Deflection yoke and color cathode ray tube comprising the deflection yoke

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 flange portion of one selected from the group consisting of the saddle shaped horizontal deflection coil and the saddle shaped vertical deflection coil has a smoothly curved contour and the ratio r = c/d is set in the range of from 2.2 to 3.5, wherein c is the maximum width and d is the maximum height.

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 flange portion of one selected from the group consisting of the saddle shaped horizontal deflection coil and the saddle shaped vertical deflection coil has a smoothly curved contour and the ratio r = c/d (c : the maximum width, d : the maximum height) is set in the range of from 2.2 to 3.5.

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 flange portion of one selected from the group consisting of the saddle shaped horizontal deflection coil and the saddle shaped vertical deflection coil has a smoothly curved contour and the ratio r = c/d (c : the maximum width, d : the maximum height) is set in the range of from 2.2 to 3.5, corner portions of the screen side flange portion of the saddle shaped coil can be located farther from the glass funnel of the cathode ray tube to sufficiently reduce the strength of the magnetic field generated in the vicinity of the corner portions of the screen side flange portion of the saddle shaped coil to the tube axis direction. As a result, since the Lorentz's force applied on the electron beam becomes smaller when the electron beam is deflected on the screen corner portions of the color cathode ray tube, a high order raster distortion at the screen corner portion becomes reduced. Since the screen side flange portion of the saddle shaped coil need not be formed with a dent or a trapezoidal shape unlike conventional arts, the coil wires of the screen side flange portion are not damaged at the time of winding the horizontal deflection coil, or contact of the dent and the glass funnel portion of the cathode ray tube at the time of attaching the deflection yoke to the cathode ray tube can be avoided.

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 flange portion of one selected from the group consisting of the saddle shaped horizontal deflection coil and the saddle shaped vertical deflection coil has a smoothly curved contour and the ratio r = c/d (c : the maximum width, d : the maximum height) is set in the range of from 2.2 to 3.5, the following advantages can be achieved. That is, since the above mentioned deflection yoke of the fifth aspect of the present invention is used, as mentioned above, a high order raster distortion at the screen corners can be reduced, and thus the image quality of the color cathode ray tube can be improved.

FIG. 1 is a diagram of a deflection yoke of the present invention viewed from the screen side.

FIG. 2 is a plan view of a deflection yoke of FIG. 1.

FIG. 3 is a diagram illustrating the magnetic field oriented to the tube axis generated at the vicinity of corner portions of the screen side flange portion of the horizontal deflection coil and the Lorentz's force applied on the electron beam when the electron beam is deflected on the screen corner portions of the color cathode ray tube of the present invention.

FIG. 4 is a diagram illustrating a high order raster distortion at the screen corners.

FIG. 5 is a graph illustrating the relationship between the ratio of the maximum width and the maximum height of the screen side flange portion of the saddle shaped horizontal deflection coil r and the amount of a high order raster distortion c.

FIG. 6 is a diagram illustrating the magnetic field oriented to the tube axis generated at the vicinity of corner portions of the screen side flange portion of the horizontal deflection coil and the Lorentz's force applied on the electron beam when the electron beam is deflected on the screen corner portions of the color cathode ray tube of the present invention.

FIG. 7 is a plan view of a color cathode ray tube of the present invention.

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.

As described in FIG. 6, in deflecting the electron beam to the screen corner portions of the color cathode ray tube, the magnetic field to the tube axis direction 78 is generated in the vicinity of the corner portions 77 of the screen side flange portion 76 of the saddle shaped horizontal deflection coil to apply the Lorentz's force 79 to the electron beam. The embodiments described in detail in the following Example 8 and the Example 9 are achieved with paying attention to the magnetic field to the tube axis direction 78 generated in the vicinity of the corner portions 77 of the screen side flange portion 76. That is, by having the shape of the screen side flange portion 76 of an approximately circular shape when viewed from the screen side with the designated ratio of the maximum width to the maximum height greater, the strength of the magnetic field to the tube axis direction 78 is intensified to reduce the high order raster distortion at the screen corners.

FIG. 1 is a diagram illustrating an Example of the deflection yoke of the present invention viewed from the screen side and FIG. 2 is a plan view of the deflection yoke of FIG. 1. As can be seen in FIG. 2, the deflection yoke comprises the saddle shaped wound horizontal deflection coil 68, the saddle shaped vertical deflection coil 69 located outside the horizontal deflection coil 68, and the ferrite core 70 located outside the vertical deflection coil 69.

As described in FIG. 1, the screen side flange portion 62 of the horizontal deflection coil 68 has the contour 63, 64 of smoothly curved lines and the ratio r=c/d (c : the maximum size of the width direction (x axis direction), d : the maximum height (y axis direction)) is set to be 2.75.

The shape of the contour of the screen side flange portion 65 of conventional horizontal deflection coils is described by the chain double-dashed lines 66, 67 in FIG. 1. The value of the above mentioned r in this case is usually 2.0. In general, since the contour 66, 67 of the screen side flange portion 65 of conventional horizontal deflection coils is formed to conform to the shape of the opposing glass funnel portion of the cathode ray tube, it becomes circular in shape. The contour 66, 67 of the screen side flange portion 65 of the horizontal deflection coil is formed to conform to the surface of the glass funnel portion of the cathode ray tube in order to minimize the energy loss by placing the screen side flange portion 65 of the horizontal deflection coil close to the electron beam.

