US2200483A

US2200483A - Twin arc lamp

Info

Publication number: US2200483A
Application number: US207045A
Authority: US
Inventors: Ernest G Ashcraft
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-05-10
Filing date: 1938-05-10
Publication date: 1940-05-14
Anticipated expiration: 1957-05-14

Description

May 14, 1940- E. G. AsHcRAFT 2,200,483

TWIN ARC LAMP Filed lay 10, 1938 5 Sheets-Sheet 1 May 14, 1940- E.l G. A'sHcRAFT 2,200,483

TWIN ARC LAMP Filed May l0. 1938 5 Sheets-Sheet 2 May 14 1940- E..G. AsHcRAr-'T 2,200,483

TWIN ARC LAMP Filed lay l0, 1938 5 Sheets-Sheet C5 /nl/enor. Ernes 6. Hshdra i".

May 14 1940- E. G. AsHcRAr-T 2,200,483

TWIN ARC LAMP Filed lay 10. 1938 5 Sheets-Sheet 4 Mmmm May 14, 1940 E..G. ASHCRAFT 2,200,483

. TWIN ARC LAMP Filed lay 10, 1938 5 Sheets-Sheet 5 Fly. 6..

'orney.

Patented May 14, 1940 UNITED STATES PATENT OFFlCE 9 Claims.

This invention relates generally to are lamps, and more particularly to arc lamps adapted especially for motion picture studio service, particularly for color photography, though not necessarily restricted to such service. A specic illustrative form of the invention relates to a type of studio arc lamp in which the carbone are disposed in vertical alignment, and is here illustratively described in a twin arc form, in which two p-airs of vertically aligned carbons are employed.

The vertical carbon twin-arc lamp as heretofore known in motion picture studio practice, employing an intermittent gravity feed. principle for advancing the upper carbons to compensate for consumption, is no longer considered appropriate for color picture service, since, owing to the intermittent feed, the intensity of the arc as well as its spectral distribution is subject to variation of a character readily perceptible in the nal picture.

In some types of twin arc lamps difficulty has been encountered due to the tendency of one pair of carbonsto be consumed at a slightly faster rate than the other. The diferential in the rate of consumption is not great for modern well made carbons, but if no equaliaing provisions are made, the difference in gap length of the two arcs may become appreciable before the carbons are completely used.

It is accordingly a primary object of the invention to provide an arc lamp capable of maintaining the spectral distribution of its emitted light substantially constant under all conditions.

A further primary object of the invention is to provide improved carbon feeding means capable of automatically maintaining a predetermined distance of separation between the carbons of an arc lamp under all operating conditions.

It is a further object of the invention to provide an improved twin or multiple are carbon feeding mechanism in which the arc gaps are equalized from time to time.

A further important object of the invention is to provide an arc lamp of the character described with improved arc striking mechanism.

A further general object of the invention is to provide improved feeding and striking mechanism for an arc lamp of the type embodying vertical carbons, capable of striking the arc by separating the carbons to a predetermined distance, and of maintaining said separation distance constant during operation of the lamp.

En accordance with the present invention, the carbone are fed toward one another' to compensate for consumption by an electric drive motor, preferably a shunt motor, which is connected across the arc, and provisions are made whereby the voltage applied across the terminals of the motor for any line voltage within a substantial working range, e. g., 10E-l2() volts, is proper to cause the motor to drive at the speed required to feed the carbons at the rate necessary to just compensate for consumption at that line voltage.

In accordance with a preferred embodiment of the invention, the arc lamp mechanism is provided with upper and lower carbon carriages, which are gradually advanced toward one another by means of a lead screw driven by the electric drive motor. rThe upper carbon carriage is adapted to loosely receive a carbon, or a pair or a multiplicity of carbons, for vertical movement therethrough, so that the upper carbons descend by gravity through the upper carriage and into engagement with the lower carbons when the are is extinguished. The lower carbons are preferably rigidly mounted on the lower carbon carriage. Means, preferably of a solenoid type, are mounted directly on the upper carbon carriage for grip-ping the upper carbons and lifting them relatively to the upper carbon carriageto strike the are when an electrical current is passed through the carbons. When the arc is extinguished, the two upper carbons descend by gravity into engagement with the lower carbons. When the are is again struck, the carbon lifting means on the upper carriage engages the two upper carbons and lifts them both exactly the same distance, to strike the arc and to position them at the proper distance of separation from the lower carbone. The arc gap lengths are thus equalized each time the are is extinguished and reignited. During burning of the arcs, the carbons are advanced toward one another at a speed which is substantially equal to their rate of consumption, as mentioned previously, so that the desired arc gap lengths are closely maintained.

