Electron gun structure

Details Electron gun structure Electron gun structure

1998-11-13

2001-07-24

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Plural beam generating or control

C313S449000, C313S447000, C315S014000

Reexamination Certificate

active

06265819

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an electron gun assembly, and in particular to an electron gun assembly for color picture tube improved in withstand voltage characteristics.
BACKGROUND ART
An electron gun assembly for color picture tube has a function of generating an electron beam and focusing and accelerating the generated electron beam according to an object. In particular, a focusing lens system formed by a plurality of electrodes becomes an important element dominating the performance of the color picture tube.
The focusing lens system of the electron gun assembly for color picture tube functions to simultaneously focus three electron beams respectively corresponding to red (R), green (G), and blue (B). A bi-potential focus lens and a uni-potential focus lens are examples of a fundamental lens form of such a focusing lens system. As a matter of fact, a combination of these fundamental lens forms is utilized in order to improve the focusing performance. For example, various composite lens systems such as tri- potential focus type (abbreviated to TPF type), multi-step focus type (abbreviated to MSF type), and quadra-potential focus (abbreviated to QPF type) are utilized.
FIG. 1
is a diagram showing the schematic structure of a QPF type electron gun assembly described in Jpn. Pat. Appln. KOKAI Publication No. 54-72667.
The electron gun assembly includes a cathode
10
, a first grid
11
, a second grid
12
, a third grid
13
, a fourth grid
14
, a fifth grid
15
, and a sixth grid
16
disposed in the cited order along the same axis. Each grid has an electron beam passing hole which passes an electron beam emitted from the cathode
10
.
The cathode
10
and the grids
11
through
16
are applied with respective predetermined potentials. The cathode
10
, the first grid
11
, and the second grid
12
emit thermions and form crossovers of electron beams. The second grid
12
and the third grid
13
form a pre-focus lens
17
to focus electron beams crossed over preliminarily. The third grid
13
, the fourth grid
14
and the fifth grid
15
form an auxiliary lens
18
. The fifth grid
15
and the sixth grid
16
form a main lens
19
.
Recently, color picture tubes are required to be larger in size and higher in definition. The electron gun assembly is also required to have shorter inter-electrode distance values and higher precision. In particular, a triode ranging from the cathode
10
to the second grid
12
was formed so as to have relatively small inter-electrode distance values, but recently the inter-electrode distance values tend to become still smaller. As the inter-electrode distance becomes shorter, not only the assembling error of each inter-electrode distance but also inter-electrode distance changes caused by the influence of heat of a heater provided for the cathode
10
need to be made smaller.
As the second grid
12
, a plate thicker than that of the first grid
11
is typically used. Thus, the heat capacity of the second grid
12
becomes large. After the heater of the cathode is ignited, it takes time until thermal stability is attained. Thus, the white balance immediately after the ignition of the heater tends to break down.
In order to solve this problem, there is disclosed in Jpn. UM Appln. KOKAI Publication No. 57-128755 an electron gun assembly including a second grid
12
having a thick flat plate
21
with a predetermined opening formed therethrough and a support
22
for fixing the thick flat plate
21
to bead glass
20
as shown in FIG.
2
. The support
22
of the second grid
12
is curved toward a side opposite to the support side of the thick flat plate
21
. In the structure of the second grid
12
, the thick flat plate
21
is not directly fixed to the bead glass
20
and consequently the area of the thick flat plate
21
can be made small. As a result, its heat capacity can be made small and consequently it becomes possible to prevent the inter-electrode distance from being changed by thermal expansion.
However, the support
22
of the second grid
12
is disposed on the side of a third grid
13
. For providing the distance between the second grid
12
and the third grid
13
with a predetermined value, therefore, it is necessary to make a portion of the third grid
13
located on the side of the second grid
12
smaller than an inside diameter
23
of an opening portion of the second grid
12
located in the support portion
22
and adopt such a structure that a face
24
of the third grid
13
opposed to the second grid
12
is surrounded by the support
22
of the second grid
12
.
Conventionally, a portion of the third grid
13
located on the side of the second grid
12
, i.e., an electrode of a third grid bottom is formed so as to have a cup-shaped structure as shown in
FIGS. 3A through 3C
or a cup-shaped structure as shown in
FIGS. 4A through 4C
.
FIG. 3A
is a top view of an electrode seen from the side of a cathode
10
.
FIG. 3B
is a sectional view of the electrode seen from an in-line direction, i.e., the horizontal direction.
FIG. 3C
is a side view of the electrode seen from a direction perpendicular to the in-line direction, i.e., the vertical direction. A bottom face
30
of the cup-shaped electrode shown in
FIGS. 3A through 3C
takes the shape of an approximately rectangle having longer sides in the horizontal direction. Furthermore, so as to make the shape of an opening portion
31
substantially the same as that of a bottom face
30
, the longer sides of the bottom face
30
are joined to longer sides of the opening portion
31
with side walls
32
extended in the tube axis direction.
FIG. 4A
is a top view of an electrode seen from the side of the cathode
10
.
FIG. 4B
is a sectional view of the electrode seen from the horizontal direction.
FIG. 4C
is a side view of the electrode seen from the vertical direction. The electrode shown in
FIGS. 4A through 4C
has projections
33
respectively for individual electron beam passing holes.
FIG. 5
is a sectional view of a part of an electron gun assembly having the cup-shaped electrode shown in
FIGS. 3A through 3C
on the bottom of a third grid seen from the horizontal direction. In this shape, the distance between a folded portion
34
of a support
22
of the second grid
12
and a side wall
32
of the bottom of the third grid
13
is small and the withstand voltage characteristics is poor. In other words, the distance between the folded portion
34
and the side wall
32
is small, and in addition a large potential difference is formed between them. This results in a problem that a leak tends to occur.
Therefore, it is conceivable to use an electrode having a narrowed width of the bottom face in the vertical direction as shown in
FIG. 6A through 6C
.
FIG. 6A
is a top view of the electrode seen from the side of the cathode
10
.
FIG. 6B
is a sectional view of the electrode seen from the horizontal direction.
FIG. 6C
is a side view of the electrode seen from the vertical direction. If the electrode shown in
FIGS. 6A through 6C
is used, the distance between the folded portion
34
of the second grid
12
and the side wall
32
of the third grid
13
can be widened, and consequently the problem of the leak is eliminated. Since the inside diameter of a side of the opening
39
of the third grid bottom becomes small, however, an electric field
36
of the auxiliary lens penetrating from the side of the fourth grid
14
to the side of the third grid
13
is affected. Thus there occurs a problem that a lens which is asymmetric in the horizontal direction and the vertical direction is formed. As a result, a beam spot formed on a screen does not take the shape of a circle but takes a distorted shape.
If the electrode taking the shape shown in
FIGS. 3A through 3C
or
FIGS. 6A through 6C
is used, either the withstand voltage characteristics or the auxiliary lens characteristics are sacrificed.
Furthermore, if the third grid bottom takes the shape shown in
FIGS. 4A through 4C
, then the distance between a support
22
of the second grid
12
an

Affiliated with

Also associated with

Rating

Electron gun structure does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Electron gun structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electron gun structure will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2454504