Patent Publication Number: US-6710531-B2

Title: CRT having a shadow mask vibration damper

Description:
FIELD OF THE INVENTION 
     This invention relates generally to cathode ray tubes (CRTs) and more particularly to a tension mask assembly having a vibration damper applied to an area of the 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 tension mask. The tension mask extends between the support blade members and is held in tension to reduce its 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 or microphonic vibration is applied to the frame. Such external vibrations may then be undesirably transferred to the tension mask. 
     SUMMARY OF THE INVENTION 
     The invention provides a CRT having a tension mask and a vibration damper to receive vibration from the tension mask. The tension mask is attached to a support frame, wherein the support frame has longs sides ( 22 ,  24 ) parallel to a major axis and shorts sides parallel to a minor axis ( 26 ,  28 ). The tension mask includes borders which are near the short sides and parallel therewith. The vibration damper comprises an elongated strip member having first and second ends mounted at respective attachment locations along the border and a major portion which is in frictional contact with the border. 
    
    
     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 the lower corner portion shown in FIG.  2 . 
     FIG. 4 is a partial perspective view similar to that of FIG. 3 for a first alternate embodiment. 
     FIG. 5 is a partial perspective view similar to that of FIGS. 3 and 4 for a second alternate embodiment of the invention. 
     FIG. 6 is a cross sectional view taken along the line  6 — 6  of FIG.  5 . 
     FIG. 7 is a partial sectional view similar to that of FIG. 3 for a third alternate embodiment of the invention. 
     FIG. 8 is a cross sectional view taken along the line  8 — 8  of FIG.  7 . 
     FIG. 9 is a partial perspective view similar to that of FIG. 3 showing a fourth alternate embodiment of the invention. 
     FIG. 10 is a cross sectional view taken along the line  10 — 10  of FIG.  9 . 
     FIG. 11 is a cross sectional view of a fifth alternate embodiment of the invention. 
    
