Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to ~rojection television and
more particularly to an improved envelope for a projection tele-
vision tube, to a projection television tube incorporating the
envelope and to a process for forming the envelope.
Projection television is a well established teehniaue.
Ho~ever, because of the high cost involved in manufaeturing the
projection televisicn tubes used, projection television has ge-
nerally been limited to expensive, complieated, large screen
units which are both diffieult to install and expensive to main-
tain in satisfaetory alignment. Thus the eomplexity and eost ofthe presently available projection television tubes have eritieal-
ly eurtailed the development and aeeeptanee of projeetion tele-
vision systems for home entertainment, a use which could represent
a very high-volume market.
Projection television systems for color projection
commonly include three tubes each having a different color (eon-
veniently referred to as red, green and blue) projecting pictures
whieh are superimposed in registry on a common view sereen. Typ-
ically, the most efficient of sueh tubes incorporate the optics
of a Schmidt-t~pe projection system and comprise a target illu-
n,inatea in a single color by a suitahle specific phosphor as an
electron beam raster, a s~herical reflector directinq the light
around the peri~hery of the target and a eorrection lens for any
spherical aberration.
Wi~hin these tubes, certain dimensions are critieal, a
fact which has heretofore given rise to the high cost of con-
structing the pro~ection tube envelol~es to achieve a high level
of reliability and reproducibility of optical characteristics.
In partieular, it is essential to locate and maintain the spacing
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be-tween the mirror surface and the target surface at a predeter-
mined value within about +0.001 to 0.002 inch (about 0.025 to
0.050 mm) Projection tubes of the prior art have therefore
been constructed to incorporate expensive and compllcated means
both to position the target during envelope and tube manufacture
and to adjust its location both during manufacture and instal-
lation. A reLatively early approach to achieving a partial
solution to this problem w~s to incorporate the mirror within
the tube envelope by forming it on that internal en~elope surface
opposing the target sur~ace. This, however, still necessitated
maintaining the critical dimensions of more than one envelope
component as well as the precise relative positioning of the
components, (See for example U,S. Patents 2,467,462, R. D.
Brown, Jr., issued April 19, 1949 and 2,637,829, V. Trad, issued
May 5, 1953.) As this art has progressed in its development,
more and more complex mechanisms have been incorporated into the
tubing envelope and associated with it to achieve and maintain
the required mirror/target aIignment and critical distance.
Thus, it is obvious that it would be highly desirable
to provide an envelope for a projection television tube which is
relatively simple in construction but which is capable of achiev-
ing during construction and maintaining during use the required
precise spatial distance between mirror and target surfaces.
It is, therefore, a primary object of this invention
to provide an improved envelope for a projection television tube
which is relatively simple to construct and which, therefore,
offers the possibility of providing less expensive components for
a projection television system. It is another object of this
invention to provide an envelope for a projection television tube
of the character described which uses the envelope components
as the sole means to position the target relative to the mirror
and which requires that only a single component of the tube
envelope be made with one very accurate dimension. It is
still another object of ~his invention to provide an envelope
for a projection television tube and the television tube incorpo-
rating it which is free of any need for means to adjust the
position of the target surface either during tube assembly or
installation of the tubes in a projection television system. Yet
a further object is to provide an envelope for a projection tele-
vision tube and a projection television tube incorporating the
10 envelope which allows minor variations in the location of the
target relative to the mirror surface to compensate for the re-
quired positioning of each of the three projection tubes in a
set relative to the projection screen used.
It is another primary object of this invention to provide
an improved process for the manufacture of projection television
tubes. An additional object is to provide a process of the char-
acter described which requires forming only one dimension of
one tube envelope component, aside from optical components, with
great accuracy. It is another object to provide such a process
20 which materially re~uces the cost of the resulting ~rojection
television tube through reduction in cost of the component parts
of the envelope used and in cost of the envelope assembly. Other
objects of the invention ~Jill, in part, be obvious and will, in
part, bc apparent hcreinafter.
According to one aspect of this invention there is
provided an envelope for a projection television tube com-
prising an end ~late, the internal surface of which defines
a spherically configured mirror; a cylindrical member affixed to
the end plate and terminating in an annular face plate sealing
30 end configurea and positioned such that a sphere in stable po-
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sition resting on thc sealing end will have its center of
curvature essentially coincident with the center of curvature
of the sphere defining the surface of the mirror; target suppoxt
means engaging the seal;.ny end and supportiny a target defining
a spherical surface having a center o~ curvature essentially
coincident with the center of curvature of the sphere determin-
ing the configuration of the face plate sealing end; and a face
plate sealed to said cylindrical member.
In a preferred embodime~t the sphere determining the
surface of the target and the sphere determining the configura-
tion of the sealing end of the cylindrical member have essential-
ly the same radi.i; and in a further preferred embodiment the
face plate serves as the target support member.
