Note: Descriptions are shown in the official language in which they were submitted.
RCA 68805A/70641
3t39~ j
This invention relates to shadow mask type cathode ray
tubes and, particularly, to such tubes having corrugated
shadow masks supported therewithin.
In a shadow mask tube, a plurality of convergent
electron beams are projected through a multi-apertured color
selection shadow mask to a mosaic screen. The beam paths
; are such that each beam impinges upon and excites only one
kind of color-emitting phosphor on the screen. General]y,
the shadow mask is attached to a rigid frame, which in
turn is suspended within the picture tube envelope.
Presently, all commercial color picture tubes have
a front or viewing faceplate portion that is either
"
spherical or cylindrical. However, it is desirable to
!' 15 develop a tube having a generally flat faceplate. There
~ are problems that must be solved before a tube having a
3 flat faceplate is commercially feasible. A major problem
involves the shadow mask. According to prior art tube
design concepts, in tubes having curved faceplates, the
shadow mask is similarly curved so that it somewhat parallels
the faceplate contour. Thus, in keeping with these prior
art concepts, in a tube with a flat faceplate, the
'i corresponding shadow mask should also have an almost flat
contour. However, such a mask has insufficient self-
supporting strength or rigidity. One way to provide this
strength or rigidity would be to put the mask under
tension as is done in some commercially available tubes
having cylindrical faceplates. However, tension methods
require undesirable and expensive frame structures.
Another way of providing strength to the mask would be
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1 give it some degree of contour. However, this may raise a
problem of doming during an initial period of tube operation,
caused by shadow mask heating and expansion when the mask is
bombarded by the electron beams.
In accordance with the invention, a shadow mask
type of cathode ray tube is improved by including a mask having
parallel corrugations. In one species of the invention, the
distance between adjacent peaks of the corrugations is at
least twice as great as the spacing between adjacent apertures
of the mask. In another species of the invention, the mask
is at least partially suspended in the tube by support means
attached at a plurality of points-along the corrugated sides
of the mask.
In the drawings:
FIGURE l is a plan view,partly in axial section, of a
shadow mask cathode ray tube having a flat faceplate.
FIGURE 2 is a partially cut-away top view of a
cathode ray tube in accordance with an embodiment of the
present invention.
FIGURE 3 is a perspective view of the mask-faceplate
assembly of the tube of FIGURE 2.
FIGURE 4 is a perspective view of a modification of
' the mask-faceplate assembly of FIGURE 3.
FIGURE 5 is a top view of a mask-faceplate assembly
, 25 suggested by prior art.
FIGURE 6 is an enlarged top view of the mask-face-
plate assembly of the tube of FIGURE 2.
FIGURES 7 and 8 are enlargements of the portions
designated 7 and 8 in FIGURES 5 and 6, respectively.
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RCA 68aO5A/70691
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1 FIGURES 9, 10 and 11 are back, top and side views,
respectively, of a cathode-ray tube cylindrical mask-faceplate
assembly.
FIGURES 12, 13 and 14 are back, top and side views,
respectively, of a cathode-ray tube spherical mask-faceplate
assembly.
FIGURE 15 is a top view of a mask-facepla-te assembly
of a cathode-ray tube in accordance with another embodiment
of the present invention.
FIGURE 16 is a top view of a mask-faceplate assembly
of a cathode-ray tube in accordance with yet another embodiment
of the present invention.
FIGIJRE 17 is a top view of a mask-faceplate assembly
of a cathode-ray tube in accordance with still another
embodiment of the present invention.
- FIGURE 18 is a section view taken at lines 18-18 in
FIGURE 17.
FIGURE 19 is an enlarged partial section view taken
at lines 19-19 in FIGURE 18.
FIGURE 1 illustrates a flat-face color television
picture tube 16, whose apertured mask 18 has a reverse
curvature to give it greater strength. A mask panel assembly
similar to that incorporated in the tube 16 of FIGURE 1 is
depicted in FIGURE 2. FIGURE 2 illustrates an apertured-mask
color television picture tube 20 constructed in accordance
with the present invention, comprising an evacuated glass
envelope 22. The envelope 22 includes a rectangularly-shaped
flat faceplate panel 24, a funnel 26, and a neck 28. A
three-color phosphor-viewing screen 30 is supported on the
3 inner surface 32 of the faceplate panel 24. An electron-gun
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RCA 68805A/70641
assembly 34, positioned in the neck 28, includes three electron
guns (not shown), one for each of the three color phosphors
on the viewing-screen 30. A rectangular apertured mask 36 is
positioned in the envelope 22 adjacent the viewing screen 30.
