Cathode ray tube with convex interior walls for added stability

Details Cathode ray tube with convex interior walls for added stability Cathode ray tube with convex interior walls for added stability

1999-02-10

2001-07-03

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Shadow mask, support or shield

C445S030000

Reexamination Certificate

active

06255766

ABSTRACT:

BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a cathode ray tube (CRT) and more particularly, to a cathode ray tube capable of effectively deflecting electron beams and having increased strength against external stress.
(b) Description of the Related Art
A CRT is a device for displaying images on a screen by vertically and horizontally deflecting electron beams generated from an electron gun and landing the deflected electron beams onto the phosphor layers formed on the screen. The deflection of the electron beam is controlled by a deflection yoke which is mounted on an exterior surface of a funnel of the CRT and forms vertical and horizontal magnetic fields. CRTs are generally employed for color televisions(TVs), monitors and high definition televisions(HDTV). And with the increasing use of the CRTs, there is a need to reduce the length of the CRT for increasing the brightness of the displayed image and for reducing the size of the final products, such as TVs, monitors and HDTVs.
In a CRT with reduced length, the electron beams should be deflected with wider-angles, and the deflection frequency and current supplied to the deflection yoke should be increased for the wider-angle deflections of the electron beams. As the deflection frequency and current increase, the deflection magnetic fields tend to leak to the outside of the cathode ray tube and the power consumption increases.
In order to decrease the magnetic field leakage, a compensation coil is generally mounted with the deflection yoke. When, however, the compensation coil is employed, the power consumption of the cathode ray tube further increases. Alternatively, in order to decrease the deflection power and the magnetic field leakage, it is conventionally preferable to decrease the neck diameter of the cathode ray tube and the outer diameter of the funnel near the neck side on which the deflection yoke is mounted, so that the deflection field effectively acts on the electron beams. When the neck diameter simply decreases, there are disadvantages that the resolution of the image deteriorates due to the reduced diameter of the electron gun, and the outer electron beams are likely to bombard the inner wall of the funnel, and thus not properly land on the phosphor layer of the screen.
In order to solve these problems, U.S. Pat. No. 3,731,129 discloses a funnel having a wider peripheral portion sealed to the periphery of the panel, and a deflection portion whose cross-sectional configuration gradually varies from a shape, substantially similar to that of the rectangular image produced on the panel, to a circular shape. Thereby, the vertical and horizontal coils of the deflection yoke are closely located to the passage of the electron beams, and deflect the electron beams with reduced deflection power and without the electron beams bombarding the inner wall of the funnel.
However, in U.S. Pat. No. 3,731,129, the configuration of interior surface of the funnel was not considered in designing the funnel having the rectangular cross section. Therefore, the electron beams are not effectively deflected, and the strength of the funnel against external pressure is not satisfactory.
To overcame the shortcoming, Japanese Laid-Open patent 10-154472 discloses the funnel of a cathode ray tube having a cross-section shown in FIG.
8
. As shown in
FIG. 8
, the funnel yoke part
22
has a maximum diameter along a direction other than the horizontal axis(X) and the vertical axis(Y), for example, a rectangular section. In
FIG. 8
, the Pi(&thgr;) represents a point at which the interior surface of the yoke part
22
and a linear line drawn from the tube axis with an angle &thgr; are met. The Piv(&thgr;) and Pih(&thgr;) represent distances from the point Pi(&thgr;) to the horizontal axis(X) and the vertical axis(Y), respectively. As shown in
FIG. 8
, the interior surface of the yoke part
22
is designed so that the Piv(&thgr;) and Pih(&thgr;) are functions of &thgr; which non-linearly increase or decrease. Therefore, the Piv(&thgr;) and Pih(&thgr;) change with at least one maximum value, and therefore the interior surface of the yoke part
22
can be convexed to the tube axis. However, the Japanese Laid-Open patent 10-154472 designs the interior surface of the yoke without considering the strength of the cathode ray tube against the external pressure and the trajectories of the electron beams. Therefore, it is required to develop the optimum configuration of the interior surface for increasing the strength of the cathode ray tube and effective deflection of the electron beams.
SUMMARY OF THE INVENTION
The present invention is directed to a cathode ray tube which substantially obviates the limitations and disadvantages of the related art.
An object of the present invention is to provide a cathode ray tube capable of effectively deflecting electron beams, and thereby reducing the deflection power consumption and having increased strength against external stress.
Another object of the present invention is to provide a cathode ray tube particularly suitable for flat-panel cathode ray tube.
To accomplish these and other advantages, the cathode ray tube according to the present invention is comprised of a rectangular panel on which a phosphor screen is formed, a cylindrical neck in which an electron gun is disposed, and a funnel formed contiguous to the panel. The funnel includes a cone part whose interior surface has a circular section at the position contiguous to the neck. The circular section is changed from the neck side to the panel side to have a non-circular section having a maximum diameter along a direction other than the horizontal and vertical axis, and perpendicular distances from a funnel axis to interior surface of the cone part are non-monotonously or non-linearly increases or decreases, and the vertical interior surface is convexed to the funnel axis with meeting the following condition,
&Dgr;H/rd<0.16
where rd represents a distance from the funnel axis to the interior surface of the funnel at the diagonal direction, and AH represents a distance from a vertical line which connects the neighboring two corner points formed at the convexed interior surface to the top of the convexed interior surface.
In addition, the horizontal interior surface can be convexed to the funnel axis with fulfilling the following condition,
&Dgr;V/rd<0.34
where &Dgr;V represents a distance from a horizontal line which connects the neighboring two corner points formed at the convexed interior surface to the top of the convexed interior surface.
The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims as well as the appended drawings.


REFERENCES:
patent: 3731129 (1973-05-01), Tsuneta et al.
patent: 5929559 (1999-07-01), Sano et al.
patent: 10-154472 (1998-06-01), None

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