Electric lamp and discharge devices – Cathode ray tube – Screen
Reexamination Certificate
2000-04-13
2002-01-29
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Screen
C313S402000
Reexamination Certificate
active
06342759
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a shadow mask type color cathode ray tube, and particularly to a color cathode ray tube having a multiplicity of dot-like electron-transmissive apertures (will be also referred to as beam apertures or simply as apertures in this specification) in the useful apertured portion of the shadow mask with horizontal and vertical pitches of the apertures varied and providing a high quality display.
In general, in a shadow mask type color cathode ray tube, a multiplicity of beam apertures are formed in the apertured portion of the shadow mask in correspondence with the shape and position of the three-color phosphor screen formed on the inner surface of the faceplate of the panel portion.
The beam apertures in the shadow mask are arranged with horizontal and vertical aperture pitches determined by some formula such that triads of red, green and blue phosphor picture elements are arranged in predetermined positions.
As such a prior art shadow mask type color cathode ray tube, there are known those in which the aperture pitches of beam apertures in the apertured portion of the shadow mask are determined by the following formulas on the basis of the slightly curved shapes of the inner surface of the faceplate and the apertured portion of the shadow mask.
In one example, the horizontal aperture pitches are nearly uniform in a central portion on both sides of and in the neighborhood of the vertical center line of the apertured portion, and become progressively greater as the left or right side of the apertured portion is approached outside of the central portion. This type is hereinafter referred to as a prior art shadow mask of the first type.
In another example, as disclosed in Japanese Patent Laid-Open Publication No. SHO 56-41648, the vertical aperture pitches of the beam apertures become progressively smaller as one goes from the horizontal center line toward the top or bottom of the apertured portion and from the vertical center line toward the left or right side of the apertured portion at the same time. This type is hereinafter referred to as a prior art shadow mask of the second type.
In a color cathode ray tube employing the prior art shadow mask of the second type, the phosphor screen is configured such that the line triads of the three phosphor dots of red, green and blue colors tilt increasingly with respect to a horizontal direction as one goes from the horizontal center line toward the top or bottom of the useful phosphor screen area and from the vertical center line toward the left or right side of the useful phosphor screen area at the same time.
FIG. 5
is a plan view showing an arrangement of part of phosphor dots in the useful phosphor screen area of a color cathode ray tube employing the shadow mask of the second type (disclosed in Japanese Patent Laid-Open Publication No. SHO 56-41648).
In
FIG. 5
, reference numeral
31
designates a faceplate;
32
is a useful phosphor screen area;
33
is phosphor dots;
33
R is red phosphor dots;
33
G is green phosphor dots;
33
B is blue phosphor dots;
34
is the vertical center line (Y axis) of the useful phosphor screen area
32
; and
35
is the horizontal center line (X axis) of the useful phosphor screen area
32
.
The faceplate
31
has a multiplicity of phosphor dots
33
in the useful phosphor screen area
32
on the inner surface thereof. The phosphor dots
33
are composed of a plurality of triads and one red phosphor dot
33
R, one green phosphor dot
33
G and one blue phosphor dot
33
B form one triad.
As shown in
FIG. 5
, the phosphor dots
33
are arranged with nearly uniform horizontal and vertical pitches such that the line triads of the three-color phosphor dots
33
tilt increasingly with decreasing distance from the corners of the useful phosphor screen area
32
, with respect to the horizontal center line
35
.
Specifically, the line triads of the three-color phosphors are nearly horizontal in each of the following portions in the useful phosphor screen area
32
: the approximately central portion and its neighborhood; the portion extending on the horizontal center line
35
from approximately the center to the right and left sides and its neighborhood; and the portion extending on the vertical center line
34
from approximately the center to the top and bottom and its neighborhood. At the four corner portions in the useful phosphor area
32
, the line triads of the three-color phosphors
33
tilt most largely with respect to the horizontal center line
35
and tilt decreasingly with respect to the horizontal center line
35
with increasing distance from the four corner portions. The tilt of the line triads of the three-color phosphors
33
with respect to the horizontal center line
35
at the four corner portions have upward slopes at the upper left-hand corner, downward slopes at the upper right-hand corner, downward slopes at the lower left-hand corner and upward slopes at the lower right-hand corner. In the following description, such an arrangement of a multiplicity of the phosphor dots
33
on the faceplate
31
is referred to as a tilt array arrangement.
In the color cathode ray tubes employing the prior art shadow mask of the first type, a multiplicity of the phosphor dots formed in the useful phosphor screen area are arranged with the horizontal aperture pitch nearly uniform in the portion on both sides and in the neighborhood of the vertical center line, and with dot pitches progressively greater toward the left or right side of the useful phosphor screen area out of the central portion. Accordingly, horizontal and diagonal pitches between two adjacent triads of phosphor dots at portions at sides and corners of the useful phosphor screen area become greater, respectively. As a result, the color cathode ray tubes employing the prior art shadow mask of the first type have a disadvantage that the resolution is deteriorated at portions at sides and corners of the phosphor screen.
In the color cathode ray tubes employing the prior art shadow mask of the second type, since the phosphor dots formed in the useful phosphor screen area are arranged in a tilt array arrangement, diagonal pitches between two adjacent triads of phosphor dots at portions at corners in the useful phosphor screen area become smaller. As a result, the color cathode ray tubes employing the prior art shadow mask of the second type have a disadvantage that the color purity tolerance at each corner portion on the phosphor screen is reduced, leading to the non-uniformity in displayed colors.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-mentioned problems and to provide a shadow mask type color cathode ray tube capable of increasing the color purity tolerance at each portion on the phosphor screen so as to prevent deterioration of the resolution, and retaining the mechanical strength of the shadow mask.
To achieve the above object, according to the shadow mask type color cathode ray tube of the present invention, beam apertures of the shadow mask are arranged such that the horizontal aperture pitches are nearly uniform in a central portion on both sides of and in the neighborhood of the vertical center line of the apertured portion and increase slightly with increasing distance from the central portion toward the left or right side of the apertured portion, and such that the vertical aperture pitches are arranged in such a manner as to slightly increase the tilt of the horizontal rows of the beam apertures as one goes from the vertical center line toward the left or right side of the apertured portion.
Here, the phosphor dots of the phosphor screen are arranged in such a manner as to satisfy the following relationship:
0.98 Pdo≦Pd≦1.02 Pdo (1)
where Pd={Ph
2
+Pv
2
}
0.5
, and where, consider two closest phosphor dots of the same color one on each of the two adjacent horizontal rows of the phosphor dots in the phosphor screen, a horizontal dot pitch Ph is a distance between the two phosphor dots of th
Antonelli Terry Stout & Kraus LLP
Clove Thelma Sheree
Hitachi , Ltd.
Patel Nimeshkumar D.
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