US2890377A

US2890377A - Color tube shield

Info

Publication number: US2890377A
Application number: US483923A
Authority: US
Inventors: Norman F Fyler
Original assignee: Columbia Broadcasting System Inc
Current assignee: CBS Broadcasting Inc
Priority date: 1955-01-25
Filing date: 1955-01-25
Publication date: 1959-06-09
Anticipated expiration: 1976-06-09

Description

June 9 1959 N. F. FYLER COLOR TUBE SHIELD Filed Jan. 25, 1955 ,INVENTOR. Norman FJFyler ATTORNEY United States Patent-O COLOR TUBE SHIELD Application January 25, 1955, Serial No. 483,923

6 Claims. 01. 315-13 This invention relates to cathode raytubes in general and to tri-color television picture tubes in particular.

One of the problems associated with tri-color picture tubes is the elimination of the effect known as halation. Halation is the false excitation of the fluorescent materials around the edge of the viewing screen. For example, if a portion of the red-producing electron beam falls on the blue-producing fluorescent material, the visible color blue will be produced.

In a shadow mask tube, the foramina in the mask prevent cross-excitation of the fluorescent materials over the greater part of the viewing screen. However, even a practical design such as that shown in United States Patent No. 2,690,518 of Fyler and Rowe, assigned to the same assignee as the present application, exhibits halation around the edge of the viewing screen. In such a tube, halation appears as a bluish fringe with green overtones around the picture. If uncontrolled, such visible evidence of halation may render a tube commercially unacceptable.

The color of the fringe around the picture is a function of the different luminous efliciencies of the presently used luminescent materials and the method of compensating for the different efliciencies. The red-producing material now being used is the least efficient; that used to produce green being next in efliciency and that used to produce blue being the most efficient. The beam currents of the guns are adjusted to keep the ratio of the beam currents inversely proportional to the luminous efliciency of the particular luminescent materials over all usefulbrightness ranges. This means that at any given brightness level the blue beam is the least intense and the red beam the most intense. Even a small proportion of the red beam reflecting off the funnel of the tube and impinging on the blue and green producing phosphors will excite such phosphors sufliciently to give a visible color.

A positioning structure for a shadow mask adjacent to the viewing screen is shown in detail in a patent application of Fyler Serial No. 506,684, dated May 6, 1955, for Color Picture Tube. This structure results in an opening being left between the outer edge of the shadow mask and the inner wall of the tube envelope. This opening has proven troublesome because as the raster is scanned, the electron beams are periodically deflected so as to fall on the inner wall of the tube envelope adjacent to the opening. Although the inner wall is coated with a conducting material, some reflection occurs. In addition, some secondary emission undoubtedly occurs. The reflected electrons and a portion of the secondarily emitted electrons are diffused through the opening on to the edges of the viewing screen. No separation of the beams has been accomplished because the beams have not passed through any of the foramina in the shadow mask. Therefore, the three beams remain mixed even after reflection. The ratio of the beam currents energizing each color-producing fluorescent material under these conditions is not inversely proportional to the luminous. 'efliciency of the various phosphors. The result is the bluish green fringe which is so objectionable. The red phosphor is also energized,

2,890,377 I fiatented June 9, 1959 2' but since its efiiciency is low, the effect is masked by the more intense blue and green.

The effect of halation has been studied and may be avoided or minimized in any one of the following ways: (1) Fitting the mask to the panel so that an intimate contlziact is made completely around the periphery of the mas 1 n (2) Designing sweep circuits so that no part of the raster is swept over the-outer edge of the mask;

(3) Blanking off overswept portions of the raster from the fluorescent screen;

(4') Reducing the active area of the fluorescent screen; (5) Equalizing .the luminous efliciency of each of the fluorescent materials used to make the viewing screen;

(6) Using a perfect conductor with a very highwork.

function as a coating on the inner walls of the tube envelope. 1

A moments consideration will serve to show that method 3 above is the best. Each of the other methods involve high cost precision work, complicated external circuitry, sacrifice of efficiency, or development of special materials n g V A second problem associated with the manufacture of color tubes arises when the funnel is joined to the panel to complete thev tube envelope. All practical methods of fabricating a color tube make it highly desirably that the tube envelope be constructed of at least two major parts. The usual parts are the rear section which includes a neck and funnel, and the viewing screen end, or panel. The electron guns are mounted in the neck and the fluorescent screen and shadow mask in the panel. Metallic flanges are usually sealed to the mating ends of the funnel and flange to permit welding'to complete the envelope. Cushioning of some kind is desirable especially during assembly of the panel and funnel. Extreme care then need notbe taken to avoid mechanical and thermal strains. At the same time, a firm evenly distributed mechanical contact must be maintained between the parts to ensure proper relative positioning of the electron guns, the shadow mask and the fluorescent screen. 7

It is an object of this invention to provide a simple device in a color picture tube to eliminate the effects of halation. I Y

It is a further object of this invention to provide self supporting positive means of positioning an anti-halation device or electron shield.

