US2774907A - Arc lamp and control system therefor - Google Patents

Description

Dec. 18, 1956 H. R. BENSON ARC LAMP AND CONTROL SYSTEM THEREFOR i 5 Iwluv kfw/M m fd n e, n V 9 N E m .w m m m .nu nn M .Nq T VH l l I l 1| 7 7. W w 4 M 3 2 f 5 ,6, i 9 @iwf/m4114151 .clp 3 e n ,7 3 m NW2 3 United States Patent" O ARC LAlVIP AND CONTROL SYSTEM THEREFOR Harold R. Benson, Maywood, lll., assigner to nuArc Co., Inc., Chicago, Ill., a corporation of Illinois Application July 6, 1955, Serial No. 520,287

12 Claims. (Cl. 314-77) The present invention relates to an arc lamp and control system therefor, and more particularly, to such a lamp having a simple control system embodying a timing mechanism for periodically adjusting the relative positions of the arc lamp electrodes and hence the arc current owing therethrough.

Arc lamps have heretofore been extensively employed in the graphic arts industry, since they provide a means for producing, in a very efficient manner, a very intense source of illumination. Conventionally, such lamps comprise carbon electrodes associated with a suitable reflector and including means for controlling the feed of the carbon electrodes. It is desirable that such arc lamps produce accurately controlled light so that definite standards for exposure in the graphic arts industry may be maintained. In United States Letters Patent 2,616,059, Benson, granted October 28, 1952, and assigned to the same assignee as the present application, there is disclosed and claimed an arc lamp with control means for providing very accurate control of the light intensity produced, regardless of the voltage of the source and regardless of the nonuniformity of the carbon electrodes employed. It has been found, as is set forth in the above-mentioned Benson patent, that by maintaining the arc current at a constant value, the desired constant light intensity is maintained at all times.

The ar-c lamp and controlling means of the abovementioned Benson patent has gone into extensive commercial use and has proven to be unusually satisfactory. In the arrangement disclosed therein, the arc current is maintained constant at all times. It has been discovered that an arc lamp with a predetermined spacing of electrodes can burn for a short period of time with only minor changes in the magnitude of the arc current due to burning away of the car-bon electrodes. There are numerous applications where a small change in arc current and hence a small change in light intensity is permissible, particularly Where the c'ost of equipment is low. Moreover, there are numerous `applications in the graphic arts industry where it would be desirable to have available an arc lamp and suitable control means which would be relatively inexpensive and yet which would maintain the arc current substantially constant. It has been noted, for example, that if an arc current of thirty amperes is permitted to ow when the electrodes are separated the desired amount, this current will decrease only a relatively few percent during a period of the order of a minute due to burning away of the carbon electrodes.

It would be desirable to provide an inexpensive arc llamp with control means which would be simple and yet which would maintain a substantially constant light intensity for the numerous applications in the graphic arts industry where the user cannot aiford to purchase the accurate control aliorded by the arc lamp of the abovementioned Benson patent.

Accordingly, it is an object of the present invention to provide an improved arc lamp and associated control system having the desirable characteristics discussed above.

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It is another object of the present invention to provide an improved arc lamp ycontrol system for use in the graphic arts industry comprising a simple, inexpensive, and highly dependable apparatus for controlling the light intensity produced by the arc lamp.

It is a further object of the present invention to provide an arc lamp control system employing means for maintaining carbon electrodes of an arc lamp within a predetermined space relationship in order to maintain approximately constant light intensity, and, in addition, to provide means for establishing reignition of the arc upon arc extinguishment.

It is another object of the present invention to provide an arc lamp control system in which a periodically actuatable device successively disposes the electrodes in the identical predetermined space relationship.

A still further object of ythe present invention is to provide an arc lamp control system wherein electrodes which are biased into contacting` engagement are separated to a predetermined extent by suit-able means and periodically this suitable means permits the electrodes to move at high speed into contacting engagement and whereupon they are again separated to the same predetermined extent.

Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specication.

For a better understanding of the present invention, reference may be had to the accompanying drawing in which:

Fig. 1 is a somewhat perspective schematic diagram of an arc lamp and control system embodying the present invention; and

Fig. 2 is a somewhat schematic diagram of a portion of Fig. 1.

