Abstract:
An inline type color cathode-ray tube deflection yoke applies a deflecting magnetic field to electron beams from a neck portion of a valve accommodating three electron guns toward the funnel portion of the valve. The deflection yoke is provided with a vertical deflection coil, auxiliary coils serially connected to the vertical deflection coil, and a U-shaped magnetic member around each of both leg portions of which the auxiliary coils are wound. The U-shaped magnetic member is arranged so that the leg portions face the neck portion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a deflection yoke attached to an inline type color cathode-ray tube and a mis-convergence correction method for a color cathode-ray tube correcting mis-convergence on the Y-axis of a screen. The present invention particularly relates to a deflection yoke and a mis-convergence correction method capable of simultaneously correcting comatic aberration and mis-convergence. 
     2. Description of the Related Art 
     There exists a color display device provided with an inline type color cathode-ray tube (to be referred to as “color CRT” hereinafter). In the inline type color CRT, electron beams are produced in a vacuum valve from electron guns for blue, green, and red, respectively. The electron beams are deflected in X and Y-axes directions by a deflection yoke made up of an electromagnetic coil and the like and reach a phosphor film through a shadow mask. 
     In the inline type color CRT stated above, electron beams pass into a heavily distorted deflecting magnetic field at the time of deflecting the electron beams in the X and Y-axes directions by means of the deflection yoke. Due to this, three electron beams disadvantageously, poorly converge. This phenomenon is called mis-convergence. 
     To solve the disadvantage, there is provided a color CRT which adopts a system called inline self-convergence system. FIGS. 1A and 1B are typical views showing the inline self-convergence system. In the inline self convergence system, a deflecting magnetic field  101  (FIG. 1A) having a pin cushion type, horizontally deflecting magnetic field distribution, and a deflecting magnetic field  102  (FIG. 2B) having a barrel type, vertically deflecting magnetic field distribution are formed. Three electron beams  10 B,  10 G and  10 R emitted from three inline electron guns aligned in the same horizontal plane are deflected by these deflecting magnetic fields  101  and  102  and converge at arbitrary points on a screen, respectively. 
     The inline self-convergence system has advantages in that it suffices to provide a small number of electrical circuits, adjustment is required infrequently and the like to converge the three electron beams  10 B,  10 G and  10 R and in that the highly accurate convergence can be realized. 
     Nevertheless, a focus voltage Vfh capable of minimizing a horizontal diameter of a spot and a focus voltage Vfv capable of minimizing a vertical diameter of a spot differ from each other and the difference between the both focus voltages ΔVf=Vfh−Vfv is negative. Namely, the convergence state of the electron beams in the vertical direction is an over-focus state. For that reason, if the distortions of the shapes of the electron beams on the periphery of the screen are finely observed, it is found that halos occur in vertical direction because of astigmatism. FIG. 2 is a typical view showing electron beam spots on a conventional screen. Electron beams  10 B,  10 G and  10 R are influenced by the magnetic field distortions of the self convergence deflecting magnetic fields  101  and  102  when passing into the fields  101  and  102 . As a result, the shapes of the electron beam spots become round at the center of the screen, which is free from deflection. However, if the electron beams are deflected to the peripheral portions of the screen, the shape of each electron beam spot becomes one having an oblong beam core  111  and a radial halo  112  generated above and below the beam core  111 , i.e., a distorted shape. The diameter of each of the distorted electron beam spots on the peripheral portions of the screen is, therefore, larger than that of the completely round spot at the center of the screen, with the result that resolution on the peripheral portions of the screen considerably deteriorates. 
     Further, because of the asymmetry of deflecting magnetic fields, comatic aberration, which causes mis-convergence occurring between the center beam (G) and the side beams (B, R) among the three electron beams as deflection frequency is higher. It is, therefore, necessary to eliminate the comatic aberration, as well. FIGS. 3A to  3 D are typical views showing mis-convergence. FIG. 4 is a typical view showing one example of a lateral raster distortion. The mis-convergence caused by the comatic aberration includes an arc distortion, as shown in FIG. 3A, in which a red line  20 R and a blue line  20 B separate from each other in lateral direction on the upper and lower ends of the screen, a distortion, as shown in FIG. 3B, in which a red line  21 R and a blue line  21 G separate from each other in longitudinal direction on the upper and lower ends of the screen, and a distortion, as shown in FIG. 3C, in which a red line  21 R and a blue line  21 B separate from a green line  21 G in longitudinal direction. Further, as shown in FIG. 3D, if a figure which should be originally a rectangle is distorted into a trapezoid  30  due to the influence of a pin cushion type magnetic field distribution and a barrel type magnetic field distribution, the distorted figure is visually inappropriate particularly for CAD, CAM or the like and causes much deficiency. Moreover, as shown in FIG. 4, if there is a parallel distortion in which a red line  21 R and a blue line  21 B are deviated from a green line  21 G in the lateral direction of the screen, a resultant image is difficult to view. 
