US2721287A

US2721287A - Multiple beam gun

Info

Publication number: US2721287A
Application number: US248357A
Authority: US
Inventors: David D Van Ormer
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1951-09-26
Filing date: 1951-09-26
Publication date: 1955-10-18
Anticipated expiration: 1972-10-18
Also published as: NL172717B; FR1065703A; NL91128C; GB721571A; BE514227A

Description

Oct. 18, 1955 D. D. VAN ORMER 2,721,287

MULTIPLE BEAM GUN Filed Sept. 26, 1951 2 Sheets-Sheet 1 INVENTOR mvidg. Immmer WW 4? A4 ATTORNEY Oct. 18, 1955 VAN QRMER 2,721,287

MULTIPLE BEAM GUN Filed Sept. 26, 1951 2 Sheets-Sheet 2 T 1 55 wi Tm as $1 75} -95 77 77 1 is x ay F5 6 pavidgva$ii2er WW d United States Patent MULTIPLE BEAM GUN Application September26, 1951, Serial No. 248,357

9 Claims. (Cl. 313-69) This invention is directed to a cathoderay tube and more particularly to the gun structure for a television picture tube.

In many television applications it is desirable that the brightness of the picture on the fluorescent screen be as great as is possible. This is particularly true in television projection type picture tubes in which the image= from the fluorescent screen of the tube is projected onto aviewing :screeni Also, some picture tubes used to produce television pictures in color'require a plurality of electron beams. I

It is an object of my invention to provide a novel gun structure for producing a plurality of electron beams. It isa further object of my invention to provide a television picture tubehaving an improved gun structure for producing a pluralityof electron beams, which are caused to converge at a'common point on the tube screen. It is another object-of my invention to provide an electron "gun structure of simplified design for producing a plurality of electron'beams which are brought to a common point of convergence.

The invention is to a picture tube having an electron gun structure for producing a plurality of electron beams. The gun is "composed of a plurality of electron emitting cathode surfaces directed toward a common axis. Spaced along the axis'from the cathode emitting surfaces is a common accelerating electrode having a single aperture surrounding the common axis. Spaced between. the cathode emitting surface and the common accelerating electrode are control grid electrode portions, each. having an aperture'therethrough overlying each of the cathode emitting surfaces. During tube operation, the electron emission from each of the cathode surfaces is brought to a common cross-over point on the common axis. Spaced along the axis from the accelerating electrode is a focussing electrode. 'The field between the accelerating and focussing electrodes has the double function of converging the beams emerging from the common cross-over point to a second common convergence point, as well as that of focussing the electrons in each beam at the point of common convergence.

The novel features which I believe to be characteristic ofmy invention are set forth with particularity in the appended claims, but the invention itself will best be understood'by reference to the following description taken in connection with the accompanying drawing, in which:

Figure l is a sectional view of a cathode ray tube showing a novel gun structure in accordance with the invention.

Figure 2 is an enlarged detailed drawing of the'type of. gun structure shown in Figure 1.

. Figure 3 is "aschematic showing of the possible operation of the novel gun structure.

Figures 4 and 5 are modifications of electron gunstructures whichr-may be used in tubes of the type shown in Figure 1. i

Figure 6 is-a sectional view showing a-portion ofa cathode rayntube. having. a. novel gun structure for.pro ducing a plurality of electron beams.

2,721,287 l atent ed Oct. 18, 1955 ice 2 Figure 7 i's'a'n enlarged-partial sectional view of the gun structure showninFigure -6.

In Figure 1 there is disclosed a cathode ray tube utilizin a plurality of-electron-beams. The tube comprises an evacuated envelope 10 having alarge conical portion 12 and a tubular neck portion'14. Mounted within the neck 'por'tion14 is an electron gun structure 16 consisting essentially of a plurality of cathode electrodes'lii. As shown in greater detail in- Figure 2 there; are two'cathodes 18 mounted symmetrically with-respect to the'axis20 of the tubular neck=portion 14. 'Cathodes 18' are essentially thinned walled metal .tubes having the end facing the bulb portion '12 closed respectively by wall portions 22 which are directed toward the axis 20 and whose surfaces substantially form an angle'of'45" with the axis 20. The surfaces of the wall portions 22 are coated with any-well known electron emitting material such as a mixture of barium and strontium oxides. Heater filaments 24 are respectively mounted within thetubular cathodes 18 to maintain the cathode surfaces 22 at thermionic temperatures during. tube operation.

