Patent Document

The invention generally relates to the application of crosswires to a tension focus mask for use in color picture tubes and, more particularly, to a method and apparatus of protecting the edges of mask frame assembly from damage during handling and providing an integral beam shield as well as stabilize the edge strands. 
     BACKGROUND OF THE INVENTION 
     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 shadow mask or a tension mask, is interposed between the electron 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 contoured to somewhat parallel the inner surface of the tube faceplate. A shadow mask may be either domed or tensioned. A type of tension mask, called a tension focus mask, comprises two sets of conductive elements that are perpendicular to each other and separated by an insulator. Two different voltages are applied to the two sets of elements to create quadropole focusing lenses in each of the mask opening, which form a focus mask. The mask openings are defined by the rectangular space between adjacent vertical lines and adjacent horizontal lines. Generally, in a tension focus mask, a vertical set of conductive lines or strands is under tension and a set of horizontal conductive elements sometimes known as crosswires overlies the strands. 
     In cathode ray tubes containing tension focus masks, the spatial integrity of the strands and crosswires is critical. The crosswires and strands must not move from their respective positions during tube operation or during tube fabrication. Any such motion of the crosswires could impact the mask strands causing electron beams to misregister with the phosphor elements, during tube operation. It is therefore desirable that the mask structural elements, especially those used to terminate the crosswires, must be rigid. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus and method of constructing a rigid busbar for the purpose of preventing damage to a tension focus mask due to handling during the manufacturing process. The apparatus includes a mask frame assembly having a set of short sides constructed by robust steel structural members. The short sides are formed from a base segment formed of a stainless steel 90° extruded angle shape having two respective ends. The 90° extruded base segment forms the bottom and side rail of the short side of the mask frame assembly. This side rail is attached on each of its respective ends to two square tubes that form the long sides of the rectangular mask frame assembly. Above the stainless steel side rail is another larger side rail formed of cold rolled steel in the shape of an angle attached on each end to the square tubes. A set of arched cantilevers are also attached to the ends of the side rails above the point where the square tube is joined to the side rail. 
     The cantilevers support a tension mask that is welded to each of the cantilevers and whose strands are parallel to the short sides of the mask frame assembly. 
     Along the outsides of the steel side rails is attached an insulating strip. A set of bus bars are then attached to the outside of the insulating strips. A plurality of crosswires are laid perpendicular to the mask strands and attached on each end to the bus bars. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view, partially in axial section, of a color picture tube, including a tension focus mask assembly according to the present invention; 
     FIG. 2 is a perspective view of the tension focus mask assembly of FIG. 1; 
     FIG. 3 is a side view, cross-sectional, of the apparatus for terminating crosswires; and 
     FIG. 4 is a side view, cross-sectional, of another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a cathode ray tube  10  having a glass envelope  12  comprises a rectangular face plate 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 face plate  22  and a peripheral flange or sidewall  24  that is sealed to the funnel  18  by a glass frit  26 . A three-color phosphor screen  28  is carried by the inner surface of the face plate  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 tension focus mask  30  is removably mounted in a predetermined spaced relation to the screen  28 . 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 tension focus mask  30  to the screen  28 . 
     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 which cause the beams to scan horizontally and vertically in a rectangular raster over the screen  28 . 
     The tension focus mask  30 , shown in greater detail in FIG. 2, includes two longs sides  36  and  38  and two short sides  40  and  42 . The two short sides  40  and  42  of the mask parallel a central minor axis, Y, of the tube. The tension focus mask  30  includes two sets of conductive lines: strands  44  that are parallel to the central minor axis y and to each other; and wires  46 , that are parallel to the central major axis x and to each other. In a preferred 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 cross wires  46  have a round cross section, having a diameter of about 1 mil and extend horizontally. In the completed mask, the strands  44  and wires  46  are separated from each other by suitable insulators such as lead-zinc-boro-silicate. 
     FIG. 3 depicts a side view, cross-section, of the tension focus mask  30  for constructing a rigid busbar. To best understand the invention, the reader should simultaneously refer to both FIGS. 2 and 3. 
     The short sides  40  and  42  of the tension focus mask  30  includes a base segment  314 , which can be seen in both FIGS. 2 and 3, formed of a stainless steel 90° angle segment having two respective ends. A massive side rail  310  is formed of an alloy steel material also in the shape of an angle and having two respective ends. Together, these two side rail segments  314  and  310  establish the structural portions of the two short sides  40  and  42 . Each side,  40  and  42  are fabricated to mirror one another. The stainless steel base segment  314  is arranged such that it is perpendicular to the long sides  36  and  38  and attached to the long side on each of its respective ends by welding. The second element, the massive side rail  310 , is arranged such that it is aligned in the same vertical plane as the first segment  314 , but the second segment  310  is positioned above segment  314  in the Z direction. 
