US3313975A

US3313975A - Electron impervious flexible shield member for electron discharge tubes

Info

Publication number: US3313975A
Application number: US380453A
Authority: US
Inventors: Frederick G Oess
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1964-07-06
Filing date: 1964-07-06
Publication date: 1967-04-11
Anticipated expiration: 1984-04-11
Also published as: GB1083406A

Description

prll 11, 1967 F G, @E55 3,313,975

ELECTRON IMPERVIOUS FLEXIBLE SHIELD MEMBER FOR ELECTRON DISCHARGE TUBES Filed July 6, 1964 3 Sheets-Sheet l w .//l/f! April 11, 1967 F. G. oEss 3,313,975

ELECTRON IMPERVIOUS FLEXIBLE SHIELD MEMBER FOR ELECTRON DISCHARGE TUBES Filed July 6, 1964 3 Sheets-Sheet 2 y maj/145% April l1, 1967 F. G. oEss 3,313,975

ELECTRON IMPERVIOUS FLEXIBLE SHIELD MEMBER FOR ELECTRON DISCHARGE TUBES Filed July 6, 1964 3 Sheets-Sheet 5 WMA/raz.

United States Patent O 3,313,975 ELECTRN HMPERVIOUS FLEXIBLE SHIELD MEMBER FOR ELECTRN DISCHARGE TUBES Frederick G. Oess, Oceanside, Calif., assigner to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed July 6, 1964. Ser. No. 380,453 6 Claims. (Cl. 313-241) This invention relates to llexilble components and the like especially for use las a shield or closure member between structures which may have irregular and/or incongruent shapes. More particularly, but not necessarily exclusively, the invention relates to cathode ray storage tubes and to flexible shielding means for eliminating undesirable illumination effects and electrical charging of the glass envelope which results in arcing or distortion o-f the visual display or electrical read-out.

The invention ilnds particular utility in direct-viewing cathode ray storage tubes wherein a relatively high velocity electron beam is employed which scans a storage tar-get in accordance with intelligence signals to establish a charge pattern on the storage target corresponding to the information to be stored and presented. The storage target is sprayed or flooded with a relatively broad beam of electrons which pass through the storage target according to the potentials of the discrete areas there-of defining t-he stored charge pattern and are then accelerated to impinge upon the 'viewing screen to create a visual replica of the stored charge pattern. rIhe operation of such cathode ray tubes is well-known and a full description thereof may be found in U.S. Patent 2,790,- 929 issued to E. E. Herman and G. F. Smith, entitled, Direct-Viewing Half-Tone Storage Device, and in U.S. Patent No. 3,086,139 issued to N. H. Lehrer and entitled, Cathode Ray Storage Tube. In ilooding the storage target with the broad beam of electrons (sometimes called viewing e-lectrons), it will be appreciated that a uniform distribution over the storage surface of these electrons is desirable, and further that all of the iviewing electrons should have substantially the same velocity, and should impinlge substantially normally on the storage surface, or elese variations in the intensity and accuracy of presentation will result. To achieve these ends, the flood or viewing electrons are collimated o'ver the entire area of the storage surface, by means of a collimating electron lens system, as is also well understood in the art.

It has been observed in the operation of direct-viewing storage tubes of the character described that ilood electrons penetrate around the edge of the target electrodes therein so a-s to strike the inner surface of the adjacent glass envelope thereby developing an undesirable charge thereon. Such glass charging results in an undesirable high electric field which distorts the uniform-ity of the visual display in a direct-viewing storage tube. In other types of storage tubes of the scan-conversion type, for example, the electrical read out is distorted Iby such charging. In some instances arcing may result which damages the electrodes of such highly expensive tubes.

In U.S. Patent 2,928,970 to K. R. Hesse, a shield means is described for preventing stray llood electrons from penetrating into the space around the periphery of the target electrodes and the side walls of the envelope. In general, Hesses shield comprises an inwardly extending ring or skirt affixed to the ring support for the collector electrode grid, for example. In addition to not disclosing means for preventing the flood electrons from entering the space between the electrodes and the glass envelope, the type of shield described by Hesse is relatively inilexible and is not easily adapted to providing a shielding action in areas involving odd and inconigruent shapes or dimensions.

