Abstract:
A color cathode ray has an electron gun which includes three cathodes for emitting three in-line electron beams and a plurality of electrodes fixed in a predetermined axially spaced relationship on insulating supports. At least one of the plurality of electrodes is cup-shaped and has a correction electrode therein, and edges of the correction electrode are formed with recesses and sloped portions. A distance L from a mouth of each of the recesses of the correction electrode to an inner wall of the at least one of the plurality of electrodes satisfies the following relationship: L′≦L≦15 μm, where L′ is a height of a burr caused in press-forming of the recesses.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of U.S. application Ser. No. 09/247,088, filed Feb. 9, 1999, now U.S. Pat. No. 6,081,068, issued Jun. 27, 2000, which is a continuation of U.S. application Ser. No. 08/916,710, filed Aug. 25, 1997, now U.S. Pat. No. 5,886,462, issued Mar. 23, 1999, the subject matter of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a color cathode ray tube, and particularly to a color cathode ray tube having precision main lens electrodes for an in-line type electron gun. 
     Color cathode ray tubes such as a color picture tube, a display tube, and the like are widely used as a receiver of TV broadcasting or as a monitor in an information processing apparatus for their high-definition image reproduction capability. 
     The color cathode ray tube of this kind includes a vacuum envelope comprised of at least a funnel having a faceplate carrying a phosphor screen on its inner surface at one end thereof, and a neck connected to the end of the funnel housing therein an electron gun structure for emitting electron beams toward the phosphor screen. 
     FIG. 15 is a schematic sectional view for explaining the configuration of a shadow mask type color cathode ray tube as one example of a color cathode ray tube to which the present invention is applied. Reference numeral  20  designates a faceplate,  21  a neck,  22  a funnel for connecting the faceplate to the neck,  23  a phosphor screen formed on the inner surface of the face plate to constitute an imaging screen,  24  a shadow mask which is a color selection electrode,  25  a mask frame for supporting the shadow mask to constitute a shadow mask structure,  26  an inner shield for shielding external magnetic fields,  27  a suspension spring mechanism for suspending the shadow mask structure on studs heat-sealed to the inner side wall,  28  an electron gun housed in the neck for emitting three electron beams Bs (×2) and Bc,  29  a deflection device for horizontally and vertically deflecting the electron beams,  30   a  magnetic device for carrying out a color purity adjustment and a centering adjustment,  31  a getter,  32  an internal conductive coating, and  33  an implosion protection band. 
     In the configuration shown in FIG. 15, the faceplate  20 , the neck  21  and the funnel  22  constitute a vacuum envelope. Three electron beams Bc and Bs×2 emitted in a line from the electron gun are horizontally and vertically deflected by magnetic fields formed by the deflection device  29  to scan the phosphor screen  23  two-dimensionally. 
     The three electron beams Bs, Bc×2 are respectively modulated by color signals of red (side beam Bs), green (center beam Bc) and blue (side beam Bs) and subjected to color selection in beam apertures in the shadow mask  24  disposed immediately in front of the phosphor screen  23  to impinge upon a red phosphor, a green phosphor and a blue phosphor of the mosaic three color phosphors of the phosphor screen  23 , thereby reproducing a desired color image. 
     FIG. 16 is a top view of main parts for explaining a structural example of an in-line type electron gun structure used for the color cathode ray tube shown in FIG.  15 . Reference numeral  10  designates a cathode,  11  a first grid electrode serving as a control electrode,  12  a second grid electrode,  13  a third grid electrode,  14  a fourth grid electrode,  15  a fifth grid electrode,  16  a sixth grid electrode,  16   a  a correction plate electrode in the sixth grid electrode  16 ,  17  an anode,  17   a  a correction plate electrode in the anode,  18  a shield cup, and  19  insulating supports (only one of two is shown). 
     In the electron gun, three electron beams generated in a triode constituted by the cathode  10 , the first grid electrode  11  and the second grid electrode  12  are accelerated and preliminarily focused by the third grid electrode  13 , the fourth grid electrode  14  and the fifth grid electrode  15 , focused as desired by a main lens formed between the opposing surfaces of the sixth grid electrode and the anode  17 , and they are directed toward the phosphor screen as shown in FIG.  15 . 
     In the electron gun of this type, the fifth electrode  15 , the sixth electrode  16  and the anode  17  constituting the focus lens are cup-shaped. Particularly, each of the grid electrode  16  and the anode  17  constituting the final lens has a single opening surrounded by an in-turned rim on mutually facing ends thereof and has a correction plate electrode  16   a ,  17   a  therein set back from the mutually facing ends thereof which has an individual aperture therein for each of the electron beams, respectively. 
