US2777084A - Plastic electrode structure for electron tubes - Google Patents

Description

2 Sheets-Sheet l Jan. 8, 1957 J. M. LAFFERTY PLASTIC ELECTRODE STRUCTURE FOR ELECTRON TUBES Filed April l2, 1952 Jan. 8, 1957 J, M, LAFFERTY 2,777,084

PLASTIC ELECTRODE STRUCTURE FOR ELECTRON TUBES Filed April 12. 19V-52V 2 sheets-sheet 2 Inventor: James IVI. Lafertg,

His Attorneg.

United States Patent PLASTIC ELECTRODE STRUCTURE FOR ELECTRON TUBES James M. Laerty, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 12, 1952, Serial No. 281,996

2 Claims. (Cl. 313-80) The present invention relates to an improved electron tube, and to a new and improved electrode structure for such tubes.

More particularly, the invention relates to an improved cathode-ray, color image-reproducing tube of the reflection type, and to a new andimproved image-reproducing electrode member construction which is ideally suited for use in electron tubes of this type.

Reflection-type cathode-ray tri-color image-reproducing electron tubes are designed primarily for use in color television receiving systems, and include an evacuated envelope for enclosing the tube components, an electron beam source positioned within the envelope, and a reilection-type color image reproducing electrode structure disposed within the tube envelope transverse to the path of the electron beam produced by the electron beam source. For a more detailed disclosure of the construction and operation of the cathode ray, color imaging reproducing tubes of this type, reference is made to applicants U. S. patent -application Serial Number 208,875, now Patent No, 2,741,720, Color Television Picture Tube, led February 1, 1951, and U. S. application Serial Number 269,978, Tri-Color Cathode Ray Image Reproducing Tube, filed February 5, 1952, however, for the purposes of the present disclosure, a brief description of the operation of such electron tubes is believed suicient. The reection-type color image-reproducing electrode structure of the tube includes an apertured, image-reproducing electrode member having a plurality of dierent color light-emitting phosphorescent materials symmetrically arranged on the face thereof opposite the electron beam source, and a transparent reilecting electrode mounted parallel to and spaced from the phosphorescent material coated surface of the apertured electrode member. When incorporated in a television receiver, the electron beam produced by the electron beam source is caused to scan over the apertured electrode member by suitably positioned horizontal and vertical deliection systems controlled by the synchronizing component of a received color television signal, and the intensity of the electron beam is controlled by the video component of the received signal in the well-known manner. As the electron beam is caused to scan back and forth over the apertured, image reproducing electrode member in tracing out the image tobe reproduced, portions of the beam will pass through the apertures and enter into the space between the apertured image reproducing electrode members andthe transparent electrode member. Each of these electrode members hasl an electric potential applied thereto which coact to establish 2,171,084 Patented Jan. 8,'-1957 ice duced by the electron tube, and is in turn determined by a large number of factors, included amongst which are the spacing between the electrode members, the value of the retarding eld, the angle of lincidence of the electron beam measured with respect to the plane of the apertured image reproducing electrode member, and the velocity of the electrons in the electron beam. In order to obtain a desired color reproduction, the known circuits of this type generally eiect color switching of the reproduced image by applying the color component of a received color television signal between lthe apertured image-reproducing electrode member and the transparent reecting electrode member to thereby vary the value of the retarding electric iield between the two electrode members in accordance with the desired color arrangement.

In this fashion, the point at which electrons are projected into the retarding electric eld through the apertures in the apertured image-reproducing electrode member, return to the image-reproducing electrode member, and therefore, the color of the reproduced image, is controlled. Hence, the color of the image reproduced is determined by the value of the retarding electric eld existing between the apertured electrode member, and the transparent reecting electrode member.

From the above discussion, it can be appreciated that, should the electric eld vary in any manner due to eX- traneous effects such as vibration of the apertured imagereproducing electrode member, the color of the image reproduced would not be correct. For this reason, it is essential that vibrations of the apertured image-reproducing electrode member be reduced to a minimum.

