Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
1999-06-04
2001-07-10
Patel, Ashok (Department: 2875)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S412000, C313S414000, C313S428000, C313S439000
Reexamination Certificate
active
06259197
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a cathode ray tube comprising an in-line electron gun with means for generating electrons and a lens system including two facing lens electrodes having apertures for allowing passage of electrons.
Such cathode ray tubes are known and are employed, inter alia, for television receivers and computer monitors.
In such a cathode ray tube, three electron beams are generated in the in-line electron gun, which electron beams extend in one plane, the in-line plane. These electron beams are deflected across a display screen in two mutually perpendicular directions by means of a deflection means. A color selection electrode, for example a shadow mask, is situated between the electron gun and the display screen. The electron gun accommodates a lens system having two lens electrodes between which, in operation, an electron-optical lens is formed. Customarily, the electron gun comprises a main lens system by means of which the electron beams are focused on the display screen, and the electron gun further comprises a pre-focusing lens system which is situated between the main lens system and the means for generating electrons.
Of great importance for the quality of the picture display is the quality of the lens system or lens systems. Relatively small deviations in the electron-optical lenses formed in and by the lens systems may adversely affect the picture quality.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a cathode ray tube having a means for improving the picture quality.
To achieve this, a cathode ray tube in accordance with the invention is characterized in that inside the electron gun, an electrode part lies against at least one of the lens electrodes, said lens electrode and the electrode part contacting each other in only two regions, on either side of the in-line plane or on either side of a plane transverse to the in-line plane and through a central aperture.
The electron-optical lenses form, in operation, between the lens electrodes and, in particular, between the apertures in the lens electrodes.
The distance between and the orientation of the facing apertures of the lens electrodes also determine the electron-optical properties (such as the strength of a lens and the astigmatism of the lens) of the lenses. In the manufacture of the electron gun, a number of electrodes and electrode parts are stacked, spacers being positioned between electrodes. A problem which relates thereto and which has been recognized by the inventors is that, in known cathode ray tubes, a lens electrode may be pushed out of alignment by an engaging electrode or electrode part, thus causing the lens electrode to assume an oblique position relative to the second lens electrode facing said lens electrode. As a result, undesirable differences occur between the lenses for the outer electrodes and/or an astigmatic deviation in the lenses occurs.
In the cathode ray tube in accordance with the invention, the lens electrode and the electrode part contact each other in only two regions, on either side of the in-line plane or on either side of a plane transverse to the in-line plane and through a central aperture. The forces exerted by the engaging part on the lens electrode are symmetrical relative to planes of symmetry of the apertures of the lens. As a result, the risk that the lens electrode is pushed out of alignment by the electrode part in the course of the manufacturing process is reduced, so that the electron-optical properties of the lens improve. The invention also relates to a method of manufacturing an electron gun, in which electrodes are stacked and separated from each other by spacers, characterized in that at least one of the spacers comprises two regions projecting from the plane of the spacer, which regions are situated on either side of the in-line plane or on either side of a plane transverse to the in-line plane and through a central aperture.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 5300855 (1994-04-01), Kweon
patent: 5828191 (1998-10-01), Shirai et al.
patent: 5986394 (1999-11-01), Jeon et al.
patent: 0265683 (1990-11-01), None
Patel Ashok
U.S. Philips Corporation
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