Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2001-08-14
2003-01-21
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C174S1130AS, C174S171000
Reexamination Certificate
active
06509693
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a core wire for a filament adapted to be heated for driving to emit electrons therefrom, such a filament and a method for mounting such a filament. Also, the present invention relates to a fluorescent display device for carrying out desired display due to impingement of electrons on phosphors and a method for manufacturing such a fluorescent display device. The fluorescent display devices include a write head for carrying out desired optical writing on a photosensitive element due to impingement of electrons emitted from a filament thereon.
Now, a conventional fluorescent display device of such a type as described above which has been generally known in the art will be described with reference to
FIGS. 6 and 7
, wherein
FIG. 6
is a partially cutaway perspective view generally showing a structure of the fluorescent display device and
FIG. 7
is a partially enlarged sectional view of the fluorescent display device of
FIG. 6
which is taken in a direction in which filaments are arranged stretchedly or while being stretched.
The conventional fluorescent display device generally designated at reference numeral
31
in
FIGS. 6 and 7
, as shown in
FIG. 6
, includes a box-like envelope
32
of which an interior is kept at a high vacuum. The envelope
32
includes a box-like casing
36
which is constituted by an anode substrate
33
made of an insulating material, a front cover
34
made of an insulating and light-permeable material and a frame-like side plate
35
made of an insulating material.
The anode substrate
33
, as shown in
FIG. 7
, is formed on an inner surface thereof positioned in the envelope
32
with a wiring layer (wiring conductor)
37
in a predetermined pattern depending on a display pattern
38
. The wiring layer
37
may be made of, for example, an thin Al film. The wiring layer
37
is formed thereon with an insulating layer
39
laminatedly or by lamination. The insulating layer
39
is formed at portions thereof corresponding to display segments
40
of the display pattern
38
with through-holes
41
, via which the wiring layer
37
is exposed. The through-holes
41
with which the wiring layer
37
is exposed each are filled therein with a conductive layer
42
by printing of a conductive paste.
The insulating layer
39
, as shown in
FIG. 7
, is formed on a surface thereof facing the front cover
34
with anode conductors
43
in a discrete manner in correspondence to the display segments
40
of the display pattern
38
so as to be electrically connected to the wiring layer
37
through the conductive layers
42
. The anode conductors
43
may be formed of a thick film by printing. The thick film may be made of, for example, either a graphite paste constituted by a graphite powder and an organic binder or an Al paste. This provides anodes
45
each for every display segments
40
of the display pattern
38
.
Above the anodes
45
, as shown in
FIGS. 6 and 7
, are arranged mesh-like grids
46
, above which cathodes
47
each constituted by a filament are arranged stretchedly or while being stretched.
The filament for each of the cathodes
47
arranged in the fluorescent display device
31
is made by coating carbonate of Ba, Sr or Ca on a tungsten core wire of from several microns to tens of microns in diameter. In order to permit each of the filaments to emit thermions, it is required to feed the tungsten with electricity to heat the filament to a temperature within a range of between 600° C. and 650° C. For example, heating of the filament of, for example, 10 mm in length to a temperature of 650° C. supposing that it is at a room temperature (24° C.) during non-heating causes the filament to elongate by about 0.3 mm because tungsten has a thermal expansion coefficient of 4.4×10
−7
. Such elongation of the filament by about 0.3 mm causes sagging of the filament, resulting in the filament contacting with the anodes
45
and grids
46
in the envelope
32
, leading to a failure in insulation. Also, such sagging of the filament causes vibration of the filament when the fluorescent display device is of the vehicle-mounted type or the like, to thereby adversely affect display of the fluorescent display device. More particularly, vibration of the filament acting as an electron emitting source causes display of the fluorescent display device to be vibrated in synchronism therewith, leading to flickering of the display, to thereby deteriorate visibility of the display.
In order to eliminate the above-described problem, the conventional fluorescent display device
31
is provided with a support structure for fixing each of the filaments while applying tension of a predetermined magnitude to the filament, to thereby prevent sagging of the filament due to thermal expansion thereof. The support structure is constituted by a support
51
acting as a stationary stretching member for fixing one end of each of the filaments and an anchor
52
acting as an elastic stretching member for elastically holding the other end of each of the filaments. This permits each of the filaments to be fixed at one end thereof on the support
51
and elastically held at the other end thereof on the anchor
52
, so that the filament may be elastically arranged between the support
51
and the anchor while being stretched therebetween.
Also, in place of the anchor
52
for elastically holding the filament, a structure which includes a coiled filament constituted by a coiled tungsten core wire formed at at least a part thereof with a coiled portion and a carbonate material electro-deposited on the coiled tungsten core wire, to thereby exhibit elasticity is known in the art. Such a coiled filament may be made as shown in FIG.
8
. More specifically, the coiled tungsten core wires each are fixed on a metal frame
62
while keeping a coiled portion
61
a
thereof stretched and then the metal frame
62
is placed in an electrolytic bath
64
in which an electrolytic carbonate solution
63
is filled. Then, a voltage at a predetermined level such as, for example, 60V is applied between the metal frame
62
and the bath
64
for a predetermined period of time (for example, 60 seconds). This permits the carbonate to be electro-deposited on the coiled tungsten core wires, resulting in coiled filaments
61
being provided. Then, the coiled filaments
61
thus provided each are welded to a metal member for fixing the filament.
Unfortunately, the above-described approaches each have a disadvantage. More particularly, the elastic anchor
52
of
FIG. 7
for absorbing sagging of the filament is expensive because it is required to subject a material for the anchor to etching and pressing. Also, manufacturing of the anchor
52
requires a holding plate for forming the anchor
52
into a frame-like shape. The holding plate must be formed into a thickness as large as 0.2 to 0.3 mm in order to overcome tension of the filament. Such an increased thickness causes the holding plate to be unsuitable for incorporation in an ultrathin fluorescent display device in which a distance between two substrates is as small as about 1 mm.
For example, use of a substrate material (for each of the anode substrate, front cover, side plate and the like) for the purpose of realizing an ultrathin fluorescent display device which has never been seen in the art causes a size of a package which permits the substrate to satisfactorily exhibit pressure resistance to be subjected to a restriction. Thus, it is required to arrange struts in the envelope. Also, the ultrathin fluorescent display device in which such thin substrates are arranged causes even a difference in level due to a thickness of the metal frame to apply stress to each of the substrates, leading to likelihood that a portion of the substrate through which the metal frame is led out cracks. Thus, it is required that the side plate is recessed at a portion thereof corresponding to a position of the flourescent display device of which the metal frame is led out by a depth corresponding to a thickness o
Ishikawa Kazuyoshi
Kogo Katsutoshi
Ogawa Yukio
Yonezawa Yoshihisa
Yoshimura Satoshi
Futaba Corporation
Tran Thuy Vinh
Wong Don
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