Abstract:
A color picture tube ( 10 ) has a tensioned mask ( 24 ) supported by a support frame ( 28 ) mounted within the tube. The mask has a significantly lower coefficient of thermal expansion than the frame. Intermediate members ( 48 ) are located between the mask and the frame. The intermediate members are of a material having a coefficient of thermal expansion similar to that of the mask. The frame has elongated tabs ( 46 ) extending therefrom. Each of the tabs is attached at one end thereof to the remaining portion of the frame. The distal ends of the tabs are welded to the intermediate members.

Description:
[0001]    This invention relates to color picture tubes having tension masks, and particularly to a tube having means for connecting a tension mask, that is made of a material having a relatively low coefficient of thermal expansion material, to a support frame, that has a significantly higher coefficient of thermal expansion.  
         BACKGROUND OF THE INVENTION  
         [0002]    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.  
           [0003]    One type of color picture tube has a tension mask mounted within a faceplate panel thereof. In order to maintain the tension on the mask, the mask must be attached to a relatively massive support 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.  
           [0004]    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 requires a support 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 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 expansion tension mask with a higher expansion support 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 support frame.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention provides an improvement in a color picture tube having a tensioned mask supported by a support frame mounted within the tube. The mask has a significantly lower coefficient of thermal expansion than the frame. Intermediate members are located between the mask and the frame. The intermediate members are of a material having a coefficient of thermal expansion similar to that of the mask. The frame has elongated tabs extending therefrom. Each of the tabs is attached at one end thereof to the remaining portion of the frame. The distal ends of at least some of the tabs are welded to the intermediate members. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    In the drawings:  
         [0007]    [0007]FIG. 1 is a side view, partly in axial section, of a color picture tube embodying the invention.  
         [0008]    [0008]FIG. 2 is a perspective view of a tension mask-frame assembly.  
         [0009]    [0009]FIG. 3 is a partial perspective view of the frame of FIG. 2.  
         [0010]    [0010]FIG. 4 is a partial perspective view of a second frame embodiment.  
         [0011]    [0011]FIG. 5 is a partial perspective view of a third frame embodiment.  
         [0012]    [0012]FIGS. 6 and 7 are elevation views of the right end of the frame of FIG. 5 in an unheated condition and in a heated condition, respectively.  
         [0013]    [0013]FIG. 8 is a partial perspective view of a fourth frame embodiment.  
         [0014]    [0014]FIG. 9 is a partial perspective view of a fifth frame embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    [0015]FIG. 1 shows a color picture tube  10  having a glass envelope  11  comprising a rectangular faceplate panel  12  and a tubular neck  14  connected by a funnel  15 . The funnel  15  has an internal conductive coating (not shown) that extends from an anode button  16  toward the panel  12  and to the neck  14 . The panel  12  comprises a substantially cylindrical or flat viewing faceplate  18  and a peripheral flange or sidewall  20 , which is sealed to the funnel  15  by a glass frit  17 . A three-color phosphor screen  22  is carried by the inner surface of the faceplate  18 . The screen  22  is a line screen with the phosphor lines arranged in triads, each triad including a phosphor line of each of the three colors. A color selection tension mask  24  is removably mounted in predetermined spaced relation to the screen  22 . An electron gun  26 , shown schematically by dashed lines in FIG. 1, is centrally mounted within the neck  14  to generate and direct three inline electron beams, a center beam and two side or outer beams, along convergent paths through the mask  24  to the screen  22 .  
         [0016]    The tube  10  is designed to be used with an external magnetic deflection yoke, such as the yoke  30  shown in the neighborhood of the funnel-to-neck junction. When activated, the yoke  30  subjects the three beams to magnetic fields which cause the beams to scan horizontally and vertically in a rectangular raster over the screen  22 .  
