CA1051501A - Color cathode ray tube having an improved one-way-only shadow mask suspension system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This application depicts a rectangular color cathode ray tube having a faceplate and a mating funnel, on the face-plate of which is a system of four suspension devices, one at each corner of the mask, for detachably supporting a non-self-rigid shadow mask adjacent a screen-bearing inner surface of the faceplate. Each of the mask suspension devices comprises mask-mounted and envelope-associated components, the devices being characterized by one of the components including spring means having a provision for retentively engaging in a male-female relationship a mating provision on the other of the components. In at least one of the suspension devices the provisions on the mask-mounted and envelope-associated components are of reverse gender from that of the diagonally opposite device to assure a one-way-only suspension of the mask on the faceplate.

Description

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This invention relates to color c~thode ray tubes of the type havirlg a shadow mask, and especially to a system for suspending a shadow mask on the faceplate o~ a color tube. Th;s invention has applicability to suspension systems for shadow masks of various types, including post deflection ~ocus masks.
This application is related to applicant's U.S. patents Nos. 3,896,3~1; 3,912,963; 3,943,399 and 3,999,09~ issued July ~2, 1975, October 14, 1975, March 9, 1976 and December 21, 1976, res-pectively; applicant's Canadian patent 1,001,207, issued December 7, 1976 and applicant's co-pending applications Serial Nos.
240,267 and 253,050, filed November 24, 1975 and May 21, 1976, respectively.
Conventional color cathode ray tubes have a shadow mask assembly which includes a heavy frame to which is welded a dished, apertured mask~ The frame is, by design, extremely rigid and provides the necessary rigidity for the mask. The mask-frame assembly is mounted in a conventional tube by a suspension system comprising three of four leaf springs which are welded to the frame at spaced points around the periphery thereof. These springs must be relatively stiff to support the heavy mask frame assembly, typically applying a ~oad of 4-5 pounds or more to the mask-frame assembly. The springs ~ , :

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have aperture~ at their distal ends whlch en~age studs projectin~ wardly from a rearward flange on the tllbe face-plate when the assen)bly is mounted in a tube. The mask-frame assembly is capable of being demounted and precisely remounted in a tube by depressing the springs to disengage the said studs. This type of system has proven to be commercially viable, however, the mask-frame assembly and the tube envelope are undesirably expensive.
The system with which this invention is involved represents a radical departure from conventional and other prior art approaches to shadow masks and shado~ mask suspension systems. A low cost9 lightweight, non-self-rigid, torsionally fle~ible ~ask is provided. The faceplate is used to impart the necessary rigidity to the mask. A novel suspension system `
is provided ~hich furnishes a mechanically rigid link between the faceplate and the maskp and yet which permits the mask to :
be co~veniently and repeatably demounted and precisely re- - i mounted in the *ube. The advantages of this system are manifold.
A primary advantage resides in the appreciable savings in tube cost. Tube cost savings result from the use, in a preferred embodimentg of an envelope having a flangeless faceplate which.
is less expensive than the conventional flanged faceplate, and from the use of a lightweight (low mass~, low cost shadow mask (preferably of one-piece, frameless construction)~
Brief Descrip~tion of the Draw ngs The features of the invention which are believed to be novel and ~nobvious are set forth with particularisy in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the acco~panying drawings, in which:
Figures A and B, located on the third sheet of drawings, are sche~atic diagrams of a four-bar linkage model ~b/_ ~ - 3 -:LO~ 2,g~
useful in llndersLand:ing the mechanical properties of a shadow ask of the type with which this inventiorl ~s concer~ed;
Yigure 1 is a perspec:tive view, partly broken a~y, of a novel color cathode ray tube as ~een from the rear, wi~h a portion of the envelope cut-away to reveal a preferred suspension system for a shadow mask implementing the principles ` of this invention;
Figure 2 represents an enlargement of a portion of :~ the screen of the Figure 1 tube;
Figure 3 is an enlarged fragmentary perspective view, shown partly sectioned and broken away, of a corner of the tube shown in Pigure 19 revealing with particular clarity one of the suspension devices for mounting the shadow mask on the tube faceplate;
Figure 4 is a sectional view taken generally along lines 4-4 in Figure 3;
Figure 5 is a highly schematic view of a faceplate ^: I
` mask assembly shown in Figures 1-4; the Figure is useful in understanding certain mask suspension priciples on which this invention is based~ `
~ Figures 6 and 7, located on the second sheet of ::
: drawings, are isolated front and side elevational views and a spring constituting part of the suspension devices shown in Figures 1, 3, and 4;
Figures 8 and 9 illustrate a mask suspension device representing one of the four devices constituting the Figures 1-4 system;
Figure 9A, located on the sixth sheet of drawings, shows an alternative bracket structure; `
Figures 10~12 are schematic perspective views of alternative mask suspension devices which may be constructed according to the principles of this invention;
Figure 13 is a side elevational view, partially mb/ - 3a -~ ' ' ` ' :

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sectioned, of a m~sk suspension devlce representln~ yet another e~bodiment of the invention;
Figure 14 i8 an isolated rear view of a bracket-spring shown ln Figl~re 13;
Figure 15 is a sectional view taken along a 1ine in Figure ]3, Figure 16 is an unfurled view of the Figures 13-15 bracket-spring; and , Figure 17 is a fragmentary perspective view similar to Fig. 3, a mask suspension device representing yet another embodiment of the invention.
A system of the character described has imposed upon it a number of requirements and constraints not presented in conventional systems in which a rigid frame is used to impart rigidity to ~he mask. Before enumerating these requirements and constraints, a discussion of certain under-lying principles will be engaged. A shadow ~ask of the ~ype ~ j - with which this invention is concerned may be modelled as a rectangul~r four bar linkage affixed to a flexible sheet.

