US2796546A - Damp rod construction for cathode ray tube grid structure - Google Patents

Description

June 18, 1957 PATTERSON 2,796,546

DAMP ROD CONSTRUCTION FOR CATHODE RAY TUBE GRID STRUCTURE Filed June 29, 1953 2 Sheets-Sheet 1 INVENTOR. Howard A. Fame/"$00 June 18, 1957 H, R, PATTERSON 2,796,546

DAMP ROD CONSTRUCTION FOR CATHODE RAY TUBE GRID STRUCTURE Filed June 29, 1953 2 Sheets-Sheet 2 INVEN TOR. Howard E Puffs/"son United States Patent? O DAIVIP ROD CONSTRUCTION FOR CATHODE RAY TUBE GRID STRUCTURE Howard R. Patterson, Oakland, Calif., assignor to Chromatic Television Laboratories, Inc., New York, N. Y., a corporation of California Application June 29, 1953, Serial No. 364,778

7 Claims. (Cl. 313-78) The present invention relates to cathode-ray tubes of the type adapted to eifect the reconstitution of polychrome images. More particularly, the invention relates to cathode-ray tubes having a grid of coplanar parallel wires positioned adjacent to a striped phosphor screen or target electrode. It also relates to means for enhancing the color fidelity of the image reproduced on this screen by inhibiting any tendency the wires of the grid may have to vibrate as a result of the cyclic application of electrical potentials thereto and/or as a result of any shock excitation of either a physical or electrical nature.

Cathode-ray tubes constructed with a grid of parallel wires located adjacent to a striped phosphor screen are already'known in the art and serve to focus the beam electrons into a pattern of thin parallel lines registered with the phosphor strips of the screen. The PDF (postdeflection-focusing) type of cathode-ray tube operation has been set forth by Ernest 0. Lawrence in various of his copending United States patent applications, such as Serial No. 219,213, filed April 4, 1951, and Serial No. 234,190, filed June 29, 1951 (now respectively U. S. Patent No. 2,692,532, granted October 26, 1954, and U. S. Patent No. 2,711,493, granted June 21, 1955).

In order to facilitate an understanding of the principles of the present invention, a brief description of one such form of single-gun PDF tube will now be given. This description should be construed as exemplary rather than limiting, since it will be seen that the invention is obviously applicable to tubes constructed along different lines. In general, however, the tube may incorporate a screen or target electrode made up of a relatively large number of very narrow component-color phosphor strips and laid down in a predetermined sequence and intended to luminesce, when impacted by the cathode-ray beam, in colors such as red, green, blue, green, red, green, for example. Obviously, when reference is hereinafter made to the color of a phosphor, what is meant is the color of the light emitted therefrom which reaches the eye of the observer. The phosphors are then aluminized, or the screen in some other manner is provided with an electrically conductive coating.

A grid assembly is located adjacent to such phosphor screen. The grid may be made up of parallel coplanar wires, and so related to the phosphor strips that, in an electron-optical sense, there is a wire aligned with each blue strip, and similarly a wire aligned with each red strip. The red wires are connected to a common terminal, while the blue wires are similarly joined together electrically.

Between the plane of the wire grid assembly and the conductive coating on the phosphor screen, there may be established a relative difference of potential of such magnitude and polarity as to create a series of converging cylindrical lenses for the electrons in the scanning beam. Such converging fields cause the beam electrons to form a fine line structure on thephosphor screen, this line structure having no necessary direct geometrical relationice It will now be appreciated that, as the beam electrons travel from the electron gun they may be focussed by the above-described lens structure into a series of lines parallel to the phosphor strips. If there is a zero potential difference between the red and blue terminals of the wire grid, then these lines formed by the beam electrons may be caused to lie within the boundaries of the green strips. If the wires associated With the red strips are made positive relative to the wires electron-optically related to the blue-strips, the beam electrons will be de= flected, and the thin lines will now lie within the boundaries of the red strips. Similarly, the electrons Will strike the blue strips when the wires associated with such strips are relatively positive with respect to the red wires. Different component coolrs are thus displayed 3C1 cording to the potential difference (if any) existing between the two sections of the grid wire assembly.