     FIGS. 17A and 17B are schematic sectional views for explaining a main lens forming electrode of the aforementioned type electrode gun. FIG. 17A is a sectional view in parallel with the in-line direction of the three beams, and FIG. 17B is a sectional view perpendicular to the in-line direction. 
     In FIGS. 17A and 17B, the sixth grid electrode  16  has a single opening  16 - 1  in the end face of the sixth grid electrode  16  opposing the anode  17 , surrounded by a rim turned in an axial distance H toward the interior of the sixth grid electrode  16 , and has a correction plate electrode  16   a  having three beam apertures therein corresponding to the number of the electron beams and disposed at a position therein set back a distance d 1  from the single opening toward the interior of the sixth grid electrode, and similarly the anode  17  has a single opening  17 - 1  in the end face of the anode opposing the sixth grid electrode  16  across a spacing g, surrounded by a rim turned in an axial distance H toward the interior of the sixth electrode  16 , and has a correction plate electrode  17   a  having three beam apertures therein corresponding to the number of the electron beams end disposed at a position therein set back a distance d 2  from the single opening toward the interior of the anode. The correction plate electrode  17   a  has an opening for passing a center electron beam and forms passageways for side electron beams in cooperation with the inner wall of the cup-shaped anode  17 . A combination of the single openings  16 - 1 ,  17 - 1  and the correction plate electrodes  16   a ,  17   a  produces an effectively large diameter electron lens. Japanese Patent Application Laid-Open No. 4-43532 Publication discloses an above-described effectively large diameter main lens formed by provision of oval rims in opposing end faces of a pair of electrodes in the main lens and correction plate electrodes set back from the respective opposing end faces toward the interiors of the respective electrodes. 
     FIGS. 18A to  18 C are schematic sectional views for explaining the shapes of the electrodes for a main lens of the conventional electron gun. Generally, the inner wall of the cup-shaped electrode  16  ( 17 ) is formed to have an axially uniform inside diameter (in major and minor axis directions) from the open end A to the opposite end B formed with a rim as shown in FIG.  18 A. The opening end A sometimes becomes narrower than the opposite end B after manufacturing process such as drawing as shown in FIG.  18 B. 
     The outside diameters of the correction plate electrode are made substantially equal to the inside diameters of the cup-shaped electrode in major and minor axis lengths. Since the correction plate electrode  17   a  disposed within the anode  17  is semi-circular or semi-oval at both ends of its major axis, only top and bottom edges of the plate electrode in the minor axis direction are welded to the inner wall of the cup-shaped electrode. 
     When the correction plate electrode  16   a  ( 17   a ) is inserted into the cup-shaped electrode  16  ( 17 ) and fixed by laser weld or the like to a position of a desired set back amount d from the electrode end face to manufacture the electrode as shown in FIG. 18C, if the inside diameter of the cup-shaped electrode is of the shape shown in FIG. 18A or FIG. 18B, it is very difficult to accurately position the correction plate electrode  16   a  ( 17   a ) within the cup-shaped electrode (the sixth grid electrode  16  or the anode  17 ). Thus, it is difficult to establish the dimension d or to secure the parallelism with respect to the single opening, resulting in deterioration of characteristics of the electron gun. 
     As described above, in the conventional electron gun structure for the cathode ray tube, the correction plate electrode is welded by laser to a position set back from the rim in-turned internally of the opposing end faces of the cup-shaped electrode, within the cup-shaped electrode of the main lens. Therefore, variations in positioning accuracy of the correction plate electrode are caused by variations in the shape of the open end of the cup-shaped electrode, resulting in an increase of astigmatism of the lens. 
     There is a further problem in that it is very difficult to adjust the positioning of the correction plate electrode after being assembled and welded. 
     FIGS. 19A to  19 C are schematic sectional views for explaining the shape of the main lens forming electrodes of the electron gun previously proposed by the present inventors, FIG. 19A is a sectional view similar to FIG. 17B illustrating the cup-shaped anode  17 , FIG. 19B is a front view of the correction plate electrode  17   a  to be welded and fixed to the interior of the cup-shaped electrode  17 , and FIG. 19C is an enlarged view of main parts of FIG.  19 B. 
     As shown in FIG. 19A, the correction plate electrode  17   a  is inserted toward the opposite end formed with a rim along the inner wall B from the open end A of the cup-shaped anode  17 , and fixed at its edges by laser weld or the like to the position of the set back amount d 2 . As shown in FIG. 19B, the correction plate electrode  17   a  has the beam aperture  17   ac  for passing a center electron beam end two cutouts  17   as  for passing side electron beams at both its sides. The cutouts  17   as  form an electron beam aperture in cooperation with the inner wall of the anode  17 . 