According to another aspect of this invention there
i.s provided a projection television tube comprising an end plate,
the internal surface of ~hich defines a spheri.cally configured
mirror; a neck sealed to the end plate; a cylindrical member
affixed tc t.he end plate and terminating in an annular face plate
sealing end configured and positioned such that a sphere in sta-
ble position resting on the sealiny end will have its centerof curvature e~sentially coincident with the center of curvature
oi the sphere defining the surface of the mirror; target support
means engaying the sealing end and supporting a target defining
a spherical surface having a center of curvature essentially
coincident with the center of curvature of the sphere determin-
ing the cor.figuration of the face plate sealing end; a face ~late
sealed to the cylindrical member; connecting means to electric-
ally connect the target and the mirror and to provide an external
annode terminal; electron ~un means sealed within the neck ar-
ranged to produce an electron beam to print a raster on the target;
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and electron beam focusin~ means.
According to a further aspect of this invention there
is provided a process for forming an envelope for a projection
television tube, comprising the steps of forming an end plate
to have a sph~rically configured mirror on its internal surface;
affixing to the end plate a cylindrical member which ter~.inates
in an annular face plate sealing end configured and positioned
such that a sphere in stable position resting on the sealing end
will have its center of curvature essentially coincident with
the center of curvature of the sphere defininy the surface of
the mirror; positioning on the face plate sealing end of the
cylindrical member a target support means configured to engage
the face plate sealing end and supporting a target defining a
spherical surface having a center of curvature when so positioned
which is essentially coincident with the center of curvature of
the sphere determinin~ the configuration of the face plate sealing
end, the positioning of the target support means in conjunction
with the height of the cylindrical me~er sexving to attain a
predetermined location of the target with respect to the mirror;
2~ and sealing a face plate to the cylindrical member thereby to
permanently affix the target in the predetermined location.
According to yet another aspect of thls invention
there is provided a process for forming a projection television
tube comprising the steps of forming an end plate to have a
spherically configured mirror n its internal surface; sealing
a neck to the end plate; providin~ a cylindrical ~ember which
terminates in an annular face plate sealing end configured and
positioned such that a sphere in stable position resting on the
sealiny end will have its center of curvature essentially coinci-
dent with the center of curvature of the sphere definlng the sur-
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face of the mirror; applying an electrically conductive coating
to the internal wall of the cylindrical member; sealing an annode
terminal through the wall of the cylindrical member; positioning
on th~ face plate sealing end of the cylindrical me~ber a ~arget
support means configured to engage the face plate sealing end
and supporting a target defining a spherical surface having a
center of curvature when so positioned which is essentially co-
incident with the center of curvature of the sphere determining
the confiquration of the face plate sealing end, the positioning
of the target support means in conjunction with the height of
the cylindrical member serving to attain a predetermined location
of said target with respect to said mirror; providing a face
plate: affixing the end plate to the cylindrical member; pro-
viding an electrical connection between the mirror and the target;
sealing the face plate to the cylindrical member thereby to
permanently affix the target in its predetermined location;
providing an electron gun assembly arranged to direct an electron
beam onto the target, and sealing the electron gun into the
neck; sealing off the neck in a manner to create a vacuum within
the tube volume; and affixing electron beam focusing means to
the neck.
The invention accordingly comprises the several steps
and the relation of one or more o such steps with respect to
each of the others, and the articles possessing the features,
properties/ and the relation of elements, which are exemplified
in the following detailed disclosure, and the scope of the in-
vention will be indicated in the claims.
For a fuller understanding of the nature and objects
of the invention, reference should be had to the following de-
tailed descrlption taken in connection with the accompanying
IL7.5
drawinqs in which
E~ig. 1 is a longitudinal cross section through theenvelope portion of one embodiment of a projection television
tube constructed in accordance with this invention;
Fig. 2 is plan view of the internal surface of the face
plate of the tube envelope of Fig. l;
Fig. 3 is an expanded, perspective view illustrating
the assembly of the projection television tube envelope of
Fig. l;
Fi~s. 4-9 illustrate in cross sectional detail dif-
ferent techniques for sealing the face plate and cylindrical
sections of the projection television tube envelope;
Figs, 10 and 11 illustrate the incorporation of heat
transfer means arranged to cool the target surface;
Figs. 12-14 are longitudinal cross sections through
two additional embGdiments of the projection television tube
envelope constructed in accordance ~ith this invention in which
the target support member comprises a target substrate affixed
to the face plate;
Pigs. 15 and 16 are longitudinal cross sections through
another embodiment of a projection television tube envelope con-
structed in accordance with this invention incorporating a sepa-
rate target support means;
Fig. 17 is a ~lan view of the target support means
used in the envelope embodiment of Figs. 15 and 16;
Fig~ 18 is a longitudina] cross section of a projection
television tube constructed in accordance with this invention
and incorporating the tube envelope of Fig. l;
Fig. 19 is a simplified diagram of a projection tele-
vision system; and
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Fig. 20 illu~trates diagrammatically the ef~ect of
a small lateral shift in the center of the fiphere defining the
target surface, relative to the mirror ~urface, to compensate
for the optics of a projection television system.