Accordingly, color control in a cathode-ray tube having a grid assembly of the above nature (whether used for PDF or not), is brought about by a cyclic change in the potentials applied to selected wires of the grid, with the electrostatic charges on the wires exerting forces the magnitude of which varies as a function of this potential change. If'the forces thus exerted vary at a fre quency close to the natural resonant frequency of the wires, the latter will vibrate, resulting in an oscillation of the line pattern on the phosphor screen. If the magnitude of this oscillation is sufficiently great, color contamination and/ or electrical shorting can occur. Even with relatively little wire vibration the electron beam may be defocussed, and image reproduction seriously impaired. It is of course, obvious that wire vibration may also result from electrical shocks received by the grid assembly, or as a result of physical shocks to which the entire cathode-ray tube may be subjected.

The above problem has been recognized. One solution is proposed in a copending United States patent application of James T. Vale, Serial No. 252,664, filed October 23, 1951 (now U. S. Patent No. 2,721,288, granted October 18, 1955), and assigned to the same assignee as the present application. In the Vale disclosure, the vibration of such a wire grid is damped, and one preferred arrangement for carrying out this objective includes an insulating cord or strand (which may be a ceramic thread) wound, or passed in-and-out, between the parallel conductors in a region near the wire frame or support.

The above-mentioned Vale method of reducing the amplitude of grid wire vibration by bringing into contact with the wires a mechanically lossy material is effective for many purposes Where some residual vibration can be tolerated. However, friction between the wires and the damping member necessitates the use of materials able in a United States patent application entitled Grid for- Color Television Tubes (also identified as Serial No. 343,887, filed March 23, 1953). This embodies the principle that the frequency of vibration of a supported wire is a function of the distance between its supports. Hence, if a wire of given length (having a certain natural resonant frequency) is rigidly held at one or more points between its ends, then the wire segments between the constraining points will have higher resonant frequencies corresponding to their shorter lengths. If these increased resonant frequencies are sufliciently higher than the driving frequency (i. e., the rate of change of potentials applied to the wires) then the tendency of the wire seg-- ments to vibrate will be materially reduced, and the amplitude of any vibration which does occur will be much lower.

One structure designed in accordance with the teaching of the identified Cook application comprises a node bar of insulating material, such as glass, extending across the grid wires, the latter being rigidly secured to the bar at spaced points.therealong. To eliminate the. electron shadow which would otherwise result from the presence of a solid object in'the path of the scanning beam, the bar is given a conductive coating over. the portion of its surface which is. out of contact withthe wires. The undesirable shadow region is thus filled in with electrons which would normally impinge other points on the target area. 7 7

Both the Vale and Cook arrangements operate satisfactorily in many tube types. However, with' advancesin tube designs and the trend toward. extremely large? 1 surface must be given a conductive= coating, and then. this coating-. must' be connected to: a. point" of proper potential. v

It becomes possible, to dispensewith a: number: of the operations made necessary by the employment of anode bar such as described above, through utilization of a plurality of straight rods, of some rigid. insulating material such as glass, which are interwoven between the grid wires in such a manner. thatthe latter are displacedvertically (normal tothe plane of: the target electrode) atevery rod, with a'djacentjwires being offset in opposite directions; Such an? arrangement is described in a copending United States patent application of Ernest 0. Lawrence, Serial No. 342,941, filed March '17, 1953, and also assigned to the same assigneeas the present application.

It is additionally found, by establishing" a certain po tential difference between the electron gun 'of the cathoderay tube and the wire grid, andalso by employing a selected composition for the rods, that a number of the scanning beam electrons'are brought into that region of the target electrode which would otherwise be shadowed. Thus an arrangement ofthe type'described in the last-mentioned Lawrence application not' only materially reduces vibration of the grid wires, but also substantially eliminates the shadow etfect without requiring notched bars; cement, electrical coatings, or con ductors-for creating and maintaining a predeterminedpo tential on the surface of the vibration-reducing components.