Briefly, the present invention comprises an arc lamp control system for controlling the light intensity produced by an arc lamp. The control system includes biasing means associated with the electrode carriages for moving the carbon electrodes into abutting or contacting relationship. In addition, there is associated with the biasing means an electromagnetic means for overcoming the biasing means to separate the electrodes a definite distance. The electromagnetic means by means of a timing means is rst periodically deenergized and then reenergized thereby quickly to permit the electrodes to move into abutting or cont-acting relationship followed by separation to this definite distance. With this arrangement, compensation for the shortening of the electrodes caused by the burning thereof is obtained. Furthermore, there is provided a reignition device associated with the electrode controlled circuit for insuring immediate reignition of the arc upon extinguishment 'thereof for any reason.

Referring now to the drawing, and particularly to Fig. l, there is illustrated an arc lamp control system, designated generally by reference numeral 5, embodying the features of the present invention. This control system -is applicable to any arc lamp in which means are provided to move the electrodes relative to each other to compensate for burning of the electrodes by the are. As illustrated, the arc lamp generally designated at o, comprises a conventional upper electrode or carbon carriage 7 and a similar lower electrode or carbon carriage 8. These carri-ages, like in the arrangement disclosed in prior Benson Patent 2,616,059 mentioned above, are illustrated as being supported by oppositely movable rack members 9 and 10, respectively. These rack membersI drivingly engage opposite sides of a gear 11 so that rota'- tion of gear 11 causes the rack members simultaneously to move in opposite directions along spaced parallel paths. Moreover, such movement of the rack members 9 and 10 causes either relative separation of the carriages '7 and 8 or relative movement toward each other.

In order to support suitable carbons between which the arc is drawn, each of the carriages is provided with clamp means for removably securing suitable carbon electrodes for movement along a common axis, which axis, of course, comprises the longitudinal axis of each electrode. As illustrated, upper carriage 7 includes a carbon clamp 12 for clampingly receiving a carbon electrode 13 while lower carriage 8 is provided with a similar clamp 14 for removably supporting a carbon electrode 15. These electrodes are coaxially disposed for relative separation or movement together along a common axis. Preferably, a suitable reflector 16 is provided to direct the light produced by the arc in a desired manner. It will be appreciated that a suitable support not shown will be provided for the above described parts of arc lamp 6. Also, it should be understood that although with the above described arrangement, both carriages move simultaneously in opposite directions, the arc lamp might include an arrangement wherein one carriage is stationary and the other is movable to produce relative movement between the electrodes.

For the purpose of causing an anc current to ow through carbon electrodes 13 and 15, they are connected into an electric circuit clearly shown in Fig. 1 of the drawing. As there illustrated, a high reactance transformer 17 is provided having a primary Winding 17a and a secondary winding 17h. The primary winding 17a is connected to a suitable source of electric energy indicated at 18 through a switch 19. The secondary winding 17b is connected to electrodes 13 and 15 by means of conductors 21 and 22 respectively. For a purpose to be described hereinafter, a winding 23a of a relay 23 is connected in series with the are .circuit including electrodes 13 and 15 as well as conductors 21 and 22. With the above escribed arrangement, when electrodes 13 and 15 have adjacent ends thereof in electrical contact, a current will ow through the arc circuit whenever switch 19 is closed. lf the electrodes are separated, an arc will 'Je drawn therebetween. This arrangement is substantially lille that disclosed in the above-mentioned Benson Patent 2,616,059.

ln accordance with the present invention, means are provided constantly to urge the electrodes 13 and 15 into the contacting engagement shown in Fig. l ot' the drawing whereby current will flow when switch 19 is clos-ed. To this end, there is provided a spring means illustrated as a torsion spring connected to a shaft 2S drivingly connected to gear 11. Spring means 24 may comprise a clock spring having one end connected to a suitable support such as the arc lamp frame schematically indicated at 26 and the other end connected to shaft 25. in this manner, as clearly shown in Fig. l, the spring 24 will tend to rotate the shaft 25 in a counterclockwise direction, thereby tending to move the racks 9 and 10 in opposite directions to cause electrodes 13 and 14 to move into the abutting relationship shown insuring electrical contact therebetween. The bias of the spring 2-l is sufciently strong to urge the carbon electrodes into electrical negagement even when the electrodes 13 and 1S have been substantially consumed by the arc during operation of the arc lamp 6. A suitable manual control knob 27 may be provided on shaft 25 whereby manual actuation of the rack members 9 and may be obtained.

