US2466329A

US2466329A - Partitioned projection cathode-ray tube

Info

Publication number: US2466329A
Application number: US732410A
Authority: US
Inventors: Samson Kurt Arthur Richard; Mcconnell Eric Douglas; Mcmullan Dennis
Original assignee: Cinema Television Ltd
Current assignee: Cinema Television Ltd
Priority date: 1946-08-02
Filing date: 1947-03-05
Publication date: 1949-04-05
Anticipated expiration: 1966-04-05
Also published as: GB615285A

Description

April 1949' K. A. R. SAMSON ET AL 2,466,329

PARTITIONED PROJECTION CATHODE-RAY TUBE Filed March 5, 1947 FIG. 2. l5 K' I I30 INVEN TORS KURT ARTHUR RICHARD SAMSON ERIC DOUGLAS MC CONNELL DENNIS MC MULLAN ATTORNEY Patented Apr. 5, 1949 2,466,329 PARTITIONED PROJECTION CATHODE-RAY TUBE Kurt Arthur Richard Samson, Beckenham, Eric Douglas McConnell, West Wickham, and Dennis MclVIullan,

to Cinema-Television Wallingford, England, assignors Limited, London, England, a corporation of England Application March 5, 1947, Serial No. 732,410 In Great Britain August 2, 1946 18 Claims.

This invention relates to improvements in cathode ray tubes. More particularly it relates to improvements in cathode ray tubes of the type employed in television receiver projection systerms.

The main object of the invention is to provide a cathode ray tube of such construction that it is convenient to use within or forming part of the envelop of the tube optical elements formed of materials (such, for example, as a synthetic resin) which continually exude gases when the gas pressure in the vicinity thereof is reduced to a low value.

A further object of the invention is to provide a cathode ray tube of such construction that it is possible to use as a portion of the envelope of the tube a very thin glass wall which has a minimum deleterious effect on an optical image projected therethrough.

According to the invention there is provided a cathode ray tube of th kind employed for the projection of optical images, comprising an envelope containing a fluorescent screen and having a wall thereof through which the optical image is arranged to be projected to a viewing screen and wherein the space within the envelop is divided into two portions, on of which has for at least a part of its boundary the inner surface of the said wall and is maintained at a higher gas pressure than the other, which contains the electron gun for the tube.

Again according to the invention there is provided a cathode ray tube of the kind employed for the projection of optical images comprising an envelope containing a fluorescent screen and having a wall thereof, through which the optical image is projected to a viewing screen and wherein a space within the envelope bounded at least in part by the said wall is partitioned off from the space containing the electron gun, so that the former space can be maintained at a higher gas pressure than is necessary for efiicient working in the space containing the electron gun.

According to a feature of the invention, the envelope also contains a concave mirror for projecting the optical image.

According to a further feature of the invention, the wall through which the optical image is projected is formed so as to provide correction for distortion of the optical image.

According to a further feature of the invention, the wall is arranged to correct for spherical aberration and coma in the image.

According to a still further feature of the invention, th two portions of the space within the envelope are continuously evacuated.

The invention is particularly applicable tocathode ray tubes of the kind described in a pending British application, No. 18,284/46, where a shell in the form of a portion of a sphere is incorporated to form a wall of the tube envelope, this shell being used to correct at least in part for the spherical aberration and coma in the projected optical image.

The invention will be hereinafter more particularly described with reference to the accompanying drawing, comprising Figs. 1 and 2, which illustrate, purely by way of example, dilierent embodiments of the invention.