However, the linear configuration of the damp rods causes the interweavingprocess to produce two substantially coplanar sets (or groups) ofgrid wires, with alternate'wires being displaced in the same general direction normal to the plane of the base plate. Application of color switching voltagesto these two sets of wires may, in some cases, result inslight color fringing due to the difference in raster size of the individual component-color fields. This is dueto the .greater efiect on the electrons in the'scanning beam of the grid Wires lying nearest to the electron gun 'ofthe cathode-ray tube, considered wtih respect to'the furthest,.or hidde'nj" grid. These means may generally be said to involve use of voltages on the two sets ofgridwires which are unbalanced to that particular degree. required to bring the respective raster areas into substantial coincidence.

It is, in many instances, desirable to incorporate within the cathode-ray tube means .for overcoming the adverse effects of grid wire vibration without at'the same time rigidly anchoring-each gridwire to the damping'member, as suggested by Cook, or utilizing elements which-sep- 4' arate the grid wires into distinct planes, as proposed by Lawrence. Such an expedient not only permits the cementitious binding material of the former arrangement to be dispensed with, along with the possibility of lateral displacement of the parallel conductors, but also eliminates the unbalanced voltagesfor the two sets of grid wires frequently required by a structure designed in ac: cordance with Lawrences teaching.

One solution of the problem set forth above is described in the present application. It recognizes the desirability of maintaining a coplanar relationship of the grid wires, and takes this into account. by employing. at least one damping element the configuration of which is specifically chosen so as not to disturb this grid wire relationship. At the same time, not only is Wire vibration reduced in magnitude, but, by extending the interweaving concept of Lawrence to a degree not attainable in the disclosure referred to,-the actual effectiveness of the damping action is greatly enhanced.

Oneobject of the present invention, therefore, is to: provide an improved'form of cathode-raytube suitable for the reconsitutiontof polychrome images;

A further object of the inventioniis to substantially 7 completely overcome, in a polychrome: cathode-ray. tube: having a grid structure of. coplanar parallel wires, anytendencytoward'vibration the wires of. the grid structure may possess either when color-changing potentials are cyclically applied thereto: or when. the grid structu'reis subjected to shocks of a physicaland/orelectrical nature;

An additional object of the:present invention istoaccomplish the above objective while at the sametimemaintaining the coplanar relationship of the grid wires;

A still further object of: the present invention isto provide, in a polychrome. cathode-ray tube having a color-controlgrid. structure of coplanar parallel wires, at least one dampingi element of non-linear configuration interwoven with the Wires of-the' color-control grid.

.Fig. I is apartly schematic representation'of-one form:

of cathode-ray tube in which the present-invention may be incorporated;

Figure 2is an enlarged'view of a portion of Figure 1;

Figure 3 is aperspective view of a portionof the wire grid assembly of Figure 1, showing in greater detail the interwoven relationship betweenthe" grid wires and damp rods;

Figure 4=is a sectional view of a portion of Figure 3 along the line 4-4; and

vFigure 5 is a'plan- View ofap'ortion of Figure 3, showing'one-preferredassociationof the grid WlI'BS' andphosphor' strips.

Referringnow to Figure l of the drawings, there is generally indicated bythe reference numeral'ltlj one type of cathode-ray tube-in'which the present invention may be incorporated. Thistub'e 10inolud'es-the usual components for developing abeam of electrons; and for deflecting this electron-beam- 12 in substantially mutually perpendicular directions was to trace a-rasteron the tube target electrode.

The target electrode-of't-ube 1-0, for ease of illustration, is disclosed as formingpartfofa separateunit or assembly 14mounted in. any suitable manner adjacent to the transparent end wall16 of the tube. end wall 16 when' suitably configured, may itself cornprise the targefel'ect'rode if convenient or desirable. For certain constructionaldetai'ls ofthe assembly 14, -reference is made to above-mentioned Vale application, .Serial No. 252,664,. as -well as to further copending applications of Renn Zaphiropoulos, Serial 'No. 307,435, filed September 2, 1952 (now U. S; Patent No. 2,683,833, gran-ted July 13,' 1954),. andSerial'No. 307,436, filed September 2, 1952'. However, inasmuch .as:.these.constructional detailsform nopart'ofthe present invention, they willibe'omittedi from the description which" follows, audit will merelybe stated that the. assembly '14" whiohincludes.a'transparentr Obviously, however; the

base plate 18, a phosphor coating 20 thereon, and agrid of parallel color-control conductors 22 adjacent to the phosphor coating 20) is positionedand supported within the tube so that the light produced by impingement of the scanning beam 12 on the phosphor coating may be viewed by an observer through the transparent end wall 16 of the cathode-ray tube.