Figs. 1 and 2 illustrate a preferred embodiment of
the projection television tube envelope of this invention; and
Fig. 3 is an expanded view of the three components forming the
envelope. A complete projection television tube incorporating
the envelope of Figs. 1-3 is shown in ~ig. 18 and described
below.
The projection television tube envelope of this in-
vention, generally designated by the reference numeral 10, is
shown in Fig. 1 to be formed of three principal components which
comprise an optically transparent face plate 11, a cylinder-like
wall member 12 which may be slightly flared, and an end plate
13 to ~hich is joined a central neck section 14. In keeping
with known practice, the annular internal surface 15 (Fig. 3)
of end plate 13 facing the internal wall of face plate 11 is
configured with the sphericity of a sphere having a center 16
and a radius ~ep That annular portion of surface 15 within en-
velope volume 17 is coated~ e.o., aluminized, to provide a mir-
ror 18. Thus, mirror 18 can be said to be a spherical segment
or, more conveniently, to he of spherical configuration, a term
used hereinafter to denote a portion of a spherical surface.
~t will, of course, be appreciated that mirror 18 is not as thick
as shown in Yig. 1. However, mirror and target surfaces are
exaggerated in the drawings for ease of identificationO
The internal surface 19 of neck 14 is coated with a
suitable electrically conductive coating, such as a colloidal
graphite coating sold under the tradename of Dag. This coating
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extendq up to and in contact with the erlge of mirror 18.
In the Schmidt ~ystem a beam of electrons is directed
against a phosphor tar~et 20 within a sp~cified target ~urface
area referred to as the raster 21 (Fig. 2). The target surface,
generally rectangular in shape, must be of a spherical configura-
tion, i.e., configured with the sphericity of a sphere of radius
Rt which has a center essentially coincident with center 16 of the
sphere defining the configuration of the surface of mirror 18.
In this manner the radial distance D~ between mirror 18 and target
20 remains essentially constant. The attaining and maintaining
of this distance Dc is critical to the manufacturing of pro-
jection television tube envelopes and the tubes incorporating
them.
In accordance with the practice of this invention the
positioning of target 20 to achieve the desired relationship with
mirror 18 is accomplished by providing the cylinder-like member,
thereinafter, for convenience, referred to as the cylindrical
member) with an annular face plate sealing end 22 configured
and positioned relative to mirror 18 such that a sphere in stable
position resting on sealing end 22 will have its center of cur-
vature essentially coincident with the center of curvature of
the sphere defining the surface of mirror 18. Thus, as diagram-
med in Fig. 1, sealing end 22 is configured with the sphericity
of a sphere of radius P.Se with a center essentially coinciding
with center 16 of the sphere of radius P~ep defining the surface
of mirror 18. Alternatively, sealing end 22 may be configured
to present a surface to position and support a s-phere of radius
Rse as detailed be1ow in conjunction with the description of
Figs. 6 and 8.
By affixing target 20 to a target support member which
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engages the sealing end 22 of cylinder-like member 12, the target
support member and the target affixed thereto may experience
small lateral motion along the sealing line without causing any
effective shifting of the target surface relative to the mirror,
Thus, a lateral motion of the target support member of up to as
much as from about 0.050 to about 0.070 inch (about 1 2S to
about 1.75 mm) from true sealing surface alignment during as-
sembl~ and sealing will not adversely affect the optical char-
acteristics of the projection tube incorporating the envelope
so constructed, since the critical distance Dc will be maintained.
Thus the role of the cylindrical member, in addition
to that of forming a portion of the envelope wall, is that of
accurately positioning the target surface relative to the
mirror surface to attain the desired, predetermined spacing
Dc. This means that the height of the cylindrical member is
the one critical dimension in the tube envelope construction7
Because the cylindrical member can take various cross sectional
configurations, a cylindrical member of predetermined height
may be defined as that cylinder-like member which, when inter-
posed between the end plate mirror and the spherical surfaceof the target holding means results in the essential coinci-
dence of the centers of curvatures of the mirror and target.
The cylindrical member thereby becomes the envelope component
serving as the sole means for positioning the target relative
to the mirror.
