US1721845A - Arc lamp and method of maintaining a uniform length of arc - Google Patents

Description

y 23, 1929- c. s. ASHCRAFT ARC LAMP AND METHOD OF MAINTAINING A UNIFORM LENGTH OF ARC Filed Aug. 1921 4 Sheets-Sheet I I if )ili 5% y 23, 1929- c. s. ASHCRAFT 1,721,845

ARC LAMP AND METHOD OF MAINTAINING A UNIFORM LENGTH OF ARC Filed Aug. 1. 1921 4 Sheets-Sheet 2 23, 1929. g, s c 1,721,845

ARC LAMP AND METHOD Ol MAINTAINING A UNIFORM LENGTH OF ARC Iii-led Aug- 1921 4 Sheets-Sheet 5 M 1/7 16 1 1511 317 2%, 1/6 J? 4:,

y 23,1929.v c.-s. AsHcRAF-r' 1,721,845

ARC LAMP AND METHOD OF MAINTAINING A UNIFORM LENGTH OF ARC Filed Aug. 1921 4 Sheets-Sheet 4 trode turned toward the lens.

Patented July 23, 1929.

UNITED STATES PATENT OFFICE.

CLARENCE S. ASHGRAFT, OF LQS AN GELES, CALIFORNIA.

ARC LAMP AND METHOD OF MAINTAINING A UNIFORM LENGTH OF ARC.

Application filed August 1, 1921. Serial No. 488,849.

This invention relates .to that type of arc lamp provided with electrically operated mechanisms functioning to feed the electrodes to compensate for disintegration thereof by action of the electric are.

An important object of the invention is to automatically maintain an arc of a predetermined length between the tips of the electrodes, thus effecting the production of a steady light.

Another important object is to hold the arc in the position to which it is adjusted so that the area illuminatedwill remain constant.

Another important object is to provide for projection of the radiation directly through the condenser lens. Prior to my discovery, it was the practice to provide a mirror to receive the radiation and project the samewithout a condenser. In lamps of such character there is produced an objectionable unilluminated spot in the center of the area which it is desired to illuminate, for the reason that the radiation reflected by the mirror is obstructed in the axis of the radiation by the positive electrode and its holding and op cratingmechanism. I have discovered that a far superior light can be produced by positioning the positive electrode in the axis of the condenser lens with the crater of said elec- I have discovered that, by employing, in combination with the condenser lens, a rotating positive electrode having its crater turned toward the condenser, there is produced a; substantially perfect light and, in so far as I am aware to the contrary, this particular combination and arrangement of elements has notbeen empltiyed prior to my discovery.

y be secured for maintaining a constant length of arc, to wit:

(a) Uniform feed motion of one of ,the electrodes to compensate for consumption thereof:

(6) Uniform feed motion of one offthe electrodes with the motion automatically interrupted from time to time to hold the are in substantially a fixed position:

(0) Uniform feed-motion of one of the electrodes in combination with either intermittent or constant feed motion of the other electrode to hold the are in fixed position and to compensate for burning away of the electrodes:

this invention the following results may ((1) Uniform feed motion of one of the electrodes, with the motion interrupted from time to time, in combination with intermittent or constant feed of the other electrode to hold the arc in fixed position and to compensate for burning of the electrodes.

My lamp is constructed to operate either to ponstantly feed the positive electrode to compensate for consumption thereof, and to intermittently feed the negative electrode to compensate for burning thereof and to pre vent a tendency to change in length of the are that would ordinarily be produced by unequal rate of burning of different portions of the negative electrode; or to feed the positive electrode uniformly and to automatically interrupt the feed motion thereof from time to time in accordance with the degree of penciling of said positive electrode so as to maintain the tip of the positive electrode in a plane that remalns at an unchanged distance from the condenser lens, or, in case a mirror is used, from such mirror, and to intermittently feed the negative electrode for the reason explained above. The best results are obtained by the latter operation.

In so far as I am aware, uniform feed of the positive carbon has not heretofore been effected, the feed being a step by step or intermittent motion. By advancing the positive electrode constantly or uniformly, the rate of feed may be timed to correspond very closely with the rate at which said electrode is consumed. It is also believed to be new to automatically interrupt the uniform motion, from time to time, to prevent advancing the positive electrode beyond a predetermined plane, regardless of the density of the particular electrode being used.

In order to feed the positive electrode at a uniform rate and interrupt the feed from time to time, as becomes advisable to maintain the crater in a predetermined plane, I have provided two electrical devices normally in balance, the lengthening or shortening of the arc'producin a consequent change in voltage which a ects the magnetic flux of the electrical devices in such a manner that they operate in unison to either advance or retract the electrode, thus shortening or lengthening the are so that the voltage across the are again becomes normal. The electrical devices for accomplishing this may be of various constructions, and I have shown them associated with a mechanically operated mechanism for producing the desired result;

but whatever the construction of said devices, by their use there are established two electromagnetic fields by utilization of the potential difference across the line, the strength of said field varying, one directly and one inversely as thevoltage across the arc.

