US2729760A - Electrode structure for cathode-ray tubes for image production in natural color - Google Patents

Description

2,729,760 ELECTRODE STRUCTURE FOR CATHODE-RAY TUBES FOR IMAGE PRODUCTION IN NATURAL COLOR Filed March 17, 1953 E. O. LAWRENCE Jan. 3, 1956 2 Sheets-Sheet 1 INVENTOR. EM 657' 0 Lawrence Wk- \T w Jan. 3, 1956 E. o. LAWRENCE ELECTRODE STRUCTURE FOR CATHODE-RAY TUBES FOR IMAGE PRODUCTION IN NATURAL COLOR 2 Sheets-Sheet 2 Filed March 17, 1953 DAMP K00 Mm w w n R R6 0 0 F MW WA m0 9 M r E United States Patent ELECTRODE STRUCTURE FOR CATHODE-RAY TUBES FOR IMAGE PRODUCTION IN NATURAL COLOR Ernest 0. Lawrence, Berkeley, Calif., assignor to Chromatic Television Laboratories, Inc., New York, N. Y., a corporation of California Application March 17, 1953, Serial No. 342,941

7 Claims. (Cl. 313-78) The present invention relates to cathode-ray tubes of the type adapted to effect the reconstitution of polychrome images through the cyclic application of colorcontrol potentials to a grid of parallel wires located within the cathode ray tube adjacent to a striped phosphor screen or target electrode.

A wire grid of the above nature may perform a dual function. That is, in addition to its use for color control, it may also serve as part of an electron lens system to focus the electrons of the scanning beam into a line pattern registered with the phosphor strips of the screen. Moreover, these two operations of the grid may be combined, or each may be carried out independently of the other. A detailed description of one form of cathoderay tube employing such principles may be found in copending United States patent applications of Ernest 0. Lawrence, Serial No. 219,213, filed April 4, 1951, and Serial No. 234,190, filed June 29, 1951, now respectively United States Letters Patent No. 2,692,532 granted October 26, 1954, and No. 2,711,493 granted June 21, 1952.

As an illustration, the phosphor strips may be laid down in the chromatic sequence to produce, when subjected to the impact of the scanning cathode-ray beam, light in the colors red, green, blue, green, red, green, etc. The grid may then be so designed that there is a wire electronoptically aligned with each red and blue strip, but none with the green. A difference of potential established between the electrical center of the wire grid, on one hand, and a conductive coating on the phosphor screen, on the other, creates a multiplicity of cylindrical electrostatic lenses which form the line pattern mentioned above. By connecting all of the wires which will control the production of red light, and hence called red wires herein, to one common terminal, and all of 'the wires which will control the production of blue light, and hence called blue wires herein, to another terminal, the voltage applied to each set of wires may then be cyclically varied to present to an observer different chromatic aspects of the image being reproduced.

Such a cyclic variation in the voltage applied to each set of Wires results in electrostatic charges on the wires exerting forces of attraction at this same rate. If the forces thus exerted vary at a frequency close to the natural resonant frequency of the wires, the latter will tend to vibrate. This vibration produces an oscillation of the line pattern on the phosphor screen, and, if the magnitude of the oscillation is sufficiently great, color contamination and/or electrical shorting may occur. In any event, the result is definitely objectionable.

Various attempts have been made to overcome the effects of grid wire vibration. In one form of structure, heretofore proposed, at least one insulating cord (such as a ceramic thread) is passed in-and-out between the parallel conductors in a region near the grid wire frame or support. This has a damping effect, and is described at greater length in a copending United States patent application of James T. Vale, Serial No. 252,664, filed October 23, 1951, which is assigned to the same assignee as the present application.

A different approach is suggested by Leslie J. Cook in a United States patent application entitled Grid Structure for Color Television Tube andalso identified as Serial No. 343,887 filed March 23, 1953. This last named application 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 intermediate its cnds, then the wire segments between the constraining points will have higher resonant frequencies corresponding to their shorter lengths. If these increased resonant frequencies are sufficiently higher than the driving frequency (i. e., the rate of change of potentials applied to the wires) then the tendency of the wire segments to vibrate will be materially decreased, 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 evenly-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 with the wires. This coating is maintained at a potential which is relatively positive with respect to the average operating potential of the grid wires. The undesirable shadow region is thus filled in with electrons which would normally impinge other points on the target area.

