Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Electron or ion beam deflecting type
Reexamination Certificate
2003-03-27
2004-12-28
Barrera, Ramon M. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Electron or ion beam deflecting type
C313S440000
Reexamination Certificate
active
06836200
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to convergence yokes which are fixed to a cathode-ray tube of projection televisions and the like and produce two-pole magnetic field for deflecting an electron beam in a horizontal direction or a vertical direction.
BACKGROUND OF THE INVENTION
With reference to
FIG. 1
, a convergence yoke comprises a ring core
1
having a horizontal coil
2
and a vertical coil
3
wound therearound. A horizontal convergence correction circuit
4
is connected to the horizontal coil
2
. A vertical convergence correction circuit
5
is connected to the vertical coil
3
. With the convergence yoke, producing uniform magnetic field within the electron beam passing area is required for suppressing the electron beam distortion caused by the deflection to improve focus performance.
It is proposed, according to the literature “SEMINAR M-4 1991 SID ‘Deflection And Convergence Technology’ Basab B. Dasgupta, Sony Corporation, San Diego, Calif.”, that winding density distribution of the coil wherein the winding angle &thgr; from the reference axis of the ring core is a variable is in proportion to cos &thgr;, whereby the magnetic field within the ring core is made uniform.
Further, Japanese Patent No. 3039988 proposes a convergence yoke wherein ratio A
3
/A
1
of a coefficient (Ak coefficient) when winding distribution is expanded in Fourier series is 0.13 to 0.50 in order to render the magnetic field strength distribution uniform.
However, with use of computer simulation, the present inventor has calculated the magnetic field strength distribution of the horizontal coil of the convergence yoke wherein the winding density distribution of the coil is in proportion to cos &thgr;, revealing that contour lines of the magnetic field strength in the ring core are shaped in oblong ellipses as shown in
FIG. 20
, and particularly the magnetic field strength has nonuniformity on an upper and lower portions of the electron beam passing area. Thus the electron beam has a gross distortion of a circular shape in cross section as shown in FIG.
24
(
a
).
Furthermore, the present inventor, with use of computer simulation, has calculated the magnetic field strength distribution of the horizontal coil of the convergence yoke wherein ratio A
3
/A
1
of Ak coefficient is 0.13 to 0.50, and winding is provided uniformly in the range of 15° to 40° in winding angle &thgr; from the reference axis (the construction according to claim
2
of the patent stated above), with the result that the magnetic field strength is not uniform at each of four corners as shown in FIG.
21
.
Further, in the case where the winding range of the convergence yoke is shifted 0.5°, i.e. the winding is provided uniformly in the range of 15.5° to 40.5° in winding angle &thgr; from the reference axis, the present inventor calculates the magnetic field strength distribution of the horizontal coil with use of computer simulation, to obtain the magnetic field strength distribution shown in FIG.
22
. In this case whereas ratio A
3
/A
1
of Ak coefficient is 0.1 departing from the scope of the invention of the patent stated above, the magnetic field strength distribution obtained is slightly more uniform than that shown in FIG.
21
. Accordingly, it is not always true that ratio A
3
/A
1
of Ak coefficient is most preferably in the range of 0.13 to 0.50.
Further, with use of computer simulation the present inventor calculates the magnetic field strength distribution of the horizontal coil of the convergence yoke wherein the winding is provided uniformly in the range of 10° to 30° in winding angle &thgr; from the reference axis (the construction according to claim
3
of the patent stated above), to obtain the magnetic field strength distribution shown in FIG.
23
. As illustrated, the magnetic field strength is extremely uneven, causing the electron beam to be distorted grossly as shown in FIG.
24
(
b
).
Furthermore, even if ratio A
3
/A
1
of Ak coefficient is in the range of 0.13 to 0.50, the magnetic field strength distribution varies greatly within this range, so that in designing the convergence yoke the coil performance cannot be determined unless the deformation caused by the deflection of the electron beam is actually measured. Presumably, the reason is that the current density distribution represented by the sum of two terms, A
1
and A
3
of Fourier series, is greatly shifted from the actual current density distribution, as shown in
FIG. 25
, so that the coil performance cannot be determined only by ratio A
3
/A
1
of Ak coefficient.
As described above, prior art has the problem that the winding distribution having the uniform magnetic field strength cannot be determined uniquely.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a convergence yoke having more uniform magnetic field strength than conventionally.
A convergence yoke embodying the present invention is characterized in that the convergence yoke comprises a ring core having a plurality of coils wound therearound, and winding density distribution of each of the coils wherein winding angle &thgr; from a reference axis of the ring core is a variable is in proportion to cos
2
&thgr;.
As compared with a conventional convergence yoke wherein winding density distribution of a coil is in proportion to cos &thgr;, the convergence yoke of the invention is greatly reduced in density as angle &thgr; is increased as shown in
FIG. 5
, so that an oblong ellipse of the magnetic field strength distribution shown in
FIG. 20
is extended upward and downward, rendering the magnetic field strength distribution shaped in concentric circles. As a result, the magnetic field strength distribution is uniform over electron beam passing area, and a cross section shape of the electron beams will not be grossly distorted owing to the deflection.
Stated specifically, the ring core
1
has wound therearound a horizontal coil
2
and a vertical coil
3
based on a horizontal coil reference axis
20
and a vertical coil reference axis
30
which are orthogonal to each other. Each of the two coils
2
,
3
has the winding density distribution described.
Further stated specifically, the plurality of coils each comprises a plurality of coil portions. Each of the coil portions is wound within a predetermined angle range wherein a winding center is in the range of 25° to 30° in winding angle &thgr; from the reference axis on each of quadrants of orthogonal coordinates, and has winding density distribution in proportion to cos
2
&thgr; within the angle range. According to the specific construction, the magnetic field strength distribution comprising diamond-shape contour lines is obtained, whereby the uniformity of the magnetic field strength becomes higher than conventionally.
Another convergence yoke of the present invention is characterized in that the yoke comprises a ring core having a plurality of coils wound therearoud, each of the coils comprises a plurality of coil portions, each coil portion is wound uniformly at a first winding density X
1
within a predetermined angle range (&thgr;s to &thgr;e) wherein a winding center is in the range of 25° to 30° in winding angle &thgr; from the reference axis on each of quadrants of orthogonal coordinates and is wound uniformly at a second winding density X
2
within an angle range (0 to &thgr;s) from 0° to the predetermined angle range in winding angle &thgr;, ratio of the second winding density X
2
relative to the first winding density X
1
is represented by an expression given below.
X
2
/
X
1
=((cos
2
&thgr;s−cos
2
&thgr;e)/2 cos
2
&thgr;s)±0.1
The convergence yoke described above has approximately uniform magnetic field strength distribution which is equivalent to that of a convergence yoke having winding density distribution in proportion to cos
2
&thgr; within the predetermined angle range (&thgr;s to &thgr;e) wherein a winding center is in the range of 25° to 30° in winding angle &thgr; from the reference axis.
As described above, with the convergence yoke of
Armstrong Kratz Quintos Hanson & Brooks, LLP
Barrera Ramon M.
Sanyo Electric Co,. Ltd.
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