The means heretofore employed for maintaining an arc.of' a prescribed length, and consequently of a given voltage, do not properly function when deviation from the normal electrical pressure occurs. When two electrodes are connected electrically, in series with a ballast resistance, to a source of electric current, in order to start the are it is first necessary to bring the electrodes in contact with each other and then draw them apart to such distance that a steady, silent arc is formed. If the voltage of the line be, for example, one hundred and ten, the voltage across the arc with the electrodes in contact will be approximately zero and that across theresistance will be approximately one hundred and ten. If the electrodes be then separated suificiently to require a pressure of fifty volts at the arc, the voltage' across the resistance will be sixty and, as the electrodes are consumed, the arc will necessarily lengthen, thus increasing the voltage necessary to maintain the are because of the increased resistance of the greater air gap between the electrodes. The normal length of are for a lamp operating on a current of one hundred and ten volts and one hundred amperes is approximately five-eighths of an inch. 'After operating the lamp or one-half minute, the arc will be increasedto about three-fourths of an inch in length, and the voltage across the arc will rise to approximately sixty. It is lmown that when two or more resistances are connected in series the sum of the voltages across the separate resistances is equal to the voltage across the combination. The are may be considered as one resistance and this, together with the ballast resistance inseries with the arc,.will constitute a combination. By this invention there is produced a balanced pull between two electro-magnetic fields, when the arc is of the predetermined length; the strength of one of said fields varying with the voltage across the arc and the'strength of the other field varying withthe voltage across the resistance so that either shortening or lengthening of the arc will unbalance the pull of the two fields, .permittingone or the other of them to predominate. And this inventibn' provides means operative by the differential magnetic pull of the fields to advance or retract an electrode according as one field or the other exerts the stronger pull, and thus re-establish the predetermined length of the are.

The accompanying drawings illustrate the invention:

Figure 1 is a plan view of an .arc lamp em bodying the invention.

Figure 2 is a side elevation of Figure 1, i

tional elevation of the lower portion of the lamp.

Figure 4 is a sectional elevation on the line indicated by 0 -40 Figure 3.

- Figure 5 is a sectional elevation on the line indicated by 11: :0 Figure 3.

Figure 6-is an enlarged fragment-a1 secfional elevation of the upper portion of the amp. I

Figure 7 is a fragmental elevation partly in section on the line indicated by ai -m Figure 6.

Figure 8 is a transverse sectional elevation on the line indicated by a2 m Figure 6.

Figure 9 is an enlarged sectional detail of a portion of the negative electrode-feeding mechanism.

Figure 10 is a diagram of the electrical connections of the lamp.

Figure 11 is an enlarged fragmental front elevation of the upper portion of the lamp.

Figure 12 is a plan section on the line indicated by w w Figure 11;

Figure 13 is a plan view of the electric unit which controls the advancement and retraction of the positive electrode.

Figure 14 is an elevation, partly in section, on line indicated byrww-, Figure 13.

Figure 15 is an enlarged sectional elevation on the line indicated by 13 -09 Figure 13.

Figure 16 is a reduced plan section on line indicated by w m Figure 15.

Figure 17 is a sectional elevation on line indicated by a:"m", Figure 4.

In this lamp there are provided electrodes arranged at an angle to one another, in this instance the positive electrode being indicated at a and the negative electrode at b. The angle between the electrodes is preferably greater than a right angle and less than 135. The positive electrode a is positioned with its axis coinciding with the axis of the condenser lens which is indicated at 1. As clearly shown in Figure 2, the crater end of the electrode a faces the condenserlens, thus substantially preventing any of the radiation issuing from the crater of the positive electrode from being obstructed by any part of the lamp mechanism. In projector arc lamps of prior construction, the rotating positive electrode other, so that the axis of the beam projected by the crater toward the lens would not coincide with the axis of the lens but would lie at varying angles thereto according to the degree of burning away of the electrode at one side in relation to the burning away at the other side. Under such conditions, the radiation strikes the lens at different angles, thus causing the projected rays to change their direction. I, therefore, constantly rotate the positive electrode, thus maintaining a crater of uniform depth and diameter and one whose rim lies substantially parallel with the condenser lens 1. T am aware that it is not new to rotate a positive electrode in order to produce this burning away, but I am not aware that a rotating positive electrode has heretofore been used in combination with a condenser lens positioned in front of the crater end of the electrode to obtain the ad vantageous results set forth above.