The invention will be best understood by now referring to the following detailed description of illustrative means embodying the invention, reference being directed to the accompanying drawings, in which:

Fig. l is a front elevation of the mechanism; shown in inoperative position, with the carbons touching;

Fig. 2 is a top plan view of the mechanism of Fig. 1;

Fig. 3 is a side elevation, parts being broken z-iway, of the mechanism of Fig. l;

Fig. 3a is a detail section taken on line 3ft-3a of Fig. 3;

Fig. 4 is an enlarged view of a portion of Fig. 1, showing the mechanism in operating position;

Fig. 5 is a section taken as indicated by the broken line 5-5 of Fig. 3;

Fig. 6 is a section taken on line 6 6 of Fig. 3;

Fig. '1 shows the electrical circuit of the arc lamp; and

Figs. 8 and 9 are graphs illustrating relations provided in accordance with the invention.

I will describe first one form of arc lamp mechanism illustrative of suitable means for carrying the present invention into practical effect.

Any suitable frame may be provided; as here illustratively shown, the frame includes upper and lower ycastings I and II connected by parallel vertical rods I2 and I3.

Tightly mounted on rods I2 and I3 are three mounting castings I4, I and I6, the rst being positioned at the upper ends of rods I2 and I3 just below upper frame member I0, the second being positioned midway of the lengths of rods I2 and I3, and the third being positioned at the lower ends of said rods, just above lower frame member II. Mounted on mountings |5 and I6 is the housing I1 for an electrical drive motor M, which is disposed with its drive shaft extending in a vertical direction. This motor housing |1 is located just to the rear of the plane dened by rods I2 and I3, and just outside rod I2 (See Figs l and 3).

Vertical motor drive-shaft I8 carries a worm I9, meshing with a worm wheel on shaft 2|, the latter having another worm 22 meshing with a worm wheel 23 tightly mounted on a vertically disposed lead screw 24. Below worm wheel 23, lead screw 24 is provided with a downwardly extending shaft portion 25 of reduced diameter, which is journaled, just below worm 23, in a bearing 26 carried by mounting I5.

Bearing 26 has a shoulder at 21 resting on mounting l5, and its upper end supports lead screw 24 by engaging the undersurface of worm wheel 23.

Pinned on shaft 25 below mounting I5 is a coaxial lead screw 30. The upper end portion of lead screw 24 and the lower end portion of lead screw 30 are suitably journaled in mountings I4 and I6, respectively. The upper carbon holder or carriage, designated generally by numeral 40, embodies a frame member a having hub portions 4I and 42 slidably mounted on parallel rods I2 and I3. Adjacent hub portion 42 frame 40a has a bore 43 within which is received the upper end of a shaft 44 extending downwardly in parallelism with rods |2 and I3, shaft 44 being rigidly secured to frame 40d as by pin 45. This shaft 44 is telescopically received by a tube 46 mounted at its lower end in mounting I6 and extending upwardly through a bore 41 in mounting I5, the upper end of tube terminating just above the latter.

A lower carbon holder or carriage 50 similarly comprises a frame 50a provided with hub portions 5| and 52 slidably receiving rods I2 and I3, and having, adjacent hub portion 5|, a bore 53 receiving the lower end of a shaft 54 extending upwardly in parallelism with rods I2 and I3, shaft 54 being rigidly secured to carriage 50 as by means of pin 55. Carriage frame 50a is provided with a bore 56 which slidably passes the aforementioned iixed sleeve 46. Upwardly extending shaft 54 is slidably received by a sleeve 51 rigidly mounted at its upper end on mounting member I4 and extending downwardly therefrom through a bore 58 in mounting I5, the sleeve terminating just below mounting I5 as clearly indicated in Fig. 4. Upper carbon carriage frame 40a is provided with a bore 59 which slidably receives sleeve 51.

