US3395305A - Cathode ray tube graticule - Google Patents

Description

July 30, 1968 L. s. YAGGY CATHODE RAY TUBE GRATICULE Filed Dec. 2, 1966 United States Patent 3,395,305 CATHODE RAY TUBE GRATICULE Leou S. Yaggy, North Carlsbad, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of California Filed Dec. 2, 1966, Ser. No. 598,849 1 Claim. (Cl. 313-92) ABSTRACT OF THE DISCLOSURE In providing a visible graticule for use in visual analysis of a cathode ray tube display, the present invention structurally incorporates an electrically conductive layer on the internal surface of the tube viewing screen and provides a phosphor pattern thereon of determined configuration which includes voids effecting a visible display of the desired graticule during tube operation. The invention is particularly advantageous in low contrast tubes wherein the provision of an effective visible graticule has heretofore been difiicult to provide. Additionally, the density of the phosphor layer may be improved as compared to prior art tubes of this type in that the patterns provided offer escape paths for secondary electrons to collect at the conductive layer. Thus storage and writing speed characteristics may be improved.

The invention relates to cathode ray tubes, generally, and has particular utility in that type of tube, which, because of operational mode, has inherent low-contrast characteristics. For example, bistable tubes are illustrative of tubes having inherent low contrast characteristics. The invention, therefore, provides a novel tube structure with a visible graticule and additionally aids in the operation of the tube.

Cathode ray tubes are frequently used for visual wave display patterns and other time and amplitude-varying phenomena. In the examination of such visual displays, it is sometimes desirable to provide a visible graticule to aid in the visual analysis of the display. Graticules generally comprise a network of perpendicularly arranged lines spaced in a predetermined relationship to each other to give visual effect to aspects of the phenomena being reviewed.

In my application Ser. No. 492,800, filed Oct. 4, 1965, Patent No. 3,356,881, I described a mode of manufacturing and providing an illuminated graticule for certain cathode ray tubes. The invention therein disclosed resulted in an illuminated internal graticule which had no effect on the contrast of a stored display. In certain lowcontrast tubes, such as bistable storage tubes, the technique described in the earlier-filed application is not particularly advantageous because of the inherent lowcontrast characteristics of such tubes. Additionally, the meshless bistable storage tube requires a combination viewing screen and illuminescent storage surface directly exposed to the electron beam, hence, the invention of my earlier-filed application cannot generally be applied thereto.

The operating principle of meshless bistable storage tubes generally requires a transparent conductive layer positioned on the glass viewing screen. A phosphor coating then covers the conductive layer to provide both luminescence and an ability to accept a charge for elapsed time image viewing. The transparent conductive layer usually acts as a collector electrode for secondary electrons which escape the storage layer during tube operation. In order to accommodate such secondary electron collection, it has heretofore been the practice to provide an extremely low-density, or sparse phosphor layer which, in effect, offers innumerable voids in its surface per- 3,395,305 Patented July 30, 1968 mitting the secondary electrons to pass therethrough and be captured by the exposed transparent conductive coating. A disadvantage of this practice is that the low-density phosphor is not conducive to providing a sharp and clear display. Additionally, writing speed is importantly reduced.

In an effort to provide an internal graticule visible during tube operation, prior art designs have deposited a grid of black lines using any suitable black material, such as carbon black, on the internal surface of the viewing screen. Thereafter, the transparent conductive layer and phosphor storage layer were deposited as described. This mode of graticule provision, while generally satisfactory, does involve the use of a foreign blacking material as well as an additional manufacturing step thus adding to the initial cost of the tube.

With the above in mind, it is a primary object of the invention to provide an internal graticule which will be visibly displayed and particularly suited to the lowcontrast type tubes described.

It is another object of the invention to provide a plurality of voids in the material distributed on the internal surface of the tube, such voids appearing as black lines on the viewing screen when the tube is operated. Specifically, the voids are positioned in relative arrangement determined by the graticule pattern desired.

It is a specific object of the invention to provide voids in the illuminescent phosphor layer which will effect a visible graticule pattern on the viewing screen during tube operation.

It is yet another object of the invention to provide voids of the type described which may be used to expose segments of a transparent conductive layer below the phosphor layer and thus act as a path for the passage of ejected secondary electrons to the conductive layer for capture and disposition.

These and other objects of the invention will become apparent in the course of the following description and from an examination of the related drawings wherein:

FIGURE 1 is a view of a segment of a cathode ray tube illustrating the graticule of the disclosed invention as it would appear on the viewing screen;

FIG. 2 is an enlarged view of the structure of FIG. 1 illustrating the pattern of phosphor disposition on the internal surface of the viewing screen taken at circle 2 of FIG. 1;

FIG. 2(a) is a view similar to FIG. 2 of an alternate mode of phosphor disposition illustrating the phosphor layer as a plurality of segregated island segments; and

FIG. 3 is a sectional view taken along line 33 of FIG. 2.