~ s will be apparent from the following detailed de-
scription, the target support member may take any of a n~er of
forms, so long as it has a sealing edge configured to engage the
sealing end of the cylindrical member, the sealing edqe being de-
fined. by the surface of that sphere which, in its stable posi-
tion, rests on the sea].ing end 22 of cyli.ndrical member 12 and
has its center essentially coincid~nt with center 16 of mirror
1~. In the tube envelope embodiment of Figs. 1-3, face plate 11
serves in the dual role of target support member and face plate,
the target being deposited directly on the internal surface
23 of face plate 11. Typically, target 20 will be formed by
vacuum depositing an aluminum fi:Lm on surface 23 and then deposit-
ing the desired phosphor over the aluminum. ~s will be seen in
Pig~ 2, the actual target area 20 is made somewhat larger in both
dimensions than the raster 21-to be printed on it, For example,
it will generally be desirable to form the target ahout 0.060 to
about 0.06~ inch (about 1.5 to about 1.75 m~,) larger than raster
21 on each of the four sides to compensate for any of the allo~-
able lateral mov~ment o~ the target support mem~er in asse~bling
and sealing the envelope.
~ .lthouyh target 20 is illustrated ~or convenience ir
the drawiny to have a considerable thickness, it should be under-
stood that fcr all practical purposes it may be considered to have
a surface coincident with internal surface 23 of face plate 11,
or of any other substrate on which it is deposited. This, in
turn, reans that the internal surface 23 of face plate 11 an~
the surface of target 20, in order to meet the requirements
for target alignment, are also confi~ured with the sphericit~
Gf a sphere essentially identical to that sphere of radius RSe.
~ence, the spherical surfaces defining face pl.ate 11 and taraet
:~ 20 can be seen to have radii Rfp and Rt which are esser.tiall~
e~ual to Rse. ~hus, in the preferred envelope embodiment shown
in Pigs. 1~3 the spherically configured face plate is affixed
to sealing end 22 in any suitable manner such as illustrated in
Figs. 4-6 and 8 to achieve the desired radial-distance Dc between
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~ .'3mirror and t~rgct.
The ~nvelope embodiment of Figs. 1-3 is constructed
of three separ~te components as shown in the expanded view of
Fig. 3. In such a case, race plate 11, cylindrical member 12
and end plate 13 with neck 14 are molded of an appropriate glass
and machined to define the desired configuration of the mirror and
sealing surfaces. In those ènvelope embodiments in which the
cylindrical me~ber 12 is to he affixed to the end plate, it is
also necessary to shape the end plate sealing end 25 of cylin-
drical member 12 to essentially conform or to present a surfacewhich essentially conforms in sphericity to that of mirror 18,
i.e., to the internal surface 15 o~ the end plate. Thus it may
be seen that the end plate sealing end of cylindrical member
12 presents a surface which is configured with the sphericity
of a sphere of radius Rep.
Plthough it is ~enerally preferable to form cylindrical
member 12 with G slight flare, it is also, of course, within the
scope of this invention to form it with any other suitable con-
figuration. It will, however, be appreciated that the critical
dimension, Dc, is determined by the distance maintained between
the target support member and mirror and that this distance is
determined solely by the height dimension of cylindrical member,
takina into account, if necessary, the thickness of any frit
layer or layers interposed between the components~
Before discussing the various techniques ~hich may be
used to seal together the components of the envelop-e, it will
be convenient to complete the description of the remaining ele-
ments of the envelope. In accordance with known techniques in
; constructing the envelope, the internal surface 26 of cylindrical
member 12 is coated with an electrically conductive coating, e.g.,
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a suitable colloidal graphite coating, and an electrical con-
nection is provided between mirror 18 and targek 20. This elec-
trical connection comprises a film strip 27 of an electrically
conductincJ material, ~.g., aluminum, coated on face plate sur-
face 23 contacting target 20 (Fig. 2) and terminating in an en-
larged contact area 28, e.g., one coated with colloidal graphite;
and an electrically conductive wire 29, e.g., of stainless steel,
shaped to force its dimpled ends into contact with area 28 and
mirror surface 18. An external anode terminal 30 is inserted
through and sealed to the wall of cylindrical member 12, by frit
31, to contact wire 29 through spring clip 32 thus providing
one of the necessary electrical contacts for the projection tele-
vision tube incorporating the envelope. Alternatively, this an-
node terminal ma~ be inserted through and sealed in the end plate.
A correcting lens 33 is held in spaced relationship to
face plate 11 by a lens supporting ring 34 which when seated on
face plate 11 results in automatically aligning lens 33 with re-
spect to the other optical components of the tube. Supporting
ring 34 is affixed to the envelope through a plurality of spaced
an~led arms 35 held to cylindrical member 12 by an adustable
band 36. Lens 33 not only serves to correct the spherical aber-
rations inherent in the optics of the system, but also, with
support ring 34, protects face plate 11. The actual design and
positioning of lens 34 is within thc capabilities of an artisan
of ordinary skill in the optical arts; and it will be apparent
that the proper seIection of correction lens with slightly dif-
ferent effective powers can he used to correct for any small
dimensional inaccuracies of the envelope.
