Patent Publication Number: US-6703777-B2

Title: Adjusting method for cathode position of an electron gun and an electron gun for a cathode ray tube

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present invention claims priority to the priority document, Japanese Patent Application No. P2000-391470 filed in Japan on Dec. 22, 2000, and incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an adjusting method for cathode position of an electron gun and a electron gun for a cathode ray tube. More particularly, after a positional adjustment is executed for a position of an apex point of a cathode to become a center of a grid aperture of a first grid, an adjustment for a distance between the cathode and the first grid is independently executed, and accordingly even a cathode having a dome shaped surface can be fixed to a right position relative to the aperture of the first grid with higher precision. 
     2. Description of the Related Art 
     An electron gun of a cathode ray tube is so constructed, for example as shown in FIG. 9, as to be mechanically linked and supported with a predetermined positional relation mutually by fixing a cylindrical shaped first grid  11 , a second grid  12 , a third grid  13 , a forth grid  14  and a fifth grid  15  to a beading glass  16 , respectively. 
     Further a cylindrical cathode structure  30  is positioned within the first grid  11  and a cathode  31  is provided on a top surface of the cathode structure  30 . In this case, when the cathode structure  30  is assembled within the first grid  11 , a grid aperture  11   h  provided at the first grid  11  and the cathode structure  30  are adjusted to be coaxial and further, a gap between the first grid  11  and the cathode  31  to be a predetermined value (it is called as a dgk-value adjustment). 
     Further a test for improving focus characteristics has been done by employing a cathode having a dome shaped surface such as an impregnate type cathode, for example, and by minimizing a work area of a cathode due to concentration of an electronic field from a first grid. 
     In a case when the surface of the cathode  31  is formed to be dome shaped, a position of the apex point of the dome shaped cathode may have dispersion at every cathode. 
     When the grid aperture  11   h  and the cathode structure  30  are adjusted to be coaxial, it sometimes occurs that the position of the apex point and a center of the grid aperture  11   h  are not coincided due to such dispersion of the apex point the cathode  31 . 
     When the position of the apex point and the center of the grid aperture  11   h  are not coincided, a track of a beam emitted from the cathode  31  is bent and it causes the problems that the shift amount of the spot formed on a phosphor screen of the cathode ray tube becomes large. 
     Further the surface of the cathode  31  is dome shaped, so that if it is not precisely adjusted for the gap between the apex point and the first grid  11  to be a predetermined space by properly detecting the position of the apex point of the cathode surface, the gap between the first grid  11  and the cathode  31  may have dispersion, and it causes a problem in which cut-off levels of R, G and B beams have dispersion due to such dispersion of the gaps. 
     SUMMARY OF THE INVENTION 
     According to the present invention, an adjusting method for a cathode position of an electron gun is presented capable of properly adjusting a position of a cathode, although an impregnate type cathode is employed as a cathode. 
     The adjusting method of the present invention includes: a step for supporting a cathode structure at a cathode holder; a step for detecting a position of an apex point of the cathode of the cathode structure supported by the cathode holder; a step for fixing the cathode holder to a first grid after executing a position adjustment for the position of the apex point of the cathode to be a center of a grid aperture of the first grid; and a step for fixing the cathode holder and the cathode structure after executing the position adjustment of the detected position of the apex point of the cathode and the first grid to be a predetermined value. 
     Further an electron gun of a cathode ray tube of the present invention comprises: a cathode colder; a cathode structure supported by the cathode holder; a cathode constituting the cathode structure; and a first grid having a grid aperture; wherein an apex point of the cathode is fixed to be positioned to a center of the grid aperture of the first grid. 
