Electric lamp and discharge devices – Electrode and shield structures – Indirectly heated cathodes
Reexamination Certificate
2001-07-26
2003-04-22
O'Shea, Sandra (Department: 2879)
Electric lamp and discharge devices
Electrode and shield structures
Indirectly heated cathodes
C313S409000, C313S037000
Reexamination Certificate
active
06552479
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube having an electron gun employing an indirectly heated cathode, and in particular to a cathode ray tube having reduced a power consumption of a heater serving as a heating element of the indirectly heated cathode.
Cathode ray tubes such as TV picture tubes and display tubes are widely used as a display means in various kinds of information processing equipment because of their capability of high-resolution image reproduction.
The cathode ray tubes of this kind include an evacuated envelope comprising a panel portion having a phosphor screen formed of phosphors coated on its inner surface, a neck portion and a funnel portion for connecting the panel portion and the neck portion, an electron gun housed in the neck portion comprising an electron beam generating section including an indirectly heated cathode, a control electrode and an accelerating electrode, and a main lens section formed of plural electrodes for focusing and accelerating an electron beam generated in the electron beam generating section toward the phosphor screen, and a deflection yoke mounted around the funnel portion for scanning the phosphor screen with the electron beam emitted from the electron gun.
FIG. 6
is a schematic cross-sectional view of a shadow mask type color cathode ray tube for explaining an example of a structure of a cathode ray tube. Reference numeral
1
denotes a panel portion,
2
is a funnel portion,
3
is a neck portion,
4
is a phosphor screen formed of phosphors coated on the inner surface of the panel portion
1
,
5
is a shadow mask serving as a color selection electrode,
6
is a magnetic shield for shielding an external magnetic field (the Earth's magnetic field) for preventing the Earth's magnetic field from changing the trajectory of electron beams. Reference numeral
7
denotes a deflection yoke,
8
is external magnets for beam adjustment,
9
is an electron gun provided with indirectly-heated cathodes for emitting three electron beams and
10
are the three electron beams only one of which is shown.
The three electron beams
10
from the electron gun
9
are modulated by video signals from an external signal processing circuit (not shown), respectively, and are projected toward the phosphor screen
4
. The electron beams
10
scan the phosphor screen
4
two-dimensionally by being subjected to the horizontal and vertical deflection magnetic fields generated by the deflection yoke
7
mounted around the transition region between the neck portion
3
and the funnel portion
2
. The shadow mask
5
reproduces a desired image by passing the three electron beams through a large number of apertures therein to the phosphor screen such that each beam impinges upon and excites only one of the three kinds of color phosphor elements in the phosphor screen.
FIG. 7
is a side elevation view of the electron gun
9
for explaining an example of a structure of the electron gun
9
used for the color cathode ray tube shown in FIG.
6
. The electron gun
9
comprises a control electrode (the first grid electrode or G
1
)
11
, an accelerating electrode (the second grid electrode or G
2
)
12
, focus electrodes (the third grid electrode or G
3
, the fourth grid electrode or G
4
, and the fifth grid electrode or G
5
)
13
,
14
,
15
, an anode (the sixth grid electrode or G
6
)
16
, and a shield cup
17
physically retained in axial predetermined spaced relationship in the order named by multiform glasses
20
, and the respective electrodes are electrically connected to respective stem pins
18
a
implanted in a stem
18
by welding to the stem pins
18
a
a tab or a lead provided to the electrodes.
In this electron gun
9
, an indirectly heated cathode structure
21
is spaced closely from the electron beam apertures in the control electrode
11
toward the stem
18
, and has heaters for heating the electron-emissive layers.
Reference numeral
19
denote bulb spacer contacts for centering the central longitudinal axis of the electron gun
9
coincident with the axis of the neck portion
3
by pressing resiliently against the inner wall of the neck portion
3
and for effecting delivery of an anode voltage from the internal conductive coating coated on the inner walls of the funnel portion
2
and the neck portion
3
to the electron gun
9
.
The indirectly heated cathode structure
21
, the control electrode
11
and the accelerating electrode
12
form an electron beam generating section (a triode portion). The focus electrodes
13
to
15
accelerate and focus the electron beams emitted from the electron beam generating section, and then a main lens formed between the focus electrode
15
and the anode
16
focuses the electron beams onto the phosphor screen.
The stem
18
is fused to close the open end of the neck portion
3
of the vacuum envelope, and signals and voltages from external circuits are applied to the respective electrodes via the stem pins
18
a
. The external magnets
8
(a magnet assembly) for beam adjustment shown in
FIG. 6
correct errors in landing of the electron beams on the phosphor picture elements caused by a delicate misalignment in axis or a delicate rotational error between the electron gun
9
and the panel portion
1
, the funnel portion
2
and the shadow mask
5
.
FIG. 8
is a cross-sectional view of the indirectly heated cathode structure
21
shown in FIG.
7
. The indirectly heated cathode structure
21
comprises bead supports
22
, an eyelet
23
, heater supports
24
, a heater
25
, a base metal
27
for supporting an electron-emissive material
26
, a cathode support sleeve
28
and a cathode cylinder
29
.
The indirectly heated cathode structure
21
is fixed on multiform glasses
20
by the eyelet
23
and the bead supports
22
. The heater
25
housed within the cathode support sleeve
28
are fixed by welding its ends (leg portions) to the heater support
24
.
FIGS. 9A and 9B
are illustrations of a structure of the heater
25
,
FIG. 9A
being a side view of the heater
25
and
FIG. 8B
being an enlarged fragmentary cross-sectional view of the encircled portion designated “A” in FIG.
9
A. As shown in
FIG. 9B
, the heater
25
comprises a tungsten wire
31
spirally wound, an alumina insulating layer
32
coated around the tungsten wire
31
, and a blackened fine-powder tungsten layer
33
coated around the alumina insulating layer
32
. The blackened layer
33
is intended for lowering the temperature required of the heater
25
by improving the heat radiation from the heater
25
, and consequently improving the reliability of the heater
25
.
In
FIG. 9A
, reference character HT denote leg portions of the heater
25
comprised of tungsten wires spirally wound in three layers, HD is a major heating portion of the heater
25
formed by winding spirally in a large diameter a tungsten coiled wire having been wound initially spirally in a small diameter (hereinafter referred to merely as a coiled coil portion), HA is a portion coated with alumina, HB is a blackened portion covered with the blackened fine-powder tungsten layer
33
, HE are portions not covered with alumina and reference numeral
39
in
FIG. 9B
denotes a hollow formed after dissolving and removing a molybdenum mandrel.
A method of forming the leg portions HT of the heater by winding tungsten wires in three layers is disclosed in Japanese Patent Application Laid-open No. Hei 11-354041 (laid-open on Dec. 24, 1999).
FIGS. 10A-10E
illustrate sequence of steps in a conventional method of fabricating the conventional heater.
In
FIG. 10A
, a tungsten wire
31
is wound spirally forward as indicated by an arrow P around a molybdenum mandrel wire
40
up to point A.
Next, as illustrated in
FIG. 10B
, the tungsten wire
31
is wound spirally backward from point A to point B as indicated by an arrow Q.
Then, as illustrated in
FIG. 10C
, the tungsten wire
31
is wound spirally forward again from point B to point C over a centerline CL for folding in a subsequent process, as indicated by an arrow
Iwamura Norio
Koizumi Sachio
Komiya Toshifumi
Antonelli Terry Stout & Kraus LLP
Dong Dalei
Hitachi , Ltd.
O'Shea Sandra
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