The base plate 18 may be of glass or other suitable material. The phosphor coating 20 is preferably in the form of a plurality of narrow strips which have the property of fiuorescing in different component colors of the image to be reconstituted, these colors, for example, being red, green and blue. These strips are laid down side-byside in a predetermined chromatic sequence. As best shown in Figures 3 and 4, the order chosen for illustration is red, green, blue, green, red, green, etc. This order, however, forms no specific part of the present invention, but is suggested as one order which has proved to be satisfactory. The phosphor coating 20 is then aluminized or otherwise provided with a thin film of electrically-conductive material on the surface toward the source of the impinging electrons.

The color-control grid adjacent to the target surface 20 is composed of a plurality of linear conductors, such as the parallel wires 22, aligned with the phosphor strips in a manner best shown in Figures 3 and 5. (Only a small section of the striped phosphor surface 29 of the target electrode is illustrated in Figure 3 in order to permit a. clear showing of the grid wire relationships.) That is, there is a grid wire associated with each red and blue phosphor strip, but none with the green. By cyclically varying the voltage of the red wires with respect to the voltage of the blue wires, different chromatic aspects of an image are successively presented. In this connection, it must be kept in mind that the drawings of the present application are not to scale, and the relative dimensions and spacings of the illustrated components are intentionally distorted for ease of presentation. In general, though, each pair of wires may, in an electronoptical sense, he considered as subtending strip areas constituting one color cycle.

In a preferred form of tube design, a potential is applied to the conductive coating on the phosphor surface 20 which is relatively positive with respect to the average, or D.-C., potential of the wires 22 of the grid assembly. This gives rise to a plurality of cylindrical electrostatic lenses, which serve to focus the electrons of the scanning beam 12 in a series of fine lines registered with the phosphor strips. However, the present invention is obviously applicable to cases where the wires 22 serve either as a color-changing device alone, as will subsequently appear, or as an electrostatic lens assembly per se, as shown for example in patent application, Serial No. 234,190 above referred to.

Although any suitable method may be employed for positioning the wires 22 so that they are adjacent to the phosphor-coated surface 20 of the target electrode, a pair of bars 24 and 26 is shown, each of these bars having on its upper surface a series of equally-spaced grooves for aligning the wires 22 and preventing internal movement at such points. The wires are respectively held taut (as best shown in Figures 1 and 2) by a plurality of hooks forming part of two retaining assemblies '28 secured to the under surface of the transparent base plate 18 beyond the boundaries of the image raster area. This general type of construction is described and claimed in Zaphiropoulos application Serial No. 307,435, referred to above.

It has been indicated that one of the principal features of the present invention consists in substantially completely overcoming any tendency toward vibration the wires of a color-control grid assembly of the class described may possess by interweaving one or more rigid rod-"like members between the wires of the color-control assembly, while at the same time retaining the coplanar wire rela- 6 tionship. One such arrangement is shown in Figures l through 5.

In this construction, three insula g rods 30, 32 and 34 of circular cross-sect-ion have been chosen for illustration, although the rod 32 alone will produce results as set forth below. In each case, however, the rods extend substantially transversely to the grid wires 22 and are interwoven therebetween; that is-over one wire, under the next, over the following wire, etc. Figure 3, 4 and 5 bring out this intervowen relationship most clearly.

