Patent Publication Number: US-6703773-B2

Title: Tension mask frame assembly of color cathode-ray tube

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application entitled Tension Mask Frame Assembly of the Color Picture Tube earlier filed in the Korean Industrial Property Office on Apr. 21, 2000, and there duly assigned Serial No. 2000-21179 by that Office. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to color cathode ray tubes (color CRTS), and more particularly, to a tension mask frame assembly of a color cathode-ray tube having an improved frame for supporting a tension mask. 
     2. Description of the Background Art 
     In color cathode-ray tubes, three electron beams emitted from an electron gun land on the red, green and blue fluorescent materials of a fluorescent film formed on a screen surface of a panel through electron beam passing holes, and excite the fluorescent materials to form an image. 
     A surface of a screen of a typical color cathode-ray tube is designed to have a predetermined curvature considering the trace of the electron beam emitted from the electron gun. The shadow mask is designed to have a curvature corresponding to that of the surface of the screen. However, the curved shadow mask bulges toward the panel by being heated by the electron beam emitted from the electron gun, which is referred to as a doming phenomenon. The doming phenomenon prevents the electron beam from accurately landing on a fluorescent surface. 
     Recently, color cathode-ray tubes are pursuing flattening of the surface of a screen in order to widen the view angle of an image and prevent distortion of an image. Accordingly, a mask having a color distinguishing function, which is installed within a cathode-ray tube, must be flattened. The mask becomes an obstacle to manufacture a cathode-ray tube having a flat screen. In order to realize a flat surface, a tension force is applied to the shadow mask of a flat cathode-ray tube. 
     A tension mask frame assembly may include a frame and a flat tension mask. The frame has first and second support members that are installed in parallel. The frame also includes first and second elastic members connected to the first and second support members. The first and second support members are spaced a predetermined distance from each other. The flat tension mask has slots formed by a plurality of strips isolated from each other at predetermined intervals, and two longer edges of the flat tension mask are welded with the first and second support members, respectively, by receiving a tensile force. 
     The strips are connected to each other by tie bars isolated from each other at predetermined intervals, thereby forming the slots. In this tension mask frame assembly, the tension mask supported by the first and second support members cannot receive a uniform tensile force over the entire surface. That is, in order to weld the tension mask to the first and second support members of the frame, first, the first and second elastic members and are pressurized and elastically deformed so that the first and second support members are displaced in facing directions. Next, in this state, both longer sides of the tension mask are welded to the first and second support members, respectively, and then the pressure having been put on the first and second elastic members is removed. At this time, the first and second support members is subjected to a restoring force by the elasticity of the first and second elastic members. This restoring force to the first and second support members is different at portions supported by the first and second elastic members than from the center portions. 
     The difference in restoring force between portions of the first and second support members is represented as the difference between tensile forces applied to the strips of the tension mask welded with the first and second support members. A tensile force applied to the strips of the tension mask is large at portions supported by the first and second elastic members and, whereas a tensile force applied to the strips is small at portions other than the portions supported by the first and second elastic members. 
     The difference in tensile force causes deformation of the slits through which electron beams pass, since the tension mask is partially diminished or expanded without sufficiently absorbing the thermal expansion amount at the center portion due to electron beams. The deformation of the slits hinders in accurate landing of electron beams emitted from the electron gun of a cathode-ray tube at predetermined positions on a fluorescent film, and makes the amount of an electron beam passing through a slot different according to portions of the tension mask. Thus, an image having a uniform resolution cannot be obtained. Also, portions on which relatively small tensile forces are applied severely vibrate even by small external impacts, so that screen jitter occurs. 
     U.S. Pat. No. 5,111,107 issued to Kume, et al. for GRID APPARATUS FOR A COLOR CATHODE RAY TUBE WHICH ELIMINATES VIBRATION OF THE GRIDS discloses a grid apparatus for color cathode-ray tubes, having a plurality of ribbon-shaped grid elements stretched in tension and attached to a frame which includes a pair of support bars and a pair of resilient support members. Metallic members which have a larger thermal expansion coefficient than the resilient support members are connected to the reverse surfaces of the resilient support members opposite the side of where the grid elements are attached. 