     Recesses  17   b  are formed by press-forming at the edges of the correction plate electrode  17   a  which contact the inner wall of the anode  17  when inserted into the anode  17 , to reduce friction with the inner wall B and secure ease of assembling. However, when the recess  17   b  is press-formed in the correction plate electrode  17   a , burrs  17   d  occur as shown in FIG.  19 C. If the protrusion L′ of the burr  17   d  is larger than the clearance between the plate electrode and the inner wall of the anode  17 , this deforms the anode  17  and the correction plate electrode  17   a.    
     In addition to burrs, variations of outside diameters of the correction plate electrode  17   a  and inside diameters of the open end of the cup-shaped electrode  17  hinder the ease of insertion of the correction plate electrode  17   a  into the cup-shaped electrode  17 . This difficulty with the insertion and variations of conditions of laser weld change the diameter of the opening in the cup-shaped electrode and the diameters of the apertures in the correction plate electrode which play the most important role in the assembled electrodes. This poses a problem in that characteristics of the electron gun is degraded by the reduced accuracy of the main lens electrode geometry and resultant increased astigmatism such that a cathode ray tube can not provide the desired performance. 
     There is a further problem in that it is very difficult to readjust the position of the correction plate electrode after it is assembled and welded to the cup-shaped electrode. 
     The same is true for the assembly of the sixth grid electrode  16  and the correction plate electrode  16   a  therefor, and the description associated with the problem is omitted. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a color cathode ray tube of high performance in which the accuracy of a main lens electrode assembly is improved by overcoming the problems described above with respect to prior art. 
     To achieve the aforementioned object, according to an embodiment of the present invention, there is provided a color cathoe dray tube including a vacuum envelope comprising a panel portion, a neck portion, and a funnel portion connecting the panel portion and the neck portion; a phosphor screen on an inner surface of the panel portion; a shadow mask suspended closely spaced from the phosphor screen in the panel portion; and an electron gun housed within the neck portion; the electron gun comprising three cathodes for emitting three in-line electron beams and a plurality of electrodes; the plurality of electrodes being fixed in a predetermined axially spaced relationship on insulating supports, at least one of the plurality of electrodes being cup-shaped and having a correction electrode therein, edges of the correction electrode being formed with recesses and sloped portions extending in a direction away from the recesses toward an inner wall of the at least one of the plurality of electrodes, and a distance L from a mouth of each of the recesses of the correction electrode to an inner wall of the at least one of the plurality of electrodes satisfying the following relationship: L′≦L≦15 μm, where L′ is a height of a burr caused in press-forming of the recesses. 
     To achieve the aforementioned object, according to another embodiment of the present invention, there is provided a color cathode ray tube including a vacuum envelope comprising a panel portion, a neck portion, and a funnel portion-connecting the panel portion and the neck portion; a mosaic three-color phosphor screen on an inner surface of the panel portion; a shadow mask suspended closely spaced from the mosaic three-color phosphor screen of the panel portion; and an electron gun housed within the neck portion; the electron gun comprising three cathodes for emitting three in-line electron beams and a plurality of electrodes; the plurality of electrodes being fixed in a predetermined axially spaced relationship on insulating supports, at least one of the plurality of electrodes being cup-shaped and having a correction electrode therein, edges of the correction electrode being formed with recesses and sloped portions, and a distance L from a mouth of each of the recesses of the correction electrode to an inner wall of the at least one of the plurality of electrodes satisfying the following relationship: L′≦L≦15 μm, where L′ is a height of a burr caused in press-forming of the recesses. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, which form an integral part of the specification and are to be read in conjunction therewith, and in which like reference numerals designate similar components throughout the figures, and in which: 
     FIGS. 1A and 1B are schematic sectional views for explaining an embodiment of an electron gun structure for a cathode ray tube, FIG. 1A is a sectional view in parallel with the in-line direction of three electron beams of the electron gun, FIG. 1B is a sectional view perpendicular to the in-line direction of the three electron beams; 
     FIGS. 1C and 1D are schematic sectional views for explaining a modification of the embodiment of FIGS. 1A and 1B, FIG. 1C is a sectional view in parallel with the in-line direction of three electron beams of the electron gun, FIG. 1D is a sectional view perpendicular to the in-line direction of the three electron beams; 
     FIG. 2 is a front view showing a state in which a correction plate electrode is welded to the interior of the cup-shaped electrode of FIG. 1A; 
