US3890528A

US3890528A - Common focusing electrode for plurality of beams and having same plurality of internal shields

Info

Publication number: US3890528A
Application number: US456078A
Authority: US
Inventors: Donald L Say; Harry E Smithgall
Original assignee: GTE Sylvania Inc
Current assignee: GTE Sylvania Inc
Priority date: 1974-03-29
Filing date: 1974-03-29
Publication date: 1975-06-17
Anticipated expiration: 1992-06-17
Also published as: DE2513281C2; DE2513281A1

Abstract

An improvement is provided in a multibeam bipotential electron gun structure for use in a cathode ray tube whereby the electrostatic focus lensing effected by the focus and accelerating electrodes is beneficially improved. The invention relates to a tube-like encompassing member that is formed integral with each of the front apertures in the focus electrode, such being fabricated in a manner to extend rearward toward a related rear aperture in the same electrode thereby effecting shielding for the respective electron beam traversing the region. This shielding provides improved symmetry of the equipotential lines of force comprising the field of the focus lensing in particularly the region of low beam velocity within the focus electrode portion of the lensing field, thereby providing a welldefined beam spot landing at the screen.

Description

United States Patent [19] Say et al.

[ June 17, 1975 [75] Inventors: Donald L. Say, Waterloo; Harry E.

Smithgall, Seneca Falls, both of N.Y.

[73] Assignee: GTE Sylvania Incorporated,

Stamford, Conn.

3,772,554 ll/l973 Hughes ..3l3/4l4X Primary ExaminerRobert Segal Attorney, Agent, or FirmNorman J. OMalley; Frederick H. Rinn; Cyril AI Krenzer [57] ABSTRACT An improvement is provided in a multibeam bipotential electron gun structure for use in a cathode ray tube whereby the electrostatic focus lensing effected by the focus and accelerating electrodes is beneficially improved. The invention relates to a tube-like encompassing member that is formed integral with each of the front apertures in the focus electrode, such being fabricated in a manner to extend rearward toward a related rear aperture in the same electrode thereby effecting shielding for the respective electron beam traversing the region. This shielding provides improved symmetry of the equipotential lines of force comprising the field of the focus lensing in particularly the region of low beam velocity within the focus electrode portion of the lensing field, thereby providing a welldefined beam spot landing at the screen.

4 Claims, 7 Drawing Figures 1 COMMON FOCUSING ELECTRODE FOR PLURALITY OF BEAMS AND HAVING SAME PLURALITY OF INTERNAL SHIELDS BACKGROUND OF THE INVENTION This invention relates to a plural beam cathode ray tube and more particularly to a multibeam bipotential electron gun structure employed in a color cathode ray tube construction.

Many cathode ray tubes currently utilized in color television applications are of the type employing a patterned multiphosphor cathodoluminescent screen interiorly disposed on the viewing panel of the envelope wherein an apertured or multiopening mask is spatially positioned relative thereto. A plurality of electron beams, emanating from an electron gun mount structure positioned within the envelope, are directed to converge at and traverse the apertured mask to discretely impinge and luminescently excite the electronresponsive phosphors of the screen therebeyond. Focusing of the individual electron beams is conventionally achieved by means of bi-potential lensing. This type of focus lensing is dependent on the ratio of the focus voltage to the respective accelerating electrode or anode voltage. For example, in bi-potential focusing, the potential applied to the focus electrode is in the order of to percent of the anode voltage, thus with an anode voltage in excess of 20,000 volts, the focus voltage is usually well above 3,000 volts. With the advent of smaller and more compact multibeam electron gun structures, unitized focusing and accelerating electrodes have been developed wherein the plurality of beams share portions of the respective single electrodes. The unitized focusing electrode is a common structure having, for example, three spaced-apart apertures in a common plane therein, one for each of the beams traversing the electrode. The associated accelerating electrode is also a common structure having a like number of related apertures therein. These two electrodes are positioned adjacent to one another in a substantially longitudinal manner to form focusing lenses for the respective electron beams traversing these electrodes. In some gun constructions, the apertures in the accelerating electrode are offset slightly from those in the related focusing electrode to form an eccentric lens. This type of offset lens is beneficial in that it not only focuses an electron beam but also initiates a desired slight deflection of the beam toward a convergent position relative to the two other related beams emanating from the gun structure. While advantageously initiating the desired convergence, it has been found that the offset focusing lens evidences a partial nonsymmetrical field which influences the beam to effect a noticeably distorted spot image at the screen.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to reduce the aforementioned disadvantages by improving the multibeam bipotential electron gun structure in a manner to achieve improved field symmetry of the focus lensing for each of the electron beams emanating therefrom.

