Deflection yoke and color cathode ray tube comprising the deflection yoke

Abstract: A deflection yoke which is capable of sufficiently reducing a high order raster distortion (gullwing) at the upper and lower edges of the screen without damaging coil wires of the screen side flange portion at the time of winding the horizontal deflection coil. A deflection yoke is formed with a saddle shaped horizontal deflection coil 1, a saddle shaped vertical deflection coil 2 located outside the horizontal deflection coil 1, and a ferrite core 3 located outside the vertical deflection coil 2. The screen side cone portion 1a of the horizontal deflection coil 1 is wound with a winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the horizontal axis as the standard. The head point in the direction of screen side tube axis 4 of the screen side cone portion 1a of the horizontal deflection coil 1 is located 30 mm away from the screen side tip portion 3a of the ferrite core 3.

Description: The present invention relates to deflection yokes and color cathode ray tubes with the deflection yokes. In the current color cathode ray tubes used as a display monitor such as windows, information is very often displayed in the peripheral regions of the screen. Therefore a technology enabling minute image display in such regions is being required. Since the raster distortion is one of the important elements in determining the image quality in the peripheral regions of the screen, the standard for the raster distortion of the screen, which depends on the magnetic field distribution of the deflection yoke itself, has become very demanding. In general, the magnetic field distribution at the screen side cone portion of a saddle shaped coil used as a horizontal deflection coil is designed to include a strong pincushion distortion in order to eliminate the raster distortion at the upper and lower edges of the screen. However, when it includes significant fifth-order pincushion distortion, an upper and lower high order raster distortion called gullwing emerges. Since a high order raster distortion such as the gullwing deteriorates the visual image quality drastically, it should be prevented. In general, the vertical magnetic field distribution of a deflection yoke used in a color cathode ray tube for display monitoring has a barrel distortion entirely from the electron gun side to the screen side with respect to the self-convergence. Then, since the raster distortion at the right and left edges of the screen has a pincushion shape when such a barrel distortion is included, the distortion is eliminated by supplying a correction current from the circuit side of the display monitor toward the horizontal deflection coil. However, since the correction current in general has a wave form to correct a third-order pincushion distortion, when a raster distortion at the right and left edges of the screen includes a gullwing which is a high order distortion, the correction current can not completely eliminate the distortion. On the other hand, as mentioned above, since the gullwing drastically deteriorates the visual image quality, it should be prevented. In order to meet such requirements, a method of reducing a high order raster distortion such as a gullwing at the upper and lower edges of the screen by forming a dent toward the central axis of the cathode ray tube at the center of the screen side flange portion of the horizontal deflection coil is proposed in US-A-4,233,582. Another method of reducing the gullwing at the upper and lower edges of the screen by having the screen side flange portion of the horizontal deflection coil of a polygonal shape is advocated in US-A-4,229,720. By analogy, these methods can be applied to a vertical deflection coil to reduce the gullwing at the right and left edges of the screen. Further, a method of reducing a high order raster distortion by forming a projection toward the electron gun side at the right and left edges of the screen side flange portion of a saddle shaped coil is proposed in JP-A-216738/1990. However, in the method disclosed in US-A-4,233,582, in the pressing process to provide a dent toward the central axis of the cathode ray tube at the center of the screen side flange portion of a horizontal deflection coil or a vertical deflection coil, there is a problem that it is highly likely that the insulating coating layer of a coil wire is damaged due to the excessive stretching of the coil wire in production. Further, if the dent is formed too deep, since the dent comes in contact with the funnel portion of the cathode ray tube when the deflection yoke is attached to the cathode ray tube, there is a problem in production or designing in that it is sometimes difficult to form a dent sufficient to remove a high order raster distortion such as the gullwing. Further, if a dent is formed too deep, since the dent comes in contact with the cone portion of the horizontal deflection coil when assembling the deflection yoke, there is a problem in production or designing in that it is sometimes difficult to form a dent sufficient to remove the gullwing. Further, in the method disclosed in US-A-4,229,720, there is a problem in production in that coil wires are liable to be deformed and damaged at the apexes of the polygon-shaped screen side flange portion of the horizontal deflection coil or the vertical deflection coil. In general, a ferrite core is used in a deflection yoke to strengthen the deflection magnetic field strength but the ferrite core also alleviates the magnetic field distortion formed