     FIG. 3 is a fragmentary perspective view showing a step for welding the correction plate electrode to the interior of the cup-shaped electrode of FIG. 1A; 
     FIG. 4A is an axial sectional view of an electron gun showing a step for welding the correction plate electrode to the interior of the cup-shaped electrode of FIG. 1A; 
     FIG. 4B is an axial sectional view of an electron gun showing a step in the interior of the cup-shaped electrode of FIG. 1C; 
     FIGS. 5A and 5B are schematic sectional views for explaining another embodiment of an electron gun structure for a cathode ray tube according to the present invention, FIG. 5A is a sectional view perpendicular to the in-line direction of the three electron beams, FIG. 5B is an enlarged view of a portion A of FIG. 5A; 
     FIGS. 6A and 6B are front views showing the constitution of the cup-shaped electrode of FIG. 5A and a plate-like electrode inserted therein, FIG. 6A is a sectional view of FIG. 5A, taken in the direction of the arrows VIA—VIA thereof, FIG. 6B is a sectional view of FIG. 5A, taken in the direction of the arrows VIB—VIB thereof; 
     FIG. 7 is a plan view for explaining in detail the shape of a correction plate electrode installed within the cup-shaped electrode of FIG. 6A; 
     FIG. 8 is an enlarged plan view of main parts of the correction plate electrode of FIG. 7; 
     FIGS. 9A and 9B are schematic sectional views for explaining another embodiment of an electron gun structure for a cathode ray tube according to the present invention, FIG. 9A is a sectional view perpendicular to the in-line direction of the three electron beams, FIG. 9B is an enlarged view of a portion A of FIG. 9A; 
     FIGS. 10A and 10B are front views showing the constitution of the cup-shaped electrode and a plate-like electrode inserted therein, FIG. 10A is a sectional view of FIG. 9A, taken in the direction of the arrows XA—XA thereof, FIG. 10B is a sectional view of FIG. 9A, taken in the direction of the arrows XB—XB thereof; 
     FIG. 11 is a plan view for explaining in detail the shape of a correction plate electrode installed within the cup-shaped electrode of FIG. 10A; 
     FIG. 12 is an enlarged plan view of main parts of the correction plate electrode of FIG. 11; 
     FIGS. 13A and 13B are schematic sectional views for explaining another embodiment of an electron gun structure for a cathode ray tube according to the present invention, FIG. 13A is a sectional view perpendicular to the in-line direction of the arrangement of the three electron beams, FIG. 13B is an enlarged view of a portion A of FIG. 13A; 
     FIGS. 14A and 14B are schematic sectional views for explaining still another embodiment of an electron gun structure for a cathode ray tube according to the present invention, FIG. 14A is a sectional view perpendicular to the in-line direction of the electron beams, FIG. 14B is an enlarged view of a portion A of FIG. 14A; 
     FIG. 15 is a schematic sectional view for explaining the constitution of a shadow mask type color cathode ray tube as one example of a color cathode ray tube to which the present invention is applied; 
     FIG. 16 is a side view of main parts for explaining a structural example of an in-line type electron gun structure used in the color cathode ray tube shown in FIG. 15; 
     FIGS. 17A and 17B are schematic sectional views for explaining a main lens forming electrode of an electron gun, FIG. 17A is a sectional view in parallel with the in-line direction of the three electron beams, and FIG. 17B is a sectional view perpendicular to the in-line direction; 
     FIGS. 18A to  18 C are schematic sectional views for explaining various shapes of a main lens forming electrode of a conventional electron gun; and 
     FIGS. 19A to  19 C are views for explaining the shape of a main lens forming electrode of an electron gun previously proposed by the present inventor, FIG. 19A is a sectional view thereof, FIG. 19B is a plan view of the correction plate electrode, FIG. 19C is an enlarged view of main parts of the correction plate electrode in FIG.  19 B. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will be described in detail hereinafter with reference to the drawings thereof. 
     FIGS. 1A and 1B are schematic sectional views for explaining one embodiment of an electron gun for a cathode ray tube, FIG. 1A is a sectional view in parallel with the in-line direction of three electron beams, and FIG. 1B is a sectional view perpendicular to the in-line direction of the three electron beams. In FIGS. 1A and 1B, the same reference numerals as those in FIGS. 17A and 17B correspond to the same functional parts. Reference numeral  16 - 1  designates to a single opening formed in the end face of the sixth grid  16  opposing the anode  17 ,  16 - 2  a step formed on the inner wall of the sixth grid electrode,  17 - 1  a single opening formed in the end face of the anode  16  opposing the sixth grid electrode, and  17 - 2  a step formed on the inner wall of the anode. 
     In FIGS. 1A and 1B, a main lens is formed between the opposing end faces of the sixth grid electrode  16  and the anode  17 . An in-turned rim is formed in the end face of the sixth grid electrode  16  opposing the anode  17 , and similarly, an in-turned rim is formed in the end face of the anode  17  opposing the sixth grid electrode  1   h . The single-openings  16 - 1  and  17 - 1  in the sixth grid electrodes and the anode oppose each other and form a main lens therebetween. Interiorly of the sixth grid electrode  16 , a correction plate electrode  16   a  is positioned at a place set back a predetermined distance from its end face opposing the anode  17 . 