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Sucll ~ mo~el i~ s~1own in r i~1urc A. ~l1e our rigicl bars o~ ~hc :Linkage a~c dcsi~n.1~ccl A, ~, C ~Incl n; ~lle sheet is labelcd S.
As is ~ell known, a four bar lil1kage is no1: inhcrcntly a rig:id structure. The rcctangular four bar linkage, in its free state, S might, e.g., quite easily be skewcd into a parallclogram geome-try. It is evident, howevcr, tha-t the Figure ~ model cannot be skewed in :its plane -to take a parallelogram shape since it is affixed to the sheet S.
The linkage, can, however, be torsionally twisted about its diagonals, as shown for example in Figure B. In Figure B, the model has been twisted as follows -- the linkage bar A has been rota-ted toward the reader ~see arrows); the linkage bar C has been rotated away from the reader. The corners l and 3 have been displaced upwardly and the corners

2 and 4 have been displaced downwardly. The sheet S is thus stressed convexly along diagonal 2-4 and somewhat concavely at the ends of diagonal l-3. The model may thus be thought of as being twisted about one of its diagonals (here shown as diagonal 1-3). It can be noted that the model configuration, a-fter twisting, is changed substantially less along its major axis a and mi.nor axis Mi, than along the diagonals. Thus a four bar linkage affixed to a flexible sheet is relatively stiff with respect to its major and minor axes (due to the rigidity of the bars), but is relatively flexible in torsion. When ` 25 torsionally flexed (twisted), about its diagonals, the corners ; are displaced, but points on the major and minor axes remain relatively sta~ionary.
As will be pointed out in more detail hereinafter, the shadow mask with which this invention is concerned is simi-lar to the described model in its mechanical characteristics.
: The principles of this invention, though not limited f;l i ~_ , ' ' ' :

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to such application, are most useful when em~odied in a color cathode ray tube having a flangcless faceplate. ~lhen such a faceplate is sealed to mating funnel after completion of the faceplate screening and mask insertion operation, the faceplate is very apt to experience a twist-wise elastic distortion due to a tolerance-related configurational mismatch be~ween the ` funnel and faceplate sealing surfaces. Any such distortion wîll be rendered a permanent deformation when the sealing cement - has cured and the sealing operation is completed. Thus, one of the necessary general requirements imposed on a mask and mask-.:
- suspension system intended for use with a flangeless faceplate is that i~ must be able to adapt to such twist-wise deformations of a aceplate with which it is mated. Stated another way, the mask must ~e capable of flexing or twisting about its diagonals in much the same way faceplat-es are apt to twist-wise deform in their contour during tube fabrication, and its suspension system must provide for such adaption. As will become evident as this description proceeds, the shadow mask and suspension system with which this in~ention is concerned are uniquely capable of meeting this requirement.
Second, and of equal significance -- with respect to any given faceplate, since the mask is non-self-rigid, the sus-pension system for the mask must effectively transfer the rigidi-ty of the facepla~e to the mask.
Ihird, the suspension system must precisely fix and hold a predetermined spatial position of -the mask as a whole relative to the faceplate against translational or rotational - displacement, in spite of any thermal expansion or contrac-tion of the mask, demounting and remounting of the mask, . 3~ or mechanical shocks.

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lollrtll, it is desirclble -that arly therlrlally irlduced movement o~ ~ny part of the mask or of any mask suspcnsion clemellt during tube opera~ion be radiaL, rather than tan-gential, since radial crrors can be compensated by adjusting iTl the beam deElect-ioll cha-racteristic, whereas tangelltial errors cannot be.
Fifth, it is desirable that the system permit the mask to be conveniently and quickly demounted and remounted, preferably automatically, since in conventional factory :Eaceplate screening practices the mask is mounted on or de-; mounted from the faceplate many times.
A sixth general requirement is that the mask sus-pension system should carry a low manufacturing cost.
A seventh requirement strikes at the heart of the present invention. Since, according to standard industry practice, the shadow mask is used as a photographic stencil in the photoscreening of the pattern of phosphor triads on the tube faceplate, it is important that a unique relative rotational orientatian of the mask and faceplate be preserved during the photoscreening operation and during the final assembly of the mask in the tube. If the said relative rotational orientation is not preserved, registration of the pattern of mask aperture with the pattern of phosphor triads derived therefrom will be lost.
In conventional three point mask suspension systems three leaf springs attached to the mask at three spaced points on the periphery thereof engage three similarly spaced studs ; embedded in a rearward flange on the faceplate. In such systems, one-way-only suspension of the mask on the face-- 30 plate is inherent. See, for e~ample, Patent No. 3,358,170 -Fiore.
In conventional four point (four spring) suspension . . . . .

systellls th~ susl)ension sl~rirl~/s are looclte(l interrnecliate the mask corners, typicaLIy on or neLIr the m-ljor and minor axes of thc m~lsk. In these systems, according to one approach, one-way-only suspension oE the mask is achieved by custom-~r~
~J attaching the springs to the mask. See, for example,/Patent No. 3,296,477. Alternatively, it is known to make one of the four studs (and the associated stud-engaging spring aperture) larger than the other three to prevent mounting of the mask in other than the desired orientation.
A corner suspension system for a rectangular-type tube being inherently symmetric about the major and minor mask a~es also does not inherently provide one-way-only mask suspension. Either of two rotational positions of the mask relative to the -facepla-te are possible. The afore-described commercially known suggestions to assure one-way-only four-point mask suspension are not believed to be optimally suited, however, to incorporation in the corner suspension system with which this invention is involved.
Other Prior Art U.S. British 2,823,328 Vincent 1,278,633 2,922,063 Haas 1,278,632 2,961,560 Fyler 1,278S635

3,497,746 Duistermaat et al 1,772,334 3,529,199 Duistermaat et al 3,537,159 Gartner 3,548,235 Duiedijk et al Objects of the In ention It is a general object of this invention to provide a color cathode ray tube having an improved suspension system especially useful for corner-suspending a low cost, non-self-~, . ~ -- ~s~

rigid, torsionally flexible shadow mask adjacent to the tuhe's faceplate.
The invention is used in a color cathode ray tube having an e~velope which includes a curved, ar)proximately rec-tangular faceplate supporting on an inner surface thereof in a central region a phosphor screen comprising a pattern of red-emissive, blue-emissive and green~emissive phosphor triads. The invention relates to the combination comprising: an approximately rectangular shadow mask having a similarly curved central portion containing a pattern of phosphor triads and a stiffening portion circumscribing the central portion; and a mask suspension system for supporting the shadow mask at a predetermined spacing from the inner surface of the faceplate, comprislng four suspension devices, one at each corner of the mask, for detachably coupling the mask to the faceplat~. The suspension devices each include an enve-lope-associated component on the faceplate in a corner region thereof for supporting the mask, and a mask-mounted component - ~ I
secured to the outside of the stiffening portion of the mask. One of the componen~s includes spring means having a provision for :: ~
retentively engaging in a male-female relationship a provision on the other of said components in at least one of the suspension devices the provisio~s on the components being of reverse gender from that of the diagonally opposite suspension device to assure ; a one~way-only suspension of the mask on the faceplate.