    
     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 a frame  20  and a pair of support blade members  40  attached to the frame  20 . The frame consists of two long sides  22  and  24 , and two short sides  26  and  28  arranged in a plane for supporting a tension mask  30 . The two long sides  22  and  24  of the frame  20  are parallel to a central major axis, X, of the CRT; and the two short sides  26  and  28  parallel a central minor axis, Y, of the CRT. The support blade members  40  are attached along the long sides  22  and  24  for supporting the tension mask  30  along blade edges  42  thereof. The mask  30  is shown in FIG. 2 as a flat planar surface for simplicity. However, it consists of a plurality of apertures  35  as best shown partially in FIGS.  3 . 
     Referring now to FIG. 3, an exploded section of the tension mask frame assembly  10  is shown. The tension mask  30  is formed from a thin sheet of metal, typically steel or invar, which is etched or otherwise processed to produce a plurality of strands  32 . Borders  36  located at opposite ends of the strands are attached to each of the support blade members  40  at an edge  42  by welding. The strands  32  extend parallel to the minor axis, Y, and a plurality of cross wires  34  are also conductive and are insulated from the strands  32  and extend parallel to the major axis, X. The combination of cross wires  34  and strands  32  form a plurality of precisely positioned apertures  35  through which the electron beam passes from the electron gun  13  to the screen  12 . These apertures  35  define an array area  37  between the borders  36 . Although the tension mask is firmly attached to and tensed between the support blade members  40 , there is no ridged support along the minor axis, Y. The tension mask  30  is therefore somewhat susceptible to vibration transfer from the support blade members  40  to the tension mask  30 . 
     The invention involves mitigating such vibrations through the use of at least one vibration damper  46 , wherein a vibration damper  46  is provided along a border  36  of the tension mask  30  parallel to the minor axis Y and extending substantially between the long sides  22 ,  24 . While only one vibration damper  46  will be described for simplicity, it should be understood that the preferred embodiment includes a pair of vibration dampers  46  each positioned along opposite ends of the tension mask  30  and damper  46  extends parallel to the minor axis Y. The vibration damper  46  is an elongated strip member, which is attached to each of the borders  36  at an attachment location  48 . The elongated strip member has first and second ends mounted to a surface along the border  36  of the tension mask  30  and a substantial portion acting upon the surface of the border  36 . The first and second ends are attached to the surface of the border  36  at attachment locations  48 . The attachment is preferably accomplished by welding but may also include attachment by adhesives or other suitable techniques. It should be understood that although the vibration damper  46  is shown here as being attached along a screen facing side of the mask  30 , it could alternatively be applied to the opposite gun facing side of the tension mask  30 . The vibration damper  46 , while fixed at both ends is in rubbing frictional contact with the shadow mask  30  along a substantial portion of its surface between the attachment locations  48 . As the tension mask  30  tends to vibrate, the vibrations are damped due to friction from the rubbing of the border  36  with the damper and induced strain energy along the damper  46 . The vibrational energy of the mask  30  can be communicated to the borders  36  by either tie bars in a web-type mask or cross wires in a strand mask. The damper  46  may optionally have a rough surface applied on the side which is in contact with the tension mask  30  in order to increase the friction between these components upon vibration. 
     The material of the vibration damper  46  may be optionally selected to have a coefficient of thermal expansion which is different from that of the tension mask  30 . Selection of such a material is preferred in applications where additional tensioning or detensioning is required along the minor axis Y of the tension mask  30  during thermal cycling. It should also be understood that while the vibration damper  46  is shown as being applied to a tension mask  30 , it is equally applicable to other types of masks such as shadow masks, tensed tie bar masks, focus masks and others. 
     FIG. 4 shows a first alternate embodiment in which the vibration damper  46  is substantially similar to that shown in FIG. 3 except that the attachment locations  148  are moved inward from the support blade member  40 . 
     FIGS. 5 and 6 show a second alternate embodiment in which the vibration damper  46  is secured to the tension mask  30  by the application of a support plate  50  fastened to the vibration damper  46  through an opening  44  in the tension mask  30 . As best shown in FIG. 6, an adhesive  52  is applied to the vibration damper  46  at the attachment location  148  within the opening  44 . The support plate  50  is then applied to the opposite side of the tension mask  30  such that it contacts the adhesive  52  through the opening  44  to sandwich the tension mask  30  between the vibration damper  46  and the support plate  50 . It should be understood in this embodiment as with each of the others, that the vibration damper  46  may be positioned on either the gun facing side or the screen facing side of the tension mask  30  while the support plate  50  is positioned on the side opposite the vibration damper  46 . 
     A third alternate embodiment is shown in FIGS. 7 and 8 wherein a support plate  50  is similarly positioned opposite the vibration damper  46  around the opening  44 . In this embodiment, however, instead of applying an adhesive  52  at the attachment location  148 , a pin  152  is utilized to secure the support plate  50  to the vibration damper  46 . Once again, it should be understood in this embodiment as with each of the others, that the vibration damper  46  may be positioned on either the gun facing side or the screen facing side of the tension mask  30  while the support plate  50  is positioned on the side opposite the vibration damper  46 . 
     FIGS. 9 and 10 show a fourth alternate embodiment in which the vibration damper  46  is applied to the tension mask  30  by simply bending a portion thereof through the opening  44 . As best shown in FIG. 10, a bent portion  49  extends through the opening  44  and around the opposite side of the tension mask  30  to sandwich the mask  30  between the bent portion  49  and the remainder of the vibration damper  46 . It should be understood in this embodiment as with each of the others, that the vibration damper  46  may be positioned on either the gun facing side or the screen facing side of the tension mask  30  while the bent portion  49  is positioned on the side opposite the vibration damper  46 . 
     FIG. 11 shows yet a fifth alternate embodiment in which a raised portion  43  is formed into the vibration damper  46 . Here, the raised portion  43  comprises a semicircular bent section extending outward from the vibration damper  46  and located near the attachment location  48  along the tension mask  30 . The raised portion  43  is especially useful in situations where materials having different coefficients of thermal expansion are utilized for the vibration damper  46 . The raised portion  43  serves to allow the vibration damper  46  to expand along with the tension mask  30  during thermal cycling without applying excessive shear forces to the attachment location  48 . The raised portion ( 43 ) elastically maintains structural integrity of the elongated strip member. It should be understood that the raised portion  43  is optionally applicable to any of the alternate embodiments discussed above. 
     Advantageously, since the vibration damper  46  is in frictional contact with the tension mask  30  over a substantial portion of its surface, it serves to improve vibration damping of the tension mask  30  along the minor axis.