` The problem of reducing vibration of the apertured eleca ret-arding electric teld in the space, and this retarding electric iield then acts on the portions of the electron beam projected thereinto, to cause the beam to be re- The particular c oloi lightI emitting type. l 'i A still further object of the invention is to provide a trode member is not a simple one, however, since the apertured, image reproducing electrode member is generally formed out of a thin metal sheet necessitated by reason of the nature of the aperture-forming process, and the need for reducing or minimizing any tendency of the apertured electrode member to reduce the intensity of the electron beam passing through the apertures therein due to shadowing, and like elfects. Because of the requirement that the apertured irnage-reproducing electrode member be constructed from a thin metal sheet, a bracing structure must be provided for preventing vibration of the member, and the provision of the bracing structure necessarily further complicates the manufacture of the reection-type, tri-color imagereproducing electron tube, and increases its cost. Additionally, because the thin metal out of which the electrode member is constructed, can be easily stressed or elongated, considerable care must be exercised in handling such members in order to prevent misaligning the apertures, etc., and the need for caution in handling the apertured electrode members while mounting the same in the electron tube envelope further complicates the manufacture of electron tubes of this type,

It is therefore one object of the present invention to provide a new and improved construction for apertured electrode members intended for use in electron tubes.

Another object of the invention is to provide a new and improved construction for apertured electrode members that is particularly suitable for use in cathode-ray, imagereproducing electron tubes, and is relatively simple in design, and eicient in operation.

A4 further object of the invention is to provide a new :and improved cathode-ray, tri-color image-reproducing new and improved tricolor, image-reproducing electron tube of the reflection type wherein any tendency of the image-reproducing apertured electrode member to vibrate, or to become misaligned due to expansion, is minimized.

A feature of the invention is the provision of an electrode member for an electron tube which comprises a plastic member having a plurality of apertures formed therein. The electrode member may have an electrically conductive coating covering at least one apertured surface thereof, and preferably has the apertures formed therein in a manner such that the projected axes of all of the apertures intersect at a common point in si: ce.

Another feature of: the invention is the provision of an electron tube which includes an envelope for enclosing the electron tube components, an electrode member constructed of a plastic material and having a plurality of apertures formed therein mounted within the envelope. an electrically conductive coating covering at least one surface of the apertured plastic member, and source of electrons supported within the envelope in a position such that the electrons produced thereby are adapted to be controlled by the apertured electrode member.

Other objects, Vfeatures and many of the attendant advantages of this invention will be appreciated more readily as the same become better understood by reference to the following detailed description, when considered in connection with the accompanying drawings, wherein like parts are identified by the same reference character, and wherein:

Fig. l is a sectional view of a preferred embodiment of an improved electron tube constructed in accordance with the invention;

Fig. 2 is an enlarged, fragmentary sectional View of a portion of an improved electrode structure incorporated in the electron tube illustrated in Fig. l, and comprising a part of the present invention;

Fig. 3 is an amplified, fragmentary', plan view of a portion of a new and improved electrode member comprising a part of the electrode structure shown in Fig. 2;

Fig. 4 is a diagrammatic illustration of the method by which the apertured electrode member shown in Fig. 2, may be manufactured;

Fig. 5 is a fragmentary cross sectional view of a portion of the electrode structure of electron tube shown in Fig. 1, and illustrates the manner in which the electrode structure is supported within the tube; and

Fig. 6 is a plan view of the new and improved apertured electrode member and mounting ring therefor.

A preferred embodiment of an improved electron tube constructed in accordance with the invention, is shown in Fig. l, and comprises a tube envelope, indicated at 11, having a hemispherical body portion 12, a transparent face portion 13, secured to one side of the hemispherical body portion 12 and adapted to be viewed by a person observing an image reproduced by the tube, and a conical neck portieri 14 secured to the side of the hemispherical body portion 12 opposite face portion 13. Mounted in the conical neck portion 14 is an electron beam source, indicated at 15, which includes an electron gun 16 supported in the end of the conical neck portion 14, a beam focusing means 17, and a vertical and horizontal beam deflection means 1,8 and 19, suitably positioned with re spect to the path of the electron beam produced by electron gun 16 and beam focusing coil 17 for causing the electron beam to be scanned over an improved, reflectiontype, image reproducing electrode structure, indicated at 21. ln operation, the electron beam is caused to scan over the surface of the image reproducing electrode structure 21 in tracing out a reproduction of the image in the previously described manner, and appears to be coming from a point source of electrons 22 located substantially midway the distance between the vertical and horizontal deflection coils 1S and 19.

As is best shown in Fig. 2 of the drawings, the improved reflection-type image reproducing electrode structure 21 includes an apertured, image reproducing electrode member 23 constructed of a relatively thick plastic material having a plurality of conica] apertures 24 formed therein in a manner such that the projected axes of all of the apertures intersect at a common point which coincides with the point source of electrons 22. The manner in which the apertures 24 are thus formed is dependent upon a particular characteristic of the plastic material out of which the electrode member 23 is constructed, and will be described more fully hereinafter. Further, while the material has been described as plastic, it should be understood that for purposes of the present disclosure, the term is to be interpreted broadly as any or all materials formed by means of chemical synthesis, including glass.

