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 (85), a saddle shaped vertical deflection coil (86) located outside the horizontal deflection coil, and a ferrite core (87) located outside the vertical deflection coil. The screen side flange portion of the horizontal deflection coil has a gap therethrough in the upper and lower direction.

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. These objects are achieved with the features of independent claim 1. 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 a gap is formed through the screen side flange portion of the horizontal deflection coil in the vertical axis direction. 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 a gap is formed through the screen side flange portion of the horizontal deflection coil in the vertical axis direction of the color cathode ray tubes. Since the color cathode ray tube 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 a gap is formed through the screen side flange portion of the horizontal deflection coil to the upper and lower orientation, the following advantages can be achieved. That is, since the above mentioned deflection yoke of the present invention is used and a high order upper and lower raster distortion of the screen is reduced as mentioned above, the image quality of the color cathode ray tube can be improved. FIG. 1 is a plan view 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 diagram illustrating a high order upper and lower raster distortion of the screen surface. FIG. 4 is a graph illustrating the relationship between the maximum size of the gap portion and a high order upper and lower raster distortion of the screen surface. FIG. 5 is a plan view of a color cathode ray tube of the present invention. FIG. 1 is a plan view illustrating an 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 can be seen in FIG. 1, the deflection yoke comprises the saddle shaped horizontal deflection coil 85, the saddle shaped vertical deflection coil 86 located outside the horizontal deflection coil 85, and the ferrite core 87 located outside the vertical deflection coil 86. The screen side flange portion 82 of the horizontal deflection coil 85 has a maximum size in the tube axis direction (z axis direction) f of 20 mm and a maximum size in the horizontal direction (x axis direction) g of 120 mm and the contour viewed from the screen side of approximately circular shape as described in FIG. 2. The screen side flange portion 82 of the horizontal deflection coil 85 has a gap portion 83 in the upper and lower direction therethrough. Here the gap portion 83 is set to have a maximum size in the tube axis direction h of 5 mm, and a maximum size in the horizontal direction i of 80 mm. The shape of the conventional screen side flange portion of a horizontal deflection coil is described by the chain double-dashed line 84 in FIG. 1. The contour is approximately the same as that of the screen side flange portion 82 of this Example but they are different for having the gap portion formed therethrough in the upper and lower direction in this Example. As described in FIG. 2, in deflecting the electron beam to the screen corner portion of the color cathode ray tube, the magnetic field to the tube axis direction 89 is generated in the vicinity of the corner portions 88 of the screen side flange portion 82 of the horizontal deflection coil 85 to apply the Lorentz's force 90 to the electron beam. However, if the contour of the screen side flange portion of a horizontal deflection coil is the above mentioned conventional shape, since the strength of the magnetic field 89 is very strong, the Lorentz's force 90 applied to the electron beam becomes greater as well. As a result, the raster distortion 91 is generated at the upper and lower edges of the screen as described in FIG. 3. The amount of the distortion j becomes 0.7 mm in the 51 cm (21") -90° color cathode ray tube, and thus the image quality becomes drastically deteriorated. On the other hand, if a gap portion 83 is formed in the upper and lower direction through the screen side flange portion 82 of the horizontal deflection coil 85 as in this Example, since coil wires do not exist in the gap portion 83, the strength of the magnetic field to the tube axis direction 89 generated in the vicinity of corner portions 88 of the screen side flange portion 82 of the horizontal deflection coil 85 becomes weak. As a result, since the Lorentz's force 90 applied on the electron beam becomes weak as well, the high order upper and lower raster distortion 91 in the screen surface described in FIG. 3 is reduced. With the maximum size in the tube axis direction h of the gap portion 83 fixed to be 5 mm, the relationship between the maximum size in the horizontal direction i of the gap portion 83 and the amount of the high order distortion of the upper and lower edges of the screen j is examined with a 51 cm (21") -90° color cathode ray tube. The result is illustrated in FIG. 4. As can be seen from FIG. 4, the amount of the high order upper and lower raster distortion j at screen surface becomes 0 when the maximum size in the horizontal direction i is 80 mm. That is, when a gap portion 83 is formed in the upper and lower direction through the screen side flange portion 82 of the horizontal deflection coil 85 having an approximately circular shape viewed from the screen side, a maximum size in the tube axis direction f of 20 mm and a maximum size in the horizontal direction of 120 mm, the high order upper and lower raster distortion on the screen surface of a 51 cm (21") -90° color cathode ray tube can be eliminated with a maximum gap size in the tube axis direction h of 5 mm and a maximum gap size in the horizontal direction i 80 mm. Although the contour of the screen side flange portion 82 of the horizontal deflection coil 85 viewed from the screen side is an approximately circular shape in this Example, the shape is not limited thereto. Further, the maximum size to the tube axis direction f, the maximum contour size to the horizontal direction g of the screen side flange portion 82 of the horizontal deflection coil 85, and the size to the tube axis direction h of the gap portion 83 are not limited to the amounts described in this Example. That is, forming a gap portion 83 in the upper and lower direction through the screen side flange portion 82 of the horizontal deflection coil 85 is the important feature of this Example. FIG. 5 is a plan view illustrating an Example of color cathode ray tubes of the present invention. As can be seen in FIG. 5, the color cathode ray tube main body 96 comprises glass panel portion 97, and glass funnel portion 33 connected to the rear part of the glass panel portion 97. An electron gun (not shown in FIG. 5) is provided behind the glass funnel portion 33. The deflection yoke, comprising the saddle shaped horizontal deflection coil 85, the saddle shaped vertical deflection coil 86 located outside the horizontal deflection coil 85 and the ferrite core 87 located outside the vertical deflection coil 86 is isolated in the rear periphery of the glass funnel portion 33. The screen side flange portion 82 of the horizontal deflection coil 85 has a gap portion 83 therethrough in the upper and lower direction. Here the gap portion 83 is set to have a maximum size in the tube axis direction h of 5 mm and a maximum size in the horizontal direction i of 80 mm. That is, the deflection yoke with the structure described above is used in the color cathode ray tube of this Example (see FIG. 1, FIG. 2). Since the deflection yoke with the structure described above is used and the screen surface becomes a preferable straight linear one without the high order upper and lower raster distortion as described above, the image quality of the color cathode ray tube is improved. Although the shape of the screen side flange portion 82 of the horizontal deflection coil 85 viewed from the screen side is an approximately circular one also in this Example, the shape is not limited thereto. The amount of the maximum size in the tube axis direction f and the maximum contour size in the horizontal direction g of the screen side flange portion 82 of the horizontal deflection coil 85, and the size in the tube axis direction h and the horizontal direction i of the gap portion 83 are not limited to those described in this Example.

Claims: A deflection yoke comprising a saddle shaped horizontal deflection coil (85), a saddle shaped vertical deflection coil (86) located outside the saddle shaped horizontal deflection coil (85), and a core (87) located outside the saddle shaped vertical deflection coil (86), characterized in that the screen side flange portion (82) of the horizontal deflection coil (85) has a gap (83) therethrough in the vertical axis direction, and extending from the vertical axis of the screen side flange portion in horizontal direction. A color cathode ray tube comprising a color cathode ray tube main body (96) which comprises a glass panel portion (97) and a glass funnel portion (33) connected to the rear part of the glass panel portion (97), and a deflection yoke as claimed in claim 1, said color cathode ray tube further comprising an electron gun located at the rear part of the color cathode ray tube main body (96).

Inventors: HONDA MASANOBU, SHIMADA KOJI, HONDA, MASANOBU, SHIMADA, KOJI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1995
Main classification: H01J29
IPC codes: H01J29