Abstract:
The invention provides a tension mask support frame assembly having a pair of support blade members attached to a frame. The support blade members are attached to opposite sides of the frame at a central location whereby each support blade member has a pair of distal ends extending from the central attachment point. A damping scrubber is disposed in the space between the support blade member and the frame near a distal end of the support blade members. Vibrations in the tension mask are thereby reduced through the transfer of the vibrations to the frame through rubbing action of the damping scrubbers.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to cathode ray tubes and more particularly to tension mask support frame assemblies having a vibration damping scrubber on a support blade member which holds a tension mask. 
     BACKGROUND OF THE INVENTION 
     A color cathode ray tube, or CRT, 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 panel of the tube and is made up of an array of elements of three different color-emitting phosphors. A shadow mask, which may be either a formed mask or a tension mask having strands, is located between the electron gun and the screen. The electron beams emitted from the electron gun pass through apertures in the shadow mask and strike the screen causing the phosphors to emit light so that an image is displayed on the viewing surface of the faceplate panel. 
     One type of CRT has a tension mask comprising a set of strands that are tensioned onto a mask support frame to reduce their propensity to vibrate at large amplitudes under external excitation. Such vibrations would cause gross electron beam misregister on the screen and would result in objectionable image anomalies to the viewer of the CRT. 
     One method of tensioning a mask utilizes a mask support frame having a pair of support blade members mounted on opposite sides of the frame parallel to the major axis of the CRT. The tension mask extends between the support blade members and is held in tension to reduce it&#39;s propensity to vibrate. A problem exists in that the support blade members supporting the mask are subject to vibration relative to the frame when external vibration is applied to the frame. Such external vibrations are then transferred to the tension mask. 
     SUMMARY OF THE INVENTION 
     The invention provides a tension mask support frame assembly for a CRT having a pair of support blade members attached to a frame. The support blade members are attached to opposite sides of the frame at a central location whereby each support blade member has a pair of distal ends extending from the central attachment point. A damping scrubber is disposed in the space between the support blade member and the frame near the support blade members&#39; distal end. Vibrations in the support blade members are thereby reduced through rubbing action of the damping scrubbers against the frame. The fundamental frequency of vibration of the support blade member is also increased by having the distal ends of the blades touching the subframe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of example with reference to the accompanying figures of which: 
     FIG. 1 is a cross sectional view of a CRT showing a tension mask support frame assembly. 
     FIG. 2 is a perspective view of the tension mask support frame assembly. 
     FIG. 3 is a partial perspective view of an end of the tension mask support frame assembly. 
     FIG. 4 is a cross sectional view taken along the line  4 — 4  of FIG.  2 . 
     FIG. 5 shows an alternative embodiment of the tension mask support frame assembly and damping scrubber of FIG.  2 . 
     FIG. 6 is another alternate embodiment tension mask support frame assembly of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a cathode ray tube (CRT)  1  having a glass envelope  2  comprising a rectangular faceplate panel  3  and a tubular neck  4  connected by a funnel  5 . The funnel  5  has an internal conductive coating (not shown) that extends from an anode button  6  toward the faceplate panel  3  and to the neck  4 . The faceplate panel  3  comprises a viewing faceplate  8  and a peripheral flange or sidewall  9 , which is sealed to the funnel  5  by a glass frit  7 . A three-color phosphor screen  12  is carried by the inner surface of the faceplate panel  3 . The screen  12  is a line screen with the phosphor lines arranged in triads, each of the triads including a phosphor line of each of the three colors. A tension mask support frame assembly  10  is removably mounted in predetermined spaced relation to the screen  12 . An electron gun  13 , shown schematically by dashed lines in FIG. 1, is centrally mounted within the neck  4  to generate and direct three inline electron beams, a center beam and two side or outer beams, along convergent paths through the tension mask support frame assembly  10  to the screen  12 . 
     The CRT  1  is designed to be used with an external magnetic deflection yoke  14  shown in the neighborhood of the funnel-to-neck junction. When activated, the yoke  14  subjects the three beams to magnetic fields which cause the beams to scan horizontally and vertically in a rectangular raster over the screen  12 . 
