US2691120A - Ionizing flash lamp - Google Patents

Description

0d. 5, 1954 BARBER 2,591,120

IONIZING FLASH LAMP Filed Oct. 28, 1948 KLAO |4 :1 L ;z 40 I I Yr K :4 -30 ,(so 38 a FIG. 3 15 L 0 POWER SUPPLY 1 INVENTOR.

. Raymond H. Barber 665;? FIG. 6 By I8 68 F Aflv- Patented Oct. 5, 1954 UNITED STATES PATENT OFFICE IONIZING FLASH LAMP Raymond H. Barber, Chicago, 111.

Application October 28, 1948, Serial No. 57,089

7 Claims. 1

This invention relates to electron discharge tubes. More specifically, the invention relates to an improvement in the physical and electrical structure of gaseous discharge tubes of the type employed in flash photography, flash signaling, stroboscopic illumination, and similar applications. The invention also provides a novel type of control circuit for initiating the gaseous discharge in such tubes.

Gaseous discharge tubes capable of producing the high-intensity, high-speed, flashes of light, particularly for use in photography and stroboscopy, are now well known. The voltage applied between the anode and the cathode to produce the discharge is commonly supplied by a condenser-type power supply. In such power supplies, a condenser is charged to a high voltage and is thereafter discharged through the electron discharge tube to produce high-intensity light. Where a two-electrode tube is employed, the voltage to which the condenser is charged exceeds the ignition or firing potential of the tube.

The present invention provides electron discharge tubes which are capable of producing light flashes of high intensity upon the application of voltages lower than those now in use. Further, the electron tubes of the present invention may be employed with relatively simple and inexpensive firing or ignition systems. One aspect of the invention provides an improved and simplified ignition or firing system for electron discharge photoflash tubes. Further, the present invention provides electron-discharge photoflash tubes of great simplicity of structure and assembly and consequent reduced cost of construction.

Generally, reduction of the cost of construction of photoflash tubes of the electron discharge type is accomplished in the present invention by a novel type of mounting means for the discharge chamber in which the gaseous discharge occurs. Such discharge chambers are commonly enclosed within light-transmitting envelopes to which are sealed insulating bases through which the contacts to the discharge chamber electrodes, and to the control electrode or grid, are made. The discharge chamber, an elongated tube which is commonly wound in the form of a helix or other tortuous shape, is usually formed of a relatively expensive heat-resistant glass, or of quartz. In order to prevent damage due to impact collision between the discharge chamber and the envelope upon subjection to vibration or shock, the discharge chamber is mounted within the envelope in such a manner as to prevent relative motion therebetween. Various means of mounting the discharge chamber withinthe envelope'have heretofore been employed. Where the mounting means, suchasa glass-to-glass seal, is of the same material 'as the discharge chamber, the envelope must likewise be of the relatively expensive material of the chamber, since differences in temperature coefficients of expansion would other- Wise prevent bonding. Furthermore, the assembly of the rigidly supported discharge chamber with the base and envelope has heretofore been a relatively expensive and complicated operation.

In the embodiment of the present invention to be herein described the discharge chamber is mounted upon the base by a resilient support such as a piece of rubber or neoprene. When the envelope is placed over the discharge chamber, the upper end of the discharge chamber contacts the end of the envelope, and the resilient support is compressed. When the envelope is sealed to the base, the resilient support remains under compression and thus holds the dischargechamber securely in contact with the envelope, so that neither the discharge chamber nor the envelope will be damaged by impact contact between the two upon vibration or shock to the assembly. The leads-to the electrodes are flexible and need not contribute in any manner to the support. Thus assembly of the photoflash tube of the present invention is far simpler than the assembly of similar photoflash tubes heretofore employed, and improved resistance to vibration and shock damage is obtained. The interior of the discharge chamber has a pair of electrodes at the opposite ends thereof, which electrodes are of conventional construction and between which electrodes the discharge takes place. The atmosphere within the discharge chamber consists of the gases that are usually employed in flash photography type electron discharge tubes so that the physical conditions within the discharge tube of the present invention are the same as in conventional well known electric discharge flash tubes.

The improved electrical characteristics of the present invention are obtained by the provision of a novel type of conducting electrode inside the envelope, but exterior to the discharge chamber. The conducting electrode is in contact with the exterior surface of the elongated discharge tube along a large portion or all of the length thereof. This electrode, in one embodiment of the invention, is connected to the cathode. In this embodiment the external electrode serves to collect electrostatic charge which otherwise remains upon the insulating walls of the discharge chamher, and to change the electric field within the discharge chamber. In this manner, the operating characteristics and starting voltage of the photoflash tube are held constant, and furthermore the operating voltage required for firing of the two-electrode tube is decreased. Furthermore, in the embodiments to be herein described, this external electrode also serves as a light reflector. Alternatively, as will hereinafter be seen, the exterior electrode may be brought to an external connection and employed as the control electrode or starting grid of the tube. In this three-electrode embodiment of the invention, the external electrode may be normally unconnected, and the equalizing of the potentials of the external electrode and one of the internal electrodes, and the consequent change of electric field conditions Within the chamber and electrostatic charge conditions on the wall of the chamber may be employed for triggering or firing the tube. Employing this property of a three-electrode tube made in accordance with the invention, the invention further provides a novel triggering or firing system far simpler than those heretofore employed.