The electron-gun assembly 34 is adapted to project three elec-
tron beams through the apertured mask 36 to strike the viewing-
screen structure 30 with the mask 36 serving as a color
selection electrode. A magnetic deflection yoke 38 is
positioned on the envelope 22 near the intersection of the
funnel 26 and the neck 28. When suitably energized, the yoke
38 causes the electron beams to scan the screen 30 in a
rectangular raster.
The apertured mask 36, further depicted in FIGURE 3,
is corrugated or somewhat sinusoidally curved along the
horizontal axis ~in the direction of the longer dimension of
the mask) with the corrugations extending vertically (between -
long sides of the mask or in the direction of the shorter
dimension of the mask). It should be understood that the term
corrugated is herein defined broadly to include various shapes
including a sawtooth waveform as well as sinusoidal shapes.
Although the mask 36 is shown without any curvature vertically,
it should be understood that a mask having some curvature along
the vertical axis also is included within the scope of the
present invention, an example of which is presented below.
The mask 36 includes a plurality of slit-shaped
apertures 40 aligned in vertical columns. In order to keep
acceptable line formation on the screen, that is maintaining
even spacing or nesting between the phosphor lines, the
horizontal spacing between aperture columns is varied as a
function of the spacing between the mask 36 and the screen 30
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RCA 68805A/70641
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1 according to the following formula:
3sq
a =
where
"a" is the horizontal spacing between aperture
columns,
"~" is the spacing between the mask and the
faceplate,
"L" is the distance from the screen to the
electron beam deflection plane, and
"s" is the spacing between a center and outer
beam at the deflection plane.
Therefore, once the mask contour "q" is established to obtain
desired strength and/or rigidity, the parameter "a" is allowed
to vary horizontally over the mask in accordance with such
mask contour. Generally, the peak-to-peak wavelength dimension
(e.g. from point A to point B) of the corrugated or sinusoidal
variation in the mask should be at least twice as great as the
spacing between adjacent apertures.
As shown in FIGURE 3, the apertured mask 36 is mounted
to the faceplate panel 24 by a plurality of flexible supports
42 positioned along corrugated sides of the mask 36 and rigid
supports 44 positioned at the straight sides of the mask 36.
Each of the flexible supports 42 is L~shaped, comprising two
flanges 46 and 48, and is attached to the faceplate panel 24
at the bottom flange 46 by suitable means such as by being
sealed with a glass frit. The second flange 48 of each flex-
ible support 42 is cantilevered out from the faceplate panel24 and provides the flexible portion of the support 42. The
mask 36 is connected to the flexible supports 42 on the
corrugated sides at points of inflection where the direation
of curvature of the mask changes. Such points are on the
centerline of the corrugated or sine-wave mask shape. The
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RCA 68805A/706~1
1 cantilever structure of the support:s 4~ permits flexibility
in the direction of the corrugationc3, i.e. in the vertical
direction (as determined by the tube in its normal operating
orientation) thus allowing for therrnal expansion of the mask
in this direction. Since the phosphor lines extend vertically,
there is no misregister caused by mask expansion in the
vertical direction. In the perpendicular or horizontal
direction, however, the supports 42 are very rigid.
Correspondingly, the supports 44 on the side of the mask 36
are rigid in both the horizontal and vertical directions and
hold the center of the mask from movement.
An alternatlve version of a mask supporting embodiment
that provides a similar type of mask suspension is shown in
FIGURE4 . In this embodiment, the flexible supports at the
top and bottom of the mask are replaced with two metal bars
50 having low expansion characteristics relative to the mask
material. For example, if the material of the mask 36 is
steel, the bars 50 may be invar. The mask 36 is connected to
the support bars 50 along the centerline of its corrugated
20 or sine-wave shaped sides. The bars 50 in turn are mounted to
the faceplate panel 24 by flexible supports 52 that are
attached near each end of each bar 50. Side supports 54 for the
mask 36 are attached to the short sides of the mask and
perform -the same function as described with respect to the
supports 44 of the previous embodiment, that of fixing the
position of the center of the mask.
An advantage of the mask support of the present invention
can be appreciated by comparing an embodiment of the
invention with an embodiment suggested by the prior art.
FIGURE 5 shows a flat faceplate 56 having a spherically
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RCA 6~805A/70641
1 contoured apertured mask 58 mounted thereto by means of
rigid support members 60. FIGURE 6 shows a similar view of
the faceplate and mask assembly of the tube of FIGURE 2. The
dashed lines 59 and 37 in FIGURES 5 and 6, respectively,
represent the configura-tion the masks take in a condition
of thermal expansion due to bombardment by the electron
beams. The spherical mask 58 of FIGURE 5, being held at
its edges by -the supports 60, domes substantially toward
the faceplate 56. However, the mask 36 of FIGURE 6 is held
at various points by the supports 42 and therefore only
domes between these support points.
