Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
2002-08-08
2003-09-23
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S414000, C313S412000
Reexamination Certificate
active
06624562
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube and particularly to a shadow mask type color cathode ray tube having an improved resolution capability. Color cathode ray tube such as color picture tubes and display tubes have been widely used as receivers of TV broadcasting or monitors in information processing equipment because of their high-resolution capability.
Generally, such color cathode ray tubes comprise a phosphor screen formed on an inner surface of a faceplate of a panel portion of an evacuated envelope, a shadow mask having a multiplicity of electron beam apertures and spaced from the phosphor screen within the panel portion, an electron gun of the in-line type for projecting electron beams toward the phosphor screen and housed in a neck portion of the evacuated envelope, and a deflection yoke mounted around a funnel portion of the evacuated envelope.
FIG. 6
is a schematic cross sectional view for explaining a construction of a shadow mask type color cathode ray tube as an example of a color cathode ray tube to which the present invention is applicable. In
FIG. 6
, reference numeral
20
is a faceplate,
21
is a neck,
22
is a funnel for connecting the faceplate
20
and the neck
21
,
23
is a phosphor screen serving as an image display screen formed on an inner surface of the faceplate
20
,
24
is a shadow mask serving as a color selection electrode,
25
is a mask frame for supporting the shadow mask
24
and for forming a shadow mask assembly,
26
is an inner shield for shielding extraneous ambient magnetic fields,
27
is a suspension spring mechanism for suspending the shadow mask assembly on studs embedded in the inner sidewall of the faceplate
20
,
28
is an electron gun housed in the neck
21
for projecting three electron beams Bs (X2) and Bc,
29
is a deflection device for deflecting the electron beams horizontally and vertically,
30
is a magnetic device for adjusting color purity and centering the electron beams,
31
is a getter,
32
is an internal conductive coating,
33
is an implosion protection band, and
34
are stem pins for supplying voltages on the electron gun
28
.
The evacuated envelope is formed of a faceplate
20
, a neck
21
and a funnel
22
. The magnetic deflection fields generated by the deflection device
29
deflect the three in-line electron beams emitted from the electron gun
28
horizontally and vertically to scan the phosphor screen
23
in two dimensions. The three electron beams Bc, Bs X2 are modulated by the green signal (center beam Bc), the blue signal (side beam Bs) and the blue signal (side beam Bs), respectively, and after being subjected to color selection by beam apertures in the shadow mask
24
disposed immediately in front of the phosphor screen
23
, impinge on respective phosphor elements of red, green and blue colors of the tricolor mosaic phosphor screen
23
to reproduce the intended color image.
FIGS. 7A
to
7
C are illustrations of a construction example of the in-line type electron gun applicable to the color cathode ray tube shown in
FIG. 6
,
FIG. 7A
is a horizontal sectional view thereof, and
FIG. 7B
is a schematic sectional view of the major portion of
FIG. 7A
, taken along the VIIB—VIIB, and
FIG. 7C
is a schematic sectional view of the major portion of
FIG. 7A
, taken along the VIIC—VIIC. In
FIG. 7A
, reference numerals Ia to Ic are cathode structures,
2
is a control grid electrode,
3
is an accelerating electrode,
4
is a focus electrode,
5
is an anode,
6
is a shield cup,
41
is a first focus sub-electrode,
42
is a second focus sub-electrode, and the first and second sub-electrodes
41
,
42
form a focus electrode
4
. Vertical plates
411
are attached to the first focus sub-electrode
41
on the second focus sub-electrode
42
side thereof such that they sandwich each of three electron beams horizontally and they extend toward the second focus sub-electrode
42
, a pair of horizontal plates
421
are attached to the second focus sub-electrode
42
on the first focus sub-electrode
41
side thereof such that they sandwich three electron beams vertically and they extend toward the first focus sub-electrode
41
, and the vertical plates
411
and the horizontal plates
421
form a so-called electrostatic quadrupole lens. The correction plate electrode
422
with a beam aperture for each of the three electron beams is disposed within the second focus sub-electrode
42
and the correction plate electrode
51
with a beam aperture for each of the three electron beams is disposed within the anode
5
.
The vertical plates
411
and the horizontal plates
421
of the electrostatic quadrupole lens, as respectively shown in
FIGS. 7B and 7C
, are such that the vertical plates
411
are comprised of four plates
411
a
,
411
b
,
411
c
and
411
d
arranged in such a manner as to sandwich side beam apertures
41
s
and a center beam aperture
41
c
in the first focus sub-electrode
41
individually and horizontally and the horizontal plates
421
are comprised of a pair of plates
421
a
and
421
b
arranged in such a manner as to sandwich side beam apertures
42
s
and a center beam aperture
42
c
in the second focus sub-electrode
42
in common and vertically.
The cathode structures
1
a
to
1
c
, the control grid electrode
2
and the accelerating electrode
3
form an electron beam generating section. Thermoelectrons emitted from the heated cathode structure
1
are accelerated toward the control grid electrode
2
by an electric potential of the accelerating grid electrode
3
and form three electron beams. The three electron beam pass through the apertures in the control grid electrode
2
, and the apertures in the accelerating electrode
3
, and after having astigmatism corrected by the electrostatic quadrupole lens disposed between the first and second focus sub-electrodes
41
and
42
, and enter the main lens formed between the second focus sub-electrode
42
and the anode
5
. The three electron beams are focused by the main lens, and after being subjected to color selection by the shadow mask, and impinge upon the intended respective phosphor elements of the phosphor screen and produce the bright spots of the intended colors.
The first focus sub-electrode
41
is supplied with a fixed voltage Vf
1
and the second focus sub-electrode
42
is supplied with a dynamic voltage Vf
2
+dVf which is a fixed voltage Vf
2
superposed with a voltage dVf varying in synchronism with deflection angles of the electron beams. The anode
5
is supplied with the highest voltage Eb via the internal conductive coating
32
(see
FIG. 6
) coated on the inner surface of the funnel
22
.
With this construction, the curvature of the image field is corrected by varying the lens strength with the deflection angle of the electron beams and astigmatism is corrected by the electrostatic quadrupole lens such that the focus length of the electron beams and the shape of the beam spots are controlled to provide good focus over the entire phosphor screen.
To obtain a normal round beam spot at the center of the phosphor screen, the horizontal and vertical effective lens diameters are approximately equalized with each other for each of the three electron beams by optimization in terms of the dimensions of the single openings common for the three electron beams in the second focus sub-electrode
42
and the anode
5
for forming the main lens portion, the dimensions of the beam apertures in the correction plate electrodes
422
,
51
disposed within the second focus sub-electrode
42
and the anode
5
, and the axial distances between the correction plate electrodes
422
,
51
and the single openings in the second focus sub-electrode
42
and the anode
5
incorporating the correction plate electrodes
422
,
51
.
With such a lens, the resolution capability of the electron beams scanning the phosphor screen was improved and reproduced the high quality image.
The prior art as described above is disclosed in Japanese Patent Application Laid-open Publicati
Shirai Shoji
Uchida Go
Antonelli Terry Stout & Kraus LLP
Guharay Karabi
Hitachi , Ltd.
Patel Nimeshkumar D.
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