It is therefore an object of the present invention to provide an improved llexible component or shielding member.

Another object of the invention is to provide an imp roved flexible shielding member for use in electron tubes.

Another object of the invention is to provide an improved cathode ray tube of the type utilizing a collimated beam of flood electrons with means to prevent the flood electrons from entering into the space between the target structures and the tube envelope.

Another object of the invention is to provide an improved flexible shielding mean-s for use in the cathode ray storage tubes of the type utilizing a collimating beam of flood electrons.

'Ilhese and other objects and advantages of the invention are realized by providing a shield member of thin, flexible material having surfaces lying in more than one plane. The flexible component or shield member of the invention may take, for example, the form of a trou-gh or rain gutter. The shield member may also comprise a straight portion having a flared out skirt portion. When disposed between adjacent structures such as the wall of an electron tube and target structures therein, the portions o-f the shielding member may be slightly flexed and under tension so as to insure snug contact between the tube wall and the target structures. To achieve flexibility and resilience in more than one plane the shield member is provided with slits transverse to its length which permit it to be bent abruptly around corners or other irregularly shra'ped portions of the target while still retaining the desired snug contact between these structures and the tube wall. By folding t-he slit portions of the shield member on themselves the flexibility function of the slits is obtained while covering the slits so that electrons, for example, may not pass therethrough.

The invention will be described in greater detail' in connection with one application thereof in a direct-viewing cathode ray storage tube by reference to the dnawings in which:

FIGURE l is a partially cross-sectional and partially schematic view of a cathode ray storage tube employing a llexi'ble flood beam shield member according to the present invention;

FIGURE 2 is a plan view of a strip of flexible material for use as a flood beam shield member according to the invention at one stage in the fabrication thereof;

FIGURE 3 is an elevational view in perspective of the strip of llexible material folded on itself along the centerline shown in FIGURE 2 for use as a llood beam shield member according to the invention at a further stage in the fabrication thereof;

FIGURE 4 is an elevational view in perspective of the strip of flexible material shown in FIGURE 3 for use as a flood beam shield member according to the invention at a further stage in the fabrication thereof;

FIGURE 5 is an elevational view in perspective of the strip of flexible material shown in FIGURE 4 for use as a ilood beam shield member according to the invention at the final stage of fabrication thereof;

FIGURE 6 is an end view partly in section of a portion -of a cathode ray tube showing t-he flexible ilood beam shield member disposed between an electrode structure and the wall portion of the tube; and

FIGURE 7 is a plan View partly in section of a portion of a cathode ray tube showing the flexible llood beam shield member disposed between an electrode structure and the wall portion of the tube.

Referring now to the drawings and to FIGURE 1 in particular, a typical half-tone visual display c-athode ray tube 2 is shown. The tube 2 comprises an evacuated envelope formed by a comparatively large cylindrical section 4 and a narrower neck portion 6 communicating therewith at one side thereof (hereinafter referred to as the neck or gun side). The neck section 6 may be disposed coaxially with the main longitudinal axis of the larger cylindrical section 4. The side of the large cylindrical section 4 opposite the neck side comprises the faceplate 8 over the 'inner surface of which may be disposed a phosphor target or viewing screen 1t) covered with a thin lm 12 of metal, such as aluminum, for example. Adjacent and coextensive with the faceplate 8 is a storage target 14 as described in U.S. Patent 3,086,139 to N. H. Lehrer and assigned to the instant assignee. The storage target 14 may comprise a nickel mesh support 15 on one side of which is disposed a thin layer or film of zinc sulide. This film or Zinc sulfide has both secondary electron emissive and bombardment induced conductivity properties. The nickel mesh may lbe supported on an annular ring 17 as shown in FIGURE 7.

Continuing to proceed with the description from the viewing screen end of the tube toward the gun section, Ka collector electrode 16 is disposed adjacent and coextensive with the storage target 14. The collector grid 16 comprises a conductive screen and it may be supported about its pheriphery by a cylindrical member or can 18 which may also serve as a collimating electrode. Alternatively, the collector grid may be disposed on a separate support ring 19 as shown in FIGURE 7.