The mechanism for producing uniform feed of the positive electrode will now be described, The positive electrode a passes loosely through a drum 2 at the axis thereof. The hub 3 Ofsaid drum is journaled by an anti-friction bearing 4 supported by a stand-- ard 5. The front plate 6 of the drum 2 is provided withinwardly projecting brackets 7, each pair of brackets supporting a stud 8 which engages in radial slots 9 formed in the brackets, said slots permitting of radial movement of the studs relative to the axis of the drum. The adjacent ends of adjacent studs 8 are connected to each other by coil springs 10 which yieldingly hold the studs 8 toward the axis of the drum. On each stud 8 between each pair of brackets 52 is rotatably mounted a spur gear 11. In the instance shown in the drawings, there are three such gears, but it is to be understood that one or more may be employed. The gears 11 engage a spiral gear 12 which is rotatably mounted on the hub 3. The spiral gear 12 is inserted in the rear end of the drum 2 and closes the rear end of the chamber 13 of said drum.

In order that rotation of the drum may produce rotation of the gears 11 about their axes, it is necessary to hold the spiral gear 12 stationary and to effect this, in-this particular instance, I provide rearwardly extending studs 14 on the gear 12 and any one of said studs is engaged by a latch 15 pivoted at 16 to the standard 5 so that the latch may be thrown into or out of the path of rotation of the studs 14. i t

On the rear end of the drum hub 3 is screwthreaded a bevel gear 17 provided with a'bore.

18 through which the electrode a extends. The gear 17 meshes with a bevel pinion 19 -fixed to the upper end of a shaft 20 which is,

naled in a bearing 24 formed in the lower portion of the standard 5. The standard 5 is mounted on the top of a casing 25 and the lower end of the shaft 23 projects into said casing and is connected by a universal joint 26 to a vertical shaft 27. The shaft 27 is journaled in a bearing 28 supported by a suitable frame 29 which is fastened to the top of the casing 25. The lower endof-the shaft 27 is provided with a bevel gear 30 meshing with a bevel pinion 31 on a jack shaft 32, The jack shaft 32 is journaled in bearings 32 carried by the frame 29. The rear end of the jack shaft 32 is provided with a worm gear 33 meshing with a worm 34 on a worm shaft 35 which is provided on its upper end with a worm gear 36 meshing with a worm 37 on the shaft 38 of an electric motor 39. The motor 39 is suspended from the top of the casing 25.

From the foregoing it will be clear that operation of the motor 39 will produce comparatively slow rotation of the electrode a and also, when the latch 15 is thrown into the path of movement of the studs 14, will produce rotation of the gears 11 in the direction indicated by the arrow (Z in Figure 6. The gears 11 project through slots 40 in the hub 3 and engage the electrode a so that when the gears 11 operate they produce endwise motion or feed of the positive electrode The various gears are so proportioned relative to the speed of operation of the motor 39 that when uninterrupted feed of the positive electrode is desired such feed is at a rate of speed corresponding as nearly as possible to the speed at which the positive electrode is consumed, so that the burning tip of the positive electrode will be maintained as nearly as possible at a uniform distance from the lens 1. Of course, it is not always possible to provide an uninterrupted feed, no matter how uniform the feed motion may be, and maintain the burning tip of the positive electrode in absolutely the same plane, and, therefore, I preferably interrupt the uniform feed motionfrom time to time in accordance with the change in diameter of the tip of the positive electrode, and such means will be described hereinafter.

The front plate 6 is provided with radial brush holders 160 carrying brushes 161 which are held with their inner concave faces 162 in contact with the periphery of plane is within a comparatively short distance from the crater end of the positive electrode when the lamp is in operation.

The construction for advancement and retraction of the negative electrode 5 will now be described. The jack shaft 32 is provided at it forward end with a bevel pinion 41 adapted to engage either one of a pair of bevel gears 42, 43, according as one or the other is moved into mesh with the pinion 41. The gears 42, 43 are fast on a shifting memloer 44 which slides longitudinally on a bushing 45. The bushing 45 is mounted on a shaft 46 and said bushing, gears 42, 43, and shifting member 44 are held against relative rotation with the shaft 46 by a pin 47, or equivalent, projecting transversely through the shaft 46, the outer end of said pin engaging longitudinal slots 48 in the hub of the gear 43 so as to permit said gear to shift longitudinally relative to the bushing 45. I

The shaft 46 is journaled in bearings 49, 50 supported by the frame 29 and the upper end of said shaft is provided with a bevel gear 51 which meshes with a bevel gear 52 shiftably mounted on a shaft 53. The gear 52 drives the shaft 53 through a pin 54 in the gear 52, said pin engaging a slot'55 extending longitudinally in the shaft 53. Thus the shaft 53 can be moved endwise without disturbing the driving connection between it and the shaft 46.