:In order to maintain a coplanar relationship of the grid wires 22, a particular configuration is imparted to each of the damp rods 30, 32 and 34. As perhaps best shown in Figure 4, this configuration may be termed zig zag in nature for convenience of description. Expressed differently, a rod which would otherwise be essentially linear is bent at points corresponding in number to the number of grid wires with which the rod is to be interwoven. The direction of bending is the same at alternate points; that is in, out, in, out, etc. as again perhaps best shown in Figure 4. The-result is a rod of undulating form, and, if the amount by which the rod is bent is chosen so that L1=the distance from the inner surface of the damp rod at any selected convolution k to the longitudinal axis xx of the damp rod L2=the distance from the inner surface of the damp rod at convolutions adjoining convolution k to the longitudinal axis x-x of the damp rod D=the diameter of the damp rod then there will be good surface contact between the rod and each of the grid wires 22 with which it is interwoven.

Each of the damp rods 30, 32 and 34 is not only interwoven with the grid wires 22 but in addition is ofiset with respect to each adjoining damp rod or rods in the sense that corresponding convolutions of adjoining rods extend in opposite directions. The construction accordingly is one in which the rod 32, for example, overlies those particular grid wires which the rods 30 and 34 go under. Reference to Figure 5 illustrates this point, and, in Figure 4, the side view of rods 30 and 32 brings out that the former (which lies in back of the rod 32) contacts each grid wire at a point which is diametrically opposed to the point at which each grid wire is contacted by the rod 32. The rod 34, although not shown in Figure 4, occupies a position relatively similar to that of the rod 30.

It Will now be appreciated that, as one portion of the grid wire assembly is subjected to an electrostatic force of a magnitude which would otherwise cause the wires thereof to leave their normal position, these wires must overcome the restraining effect of the damp rod with which they are in contact. However, this same damp rod contacts another portion of the grid wire assembly the wires of which are not subject to a force of this particular value. In fact, the direction in which the force on the last-mentioned grid wire portion is changing may be directly opposed to the direction of changes of the force acting on the first group of wires. The damp rods, by contacting all of the wires, act as an equalizing, or balancing medium which almost completely cancels out any tendency toward movement the individual wires of the color-control grid structure may possess.

Although any number of zig-zag damp rods may obviously be employed, three rods each .003" to .005 in diameter have been found suitable in actual tube constructions.

In order to insure that each of the rods 30, 32 and 34 remains in its proper position as shown in the drawings, a small amount of binding material, such, for example,

as Sauereisen cement, may be applied near the two extremities of each rod. As illustrated in Figure 3, this binding inaterial identified by the reference numeral 36, secures the respective ends of each rod-to whatever number-'of-gr'id wires (such as threeor tour) that-are contaetedbythe'cement. This positions each rod with respect to the wires and prevents any-relative movement therebetween 'in the plane of the latter. Inasmuch as the two extremities of each rod respectively lie outside the raster area of the target electrode,thereis no noticeable eifect produced by -the cement on the image presented to an observer. 'While "this process is entirely satisfactory, other-methods of holding the rods in place are possible and are intended to 'fall within the scope of the present disclosure. It will be appreciated, however, thatcertainzconditions of wire spacing and/ or damp rod diametentor example, make 'it possible to omit the binding material entirely .as the rods will remain in position without such aid.

Any material maybe used for the damp rods 30, 32 and 34 which will produce satisfactory results, especially if this material be of a vitreous nature. One substance which has been found to be especially suitable is what is known commercially has ..Gl2-glass. When damp rods having such a composition are utilized, it is noticed that the electron'shadow (which each damp rod would normally be expected to cast=upon the phosphor-coated surface 2% of the target electrode, and which condition is recognized in copending Cook application Serial No. 343,887 filed March 23, 1953) is not visible 'when V1/ V2 is roughly equal to A, where V2 isthe potential difierence from the cathode to screen 20 and V1 is the mean potential difference-from the cathode to the wire grid .22. Reducing this voltage ratio causes an increasing amount of shadow.

It should be understood that use in the present application of the expression adjacent to in describing the spatial relationship of the wire grid and target electrode is to be interpreted as describing a condition wherein the wire grid lies in a plane slightly spaced apart from the plane of the target electrode, and .is not to be confused with a case where these two members are contiguous, or actually in physical contact with one another.