It will be understood, that when the electrodes 13 and are in electrical contact as shown in Fig. l of the drawing no arc will be drawn even though a current llows through these electrodes and consequently, no light will be produced. It is, therefore, necessary that the electrodes 13 and 15 be disposed in spaced relationship in order to draw an arc therebetween to produce the desired illumination. In accordance with the present invention, there is provided a mechanism which will insure separation of the electrodes 13 and 15 to the same predetermined extent whenever rendered effective, thereby drawing an arc which will insure a predetermined current ow. It will be understood that a constant current llow insures a constant light intensity so by maintaining a constant current ow, a constant light intensity is obtained.

To provide the same electrode separation each time the mechanism for separating the electrodes is actuated, there is employed, as illustrated in the drawing, a solenoid `actuated ratchet means generally indicated at 29, comprising the solenoid 3l), a ratchet wheel 31, and associated interrelated elements. Specifically, the solenoid 30 includes an armature 30a and a winding 301;. The armature 39a is connected to a bar 32 to reciprocate the latter in response to energization and deenergizaticn of the winding 3G11. Suitably mounted on reciprocal bar 32 is a pawl 33 for engaging the teeth ot ratchet wheel 31 which latter is drivingly connected to shaft 25. The ratchet teeth of ratchet wheel 31 are directed so that upon energization of solenoid Eil, the ratchet wheel is rotated in a clockwise direction to separate the carbon electrodes 13 and 15 a definite distance determined by the length of the stroke of solenoid 30. lt will be appreciated that regardless of which tooth of ratchet wheel 31 is engaged by pawl 33 the electrodes 13 and 15 will always be separated to the same extent with each energization of solenoid 30, since the spring 24 will always cause the carbon electrodes to be in contacting engagement as shown, immediately preceding energization of the winding 36]) of solenoi 3l). A suitable spring means such as leaf spring 34 is preferably provided to insure engagement of pawl 33 with ratchet wheel 31. Obviously, solenoid 36 must be capable of overcoming the biasing force ot spring 24 so that upon cnergization thereof the carbon electrodes 13 and 15 are quickly separated to the desired distance. Moreover, it will be appreciated that upon deenergization of soleniod 30, spring 24 will quickly move armature 30a to its deenergized position and carbon electrodes 13 and 15 into contacting engagement.

For the purpose of preventing too rapid a separation of the carbon electrodes 13 and 15, with the possible extinguishment of the arc drawn therebetween upon energization of solenoid 30, a suitable dashpot 36 is provided. As illustrated, dashpot 36 is connected to retard movement of bar 32 and, consequently, retard relative movement of carbon electrodes 13 and 15. It will be understood that any suitable retarding means may be employed and dashpot 36 is shown in the drawing as comprising a cylinder 37 and associated plunger 38. The plunger 38 is connected to reciprocating bar 32 by means indicated as 39. A suitable spring, not shown, will be interposed between the upper side of plunger 3S and the top of cylinder 37, as viewed in Fig. l ot the drawing, in order to bias the pawl .33 to the position shown in Fig. 2. Suitable adjustable needle valve means i0 and 41 or the like may be provided to adjust the effective dashpot action of the dashpot 36 for either direction of movement. Thus, the dashpot will prevent extinguishing the arc drawn by too rapid separation of the electrodes, and will also prevent spring 24 from bringing the electrodes into engagement with such high speed as to damage the carbon electrodes or supporting mechanism. The position of pawl 33 when solenoid 3d is deenergized is best shown in Fig. 2 of the drawing.