It is another object of the invention to provide an improvement in a cathode ray tube multibeam bipotential electron gun structure whereof the beams projected therefrom are focused on the screen as spots free of astigmatic distortions.

These and other objects and advantages are achieved in one aspect of the invention by an improvement in the multibeam bipotential electron gun structure of the cathode ray tube. For example, in a three beam electron gun structure, focusing of the individual beams is accomplished by lensing effected by the focusing and accelerating electrode members. The focusing electrode is a common member having three from and rear spatially related apertures therein. Each of the front apertures has a tube-like encompassing member formed integral therewith and fabricated in a manner to extend rearward toward a related smaller-dimensioned rear aperture, thereby effecting shielding for the respective electron beam passing therethrough. A common accelerating electrode member is adjacently positioned ahead of the focusing electrode. This accelerating electrode has three spaced-apart apertures located therein which substantially mate with the front apertures of the focusing electrode member. At least two of the accelerating electrode apertures are eccentrically aligned relative to the related focusing electrode front apertures to form therebetween offset electrostatic lensings for focusing the respective individual electron beams trave rsing that particular region. Each of the focusing electrode shielding members provides a marked enhancement of beam focusing by effecting improved symmetry of the equipotential lines of force in particularly the region of low beam velocity in the focusing electrode portion of the electrostatic lensing field. The improved symmetry of the focus lensing influences the shaping of the beam passing therethrough to provide a substantially small and well-defined beam spot landing at the screen.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a sectional view of the color cathode ray tube illustrating componental portions thereof;

FIG. 2 is an enlarged partially sectioned view of a multibeam electron gun structure wherein the invention is shown;

FIG. 3 is a slightly enlarged plan view illustrating the forward portion of the grid three electrode member taken along the line 33 of FIG. 2',

FIG. 4 is a prior art illustration delineating an enlarged sectional view showing the relationship of a single focusing electrode aperture to a single accelerating electrode aperture whereof the equipotential lines of the non-symmetrical offset lensing field are indicated;

FIG. 5 is a sectional view showing a single accelerating electrode aperture related to a single focusing electrode aperture incorporating the invention wherein the modified symmetrical lensing field is indicated;

FIG. 6 is a partial sectional view of an inline multibeam electron gun showing the focusing electrode and the accelerating electrode relationship with the invention delineated in the focusing electrode member; and

FIG. 7 is a plan view illustrating the forward portion of the common inline focusing electrode member taken along the line 77 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following specification and appended claims in connection with the aforedescribed drawings.

With reference to the drawings, there is illustrated in FIG. 1 a partially sectioned multibeamed color cathode ray tube 11 having an encompassing envelope comprised of an integration of a neck portion 13, a funnel portion 15, and a face or viewing panel portion 17. A patterned screen 19 including a repetitive plurality of color-emitting phosphor components is suitably disposed on the interior surface of the viewing panel 17. A multi-opening mask member 21 is positioned within the viewing panel, by means not shown, in a manner whereof the multi-opening portion 23 is spatially related to the patterned screen 19. Extending into the neck portion 13 is a skirt of a high voltage internal conductive coating 25 which is a continuation of the coating covering the interior surface of the funnel portion 15 of the tube envelope. Positionally encompassed within the neck portion is a multibeam bipotential electron gun structure 27 having a longitudinal axis 29 therethrough. Two of the plurality of

individual electron beams

31 and 33 are shown emanating from the gun structure, whereupon they are convergently directed toward the patterned screen 19. Mounted exteriorly upon the envelope, in substantially the neckfunnel transition region 35, is a yoke 37 or deflection coil arrangement which is formed and energized to impart scanning motion to the referenced

electron beams

31 and 33. Positioned behind the yoke means, on the exterior of the neck portion 13 of the envelope, are magnet means 39 and 41 of the dynamic convergence device, two of which are shown. The magnetic fields emanating from the respective magnet means effect converging influences on the respective beams as they traverse the convergence cage 43 attached to the forward end of the multi-beamed electron gun structure 27.