     The mis-convergence stated above is normally considered to derive from the deviation between the mechanical center of three electron beams and that of a deflecting magnetic field from the viewpoint of the electron guns of a color CRT. Further, the mis-convergence is considered to derive from a design in which a variable resistor for deflecting current control provided on a deflection coil simultaneously corrects comatic aberration and the distortion of an image from the viewpoint of a deflection yoke. 
     To solve the above-stated disadvantages, there has been conventionally proposed a mis-convergence correction method using a deflection yoke provided with a pair of E-shaped magnetic members (Japanese Patent Application Laid-Open No. 9-17355). FIG. 5 is a typical view showing a conventional deflection device disclosed by Japanese Patent Application Laid-Open No. 9-17355. FIG. 6 is a typical view showing magnetic fields generated by the conventional deflection device. 
     This conventional deflection device has a pair of E-shaped magnetic members  41  and  42  provided on a deflection yoke bobbin attached to the neck portion  40  of a color CRT. Coma correction coils  51   a  and  51   c  are wound around the leg portions  41   a  and  41   c  of the E-shaped magnetic member  41  on both ends thereof, respectively. A coma correction coil  51   b  is wound around the central leg portion  41   b  of the E-shaped magnetic member  41 . Likewise, coma correction coils  52   a  and  52   c  are wound around the leg portions  42   a  and  42   c  of the E-shaped magnetic member  42  on the both ends thereof, respectively. A coma correction coil  52   b  is wound around the central leg portion  42   b  of the E-shaped magnetic member  42 . 
     In the conventional deflection device constituted as stated above, a pin cushion type deflecting magnetic field  60   a  is generated between the leg portions  41   a  and  42   a,  and a pin cushion type deflecting magnetic field  60   c  is generated between the leg portions  41   c  and  42   c  as shown in FIG. 6. A barrel type deflecting magnetic field  61   b  is generated between the leg portions  41   b  and  42   b.  As a result, astigmatism and mis-convergence can be simultaneously corrected. 
     Although the conventional mis-convergence correction method stated above has an advantage in that astigmatism and mis-convergence can be simultaneously corrected by simple means relatively easily, the following disadvantages are still to be solved. 
     Since three coma correction coils are provided for each E-shaped magnetic member, the mold structure of a supporter for an E-shaped magnetic member becomes complicated. Consequently, production cost is increased and it is economically difficult to work this method. 
     Furthermore, as shown in FIG. 4, while the horizontal deviation between the red line  21 R and the blue line  21 B, and the green line  21 G on the upper and lower ends of the screen are small, the vertical deviation between the red line  21 R and the blue line  21 B, and the green line  21 G on the left and right ends of the screen is large. For that reason, there is a fundamental limit to correcting deviations. 
     Moreover, as shown in, for example, Japanese Patent Application Laid-Open No. 11-40079, an E-shaped magnetic member is to be arranged on the electron gun-side rear end portion of a deflection yoke. FIG. 7 is a typical view showing how the E-shaped magnetic member is disposed. FIG. 8 is a typical view showing mis-convergence resulting from asymmetry of magnetic flux densities. The arrangement shown therein is undesirable from the viewpoint of the structure of the deflection yoke for the following reasons. As shown in FIG. 7, a low hysteresis, high permeable magnetic member  74  is normally attached to a bobbin  73  while intersecting a leakage magnetic flux from a horizontal deflection coil  72  on the rear end portion of the deflection yoke  70  on an electron gun  71  side. This is intended to correct mis-convergence generated because the magnetic flux distribution densities of lines  22 G,  22 B and  22 R become asymmetric on the left and right positions of a screen as shown in FIG.  8 . In case of employing the E-shaped magnetic member, therefore, such a mis-convergence correction method cannot be adopted. 
     In these circumstances, a mis-convergence correction method other than a method of providing a coma correction coil on an E-shaped magnetic body is desired. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a deflection yoke and a mis-convergence correction method for a color cathode-ray tube which can be manufactured at low cost and which can ensure the correction of both astigmatism and mis-convergence. 
     According to one aspect of the present invention, a deflection yoke for inline type color cathode-ray tube with a valve accommodating three electron guns and having a neck portion and a funnel portion comprises a vertical defection coil which defects beams emitted from the three electron guns in a vertical direction of a screen, auxiliary coils connected in series to the vertical deflection coil, and a U-shaped magnetic member having leg portions and being arranged such that the leg portions face the neck portion of the valve. The auxiliary coils are wound around each of the leg portions of the U-shaped magnetic member. 