From the above description it will be noted that Whenever solenoid 30 is energized the carbon electrodes 13 and 15 are separated to draw an arc therebetween. Since these electrodes are always separated to the same predetermined extent, a predetermined arc current and predetermined light intensity will result immediately upon separation thereof. The arc will burn away the ends of the electrodes between which the arc is drawn, and as the arc gap Iincreases in length, the arc current will decrease and so will the light intensity. If the solenoid 30 is periodically deenergized followed by immediate reenergization, a fairly constant light intensity will be maintained, since upon reenergization the desired electrode separation is always obtained. Accordingly, the winding 30b of solenoid 30 is connected across voltage source 18 in series with switch 19 through conductors 43 and 44, normally closed contacts 45a of a timing switch 45, a conductor 46, contacts 23b of relay 23, and a conductor 47. It will be understood that transformer 17 might be provided with an additional secondary winding to provide a source of voltage for solenoid 36. Also, where two arc lamps are to be energized from a single transformer, obviously transformer 17 may be provided with another winding like 17b for a second lamp. The opening of either contacts 45a of switch 45 or contacts 23b of relay 23 will cause deenergization of solenoid 30. However, the contacts 23b of relay 30 will be closed whenever an arc current flows, whether the electrodes 13 and 15 are together as shown in Fig. 1 of the drawing, or separated.

ln order periodically to open switch contacts 45C with the resultant deenergization of solenoid 30, there is provided `a timing motor 49 connected to drive a cam 54) at a predetermined speed, such as one revolution per minute. Moreover, cam 50 is positioned to actuate switch 45 to open contacts 45a for a brief period once per minute. As illustrated, timing motor 49 is connected across voltage source 18 in series with switch 19. Thus, Whenever switch 19 is closed, timing motor 49 will cyclically open contacts 45a for a brief period during `each cycle. It should be understood that, although it has been found quite satisfactory to open contacts 45a for a brief instant once per minute, the cyclic period might be shorter if more constant light intensity is desired, or in some cases the cyclic period might even be longer.

in View of the detailed description included above, the operation of the arc lamp and control means therefor will be understood by those skilled in the art. It will be appreciated that the timing mechanism described above causes energization of the solenoid 30 for the bulk of the cyclic period, but for an instant during a cycle, such as once per minute, Where the cyclic period is one minute, the solenoid 30 is deenergized for just an instant. Upon deenergization of the solenoid 30, the pawl 33 is moved downwardly out of engagement with the ratchet member 31, thereby permitting the spring 24 to rotate the shaft 25 and the gear 11 in such a manner as to move the electrodes 13 and 15 into contacting engagement for the instant during which the switch 45 is open. Immediately upon energization of the solenoid 36, the pawl 33 is moved into engagement with the ratchet 31, thereby rotating the shaft 25 and the gear 11 in order to separate the electrodes 13 and 15 a predetermined distance to draw an arc of the desired light intensity. It will be understood that electrode carriages 7 and 8, although occupying different initial positions depending upon the length of electrodes 13 and 15, are always moved apart the same .amount upon energization of solenoid 30. The repeated operation of the timing mechanism periodically deenergizing the solenoid 30 causes the electrode carriages 7 and S to move successively closer and closer to one another as the carbon electrodes 13 and 15 are consumed during use. ln this manner, for an instant during each cycle, the electrodes 13 and 15 are brought into abutting relationship, and for the balance of the cycle they are disposed in a predetermined spaced relationship calculated to produce an arc having a substantially constant and desired light intensity. It will be appreciated that the timing mechanism may be designed to actuate the solenoid 3i) and dispose the electrodes in abutting relationship more frequently than once per minute, but in a commercial embodiment employing the present invention, a one-minute cycle was found to produce a variation in light intensity of the order of only 5%, which is acceptable for many applications. Thus, there is provided an exceptionally simple, easily operable, and completely dependable arc lamp control system for maintaining a substantially constant light intensity.

ln the event that the arc created between the electrodes 13 and 15 is unexpectedly extinguished, the relay 23 acts as a reignition device by interrupting at its contacts 23b the energization circuit of winding 30a of solenoid 30 independently of the timer mechanism and regardless of the condition of switch 45. So long as current ows through the electrode circuit, whether or not an arc is drawn, the relay 23 remains energized to close contacts 23b. As shown in Fig. l, the relay 23 has just been energized by increased current iiow caused by movement of the electrodes into contacting engagement but its armature has not yet moved into its energized position in electrical engagement across the contacts 23b.