     The tension mask support frame assembly  10 , as shown in FIG. 2, includes two long sides  22  and  24 , and two short sides  26  and  28 . The two long sides  22 ,  24  of the tension mask support frame assembly  10  are parallel to a central major axis, X, of the CRT; and the two short sides  26 ,  28  parallel a central minor axis, Y, of the tube. The two long sides  22 ,  24  and two short sides  26 ,  28  form a continuous planar mask support frame  20  along those major and minor axes. The frame  20  comprises an elongated wall portion  23  extending along the top peripheral surfaces of the long sides  22 ,  24  and short sides  26 ,  28 . 
     The tension mask support frame assembly  10  includes a tension mask  30  (shown here diagrammatically as a sheet for simplicity) that contains a plurality of metal strips (not shown) having a multiplicity of elongated slits (not shown) therebetween that parallel the minor axis, Y, of the tube. The tension mask  30  is fixed to a pair of support blade members  40  which are fastened to the frame  20  at mounting locations  33 . The support blade members  40  may vary in height from the center of each support blade member  40  longitudinally to the ends of the support blade member  40  to permit the best curvature and tension compliance over the tension mask  30 . 
     Referring now to FIGS. 3 and 4 the damping scrubber  32  is attached on the bottom of the support blade member  40  near its distal end. The damping scrubber  32  is best shown in FIG. 3 as being positioned against the elongated wall portion  23  of the frame  20 . As best shown in FIG. 4, the damping scrubber  32  has a central  10  portion  34  and a pair of resilient legs  36  extending therefrom. The resilient legs  36  extend from the central portion  34  at an angle toward the wall portion  23  and include curled sections  38  formed at their free ends. The central portion  34  is attached to the bottom surface of the support blade member  40  by welding or any other suitable means such as a high temperature adhesive. It should be understood that the central portion  34  of the damping scrubber  32  may alternatively be attached either to the support blade member  40  or to the frame  20 . The damping scrubber  32  is positioned between the support blade member  40  and frame  20  such that the curled sections  38  are in scrubbing or frictional contact with the wall portion  23  and the resilient legs  36  are preloaded and flexed against the wall portion  23 . During vibrations, these curled sections  38  scrub against the wall portion  23  to dampen the vibration imparted to the frame  20  which tend to deflect the distal ends of the support blade member  40  and thereby reduce the duration of vibrations of the tension mask  30 . The resilient legs  36  ensure contact, and thus friction, and provide a force that raises the resonance of the support blade member  40 . Such increase in resonance reduces the amplitudes of motion by separating them from other natural frequencies of the mask-frame assembly. 
     An advantage of the present invention is that, the resilient legs  36  flex closer together and further apart cyclically as the frame  20  and support blade member  40  move away and towards one another respectively. These flexures cause the resilient legs  36  to rub against the frame  20  with each cycle of motion to dampen the effects of vibration on the support blade member  40  thus shortening their duration. 
     FIG. 5 shows an alternate embodiment of the support blade member  50 . In this support blade member  50  an opening  51  is formed along a frame facing wall  53 . An integral damping scrubber  52  extends from the frame facing wall  53  into the opening  51 . The damping scrubber  52  consists of a resilient leg  56  extending into the opening  51  from an attachment end  55  having a curled section  58  disposed at a free end. The resilient leg  56  is preloaded outward from the frame facing wall  53  such that when installed, it resiliently engages the wall portion  23  of the frame  20 . The contact of the resilient leg  56  against the wall portion  23  similarly dampens the vibration imparted to the frame  20  thereby reducing the vibration on the tension mask  30 . 
     The resiliency of the resilient leg  56  may be adjusted by adding features to its attachment end  55 , for example the material of the resilient leg  56  may be thinned at the attachment end  55  or edges of the attachment end  55  may be coined to provide varying degrees of resiliency. These features may act as a hinge to cantilever the resilient leg  56  at various levels of resiliency. While the resilient leg  56  is shown here as being preferably integral with the frame facing wall  53 , the leg may be attached to the frame by other suitable means and extend into the frame opening  51  as shown in FIG.  5 . 
     In another alternate embodiment as shown in FIG. 6, the resilient leg  66  may be attached at the distal end of the support blade member  60  instead of extending into an opening along the frame facing wall. This resilient leg  66  is otherwise similar to the resilient leg  56 . 
     The foregoing illustrates some of the possibilities for practicing the invention. Many other embodiments are possible within the scope and spirit of the invention. It is, therefore, intended that the foregoing description be regarded as illustrative rather than limiting, and that the scope of the invention is given by the appended claims together with their full range of equivalents.