     In the present invention, the auxiliary coils wound around the U-shaped magnetic member are connected to the vertical deflection coil in series. Therefore, a quadruple magnetic field lens function resulting from a type of quadruple coils is generated. As a result, a pin cushion distortion in the vertical direction of a screen can be corrected and mis-convergence can be corrected, as well. 
     According to another aspect of the present invention, a mis-convergence correction method for a color cathode-ray tube provided with the above-described deflection yoke, the method comprises the step of adjusting each of inductances of the auxiliary coils. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are typical views showing an inline self-convergence system; 
     FIG. 2 is a typical view showing electron beam spots on a conventional screen; 
     FIGS. 3A to  3 D are typical views showing mis-convergence; 
     FIG. 4 is a typical view showing one example of lateral raster distortions; 
     FIG. 5 is a typical view showing a conventional deflection device disclosed by Japanese Patent Application Laid-Open No. 9-17355; 
     FIG. 6 is a typical view showing magnetic fields generated by the conventional deflection device; 
     FIG. 7 is a typical view showing a disposing place where an E-shaped magnetic member is disposed; 
     FIG. 8 is a typical view showing mis-convergence derived from asymmetry of magnetic flux densities; 
     FIG. 9 is a front view showing a deflection yoke in a first embodiment according to the present invention; 
     FIG. 10 is a circuit diagram showing connecting relation among coils in the first embodiment; 
     FIG. 11 is a circuit diagram showing a method of creating an image on the upper half of a screen in the first embodiment; 
     FIGS. 12A and 12B are typical views showing lateral raster distortions in the first embodiment; 
     FIG. 13 is a front view showing a deflection yoke in a second embodiment according to the present invention; 
     FIG. 14 is a circuit diagram showing connecting relation among coils in the second embodiment; and 
     FIG. 15 is a typical view showing lateral raster distortions in the second embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will be concretely described hereinafter with reference to the accompanying drawings. FIG. 9 is a front view showing a deflection yoke in a first embodiment according to the present invention. FIG. 10 is a circuit diagram showing connecting relation among coils in the first embodiment. 
     In the first embodiment, two U-shaped magnetic members Ucc 1  and Ucc 2  are provided. The U-shaped magnetic members Ucc 1  and Ucc 2  are arranged so as to put the neck portion (not shown) of a color CRT between the both tip ends of the respective leg portions of the U-shaped magnetic members Ucc 1  and Ucc 2 . An upper left auxiliary coil L 1  and an upper right auxiliary coil R 1  are wound around the leg portions of the U-shaped magnetic member Ucc 1 , respectively, and a coma correction coil CO 1  is wound around the central portion of the member Ucc 1 . Likewise, a lower left auxiliary coil L 2  and an lower right auxiliary coil R 2  are wound around the leg portions of the U-shaped magnetic member Ucc 2 , respectively, and a coma correction coil CO 2  is wound around the central portion of the member Ucc 2 . 
     Further, in the first embodiment, vertical coils V 1  and V 2  are connected in series to a deflection coil terminal Hot. A variable resistor VR for deflecting current control is connected in parallel to the vertical coils V 1  and V 2 . A contact Vrm of the variable resistor VR is connected to the node between the vertical coils V 1  and V 2 . On the upper half of a screen, electron beams are deflected in vertical direction by the vertical coil V 1 . On the lower half of the screen, electron beams are deflected in vertical direction by the vertical coil V 2 . Further, the coma correction coils CO 1  and CO 2  are connected in series to the vertical coil V 2 . In addition, correction coil bodies U and D are connected parallel to each other between the coma correction coil CO 2  and a deflection coil terminal Cold. 
     In the correction coil body U, a rectifier diode D 1 , the upper left auxiliary coil L 1  and the upper right auxiliary coil R 1  are connected in series between the coma correction coil CO 2  and the deflection coil terminal Cold. The rectifier diode D 1  is arranged such that the anode of the diode D 1  is connected to the coma correction coil CO 2 . Further, the both ends of a variable resistor VR 1  are connected to the node A between the diode D 1  and the upper left auxiliary coil L 1  and the terminal Cold-side terminal B of the upper right auxiliary coil R 1 , respectively. A contact Vr 1 m of the variable resistor VR 1  is connected to the node N 1  between the upper left auxiliary coil L 1  and the upper right auxiliary coil R 1 . The correction coil body U constituted as stated above corrects a lateral raster distortion of an image on the upper half of the screen. 
