Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Electron or ion beam deflecting type
Reexamination Certificate
2001-08-29
2003-04-08
Barrera, Ramon M. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Electron or ion beam deflecting type
C335S302000, C335S303000, C264S328800, C264S429000
Reexamination Certificate
active
06545578
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to deflection yokes for deflecting the electron beam to be emitted by a cathode-ray tube.
BACKGROUND OF THE INVENTION
With reference to FIGS.
10
(
a
) and
10
(
b
), two annular centering magnets
7
,
7
are mounted on a deflection yoke
6
at its neck end. The centering of an electron beam can be adjusted by rotatingly moving the magnets
7
,
7
.
The centering magnet
7
is molded in an annular form as shown in
FIG. 11
from a resin containing a finely divided magnetic material mixed therewith (hereafter referred to as the “magnetic resin”). The magnet is magnetized to an N pole
73
and an S pole
74
at two portions which are displaced from each other by 180 degrees about the center axis of the annular form to serve as a two-pole magnet. The centering magnet
7
has a pair of adjusting knobs
70
,
71
projecting from the two portions where the N pole
73
and the S pole
74
are provided. The annular form of the centering magnet
7
is symmetrical about an extension (line E—E) of a diametrical line connecting the center point
75
of the N pole
73
to the center point
76
of the S pole
74
, and is also symmetrical about an extension (line F—F) of a diametrical line orthogonal to the line E—E.
Examples of useful finely divided magnetic materials are those of the alnico (Al—Ni—Co) type, ferrite type or rare-earth elements. Finely divided alnico magnetic materials are widely used from the viewpoint of magnetic intensity, temperature characteristics, cost and productivity.
However, the conventional centering magnet
7
prepared from a magnetic resin containing a finely divided alnico magnetic material mixed therewith has the problem that the images displayed on a picture tube of electron beam are low in resolution because of an uneven distribution of the finely divided magnetic material.
FIG. 12
shows the distribution of finely divided magnetic material in the centering magnet
7
. The content of the magnetic material
31
is greater toward the N pole
73
and decreases toward the S pole
74
presumably because the finely divided alnico magnetic material is greater than ferrite magnetic materials in particle size.
In the molding step wherein the magnetic resin is used, the magnetic resin is poured into a mold
8
having an annular hollow portion
80
through a resin gate opening
81
thereof as shown in FIG.
13
and then divided into two resin streams along the annular form of the hollow portion
80
. The divided streams thereafter flow together. Consequently, the content of the finely divided magnetic material is small toward the resin gate opening
81
and increases at a confluent portion
79
shown in
FIG. 12
where the two resin streams meet, with the result that uneven magnetization occurs in the centering magnet
7
having the N pole
73
and the S pole
74
formed by magnetization, between the S pole (
74
) side having a small magnetic material content and the N pole (
73
) side with a great magnetic material content.
FIG. 14
shows a distribution of lines of magnetic force produced across the central aperture
78
of each of centering magnets
7
,
7
which are arranged in a pair as positioned in opposite relationship in polarity. As illustrated, lines of magnetic force emanating from the N pole
73
toward the S pole
74
are arranged concentrically on the N pole (
73
) side of high magnetic material content and dispersed on the S pole (
74
) side of low magnetic material content, thus spreading out from the N pole
73
toward the S pole
74
. Accordingly, the point of change of polarity from the N pole
73
to the S pole
74
on the centering magnet
7
is positioned closer to the N pole
73
than the line F—F, resulting in a difference between the distance from the N pole
73
to the point of polarity change and the distance from the S pole
74
to the point. When the two centering magnets
7
,
7
are superposed on each other as positioned in opposite relationship in polarity, the lines of magnetic force emanating from one of the magnets
7
,
7
will consequently intersect those from the other magnet as seen in FIG.
15
.
FIG. 15
shows that the two centering magnets
7
,
7
are positioned at an angle of zero relative to each other. When the relative angle is altered from this position, the lines of magnetic forces of the two magnets
7
,
7
combine, and the combined lines of magnetic force exert on the electron beam a magnetic force for the adjustment of centering (adjusting magnetic force). Even if the two centering magnets
7
,
7
are set in the position of relative angle of zero as shown in
FIG. 15
in the case where no adjustment is needed for centering, the distribution of the lines of magnetic forces of the magnets
7
,
7
is not symmetrical about the line F—F, and the magnets
7
,
7
therefore fail to offset each other in magnetic lines. As a result, the combined magnetic lines set up a four-pole residual magnetic field over the central apertures
78
,
78
of the two magnets
7
,
7
as indicated by allows in FIG.
16
.
Accordingly, the electron beam
9
having a circular cross section and passing through the central apertures
78
,
78
of the magnets
7
,
7
is expanded in one direction and contracted in other direction orthogonal to the direction by being magnetically acted on by the four-pole residual magnetic field to deform to an elliptical form in cross section. This impairs the performance of image focusing on the screen of the picture tube of electron beam to form images of low resolution.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a centering magnet adapted to eliminate the adjusting magnetic force when there is no need for centering adjustment, a deflection yoke provided with such centering magnets, and a process for producing the centering magnet.
The present invention provides a first centering magnet which is molded in an annular form from a magnetic resin, the centering magnet having two portions opposed to each other as displaced from each other by 180 degrees about a center axis of the annular form thereof and magnetized to an N pole and an S pole respectively, the content of finely divided magnetic material varying circumferentially of the annular form, the distribution of the content being symmetrical about a straight line (line B—B) orthogonal to a straight line (line A—A) through a center point of the N pole and a center point of the S pole.
The invention provides a first deflection yoke having two first centering magnets mounted thereon in combination.
The distribution of the content of the finely divided magnetic material in the first centering magnet of the invention is symmetrical about the line B—B, so that the distribution of the lines of magnetic force emanating from the N pole toward the S pole is similarly symmetrical about the line B—B.
With the first deflection yoke of the invention, the distribution of the lines of magnetic force emanating from the N pole toward the S pole in each centering magnet is symmetrical about the line B—B, so that when the two centering magnets are superposed on each other as positioned in opposite relationship in polarity, the lines of magnetic forces emanating from one of the two magnets offset those of the other magnet, setting up no four-pole residual magnetic field due to the combination of magnetic lines. This eliminates the magnetic force for the adjustment of centering.
The present invention further provides a second centering magnet molded in an annular form from a magnetic resin, with a plurality of positions arranged symmetrically about a diametrical line of the annular form and each serving as the most upstream position for a flow of the resin for molding, the centering magnet being magnetized to an N pole and an S pole respectively at two portions intersecting the diametrical line or at two portions 90 degrees out of phase with the two portions respectively.
The invention provides a second deflection yoke having two second centering magnets mounted thereon in combination.
The plurali
Armstrong Westerman & Hattori, LLP
Barrera Ramon M.
Sanyo Electric Co,. Ltd.
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