Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
1999-01-27
2001-09-25
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S421000, C313S426000, C313S441000, C313S444000
Reexamination Certificate
active
06294866
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube having an electron gun configured to project three electron beams toward a phosphor screen.
In color cathode ray tubes for use in TV receiver sets or monitors, spot shapes of the electron beams on the screen have to be properly controlled with increase in beam deflection to provide good focus and high resolution over the entire phosphor screen (also referred to merely as the screen or the picture area).
FIG. 5
is a longitudinal cross-sectional view of a color cathode ray tube for explaining its overall structure, to which the present invention is applied. Reference numeral
31
denotes a panel portion for carrying a screen,
32
is a neck portion for housing an electron gun,
33
is a funnel portion for connecting the panel portion
31
and the neck portion
32
,
34
is a phosphor screen coated on the inner surface of the panel portion
31
,
35
is a shadow mask serving as a color selection electrode,
36
is a mask frame for supporting the shadow mask
35
,
37
is a magnetic shield for shielding external magnetic fields,
38
is springs for suspending the shadow mask
35
,
39
is an electron gun for projecting three electron beams arranged in a line,
40
is a deflection yoke,
41
is a magnet assembly for centering the beams and adjusting color purity and convergence of the beams, B denotes three electron beams arranged in a line (two side beams SB and one center beam CB).
The vacuum envelope of this color cathode ray tube is formed of the panel portion
31
, the neck portion
32
, and the funnel portion
33
around which the deflection yoke
40
is mounted. The electron gun
39
housed in the neck portion
32
projects the three in-line beams B toward the phosphor screen
34
. The deflection yoke
40
mounted around the transition region between the funnel portion
33
and the neck portion
32
generates the magnetic field for deflecting the three electron beams B from the electron gun
39
in two horizontal and vertical directions. The shadow mask
35
is welded to the mask frame
36
, and the mask frame
36
is suspended within the panel portion
31
by engaging its suspension springs
38
fixed to its peripheral portions with panel pins embedded in the inner surface of the panel portion
31
such that the shadow mask is spaced a predetermined distance from the phosphor screen
34
.
FIG. 6A
is a vertical cross-sectional view of a three in-line beam electron gun in a color cathode ray tube for explaining a dimensional relationship of the present invention and the prior art, and
FIG. 6B
is a cross-sectional view taken along line VIB—VIB of FIG.
6
A. Reference numeral
1
denotes a cathode structure,
2
is a beam control electrode,
3
is an accelerating electrode,
4
is a focus electrode,
5
is an anode and
6
is a shield cup. The focus electrode
4
is divided into a first focus sub-electrode
4
-
1
and a second focus sub-electrode
4
-
2
. The cathode structure
1
, the beam control electrode
2
and the accelerating electrode
3
constitute an electron beam generating section.
Thermoelectrons emitted from the heated cathode structure
1
are accelerated toward the beam control electrode
2
by the potential of the accelerating electrode
3
to form three electron beams. The three electron beams pass through the apertures in the beam control electrode
2
, then pass through the apertures in the accelerating electrodes
3
, are slightly focused by a prefocus lens formed between the accelerating electrode
3
and the first focus sub-electrode
4
-
1
, then are accelerated and enter a main lens
7
formed between the second focus sub-electrode
4
-
2
and the anode
5
. After they are focused by the main lens
7
, they pass through apertures in the shadow mask
35
and are focused on the phosphor screen
34
to form three beam spots on the phosphor screen
34
.
Four vertical parallel plate-like electrodes
411
,
412
,
413
,
414
(only
413
is visible) and two horizontal parallel plate-like electrodes
421
,
422
are attached to the first focus sub-electrode
4
-
1
and the second focus sub-electrode
4
-
2
, respectively, to form an electrostatic quadrupole lens
8
therebetween.
The electrostatic quadrupole lens
8
are formed by the four vertical parallel plate-like electrodes
411
,
412
,
413
,
414
(only
413
is visible) disposed to sandwich, in a direction of the in-line beam arrangement, respective beam apertures in the end of the first focus sub-electrode
4
-
1
facing the second focus sub-electrode
4
-
2
and electrically connected to the first focus sub-electrode
4
-
1
, and a pair of horizontal parallel plate-like electrodes
421
,
422
disposed to sandwich, in a direction perpendicular to the in-line beam arrangement, three beam apertures
4
-
2
a
,
4
-
2
b
,
4
-
2
c
in the end of the second focus sub-electrode
4
-
2
facing the first focus sub-electrode
4
-
1
and electrically connected to the second focus sub-electrode
4
-
2
.
As shown in
FIG. 7
, a fixed voltage Vf
1
is applied to the first focus sub-electrode
4
-
1
, and a dynamic voltage (Vf
2
+dVf) varying in synchronism with deflection of the electron beams scanned on the phosphor screen
34
is applied to the second focus sub-electrode
4
-
2
. The anode
5
is supplied with the highest voltage Eb (anode voltage).
With this structure, the strength of the main lens
7
is varied with deflection of the electron beams to correct the curvature of the image field, astigmatism is corrected by the electrostatic quadrupole lens
8
formed by the first and second focus sub-electrodes
4
-
1
,
4
-
2
with deflection of the electron beams such that focus lengths of the electron beams and the shapes of the beams on the phosphor screen are controlled to provide good focus over the entire phosphor screen
34
.
The electrostatic quadrupole lens
8
is configured such that the quadrupole lens is formed in a space where two horizontal parallel plate-like electrodes
421
,
422
and four vertical parallel plate-like electrodes
411
,
412
,
413
,
414
overlap each other. The strength of the quadrupole lens increases with increase in the overlapped length of the plate-like electrodes.
The above-described electrostatic quadrupole formed by the first and second sub-electrodes
4
-
1
,
4
-
2
of the focus electrode
4
in an electron gun are disclosed in Japanese Patent Application Laid-Open No. Sho 61-250934, for example.
The prior art electrostatic quadrupole lens is formed by combination of plate-like electrodes, in a space where horizontal parallel plate-like electrodes and vertical parallel plate-like electrodes are spaced a relatively great distance from each other, a uniform quadrupole lens is produced in the space, but in space where they are spaced a relatively short distance, a greatly distorted quadrupole lens is generated in the space.
When the trajectory of electron beam B is bent in the electron gun due to manufacturing variations in electron guns or color cathode ray tubes, and as a result the electron beam B traverse corners off the axis of the electrostatic quadrupole lens as illustrated in
FIG. 6B
, the problem arises in that they are influenced by the distorted quadrupole lens action, produce greatly distorted beam spot shapes including a core C and a halo H on the phosphor screen as illustrated in
FIG. 6
c
and deteriorate focus characteristics resulting in degradation of resolution.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the aforementioned problems with the prior art and to provide a color cathode ray tube having an electron gun capable of preventing deterioration in focus characteristics and in resolution in spite of manufacturing variations in the electron gun or the color cathode ray tube.
In accordance with one embodiment of the present invention, there is provided a color cathode ray tube comprising a phosphor screen, an electron beam generating section for generating three in-line electron beams, a focus electrode and an anode, the
Kato Shin-ichi
Nagaoka Masafumi
Shirai Shoji
Uchida Go
Antonelli Terry Stout & Kraus LLP
Haynes Mack
Hitachi , Ltd.
Patel Nimeshkumar D.
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