Referring now to Fig. 1, a cathode ray tube comprises a glass neck. 1 incorporating an electron gun 2, a cylindrical metal member 4, having secured thereto at one end a spherical metal cover 3 having an aperture to which issealed the neck I, and sealed at the other end to the edge of a transparent shell 5, which may have the form of a portion of a sphere, as described in the pending British application, No. 18,284/46, and is designed to correct at least in part-for the spherical aberration and coma in the optical image which is projected therethrough. The image is obtained from a fluorescent screen supported within the cylinder l, on a curved support 6, aligned with neck I, and is projected through the shell 5, by means of a concave spherical mirror 1, also positioned within the cylinder A, and provided with a central aperture aligned with the neck I. The mirror I and shell 5 have different radii of curvature but are concentric. A thin plane glass partition 8, divides the space within the envelope into two parts 9 and Ill, whichare both continuously evacuated by means of an exhausting system H, comprising diffusion and backing pumps. The space 9, is evacuated by the diffusion pumpand the backing pump, while the space lil is evacuated by the backing pump. The mirror 1 is formed of glass and consequently the space ii can be evacuated so that a hard vacuum is obtained. The shell 5 may be formed of a synthetic resin (for example, the plastic known under the trade name of Perspex) which continuously exudes gas when the pressure in part it is substantially reduced. This will bev immaterial as the vacuum in space it] need only be of the order which can be produced by the backing pump of exhausting system H and still will not interfer with the eificiency of the electron bombardment of the fluorescent screen in space 9.

The arrangement illustrated in Fig. 1 can be modified in any of the following ways without exceeding the spirit and scope of the invention.

(1) An aspherical correcting plate can be positioned between the partition 8 and the shell at the center of curvature of the latter and can be used to provide correction for spherical aberration and coma in addition to that provided by the shell 5.

(2) The partition 8, instead of being made of plane glass, can comprise an aspherical plate designed to correct for spherical aberration and coma. In this case the partition will be positioned coincident with the center of curvature of the shell.

(3) A thick, flat synthetic resin sheet can be substituted for the shell and the aspherical correcting plane positioned between this sheet and the partition as in modification (1) above.

(4) A thick, fiat synthetic resin sheet can be substituted for the shell 5, and the partition 8 can comprise the aspherical correcting plate as in modification (2) above.

Referring now to Fig. 2, the cathode ray tube comprises an inner envelope in the form of a glass neck l3 (housing the electron gun, 13a) and a very thin glass main body 14, and an outer envelope in the form of a metal cylinder It, having secured thereto a spherical metal cover !5, with a central aperture forming a gastight joint with the neck 13, and a spherical shell ll, similar to the shell 5 of Fig. 1. The inner and outer envelopes are separately evacuated by means of an exhausting system 18, comprising diffusion and backing pumps. The inner envelope is evacuated by the diffusion pump and the backing pump while the outer envelope is evacuated by the backing pump. The fluorescent screen is formed upon a convex metal support I9, which may be formed on a convex inner surface of the inner envelope or may be mounted within the inner envelope or may be suitably sealed to the glass to form part of the wall of the envelope. The support I9, may be water cooled by means of a water jacket 20. The pipe work extending to the water jacket 20 is not shown.

The optical image from the fluorescent screen is projected through the shell 11, by means of a concave spherical mirror 2!, which, unlike the mirror I of Fig. 1, can be formed of a synthetic resin, due to the fact that it is not located in the portion of the envelope housing the electron gun where a hard vacuum is essential. The mirror 2! and shell I! have difi'erent radii of curvature, but are positioned so as to have a common center of curvature. The shell I! will be formed of a transparent synthetic resin. As the body I l of the inner envelope can be formed of very thin glass owing to the low gas pressure in the outer envelope, the wall of this body will not distort the optical image to too great an extent. The exhausting system I 8 continuously evacuates both the inner and outer envelopes, the outer envelope, which includes the mirror 2| and shell n, both of which are formed of a material which exudes gases being, as hereinbefore mentioned, connected to the backing pump.

Additional correction for spherical aberration and coma can be introduced by positioning an aspherical correcting plate between the fluorescent screen and the shell 11, at the center of curvature of the shell. A thick, flat, synthetic resin sheet can be substituted for sheet 11, when an aspherlcal correcting plate is used. The construction shown in Fig. 2 has the advantage as compared with the construction shown in Fig. 1 that the space to be evacuated to the lower gas pressure can be considerably smaller and therefore the pumping apparatus can be simplified.