     According to the present invention, a cathode structure having a cathode with a dome shaped surface is mounted within a cathode holder. A position of the apex point of the cathode in the cathode structure supported by the cathode holder is detected and then the cathode holder is fixed to the first grid after a position adjustment where a position of an apex point of the cathode is coincided with a center of the grid aperture of the first grid. Further the cathode holder and the cathode structure are fixed after executing the position adjustment in which the gap between the detected position of the apex point of the cathode and the first grid becomes a predetermined value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1A is a top view of a first grid; 
     FIG. 1B is a sectional view of the first grid taken along a line I—I in FIG. 1A; 
     FIG. 2 is a schematic sectional view of a cathode structure; 
     FIG. 3 is a sectional view of a sleeve holder; 
     FIG. 4A is a top view of a cathode fixing jig; 
     FIG. 4B is a side view of the cathode fixing jig in FIG. 4A; 
     FIG. 5 is a plan view of a grid position adjustment jig; 
     FIG. 6 is a sectional view of the grid position adjustment jig taken along a line II—II in FIG. 5 and a cathode structure supporting jig; 
     FIGS. 7A to  7 D are charts showing a process for assembling the cathode structure; 
     FIG. 8 is a schematic sectional view of a first grid on which the cathode structure is mounted; and 
     FIG. 9 is a partial side view of the electron gun. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Here-in-after, one embodiment of the present invention is explained with reference to the attached drawings. 
     As shown in FIG. 1A, a first grid  11  has a grid aperture  11   h -R for R (red) beam, a grid aperture  11   h -G for G (green) beam and a grid aperture  11   h -B for B (blue) beam. At a longer side portion of the first grid  11 , a fixing terminal  11 T is formed in a projected form, where the first grid  11  is bonded to a beading glass  16  when it is fixed to the beading glass  16 . 
     Further to the first grid  11 , a substrate holder  11   b  is welded the first grid  11  to support a ceramic substrate  20  as shown in FIG.  1 B. An insertion aperture  21 -R for inserting a cathode structure  30  is provided at the ceramic substrate  20  at a position opposed to the grid aperture  11   h -R for the R beam. Similarly, insertion apertures  21 -G for G beam and  21 -B for B beam for inserting respective cathode structures  30  (depicted by a two-dot-chain line) are provided at position opposed to the grid aperture  11   h -G and grid aperture  11   h -B. Further sleeve rings  22 -R,  22 -G and  22 -B are provided on periphery of the insertion apertures  21 -R,  21 -G and  21 -B, respectively at a face of the of the ceramic substrate  20 , where the face is the other side to the face opposed to the first grid  11 . 
     FIG. 2 shows a schematic sectional view of the cathode structure  30  positioned within the first grid  11 . Such impregnate type cathode  31  having a dome shaped surface is fixed to a cap  32  and further a first sleeve  33  is mounted on the cap  32 . 
     Each end of three straps  35  is connected to one side of the first sleeve  33  at even interval and the each of other end of the straps  35  is connected to a tip of a second sleeve  34 , respectively. Accordingly, when the first sleeve  33  to which the cathode  31  and the cap  32  are fixed is inserted into the second sleeve  34 , the first sleeve  33  is supported by the strap  35  so as not to move in the direction perpendicular to an axial direction of the cathode structure  30 . Further by fixing the other end of the strap  35  to the tip of the second sleeve  34 , the first sleeve  33  is also kept unmoved to the axial direction of the cathode structure  30 . The first sleeve  33  is supported by way of the strap  35 , so that when the cathode  31  is heated by a heater that is mounted within the first sleeve  33 , the heat is prevented from escaping to the second sleeve  34 , and accordingly, the cathode  31  can be efficiently heated. A sleeve shield  36  is mounted inside of the second sleeve  34  to which the first sleeve  33  is connected by way of the strap  35 . 
     FIG. 3 is a sectional view of a sleeve holder  40  for fixing a cathode structure  30 -R for a R (red) beam, a cathode structure  30 -G for a G (green) beam and a cathode structure  30 -B for a B (blue) beam to the ceramic substrate  20 , where the cathode structure  30 -R, the cathode structure  30 -G and the cathode structure  30 -B are inserted into respective inserting apertures  21 -R,  21 -G, and  21 -B of the ceramic substrate  20 . The sleeve holder  40  is formed in a cylindrical shape and an inside diameter of the sleeve holder  40  is formed slightly larger than an outer diameter of the second sleeve  34  so as to slidably support the inserted cathode structure  30 . Further a collar portion  41  to be welded to the sleeve ring  22  is formed at an end of the sleeve holder  40  that becomes a cathode side when the cathode structure  30  is inserted. 
     When the cathode structure  30  constructed as above is installed within the first grid  11  by way of the sleeve holder  40 , a position of an apex point of the cathode  31  provided on top of the cathode structure  30  and a center of the grid aperture  11   h  are adjusted to be coincided to each other by a cathode fixing jig, and after that the cathode structure  30  is adjusted to be a right position so as for a gap between the apex point of the cathode  31  and the first grid  11  to be a predetermined value. 
