CA1038024A - Laser power supply - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method of energizing a laser source stimulating flash lamp directly from an AC power line. Uncontrolled diodes couple the anode and cathode of the flash lamp directly to the AC line. The lamp is triggered by a separate triggering circuit which produces its trigger pulse at a predeter-mined phase of the AC power source. The use of high current carrying con-trolled rectifiers and large energy storage devices is thereby eliminated.

Description

~3~Q2~

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 31~2~
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

z~
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 ~3~

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 ~3~Q2~
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 ~0;~80~
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.

~a3~Q~
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.

1~)38~2~
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.

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In combination: means for producing light by ionization of a gas;
uncontrolled rectifying means coupling said light producing means to a source of power, said source of power having a plurality of phases, and said ionization being continuously sustained for a period of time longer than the time 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.

2. The combination of Claim 1 wherein said source of power has three phases, said phases being Y-connected.

3. The combination of Claim 1 wherein said source of power has three phases, said phases being delta-connected.

4. The combination of Claim 1 wherein said applying means comprises in combination: means for counting the number of said pulses; and switch means for coupling said pulses to said light producing means, said switch means operating in response to said counting means.