Abstract:
A method and apparatus for applying crosswires to a tension mask. The method includes winding crosswires around various drum assemblies and then using transfer devices to remove sections of crosswires and transfer them to tension mask frame assemblies.

Description:
This invention generally relates to color picture tubes and, more particularly, a method and apparatus for transferring and applying crosswires from a drum unit assembly to a tension mask assembly. 
     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 face plate of the tube and is made up of an array of elements of three different color emitting phosphors. A color selection electrode, also referred to as a shadow 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 contoured to somewhat parallel the inner surface of the tube face plate. A tension mask can be a strand tension mask, tie-bar tension mask or tension focus mask. A tension focus mask comprises two sets of conductive lines that are perpendicular to each other and separated by an insulator. Different voltages are applied to the two sets of lines to create focusing lenses in each of the mask openings. 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. 
     In assembling a tension focus mask, it is required to assemble the wires and strands with a high degree of accuracy to achieve consistent spacing between the strands and between the wires to optimize visual performance. It is, therefore, desirable to develop techniques for assembling tension focus masks that will provide precise spacing between the vertical conductive elements and between the horizontal conductive element. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for transferring and attaching crosswires from a drum assembly to a mask frame assembly. The method includes providing a plurality of crosswires that have been rolled onto a drum assembly. The crosswires are then transferred from the drum assembly to a mask frame assembly. In one embodiment, the crosswires are transferred directly onto a mask frame assembly from a drum assembly. In other embodiments, a transfer apparatus is used to transfer the crosswires from the drum assembly to the mask frame assembly. 
     In the first embodiment, a drum assembly that has had crosswires rolled onto it, unrolls the crosswires onto a mask frame assembly. In this method, both the mask frame assembly and the drum assembly are rotating about a separate different axis point and are moving in a reciprocating manner as the crosswires are transferred from the drum to the mask frame. In a second embodiment, crosswires that have been wound around a drum assembly are cut by a transfer device and moved from the drum assembly onto the mask frame assembly. In a third embodiment, crosswires wound around a drum are transferred from the drum to the mask frame assembly by a mask frame transfer device that contains a self-tensioning device that allows the crosswires to be straightened and tensioned as they are cut from the drum assembly and transferred to a mask frame assembly. 
    
    
     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-frame-assembly mask according to the present invention; 
     FIG. 2 is a perspective view of the tension focus mask-frame-assembly of FIG. 1; 
     FIGS. 3A,  3 B and  3 C are three perspective views of the apparatus of a first embodiment of the invention; 
     FIGS. 3D and 3E are two side views of the apparatus of a first embodiment of the invention; 
     FIGS. 4A,  4 B and  4 C are a perspective view of the apparatus of an alternative embodiment; and 
     FIGS. 5A,  5 B,  5 C,  5 D and  5 E are a perspective view of the apparatus of another alternative embodiment. 
    
    
     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 sealing 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 . Tension focus mask  30  has a differential voltage coupled across the strands and wires. 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 . 
     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 . 
     The 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 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 one embodiment, the strands  44  are flat strips that extend vertically, having a width of about 0.005 to 0.020″ and a thickness of 0.001 to 0.008″, and the crosswires  46  have a round cross section, having a diameter of 0.0005 to 0.003″ and extend horizontally. In the completed mask, the strands and wires are separated from each other by suitable insulator such as lead-based frit. 
     FIGS. 3A through 3E depict various views of the system  300  of one embodiment of the invention. This system  300  comprises a drum unit  301  in concert with the mask frame assembly  304 . The drum unit  301  consists of a drum  302 , crosswires  46  and transfer bars  306 . 
     The transfer bars  306  are temporarily affixed in a vertical orientation parallel to the axis of the drum unit  301  and perpendicular to the crosswires  46 . The crosswires  46  are wound around the drum unit  301  over the transfer bars  306  in sections long enough to complete one tension focus mask  30 . The circumference of the drum unit  301  may be a multiple of the length of a mask frame assembly  304  thereby facilitating the creation of a plurality of tension focus masks  30  for each revolution of the drum unit  301 . After winding the crosswires  46  around the drum unit  301  and over the transfer bars  306 , the crosswires  46  are glued to the transfer bars  306  at the point of contact. 
     The transfer process begins with a transfer bar  306  being attached to the mask frame assembly  304 . A transfer bar  306  is affixed to a portion of the mask frame assembly  304  at a point before the mask frame element  314  begins. The crosswires  46  are then transferred to the mask frame assembly  304  and a second transfer bar  306  is affixed to a portion of the mask frame assembly  304  at a point after the mask frame element  314  ends. An adhesive is then applied to crosswires  46  at a point where the crosswires  46  go over the bus bars  312 A and  312 B and the adhesive is allowed to cure. After curing, the crosswires  46  are cut from the transfer bars  306  and the mask frame element  314  is removed from the mask frame assembly  304 . 