Having thusdescribed the invention, what'is claimed is:,

1. .A vibration-inhibiting element for .a cathode-ray tube designed for the reconstitution of polychrome images and having-a grid structure of coplanar parallel wires lying between the cathode-ray beam developingmeans of said tube and the target electrode scanned tthereby and substantially adjacentto the target, .said vibrationinhibiting element comprising a nonlinear rod of substantially inflexible insulating material extending substantially transverselyto the parallel wires of said vgrid structure and interwoven therebetweenin such a manner as to retain a coplanar wire relationship.

2. A vibration-inhibiting element according to claim 1, in which the non-linearity of said rod is of a zig zag nature. V y

3. A vibration-inhibiting assembly for a cathode-ray tube designed for the reconstitution of polychrome images, said tube having a planar-surfaced target electrode and a grid structure ofcoplanar parallel wires lying adjacent to the -planar surface of said target electrode, said vibration-inhibiting assembly including a plurality of ;rodlike insulating members each having a permanent .Zigzag configuration, each extending substantially transversely to the parallel wires of said grid structure-and interwoven therebetween, the zig-zag configuration of each of the said rod-'likemembers being such that the interwoven relationship of each said zigzag member with the parallel wires of .said grid structureresults in the iormer contacting each of the said wires and at the same .timesubtantially retains the said'coplanar grid wire relationship.

4. A'vibration-inhibiting assembly according to claim 3, in which any selected one of the said plurality -of rod-like members contacts .each particular wire of said grid structure at a point which is substantially diametrically opposed to the point at which such particular wire is contacted by the one or more rod-like members lying adjacent to the said oneselected member.

5. A zig-zag damp rod of insulating material for inhibiting vibration of the tautly stretched linear conductors forming a color control grid structure of a cathode-ray tube designed for the production of polychrome images, said linear conductors lying adjacent to the target electrode of said cathode-ray tube, said damp rod extending transversely to the conductors of the grid and interwoven therewith and being essentially of a linear nature and substantially inflexible but being bent in-and-out at points substantially corresponding in number to the number of linear conductors making up said grid structure, the direction of bending of sa-iddamp rod being the same at alternate points, so that the said bent rod 'is substantially symmetrical about its longitudinal axis and adjacent conductors of the grid lie on opposite sidesof the rod.

6. In a cathode-ray'tube designed for the production of polychrome im-ages,..the combination of a color-control grid-structure of parallel wires arranged in coplanar rela tion in a plane adjacent to the target electrode of said cathode-ray tube, and at least one rod-like element of substantially inflexible insulating material respectively bent in-and-out at equally spaced points corresponding in number essentially to the number of parallel wires making up said grid structure, said rod-like element being adapted for interweaving with the said parallel wires without disturbingthe coplanar relationship of the latter, whereby the tendency of said-wires to vibrate whencolorcontrol potentials are applied to said grid structure will be strongly inhibited.

7. A vibration-inhibited color grid assembly for a cathode-ray tube adapted for thereconstitution of images in color on the tube target surface, which comprises a color-control grid structure constituted of a multiplicity of linear conductors all in substantially coplanar 'relationship and supported from and located by the tube wall in tautly stretched'relationship adjacent to the target, a non-linear rod of insulating material extending transversely to the linearconductors of the grid and interwoven therewith, the rod non'linearity being of a-generally zig-zag configuration with a zig-zag pitch being such as to place adjacent linear conductors of the grid on opposite sides of the rod and alternate linear 'conductors on the same side of the rod and the-displacement of each zigzag bend from linearity being-such that when each linear conductor of the grid rests adjacent to the rod on oneside or the other thereof-and the'group of linear conductors forming :the grid is maintained by the rod in substantially non-vibratory coplanar relationship.

References Cited in the file of this patent UNITED STATES PATENTS 2,072,638 'Jobst ,Mar. 2, 1937 2,231,691 Snyder Feb. 11, 1941 2,416,056 Kallmann Feb. 118, 1947 2,441,791 Schroeder Aug. 10, ,1948 2,461,515 Bromwell Feb. 15, '1949 2,568,448 Hanson Sept. 18, 1951 2,653,263 Lawrence Sept. '22, 1953 2,757,303 Silverman July' 31, 1956

Images