which, in turn, is pivoted at 61 to the up-v per end of a core or armature 62 adapted to be pulled downwardly by an arc-establishing coil 63. Such coils are in common use for strikingthe are and their operation is well understood in this art. Retraction of the core 62 is effected by a coil spring 63' fastened at one end to the arm 57 and at its opposite end to the frame 29. The shaft 53 is journaled in bearings 64, 65Imounted on the standard 5 and is provided with a worm 66. Extending parallel with and on opposite sides of the shaft 53 are guide rods 67 slot 7O communicating with. the opening 69,

and extending through said slot and normally engaging the worm 66 is a toothed member 71 pro ecting from an arm 72 which is pivoted at 73 to the carriage 68. Engaging the arm 72 is a coil spring 74 tending to yieldingly hold the toothed member 71 in engagement with i-the worm 66. The spring 74 is mounted in a yoke 75 projecting from the-carriage 68 at right angles to the axis of the spring. It is clear that, when the toothed member 71 is in engagement with the worm 66, turning of the shaft 53 will cause translation of the carriage 68. The carriage 68 carries a standard 76, and fastened to one face of said standard by screws 77 is one section of a split sleeve 78 which constitutes the negative electrode holder, the electrode 5 being clamped between the sleeve sections. The free sleeve section is yieldingly held toward the other sleeve section by endless coil springs 79 mounted in annular grooves 80 in the periphery of the sleeve, the bore of said sleeve being of slightly less diameter than the negative electrode so that the electrode will be securely clamped to the standard 76.

From the foregoing it will be clear that energization of the coil 63 will retract the negative electrode from the positive electrode, and it is also clear that according as the gear 42 or 43 engages the pinion 41 operation of the motor 39 will move the negative electrode away from or toward the positive electrode.

The means for operating the shifting member 44 to advance or retract the negative elec-.

trode will now be described The shifting member 44 is provided with an annular groove 81 engaged by a shifting fork 82 which projects from a shaft 83 reciprocative- 1y mounted in bearings 84 provided on the frame 29. The upper end of the shaft 83 is fastened by nuts 85, 86 to an arm 87 pivoted at one end in a lever 88 which is fulcrumed at 89 on the frame29. The lever 88 is provided at its opposite ends with armatures 90, 91, actuated, respectively, by electro- magnets 92, 93, positioned above the levelof the armatures and normally spaced therefrom when the gears 42, 43 are both disengaged from the gear 41. From the foregoing it is clear that energization of the electro-magnet 92 will throw the gear 42 in'mesh with the gear 41 and that energization of the electro-magnet 93 will throw the gear-43 into mesh with the gear 41, thus to effect the endwise movement of the negative electrode as hereinbefore described. Thelever 88 is normally held in neutral position, that is with both gears 42,

43 disengaged from the gear 41, By coil springs 94 fastened at one end to the armatures 90, 91,v respectively, and at their opposite ends to the bearing 49.

Mention has. been heretofore made of means which I have provided 'for interrupting the feed of the positive electrode from time to time, if the positive electrode be fed uniformly at a higher rate of speed than the rate of burning of said electrode.- When these means are employed, it is preferable that the driiging, connections between the motor and the gears 11 or the motor speed be such as to cause a much faster advancement of the positive electrode than the rate at which said electrode is consumed, so that when the positive electrode is burned away a predetermined amount at its tip, such advancement of the positive electrode will very quickly compensate for the burning thereof. In actual operation, the positive electrode becomes tapered at its burning end and this taper is ordinarily called penciling and is indicated at c in Figure 2. The penciling extends from the tip to a protecting plate indicated at 95, the positive elect-rode passing through an orifice 96 provided in said plate.

Engaging the electrode a in front of the plate 95 is a roller 97 rotatably mounted on one end of an arm 98 which is pivoted at 99 to the plate 95. The roller end of the arm 98 is positioned in front of the plate 95 and said arm is bent and passes through a slot 100 in the plate 95 so that a portion of the arm 98 extends rearwardly of said plate. This rear end of the arm 98 is provided with an electric contact 101 adapted, when the roller moves toward the axis of the electrode, to engage a stationary electric contact 102 mounted in an electric insulating block 103 which is fastened to the rear face of the plate 95. The contacts 101 and 102 are normally held toward each other and the roller 97 pressed against the periphery of the positive electrode by the action of a coil spring 104 which is fastened at oneend to the rear portion of the arm 98 and at its other end to the insulating block 103.

