Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1998-08-25
2001-02-27
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S261000, C313S417000, C313S240000, C313S456000
Reexamination Certificate
active
06194822
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to multi-electron beam, multi-grid electron guns for use in color cathode ray tubes (CRTs) and is particularly directed to apparatus for properly aligning electron gun grids having eccentric beam passing apertures during electron gun assembly.
BACKGROUND OF THE INVENTION
Color CRTs as used in television receivers and computer terminals employ multiple electron beams for providing a video image comprised of the primary colors of red, green and blue on a display screen. Typically, three electron beams are directed onto and scan the display screen in a raster-like manner. A common color CRT design has the three electron beams arranged in an inline array. An electron gun in the color CRT typically employs plural cathodes for generating energetic electrons in combination with apertured, charged grids aligned along the electron gun's longitudinal axis. Each of the charged grids typically includes three inline beam passing apertures for forming the energetic electrons into three separate beams and for focussing the beams on the CRT's display screen.
In order to provide a high quality color video image on the CRT's display screen, each of the gun's charged grids must be in precise position and alignment along the electron gun's longitudinal axis. An alignment jig incorporating three spaced mandrels is typically used for positioning and aligning the grids during electron gun assembly. Where the three inline electron beam passing apertures are circular, cylindrically shaped mandrels are employed for engaging those portions of the grid defining the three inline apertures therein. The cylindrically shaped mandrels provide the requisite alignment precision of the grids necessary for electron gun assembly.
However, in some cases non-circular beam passing apertures are provided in the electron gun grid for improved video image quality. For example, the two outer electron beam passing apertures may be provided with an asymmetric, e.g., eccentric, shape to compensate for the asymmetric electrostatic field applied to the two outer electron beams. This asymmetric electrostatic field arises from the inline alignment of the three electron beams and the shape of the common lens portions of grids in the electron gun's main focus lens. The use of a cylindrical mandrel inserted in an asymmetric beam passing aperture typically gives rise to rotation of the grid during electron gun assembly. Rotation of the grid misaligns the grid's electron beam passing apertures resulting in a degradation of video image quality presented on the CRT's display screen.
The present invention addresses the aforementioned limitations of the prior art by providing for the precise alignment of grids having asymmetric beam passing apertures during electron gun assembly. The present invention also provides apparatus for the stable and secure positioning of electron gun grids during electron gun assembly.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to facilitate the accurate positioning and alignment of asymmetric apertured grids in a multi-grid electron gun.
It is another object of the present invention to provide apparatus for preventing rotation of a grid having eccentric electron beam passing apertures during assembly in a multi-beam electron gun as used in a color CRT.
Yet another object of the present invention is to provide a support mechanism for securely maintaining an electron gun grid in fixed position during electron gun assembly.
This invention contemplates an alignment jig for aligning a grid during assembly of an electron gun, wherein the grid includes three inline electron beam passing apertures including a center circular aperture and two outer asymmetric apertures, the alignment jig comprising a first support member; three generally cylindrical mandrels attached to and arranged in a spaced, parallel, inline array on the support member, wherein each of the mandrels is adapted for insertion in a respective aperture of the grid for supporting the grid during electron gun assembly; a first keying member disposed on the grid; and a second support member adapted to receive the grid, the second support member including a second keying member adapted for complementary engagement with said first keying member for maintaining the three apertures of the grid in precise alignment with the three mandrels.
This invention further contemplates an arrangement for engaging and maintaining a grid in fixed position during assembly in an electron gun, wherein the grid is generally rectangular in cross section having first and second opposed lateral walls, the arrangement comprising first and second grooves respectively disposed in respective outer portions of the first and second lateral walls of the grid; a support frame; and first and second engaging mechanisms attached to the support frame, wherein the first and second engaging mechanisms are inwardly biased by an inwardly directed force and are adapted for insertion in the first and second grooves, respectively, for maintaining the grid in fixed position during electron gun assembly, and wherein the grid may be released and removed from the engaging mechanisms by overcoming the inwardly directed force.
REFERENCES:
patent: 2721374 (1955-10-01), Pilas
patent: 4976643 (1990-12-01), Lee
patent: 5430350 (1995-07-01), Chen et al.
Chang Shung-Lin
Lee Hsiang-Sung
Wang Chi-Tsan
Yeh Chun-Hsien
Chunghwa Picture Tubes Ltd.
Emrich & -Dithmar
Patel Ashok
Williams Joseph
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