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Descri~tion_of the ~ref~r-r d E~)od_nent This inven-tion is directed to providing ~n i~p~o~ecl shadow mask suspension system which is especially useful for suspending upon the envelope of a color cathode ray tube a lightweight, torsionally flexible shadow mask such as is des-cribed and claimed, for example, in the referent U.S. patent No.
3,912,963~ As used herein, the term "shadow mask" is intended to encompass all tubes, including post deflection focus ("PDF") tubes, in which a color selection mask or electrode achieves a shadowing effect, whether total or only partial (as in a PDF tube).
The present suspension system includes four suspension devices, one on a~ each corner of the mask. The general concept, however, of a lightweight, non-self-rigid, torsionally flexible, rectangu-lar shadow mask which is supported at its four corners so as to permit it to conform to the contour of a cathode ray tube face- - i plate was first described and claimed in the above-noted Canadian patent No. 1,001,207.
Figures 1 4 illustrate a color cathode ray tube 2 incorporating a mask suspension system which implements the ; principles of this invention. The tube 2 is depicted as having an envelope comprisins a funnel 4 sealed to a rectangular flange-~; less faceplate 6. The tube 2 includes a lightweight, rectangular, non-self-rigid, torsionally flexible shadow mask 12 of novel character described in detail and claimed in the referent U.S.
patent No. 3,912,963.
Before engaging in a discussion of the structural details of the mask 12 and its novel suspension system, a brief P~, . j c/" - .

: e~pla.nati.on ~ill be gi.vcn of certa~ mask s~lspension principles wlderly;ng the system with which this :invcnt.ion is concerned, particularly with reference to Figure 5. In Figure 5 there is sllo~n, in schematic :form, a faceplate 6 on which is ` 5 mounted a shadow mask 12. The suspension systcm for the .
;. shadow mask is shown as comprising four suspension devices 26, one in each corner of the faceplate on a faceplate diagonal.
.~ The prefcrred structures for the suspension devices 26 wi~l be. described in more detail hereinafter. Only those parts of the suspension devices 26 which are pertinent to this . discussion of principles will be mentioned at this point.
Each of t.he suspension devices includes an envelope-associated component, here shown as a stud 27, having thereon a provision for coupling the stud to a mask-mounted component ,~
of the suspension device 26. The suspension devices each also include a mask-mounted component, here shown as comprising a bracket 28 on whlch~is mounted a leaf spring 30 having a pro-vision for engaging the provision on the stud 27.
; ~ In the system with which this invention is concerned, :.~ 20 the faceplate 6 is used, in effect, to impart rigidity to the mask 12. The suspension system acts as a rigid coupling between the faceplate 6 and the mask 12~ Yet, by the provision of the . spring suspension system, the mask 12 may be demounted and pre-cisely remounted a number of times, a capability required by . ~ 25 conventional faceplate screening operations. When the leaf ~:~ spring 30 is deflected, the provision on the spring moves to .~ achieve stud disengagement with an arc of motion in a plane preferably including a tube diagonal and the mask/tube axis 29 ~:
~the mask and the faceplate being coaxial).
: 30 As shown in Figure 5, the said diagonal for the studs ~ 27 in the left front and right rear corners of the faceplate 6 , ~ ~5~ S~ ~

is designcltec~ . Thc said ylane in which the provision on the syring moves when the spring 30 is deflected is designated Pl in Figure S. Line D2 represents thc other diagonal; the plane P2 is the plane in which the provision on the suspension devices in the left rear and rlght front corners of the ~igure 5 face-plate move when their associated springs 3U are deflected.
Because the non-self-rigid mask 12 is easily flexed about i~s diagonals, and due ~o the corner mountin~ thereof,~
the mask LS capable of conforming to twist-wise de-formation of - 10 the faceplate 6 on which the mask is mounted. Further, by introducing the suspens~on forces along the diagonals in the said planes Pl and P2, the mask corners are immobilized and the mask is held firmly and precisely positioned l~ith respect to the faceplate 6. By the fact that the force exerted by the spring IS; 30 on the mask 12 (when the mask is mounted) is along a diagonal, no subs~antial moment which might tend to distort the mask is imposed thereon.
As wi~ll be described in more detail hereinafter, each of the springs 30 is caused to have a relatively low spring rate 20 ~ e. in flexure out of its plane, yet be extremely stiff in its own plane.~ It can be seen that by this fact, the mask 12 is capable of being repeatably~and precisely fixed in its spatial~
location reIative to the faceplate, without its being deformed or distorted by the imposition of excessive loads or moment loads Z5 thereon. A full description of the suspension system and its . .
components will be given below.
Referring now also to Figures 1-4, the illustrated ` tube 2 is shown as having on the inner surface of the faceplate l 6 a phosphor screen 7 (see Figure 2). The screen is illustrated `( 30 as comprising any array of vertica]ly oriented, horizontally repeating triads of red-emissive, blue-emissive and green-! , ~ . . ' : -: :

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emis~lve pllo~pllor clelllell~s 8~, 8n and 8G. Tlle screen is preferably oE tlle nega~lve guardball(l, black ma~rl~ type as taught in U.S. patent 3,146,368. An aluminum layer is sllown at ll. ~ black grilLe 10 comprises In ~hls embodimen~ u pat te~n of light-absorptive bands separating the phosphor elements 8R9 8B and 8G.
The shadow mask 12 has a pattern of "slot" or "slit" apertures 14, spaced by "tie-bars" 16, which define beam landings 15. The shadow mask is, in general terms, des~
cribed and claimed in U.S. patent No. 3,912,963. Briefly, the shadow mask 12 is non-self-rigid and may conveniently be of a - frameless, one piece construction metal-formed from a single sheet of electrically conductive materials such as 6 mil thlck, cold-rolled steel. An integral skirt 18 shields the screen 7 from stray and overs~anned electrons. The skirt 18 and inte- --!
grally formed channel 20 and edge lip 24 enhances the stiff~
ness of the mask with respect to its major and minor axes, while permitting the mask to flex with respect to its diagonals ~ `
and thereby conform, when mounted to the contour of the face-plate. ~ -~
The tube is shown as including a neck 31, within ~`~ ~hich is contained an electron gun assembly. The electron gun ;~
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assembly may take any of a variety of constructions, but in the illustrated embodiment wherein the mask is a slot mask coopera~lng with a screen of the "line"-type, the electron gun ;.i - . :: ~
assembly preferably is of the "in-line"-type, comprising three sepa~ate guns 32, 33, 34 generating three coplanar beams 35, 36, and 38 which ca~ry, respectively, red-associatedg blue-associated and green-associated color video information. The electron gun assembly is electrically accessed through pins 40 in the base 42 of the tube.
A mask suspension system constructed according to this inyention will now be described. Figures 3 and 4 show ,~
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a preferred maslc suspen6ion dcvlce 26 whlch ls employed on three of the four corners of the mask 12. As ~ill be descrlbed in more de~all below, the suspenslorl device on the fourth corner is str~ctured difEerently from the remaining three de~ices and in such a way as to assure suspension of the mask in a unique rotational orientation relative to the faceplate.
Further, the device for the fourth corner must hold the proper 11~11 spacing (the spacing between the mask and the screen-bearing Eaceplate surface), while allowing the fourth corner of the mask to seek an equilibrium position in its own i plane. However, before discussing the fourth corner suspension -~ de~ice, the preferred structure and operation of the ., remaining three devices 26 will be descrlbed.