Adapted to be operated by closing of an electric circuit through the electric contacts 101, 102, are means operating to hold the gear 12 against rotation so that the electrode a will be fed by operation of the motor 39, even though the latch 15 be thrown out of the path of travel of the studs 14, said means being inoperative to hold the gear 12 against turning when the contacts 101, 102 are separated and rotation of the gear 12 by planetary movement of the gears 11 preventing rotation of the gears 11 around their own axes so that no feed of the positive electrode occurs when the contacts 101, 102 are separated. These gear-holding means are constructed as follows: Any one of the studs 14 is adapted to come into engagement with a detent 105 passing through an opening 106 in the standard 5. The detent 105 is pivoted at 107 to a lever 108 which, in turn, is pivoted at 109 to the standard '5. .The arm 108 is yieldingly held with the detent 105 normally out of the path of travel of the studs 14 by a coil spring 110 fastened at one end to the lever'108 and at its opposite end to a bracket 111 projecting from the standard 5. The lever 108 is provided with an armature 112 adapted to be attracted by an electro-magnet 113 to move the lever 108 against the pull of the spring 110 so as to throw the detent 105 into the path of travel of the studs 14 when the electro-magnet is energized. The electro-magnet 113 is mounted on the bracket 111. When the detent'105 is moved out of position to stop rotation of the gear 12, oper'- ation of the motor 39 will fail to feed the positive electrode, though said positive electrode will continue to be rotated. Cf course, when it is desired to automatically interrupt the uniform feed movement of the positive electrode a, the latch 15 will be retracted'so as to make it inoperative to stop rotation of the gear 12, in order that holding of the gear 12 against rotation can only be effected by the detent 105 when said detent has been actuated by energization of the electro-magnet 113, as above described.

Since the electric current is passed to the positive electrode through the bushing 3 and bevel gear 17, I provide an electric contact or brush 114 to engage the rear face of the gear 17, said contact being provided with an orifice 115 through which the positive elec trode extends. The contact 114 forms one end of an angular arm 116 which is pivoted at .117 to the standard 5. The contact 114 is yieldingly held against the gear 17 by a coil spring 118, fastened at one end to the arm 116 and at its opposite end to the standard 5.

The contact 114 may be supplied with electric current through a terminal 119 which is fastened by screws 120 to said contact.

The'electrical connections for the mechanisms hcreinbefore described, clearly'shown in Figure 10, are as follows: The negative current supply main 121 connects with a resistance 122 which supplies current to the negative electrode 6 through a wire 167 connected with the member 76 and said wire 167 is connected by a wire 123 to one end of the coil of the electro-magnet 113, the other end of said coil being connected by a wire 124 to the contact 102. The contact 101 is grounded as indicated at 125. The negative current wire 167 is connected on one side of the resistance 122 by a wire 126 to one end of the arc-establishing coil 63 and the other end of said coil is connected by a wire 127 to the main 121 on the other side of the resistance 122.

The line carrying the positive current is indicated at 128 and electric current is furnished to the positive electrode through the terminal 119. In the diagram the wires 128 and 167 are shown connected to the electrodes a,

I'll

The relay 136 is provided with two electroma ets 137, 138 arranged in opposition to eac other on opposite sides of an armature or a pair of armatures 139, 139' so that the electro-magnetic fields produced "by the electromagnets will exert their pull in opposite directions on the armature or armatures. The armatures 139, 139 are mounted on opposite sides of an arm 139" which thus operatively connects said armatures. thus constitute, in effect, a single armature and it is obvious that the spirit of the invention will be conformed to by the alternative constructions. The arm 139" is interposed between the contacts 134, 135 so as to engage either of them according as the arm is moved to one side or the other. The strengths of the electro-magnets137, 138 are proportioned relative to the distance at which the electro-magnets are s aced from the armatures so that the pull 0 said electro-magnets on the armatures will be equal for a predetermined difference of voltage of the electric current in the electro- magnets 137, 138 for a reason that will appear more clearly hereinafter.

One end of each of the coils of the electromagnets' 137, 138 is connected by a common wire 140 to the wire 167. The other end of the coil of the electro-magnet 137 is connected by a wire 141 with the main 121, the resistance 122 being connected in between the wires 140 and 141, so that the electro-magnet 137 is connected across said resistance. The other end of the electro-magnet 138 is connected by a wire 142 to the main 128. The arm 139" receives the positive current through a wire 143, which, in this instance, is connected to the wire 142.

