Abstract:
A method and apparatus of maintaining spacing between tension mask strands in a tension mask. The method includes providing a tension mask with strands connecting therebetween and attaching a set of barrier ridge elements to a first side of the strands. Next, the tension mask is tensioned and affixed to a mask frame to form a mask frame assembly.

Description:
[0001]    This invention generally relates to color picture tubes and, more particularly, a method and apparatus for fabricating tension masks for color picture tubes.  
         BACKGROUND OF THE INVENTION  
         [0002]    A color picture tube includes an electron gun for forming and directing three electron beams to a screen of the tube. The screen is located on the inner surface of the faceplate of the tube and is made up of an array of elements of three different color emitting phosphors. An aperture mask, which may be either a domed mask or a tension 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 mask is a thin sheet of metal, such as steel, that is contoured to somewhat parallel the inner surface of the tube faceplate. A focus mask comprises two sets of conductive lines that are perpendicular to each other and separated by an insulator. When different potentials are applied to the two sets of lines to create multiple focusing lenses in each of the mask openings, the mask is referred to as a focus mask. One type of focus mask is a tension focus mask, wherein at least one of the sets of conductive lines is under tension. Generally, in a tension focus mask, a vertical set of conductive lines or strands is under tension and a horizontal set of conductive lines or wires overlies the strands.  
           [0003]    In assembling a strand tension mask, it is required to assemble the strands with a high degree of accuracy to achieve consistent spacing between the strands.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides a method and apparatus for maintaining uniform spacing between the strands of a tension mask. The apparatus includes providing a set of barrier ridges and affixing them to a tension mask. The barrier ridge is aligned perpendicular to the strands of the tension mask and affixed to the frame near the ends of the tension mask. The barrier ridges traverse the length of the tension mask and act to keep the mask strands parallel and equidistantly spaced from each other when faced with applied stress during mask welding and subsequent thermal processing. After the barrier ridges are affixed to the frame, the tension mask is mounted to the mask frame. The barrier ridges are affixed to the frame inside the frame and directly under and in contact with the mask strands. When the tension mask is mounted to the mask frame, the barrier ridges lay inside the mask frame, and between the mask frame and the array region of the tension mask that produces visible image on the screen. The mask strands are in frictional contact with the barrier ridge. They may also be adhered to the ridge by a suitable adhesive such as Kasil.  
           [0005]    During mask-to-frame welding, mask strands are welded directly to the cantilever of the frame. Because of the frictional force exerted by the barrier ridge, mechanical stresses applied to strands along the weld contact points are isolated to the regions of the strands of the contact points. Therefore, the portions of the strands between the barrier ridges are, advantageously, less affected by the mechanical stresses and maintain their positions. After the tension mask is affixed to the mask frame, the entire mask frame assembly is used in manufacturing a color picture tube. As such, the assembly is processed through a series of thermal cycles. The barrier ridges expand and contract in unison with the mask frame. By attaching the tension mask strands to the barrier ridges, spatial integrity between the strands is thus maintained during the manufacturing of the strand tension masks, subsequent processing and tube operation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a side view, partially in the axial section, of a color picture tube, including a strand tension focus mask-frame-assembly according to the present invention;  
         [0007]    [0007]FIG. 2 is a perspective view of the strand tension focus mask-frame-assembly of FIG. 1;  
         [0008]    [0008]FIG. 3 is a front view of a tension mask frame of FIG. 2 prior to attachment of the strand tension mask;  
         [0009]    [0009]FIG. 4 is a front view of the strand tension mask of FIG. 2 prior to welding to the tension mask frame;  
         [0010]    [0010]FIG. 5 is a front view of a tension mask of FIG. 4 depicting the locations of the tension mask which will contact the barrier ridges on the mask frame; and  
         [0011]    [0011]FIG. 6 is a front view of the tension mask assembly according to the present invention; this drawing illustrates the relationship between the locations of the mask frame, the barrier ridges and the mask skirt. 
