Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-09-25
2002-09-10
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S407000, C313S408000, C313S313000
Reexamination Certificate
active
06448702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a cathode ray tube, more particularly to a color cathode ray tube, and most particularly to an internal magnetic shield which is a part of a color cathode ray tube.
2. Description of the Related Art
FIGS. 1
to
4
illustrate conventional color cathode ray tubes. Hereinbelow is explained an internal magnetic shield as a part of a color cathode ray tube.
FIG. 1
is a longitudinal cross-sectional view of a conventional shadow-mask type color cathode ray tube
700
.
The illustrated color cathode ray tube
700
is comprised of an electron gun
709
emitting electron beams
710
, a funnel
708
which has a length in a direction of a longitudinal center line of the color cathode ray tube
700
and is open at one end and in which the electron gun
709
is located, a face panel or a screen
707
which is open at one end and connected to the funnel
708
such that the funnel
708
and the face panel
707
define a closed space therein, a fluorescent film
706
adhered onto an inner bottom of the face panel
707
, an internal magnetic shield
701
which is located in the space and which is open at opposite ends such that electron beams
710
emitted from the electron gun
709
pass therethrough and reach the fluorescent film
706
, a mask frame
703
fixedly adhered to the internal magnetic shield
701
and extending towards the face panel
707
from a distal end of the internal magnetic shield
701
, a shadow mask
702
located in the space in facing relation with the fluorescent film
706
and supported by the mask frame
703
, stud pins
705
arranged on an inner wall of the face panel
707
, hook springs
704
each fixed at one end on an outer wall of the mask frame
703
and detachably engaged at the other end to the stud pin
705
, and a deflecting yoke
711
located around the funnel
708
.
FIG. 2
is a backward perspective view of the internal magnetic shield
701
, the shadow mask
702
and the mask frame
703
with portions broken away for clarity.
As illustrated in
FIGS. 1 and 2
, the internal magnetic shield
701
has a flange portion
701
a
at one end closer to the face panel
707
, and the mask frame
703
also has a flange portion
703
a
at one end remoter from the face panel
707
. The flange portions
701
a
and
703
a
are fixed to each other, and hence, the internal magnetic shield
701
and the mask frame
703
are fixed to each other such that the mask frame
703
extends towards the face panel
707
from the internal magnetic shield
701
.
As is obvious in view of
FIGS. 1 and 2
, a distal end or the flange portion
701
a
of the internal magnetic shield
701
is located remoter from the face panel
707
than the shadow mask
702
, that is, located closer to the electron gun
709
than the shadow mask
702
.
FIG. 3
is a longitudinal cross-sectional view of a conventional aperture grill type color cathode ray tube
900
.
The illustrated color cathode ray tube
900
is comprised of an electron gun
909
emitting electron beams
910
, a funnel
908
which has a length in a direction of a longitudinal center line of the color cathode ray tube
900
and is open at one end and in which the electron gun
909
is located, a face panel or a screen
907
which is open at one end and connected to the funnel
908
such that the funnel
908
and the face panel
907
define a closed space therein, a fluorescent film
906
adhered onto an inner bottom of the face panel
907
, an internal magnetic shield
901
which is located in the space and which is open at opposite ends such that electron beams
910
emitted from the electron gun
909
pass therethrough and reach the fluorescent film
906
, a mask frame including first frames
903
B fixed to the internal magnetic shield
901
and second frames
903
A fixed to the first frames
903
B, an aperture grill
902
located in the space in facing relation to the fluorescent film
906
and supported by the second frames
903
A, stud pins
905
arranged on an inner wall of the face panel
907
, hook springs
704
each fixed at one end on an outer wall of the second frame
903
A and detachably engaged at the other end to the stud pin
905
, and a deflecting yoke
911
located around the funnel
908
.
FIG. 4
is a backward perspective view of the internal magnetic shield
901
, the aperture grill
902
, the first frames
903
B and the second frames
903
A with portions broken away for clarity.
As illustrated in
FIGS. 3 and 4
, the internal magnetic shield
901
has a flange portion
901
a
at one end closer to the face panel
907
. The first frames
903
B are fixed on the flange portion
901
a
, and the second frames
903
A are fixed across the first frames
903
B in a direction perpendicular to a direction in which the second frames
903
B extend.
As is obvious in view of
FIGS. 3 and 4
, a distal end or the flange portion
901
a
of the internal magnetic shield
901
is located remoter from the face panel
907
than the aperture grill
902
, that is, located closer to the electron gun
909
than the aperture grill
902
.
The conventional color cathode ray tubes
700
and
900
illustrated in
FIGS. 1
to
4
are designed to include the internal magnetic shields
701
and
901
to prevent that the electron beams
710
and
910
deflected by the deflecting yokes
711
and
911
in a predetermined direction are further deflected by external magnetic field such as earth magnetism in a wrong direction. To this end, the internal magnetic shields
701
and
901
are generally designed to be composed of ferromagnetic substance and to magnetically shield the electron beams
710
and
910
by surrounding orbits of the electron beams
710
and
910
to prevent the electron beams
710
and
910
from being unpreferably influenced by external magnetic fields.
As mentioned earlier, the distal ends of the internal magnetic shields
701
and
901
in the conventional color cathode ray tubes
700
and
900
are located behind the shadow mask
702
and the aperture grill
902
, that is, located remoter from the face panels
707
and
907
than the shadow mask
702
and the aperture grill
902
. As a result, both a space between the shadow mask
702
and the fluorescent film
706
and a space between the aperture grill
902
and the fluorescent film
906
are not magnetically shielded.
Accordingly, in the shadow mask type color cathode ray tube
700
illustrated in
FIGS. 1 and 2
, the electron beams
710
are influenced by external magnetic fields in a space between the shadow mask
702
and the fluorescent film
706
, and hence, deflected in a wrong direction. As a result, the fluorescent film
706
receives the electron beams
710
at a location other than a desired location, and hence, a color other than a desired color is produced from the fluorescent film
706
.
In the aperture grill type color cathode ray tube
900
illustrated in
FIGS. 3 and 4
, since the first and second frames
903
A and
903
B have almost no magnetic shielding effects, the electron beams
910
are influenced by external magnetic fields in a space between the distal ends or flange portion
901
a
of the internal magnetic shield
901
and the fluorescent film
906
. As a result, the electron beams
910
are deflected in a wrong direction, and the fluorescent film
906
receives the electron beams
910
at a location other than a desired location, and hence, a color other than a desired color is produced from the fluorescent film
906
.
Since the aperture grill type color cathode ray tube
900
has a wider space not magnetically shielded than the shadow mask type color cathode ray tube
700
, the color cathode ray tube
900
is more harmfully influenced by external magnetic fields than the color cathode ray tube
700
.
A conventional color cathode ray tube was designed to additionally include an external magnetic sensor, a landing compensation coil and so on so as to cancel influence exerted by external magnetic fields. As a result, the conventional color cathode ray tube was accompanied with prob
Kamada Akihiro
Morohashi Takashi
McGinn & Gibb PLLC
NEC Corporation
Patel Vip
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