The illustrated mask suspension devices 26 each -~ include envelope-associated means on the tube faceplate. `
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Whereas numerous other envelope-associated means are contem-~` plated, in the Figures 1-4 embodiment the envelope-associated means is shown as taking the form of a stud 27. The stud -~1 ', ' : "
27 does not, per se, constitute an aspect of this invention, being descrlbed and claimed in the referentcopending application ~; ~ Serial No. 240,267.
The stud 27 is preferahly a sheet-metal stamping ~ ;
and is illustrated as having a channel shape with a forwardly ;
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extending face 48 containing an integral protuberance or lug ~`
i~ ~ 50 and two legs 52, 54 which are embedded in (of which may, in another form, be cemented to) the faceplate 6. `s ;
~`~` - The spaced legs 52, 54 permit screening fluids suffused across the faceplate during the faceplate screening : . .. . .
operations to pass through the stud 27 without clogging it ~ 30 and without creating reflection marks in the end-product ~-,1 ' pb~ -14-", . .. . . .

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screen. As will b~come eviden~ a8 ~hi~ descrlption proceeds, the positioning of the s~ud 27 and particularly the lllg 50 must be to wi~llin very tight tolerances in order that the shadow Illask 12 will be suspended precisely at the deslred "Q" spacing.
In accordance ~ith the Figures 1-4 embodiment of the present invention, the æuspension device 26 also includes mask-mounted means for retentively and detachably engaging the envelope-associated means (here shown as the stud 27). The mask-mounted means may take various forms, but is here shown as including a stiff bracket 28 externally surrounding and embracing a corner of the mask 12, and a cantilevered leaf ~;
spring 30 (described below) affixed to the bracket 28 and having provision for retentively engaging the stud 27. ~`
The bracket 28, per se, donstitutes an aspect of an invention described and cLaimed in the referent U.S. Patent No. 3,999,098, ~' and the spring 30 an aspect of an invention described ~- ;
~' and claimed in the referent copending application Serial No.
- 253,050. ~ -- 20 The bracket 28 extends around a corner of the mask ~-on the outside and in the plane thereof. The bracket 28 is secured to the ~ask on at least three points 9 two points being located one each on adjoining sides of the mask corner to impart tangential rigidity to the bracket connection. A -third point is located spaced from a line joining the two ::
points so as to impart rigidity to the bracket connection in `~ ;
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~,`! a plane parallel to and passing through the mask axis. The ~
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bracket 28 is illustrated as including a head 60 having a ;~
radially outwardly directed face surface 62 preferably ;
extending parallel to the mask/tube axis 29 when the mask is operati~ely mounted within a tube, The bracket 28 in- -.

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cl~lcs a pclil o~ (livcrging arllls 63, fi~ cxterlclin~ transvcrscly to thc mask/tllbc axis 29. Thc arms 63, 6~ each have a provision, llere shown as dimples 70, 72, intended to be welded to a mask surface, here shown as tllc back surface 74 of channel 20.
The arms 63, 64 have a pair of Willgs 66, 68 bent out of the plane of the arms 63, 6~. Each of the wings 66, 68 has an area on its distal end, here shown as dimples 76, 68, intended to be welded to a side surface of the mask, here shown as side surEace 80 of the channel 20. The wings 66, 68 have, at a point between the supporting arms 63, 64 and the proximate dimple, a provision having a radial yield prior to attachment, here shown as thinned-down sections 82, 84. lhe thinned-down section in each of the wings 66, 68 provides a radial yield (out of the plane of the wing) beEore welding, ~` lS but yet provide high rigidity in the mask's axial direction.
The bracket 28 may, for example, be formed from 60 mil thick cold-rolled steel.
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` ~ ~ Although it is believed that the mask 12 will not re-quire any "Q" compensation, i.e., deliberate variation of 20 ~ the mask-to-faceplate spacing ~the "Q" distance) to compensate for thermally induced mask expansion and contraction, in any . . -; application where such may be desired, it can be provided ; .
- by causing the bracket 28 to be composed, a1 least in its crucial parts9 of a laminated (face-bonded) bimetallic ~, -~ 25 material. Figure 9A shows such a bracket wherein the two components of the laminate structure are shown at 95 and 96 ; and represent metals having suitably different coefficients of expansion. Other properties and features of the bracket and preferred methods of assembly will be described and will be ` 30 better understood after a discussion of the spring 30.
The spring 30 is shown as being welded at one end to the .. . .

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f~lce su-rfclce 62 of the head 60 oE bracket 28 and ln the illus~rated embo~imcnt exten~s towarcl thc ~aceplate. A
provision on the distal end of the spring, here shown as an aperture 86, retentively receives the mating lug 50 on the stud 27 when ~he mask 12 is operatively mounted in a tube.
The leaE spring 30 is shown in isolation in Figures 6 and 7. In the illustrated embodiment, the periphery of the aperture 86 has been stamped to assume a shape which will discourage frictional "hanging up" of the spring 30 on the lug 50.
It is here noted that the lug could as well constitute part of the mask-mounted component and the aperture could be in the stud 27. I-lowever, in that case, the reaction force imposed by the stud aperture on the lug would be displaced from the . ` ~
~l plane of the spring, producing a moment on the spring. The ,;., : :
15~ possible result ~though unlikely) of the application of such a moment to the spring is a misengagement of lug and aperture whlch mlght alter the position of the mask relative to the faceplate, or the mask geometry. The illustrated arrangement ; ~ ~with the aperture in the spring rather than in the stud) ~ ~ 20 ; precludes this possibility.
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~` ~ As briefly discussed above in connection with Figure ; . -5, the lea~ spring is cantilevered such that it deflects with -~ an arc of motion in a plane perpendicular to the mask and preferably passing through the mask/tube axis in order that forces exerted on the mask by the spring are substantially radial. The force exerted by the spring 30 is preferably ~!
substantially along a mask diagonal to preclude the imposition ~; of any substantial moment (in the plane Pl or P2 ~ Figure 5)on the mask which might cause the mask to be deformed.
It would be ideal if the mask, particularly a non-self-rigid mask such as mask 12, were subjected to zero loading , ~ -17-.. , .,. ,. . ... ... . .. , . :

