US2738437A - Color grid structure for cathode-ray tube designed for polychrome image reproduction - Google Patents

Description

March 13, 1956 w. A. LLOYD 2,738,437

COLOR GRID STRUCTURE FOR CATHODE-RAY TUBE DESIGNED FOR POLYCHROME IMAGE REPRODUCTION Filed Aug. 28, 1953 FIG. 3

IN V EN TOR. W/wAM 11. w

United States Patent O COLOR GRID STRUCTURE FOR CATHODE-RAY TUBE DESIGNED FOR POLYCHROME IMAGE REPRODUCTION William A. Lloyd, El Cerrito, Calif., assiguor to Chromatic Television Laboratories, Inc., New York, N. Y., a corporation of California Application August 28, 1953, Serial No. 377,209

6 Claims. (Cl. 313-48) The present invention relates to cathode-ray tubes of the type adapted to elfect the reconstitution of polychrome images. More particularly the invention relates to a color grid structure for such cathode-ray tubes which is characterized by ease of assembly and ability to enhance the fidelity of the reconstituted image.

Cathode-ray tubes having a grid of parallel wires located adjacent to a striped phosphor screen are now known in the art. Such a structure may in some instances serve to focus the beam electrons into a pattern of thin lines nominally registered with the discrete phosphor areas of the screen, as set forth by ErnestO. Lawrence in certain of his copending United States patent applications, such as Serial No. 219,213 filed April 4, 1951, now U. S. Patent #2,692,532 granted October 26, 1954, and Serial No. 234,190 filed June 29, 1951.

One type of cathode-ray tube incorporating this prin-' ciple, which may be termed post-deflection-focusing, is designed with a relatively large number of narrow component-color phosphor strips laid down in a predetermined sequence to form a screen, or target electrode. These phosphor strips luminesce, when impacted by the cathode-ray beam, in various component colors of the image to be synthesized. Purely as an example, the order in which the phosphor strips are laid down may be red, green, blue, green, red, green, etc., bearing in mind that the color of the phosphor as used herein refers to the color of the light emitted therefrom which is seen by an observer. An electrically conductive coating overlies the phosphor strips, and is produced in some preferred manner such as by aluminization.

In order that the path of an electron arriving at the phosphor screen from the cathode emitter may be controlled in a selective manner in the vicinity of the target, a grid assembly is located adjacent to the phosphor screen, and, with the latter, comprises a color grid structure of the type to which the present invention is particularly applicable. Such a grid is formed of a large number of wires or linear conductors, extending in the same direction as the phosphor strips and lying in the path of electrons directed to the target electrode from the electron gun of the cathode-ray tube. The wires of the grid assembly are electron-optically related to the phosphor strips so that, in this electron-optical sense, there is a wire aligned with each blue strip, and-similarly a wire aligned with each red strip: It should be borne in'mind that this electron-optical alignment incorporateswhatever spacing corrections are necessary to compensate'for variations introduced into the tube operation by changes in the instantaneous angle of impingement 'of the cathode-ray beam as it scans the target, and'also by changes in deflection sensitivity at portions of the target electrode asymmetrically located with respect to the tube axis. However, these corrections form no part of the present invention, and are mentioned merely as an aid in understandingthe operation of a tube of the nature set forth. All of'the Wires associated with the red" strips are connected to a common terminal, while the blue wires are similarly joined together electrically.

Between the actual or nominal plane of the wire grid assembly and the conductive coating on the phosphor strips a diiference of potential is established. By properly choosing the magnitude and polarity of this potential difference, a series of converging electrostatic fields for the beam electrons is created. These converging fields which may be likened in an optical sense to cylindrical lenses) cause the beam electrons arriving at the wire grid from the electron gun of the, tube to form a fine line structure on the phosphor target. It will be appreciated that the particular scanning operation by means of which the beam electrons are caused to trace a raster at the plane of the grid wires has no direct geometrical relationship to the actual line structure developed on the target electrode, the latter being determined solely by the configuration of the wires of the grid assembly.

Inasmuch as the grid wires, as stated above, are electron-optically aligned with the phosphor strips, a zero potential diflerence between the red and blue terminals of the grid will result in the beam electrons undergoing a focusing action alone, and hence these electrons may be caused to impinge the target within the boundaries of a particular strip such as green. If the conductors associated with the red strips are then made positive relative to the conductors electron-optically related to the blue strips, the beam electrons will be subjected to an auxiliary or micro deflection over and above that due to the deflection providing the raster, so that the lines of impingement of such electrons will now lie within the respective boundaries of the red strips. Similarly, electrons will strike the blue strips when the wires associated withsuch strips are suitably positive with respect to the red wires. Diiferent component colors of the image are thus displayed according. to the potential difierence (if any) existing between the two sections of the grid wire assembly.