     The correction plate electrode  16   a  is positioned by pressing it against the step  16 - 2  formed within the sixth grid electrode  16  and is welded to the sixth grid electrode  16 . The step  16 - 2  is formed by enlarging the inside diameter of the sixth grid electrode  16 . Also interiorly of the anode  17 , a correction plate electrode  17   a  is positioned at a place set back a predetermined distance set back from its end face opposing the sixth grid electrode  16 . 
     The correction plate electrode  17   a  is positioned by pressing it against the step  17 - 2  formed within the anode  17  and is welded to the anode  17 . The step  17 - 2  is formed by enlarging the inside diameter of the anode  17 . FIG. 2 is a plan view showing a state in which a correction plate electrode is welded to the interior of the cup-shaped electrode, as viewed from the rim side of the sixth grid electrode or the anode. 
     In FIG. 2, the correction plate electrode  16   a  ( 17   a ) welded interiorly of the cup-shaped electrode (sixth grid electrode  16 , anode  17 ) is formed with three electron beam apertures  16   as  ( 17   as ),  16   ac  ( 17   ac ) and  16   as  ( 17   as ) adjacent to but spaced from the single opening  16 - 1  ( 17 - 1 ) in the cup-shaped electrode. This main lens structure provides a large-diameter lens. 
     FIG. 3 is a fragmentary perspective view showing a step provided for positioning the correction plate electrode in the interior of the cup-shaped electrode. The steps  16 - 2  and  17 - 2  are formed by enlarging the inside diameters of the cup-shaped sixth grid electrode  16  and the anode  17 . The steps can be formed simultaneously with the press-forming of the cup-shaped electrode. 
     FIG. 4A is an axial sectional view of an electron gun showing a step for positioning the correction plate electrode in the interior of the cup-shaped electrode. In FIG. 4A, the correction plate electrode is omitted. 
     In FIG. 4A, the step  16 - 2  ( 17 - 2 ) is formed at a position set back by “d” in an axial direction from its end face which is opposing the other cup-shaped electrode and which is formed with a rim. This step enables the inside diameter W 1  at the open end opposite the end face formed with a rim to be larger than the inside diameter W 2  in the vicinity of the end face opposing the other cup-shaped electrode to facilitate the insertion of the correction plate electrode into the cup-shaped electrode, establishes the amount “d” of the setback with accuracy. 
     In FIG. 4A, as a specific example, the height M and the set back amount d are 7 mm and 3.5 mm, respectively, W 1 −W 2 =0.04 mm. 
     In the embodiment illustrated in FIGS. 1A and 1B, the correction plate electrodes  16   a  and  17   a  are positioned by pressing them against the step  16 - 2  formed within the sixth grid electrode  16  and the step  17 - 2  formed within the anode  17 , and are welded to the sixth grid electrode and the anode  17 , respectively. But it is not essential for the present invention to position the correction plate electrodes  16   a  and  17   a  by using the steps  16 - 2  and  17 - 2 , respectively. 
     A modification of the embodiment shown in FIGS. 1A and 1B will be described with reference to FIGS. 1C,  1 D and  4 B. FIG. 1C is a sectional view in parallel with the in-line direction of three electron beams of the electron gun for a cathode ray tube, FIG. 1D is a sectional view perpendicular to the in-line direction of the three electron beams, and FIG. 4B is an axial sectional view of the cup-shaped sixth grid electrode  16  and the cup-shaped anode  17 . In FIG. 4B, a region having an inside diameter W 2  extends from the end face formed with a single opening  16 - 1  ( 17 - 1 ) to a distance f which is greater than the distance d 1  or d 2  indicated in FIG.  1 C. In FIG. 1C, the correction plate electrode  16   a ′ is inserted beyond the step  16 - 2  into a region having the inside diameter W 2  and is welded by a laser at a distance of d 1  from the single opening  16 - 1  and the correction plate electrode  17   a ′ is inserted beyond the step  17 - 2  into a region having the inside diameter W 2  and is welded by laser at a distance of d 2  from the single opening  17 - 1 . In this case the outer dimensions of the correction plate electrodes  16   a , and  17   a ′ are made smaller than those of the correction plate electrodes  16   a  and  17   a  in the embodiment illustrated in FIGS. 1A and 1B. The dimensions M, W 1  and W 2  in FIG. 4B are the same as in FIG.  4 A. The dimension f in FIG. 4A is 4.1 mm. The thickness of the correction plate electrodes  16   a , and  17   a ′ is 0.6 mm. 