Now referring more particularly to Figures 13 to 16, inclusive, showing the balanced relay 136, the contacts 134, 135 are seen to be adjustably screw-threaded through an insulation block 144 which is supported by a standard 145 of-a U-shape frame 146 that is fastened to and insulated from a base 147. The standard 145 is provided with a horizontally-extending T-shape bracket 148 having spaced downwardly-extending ears 149 carrying tension-adjusting screws 150 to which are connected the outer ends of coil springs 151 that have their inner ends connected with an upwardly-extending finger 152 of the arm 139". The tension of the springs 151 is adjusted to normally hold thearm 139" substantially mid-way between the adjacent faces of the contacts 134, 135 when the electro-magnets137, 138 are not energized. The

' arm 139" projects from a vertical pivot 153 which is journaled at its opposite ends in bearings 154 and 155, the bearing 154 being at the upper end of a standard 156 of the frame 146, and the bearing 155 being at the lower portion of the said frame. The outer ends of The armatures" first insuflicient to cause engagement of the burning back of the positive electrode, there-- by tapering the tip of said electrode sufiiciently to permit the contacts 101, 102 to close the electric circuit through the electro-magnet 113, said electro-magnet will operate to push the detent into the path of travel of the studs 14, thus stopping rotation of the gear 12. As soon as this occurs planetary rotation of the gears 11 will rotate said gears about their axes and said gears, being in engagement with the positive electrode, will feed said positive electrode. This feed movement is relatively fast so that the tip of the positive electrode is very quickly positioned the same distance from the condenser lens 1 as when the lamp was started into operation. The feeding forward of the positive electrode in this wise actuates the arm 98 to open the contacts 101, 102 so that the electro-magnet 113 will no longer hold the detent 105 in the path of travel of the studs 14 and the spring operates to retract said detent, thus permitthus increasing the length of the arc and, consequently, increasing the voltage across the are. This increase of voltage across the arc produces increased voltage ofthe current in the electro-magnet 138, and produces lower the electro- magnets 137, 138 are fastened t /voltage of the current in the electro-magnet standards 157 which are connected byka trans- 137 because of the drop in voltage of the re- 8 3 sistance 122. This change of voltage in the electro- magnets 138, 137 produces a stronger magnetic field adjacent the armature 139' than adjacent the armature 139. The armature 139 is, therefore, drawn against the contact 135, thus closing the circuit through the electro-magnet 93, which thereupon actuates the armature 91 to cause shifting of the gear 43 into mesh with the gear 41, whereupon the motor 39 turns the shaft 53 counter-clockwise, looking at the rear end of the said shaft, so as to feed the carbon holder 78 and its electrode 7) toward the electrode a.

If the arc should become shorter than the predetermined length, thus decreasing the voltage across the are, the voltage in the electro-magnet 137 will rise and that in the electro-magnet 138 will lower, thus producing an unbalanced electro-mag'netic field. in this case, the stronger field being adjacent the armature 139, said armature will be drawn against the contact 134, thus energizing the electro-magnet 92 which thereupon functions to shift the gear 42 into mesh with the gear 11, thereby producing rotation of the shaft 53 in the opposite direction to that produced when the length of the are increases. This causes movement of the electrode holder 78 away from the electrode a to increase the air gap between the electrodes and thus increase the voltage across the arc to that predetermined for operation of the lamp.

It will be clear from the foregoing that I have provided mechanism operating to automatically feed the electrode a at an uninterrupted uniform speed corresponding substantially to the rate of consumption of said electrode, and that I have also provided automatic means to feed the electrode a at intervals determined by actual consumption of said electrode, irrespective of the increase or diminution in the length of the are, so as to maintain its tip as nearly as possible in a plane lying at a predetermined distance from the condenser lens 1. a The means for thus feeding the electrode a are governed by the change in diameter of the peneiling portion 0 of said electrode.

It is also clear that deviation. in the spacing of the electrodes from each other is utilized to produce unbalancing of the magnetic pull of two elect-ro-magnetic fields, one field being created by the potential difference across the arc and both fields being created bythe potential difference across the line.

Referring to the electrical connections of the electro- magnetcoils 137, 138, it may be observed that said coils are connected in series across the mains andthatf the coil 138 is shunted across the arc. Assuming in the operation of the lamp a normal voltage across the arc of fifty-two and fifty-eight volts across the rheostat, the coil 137 will be wound with fifty-eight turnsof wire to every fifty-two turns irithe coil 138. Since the two coils are in series, the same current flows through both and the coil 137 has more ampere turns than the coil 138 and, therefore, a greater magnetic pull. Because of this the core of the coil 138 is positioned a greater distance from the armature 139 than is the core of the coil 137 from the armature 139. These distances may be determined by connecting the coils across the mains and temporarily disconnecting the junction wire. \Vhen the distances are correct, both coils have an equal pull on their associated armatures and no movement of the arm 139" will take place. If new the voltage across the coils 137, 138 be measured, it will be found to be fifty-eight and fifty-two, respectively, with the voltage across the mains at one hundred and ten. If now the junction wire be connected there will be no movement of the arm 139 so long as the voltage across the arc is fifty-two. When the voltage across the are rises or falls, the differential magnetic'pull will cause operation of the arm 139" as hereinbefore described. Thus there is normally a magnetic balance when the voltage across the are is equal to the drop across the coil 138, and any other voltage across the arc will upset the balance and cause a movement of the armature 139 toward or from the coil 138, depending upon whether the arc voltage rises above or falls below the predetermined ratio of 52:110.