     FIG. 4A shows a schematic plan view of the cathode fixing jig and FIG. 4B is a schematic front view thereof. A two-dot-chain line in FIG.  4 A and FIG. 4B designates respective positions of a measuring machine  58 , an grid position adjustment jig  60  and a cathode structure supporting jig  80 , and those will be described later. Further in this schematic front view in FIG. 4B, later-described laser output apparatuses  53 - 2 ,  53 - 3 ,  55 - 2  and  55 - 3  are neglected for simplifying the drawing. 
     The grid position adjustment jig  60  and a table  52  for mounting the cathode structure supporting jig  80  are provided on a frame  51  of the cathode fixing jig  50 . Three laser output apparatus  53 - 1 ,  53 - 2  and  53 - 3  are provided, for example, for laser-welding the sleeve ring  22  on the ceramic substrate  20  and the collar portion  41  on the sleeve holder  40  around the table  52 . 
     The laser output apparatus  53 - 1  is fixed on a supporting substrate  54 - 1  so as to irradiate the laser beam askew in an upward direction. In addition, a focus position of the laser beam is adjusted to be a junction face where the sleeve ring  22  of the ceramic substrate  20  supported by the grid position adjustment jig  60  and the collar portion  41  of the sleeve holder  40  supported by the cathode structure supporting jig  80  are in junction. Similarly the laser output apparatus  53 - 2  and  53 - 3  are also fixed so as to irradiate the laser beam askew in the upward direction, and also are adjusted to have a focus position at a junction face of the sleeve ring  22  and the collar portion  41 . 
     Three laser output apparatus  55 - 1 ,  55 - 2  and  55 - 3  are provided around the table  52  for welding the second sleeve  34  and the sleeve holder  40  of the cathode structure  30 , for example. 
     The laser output apparatus  55 - 1  is fixed to the supporting substrate  56 - 1  to irradiate the laser beam in a horizontal direction. A focusing position of the laser beam is adjusted to a superposed position of the second sleeve  34  of the cathode structure  30  supported by the cathode structure supporting jig  80  and the sleeve holder  40  mounted on the ceramic substrate  20 . Similarly, the laser output apparatus  55 - 2  and  55 - 3  are also adjusted to irradiate the laser beam to the horizontal direction and the focus point of the laser beam is adjusted to a superposed position of the second sleeve  34  and the sleeve holder  40 . 
     Further a measuring machine  58  is positioned above the grid position adjustment jig  60 , wherein the measuring machine  58  detects the grid aperture  11   h  of the first grid  11  supported by the grid position adjustment jig  60  and the position of the apex point of the cathode structure  30  supported by the cathode structure supporting jig  80 . 
     FIG. 5 shows a schematic front view of the grid position adjustment jig  60 . 
     The first table  62  is mounted on the base substrate  61  slidably in an X direction in the figure. Further the second table  63  is mounted on the first table  62  slidably in a Y direction in the figure. Further a table  64  having an opening  64   a  is fixedly mounted at the second table  63  for mounting the grid fixing member  70  (as shown by a two-dot-chain line in the figure). In this case, openings are provided at the base substrate  61 , the first table  62  and the second table  63  corresponding to a position of the opening  64   a  of the table  64 . 
     A position adjustment apparatus such as a micro-meter  65  is provided at one side of the first table  62  by fixing on the base substrate  61 , where such side of the first table  62  is perpendicular to the X direction. A spindle  65   a  of the micro-meter  65  is impinged on a side end face of the first table  62 . Further a pressing portion  66  fixed to the base substrate  61  is provided and a shaft  66   a  of the pressing portion  66  is impinged on the side end face of the first table  62  and then the first table  62  is pressed against the micro-meter  65 . Accordingly, the position of the grid fixing member  70  can be adjusted minutely in the X direction by rotating a thimble  65   b  of the micro-meter  65  so as to vary a protruding amount of the spindle  65   a.    
