Abstract:
A cathode ray tube has a tensioned mask supported by a support frame. The tension mask being susceptible to vibration and adapted for mounting in tension within the cathode ray tube. The tension mask includes damper wire support springs attached to, and extending from, opposite sides of the tension mask support frame. The damper wire support springs having a compliance section supporting a damper wire in contact with and across the surface of the tension mask for damping vibrations in the mask.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to cathode ray tubes and, particularly, to an improved means for damping vibrations in such tubes having a tension mask. 
     BACKGROUND OF THE INVENTION 
     As is known in the art, a cathode ray tube is generally constructed of a glass envelope and includes an electron gun located within a neck portion of the envelope for generating and directing three electron beams to the screen of the tube. The screen is located on the inner surface of a faceplate panel of the tube and is made up of an array of elements of three different color emitting phosphors. A color selecting electrode, which may be either a shadow mask or a focus mask, is interposed between the gun and the phosphor screen to permit each electron beam to strike only the phosphor elements associated with that beam. Each electron beam is scanned by an electromagnetic deflecting device for impingement on a desired phosphor of the phosphor screen. 
     In conventional color cathode ray tubes having two-dimensionally curved color selecting electrodes or shadow masks, the curvature of the mask and its thickness causes it to be structurally self-supporting. Another type of commercial shadow mask is tensioned on a support frame and is not self-supporting as is the two-dimensionally curved type. The tension shadow mask contains a plurality of very thin parallel vertically extending strands maintained at high tension. In another type of tension mask, the frame supporting the mask is designed to permit the mask to de-tension during thermal treatment of the tube. The afore-described cylindrical tension shadow mask configurations are prone to vibrations, as may be caused by external mechanical pulses, or by a speaker in an associated television receiver, for example. The resonant frequency of vibration of the mask will vary depending on the mechanical parameters of and tension in the mask. Any vibration of the mask will cause electron beam landings to be out of registry with their respectively associated phosphor elements, causing color impurities in the reproduced images. 
     Various means have been suggested for damping the resonant vibrations described above. One example for damping the vibration of a tension mask includes damping wires stretched across the mask to damp vibrations in the mask strands by relative motion between the strands and the wires. The damping wires can be held against the mask strands because of the curved nature of the mask. The ends of the wires are secured to the frame supporting the tension mask by tabs which hold the wires under light tension. With such an arrangement, the strands are resiliently pressed by the wires and, therefore, are not likely to vibrate by external mechanical shocks or electron beam bombardment. Disadvantages inherent in a mask assembly of this type include variations in the height of the tabs which could either cause the wires not to touch the strands or press on them to cause noticeable deflection of the strands so as to prevent damping of their motions. The problem is exacerbated by the use of tension masks having specific tension distributions across the mask or in de-tension mask frames resulting in relatively low strand stretching forces. 
     This invention is directed to providing a solution to the problem of damping resonant vibrations in a tension shadow mask and thus avoiding a deterioration of picture quality caused by external vibrations. 
     SUMMARY OF THE INVENTION 
     The present invention provides a cathode ray tube having a color selection electrode tension mask attached to a support frame. The tension mask includes damper wire support springs attached to, and extending from, opposite sides of the tension mask support frame. The damper wire support springs having a compliance section supporting a damper wire in contact with and across the surface of the tension mask for damping vibrations in the mask. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the present invention may best be understood by reference to the following description of preferred embodiments of the invention taken in conjunction with the accompanying drawings, in the figures of which like reference numerals identify like elements, and in which: 
     FIG. 1 is a top view, partly in axial section, of a color picture tube embodying the invention. 
     FIG. 2 is a perspective view showing an embodiment of the damper wire support springs on a tension mask and support frame according to the present invention. 
     FIG. 3 is a detail view in perspective of a representative one of damper wire support springs according to the invention. 
     FIG. 4 is a view similar to FIG. 3 depicting an alternative embodiment of the damper wire support springs. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a color picture tube  10  having a glass envelope  12  comprising 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 the wide portion of the funnel and to the neck  16 . The panel  14  comprises a substantially flat external viewing faceplate  22  and a peripheral flange or sidewall  24 , which 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 faceplate  22 . The screen  28  is a line screen with the phosphor line arranged in triads, each triad including a phosphor line of each of the three colors. A color selection electrode or tension shadow mask  30  is removably mounted in predetermined spaced relation to the screen  28 . An electron gun  32 , shown schematically by dashed lines in FIG. 1, is centrally mounted within the neck  16  to generate and direct three inline electron beams  34 , 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  36  shown in the neighborhood of the funnel-to-neck junction. When activated, the yoke  36  subjects the three beams to magnetic fields which cause the beams to scan horizontally and vertically in a rectangular raster over the screen  28 . 
