Information
-
Patent Grant
-
6242852
-
Patent Number
6,242,852
-
Date Filed
Monday, May 3, 199925 years ago
-
Date Issued
Tuesday, June 5, 200123 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 313 270
- 313 337
- 313 346 DC
- 313 346 R
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International Classifications
-
Abstract
A heater is built in an inner sleeve of an electron gun, and an impregnated type cathode is fixed at an end portion, on the grid electrodes side, of the inner sleeve. The inner sleeve, having an outside diameter ranging from about 1.0 mm to 1.4 mm and a length substantially equal to a primary spiral length of the heater is inserted in an outer sleeve. The outer sleeve has on the grid electrodes side a small-diameter portion having an outside diameter ranging from about 2.2 mm to about 2.6 mm and on the base end side a large-diameter portion having an outside diameter ranging from about 2.6 mm to 3.0 mm. The inner sleeve is inserted in the small-diameter portion and is fixed thereto by means of strap-like tabs. A holder is fixed around the outer peripheral portion of the large-diameter portion, and is assembled in a ceramic disk via the holder.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an electron gun used for a CRT (cathode ray tube) or the like, and particularly to an electron gun in which an impregnated type cathode is provided in a heater built-in inner sleeve and the inner sleeve is connected to and supported by an outer sleeve by means of strap-like connecting members, called, tabs. In more particular, the present invention relates to an electron gun capable of leesening the diameter of the inner sleeve for reducing radiation heat propagating to grids and the like, thereby reducing power consumption in combination with prevention of inconveniences such as plane stray.
As shown in
FIGS. 1 and 2
, a CRT includes a tube main body T having a face panel portion F and a neck portion N, wherein an aperture grill AG and a fluorescent layer L are provided on the face panel portion F, and an electron gun E is provided on the neck portion N. The electron gun E, if it is of a Trinitron type, has prefocus lens system having three cathodes KB, KG and KR and, a first grid electrode G
1
and a second grid electrode G
2
; a main lens system having a third grid electrode G
3
, a fourth grid electrode system G
4
AB, G
4
C, G
4
DE, and a fifth grid electrode G
5
; and a deflection system having a convergence deflection plate CP and a shield CS. In
FIG. 2
, reference character DY designates a deflection yoke.
In recent years, to improve the controllability of electron beams, the electron gun E is configured such that the cathode (hereinafter, represented by reference character K) and the first and second grid electrodes G
1
and G
2
are integrally assembled into a cathode structure A.
The cathode structure A is, as shown in
FIGS. 3 and 4
, configured such that the cathode K is fixed at an end portion, on the grid electrodes G
1
and G
2
side, of a heater
11
built-in inner sleeve
10
; the inner sleeve
10
is inserted in an outer sleeve
20
and is fixed thereto by means of strap-like tabs (not shown); the outer sleeve
20
is mounted on a ceramic disk
22
via a holder
21
; and the first grid G
1
is directly provided on the ceramic disk
22
and the second grid electrode G
2
is provided on the ceramic disk
22
via a spacer
23
. In
FIG. 3
, reference numeral
30
designates a lead for making the grid electrode G
1
conductive, and in
FIG. 4
, reference numeral
17
designates a cap for mounting the cathode.
In recent years, an impregnated type cathode K in which a porous base such as a tungsten sintered body is filled with a cathode material has been developed and has come to be used for the electron gun E shown in
FIGS. 3 and 4
in place of a conventional oxide cathode.
As is known, the impregnated type cathode has an advantage that the electron emission density is higher than that for the oxide cathode, and therefore, the electron gun E using the impregnated type cathode K is advantageous in enhancing the performance of the CRT.
However, in the electron gun E using the above impregnated type cathode K it is essential to heat the impregnated type cathode K at a high temperature because the operational temperature of the impregnated type cathode K is higher than that of the oxide cathode. That is to say, the operational temperature of the oxide cathode is about 800° C., while the operational temperature of the impregnated type cathode K is about 1000° C.
As a result, there occur a first problem that a calorie transferred from the built-in heater
11
to the first and second electrodes G
1
and G
2
by way of the inner sleeve
10
, outer sleeve
20
and ceramic disk
22
is large, thereby to increase the power consumption of the heater
11
; a second problem that when the grid electrodes G
1
and G
2
are over-heated at high temperatures, Ba and BaO are evaporated and scattered from the cathode K and are deposited on the grid electrodes G
1
and G
2
to form emission sources ES (see FIG.