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by its support system. Ilowcver, such :iS not bclieved to be possible in a spring-type support system structwre~ Eor a rapid, precise and convenient demounting and remounting of the mask. It is advantageous, however, to cause the mask loading force to be as low as possible, for a given minimum necessary spring de:~lection, consistent with the many other mask support requirements and constraints. An excessive load exerted on the mask will cause it or its suspension system to deform. This is an especially serious problem during thermal cycling of the tube, as when the faceplate and funnel are frit-sealed at 4003C or more.
The mask expands to its greatest dimensions under such conditions and maximum ~ask loads are generated. Yet the spring 30 must exert suf-ficient force that upon mechanical shocklng o the~tube, ~he shadow mask will not be disengaged.
Preferably the spring 30 has a relatively low spring rate, i.e. stress-versus-deflection characteristic, in order to minimize the variations in spring forces lmposed on thé
mask as a result of tolerance-related variations in spring .. ", deflection. Such tolerance-related variations may be caused, e.g.j by~tolerance errors in the configuration or mounted geometry of bracket 28, or in the location of the~stud 27 on the faceplate 6.
The spring is very stlff in its own plane,~and pre-25~ ferably also in torsion (particularly in applications, as ' described above, where the spring carries the lug and the - ~ stud has the lug-receiving aperture) in order that three of , ~ the suspension devices acting in concert will precisely fix : and hold the mask in a predetermined spatial position re--~ ~ 30 lative to the faceplate against translational or rotational displacement, in spite of any thermal expansion or contraction ~.~).51~
of thc mask, ~e~no~lrl~ g ~ d remoun~:ing of tlle mask, or mech~ntcal shockæ. It can be seen by reference to Figure 5, for example, tllat witl~ threc o the fo~lr .Ieaf sprillg~ being very stiEf in their respective planes, and with thelr distal ends constrained, the mask i8 completely immobilized and its position relative to the faceplate fixed.
The suspension system of the present invention dif-~ fers in a number of respects from the prior art suspension :; ,:
systems described and claimed in the referent U.S~ Patent ,. ....................................................................... .
Nos. 3,896,321 and 3,943,399. The springs of the systems described in those applications are folded and have a small ; amount of flexibility in the tangential direction. In the system of the present invention, at least three of the four mask suspension devices employ leaf springs which are ~ non-folded and otherwise caused to have an insignificant ~; -1 , . . . . . .. ..
- amount of flexlbility in the tangential direction. The result is an il~proved capability of accurately and repeatably positioning the mask relative to the faceplate in spite of -~,~ thermal and mechanical influences.
As noted above in the background discussion, the ` - spring 30, being corner-located, must be compact, have a `~
relatively small deflection, must not be over-stressed during -~
~ demounting or remounting or during thermal recycling of the -~
- tube, and desirably should otherwise meet the afore;described ,: , - , - - ,., ~ ~, :
-~ requirements imposed thereon.
It is noted that in the design of a system of the character herein described and claimed~ the effective length (i.e., cantilevered length "1"~, the width "w", and the thickness "t" of the spring are all of extreme importance.
As noted, the deflection of the spring required to demount or remount the mask must be sufficiently large to permit :'~., ' ' ',: ' ; ~ ,:

pb/

~5~
tllcse opera~ions to bo reaclily performcd manually or with au~omate~l cquipment, and yct the de~lection cannot be so great so ; as to require an intolerably large amount of space in the tubeenclosure. The spring must be thin to prevent excessive stressing thereof upon deflection, yet not so thin as to ` buckle when the tube is drop-tested ~a tes~ which exerts - up to 45 G's on the mask suspension system). Tlle thickness of the spring must also be taken into consideration in connection with welding oE the spring to a support member, if such is necessary.
As noted, the load imposed by the spring on the mask must be adequate to prevent dislodgement of the mask in the event of mechanical shocks, and yet cannot be so great as to de~orm the mask, particularly during thermal cycling lS of the tube wherein the mask is thermally enlarged in size.
, .1 Further, the load value must be relatively insensitive to thermal cycling of the tube. The spring parameters must be chosen, along with the material considerations, such that over-stressing of the spring will not rcsult. -It has been found that ~for constant load) if, e.g., while holding other parameters fixed, the width of the spring i,,, :
is increased, the bending stresses on the spring will be re-duced; however, the de-flection ~for a given load~ is apt to ~ be undesirably reduced. But, to increase the de-flection to an acceptable value, it is apt to be necessary to reduce the thickness of the spring below a minimum thickness which will enable the completed tube to pass the drop tests or ~; which will cause the bending stresses on the sprlng to increase to an undesirable level.
Further, it has been found that if the width of the ", ` spring is excessively decreased, the spring is apt ~o lose its /

~ , . . .

~L()5~

, . .
ncccssary tallgcnt]al stiffness tin its own plane), and, ~for a fixcd deflection, the applied load is apt to drop below an - acceptable value.
~f tlle efcctive length of thc spring is reduced , S too far, the radial stresses will increase beyond a per- -missible limit. Tncreasing the effective length of the spring will result in a reduction in the radial stresses in the spring, but is apt to result in an intolerably reduced applied load on the mask. The space requirement also increases with increasing spring length.
Taking all these and other :Eactors i.nto consideration, ~`~ the ratio of the width "w" to the thickness "t" of the leaf spring 30 is caused~to be between about 25 and 300, and the effective length "1" thereof is between about .5w and l.5w.
lS~ ~ The desirable part of the range of the length-to-width ratio ~ has been found to be where the effective width is approximately !~ ~ equal to the effective length of the spring, ldeally about 9 "1". The loading of the mask by the spring has been found desirably to be between about .34 pounds and 2.4 pounds for Zo ~ ~ a~spring deflection of between about 50-270 mils. Ideally, ~the loading is about .7 pounds and the spring deflection about 90 mils. In a system constructed and very succes~fully tested, the spring had a bend angle 'iO" (see bend line 88 in Figure 7) of about 6. The active length "1" of the spring from the bend line to the center line of the aperture , ~;, , : ~ 86 was about .7 inch ~the overall spring length was about ~ .95 inch). The width of the spring was about .79 inch and ; the spring was composed of .008 inch 17-7 PH stainless steel, heat-treated to a condition RF 950.
~. .
It is an aspect of this invention to provide--a mask suspension system for supporting a shadow mask at a pre-. : -v~

