Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
1998-10-28
2001-05-29
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S414000, C313S451000
Reexamination Certificate
active
06239546
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a color cathode-ray tube, and more particularly to a configuration of electrodes forming a main lens of an electron gun.
BACKGROUND OF THE INVENTION
Generally, a color cathode-ray tube apparatus has an envelope comprised of a panel and a funnel joined to the panel to form one component. Three electron beams emitted from an electron gun arranged inside a neck of the funnel are deflected by horizontal and vertical deflection magnetic fields generated by a deflector mounted outside the funnel. While scanning horizontally and vertically, the three electron beams strike a phosphor screen formed on the inner face of the panel so as to oppose a shadow mask. Thus, the color cathode-ray tube apparatus displays color images.
In such a color cathode-ray tube apparatus, in order to display images with high resolution on the phosphor screen, it is necessary to make a spot diameter on the phosphor screen as small as possible by reducing the effect of spherical aberration through enlarging the effective lens aperture of a main lens in the electron gun.
A main lens of an electron gun used for a conventional color cathode-ray tube is described, for example, in Unexamined Japanese Patent Application No. Tokkai Hei 3-152834 and Unexamined Japanese Patent Application No. Tokkai Hei 4-133247. As shown in
FIG. 14
, the main lens is comprised of a focusing electrode
13
with an end face (a bottom
13
c
) and a final accelerating electrode
14
with an end face (a bottom
14
c
) adjacent to the focusing electrode
13
. The end face of the focusing electrode
13
and that of the final accelerating electrode
14
oppose each other. Each end face has an oblong electron-beam through-hole having its major axis in the horizontal direction. The main lens contains field forming electrode plates
13
a
and
14
a
, each of which has three electron-beam through-holes at the position recessed from its end face.
The focusing electrode
13
is welded on a surface
74
contacting with an auxiliary focusing electrode
12
on a cathode side. The focusing electrode
13
is fixed to an insulating support
21
(made of weld glass bead) through bracket portions
75
formed on the upper and lower faces of the auxiliary focusing electrode
12
in the vertical direction or through buried portions
76
formed on the upper and lower faces of the focusing electrode
13
in the vertical direction. The final accelerating electrode
14
is fixed to the insulating support
21
through bracket portions
77
or buried portions
78
formed on its upper and lower faces in the vertical direction.
The focusing electrode
13
and the final accelerating electrode
14
are fixed to the insulating support
21
by heating the insulating support
21
to a high temperature to soften it and forcing the bracket portions
75
and
77
or the buried portions
76
and
78
into the insulating support
21
.
At that time, an opening
13
b
of the focusing electrode
13
is subject to a force. Therefore, while the length of the opening
13
b
decreases in the vertical direction, the length of an opening at the bottom
13
c
of the focusing electrode
13
increases in the vertical direction. In this case, the field forming electrode plate
13
a
functions as a supporting point. Consequently, the focusing power of the main lens in the vertical direction decreases while that in the horizontal direction increases. Thus, an electron beam spot that should be focussed on a phosphor screen optimally (in a just-focusing condition) is in an over-focusing condition in the horizontal direction and in an under-focusing condition in the vertical direction. As a result, there has been a problem that the spot of an electron beam on the screen increases in diameter or is distorted.
The difference between the focus condition in the horizontal direction and that in the vertical direction varies depending on how a force is applied in forcing the focusing electrode
13
into the insulating support
21
, thus causing variations in every cathode-ray tube.
The same problem may also occur in fixing the final accelerating electrode
14
to the insulating support
21
.
SUMMARY OF THE INVENTION
The present invention aims to solve such problems. In the present invention, when fixing a focusing electrode and a final accelerating electrode to an insulating support, a force to which bracket portions or buried portions of the focusing electrode and the final accelerating electrode are subjected is reduced, thus preventing the deformation of the focusing electrode and the final accelerating electrode.
In order to attain the above-mentioned object, the present invention employs the following configuration.
A color cathode-ray tube of the present invention comprises an electron gun having a main lens. The main lens comprises a focusing electrode and a final accelerating electrode, each of which has an opening portion on one end and a bottom having an electron-beam through-hole on the other end. The focussing electrode and the final accelerating electrode are arranged with their bottoms opposing each other at a predetermined distance. At least one of the focussing electrode and the final accelerating electrode has an field forming electrode plate and a reinforcing electrode plate. The field forming electrode plate is provided inside the electrode at a position recessed from its bottom. The reinforcing electrode plate has at least one opening through which an electron beam passes and is connected to the opening portion side. The reinforcing electrode plate has a supporting portion and is fixed to an insulating support with the supporting portion projecting further outside than a peripheral surface of the opening portion.
Therefore, when fixing the focusing electrode and the final accelerating electrode to the insulating support, the reinforcing electrode plate absorbs the force to which the bracket portions or the buried portions are subjected, thus preventing the deformation of the focusing electrode and the final accelerating electrode.
In the configuration described above, the reinforcing electrode plate may have only one opening through which a center electron beam out of three electron beams passes. Additionally, both sides of the reinforcing electrode plate may be formed in a nearly circular-arc shape, and the each portion having the nearly circular-arc shape may partially surround the electron beam located at each side of the center electron beam respectively.
Further, in the configuration described above, the reinforcing electrode plate may have a hood adjacent at least one of the three electron beams. The hood projects forward or backward with respect to the traveling direction of the electron beam.
These structures enable a spot diameter on a phosphor screen to be adjusted by adjusting an electric field lens using a reinforcing electrode plate.
REFERENCES:
patent: 5142189 (1992-08-01), Sugahara et al.
patent: 5235241 (1993-08-01), Van Eck et al.
patent: 5656884 (1997-08-01), Lee
patent: 5661363 (1997-08-01), Iguchi et al.
patent: 5932958 (1999-08-01), Watanabe et al.
patent: 4-133247 (1992-05-01), None
Natsuhara Masao
Wada Yasufumi
Yamamoto Yasuyuki
Matsushita Electronics Corporation
Merchant & Gould P.C.
Patel Vip
Williams Joseph
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