US2396436A - Arc lamp and method of operating same - Google Patents

Description

March 12, 1946. E, c, RICHARDSON 2,396,436

ARC LAMP AND METHOD OF OPERATING SAME Filed Oct. 19, 1943 I 3 Sheets-Sheet 1 INVENTORQ 44450 CI fl/a/qeaso/w A ORN.

March 12, 1946.

E. c. RICHARDSON ARC LAMP AND METHOD OF OPERATING 'SAME Filed Oct. 19, 1943 3 Sheets-Sheet 2 INVENTOR. am; 6. 2x01420504,

March 12 E. RICHARDSON ARC LAMP AND METHOD OF OPERATING SAME Fild Oct. 19, 1945 3 Sheets-Sheet 3 INVENTOR. 24152 6 fl/a/ wpso/g Patented Mar. 12, 1946 ARC LAMP AND METHOD OF OPERATING SAME Elmer 0. Richardson, Los Angeles, Calif, assignor to Mole-Richardson (30., Los Angeles, Calif, a

limited partnership Application October 19, 1943, Serial No. 506,812

6 Claims.

My invention relates to are lamps and has particular reference to an arc lamp construction and method of operating the same by which quantity and quality of the light produced by the lamp may be accurately maintained at a uniform value.

In the operation of arc lamps, the most desirable characteristic to be maintained is uniformity of quantity and quality of light produced by the lamp. For military purposes, such as military searchlights, it is desirable to constantly maintain the crater of the positive carbon at the focal plane of the mirror or lens system employed with the lamp so as to maintain a concentration of maximum brilliance in a tight well focused beam. For other purposes, such as illumination of motion. picture sets, the most desirable characteristic is that of maintaining uniformity of quality and quantity of illumination while extreme accuracy of focus is of less importance.

If the rate of forward feed of the carbons can be accurately maintained equal to the rate at which the carbons burn away, both of the foregoing desirable results may be achieved. With the feed so maintained, lamps for military purposes can be operated so as to accurately maintain the crater of the positive carbon at the focal plane of the lens or mirror system by supplying the lamp with voltages maintained uniform within close limits. For motion picture sets or other purposes where focusing is not of primar importance, the quantity and quality of the light, particularly at high intensities, can be maintained at uniform values by arranging the feeding of the carbons ata uniform rate equal to the rate at which they burn away, even though the voltages supplied to the lamp may vary between relatively wide limits. the arc lengthening or shortening until the amperage across the arc reaches the value at which the carbons will burn away at the same rate at which they are fed forward.

Previous arc lamp constructions and methods of feeding the carbons have not been satisfactory for the accomplishment of either of these purposes for the reason that the forward feed of the carbons, particularly the positive carbon, could not accurately be coordinated with the burning rate of the carbon, with the result that the crater end of the positive carbon would wander forwardly and rearwardly even though uniform voltage was applied thereto or if the arc length was set to some specified value for a given voltage variation from that voltage resulted in a change in the arc current and variation of the intensity of the light.

It is thereforean object of invention to provide a method of operating an arc lamp. in which the forward feed of the carbons, particularly the positive carbon. is so definitely and accurately coordinated with the burning rate of the carbon that the carbon is fed forwardly at the same rate at which it is consumed.

Another object of my invention is to provide a method of operating an arc lamp, in which if the lamp is supplied with substantially uniform voltage the crater of the positive carbon will be accurately maintained at the focal plane or" the lens or mirror system while if the lamp is supplied with voltages of varying values, the current across the arc will be automatically maintained at a uniform value.

Another object of my invention is to provide an arc lamp structure in which the carbons, particularly the positive carbon, are continuously fed forward at a uniform rate equal to the burning rate of the carbon.

It is also an object of my invention to provide a method of operating an arc lamp, in which the positive carbon is continuously fed forward at a rate equal to the burning rate of the positive carbon while the negative carbon is fed forwardly at a different rate equal to one which corresponds to the burning rate of the negative carbon.

It is a still further object of my invention to provide an arc lamp structure, in which the positive carbon is fed forwardly in a continuous motion by means of an electric motor drive, in which the speed of ,the motor is so accurately controlled as to feed the carbon forward at the burning rate of the carbon.

It is additionally an object of my invention to provide an arc lamp structure as set forth in the preceding aragraph, in which the negative carbon is fed forwardly in minute steps, the frequency of which is controlled by the speed of the same motor which feeds the forward carbon.