While there has been illustrated and described a particular embodiment of the present invention, it will be understood that numerous changes and modifications thereof may occur to those skilled in the art. It is intended in the appended claims to cover all those changes and modifications as fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

l. In an arc lamp, the combination of a pair of electrodes mounted for relative movement toward and away from each other, biasing means for continually urging said electrodes into contacting engagement, means for producing a predetermined relative separation of said electrodes against the force of said biasing means to draw an arc of a predetermined length, and timing means for cyclically maintaining said last mentioned means effective for the major portion of the cycle but rendering it ineffective for a short instant during each cycle, thereby periodically adjusting the length of said arc to produce a sub- :stantially constant light intensity.

2. An arc lamp comprising a pair of electrodes between which an arc is adapted `to be drawn, the combination Vof a pair of electrode carriages each capable of supporting lone of said electrodes, means including a gear and rack mechanism for causing simultaneous movement in opposite directions of said carriages, spring means -f'or urging said gear in such a direction to tend to move said electrodes into contacting engagement, a ratchet d-rivingly connected to said gear, solenoid means, .a pawl connected Ito said solenoid means for actuating said ratchet to separate said electrodes a iixed predetermined distance in response to energization of said solenoid means and against :the force of said spring means, ya switch connected in the energization circuit of said solenoid means, and timing means for periodically actuating said switch to the open position to deenergize said solenoid means for a `brief instant during each period whereby said spring means moves said electrodes int-o contacting engagement and subsequent reenergization lof said solenoid means causes separation of said electrodes to said fixed predetermined distance.

3. The arc lamp of claim 1 `wherein said means for producing a predetermined lrela-tive sepa-ration of said electrodes comprises a solenoid operated ratchet mechanism which by Virtue 4of the constant throw 4of the solenoid forming part lof the solenoid actuated ratchet mechanism insures the same separation of the electrodes whenever the solenoid is energized.

4. An arc lamp lcomprising a pair of electrodes between which an `arc is adapted to be drawn, the combination of a pair of electrode carriages each capable of supporting one of said electrodes, means including a gear and rack mechanism for causing simultaneous movement in opposite directions of said carriages, spring means for urging said gear in such la direction to tend to move said electrodes into contacting engagement, a

ratchet drivingly connected to said gear, solenoid means, a pawl connected to said solenoid means for actuating said ratchet to separate said electrodes a fixed predetermined distance in response to energization of said solenoid means and against -the force of said spring means, `a switch connected in the energization circuit of said solenoid means, timing means for periodically actuating said switch to the open position to deenergize said solenoid means for a brief instant during each period whereby said spring means moves ysaid electrodes into contacting engagement and subsequent reenergization of said solenoid means causes separation of said electrodes to said tixed predetermined distance, and d-ashpot means for retardingthe action of said solenoid means.

5. The arc lamp of claim 2 `wherein dashpot means are provided to retard the opera-tion of both said spring means and said solenoid means.

6. An arc lamp control system for controlling the light intensity produced by yan arc, comprising a pair of electrodes, a pair of holders, one for supporting each of said electrodes, means `for moving said holders relative 4to one another, spring biasing means for normally urging the ends of said electrodes between which the Iarc is drawn into contacting engagement, electromagnetic means for producing relative separation of said electrodes to a predetermined distance against the force of said spring biasing means, and a timing apparatus `for normally energizing and for momentarily deenergizing said electromagnetic means in a cyclic manner, the momentary deenergization of said electromagnetic means rendering said biasing means effective momentarily to move said ends of said electrodes into contacting engagement, said timing apparatus thereby cyclically moving said electrodes into contacting engagement and then separating said ends of said electrodes by the same predetermined amount once each cycle, whereby the arc light intensity produced remains fairly constant throughout successive cycles of operation.

7. The arc lamp of claim 1 wherein means are provided to insure immediate reignition `of the `arc Should it be extinguished.

