Note: Descriptions are shown in the official language in which they were submitted.
WO 92/02947 2~ 6~ 3~ 7 Pcr/USgl/04997
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THIN CONFIGU~ATION
FLAT FORM VACUUM-SEALED ENVELOPE
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Background of the Invention
This is a continuation-in-part of application serial no. 07/562,251 filed
S August 3, 1990.
This invention relates in general to the construction and operation of
glass envelopes containing internal elements and/or gases under partial
vacuum, such as lamps and various electronic devices. More particularly,
this invention relates to vacuum tubes~ incandescent lamps, fluorescent
i 10 lamps and other devices which employ glass envelopes to allow internal
elements to operate in isolated atmospheres under partial vacuum
conditions.
Vacuum tubes, incandescent lamps, fluorescent lamps, electronic devices
and the like employ glass envelopes that enclose the internal elements in
15 gaseous atmospheres at very low pressure or partial vacuum conditions.
A fundamental problem with such a type of glass envelope is that it must
withstand atmospheric pressure without breaking. Prior art designs
achieve this by form;llg the envelopes in spherical, tubular, or
combina~ion spherical/tubular shapes which have inherent resistance to
20 the externally applied compression forces of atmospheric pressure.
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The need has been recognized for vacuum-sealed glass envelopes which
have a very thin and flat configuration for use in vacuum-sealed devices
of the type described. Among the devices which would benefit through
the use sf thin configuration flat form envelopes are electron tubes in
5 which the elements are arrayed sequentially or in a plane. Other
examples are vacuum fluorescent or incandescent filament display
; devices having elements which are viewed through the glass envelope.
Heretofore such devices have used flat glass envelopes, but their size has
been severely limited because as the span vidth increases the glass
10 thickness must correspondingly increase to resist atmospheric pressure.
Other examples that could benefit from flat form envelopes are lamps,
such as fluorescent lamps, which heretofore have been produced in
tubular form so as to withstand atmospheric pressure.
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In the prior art, glass vacuum envelopes of flat configuration can be
15 constructed su~lcient to sustain atmospheric pressure by using thick glass
plates, but in such case the vacuurn tube becomes undesirably thick and
heavy. For example, a flat fluorescent lamp of 154 rnrn x 112 rnm planar
dimensions requires a heavy glass of 18 mm thickness weighing 450
grams. A fluorescent lamp of such a design is impractical for many
20 applications, such as LCD back lighting.
The prior art includes panel lamp designs of the type disclosed in U.S.
patent no. 3,226,950 to Christy and U.S. patent no. 3,646,383 to Jones et
al. As disclosed in those patents, the front and back plates of the panels
are shaped with multiple embossments that match when fitted together
25 to create a labyrinth channel. The panels are of relatively large scale
with a thickness on the order of one inch or more. Wide flat bearing
surfaces are forrned between the channels. This creates brightness
uniformity problerns. In the patents the provision to alleviate the
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. brightness uniformity problem requires special shapes and dimensions in
the walls of the embossments.
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Certain prior art flat vacuum tube designs have been proposed in which
separate support elements or other artifacts are inserted between the
S front and back glass plates. This technique is commonly used in many
types of display devices. An example is United States patent 4,767,965
to Yamano, et al. In the Yamano patent flat glass plates are supported
by separate spacer pieces which can be either glass pipes, glass balls, half
discs ar mounds of deposited frit material. Moreover, the use of the
10 separate spacers increases the complexity and cost of fabrication, and the
spacers can be interruptive or incompatible with the vacuum tube
function. For example, the spacers can create non-lighted areas when
used within a ~lat fluorescent lamp.
Objec~nd Summarv of the Invention
15 It is a general object of the invention to provide a vacuum-sealed
envelope of very thin and flat configuration for use in vacuum tubes,
incandescent lamps, fluorescent lamps, electronic devices and other
- structures in which internal elements and/or gases are contained under
; partial vacuum conditions.
: 20 Another object is to provide a vacuum-sealed envelope of the type
described which is in flat form for enhancing the spatial relationship of
the elements and parts mounted internally within the envelope, such as
in a sequential element array or in a planar array.
Another object is to provide a flat forrn envelope of the type described
25 which provides enhanced visual characteristics, such as for vacuum
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fluorescent or incandescent filament display devices in which elements
are actually viewed through the glass envelope.
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Another object is to provide a vacuum-sealed envelope of the type
described which provides a more desirable overall form factor in relation
- 5 to the equipment into which the envelope must fit, such as the back light
for a liquid crystal display, instrument panel, aircraft lighting, surface
mounted lights and the like.