     A position adjustment apparatus such as a micro-meter  67  is provided at one side of the second table  63  by fixing on the base substrate  61 , where the side of the second table  63  is perpendicular to the X direction. A spindle  67   a  of the micro-meter  67  is impinged on a side end face of the second table  63 . Further a pressing portion  68  fixed to the base substrate  61  is provided and a shaft  68   a  of the pressing portion  68  is impinged on the side end face of the second table  63  and the second table  63  is pressed against the micro-meter  67 . Accordingly, the position of the grid fixing member  70  can be adjusted minutely in the X direction by rotating a thimble  67   b  of the micro-meter  67  so as to vary a protruding amount of the spindle  67   a.    
     Thus constructed grid position adjustment jig  60  is mounted and fixed to a base substrate  81  of a cathode structure supporting jig  80  as shown in FIG.  6 . In this case, FIG. 6 shows a schematic view of the grid position adjustment jig  60  taken along a line II—II in FIG.  5 . Further a schematic sectional view of the opening of the table  64  taken along a line III—III is also depicted. 
     An elevating desk  82  is mounted on the base substrate  81  slidably in the vertical direction (a Z direction in the figure). Further a micro-meter  83  is fixedly mounted on the base substrate  81  as the position adjustment apparatus and the spindle  83   a  of the micro-meter  83  is fixed to the elevating desk  82 . Further a supporting portion  84  is provided on an upper surface of the elevating desk  82  for supporting the cathode structure  30  and the sleeve holder  40 . In the figure, a schematic sectional view of the supporting portion  84  is depicted. In this case, the positions of the cathode structure  30  supported by the supporting portion  84  and the sleeve holder  40  can be adjusted in the vertical direction by rotating the thimble  83   b  of the micro-meter  83  so as to vary a protruding amount of the spindle  83   a  of the micro-meter  83 . 
     The grid fixing member  70  is mounted to the opening of the table  64  in the grid position adjustment jig  60 . The grid fixing member  70  includes a table  71  to receive the first grid  11  and a supporting lever  72  for supporting the first grid  11  mounted on the table  71 . The grid aperture  11   h  of the first grid  11  is open condition at the table  71 . 
     The grid fixing member  70  is mounted on the grid position adjustment jig  60  and the grid position adjustment jig  60  is further mounted on the cathode structure supporting jig  80  so that the sleeve ring  22  of the ceramic substrate  20  mounted on the first grid  11  becomes to be on a side of the cathode structure supporting jig  80 . Further the position of the grid fixing member  70  is adjusted by the micro-meters  65  and  67  and the cathode  31  of the cathode structure  30  supported by the supporting portion  84  is fixed to be detected by the measuring machine  58  through the grid apertures  11   h -R,  11   h -G and  11   h -B of the first grid  11 . 
     FIGS. 7A to  7 D are charts for explaining mounting operations of fixing the cathode structure  30  on the first grid  11  by the cathode fixing jig  50 . As shown in FIG. 7A, a cathode structure supporting portion  841  for fixing the position of the cathode structure  30  at a center of a tip of the supporting portion  84  provided on the cathode structure supporting jig  80 . Further a groove  842  is formed around the cathode structure supporting portion  841  and a resilient member such as a coil spring  843  is loosely inserted in the groove  842 . A movable supporting member  844  is provided to slidably support the collar portion  41  of the sleeve holder  40  in the vertical direction (the Z direction in the figure), wherein the movable supporting member  844  is loosely inserted in the in the groove  842  in which the coil spring  843  is loosely inserted. 
     In this case, when the cathode structure  30  is mounted on the first grid  11 , the cathode structure  30  is supported by fixing its position by the cathode structure supporting portion  841 , and also, the collar portion  41  of the sleeve holder  40  is supported by the movable supporting member  844 . Further, the apex point of the cathode  31  provided at a tip of the cathode structure  30  supported by the supporting portion  84  is detected by the measuring machine  58  by way of the grid aperture  11   h -R, for example, of the first grid  11 . 
     A measuring machine capable of detecting the apex point of the cathode  31  such as a focal depth measuring machine or a three dimensional surface form measuring machine which can detect the apex point by applying interference between an irradiating light and a reflecting light are used as a measuring machine  58 . 
     A positioning adjustment to execute a fine adjustment of a position of the first grid  11  by the micro-meters  65  and  67  so that the apex point of the cathode  31  detected by the measuring machine  58  becomes a center of the grid aperture  11   h -R. 