The net effect of this doming is illustrated in
FIGURES 7 and 8, which are enlargements of the indicated
areas of FIGURES 5 and 6, respectively. As shown in FIGURE
7, the landing spot of an electron beam 6~ passing through
an aperture 64 of the heated domed mask 59 is displaced a
distance E from the landing spot of an electron beam 62
passing through an aperture 68 of an unheated mask 58.
~owever, in a tube using the present invention, displacement
of the heated mask is much less. FIGURE 8 shows the
position of the heated mask 37 only slightly moved from
the position of the unheated mask 36. The resultant shift
of the beam spot is designated E', which from the
illustrations can be seen to be considerably less than the
shift encountered with the prior art tube because of the
reduced mask movement.
Although the invention has been described with
respect to a flat facepla-te, it should be appreciated that
the invention is also applicable if the faceplate has
curvature. FIGURES 9,10 and 11 depict a faceplate panel
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RCA 68805A/70641
l37
1 assembly 70 having a rectangular faceplate 72 that is
cylindrically curved and to which an apertured mask 74 is
mounted by means of flexible and rigid supports, 76 and 78,
respectively. The mask 74 is corrugated with the points of
inflection of the corrugations lying in a curved or
cylindrical plane. The flexible supports 76 extend from
the faceplate 72 and are attached to the long sides of
the mask 74 at the points of inflection. The rigid
supports 78 also extend from the faceplate 72 and are
attached to the mask 74 at the center of its short sides.
In another embodiment, illustrated in FIGURES 12, 13
and 14, a faceplate panel assembly 80 is shown with a
spherically curved faceplate 82. A mask 84 is attached
to the faceplate 82 by means of flexible and rigid
supports 86 and 88, respectively. The mask 84 is
spherically curved similar to the faceplate 82 and has
^vertically extending corrugations superimposed thereon.
~ike the previous embodiment, the flexible supports 86
extend from the faceplate 82 and are attached to the
points of inflection along the long sides of the mask
84 and the rigid supports 88 are attached to the centers
of the short sides of the mask.
Although the preceding embodiments have been shown
with the corrugated masks attached to the supports at
the points of inflection at the corrugated sides of the
~asks, the scope of the invention can include other
mounting points of mutual correspondence. For example, the
mounting points may be at any other regular points on the
i mask that are a fixed distance from a reference plane, such
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1 as at the points on the mask nearest the faceplate panel.
FIGURES 15 and 16 show such a mask support system. In
FIGURE 15, a corrugated mask 90 is shown mounted to a flat
faceplate panel 92 by means of flexible and rigid supports
94 and 96, respectively. The flexible supports 94 are
affixed to the panel 92 and are attached to the corrugated
sides of the mask at points on the mask closest to the
faceplate panel.
Correspondingly, FIGURE 16 shows a corrugated mask
98 mounted at its corrugated sides to a faceplate panel
100 with metal bars 102 which are attached to and at least -
partially supported by flexible supports 104 similar to
those shown with respect to the embodiment of FIGURE 4.
It should be appreciated, however, that the effect of doming
in the embodiments of FIGURES 15 and 16, although much less
than in the single arch example o~ FIGURE 5, will be somewhat
greater than in the embodiment of FIGURE 6 (wherein the mask
is supported at points of inflection) since the mask span
between supports is greater.
In all of the foregoing embodiments, the mask
supports have been shown extending directly from the
edges of the viewing portion of the tube faceplate as
illustrated examples. This is only one possible arrangement
of the supports within the scope of the present invention.
The supports also can be extended from the sidewalls of
the tube faceplate instead of from the viewing portion.
Alternatively, the supports can also extend between the mask
and a frame which in turn is suspended within the tube
faceplate.
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1 FIGURES 17, 18 and 19 illustrate another embodiment
according to the present invention, wherein a corrugated
rectangular apertured mask 110 is attached to a peripheral
frame 112. The frame 112 is suspended within a flat
rectangular faceplate panel 114 by a plurality of spring
supports 116 that are removably mounted on conical studs 118
embedded within a peripheral sidewall 120 of the panel 114.
The attachment of the mask 110 to the frame 112 is made by
means of a plurality of tabs 122 formed integrally as part
of the mask structure. Each tab 122 extends from a side of
the mask 110 at a point of inflection on the corrugated
cross-section and is welded to a flange of the frame 112.
Two additional tabs 124 are iocated at the center of the
two opposite vertical sides of the mask to prevent vertical
displacement of the mask during tube operation.
The tabs 122 and 124 are preferably formed by adding
their outline to the photographic masters that are used to
expose the aperture pattern during mask fabrication. The
final shape of the mask and tabs are then defined when the
mask is etched.
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