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- The invention in summary provides a thin configuration vacuum
envelope comprising, in certain embodiments, a flat wall plate spaced in
10 parallel relation from a shaped wall plate. The shaped plate is integrally
formed with a support structure comprised of spaced-apart ridges having
side walls which converge together at apexes and support the opposing
surface of the flat plate. The ridge apexes contact the plate at narrow,
substantially line contact paths which produce minimal degradation of
15 brightness uniformity. The cavity between the plates is hermetically
sealed for confining elements of the lamp or other device and/or gases
within a partial vacuum. In other embodiments, the envelope comprises
a pair of shaped wall plates having projecting portions which are in
contact when the plates are mounted together.
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20 The foregoing and additional objects and features of the invention willappear from the following specification in which the several
embodiments have been described in connection with the accompanying
drawings.
Brief Description of the Drawin~
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25 FIG. 1 is a perspective view, partially cut away, of a flat fluorescent lamp
illustrating one preferred embodiment of the invention;
W092/02947 2a57`377PCI/US91/04997
~IG. 2 is a cross-sectional view, to an enlarged scale, of the lamp of
: FIG. 1;
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FIG. 3 is an enlarged cross-sectional view of portions of the channel
segments of the lamp of FIG. 1;
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5 FIG. 4 is a schematic view of another embodiment providing a flat lamp
with a parallel channel pattern;
FIG. 5 is a schematic view of another embodiment providing a flat lamp
with a serpentine cbannel pattern;
FIG. 6 is a schematic view of another embodiment providing a flat lamp
10 having a plurality of serpentine channels which are clustered together.
.
FIG. 7 is a perspective view, partially cut away, of a flat fluorescent lamp
:. illustrating one preferred embodiment of the invention;
.
: FIG. 8 is a fragmentary cross-sectional view, to an enlarged scale, of a
portion of the lamp of FIG. 7;
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Detailed Description of the Invention
Referring to the drawings, FIGS. 1, 2 and 3 illustrate one preferred
:~ embodiment of the invention providing a flat form fluorescent lamp 10.
While the invention will be described in relation to fluorescent lamp
applications, it is understood that the invention encompasses other
20 applications, such as vacuum tubes, incandescent lamps, electronic
devices and various other sirnilar devices of the type incorporating glass
.
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envelopes enclosing a partial vacuum in which the internal elements
operate and/or in which gases are contained.
Fluorescent lamp 10 is compnsed of a shaped wall plate 12 mounted
over a flat wall plate 14 to provide a thin, flat forrn envelope for
5 confining a partial vacuum or gaseous atmosphere. The wall plates are
comprised of a suitable transparent or translucent vitreous material such
as clear glass.
In a typical application, the flat plate is the back side of the lamp while
the shaped plate is the front side through which light is transrnitted. In
10 other applications for the lamp, the flat plate could be the front side for
transmitting light. The non-light-transmitting back side could be
fabricated from an electrically conductive substrate, preferably metal,
covered with a glass layer. The substrate would be a suitable metal such
as stainless steel with therrnal expansion properties compatible with the
15 glass of the layer. The side of the back plate with the glass layer would
face the front plate and be sealed about the outer periphery. Depending
upon the reqllirements of a particular application, the metal substrate
with its glass layer could define either the shaped plate or the flat plate
:~ of the envelope.
20 A support structure is integrally formed on the inside of the shaped plate
and comprises a plurality of spaced-apart ridges 16, 18, 20 which project
into juxtaposition with the opposing inner surface 22 of the flat plate.
The ridges serve as spacers which support the plates in parallel, spaced-
apart relationship to forrn elongate cavities or channels 24-30 between
25 the ridges. As required, the ridges can be sealed to the flat plate by
means of a glass frit for sealing between the adjacent channels.
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As best shown in FIG. 3, the plate ridges 16-20 are formed with a cross
section in which a pair of side walls 32, 34 converge at a predetermined
included angle ,~. The side walls of each ridge merge at a sharp apex 35
that contacts inner surface 22 of the flat plate along a very narrow
S contact path, which can be considered substantially a line contact. The
side wall angle ,s preferably is in the range of 40 to 90, and in the
illustrated embodiment this angle is 90.
The configuration and size of the wall plates in the invention provides
implosion resistance against atmosphenc pressure when the channels are
10 evacuated. Depending upon the particular application, the plate wall
thickness Tp is principally a function of the span width Wr between the
ridges. With a relatively large span width Wr the plate thickness Tp is
correspondingly greater so that the plates have sufficient structural
strength for implosion resistance. The invention also provides a specific
15 cross-sectional dimensional aspect ratio Wr:HC in the range of 5:1 to
10:1. The dimensional aspect ratio HC:Tp is also in the range 1.5:1 to
3:1. In a typical application for a fluorescent lamp where the charmels
are sized so that Ws = 0.400" and ~c = 0.0607 then the wall plate
thickness Tp is sized in the range of 0.02" to 0.045't. This produces an
20 overali lamp thickness Tl in the range of 0.100" to 0.150".