Another object of my invention is to provide an arc lamp structure of the character set forth hereinbefcre, in which the amount of movement given the negative carbon at each step may be varied through a substantially infinite range of values.

Other objects and advantages of my invention will be apparent from a study of the following specifications, read in connection with the accompanying drawings, wherein Fig. 1 is a side elevational view partly in section of an electrode holding and feeding mechanism which may be employed in the practice of my invention;

Fig. 2 is a horizontal sectional View taken along the line IIII of Fig. 1;

Fig. 3 is a detail horizontal sectional view of a clutch mechanism employed in the practice of my invention;

Fig. 4 is a vertical sectional view through the clutch mechanism shown in Fig. 3;

Fig. 5 is an enlarged sectional view of the rotating and feeding mechanism employed for the positive carbon;

Fig. 6 is a detail sectional view taken along line VIVI of Fig. l; and

Fig. 7 is a detail View of a portion of the electrode and holding and forward feed mechanism shown in Fig. 1.

Referring to the drawings, I have illustrated an arc lamp construction which may be employed for the practice of my invention as comprising a base plate l, to which is secured as by means of bolts 2 a vertically extending hollow post 3, upon the upper end of which is mounted the positive carbon rotating and feeding mechanism indicated generally at "1. Attached to the front of the post 3 is a forwardly projecting bracket 5 which carries the negative electrode feeding mechanism indicated generally at 55.

By referring particularly to Figs. 1, 2 and 7, it will be observed that the positive electrode P is adapted to be rotated and fed forwardly by means of feeding mechanism substantially corresponding to that illustrated and described in my earlier Patent No. 2,060,347, issued November 1936. Such feeding and rotating mechanism for the purpose of the present invention may be briefly described as comprising a pair of spur gears 1 and 8 mounted upon the forward end or head 9 of a sleeve Ill mounted for rotation in the head l as by means of a bearing M. The spur gears l and 8 are urged toward each other by means of springs l2 so as to grip between them the positive carbon P which extends through the sleeve iii and as the sleeve is rotated the positive carbon will be rotated therewith.

The forward feed of the positive carbon is accomplished by means of the engagement of the spur gears l and 8 with a scroll gear i3 formed upon the front face of a bushin it which surrounds the sleeve it and is adapted to be rotated relative to the sleeve H3. tatably mounted in the head structure by means of a bearing l5. Power for rotating the sleeve is applied through a sleeve driving shaft !6 coupled to the sleeve by means of bevel gears I? while power for rotating the scroll gear i3 is applied through a scroll driving shaft i8 coupled to the bushing M by means of bevel gears I9. Thus by rotating the sleeve if at any desired constant speed of rotation and rotating the scroll gear A3 at a different constant speed of rotation, the positive carbon will be both continuously rotated and continuously fed forward at a rate of speed which is determined by the difference in the speed of rotation of the shafts it and i8.

The shafts l6 and 58 are adapted to be driven at the desired speeds by means of a train of gears 20, preferably mounted upon the under side of the base plate i and comprising a driving gear 2| driven at a predetermined constant speed by means of a motor 22 which is provided with a mechanical or electrical speed governor 23 of any suitable type, the motor illustrated in Fig. 1 being provided with a governor of the type illustrated and described in United States patents to Royal Lee, Nos. 1,630,394 and 1,7611%. While the governors illustrated and described in the Lee patents comprise mechanical governors which operate to open and close the motor circuits, it is to be understood that wherever the words mechanical governor are used in this specification, it is intended to mean any device which is responsive to the speed of the motor to impose a mechanical on the motor or to so control the motor circuits as to provide in effect an electrical brake which will result in the maintaining of the motor speed at an, accurately The bushing it is rocontrolled constant value, as distinguished from electrical devices for regulating the voltage or the current supplied to the motor circuit in an attempt to control the motor speed by variations of current and voltage supplied thereto.

By referring particularly to Figs. 1 and 2, it will be noted that the driving gear 2i drives a smaller gear 2 3 which is coupled by means of a stub shaft 25 to a larger gear 26, which is in turn meshed with an idler gear 2? to drive a gear 23 fixed upon a stub shaft 29, which is in turn coupled to a rod 3i! adapted to drive the positive carbon rotating shaft 56.