Advantages of the invention, not hereinbefore alluded to, are as follows: The lamp is economical to use. The length of the positive electrodes in general use is twelve inches. By-

placing the brushes and feed rollers in substantially the .same plane and quite close to the crater tip of the electrode, it is possible to use all but approximately two inches of the electrode. without the use of an adapter, thereby obtaining an efiiciency of 83%70 as against a probable efficiency of or with the old lamps now in use. The low carbon loss in this lamp results without the least injury to the mechanism.

Another advantage is simplicity. In this lamp there are but four moving parts to the positive electrode holder, as compared with nine or ten to the holders now in use. It is obvious that the fewer the parts required for satisfactory operation the more reliable the lamp will be in use and the lower the cost of production of the lamp.

The lamp is dependable in operation, one reason being because of the provision of the anti-friction bearing. The use of such hearing insures against a frozen bearing, which results from the use of the ordinary bearing because of the extremely hightempenature. The spiral gearing provided for feeding of the positive electrode is self-cleaning, due to the fact that the spiral hoopgear has a brushing action upon the electrode feeding gears. Thus no grit or dirt can so clog the gearing as to impede feed of the positive electrode.

By reason of the system of springs connecting the ends of the gear shafts 8 to one another, an equalizing effect is produced so that all of the gears 11 must exert the same pressure upon the positive electrode. This makes it impossible for the gears 11 to rotate about their axes without imparting motion to the positive electrode.

With lamps of prior construction now in use,itis not possible to employ positive electrodes varying in diametermore than a slight amount, approximately one-thirty-second of an inch. Electrodes furnished by the manufacturers often vary more than one-thirtysecond of an inch in diameter, and when this is the case it is necessary to discard such electrodes, which besides being wasteful is the cause of expensive delays. Such delays are particularly annoying and expensive in the motion picture industry, in which my'lamp is especially useful for photographing purposes. Because of the provision of a spiral gear having several turns, considerable lati: tude of movement of the gears 11 toward and from the positive electrode is possible, so as to automatically accommodate the gears l1 to positive electrodes varying considerably in diameter from one another.

The lamp is easy to operate since, when a fresh positiveelectrode is to be inserted, all that is necessary is to push it into place, either from the front or rear. This may done without fear of damaging the gears 11 or brushes, no matter how carelessly it may be done.

Another advantage is accessibility for mak ing repairs. .The simplicity and ruggedness .old, the substitution may be effected without of construction practically preclude breaking of'the lamp, but in event of it becoming necessary to substitute new parts in place of the the removalofany part excepting that which is to be replaced, thereby effecting asavmg of time in repairing the lamp, and this, 1n

turn, minimizes the time necessary for the lamp to remain out of commission.

The are voltage is very sensitive to change in length of the air gap between the electrodes, and as the feedmotion of the positive electrode is very steady I can, therefore, control the length of are more accurately than has heretofore been'possible, this being due to the functioning of the balanced relay 136.

-- I claim: 1. In an arc lamp, the combination of an electrode holder; a positive electrode shiftably mountedin said holder; a negative electrode opposed to the positive electrode; and

means to automatically feed the positive elec-- trode at a uniform speed but slightly higher.

than-that of the burning away of said posi tive electrode and to interrupt the feeding at intervals to prevent advancing the tip of the positive electrode bay nd a predetermined plane, said means comprising a spiral gear and adapted to rotate therewith about the axis of said holder, a spur gear resiliently supported upon the electrode holder, said spur gear being adapted to revolve about the axis of said electrode holder, to engage said spiral gear so as to be rotated about its axis when revolving in a planetary movement, about the axis of said spiral gear, and means for holding said spiral gear stationary.

2. In an arc lamp, the combination of: an electrode holder; a positive electrode shiftably mounted in said holder; a negative electrode opposed to the positive electrode; means to rotate the positive electrode; and means operative at will and'cooperating with the electrode-rotating means to effect automatically uniform feeding of the positive electrode or to automatically interrupt the feed of said positive electrode, said means comprising a spiral gear frictionally mounted on said electrode holder and adapted to rotate therewith about the axis of said holder, a spur gear resiliently supported upon the electrode holder, said spur gear being adapted to revolve about the axis of said electrode holder, to engage said spiral gear so as to be rotated about its axis when revolving in a planetary movement about the axis of said spiral gear, a projection on said spiral gear and means for either manually or automaticallyintercepting said projection to inhibit rotation of said spiral gear.