Figs. 4-9 illustrate in cross sectional detail several
30 ways in which~face plate 11, cylindrical member 12 and end plate
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13 of the envelope embodiment of Yigs. 1-3 may be sealed together.
In the sealing modifi~ation of Figs. 4 and 5, the face plate
sealing end 22 of cylindrical member 12 is ground to hav~ the
required s~hericity and the end plate sealing end 25 i5 ground
to the same sphericity as mirror 18. Sealing is accomplished
through the use of two layers o~ frit 39 and 40 (typicall~ a
commercially available lead oxide frit) between the face plate
and cylindrical-member and between the cylindrical member and
end plate, respectively. It will be appreciated that in this
sealing embodiment it is necessary to accurately control the
thickness of frit layers 39 and 40 and to subtract the combined
thicknesses of these frit layers in calculating the height
dimension of cylindrical member 12 which controls the distance,
Dc, between the target and mirror.
The actual thickness of frit layers 39 and 40 may be
controlled by the use of shim means shown in the modification
of Fig. 5 to be accurately graded beads 41 formed of a glass
having a melting point sufficiently higher than the activation
temperature of the frit material so that they will retain their
origir.al shape during sealing. It is also, of course, desirable
t~.at the glass from which the beads 41 are formed has a coeffi-
cient of thermal expansion essentially the same as that from
which the components of the envelope are made. Other suitable
shim means such as shcrt glass rods or tetrahedrons of appropriate
dimensiGns may be used. In general, it will be preferable to
use frit thicknesses ranging between about 0.005 and about 0.015
inch (about 0.1 and about 0.4 mm). Thus, 0.010 inch (0.25 mm)
diameter glass beads may be cited as exemplary shim means.
Figs. 6-9 illustrate several sealing modifications
which do not require the making of allowances for frit thick-
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ness in determirlin~ and achieving the desired accurate heiyht
dimension of the cylindrical member. In the modlfication of
Fig. 6, surface 22 of cylindrical member 12 is ground to have
the desired sphericity and then a frit groove 42 is cut out
to contain frit A3, taking care to maintain the integrity of
internal line contact 44 so that it and the remaining portion
of surface 22 present a sealing surface with the desired spher-
icity~ In similar manner, surface 15 of end plate 13 has a
frit groove 45, containing frit 46, cut in it to provide a con-
tact line 47 which, with the remaining portion o surface 15,provides the required sealing surface. Alternatively, as shown
in Fig. 7, a frit groove 48 may be cut in sealing end 25 of the
cylindrical-member, retaining a portion of spherically confi~ured
end surface 25 and creating a co~tact line 4g on the spherical
surface with radius Rep.
Fig. 8 illustrates a sealing modification in which
two parallel circular contact lines 50 and 51 in face plate
sealing end 22 of cylindrical member 12 are provided for seat-
ing face plate 11 serving as the target support member. Between
these contact lines a frit space 52 is provided. It will, of
course, be appreciated that both contact lines 50 and 51 must
lie on the required spherical surface of the sphere with radius
RSe, corresponding to surface 22 of the face plate sealing end
of cylindrical member 12. Thus, these two parallel contact
lines 50 and 51 meet the requirement of presenting a surface
which conforms in sphericity to the prescribed sphere of radius
P~se and center 16. E~arallel contact lines 53 and 54, defining
frit space 55 between them, may also be cut in the peripheral
surface of end plate 13 to seal cylindrical member 12 thereto.
Finally, as ~hown in Pig. 9, the peripheral surface of end
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plate 13 may be Pormed to have an essentially flat ~urface 56
so that the end plate sealing end 25 of cylindrical member 12
form a contact line 57 with the end plate and leaves a frit
space 58 for sealing.
It will be apparent that a number of combinations of
sealing surfaces may bc used in constructing the projection
television tube envelope and tube of this invention so long as
the face plate sealing end surface of the cylindrical memher
is configured as previously defined.
The face plate configuration of the projection tube
of this invention permits the incorporation of external cooling
means for the target, thus offering the possibility of attain-
ing a higher light level and a longer tube life. As shown in
Fig. 10, a ccntoured plate 60 formed of a material-having rela-
tively hish heat conductivity, e.g., copper, is bonded to ma~e
thermal contact with the external surface 61 of face plate 11
and positioned to correspond with the position of target 20.
Extending upward from plate 60 and in heat transfer contact
therewith is a post 62 having one or more heat dissipating
fins 63 affixed thereto.
Fig. 11 illustrates a modification of the external
cooling means of Fig. 10 in that the plate 60 is set in a well
; ~4 cut in face plate surface 61. Inasmuch as the thickness of
the face plate wall through which target heat is transferred
~ by conduction to plate 60 is less than in the arrangement of
:~: rig. lo, the cooling of targct 20 is somewhat more efficient
;~ in tbe arrangement of Fig. 11. .
