Self-Converging Deflection Yoke

The present invention relates to a deflection yoke for a color television receiver, and more particularly to a deflection yoke capable of reducing a pincushion distortion of a raster scanned on a faceplate of a picture tube.

In a conventional television receiver, a raster scanned on the faceplate of the picture tube includes much distortion and nonconvergence. In a self-converging deflection yoke for a color picture tube having inline electron guns, convergence is compensated by forming a magnetic field generated by a horizontal deflection coil into a pincushion field and forming a magnetic field generated by a vertical deflection coil into a barrel field, as is well known in the art. Accordingly, as for the pincushion deflection distortion (hereinafter referred to simply as pincushion distortion) at the left and right edge of a screen of a color television receiver, in addition to an inherent pincushion distortion due to a radius of curvature of the picture tube, a further pincushion distortion is added by the fact that the vertical deflection magnetic field is formed into an intensified barrel field in order to compensate for the convergence, resulting in the movement of electron beam normal to magnetic line of force created by the vertical deflection coil. A pincushion distortion compensation circuit is, therefore, usually provided to compensate for such pincushion distortion at the left and right edge of the screen. In order to simultaneously compensate for the convergence and the pincushion distortion by a deflection coil only, without using the pincushion distortion compensation circuit, it is necessary to form that portion of the vertical deflection magnetic field which faces the screen into a pincushion shape to compensate for the pincushion distortion, and at the same time to form that portion of the vertical deflection magnetic field which faces the electron guns into a barrel shape which is intensified enough to balance out the pincushion magnetic field on the screen side, to compensate for the convergence.

FIG. 1 shows a perspective view of a deflection yoke. A major section of the deflection yoke 1 includes a saddle-shaped horizontal deflection coil 2, a toroidal vertical deflection coil 3, a core 4 and a separator 5.

FIGS. 2A and 2B show the vertical deflection coil 3 which forms a pincushion magnetic field on the screen side and an intensified barrel magnetic field on the electron gun side. FIG. 2A is a perspective view and FIG. 2B is a front view. A feature of the vertical deflection coil 3 resides in that a winding angle .phi..sub.2 of a coil 6, wound on the core 4, at a larger opening 4a located on the screen side is smaller than a winding angle .phi..sub.1 at a smaller opening 4b located on the electron gun side. A drawback of this vertical deflection coil 3 resides in that a wire 7 is apt to slip on the surface of the core 4 and hence it is difficult to attain proper winding angles .phi..sub.1 and .phi..sub.2 because the wire 7 of the coil 6 wound at positions having larger winding angles .phi..sub.1 and .phi..sub.2 is wound obliquely to the core 4.

In the vertical deflection coil used for a picture tube having a large pincushion distortion such as a wide deflection angle picture tube, e.g. 90.degree. deflection picture tube, the winding angle .phi..sub.1 of more than 150.degree. and the winding angle .phi..sub.2 of approximately 80.degree. are required. Therefore, the wire 7 wound at the position of the winding angle .phi..sub.1 is especially apt to slip. It is, therefore, necessary to form the magnetic field on the electron gun side into an intensified barrel field without increasing the winding angle .phi..sub.1 at the opening 4b located on the electron gun side to over 150.degree..

It is an object of the present invention to provide a deflection yoke having means for producing an intensified barrel magnetic field without materially increasing a winding angle at a smaller opening.

It is another object of the present invention to provide a deflection yoke in which a wire wound at a large winding angle position does not slip on a surface of a core.

The deflection yoke in accordance with the present invention comprises a vertical deflection coil having a smaller winding angle at a larger opening than a winding angle at a smaller opening, and a magnetic material piece disposed inside the vertical deflection coil. The deflection yoke of the present invention further includes a core having its end surfaces deformed or auxiliary ring for locking the wire. The deformed end surfaces of the core or the auxiliary ring are notched in sawtooth shape to prevent the wire of the vertical deflection coil from slipping.