3. In an arc lamp, the combination of: an electrode holder; an electrode shiftably mounted in said holder; a flat spiral gear frictionally mounted on saidelectrode holder and adapted to rotate therewith about the axis of said holder; a spur gear resiliently supported upon the electrode holder, said spur gear being adapted to revolve about the axis of said electrode holder, to engage said spiral gear so as to be rotated about its own axis when rotated around the axis of the spiral gear and to resiliently press upon said electrode; and means for holding said spiral gear stationary.

4. In an arc lamp, the combination: of: an electrode holder; an electrode shiftably mounted in said holder; a fiat spiral gear frictionally mounted on said electrode holder and adapted to rotate therewith about the 5.. In an arclamp, the combination of :an

electrode holder; an electrode shiftably mounted in saidholder; a flat spiral gear frictionally mounted on said electrode holder gear so as to be rotated about its own axis when revolving in a planetary movement about the axis of said spiral gear, and to resiliently press upon said electrode and means set into operation by burning away of the electrode for holding said spiral gear stationary.

6. In an arc lamp, the combination of: a shiftably mounted electrode; means for shifting said electrode; a member yieldably engaging the periphery of the electrode near the crater endthereof; and means operative by movement of said member toward the axis of I said electrode to cause said electrode-shifting means to shift said electrode, and by movement of said member away from the axis of said electrode to cause said electrode-shifting means to rest.

7. In an arc lamp, the combination of: a shiftably mounted electrode; means for shifting the electrode, said means including revolving enmeshed gears relatively stationary when said shifting means are inoperative; a member yieldably engaging the periphery of said electrode near the crater end thereof; and means operative by movement of said member toward the axis of said electrode'to cause relative movement of said gears so that said electrode will be shifted.

8. In an arc lamp, the combination of: an electrode holder; an' electrode shiftably mounted in said holder; and mechanism for I converting a rotary motion of said holder .into a linear motion for feeding said electrode, said mechanism including a spiral gear frictionally mounted on said electrode holder and adapted to rotate therewith about the axis of said holder, a spur gear resiliently supported upon the electrode holder and engaging said spiral gear so as to rotate upon its own axis when revolved in a planetary movement about the axis of the spiral gear, said spur gear resiliently engaging the periphery of said electrode, and means for producing a relative movement between the said gears so as to rotate the said spur gear.

9. In an arc lamp, the combination of: an electrode holder; and electrode shiftably mounted in said holder; and mechanism for converting a rotary motion of said holder into a linear motion for feeding said electrode, said mechanism including a spiral gear frictionally mounted on said electrode holder and adapted to rotate therewith about the axis of said holder, a spur ear resiliently supported upon the electro e holder and engagmg said spiral gear soas to rotate upon its own axis when revolved in a planetary movement about the axis of the spiral gear, said spur gear resiliently engaging the periphery of said electrode, and means for retarding the rotation of said spiral gear thereby causing said spur gear to revolve.

10. In an arc lamp, the combination of: an electrode holder; a positive electrode shiftably mounted in said holder; a negative electrode opposed to the positive electrode; a spiral gear frictionally mounted on said electrode holder and adapted to rotate therewith about the axis of said holder; and a spur gear resiliently supported upon the electrode holder and having peripheral frictional engagement with the positive electrode for feeding same when the spur gear is rotated relative to said electrode, said spur gear being adapted to revolve about the axis of said electrode holder and to engage said spiral gear so as to be rotated about its axis for advancing said positive electrode when revolving in a planetary movement about the axis of said spiral gear.

11. In an arc lamp, the combination of: an electrode holder; a positive electrode shiftably mounted in said holder; a negative elec trode opposed to the positive electrode; a spiral gear-frictionally mounted on said electrode holder and adapted to rotate therewith about the axis of said holder; a spur gear resiliently supported upon the electrode holdor and having peripheral frictional engagement with the positive electrode for feeding same when the spur gear is rotated relative to said electrode, said spur gear being adapted to revolve about the axis of said electrode holder and to engage said spiral gear so as to be rotated about its axis for advancing said positive electrode when revolving in a planetary movement about the axis of said spiral gear; and means for holding said splral gear stationary'for causing said planetary movement.

12. In an arc lamp, the combination of: an electrode holder; a positive electrode shiftably mounted in said holder; a negative electrode opposed to the positive electrode; a spiral gear frictionally mounted on said electrode holder and adapted to rotate therewith about the axis of said holder; a spur gear resiliently supported upon the electrode holder and having peripheral frictional engagement with the positive electrode for feeding same when the spur gear is rotated relative to said electrode, said spur gear being adapted to revolve about the axis of said electrode holder and to engage said spiral gear so as to be rotated about its axis for advancing said positive electrode when revolving in a planetary movement about the axis of said spiral gear and means for retarding rotation of sald spiral gear for causing said planetary movement.

Signed at Los Angeles, California, this 26th day of July 1921.

CLARENCE S. ASHCRAFT.

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