     In the grid apparatus having such a configuration, during heat treatment, thermal creep of the grid elements is prevented so that the tension of the grid elements will remain high when the normal temperature state is resumed. However, in the above-described color cathode-ray tube grid apparatus, the support bars are supported only by the resilient support members, so that the aforementioned problems remain. 
     Further exemplars of the art are U.S. Pat. No. 5,355,049 issued to Sung for ASSEMBLY OF SHADOW MASK FRAME WITH INNER SHIELD FOR COLOR CATHODE RAY TUBE, U.S. Pat. No. 5,898,259 issued to Reyal for SHADOW MASK FRAME OF A CATHODE RAY TUBE, ITS PROCESS OF MANUFACTURE, AND SUSPENSION ELEMENT OF A SHADOW MASK FRAME, U.S. Pat. No. 4,678,963 issued to Fonda for SHADOW MASK FOR A COLORED IMAGE TUBE AND IMAGE TUBE COMPRISING THE SAME, U.S. Pat. No. 5,877,586 issued to Aibara for SLOT-TYPE SHADOW MASK, U.S. Pat. No. 5,030,880 issued to An for SHADOW MASK FOR COLOR CATHODE RAY TUBE, U.S. Pat. No. 3,652,895 issued to Tsuneta et al. for SHADOW-MASK HAVING GRADUATED RECTANGULAR APERTURES, U.S. Pat. No. 5,856,725 issued to Ueda for SHADOW MASK WITH EDGE SLOTS CONFIGURATION, U.S. Pat. No. 4,168,450 issued to Yamauchi et al. for SLOT TYPE SHADOW MASK, U.S. Pat. No. 4,300,069 issued to Nolan for COLOR PICTURE TUBE HAVING IMPROVED SLIT TYPE SHADOW MASK AND METHOD OF MAKING SAME, U.S. Pat. No. 4,973,283 issued to Alder et al. for METHOD OF MANUFACTURING A TIED SLIT MASK CRT, U.S. Pat. No. 4,942,332 bit issued to Alder et al. for TIED SLIT MASK FOR CATHODE RAY TUBES, U.S. Pat. No. 5,523,647 issued to Kawamura et al. for COLOR CATHODE RAY TUBE HAVING IMPROVED SLOT TYPE SHADOW MASK, U.S. Pat. No. 6,057,640 issued to Aibara for SHADOW MASK FOR COLOR CATHODE RAY TUBE WITH SLOTS SIZED TO IMPROVE MECHANICAL STRENGTH AND BRIGHTNESS, U.S. Pat. No. 6,140,754 issued to Ko for STRUCTURE OF SHADOW MASK FOR FLAT CATHODE RAY TUBE, U.S. Pat. No. 4,794,299 issued to Chiodi et al. for FLAT TENSION MASK COLOR CRT FRONT ASSEMBLY WITH IMPROVED MASK FOR DEGROUPING ERROR COMPENSATION, U.S. Pat. No. 4,915,658 issued to Lopata et al. for REFERENCE AND SUPPORT SYSTEM FOR FLAT CRT TENSION MASK, U.S. Pat. No. 5,932,957 issued to Ragland, jr. for CATHODE-RAY TUBE HAVING DETENTIONING ROD ASSEMBLY FOR A TENSION MASK FRAME, U.S. Pat. No. 5,644,192 issue to Ragland, jr. for COLOR PICTURE HAVING A TENSIONED MASK AND COMPLIANT SUPPORT FRAME ASSEMBLY, and U.S. Pat. No. 4,495,437 issued to Kume et al. for GRID APPARATUS FOR USE WITH A COLOR CATHODE RAY TUBE. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a tension mask frame assembly for a color cathode ray tube in which a partial distortion of the tension mask due to application of non-uniform tensile forces to the tension mask supported by the support members of a frame is prevented by improving the structural integrity of the support members, so that the electron beam color distinguishing function of a tension mask is improved. 
     To achieve the above objects, the present invention provides a tension mask frame assembly for a color cathode-ray tube, the assembly including a tension mask having a plurality of strips isolated from each other at predetermined intervals on a thin plate to form slots, and tie bars for partitioning slots at a predetermined pitch interval by connecting adjacent strips to each other; and a frame having a pair of support members for supporting the longer sides of the tension mask, a pair of elastic members, the ends of which are connected to both ends of each of the support members so that the support members are isolated from each other a predetermined distance, and a reinforcing member having both ends coupled to both ends of the exterior side surface of each of the support members and its center portion contacting with the exterior side surface of each of the support members, the reinforcing member for elastically restoring the support members in a direction where a tensile force is applied to the strips. 