     In this modification, the inside diameter W 1  of the cup-shaped sixth grid electrode  16  and the cup-shaped anode  17  on their open end side can be made sufficiently larger than the outer dimensions of the correction plate electrodes  16   a , and  17   a ′, and the correction plate electrodes can be inserted smoothly into the vicinity of their weld positions without deforming the electrodes, and are welded to the sixth grid electrode  16  and the anode  17  at predetermined positions in a region having the inside diameter W 2  after they are positioned accurately by using an electrode assembling jig. 
     According to the above-described embodiment, it is possible to provide precision main lens electrodes for an electron gun structure for a high performance cathode ray tube. 
     The present invention can be applied to not only the above-described main lens electrodes but also various electrodes for an electron gun including other similar electrodes therein. 
     According to the present invention, the assembly of the correction plate electrodes in the electrode of the type in which the correction plate electrodes are inserted into and fixed to the cup-shaped electrode becomes easy and the positioning of the correction plate electrodes can be established with high accuracy, thus a cathode ray tube of high image quality is provided. 
     FIGS. 5A and 5B are schematic sectional views for explaining a further embodiment of an electron gun structure for a color cathode ray tube according to the present invention, 
     FIG. 5A is a sectional view perpendicular to the in-line direction of the three electron beams, and FIG. 5B is an enlarged view of the encircled portion designated at A of FIG.  5 A. 
     In FIGS. 5A and 5B, the same reference numerals as those in FIGS. 17A,  17 B,  19 A,  19 B and  19 C correspond to the same functional parts. Reference numeral  17   b  designates a recess, and  17   c  designates a sloping portion described later. While FIGS. 5A and 5B illustrate the constitution of the anode  17 , the same is true for the sixth grid electrode  16 . 
     In FIGS. 5A and 5B, the end face of the sixth grid electrode  16  facing the anode  17  is turned in to form a rim, and similarly, the end face of the anode  17  facing the sixth grid electrode  16  is also formed with a rim. The single openings  16 - 1  and  17 - 1  face each other to form a main lens therebetween. 
     As explained in connection with FIGS. 17A and 17B, interiorly of the sixth grid electrode  16  is installed the correction plate electrode  16   a  with a desired amount of set back from its end face opposing the anode  17 , and interiorly of the anode  17  is installed the correction plate electrode  17   a  with a desired amount of set beck from its end face opposing the sixth electrode  16 . 
     The correction plate electrode installed in the cup-shaped electrode has the shape as described below. Take the anode  17  and the correction plate electrode  17   a , for instance, the correction plate electrode  17   a  installed within the anode  17  has a recess  17   b  for facilitating the insertion into the cup-shaped electrode and a sloping portion  17   c  described later to avoid difficulties in insertion caused by burrs. 
     The correction plate electrode  17   a  is inserted into a desired position of the anode  17  and welded and fixed by laser or the like. FIGS. 6A and 6B are views showing the constitution of the cup-shaped electrode of FIG. 5A and a correction plate electrode inserted therein, FIG. 6A is a sectional view of FIG. 5A, taken in the direction of the arrows VIA—VIA thereof, and FIG. 6B is a sectional view of FIG. 5A, taken in the direction of the arrows VIB—VIB thereof. 
     In FIG. 6A, the correction plate electrode  17   a  housed in the anode  17  has a center electron beam aperture  17   ac  and side electron beam apertures  17   ac . The recesses  17   b  are formed above and below the center electron beam apertures  17   ac  in the center portion of the plate electrode, and the correction plate electrode has four sloping edges  17   c  which approach the edges of the center electron beam aperture in the in-line direction of the three electron beams from the corners of the plate electrode. 
     The correction plate electrode  16   a  housed in the sixth grid electrode  16  likewise has a center electron beam aperture  16   ac  and side electron beam apertures  16   as , as shown in FIG.  6 B. The recesses  16   b  are formed above and below the center electron beam apertures  16   ac  in the center portion of the plate electrode, end the correction plate electrode has four sloping edges  16   c  which approach the edges of the center electron beam aperture in the in-line direction of the three electron beams from the corners of the plate electrode. 
     FIG. 7 is a plan view for explaining in detail the shape of a correction plate electrode installed within the cup-shaped electrode of FIG. 6A. A description will be made taking the plate electrode  17   a  installed on the anode  17  of FIG. 6A as an example. FIG. 8 is an enlarged plan view of main parts of FIG.  7 . 
     In FIGS. 6A,  7  and  8 , the correction plate electrode  17   a  is formed at the edge thereof with recesses  17   b  as well as sloping edges  17   c . As shown enlarged in FIG. 8, the sloping edges  17   c  slope gradually downward to the recesses  17   b  from both ends of the edge of the plate electrode by a height L exceeding a height L′, of burrs  17   d  caused in press-forming, that is, the height L of the corners of the plate electrode and the height L′ of the burrs  17   d  measured in a direction perpendicular to the three beam in-line direction with respect to the mouth of the recesses satisfy the relationship L′≦L. 