A flood gun 30 is provided in the larger cylindrical portion 4 and may be disposed on the longitudinal axis of the tube 2. The flood gun 30 comprises a cathode 32 and an intensity electrode 34 which encloses the cathode 32 except for its small aperture 36 disposed over the centrail portion of the cathode 32. An annular electrode 38 is disposed adjacent the intensity electrode 34 and coaxially with respect to the longitudinal axis of the tube 2 which also passes through the center of the aperture 36 in the intensity electrode 38.

The neck portion 6 of the tube 2 houses a rst electron gun 40 which may be of conventional construction, for providing an electron beam of elemental cross-sectional area. The gun 40 comprises a cathode 42 and includes an intensity electrode grid (not shown) and -a cylindrical lbeam forming section 46. Horizontal deecting plates 48 and vertical deiiecting plates 48 for controlling the deflection of the electron beam generated by the electron `gun are also provided. Also shown as housed in the neck portion 6 of the tut e 2 is a second electron gun Str of conventional construction for providing a second electron beam of elemental cross-sectional area. The gun 50 comprises a cathode 52 and Iincludes an intensity electrode grid (not shown) tand a cylindrical beam forming section 66. Horizontal and vertical deiiecting plates 58 and 58' respectively, are likewise provided. While electrostatic deflection means are shown, the electron beams from the two guns may be magnetically focused and deiiected, in which cases separate neck portions may be desirable. Hereinafter the rst electron gun 40 will be referred to as to storage gun while the second electron gun 50 will be referred to as the live gun, and it will lbe understood that the second gun is switched to provide live presentations and selective erasure on a timesharing basis las described in the aforementioned patent to Lehrer.

An equipotential region is maintained throughout the neck portion 6 and the large cylindrical section 4 of the tube 2 by means of a conductive layer 44 which may be coated over the interior surfaces of the tube as shown.

The electron beams produced by the two electron guns 40 and 50 are caused to scan the storage target 14 and/ or viewing screen by means of horizontal and vertical deflection voltages generated by the horizontal and vertical deflection generators 60, 62 and 64, and 66 respectively.

The storage target characteristic is such that with a beam energy of about 1.0 kv., positive charging (which means charging the potential of the storage surface) is at a maximum and is almost entirely due to the secondary electron emission phenomena, any charging due to bombardment induced conductivity being negligible and rather completely over-ridden by the secondary electron emission effect. Thus with a primary beam energy of from l-4.5 kv. negative the storage target is charged positively by the secondary emission phenomenon.

At about 4.5 kv. secondary emission still occurs but bombardment induced conductivity effects will have increased to the point where both phenomena charge the storage surface in equal but Opposite electrical senses, hence the storage surface potential will be relatively undisturbed when the storage target is bombarded by a beam of about 4.5 kv. With beam energies greater than about 4.5 kv. the bombardment induced conductivity effect increases further and rather completely overrides the secondary emission effect which continues to diminish. The net charging effect on the storage surface hence is to drive it `negatively toward the equilibrium potential, by the bombardment induced conductivity effect.

It will thus be appreciated that the storage target utilizes two phenomena to produce charging effects in opposite electrical senses which effects may be balanced so as t0 result in no net charging effect in either electrical sense. This is possible because there is a continuous range of electron beam energy level where both the secondary electron emission and bombardment induced conductivity occur and because at different portions of this range either of these phenomena can be made dominant or the tube phenomena can be balanced. The capability of balancing these two phenomena permits one to write-through the storage target so as to present direct or live information without altering the potentials on the storage target.

In operation, the potential of the storage dielectric is initially made negative with respect to the cathode 32 of the ood gun 3G. Under these circumstances flood electrons from the gun 30 will be prevented from penetrating the storage target 2. Hence the flood or Viewing electrons cannot reach the viewing screen and excite it into luminescence.

