Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2002-04-30
2004-08-03
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S417000, C313S456000, C445S060000, C445S034000
Reexamination Certificate
active
06771015
ABSTRACT:
This application claims the benefit of the Korean Application No. P2002-11650 filed on Mar. 5, 2002, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an electron gun for a cathode ray tube, and more particularly, to an electron gun having guide holes formed for use in alignment of the electron gun for a cathode ray tube.
2. Discussion of the Related Art
As shown in
FIG. 1
, a conventional color cathode ray tube includes a panel
1
and a funnel
2
made of glass material, a bulb
3
for maintaining 10-7 torr vacuum level, an electron gun
6
housed in a neck portion
4
formed in the bulb
3
for emitting electron beams
5
, a shadow mask
8
which makes three electron beams
5
emitted from the electron gun
6
selectively collide with a three-color fluorescent screen
7
, such as red (R), green (G), and blue (B), which coats the panel
1
, and a deflection yoke
9
disposed in an external portion of the funnel
2
to deflect electron beams
5
emitted from the electron gun
6
.
Especially,
FIG. 2
depicts a Uni-Bi type electron gun for use in monitors. The electron gun
6
includes a cathode
10
for emitting thermoelectrons, first and second electrodes
11
and
12
for controlling the thermoelectrons emitted from the cathode
10
, a third electrode
13
which is configured to an observation direction (Z—Z) to form a prime electrostatic focusing lens for focusing the electron beams
5
on the fluorescent screen
7
, a fourth electrode
14
, a focus electrode
15
, an anode electrode
16
, and a shield cup
17
arranged in line, being fastened using a non-insulating bead glass
18
.
Although it is not shown in
FIG. 2
, the amount of the thermoelectrons emitted from the cathode
10
through heat generation of a heater installed at the inside of the cathode
10
is controlled by the cathode
10
and the voltage of the first electrode
11
, and is accelerated by the second electrode
12
. In general, the voltage amounting to approximately below 1000 volts is applied to the second electrode
12
and the fourth electrode
14
, and 20% to 40% of the voltage applied to the anode electrode
16
is applied to the third electrode
13
and the focus electrode
15
. In the meantime, an electrostatic lens formed inbetween the second electrode
12
and the third electrode
13
, and another electrostatic lens (it is also called a shear focusing lens), which is formed by the third electrode
13
, the fourth electrode
14
and the focus lens
15
, determines an incident angle, which is the angle of the electron beam
5
incident upon the prime lens. In fact, the prime electrostatic focusing lens (or the prime lens) is formed between the anode electrode
16
and the focus electrode
15
, when a high voltage ranging from 20,000 to 35,000 Volts is applied to the anode electrode
16
and about 20% to 40% of the same voltage is applied to the focus electrode
15
that is neighboring to the anode electrode
16
by the space about 1.0 mm.
Therefore, the electron beams formed in a triode portion including the cathode
10
, the first electrode
11
, and the second electrode
12
forms cross over therein. At first, the electron beams are focused by the shear focusing lens including the third electrode
13
, the fourth electrode
14
and the focus electrode
15
, and the electron beams are focused by the prime lens including the focus electrode
15
and the anode electrode
16
for the second time, and then forms an image on the screen.
Meanwhile, to actually utilize such electrodes, there needs a process called a beading process for fastening the center of those electrodes and relative positions. In the process, the positions of the electrodes are determined using a beading jig, and the relative position of each electrode is fastened by compressing a bead glass
18
that has been heated at a high temperature over 1000° C. to the electron gun and cooling the heated bead glass.
FIG. 3
illustrates the beading jig
21
generally being used now. Here, mandrills
22
a
,
22
b
and
22
c
are used for determining the position of the three electron beam passage holes. The diameter of the mandrill is approximately 10 to 20 &mgr;m smaller than that of the electron beam passage holes, which is inserted into each electrode in sequence, and a spacer
23
for adjusting the space between the electrodes is used.
As the cathode ray tube gets highly dense, particularly the diameter of the electron beam passage hole of the first electrode
11
is very small like below 0.4 mm, and the thickness of the peripheral electrode of the beam passage hole is very thin like around 0.1 mm. Therefore, once the mandrill is inserted and the beading process is carried out, the electron beam passage holes are severely deformed, often causing defocusing or aberration.
To overcome the problems described above, what people tried was installing separate guide holes
30
a
and
30
b
to determine the positions as shown in
FIG. 4
, and added guide pins
34
a
and
34
b
to the beading jig
31
as depicted in
FIG. 5
to make the beading process possible using the guide holes. In addition, the mandrills
32
a
,
32
b
and
32
c
do not have their own pins because they should not be in touch with the electron beam passage holes of the first electrode
35
and the second electrode
36
. It is so because if the mandrills
32
a
,
32
b
and
32
c
do not pass through the electron beam passage holes of the first electrode
35
and the second electrode
36
, the beam passage holes
35
a
,
35
b
and
35
c
of the first electrode
35
would not be damaged by the force generated from the compression of the bead glass during the beading process, so the defocusing problem due to the electrode deformation can be successfully prevented.
However, now that each electron beam passage hole associated with the first electrode
35
, the second electrode
36
and the third electrode
37
is not necessarily set up on the basis of an individual electron beam passage hole, but the position determining holes, or the guide holes
30
a
and
30
b
, set up the passage holes, and the positions of each electron beam passage holes that influence the actual electron beam's focus are largely determined by the relative positions of the center of the guide holes and the electron beam passage holes, it is always possible to have the defocusing problem due to a discrepancy between the centers of the beam passage holes by one-sided halo.
With reference to
FIG. 6
, the followings explain how to calculate the aberration of the electron beam passage holes of the triode electrode in accordance with the relation between the guide holes
30
a
and
30
b
of the triode electrode and the guide pins
34
a
and
34
b
of the beading jig
31
.
Typically, the size of the guide holes
30
a
and
30
b
has ±5 &mgr;m of precision, and the distance between two guide holes, being a relatively large value, has ±10 &mgr;m of precision. Suppose that the size of the guide holes is 1.000±0.005 mm, and the distance between the two guide holes is 20.0±0.010 mm. Then, the size of the guide pins
34
a
and
34
b
of the beading jig
31
for production is determined as follows. First of all, the minimum size of the guide holes
30
a
and
30
b
, 0.995 mm, is subtracted by twice of the deflection distance aberration between the two guide holes, 0.020 mm (2×0.010 mm), to yield 0.975 mm. Then, 0.975 mm is again subtracted by twice of the margin for the guide holes
30
a
and
30
b
, and the guide pins
34
a
and
34
b
for securing assembly, 0.010 mm (2×0.005 mm), to yield 0.965 mm. Of course, it is always possible that the guide pins
34
a
and
34
b
have manufacturing error, but since it is relatively very small, the error can be disregarded. This means that the final size of the guide pins
34
a
and
34
b
is 0.965 mm, and a possible maximum position error according to the sizes of the guide holes and the guide pins is (1.005−0.965)/2, or 0.020 mm.
Because
LG Philips Displays Korea Co., Ltd.
Patel Nimeshkumar D.
Perry Anthony
LandOfFree
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