The upper and lower carbon carriages are thus mounted for vertical movement along the described guide members. Releasable connections are provided between said carriages and

lead screws

24 and 30, which are of opposite pitch, so that when said lead screws are rotated, the carbon carriages will be moved toward one another, and so that the connections between the carbon carriages and the lead screws may be released for quick adjustment oi the carriages along' the lead screws.

Thus the upper carbon carriage has a pair of vertically spaced rearwardly extending plates or brackets 65, between which are pivotally mounted a pair of levers 66. As shown in the drawings, each lever 06 has a hub 61 pivotally mounted on a pin 68 extending between brackets 65. The forwardly extending arms 10 of levers 00 are provided with nut elements 1| adapted to threadly engage opposite sides of lead screw 24. A spring 14 between the rearward arms I5 of levers 56 spreads arms 15 to hold nut elements 1| in yielding engagement with lead screw 24. The rearward ends of arms 15 are provided with finger pieces 15 by which arms 15 may be conveniently grasped to move them together for the purpose of releasing 'threaded elements 1|, and therefore upper carbon carriage 40, from the lead screw.

Lower carbon carriage 50 is provided with rearwardly extending brackets 80, between which are pivotally mounted manually releasable lead screw engaging levers 66 which may be exactly similar to the levers 00 on the upper carbon carriage, levers on the lower carriage having nut elements 1| adapted to releasably engage lower lead screw member 30, as clearly indicated in the drawings.

Lower carbon carriage 50 has two arms 90, to the outer ends of which are secured carbon holders 9 I, which may be of any suitable type adapted to receive and clamp the lower ends of a pair of vertical carbons 92. As here shown, holders 9| contain split bushings 9 I a adapted to clamp carbons 92 when screws 9|b are tightened. Carbon holders 9| are provided with threaded studs 94 which extend through arms 90, nuts 95 being screwthreaded on said studs to secure the carbon holders in assembly with the arms of the l carriage. Electrical connectors 96 clamped between nuts 95 serve to conduct electrical current to the carbon holders. The carbon holders and studs 94 are insulated from arms 90 by suitable insulation such as indicated at 91.

Brackets |03 and |04 at the outer end of each of arms |0| and |02 are provided, in alinement with lower carbons 92, with perforations |05 CII adapted to slidably receive vertical upper carbons ll. Electrical connectors lllJa are clamped directly on the upper ends of carbons llll. Carbons lill descend by gravity through brackets m3 and itil into engagement with the upper ends of carhons all when the arc is extinguished, and are engaged and lifted with relation to the upper carbon carriage to strike the arc by means supported by and travelling with 'the carriage itself. While various means may be provided to accomplish this purpose, I here i1 ustrate a simple mechanism comprising carbon engaging clutches in the form of flat plates l2il, one for each carbon, each having a carbon receiving perforation l2! midway between its ends which is somewhat larger in diameter than the diameter of the carbon, and being positioned between the aforementioned brackets lllt and lilrl, as illustrated. Clutch plates lli) normally, that is, when the arc is not burning, rest down on lower brackets lfl, illustrated in Fig. l. Each plate lill has at one end a perforation l2?! somewhat loosely receiving a screw llltl which also downwardly through bracket llill. A nut llt on the lower end of screw 23. below bracket llll, is so positioned as to permit plate l2@ to be lifted to the position illustrated in Fig. 1l, at which point the head or the screw acts as a stop preventing further upward move ment of the plate.

Plates lli are adapted to be lifted by means of links it@ connected to their other ends, the latter being looped at their upper ends aroundin sulation sleeves mounted on a horizontal rod |3ll. Rod i3d passes through a central mounting |35, which is secured on and carried by the outer swinging end oi a lever member lli. Collars lllla set on rod on opposite sides of mounting |35 corinne the rod against endwise displacement.