4
), and thermal electrons are emitted from these emission sources ES, to increase the stray emission intensity, thereby exerting adverse effect not only on an image quality but also on the focus characteristic, resulting in a phenomenon (so-called plane stray) in which the center of the screen becomes bright after completion of the deflecting operation; and a third problem that a leakage current from the grid electrodes G
1
and G
2
is increased, to cause a malfunction of the circuit.
It is known that the above problems can be somewhat solved by reducing the area of the inner sleeve
10
, that is, reducing the diameter of the inner sleeve
10
, thereby reducing the radiation heat from the inner sleeve
10
.
If the diameter of the inner sleeve
10
is reduced, however, a gap between the inner sleeve
10
and outer sleeve
20
becomes large, so that a calorie propagating by thermal transmission is increased, to make large the power consumption of the heater required to keep the temperature of the inner sleeve at about 1000° C., and it is required to ensure the supporting rigidity of the inner sleeve
10
fixed to the outer sleeve
20
by enlarging the dimension such as the thickness of each tab in accordance with the gap between the inner sleeve
10
and outer sleeve
20
, to increase a calorie propagating by thermal conduction.
To reduce radiation heat, it may be considered to reduce not only the diameter of the inner sleeve
10
but also the diameter of the outer sleeve
20
; however, if the diameter of the outer sleeve
20
is reduced, a work of connecting the outer sleeve
20
with the holder
21
upon assembly of the outer sleeve
20
in the ceramic disk
22
is complicated, and increases to increase the number of assembling steps, thereby increasing the manufacturing cost.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention has been made, and an object of the present invention is to provide an electron gun capable of reducing the caloric amount propagating to grid electrodes due to thermal conduction and thermal radiation, reducing the power consumption of a heater, preventing inconveniences such as plane stray, and simplifying the assembly of the electron gun.
To achieve the above object, according to the present invention, there is provided an electron gun including: a heater built-in inner sleeve at the leading end of which an impregnated type cathode is provided; an outer sleeve in which the inner sleeve is inserted; and strap-like connecting members for connecting the inner sleeve to the outer sleeve at a plurality of positions spaced at intervals in the peripheral direction such that the inner sleeve is disposed coaxially with the outer sleeve, the impregnated type cathode is positioned at the leading end of the outer sleeve, and the inner sleeve is separated from the outer sleeve with an annular space kept therebetween; wherein the outer sleeve has on the leading end side a small-diameter portion having a diameter smaller than that of the remaining portion of the outer sleeve on the base end side; the inner sleeve is positioned in the small-diameter portion; and the leading end of the small-diameter portion is connected to the base end of the inner sleeve by means of the strap-like connecting members.
Further, in the electron gun of the present invention, since the diameter of the inner sleeve is reduced (specificallly to a value ranging from about 1.0 mm to about 1.2 mm) and the small-diameter portion having a small diameter (specifically in a range of about 2.2 mm to about 2.6 mm) on the leading end side of the outer sleeve, a suitable gap can be formed between the inner sleeve and the small-diameter portion of the outer sleeve without reducing the diameter of the portion on the base end side of the outer sleeve (specifically while ensuring the outside diameter of the portion in a range of about 2.6 mm to about 3.0 mm).
Accordingly, it is possible to reduce a caloric amount propagating by thermal radiation and thermal transmission toward the grid electrodes, to avoid the enlargement of the tab thereby reducing the caloric amount propagating by thermal conduction, and to facilitate the assembly of the outer sleeve in the ceramic disk using the large-diameter portion of the outer sleeve.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a schematic sectional view of a CRT to which an electron gun is applied;
FIG. 2
is a conceptional view of the CRT to which the electron gun is applied;
FIG. 3
is a schematic view of a related art cathode structure;
FIG. 4
is a schematic sectional view showing, on an enlarged scale, a portion of the related art cathode structure;
FIGS. 5A and 5B
are schematic views of a cathode structure of an electron gun according to one embodiment of the present invention, wherein
FIG. 5A
is a sectional front view, and
FIG. 5B
is a plan view;
FIGS. 6A and 6B
are views showing an essential portion of the cathode structure, wherein
FIG. 6A
is a sectional front view, and
FIG. 6B
is a plan view; and
FIG. 7
is a front view of a heater used for the cathode structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.
FIGS. 5A and 5B
,
FIGS. 6A and 6B
, and
FIG. 7
show an electron gun according to one embodiment of the present invention, wherein
FIGS. 5A and 5B
are schematic views of a cathode structure of the electron gun;
FIGS. 6A and 6B
are enlarged views showing an essential portion of the cathode structure; and
FIG. 7
is a front view of a heater used for the cathode structure.
