tube and laser rod. For exampleJ the flash tube could be in
the form of a helix wound around the laser rod, the combination of which is
located at the center of a mirrored cylindrical cavity. Also, two or more
such flash tubes could be used. ~he invention may be used to advantage in
laser drilling operations as well as in laser wolding applica~ions.
Although preferred embodiments of the invention have been des-
cribed, numerous modifications and alterations thereto would be apparent to
one skilled in the art WOt]lOut departing from the spirit and scope of thc
present invent:ion.