     The dimensions X, Y of the anode  17  in FIG. 6A are 22 mm and 16 mm, respectively; the dimensions P, Q of the correction plate electrode  17  in FIG. 7 are 4 mm, 12 mm, respectively; and a value L of 10 μm is chosen for the plate electrode of a thickness in the range of 0.3 mm to 1.0 mm. It has been found that the value L of 15 μm or less is sufficient. 
     With this structure, it is possible to prevent the anode  17  or the plate electrode  17   a  from being deformed due to the burrs  17   d  when the correction plate electrode  17   a  is inserted into the anode  17 . In case of assembling the sixth grid electrode  16  and the plate electrode  16   a , deformation of the sixth grid electrode  16  and the plate electrode  16   a  are likewise prevented by the provision of the sloping portion. 
     It is possible to provide a high performance cathode ray tube having precision main lens electrodes according to the above-described embodiment. Of course, the present embodiment can be combined with the embodiments explained in connection with FIGS. 1A to  4 B. 
     It is noted that the present invention can be applied not only to the aforementioned main lens electrodes but also to various electron gun electrodes having similar internal electrodes. 
     According to the present invention, it becomes easy to assemble the correction plate electrode into the electrode of the type in which the correction plate electrode is inserted into and fixed to the cup-shaped electrode, and it is possible to establish the position of the correction plate electrode with high accuracy, thus a high quality cathode ray tube can be provided. 
     FIGS. 9A and 9B are schematic sectional views for explaining another embodiment of an electron gun structure for a cathode ray tube according to the present invention, FIG. 9A is a sectional view perpendicular to the in-line direction of the three electron beams, and FIG. 9B is an enlarged view of the encircled portion designated A of FIG.  9 A. 
     In FIGS. 9A and 9B, the same reference numerals as those in FIGS. 17A and 17B correspond to the same functional parts. Reference numeral  17   c  designates tongues. While FIGS. 9A and 9B show the constitution of welding portions of the correction plate electrode  17   a  inserted into the anode  17 , it is to be noted that the correction plate electrode  16   a  inserted into the sixth grid electrode  16  is also provided with tongues similar to those formed in the electrode  17  except the correction plate electrode is provided with three electron beam apertures. 
     In FIG. 9A, the end face of the sixth grid electrode  16  opposing the anode  17  is turned in to form a rim, the end face of the anode  17  opposing the sixth grid electrode is turned in to form a rim, the two single openings  16 - 1  and  17 - 1  of the two cup-shaped electrodes face each other and form a main lens therebetween. 
     As explained in connection with FIG. 17A, the correction plate electrode  16   a  is provided within the sixth grid electrode  16  with a desired amount of set back from its end face opposing the anode  17 , and the correction plate electrode  17   a  is provided within the anode  17  with a desired amount of set back from its end face opposing the sixth electrode  16 . 
     Tongues  17   c  are drawn integrally from the electrode material and configured to project inwardly and axially on the wall surface of the cup-shaped anode  17  extending in the in-line direction of the three electron beams. Two tongues  17   c  are arranged in a line corresponding to each of two sides of the correction plate electrode parallel with the in-line direction as described later. 
     The correction plate electrode installed in the cup-shaped electrode has a shape as described below. Taking the anode  17  and the correction plate electrode  17   a  as an example, the correction plate electrode  17   a  installed within the anode  17  has the outside diameter slightly smaller than the inside diameter of the anode  17  to facilitate the insertion thereof in assembling. 
     The top and bottom edges of the correction plate electrode  17   a  are positioned to oppose the tongues  17   c  on the inner wall of the anode  17  and welded to the tongues by laser or the like. 
     FIGS. 10A and 10B are views showing the constitution of the cup-shaped electrodes and correction plate electrode inserted therein, FIG. 10A is a sectional view of FIG. 9A, taken in the direction of the arrows XA—XA thereof, and FIG. 10B is a sectional view of FIG. 9A, taken in the direction of the arrows XB—XB thereof. 
     In FIG. 10A, the correction plate electrode  17   a  housed in the anode  17  has a center electron beam aperture  17   ac  and side electron beam apertures  17   as , and the recesses  17   b  are formed above and below the center electron beam apertures  17   ac  in the center portion of the plate electrode, and the sides of the plate electrode parallel with the in-line direction of the electron beams are welded to the tongues  17   c  formed in the inner walls of the anode  17 . 