8. In an arc lamp comprising -a pair of electrodes between which an arc is adapted to be drawn, movable upper and lower electrode carriages, means Ifor supporting one of said electrodes from each of said carriages in colinear relationship, -a flrst rack connected to said upper electrode carriage, a second rack connected to said lower electrode carriage, the longitudinal axes of said racks being disposed in spaced parallel relationship, a gear for engaging both of said racks to cause simultaneous mov,.- ment of said rack-s in opposite directions upon rotation of said rack, a shaft connected to said gear, spring biasing means associated with said shaft for moving said racks to cause said electrodes to move towards each other into contacting engagement, normally energized electromagnetic lmeans mechanically associated with said shaft for overcoming the force of said spring biasing means to move said electrodes apart a predetermined distance, va dashpot connected to said electromagnetic means for retarding the action of said electromagnetic means and reducing the rate of separation of said electrodes, and a timer mechanism `for deenergizing momentarily yand periodically Vsaid electromagnetic means 'to permit said electrodes to move int-o contacting engagement under the force of said biasing means, so that upon reenergization of said electromagnetic means said electrodes are moved apart said predetermined distance regardless of the amount of electrode shortening caused by arc burning, said timer mechanism maintaining said electromagnetic means energized for all but an instant of each period of operation.

9. An arc lamp comprising a pair of electrodes between which an -arc is adapted to be drawn, the combination of a pair of electrode carriages each capable of supporting one of said electrodes, means including a `gear and rack mechanism for causing simultaneous movement in opposite directions of said carriages, spring means for urging said gear in such a direction to tend to move said electrodes into contacting engagement, a ratchet `drivingly connected to said gear, solenoid means, a pawl connected to said solenoid means for actuating said Iratchet Ito separate said electrodes a xed predetermined distance in response to energization of said solenoid means and against lthe lforce of said spring means, `a switch connected in the energization circuit of said solenoid means, timing means for periodically actuating said switch to the open position to deenergize said solenoid means for a brief instant during each period whereby said spring means moves said electrodes into contacting engagement and subsequent reenergization of ysaid solenoid means causes separation of said electrodes to said fixed predetermined distance, and independent means for deenergizing said solenoid whenever for any reason the arc drawn between said electrodes is extinguished.

10. The arc lamp of claim 9, wherein said independent means comprises a relay having its winding connected in series with the arc circuit.

l1. An arc lamp comprising a pair of electrodes between which an arc is adapted to be drawn, an electrical circuit including a power source for energizing said electrodes, a pair of electrode carriages each supporting one of said eiectrodes, means including a gear and rack mechanism for causing simultaneous movement of said carriages toward or away from each other, spring means for biasing said gear for movement in a direction to move said. electrodes into contacting engagement, ratchet means drivingly connected to said gear, electromagnetically operated means including a pav/l for actuating said ratchet means to separate said electrodes a fixed predetermined distance against the force of said spring means, and means responsive to decrease of current in said electrical circuit below a predetermined value for rendering said electromagnetically operated means ineffective in order to move said electrodes into contacting engagement by the energy stored in said spring means whereupon the current ow in said circuit is increased to again actuate the electromagnetically operated means and move the electrodes said predetermined distance apart.

12. An arc lamp comprising a pair of electrodes between which an arc is adapted to be drawn, an electrical circuit including a power source for energizing said electrodes, a pair of electrode carriages each supporting one ct said electrodes, means including a gear and rack mechanism for causing simultaneous movement of said carriages toward or away from each other, spring means for biasing said gear for movement in a direction to move said electrodes into contacting engagement, ratchet means drivingly connected to said gear, electromagnetically operated means including a pawl for actuating said ratchet means and operable to move each of said electrodes a fixed predetermined distance against the force of said spring, means for supplying current to draw an arc bctween said electrodes having a predetermined intensity, a circuit for energizing the electromagnetically operated means, a switch connected in said circuit, and means responsive to the current flow to the electrodes for controlling the actuation of said switch to render said electromagnetically operated means ineiective whereby said electrodes are momentarily moved into contacting engagement when said current falls below a predetermined value and are then moved said predetermined distance apart unten the current flow is restored to said predetermined value.

References Cited in the tile of this patent UNlTED STATES PATENTS

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