In this embodiment, parts corresponding to those of the above-described prior art electron gun shown in
FIGS. 1
to
4
are designated by the same reference numerals (characters), and explanation and graphic representation thereof are partially omitted.
Referring to
FIGS. 5A and 5B
, a cathode structure A is obtained by loosely inserting an inner sleeve
10
at the leading end of which an impregnated type cathode K is provided in an outer sleeve
20
, fixing the inner sleeve
10
to the outer sleeve
20
with tabs
29
, and assembling the outer sleeve
20
in a ceramic disk
22
via a holder
21
.
As shown in
FIGS. 6A and 6B
, the inner sleeve
10
is a cylindrical member having an outside diameter “d” ranging from about 1.0 mm to about 1.4 mm and a length “
1
” (exclusive of a portion mounting the cathode K) ranging from about 3 mm to about 6 mm (preferably, ranging from about 4 mm to 5 mm). A heater
11
is built in the inner sleeve
10
in proximity to the impregnated type cathode K. As will be described later, the inner sleeve
10
is loosely inserted in a small-diameter portion of the outer sleeve
20
.
Referring to
FIG. 7
, the heater
11
is specified such that a secondary spiral length H2 (the length of a spirally wound portion) is in a range of about 75% or less of the length “
1
” of the inner sleeve
10
(concretely, in a range of about 3 mm or less); a primary spiral length H1 (the sum of the length of the spirally wound portion and the length of a straight portion) is substantially equal to or less than the length “1” (that is, about 3 mm to about 6 mm, preferably, about 4 mm to 5 mm) of the inner sleeve
10
; and the number of primary turns is about 165±3. The heater
11
generates heat by a voltage of about 5.0 V applied thereto, to heat the impregnated type cathode K.
The outer sleeve
20
is a cylindrical member having on the leading end side a small-diameter portion
20
a
having an outside diameter D1 ranging from about 2.2 mm to about 2.6 mm and having on the base end side a large-diameter portion
20
b
having an outside diameter D2 ranging from about 2.6 mm to 2.8 mm. The length of the small-diameter portion
20
a
is substantially equal to or more than the length “1” of the inner sleeve
10
.
The inner sleeve
10
is loosely, coaxially inserted in the small-diameter portion
20
a
of the outer sleeve
20
with an annular gap kept therebetween, and is fixed thereto at positions spaced at equal intervals in the circumferential direction by means of a plurality of tabs (strap-like connecting members)
29
. Each tab
29
is a strap-like (or strip-like) member having a thickness of about 0.02 mm and a width of about 0.35 mm. Both ends of the tab
29
in the longitudinal direction are welded to the leading end of the small-diameter portion
20
a
of the outer sleeve
20
and to the base end of the inner sleeve
10
.
The holder
21
is fixed around the outer periphery of the base end of the large-diameter portion
20
b
of the outer sleeve
20
by resistance welding, brazing or the like, and the outer sleeve
20
, and the ceramic disk
22
is assembled to the outer sleeve
20
via the holder
21
. As described above, the first grid electrode G
1
is directly mounted on the ceramic disk
22
, and the second grid electrode G
2
is mounted on the ceramic disk
22
via the spacer
23
.
In this embodiment, the diameter of the inner sleeve
10
at the leading end of which the impregnated type cathode K is provided is reduced; the diameter of a portion of the outer sleeve
20
is reduced to form the small-diameter portion
20
a
; and the inner sleeve
10
is loosely inserted in the small-diameter portion
20
a
and is fixed thereto by means of the tabs
29
.
To be more specific, the inner sleeve
10
is formed such that the outside diameter “d” thereof becomes about 1.0 to 1.2 mm and the small-diameter portion
20
a
of the outer sleeve
20
is formed such that the outside diameter D1 thereof becomes about 2.2 to 2.6 mm, and the inner sleeve
10
is inserted in the small-diameter portion
20
a
with a gap kept therebetween.
Accordingly, it is possible to reduce the caloric amount propagating by thermal radiation from the inner sleeve
10
, and since a suitable gap is kept between the inner sleeve
10
and the small-diameter portion
20
a
of the outer sleeve
20
, it is possible to reduce a calorie propagating by thermal transmission.
As a result, it is possible to prevent the grid electrodes G
1
and G
2
from being heated at high temperatures, to reduce the power consumption of the heater
11
, and to rigidly fix the inner sleeve
10
to the outer sleeve
20
without enlarging the tabs
29
.