by the deflection coil itself (hereinafter abbreviated ferrite core effect on the field distribution). Therefore even if the horizontal magnetic field distortion is controlled by the winding distribution of the deflection coil to minimize the deflection aberration, since the magnetic field distortion is alleviated by the ferrite core effect on the field distribution of the ferrite core, there is a problem that the correction sensitivity of the deflection aberration deteriorates to that extent. In the method disclosed in JP-A-216738/1990, in the pressing process to provide a projection at the right and left edges of the screen side flange portion of the saddle shaped coil, there is a problem in that it is highly likely that the insulation coating layer of a coil wire is damaged due to the excessive stretching of the coil wire in production. Further, if the projection is formed too high, since the horizontal deflection coil, the vertical deflection coil and the ferrite core come in contact with each other when the deflection yoke is assembled, there is a problem in production or designing in that it is difficult to form a projection sufficient to remove a high order raster distortion. In order to solve the above mentioned problems of conventional arts, an object of the present invention is to provide a deflection yoke which can sufficiently decrease a gullwing without the risk of damaging coil wires of the screen side flange portion at the time of winding of the horizontal deflection coil or the vertical deflection coil. Another object of the present invention is to provide a deflection yoke which can sufficiently decrease a high order raster distortion without the risk of damaging the coil wires of the screen side flange portion of the saddle shaped coil at the time of wiring the saddle shaped coil, or contacting the horizontal deflection coil, the vertical deflection coil and the ferrite core with each other at the time of assembling the deflection yoke. It is a further object of the present invention to provide a deflection yoke which can sufficiently decrease a high order raster distortion without the risk of damaging the coil wires of the screen side flange portion at the time of winding the saddle shaped coil or the horizontal deflection coil, or contacting the saddle shaped coil or the horizontal deflection coil to the glass funnel at the time of attaching the deflection yoke. It is another object of the present invention to provide a color cathode ray tube which can sufficiently decrease a high order raster distortion such as the gullwing to improve the image quality. In order to achieve the above mentioned objects, an aspect of deflection yokes of the present invention comprises at least a saddle shaped horizontal deflection coil, a saddle shaped vertical deflection coil located outside the saddle shaped horizontal deflection coil and a core located outside the saddle shaped vertical deflection coil, wherein the screen side cone portion of at least one selected from the group consisting of the saddle shaped horizontal deflection coil and the saddle shaped vertical deflection coil projects to a position not affected by the ferrite core effect on the field distribution of the core. An aspect of color cathode ray tubes of the present invention comprises a color cathode ray tube main body comprising a glass panel portion and a glass funnel portion connected to the rear part of the glass panel portion, and a deflection yoke comprising at least an electron gun located at the rear of the cathode ray tube main body, a saddle shaped horizontal deflection coil located at the rear periphery of the cathode ray tube main body, a saddle shaped vertical deflection coil located outside the saddle shaped horizontal deflection coil and a core located outside the saddle shaped vertical deflection coil, wherein the screen side cone portion of at least one selected from the group consisting of the saddle shaped horizontal deflection coil and the saddle shaped vertical deflection coil projects to a position not affected by the ferrite core effect on the field distribution of the core. In the above mentioned aspect of deflection yokes of the present invention, it is preferable that the head point in the direction of screen side tube axis of the screen side cone portion of the horizontal deflection coil is located in the range of from 20 mm to 60 mm away from the screen side tip portion of of the core. The head point in the direction of screen side tube axis of the screen side cone portion of the horizontal deflection coil herein refers to the top portion of the projection of the screen side cone portion at the point crossing the tube axis. In the above mentioned aspect of deflection yokes of the present invention, it is preferable that the screen side cone portion of the horizontal deflection coil is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the horizontal axis as the standard. In the above mentioned aspect of color cathode ray tubes of the present invention, it is preferable that the head point in the direction of screen side tube axis of the screen side cone portion of the horizontal deflection coil is located in the range of from 20 mm to 60 mm away from the screen side tip portion of of the core. In the above mentioned aspect of color cathode ray tubes of the present invention, it is preferable that the screen side cone portion of the horizontal deflection coil is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the horizontal axis as the standard. In the above mentioned aspect of deflection yokes