Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-06-21
2003-08-12
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S404000, C313S407000
Reexamination Certificate
active
06605890
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube, and in particular to a color cathode ray tube having a so-called slot type shadow mask.
A color cathode ray tube used for a TV receiver, or a monitor for a personal computer or other information equipment is formed of a vacuum envelope comprising a face panel having a mosaic phosphor screen coated with plural-color phosphors (usually red, green and blue), a neck housing an electron gun and a funnel for connecting the neck to the face panel.
A deflection yoke is mounted around the outside of the transition region between the funnel and the neck, and intensity-modulated electron beams emitted from the electron gun are scanned horizontally and vertically on the phosphor screen by horizontal and vertical deflection magnetic fields generated by the deflection yoke to reproduce an image.
A shadow mask is closely spaced from the phosphor screen, and serves as a so-called color selection electrode for making each of a plurality of electron beams (usually three beams for red, green and blue, respectively) emitted from the electron gun impinge on only phosphor elements of a corresponding color.
Various types of shadow masks are known, and among them is a slot type shadow mask having a plurality of strips (long narrow pieces) extending in a direction perpendicular to a horizontal scanning direction of the electron beams emitted from the electron gun and a plurality of bridge portions for connecting two adjacent strips such that each of rectangular electron beam apertures (which are called “slots”) is defined by two adjacent strips and two adjacent bridge portions. This slot type shadow mask is tensed along the direction perpendicular to the horizontal scanning direction of the electron beams, for example, and it is known that it vibrates when an external shock is applied to it. If the shadow mask vibrates, the position of the electron beams passing through a slot is deviated, and thereby landing positions of the electron beams are deviated from their intended phosphor elements and the reproduced image also vibrates resulting in deterioration of image quality. Further, there is a case in which this vibration damages the shadow mask itself and therefore it is impossible to reproduce a normal image.
To prevent such vibration of the shadow mask, there is a technique to superpose a vibration-preventing wire on a slit extending in the direction perpendicular to the horizontal scanning direction of the electron beams (the vertical direction) and thereby to absorb the vibration, as disclosed in Japanese Patent Application Laid-open No. Hei 8-227,667.
FIG. 14
is a schematic perspective view of a prior art slot type shadow mask provided with a vibration-preventing structure. A shadow mask
8
is depicted as a constituent component of a shadow mask structure
7
stretched over mask frames
9
a
,
9
b.
The pair of mask frames
9
a
,
9
b
are fixed to support frames
10
a
,
10
b
to form a peripheral frame, and the shadow mask
8
is stretched over the mask frames
9
a
,
9
b
. In the shadow mask
8
, a large number of slot type electron beam apertures
20
are defined by a plurality of strips
21
extending in a direction (the Y-axis direction) perpendicular to a horizontal scanning direction (the X-axis direction) of the electron beams emitted from the electron gun and a plurality of bridge portions
22
for connecting two adjacent strips
21
to form an apertured area.
Vibration-preventing wires
12
are superposed on the respective strips
21
in a direction in which the strips
21
extend, and are fixed to the wire supports
11
a
attached to the mask frames
9
a
,
9
b
. The wire supports
11
a
are made of resilient material and apply a desired tension to the vibration-preventing wires
12
.
On the other hand, Japanese Patent Application Laid-open No. Hei 5-198,271 discloses a color cathode ray tube in which a shadow mask comprised of strips only without no bridges (i.e., a shadow mask formed of a parallel array of narrow strips held together only at the ends) and a vibration-preventing wire is stretched over a surface of the shadow mask in the horizontal scanning direction and is pressed against the surface of the shadow mask to attenuate the vibration as much as possible. Incidentally, a plurality of vibration-preventing wires of this type are usually disposed in the horizontal scanning direction of the electron beams.
SUMMARY OF THE INVENTION
In the prior art shadow mask, it is difficult to make the vibration-preventing wire contact the surface of the shadow mask securely, and it is also inevitable for the vibration-preventing wire to be disposed to traverse the electron beam apertures.
Therefore, there have been pointed out problems that vibration of the shadow mask caused by external shock do not attenuate in a short period of time, or a horizontal black line appears in a reproduced image due to shadow in a phosphor screen caused by collision with the vibration-preventing wire, of the electron beams which are intended to pass through the electron beam apertures, resulting in deterioration of image quality.
It is an object of the invention to provide a color cathode ray tube having vibration of the shadow mask prevented without incurring deterioration in the image quality by eliminating the above problems with the prior art.
To achieve the above objects, in a shadow mask of the present invention, holes for positioning a vibration-preventing wire are opened at positions corresponding to ends of the strips, outside an apertured area of the shadow mask, and the vibration-preventing wire is passed through the holes and stretched.
The representative configurations of the present invention are as follows:
In accordance with the present invention, there is provided a color cathode ray tube comprising a vacuum envelope including a panel, a neck and a funnel for connecting the panel and the neck, an electron gun housed in the neck, a phosphor screen coated on an inner surface of the panel, and a shadow mask closely spaced from the phosphor screen and housed in the panel, the shadow mask having a plurality of strips extending in a direction perpendicular to a horizontal scanning direction of electron beams emitted from the electron gun and a plurality of bridge portions connecting adjacent ones among the plurality of strips, the shadow mask being formed with an apertured area having a plurality of slot-shaped electron beam apertures therein, each of the plurality of slot-shaped electron beam apertures being defined by two adjacent ones among the plurality of strips and two adjacent ones in the direction perpendicular to the horizontal scanning direction among the plurality of bridge portions, the shadow mask being provided with at least one wire held under tension in the extending direction of the plurality of strips so as to be superposed on a surface of one of the plurality of strips in the apertured area, and the surface of the one of the plurality of strips being a surface of the one of the plurality of strips facing the electron gun.
In accordance with the present invention, there is provided a color cathode ray tube comprising a vacuum envelope including a panel, a neck and a funnel for connecting the panel and the neck, an electron gun housed in the neck, a phosphor screen coating on an inner surface of the panel, and a shadow mask closely spaced from the phosphor screen and housed in the panel, the shadow mask having a plurality of strips extending in a direction perpendicular to a horizontal scanning direction of electron beams emitted from the electron gun and a plurality of bridge portions connecting adjacent ones among the plurality of strips, the shadow mask being formed with an apertured area having a plurality of slot-shaped electron beam apertures therein, each of the plurality of slot-shaped electron beam apertures being defined by two adjacent ones among the plurality of strips and two adjacent ones in the direction perpendicular to the horizontal scanning direction among the plurality of br
Kawasaki Hiroshi
Nakamura Takao
Tanabe Hideo
Watanabe Mitsuru
Hitachi , Ltd.
Patel Ashok
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