Abstract:
The present invention provides an improved support blade structure for use on a tension mask frame assembly. The support blade structure is formed of a material having a first coefficient of thermal expansion and includes fastening portions and an insert member connected at a generally central location to the support blade structure. The insert member is formed of a material having a second coefficient of thermal expansion and has a plurality of apertures extending in a row along its length. The aperatures are dimensioned to be larger than the fastening portions passing therethrough to loosely connect the insert member to the support blade structure. This allows the insert member to be connected at the center while it&#39;s end are free to slide relative to the support blade structure during thermal cycling.

Description:
FIELD OF THE INVENTION 
     This invention relates to color picture tubes having tension masks, and more particularly to a tension mask frame assembly having a mask support blade structure with an insert for supporting the tension mask. 
     BACKGROUND OF THE INVENTION 
     A color picture tube includes an electron gun for generating and directing three electron beams to the screen of the tube. The screen is located on the inner surface of a faceplate of the tube and is made up of an array of elements of three different color emitting phosphors. A color selection electrode, which may be either a shadow mask or a focus mask, is interposed between the gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam. A shadow mask is a thin sheet of metal, such as steel, that is usually contoured to somewhat parallel the inner surface of the tube faceplate. 
     One type of color picture tube has a tension mask affixed to two parallel support frame members under tension and mounted within a faceplate panel thereof. In order to maintain the tension on the mask, the mask must be attached to a relatively massive frame. Although such tubes have found wide consumer acceptance, there is still a need for further improvement, to reduce the weight and cost of the mask-frame assemblies in such tubes while maintaining the necessary tension on the mask. 
     It has been suggested that a lighter frame could be used in a tension mask tube if the required tension on a mask is reduced. One way to reduce the required mask tension is to make the mask from a material having a low coefficient of thermal expansion. However, a mask from such material would require a frame of a material having a similar coefficient of thermal expansion, to prevent any mismatch of expansions during thermal processing that is required for tube manufacturing, and during tube operation. Because the metal materials that have low coefficients of thermal expansion are relatively expensive, it is relatively costly to make both the mask and frame out of identical or similar low expansion materials. Therefore, it is desirable to use the combination of a low coefficient of thermal expansion tension mask with a higher coefficient of thermal expansion frame, and to provide a solution to the problem that exists when there is a substantial mismatch in coefficients of thermal expansion between a tension mask and its frame. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved mask support blade structure for use on a tension mask frame assembly. The support blade structure is formed of a material having a first coefficient of thermal expansion and includes fastening portions and an insert member. The insert member is formed of a material having a second coefficient of thermal expansion and includes a plurality of apertures extending in a row along its length. The insert member is connected to the support blade structure with at least one fastening portion at a generally central location along the length of the insert member. The remaining fastening portions connect the insert portion to the support blade structure through the apertures which are dimensioned to be larger than the fastening portions such that the fastening portions loosely fit into the apertures of the insert member. This allows the insert member to be fixed at the center while its&#39; ends are free to slide relative to the support blade structure during thermal cycling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying figures of which: 
         FIG. 1  is a cross sectional view of a color picture tube having a tension mask frame assembly mounted behind the face plate panel. 
         FIG. 2  is a perspective view of the tension mask frame assembly shown in FIG.  1 . 
         FIG. 3  is a front view of a support blade structure. 
         FIG. 4  is cross sectional view taken along the line  4 — 4  of FIG.  3 . 
         FIG. 5  is a perspective view of the support blade structure during assembly. 
         FIG. 6  is a partial cross sectional view of the support blade structure taken along line  6 — 6  of  FIG. 4  showing the insert apertures and support blade structure portions passing therethrough. 
         FIG. 7  is a partial cross sectional views taken along the line  7 — 7  of  FIG. 4  showing the relative position between the insert and support blade structure before thermal cycling. 
         FIG. 8  is a partial cross sectional view taken along the line  7 — 7  of  FIG. 4  showing the relative position between the insert and support blade structure during thermal cycling. 
         FIG. 9  is a cross sectional view similar to that of  FIG. 4  for an alternate embodiment of the support blade structure. 
         FIG. 10  is a partial cross sectional views similar to  FIG. 7  showing the relative position in the alternate embodiment insert and support blade structure before thermal cycling. 
         FIG. 11  is a partial cross sectional view similar to  FIG. 8  showing the relative position in the alternative embodiment insert and support blade structure during thermal cycling. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a color picture tube  1  having a glass envelope  2  comprising a rectangular faceplate panel  3  and a tubular neck  4  connected by a funnel  5 . The funnel  5  has an internal conductive coating (not shown) that extends from an anode button  6  toward the panel  3  and to the neck  4 . The panel  3  comprises a viewing faceplate  8  and a peripheral flange or sidewall  9 , which is sealed to the funnel  5  by a glass frit  7 . A three-color phosphor screen  12  is carried by the inner surface of the panel  3 . The screen  12  is a line screen with the phosphor lines arranged in triads, each of the triads including a phosphor line of each of the three colors. A color selection tension mask frame assembly  10  is removably mounted in predetermined spaced relation to the screen  12 . An electron gun  13 , shown schematically by dashed lines in  FIG. 1 , is centrally mounted within the neck  4  to generate and direct three inline electron beams, a center beam and two side or outer beams, along convergent paths through the tension mask frame assembly  10  to the screen  12 . 