         [0017]    The tension mask  24 , as shown in FIG. 2, is attached to a peripheral frame  28  that includes two long sides  32  and  34 , and two short sides  36  and  38 . The two long sides  32  and  34  of the frame parallel a central major axis, X, of the tube; and the two short sides  36  and  38  parallel a central minor axis, Y, of the tube. The tension mask  24  includes an apertured portion that contains a plurality of metal strips having a multiplicity of elongated slits therebetween that parallel the minor axis of the mask.  
         [0018]    Details of the frame  28  are shown in FIG. 3. The long sides of the frame  32  and  34  have an L-shaped cross-section formed by two flanges  40  and  42 . One flange  40  is in the X-Y plane, perpendicular to the central longitudinal Z axis of the tube. The second flange  42  is in the X-Z plane, extending perpendicularly to the Y axis. The short sides  36  and  38  also have an L-shaped cross-section, but could be shaped in other cross-sections, such as square, rectangular or even solid. The second flange  42  includes a plurality of slits  44  therein that extend from near the proximal end connection with the first flange  40  to the distal edge of the second flange. The slits  44  define a series of tabs  46  in the frame  28 . In this embodiment, each of the tabs  46  is welded near its distal end to an intermediate member  48 . In other embodiments, the intermediate members  48  need not be attached to all of the tabs  46 . Each intermediate member  48  extends the length of a long side,  32  and  34 , and overlaps the second flange  42  that includes the tabs  46 . The mask  24 , as shown in FIG. 2, is attached between the distal edges of two parallel intermediate members  48 , that are attached to the two long sides  32  and  34  of the frame  28 . The intermediate members  48  are of a material that has a low coefficient of thermal expansion, similar to that of the mask  24 . Therefore, expansion mismatch between the mask and the frame, caused by changes in temperature, does not occur and mask wrinkling during tube manufacturing and mask/frame warping during tube operation do not occur.  
         [0019]    In one embodiment, the L-shaped frame is made from 4130 steel, and the intermediate members and mask are made of low expansion materials, such as Invar. The L-shaped frame is 1.27 mm (0.050″) thick, and the intermediate members  48  are 3.05 mm (0.120″) thick. In general, thicknesses of the component parts of the complete frame assembly are determined by considering mask thickness, the flexibility of the total mask-frame assembly and the desired warp misregistration limits.  
         [0020]    Further embodiments are shown in FIGS. 4 through 9. Each of the embodiments utilizes two intermediate members, that are either the same or similar to the members  48  used in the first embodiment.  
         [0021]    The frame  50  of FIG. 4 is similar to the frame  28  of FIG. 3, except that along each long side  32 ′ an angled portion  52  extends between two flanges  40 ′ and  42 ′ to form a triangularly shaped cross-section. The angled portion  52  includes a plurality of slits  54  that are aligned with slits  44 ′ in the second flange  42 ′ An intermediate member  48 ′ is located between the flange  42 ′ and the angled portion  52 . The formation of a triangular cross-section provides for a rigid frame, even with thinner material than that required for the frame  28  of FIG. 3.  
         [0022]    [0022]FIG. 5 shows a frame  56  that includes slits  58  having varied spacings to form narrower and wider sections,  60  and  62 , respectively, in a second flange  64 . The narrower sections  60  are the tabs to which the intermediate member  48  is attached. FIGS. 6 and 7 show the end tab of the frame  56  of FIG. 5, in an unheated condition and in a heated condition, respectively. When the frame is heated, it expands more than does the intermediate member  48 . Compensation for this expansion differential, to maintain the position of the intermediate member  48 , is provided by the flexure of the tab.  
         [0023]    [0023]FIGS. 8 and 9 show two additional frames  66  and  68 , respectively. Each of these frames has tabs that are enclosed within unopen cutouts in a flange of the frame. In the frame  66  of FIG. 8, a plurality of tabs  70  extend down from the distal edge of a flange  72 , and are attached by welding to an intermediate member  74 . In the frame  68  of FIG. 8, a plurality of tabs  76  extend upward toward the distal edge of a flange  78 , and are attached by welding to an intermediate member  80 .