Indesigning one color grid structure of the above type, the grid wires are chosen to be essentially coplanar, and are maintained in position relative to the phosphor strips of the target by means of spacer elements. The spacing between the plane of the grid wires and the phosphorcoated surface of the target is critical in many respects and must remain substantially unchanged during operation of the cathode-ray tube. One preferred construction in which the grid wires and the target electrode are formed as a unit is illustrated and described in a copending United States patent application of Renn Zaphi-' ropoulos, Serial No. 307,435 filed'September 2, 1952.

In the Zaphiropoulos assembly, a light-transmissive base plate (which may be of glass) is employed as a target backing. This base plate is secured to a grid frame by the strand conductors, or wires, of the grid. A pairof spacer elements is aflixed to one surface of the base plate, and defines a window, or target area, therebetween which may be coated with phosphor strips having the desired color characteristics. Means are provided for securing the electrically-conducting wiresto the frame s9 that these wires extend across the window, or target area, of the-base plate and are positioned therefrom by the spacer ele ments. In one embodiment, the grid wires, or linear conductors, are divided into two sets of alternate strands, and suitable means are provided for applying potentials to each set of strands. In this particular showing, the frame is divided into two sections, with each section serving a separate set of strands and also being electrically insulated from the other.

It will thus be recognized that in this form of construction the glass plate is sandwiched between the wires of the grid, onone hand, and the two frame'portions on the other. These two frame portions are pressed 3 together by the tension of the wires associated with the outer frame portion, and this pressure acts to hold the frames, base plate and wires in a unitary assembly. Some form of insulation between the two sections of the frame is required in order to permit different potentials to be applied to the two sets of grid wires.

While two sections of a frame of the type above suggested may be separated by a layer of glass tape or mica, it has been found that the glass tape, or ribbon, which is commercially available is generally too thin for dependable operation under normal conditions. Using such tape has ofttimes caused electrical shorting between the two sets of grid wires. Furthermore, it results in occasionally loose fibers within the cathode-ray tube, and these fibers may have a deleterious effect upon the quality of the reproduced image. With respect to mica insulation, this substance is comparatively expensive, and, furthermore, it is quite difficult adequately to de-gas during tube bakeout. One further disadvantage common to both of these types of insulation is that they are difficult properly to install when the grid is wound, and hence the cost of the resulting color grid structure is increased.

According to a feature of the present invention, the above difficulties are overcome by utilizing a form of insulating material between the two frame sections which is relatively inexpensive and which achieves all necessary insulation without being ditficult to de-gas and without possessing a tendency to deposit loose fibers within the cathode-ray tube envelope. Still further, the insulating substance described in the present application is noncompressible and hence results in a color structure in which the wires may be maintained under a higher degree of tension than they are in the case where some flexible insulating material such as glass tape is employed. In addition, the insulating material employed in the present invention is more readily installed than either glass tape or mica, and hence assembly of the color grid structure is facilitated and manufacturing cost decreased.

One object of the present invention, therefore, is to provide an improved form of color grid structure suitable for incorporation into a cathode-ray tube designed for polychrome image reproduction.

A still further object of the invention is to provide an improved means for insulating the two frame sections of a color grid structure which possesses none of the dis advantages of the means formerly employed for this purpose.

An additional object of the invention is to provide a color grid structure for cathode-ray tubes which may be easily constructed at minimum cost.

Other objects and advantages of the invention will be apparent from the following description of a preferred form thereof and from the drawings, in which:

Figure 1 is a semi-diagrammatic view of a cathode-ray tube showing in cross-section a color grid structure, or target assembly, in accordance with the present invention;

Figure 2 is a plan view of the color grid structure or target assembly, of Fig. 1 as seen from the electron gun end of the cathode-ray tube;

Figure 3 is a cross-sectional view of a part of the color grid structure of Fig. 2; and

Figure 4 is a plan view of a portion of the target area of Fig. 2, showing one preferred relationship between the grid wires and phosphor strips.