     FIG. 2 is a perspective view of the tension mask  30  mounted on a frame  38 . The tension mask  30  includes two long sides  40  and  42 , and two short sides  44  and  46 . The two long sides  40  and  42  of the tension mask parallel the central major axis, X, of the tube; and the two short sides  44  and  46  parallel the central minor axis, Y, of the tube. The tension mask  30  includes an active apertured portion  48  that contains a plurality of parallel vertically extending strands  50 . A multiplicity of elongated apertures  52 , between the strands  50 , parallel the minor axis Y of the tube. The electron beams pass through the apertures  52  in the active apertured portion  48  during tube operation. 
     The frame  38  includes four sides: two long sides  54 , substantially paralleling the major axis X of the tube, and two short sides  56 , paralleling the minor axis Y of the tube. A damper wire  58  extends across the tension shadow mask  30  perpendicular to the apertures  52 . Damper wire support springs  60  are secured to and extend from the short sides  56  of the frame  38  on the outside peripheral portion of the tension shadow mask  30 . The damper wire support springs  60  include compliance section  62  supporting the damper wire  58  on the screen side of the tension shadow mask  30  in contact with the strands  50  of the tension shadow mask  30  for damping vibrations in the mask. 
     FIG. 3 is a view of the damper wire support spring  60  for a tension mask according to the invention. The damper wire support spring  60  includes a holding member  64  for securing the damper wire support spring  60  to the short sides  56  of the frame  38  and a compliance section  62  for supporting the damper wire  58  in contact with the strands  50  (as shown in FIG.  2 ). The compliance section  62  is a relatively thin spring member  66  secured to the free end of the holding member  64 . The spring member  66  extends from the free end of the holding member  64  and curves inward in a bias position toward the central active apertured portion  48  of the tension shadow mask  30  (as shown in FIG.  2 ). Attached to the spring member  66  is the damper wire  58 , by spot welding for example, whereby the damper wire  58  is held in position between the damper wire support springs  60  and against the strands  50  such that it is permitted a degree of “play” or movement, referred herein to as “compliance,” in response to mask pre-loading or side-loading forces. It will be understood that the damper wire  58  may also be attached to the holding member  64 , by spot welding for example, so long as the damper wire  58  is supported by the compliance section  62 . 
     The damper wire support spring  60  is manufactured by forming separately the holding member  64  and the spring member  66  and then combining them with each other so that the dimensions of each portion can be set individually according to the required compliance. In a preferred embodiment, the spring member  66  is made from a suitable material having a thickness in the range of about 0.001 to 0.003 inches (0.25-0.76 mm) and a width of about 0.05 to 0.20 inches (12.7-50.8 mm) to permit compliance of the damper wire  58  in the direction normal to the mask, or X-Y plane of the tube, as well as compliance in the direction tangent to the surface of the tension shadow mask  30 . It will be appreciated, of course, that the spring member  66  might also be constructed with alternative dimensions if desired. 
     FIG. 4 is a depiction of another embodiment of the present invention. In this embodiment, the compliance section  62  of the damper wire support spring  60  supporting the damper wire  58  is of a unitary construction with an L-shaped section having a cut out region  68 . The damper wire support spring  60  is formed from a single sheet of material and the cut out region  68  is introduced in a condition so that the compliance on the damper wire  58  becomes substantially the same as achieved by the embodiment shown in FIG.  3 . With the cut out region  68 , however, the damper wire  58  is not carried by the bent contour and spring bias of the spring member  66  as shown in FIG. 3, but rather works to apply a pre-load force on the free end of the damper wire support spring  60  for compliance. In either embodiment, the compliance of the damper wire support spring  60  secures the damper wire across the mask to the strands  50  such that the damper wire is free to move somewhat in response to forces associated with variations in the deflections and tension distribution in the mask. 
     According to the present invention, the compliance provided by the vibration damping means maintains the effectiveness of the damper wire in spite of significant changes in the resonant frequency of the tension mask which may result from heating and cooling of the mask or from external mechanical shocks to the tube. Even if the tension distribution across the mask results in relatively low strand stretching forces, the damper wire support spring  60  provides compliance in the damper wires  58  to maintain contact with the strands  50 . Consequently, the deterioration of picture quality caused by external vibration or thermal cycles can be prevented. 
     While the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention. For example, the number of damper wire support springs  60  may be increased to support additional damper wires so as to provide sufficient dampening of the tension mask. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention, which is set for the in the following claims.