The nature of the invention, and the manner in which the objects and advantages above described, together with other objects and advantages which Will be apparent, will best be understood from a description of the embodiments of the invention illustrated in the drawing, in which:

Figure l is a central vertical sectional view, partly in elevation, of a photofiash tube made in accordance with the invention;

Figure 2 is a horizontal sectional view of the photofiash tube of Figure 1 taken along the line 22 in the direction indicated by arrows;

Figure 3 is a fragmentary vertical sectional view corresponding to Figure 1 illustrating a modification of the invention;

Figure 4 is a fragmentary vertical sectional view corresponding to a portion of the illustration of Figure 1 and illustrating a further modification of the invention;

Figure 5 is a schematic electrical diagram, partly in block form, illustrating a discharge or firing system constituting a portion of the invention; and

Figure 6 is a schematic electrical diagram illustrating a modification of the system of Figure 5.

In the photoflash tube 8 of Figure 1, the discharge chamber l0, constituting an elongated tube of pyrex or other heat-resistant glass, is wound substantially in the form of a helix, having a plurality of turns I2. The lowermost turn I2 terminates in a vertical extension M parallel With the axis of the helical discharge chamber I0. At the end of the downwardly extending portion [4 is a shoulder portion formed by a nipple I6 of reduced cross section. A cathode i8 is supported within the vertical extension M by a wire sealed in the nipple IT. The uppermost turn 22 of the helical discharge chamber l0 flattens out from the helical shape of the helical turns 2 to the shape of a portion of a plane circle. The uppermost turn 22 lies in a plane approximately perpendicular to the axis of the helical discharge tube l0. Sealed in the end of the uppermost turn 22 is an anode 24 of the type now conventional in such discharge tubes. The anode 24 is connected to a flexible wire 26 which extends down the axis of the discharge tube or chamber IE) to the bottom of the assembly. Within the discharge tube ID there is the conventional atmosphere usual in such flash photography glow discharge tubes, as, for instance, described in Patents 2,281,579 or 2,351,603 or 2,399,222, or 2,467,472.

Within the helix formed by the discharge chamber I0 is a conducting electrode 28 formed of a rectangular sheet of springy metal such as a resilient alloy of aluminum. The electrode 28 is rolled to a diameter slightly larger than the inner diameter of the helical discharge chamber l8. Therefore the electrode 28 is under slight compression by contact with the inner surfaces of the helical discharge chamber In, in this manner establishing firm contact with the successive turns [2 of the helix. In order to maximize the contact between the electrode 28 and the discharge chamber !B, the width of the sheet from which the electrode 28 is formed is slightly smaller than the inner circumference of the discharge chamber lfl, thusleaving a slit 31} extending vertically from the top to the bottom of the electrode 28. Provision of the slit 32 prevents overlapping of the ends of the sheet forming the electrode 28, and thus minimizes the loss of contact which would be caused by such overlapping. Preferably the electrode 28 is highly polished in order to serve as a light reflector, in addition to its electrical functions to be described below.

The assembly thus far described is contained in a tubular envelope 32, of any inexpensive glass. The upper end of the envelope 32 is domeshaped. The lower end 36 of the envelope 32 is open and is inserted into a cup-shaped base 38, of insulating plastic, the envelope 32 being cemented to the base 33 at at. The base 38 has prong contacts 42, 43 and 45 extending through the bottom thereof.

The nipple or shoulder portion (5 of the lower extension [4 of the discharge chamber I ii is journalled in a short length of rubber or neoprene tubing M. The bottom of the tubing spacer it rests upon the base. The nipple or shoulder portion It is disposed directly above one of the base prongs 42, and a wire 46 is soldered into the prong 42 at its lower end and to the electrode lead wire 20 at the upper end of the wire '49. The uppermost winding 22 of the discharge chamber I0 is pressed against the dome-shaped upper end 34 of the envelope 32, and the spacer support 44 is compressed between the base 38 and the lower extension [4 of the discharge chamber it). Thus the discharge tube or chamber Ill is held rigidly in place within the envelope 32. The wire 26, which is, as stated above, connected to the anode 24, is soldered to another of the prong contacts 43, and an additional wire 58 is soldered at its upper end to the resilient electrode 28 and at its lower end to a third prong contact 45.