Referring now to the drawings, there is shown in Fig. l

a cathode-ray tube, certain parts of which are conven-.

tional. For example, in the neck end of the tube, and within the envelope 10, there is an indirectly-heated cathode 12 which acts as a source of electrons for development into a scanning beam. The latter is indicated schematically by the trace 14. Adjacent to, and partially surrounding the cathode 12, is a control grid or electrode 16 suitably apertured to permit the passage of electrons which are subsequently formed into the beam 14. The

control grid 16 functions in the usual manner to modulate the emitted stream of electrons in accordance with the potential applied thereto relative to the cathode 12. Also in the neck of the tube there is provided a'first anode 13 to which suitable potentials may be applied so as to result in the initial acceleration of the electrons emitted from the cathode 12. Adjacent to the first anode there is positioned a second anode 20 for supplying an additional acceleration to the electrons and also for focusing the developed beam.

Deflecting coils comprising a horizontal pair 24 and a vertical pair 26 are provided for the usual scanning purposes. Obviously the terms horizontal and vertical are used herein in a descriptive sense only. Thus the electron beam 14 is caused to scan a target, or translucent backing area 22, to produce light which is visible through the end wall 28 of the envelope 10.

The translucent base plate 22 may be secured in the viewing end of the cathode-ray tube in many different ways. One possible method is shown in Fig. 2, and incorporates a contoured support, or frame section 30, adapted to fit Within the envelope of the tube and hence maintain the base plate 22 in position adjacent the end wall 28. The frame section 30 is accordingly provided with a plurality of lugs 32 which are shown in Fig. 2 as having a contour generally similar to the internal periphery of the envelope 10. In the case of a metal envelope 10, small angles 34 may be Welded to the inside surface of the envelope at positions where it is desired to attach the lugs 32. The lugs are joined to the angles by means of bolts or rivets 36 which preferably pass through ceramic bushings (not shown) and which are provided with insulating discs on each end to isolate electrically the support for frame section 30 from the envelope 10. Other means of attachment may be employed especially when glass instead of metal envelopes are used. However, since these constructional features form no part of the present invention, and furthermore are mentioned in the above-referred-to Zaphiropoulos application, no further details regarding them will be set forth herein.

About the support, or frame section 30 and the base plate 22 there are stretched electrically-conducting strands which appear as shown in Fig. 2 when viewed from the electron beam source. These strands are generally identified by the reference numeral 38 in the drawings. Aflixed to the surface of the target 22 against which the electron beam is adapted to impinge is a pair of insulating spacer elements respectively designated by the numerals 40 and 42 (Fig. 2). These spacers, as well as the translucent base plate 22, may comprise bore-silicate glass, but in any event should possess the same coefiicient of expansion. These spacer elements provide the dual functions of aligning and supporting in substantially coplanar relation to the strands 38 at a uniform distance from the surface of the target 22.

In order that each pair of adjacent strands 38 may serve as an electron lens to focus the beam electrons into a substantially linear trace on the target 22, and at the same time to provide structure for deflecting the focused trace from one phosphor area to another, means are provided for separating the strands 38 into two electrically insulated sets of conductors. In accordance with the present invention, this means includes a two-section frame, comprising a pair of continuous loops or rectangular forms as indicated by the showing of Figs. 2 and 3. Thus an additional member 44 is employed in conjunction with the frame section 30 described in connection with Fig. 2. This frame section 44 may be generally similar in outline and general configuration to that of the frame section 30, except that it does not possess the lugs 32. As indicated by the cut-away portion of Fig. 2, the frame section 44 underlies the frame section 30 as viewed from the cathode end of the tube and is maintained in spacedapart relation therefrom by the presence of a pair of insulating separators consistingof the vitreous rods 46.

As is apparent from Fig. 3, the continuous frame member 30 is disposed adjacent to that side of the target 22 which faces the end wall 28 of the cathode-ray tube. An aluminized phosphor coating 48, preferably in accordance with the showing of Fig. 4, is deposited on the opposite (or gun) side of the target 22 between the glass spacer elements 40 and 42.