As is best shown in Fig. 2 of the drawings, the aperture image reproducing electrode member 23 has a conductive coating Z5 of aluminum or some similar material, covering both of the apertured surfaces thereof, and secured over the electrically conductive coating are a plurality of different-color light-emitting phosphorescent ma` terials 26, 27 and 28. The different color light-emitting phosphorescent materials are preferably disposed in symmetrically and concentrically arranged arcuate rows spaced intermediate the apertures 24 which are likewise preferably arranged in concentric arcuate rows having varying length radii and a common center point, in the manner best seen in Figs. 3 and 4 of the drawings. For a more complete description of the exact geometrical layout of the apertures 24 and different color light-emitting phosphorescent materials 25 through 23 with respect to each other, and with respect to the point source of elect'rons 22, reference is made to applicants above identified U. S; Patent application Serial Number 269,978.

Referring again to Fig. 2 of the drawings, the imagereproducing electrode structure 21 further includes a transparent relle'cting electrode member 29 raving a transparent electrically conductive coating 39 en the face thereof adjacent the phosphorescent material coated surface of apertured, image reproducing electrode iember 23. in operation, the apertured, image reproducing electrode member 23 is adapted to have a relatively high positive p'otential applied thereto, and the transparent reflecting electrode member 29 has a comparatively low electric potential applied thereto, so that a retarding electric held is established between the space intermediate electrode members 23 and 29. This re tat-ding electric tield tends to cause electrons entering into the space through the apertures 24 in electrode` Viember 23 to be reilected back to electrode member 23, and to impingc upon one of the different color lightemitting phosphorescent materials to excite the same and thereby cause it to emanate a characteristic color light. The distance that an electron strikes the apertured electrode member 23 when measured from thtl aperture through which the electron entered the retardrtg electric field, is given by the mathematical expression:

where S is the displacement between the point on member 23 through which the electron beam enters the reA tarding field and the point on which the reflected beam impinges, -d is the distance in centimeters between the electrode members 23 and 29, Vo is the potential of the apertured electrode member 23, Vc is the potential of the reecting electrode member 29, and a is the angle yof incidence of the electron beam with respect to a normal to the plane of the apertured electrode member 23. From an inspection of Expression 1 it can be readily appreciated `that any variation in the spacing d between the electrode members 23 and 29, will affect the displacement S that the reflected electron beam will travel prior to impinging upon a desired color phosphorescent material on electrode member 23. Consequently,

should the electrode member 213, be subject to vibration, or should the apertures therein Vbe thrown out ot alignment, control over the high-i of an electron through the retarding electric held would be lost, and an undesired color light-emitting phosphorescent material could be excited.

Because existing techniques for constructing the apertured electrode members require the use of thin metallic sheets that are highly subject to becoming misaligued, or to vibrate, elaborate precautions must be taken during the manufacture of presently-known i'eilectioiitype cathode-ray :tri-color image-reproducing electrode members of this type in order to prevent misalignment or" the apertures, and the electrode members must be supported by some form of bracing structure in order to prevent such Vibrations. Because the measures taken to overcome the above-cited objections tend to complicate the manufacture of electron tubes of this type, and increase its cost, the electrode structure comprising the present invention was developed as a more desirable means of solving the problem.

By providing the relatively thick, plastic apertured electrode member 2,3 illustrated in Figs. l and 2, the present invention overcomes the necessity for extra precautions required in handling thin apertured metal members, and does away with the need tor bracing structure to prevent vibration of such members. The a-ertured electrode member 23 is constructed of a light sensitive plastic material (one suitable material being that which is manufactured and sold by the. Corning Glass Works as Laboratory Product #XdSBRG under the trade name Fotoform Glass). This material initially' has a more or less amorphous structure which is transparent to ultra-violet light. By exposing portions of the member constructed of this material to ultra-violet light, and subsequently by heating the member in a bal;- ing process, the exposed portions of the member are converted to a more or less crystalline structure. This crystalline structure, when submitted to an etching bath of a proper reagent such as hydrolluoric acid, will be pret'- erentially etched over those portions of the member which were not exposed to the ultra-violet light. lt has been empirically determined that the etching of the exposed portions of the member is in the neighborhood ot times as greateas that of the unexposed portions, consequently, the material is ideally suited for having apertures formed therein along desired directional axes.