For greater exposition, reference is directed to FIGS. 2 and 3 wherein the improved multi-beam bipotential electron gun structure 27, incorporating an embodiment of the invention, is exemplarily illustrated as a three-beam delta arrangement whereof the respective beams are positioned in a substantially equispaced offaxis orientation. In a multibeam gun structure, each of the respective beams traverses a substantially longitudinal arrangement of several functionally related electrode members embodying, as for example, apertured grid electrodes one through four positioned in sequential orientation from a related cathode or electron generating component. These several electrode members are positionally held in spaced relationship with respect to each other by a plurality of insulative support rods 45, of which two are shown. In greater detail, a single or central ray of an exemplary electron beam 33 is shown as emanating from the electron-emissive thermionic cathode 47, whereupon the beam is initially shaped and influenced by the apertured individual grid one control electrode 49 and thence directed through the apertured grid two or screen electrode 51. The travelling beam then enters one of the rear apertures 53 formed in the rear aperture plane 55 of the composite common grid three focus electrode member 57, and proceeds therethrough leaving by a larger aperture 59 formed in the front aperture plane 61 of that member; whereupon the beam enters a related aperture 63 in the common grid four accelerating electrode 65 to which is terminally attached the aforementioned convergence cage assembly 43. g

The unitizdf'focuselectrode 57, of delta beam arrangement, is illustrated as being fabricated of two substantially cupshaped

members

67 and 69 which are suitably integrated by peripherally applied bonding at the respectively mated flanges 71 and 73. FIG. 3 presents a view looking into the forward member 69 from the flange 73. As shown, discretely configurated portions of the peripheral flange are typically embedded in the spaced-apart support rods 45 to provide rigid positional support for the electrode member in the composite gun structure 27.

The invention relates to an improvement in the common grid three focus electrode structure 73, wherein each of the front apertures 59 in the front aperture plane 61 is, for example, substantially circular in shape and has a tube-like encompassing member 77 integral with the front aperture plane, such member being formed in a manner to extend rearward therefrom toward the related smaller-dimensioned rear aperture 53 oriented in the rear aperture plane 55 of that electrode member. Thus, each tube-like member 77 effects shielding for the respective electron beams passing therethrough. These shielding means are substantially similar for the several beams concerned. For example, they are usually of substantially equal internal crosssectional dimensionings, and are preferably substantially cylindrical in shape.

The aperture plane 64 of the grid four accelerating electrode member 65 has a plurality of spaced apertures 63 therein which are of dimensions substantially larger than the spatially related front-oriented apertures 59 in the grid three electrode member 57. At least two of the larger-dimensioned grid four apertures 63 are eccentrically aligned relative to the related smallerdimensioned grid three front apertures 59, to form offset non-symmetrical electrostatic lenses for focusing the respective electron beams traversing the respective region.

In referring particularly to FIG. 3, the offset relationship of the

apertures

59 and 63, pertaining to the focus lensing, is illustrated, for example, for one set of apertures as being substantially in radial orientation 0 with reference to the gun axis 29, whereby the periphery of the accelerating electrode aperture 63 is phantomed to indicate its distal eccentricity D to the periphery of the focus electrode aperture 59. The opposed peripheral portions of the two radially oriented apertures that are proximal P to the gun axis 29 are substantially mated in longitudinal alignment. The offset lensing so effected, not only focuses the electron beam, but also initiates a beneficial deflective influence which imparts a slight convergent attitude to the beam with respect to the two other beams formed in the gun structure.

For a functional explanation of the invention, attention is directed to FIGS. 4 and 5 wherein lensings affecting the focusing and trajectories of the beams are portrayed. FIG. 4 is an enlarged portional art view illustrating a single grid three aperture in relationship to a spatially related single grid four aperture whereof an offset or eccentric focusing lens is effected. The grid four accelerating electrode 65', sometimes referenced as an anode, has a relatively high anode voltage, for example, the potential may be in excess of 20 kv. The related grid three focusing electrode 57 has a lower potential applied thereto which, for example, may be in the order of 4 to 5 kv. Both apertures 59' and 63' in the prior art structures are defined by relatively short or small re-entrant lips. The apertural interaction of the diverse grid three-grid four potentials effects an electrostatic focusing lens whereof the equipotential lines 79 in particularly the low voltage grid three electrode 57' region are non-symmetrically oriented. The focusing of the electron beam 33' traversing this lensing is detrimentally influenced by astigmatism or distortion introduced by this nonsymmetrical field. For example, the near presence of the wall 81 of the focus electrode 57' and the short re-entry lips 83 surrounding the aperture 59' are contributory to allowing the equipotential lines 79', especially in the low-voltage region, to loop back of the aperture in a nomsymmetrical manner. This displacement of the lensing field within the focus grid produces a detrimental uncontrolled bending or astigmatic influence on the beam in a region of low velocity whereat the electrons are easily deflected. Such action aggravates beam spot distortion at the screen. The beneficial aspects of the invention are illustrated in FIG. 5, which is an enlarged portional view, wherein the grid three aperture 59 is shown as being formed to have an integral tube-like encompassing or shielding member 77 extending rearward therefrom into the volume of the focus electrode structure 57. It is preferable for the shielding member to have a length 2 at least equally 50 percent of the radius r of the aperture 59 or of the resultant like dimensioned lens: e Z 0.50 r. Such longitudinal definitive shielding effects substantially symmetrical shapings of the equipotential lines of force in the low voltage portion of the lensing field, substantially within the critical portion of the focus electrode member, thereby providing enhanced beam spot focusing at the screen that is free of astigmatic distortion.