The projectlon television tube envelope embodiments
shown in Figs. 12-14 use the face plate as a part of the target
support means while providing flexlbility in the tube optlCs.
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.
In the envelope embodiment of Figs. 12 and 13, in which the same
reference numbers are used to identlfy like elen,ents of Fig. 1,
the face plate 11, cylindrical member 12 and end plate 13 are
configured as described in connection with Figs. 1 and 3 and
sealed by any suitable technique such as one of those de-
scribed in conjunction with Figs. 4-9. However, the target
20, deposited as previously described, is on the surface of
a substrate 70 preferably formed of the same glass as the en-
~elope or of a glass having essentially the same coefficient
of thermal-expansion as the envelope glass. Target substrate
70 preferably has two or more feet 71, the surfaces 72 of
which are ground to have the same sphericity as internal wall
23 of face plate 11 to accurately locate target 20 on face
plate 11 when affixed thereto with frit 73 which is applied
in a quantity to-fill a pGrtiOn of the sp~ce between substrate
70 and s~rface 23. Thus, the t~rget support means in this
embodiment is comprised of f~ce plate 11 and ta~get substrate
70 affixed thereto.
In the e~bodiment of Fig. 12, the target substrate
provides a target 20 having a surface configure~ Wi th the
sphericity of a sphere of radius ~t and a center which essen-
tially coincides with center 16 of the mirror-defining spherical
surface. Thus, although Rt is somewhat greater than Rse, the
conditions set forth for the support of the target relati~e to
the mirror are met since small lateral excursions of face
plate 11 with target substrate 70 affixed thereto will have vir-
tually no effect on the radial distance, ~c' between target
and mirror.
In order to provide the electrical connection between
target 20 and mirror 18, a narrow film of aluminum 74, or other
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electrically conductive material, (Fig. 13) may be deposited
beginning at the target edge and running along the side and
substrate surface opposite the target surface to make contact
thxough a conductive clip 75 with a conductive film 27 deposited
on surface 23 of face plate 11 and terminating in a contact area
28 as shown in Fig. 2. The remaining connection through a wire
29 is identical to that shown in Fig. 1. It is, of course,
within the scope of this invention to provide any other suit
able electrical connection between the target, anr.od~ terminal
and mirror.
The optics of the embodiment of Fig. 12 are such that
a correction lens need not be used since face ~late 11 may
serve that purpose. This is made possible because there is
some freedom in this arrangement to locate the face plate with
respect tG the mirxor; and, if required, the surfaces of the
face plate may be configured with reference to the mirror sur-
face to enhance its optical corrective characteristics. It is
also, of course, possikle and ~7ithin the scope of this invention
to add to the embodiment of ~ig. 12 an appropriately configured
corrective l~ns in the manner shown in FigO 1 to provide a tele-
vision projection tube of the highest performance capabilities.
The projection television tube envelope of Fig. 14
employs a target substrate 80 affixed by frit 81 to a flat
face plate 82 as the target support means engaging the cylin-
drical member sealing end surface 22. In this embodiment the
peripheral enga(~ing surface 83 of face plate 82 is ground to
have the sphcrlcity of a sphere of radius P~Se and the target
substrate 80 to have the sphericity of a sphere of radius Rt,
both having centers of curvature essentially coincident with
that of the sphere of radius ~ep defining the mirror surface.
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It will be apparent that this embodiment also meets the require-
ments for the envelope components.
The use of an essentially flat face plate necessitates,
for qood performance, the incorporation of ~ correction lens 85
supported on a lens support B6 which is sealed to the outer rim
of face plate 82. The configuration of lens 85 is known in
the art and it is positioned so that its optical center es-
sentially coincides with spherical center 16; and in the as-
sembly of the envelope components, lens 85 is located by well-
known optically observed self-imaging techniques.
In the tube envelope embodiment shown in Figs. 15-17
the end ~late 90 and cylindrical member 91 are formed as an in-
tegral piece 92 prior to the sealiny of the face plate to the
cylindrical member. Thus, cylindrical member 91 may be flame
sealed to end plate 90 or these two components may be initially
moldec as an intesral piece. This arrangement is, of course,
applicable to an~ of the tube envelope embodiments of this in-
vention. Alternatively,the envelope of Fig. 15 may be constructed
of a separate end plate and cylindrical member as previously
described. The embodiment of Figs. 15-17 also incorporates a
target holding means which is separate and distinct from the
face plate. In this arrangement the inner surface95 of the face
plate sealing end of cylindrical member 91 is ground to have the
required sphericity, i.e., that of a sphere of radius Rse; and
the outer surface 96 is ground flat to support and have sealed
thereto, through frit 97, a flat, circular face plate 98 (see
Fig. 16).