When the magnetic material piece is disposed inside the vertical deflection coil, the shape of the vertical deflection magnetic field changes. Since the lines of magnetic force around the magnetic material piece pass in the body of the magnetic material piece or attracted thereto, the barrel magnetic field is further enhanced. Where the barrel magnetic field is enhanced, the pincushion magnetic field may be formed on the screen side. Accordingly, the pincushion distortion can be relieved.

If the end of the end surface of the core is normal to the wire of the vertical deflection coil, a force acting on the wire is normal to the end of the end surface and the slip of the wire on the end surface is prevented. The core of the deflection yoke of the present invention has its end surfaces notched in the sawtooth shape and the ends of the notched end surfaces are arranged to be normal to the wire of the vertical deflection coil, or the auxiliary ring having sawtooth-notched end surfaces is disposed over the end surfaces of the core. Consequently, the wire wound at the large winding angle position is prevented from slipping on the surface of the core.

FIG. 1 is a perspective view of a prior art deflection yoke.

FIG. 2A is a perspective view of a vertical deflection coil of the prior art.

FIG. 2B is a front view of the vertical deflection coil shown in FIG. 2A.

FIG. 3 is a front view of a deflection yoke of the present invention.

FIG. 4 is a sectional view of the deflection yoke of the present invention.

FIG. 5 shows a distribution graph of lines of magnetic force of a barrel magnetic field.

FIG. 6 shows a graph illustrating shapes of a pincushion magnetic field and a barrel magnetic field.

FIG. 7 is a side elevational view of a vertical deflection coil having an auxiliary ring of sawtooth shape.

FIG. 8 is a side elevational view of a vertical deflection coil wound on a core having its end surfaces deformed into sawtooth shape.

The preferred embodiments of the present invention will now be explained. Referring to FIG. 3, a deflection yoke 20 of the present invention includes a magnetic material piece 8 of iron or permaloy plate of rectangular or pedestal shape disposed inside a coil 6 of a vertical deflection coil 3. The magnetic material piece 8 is attached by bond or the like at a position closer to a smaller opening 4b in an inside of the coil 6, being separated from a larger opening 4a by 1/2-3/4 of a full distance between both openings. The width l.sub.1 of the magnetic material piece 8 is approximately 1/5-1/2 of the distance from the larger opening 4a of the vertical deflection coil to the smaller opening 4b. The length of the magnetic material piece 8 is chosen such that an angle .phi..sub.3 looking into the magnetic material piece 8 from a center 0 is approximately 30.degree.-70.degree. C. By this magnetic material piece 8, the magnetic field on the side of the smaller opening 4b is formed into an intensified barrel field. In FIG. 3, a separator 5 is not shown. FIG. 4 shows a side sectional view of the deflection yoke 20 of the present invention, which clearly shows that the magnetic material piece 8 is attached to the vertical deflection coil 3 on the side of the smaller opening 4b. The magnetic material piece 8 may be attached to a horn-shaped portion 5b of the separator 5 instead of the vertical deflection coil 3, at a position close to a smaller opening 5a of the separator 5. In this case, a similarly intensified barrel field to that produced when it is attached to the vertical deflection coil 3 can be formed.

FIG. 5 shows a distribution graph of the lines of magnetic flux in the barrel magnetic field formed by the magnetic material piece 8, as looked from the larger opening side. The lines of magnetic force shown by dotted lines show lines of magnetic flux in the absence of the magnetic material piece 8 and the solid lines of magnetic flux show lines of magnetic flux in the presence of the magnetic material piece 8. Since the dotted lines of magnetic flux are altered to the solid lines of magnetic flux, the barrel magnetic field is enhanced.