     In the correction coil body D, a rectifier diode D 2 , the lower left auxiliary coil L 2  and the lower right auxiliary coil R 2  are connected in series between the coma correction coil CO 2  and the deflection coil terminal Cold. The rectifier diode D 2  is arranged such that the cathode of the diode D 2  is connected to the coma correction coil CO 2 . Further, the both ends of a variable resistor VR 2  are connected to the node E between the diode D 2  and the lower left auxiliary coil L 2  and the terminal Cold-side terminal F of the lower right auxiliary coil R 2 , respectively. A contact Vr 2 m of the variable resistor VR 2  is connected to the node N 2  between the lower left auxiliary coil L 2  and the lower right auxiliary coil R 2 . The correction coil body D constituted as stated above corrects a lateral raster distortion of the image on the lower half of the screen. 
     Next, the operation of the deflection yoke constituted as stated above in the first embodiment will be described. FIG. 11 is a circuit diagram showing a method of creating an image on the upper half of the screen in the first embodiment. 
     If the image on the upper half of the screen is created by vertical deflection, a saw-tooth deflecting current is applied by a vertical deflection circuit (not shown) from the deflection coil terminal Hot toward the deflection coil terminal Cold. As a result, the vertical deflection is conducted only by the vertical coil V 1  in a vertical deflecting portion of the deflection yoke. Also, while a current flows in the correction coil body U, no current flows in the correction coil body D, by the rectification functions of the diodes D 1  and D 2 . Accordingly, electron beams are closer to and greatly influenced by the vertical coil V 1  and the coma correction coil CO 1 , but hardly influenced by the vertical coil V 2  and the coma correction coil CO 2 . The vertical coil V 2  and the coma correction coil CO 2  may be considered to be substantially short-circuited as indicated by broken lines in FIG.  11 . 
     Next, the vertical deflection operation on the upper half of the screen will be described in more detail. First, the power of the color CRT is turned on, electron beams are emitted from electron guns, the electron beams are struck against a phosphor film on the inner surface of a face portion through the deflection yoke and a shadow mask, thereby forming a raster (which means an image). In the correction coil body U, a bridge circuit is made up out of divisional resistors Rg and Rh of the variable resistor VR 1 , the upper left auxiliary coil L 1  and the upper right auxiliary coil R 1 . The ratio of a current flowing in the upper left auxiliary coil L 1  to that flowing in the upper right auxiliary coil R 1  is, therefore, determined by the potential division ratio of the divisional resistors Rg and Rh. Thus, by adjusting resistance values of the divisional resistors Rg and Rh, it is possible to adjust outline of individual small beam spots. 
     FIGS. 12A and 12B are typical views showing lateral raster distortions in the first embodiment. A distortion quantity ac between a red line  21 R and a blue line  21 B, and a green line  21 G, and a distortion quantity ac between the red line  21 R and the blue line  21 B vary according to the resistance values of the divisional resistors Rg and Rh and the inductances of the upper left auxiliary coil L 1  and the upper right auxiliary coil R 1 . Therefore, fine adjustments can be made to these distortion quantities by the contact VR 1 m of the variable resistor VR 1  and the divisional resistors Rg and Rh. That is to say, the currents flowing in the upper left auxiliary coil L 1  and the upper right auxiliary coil R 1  generate magnetic fluxes Φ 1  and Φ 2  in the vicinity of the both end portions of the U-shaped magnetic member Ucc 1 , respectively, whereby the vertical positions of the individual electron beams B and R can be corrected. 
     Further, the variable resistor VR for deflecting current control can correct a trapezoidal image distortion independently of the correction of comatic aberration as in the case of the conventional method. 
     In case of creating an image on the lower half of the screen by vertical deflection, saw-tooth deflecting current may be applied by the vertical deflection circuit from the deflection coil terminal Cold toward the deflection coil terminal Hot. As a result, a comatic aberration and an image distortion can be corrected in the same manner as that on the upper half of the screen. It should be noted, however, that distortion quantities are not always the same as those in the case of the vertical deflection on the upper half of the screen. In most cases, distortion quantities differ between the upper half and the lower half of the screen. It is, therefore, preferable to change settings for the diode D 2 , the lower left auxiliary coil L 2 , the lower right auxiliary coil R 2 , the variable resistor VR 2  and the like. 
     As can be seen from the above, according to the first embodiment of the present invention, a quadruple magnetic field lens may be composed of comatic aberration magnetic fields generated from the coma correction coils CO 1  and CO 2  wound around the U-shaped magnetic members Ucc 1  and Ucc 2  and the magnetic fluxes Φ 1  and Φ 2  generated in the vicinity of the both ends of the U-shaped magnetic members Ucc 1  and Ucc 2  and the like. This quadruple magnetic field lens enables the correction of mis-convergence. 