As here illustratively shown, lever ltli is in the form of a rod which is bent double, its two ends being received in openings lSl in mounting lilo, and being secured thereto by screws |313. The two arm portions ldt of the rod extending rearwardly from mounting. lao are bent upwardly at lts, so as to pass through loops Mil formed in the ends ot clips lill pivotally mounted at ldlc on arms lllti (see Fig. 5), and are then bent rearwardly, as at l 32, to form portions |123 passing around opposite sides of lead screw 24. The loop end oi the rod, rearwardly of lead screw 2t, engages in a notch formed in the upper end of the vertically movable plunger l5! of a solenoid .e pin 53 closes notch i553 above the loop end ot lever llit, so that when solenoid lll?! is energized and pulls plunger lill in a downward direction, pin. L53 will engage and pull down the loop end of lever |36. Lever lli is thus iucrumed by pivotally mounted clips lill. A liiii connected between mounting lllli and carriage frame dll returns lever 536 and solenoid plunger lill to the positionoi Figs. l and 3 when the solenoid is deenergized.

Solenoid plunger lill is slide-ble through -a sleeve itil extending through and tightly fitted in bracket arms between levers till (Fig. 5), the solenoid bei secured to the lower end of said sleeve, so that it is mounted directly on or is carried by the vertically travelling upper carbon carriage. Thus, as illustratively shown in Fig. 3, the lower portion of sleeve lftll is reduced, as at ll, and the case of solenoid is mounted thereon as by meansr of a press Fig. 'l shows the electrical circuit for the arc lamp. The upper member of one pair of carbons is connected by circuit conductor llll to one terrninal of the winding of solenoid lili, the other terminal of which is connected through a usual voltage reducing resistance or grid lll and through line switch |96 to the positive side of the line, as indicated. The lower carbon t2 of the other pair is connected by lead |12 through switch |90 to the negative side of the line. The upper carbon of the latter pair and the lower carbon of the Iformer are connected by a conductor Illia., so that the 'two pairs of carbons are series connected across the line. The shunt drive motor M for lead screws 24 and 3l) is connected by leads l 'irl and |15 across the positive and negative leads ll'l and Il? going to the carbone, one of said leads, here lead l'l5, including resistor lllic, which may be variable, and is so indicated in Fig. '2. The shunt field winding f of motor M is preferably connected across resistor lla as well as the armature of the motor, as indicated. With this arrangement, the speed of the motor is more sensitive to the adjustment of resistor llct. I have stated that lead lll] goes to the positive side of the line and lead ll'2 to the negative side of the line; it is to be understood, however, that this is not necessary, and that the lamp will operate with the reverse polarity as well. Resistor lll, ordinarily called the grid, is used since the usual available D. C. voltis excessive for the carbons used in this type of lamp.

rilhe voltage across the motor armature during running conditions is the voltage across the two series connected arcs, less the lR drop in resistor l'lc. Motor M runs at a speed proportional to Athis impressed voltage, driving the two carbon carriages toward one another' to compensate for consumption of the carbons.

When the arc is extinguished, the mechanism stands in the position of Figs. l. and 3, with solenoid |52 deenergized, and lever llli held by spring |65 with its forward arm portions in downward position. Clutch plates l2@ are therefore resting on brackets ld, and upper carbone lill are free to slide by gravity through brackets H93 and itil until their lower ends engage the upper ends of lower carbone When line switch |93 is closed, electrical current flows through circuit llt, lill and through the carbone, then touching. Solenoid accordingly energized, and pulls plunger llil down. This swings lever lilli to elevate rod i3d, which lifts links ll to pull clutch plates to their upper, tilted position ol lig. ll. As the cli` ch plates are nrst tilted in this action, they d carbons lill, and as they are then elevated to the position of Fig. Al, they lift the carbone, thereby striking the arc. The distance the carbone are lifted depends of course upon the adjustment ci stop screws 623, which are so adjusted that the carbons will be lifted a distance exactly to the separation distance between the tips ol the carbons for proper operation. This separation distance is typically IIhe arc being struck, a potential difference is established thereacross, and shunt motor M begins to run. When the arc is subsequently extinguished, as by opening switch llill, solenoid ll is deenergized, lever ltty is accordingly released and moves to allow clutch plates to descend to brackets Upper carbone llt are accordingly released by the upper carriage, and descend by gravity until their lower ends engage the upper ends of lower carbons 92. When line fro switch is then again closed, solenoid l5! is again energized and causes the carbons to be lifted to strike the arc, the carbons again being moved at once to their proper equal separation distance,

Thus it is characteristic of the invention that the upper carbons are loosely held by the upper carriage when the arc is extinguished, and that when the arc is struck, means on the upper carriage engage the upper carbons and lift them by a distance equal to their normal distance of separation from the lower carbons. The shunt drive motor driving the upper and lower carriages then closely maintains this separation distance during burning of the arcs, as will be more fully discussed infra.

