Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2002-12-24
2004-04-27
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C220S00210A, C220S00230A
Reexamination Certificate
active
06727641
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to an improved technology for a pyramid-shaped yoke portion that is formed to be continuous to a body portion of a funnel for a cathode ray tube (CRT).
2. Description of Related Art
As is well known, a cathode ray tube mainly comprises a panel having a substantially rectangular image display portion and a funnel that is sealed to the panel to allow electron beams to pass therein. The funnel comprises a large opening portion with a substantially rectangular shape, a small opening portion with a substantially circular shape to which a cylindrical neck tube for installing an electron gun therein is connected, a substantially funnel-shaped body portion, and a yoke portion, on which a deflection yoke is externally mounted, being continuous to the body portion at the side of the small opening portion.
In the cathode ray tube with the above elements, because the deflection yoke is a large consuming source of electric power, it is very important to reduce the consumption of electricity of the deflection yoke to save and reduce the total consuming power of the cathode ray tube. To reduce the consuming power of the deflection yoke, an approach is known where the neck tube of the funnel can be shrunk to a small diameter and the outer diameter of the yoke portion on which the deflection yoke is mounted is reduced.
However, because the electron beams, which are emitted from the electron gun inside the neck tube, pass nearby the inner wall of the yoke portion, as the outer diameter of the neck tube or the yoke portion is reduced, the electron beams, which directs toward the diagonal portion that forms a maximum deflection angle, might collide with the inner wall of the yoke portion. As a result, there is a problem that a good image cannot be obtained.
In order to solve such a problem, a pyramid shape, which changes gradually from circular shape to a substantially rectangular shape in the direction from the neck tube side to the panel side, has been practically used. If the outside of the yoke portion is the pyramid shape, the diameters in the major and minor axis directions of the deflection yoke can be reduced, and therefore, the deflection coils corresponding to the major and minor axis directions can approach the electron beams. In this way, the electron beams can be more efficiently deflected, and advantageously, the deflection power can be reduced.
Similarly, in order to keep the electron beams, which directs toward the diagonal portion of the inner diameter of the yoke portion, from colliding with the internal wall thereof, a pyramid shape, which changes gradually from circular shape to a substantially rectangular shape in the direction from the neck tube side to the panel side, has been practically used.
In this situation, for example, referring to Japanese Laid Open No. 11-120940 or No. 11-176355, when the inner face of the yoke portion is formed with a pyramid shape, the diagonal portion is formed with an arc-shaped curved portion in consideration of the moldability or the strength. The curved portions at the major and minor axis sides are circular arc shapes with substantially the same radii with respect to the diagonal axis as a reference. It is usual that the shape of the inner face of the yoke portion is substantially corresponding to an ideal passing area of the electron beams.
The diagonal axes of the yoke portion are generally set corresponding to a passing area of the electron beams.
However, distortions often occur in the actual passing area of the electron beams due to the accuracy of the deflection yoke and the like. Therefore, the diagonal axis of the yoke portion, in fact, has a directional deviation with respect to the passing area of the electron beams.
In the cathode ray tube having the above characteristic, if the curved portion formed at the diagonal portion of the yoke portion has arc shapes with substantially the same curvature radii at the major axis side and the minor axis side with respect to the diagonal axis as a reference, the electron beams with a maximum deflection angle will collide with a partially curved portion at any one side thereof. Therefore, a good image cannot be obtained.
In order to solve this problem, as shown in
FIG. 8
, a diagonal inner-face curved portion
8
and a diagonal outer-face curved portion
9
of a diagonal portion
7
are expanded by a single circular arc, while a constant distance between the diagonal portion
7
of the yoke portion
6
and the tube axis is maintained. However, the design and manufacture of a mold for the funnel, the design and manufacture for the deflection yoke, and a variety of other portions related to producing the cathode ray tube have to be completely changed. Thus, a lot of trouble or effort is caused and the cost becomes large.
Alternatively, to thin the thickness of the yoke portion entirely has also been considered. But, if the thickness is made too thin, there are problems in molding or strength, so that there is a limitation to thinning the thickness of the yoke portion and this strategy cannot be an effective solution.
SUMMARY OF THE INVENTION
According to the foregoing description, it is an object of the present invention to provide a funnel for a cathode ray tube, wherein by simply and effectively improving a diagonal portion of a yoke portion, it is not necessary to basically modify the mold or the deflection yoke, etc. and therefore, the electron beams can be suitably kept from colliding with the yoke portion, so as to be able to obtain a good image.
In order to achieve the object, the present invention provides a funnel for a cathode ray tube having a large opening portion with a substantially rectangular shape, a small opening portion with a substantially circular shape to which a cylindrical neck tube is connected, a funnel-shaped body portion continuous from the large opening portion, and a pyramid-shaped yoke portion continuous from the body portion to the small opening portion, comprising a diagonal inner-face curved portion is formed on an inner face of a diagonal portion of the yoke portion, wherein the diagonal inner-face curved portion comprises a partially inner-face curved portion at a major axis side and a partially inner-face curved portion at a minor axis side, both of which are imaginarily divided to each other with respect to a diagonal axis as a reference, and wherein at least one of the partially inner-face curved portions at the major axis side and the minor axis side swells to the outward side.
The term “swells to the outward side” means that at a cross-sectional plane perpendicular to the tube axis, at least one of the partially inner-face curved portions swells to the outward side (to the outer-face side of the yoke portion) than an imaginary extension line that extends along the inner face of the major side or the minor side, which form the yoke portion, toward the diagonal axis side. Therefore, when the inner faces of the minor side and the major side are respectively formed by circular arcs, the term “swells to the outward side” means that at least one of the partially inner-face curved portions swells to the outward side than an imaginary extension line of the circular arc. Moreover, in detail, the term “swells to the outward side” means that with respect to an imaginary reference curved line (a conventional curved line) whose curvature varies slowly from a central point of the inner face of at least one of the major axis side and the minor axis side toward the diagonal axis, the partially inner-face curved portion of at least one of the major axis side and the minor axis side swells to the outward side due to the changing of the curvature thereof greater than that of the imaginary reference curved line in the halfway of the imaginary reference curved line. In addition, when one of the partially inner-face curved portions of the major axis side and the minor axis side swells to the outward side, the one partially inner-face curved portion swells to the outward side relative to
Nippon Electric Glass Co. Ltd.
Patel Ashok
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