The tarqet support means 100, shown in a top plan
view in Fig. 17, comprises a circular positioning and seating
ring 101 from which narrow supportinq spokes 102 extend inwardly
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.
,
r;1 ~
to hold target substrate 103 on which target 20, defining raster
21, i5 deposited. It will be appreciated from Figs. 15-17 that
target support means 100 is shaped to have the configuration
of a segment of a sphere with radius Rt (essentially equal to
Rse) to provide the required surface configuration for target 20
and the enga~ement of targct positioning and seating ring 101
with spherically configured sealing surface 95 of the cylindrical
member. Thus through the use of this spherically configured
target support means and the spherically configured surface 95
(or one which conforms to a spherical surface such as shown
in Fig. 8) the desired positioning of the entire target surface
20 with respect to mirror 18 is assured. The target support
means 100 are preferably formed from stainless steel using well-
known etching techniques.
In order to maintain continuous engagement of target
support ring 101 with surface 95, a plurality of spring clips
104 is located around the target support between the internal
wall 105 of face plate 98 and ring 101. If target support means
100 is formed of an electrically conducting metal it may serve
as an electrical connection between the target and wire 2g.
Alternatively, as shown in Figs. 16 and 17, the electrical con-
nection between the target and mirror may be through a thin
conductive strip 106 terminating in an enlarged conductive area
107 and wire 29 contacting area 107 in the ~anner descri~ed
for the envelope of Fig. 1.
It will be apparent from the above detailed descrip-
tions of the embodi~ents of the projection television tube en-
velope which are illustrated as exemplary of the inventlon,
that many combinations of target support means, envelope con-
figurations,,sealing techniques and electrical connections
L7;~
within the tube are possible.
Fig. 18 is a longitudinal cross section of a pro-
jection television tube constructed in accordance with this in-
vention, that is one includiny the tube envelope of this inven-
tion~ The tubc envelope illustrated in the tube of ~ig. 18 is
that of Fig. 1-3. The tube may, however, use any of the envelope
embodiments shown or described. In kee~ing with well-accepted
projection television tube design, neck 14 is sealed off to
provide fluid-tight evacuated envelope volume 17. An electron
gun 110 of well-known design is sealed in neck 14 and is shown
to comprise a cathode 111 with associated heater 112, grids 113
and 114 and anode 11~ which is electrically connected to annode
terminal 30 through the electrical conducting coating 19 which
extends down through the internal wall of neck 14 to make con-
tact with annode 115, mirror 18, and wire 29. The projection
tele~-ision tube has a magnetic focusing lens assembly 116, a
convergence controllir.g means 117 and deflection controlling
means 118, all of ~hich are standard components.
In the precedlng detailed descriptions of the television
projection tube envelope~end of the tube incorporating the en-
velope in accordance with this invention, the centers of curva-
tures of the spheres defining the contours of the mirror, the
target surface and the face plate sealing end surface of the
cylindrical men~er have been defined as being essentially coinci-
dent. This term as used herein is meant to include any combina-
tiGn oi the locii of these centers which satisfies the require-
ment that the radial distance, Dc, from any poi~t on the target
surface to the mirror surface is a constant value within a Fre-
determined tolerance range which permits the achievement of
the deslred optical characteristics and performance of the tube.
:
-22-
.
'7~
As will be apparent to tho~e skilled in the ar~, the real centers
of curvatures of the optical element~ may be slightly displaced
to achieve the optimum optical design which compensates for work-
ing at a finite distance.
Thus, for example, in a televisi.on projection tube of
what might be termed a "standard size" having a radial distance,
Dc, from target to mlrror of about four inches (about 10 cm)
the tolerance r~r,ge for Dc is from about ~.002 to about 0.00
inch (fro~ about 0.050 to about 0.10 mm) greater or less than
the predetermined radial distance. This, in turr" means that for
such a "standard-size" tube, a slight shifting of the locus of
the center of curvature of the s~here corresponding to the target
surface either up or down on the tube a~is and/or laterally
a~ay from the axis ~hich results in a lateral motion of the
target support ~eans of no greater than about one-sixteenth
of ar. inch ~about 0.06 to about 0.07 inch or about 1.~ to abcut
1.75 mm) fror perfect ali~nment can be tolerated during assembly
and sealing.
In fact, a slight lateral shifting of the locus of
the center of curvature defining the target surface configura-
tion fro~, the tube axis is required in a tele~ision projection
system which uses three separate projection tubes, one each for
projecting red, blue and green images. It is not, of course,
ph~sically possible to position three tubes to have their ax~s
coincident and the a~es cannot be parallel since the images rom
: : the three tubes must meet and be precisely superimposed on the
screen. Moreover, as will be seen diagrammed in Fig. 19, in
order to provide a direct line of sight from the screen 125 to
the viewer 126, it: is necessary to-direct the images from the
three tubes housed in projecti.on system 127, at an angle, e.g.,
:~ ~ ~23-
7;~
from about S to 10. Thus, it is highly desirable if the pro-
jection television tube is built to Gompen.sate for these factors.