Cathodes 18 are fixedto a common insulating ceramic disc 26 which is mountedwithin a tubular control grid electrode 28 closed by wall-portion 30 adjacent the cathode surface 22. The control grid electrode wall portion 30 is formed with: a concave or depressed portion 32 of substantially conical shape-which extends down-over the cathode emitting surface 22. The wall portion 32 is closely spaced from the cathode surface 22 in the order of from 3 to 5 mils and substantially parallel to the emitting surface 22. A:plurality of apertures 34 are provided through the portions-of the-wall 32 overlying the central portions of the emitting cathode surfaces 22.

.Spaced along=the axis 20 from electrode 28 is a short tubular accelerating electrode 36, closed atits-end facing the cathodes 18 by a -wall portion 38 having a single large aperture 40 surrounding axis 20. Wall 38 maybe displaced in theregionabout aperture 40 to extend toward the depressed portion 32 of the control grid 28.

iDuring tube operation, the cathode surfaces 22 are heated andwill emit a copious number of electrons. Control electrode 28 is normally operated at some voltage negative to thepotential of the cathodesurfaces 22;and accelerating electrode 36 is --maintained at a positive-potential in the'order of volts above cathode.potential. -The electronemission from each cath- V ode surface 22 is formed into an individual electron beam; Each. cathode emitting surface with its corresponding control-electrode portion 32 and the anode electrode portion 38 forms an electrostatic electron lens which draws the-electrons from the cathode through the corresponding'grid aperture 34 into the accelerating electrode aperture 40. The electrons passing through each grid aperturel34 are compressed or brought to focus by the electrostatic field into a concentrated region normally known as the first cross-over point. Thus, each electron beam:presents a region or point where the electronbeam is at aminimum cross-sectional area. This. formation of a' cross-overpoint in each electron beam is well-recognized'and is set forth, for example, in' the book Television by V. K. Zworykin and G. A. Morton, published by John'Wiley and Sons Inc., New York, as we'llas in -U. S. Patent 2,581,487 to D. A. Jenny, issued January 8, 1952; With the voltages indicated and: the structural arrangement of the electrode surfaces shown,- it is possible to cause the cross-over point of each electronibeam to coincide on axis 20 at a common point 42 with the cross-over pointsof the other beamsrespectively. From. this common crossover-poinn'the electronv beamsfromthe cathode surface 22- will diverge from each: other as independent electron beams- 44. Furthermore, the trajectories of the electrons in each beam 44 will be divergent so that after passing through the common point 42, each electron beam begins to spread. It is not at all clear whether the beams actually cross each other or merely form a region of minimum cross sectional area. As illustrated in Figure 3a, the beams 44 may only approach each other and be mutually reflected from each other and thus appear to diverge from a virtual crossover point 42. Or, as shown in Figure 3b the beams may actually cross over one another but again appear to diverge from a virtual point 42.

As shown in Figure 1, and spaced along the axis 20, is a second accelerating electrode 46 operated at a voltage in the order of 18,000 volts. The large end of the bulb of envelope is closed by a glass face plate 47 on the surface of which is deposited phosphor material to provide luminescence when struck by the electron beams 44. Adjacent to the phosphor screen 48 there is formed, as a conductive coating 50, a collector electrode extending as shown in Figure 1 from a point adjacent the phosphor screen down into the neck portion of the tube envelope beyond the upper end of the tubular electrode 46. The accelerating electrode 46 is electrically tied to the conductive wall coating 50 by spring fingers 52 fastened to electrode 46 and making spring contact with the conductive coating 50.

