Electric lamp and discharge devices – Cathode ray tube – Plural beam generating or control
Reexamination Certificate
2000-12-18
2003-05-13
Kim, Robert H. (Department: 2882)
Electric lamp and discharge devices
Cathode ray tube
Plural beam generating or control
C313S412000
Reexamination Certificate
active
06563258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube, and in particular to a cathode ray tube capable of improving withstand voltage characteristics and displaying high-resolution color images by ensuring of high precision of dimensions and shapes of cup-shaped electrodes among a plurality of electrodes of an electron gun housed in its vacuum envelope.
Color cathode ray tubes such as a color picture tube and a display tube, which are typical cathode ray tubes, are widely used for reception of TV broadcast and monitors of various kinds of information processing equipment because of their high-definition image reproduction capability.
Color cathode ray tubes of such a kind have a vacuum envelope comprised of a panel, a neck and a funnel for connecting the panel and the neck, a phosphor screen formed on an inner surface of the panel, and an electron gun housed in the neck for projecting electron beams toward the phosphor screen. Especially, widely used are color cathode ray tubes employing an in-line type electron gun for projecting a plurality of electron beams parallel with each other in a horizontal plane.
FIG. 5
is a side view of an essential part of an embodiment of a configuration of an in-line type electron gun used for a color cathode ray tube, viewed in a direction perpendicular to a direction of the in-line arrangement of the electron beams.
In
FIG. 5
, reference numeral
31
denotes cathodes,
32
is a first electrode serving as a control electrode,
33
is a second electrode serving as an accelerating electrode, and the cathodes
31
, the first electrode
32
and the second electrode
33
form an electron beam generating section. Reference numeral
34
denotes a third electrode, and
35
is a fourth electrode.
In this example, the fourth electrode
35
is formed of two cup-shaped electrodes
35
a
and
35
b,
and they serve as two focus electrodes. Reference numeral
36
denotes a fifth electrode, and the fifth electrode
36
and the cup-shaped electrode
35
b
of the fourth electrode
35
form a main lens therebetween. Reference numeral
37
denotes a shield cup, which is welded to the fifth electrode
36
. The cathodes
31
and the first to fifth electrodes
32
-
36
are spaced with predetermined spacings and fixed in the predetermined order by a pair of insulator support rods (multiform glasses)
38
.
Reference numeral
39
denotes a stem, and the cathodes and the electrodes are supplied with display signals or operating voltages via stem pins
40
sealed through the stem
39
. Three electron beams are generated by the electron beam generating section which is a triode section comprised of the cathodes
31
, the first electrode
32
and the second electrode
33
, and are accelerated and focused by the third electrode
34
, the fourth electrode
35
and the fifth electrode
36
such that the three electron beams are subjected to a desired focusing action by the main lens formed between opposing end faces of the fifth electrode
36
and the electrode
35
b
of the fourth electrode
35
and then directed toward the phosphor screen.
In this type of an electron gun, the first electrode
32
and the second electrode
33
are plate-like electrodes, and the third electrode
34
, the fourth electrode
35
and the fifth electrode
36
are cup-shaped single-electrodes, respectively, or compound electrodes fabricated by welding together plural electrode members including a cup-shaped electrode member and a plate-like member, respectively.
FIGS. 6A
to
6
C are illustrations for explaining details of the fifth electrode
36
which is one of cup-shaped electrodes used in the electron gun of
FIG. 5
,
FIG. 6A
is a plan view of the fifth electrode
36
,
FIG. 6B
is a front view thereof, and
FIG. 6C
is a cross-sectional view of the fifth electrode
36
taken along line VIC—VIC of FIG.
6
A.
As shown in
FIGS. 6A
to
6
C, the cup-shaped fifth electrode
36
has a generally rectangular flange
36
f
and a tubular portion
36
b
rising approximately perpendicularly and continuously from the flange
36
f.
The tubular portion
36
b
has an approximately oval opening in a cross section perpendicular to an axis
36
c
of the tubular portion
36
b,
that is, an approximately oval opening of the shape having two arcs
36
b
1
at both ends thereof and two straight lines
36
b
2
at the central portions joining the two arcs
36
b
1
. The three electron beams pass through the approximately oval opening. Reference numeral
36
d
denotes a turned-up portion, which is turned up inwardly from a top surface
36
e
of the tubular portion
36
b
to extend toward the flange
36
f.
In some cup-shaped electrodes, the turned-up portion
36
d
is omitted.
The flange
36
f
comprises arc-shaped flange portions
36
f
1
and straight flange portions
36
f
2
which are formed outside of the tubular portions
36
b.
A structure of such a cup-shaped electrode is disclosed in Japanese Patent Application Laid-open No. Sho 55-74036 (laid-open on Jun. 4, 1980), for example.
Generally, such cup-shaped electrodes are fabricated by punching out sheets of desired dimensions from a long strip of a material, and then performing various operations such as the drawing of the sheets, heat treatment, and putting the drawn parts in final shape.
SUMMARY OF THE INVENTION
In the above prior art cup-shaped electrode, there has been a problem in that defects such as defective outside dimensions occur in the flange
36
f
after the drawing process, as indicated by broken lines
61
,
62
in
FIGS. 6A and 6B
.
As described above, such cup-shaped electrodes are fabricated by the process steps including the drawing process steps. The tubular portion
36
b
has an approximately oval cross section in a plane perpendicular to the axis
36
c
of the tubular portion
36
b
, and consequently, in the drawing process step in which the tubular portion
36
b
is formed to rise from the flange
36
f
, the arc-shaped portions
36
w
1
of the tubular portion
36
b
are subjected to drawing action, but the straight portions
36
w
2
of the tubular portion
36
b
are subjected to bending, action, that is to say, the work piece is subjected to different forming actions depending upon the positions of the work piece in the same processing step. As a result, the arc-shaped portions
36
w
1
and the straight portions
36
w
2
differ from each other in the amount of excess material capable of flowing elsewhere, and consequently, the thickness of the arc-shaped flange portions
36
f
1
becomes greater than that of the straight flange portions
36
f
2
.
The parts as drawn are subjected to heat treatment, and then are press-forming the whole parts including the flange
36
f
into final shape by using a die. If the parts of the above-mentioned shape were intended to be press-formed into final shape, it was difficult to ensure the flatness of the flange
36
f
and the parallelism of the flange
36
f
with the top surface
36
e,
and further the tubular portion
36
b
tilted with respect to the normal to the flange
36
f
, and as a result, the desired shapes and dimensions of the electrodes were not obtained, and further desired interelectrode spacings and concentricity between electron beam apertures which are important factors in withstand voltage and resolution characteristics could not be obtained in assembling the electron gun, and consequently adverse effects were caused to characteristics of the color cathode ray tube.
As measures to solve such various problems, there is a special technique to press-form the thick arc-shaped flange portions
36
f
1
by pressing the flange portions
36
f
1
against the shaping die strongly, but it complicates the processing steps and also the arc-shaped flange portions
36
f
1
expand locally and outwardly as indicated by broken lines
62
in
FIG. 6A
, and edges of the arc-shaped flange portions
36
f
1
become pointed in a longitudinal cross section and cause a problem in withstand voltage characteristics.
On the other hand, to prevent the above-mentioned local and outward ex
Mera Takeshi
Miura Masato
Antonelli,Terry,Stout & Kraus, LLP
Gemmell Elizabeth
Hitachi , Ltd.
Kim Robert H.
LandOfFree
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