Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2000-02-04
2002-05-28
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S431000, C313S413000, C313S433000, C313S437000, C313S440000, C313S442000, C335S210000, C335S213000
Reexamination Certificate
active
06396206
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube such as a TV, a monitor, or the like, and particularly to a cathode ray tube apparatus which realizes a flat screen using a press-molded mask for selecting colors.
In general, a cathode ray tube apparatus comprises a vacuum envelope which includes a panel having a substantially rectangular display portion, a funnel connected continuously to the panel, and a cylindrical neck connected continuously to the small diameter end of the funnel. A deflection yoke is installed thereon from the end portion of the neck on the funnel side to the small diameter portion of the funnel.
A phosphor screen having a dotted or striped three-color phosphor layer which radiates in blue, green, and red is formed on the inner surface of the panel. Also, a shadow mask (for selecting color) having a surface which faces the phosphor screen and has a number of electron beam passage apertures formed at a predetermined layout pitch is arranged to face the phosphor screen. Further, an electron gun which emits three electron beams is provided inside the neck.
In the cathode ray tube apparatus described above, the electron beams emitted from the electron gun are deflected in the horizontal and vertical directions by horizontal and vertical magnetic fields generated by the deflection yoke, so the phosphor screen is scanned horizontally and vertically through the shadow mask thereby displaying a color image.
At present, as a color cathode ray tube apparatus of this kind, a color cathode ray tube of self-convergence inline type is used widely. This apparatus adopts an electron gun of inline type which emits three-electron beams consisting of a center beam and a pair of side beams which are arranged in line and run on the same horizontal plane. The horizontal deflection magnetic field generated by the deflection yoke is arranged in a pin-cushion shape while the vertical deflection magnetic field is arranged in a barrel shape, and the three electron beams arranged in line are deflected by these horizontal and vertical deflection magnetic fields. In this manner, the three electron beams can be converged over the entire screen without requiring any special correction means.
In recent years, there has been a strong demand for flatness of the screen in this kind of color cathode ray tube. In order to achieve this flatness, it is necessary to flatten the panel. However, if the panel is flattened, the shadow mask must also be flattened. As a result, the following problem arises.
In general, in a color cathode ray tube apparatus, three electron beams are converged on the center of a phosphor screen mainly by a purity convergence magnet attached to the deflection yoke in the neck side. The three electron beams pass through the electron beam passage apertures of the shadow mask at a predetermined angle and respectively land on predetermined phosphor layers. To optimize landing margins thereof in relation to the phosphor layers, it is necessary to set optimally the distance between the inner surface of the panel and the shadow mask.
Where q is the distance in the tube-axis direction between the shadow mask and the inner surface of the panel, &sgr; is the distance between the center beam
3
G and each of the pair of side beams
3
B and
3
R on the inner surface of the panel, and Ph is the pitch of the landing position of the center beam
3
G in the in-line direction of the three electron beams on the inner surface of the panel, &sgr; and Ph must be substantially constant over the entire surface of the phosphor screen in order to attain uniformness of the screen resolution. Consequently, if the panel is flattened, the shadow mask must also be flattened so that q is substantially constant, in order to make &sgr; and Ph substantially constant on the entire phosphor screen.
In general, however, the shadow mask is manufactured by shaping a shadow mask material, which has a flat thin-plate-like shape and electron beam passage apertures formed by photo-etching, into a predetermined curved surface. This shaping is carried out in a manner that the non-aperture portion of the mask material which surrounds a region where electron beam passage apertures are formed is clamped and fixed by a die and a Planck holder and the aperture-formed region is bulged by a punch and a knockout. Therefore, if the shadow mask is flattened and the amount of an extension caused by the bulging is reduced, sufficient plastic deformation cannot be obtained and the mask material therefore cannot be shaped into a predetermined curved surface. Also, the shaping strength of the shadow mask is deteriorated to cause deformation easily.
As a measure for solving this problem, between the phosphor screen and the cathode of the electron gun which emits three electron beams
3
B,
3
G, and
3
R arranged in line to the phosphor screen, there are provided two orbital correction means by which the force for correcting the pair of side beams
3
B and
3
R toward the center beam
3
G is changed between the center and the peripheral portion of the phosphor screen are provided. As a result of this, the virtual distance Sg between the center beam
3
G and each of the side beams
3
B and
3
R in the in-line direction of the three electron beams between the center and the peripheral portion of the phosphor screen varies such that the virtual distance Sgc
1
when the electron beams run toward the peripheral portion is smaller compared with the virtual distance Sgc
0
when the beams run toward the center of the screen.
These two orbital correction means are arranged such that generated forces Fr
0
and Ff
0
are set to zero with respect to three electron beams
3
B,
3
G, and
3
R running toward the center of the phosphor screen and the side beams
3
B and
3
R are over-converged by means of a force Fr
1
generated by the neck-side orbital correction means with respect to three electron beams
3
B,
3
G, and
3
R running toward the peripheral portion. Further, the side beams
3
B and
3
R are under-converged by means of a force Ff
1
generated by the panel-side orbital correction means.
As a result of this, the virtual distance Sg at the cathode decreases from Sgc
0
at the center of the phosphor screen to the Sgc
1
at the periphery thereof, so that the distance q between the inner surface of the panel and the shadow mask in the tube-axis direction at the peripheral portion of the phosphor screen can be increased by &Dgr;q=q−q
0
in relation to the distance q
0
between the inner surface of the panel and the shadow mask in the tube-axis direction at the center of the phosphor screen.
However, if there are provided orbital correction means for over/under-converging the pair of side beams
3
B and
3
R in correspondence with the position of the phosphor screen, as described above, a problem arises in that the convergence characteristic of the three electron beams
3
B,
3
G, and
3
R is deteriorated as the amount of the orbital correction increases.
SUMMARY
The present invention has been made in view of the above problem, and its object is to provide a color cathode ray tube apparatus which is capable of improving the convergence characteristic of three electron beams over the entire phosphor screen even if a flat panel is combined with a shadow mask shaped to have a curved surface which is hardly deteriorated in processability and shaping strength.
To achieve the above object, a color cathode ray tube apparatus according to the present invention comprises: a vacuum envelope including a substantially rectangular panel having first and second axes which pass through a tube axis and are perpendicular to each other, a funnel connected to the panel, and a neck connected to an end of a small diameter portion of the funnel. Additionally, the color cathode ray tube comprises a phosphor screen formed on an inner surface of the panel; a mask for selecting colors, the mask having a surface which faces the phosphor screen with a predetermined distance, and a number of electron beam passage apert
Ibuki Hiroaki
Sano Yuuichi
Yokota Masahiro
Haynes Mack
Kabushiki Kaisha Toshiba
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