The use of a plurality of beams in a tube of the type described in Figure 1 is to produce a brighter picture on the fluorescent screen 48. One such application would be a projection type picture tube in which the picture formed on screen 48 is projected onto a large viewing screen. In a projection type picture tube, it is necessary that the electron beams 44 be brought to a sharp focus at a common point on the surface of the fluorescent screen 48. This is done by the use of a focussing coil 54 mounted on the tube neck 14. Coil 54 is positioned and operated so that the common virtual cross-over point 42 lies on the axis of the focussing field of coil 54 and the electrons appearing to leave point 42' are focussed to a sharp point on the fluorescent screen 48. Thus, coil 54 has a double function: the plurality of electron beams 44 emerging from the common cross over point 42 are brought to a point of common convergence on the fluorescent screen 48, and also, the electrons of each beam are focussed within the beams themselves so that each beam is brought to a small spot at the common point of beam convergence. The result is similar to that described in the application of Hannah C. Moodey, Serial No. 166,416, filed June 6, 1950.

A conventional type deflecting yoke 56 is used for scanning the electron beams 44 simultaneously over the surface of the fluorescent screen 48 in any desired manner. Defiecting yoke 56 consists normally of two pairs of deflecting coils, each pair connected together in series to a source of sawtooth voltages for providing respectively line and frame scansion of the beam over the screen surface, The structure and function of such a deflection yoke is conventional and well known.

In Figure 2, the gun structure is different from that shown in Figure 1. Spaced along the axis of the tube is a tubular accelerating electrode ,58 adapted to be operated at around 4,300 volts. A wall coating 51, similar to that disclosed in the tube of Figure 1 extends down the neck portion 14 of the tube envelope and overlaps the adjacent end of the accelerating tubular electrode 58. The wall coating 51 is operated in the order of 18,000 volts to provide between it and the accelerating electrode 58 an electrostatic focussing and converging field. In Figure 2, the cathode surfaces are symmetrically disposed with respect to tube axis 20 and the other gun parts all coaxially fixed to the tube neck 14, so that beams 44 enter the field between

electrodes

58 and 51 symmetrically spaced from the field axis. Thus, as in thecase of the magnetic focussing field of coil 54 in Figure 1, this focussing field causes the electron beams 44 to converge on the common axis and also brings each beam 44 to a focus point at the fluorescent screen. Thus, in Figure 2 the electrostatic field between

electrodes

58 and 51 is used for simultaneous beam convergence and beam focussing.

The cathode arrangement shown in Figures 1 and 2 need not be limiting, other alternative forms are possible and which also utilize the invention. For example, in Figure 4 there is disclosed a gun structure comprising a plurality of cathode electrodes 60, which are essentially tubular members having filamentary heaters 62, therein for heating the respective cathodes to electron emitting temperatures. There are provided electron emitting surfaces 64 projecting from an end of each cathode cylinder. The emitting cathode surfaces 64 extend at an angle to a common axis 66 of the electron gun and are coated with electron emitting material for providing a source of electron emission during tube operation. Surrounding the cathodes 60 is a common control grid 68 similar to electrode 28 disclosed on Figures 1 and 2. As described above, for electrode 28, control electrode 68 has a depressed or concave wall portion 70 extending down over the emitting cathode surfaces 64 and closely spaced at a uniform distance from the cathode surfaces.

Overlying each emitting cathode surface 64, there is positioned an aperture through the wall portion 70 to provide passage therethrough of electrons from the cathodes. Spaced along axis 66 and similar to electrode 36, shown in Figures 1 and 2, is a tubular accelerating electrode 74 having wall portion 76 with a central aperture 78. Portions of wall 76 forming aperture 78 extend into the concave portion 70 of electrode 68. As previously described for Figures 1 and 2, the electrodes shown in Figure 4 form the electrons emitted by cathode portions 64 into beams having a common crossover point on the axis 66. The beams diverge from this common crossover point as a plurality of beams which may be brought to a common point of convergence and focus as described above for Figures 1 and 2.