Referring now to Fig. 4 of the drawings, a schematic diagram of one suitable method for forming the apertures in the radiant energy sensitive member Y23 is disclosed. A blank sheet of the radiant energy sensitive plastic material having the desired thickness is first covered with a contact negative 31 which is opaque to ultraviolet light rays. The Contact negative 3l has a series of concentrically arranged rows of apertures vtherein with all of the rows of apertures being subtended by varying length radii having a common center point. A point source of ultra-violet light 33 positioned at the center of a transparent, spherical housing, on the same side of member 23 as negative 3l on a line perpendicular to the plane of the member 23 and passing'through the common center point 32 of the varying length radii subtending the concentrically arranged rows of apertures in vthe contact negative 31. By arranging the point source of ultra-violet light 33 in this fashion, the source 33 occupies the same position that the point source electrons 22 would occupy upon the nished electrode member Z3 being mounted in a tri-color, rellecting-type image-reproducing electron tube. Since both ultra-violet light rays and electrons travel in substantially s mightline paths, the ultra-violet light from the point source 33 will mark out paths in the member 23 which electrons originating from substantially the same location would pass with a minimum of attenuation.

ln order to assure that the path of travel of the ultra.-

" 'ber 29.

6 violet rays through the member 23 is substantially along a straight line directed throughthe point source 33, itis necessary to consider the effect of refraction of the light beams upon the same passing into member 23. If the medium surrounding member 23 were air or any other substance having an index -of refraction diierent from that of the member 23, refraction would take place, and hence, the paths that the ultra-violet rays follow through the member would not be along straight line paths passing through the point source V33. For this reason the point source 33 is enclosed at the center within a transparent spherical housing at the center thereof, and the entire arrangement including member 23, is submersed in a medium that has the same index of infraction/to ultrafviolet light as the member 23, and is transparent to ultra violet light. By constructing apertured electrode member 23 in this fashion, it will be assured that upon the member being mounted within an elecron tube envelope in a manner such that the electron source 22 corresponds to the position of the point source of ultra-violet ray 33, electrons traveling in a straight-line path from the point source A2,2 will pass through the conically-shaped apertures in member 23 with a minimum of attenuation. Subsequent to irradiation light sensitive member `23 to ultraviolet light in the above-described fashion, the irradiated member is subjected to a suitable etching bath in a manner such that only the side thereof to which the contact negative 31 wasixed, is exposed to the action of the bath. Preferential etching of the portions of member 23 exposed to the ultra-violet light lthen takes place to for-m the conically-shaped apertures 24 therein, as is best shown in Fig. 2. Following this operation, an electrically conductive coating 425 is formed on both surfaces of the apertured electrode member, and at least on the surface of mem-ber l23 adapted to be disposed adjacent reffecting electrode member 29. The electrically conductive coating may comprise aluminum or some other conductive metal and may be formed on the apertured member by inserting the same in a bath, or by any other suitable method. Following the coating of the apertured member with the electrically conductive surfacepthe surface of the member adapted to be disposed adjacent reilecting electrode member 29 has the plurality of different color light-emitting phosphorescent materials formed thereon in a manner described more fully in the above-identied U. S. Patent application Serial No. 269,978. Briey, however, the phosphorescent materials are arranged in concentric lines having varying length radii disposed intermediate the concentric rows of apertures as illustrated in Fig. 3 of the drawing.

Upon completion of the phosphorescent material print- 4ing process, the completed apertured image-reproducing electrode member 23 is then mounted in assembled relationship with the transparent reilecting electrode mem- For this purpose, a plurality of electrically conductive lJ-shaped clamps 35 are provided with one clamp being disposed at each of four corners of the electrode members. As is best shown in Fig. 5 0f the drawings, the electrode members 23 and 29 are maintained in spaced-apart, parallel relationship between the ends of the legs vkof the U-shaped clamps 35 by means of a pair of spacer blocks 36 and 37, and a clamping plate 38 that is annular in shape, and constructed of an electrically conductive material. Both of the spacer blocls 36 and 37y are constructed of an electrically conductive glass having a relatively high resistivity to the how of electric current, and are positioned on opposite sides of transparent reilecting electrode member 29. The spacer block 36 is disposed with one end thereof engaging the surface of the transparent reflecting electrode member 29 adjacent tube face 13, and the other end thereof seated in a groove in a free end of a U-shaped clamp 35. The spacer block 37 is disposed between the transparent electrically conductive face of member 29 and image-reproducing electrode member 23 with the annular clamping plate 38 positioned between the apertured image-reproducing electrode member 23 and the free end of the leg portion of the U-shaped clamp. The entire assembly is then held together by means of an adjusting screw 39 seated in the ends of one of the leg portions of each of the U-shaped clamps 35, the adjusting screws being adapted to engage the end of spacer blocks 36 so that upon adjustment of the screw, all of the members are placed under compression.