Both the Vale and Cook arrangements operate completely satisfactorily in many tube types. However, with advances in tube designs and the trend toward extremely large size tubes it is found that the former scheme often is not the most desirable, particularly for mass production operations, completely to prevent vibration. The Cook construction is highly eficient in its use but because of the fact that extreme care must be taken to guard against lateral displacement of the parallel grid wires when the node bar is secured thereto it tends in some tube types to increase manufacturing costs. Furthermore, a section of the node bar surface must be given a conductive coating, and thenthis coating must be connected to a point of proper potential.

It has now been found that it is possible in certain tube types to dispense with a number of the operations made necessary by the employment of a node bar such as described above. This result is accomplished through the 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 that the latter are displaced vertically (normal to the plane of the target electrode) at every rod, with adjacent wires being offset in opposite directions.

It has additionally been found, by establishing a certain potential difference between the electron gun of the tube and the wire grid, and also 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. It is believed that this result is produced by the secondary emission effect of the material from which the rods are made, and that the loss of secondary electrons by this material establishes an electrostatic field in the neighborhood of the rods which deflects the beam electrons into the shadow region of the target electrode. In any event, an arrangement of the type herein described either eliminates or materially reduces the.

shadow eflect without requiring notched bars, cement, electrical coatings, or conductors for creating and maintaining a predetermined potential on the surface of any of the vibration-reducing components.

One object of the present invention, therefore, is to provide an improved form of cathode-ray tube suitable for the reconstitution of images in substantially true and natural color.

A furtherobject of the present invention is to substantially completely overcome,in a polychrome cathoderay tube having a color-control grid structure of parallel wires, any vibrational tendency which the wires of the grid structure may possess when color-changing potentials are cyclically applied thereto.

An additional object of the invention is to provide, in a polychrome cathode-ray tube having a grid structure of coplanar parallel wires adjacent to the tube targetelectrode, means for reducing, or. substantially eliminating, any electron shadows which might otherwise result from the employment of aplurality of vibration-reducing elements in conjunction with the wire grid.

A still further object of the invention is to accomplish with this vibration reduction a substantial elimination of the electron shadows by utilizing inherent properties of the vibration-reducing elements themselves, thus dispensing with any separate electrical connections or leads between such elements and other portions of the cathode-ray tube.

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

Figure 1 is a partly schematic representation of one form of cathode-ray tube in which the present invention may be incorporated;

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

Figure 3 is a perspective view of a portion of the wire grid assembly of Figure 1, showing in greater detail the interwoven relationship between the grid wires and damp rods; and

Figure 4 is a plan view of aportion of Figure 3, showing one preferred association of the grid wires and phosphor strips.

Referring now to Figure l of the drawings, there is generally indicated by the reference numeral 10 one type of cathode-ray tube in which the present invention may be incorporated. This tube It) includes the usual components for developing a beam of electrons, and for defleeting this electron beam 12 in substantially mutually perpendicular directions so as to trace a raster on the tube target electrode. Since these basic operational features are well known in the television art, no detailed description is believed necessary, although reference is made to the aforementioned Lawrence applications Serial No. 219,213 and Serial No. 234,190 for a' more extended explanation.

The target electrode of tube It for ease of illustration, is disclosed as forming part of a separate unit or assembly 14 mounted in any suitable manner adjacent to the transparent end wall 16 of the tube. Obviously, however, the end wall 16 when suitably configured may itself comprise the target electrode if convenient or desirable. For certain constructional details of the 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 United States Patent No. 2,683,833 granted July 13, 1954, and Serial No. 307,436, filed September 2, 1952. However, inasmuch as these constructional details form no part of the present invention, they will be omitted from the description which follows, and it will merely be stated that the assembly 14 (which includes a transparent base plate 18, a phosphor coating 20 thereon, and a grid of parallel color-control conductors 22 adjacent to, but spaced apart from, the phosphor coating 24)) is positioned and supported within tube 10 so that the light produced by impingement of the scanning beam 12 on the phosphor eoatinglii may be viewed by m observer through the transparent end wall 16 of the cathode-ray tube.