Figure 5 shows a plurality of cathode electrodes 80, similar to electrodes 18 of Figures 1 and 2 but positioned with their axes in a common plane rather than parallel to each other. The cathode emitting surfaces 82 retain the same relative positions as the emitting surfaces 22 in Figure 2. With this arrangement, the overall length of the gun structure may be decreased. Leads 84 from the cathode heaters 86 are brought out through the sides of the cathode cylinders. Also, the control grid 88 is considerably shortened in its length and is also closed by a wall portion 90 at its lower end. However, the control portion 92 overlying the cathode emitting surfaces has the same configuration as shown in the previous modifications. Also, an accelerating electrode 94 is identical to previously described accelerating electrodes 36 and 76. The formation of the electron beams with the structure of Figure 5 is identical to that described above for the other modifications.

Figures 6 and 7 show a sectional view of an alternate form of gun structure for providing a plurality of electron beams. In this gun structure a cathode 96 consists of a single tubular member closed at its upper end by a conical shaped wall 98. The outer surface of the conical wall 98 is coated with oxide materials for providing a source of electrons. Cathode tube 96 is mounted on a ceramic spacer 99 which is fixed within a control grid cylinder 97 by being clamped between a spacer ring and a retainer ring 93 welded to the control grid wall 97. The end of the control grid adjacent the electron emitting portion 98 is closed by a wall portion 91 having a conical concave portion 89 closely spaced uniformly from the cathode emitting portion 98. The concave wall portion 89 of the control grid has a plurality of apertures 87 overlying the cathode emitting surface 98 for the passage of electrons therethrough. Axially spaced from the control grid 97 is an accelerating grid electrode 85 having a central opening 83 arranged'coaxially with the cathode and control electrode members. The periphery portions forming aperture 83 of the accelerating grid 85 are bent downward as is shown in Figure 7 to partially extend into the cavity of the control grid wall portion 89. Axially spaced from accelerating grid 85 is a second accelerating electrode 79, formed, as is shown in Figure 6. Spring fingers 77 space the gun structure from the tube neck 14 as Well as center the gun on the neck axis. A conductive coating 75 similar to wall coating of Figure 2 is used as a third accelerating and focussing electrode and extends from the gun structure to a point adjacent the fluorescent screen at the other end of the tube (not shown).

As shown in Figure 7 the three control grid apertures 87 are positioned in a triangular arrangement. In a successfully operated tube of the type shown in Figures 6 and 7, the apertures 87 were substantially, 31 mils in diameter and the control grid wall 89 was spaced substantially 5 mils from the cathode emitting portion 98. The accelerating electrode 85 was spaced substantially 40 mils from the control grid electrode 97. The slope of the

conical wall portions

89 and 98. were approximately 45 from the vertical. This arrangement of parts was such that the electrons passing through the grid apertures 87 were brought to a common crossover point on the gun axis. From this common point the electrons from each aperture 87 emerged as a beam. The several beams were divergent fromeach other but retained their symmetry of position around the axis of the gun. With the gun structure shown in Figures 6 and 7, the focussing field between electrodes 79 and 75 provided a field for bringing the beams to a common point of convergence at the fluorescent screen. Furthermore, thisfield focusses the electrons in each beam to a fine point at the common point of beam convergence.

In the invention as described above the angle that the cathode emitting surfaces made with the gun axis has been described as substantially 45. This particular angle is not limiting but is one which has proved satisfactory. If the angle of the cathode surface to the axis of the gun is made sharper or smaller it would be necessary to increase the accelerating electrode voltage to bring the crossover point of the several beams to a common point on the tube axis.

The distance of the crossover point of each beam from the cathode surface is determined by the size of the control grid aperture as well as by the cathode-to-control grid spacing. The crossover points of the beams can be brought to a common point on the axis by positioning the cathode emitting surfaces at the-required angle to the gun axis and also spacing the cathode emitting surfaces from each other the proper distance. The voltage of the accelerating'electrode also determines the angle of beam divergence from. the gun axis. Thus, adjustment of the accelerating electrodevoltage is made to conform with the strength of the focussing coil field as well as the length of the tube.

In tubes of the type described, because of theincreased cathode area, fromwhich electrons can be emitted, less control grid drive will be needed to provide a given picture brightness. Or fora given grid drive voltage the brightness will be greater depending upon the number of beams. i W

Plural beam electron guns also may be used in such applications as color television picture tubes. For example, the modifications of Figures 1 and 2 for example may be substituted for the gun structure shown in the tube disclosed in the above cited application of Hannah C. Moodey.