     In the present invention, preferably, both ends of each of the reinforcing members are secured at positions on the exterior side surface of each of the support members where the support members are supported by the elastic members, and the center portion thereof is joined to the center portion of the exterior side surface of each of the support members supported by the elastic members. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of this invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
     FIG. 1 is a perspective view of a tension mask frame assembly for a flat color cathode-ray tube; 
     FIG. 2 is a graph showing tensile forces applied to portions of a tension mask supported by a frame; and 
     FIG. 3 is an exploded perspective view of a tension mask frame assembly according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an example of a tension mask frame assembly for a color cathode-ray tube. Referring to FIG. 1, the tension mask frame assembly includes a frame  10  and a flat tension mask  20 . The frame has first and second support members  11  and  12  installed in parallel and first and second elastic members  13  and  14  connected to the first and second support members  11  and  12  such that the first and second support members  11  and  12  are spaced a predetermined distance from each other. The flat tension mask  20  has slots  22  formed by a plurality of strips  21  isolated from each other at predetermined intervals. The two longer edges  26  and  28  of the flat tension mask  20  are welded with the first and second support members  11  and  12 , respectively, by receiving a tensile force. 
     The strips  21  are connected to each other by tie bars  23  isolated from each other at predetermined intervals, thereby forming the slots  22 . In this tension mask frame assembly, the tension mask  20  supported by the first and second support members  11  and  12  cannot receive a uniform tensile force over the entire surface. 
     That is, in order to weld the tension mask  20  to the first and second support members  11  and  12  of the frame  10 , first, the first and second elastic members  13  and  14  are pressurized and elastically deformed so that the first and second support members  11  and  12  are displaced in facing directions. Next, in this state, both longer sides  26  and  28  of the tension mask  20  are welded to the first and second support members  11  and  12 , respectively, and then the pressure having been put on the first and second elastic members  13  and  14  is removed. At this time, the first and second support members  11  and  12  are subjected to a restoring force by the elasticity of the first and second elastic members  13  and  14 . This restoring force to the first and second support members  11  and  12  is different at portions of the support members  11  and  12  supported by the first and second elastic members than from the center portions of the first and second support members  11  and  12 . 
     The difference in restoring force between portions of the first and second support members  11  and  12  is represented as the difference between tensile forces applied to the strips  21  of the tension mask welded with the first and second support members. As shown in the graph of FIG. 2, a tensile force applied to the strips of the tension mask  10  is large at portions supported by the first and second elastic members  13  and  14 , whereas a tensile force applied to the strips  21  is small at portions other than the portions supported by the first and second elastic members  13  and  14 . 
     The difference in tensile force causes deformation of the slits  22  through which electron beams pass, since the tension mask  20  is partially diminished or expanded without sufficiently absorbing the thermal expansion amount at the center portion due to electron beams. The deformation of the slits  22  hinders an accurate landing of electron beams emitted from the electron gun of a cathode-ray tube at predetermined positions on a fluorescent film, and makes the amount of an electron beam passing through a slot different according to portions of the tension mask. Thus, an image having a uniform resolution cannot be obtained. Also, portions on which relatively small tensile forces are applied severely vibrate even by small external impacts, so that screen jitter occurs. 
     Referring to FIG. 3, a tension mask frame assembly for a color cathode-ray tube includes a tension mask  40  having an electron beam color distinguishing function, and a frame  50  for supporting the tension mask  40  while applying a predetermined tensile force to the tension mask  40 . 
     In the tension mask  40 , a plurality of strips  41  spaced at predetermined intervals  47  are formed on a thin plate  46 , and adjacent strips  41  are connected to each other via a tie bar  42  having a predetermined horizontal pitch  48  to thus form a plurality of slots  43 . Dummy bridges  44  extending from adjacent strips  41  are formed on each of the slots  43  defined by a tie bar  42  and adjacent strips  41 . Each one of the dummy bridges  44  is made up of first and second protrusions  44   a  and  44   b  extending from two adjacent strips in facing directions. Here, the first and second protrusions  44   a  and  44   b  extending in facing directions do not contact each other. The dummy bridges are not necessarily required by the tension mask. 