Another gear 35 fixed upon a stub shaft 32,

' which is coupled by means of a rod 33 to the scroll rotatin shaft iii, is adapted to be driven from the gear 23 by means of an idler gear 3% which meshes with the gears 28 and 35. By selecting the relative diameters of the gears 23 and Si, the two shafts it and 18 may be driven at any desired difference in speeds.

Using a motor drive having a positive speed governor which will maintain the speed of the motor at a constant value with variations mainained within minute limits, it follows that the rate of forward feed of the positive carbon P will be at an accurately controlled constant rate.

Thus if the burning rate of the particular positive carbon to be employed in the lamp is known, and the quality of present day are lamp carbon electrodes is such that the burning rate is capable of accurate ascertainment, the speed of rotation of the mechanically governed motor and the gear ratios to be employed are selected such that the rate of forward feed of the carbon is exactly equal to the rate at which the carbon burns away.

Hence in any situation where it is desirable to maintain the crater positive carbon at the focal plane of the lens or mirror system with great accuracy, as for example in military searchlights, all that is required is to supply the lamp with a voltage which is maintained substantially uniform.

By properly controlling the rate of feed of the negative carbon N in proportion to its burning rate, an arc of constant length is maintained so that in the event that slight inaccuracies in the composition of the positive carbon should momentarily change the burning rate of the positive carbon, the resultant small change in arc length would cause the positive carbon to burn more rapidly or more slowly until the crater was restored to its desired position at the focus of the optical system.

To control the rate of feed of the negative carbon N, I mount this carbon upon a carriage 35 which is slidably supported upon the frame 5. The carriage 35 is provided with a nut structure 36 threadedly engaging a feed screw 37 adapted to be rotated by means of power supplied through a pair of bevel gears 35 which are in turn driven by means of a shaft 39 mounted in the base plate I. The shaft 39 is adapted to be rotated in a step by step motion through a clutch 4!: which in effect constitutes a ratchet having an infinite number of teeth so that the amount of motion given to the shaft 39 for each step and the frequency of such steps in a given period of time may be so arranged as to feed the negative carbon N toward the positive carbon P at the burning rate of the negative carbon N. By employing a substantially large number of small steps, the effect will be to pr0- duce a substantially continuous feeding movement to the negative carbon N corresponding to the previously ascertained burning rate of this carbon.

I prefer to drive the negative carbon from the same source of power as is employed to control the feed of the positive carbon P so that the uniformity of feed control which has already been provided for the positive carbon may also be employed to produce uniformity in the feed rate of the negative carbon N.

For this purpose I provide upon one of the gears of the gear train 2|3| a cam 4|. As illustrated in Figs. 1 and 2, this cam is mounted upon or formed integrally with the last gear 3| in the train, upon which cam rides a lever 42, preferably having a roller 43 interposed between the lever and the cam. The lever 42 is of any desired length, pivoted at 44 and normally urged against the cam 4| by means of a tension spring 45 so that the outer end 45 of the lever is moved in a clockwise direction, as viewed in Fig. 2, by means of the spring 45 and is moved in a counterclockwise direction by the roller 43 riding upon the high point or points of the cam 4|.

The outer or free end of the lever 46 is connected by means of a connecting rod or link 41 to a lever 48 on the driving member of the clutch 4G. The clutch or ratchet, as is best seen in Figs. 2, 3 and 4, comprises a driving member 49 in the form of a circular disk, the upper surface of which is cut away to form an upstanding central boss 50, about which extends a pair of semi-annular shoes |a and 5|b, one end of each of the shoes having a transverse notch or recess 52 formed therein so that the adjacent ends of the two shoes may seat upon a pin 53, either attached to the driving member 49 or freely floating thereon.

The opposite ends of the shoes 5|a--5|b are disposed adjacent the expander 54 which may be a rectangular head formed upon a pin 55 extending through the driven member 49 and the outer end of which is rigidly secured as by a pin 56 to the lever 48.

The driven member 57 of the clutch is formed as a circular cup which surrounds the shoes SM and 5|b, the driven member being secured as by a pin 58 to the shaft 39, which is rotatably mounted in the driven member 49 as by means of a bearing 59 extending through a central bore in the boss 50, the shaft 39 being retained in place as by means of forming an enlarged head 60 thereon received in a counter-bore or recess 6| extending from the under side of the driven member 49.