of the present invention, it is preferable that the head point in the direction of screen side tube axis of the screen side cone portion of the vertical deflection coil is located in the range of from 10 mm to 60 mm away from the screen side tip portion of the core. In the above mentioned aspect of deflection yokes of the present invention, it is preferable that the screen side cone portion of the vertical deflection coil is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the vertical axis as the standard. In the above mentioned aspect of color cathode ray tubes of the present invention, it is preferable that the head point in the direction of screen side tube axis of the screen side cone portion of the vertical deflection coil is located in the range of from 10 mm to 60 mm away from the screen side tip portion of the core. In the above mentioned aspect of color cathode ray tubes of the present invention, it is preferable that the screen side cone portion of the vertical deflection coil is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the vertical axis as the standard. Since the above mentioned aspect of deflection yokes of the present invention comprises at least a saddle shaped horizontal deflection coil, a saddle shaped vertical deflection coil located outside the saddle shaped horizontal deflection coil and a core located outside the saddle shaped vertical deflection coil, wherein the screen side cone portion of at least one selected from the group consisting of the saddle shaped horizontal deflection coil and the saddle shaped vertical deflection coil projects to a position not affected by the ferrite core effect on the field distribution of the core, wherein the screen side cone portion of at least one selected from the group consisting of the saddle shaped horizontal deflection coil and the saddle shaped vertical deflection coil projects to a position not having the ferrite core effect on the field distribution of the core, if the condition of horizontal magnetic field distortion or the vertical magnetic field distortion to minimize the high order raster distortion (gullwing) at the upper and lower edges or the right and left edges of the screen is achieved, the gullwing can be effectively reduced. Further, since the gullwing can be reduced effectively, the screen side flange portion of the horizontal deflection coil or the vertical deflection coil can be formed in approximately a circular shape without forming a dent in the screen side flange portion of the horizontal deflection coil or the vertical deflection coil, or having a polygon shaped screen side flange portion of the horizontal deflection coil or the vertical deflection coil as in conventional arts. As a result, problems such as the damage in production to the coil wires of the screen side flange portion at the time of winding the horizontal deflection coil or the vertical deflection coil can be prevented. Since the above mentioned aspect of color cathode ray tubes of the present invention comprises a color cathode ray tube main body comprising a glass panel portion and a glass funnel portion connected to the rear part of the glass panel portion, and a deflection yoke comprising at least an electron gun located at the rear of the cathode ray tube main body, a saddle shaped horizontal deflection coil located at the rear periphery of the cathode ray tube main body, a saddle shaped vertical deflection coil located outside the saddle shaped horizontal deflection coil and a core located outside the saddle shaped vertical deflection coil, wherein the screen side cone portion of at least one selected from the group consisting of the saddle shaped horizontal deflection coil and the saddle shaped vertical deflection coil projects to a position not affected by the ferrite core effect on the field distribution of the core, the following advantages can be achieved. That is, since a deflection yoke of the first aspect of the present invention is used effectively to reduce the gullwing as mentioned above, the image quality of the color cathode ray tube can be improved. In the above mentioned preferable embodiment of the first aspect of deflection yokes of the present invention in which the head point in the direction of screen side tube axis of the screen side cone portion of the horizontal deflection coil is located in the range of from 20 mm to 60 mm away from the screen side tip portion of the core, the ferrite core effect on the field distribution of the core to the screen side cone portion of the horizontal deflection coil becomes smaller. In the above mentioned preferable embodiment of the aspect of deflection yokes of the present invention in which the screen side cone portion of the horizontal deflection coil is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the horizontal axis as the standard, the condition of horizontal magnetic field distortion to minimize the gullwing can be easily achieved. This is because the fifth-order pincushion distortion, which generates gullwing, emerges at the wires at the screen side cone portion of the horizontal deflection coil which is wound in the winding angle range from 1° to 18° with the horizontal axis as the standard. By comparatively reducing the winding distribution at the winding angle from 1° to 18°, the fifth-order pincushion distortion can be decreased to curb the generation of the gullwing. In the above mentioned preferable embodiment of the aspect of color cathode ray tubes of the present invention in which the head point in the direction of screen side tube axis of the