Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
1997-11-03
2003-05-27
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S408000
Reexamination Certificate
active
06570310
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shadow-mask type color-generating cathode-ray tube (color CRT) and more particularly, to a shadow-mask type color CRT equipped with a slot type shadow mask, which reduces the moire phenomenon without deteriorating its vertical resolution.
2. Description of the Prior Art
As shown in
FIG. 1
, a shadow mask
18
of a conventional shadow-mask type color CRT has a number of slots
17
allowing selectively electron beams emitted from three electron guns to arrive at a phosphor screen through the mask
18
. The three electron beams for red (R), green (G) and blue (B) colors are deflected by horizontal and vertical deflecting magnetic fields generated by a deflection yoke in the horizontal and vertical directions X and Y of a face panel.
The three electron beams are horizontally scanned over the entire phosphor screen. On the other hand, the beams passing through the slots
17
in the shadow mask
18
strike the corresponding phosphor stripes arranged in the entire phosphor screen and excite them. Thus, a wanted color image is displayed on the face panel.
The slots
17
, all of which have the same roughly rectangular shape, are regularly arranged to form a mosaic in the horizontal and vertical directions X and Y of the face panel. In other words, the slots
17
are arranged in a staggered pattern. Between any vertically adjacent slots
17
, a bridge area
19
is formed to maintain the mechanical strength of the shadow mask
18
.
Specifically, a given number of the slots
17
are arranged at a fixed vertical pitch Pv in the vertical direction Y, forming a slot column
17
a.
Another given number of the slots
17
are arranged at the same fixed vertical pitch P
V
in the vertical direction Y, forming another slot column
17
b.
A plurality of the slot columns
17
a
and a plurality of the slot columns
17
b
are alternately arranged in parallel in the horizontal direction Y. The columns
17
a
and
17
b
are arranged at a fixed horizontal pitch P
H
.
The slot
17
in any one of the slot columns
17
b
is shifted in the vertical direction Y with respect to a corresponding one of the slots
17
in an adjacent one of the columns
17
a
by a half of the vertical pitch P
V
, i.e., (½)P
V
. In other words, the slots
17
are arranged so that, in any adjacent slot columns
17
a
and
17
b,
the horizontal center line of the bridge area
19
equally divides the opposed slot
17
into two in the vertical direction Y.
The fixed vertical pitch Pv is typically set at a value from 0.6 mm to 1.0 mm.
Each of the bridge areas
19
provides an electron-beam stopping area, which tends to create a shade on the phosphor screen, resulting in reduction in brightness. Also, the smaller the spot diameter of the electron beams, the larger the contrast on the phosphor screen, which makes the moire phenomenon remarkable.
To solve this problem, conventionally, the vertical pitch P
V
is varied to minimize the visibility of the moire within the shadow mask
18
.
However, with the conventional shadow-mask type color CRT as stated above, when this CRT with the vertical pitch P
V
of 0.6 to 1.0 mm is used as a visual display terminal (VDT) in such an application as a computer display terminal, the shades produced by the bridge areas
19
tend to prevent the phosphor stripes from fluorescing at a part of the character and/or figure to be displayed, because the CRT requires a high resolution. This results in that the character cannot be read and/or the background and/or figure looks rough and non-uniform, making reading of the character still more difficult.
These shades further cause another problem of resolution deterioration.
Additionally, another conventional color CRT was disclosed in the Japanese Non-Examined Patent Publication No. 2-103847 published in April 1990. In this CRT, the vertical width B
W
of the bridge areas is varied at random under the condition of &Dgr;≧B
W
, where &Dgr; is a shift for any adjacent slot columns.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a color CRT equipped with a slot-type shadow mask that enables to reduce the moire phenomenon without deteriorating its vertical resolution.
The object together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A shadow-mask type color CRT according to the present invention includes a shadow mask fixed apart from a face panel and opposed to a phosphor screen. The mask has slots allowing selectively electron beams to arrive at the phosphor screen through the mask. Each of the slots has an vertically elongated shape. The slots are arranged horizontally at a fixed horizontal pitch, and vertically at a fixed vertical pitch. At least two of the vertically adjacent ones of the slots have a bridge area therebetween. Each of the bridge areas serves as an electron-beam stopping area. In addition, at least of the two horizontally adjacent ones of the slots are vertically shifted at a fixed value equal to or greater than a half of the vertical pitch. The electron beams are scanned perpendicular to the slots. The vertical pitch of the slots is set at a value ranging from 0.2 mm to 0.5 mm.
With the color cathode-ray tube according to the present invention, the slots of the shadow mask, which have a vertically elongated shape, are arranged horizontally at a fixed horizontal pitch and vertically at a fixed vertical pitch. Also, horizontally adjacent slots are vertically shifted at a fixed value equal to or greater than a half of the vertical pitch. Further, the vertical pitch of the slots is set at a value ranging from 0.2 mm to 0.5 mm. As a result, the moire phenomenon can be reduced without deteriorating its vertical resolution.
In a preferred embodiment, each of the bridges has a fixed vertical length ranging from 0.02 mm to 0.08 mm. In this case, the moire phenomenon can be further reduced without deteriorating its vertical resolution.
In another preferred embodiment, the vertical pitch of the slots is set at a value ranging from 0.2 mm to 0.275 mm or from 0.2 mm to 0.28 mm corresponding to a raster (or screen) size of the tube. In this case, the moire phenomenon can be suitably reduced corresponding to the raster (or screen) size without deteriorating its vertical resolution.
REFERENCES:
patent: 4672260 (1987-06-01), Prazak, III
patent: 4859901 (1989-08-01), Thompson-Russell
patent: 5079477 (1992-01-01), Yamamoto
patent: 5162694 (1992-11-01), Capek et al.
patent: 5730887 (1998-03-01), Simpson et al.
patent: 2-103847 (1990-04-01), None
K. Naiki et al.,15-Inch Flat Face Vary High Resolution Color Display Tube, NEC Res. & Develop., No 90, Jul. 1988.*
H. Yoshida et al.,High Resolution Color Display Tubes for Display Terminals, Hitachi Review vol. 32, No 1, 1983 (No month).*
K. Hirabayash et al.,High Resolution Color Display TubeNational Technical Report vol. 25 No. 2, Apr. 1979.
Day Michael H.
NEC Corporation
Sughrue & Mion, PLLC
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