US2609519A - Arc lamp or the like - Google Patents

Description

Sept. 2, 1952 R. c. BEITZ 2,609,519

ARC LAMP OR THE LIKE Filed July 21, 1950 I NVENTOR E/HHED C. BE/TZ Patented Sept. 2, 1952 ARC LAMP OR THE LIKE Richard C. Beitz, Amherst, N. Y., assignor to American Optical Company,

Southbridge,

Mass., a voluntary association of Massachusetts Application July 21, 1950, Serial No. 175,058

This invention relates to are lamps, welding apparatus and the like wherein one or more movable electrodes or the like are employed, and more particularly to electrical and mechanical means for automatically moving such electrode or electrodes for automatically effecting an arc and for adjusting the arc to a proper predetermined size when the apparatus is placed in operation, as well as for automatically advancing said electrode or electrodes thereafter toward the are when required for maintaining said are at a substantially constant size as the electrode or electrodes are consumed during use.

While the invention is especially useful in arc lamps which are to be used with photomicrographic apparatus wherein a substantially constant high intensity light source is needed and wherein freedom from vibration during photographing and such, particularly atvextremely high magnifications, is essential, it nevertheless has general utility for controlling the size of arc in projectors, welding apparatus, electric arc furnaces and the like. Accordingly, hereinafter when the words electrode or electrodes are used, it should be kept in mind that they are intended to apply to the electrically conductive arc sustaining members or materials ordinarily encountered in such apparatus. The apparatus of the present invention is of such construction and arrangement that it may be, by the mere pressing of a switch, alternatively used on A. C. or D. C. current. Also the operating mechanism of the present invention is of such high sensitivity that when the same is being used in an arc lamp, no appreciable visible change in intensity of the arc will be noticeable during ordinary use thereof.

' It is, accordingly, an object of the present invention to provide in an arc lamp or like apparatus efiicient, highly sensitive and inexpensive means for gripping and guiding an electrode or a pair of electrodes and for automatically moving the same so as to establish an are, so as to immediately thereafter automatically adjust the arc to proper predetermined size and so as to maintain the are substantially constant during continued use thereof.

It is an additional object of the invention to provide in an arc lamp or like apparatus automatically operable means of the type described which may be readily operated on alternating or direct current, as desired, while still retaining the high degree of sensitivity desired.

" It is, also, an object of the invention to provide in apparatus of the character described, readily adjustable means for altering the prede- 6 Claims. (01. 314-71) termined size of are which is to be automatically maintained during operation of the apparatus.

Other objects and advantages of the invention will become apparent from the detailed description which follows when taken in conjunction with the accompanying drawing in which:

The single diagrammatic figure thereof indicates parts of an arc lamp or the like and the electrical and mechanical means for operating same.

Referring to the drawing in detail, there is shown at l2 and M, respectively, a pair of electrodes or carbons which may serve to establish and maintain an arc of suitable size at a point is in an arc lamp or the like. Mechanism for advancing these electrodes toward each other is diagrammatically shown herein and comprises suitable means for attaching the electrodes to a pair of endless chains or belts l5 and H, which are caused to move in opposite directions for advancing the electrodes. The belts I5 and I1 are actuated by means of a pair of shafts l8 and l 9 geared together by means of gears 20 and 22. In the drawing, electrode I4 is shown as somewhat thicker in diameter than electrode l2 and gear 22 is of greater size than gear 20 for the purpose of obtaining the proper rate of advance of the electrodes as they are consumed, While the apparatus will be first described for use with D. C. current, it should be noted that in cases where" an A. C. current is to be employed for operation of the arc, electrodes of different sizes might be employed instead of the ones shown. Gear 22 is actuated by shaft l9 which is in turn driven by reduction gear means 24 driven by a motor 26. In a preferred construction, means 24 and motor 26 may be suitably incorporatedin a unitary electric motor housing with gear means 24 having a speed reduction ratio in the neighborhood of to 1. Whileendless belts have been shown in the drawing to move the electrodes, it will be obvious that grooved pressure rollers could be arranged, as is well known in the art, to move the electrodes l2andl4.