Having assembled the electrode members 23 and 29 in parallel, spaced-apart relationship, the electrode structure is then mounted within the tube envelope 12 by means of a plurality of projections 41, shown in Fig. 6 of the drawing, formed on the clamping plate 38. The projections 41 may be located substantially at the point of intersection of an equilateral triangle, and have backwardly turned ear portions 42, best seen in Fig. l of the drawings. The ear portions 42 are shaped to fit the contour of the tube envelope 12, and are secured thereto by means of a plurality of bolts brazed to the surface of the envelope 12 so as to maintain the interior of the envelope vacuum-tight. Having mounted the imagereproducing electrode structure within the tube envelope, an operating potential is supplied to the apertured imagereproducing electrode member 23 through the electrically conductive tube envelope 12 and member 38, and an operating potential is supplied to the transparent reflecting electrode member 29 through a resilient contact arm 43 secured to an electrically conductive post 44 that is supported within a cup-shaped insulating support 45 having a bore in the end thereof which sealably seats the conductive post 44. In this manner, an operating potential is supplied to the reecting electrode member 29 which is dlifferent from the operating potential supplied to the apertured image-reproducing electrode member 23.

In operation, the two different electric potentials supplied to the apertured, image-reproducing electrode member 23 and the transparent reecting electrode member 29, produce a retarding electric eld in the space between the two electrode members. This retarding electric field acts on the portions of the electron beam passing through the apertures in the electrode member 23, as it is scanned over the apertured electrode member in tracing out the image to be reproduced, and reflects the same to cause them to inpinge desired ones of the different color light-emitting phosphorescent materials formed on the face of the image reproducing electrode member 23. As the spacing between the electrode members will to a large extent affect the value of the retarding field, and this spacing is maintained substantially constant because of the inability of the relatively thick plastic electrode member 23 to vibrate, extraneous disturbances will have no effect on the operation of the tube, and a true color reproduction will be obtained.

Froin the foregoing description, it can be readily appreciated that the invention provides a new and improved aperturcd electrode structure for use in electron tubes, and particularly for use in cathode-ray, color image reproducing electron tubes of the reflection type. The new and improved electrode member is relatively simple to manufacture, and eicient in operation since by reason of the manner of its manufacture, the apertures formed therein are conical in shape, and are directionally disposed along axes which electrons would normally tend 8 to follow, so that shadowing due to the structure is rcduced to a minimum. Further, by reason of its relative thickness, the new and improved structure requires little or no mechanical bracing so that the manufacture of electron tubes utilizing the structure is simplified, and the cost thereof reduced.

Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that changes may be made herein which are within the full intended scope of the present invention, as defined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A luminescent electrode stnlcture for a cathode ray image reproducing tube comprising a glass sheet having an ultraviolet-light sensitive area therein and a plurality of preferentially etched uniformly tapered apertures formed in said area, each of said apertures extending through said sheet in a direction toward a common point in space at one side of said sheet, each of said apertures increasing in diameter toward said point, and the maximum diameter of each of said apertures being substantially less than the thickness of said sheet, an electrically conductive surface coating on the other side of said sheet, and a plurality of symmetrically arranged phosphorescent materials of different color characteristics on said coating to reproduce an image in color.

2. A cathode ray image reproducing tube comprising a vacuum-tight envelope, a luminescent electrode structure mounted within said envelope including a glass sheet having an ultraviolet-light sensitive area therein, a plu rality of preferentially etched uniformly tapered apertures formed in said area, the maximum diameter of each of said apertures being substantially less than the thickness of said sheet, an electrically conductive coating covering at least one surface of said sheet, an electron beam source supported within said envelope in a position such that an electron beam produced thereby is scanned over said area, said apertures being oriented so that their projected axes intersect at a common point within said envelope, said electron beam source being effectively located at said point, a plurality of symmetrically arranged phosphorescent materials of different color characteristics secured to said coating, and a transparent reflecting electrode member mounted within said envelope adjacent to and spaced from said materials to reproduce an image in color.

References Cited in the tile of this patent UNITED STATES PATENTS 1,857,929 McFarland May 10, 1932 2,250,283 Teal July 22, 1941 2,416,056 Kallmann Feb. 18, 1947 2,506,604 Lokker et al. May 9, 1950 2,547,638 Gardner Apr. 3, 1951 2,558,019 Toulon .lune 26, 1951 2,577,038 Rose Dec. 4, 1951 2,606,303 Bramley Aug. 5, 1952 2,611,100 Faulkner et al. Sept. 16, 1952 2,622,220 Geer Dec. 16, 1952 2,663,821 Law Dec. 22, 1953

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