Abstract:
The present invention provides an improvement in a color picture tube having a tension mask supported by a support frame mounted within said tube. The mask has a significantly lower coefficient of thermal expansion than the frame. The frame has two substantially parallel cantilevered members, each member has a distal edge to which the tension mask is attached. At least one of the distal edges has two sections separated by a gap therebetween. The two sections include an inner section and an outer section. The mask is glued to the inner section and is welded to the outer section.

Description:
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 
     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 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. 
     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, such as Invar. However, a mask from such material would require 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 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 expansion tension mask with a higher expansion support frame. However, a thermal expansion mismatch between mask and frame often results in mask wrinkles following thermal processing, which may involve temperatures as high as 450° C., such as during frit sealing. One solution to deal with this expansion mismatch is to individually weld each mask strand to the frame. It has been found that such individual welding of the strands of a tension mask to a frame causes the mask strands to become misaligned, when existing roller welders are used. 
     The present invention addresses a need for a solution to the problem, of attaching a tension mask to a frame, 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 
     The present invention provides an improvement in a color picture tube having a tension mask supported by a support frame mounted within the tube. The mask has a significantly lower coefficient of thermal expansion than the frame. The frame has two substantially parallel cantilevered members, each member having a distal edge to which the tension mask is attached. At least one of the distal edges has two sections separated by a gap therebetween. The two sections include an inner section and an outer section. The mask is glued to the inner section and is welded to the outer section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a side view, partly in axial section, of a color picture tube embodying the invention. 
     FIG. 2 is a perspective view of a tension mask-frame assembly. 
     FIG. 3 is a partial perspective view of the mask-frame assembly of FIG.  2 . 
     FIGS. 4 through 7 are side views of a cantilevered flange of the frame of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 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 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 . 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 . 
     The tension mask  24 , as shown in FIGS. 2 and 3, 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 strands  39  having a multiplicity of elongated slits  41  therebetween that parallel the minor axis of the mask. Each slit  41  extends between the two long sides  32  and  34  of the mask  24 . 
     As shown in greater detail in FIG. 3, each of the two long sides  32  of the frame  28  includes a rigid section  40  and a compliant member  42  cantilevered from the rigid section. The rigid sections  40  are hollow tubes, and the compliant members  42  are metal plates. The compliant members  42  substantially parallel each other and may vary in height from the center of each section longitudinally to the ends of the sections, to permit the best tension compliance over the mask. Each of the short sides  36  and  38  (not shown) has an L-shaped cross-section upper portion  44  parallel to and separated from a flat bar-shaped lower portion  46 . 
     Each compliant member  42  has a distal edge  48  to which the strands  39  of the tension mask  24  are attached. The distal edge  48  of at least one of the compliant members  42  has two sections  50  and  52  separated by a gap  54  therebetween. The two sections  50  and  52  include an inner section  50  and an outer section  52 . The mask  24  is glued to the inner section  50  and is welded to the outer section  52 . 
     FIGS. 4 through 7 illustrate the steps taken to attach the mask  24  to compliant members  42  of the frame  28 . First, the mask  24  is stretched between the two compliant members  42 , as shown in FIG.  4 . Next, forces F 1  are applied to the compliant members  42  to move them slightly together, and glue  56  is applied to seal the mask strands  39  to the inner sections  50  of the compliant members  42 , as shown in FIG.  5 . After the glue  56  has dried, the forces F 1  are changed to reduced forces F 2 , other forces F 3  are applied to the outsides of the outer sections  52 , and the mask strands  39  are attached to the outer sections  52  by welds  58 , as shown in FIG.  6 . The sum of the forces F 2  and F 3  should be such that the joint produced by glue  56  is not substantially moved, while a light tension in the mask is maintained. The generated spring force between the inner and outer sections  50  and  52  should be similar to the desired final mask tension. Once the mask is welded, a border  60  of the mask  24  is trimmed, and the forces F 2  and F 3  are released from the frame, as shown in FIG.  7 . Utilization of this two-attachment process ensures that the positions of the strands are maintained by the glue when the welds are made. 
     To achieve the proper tension forces in the mask  24  along the entire length of the compliant members  42  requires either that the forces F 3  on the outer sections  52  of the cantilevered compliant members  42  be varied along the mask, or that the spring constant of the outer sections  52  be varied along the compliant members  42 . This latter technique of varying the spring constant can be achieved in many different ways. For example, the thickness of the outer section  52  can be varied either by machining, by moving the position of the gap  54 , or by varying the depth of the gap  54 . 
     Utilization of a tube design that allows for two step attachment of a tension mask, permits attachment of individual strands of a tension mask, while preventing misalignment of the strands relative to a mask frame. This advantage is achieved because the first step of gluing the strands  39  to the inner sections  50  holds the strands in place until they can be welded to the outer sections  52 . 
     In one preferred embodiment, the rigid sections  40  of the long side members  32  and  34  are hollow square tubes of 4130 steel having a wall thickness of 0.175 cm. The thickness of the compliant members is determined by considering mask thickness, the flexibility of the total mask-frame assembly and the desired warp misregistration limits. In a further preferred embodiment, the compliant members  42  are plates of 4130 stainless steel that are 0.157 cm thick. The two L-shaped upper portions  44  are preferably of CRS-1018 steel having a thickness of 0.318 cm. The two bar-shaped lower portions  46  are preferably of 300 Series stainless steel having a thickness of about 3 cm, which has a different coefficient of thermal expansion than does the CRS-1018 steel of the upper portions  44 . When the frame  28  is heated, the lower portions  46  expand more than do the upper portions  44 . 
     Although the rigid sections  40  have been shown as hollow square tubes, other preferred configurations, such as those having L-shaped, C-shaped or triangular-shaped cross-sections, are also possible for these sections. Furthermore, although the short sides  36  and  38  of the frame  28  have been shown as having L-shaped cross-sections, other preferred configurations may be used, such as C-shaped, triangular shaped or box-shaped.