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The preferred method of fabricating the shaped wall plate is by use of a
suitable mold, not shown, having surfaces which correspond to the
desired shape. The mold is heated, and then pre-heated glass sheets are
pressed between the mold surfaces so that the plastic glass flows into
25 conformance with the mold curvature. The flat and shaped wall plates-
are then assembled together so that the ridges contact the opposing flat
plate. A small spacing, not shown, is initially provided along the
peripheral rims of the plates to facilitate forming a vacuum tight seal. A
suitable glass frit, not shown, is glazed in the peripheral spacing to seal
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the edges of the envelope. Discharge electrodes 36, 38 are then
mounted on a pair of electrode substrates 40 and 42 which are inserted
at opposite ends of the cavities before the plates are sealed. Inleads 44,
46 are printed or otherwise adhered to the substrates for connecting the
S electrodes with a suitable AC drive control circuit, not shown.
Either or both of the inner surfaces 22 and 48 of the respective glass
plates 12 and 14 are coated with a suitable activated powdered phosphor
such as Magnesium Tungstate or calcium
Fluorochlorophosphate:Antimony:Manganese. The cavities 24-30 are
10 exhausted to a partial vacuum by means of suitable exhaust tubes (one is
shown at 50) or other means. An ionizable medium comprising a
mixture of inert gas such as Argon and a small percentage of Mercury
gas is then charged into the cavities. Gas pressure v~rithin the gas
cavities preferably is within the range of three to thirty torr.
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15 During operation free electrons are accelerated by the electric field
applied between the electrodes at opposite ends of the channels. When
these electrons collide with neutral atorns/molecules the latter are
ionized when sufficient voltage is applied. This creates ion-electron
pairs. The ions are swept to the electrode surfaces and can provide
20 secondary electrons when colliding with the electrode surfaces. These
secondary electrons are swept toward the other electrode creating
additional ion-electrons. At sufficient voltage an avalanche or arc occurs
causin~ the gas to be highly ionized creating many ion-electron pairs as
well as many excited atoms/molecules. When these excited
25 atoms/molecules decay to their ground state they give off photons of
energy. The partial pressure of Mercury is particularly rich in radiating
ultraviolet photons. The phosphor coating absorbs the ultraviolet
radiation and re-radiates at wave lengths visible to the human eye.
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As required by the area size requirements of a particular application, the
length and width dimensions of the plates can be scaled up by repeating
or extending the various matrix patterns for the projecting portion
described in the foregoing embodiments.
S FIG. 4 illustrates an embodiment providing a flat lamp 51 in which the
channels are arranged in parallel paths. The shaped wall plate 52 is
formed with four spaced-apart ridges 54-60. When the ridges are
mounted in juxtaposition with the flat plate, five elongate parallel
channels 62 are defined for containing the gaseous atmosphere under
10 partial vacuum. Discharge electrodes 64, 66 are mounted in the
opposite ends of each channel. Inleads 68, 70 connect the electrodes
into a drive control circuit 72 which in turn receives power from ~AC
: source 74. Control circuit 72 synchronously drives all five channels by
simultaneously applying continuously variable voltages to the discharge
15 electrodes. Any suitable synchronous drive control circuit design can be
used for this purpose. When the channels are synchronously driven in
this manner, the voltage differentials between channels are not high,
thereby obviating the requirement to create tight interchannel sealing
along the ridges. There is little channel-to-channel breakdown across
20 the ridges even where the channel barriers are narrow and unsealed.
FIG. 5 illustrates another embodiment providing a flat lamp 76 having
multiple channels in a serpentine path for the flow of current through
the ionized gases. In the illustrated embodiment four channels 78 are
defined by three spaced-apart ridges 80-84 formed in a shaped plate 86.
25 Each ridge has an end 88 which terminates short of the ends of the
channels so that the ends of the adjacent channels are in open
communication. The terminated ends of the ridges alternate to define
the serpentine path. In this embodiment the lines of contact between
the ridges and the opposing flat plate are sealed to electrically isolate
wo 92/02947 2 0 ~ 7 3 7 7 -lo- Pcr/US9l/o4997
adjacent channels. The serpentine pattern creates relatively higher
; interchannel voltage potentials which would otherwise create channel-to-
channel breakdown across unsealed channel barriers. Discharge
electrodes 90, 92 are mounted at the closed ends of the channels on
5 either side of the envelope. Inleads 94, 96 connect the electrodes with a
drive control circuit 98 which in turn is coupled with AC power source
100. The size of the lamp envelope can be scaled up by increasing the
number ~f channels in the serpentine pattern, as required by the
particular application.
10 FIG. 6 illustrates an embodiment providing a flat lamp 102 having a
plurality of separate serpentine channels arranged in multiple clusters.