By forming the shoes 5|a and 5|b and the eX- pander 54 of such dimensions that when the expander is disposed in its non-operative or central position as shown in Fig. 3, the exterior surfaces of the shoes 5|a and 5!!) are just free of contact of the interior walls of the driven member 57. The driving member 49 may be rotated freely with respect to the driven member 5?. However, upon the rotation of the expander 54, the shoes 5|a and 5|b will be expanded outwardly into frictional engagement with the driven member 57 and will rotate the driven member 57 with the driving member 49.

Thus it will be apparent that by providing upon the lower face of the driven member 49 a stop 62 (see Figs. 1 and 2), the movement of the lever 48 in a clockwise direction will be limited such that the expander 54 will assume its central or non-operative position, while movement of the lever 43 in a counterclockwise direction will not be so limited but will rotate the expander 54 to clutch the driving and driven members of the clutch together. Thus as the lever 42 is oscillated by the spring and the cam 4|, the shaft 39 will be rotated in a counterclockwise direction as viewed in Fig. 2.

The extent of the rotary motion produced upon each oscillation of the lever 42 may be readily determined by determining the arc through which the lever 42 will move and in order to permit of the greatest degree of adjustability I prefer to provide the cam 4| with high and low points of such dimensions relative to each other that the lever 42 will be swung through a considerabie arc and then I limit the actual movement of the lever 42 by limiting the extent of its clockwise movement as by rneansof providing a stop screw 63 adapted to engage 2. lug E4 on the lever 42 to limit the swing of the lever 42 as it attempts to follow down upon the low point of the cam 41.

Thus by mounting the stop screw 63 in a threaded boss 65 formed upon the base plate and extending to one edge of the base plate where access to the screw 63 may be readily had, the amount of rotarymovement produced by each oscillation of the lever 42 may be given an infinite number of values.

It will be apparent that the gear 3| will be rotated at a relatively low speed and upon each revolution the negative carbon N will be given two minute feed steps and since the gear 3! is rotated at a definite constant speed by means of the governor controlled motor 22 the feeding rate of the negative carbon N will be maintained at a constant'value. It will be understood, however, that if the burning rate of a selected negative carbon is such that a higher rate of feed is required, either a cam with a greater number of high points may be employed to produce a greater number of steps per revolution of the gear 3| or the length of the throw of the lever 42 may be increased by backing off the stop screw 63 until the desired feeding rate is achieved.

It will be understood by those skilled in this art that the carriage 35 of the negative carbon may be moved independently of the negative carbon feed herein described whenever .it is desired to strike the arc as by providing a lever 10 pivoted at 1| upon the frame 5, one end of the "lever being pivoted as at 72 to the lower end of the feed screw 31, the upper end of which is coupled, as by means of a pin 73 and slot 74, to the bevel gears 38 such as to permit axial movement of the feed screw 37 relative to the gears 38 but maintaining the rotary drive relation between these members. Thus actuation of the lever 'lil in a clockwise direction will slide the carriage 35 and the feed screw 37 upwardly toward the positive carbon P and permit the ready striking of the arc. The operation of the lever 1|] may be either manual as by providing a finger-piece 75 thereon, or it may be actuated electrically as by means of a magnet 76, the armature of which is coupled by means of a bar 11 and links 16 and 19 to the lever 19, a suitable dash pot 8i! being interposed in this linkage for retarding the motion of the carriage 35 in the conventional manner. It will be observed from the foregoing that I have provided an arc lamp in which the burning rates of the carbons are employed to maintain both the positive and the negative carbons at predetermined locations in the lamp by so accurately controlling the feed of these carbons toward each other that as the ends of the carbons are burned away the carbons are fed forwardly at the same rate as the carbons burn.

Thus the arc length is maintained at a substantially constant value to produce the desired brilliance of the arc while the crater at the end of the positive carbon is accurately maintained at the focal point of the optical system employed with the lamp. For example, a positive carbon which has a burning rate of 18 inches per hour can be readily fed forwardly at the rate of 18 inches per hour while a negative carbon employed therewith may have a burning rate of 2 inches per hour and may be accurately fed at this rate.

In structures actually built and tested, in which the voltage was maintained within a limit of 1 :2 volts, the positive crater was maintained at the focal point within i limits of .040 inch more than 50% of the time, within .060 inch 90% of the time and within L .100 inch at all times.