     The massive side rail segment  310  is also affixed to the long sides  36  and  38  on each of its&#39; respective ends, perpendicular to the long sides  36  and  38  similar to that of the base segment  314 . 
     The arrangement of the segments  314  and  310  forms the short sides  42  and  40 . This arrangement allows workers and technicians to grasp the tension focus mask  30  without handling the mask portion of the assembly. The side rails also prevent damage when mask frame assemblies are jarred impacted by objects or other mask assemblies during fabrication. The cross wires  46  are especially fragile and require the utmost care to avoid damage. 
     The massive side rail segment  310  further comprises a set of elements that aids in the performance of the mask frame assembly and allows the assembly to be used as a tension focus mask or a color selection electrode. These elements include a beam shield  302 , an insulator/spacer  308  and a rigid busbar  306 . 
     The beam shield  302  is formed along the upper inside portion of the massive side rail  310 . The beam shield  302  runs the entire length of the massive side rail  310  and prevents stray electrons from the electron gun  32  of the CRT  10  from scattering and landing on the screen to produce an anomalous effect in the edge regions during use. 
     The insulator/spacer  308  is affixed to the outside of the massive side rail  310 . The insulator/spacer  308  is sandwiched between the side rail  310  and the busbar  306 . The insulator/spacer  308  acts to provide electrical insulation for preventing busbar  306  from making electrical contact with the massive side rail  310 . The busbar  306  is attached to the outside of the insulator/spacer  308  and runs the length of the short side  40  and  42  of the tension focus mask  30 . 
     A plurality of crosswires  46  of the focus mask are applied over strands  44  and terminate on the busbar  306 . The crosswires  46  are laid parallel to one another and equidistantly spaced from each other. The crosswires  46  are affixed to the busbar  306  by, for example, a structural adhesive  304 , such as carbon loaded KASIL, applied across the top portion of the busbar  306 . After the adhesive  304  has dried or cured, the crosswires  46  are trimmed flush to the busbar  306 . 
     During operation of tube  10 , a voltage difference, not shown, is applied between crosswires  46  and strands  44 . The voltage is applied to crosswires  46  via the conductivity of busbar  306 . Thereby, focus action is provided, in a known manner. 
     The tension focus mask  30  is assembled in three separate processes. In the first process the frame portion is assembled, while in the second process the etched mask strands  44  are affixed to the tension focus mask  30  and finally in the third process, the crosswire  46  are attached. This forms the frame portion of the tension focus mask  30 . 
     Once all the elements have been properly aligned and assembled, a plurality of crosswires  46  are laid across the top of the busbar  306 . The crosswires  46  are glued using a fast-curing, high-temperature adhesive  304  such as carbon loaded KASIL to the top of the busbar  306 . After attachment, the crosswires  46  may be trimmed flush with the busbar  306 . 
     Short sides  40  and  42  are reinforced with a rigid busbar  306  for the purpose of preventing damage to tension focus mask  30  due to handling during the manufacturing process. Rigidity refers to the ability of the busbar  306  to resist deformation, during manufacture of the CRT  10  and in use. The busbar  306  is formed to be rigid so as to prevent a transmittal of force to crosswires  46  from, for example, side rail  310 . Thereby, advantageously,beam misregister is prevented during use of the CRT  10 . For preventing beam misregistration, the deviation of the beam landing location from the ideal on the screen  28  may not be more than 2-4 mils depending on the screen  28  size. 
     This rigid busbar apparatus allows technicians and workers to handle the tension focus mask  30  by the short sides  40  and  42  at base segments  314 , thus preventing physical contact with tension focus mask  30  that could potentially damage the crosswires  46  and strands  44 . 
     FIG. 4 is a side view, cross-sectional, of another embodiment of the present invention. In this embodiment, a rigid busbar  306 ′ is supported by a frame assembly  320 ′. Rigid busbar  306 ′ is made of an insulator such as glass. An electrically conductive layer, not shown, provides a connection for a focus voltage, not shown. In this embodiment as in the previous embodiment, the rigid busbar  306 ′ prevents the tension focus mask crosswires  46  from damage or shifting during manufacture and use. A busbar clip  314 ′ secures the rigid busbar  306  to the mask frame  320 ′. An adhesive  304 ′ that may be structural or non-structural is used to adhere the crosswires  46  to the rigid busbar  306 ′. The adhesive  304 ′ is applied over the crosswires  46  onto the busbar  306 ′ and allowed to cure or dry. As in the previous embodiment, the rigid busbar  306 ′ will not deform during manufacture and will prevent electron beam misregistration. 
     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.

Technology Category: 5