It Will readily be seen that the manner in which the discharge chamber H3 is supported within the envelope 32 affords a construction which is extremely simple to assemble, yet highly reliable and durable in operation. After insertion of the electrode 28 in the helical discharge chamber I9, the spacer sleeve or tube 44 is fitted over the nipple or shoulder portion IS with the Wire 23 depending from cathode support wire 20. The discharge chamber 10 is then inserted in the envelope 32. The lower end 36 of the envelope 32 is then inserted into the base 38, with the wires 56, 26 and 50 extending into the respective prong contacts 42, 43 and 45. The contacts 32, Z3 and 45, which are prefilled with solder, are then heated and allowed tocool and the cement 4c is pp ied. H

It has been found that the voltage between the cathode It and the anode 2 3 which produces discharge in the chamber It is much lower when the electrode 28 is connected to one of the internal electrodes it or M, particularly to the cathode l8, than is the case when the external electrode 28 is omitted or is left unconnected. This difference in firing potential is believed to be due to the change of the electric field within the discharge chamber IG and the dissipation of the effects of electrostatic charges on the insulating walls of the discharge chamber I9. It is found that the dilference in anode-to-cathode firing potential between the condition in which the electrode 28 is floating and that in which it is connected to the cathode I8 is further increased by coating the interior of the helix, which is in contact with the electrode 28, with a conducting coating 69, such as aluminum paint, as illustrated in Figure 4. Preferably the coating 60 is baked to cause carbonization of the pigment vehicle where aluminum paint is employed. Colloidal graphite or similar conducting films may likewise be employed, but aluminum paint is preferred because of high light reflection.

The difference in firing potential above described may be employed to provide a photofiash firing system far more simple than those heretofore in use. In Figure 5 is shown a system Wherein the firing circuit consists only of a shorting switch rather than the complex and expensive high-voltage relays, thyratrons, and spark coils heretofore employed. The circuit consists of a conventional power supply '52 (shown in block form), charging resistor 6d, and storage condenser 66, the latter bein connected between the anode 24 and the cathode it of the photofiash tube 8. The cathode I8 is connected to the control electrode 23 through a simple make-andbreak switch 58, which may be the switch now commonly incorporated in cameras for synchronization of photoflash exposures. In Figure 6 is shown a modification of the circuit of Figure 5 wherein a condenser it, of small capacitance, is inserted in series with the switch 68 between the cathode is and the control electrode 28. Insertion of the condenser 70 is an optional modification which may be made for purposes of protecting the equipment against accident. It will be noted that in the circuit of Figure 5, accidental shorting of the anode 2:5 to the control electrode 28, as by damage to the photoflash tube 8, would short-circuit the condenser 56 upon the closing of the switch 58. The possibility of damage to the system from such an occurrence is avoided by the use of the condenser it.

The embodiment of the photofiash tube of the invention illustrated in Figure 1 and described above is a three-electrode electron discharge photoflash tube. As illustrated in Figure 3, the electrode 28 may advantageously be employed in two-electrode photofiash tubes. In the photofiash tube ll of Figure 3 the wire which is connected to the exterior electrode 28 is connected directly to the contact 42 which is connected with the cathode l8. The exterior electrode 28 is thus directly connected electrically to the cathode 3 within the envelope 32. The two-electrode tube of this embodiment offers great advantage over other two-electrode structures in that the operating characteristics of the tube remain relatively constant, bein unaffected by the increase or decrease of electrostatic charge upon the wall of the discharge chamber it. Furthermore, the voltage at which the two-electrode tube fires is substantial-1y reduced by the presence of the exterior electrode 2% connected to the cathode [8.

It will be understood that the invention may be embodied in many forms other than the preferred forms herein illustrated and described. For example, persons skilled in the art will readily adapt the invention to electron discharge photo-flash tubes wherein the discharge chambers assume forms far different from that herein illustrated. Likewise many other designs may be reached for the electrode 28, although the form herein illustrated offers great advantage. Furthermore, the manner of mounting herein described may be greatly modified without departing from the broader aspects of the teachings of the invention. Furthermore, many circuits other than the circuits herein illustrated will be designed to utilize the teachings of this aspect of the invention. Accordingly, the scope of the patent protection to be afforded the invention should not be limited by the description included herein, or the drawing appended hereto, but, in accordance with the patent laws, shall be limited only by the scope of the appended claims.