By operating arc lamps in this manner, it will be apparent that the divergence of the beam projected may be closely maintained at a constant value and the brilliance of illumination is likewise maintained at a constant value throughout the operation f the lamp.

When the structure and method hereinbefore described are to be employed for motion picture set illumination where it is desirable to maintain a constant brilliance and quality of light, particularly in the making of color pictures in which the maintenance of the spectrum values is of great importance, this result is accomplished even though the voltage values supplied to the lamp may vary between relatively wide limits; for example, with the lamp designed to operate with a given arc length and a given current, any reduction in voltage supplied to the lamp will result in a shortening of the arc until the current across the arc reaches the value at which the positive carbon will be burned away at the same rate at which it is fed forward and this current will be the current for which the lamp was originally set. Thus though the arc length is less the current is the same and the brilliance, quantity and quality of illumination from the lamp is maintained at a constant value.

While I have shown and described the preferred embodiment of my invention, I do not desire to be limited to any of the details of construction shown and described, except as defined in the appended claims.

I claim:

1. ihe method of operating an arc lamp employing a positive and a negative electrode to maintain the crater of the positive electrode at a fixed location when the voltage supplied to the lamp is constant or to maintain the are current constant when the supply voltage is variable, which comprises determining the rates at which each of electrodes burns away at a given intensity of arc, employing a motor to feed the positive electrode forwardly in a uniform continuous motion, mechanically governing the speed of the motor to maintain the rate of such motion at a constant value equal to the burning rate of said positive electrode, and feeding the negative electrode toward the positive electrode by the same motor and at a rate of speed which bears the same ratio to the rate of feed of the positive electrode as the burning rate of the negative electrode bears to the burning rate of the positive electrode.

2. In an arc lamp, a positive electrode and a negative electrode, means for feeding said positive electrode forwardly in a continuous motion, a motor for driving said feeding means, and a governor responsive to the speed of said motor for controlling the motor speed to maintain the speed of feeding the positive electrode at a constant value equal to the speed at which said electrode burns away.

3. In an arc lamp, a positive electrode and a negative electrode, means for feeding said positive electrode forwardly in a continuous motion, a motor for driving said feeding means, a governor responsive to the speed of said motor for controlling the motor speed to maintain the speed of feeding the positive electrode at a constant value equal to the speed at which said electrode burns away, and means for feeding the negative electrode toward the positive electrode by the same motor at the same relative rate of speed as the burning rate of the negative electrode bears to the burning rate of the positive electrode.

4. In an arc lamp, a positive electrode and a negative electrode, means for feeding said positive electrode forwardly in a continuous motion, a motor for driving said feeding means, a governor responsive to the speed of said motor for controlling the motor speed to maintain the speed of feeding the positive electrode at a constant value equal to the speed at which said electrode burns away, means for feeding the negative electrode toward the positive electrode in a step by step motion of minute steps, and means coupling said negative electrode feeding means to said motor for driving said feeding means at a rate equal to the burning rate of the negative electrode.

5. In an arc lamp, a positive electrode and a negative electrode, means for feeding said positive electrode forwardly in a continuous motion, a motor for driving said feeding means, a governor responsive to the speed of said motor for controlling the motor speed to maintain the speed of feeding the positive electrode at a constant value equal to the speed at which said electrode burns away, means for feeding the negative electrode toward the positive electrode in a step by step motion of minute steps, means coupling said negative electrode feeding means to said motor for actuating said feeding means at a predetermined frequency, and means for adjusting the length of each step, whereby the rate of feeding of said negative electrode may be adjusted to be equal to the rate at which the negative electrode burns away.

6. In an arc lamp, a positive electrode and a negative electrode, means for feeding said positive electrode forwardly in a continuous motion, a motor for driving said feeding means, a governor responsive to the speed of said motor for controlling the motor speed to maintain the speed of feeding the positive electrode at a constant value equal to the speed at which said electrode burns away, means for feeding the negative electrode toward the positive electrode in a step by step motion of minute steps comprising a driving member and a driven member rotatable relative to each other, means for oscillating the driving member and means for clutching said members together when said driving member is moving in one direction at any rotative position relative to said driven member, means coupling said driving member to said motor to oscillate said member at a predetermined frequency relative to the speed of the positive electrode feed, and means for adjusting said coupling means to vary the arc of oscillation of said driving member to determine the length of each feeding step applied to said negative electrode.

ELMER C. RICHARDSON.

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