The electrode [2 is connected by suitable means to a main electrical conductor 28 while electrode I4 is connected to a terminal of a three-wayseparable connector 30 and then at 32 is connected to one end of a heavy-duty ballast resistor 3.4. The opposite end 35 of the ballast resistor is in turn connected to another terminal of separable connector 30 and then to a second main electrical conductor 36, so that external electric current may be supplied to the apparatus by means of conductors 28 and 36. The reason for using a armature 38 and a pair of field coils t9 and 4-2,

with one terminal of the armature and of each field coil connected together ata common. point. Such a motor is often referred'to as a, split-field series type motor since the twofield coils thereof act in opposition to each other in accordance with the current flowing therethrough. and,

through the armature and the direction of operation of the motor accordingly depends upon which field coil magnetic fiux dominates. In the present invention, the opposite freeterminal of the field coil 40 is connected to a resistor 44, of suitable electrical characteristics, which in turn is connected to main conductor 28. The opposite free terminal of the other field coil '42 is in turn connected to a, suitable fixed resistor 46 of suitable electrical characteristics which in turn is connected to an adjustable resistor 48 and this resistor. in turn is connected to main conductor 36. The opposite free terminal of the armature 38 is connected through the separable connector 30 preferably to an intermediate point 50 on ballast resistor 34 adjacent the end 32 of the resistor to which electrode it is connected or even at this end as determined by the operative characteristics of the control circuit and the mechanical characteristics of the arc lamp as will be presently described.

It will benoted that the electrical system just described is in effect a Wheatstone bridge circuit in which two arms of the bridge extending from point 56 common with conductor 28 through the electrodes [2 and M and, ballast resistor 34 to point 58 common with conductor 36 constitute a primary circuit 54,,with the point 50 common to these two arms. The other two arms of this Wheatstone bridge are formed by field coil 45 and resistor 44 and by the field coil 42 and resistors 46 and 48, respectively, and together constitute. a secondary circuit 69. The common point previously referred to and to which one armature terminal is connected is. indicated at 62, while the opposite armatureterminal thereof is connected to point 50, and preferably intermediate the armature and point 62 a normallyclosed precision snap-action switch 63 or thelike is connected.

The Wheatstone bridge control circuit just described operates in the following manner. Assuming that the lamp is to be operated on D. C.

current and that the electrodes are in spaced.

relation at the time it is to be placed in operation by connecting the conductors to this "source of power, the electric current being supplied will fiowfrom point 58 mainly through ballast resistor 34 to point 50 and then through armature 38 and switch 63 to point 62. Only a negligible amount of current will pass through resistors 46 and 48 and field coil 42 to point.62 due to the high impedance and resistance thereof as compared with that through the armature and ballast. Current from point 62 will pass through field coil 40 and resistor 44 to point 56. When such flow of current occurs motor 26 will be energized to operate the drive mechanism for the electrodes in a forwardly direction thereby advancing the electrodes toward point i6 and this advance will be rapid since the current fiow through the armature at this time will be comparatively large. This forward travel will continue until contact between the electrodes is established.

Immediately thereafter the resistance through the electrode containing arm of the bridge will drop, thereby allowing nearly all or the greater part of the main line voltage to be developed ,across the part of the ballast between points and 58. Accordingly, only negligible current will flow-at suchxtime through the arm of the bridge containing field coil because of the high impedence' and resistance therein. Thus coil 52 and armature 38 will be subjected to the main line voltage, thereby energizing motor 26 to operate in the opposite direction. This will cause the electrodes I2 and l l to move. apart.

until the resistance in the electrode containing arm of the bridge including the resistance across, the are at It builds up to such a point that the bridge circuit is substantially in balance, with the potentials at points 58 and 62 substantially.

equal. Of course, mechanical friction and such will always be present and will tend. to prevent the motor from retracting the electrodes all the way to provide a perfectly balanced bridge. Consequently, the armature will remain. stationary while the electrodes burn back to. and sufiiciently beyond this balanced condition so as to increase the voltage drop in this arm of the bridge relative to that in the arm between points Y and 58 and thus produce an out-of-balance condition of sufficient magnitude to cause field coil til to be energized more strongly than field coil 42. This condition will cause armature 38 to rotate in a forward direction at a very low rate of speed, particularly when a reduction gear unit with aratio of approximately to 1 is provided in the driving system for shaft l9, and in a more or less continuous manner.

The forward rotation of the armature. to ad vance the electrodes or carbons will not always be of a uniformrate; since certain conditions, such ashard andsoft spots in the carbons, may cause the carbons at times to burn away at varying rates. However, when these variations occur, the speed of the motor will change in such a way as to maintain the current through the ballast and the electrodes at a substantially constant value, which is synonymous with keeping the ratio of the voltage drops across the ballast: resistor and across thecarbons at a substantially constant value. 7 v

It will be noted that the armature is connected at the intermediate point 59 in the ballast resistor instead of being connected at the end 32.