     
    
     DETAILED DESCRIPTION  
       [0012]    [0012]FIG. 1 shows a cathode ray tube  10  having a glass envelope  12  comprises a rectangular faceplate panel  14  and a tubular neck  16  connected by a rectangular funnel  18 . The funnel  18  has an internal conductive coating (not shown) that extends from an anode button  20  to a neck  16 . The panel  14  comprises a viewing faceplate  22  and a peripheral flange or sidewall  24  that is sealed to the funnel  18  by a glass sealing frit  26 . A three-color phosphor screen  28  is carried by the inner surface of the faceplate  22 . The screen  28  is a line screen with the phosphor lines arranged in triads, each triad including a phosphor line of each of the three colors. A cylindrical tension mask  30  is removably mounted in a predetermined spaced relation to the screen  28 . The mask may be either a tension focus mask or a tension mask. An electron gun  32  (schematically shown by the dashed lines in FIG. 1) is centrally mounted within the neck  16  to generate three in-line electron beams, a center beam and two side beams, along convergent paths through the mask  30  to the screen  28 .  
         [0013]    The tube  10  is designed to be used with an external magnetic deflection yoke, such as the yoke  34  shown in the neighborhood of the funnel to neck junction. When activated, the yoke  34  subjects the three beams to magnetic fields that cause the beams to scan horizontally and vertically in a rectangular raster over the screen  28 .  
         [0014]    A strand tension focus mask  30 , shown in greater detail in FIG. 2, includes two long sides  36  and  38  and two short sides  40  and  42 . The two long sides  36  and  38  of the mask parallel a central major axis, x, of the tube. The tension mask  30  includes two sets of conductive lines: strands  44  that are parallel to the central minor axis y and to each other; and crosswires  46 , that are parallel to the central major axis x and to each other. The crosswires  46  are coupled to busbars (not shown) on their distal ends and lie above the mask strands. In one embodiment, the strands  44  are flat strips that extend vertically, having a width of about 13 mils and a thickness of about 2 mils, and the crosswires  46  have a round cross section, having a diameter of approximately 1 mil and extend horizontally. In the completed mask, the strands and crosswires  46  are separated from each other by a suitable insulator such as lead frit.  
         [0015]    [0015]FIG. 3 is a front view of a mask frame  300  similar to that of FIG. 2. The mask frame  300  is comprised of a set of segments attached together to form a generally rectangular shape. Segments  302  and  304  represent the vertical elements of the mask frame  300 . The mask frame  300  also includes horizontal segments  306  and  308 . Element  310  is a representation of an aperture formed inside the mask frame  300 . Cantilevers  312 A and  312 B are outer portions of the mask frame  300 . These cantilevers  312 A and  312 B are the areas to which strands  44  of stand alone tension mask  400  of FIG. 4 are welded. Barrier ridges  313 A and  313 B shown in FIG. 3, are attached to the mask frame  300  and help to make up part of the horizontal segments  306  and  308 . FIG. 6 represents how a tension mask  400  is generally affixed to a mask frame  300 .  
         [0016]    [0016]FIG. 4 is a front view of the stand alone tension mask  400  that is used, when assembled, in the arrangement of FIG. 2. The free tension mask  400  is formed of a flat thin sheet of material that has been etched to form a plurality of strands  44  between two edge portions  404 A and  404 B. Edges  404 A and  404 B are used for handling purposes prior to mask frame welding and are removed or severed afterward. FIG. 5 is a front view of the tension mask  400  of FIG. 4, depicting the locations of attachment points  402 A and  402 B of the free tension mask  400  which will be in frictional contact with the barrier ridges  313 A and  313 B. The barrier ridge elements  313 A and  313 B are aligned (as discussed below) generally perpendicularly to the mask strands  44 . Next, FIG. 6 is a front view of the tension mask assembly according to the present invention; this drawing illustrates the relationship between the locations of the mask frame  300 , the barrier ridge elements  313 A and  313 B, the mask edge portions  404 A and  404 B and the locations of attachment points  402 A and  402 B prior to severing the borders  404 A and  404 B.  