~letermill~d 9p~.1Cir)g f rOIII t:l~e lrlll~r SUr.:1Ce of a color CRT
faceplate. Tlle system oE ~hls inventlon comprl~es ~our ~uspenslon deviccs, Olle ~t cacll corner of the m~lsk, ~or detachably coupllng the mask ~:o the faceplata. 'rhe suspenslon devices each incl~lde an envelope-associated component on the ~: faceplate in a corner reglon thereof for supporting the mask ~' and a mask-mounted component secured to the outslde of a stiffening portion around the periphery of the mask.
One of the components includes spring means having a provlsion for retentively engaging, in a male-female relationship, a provicion on the other of the components. In the illustrated preferred embodiment in three of the suspension devices the engagement provisions on the components are of reverse gender from that of the fourth suspension device to assure a one-way- ~ -only suspension of the mask on the faceplate.
'~ In the preferred embodimentunder description, the .
Eour sus~ension devices have a spring attached to a corner of the mask by an intermediate mounting bracket 28. In this ' embodlment, in three of suspension devices the male and female ~' ' 20 engagement provisions on the mask~mounted and envelope-;~ associated components comprise a projecting lug (lug 50 in the ' Figures 1-4 embodiment) which engages an aperture (aperture 86 in the spring 30 of the Figures 1-4 embodiment)0 As ~-;
described,-'ln accordance with this invention, the fourth sus- '~
~- pension device has mask-mounted and envelope-associated ~:
componen~s having provisions which engage in a male-female `~
relationship, but the gender of the provisions is the opposite - of that in the other three devices.
Referring now particularly to Figure 8, there is shown a suspension device which is preferably employed as the ~' four'th suspension device in a system, according to this ~: :
' . . . .

pb/ -22-invention the remaill~ng t~irce~ eviccs of which are as described above. Ihe Pigurc 8 (fourth) suspension device includes a stud 92 having a construction similar to that of s~ud 27. One major difference however, is that the mask engagement provision in the stud is an aperture 94 rather than a lug. The mask-mounted component is generally similar to the mask-mounted component of the devices 26, but has a lug 98 at its distal end, rather than an aperture. The lug is here shown as being Lntegral with the spring 100, but alternatively may be made initially as a separate element.
It is seen then that the provisions on the mask-mounted and envelope-associated components of the suspension device ` ~ shown~in P~igure 8 engage in a male-female relationship, but that the gender of the relationship is reversed ~ith respect ~;~ 15 to that of the other three suspension devices in the system.
By thls expedlent, in accordance with t~his invention the mask can be mounted on~the~faceplate only in~a predetermined unique rotational orientation with respect thereto. If for example,~the mask were attempted to be attached to 20~ the faceplate 180 rotated from its prescribed po~sition, in one corner a~lug in one of the studs 27 would address "
the lug 98 extending from the spring 100. Engagement be-` tween two lugs would, of course, be impossible. In the diametricall~y opposed corner, and aperture 86 in one of the ~ springs 30 would address aperture 94 in~the stud 92. Again, engagement between two addressing apertures would be impossible.
The fourth suspension device preferably also has a provision for permitting the fourth corner of the mask to seek an equilibrium position in the plane of the mask, while cooperating with the other devices in precisely Eixing the '~ , .- ~. ` ~ . ; ` `

