Abstract:
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 includes an active apertured portion formed by a plurality of parallel vertically extending strands, between which are elongated operational apertures through which electron beams pass during operation of the tube. Top and bottom border portions, outside the active apertured portion of the mask, have additional apertures therein that are aligned with the longitudinal centerlines of the strands.

Description:
This invention relates to color picture tubes having tension masks, and particularly to a tube having means for connecting a tension mask to a support frame, such that the stresses on the mask caused by thermal expansion of the frame are minimized or reduced. 
     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. 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 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. 
     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 includes an active apertured portion formed by a plurality of parallel vertically extending strands, between which are elongated operational apertures through which electron beams pass during operation of the tube. Top and bottom border portions, outside the active apertured portion of the mask, have additional elongated apertures therein that are aligned with the longitudinal centerlines of strands. 
    
    
     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 front view of a tension shadow mask. 
     FIG. 3 is a front view of a small section of a border portion of the mask of FIG.  2 . 
     FIG. 4 is a perspective view of a corner of a tension shadow mask-frame assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 5 and 6 are front views of small sections of two different alternative embodiments of tension mask border portions. 
     FIG. 7 is a front view of a small section of the tension mask of FIG. 5, illustrating a bellows action of the mask during frame expansion. 
     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 rectangular funnel  15 . The funnel  15  has an internal conductive coating (not shown) that extends from an anode button  16  to the wide portion of the funnel and to the neck  14 . The panel  12  comprises a substantially flat external 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 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 , shown in FIGS. 2 and 3, includes two long sides  32  and  34 , and two short sides  36  and  38 . The two long sides  32  and  34  of the mask parallel a central major axis, X, of the mask; and the two short sides  36  and  38  parallel a central minor axis, Y, of the mask. The tension mask  24  includes an active apertured portion  40  that contains a plurality of parallel vertically extending strands  42 . The strands  42  in the active apertured portion may or may not include connecting tie bars (not shown). A multiplicity of elongated operational apertures  44 , between the strands  42 , parallel the minor axis Y of the mask. The electron beams pass through the operational apertures  44  in the active portion  40  during tube operation. Each operational aperture  44  extends into two border portions  46  and  48  at the long sides  32  and  34 , respectively, of the mask. The strands  42  are split by the inclusion of elongated additional apertures  45  that are aligned with the longitudinal centers of the strands. The additional apertures  45  overlap the operational apertures  44  in a spaced interdigitated fashion. The purpose of the additional apertures  45  in the border portions  46  and  48  of the mask  24  is to accommodate a greater expansion of the frame  50  compared to that of the mask  24 , without causing appreciable relocation of the mask strands  42  in the active portion  40  of the mask. 
     A frame  50 , for use with the tension shadow mask  24  is partially shown in FIG.  4 . The frame  50  includes four sides: two long sides  52 , substantially paralleling the major axis X of the tube, and two short sides  54 , paralleling the minor axis Y of the tube. Each of the two long sides  52  includes a rigid section  56  and a compliant section  58  cantilevered from the rigid section. The rigid sections  56  are hollow tubes, and the compliant sections  58  are metal plates. Each of the short sides  54  has an L-shaped cross-section upper portion  60  parallel to and separated from a flat bar-shaped lower portion  62 . The two long sides  32  and  34  of the tension mask  24  are welded to the distal ends of the compliant sections  58 . Although the present invention is described by way of embodiments using the frame  50 , it is to be understood that many other types of tension frames could also be used for the present invention. 
     Other embodiments of mask borders having different patterns of additional apertures are shown in FIGS. 5 and 6. In a mask  66 , shown in FIG. 5, additional apertures  68  are located between operational apertures  70 , adjacent to large tie bars  72  in the operational apertures that connect strands  74  of the mask. The additional apertures  68  are centered on the longitudinal centerlines of the strands  74 , and overlap portions of the operational apertures  70  above and below the tie bars  72 . In another mask  76 , shown in FIG. 6, additional apertures  78  are located between operational apertures  80 , adjacent to large tie bars  82  in the operational apertures that connect strands  84  of the mask. The remaining portions of the operational apertures  80 , near the mask border edges, include smaller tie bars  86 . The additional apertures  78  are centered on the longitudinal centerlines of the strands  84 , and overlap portions of the operational apertures  80  above and below the large tie bars  82 . 
     The dimensions given in FIGS. 3,  5  and  6  are representative values for a tension mask approximately 49.5 cm by 41.3 cm. The mask material is Invar, about 0.10 mm (4 mils) thick, and the frame material is steel. 
     All known commercially used tension shadow mask tubes have had solid border portions at the mask-to-frame weld points. This was acceptable when the mask and frame were made from similar expanding materials. However, when a mask and frame differ greatly in coefficients of thermal expansion, such solid border portions will deform, thereby permanently deforming the active portion of the mask during thermal processing of the tube. The additional apertures of the present invention aid in preventing substantial distortion in the active portion of the mask by providing a “mechanical filter” that accommodates any individual strand attachment errors or movements during processing or tube operation. FIG. 7 illustrates the effect that expansion of the frame compliant section  58  has on the mask  66  of FIG.  5 . Expansion of the compliant section  58  results in a bellows action on the additional apertures  68  in the mask, whereby the mask expands in the direction of the thermal expansion of the compliant sections  58 .