screen side cone portion of the horizontal deflection coil is located in the range of from 20 mm to 60 mm away from the screen side tip portion of the core, since the gullwing can be effectively reduced as mentioned above, the image quality of the color cathode ray tube can be improved. In the above mentioned preferable embodiment of the aspect of color cathode ray tubes of the present invention in which the head point in the direction of screen side tube axis of the screen side cone portion of the vertical deflection coil is located in the range of from 10 mm to 60 mm away from the screen side tip portion of the core, the ferrite core effect on the field distribution of the core to the screen side cone portion of the vertical deflection coil becomes smaller. In the above mentioned preferable embodiment of the aspect of deflection yokes of the present invention in which the screen side cone portion of the vertical deflection coil is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the winding angle range from 18° to 30° with the vertical axis as the standard, the condition of vertical magnetic field distortion to minimize a high order raster distortion such as the gullwing at the right and left edges of the screen can be easily achieved. This is because the fifth-order pincushion distortion, which generates gullwing, emerges at the wires at the screen side cone portion of the vertical deflection coil which is wound in the winding angle range from 1° to 18° with the vertical axis as the standard. By comparatively reducing the winding distribution at the winding angle of from 1° to 18°, the fifth-order pincushion distortion can be decreased to curb the generation of the gullwing. In the above mentioned preferable embodiment of the aspect of color cathode ray tubes of the present invention in which the head point in the direction of screen side tube axis of the screen side cone portion of the vertical deflection coil is located in the range of from 10 mm to 60 mm away from the screen side tip portion of the core, since the gullwing can be effectively reduced as mentioned above, the image quality of the color cathode ray tube can be improved. FIG. 1 is a side view of Example 1 of a deflection yoke of the present invention. FIG. 2 is a diagram of the deflection yoke of FIG. 1 viewed from the screen side. FIG. 3 is a graph illustrating the distortion condition of the horizontal magnetic field distribution to minimize the gullwing and the horizontal magnetic field distribution to generate the gullwing in Example 1 of the present invention. FIG. 4 is a graph illustrating the condition of the horizontal magnetic field distribution without the ferrite core effect on the field distribution and the condition of the horizontal magnetic field distribution with the ferrite core effect on the field distribution in Example 1 of the present invention. FIG. 5 is a graph illustrating the relationship of the ferrite core effect on the field distribution, and the distance between the head point in the direction of screen side tube axis at the horizontal saddle coil screen side cone portion and the ferrite core screen side tip in Example 1 of the present invention. FIG. 6 is a plan view of a color cathode ray tube of Example 2 of the present invention. FIG. 7 is a plan view of a deflection yoke of Example 3 of the present invention. FIG. 8 is a section view taken along the line VIII-VIII of FIG. 7. FIG. 9 is a graph illustrating the distortion condition of the horizontal magnetic field distribution to minimize the gullwing and the condition of the horizontal magnetic field distribution to generate the gullwing in Example 3 of the present invention. FIG. 10 is a graph illustrating the condition of the horizontal magnetic field distribution without the ferrite core effect on the field distribution and the condition of the horizontal magnetic field distribution with the ferrite core effect on the field distribution in Example 3 of the present invention. FIG. 11 is a graph illustrating the relationship of the ferrite core effect on the field distribution, and the distance between the head point in the direction of the screen side tube axis of the vertical deflection coil screen side cone portion and the ferrite core screen side tip in Example 3 of the present invention. FIG. 12 is a plan view of a cathode ray tube of Example 4 of the present invention. The present invention will be further described with reference to Examples. <Example 1> FIG. 1 is a side view illustrating the first Example of deflection yokes of the present invention and FIG. 2 is a diagram of the deflection yoke of FIG. 1 viewed from the screen side. As described in FIG. 1, the deflection yoke comprises a saddle shaped horizontal deflection coil 1, a saddle shaped vertical deflection coil 2 located outside the horizontal deflection coil 1, and a ferrite core 3 located outside the vertical deflection coil 2. The screen side cone portion la of the horizontal deflection coil is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the winding angle range from 18° to 30° with the horizontal axis as the standard. The "winding angle" here is the term to describe the area occupied by the wound deflection coil viewed from the screen side by the angle with respect to the horizontal axis (X axis). The head point in the direction of screen side tube axis 4 is located 30 mm away from the screen side edge portion 3a of the ferrite core 3. Further, the screen side flange portion 5 is formed from the head point in the direction of screen side tube axis 4 of the screen