     Next, the second embodiment according to the present invention will be described. FIG. 13 is a front view of a deflection yoke in the second embodiment according to the present invention. FIG. 14 is a circuit diagram showing connecting relation among coils in the second embodiment. 
     In the second embodiment, as in the case of the first embodiment, an upper left auxiliary coil L 1 , an upper right auxiliary coil R 1  and a coma correction coil CO 1  are wound around a U-shaped magnetic member Ucc 1 . A lower left auxiliary coil L 2 , a lower right auxiliary coil R 2  and a coma correction coil CO 2  are wound around a U-shaped magnetic member Ucc 2 . 
     Further, as in the case of the first embodiment, vertical coils V 1  and V 2 , a variable resistor VR and the coma correction coils CO 1  and CO 2  are connected to a deflection coil terminal Hot. In the second embodiment, however, one correction coil body G is connected between the coma correction coil CO 2  and a deflection coil terminal Cold. 
     In the correction coil body G, the upper left auxiliary coil L 1 , the lower left auxiliary coil L 2 , the upper right auxiliary coil R 1  and the lower right auxiliary coil R 2  are connected in series between the coma correction coil CO 2  and the deflection coil terminal Cold in this order. Also, a variable resistor VR 3  is connected in parallel to these four coils. Namely, one end of the variable resistor VR 3  is connected to the node J between the coma correction coil CO 2  and the upper left auxiliary coil L 1 , and the other end thereof is connected to the terminal Cold-side terminal K of the lower right auxiliary coil R 2 . A contact Vr 3 m of the variable resistor VR 3  is connected to the node N 3  between the lower left auxiliary coil L 2  and the upper right auxiliary coil R 1 . 
     In other words, in the second embodiment, the correction coil body G, instead of the correction coil bodies U and D in the first embodiment, is connected between the deflection coil terminals Hot and Cold and connected in series to the vertical coils V 1 , V 2  and the coma correction coils CO 1  and CO 2 , as shown in FIG.  14 . 
     Next, the operation of the deflection yoke in the second embodiment constituted as stated above will be described. In the second embodiment, the screen is not vertically divided and the entire screen is collectively subjected to vertical deflection. FIG. 15 is a typical view showing lateral raster distortions in the second embodiment. 
     In the second embodiment, the variable resistor VR 3  is divided into divisional resistors Ri and Rj by the contact Vr 3 m. The divisional resistors Ri and Rj, the upper left auxiliary coil L 1 , the lower left auxiliary coil L 2 , the upper right auxiliary coil R 1  and the lower right auxiliary coil R 2  constitute four side resistors of a bridge circuit as a whole. 
     Therefore, currents flowing in the upper left auxiliary coil L 1 , the lower left auxiliary coil L 2 , the upper right auxiliary coil R 1  and the lower right auxiliary coil R 2  are simultaneously determined by a potential division ratio determined by the divisional resistors Ri and Rj. As a result, as shown in FIG. 13, magnetic fluxes Φ 3  and Φ 5  are generated by the currents flowing in the upper left auxiliary coil L 1  and the lower left auxiliary coil L 2 , respectively, and magnetic fluxes Φ 4  and Φ 6  are generated by the currents flowing in the upper right auxiliary coil R 1  and the lower right auxiliary coil R 2 , respectively. A quadruple magnetic field lens function by these magnetic fluxes Φ 3 , Φ 4 , Φ 5  and Φ 6  is exerted to the electron beams B and R on the both sides. Accordingly, as shown in FIG. 15, a distortion quantity ad between a red line  21 R and a blue line  21 B, and a green line  21 G can be simultaneously corrected. 
     As can be understood from the above, according to the second embodiment, the distortion quantity ad can be simultaneously corrected on the entire screen, compared with the first embodiment. It is noted, however, that the first embodiment is excellent to the second embodiment in correction accuracy. 
     As stated so far, according to the deflection yoke and the mis-convergence method for a color CRT of the present invention, it is possible to obtain the quadruple magnetic field lens function derived from auxiliary coils by using the U-shaped magnetic member instead of the E-shaped magnetic member. It is, therefore, possible to correct lateral raster distortion independently of the correction of image distortion. This can ensure the correction of excessive mis-convergence on the vertical deflection portion of the deflection yoke in the Y-axis direction of the screen. Besides, since the U-shaped magnetic member can be also used together with the existing magnetic member for coma correction coils, it is possible to suppress the increase of production cost. Thus, the present invention is economically excellent, as well.