     Next, when a fine adjustment of the position of the first grid  11  is completed, the sleeve ring  22  provided on the ceramic substrate  20  and the collar portion  41  of the sleeve holder  40  are bonded by moving the supporting portion  84  in a direction of the first grid  11  as designated by an arrow in FIG. 7B by operating the micro-meter  83 . Further, the sleeve ring  22  and the sleeve holder  40  are laser-welded by irradiating a laser beam on this bonding surface from laser output apparatuses  53 - 1 ,  53 - 2  and  53 - 3 . 
     When the laser welding process for the sleeve ring  22  and the sleeve holder  40  is completed, a dgk-value (dimension between a grid and a cathode) designating a distance between the surface of the first grid  11  and the apex point of the cathode  30  is adjusted to be a predetermined value by further moving the supporting portion  84  in the direction of the first grid  11  as designated by an arrow in FIG. 7C by further operating the micro-meter  83 . 
     In this case, when the height of the apex point is constant, the dgk-value is easily adjusted to be a predetermined value based on the designated value of the micro-meter  83  with the position of the surface of the first grid  11  as a reference position of the micro-meter  83 . Further when there is dispersion in the height of the apex points, the apex point is detected by the measuring machine  58 , and the dgk-value adjustment process is executed to be a predetermined value by measuring the position of the apex point and the surface of the first grid  11 . 
     When the dgk-value adjustment process is completed, the second sleeve  34  and the sleeve holder  40  are laser-welded by irradiating the laser beam from the laser output apparatus  55 - 1 ,  55 - 2  and  55 - 3  on the superposed position of the second sleeve  34  of the cathode structure  30  and the sleeve holder  40 . In this case, the cathode structure  30  is to be fixed to the first grid  11  through the sleeve holder  40 . Further stress applied to a laser-welded portion of the sleeve ring  22  and the sleeve holder  40  is avoided because the movable supporting member  844  is to be sliding in the groove  842 , even if the supporting portion  84  is moved in a direction of the first grid  11  after the laser-welding of the sleeve ring  22  and the sleeve holder  40 . 
     Further when the fixing of the cathode structure  30  to the first grid  11  is completed, the supporting portion  84  is moved to a position opposite to the first grid  11  as shown in FIG. 7D by the micro-meter  83 . 
     After that, another cathode structure  30  is mounted to the supporting portion  84  and the first grid  11  is moved to the X direction so that another grid aperture is positioned at the cathode structure  30  supported on the supporting portion  84  and a sequential set of above-described processes as shown in FIG. 7A to FIG. 7D is again executed. 
     As described above, the sleeve ring  22  and the sleeve holder  40  are welded together by the laser beam after the centers of the grid apertures  11   h -R,  11   h -G, and  11   h -B are adjusted to be coincided with the apex point by detecting the apex point of the cathode  31 . Further, the sleeve holder  40  and the cathode structure  30  are welded together by the laser beam after adjusting the gap between the first grid  11  and the apex point to be a predetermined value. Accordingly as shown in FIG. 8, even if there are dispersion in the cathode structure  30  to be fixed to the position of the grid aperture  11   h -R and the center axis of the grid aperture  11   h -R is not coincided with the position of the apex point, it is possible to adjust the position of the apex point with the center of the grid aperture  11   h  and further to mount the cathode  31  so that the gap between the first grid  11  and the apex point becomes a predetermined value. 
     In this case in the above-described embodiment, the sleeve holder  40  and the cathode structure  30  are welded after welding the sleeve ring  22  and the sleeve holder  40 , but the sleeve ring  22  and the sleeve holder  40  is able to be welded with a predetermined gap between the first grid  11  and the apex point of the cathode  31  after welding the sleeve holder  40  and the cathode structure  30  by adjusting the center of the grid aperture  11   h  and the apex point of the cathode  31 . 
     Further the above-mentioned cathode fixing jig and the grid position adjustment jig are just employed as exemplified models and not limited to the embodiments. In addition, the positional adjustment for the first grid and the position adjustment for the cathode structure are possible to be automated by utilizing signals from the measuring machine or the like. 
     As described above, a positional adjustment process of the position of the apex point of the cathode and the center of the grid aperture on the first grid is independently done on the dgk-value adjustment process for positioning the gap between the detected position of the apex point of cathode and the first grid to be a predetermined value. Accordingly, even a coating type cathode having dome shaped surface is employed, mounting operation of the cathode onto the first grid is accomplished with high precision.