To store and display information, the storage target 14 is scanned by an electron beam with elemental crosssectional areas having an energy level relative to the storage surface of about 2.5 kv. or less. As indicated previously, this beam may be generated by means of the electron gun 40. The scanning of the storage target with such an electron beam results in the storage target becoming charged positively by the phenomenon of secondary emission. lt will be understood that the electron `beam produced by the gun 40 is modulated and scanned in accordance with information representative signals derived and applied by conventional techniques and the beam is deected horizontally and vertically by means of

deection plates

48 and 48. The secondary electrons emitted from the storage target 14 and areas thereof impinged by the beam from the electron gun 40 are collected by the collector grid 16. Viewing or flood electrons from the ilood gun 30 may then pass through the storage target 14 at these areas of positive potential and are then accelerated until they impinge upon the phosphor layer 10 of the viewing screen. In this manner the information is displayed and may be maintained and viewed as long as desired.

Non-stored or live information may also be simultaneously displayed by scanning the viewing screen 1i) with an electron beam of the electron gun SG. As explained previously, in order to write or display such live information, a beam having an energy level of about 4.5 kv. negative is required. The live gun may be caused to selectively erase stored potentials on the storage target 2 by operating the gun at its normal energy level of 6.0 kv. The impingement of a beam of this energy level on portions of the storage target results in these portions being charged negatively with respect to the flood gun cathode 32 whereby flood electrons are prevented from penetrating the storage target at these portions.

The :foregoing detailed description of a direct-viewing storage tube and its operation has been set forth herein in order that it may be fully appreciated how undesirable electrical fields and the like can adversely effect the operation of such complex 'electron tubes. A more complete detailed description of the operation of such storage tubes may be found in the aforementioned patent to Lehrer.

Since the flood electrons are formed into a broad beam having a cross-sectional area actually greater than that needed to blanket the entire storage target 14 as shown in FIGURE l, it wil-l be appreciated that peripheral portions of the flood beam may easily pass around the periphery of the storage target. In some instances the impingement of these peripheral flood electrons on the periphery of the viewing screen results in an undesirable bright ring of light around the display. More seriously, however, these flood electrons have tended to charge the glass portions of the tube envelope adjacent the storage and viewing target structures causing high fields which distort the uniformity of the visual display, and in some instances causing arcing which damages the electrode structures. In order to prevent electrons, principally those from the flood gun but also from the writing gun, a shield 70 is provided, according to the invention, between the target structures and the glass wall of the tube envelope so as to intercept these electrons.

The shield member 70 comprises a flexible strip of metal which may be formed into the shape of a trough of slightly larger diameter than the space between the tube wall and the adjacent target structure so as to ensure snug contact therebetween. Since the target structure may not always be of symmetrical shape (i.e., circular) it is necessary that the shield member be capable of adapting to a range of lspacings and/or odd shapes between the tube wall and the target structure. Furthermore, the shield member of the invention should not be restricted for use in applications requiring precise mechanical spacings and tolerances between target elements and envelopes. It will be appreciated that in -order to properly solve the problem of providing such a shield member flexibility in more than one plane is necessary. Thus, the formation of flexib-le material in the shape of a trough or rain gutter or the like results in its opposed sides being resilient and such a trough can be inserted and compressed between two parallel parts so as to obtain snug contact therewith. However, such a trough, though made of flexible material, exhibits little or no flexibility in directions transverse to its length. Hence, in attempting to use such a flexible member between parts which are curved or angular, either the trough becomes distorted and exhibits gaps in contact with the parts or it cannot follow the required path.

These problems are solved by the shield of the present invention by providing a flexible strip 70 with slits 72 therein transverse to the length thereof as shown in FIG- URE 2. In bending such a strip in a curved or angular fashion along its length, the slits will tend t-o open up and exhibit gaps, which would permit electrons to penetrate therethrough when using such a shield in an electron tube. To avoid this result, the strip member 70 is folded completely on itself and the slits 72 are disposed so as to be at other than 4right angles with respect to the fold line. Thus, as will be seen from FIGURE 3, upon folding the strip on itself the slits are prevented from being aligned and are in fact covered by the opposed solid (unslitted) portions of the strip. It will be understood that as used herein and in the appended claims the term slit is intended to refer to a linear opening in a plane surface of metal which opening terminates within the metal surface and does not extend to an edge thereof.