What is claimed is:

1. In an electron discharge flash tube, in combination: an insulatin base having contacts at the outside thereof; a tubular envelope made of a light transmissive material and having an open end secured to said base and having a domeshaped closed end; a sealed helical discharge tube made of a light transmissive material and having an ionizable gas sealed therein, said discharge tube having a plurality of helical turns and an outermost turn lying at least partially in a plane perpendicular to the longitudinal axis of the helix, the innermost turn having an extension parallel with said axis and having an end of reduced diameter; a cathode electrode sealed within said extension; a flexible wire connecting said cathode to one of said contacts in said base; a hollow cylindrical elastic support member sleeved over said end of reduced diameter and supporting said discharge tube upon said base, said wire extending through said support member and said support member being compressed between said discharge tube and said base to force said outermost turn of the tube against said domed end of the envelope; a curved sheet of resilient conducting metal within said helix and coaxial therewith, said sheet being radially compressed by contact with the surface of the helix; a conducting Wire connecting said sheet to one of said contacts; an anode electrode within said discharge tube at the outermost end thereof; and a flexible Wire connecting said anode to one of said contacts apart from the contact to which said cathode is connected.

2. A light source comprising an evacuated tube of helical shape, electrodes at the opposite ends of the tube, an ionizable gas sealed within the tube, and a layer of electrically conducting material contacting the outside of the tube along the inside of the helix and extending around and encompassing the axis of the helix at each complete turn of the helix and being entirely on the side of the tube which faces toward the axis of the helix.

3. In an electron discharge flash tube, in combination: an insulating base having contacts extending therethrough, a light transmitting envelope having an open end secured to said base and having a dome-shaped closed end; a helical tubular light transmitting discharge chamber having an ionizable gas sealed therein and formed of a plurality of helical turns and an outermost turn lying at least partially in a plane perpendicular to the axis of said helix; a first electrode sealed within the inner end of said helical discharge chamber; a flexible wire connectin said electrode to one of said prong contacts in said base; a single resilient insulating support member supporting said, discharge chamber upon said base, said support member being compressed between said chamber and said base to force said outermost turn of the chamber against said domed end of the envelope; a conducting sleeve of reflecting resilient metal within said helix and coaxial therewith, said sleeve being radially compressed by contact with the inner surface of the helix; a rigid conducting support member supporting said sleeve upon said base and connecting said sleeve to one of said contacts; a second electrode within said chamber'at the outermost end thereof; and a flexible wire connecting said second electrode to one of said contacts in the base.

4. In a flash tube of the gaseous discharge type. in ccmbination: a helically wound elongated cylindrical discharge chamber comprising a tube made of a light pervious material and having electrodes at the ends thereof, an ionizable gas sealed in said chamber, a conducting resilient sleeve coaxial with the helix formed by said chamber, said sleeve being formed of a sheet of resilient metal rolled in the form of a cylinder, and being under compression by contact with the interior surfaces of the turns of said helix, and conductors extending circuit connections to the electrodes, at least one of the conductors extending through the cylinder lengthwise thereof.

5. In a flash tube of the gaseous discharge type, in combination: a helically wound elongated cylindrical discharge chamber comprising a tube made of a light pervious material and having electrodes at the ends thereof, an ionizable gas sealed in said chamber and a conducting resilient sleeve within and coaxial with the helix formed by said chamber, said sleeve being under compression by contact with the interior surfaces of the turns of said helix.

6; In a flash tube of the gaseous discharge type, in combination: a light pervious helically wound elongated cylindrical discharge chamber having anode and cathode electrodes at the ends thereof, an ionizable gas sealed in said chamber an external conducting electrode within the helix and extending parallel with the axis of the helix formed by said chamber and in contact with the surfaces of successive turns of said helix and extending substantially 360 around the axis of the helix at each turn thereof.

7. In a flash tube of the gaseous discharge type, in combination, an elongated, light pervious insulated helical discharge chamber having an ionizable gas sealed therein and said chamber having anode and cathode electrodes at the ends thereof, a conducting electrode extending substantially 360 around the axis of the helix at each turn of the helix and being in contact with the exterior surface of said chamber along the length thereof within the helix, a source of direct voltage connected between said anode and cathode, and mechanical switching means instantaneously equalizing the potentials of one of said first mentioned electrodes and said exterior electrode.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,961,749 Ewest June 5, 1934 2,194,300 Found Mar. 19, 1940 2,201,166 Germeshausen May 21, 1940 2,262,177 Germer Nov. 11, 1941 2,272,513 Courdil Feb. 10, 1942 2,316,348 Mahlck Apr. 13, 1943 2,351,603 Edgerton June 20, 1944 2,399,222 G-errneshausen Apr. 30, 1946 2,467,472 Goshorn Apr. 19, 1949 ,480,122 Daniels Aug. 30, 1949 FOREIGN PATENTS Number Country Date 19,132 Sweden Oct. 15, 1903 525,943 Great Britain Sept. 6, 1940

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