side cone portion la of the horizontal deflection coil 1 continuously. As described in FIG. 2, the screen side flange portion 5 of the horizontal deflection coil 1 is wound approximately in a circular shape. The gullwing, which is a high order raster distortion at the upper and lower edges of the screen, arises from the distortion of the horizontal magnetic field distribution in the vicinity of the screen side aperture of the deflection yoke. The horizontal magnetic field distribution condition of the deflection yokes of the present invention is set as described by the solid line 6 in FIG. 3 to minimize the gullwing, and the distortion of the horizontal magnetic field distribution generated by the gullwing is as described by the broken line 7 of FIG. 3. That is, the horizontal magnetic field distribution described by the broken line 7 includes the fifth-order pincushion distortion. The fifth-order pincushion distortion is generated by the wires of the screen side cone portion la of the horizontal deflection coil 1 wound in the winding angle range from 1° to 18° with the horizontal axis as the standard. Screen side cone portion la of the horizontal deflection coil 1 of this Example has been appropriately adjusted in advance to have a relatively sparse winding distribution in the range of the winding angle from 1° to less than 18° and a relatively dense winding distribution in the range from 18° to 30°. By this procedure, since the fifth-order pincushion distortion is reduced, the condition of the horizontal magnetic field distribution to minimize the gullwing as described by the solid line 6 in FIG. 3 can be achieved. However, if the ferrite core 3 is provided to the screen side cone portion la of the horizontal deflection coil 1 which has been adjusted with respect to the distortion condition of the horizontal magnetic field distribution accordingly, since the ferrite core effect on the field distribution of the ferrite core 3 alleviates the distortion condition of the horizontal magnetic field distribution, the optimum distortion condition of the horizontal magnetic field distribution to minimize the gullwing as described by the solid line 8 in FIG. 4 changes to the condition described by the broken line 9 in FIG. 4. As a consequence, the gullwing can not be corrected appropriately. Since the ferrite core effect on the field distribution of the ferrite core 3 deteriorates the deflection aberration correction sensitivity by the horizontal magnetic field distribution, when the distortion condition of the horizontal magnetic field distribution needs to be measured precisely, it should be measured without the presence of the ferrite core 3. FIG. 5 is a graph illustrating the relationship between the ferrite core effect on the field distribution of the ferrite core, and the distance between the head point to the direction of screen side tube axis of the screen side cone portion of the horizontal deflection coil and the screen side edge portion of the ferrite core. As can be seen from the FIG. 5, when the distance between the head point in the direction of screen side tube axis 4 of the screen side cone portion la of the horizontal deflection coil 1 and the screen side edge portion 3a of the ferrite core 3 ℓ is 20 mm or more, the ferrite core effect on the field distribution is attenuated to less than 10 %. From this observation, the distance between the head point to the direction of screen side tube axis 4 of the screen side cone portion 1a of the horizontal deflection coil 1 and the screen side edge portion 3a of the ferrite core 3 ℓ is set to be 30 mm in this Example. By this, since the ferrite core effect on the field distribution of the ferrite core 3 to the screen side cone portion la of the horizontal deflection coil 1 becomes smaller, the optimum distortion condition of the horizontal magnetic field distribution to minimize the gullwing as described by the solid line 8 in FIG. 4 can be achieved. As mentioned above, if the screen side cone portion la of the horizontal deflection coil 1 is wound with the winding angle in the range of from 1° to 80° with a higher density of winding distribution in the range of the winding angle from 18° to 30° with the horizontal axis as the standard, and the head point in the direction of screen side tube axis 4 of the screen side cone portion la of the horizontal deflection coil 1 is located 30 mm away from the screen side edge portion 3a of the ferrite core 3, the gullwing can be effectively reduced. As a result, since the screen side flange portion 5 of the horizontal deflection coil can be formed in approximately a circular shape as mentioned above unlike conventional arts, namely, without the need to be formed with a dent shape in the screen side flange portion 5 of the horizontal deflection coil 1 or having a polygon shaped screen side flange portion 5 of the horizontal deflection coil, problems such as the damage of the coil wires of the screen side flange portion 5 at the time of winding the horizontal deflection coil 1 in production can be avoided. Although the screen side cone portion 1a of the horizontal deflection coil 1 is wound in the winding angle range of from 1° to 80° with a higher density of winding distribution in the winding angle range from 18° to 30° with the horizontal axis as the standard in this Example, the structures are not limited thereto and the range of winding angles is not specifically limited as long as the distortion condition of the horizontal magnetic field distribution to minimize the gullwing can be achieved. Besides, although