The vacuum in the space 9 of Fig. 1 or the inner envelope of Fig. 2 will be of the order of 10- mm. of mercury and the vacuum in the space H! of Fig. 1 or the outer envelope of Fig. 2 will be of the order of .1 mm. of mercury.

What is claimed is:

1. In a television projector, a first envelope enclosing a fluorescent screen and an electron gun for projecting a beam of electrons thereon, a second envelope surrounding the outside surface of a part of the wall of the first envelope, a transparent plastic window in said second envelope, means for creatin a partial vacuum inside the second envelope, means for intercepting and reflecting light from the fluorescent screen to project it through said window portion of the Wall of the second envelope.

2. In a television projector as in claim 1, in which the first and second envelopes have a common portion of their walls which is relatively thin and transparent, one side of this wall being on the inside of the first envelope and the other side thereof being on the inside of the second envelope, the wall being strong enough to withstand gas pressure against its side which is inside the second envelope equal to the pressure differential between a hard vacuum and a partial vacuum.

3. In a television which the first and projector as in claim 1, in second envelopes are sealed together and have a common portion of their Walls, the common portion being of sufi'icient strength to withstand atmospheric pressure on its outside when a hard vacuum has been produced within it, and the means for intercepting and reflecting comprises a perforated, curved mirror Within the second envelope disposed with its perforation around the first envelope and a concave surface facing through the first envelope the surface of the fluorescent screen upon which the electron beam is projected.

4. In a television projector as in claim 1, in which the first and second envelopes are sealed together and have a common portion of their walls, the common portion being of suflicient strength to withstand atmospheric pressure on its outside when a hard vacuum has been produced within it and the means for intercepting and reflecting comprises a perforated, concave mirror within the second envelope disposed with its perforation around the first envelope and its concave surface facing through the first envelope the surface of the fluorescent screen upon which the electron beam is projected, the fluorescent surface being convex toward the mirror and optic-ally coaxial therewith.

5. In a television projector as in claim 1, in which the first and second envelopes are sealed together and have a common portion of their walls, the common portion being of sufficient strength to withstand atmospheric pressure on its outside when a hard vacuum has been produced within it, and the means for intercepting and reflecting comprises a perforated, curved mirror within the second envelope disposed with its perforation around the first envelope with a concave surface facing through the first envelope the surface of thefluorescent screen upon which the electron beam is projected, the mirror comprising a plastic material.

6. In a television projector as in claim 1, in

5 which the first and second envelopes are sealed together and have a common portion of their walls; the common portion being of sufficient strength to withstand atmospheric pressure on its outside when a hardvacuum has been produced within it, the means for intercepting and reflectingcomprises a perforated, concave mirror within the second: envelope disposed'with its perforation around-the first envelope with a concave surface facing through the first envelope the surface of the fluorescent screen upon which the electron beam is projected, the fluorescent surface is convex toward the mirror and optically coaxial therewith, and the mirror comprises a plastic material.

'7. In a television projector as in claim 1, in which the first and second envelopes have a common portion of their walls which is relatively thin and transparent, one side of this wall being on the inside of the first envelope and the other side thereof being on the inside of the second envelope, the wall being strong enough to withstand a positive gas pressure against its side on the inside of the second envelope which is equal to the pressure differential between a hard vacuum and a partial vacuum, the means for intercepting and reflecting comprises a perforated, curved mirror facing the surface of the fluorescent screen upon which the electron beam is projected and reflecting light therefrom through the common wall as well as through the window portion of the wall of the second envelope, and the beam is projected onto the screen through the perforation in the mirror.