FIG. 6 shows shapes of the pincushion magnetic field and the barrel magnetic field, in which an abscissa represents a center axis z of the deflection yoke 20 shown in FIG. 4. A strength B of the vertical magnetic field in the deflection yoke is generally expressed by:

where B.sub.o is a strength of the magnetic field at any point on the z-axis and represents a strength of magnetic field in x-axis direction normal to the plane of drawing. A strength of magnetic field at a position displaced in y-axis direction from that point on the z-axis which assumes the magnetic field strength B.sub.o is given by the magnetic field strength B. B.sub.2 is a constant. An ordinate in FIG. 6 represents B.sub.2 /B.sub.o. If B.sub.2 /B.sub.o >0, the pincushion magnetic field is formed, if B.sub.2 /B.sub.o =0, a uniform magnetic field is formed, and if B.sub.2 /B.sub.o >0, the barrel magnetic field is formed. In FIG. 6, a solid line 16 shows a shape of the magnetic field in the presence of the magnetic material piece 8, and a broken line shows a shape of the magnetic field in the absence of the magnetic material piece 8. The z-axis of FIG. 6 corresponds to the z-axis shown in FIG. 4. It is seen from FIG. 6 that when the magnetic material piece 8 is attached, the barrel magnetic field is enhanced on the smaller opening side. As a result, the winding angle .phi..sub.1 may be in the order of 150.degree. and need not be more than 150.degree..

Referring to FIG. 7, in the deflection yoke 20 of the present invention, there are provided auxiliary rings 11a and 11b on end surfaces 4c and 4d of the core 4 to prevent the wire 7 of the vertical deflection coil 3 from slipping on the end surfaces 4c and 4d of the core 4. When the wire 7 intersects a center line 18 with an angle .theta..sub.3, end surfaces of the auxiliary rings 11a and 11b are divided into small areas 12 and 13 in sawtooth shape with the small areas 12 and 13 intersecting a plane normal to the center line at angles of .theta..sub.4 and .theta..sub.5, respectively. When the angles .theta..sub.4 and .theta..sub.5 are equal to the angle .theta..sub.3, tensile force acting on the wire 7 is normal to the small areas 12 and 13 and hence the wire 7 does not slip.

In FIG. 8, the wire 7 of the vertical deflection coil 3 is wound on a core 24 having its end surfaces 4c and 4d deformed into sawtooth shape. The end surfaces 4c and 4d of the core 24 have small areas 14 and 15 formed in sawtooth shape, like in the case of the auxiliary rings 11a and 11b shown in FIG. 7. The wire 7 wound on the end surfaces 4c and 4d is prevented from slipping by the small areas 14 and 15 by the same reason described above in connection with the auxiliary rings of FIG. 7.

In the deflection yoke, the overall magnetic field spreading from the smaller opening on the electron gun side to the larger opening on the screen side influences the convergence, but the pincushion distortion is largely influenced by the magnetic field on the larger opening side. This is because the distance between the electron beam and the deflection coil when the electron beam is deflected is shorter on the larger opening side than on the electron gun side, and the electron beam on the larger opening side of the deflection coil travels through curved ends of the lines of magnetic flux so that the magnetic field on the larger opening side largely influences the pincushion distortion. It is seen from the above that the magnetic field distribution necessary to simultaneously compensate for both the nonconvergence and the pincushion distortion at the left and right edge of the screen only by the deflection yoke, is the vertical deflection magnetic field which forms the pincushion magnetic field on the larger opening side and the barrel magnetic field on the smaller opening side. Thus, the deflection yoke of the present invention can simultaneously compensate for both the misconvergence and the pincushion distortion at the left and right edges of the screen.

As described hereinabove, in accordance with the deflection yoke of the present invention, in order to form different shapes of magnetic field on the larger opening side and the smaller opening side, that is, in order to form the pincushion magnetic field on the larger opening side and form the barrel magnetic field on the smaller opening side, the winding angle of the vertical deflection coil at the larger opening is changed from that at the smaller opening, that is, the winding angle of the vertical deflection coil at the smaller opening is made larger than that at the larger opening. Furthermore, the magnetic material piece is disposed inside the vertical deflection coil to enhance the barrel magnetic field. As a result, the deflection yoke of the present invention can compensate for both the misconvergence and the pincushion distortion at the left and right edges of the screen.

Furthermore, the deflection yoke of the present invention includes a core having its end surfaces formed in sawtooth shape or auxiliary rings having sawtooth-shaped end surfaces. Accordingly, the wire of the vertical deflection coil is prevented from slipping on the end surfaces of the core although the wire of the vertical deflection coil is wound at the smaller opening with a large winding angle.