The base plate 18 may be of glass or othersuitable material. The phosphor coating 20 is preferably in the form of a plurality of narrow strips which have the property of fluorescing in different component colors of the image to be reconstituted, these colors in the usual tricolor additive system, being red, green and blue. These strips are laid down side-by-side 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 part of the present invention, reference again being made to Lawrence application Serial No. 234,190 for further details. The phosphor coating 20 is then aluminized or otherwise provided with a thin film of electricallyconductive material on the side toward the source of the impinging electrons.

The color-control grid adjacent to the target surface;

20 is composed of a plurality of parallel wires 22 aligned with the phosphor strips in a manner best shown in Figures 3 and 4. (Only a small section of the striped phoSPhor surface 2th 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 that the relative dimensions and spacings of the illustrated components are intentionally distortedfor ease of presentation. In general, though, each pair of wires may, in an electron-optical sense, be 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 thegrid assembly. This gives rise to a plurality of cylindrical. electrostatic lenses, which serve to focus the electrons of the scanning beam 12 into a series of fine lines, registered with the phosphor strips. wires 22 perform the dual function of a lens grid and a color control element. However, the present invention is obviously applicable to cases where the wires 22 serve as a color-changing device alone, as will subsequently appear.

Any suitable method may be employed for positioning the wires 22 so that they are spaced apart from the plane of the target by a distance which is only a small fraction,

of the length of the electron path from the source to the target, and in such relationship that it is closer to the target than any other active tube elementas,sueh, the

grid wires will herein be described as adjacent to the phosphor-coated surface 20 of thetarget electrode. Ac;

cordingly, reference to the words .adjaeent to is not to be confused with a case where these two membersare contiguous, or actually in physical contact withoneanaother. This is provided herein by a pair of bars 24and 26 which is so shown that each of these bars has, on its upper surface a V series of equally-spaced grooves, for

aligning the wires 22 and preventing internal'movement; thereof 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 assemblieszfi secured to the under surface of the transparent base plate 13 beyond the boundaries of the image raster area. This;

general type of construction is described and claimed ins Zaphiropoulos application, Serial No. 307,435 referred: to above.

it has been indicated that one ofthe principal features of the present invention consists in substantially com-,

pletely overcoming any tendency toward vibration; the

wires-pf a color-controlgrid-assembly of the class; described maypossess byinterweaving one ormore ,rigid Thus, in effect, the

rod-like members between the grid wires of the colorcontrol assembly. One such arrangement is shown in Figures 1 through 4. In this construction, at least two rods and 32 are required, the rod 30 being located nearest to the spacer bar 24 and substantially parallel thereto, and the rod 32 being nearest to the spacer bar 26. In each case, the damp rods extend transversely to the grid wires 22, and are interwoven therebetween; that is, over one wire, under the next, over to the following wire, etc. Figures 3 and 4 bring out this interwoven relationship most clearly.

From the sectional views of Figures 1 and 2, it will be seen that the interweaving process causes the wires 22 to fall into two substantially coplanar sets, or groups, with alternate grid wires being displaced in the same direction (normal to the plane of the base plate 18). It will now be understood why at least two rods are required in order to maintain a parallel wire relationship. However, additional rods (shown in Figures 1 and 3 as 34, 36 and 38) are frequently desirable for optimum damping. In fact, a total of six rods incorporated in a cathode-ray tube of the type described has produced satisfactory results in practice. Although the dimensions of the damp rods will be determined by the size of the raster area, the composition and tension of the grid wires, etc., nevertheless rods 3-5 mils (.003.005") in diameter have proven suitable. It has also frequently been found advantageous to choose the center rod (#36 in Figures 1 and 3) slightly thicker (1 mil, for example) to insure its contact with at least a majority of the wires 22. Under certain conditions, all of the inner rods (#34, 36, 38, etc.) may thus be made thicker with good results.