     The tube  1  is designed to be used with an external magnetic deflection yoke  14  shown in the neighborhood of the funnel-to-neck junction. When activated, the yoke  14  subjects the three beams to magnetic fields which cause the beams to scan horizontally and vertically in a rectangular raster over the screen  12 . 
     The tension mask frame assembly  10 , as shown in  FIG. 2 , includes a frame  20  comprising two long sides  22  and  24 , and two short sides  26  and  28 . The two long sides  22 ,  24  of the frame are parallel to a central major axis, X, of the tube; and the two short sides  26 ,  28  parallel a central minor axis, Y, of the tube. Although the tension mask frame assembly  10  is shown here diagramatically as a sheet for simplicity, it includes an apertured mask  30  that contains a plurality of metal strips (not shown) having a multiplicity of elongated slits (not shown) therebetween that parallel the minor axis of the mask  30 . A support blade structure  40  is fastened to the frame  20  and may vary in height from the center of each section longitudinally to the ends of the sections to permit the best curvature and tension compliance over the mask  30 . 
     Referring to  FIG. 3 , the support blade structure  40  has a mask receiving edge  43  located on insert member  60  which extends from a front side wall  48 . The mask receiving edge  43  may be appropriately contoured so that the applied mask conforms with the inner surface of the panel  3 . Further detail of the support blade structure  40  can be seen in  FIGS. 4 and 5 . A first half  41  is joined to a second half  45  to form a closed tubular structure which contains the insert member  60 . The first half  41  forms a bottom wall  44  and a front side wall  48  of the tubular structure. The second half  45  forms a rear side wall  46  and a top wall  42  of the tubular structure. As best shown in  FIG. 5 , a series of projections  47  and recesses  49  extend along an edge of the bottom wall  44 . A plurality of fastening portions, or insert-securing tabs  51 , extend from an edge of the front side wall  48 . Each insert-securing tab  51  has a stop surface  52  which separates a narrow portion  54  from a wide portion  56 . 
     Turning now to the second half  45 , the rear side wall  46  has a plurality of projections  55  separated by recesses  53  extending along an edge. Similarly, the top wall  42  has a plurality of projections  66  separated by recesses  68 . 
     Referring to  FIGS. 4-8 , the insert member  60  is formed from a plate having a thickness which is greater than the thickness of the tension mask  30  and is profiled to have a mask receiving edge  43  and a back surface  61 . A central tab receiving opening  62  is preferably formed around a centerline C which is centrally located along the length of the insert member  60 . It should be understood by those reasonably skilled in the art that although it is preferred to have a single central tab-receiving opening around the centerline C, this central tab receiving opening may alternately consist of a plurality of central tab receiving openings located in the vicinity of the center line C. A plurality of outer tab receiving openings  64  each being dimensioned to be larger than the central tab-receiving opening  62  extends in a row outward from the central tab receiving opening  62 . The support blade member  40  is assembled as best shown in  FIG. 5  by first urging the insert-securing tabs  51  though the central and outer tab receiving openings  62 ,  64  of the insert member  60 . The first half  41  along with the insert member  60  are then fastened to the second half  45  such that the projections  47  fit into recesses  53  and projections  55  fit into recesses  49 . Similarly, the narrow portions  54  of the insert-securing tabs  51  fit into recesses  68 . Each of the respective projections  47 ,  55 ,  66 , and insert-securing tabs  51  may then be preferably fastened to each other as for example, by welding. The first and second halves  41 ,  45  may alternatively be secured to each other by an interference fit between the projections  47 ,  55 ,  66  and the recesses  49 ,  53 ,  68  or by selectively welding portions of each half. Alternatively, the first and second halves  41 , 45  maybe constructed of one piece so as to be folded and secured along each edge with insert-securing tabs  51  and recesses  68 . 
     The support blade structure  40  is then fixed to the frame  20  along the rear side wall  46 . Once the tension mask  30  is applied to the mask receiving edge  43 , a force cantilever is applied to the insert member  60  causing it to rotate about a point where it contacts the front side wall  48  of the first half  41 . The back surface  61  is therefore urged against an inner surface of the top wall  42  causing the insert member  60  and the tension mask  30  to remain correctly positioned. 