The purpose for thisis to provide at all times,

a certain small amount of resistance in the arm of the bridge containing the electrodes and, between points Ell-and 56, thereby giving greater driving torque in the forward direction of rotation of the motor than in the reverse direction. Also frictionalresistance in the operating parts of the driving mechanism and such. willafterthe. arm is; struclr and before the motor becomes operative to move the electrodes forwardl'y, and thereafter the motor will always tend to drive in a forwardly direction; thus preventing hunting which might otherwise result when a more evenly balanced bridge condition exists.

The ratio of the resistance in the secondary circuit 60 as compared to the primary circuit 54 may be varied slightly by adjustment of the relatively light weight resistor 48 and this control may be used to vary within desired limits the normal spacing which is to be maintained at gap it during normal operation of the apparatus. In fact resistance 48 could be placed in either arm of the secondary circuit 60 and could be readily arranged to provide the control desired.

When the lamp is to be used with alternating current, electrodes of equal diameter may be substituted in place of electrodes 12. and [4. The only other change needed for operation on A. C. current then would be either the omission of resistors 44 and 46 from the secondary circuit 60 of the bridge or if desired, and as shown in the drawing, the resistance 14 and 46 could be in effect eliminated by the closing of switches 64 and 66 for short circuiting the resistors. In fact, such might be accomplished, as is obvious, by the mere use of a single double-pole switch controlling both resistances at the same time.

The-normally closed switch 63 in the armature circuit is so positioned that it may be actuated by a cam 68, when the electrode l2 has been substantially consumed, for interrupting the current fiow through the armature 38 and thereby preventing further forward movement of the driving mechanism. For convenience during operation of the lamp, there is provided a normally open switch 16 arranged in series with a pilot light 12 and connected to points 50 and 56, which will be energized when switch is closed and this switch is preferably so positioned relative to cam 68 and switch 63 that shortly prior to the end of the operating stroke of the mechanism a warning signal will be given by the pilot light so the operator may replace the carbons before attempting to use the lamp for any appreciable period of time thereafter. Such has been found to be useful particularly in photomicrographic work requiring exposures of appreciable duration, thus avoiding undesired interruption of the arc during such photographing of specimens and the like. While opposed movable electrodes are shown and described above, it will be understood that, when desired, only one electrode need be movable for utilizing the automatic control means disclosed.

Having described my invention, I claim:

1. In an apparatus of the character described, the combination of a pair of electrodes for establishing and sustaining an arc therebetween, a ballast resistor having one end thereof connected to one of said electrodes, a pair of main conductors, respectively, so as to provide a sectrodes and to the opposite end of said ballast resistor, respectively, so as to place same in series relation in a primary circuit, gripping and guiding means constructed and arranged so as to move at least one of said electrodes toward and away from the other when actuated, driving means including a rotatable electric motor for actuating said gripping and guiding means, said motor having a pair of field coils and an armature with a lead from each connected together at a common point, said field coils being arranged in said motor in opposed relation to each other s0-- as to tend to rotate said'motor in opposite directions when energized, means for connecting the opposite leadsof said field coils to said main conductors connected to the other of said elecondary circuit therebetween, and means for connecting the other lead of said armature to said primary circuit at a point adjacent the connection of said one electrode to said ballast resistor,

2. In an apparatus of the character described, the combination of a pair of electrodes for establishing and sustaining an arc therebetween, a ballast resistor having one end thereof connected to one of said electrodes, a pair of main conductors connected'to the other of said electrodes and to the opposite end of said ballast resistor, respectively, so as to place same in series relation in a primary circuit, gripping and guiding means constructed and arranged so as to move at least one of said electrodes toward and away from the other when actuated, driving means including a rotatable electric motor for actuating said gripping and guiding means, said motor having a pair of field coils and an armature with a lead from each connected together at a common point, said field coils being arranged in said motor in 0D- posed relation to each other so as to tend to rotate said motor in opposite directions when energized, means for connecting the opposite leads of said field coils to said main conductors, respectively, so as to provide a secondary circuit therebetween, and means for connecting the other lead of said armature to said ballast resistor at a point intermediate the ends thereof.