It is an important feature of my invention that the separation distances between the carbons are equalized each time the arc is extinguished and re-strucir, since the carbon holding clutch plates then take a new hold on the upper carbons and lift them both to exactly the same separation distance from the lower carbons. In motion picture studio service the lamp of course does not normally burn for periods longer than say about ten minutes at a time, and in such a short period of time no appreciable difference in the distances of separation of the carbons, i. e., none of which will have any noticeable effect on the quality of the light, will occur. And since the separation distances of the carbons are automatically equalized each time the arc is extinguished and re-struck, there is never any greater than a negligible differential between the lengths of the two gaps, and any such differential as may exist will be so slight that it may be disregarded.

When new carbons are to be placed in the lamp, levers 55 are operated to release the carbon carriages from the lead screws, and the carriages may then be readily and quickly moved to the outer ends of the guide rods. New carbons are then inserted, after which the lower carbon carriage is adjusted to bring the upper ends of the lower carbons to the proper working height. The lamp is then in readiness for operation.

Reference is now directed to Figs. 8 and. 9. Fig. 8 is a graph in which curve 2B!! represents the relation between the impressed line voltage and the average of the rates of consumption, in inches per hour, of the positive and negative carbons of one arc. It is of course understood that, assuming equal diameter positive and negative carbons, the positive carbon is consumed slightly faster than the negative carbon. Curve 23B does not express the exact rate of consumption of either the positive or the negative carbon, but the average of the individual rates of consumption of the two. The line voltage may be assumed to vary from to 120 volts. This voltage is reduced somewhat by the drop across resistor lll, while the impressed voltage across each arc is of course half of the voltage measured across the two pairs of carbons. Thus for a line voltage of volts, there may be an average potential of 33 volts across each arc. The curve of Fig. 8 thus represents the relation between the impressed line voltage and the average of the rates of consumption of the two carbons.

Fig. 9 shows two curves representing the relations for two different lamp mechanisms between the impressed line voltage and the speed, in inches per hour, at which each one of the carbons is advanced. It will be understood that the speed of advance of one of the carbons may be calculated by dividing the motor speed by the drive ratio between the motor and the speed of travel of the corresponding carriage or holder for the carbon.

In the present embodiment of the invention, the speeds of the two carbon carriages are made equal, though it is obvious they may if desired be made sufliciently `different so as just to compensate for the difference in rates of consumption of the positive and negative carbons. It will be evident that with the speeds of advance of the two carbons exactly equal to one another, and also maintained equal to the average of the rates of consumption of the positive and negative carbons, the position of the arc gap will gradually drift in the direction of the positive carbon, at a speed equal to the differential of the speed of consumption of the positive and negative carbons. This drift is comparatively slight, however, and introduces no difliculty.

Curve 2li! represents a lamp mechanism in which, for one given line voltage only, the rate of carbon feed is just equal to the average of the rates of carbon consumption for that given line voltage, as .read from the graph of Fig. 8. Thus, for voltage A, the rate of carbon feed is just equal to the average of the rates of carbon consumption, and if the graph of Figs. 8 and 9 were superimposed, curves 29B and 2li! would coincide at one point a. At other impressed line voltages, however, there is no point of substantial coincidence on both curves ZUG and 2531, and the carbons will therefor no longer be fed at rates equal to their average rate of consumption, with the result that the arc gap will either widen or close.