     Turning now to  FIG. 6 , the insert-securing tabs  51  are inserted into the recesses  68  of the top wall  42  until the stop surfaces  52  abut the projections  66 . As best shown in  FIGS. 6 and 7 , the central tab receiving opening  62  is dimensioned to form a tight fit with the wide portion  56  of the insert-securing tab  51  inserted therein. The outer tab receiving openings  64  are dimensioned to loosely receive the wide portions  56  of the insert-securing tabs  51  inserted therein. It should be understood that either the tab receiving openings  62 ,  64  or the wide portions  56  may be dimensionally altered to create this tight fit or loose fit as required. It should also be understood that either one or several tabs  51  around the center may be dimensioned to have a tight fit with the respective openings  62 ,  64  to connect the insert member  60  to the support blade structure  40 . 
     During thermal cycling, because the first and second halves  41 ,  45  are formed of a relatively high coefficient of thermal expansion material and the insert member  60  is formed of a relatively low coefficient of thermal expansion material, the first half  41  and front side wall  48  will expand more rapidly than the insert member during heating. As shown in  FIG. 8 , during expansion, the relative movement between the insert member  60  and the first half front side wall  48  is controlled about the center line C. Expansion of the front side wall  48  occurs in the directions indicated by the arrows E in FIG.  8 . The central tab receiving opening  62  keeps its respective insert-securing tab  51  centrally positioned while allowing the remaining insert-securing tabs  51  to move outward in the direction E, or along the longitudinal length of the insert member  60 , within the outer tab receiving openings  64 . It should be noted in  FIG. 8  that expansion will occur such that the insert securing tabs closest to the center will move within their respective outer tab receiving openings a smaller distance than those located further towards the outer edges of the insert member  60 . The outer tab receiving openings closest to the center line C therefore have a greater clearance on their outer edges while the outer tab receiving openings  64  closest to the outer edges of the insert member  60  have a greater clearance on their inner edges. 
     An alternate embodiment of the invention is shown in  FIGS. 9-11 . The cross sectional view of  FIG. 9  shows the tension mask  30  similarly fixed to a contoured mask receiving edge  143  of the alternate insert member  160 . The alternate support blade structure  140  is different in that it does not form a closed tubular structure, but instead consists only of a single support member  145  thus eliminating the need for a second half to close the tubular structure. The single support member is similarly fastened to the frame  20 . A top wall  142  extends from the rear side wall  146  to receive the insert member  160 . Here, however, the insert member  160  is fixed to an outer surface of the top wall  142 . The mask  30  also may function as holding or compressing the insert member  160  against the top wall  142  while in tension. It should be understood, however, that in this embodiment, the insert member  160  could alternately be fixed to the inner surface of the top wall  142  provided the fastening portion secures the insert member  160  to the top wall  142  so as to maintain adequate support for the mask  30 . As shown in the present embodiment, fastening portions such as a fasteners  151  pass through fastener receiving openings  162 , 164  in the insert member  160 . The central fastener receiving opening  162  and the outer fastener receiving openings  164  are urged differently from the embodiment of  FIGS. 1-8  in order to receive the fastener  151 . It should be understood that while the central fastener receiving opening  162  is preferably shown here to be circular and the outer fastener receiving openings  164  are preferably shown here to be oval, these openings may be formed in other shapes to receive different shaped fasteners. As best shown in  FIG. 10 , this alternate embodiment is similar to that of  FIGS. 1-8  in that the central fastener receiving opening  162  is dimensioned to form a tight fit with the fastener  151  received therein while the outer fastener receiving openings  164  dimensioned to loosely receive the fasteners  151  and allow for them to move within the outer fastener receiving openings  164  during thermal expansion. Consequently, it should be understood that the insert member  160  may be connected to the support member by any suitable central fastening portion such as, for example, by welding.  FIG. 11  shows the relative motion between the fasteners  151  and outer fastener receiving openings  164  during a heating cycle. Since the relative motion between these components is similar to that described with reference to  FIG. 8 , it will not be repeated here. It should be noted that the insert member in both embodiments is preferably selected to have a coefficient thermal expansion which is closely matched with that of the mask  30 . This allows both components to expand and contract together during thermal cycling to better control the positional accuracy of the mask during processing. 
     An advantage of the present invention is that a relatively high coefficient of thermal expansion inexpensive material may be utilized to create support blade structure  40 ,  140  while a small amount of relatively expensive low coefficient of thermal expansion material may be utilized for an insert member  60 . The structure of the invention allows for relative motion between the insert member  60 ,  160  and support blade structure  40 ,  140  in a controlled manner about a center to insure that the tension mask  30  remains precisely positioned behind the faceplate panel  3  during thermal cycling which occurs into processing. 
     The foregoing illustrates some of the possibilities for practicing the invention. Many other embodiments are possible within the scope and spirit of the invention. It is, therefore, intended that the foregoing description be regarded as illustrative rather than limiting, and that the scope of the invention is given by the appended claims together with their full range of equivalents.