     The mask frame assembly  304  is comprised of a mask frame fixture  316 , and a mask frame element  314 . The mask frame element  314  is attached to the mask frame fixture  316 . The mask frame element  314  further comprises a set of mask strands  44  that have been welded to the mask frame element  314  and a rotating and reciprocating axle  308  that is affixed to the mask frame assembly  304 . Before the process of positioning the crosswires  46  onto the mask frame assembly  304  begins, an insulator has been applied to the mask strands  44 . 
     FIG. 3A depicts the crosswires  46  being attached to the mask frame assembly  304 . As can be seen in FIG. 3B, the mask frame  304  begins to rotate in a clockwise fashion about the axle  308  that is affixed to the back  303  portion of the mask frame assembly  304 . As the mask frame assembly  304  rotates clockwise, drum unit  302  rotates counter  30  clockwise unrolling and seating transfer bar  306 A against the mask frame assembly  304 . The transfer bar  306  is attached to the mask frame assembly  304  by an appropriate means. This may include but is not limited to gluing, welding or clamping. 
     Both mask frame  304  and drum assembly  302  move back and forth in a horizontal plane. This back and forth motion allows a specific amount of tension to be applied while maintaining a minimum gap between the drum assembly  302  and the mask frame  304 , and thus insuring uniform spacing between the crosswires  46 . 
     FIG. 3C depicts the second transfer bar  306 B being attached to the mask frame  304 . The drum  302  has moved back toward the mask frame  304  and the mask frame  304  toward the drum  302  maintaining the smallest gap possible between the drum  302  and the mask frame  304 . The transfer portion of the process ends as the transfer bar  6 B reaches the opposite side of the mask frame assembly  304  and is affixed in place. 
     FIG. 3D depicts a side view of the mask frame assembly  304 . In this view, the transfer bars  306 A and  306 B along with the crosswires  46  have been transferred to the mask frame assembly  304 . Clearly shown in this figure are the busbars  312 A and  312 B that are affixed to the mask frame element  314 . The bus bars  312 A and  312 B are glued to the crosswires  46 . After the glue has cured, the crosswires  46  are cut at points between transfer bars  306 A and  306 B and bus bars  312 A and  312 B. 
     FIG. 3E depicts a side view of the mask frame assembly  304  showing the mask frame element  314  being detached from the mask frame fixture  316 . Clearly shown are crosswires  46  cut from the busbars  312 A and  312 B and mask frame element  314  being removed from the mask frame fixture  316 . 
     FIGS. 4A,  4 B and  4 C are a perspective view of the apparatus  400  of an alternative embodiment  400  of the invention. FIGS. 4A-4C show an apparatus comprising three components. The first is the drum unit  400  shown in FIG. 4A, the second shown in  4 B is a transfer device  406 , as seen from the top with a mask frame  30  and a set of crosswires  46  sandwiched between, and the third seen in perspective, shown in FIG. 4C is a mask frame assembly  30 . In this embodiment, wire spools  402  wind crosswires  46  around a large rotating drum assembly  404  before being transferred by a second apparatus  406  to a mask frame assembly shown in FIG.  4 B. The wire spools  402  are positioned very close to the drum assembly  404 . A low tension force is maintained in the crosswires  46  that helps to provide uniformity of spacing between the crosswires  46 . 
     The second apparatus  400  of this embodiment as depicted in FIG. 4B, is a transfer device  406 . The transfer device  406  comprises an electromagnetic holder  408 , a contoured attachment point  410 , a cutter  412 , a vacuum conformer  414 , and an automatic busbar attacher  416 . The transfer device  406  is formed to match the contour of the surface  401  of the drum assembly  404 . The transfer device  406  is large enough to cover a portion of crosswires  405  as depicted in FIG. 4A that will be used to create a single tension mask. This portion of crosswires  405  is shown without the transfer device  406  for clarity. 
     In practice, transfer device  406  is applied to the outer surface  401  of the drum  404 . The transfer device  406  is pressed against the outside surface  401  of the drum  404  and an electromagnetic device  408  activated. As the electromagnetic device  408  becomes active, the crosswires  46  and transfer bars  306 A and  306 B become fixed relative to themselves and the device  408 . The drum  404  may be formed of any non-magnetic material so as not to interfere with the operation of the transfer device. After the crosswires  46  have been fixed magnetically relative to themselves and the electromagnetic device  408 , a cutter  412  is activated to cut the crosswires  46  on the drum  404 . After cutting the crosswires  46 , the transfer device  406  is removed from the drum  404  and placed onto a mask frame  30  as seen in FIG. 4B where the crosswires  46  are affixed onto the mask frame  30 . Before the crosswires  46  are applied to the mask strands  44 , an insulator is applied to the mask strands  44 . 