Curve 202 of Fig. 9 represents the condition established in accordance with the present invention. By proper adjustment of the voltage impressed across the drive motor, and proper choice of the drive ratio between the motor and the carbons, curve 202 is matched to curve 2% of Fig. 8, and if Figs. 8 and 9 were superimposed, curves 20!! and 282 would approximately coincide for at least the range of impressed line voltages for which the mechanism is designed, e. g., for a range of line voltages ranging from 105-120 v. It will be evident from a comparison of curves 203 and 282 that for any line volage within the range from B to C, the rate of carbon feed will exactly or substantially equal the average of the rates of carbon consumption. Accordingly, assuming the carbons to have initially been separated to a proper distance, that distance will be maintained regardless of variations in line voltage, the speed of the motor varying with changes in line voltage, but varying always so as to keep the rate of carbon feed equal to the average of the rates of carbon consumption. The distance of carbon separation, and therefore the spectral distribution of the emitted light, accordingly remains constant for any change in line voltage at least as great as from 105 to 120 volts.

The method of and means by which the carbon feed characteristic for changing impressed voltage is matched to the carbon consumption characteristic for changing impressed voltage, as accomplished by the present invention, will now be described. The impressed line voltage-carbon consumption characteristic curve is of course governed by the consumption characteristics of the carbons to be used. The impressed line voltage-carbon feed characteristic depends upon several factors, among which are the magnitude of the voltage actually impressed across the Sli terminals of the motor, and the drive ratio between the motor and the carbon advancing means. Accordingly, in the present simple illustrative embodiment of the invention, resistor la is used in series with the armature of motor M, and preferably inside of field winding f, and this resistor is adjusted to establish the motor speed characteristic at such a value as will give the characteristic sought for a properly chosen drive ratio. It is believed the invention may best be illustrated by here giving data on one typical practical embodiment of the inveniton, though it is to be understood, of course, that these figures are illustrative only of one practical work-out of the invention and are not to be taken in a limitative sense. With this understanding, it may be assumed that the lamp is to use cord, copper coated carbons, l-sg in diameter, of the type produced by National Carbon Co., and known as Motion Picture Studo carbons. Resistance VH, usually known as the grid, may be of a resistance of about 1.1 ohms, so that for a line voltage of 115 v., the voltage across the series connected carbons will be approximately 66 v., or 33 v. across each arc. Resistor I'iEa, is then adjusted to a resistance of substantially 100 ohms. This resistance may require somewhat ne adjustment to establish the precise characteristic sought. Motor M may typically be an ordinary 115 v. direct current shunt motor, rated at .5 a. and V40 H. P. The proper drive ratio between the shaft of motor M and each of the carbons is then 1728 to 1.

A lamp mechanism having these characteristics maintains the lengths of its two arc gaps very closely for variations in line voltage between 105 and 120 V. Some slight change in gap length is detectable but not sufficient to vary the spectral distribution of the emitted light by a degree which is at all undesirable from the standpoint of motion picture color photography. Of course, under present studio conditions, a line voltage variation of no greater than approximately four or ve Volts is ordinarily encountered, and in present practice, therefore, it will ordinarily be amply sufcient if the lamp maintains a substantially constant gap for a range of line voltages as great as say four or ve volts. The degree of voltage variation necessary to be provided for will thus depend in given cases upon conditions as they are encountered in studio service. The specic lamp as herein disclosed is capable of maintaining a substantially constant gap for a wider range of line voltages than is ordinarily met with, namely, for a range as great as fifteen volts. Such acondition is advantageous, however, even when the line voltage varies with a range of a very few volts, since with a lamp designed to maintain the gapwidth substantially constant for a greater range of voltages than will actually ordinarily be encountered, there is assurance that the gap will be very steady with lesser voltage variations than do occur with relative regularity.

The instantaneous voltage across one arc, if examined carefully, may be found to vary as much as plus or minus two volts in a somewhat irregular way due to air currents and non-uniformity of core materials of the carbons. Voltage variations from this cause are transitory in character, however, and do not appreciably affect moto-r speed because of the momentum of the motor and parts driven thereby. Moreover, the plus and minus voltage variations when averaged over a short period of time will nearly cancel and for practical purposes may be neglected. The variations in voltage introduced by changing line voltage, on the other hand, are essentially more gradual, and are the variations with which the present invention is concerned.

It is of course true that the intensity of the emitted Alight is substantially lower at a line voltage of 105 v. than at a line voltage of 120 v. This condition is not at all serious, however, since it may readily be compensated by use of more or less lamps. What the present lamp does accomplish, which so far as my knowledge goes, is entirely novel, is to maintain the spectral distribution or color value of the emitted light substantially constant under all conditions encountered in studio service, an accomplishment of utmost importance to color motion picture photography.