Each extremity of the frame section 30 associated with a termination of the grid wires 38 is provided with a notch or indentation 50 cut into that surface thereof which is opposite to the one contacting the target backing 22. This notch 50 extends parallel to that edge of the frame section 30 to which the grid conductors 38 are to be attached in a manner set forth below. The vitreous rods 46 (which may be of glass) are adapted to be in part receivable within these notches, and the former are chosen to be of such diameter that the frame section 44(when resting upon the glass rods 46 as shown in Fig. 3) is maintained in spaced-apart relationship from the outer surface of the frame section 30. It will be apparent from Fig. 3 that when the grid wires or conductors 38 are looped around the slotted edge (not shown) of the frame section 44 in the manner described below, and when a suitable tension is imparted thereto, then the frame section 44 acts to hold the glass rods 46 firmly seated within their respective notches. Inasmuch as the glass rods 46 are not compressible, there can be no electrical contact between the frame sections 30 and 44 regardless of the degree of tension imparted to the grid conductors.

Although fully set forth in the Zaphiropoulos application mentioned above, it might be stated that the edges 52 and 54 of the frame sections 30 and 44, respectively are slotted to permit the grid wires 38 to be looped therearound, with alternate wires being looped around the same particular frame section. Those alternate ones of the grid wires 38 to which a particular potential is to be applied are looped around the slotted edge 52 of the frame section 30, while the remaining ones of the grid Wires 38 to which a different potential is to be applied are looped around the slotted edge 54 of the frame section 44. To establish and maintain a proper spacing of the wires, the spacer bars 40 and 42 are precisely notched or slotted in some preferred manner such as described in the above-mentioned Zaphiropoulos application. Also, if desired, the edges of the backing plate 22 around which the wires are passed may be provided with slots each adapted to receive an individual conducting strand 38.

One set of alternate conductors is thus in contact with the frame section 30, and a single terminal connection to this frame section will provide for the application of a substantially uniform potential to the wire strands associated therewith. The second set of conducting strands is formed in the same manner as the first set. The glass rods 46 provide completely adequate insulation between the frame sections 30 and 44, and, if desired, a cementitious composition known by the trade name Insalute may be applied to the notched edges 52 and 54 of the frame sections 30 and 44 respectively in order to insure that the wires remain in the notches formed in the edges of the frame sections.

The relative position of the conducting strands, or grid wires, 38 and the red, green, and blue phosphor strips which are applied to that surface of the target 22 impacted by the electron scanning beam is shown in Fig. 4. Although the particular arrangement of the phosphor strips forms no part of the present invention, nevertheless a desirable arrangement has been shown to consist of alternate red and blue strips with a strip of green interposed therebetween. The strip widths are chosen in accordance with tube design so as to provide electro-optical rather than physical relationships between the grid wires and the phosphor strips. Each adjacent pair of grid wires accordingly is designed to subtend in an electro-optical sense a portion of the target electrode surface which includes phosphor areas of each of the component colors. Generally speaking, it may be said that the distance between adjacent grid Wires is substantially equal in one dimension to a single elemental area of the image to be resolved by the cathode-ray tube.

Inasmuch as one of the principal objects of the present invention is to eliminate certain disadvantages of other color grid structures, such as 1) the possibility of electrical shorting between the frame sections 30 and 44, (2) the tendency of certain materials such as glass tape to deposit loose fibers within the envelope of the cathoderay tube, and (3) the high cost of insulating material, such as mica, it will be seen that the glass rods 46 possess none of these drawbacks. In addition to being readily available and of low cost, these rods will provide any degree of insulation desired between the frame sections 3t) and 44 depending upon the diameter of the particular glass rod employed. Since they are obviously non-compressible, this degree of insulation will be maintained throughout the life of the cathode-ray tube. Although it is desirable to employ continuous, or one-piece, rods to separate the frame sections 30 and 44, it is clearly within the scope of the invention to use segments of a rod disposed at intervals, leaving an air gap between the frame sections at the remaining locations.

Although the rods 46 have been described above as being formed of vitreous material such as glass, it will be apparent that other ceramic compositions may be substituted therefor as long as they possess the proper insulating characteristics and are substantially non-compressible. Furthermore, although the rods 46 have been illustrated and described as being substantially circular in cross-section, it is clearly feasible to utilize a particular shape of rod which will more nearly correspond to the outline of its respective notch 50. Furthermore, whether this glass rod 46 contacts the frame section 44 in a fine line or over a greater surface area is immaterial insofar as the principles of the present invention are concerned.