In particular, since the heater
11
housed in the inner sleeve
10
is specified such that the secondary spiral length H2 is as short as about 3 mm or less; the primary spiral length H1 is as short as the length “1” of the inner sleeve
10
or less; the number of the primary turns is as small as about 165; and the applied voltage is as low as about 5.0 V, the thermal efficiency of the heater
11
can be improved and also the power consumption of the heater
11
can be reduced.
Since the ceramic disk
22
is assembled to the large-diameter portion
20
b
, having the outside diameter D2 ranging from about 2.6 mm to about 3.0 mm, of the outer sleeve
20
via the holder
21
, the assembling work of the outer sleeve
20
can be simplified and the holder
21
can be forcibly fixed to the large-diameter portion
20
b
. That is to say, if the outside diameter of the outer sleeve
20
is made small, it becomes difficult to fix the holder
21
to the large-diameter portion
20
b
by resistance welding, brazing or the like; however, in this embodiment, the outside diameter D2 of the large-diameter portion
20
b
is not largely affected by the diameter “d” of the inner sleeve
10
because the inner sleeve
10
is not positioned in the large-diameter portion
20
b
of the outer sleeve
20
, so that the degree of freedom in setting of the outside diameter D2 of the large-diameter portion
20
b
is large, and accordingly the outside diameter D2 can be made somewhat larger, to thereby facilitate the assembling work of the outer sleeve
10
.
In the above embodiment, the applied voltage of the heater
11
is set at 4.5 V; however, it may be set at a value lower than 4.5 V.
Further, in the above embodiment, the size of the tab
29
is specified such that the thickness is 0.025 mm and the width is 0.30 mm; however, the size of the tab
29
may be set at a smaller value for reducing the caloric amount propagating by thermal conductance.
While the embodiment of the present invention has been described using the specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing the spirit or scope of the following claims.
Claims
- 1. An electron gun comprising:a heater built-in inner sleeve having provided at a leading end thereof an impregnated type cathode, wherein an outside diameter of said heater built-in inner sleeve is in a range of substantially 1.0 mm to 1.2 mm; an outer sleeve in which said heater built-in inner sleeve is inserted; and a plurality of strap-like supporting members attached at first ends thereof at a respective plurality of positions spaced at regular intervals in a peripheral direction to a leading end of said outer sleeve and attached at second ends thereof to a base end of said inner sleeve opposite said leading end, such that said heater built-in inner sleeve is disposed coaxially with said outer sleeve, said impregnated type cathode is positioned at the leading end of said outer sleeve, and said heater built-in inner sleeve is separated from said outer sleeve by an annular space therebetween, wherein said outer sleeve has on the leading end a small-diameter portion having a diameter smaller than a diameter of the remaining portion of said outer sleeve on a base end, said heater built-in inner sleeve is positioned in said small-diameter portion, and the leading end of said small-diameter portion of said outer sleeve is connected to the base end of said inner sleeve by said plurality of strap-like connecting members.
- 2. The electron gun according to claim 1, further comprising: a holder fixed around an outer peripheral surface of the base end of said outer sleeve;a ceramic disk assembled to said outer sleeve via said holder and a first grid electrode G1 and a second grid electrode G2 assembled to said ceramic disk, thereby forming a cathode structure.
- 3. The electron gun according to claim 1, wherein an outside diameter of said small-diameter portion of said outer sleeve is in a range of substantially 2.2 mm to 2.6 mm, and an outside diameter of a remaining portion of said outer sleeve on the base end is in a range of substantially 2.6 mm to 2.8 mm.
- 4. The electron gun according to claim 1, wherein a primary spiral length of a heater in said heater built-in inner sleeve is substantially equal to a length of said heater built-in inner sleeve, and a secondary spiral length of said heater is about 75% or less of the length of said heater built-in inner sleeve.
- 5. The electron gun according to claim 4, wherein each of the length of said heater built-in inner sleeve and the primary spiral length of said heater is in a range of substantially 4 mm to 5 mm, and the secondary spiral length of said heater is substantially 3 mm or less.
Priority Claims (1)
Number |
Date |
Country |
Kind |
10-126455 |
May 1998 |
JP |
|
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
5780959 |
Pruvost et al. |
Jun 1998 |
|
6016026 |
Lee |
Jan 2000 |
|
Foreign Referenced Citations (2)
Number |
Date |
Country |
0436360 |
Jul 1991 |
EP |
0778604 |
Jun 1997 |
EP |