     FIG. 4C depicts a perspective view of a mask frame  30  with strands  44  welded in place before crosswires  46  are attached. Crosswires  46  are attached perpendicular to the strands  44  on the mask frame  30 . Before contact is made with the mask frame  30  by the crosswires  46 , an adhesive is applied to the mask strands  44  of the mask frame  30 . The electromagnetic transfer device  408  is applied directly to the mask frame  30  and the crosswires  46  are allowed to bond with the mask strands  44  before the electromagnetic transfer device  408  is deactivated and removed. 
     FIG. 5A is a perspective view of the apparatus of another alternative embodiment. In this embodiment, multiple wire spools  502  wind crosswires  46  around a drum assembly  504  before being transferred by a second apparatus, as seen in FIGS. 5B-5E, to a mask frame assembly. The drum assembly  504  is preferably fabricated such that its diameter is between 8 and 10 feet. The drum assembly  504  is equipped with a system for uniformly spacing the crosswires  46  as they are wound around the drum. 
     FIGS. 5B,  5 C and  5 D are perspective views of the second part of the invention is the wire transfer mechanism  550 . The wire transfer mechanism  550  is used to transfer the wound crosswires  46  from the drum assembly  504  to a mask frame (as shown in the previous embodiment). The wire transfer mechanism  550  is comprised of a frame  552  which is formed by two segments  554  having two respective ends and being parallel to each other in a substantially horizontal plane connected by a set of sliding vacuum chuck assemblies  556 . The vacuum chuck assemblies  556  are kept in tension by a pair of expansion springs  570  disposed around the frame segments  554  and between each of the sliding chuck assemblies  556 . 
     Each sliding vacuum chuck assembly  556  consists of a crossbar  558  having two respective ends. On each of the respective ends of the crossbar  558  is affixed perpendicularly, and on each end, a section of hollow tubing  560  whose diameter is larger than that of the frame segments  552 . Both sections of hollow tubing  560  are substantially parallel to each other and perpendicular to the crossbar  558 . 
     The sliding vacuum chuck assembly  556  further comprises a pivoting vacuum chuck assembly  580  that is disposed across the bottom portion of the crossbar  558 . The pivoting vacuum chuck assembly  580  includes a vacuum chuck  582 , a set of clamps  584  and a leaf spring assembly  586  that is disposed between the vacuum chuck  582  and the crossbar  558 . The pivoting vacuum chuck assembly  580  is specifically designed to be clamped onto the drum assembly  504  and to grab onto and hold the crosswires  46 . A set of clamps  584  disposed on the transfer mechanism  550  lock into small recesses  583  on the drum  504 . The recesses  583  allow the clamps  584  to mate and lock securely into place. 
     The wire transfer mechanism  550  is assembled by placing two frame segments  554  through each end of the hollow tubing  560  that is attached to the crossbar  558 . After the frame bars are placed through the hollow tubing  560 , they are slidably moved down to their respective ends that contain a stop  555 . The stop  555  is a removable obstruction that prevents hollow tubing  560  from falling off the ends of the frame segment  554 . Expansion springs  570  are now placed over frame bars  554  until they are stopped by the structure of the hollow tubing  560 . A second sliding chuck assembly  556  is now slid in place over the two frame segment  554  by inserting the frame segment  554  into the apertures of the hollow tubing  560 . Once in place, sliding chuck assembly  556  is retained on frame segment  554  by a removably affixed stop  555 . At this point, the expansion springs  570  are under little, if any, compression. 
     In practice, after crosswires  46  are wound around drum  504 , wire transfer mechanism  550  may now be applied. First, wire transfer mechanism  550  is placed under compression by moving the sliding chuck assemblies  556  toward each other. As sliding chuck assemblies  556  are moved toward each other, a set of spacers  572  are employed to hold the compressed sliding chuck assemblies under tension. 
     The wire transfer mechanism  550  is then clamped onto the drum assembly  504  by clamps  584 . The pivoting vacuum chuck assembly  580  is activated causing the crosswires  46  to become adhered to the vacuum chuck  582 . A cutter (not shown) is then used to cut the crosswires  46  from the drum assembly  504  to form a crosswire segment. At this point, the crosswires  46  are being held by the wire transfer mechanism  550 . As the wire transfer mechanism  550  is then unclamped and removed from the drum assembly  504 , the spacer  572  is removed from the wire transfer mechanism  550  causing the compression springs  570  to expand, thus holding the crosswires  46  in tension. This tension allows the crosswires  46  to maintain proper uniform spacing. The wire transfer mechanism  550  is then moved to a mask frame assembly as described with respect to previous embodiments where the crosswires  46  can be transferred to the mask frame as described with respect to previous embodiments. 
     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.