~05~
~Q~ sl,acillg Or thc mask. To ~his e~tl, rcEcrring again ~, to l:igures 8 alld 9~ the stu~ aperture 9~ is clongated in a direction l)arallel to the faceplate inner surfacc when the stud is mounted. The lug 98, upon engagemcnt with the clongated aperture ~4 pcrmits -~he fourth corner of the mask to seek an equilibrium position in its own plane (which position is dictated by the other three suspension devices), .
and yet the proper ~Q~ spacing between the mask and the faceplate inner surface at the fourth corner is maintained.
Alternatively, redundancy compensation may be achieved by structuring the aperture and stud in the fourth suspension device to fit immovably, (as is the case in the above-des-cribed other three devices Z6) and causing the spring -to be . . .
of such construction that it is resilient in the faceplate's ~` 15 tangential direction (when mounted). For example, the spring could be in the form of a~resilient slender and reed.
., . :
~ It should be understood that9 whereas in the Figures -~ 1-9 embodiment, in three of the suspension devices the 20 ~ female engagement provision is on the mask-moun~ed component and in the fourth it is on the envelope-associated component, ; another system according to the teachings of this lnvention could have the converse arrangement-i.e., in three of the suspension devices the made engagement provision could be on Z5 the mask-mounted component and in the fourth device it could be on the envelope-associated component.
; !
``` The present invention may be implemented in a variety of other systems. Whereas in the Figures 1-9 suspension devices the lea spring constituting part of the mask-mounted component extends toward the faceplate, other configurations are possible.
. , .
-2~-'''.

~05151~

For cxa~ple, r igure io S}IOWs a suspcllsion device wherein a leaf spring 102 exte~llds away from the faceplate. A system could be constructed according to this invention wherein one of the Figure 10 devices has the spring carrying a lug 104 for engaging an aperture 106 iTI a s-tud 108 embedded in the ! faceplate 110. In -the remaining three devices, the spring contains the aperture and the lug is on the stud. lhis arrangement has the advantage over the afore-described structure that as the mask 112 expands, due to thermal heating of the mask during tube operation, the mask will :
-~ be moved slightly closer to the screen anl thereby compen~
` sate for mask-expansion-related color degradation in thereproduced images. Conversely, in yet another embodiment, ! :
one female and three male engagement provisions could be 15~ carried by the mask, rather than by the~envelope.
Pigure ll shows a suspenslon devlce wherein a canti-levered spring 114 is mounted on a stud 116 and ex~ends ;away from~the faceplate 118. The spring has a~lug 120 formed at its distal end which is adapted to engage from 20~ ~ the inside~an aperture 1~22 in a bracket 124 carried by a corner of~the shadow mask 126~to embody a device such as~shown ln Figure ll~ln a~system~according to thls invention, elther the mask or the envelope could be structured to support one female engagement and three male provisions.
25 ~ Figure 12 shows yet another arrangement wherein the ;
cantilevered leaf spring 128 is mounted by a faceplate- ~
embedded stud 130 so as to extend away from the faceplate 131.
The spring has at its distal end an aperture 132 adapted to ~. .
retentively receive a lug 134 extending from a bracket 136 on 30 a corner of shadow mask 138. Again, in accordance with this invention, the three female and one male engagement pro-visions can be located either on the mask or on the envelope.
.

~s~s0~

Figures 13-16 illustratc an embodilllcnt oE the in-vention whereill -the spring an(l a supporting hracket are formed integrally from a single element of shcet material In Figures 13-16 there is depicted a corner of a color cathode ray tube, ancl particularly a suspension device for suspending a corner of a shadow mask 140 adjacent the inner - surface of a faceplate 142. The suspension device is illustrated as comprising an integral one-piece bracket-spring member 114. The member 114 ;s welded to the mask 140 at three areas 146, 148, 150 and has at its distal end an aperture 152 for retentively receiving a lug constituting part of a mask-supporting stud 156. The bracket-spring member is shown ` unfurled (before being stamped) in Figure 16. After stamping, the three tabs 158, 160, 162 are formed to have dimples 164, 166, ; 15 168 which are welded to a channel 170 constituting part of the -; ~ mask 140. As shown, the center dimple 166 is welded on the - ~ inside of the channel 170 and the outside dimples 164, 168 are welded to the outside of the channel 170. The bracket~
spring member has two basic portions, divided by their function--a bracket portion 172 and a spring portion 174.
The bracket portion 172 has formed integrally there-: ~
in stiffening corrugations 176 and is otherwise formed for enhanced stiffness. The spring portion 174 is similar in structure, function and operation to the spring 30 in the Figures 1-9 embodiment.
In accordance with this invention, it is preferred that the Figures 13-16 device be located on three mask corners.
The suspension device for the fourth corner would have a lug formed in or attached to the distal end of the bracket spring member 114. The stud in the fourth corner device-would, of course, have a mating aperture.
. . ~ .

~ -26-~ 6~5 :'.
~ lterrl,ltivcly, as al70ve, thc gcnder of cacll of the cngagcment : prov:i.sions collld be reversed.
--. It should be unders~ood -that, as in the figures 1-9 embodimcnt, redundancy compensation is pre:Eerably provided ~ 5 at the fourth corner device (the device with reverse gender : engagement provisions) in the embodiments discussed abovewith respect to ~igures 10-13. ~ither o:f the disclosed ;:: redundancy compensation approaches rnay be followed.
It is important that the leaf spring in each and all embodiments of the invention have the proper position relative . : to the associated studs. Referring for example to the Figures 1-9 embodimen~, it is important that the bracket 28 be preci-sion-mountable in prescribed radial and tangential position on the mask 12 in order that the leaf spring 30 have a predeter-mined appropriate position relative to the stud 27, and in order that the bracket 28 does not interfere with the stud 27 .~ or other:envelope or envelope-associated skructures. It is also .
important that the loading of the spring 30 against the stud 27, and thus the loading of the mask 12, be within a prescribed ~range o-f loading values and be relative constant from unit-to-unit.
: There will now be described a method for assembling the mask-mounted component of certain of the mask suspens on de-. 30 : ' ':

1(3~
vices (devlc-~ 26 in tlle l~ig~lres 1~9 embo~liment for example) in order to meet the afore-~tated reclulren~ents.
This method i8 most relevant to the sub~ect matter of referent V.S. Patent No. 3,999,U98. It i8 important that the face surface 62 on the head 60 of the bracket 28 be parallel to the mask axis and at rl prescribed radial distance therefrom. To assure this, a fixture is provided havlng a flat surface positioned at the precLse radial distance from the mask axis and oriented with precise parallellsm to the mask a~is. Before welding of the bracket 28 to the mask 12, the face surface 62 is brought into intimate engagement with ;-said surface of the fixture. The bracket is then lowered parallel to the tube-mask axis until the dimples 70, 72 make engagement with the back surface 74 of the channel 20 by prebending the wings 66~68J at the point of the thinned down sections 82, 84 inwardly through an angle sufficient to insure that the wings 66, 68 are sure to engage the said surace 80 of a mask being operated on, it is assured that the dimples 70, 72 as well as the dimples 76, 78, will engage the mask 12 when the bracket 28 is proper~y positioned by the aforesaid fixture. The four di~ples 70; 72, 76, and 78 are then welded ~o the mask, assuring a proper positioning of the bracket 28 on the mask 12.
To assure a proper positioning of the aperture 86 in the spring 30 relative to the apertured central portion ~;
of the mask 12, and thus to insure the proper "Q" spacing of the mask, the spring 30 is welded on thè face surface 62 of the bracket head 60 while the aperture 86 is positioned in a fixture which assures the correct "~" spacing of the mask from the phosphor screen.
Reiterating, a feature of the suspension device 26 . . s ,' ~

.- ' pb/ -28-~051 ~ ~ ~

is thc Eo~lr l)oint attachlncllt of tho brackot 70 (two pOillts on the top su-rEacc 74 of the ch.lnnel 20 and two on the side surEace ~0). This pcrmits the bracket 28 to be aligned in an assembly fixt-lre with the bracket face surface 62 parallel to the tube/mask axis and perpendicular to the intersecting mask diagonal, while allowing the dimples 70, 72, 76, and 78 to seat firmly on the mask. When the welds are made at the four dimples, the bracket is -fully restrained in all axes, maintaining the desired orientation of the bracke-t face surface 62 with high stiffness. This ;~ is accomplished with no significant stresses in the mask and bracket, an important ingredl-ent in the achievement of a high degree of tube performance.
The thinned-down sections 82, 84 on the wings 66, 68 permit the additional location control required to maintain the bracket face surface 62 at the proper radial distance .