The phosphor screen of the tube in the Moodey application consists of dots of phosphor material arranged in groups of three. The phosphor dots of any one group fluoresce respectively with a red, green or blue color when struck by an electron beam. Spaced from the fluorescent screen is a vmasking plate having an aperture positionedabove the center of each group of three phosphor dots. As disclosed in detail in the Moodey application three electron beamsare used, each beam coming from a diflerentdi'rection so that the electrons from the beams in passing through an aperture of the masking screen will strike only one of the three dots depending upon the direction of the electron beam. For such a modification the gun structures shown in Figures 1 and 2 may consistof three cathode electrodes spaced from each other in a triangular arrangement and with a control grid electrode 18 having three apertures 34 to provide three beams. Each beam then will approach the masking electrode of the color'tube from a different angle and will strike only the phosphor dot fluorescing with a single color. The .color signals used to modulate each beam respectively can be applied between each of the cathode electrodes and the control grid electrode 28. As a further modification, the central grid 91 in the tube of Figures 6 and.7 may be madein several parts, each part with a single control aperture 87.v The signal modulations can then be applied between cathode 96 and each control grid part respectively. Thus the beams may be independently controlled.

The modifications of Figures 4 and 5 may also be used in .a similar manner for a color television tube of the type described in-the Moodey application.

What is claimed is:

1. An electron gun structure for forming a plurality of electron .beams along respective paths, said gun structure comprising, a cathode electrode having a concave electron emitting surface, an accelerating electrode having a single apertured portionspaced coaxially from said concave cathode emitting surface along the axis of said concave surface, and aplurality of control grid electrode portions positioned between said cathode emitting surface and said apertured accelerating electrode portion, each of said control grid portions having an aperture overlying said cathode emitting surface, said apertures being symmetrically disposed about said cathode axis.

2. An electron gun structure for forming a plurality of electron beams along respective paths, said gun structure comprising, a cathode electrode having a concave electron emitting surface, an accelerating electrode having a single apertured portion spaced coaxiallyfrom said concave cathode emitting surface along the axis of said concave surface, a control grid electrode positioned between said cathode emitting surface and said apertured accelerating electrode portion, said control electrode having a portion'substantially equidistant from said concave cathode surface, said control grid electrode portion having a plurality of apertures therethrough overlying said concave cathode'surface and symmetrically disposed about said cathode axis.

3. An electron gun structure for forming a plurality of electron beams along respective paths, said gun structure comprising a-cathode electrode having a concave conical electron emitting surface, a tubular accelerating electrode coaxially spaced from said conical cathode emitting surface along the axis of said concave cathode surface, said accelerating electrode having an apertured portion overlying said'conical cathode surface,.a control electrode positioned between said cathode emitting surface and said accelerating electrode, said control electrode having a conical portion overlying and spaced substantially equidistant from said conical cathode surface, said conical control electrode portion having a plurality of apertures therethrough for the passage of electrons from said cathode surface, said control electrode apertures being symmetrically positioned about said cathode axis.

4. An electron gun structure for forming a plurality of electron beams along respective paths, said gun structure comprising cathode means having a plurality of electron emitting surfaces disposed symmetrically about a common axis of symmetry, and electrode means for forming an electron lens field for focussing the electrons from said cathode surfaces to a common point on said axis, said electrode means including an accelerating electrode having a single apertured portion spaced from and adjacent to said cathode surfaces on the axis of symme'try, and a plurality of control grid electrode portions positioned between said cathode emitting surfaces and said apertured accelerating electrode portion, each of said control grid portions having a single aperture overlying one of said cathode emitting surfaces, said control grid apertures being symmetrically positioned about said axis of symmetry.

5. An electron gun structure for forming a plurality of electron beams along respective paths, said gun structure comprising cathode means having a plurality of electron emitting surfaces symmetrically disposed about a common axis, an accelerating electrode having a portion with a single aperture coaxially spaced from and adjacent to said cathode surfaces along said common axis, a control grid electrode enclosing said cathode surfaces and including portions positioned between said cathode surfaces and said accelerating electrode, one of said control electrode'portions overlying each of said cathode surfaces and having a single aperture therethrough, said control grid apertures being symmetrically positioned about'said common axis.