the head point in the direction of screen side tube axis 4 of the screen side cone portion la of the horizontal deflection coil 1 is located 30 mm away from the screen side edge portion 3a of the ferrite core 3 in this Example, the position of the head point in the direction of screen side tube axis 4 of the screen side cone portion 1a of the horizontal deflection coil 1 is not limited thereto and the same effect can be achieved if it is located in the range of from 20 mm to 60 mm away from the screen side edge portion 3a of the ferrite core 3. If the head point in the direction of screen side tube axis 4 of the screen side cone portion la of the horizontal deflection coil 1 is located more than 60 mm away from the screen side edge portion 3a of the ferrite core 3, the total length and the diameter of the coil become very large, and thus it is unpractical. <Example 2> FIG. 6 is a plan view illustrating the second Example of color cathode ray tubes of the present invention. As can be seen in FIG. 6, the color cathode ray tube main body 9 comprises the glass panel portion 10, and the glass funnel portion 11 connected to the rear part of the glass panel portion 10. An electron gun (not shown in FIG. 6) is provided behind the glass funnel portion 11. The deflection yoke, comprising the saddle shaped horizontal deflection coil 1, the saddle shaped vertical deflection coil 2 located outside the horizontal deflection coil 1 and the ferrite core 3 located outside the vertical deflection coil 2, is located in the rear periphery of the glass funnel portion 11. The screen side cone portion 1a of the horizontal deflection coil 1 is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the horizontal axis as the standard. The head point in the direction of screen side tube axis 4 of the screen side cone portion 1a of the horizontal deflection coil 1 is located 30 mm away from the screen side edge portion 3a of the ferrite core 3. Further, the screen side flange portion 5 is formed from the head point in the direction of screen side tube axis 4 of the screen side cone portion 1a of the horizontal deflection coil 1 continuously. The screen side flange portion 5 of the horizontal deflection coil 1 is wound approximately in a circular shape. That is, the deflection yoke described in the above mentioned Example 1 is comprised in the color cathode ray tube of the present Example (see FIG. 1 and FIG. 2). Since the deflection yoke with the structure described in the above mentioned Example 1 is used and the optimum distortion condition of the horizontal magnetic field distribution to minimize a high order raster distortion (gullwing) at the upper and lower edges of the screen can be easily achieved, the image quality of the color cathode ray tube can be improved. Although the screen side cone portion 1a of the horizontal deflection coil 1 is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the horizontal axis as the standard in this Example, the structures are not limited thereto and the range of winding angles is not specifically limited as long as the distortion condition of the horizontal magnetic field distribution to minimize the gullwing can be achieved. Besides, although the head point in the direction of screen side tube axis 4 of the screen side cone portion 1a of the horizontal deflection coil 1 is located 30 mm away from the screen side edge portion 3a of the ferrite core 3 in this Example, the position of the head point in the direction of screen side tube axis 4 of the screen side cone portion 1a of the horizontal deflection coil 1 is not limited thereto and the same effect can be achieved if it is located in the range of from 20 mm to 60 mm away from the screen side edge portion 3a of the ferrite core 3. If the head point to the direction of screen side tube axis 4 of the screen side cone portion 1a of the horizontal deflection coil 1 is located more than 60 mm away from the screen side edge portion 3a of the ferrite core 3, the total length and the diameter of the coil become very large, and thus it is unpractical. 〈Example 3〉 FIG. 7 is a plan view illustrating the third Example of deflection yokes of the present invention. As can be seen in FIG. 7, the deflection yoke comprises the saddle shaped wound horizontal deflection coil 12, the saddle shaped vertical deflection coil 13 located outside the horizontal deflection coil 12, and the ferrite core 14 located outside the vertical deflection coil 13. The screen side cone portion 13a of the vertical deflection coil 13 is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the vertical axis as the standard. The head point in the direction of screen side tube axis 15 is located 20 mm away from the screen side edge portion 14a of the ferrite core 14. Further, the screen side flange portion 16 is formed from the head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 continuously. As described in FIG. 8, the screen side flange portion 16 of the vertical deflection coil 13 is wound approximately in a circular shape. The gullwing at the right and left rasters arises from the distortion of the vertical magnetic field distribution in the vicinity of the screen side aperture of the deflection yoke. The condition of the vertical magnetic field distribution of the deflection yokes of the present invention is set as described by the solid line 17 in FIG. 9 to minimize the gullwing, and the distortion of the vertical magnetic field distribution generated by the gullwing becomes as described by the broken line 18 of FIG. 9. That is, the vertical magnetic