This compensation is readily accomplished in the
practice of this invention by a slight lateral shift of the
target center of curvature within the limits previously defined.
This may be seen in Fig. 20 wherein the magnitude of this lateral
shift is exaggeratered better to illustrate the effect. It ~7ill
be seen that when the center 16 of the target suface 20 is
shifted to 16a, the target surface 20a also shifts which results
in a slight but effective shift of the beam emitted by the tube,
thus making it possible to use three projection tubes to pre-
cisely superimpose their images on a screen~ Generally, such a
slight lateral shift of the target center oE curvature will range
from about 0.005 to about n.OlQ inch (from about 0.13 to about
0.25 mm). Such a latexal shift, while accomplishing the desired
focusing of the beam, ~ill not violate the prescribed tolerance
range for Dc. Moreover, any consequent departure, ~ithin the
establishecl set limits, from the ideal position will not cause
any observable degradation ~ithin the color television require-
mer.ts.
~ he components comprising the envelope, (face platecylindrical mem~er, end plate an~ tubulation for the neck) are
pre erably formed from an electronic glass, the glass in each
component havincJ a coefficient of thermal expansion as nearly
as possible the same as that of the other components in any
one envelope. It is also possible to form the cylindrical mem-
ber of a ceramic material or metal so long as it also has a
coefficient of thermal expansion approximating that of the glass
in thc other components.
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'7~
The process of this invention may be il~ustrated using
the formation of the projection television tube of Fig. 18 as
an example. The three components of the envelope and a section
of tubing to be used as the neck tube are molded and the optical
surfaces of the face plate and end plate as well as the seal-
ing surfaces of the cylindrical member are ground and polished
to the desired configurations. The optical surfaces of th~
components are then completed. The target, conductive strip
and terminating conductive area are deposited on the internal
surface of the face plate. The location of the target within
the required area on the face plate surface may be accomplished,
for example, by the use of a photosensitive binder in the manner
employed in the manufacture of direct-view television tubes.
The internal surface of the cylindrical member is coated ~ith
an opaque conductive coating, the annode terminal is sealed in
the ~!all and the conductive ~Jire is attached. The mirror is
deposited on the end plate surface and the electrically conduc-
tive coating is applied to the internal neck joint surface of
the face plate and the internal surface of the neck tubulation
to a predetermined line. The open neck tubulation is then flame
sealed to the end plate. ~t this point, the required amcunt of
frit is applied to the two sealing ends of the cylindrical member
and the face plate and end plate are positioned on the cylindri-
cal member for sealing of the envelope assembly by bakina in an
oven. This positioning is accomplished by aligning the outer
edges of the face plate and cylindrlcal member and seating the
cylindrical member on the end plate to ensure complete continuous
contact therewith.
In a typical bakir.g and sealing cycle, 45 minutes are
taken to bring the envelope assembly up to the frit activation
-25-
temperature of about 44SC. This activation temperature level
is maintained for about 30 minutes and then about one and one-
half hours are used for cooldown. It has been found preferable
during the later part of the warmup and early part of the frit
activation heating portions of the cycle to raise the temper-
ature o~ the cylindri.cal member near the face plate to some-
what above, e.g., about 30~C above, the temperature of the face
plate. This may be done by directing infrared radiation locally
on the appropriate area of the cylindrical mem~er surface.
This additional localized heating is believed to control the
direction of induced strains and thus to form a st~onger tube
envelope.
In accordance ~ith known practice, the components
of the electron gun are then flame sealed into the tube neck,
the temperature of the tube is raisea to between 3~0C and
~00C, the cathode is electrical].y activated, and finally the
en~ of the nec~ is sealed off. Finally, the correcting lens is
attached in the r.,ar,r.er previGusly described and the external
focusing means affixed to the neck.
lt is apparent from the above detailed description of
the prG jection television tube envelope, of the completed tube
and of the process for forming the envelope and the tube, that
this invention provides a true advancement in the projection
television art by providing a relatively simFle, inexpensive,
optically acceptable television projecti.on tube~ This advance-
ment is achieved through the configuration of the components
formins the tube envelope and by the use of these envelope com-
ponents as the sole means to position the target relative to
the mirror. Moreover, only one component, the cylindrical mem-
ber, need be formed with one very accurate dimension.
: -26-
L7~
It will thus be seen that the ob~ects set forth above,
among those made apparent from the preceding description, are
e~ficiently attained and, since certain changes may be made in
carrying out the above process and in the articles set forth
without departing from the scope of the invention, it is in-
tended that all matter contained in the above desciption or
shown in the accom~,anying drawings shall be interpreted as il-
lustrative and not in a limitinc sense.
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