The invention is also applicable to a multibeam inline electron gun structure, of which a portional sectioned region embodying the focus and accelerating

electrodes

89 and 91 is illustrated in FIGS. 6 and 7. In this type of gun construction, the related electrode components for controlling each of the respective beams are positioned in a substantially longitudinal manner, on a substantially common plane, to provide a center onaxis beam 93 with

related beams

95 and 97 equi-spaced on either side thereof; the center rays of the respective beams being indicated in the FIGS. 6 and 7. At least the side-related electrode arrangements include focus electrode apertures 99 having tube-like shielding members 101 that are of substantially equal lengths. The sideoriented accelerating electrode apertures 103 are usually offset relative to the corresponding focus electrode apertures 99 to provide the benefits of eccentric lensing. Such offset orientation is indicated in phantom in FIG. 7, which presents a view looking into the forward member 105 of the two-piece focus electrode 89 from the plane of the flange 107. Configurated portions of the peripheral flange are suitably embedded in the longitudinal support rod members 45' to provide rigid positional support for the common inline focusing electrode in conjunction with the associated electrodes comprising the composite electron gun structure 87.

Thus, there is provided an improvement in a cathode ray tube multibeam bipotential electron gun structure, wherein shielding is included in the common focus grid electrode in a manner to effect improved symmetry of the equipotential lines of force comprising the electrostatic focus lensing to provide welldefined beam spot landings on the screen.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. An improvement in a cathode ray tube multibeam bipotential electron gun structure having a longitudinal axis therethrough and having electron generating means therein formed to emit a plurality of separately controlled electron beams whereof each beam emanates from a substantially longitudinal arrangement of several related apertured grid electrodes positioned in sequential orientation in front of a rear positioned cathode component, said improvement being in the forward region of said electrode arrangement and comprising:

a common focusing electrode member having a forward oriented front aperture plane spaced longitudinally from a rearward oriented rear aperture plane, said planes having a similar plurality of substantially circular related apertures therein, each of said front apertures having a defined tube-like extensive encompassing member of substantially cylindrical shaping integral with said front aperture plane and fabricated to extend rearward therefrom toward a related smaller-dimensioned rear aperture formed in said rear aperture plane to effect shielding for the respective electron beam passing there through; each of said tube-like shielding members being of substantially equal cross-sectional dimensioning and having a length at least equaling 50 percent of the radius of the associated front aperture; and

a common accelerating electrode member positioned forward of said focusing electrode member and having an aperture plane proximal to the front aperture plane of said focusing electrode member, said accelerating electrode aperture plane having a plurality of apertures therein substantially mating in a spatial manner with the front oriented aper tures of said focusing electrode member, at least two of said accelerating electrode apertures being eccentrically aligned relative to said related focusing electrode front apertures to form nonsymmetrical electrostatic lenses for focusing the respective individual electron beams traversing the particular region; each of said focusing electrode shielding members providing enhanced beam focusing by effecting improved symmetry of the equipotential lines of force in particularly the region of low beam velocity in the focusing electrode portion of said electrostatic lensing field.

2. The multibeam electron gun improvement according to claim 1 wherein said gun structure is a three beam delta arrangement whereof the related electrode components for each of the respective beams are positioned in a substantially equal off-axis orientation.

3. A multibeam electron gun improvement according to claim 1 wherein said plural beam gun structure is a three beam inline arrangement whereof the related electrode components for the respective beams are positioned in a manner to provide a center on-axis beam with related beams equi-spaced on either side thereof, and whereof at least the side-related electrode arrangements include focusing electrode tubelike shielding members of substantially equal lengths.