It is also an object of this invention to furnish a cushioning pad between the paneland funnel portions of the tube to prevent injury to either portion during assembly.

In general,"the'objects of the present invention are attained by placing a conductive element substantially perpendicular to the path of electrons reflected off; the funnel or emanating therefrom due to secondary emission, thusintercepting or preventing such electrons from impinging on the luminescent screen. The conductive element is held in position perpendicular to the longi-' tudinal axis of the tube by pressure exerted on either side by the panel and funnel after the two parts are secured together. At the same time, serrations in the con ductive element allow the conductiveelement to deform slightly in response "to such pressure, thus prevening excessive strains in the glass of which the panel and funnel are made. Motion of the anti-halation screen in a direction perpendicular to the longitudinal axis of the tube is prevented by a lip on the periphery of the conductive element. This lip is substantially perpendicular to the plane of the main part of the conductive element and is preferably formed as an integral part of the conductive element. During assembly, this lip is matched with an indentation previously fashioned in either the v j panelor funnel of the completed tube. For a better .3 understanding of this invention, reference should be made to the drawing in which:

Fig. 1 is an orthogonal view of a practical embodiment of this invention; and

Fig. 2 is a view of the shieldnf Fig. 1 in ,place ina color picture tube. Only the electron beam ,produeing red is depicted.

Referring to Fig. 1, the threemainparts of a preferred embodiment of -an-e.le1ctron shield 13 may be seen. The inner portion 11 of the shield 13, the central portion 15 and the lip 20'may advantageously be formed from a single electrically conductive sheet. The .lip 20 is preferably-a flange=projecting substantially @at .right angles to the plane of the remaining portions 11, .15 of the shield 13. The-central'portion 15.01? the shield13 .may be serrated or-crimpedifrom theinner :edge :of the :lip 20 to provide a resilient surface .of any .desired dimensions. The typeofcrimping is mot material. The inner portion 11 of the shield 13 projects inwardly .from the central portion 15 a predetermined amount to form an aperture of any desired size and shape.

Alternative ways of constructing a shield which will perform some or all the functions performed by the preferred embodiment will suggest themselves to :anyone skilled in the art. Among such ways are the extension of either or both the Eflanges 17 18 (shown in Fig. 2) inwardly inplace-of the shield 13., shaping a shield from a resilient electrically conductive material :such as woven wire, or crimping the inner portion 11 of'the'shield 13. However, in order toobtain the :required shielding, cushioning and-positioning, the embodiment :shown is preferred.

The operation of .the electron .shield .13 may be seen by referring to Fig. 2. .The panel 16 has a flange 17 sealed thereto; the :funnel 12 has a second flange .18 sealed thereto. The flanges 17 and 18 :are similarly shaped for manufacturing economy and convenience .of assembly. Each flange 17' and 1.8 has a groove 21 of sutficient :depth and diameter :to accommodate the lip 20 f the shield 13. Whenthe'lip 20 is :placed in one of the grooves 21, the crimped .central portion covers the

flange

17 or 18 inwardly :of the :groove 21. The shield 13 is thus restrained from any substantial radial movement. After the lip 20-is insertedgin the selected groove 21, the remaining section of'thewtube envelope is positioned so that the outer edges of the flanges 17 and Y18 are adjacent to each other. .A compressive forceeis exerted on the central portion ofzthe xelectronzshield 13 by so moving the

flanges

17, 18 intorjuxtaposition. The resiliency of'the central portion .15 cushionsany shock. While the

flanges

17, 18 are :thus held, :a weld '19 is formed between the ,outerperipher ies of the

flanges

17, 18. This weld 19 holds the parts firmly in place.

When the assembled :tube is :placed in operation the following occurs. The deflected red electron beamzoriginating at'electron :gun 23 isrepresented by the fascicled arrows such as those numbered 22. The spacing between the arrows roughly represents the electron-density variations across the beam. The broken arrows such as those numbered 22:: represent: that portion ofthe :electron beam which is reflected off the inside of the :funnel '12. The broken arrowssuch as those numbered22b represent those electrons which are secondarily emitted from the inner wall .of the funnel ,12. The dotted arrows such as those numbered 220 represent the ,path the electrons would take without the electron shield in place.