As described in FIG. 3, in deflecting the electron beam to the screen corner portion of the color cathode ray tube, the magnetic field to the tube axis direction 72 is generated in the vicinity of the corner portions 74 of the screen side flange portion 62 of the horizontal deflection coil 68 to apply the Lorentz's force to the electron beam. However, if the contour 66, 67 of the screen side flange portion 65 of a horizontal deflection coil has a circular shape like conventional arts, since the screen side flange portion 65 is placed closer to the electron beam, the strength of the magnetic field applied to the electron beam 72 becomes very strong. As a result, since the Lorentz's force applied to the electron beam becomes greater as well, the high order raster distortion 75 is generated at screen corner portions as described in FIG. 4. The amount of distortion e becomes 0.6 mm in a 41 cm (17") -90° color cathode ray tube, thus the image quality is drastically deteriorated.

On the other hand, in the horizontal deflection coil 68 with the contour 63, 64 of the screen side flange portion 62 of a smoothly curved line of this Example, if the ratio r=c/d (c : the maximum width (x axis direction), d : the maximum height (y axis direction)) of the screen side flange portion 62 is greater than 2.0, since the corner portions 74 of the screen side flange portion 62 become farther from the glass funnel portion as described in FIG. 25, the strength of the magnetic field to the tube axis direction 72 generated at the portions becomes weaker relative to conventional circular shaped ones. As a result, since the Lorentz's force 73 applied on the electron beam becomes weaker as well, the high order raster distortion 75 at screen corner portions described in FIG. 4 is reduced.

The relationship between the ratio r=c/d (c : the maximum width, d : the maximum height) of the screen side flange portion 62 of the horizontal deflection coil 68 and the amount of the raster distortion e at screen corners is examined with a 41 cm (17") -90° color cathode ray tube. The result is illustrated in FIG. 5. As can be seen in FIG. 5, the amount of the high order raster distortion e at screen corner portions e becomes 0 when r=2.75. That is, in a horizontal deflection coil 68 with the contour 63, 64 of the screen side flange portion 62 of a smoothly curved line, by setting the ratio r=c/d of the screen side flange portion 62 to be 2.75, the high order raster distortion at screen corner portions of a 41 cm (17") -90° color cathode ray tube can be eliminated.

Although the value for the ratio r=c/d of the screen side flange portion 62 of the horizontal deflection coil 68 of 2.75 is used in this Example, the value is not limited thereto and the value of r can be in the range from 2.2 to 3.5. When the value of r is 2.2 or more, since the amount of the high order raster distortion e at screen corner portions becomes 0.3 mm or less (see FIG. 5), and there would be no practical problems. On the other hand, if the amount of r is greater than 3.5, a high order raster distortion is generated in the direction opposite to that of FIG. 26, which is not preferable.

Further, although the embodiment wherein the screen side flange portion 62 of the horizontal deflection coil 68 has the contour of smoothly curved lines and the ratio r=c/d (c : the maximum size of the width direction, d : the maximum height) is set to be in the range from 2.2 to 3.5, the present invention is not limited to the embodiment. And the same effect of reducing a high order raster distortion can be achieved in an embodiment wherein the screen side flange portion of the saddle shaped vertical deflection coil 69 has the contour of smoothly curved lines and the ratio r=c/d (c : the maximum size of the width direction, d : the maximum height) is set to be in the range from 2.2 to 3.5.

FIG. 7 is a plan view illustrating an Example of the color cathode ray tube of the present invention. As can be seen in FIG. 7, the color cathode ray tube main body 80 comprises the glass panel portion 81, and glass funnel portion 33 located to the rear part of the glass panel portion 81. An electron gun (not shown in FIG. 7) is provided behind the glass funnel portion 33. The deflection yoke, comprising the saddle shaped horizontal deflection coil 68, the saddle shaped vertical deflection coil 69 located outside the horizontal deflection coil 68 and the ferrite core 70 located outside the vertical deflection coil 69, is located in the rear periphery of the glass funnel portion 33. That is, the deflection yoke with the structure shown in the Example is used in the color cathode ray tube of this Example (see FIG. 1, FIG. 2). The screen side flange portion 62 of the horizontal deflection coil 68 is formed to have a contour 63, 64 of a smoothly curved line with the ratio r=c/d (c : the maximum width, d : the maximum height) of the screen side flange portion 62 of the horizontal deflection coil 68 is set to be 2.75. Since the deflection yoke with the structure described in the above mentioned Example is used and the high order raster distortion 75 is reduced at screen corner portions as described above, the image quality of the color cathode ray tube is improved.

Although the case with the ratio r=c/d of the screen side flange portion 62 of the horizontal deflection coil 68 of 2.75 is used in this Example, the value is not limited thereto and the value of r can be in the range of from 2.2 to 3.5.

As mentioned above, in general, the screen side magnetic field of a deflection yoke is much more sensitive than the electron gun side magnetic field with respect to controlling a raster distortion. Therefore, a method of controlling a raster distortion by the magnetic field generated by the screen side flange portion of a saddle shaped coil is highly effective.

As described in FIG. 6, in deflecting the electron beam to the screen corner portion of the color cathode ray tube, the magnetic field to the tube axis direction 78 is generated in the vicinity of the corner portions 77 of the screen side flange portion 76 of the saddle shaped horizontal deflection coil to apply the Lorentz's force 79 to the electron beam. The embodiments described in detail in the following Example 10 and the Example 11 are achieved with paying attention to the magnetic field to the tube axis direction 78 generated in the vicinity of the corner portions 77 of the screen side flange portion 76. That is, by having a gap portion in the upper and lower direction through the screen side flange portion 76 of the saddle shaped horizontal deflection coil, the strength of the magnetic field to the tube axis direction 78 is weakened to reduce the high order raster distortion at the screen surface.