     The plate electrode  16   a  housed in the sixth grid electrode  16  likewise has a center electron beam aperture  16   ac  and side electron beam apertures  16   as , as shown in FIG. 10B, and the recesses  16   b  are formed above and below the center electron beam apertures  16   ac  in the center portion of the plate electrode, and the sides of the plate electrode parallel with the in-line direction of the electron beams are welded to the tongues  16   c  formed in the inner walls of the sixth grid electrode  16 . 
     FIG. 11 is a plan view for explaining the shape of a correction plate electrode according to the present embodiment installed within the cup-shaped electrode, taking the correction plate electrode  17   a  installed on the anode  17  of FIG. 10A as an example. FIG. 12 is an enlarged view of main parts of FIG.  11 . 
     In FIGS. 11 and 12, the sides of the correction plate electrode  17  parallel with the in-line direction are formed with a recess  17   b . The amount of projection of the tongues  17   c  formed on the inner wall of the anode  17  is formed so that the clearance L between the inner wall of the anode and the mouth of the recesses  17   b  exceed the height L, of burrs caused when the recesses  17   b  are press-formed, to satisfy L′≦L. 
     Also in this case, L of 10 to 15 μm is sufficient like in the previous embodiment. 
     With this structure, deformation of the anode  17  or the plate electrode  17   a  caused by the contact of the burrs  17   d  with the inner wall of the anode when the correction plate electrode  17   a  is inserted along the inner wall of the anode  17  can be prevented. 
     Also with respect to an assembly of the sixth grid electrode  16  and the correction plate electrode  16   a , deformation of the sixth grid electrode  16  or the correction plate electrode  16   a  can be likewise prevented. The width in the in-line direction of the correction plate electrode  16   a  is also formed to be slightly smaller than the corresponding inside diameter of the sixth grid electrode  16 . 
     According to the above-described embodiment, it is possible to provide precision main lens electrodes for an electron gun for a high performance cathode ray tube. 
     FIGS. 13A and 13B are schematic sectional views for explaining another embodiment of an electron gun structure for a cathode ray tube according to the present invention, FIG. 13A is a sectional view perpendicular to the in-line direction of the arrangement of the three electron beams, and FIG. 13B is an enlarged view of a portion A of FIG.  13 A. 
     In FIGS. 13A and 13B, the same reference numerals as those in FIG. 9A correspond to those of the same functional parts in FIG.  9 A. Reference numeral  17   c ′ designates tongues. While FIGS. 13A and 13B show the constitution of welding portions of the correction plate electrode  17   a  inserted into the sixth grid electrode  17 , it is to be noted that the sixth grid electrode  16  is also provided with tongues similar to those formed in the anode  17  except that the correction plate electrode  16   a  inserted in the sixth grid electrode  16  is provided with three electron beam apertures. 
     The projection formed on the inner wall of the cup-shaped electrode in this embodiment is tongues  17   c ′ configured to project inwardly and perpendicularly to the tube axis and drawn integrally from the electrode material. The correction plate electrode  17   a  is welded and fixed to the tongues  17   c ′ by laser. Other constitutions are similar to those of the previous embodiment. 
     Also in this embodiment, it is possible to provide precision main lens electrodes for an electron gun for a high performance cathode ray tube. 
     FIGS. 14A and 14B are schematic sectional views for explaining still another embodiment of an electron gun structure for a cathode ray tube according to the present invention, FIG. 14A is a sectional view perpendicular to the in-line direction of the three electron beams, and FIG. 14B is an enlarged view of a portion A of FIG.  14 A. 
     In FIGS. 14A and 14B, the same reference numerals as those in FIGS. 9A and 9B correspond to the same functional parts. Reference numeral  17   c ″ designates projections. While FIGS. 14A and 14B show the constitution of welding portions of the correction plate electrode  17   a  inserted into the anode  17 , it is to be noted that the sixth grid electrode  16  is also provided with projections  16   c ″ similar to those formed on the anode  17  except that the correction plate electrode is provided with three electron beam apertures. 
     The projections  17   c ″ formed on the inner wall of the cup-shaped electrode according to this embodiment are configured to project radially inwardly and are drawn integrally from the electrode material. The correction plate electrode  17   a  is welded and fixed to the projections  17   c ′ by laser. Other constitutions are similar to those of the previous embodiments. 
     Also in this embodiment, it is possible to provide precision main lens electrodes for an electron gun for a high performance cathode ray tube. 
     The present invention can be applied not only to the main lens electrodes but also to various electron gun electrodes having other similar internal electrodes. 
     According to the present invention, it becomes easy to assemble the correction plate electrode in the electrode of the type in which the correction plate electrode is inserted into and fixed to the cup-shaped electrode, it is possible to position the correction plate electrode with high accuracy, and thus a high quality cathode ray tube is provided.