In order to maintain each of the rods 30, 32 and 34 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 material, identified by the reference numeral 36, secures the respective ends of each rod to whatever number of grid wires (such as three or four) that are contacted by the 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 be outside the image raster area of the target electrode, there is no.

noticeable effect produced by the cement on the image presented to an observer. While this 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.

Any material may be 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 as C-12 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 20 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 the ratio of the tube gun voltage to the average voltage of the grid wires 22 roughly equals 1:3. Reducing this voltage ratio causes an increasing amount of shadow. As previously brought out, it is believed that this result is produced by the secondary emission effect of the material from which the rods are made, and that the loss of secondary electrons by this material establishes an electrostatic field in the neighborhood of the rods which defleets the electrons into the shadow region of the target electrode. In the above-mentioned Cook application, Serial No. 343,887, a structure positioned so as to intercept a scanning beam, and having the properties of a dielectric, is caused to cast an electron shadow of negligible proportions on the surface of a target electrode through the expedient of rendering at least a portion of the surface of the beam-intercepting structure electrically conductive, and then connecting this conducting surface to a point of suitable potential. In the present application, substantially the same effect is brought about by establishing an electrostatic field in the neighborhood of the rods, this electrostatic field being produced by properly selecting, with reference to the potential difference between the electron gun of the tube and the Wire grid, the secondary emission ratio of the material from which the damp rods are composed.

Having thus described the invention, what is claimed is:

1. A vibration-inhibiting assembly for a cathode-ray tube designed for the reconstitution of polychrome images, said tube having a planar-surface target electrode and a color-control grid structure of parallel wires lying adjacent to the planar surface of said target electrode, said vibration-inhibiting assembly including a pair of rodlike members of insulating material each extending substantially transversely of the wires of said grid structure and interwoven therebetween so as to displace each of the said grid wires in a direction approximately normal to the planar surface of said target electrode, with each of the said grid wires being so displaced in the same direction by each rod and with adjacent wires being displaced in opposite directions relative to the said target electrode, thereby to form between said rods two sets of parallel grid wires respectively lying in distinct planes each of which is substantially parallel to the planar surface of said target electrode.

2. A vibration-inhibiting assembly according to claim 1, further comprising at least one additional rod-like member of insulating material disposed in substantially parallel relation to the two members of said pair and lying therebetween.

3. A vibration-inhibiting assembly according to claim 2, in which the additional rod-like member has a diameter greater than the diameter of either of the two members of said pair.

4. A vibration-inhibiting element for a cathode-ray tube designed for the reconstitution of polychrome images and having a color-control grid structure of parallel wires lying between the cathode-ray beam developing means of said tube and the target electrode scanned thereby, said vibration-inhibiting element comprising a rod of substantially inflexible insulating material extending substantially transversely to the parallel wires of said grid structure and interwoven therebetween, said rod contacting each of said wires at not more than a single point.

5. A vibration-inhibiting element according to claim 4, in which the substantially inflexible insulating material of which the said rod is composed has a secondary emission factor greater than unity.

6. A vibration-inhibiting element according to claim 4, in which the substantially inflexible insulating material of which the said rod is composed is of a vitreous nature.

7. A vibration-inhibiting element for a cathode-ray tube designed for the reconstitution of polychrome images and having a grid structure of parallel wires lying adjacent to one surface of the target electrode scanned by the electron beam of said cathode-ray tube, said vibration-inhibiting element comprising a rod of substantially inflexible insulating material extending substantially transversely to the parallel wires of said grid structure and interwoven therebetween.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,672 .Okolicsanyi June 23, 1953 2,416,056 Kallmann Feb. 18, 1947 2,461,515 Bronwell Feb; 15, 1949 2,535,307 Mankin et a1. Dec. 26, 1950 2,590,764 Forgue Mar. 25, 1952

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