field distribution described by the broken line 18 includes the fifth-order pincushion distortion. The fifth-order pincushion distortion is generated by the wires of the screen side cone portion 13a of the vertical deflection coil 13 wound in the winding angle range from 1° to 18° with the vertical axis as the standard. Screen side cone portion 13a of the vertical deflection coil 13 of this Example has been appropriately adjusted in advance to have a relatively sparse winding distribution in the range of the winding angle from 1° to less than 18° and a relatively dense winding distribution in the range of the winding angle from 18° to 30°. By this procedure, since the fifth-order pincushion distortion is reduced, the condition of the vertical magnetic field distribution to minimize the gullwing (as described by the solid line 17 in FIG. 9) can be achieved. However, if the ferrite core 14 is provided to the screen side cone portion 13a of the vertical deflection coil 13 which has been adjusted with respect to the distortion condition of the vertical magnetic field distribution accordingly, since the ferrite core effect on the field distribution of the ferrite core 14 alleviates the distortion condition of the vertical magnetic field distribution, the optimum distortion condition of the vertical magnetic field distribution to minimize the gullwing as described in the solid line 19 in FIG. 10 changes to the condition described by the broken line 20 in FIG. 10. As a consequence, the gullwing can not be corrected appropriately. Since the ferrite core effect on the field distribution of the ferrite core 14 deteriorates the deflection aberration correction sensitivity by the vertical magnetic field distribution, when the distortion condition of the vertical magnetic field distribution needs to be controlled precisely, it should be controlled without the presence of the ferrite core 14. FIG. 11 is a graph illustrating the relationship between the ferrite core effect on the field distribution of the ferrite core, and the distance between the head point in the direction of screen side tube axis of the screen side cone portion of the vertical deflection coil and the screen side edge portion of the ferrite core. As can be seen from the FIG. 11, when the distance between the head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 and the screen side edge portion 14a of the ferrite core 14 is 10 mm or more, the ferrite core effect on the field distribution is attenuated to less than 10 %. From this observation, the distance between the head point to the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 and the screen side edge portion 14a of the ferrite core 14 is set to be 20 mm in this Example. By this, since the ferrite core effect on the field distribution of the ferrite core 14 to the screen side cone portion 13a of the vertical deflection coil 13 becomes smaller, the optimum distortion condition of the vertical magnetic field distribution to minimize the gullwing as described by the solid line 19 in FIG. 10 can be achieved. As mentioned above, if the screen side cone portion 13a of the vertical deflection coil 13 is wound with the winding angle in the range of from 1° to 80° with a high density of winding distribution in the range of the winding angle from 18° to 30° with the vertical axis as the standard, and the head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 is located 20 mm away from the screen side edge portion 14a of the ferrite core 14, the gullwing can be effectively reduced. As a result, since the screen side flange portion 16 of the vertical deflection coil 13 can be formed in approximately a circular shape as mentioned above, without the need to form a dent shape in the screen side flange portion 16 of the vertical deflection coil 13 or have a screen side flange portion 16 with a polygon shape of the vertical deflection coil 13, problems such as the damage in production to the coil wires of the screen side flange portion 16 at the time of winding the vertical deflection coil 13 can be avoided. Although the screen side cone portion 13a of the vertical deflection coil 13 is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the vertical axis as the standard in this Example, the structures are not limited thereto and the range of winding angles is not specifically limited as long as the distortion condition of the vertical magnetic field distribution to minimize the gullwing can be achieved. Besides, although the head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 is located 20 mm away from the screen side edge portion 14a of the ferrite core 14 in this Example, the position of the head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 is not limited thereto and the same effect can be achieved if it is located in the range of from 10 mm to 60 mm away from the screen side edge portion 14a of the ferrite core 14. If the head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 is located more than 60 mm away from the screen side edge portion 14a of the ferrite core 14, the total length and the diameter of the coil become very large, and thus it is unpractical. 