     The frame  50  for supporting the tension mask formed as described above includes first and second support members  51  and  52  for supporting the longer sides of the tension mask  40 , respectively, and first and second elastic members  53  and  54  which connect the support members  51  and  52  to each other and support them. The first and second support members  51  and  52  include supporters  51   a  and  52   a  that are welded with the longer sides,  56  and  58  respectively, of the tension mask  40 , respectively, and flanges  51   b  and  52   b  extending inwardly from the supporters  51   a  and  52   a , respectively. A reinforcing member  60  for uniformly maintaining the supporting force of each of the first and second support members  51  and  52  to the tension mask is installed on the outer side of each of the supporters  51   a  and  52   a.    
     Preferably, both ends of the reinforcing member  60  are secured near portions of each of the first and second support members  51  and  52  contacting the ends of the first and second elastic members  53  and  54 . However, both ends of the reinforcing member  60  can be welded with both ends of each of the first and second support members  51  and  52 . The center portion  60   a  of the reinforcing member  60  is joined to the center of each one of the first and second support members  51  and  52 . The center portion of the reinforcing member  60  between portions of each one of the first and second support members  51  and  52  is coupled to the first and second elastic members  53  and  54 , such that the reinforcing member  60  restores the first and second support members  51  and  52  elastically outward. It is apparent that the position of the junction is not limited to this embodiment and can vary according to the tension state of a tension mask supported by the first and second support members  51  and  52 . 
     The reinforcing member  60  is made of a flat bar having a width that is smaller than or equal to the width of the supporters  51   a  and  52   a , and both ends of the reinforcing member  60  are coupled to the supporters  51   a  and  52   a  have folded portions  61  and  62  so that portions other than both ends and the center portion  60   a  are isolated from the supporters  51   a  and  52   a.    
     In the operation of the tension mask frame assembly for a color cathode-ray tube according to the present invention having such a structure, the first and second support members  51  and  52  are pressurized in facing directions so that the first and second elastic members  53  and  54  which support the first and second support members are elastically deformed. At this time, the reinforcing members  60  are welded with the pressurized first and second support members  51  and  52  while their respective center portions are being pressed down on the first and second support members  51  and  52 . 
     In this state, the longer sides of the tension mask  40  are welded with the supporters  51   a  and  52   a  of the first and second support members  51  and  52 , respectively. After the welding is completed, the pressures applied to the first and second support members  51  and  52  and the reinforcing member  60  are removed, so that a tensile force is applied to the tension mask  40  by the restoring force of the first and second elastic members  53  and  54 . Considering the fact that it is difficult to pressurize the first and second support members with which the reinforcing member  60  is welded, the reinforcing member  60  can be welded with the upper portion of the outer side surface of the first and second support members. 
     Here, since the center of each of the supporters  51   a  and  52   a  of the first and second support members  51  and  52  is supported by the center portion  60   a  of the reinforcing member  60 , the deformation force of the first and second supporters  51  and  52  by the tensile force of the tension mask  40  can be reduced. To be more specific, the center portions of the first and second support members  51  and  52 , which are the farthest from portions supported by the first and second elastic members  53  and  54 , are the most severely deformed due to the least supportive reaction from the elastic members  53  and  54 . The center portions  60   a  of the reinforcing members  60 , the ends of which are supported by portions where the first and second support members  51  and  52  are welded with the first and second elastic members  53  and  54 , are welded with the center portions of the first and second support members, respectively, such that the maximumly-deformed portions of the first and second support members  51  and  52  are elastically restored in directions opposite to the deformation directions by the reinforcing member  60 . Therefore, the deformation force of the center portion of the first and second support members  51  and  52  increases in a direction where a tensile force is applied to the strips, and thus the tension of the center portion of the tension mask  40  increases, so that the tension mask is subjected to a uniform tensile force. 
     In the tension mask frame assembly for a color cathode-ray tube according to the present invention having such a structure, elastic restoration energy can be increased by the reinforcing member  60  supported by the supporters for securing the tension mask  40 . Thus, a uniform tensile force is applied to the tension mask supported by the supporters. 
     Although the invention has been described with reference to a particular embodiment, it will be apparent to one of ordinary skill in the art that modifications to the described embodiment may be made without departing from the spirit and scope of the invention.