Having thus described the invention, what is claimed is:

1. An electrode assembly for a cathode-ray tube, said electrode assembly comprising a light-transmissive electrically-insulating base plate, a pair of essentially planar electrically conductive frame sections positioned side-byside both with respect to one another and with respect to a surface of said base plate facing the end wall of said cathode-ray tube, each of said pair of frame sections having two extremities respectively associated with oppositely-disposed edges of said base plate, a pair of spacer bars aifixed to that surface of said base plate facing the electron gun of said cathode-ray tube, said pair of spacer oars respectively lying adjacent and substantially parallel to the said oppositely-disposed edges of said base plate so as to include therebetween a raster area, a first electricallyconducting means in the form of a first set of substantially parallel linear conductors secured in position at the said oppositely-disposed extremities of one of said pair of frame sections and extending from one of said extremities around that edge of said base plate associated therewith, over one of said spacer bars, across the raster area of said base plate, over the other of said spacer bars, and around the opposite edge of said base plate to the other extremity of said one frame section, a second electrically-conducting means in the form of a second set of substantially parallel linear conductors secured in position at the said oppositely-disposed extremities of the other of said pair of frame sections and extending from one of said extremities around that edge of said base plate associated therewith, over one of said spacer bars, across the raster area of said base plate, over the other of said spacer bars, and around the opposite edge of said base plate to the other extremity of said other frame section, the linear conductors 'of said first and second sets being interspersed across said raster area so that the conductors of said first set lie between the conductors of said second set, and a pair of cylindrical insulating elements interposed between the two frame sections of said pair for holding the latter in spacedapart relation, whereby a difference of potential may be applied therebetween and hence between said first and second set of linear conductors.

2, The combination of claim 1 in which the said pair of cylindrical insulating elements are composed of non-compressible material.

3. The combination of claim 2 in which the non-compressible material of which the said cylindrical insulating elements is composed is of a vitreous nature.

4. The combination of claim 2 in which the said cylindrical insulating elements are glass rods.

5. An electrode assembly for cathode-ray tubes, said electrode assembly comprising a light-transmissive electrically-insulating base plate, a pair of essentially planar electrically-conducting frame sections positioned side-byside both with respect to one another and with respect to a surface of said base plate facing the end wall of said cathode-ray tube, each of said pair of frame sections having two extremities respectively associated with oppositely-disposed edges of said base plate, a pair of spacer bars affixed to that surface of said base plate facing the electron gun of said cathode-ray tube, said pair of spacer bars respectively lying adjacent and substantially parallel to said oppositely-disposed edges of said base plate so as to include therebetween a raster area, a first electricallyconducting means in a form of a first set of parallel linear conductors secured in position at the said oppositely-disposed extremities of one of said pair of frame sections and extending from one of said extremities around that edge of said base plate associated therewith, over one of said spacer bars, across the raster area of said base plate, over the other of said spacer bars, and around the opposite edge of said base plate to the other extremity of said one frame section, a second electrically-conducting means in the form of a second set of substantially parallel linear conductors secured in position at the said oppositely-disposed extremities of the other of said pair of frame sections and extending from one of its extremities around that edge of said base plate associated therewith, over one of said spacer bars, across the raster area of said base plate, over the other of said spacer bars, and around the opposite edge of said base plate to the other extremity of said other frame section, the linear conductors of said first and second said sets being interspersed across said raster area so that the conductors of said first set lie between the conductors of said second set, the surface of one of the said frame sections being provided with a pair of notches respectively extending adjacent and parallel to its said oppositely-disposed extremities, a pair of cylindrical insulating elements composed of non-compressible material re spectively receivable in part in said pair of notches so as to be interposed between the two frame sections of said pair for holding the latter in spaced-apart relation, whereby a difference of potential may be applied therebetween and hence between the said first and second set of linear conductors.

6. An electrode assembly for a cathode-ray tube, said electrode assembly comprising a pair of frame sections each having wire-engaging means on oppositely-disposed edges thereof, a transparent plate, a continuous wire wound back-and-fourth across one surface of said plate and held by the wire-engaging means of one of the said frame sections so as to clamp said one frame section to the other surface of said plate, at least two non-compressible electrical insulators respectively disposed adjacent the wire-engaging means of said one frame section, and a second continuous wire wound back-and-forth across the said one surface of said plate and held by the wire-engaging means of the other of said frame section to said one frame section through the said electrical insulators, whereby such insulators act to maintain said two frame sections in spaced-apart relation.

References Cited in the file of this patent UNITED STATES PATENTS 2,444,740 Jonker July 6, 1948 2,461,515 Bronwell Feb. 16, 1949 2,535,307 Mankin et al Dec. 26, 1950 2,590,764 Forgue Mar. 25, 1952 2,653,263 Lawrence Sept. 22, 1953

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