Directing attention to FIGS. 1-3, numeral 10 indicates a segment of the glass viewing screen of a conventional cathode ray tube having a viewing surface at 12. In conventional bistable cathode ray tubes a thin transparent coating 14, which is electrically conductive, is first positioned on the internal surface 16 of the viewing screen 10. Any suitable transparent material may be used, tin oxide having been found satisfactory. In normal practice a thin coating of phosphor is then placed over the internal surface of the transparent film 14. The phosphor provides the visible light pattern in that it will fluoresce when struck by an appropriate electron beam.

In the construction of the phosphor coating, the present invention teaches the preparation of a slurry of phosphor particles colloidally disposed within a solution of an ultraviolet-sensitized polyvinyl alcohol. The slurry is then placed over the surface of the transparent coating 14 and dried. Thereafter, a mask is provided similar to the mask disclosed in my referenced copending application and positioned over the dried slurry. The mask may be formed to define the graticule pattern desired. The arrangement is then exposed to an appropriate source of ultraviolet radiation, the mask intercepting the ultraviolet rays where graticule voids are desired. The exposed areas of the slurry become hard while the unexposed areas may be washed away after completion of the ultraviolet radiation step. This type of phosphor printing technique is conventional and well known in the art and will not be further described in detail.

After exposure and further processing, the internal surface 16 of the tube comprises first the transparent conductive coating 14 and uniformly disposed and separated segments or sections of phosphor 18, 18. The phosphor sections 18 define primary voids therebetween as at 20, 20, said voids 20 being arranged in perpendicular relationship to each other to provide major graticule lines visible during tube operation, as shown by lines 21, 21 in FIG- URE 1. In a preferred embodiment of the invention the voids 20 may be of an order of approximately .010 wide. Operating the tube with this construction, the voids 20, 20, will appear as the dark lines 21 on the viewing screen in the desired graticule pattern.

Additionally, segments 18 may define smaller voids therebetween as indicated by relatively narrow openings 22, 22, within each phosphor segment 18. They may be provided by appropriate additions to the mask and using the procedures noted above.

The secondary voids 22 may be extremely narrow, e.g., .001" wide, so as to be effectively invisible during tube operation. Alternately, they may be wide enough (.005 to be visible without the high definition of voids 20. When thus visible, they would provide smaller visible increments to the graticule pattern as shown by hair lines 25, 25 in FIG. 1.

FIG. 2(a) is a substantially enlarged view similar to FIG. 2 and illustrates a modification of the structure shown therein. Small discrete independent segments of phosphor 18a are provided. In total, the segments may still define the major voids 20. Minor voids 2211 may be provided between each segment 18a. The voids 220: may be dimensioned to be visible during tube operation as above described. Alternately, the voids 22a may be dimensioned to be invisible yet serve as paths for collection of secondary electrons by conductive layer 14. If desired both invisible and visible voids may be provided in the structures described.

In the operation of the embodiment shown in FIGS. 1-3, it will readily be understood that as the viewing screen is bombarded by an appropriate electron source, the phosphor segments 18 fluoresce and the intelligence pattern thereof will be visible at the surface 12. At the voids 20 and 22, the fluorescing effect will be absent because of the lack of phosphor coating in such voids. The voids, therefore, will appear as visible black lines at the viewing screen 12 and thus offer the desired visible graticule pattern.

The phosphor segments 18 and 18a may be used as a storage target as is well known in the art. Under writing electron bombardment the phosphor segments emit secondary electrons and the voids 20, 22, and 22a serve as openings or paths whereby the emitted secondary electrons may travel to the conductive coating 14. Thus, a sparse or low-density phosphor pattern need not be used and the clarity and resulting sharpness of the displayed image importantly improved.

The invention thus provides a simple, easily manufactured structure particularly suited to the provision of a visible internal graticule for those cathode ray tubes which have inherent lowcontrast characteristics. The invention, however, conceivably may be applied to other type display tubes.

These features and advantages of the invention are by way of illustration only and the invention may be modified in many particulars all within the general scope thereof.

What is claimed is:

1. In a cathode ray tube,

the combination of a transparent image screen,

a continuous uninterrupted transparent conductive layer positioned on the internal surface of the screen,

a plurality of illuminescent phosphor segments distributed over the inner surface of the conductive coating,

said segments defining therebetween primary voids having no phosphor distributed therein,

secondary voids defined by said segments, said sec ondary voids having no phosphor distributed therein and being distributed over the screen in uniform patterned relationship to each other and to the primary voids,

said voids being arranged in generally perpendicular relation to each other and of uniform pattern over the screen to define a visible dark-lined graticule pattern on the screen during tube operation and phosphor fluorescence,

the width of the secondary voids being less than the width of the primary voids whereby the components of the dark-lined pattern due to the primary voids are of a visibly darker intensity than the dark-lined pattern due to the secondary voids,

said voids providing travel paths for secondary electrons emitted from said phosphor segments to said conductive coating.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 10/ 1943 Switzerland.

4/1943 France.

ROBERT SEGAL, Primary Examiner.

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