After the flexible strip has been folded on itself as in FIGURE 3, it may then be given any predetermined shape along its length such as a trough as shown in FIG- URES 4 and 5 with one side of the trough being made relatively flat or straight to facilitate the welding or the like of the shield member to a target structure which may be the cylindrical collimating member or can 13 as shown in detail in FIGURES 6 and 7.

In a typical embodiment the flexible electron shield member Iof the invention was fabricated from a strip of stainless steel about 1.312 in width and about 0.003 thick. The slits are `disposed at an angle of about 6 off normal with respect to the center fold line and are about 0.187" apart and extend to about 0.250 from the edge of the strip. With these dimensions `and angular relationships, folding of the strip .lengthwise upon itself results in covering the slits by the solid portions of the strip on the opposing surface.

There thus has been described and shown a novel, flexible shield member for electron tubes, especially of the direct-viewing storage tube, which is impervious t0 penetration of electrons and is particularly useful for preventing flood lelectrons from penetrating a space between a target structure and a glass envelope of a directviewing storage tube.

What is claimed is:

1. A flexible element comprising a strip of flexible material folded upon itself along its length on a fold line and having parallel slits therein transverse to said fold line at an angle of less than with respect thereto.

2. An electron impervious flexible shield member for electron tubes comprising a strip of flexible metal folded upon itself along its length on a fold line and having parallel slit-s therein transverse to said fold line at an angle of less than 90 with respect thereto.

3. In combination, a direct-viewing storage tube of the type having an envelope with a target member therein adapted to be disposed in the path of a flood beam of electrons, an electron impervious flexible shield member disposed between said envelope and said target member and comprising a strip of flexible metal folded along its length on a fold line having parallel slits therein transverse to said fold line at an angle of less than 90 with respect thereto.

4. In combination, a direct-viewing storage tube of the type having an envelope with a target member therein adapted to be disposed in the path of a flood beam of electrons, a troughashaped electron impervious flexible shield member disposed between said envelope and said target member and comprising a strip of flexible metal folded along its length on a fold line and having parallel slits therein transverse to said fold line at an angle of less than 90 with respect thereto.

5. In combination, a direct-viewing storage tube of the type having an envelope with a target member therein adapted to be disposed in the path of a flood beam of electrons, an electron impervious flexible shield member disposed between said envelope and said target member 'and comprising a strip -of flexible metal at least partially doubled upon itself so as to form said strip in the shape of a trough extending along its length, the opposed side portions of said trough-shaped strip being in contact, respectively, with said envelope on said target member, said trough-shaped shield member comprising a strip of flexible metal folded along its length on a fold line and having parallel slits therein transverse to said fold line at an angle of less than 90 with respect thereto.

6. In combination, a directaviewing storage tube of the type having a glass envelope with a st-orage target member therein adapted to be disposed in the path of a flood beam of electrons, an electron impervious flexible shield member disposed between said envelope and said target member and comprising a strip of flexible metal at lleast partially doubled upon itself so as to form said strip in the shape of a trough extending along its length, the opposed side portions of said trough-shaped strip being in contact, respectively, with said envelope on said target member, said trough-shaped shield member comprising a strip of flexible metal folded along its length on a fold line and having parallel slits therein transverse to said fold line at an angle of less than 90 with respect thereto.

References Cited by the Examiner UNITED STATES PATENTS Samuel 313-278 Paehr 313-313 X Bareiss 313-40 Norton 72-324 Van Rijessel et al. 315-11 X Hack 29-501 Whyman 313-68 Kiasek 29-155.55

10 JOHN W. HUCKERT, Primary Examinez'.

A. I. JAMES, Assistant Examiner.

Claims

4. IN COMBINATION, A DIRECT-VIEWING STORAGE TUBE OF THE TYPE HAVING AN ENVELOPE WITH A TARGET MEMBER THEREIN ADAPTED TO BE DISPOSED IN THE PATH OF A FLOOD BEAM OF ELECTRONS, A TROUGH-SHAPED ELECTRON IMPERVIOUS FLEXIBLE SHIELD MEMBER DISPOSED BETWEEN SAID ENVELOPE AND SAID TARGET MEMBER AND COMPRISING A STRIP OF FLEXIBLE METAL