3. In an apparatus of the character described, the combination of a pair of electrodes for establishing and sustaining an arc therebetween, a ballast resistor having one end thereof connectedto one of said electrodes, a pair of main conductors connected to the other of said electrodes and to the opposite end of said ballast resistor, respectively, so as to place same in series relation in'a primary circuit, gripping and guiding means constructed and arranged so as to move at least one of said electrodes toward and away from the other when actuated, driving means including a rotatable electric motor for actuating said gripping and guiding means, said motor having a pair of field coils' and an armature with a lead from each connected together at a common point, said field coils being arranged in said motor in opposed relation to each other so as to tend to rotate said motor in opposite directions when energized, means for connecting the opposite leads of said fieldcoils to said main conductors, respectively, so as to provide a secondary circuit therebetween, said last mentioned means including a readily adjustable resistor in series relation in said secondary circuit for controlling the normal spacing of said electrodes during the operation thereof, and means for connecting the other lead of said armature to said primary circuit at a point adjacent the connection of said one electrode to said ballast resistor.

4. In an apparatus of the character described, the combination of a pair of electrodes for establishing and sustaining an arc therebetween, a ballast resistor having one end thereof connected to one of said electrodes, a pair of main conductors connected to the other of said elec trodes and to the opposite end of said ballast resistor, respectively, so as to place same in series relation in a primary circuit, gripping and guiding means constructed and arranged so as to move at least one of said electrodes toward and away from the other when actuated, driving means including a rotatable electric motor for actuating said gripping and guiding means, said motor having a pair otfield coils and an armature with a lead from each connected together at a common point-said. field coils being arranged in saidv motorin opposedrelation to each other so as to tend to rotate said-motor in opposite directions when energized,,,means' for connecting the opposite leads of said field coils to said main conductors, respectively,,so .asto provide a secondary circuit therebetween, said'last mentioned means including a. readily adjustable esistor in seriesrelation in said secondary circuit for controlling the normal spacing of said electrodes during the operation thereof, and meansfor connecting the other-lead of said armature to said ballast resistor at a point intermedi ate the ends thereof.

5. In apparatus of the character described and adapted to operate selectively upon alternating or direct current, the combination of. a pairof electrodes for establishing and sustaining an arc therebetween, a ballast resistor having one end thereof connected to one of said electrodes, a pair of main conductors, connected to the other of saidelectrodes and to the oppositeendof said ballast-resistor, respectively, so as to place same in series relation in a primary circuit, gripping and guiding means constructed and'ar-ranged'so as to move at least one of said electrodes toward and away from the otherwhen actuated, driving means including; arotatable electric motor for actuating said grippingandguiding means, said motor having a pair of field coilsv andan armature with a lead from each connected together at, a common point, said field coils :being. arranged in said motor in Opposed relation to each other so asto tend: torotate said motor in opposite directions whenenergized, means for connecting thejoppositeleads ofsaid fieldic-oils to said main conductors, respectively, for .operationon direct current, said lastmentioned means including .a resistor of predetermined value .in series relation with each field coil therebyproviding a secondary circuit between .said'conductors which includes said common point, readily operable switch: means connected across each resistor and operable to eliminate thereffect of said resistors inssaid secondary circuit when it is desired to operate said apparatus on alternating current, and: means connecting-the other lead of said armature to said, primary circuit at a point adjacent the conneotionroi said one electrode to said ballast resistor.

6. In apparatus of the character described and adapted to operate selectively upon alternating or direct current, the combination of a pair of electrodes for establishing and sustaining an arc therebetween, a ballast resistor having one end thereof connected to one of said electrodes, a pair of main conductorsconnected to the other of said electrodes and to the opposite end of said ballastresistor, respectivelmso as to place same in series relation in a primary circuit, gripping and'guiding means constructed and arranged so as to move: at least-one of said. electrodes toward and away from the other when actuated, driving means including .a rotatableelectric motor for actuating said: gripping and guiding means, said motor having a pair of field coils and an armature wit-h a lead from each connected together at a common point, said field coils being arranged in said motor in opposed relation to each other so as to tend torotate said mot-or in opposite directions when energized, means for connecting the opposite leads of said field coils to said main conductors, respectively, for operation on direct current, said last mentioned means including a resistor of predetermined value in eries relation with each field coil thereby providing a secondary circuit between said'oond'uctors which includes said common point, readily operable switch means connected across each resistor and operable to eliminate the effect of said resistors in said'secondary circuit when it is desired to operate said apparatus on alternating current, said secondary circuit also including a readily adjustable resistor for controlling the normal spacing of said electrodes during the operation thereof, and means for connecting the other lead of said armature to said primary circuit at a point adjacent theconnection of said one electrode to said ballast resistor.

RICHARD (3. BEITZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS -lumber Name Date 315,564 Sparrow Apr. 14, 1885 1,795,707 Blymyer Mar. 10, 1931 1,897,990 Smyser Feb. 14, 1933 2,057,521 Harding Oct. 13, 1936 2,462,207 Mershon Feb. 22, 1949

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