         [0017]    To best understand the invention, the reader should simultaneously refer to FIGS. 3, 4,  5  and  6 . The mask aperture area, or viewable array region,  406  in which the mask strands  44  traverse, is an area in which it is essential for mask strands  44  to maintain proper spatial integrity in relation to the mask frame  300  during assembly of the mask frame assembly  30  and the picture tube  10 . If proper spatial integrity is not maintained between the individual mask strands  44  and the mask frame  300 , the electron beam is caused to misregister, relative to its intended phosphor target, thus creating a visible optical anomaly on the phosor screen  28 , typically affecting color purity or causing visible streaks. It is therefore desirable to maintain parallel and uniform spacing between the mask strands  44 . Commonly used mask frame  300  materials include but are not limited to steel alloys or iron-nickel alloys.  
         [0018]    As mentioned above, the free tension mask  400  is formed of a flat thin sheet of material that has been etched to form a plurality of strands  44  between two edge portions  404 . Each strand  44  is substantially parallel to the other, and each strand  44  is spaced at a precise distance apart from the other. The material of the free tension mask  400  is formed of is generally a steel or an iron nickel alloy.  
         [0019]    Direct welding of each of mask strands  44  to the cantilevers  312 A and  312 B is necessary in that it allows each individual mask strand  44  to be isolated from the other mask strands  44  during tube fabrication and operation. The barrier ridges  313 A and  313 B to which the mask strands  44  are in frictional contact isolate each mask strand  44  from other mask strands  44  during the welding of the mask strands  44  to the cantilevers  312 A and  312 B.  
         [0020]    [0020]FIG. 5 is a rear view of the tension mask  400  of FIG. 4, depicting the locations of attachment points  402 A and  402 B of the free tension mask  400  barrier ridges  313 A and  313 B of the present invention. The mask strands  44  are attached perpendicularly to the barrier ridges  313 A and  313 B as mentioned above. The barrier ridges are mechanical components of the mask frame  300 . The barrier ridges  313 A and  313 B as well as the cantilevers  312 A and  312 B have accurate contours.  
         [0021]    The barrier ridges  313 A and  313 B to which the mask strands  44  contact prevent the mask strands in the area of the barrier ridges  313 A and  313 B from losing spatial integrity in relation to each other and to the mask frame  300 . The friction between mask strands  44  and barrier ridge  313 A or  313 B prohibits mask strands  44  from moving laterally, during the welding process of mask strands  44  to cantilever  312 A or  312 B, respectively. Strands  44  may be added to barrier ridges  313 A and  313 B using suitable adhesive such as Silicate glass for further prohibiting the lateral movement of strands  44 .  
         [0022]    [0022]FIG. 6 is a top view of the tension mask assembly  30  according to the present invention; this drawing illustrates the relationship between the locations of the mask frame  300 , the barrier ridges  313 A and  313 B and the mask edge portions  404 A and  404 B. The free tension mask  400  is inserted into, and placed under tension, by a stretching fixture (not shown). The tension created by the stretching fixture maintains the spatial integrity of the mask strands  44 . The tension mask  400  is then laid across and brought into contact with the mask frame  300 . At this point, the locations or attachment points  402 A and  402 B of the free tension mask  400  contact the barrier ridges  313 A and  313 B.  
         [0023]    The strands  44  are then attached to the cantilevers  312 A and  312 B by welding or other attachment method. The method of welding the strands  44  to the mask frame  300  is accomplished by, but not limited to, seam, resistance, spot, laser, and tack welding. After the mask strands  44  have been affixed to the cantilevers  312 A and  312 B, the entire mask frame assembly  30  is prepared for further processing.  
         [0024]    As the embodiments that incorporate the teachings of the present invention have been shown and described in detail, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings without departing from the spirit of the invention.