I have now illustrated my invention embodied in a twin arc type of lamp employing vertically alined carbons, in which both carbons are fed, and are fed at the same speed. It is of course obvious that my invention is also applicable to other types of arc lamps, and is applicable whether both carbons of each arc are fed at the same or different speeds, or only one carbon off each arc is fed. If but one carbon of each pair is fed, for example, it will simply be fed at twice the speed as in the case of both carbons being fed at equal speeds. The fundamental basis of the invention, namely, matching of the impressed voltage-carbon feed characteristic to the impressed voltage-carbon consumption characteristic, for the range of line voltage encountered in practice, rather than for a single line voltage, is thus applicable to all such situations. An arc lamp mechanism in accordance with the present invention is stable in operation` and maintains the predetermined length of its arc gap for all conditions encountered in the eld. No hand feed for readjustment from time to time of the arc gap is required, and no operator need stand in constant attendance. The lamp requires only that the arcs be struck, which is done automatically when the line switch is closed, and then automatically maintains its arc gaps with all the necessary constancy and accuracy called for by present color motion picture photography practice without further attention.

I have now shown and described one present illustrative embodiment of the invention; it will of course be understood that this is for illustrative purposes only and that the present invention is applicable to other types of arc lamps as well. It should also be understood that while I have referred to my invention chiefly in connection with color motion picture photography, its full field of application is much wider than this, as it is also applicable to projection of color motion pictures, or to studio or projector use with black and white lm, or to any other service calling for a stable arc lamp.

I claim:

l. In an arc lamp the combination of a frame, upper and lower carbon carriages mounted for vertical movement on said frame, drive means on said frame operatively connected with both said carbon carriages for continuously and uninter'ruptedly advancing said carriages toward one another, a carbon holder on said lower carbon carriage for tightly gripping a lower carbon, an upper carbon guide on said upper carbon carriage having a carbon guideway adapted for free passage of the upper carbon and located in alinement with the lower carbon gripped by the carbon holder on said lower carriage, and a carbon clutch and operating means therefor associated with said upper carriage for gripping said upper carbon and elevating it a predetermined distance through said carbon guide.

2. In an arc lamp, the combination of a frame, upper and lower carbon carriages mounted for vertical movement on said frame, drive means on said frame operatively connected with both said carbon carriages for continuously and uninterruptedly advancing said carriages toward one another, a carbon holder on said lower carbon carriage for tightly gripping a lower carbon, an upper carbon guide on said upper carbon carriage having a carbon guideway adapted for free passage of the upper carbon and located in alinement with the lower carbon gripped by the carbon holder on said lower carriage, and a carbon clutch and operating means therefor mounted on and travelling with said upper cairiage for gripping said upper carbon and elevating it a predetermined distance through said carbon guide.

8. In an arc lamp the combination of a frame, upper and lower carbon carriages mounted for vertical movement on said frame, drive means on said frame operatively connected with both said carbon carriages for continuously and uninterruptedly advancing said carriages toward one another, a carbon holder on said lower carbon carriage for tightly gripping a lower carbon, an upper carbon guide on said upper carbon carriage having a carbon guideway adapted for free passage of the upper carbon and located in alinement with the lower carbon gripped by the carbon holder on the said lower carriage, a carbon clutch on said upper carriage operable to grip and elevate said upper carbon a predetermined distance through said carbon guide, and electromagnetic clutch operating means mounted on said upper carriage and operatively connected with said clutch in a manner to cause said clutch to grip and elevate said carbon when electrically energized and to hold said clutch in carbon elevated position until deenergized.

4. In an arc lamp, the combination of a frame, upper and lower carbon carriages mounted for vertical movement on said frame, drive means on Said frame operatively connected with both said carbon carriages for continuously and uninterruptedly advancing said carriages toward one another', a carbon holder on said lower carbon carriage for tightly gripping a lower carbon, an upper carbon guide on said upper carbon carrage having a carbon guideway adapted for -free passage of the upper carbon and located in alinement with the lower carbon gripped by the carbon holder on the said lower carriage, a carbon clutch on said upper carriage operable to grip and elevate said upper carbon a predetermined distance through said carbon guide, electromagnetic clutch operating means mounted on said upper carriage and operatively connected with said clutch in a manner to cause said 'clutch to grip and elevate said carbon when electrically energized and to hold said clutch in carbon elevated position until deenergized, and an electrical energizing circuit connecting said carbons and said electromagneticmeans in series.