〈Example 4〉 FIG. 12 is a plan view illustrating the fourth Example of color cathode ray tubes of the present invention. As can be seen in FIG. 12, the color cathode ray tube main body 21 comprises the glass panel portion 22, and glass funnel portion 23 connected to the rear part of the glass panel portion 22. An electron gun (not shown in FIG. 12) is provided behind the glass funnel portion 23. The deflection yoke, comprising the saddle shaped horizontal deflection coil 12, the saddle shaped vertical deflection coil 13 located outside the horizontal deflection coil 12 and the ferrite core 14 located outside the vertical deflection coil 13, is located in the rear periphery of the glass funnel portion 23. The screen side cone portion 13a of the vertical deflection coil 13 is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the vertical axis standard. The head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 is located 20 mm away from the screen side edge portion 14a of the ferrite core 14. Further, the screen side flange portion 16 is formed from the head point to the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 continuously. The screen side flange portion 16 of the vertical deflection coil 13 is wound approximately in a circular shape. That is, the deflection yoke described in the above mentioned Example 3 is used in the color cathode ray tube of the present Example (see FIG. 7, FIG. 8). Since the deflection yoke with the structure described in the above mentioned Example 3 is used, and since the optimum distortion condition of the vertical magnetic field distribution to minimize a high order raster distortion (gullwing) at the right and left edges of the screen can be easily achieved, the image quality of the color cathode ray tube can be improved. Although the screen side cone portion 13a of the vertical deflection coil 13 is wound in the winding angle range from 1° to 80° with a higher density of winding distribution in the range from 18° to 30° with the vertical axis as the standard in this Example, the structures are not limited thereto and the range of winding angles is not specifically limited as long as the distortion condition of the vertical magnetic field distribution to minimize the gullwing can be achieved. Besides, although the head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 is located 20 mm away from the screen side edge portion 14a of the ferrite core 14 in this Example, the position of the head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 is not limited thereto and the same effect can be achieved if it is located in the range of from 10 mm to 60 mm away from the screen side edge portion 14a of the ferrite core 14. If the head point in the direction of screen side tube axis 15 of the screen side cone portion 13a of the vertical deflection coil 13 is located more than 60 mm away from the screen side edge portion 14a of the ferrite core 14, the total length and the diameter of the coil become very large, and thus it is unpractical. In general, the magnetic field at the screen side of a deflection yoke is much more sensitive than the magnetic field at the electron gun side with respect to controlling the raster distortion. Therefore, methods such as controlling the raster distortion in the magnetic field generated by the screen side flange portion of the saddle shaped coil are highly effective.

Claims: A deflection yoke comprising a saddle shaped horizontal deflection coil, (1; 12) a saddle shaped vertical deflection coil (2; 13) located outside the saddle shaped horizontal deflection coil, and a ferrite core (3; 14) located outside the saddle shaped vertical deflection coil, characterized in that the screen side cone portion (1a; 13a) of at least one selected from the group consisting of the saddle shaped horizontal deflection coil (1; 12) and the saddle shaped vertical deflection coil (2; 13) projects to a position not affected by the effect of the ferrite core (3; 14) on the field distribution. The deflection yoke according to claim 1, wherein the head point (4) in the direction of screen side tube axis (7) of the screen side cone portion (1a) of the horizontal deflection coil (1) is located in the range (ℓ) of from 20 mm to 60 mm away from the screen side tip portion (3a) of the core (3). The deflection yoke according to claim 1 or 2 wherein the screen side cone portion (1a) of the horizontal deflection coil is wound with a winding angle range of 1° to 80° with a higher density of winding distribution in the winding angle range from 18' to 30' with the horizontal axis (x) as the standard. The deflection yoke according to claim 1, 2 or 3, wherein the head point (15) in the direction of screen side tube axis (z) of the screen side cone portion (13a) of the vertical deflection coil (13) is located in the range of from 10 mm to 60 mm away from the screen side tip portion (14a) of the core (14). The deflection yoke according to any one of claims 1 to 4, wherein the screen side cone portion (13a) of the vertical deflection coil (13) is wound with a winding angle range of 1° to 80° with a higher density of winding distribution in the winding angle range from 18° to 30° with the vertical axis (y) as the standard. A color cathode ray tube comprising a color cathode ray tube main body (9; 21) which comprises a glass panel portion (10; 22) and a glass funnel portion (11; 23) connected to the rear part of the glass panel portion, and a deflection yoke according to any one of claims 1 to 5, wherein the deflection yoke comprises an electron gun located at the rear part of the color cathode ray tube main body (9; 21), and wherein the saddle shaped horizontal deflection coil (1; 12) is located at the rear periphery of the color cathode ray tube main body (9; 21).

Inventors: HONDA MASANOBU, SHIMADA KOJI, HONDA, MASANOBU, SHIMADA, KOJI
Applicants: MATSUSHITA ELECTRONICS CORP, MATSUSHITA ELECTRONICS CORPORATION
Application year: 1995
Main classification: H01J29
IPC codes: H01J29