8. In a television projector as in claim 1, in which the first and second envelopes have a common portion of their walls which is relatively thin and transparent, one side of this wall being on the inside of the first envelope and the other side thereof being on the inside of the second envelope, the wall being strong enough to withstand a positive gas pressure against its side on the inside of the second envelope equal to the pressure differential between a hard vacuum and a partial vacuum, the means for intercepting and reflecting comprises a perforated, concave mirror facing the surface of the fluorescent screen with which the electron beam is projected and reflecting light therefrom through the common wall as well as through the window portion of the wall of the second envelope, the beam is projected onto the screen through the perforation in the mirror, and the fluorescent surface is convex toward the concave mirror and has a common optical axis therewith.

9. In a television projector as in claim 1, in which the window portion of the second envelope comprises an optical element for correcting spherical aberrations produced by the means for intercepting and reflecting.

10. In a television projector as in claim 1, in which the window portion is of substantially uniform thickness, its inner and outer surfaces are shaped as portions of the surfaces of concentric spheres, and it corrects, at least in part, for aberrations produced by the means for intercepting and reflecting.

11. In a television projector as in claim 1, in which the first and second envelopes have a common portion of their walls which is transparent, one side of this wall being on the inside of the first envelope and the other side thereof being on the inside of the second envelope, the wall being strong enough to withstand positive gas pressure against its side which is inside the second envelope equal to the pressure differential between a hard vacuum and a partial vacuum, the common wall comprising a correcting plate for at least partially correcting aberrations produced-by the means for interceptingand reflecting.

12. In a television projector, a first envelope whose walls include at least one transparent and relatively thin portion, a fluorescent screen in the first envelope, gun means in the first envelope for producing a beam of electrons and projecting it into the screen, means for scanning the Screen with the beam, a second envelope surrounding the outside surface of a thin portion of the wall of the first envelope, the second envelope having relatively thick walls comprising a window portion of a transparent plastic material, means for pumping gas from the space inside the second envelope to the space outside of it to form a partial vacuum, means for intercepting and reflecting light from the screen to controllably project it through a window portion of the wall of the second envelope.

13. In a television projector as in claim 12, in which the window portion comprises a correcting plate for correcting at least in part aberrations produced by the means for intercepting and refleeting.

14. In a television projector as in claim 12, in

which the window portion is formed to correct, at least in part, aberrations produced by the means for intercepting and reflecting.

15. In a television projector as in claim 12, in which the first and second envelopes are sealed together and have a common portion of their walls 35 which is strong enough to withstand atmospheric pressure on its outside when there is a hard vacuum inside of it, the means for intercepting and reflecting comprises a perforated, spherical mirror which is disposed With its perforation 40 around the first envelope and is concave toward the fluorescent screen, the screen and the mirror are separated by the first envelope, the fluorescent screen is convex toward and optically coaxial with the mirror, and the fluorescent screen is supported on a metal support comprising part of the first envelope.

16. In a television projector as in claim 12, in which the first and second envelopes are sealed together and have a common portion of their walls which is strong enough to withstand atmospheric pressure on its outside when there is a hard vacuum inside of it, the means for intercepting and reflecting comprises a perforated spherical mirror which is disposed with its perforation around the first envelope and is concave toward the fluorescent screen, the screen and the mirror are separated by the first envelope, the fluorescent screen is convex toward and optically coaxial with the mirror, the fluorescent screen is supported on a metal support comprising part of the first envelope, and cooling means are included which are adjacent to the outside surface of the metal screen support for cooling the fluorescent screen.

17. In a television projector as in claim 1, and

' means for producing a hard vacuum in the first envelope.

18. In a television projector as in claim 12, in which the envelopes are made of metal except for the plastic window in the second envelope.

KURT ARTHUR RICHARD SAMSON. ERIC DOUGLAS MCCONNELL. DENNIS MCMULLAN.

(References on following page) Name Date Bowie Feb. 6, 1940 Bedford Aug. 18, 1942 Epstein Sept. 15, 1942 FOREIGN PATENTS Country Date Great Britain June 16, 1938 Great Britain Dec. 3, 1943