In the illustrated embodiment three clusters 104-108 are provided. Each
cluster is forrned by a pattern of three ridges, for example ridges 11~114
for cluster 104. Alternate ends of the ridges are terminated short to
15 provide open cornmunication between the ends of each channel pair in
the manner described for the embodiment of FIG. 5. Pairs of electrodes
116, 118 are provided for each cluster, and the electrodes are mounted
in the closed ends of the channels at either side of the respective
. clusters. An AC power source 120 and drive control circuit 122 are
20 connected to the electrodes through inleads 124, 126. Drive circuit 122
can either independently drive the clusters, or the clusters could be
driven in parallel, as required by the particular application.
The previously described parallel, serpentine or cluster serpentine
configurations can also be fabricated by the two shaped plate
25 construction described below. The line contact formed by opposing
ridges can be either glass frit sealed for prevention of voltage
breakdown, or not sealed if the voltage potential does not require
sealing. ;
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FIGS. 7 and 8 show another embodiment providing a fluorescent lamp
130 with shaped wall plates which are in facing relationship. Lamp 13û
is comprised of generally planar top glass plate 132 and bottom glass
plate 134 which are mounted together and sealed about their peripheral
5 edges 136 and 138. In the illustrated embodiment the top and bottom
plates are each formed with support structures which comprise a matrix
of projecting portions 140 and 142. The support structures are generally
arch-shaped in cross-section and form linear parallel ridges 144 and 146.
The linear portions of the plates which form the walls of the ridges
10 curve toward each other (see FIG. 8) where they are in bearing contact
along the apexes of the ridges. The curved walls create arch structures
which provide high column strength against compression forces.
The top and bottom plates are mounted so that their corresponding
ridges are in contact. The lines of contact along the matching ridges
15 provide the linear bearing areas 148 for the compression forces. The
ridges hold the flat portions of the top and bottom plates spaced apart at
a predetennined gap distance so that elongate, parallel cavities 150, 152
are formed between the two plates. All of the cavities are internally
. open to each other so that the cavities combine to form one sealed
20 envelope for confining the gaseous atmosphere under partial vacuum.
The length of the gas cavities, and the number of cavities, is dependent
upon the required size of the lamp. As an example, for a lamp surface
area of 77.42 cm2 the thickness of each glass plate is 0.7 mrn, the height
of each gas cavity is 1.4 mm, and the spacing between the ridges is
25 9.5 rnm. Each projecting portion extends 0.7 mm from the inner surface
of the respective plate, and the radius of curvature of each ridge wall is
1.5 mm.
The preferred method of fabricating the top and bottom plates is by use
of a suitable mold having surfaces which correspond to the desired shape
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of the plates. The mold is heated, and then pre-heated glass sheets are
pressed between the mold surfaces so that the glass flows into
conformance with the mold curvature. The top and bottom plates are
then assembled together so that the ridges contact each other. A small
5 spacing, not shown, is provided along the periphery of the plates to
facilitate forming a vacuum tight seal. A suitable glass frit, not shown, is
glazed in the peripheral spacing to seal the edges of the envelope.
Suitable electrodes 154 mounted on a pair of electrode substrates 155
and 156 are inserted at opposite ends of the cavities before the plates
10 are sealed. In addition, the inner surfaces 157 of the glass plates are
- coated with a suitable activated powdered phosphor such as Magnesium
Tungstate or calcium Fluorochlorophosphate:Antimony: Manganese.
The cavities 150, 152 are exhausted to a partial vacuum by means of an
exhaust tube 159. A mixture of inert gas such as Argon and a small
15 percentage of Mercury gas is then charged into the cavities. Gas
pressure within the gas cavities preferably is within the range of three to
thirty torr. A suitable power source, not shown, drives the electrodes
with AC voltage through an external circuit which connects through
conductors 158, 160 formed on the electrode substrates at opposite ends
20 of the lamp;
As required by the area size requirements of a particular application, the
length and width dimensions of the plates can be scaled up by repeating
or extending the various matrix patterns for the projecting portion
described in the foregoing embodiments. This can be achieved without
25 increasing the glass thickness because with the invention an enlargement
of the matrix pattern does not affect the column strength of the
individual modules or cells of the matrix.
The invention also contemplates that the projecting portions of the wall
plate support structure can be shaped in other configurations consistent
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with the particular material and wall thickness of the glass. The arch
; configuration of the projecting portions could also be varied inaccordance with particular requirements provided that adequate column
strength results. The walls of the projecting portions could also be
S substantially flat, and an example of this would be ridges of truncated
cross-sectional shape.
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While the foregoing embodiments are at present considered to be
preferred it is understood that numerous variations and modifications
may be made therein by those skilled in the art, and it is intended to
10 cover in the appended claims all such variations and modifications as fall
within the true spirit and scope of the invention.
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