The inner portion of electron shield 13 is positioned in the path of the reflected portion .of'the e'lectronbeam 22a and in the path of substantially all the secondarily emitted electrons 22b which could impinge on the luminescent screen. The electron shield 13 is substantially normal to the path of the reflected and secondarily emitted electrons 22a, 22'b'so that any electrons reflecting off the shield '13tdo not reachthe luminescent screen on the .panel 16 eitherzthrough 501' around the shadow,

mask .24. Any electrons such as those represented by the arrow 22c which would, in the absence of the shield 13, impinge on the luminescent screen after reflection near the edge thereof are intercepted by the shield 13. If the main part of the beam 22 is deflected to the position of the arrow 22c, reflection in the absence of the shield 13 would :be intensified. An electrical contact 14 bleeds 01f any charge which tends to build up on the electron shield 13, keeping the shield 13 at the same potential as the inner wall of the panel 16 and funnel '12.

Although the invention "has been illustrated and described in connection with one practical color television picture tube in which it has been incolporated, it is believed that the concept of simultaneously providing a simple electron shield and cushioning device which may be positively positioned in the tube to eliminate halation and breakage in manufacturing is such that other embodiments will suggest themselves to those skilled in the art. In particular, it should be noted that the shape of the viewing screen of the picture tube in which an electron shield such as that shown and described is not restricted. A viewing screen of any shape other than the described circular shape may be protected by a shield of appropriate outline. Such other embodiments are believed to be within the spirit and scope of the present invention as defined in the appended claims.

What is claimed is:

1. A tri-color television picture tube having a two-part envelope, a :viewing screen disposed on a portion of the inner surface of one part of said envelope and including, a resilient annular ring frictionally positioned between said parts of said envelope and projecting inwardly of said envelope adjacent the viewing screen of said tube, said ring being fabricated from an electrically conductive material, and means .for maintaining said ring at the same electric potential as .the said part of said envelope which includes said viewing screen.

.2. In a cathode ray tube, an annular electron shield comprising, a substantially flat electrically conductive inner portion, a \cn'mped central portion integral with said flat portion and a peripheral fold substantially perpendicular to the plane of said inner portion.

3. In :a cathode ray'tube having a panel and funnel, an electron shield comprising, an annular electrically conductive ring, a crimped'portion outwardly adjoining said annular ring and means for retaining said ring in the inter-stice between said panel and funnel.

'4. An electron shield for cathode ray tubes comprising, an inner portion, a central portion and a peripheral portion, said portions being formed from a single sheet of electrically conductive material, said inner portion having an aperture of predetermined size formed therein, said central portion being crimped, and said peripheral portion being substantially perpendicular to said central portion.

5. In a multi-color cathode ray tube for television picture presentation, an electron shield and positioning apparatus comprising, an annular electrically conductive element, the cross-section of the outer edge of said annular conductive element being shaped to fit a predetermined cross-section of said tube, the inner edge of said annular conductive element being substantially parallel to said outer edge, corrugations being formed in the said annular conductive element, said :annularconductive element being disposed in said tube substantially perpendicularly to the longitudinal axis thereof to mask the edges of the viewing screen therein.

6. In a tri-color shadow maskpicture tube having a panel and an adjacent funnel portion to form an envelope, a fluorescent viewing screen disposed on a portion of the inner surface of said panel and means for simultaneously deflecting three electron beams originating in said funnel portion, a cushioning and shieldingdevice comprising, a "resilient portion .frictionally mounted in theintersticeXbetween:said panel and said tunnel, a cir- 5 6 cumferentially positioning portion disposed about the References Cited in the file of this patent outer edge of said panel, and a flat annular portion UNITED STATES PATENTS inwardly adjoining said resilient ring portion and projecting inwardly of said interstice to intercept a pref g g g -55 2 gig determined ortion of said deflected electron beams, h 5 2659026 2 9 1953 inner edge of said annular portion having substanti lly 3 em 5 1954 the same shape as the proj d P p y of said View 5 er l l S t 10 1957 ing screen on the plane of said fiat annular p0rti0n, sai 2806165 L cQm en 1 1 57 annular portion, said resilient portion and said ciraw 9 cumfe'rentially positioning portion being electrically 10 conductive.