6. An electron gun structure for'forming a plurality of electron beams along respective paths, said gun structure comprising a plurality of tubular cathode electrodes each having an electron emitting surface at an angle to the axis of the respective tubular cathode, said electron emitting cathode surfaces symmetrically disposed about and facing a common axis of symmetry, a tubular accelerating electrode spaced along said common axis from said cathode emitting surfaces and having an end wall portion overlying said cathode surfaces, said accelerating electrode wall portion having a single aperture coaxially spaced from and adjacent to said cathode surfaces along said common axis, a single control electrode positioned between said cathode emitting surfaces and said accelerating electrode, said control electrode having a conical portion overlying and spaced substantially equidistant from each of said cathode surfaces, said conical control electrode portion having a plurality of apertures therethrough symmetrically disposed about said common axis and with one control electrode aperture adjacent each cathode emitting surface for the passage of electrons from said cathode surfaces.

7. An electron discharge device comprising, electrode means for producing a plurality of electron beams along respective paths having a common general direction, a target electrode mounted transversely to said beam paths, said beam producing electrode means including a plurality of electron emitting surfaces, a common control electrode and a common accelerating electrode spaced successively from the electron emitting surfaces to form an electron lens field for forming electrons from said surfaces into individual beams and for focussing said beams substantially to a common point, and electron lens field producing means spaced along said beam paths between said beam producing means and said target electrode for providing a common beam converging field having an axis passing through said common point for converging and focussing said beams at a second common point on said target electrode.

8. A cathode ray tube comprising, electron beam producing means including a plurality of cathode electrodes each having an electron emitting surface for producing a plurality of electron beams along respective paths having a common general direction, a target electrode mounted transversely to said beam paths, and means spaced between said beam producing means and said target electrode for producing a lens field having an axis extending substantially normal to said target electrode for converging said electron beams onto said target electrode, said beam producing means including a plurality of electrodes for producing an electrostatic field for forming the electrons from each cathode surface into separate beams respectively and for focusing said beams to a common point on said lens field axis between said lens field producing means and said cathode electrodes, said cathode surfaces being symmetrically disposed about said lens field axis, said plurality of electrodes including a common control electrode positioned between said cathode surfaces and said common point of beam focus,

and a common anode electrode having a single aperture on said lens field axis adjacent said common point of beam focus, said control electrode having a single aperture over each cathode surface.

9. A cathode ray tube comprising, electron beam producing means for producing a plurality of electron beams along respective paths having a common general direction, a target electrode mounted transversely to said beam paths and an electron field producing means spaced between said beam producing means and said target electrode for producing a lens field having an axis extending substantially normal to said target electrode for converging said electron beams onto said target electrode, said beam producing means including a plurality of cathode electrodes each having an electron emitting surface and a plurality of other electrodes for producing an electrostatic field for focussing the electrons from each cathode surface to a common point on said lens field axis between said beam producing means and said cathode electrodes, said cathode electrodes each comprising a tubular member with said electron emitting surface positioned at an angle to the axis of said tubular member, said cathode surfaces positioned symmetrically about and facing said lens field axis, said other electrodes including a common control electrode having portions overlying and parallel to said cathode surfaces, said control electrode portions each having a single aperture therethrough, and a common accelerating electrode having portions equidistantly spaced from said control grid portions and having a single aperture on the axis of said lens field.

References Cited in the file of this patent UNITED STATES PATENTS 1,979,392 Lubcke Nov. 6, 1934 2,035,623 Sukumlyn Mar. 31, 1936 2,122,095 Gabor June 28, 1938 2,163,256 Du Mont June 20, 1939 2,457,175 Parker Dec. 28, 1948 2,490,308 Klemperer Dec. 6, 1949 2,547,415 Silverman Apr. 3, 1951 FOREIGN PATENTS 169,756 Switzerland Sept. 1, 1934 704,803 Germany Apr. 7, 1941