Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Reexamination Certificate
1999-07-15
2001-09-04
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
C313S495000, C313S456000, C313S252000
Reexamination Certificate
active
06285121
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a flat-type image display apparatus used for a television receiver, a computer-terminal display unit, or the like.
BACKGROUND ART
Recently, the development for reducing the thickness of color image display apparatus has been carried out actively. Particularly, for example, Publication of Unexamined Japanese Patent Application (Tokkai-Hei) No. 3-67444 proposes a flat-type image display apparatus employing a beam scanning method in which the distance from a cathode to an anode is shortened significantly compared with a conventional cathode-ray tube (CRT) system. In the flat-type image display apparatus, a screen is divided into a plurality of sections vertically. An electron beam is deflected vertically to display a plurality of lines on each section. Further, the screen is also divided into a plurality of sections horizontally. In each section, phosphors of R, G, and B emit light sequentially. An amount of electron beams irradiated onto the phosphors of R, G, and B is controlled by the received color picture signals. Thus, a television picture is displayed as a whole.
In the above-mentioned flat-type image display apparatus, an electrode unit in which the distance from a cathode to an anode is shortened significantly and linear hot cathodes (hereafter referred to as “linear cathodes”) as electron beam sources are housed in a flat-box type vacuum case. Electrodes forming the electrode unit are provided with small holes or slits for deflecting, focusing, and controlling electron beams emitted from the linear cathodes. The electron beams go through the electrodes while being controlled by the holes or slits in each electrode and accelerated to the anode to cause light emission of phosphors applied to the anode, thus displaying images.
FIG. 7
is an exploded perspective view showing the internal structure of a flat-type image display apparatus. In the flat-type image display apparatus, a back electrode
1
, linear cathodes
2
(in the figure, only four linear cathodes are shown) extending horizontally, an electron beam extracting electrode
3
, a signal electrode
4
, focusing electrodes
5
and
6
, a horizontal deflection electrode
7
, and a vertical deflection electrode
8
are arranged sequentially. These sheet-like electrodes
3
-
8
are superposed via insulators and spacers, thus forming an electrode unit
11
. The electron beam extracting electrode
3
is provided with electron beam extracting holes
12
. Electron beams
13
emitted from the linear cathodes
2
are extracted through the holes
12
so as to form an apparent one electron beam per hole. An extracted electron beam
13
is controlled, focused, and deflected by the respective electrodes
4
-
8
to scan a subsection
14
on the anode screen.
The phosphors of R, G, and B are printed and applied onto screen sections, for example,
14
-
16
in the inner side of a front case
9
that is a flat-box type front glass case. Further, a metal-backed layer is formed on the sections
14
-
16
to apply high voltage. The electron beams are accelerated to have high energy and strike the metal-backed layer, thus exciting the phosphors so that the phosphors emit light. The electron beam
13
allows the subsection
14
of the screen to emit light to display a part of an image. Similarly, other electron beams cause light emission of all the other subsections, such as the subsection
16
, to display images. Thus, a desired image is displayed on the whole screen. A rear case
10
and the front case
9
are combined and sealed, and then a vacuum is drawn on its inside, thus forming a flat-type image display apparatus.
FIG. 8
is a perspective view showing the appearance of a sealed flat-type image display apparatus. The front case
9
and the rear case
10
are baked to be sealed with low melting point glass. Numeral
17
indicates an exhaust pipe for drawing the vacuum inside the case, numeral
18
a high-voltage terminal of the anode, and numeral
19
outgoing terminals for controlling various electrodes forming the electrode unit. By connecting a driving circuit, a signal processing circuit, or the like to these terminals externally, the flat-type image display apparatus functions as a television receiver or a display unit.
Internal components constructing the aforementioned flat-type image display apparatus are exposed to high temperature repeatedly in a sealing step in the assembly and fabrication process and during operation of the apparatus as an image display apparatus. In other words, in the assembly and fabrication process, the apparatus is exposed to a high temperature of about 500° C. both in fixing a plurality of fixing stands for attaching various electrodes to the glass rear case using low melting point glass and in combining and baking the front case and the rear case to seal the case using low melting point glass at a peripheral adhering portion of the case. Further, for example, a process of drawing high vacuum inside the glass case after sealing the glass case is carried out in a heating furnace at about 300-350° C. Thus, the apparatus is heated repeatedly. During the operation of the apparatus as an image display apparatus, a number of linear cathodes stretched in a plane are heated to a high temperature of 600-700° C. for generating electron beams. Due to such heat radiation, the various internal electrodes also are exposed to high temperature.
In order that a proper beam spot scans precisely the screen surface on which phosphors have been printed to avoid deviation of beam position on the screen so as to display vivid images with high precision even if the apparatus is exposed to high temperature in the aforementioned assembly and fabrication process and during the operation, the apparatus must have accuracy on a micron level and the accuracy must be maintained. However, generally objects exposed to high temperature repeatedly are subjected to thermal deformation such as expansion and contraction repeatedly due to the temperature change. Therefore, in order to allow the repeated exposure to high temperature and the maintaining of high accuracy to be compatible, problems of physically incompatible occurrences must be solved.
Particularly, while a flat-type image display apparatus has a flat shape, it is necessary to form the apparatus so as to have a glass-plate-like case body with a front case and a rear case, both of which are thick to have a thickness of about 10 mm, to obtain a resist pressure of the outside air by drawing high vacuum inside the case, thus causing extremely high thermal stress in the above-mentioned assembly process at high temperature.
The problems to be solved in a conventional example will be explained with reference to
FIGS. 9 and 10
as follows.
FIG. 9
is a plan view showing an example of the arrangement of electrode support plates and electrode fixing plates for fixing an electrode unit including various electrodes that is attached to the inner face of a rear case of a conventional flat-type image displaying apparatus. In addition,
FIG. 9
schematically shows a state in which thermal expansion and distortion occur in the above-mentioned heating processes.
FIG. 10
is a partial cross-sectional view showing a schematic structure of the flat-type image display apparatus shown in
FIG. 9
in which the electrode unit is attached by fixing the electrode support plates and the electrode fixing plates that are assembled in a parallel-crosses form to fixing stands.
In
FIG. 9
, arrows A, B, C, . . . , P show thermal stress lines seen in a plane, and an alternate long and short dash line shows a slightly exaggerated distortion condition in which a rear case
10
, electrode support plates
20
, and electrode fixing plates
21
have been expanded and deformed due to the thermal effect as a result of the thermal stress.
Fixing stands
22
for fixing the electrode support plates
20
and the like to the rear case
10
are displaced according to the expansion and contraction of the glass-plate like rear case
10
, which is not shown in the figure. The
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Patel Ashok
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