4. An improvement in a cathode ray tube employing a multibeam bipotential electron gun structure whereof the individual plural beams are directed to selectively impinge a patterned cathodoluminescent screen discretely spaced therefrom, said improvement being in the multibeam electron gun structure wherein each of the respective beams emanates from a substantially longitudinal arrangement of several related apertured grid electrodes positioned in sequential orientation in front of a rear positioned related cathode component, said tube improvement being in the forward region of said electrode arrangement and comprising:

a common electrode member having a forward oriented front aperture plane spaced longitudinally from a rearward oriented rear aperture plane, said planes having a similar plurality of related apertures therein, each of said front apertures having a defined tube-like encompassing member of substantially cylindrical shaping integral with said front aperture plane and fabricated to extend rearward therefrom toward a related smallerdimensioned rear aperture formed in said rear aperture plane, and having a length at least equalling 50 percent of the radius of the associated front aperture to effect shielding for the respective electron beam passing therethrough; and

a common accelerating electrode member positioned forward of said focusing electrode member and having an aperture plane proximal to the front aperture plane of said focusing electrode member, said accelerating electrode aperture plane having a plurality of apertures therein substantially mating in a spatial manner with the front oriented apertures of said focusing electrode member, at least two of said accelerating electrode apertures being eccentrically aligned relative to related focusing electrode front apertures to form non-symmetrical electrostatic lenses for focusing the respective electron beams traversing the particular region; each of said focusing electrode shielding members providing enhanced beam spot focusing on said screen by effecting improved control of the equipotential lines of force in particularly the region of low beam velocity in the focusing electrode portion of said electrostatic lensing field.

Claims

1. An improvement in a cathode ray tube multibeam bipotential electron gun structure having a longitudinal axis therethrough and having electron generating means therein formed to emit a plurality of separately controlled electron beams whereof each beam emanates from a substantially longitudinal arrangement of several related apertured grid electrodes positioned in sequential orientation in front of a rear positioned cathode component, said improvement being in the forward region of said electrode arrangement and comprising: a common focusing electrode member having a forward oriented front aperture plane spaced longitudinally from a rearward oriented rear aperture plane, said planes having a similar plurality of substantially circular related apertures therein, each of said front apertures having a defined tube-like extensive encompassing member of substantially cylindrical shaping integral with said front aperture plane and fabricated to extend rearward therefron a related smaller-dimensioned rear aperture formed in said rear aperture plane To effect shielding for the respective electron beam passing therethrough; each of said tube-like shielding members being of substantially equal cross-sectional dimensioning and having a length at least equaling 50 percent of the radius of the associated front aperture; and a common accelerating electrode member positioned forward of said focusing electrode member and having an aperture plane proximal to the front aperture plane of said focusing electrode member, said accelerating electrode aperture plane having a plurality of apertures therein substantially mating in a spatial manner with the front oriented apertures of said focusing electrode member, at least two of said accelerating electrode apertures being eccentrically aligned relative to said related focusing electrode front apertures to form nonsymmetrical electrostatic lenses for focusing the respective individual electron beams traversing the particular region; each of said focusing electrode shielding members providing enhanced beam focusing by effecting improved symmetry of the equipotential lines of force in particularly the region of low beam velocity in the focusing electrode portion of said electrostatic lensing field.

3. A multibeam electron gun improvement according to claim 1 wherein said plural beam gun structure is a three beam inline arrangement whereof the related electrode components for the respective beams are positioned in a manner to provide a center on-axis beam with related beams equi-spaced on either side thereof, and whereof at least the side-related electrode arrangements include focusing electrode tube-like shielding members of substantially equal lengths.

4. An improvement in a cathode ray tube employing a multibeam bipotential electron gun structure whereof the individual plural beams are directed to selectively impinge a patterned cathodoluminescent screen discretely spaced therefrom, said improvement being in the multibeam electron gun structure wherein each of the respective beams emanates from a substantially longitudinal arrangement of several related apertured grid electrodes positioned in sequential orientation in front of a rear positioned related cathode component, said tube improvement being in the forward region of said electrode arrangement and comprising: a common electrode member having a forward oriented front aperture plane spaced longitudinally from a rearward oriented rear aperture plane, said planes having a similar plurality of related apertures therein, each of said front apertures having a defined tube-like encompassing member of substantially cylindrical shaping integral with said front aperture plane and fabricated to extend rearward therefrom toward a related smaller-dimensioned rear aperture formed in said rear aperture plane, and having a length at least equalling 50 percent of the radius of the associated front aperture to effect shielding for the respective electron beam passing therethrough; and a common accelerating electrode member positioned forward of said focusing electrode member and having an aperture plane proximal to the front aperture plane of said focusing electrode member, said accelerating electrode aperture plane having a plurality of apertures therein substantially mating in a spatial manner with the front oriented apertures of said focusing electrode member, at least two of said accelerating electrode apertures being eccentrically aligned relative to related focusing electrode front apertures to form non-symmetrical electrostatic lenses for focusing the respective electron beams traversing the particular region; each of said focusing electrode shielding members providing enhanced beam spot focusing on said screen by effecting improved control of the equIpotential lines of force in particularly the region of low beam velocity in the focusing electrode portion of said electrostatic lensing field.