5. In an arc lamp, the combination of upper and lower carbon supporting devices, means on said lower carbon supporting device for gripping a lower carbon, an upper carbon guide having a carbon guideway adapted for free passage of the upper carbon and located in alinement with the lower carbon gripped by the lower carbon supporting device, drive means for effecting continuous uninterrupted relative movement of said carbon supporting devices toward one another along a direction line parallel to said carbons, a normally released carbon gripping and lifting clutch associated with the upper carbon-supporting device operable to grip and then elevate the lowered upper carbon a predetermined distance relative to the upper carbon-supporting device, a clutch-operating electromagnet mounted on the upper carbon supporting device and arranged for operation of said clutch to grip and so elevate said carbon when energized and to sustain said carbon in such relatively elevated position until deenergized, and electrical connections through which said electromagnet is energized whenever electrical current passes through said carbons.

6. In an arc lamp, the combination of upper and lower carbon supporting devices, means on said lower carbon supporting device for gripping a lower carbon, an upper carbon guide on said upper carbon supporting device having a carbon guideway in alinement with said lower carbon supporting device, drive means for effecting continuous uninterrupted relative movement of said carbon supporting devices toward one another, an electromagnet mounted on said upper carbon supporting device, a carbon gripping and lifting member associated with the upper carbon-supporting device comprising a clutch plate surrounding said upper carbon and limitedly movable with relation to said carbon supporting device between a lowered substantially horizontal position and an upper tilted position, said plate releasably passing said carbon when in said lowered, substantially horizontal position, and gripping and then elevating said carbon when tilted and then elevated to said upper, tilted position, means, including an operative connection with one end of said clutch plate, operated by said electromagnet to so tilt and elevate said clutch plate, and to sustain said clutch plate in said tilted and elevated position until deenergized. and electrical connections through which said electromagnet is energized.

'7. In an arc lamp, the combination of upper and lower carbon supporting devices, means on said lower carbon supporting device for gripping and supporting a plurality of lower carbons in parallel positions, a corresponding plurality of upper carbon guides on said upper carbon supporting device having carbon guideways in alinement with the respective lower carbons, drive means for effecting continuous uninterrupted relative movement of said carbon supporting devices toward one another along a line of travel parallel to said carbons, and arc striking means supported by the upper carbon-supporting device including a plurality of carbon gripping and lifting devices normally released from the upper carbons, electromagnetic means operating said devices to grip and elevate said carbons a predetermined distance when energized with an electric current and to sustain said carbons in such relatively elevated position until deenergized, and an electrical energizing circuit connecting pairs of corresponding upper and lower carbons and said electromagnetic means in series.

8. In an arc lamp, the combination of a frame, upper and lower carbon carriages mounted for vertical movement on said frame, drive motor means on said frame operatively connected with both said carbon carriages for continuously and imiiormly advancing said carriages toward one another, a carbon holder on said lower carbon CJI carriage for tightly gripping a lower carbon, and an upper carbon clutch on said upper carriage for gripping the upper carbon when the latter is in end to end engagement with the lower carbon and elevating it a predetermined distance relative to the upper carbon carriage.

9. In an are lamp, the combination of a frame, upper and lower carbon carriages mounted for vertical movement on said frame, drive motor means on said frame operatively connected with both said carbon carriages for continuously and uniformly advancing said carriages toward one another, a carbon holder on said lower carbon carriage for tightly gripping a lower carbon, an upper carbon clutch on said upper carriage for gripping the upper carbon when the latter is in end to end engagement with the lower carbon and elevating it a predetermined distance relative to the upper carbon carriage, and electromagnetic clutch operating means for causing said clutch to grip and elevate said upper carbon, said electromagnetic means being mounted on and travelling with said upper vertically travelling 10 carriage.

ERNEST G, ASHCRAFT.