~ ~ from the tube axis by providing radial yield prior to ~ :
welding. The wings are slightly over-bent inwardly and are allowed to "give" when the bracket is fixed on the mask at the correct radial position. The thinned-down sections 82, 84 thus provide a low-force yield point for ` ~ accommodation o-f manufacturing tolerances. Note that any `~ residual stresses at this yield point results only in a ~ ~ pinching of a corner of the mask and do not contribute `~ 25 to any significant bracket or mask distortion or movement.
~! :
; Also, after welding, no further bending loads can be :, applied to the thinned-down sections 82, 84 about the ~ weak axis thereof; the width of the thinned-down sections - along the "long" or "strong" axis still serve to maintain the rigidity of the bracket 28 in the fixtured location.
A second method for assembling the bracket 28 and '~;

lOS~5 spring 30 on a ma~k 12 will now be ~escribcd. Rathcr than attaciling the bracket 28 to a mask by the use of an appro- I
priate fixture, and then attaching the spring 30 to the bracket 28, the bracket 28 and spring 30 may be welded together while re-ferellcing both to a dummy or simulated mask having nominal mask dimensions. The bracket/spring assembly is then welded at the ~our dimples 70, 72, 76, 78 to an actual mask. Because the mask 1~ is formed accurately by a high precision die, dimensional variations ~ 10 from mask to mask are small. Such variations result ;~ only in minor spring force changes, but because of the described fixturing means, the "Q" spacing will remain un-changed. To assembly the bracket/spring assembly to a mask, the assembly is positioned ln a fixture with reference to the ~15 sprlng aperture 8S (for proper mask "Q" spacing3 and with reference to the face surface 62 (for radial and tangential orientation) ,, and is then welded at the dlmple points to the mask.
Whereas the invention has been described with respect to~exemplary embodiments thereof, it is evident that many al-, terations, modiEications and variations will be apparent to those skilled in the art in light of the above disclosure.
-For example, whereas the above-described mask suspension system is most useful, for the reasons given, when applied in a tube having a flangeless faceplate, the suspension -~ 25 system o~ this invention, because of the substantial cos* `
savings it offers, may be incorporated in a tube of a type :
having a conventional flanged faceplate, as shown for ` example at 180 in the Figure 17. The above teachings made with reference to Figures 1-16 may be incorporated in systems . ', .

~5~5(~

havirlg the fl;;lnge rnollnting ~e.~ rc shown ;n [1igure l7.
igule 17 shows a shadow mask 182, which may be of the character described above with respect to ~igures 1-4, suspend~d adjacent -to the screen-bearing inncr surface 184 of the ~ 5 faceplate 180 by four corner-located mask suspension devices j~ 186. The mask suspension deviccs :L86 may be constructed similar to the mask suspension devices shown in Figures 1-4 except that the stud, rather than being a stud as shown at 27 which is embedded in an extension of the screen-bearing inner surface of the faceplate, is a modified stud 188 having a pair of legs 190, 192 which are embedded one in each corner.
of the rearward flange 194 on the faceplate 180.
Whereas the structure depicted in the above described ;~ embodiments are believed ~o be preferred, numerous modifications and variations may be employed within the spirit and scope of the present invention. Whereas a preferred spring structure has been shown, other spring structures and arrangements are contemplated to be within the purview o-f this invention. Other ", ~ male and/o-r female engagement structures than the lug and -aperture arrangements shown are contemplated. Accordingly, I intend to embrace all such alterations, modifications ~` and variations which fall within the spirit and scope of this invention.

...

,' `

j -31-. .

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. For use in a color cathode ray tube having an envel-ope which includes a curved, approximately rectangular face-plate supporting on an inner surface thereof in a central region a phosphor screen comprising a pattern of red-emissive, blue-emissive and green-emissive phosphor triads, the combin-ation comprising:
an approximately rectangular shadow mask having s similarly curved central portion containing a pattern of apertures registered with said pattern of phophor triads and a stiffening portion circumscribing said central portion; and a mask suspension system for supporting said shadow mask at a predetermined spacing from said inner surface of said faceplate, comprising four suspension devices, one at each corner of the mask, for detachably coupling said mask to said faceplate, said suspension devices each including an envelope-associated component on said faceplate in a corner region thereof for supporting said mask, and a mask-mounted component secured to the outside of said stiffening portion of said mask, one of said components including spring means having a provision for retentively engaging in a male-female relationship a provision on the other of said components in at least one of said suspension devices the provisions on said components being of reverse gender from that of the diagonally opposite suspension device to assure a one-way-only suspension of said mask on said faceplate.

2. The apparatus defined by claim 1 wherein said mask-mounted component in each device includes a bracket secured to said stiffening portion of said mask so as to extend around a corner on the outside and in the plane thereof, wherein said envelope-associated component comprises a metal stud embedded in the faceplate, and wherein said spring means com-prising a cantilevered leaf spring attached at one end to said bracket and having at its distal end said provision for engaging said provision on said stud.

3. The apparatus defined by claim 2 wherein in three of said suspension devices, said studs each have a projecting lug constituting said stud provision and said springs each have an aperture for retentively receiving said studs, and wherein in the fourth device said spring has a projecting lug and said stud has an aperture for retentively receiving said spring lug.

4. The apparatus defined by claim 3 wherein in said fourth suspension device, said aperture in said stud is elongated in a direction parallel to the faceplate inner surface to permit the mask corner supported by the fourth suspension device to seek and find an equilibrium position in the plane of the mask dic-tated by the remaining three devices, while maintaining a predetermined mask-to-faceplate distance for that corner of the mask.

5. For use in a color cathode ray tube having an en-velope which includes a curved, approximately rectangular, flange-less faceplate supporting on an inner surface thereof, in a central region, a phosphor screen comprising a pattern of red-emissive, blue-emissive and green-emissive phosphor element triads, the combination comprising:
an approximately rectangular, non-self-rigid shadow mask with a central portion having a curvature related to that of the faceplate and containing a pattern of electron-transmissive apertures registered with said pattern of phosphor triads, said shadow mask also having a stiffening portion circumscribing said central portion which causes said mask to be relatively stiff with respect to its major and minor axes, yet relatively torsionally flexible with respect to its diagonals; and a mask suspension system for detachably supporting said shadow mask at a predetermined spacing from said inner surface of said faceplate, comprising four suspension devices, one at each corner of the faceplate, for mechanically coupling said shadow mask to said faceplate, said suspension devices each including a faceplate-mounted component in the form of a stud embedded in said faceplate inner surface on a diagonal of said faceplate, and further including a mask-mounted component secured to the outside of said stiffening portion of said mask, said mask-mounted com-ponent including a cantilevered leaf spring having provision for detachably engaging a provision of said stud in a male-female relationship and substantially along a mask diagonal, in three of said suspension devices the provisions on said components being of reverse gender from that of the fourth suspension device to assure a one-way-only suspension of the mask on the faceplate.

6. The apparatus defined by claim S wherein in said three suspension devices, said studs each have a projecting lug constituting said stud provision and said springs each have an aperture for retentively receiving said studs, and wherein in said fourth device said spring has a projecting lug and said stud has an aperture for retentively receiving said spring lug.

7. The apparatus defined by claim 6 wherein in said fourth suspension device, said aperture in said stud is elongated in a direction parallel to the faceplate inner surface to permit the mask corner supported by the fourth suspension device to seek and find an equilibrium position in the plane of the mask dic-tated by the remaining three devices, while maintaining a pre-determined mask-to-faceplate distance for that corner of the mask.