Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2000-12-08
2003-03-11
Kim, Robert H. (Department: 2882)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S403000, C313S408000
Reexamination Certificate
active
06531812
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a shadow mask for a flat cathode ray tube and more particularly, to a shadow mask for a flat cathode ray tube capable of achieving the decrement of the phenomena of moire and the improvement of luminance and controlling a bridge shadow thereof.
DISCUSSION OF RELATED ART
Generally, a display device is made to provide information not in an audible manner but in a visible manner, such that it should be designed based upon the characteristics of the eyes of man. In other words, a determination standard for a quality of the display device is the eyes of man.
On the other hand, the eyes of the man can distinguish the difference of colors and brightness, and in case of scientifically explaining the capability of distinguishing the difference of brightness repeated regularly, two factors are used: an angular spatial frequency; and a modulation depth. In more detail, the angular spatial frequency factor is determined based upon the interval of the period repeated regularly and the viewing distance, and the modulation depth factor indicates the degree of the difference of brightness.
Furthermore, the eyes of man can distinguish the difference of brightness at a specific frequency band, even if the difference is negligibly small, but they fail to distinguish the difference of brightness at another specific frequency band, even if the difference is substantially large. This can be checked in FIG.
3
.
In this case, a vertical pitch of electron beams and a vertical pitch of a shadow mask, as commonly used, are positioned at a frequency band which is not sensitive to the eyes of man. Therefore, the respective vertical pitches are not sensed to the eyes of man, but their interaction enables the wavelength thereof to be extended to thereby form a new pattern that is sensitive to the eyes of man.
In other words, it is natural that the superposition of two waves having different periods from each other produces a wave having new period and amplitude. Such the principle of superposition appears in a color cathode ray tube which adopts a shadow mask and is deflected by a deflection yoke to execute a sequential scanning, which is called the phenomena of ‘moire’.
In order to remove the phenomena of moire appearing on the screen, on the other hand, a previously determined scanning manner is fixed and then, a vertical pitch of the shadow mask or spot shape and profile of the electron beams should be well designed. However, it is really difficult to design the electron beams capable of having the characteristics meeting the removal of the phenomena of moire in connection with various kinds of other characteristics.
Therefore, most of designers give their concentration on improving a quality of the shadow mask, and to analyze and design the shadow mask, Fourier series and Fourier transform are generally used.
The phenomena of moire mentioned in the present invention are the phenomena of raster moire appearing as the horizontally striped patterns on the screen.
On the other hand,
FIG. 1
shows the configuration of a general flat cathode ray tube.
As shown in
FIG. 1
, the general flat cathode ray tube includes: a panel glass
3
; a shadow mask
5
that is fixed on the reverse surface of the panel glass
3
in the state where a tension force is applied to a fixed rail (which is omitted in the drawing) by a frit glass and has a plurality of apertures of round or slot shape functioning to discriminate colors of the electron beams; a magnetic shield
6
that is secured on the inner surface of the panel glass
3
and serves to prevent the ways of the electron beams from being changed due to an external earth magnetic field or a leaking magnetic field; a funnel glass
4
that is fixed on the panel glass
3
by means of the frit glass and formed integrally with a neck portion on the rear portion thereof; an electron gun
1
that is sealed into the neck portion of the funnel glass
4
and emits the electron beams of R, G and B colors; and a deflection yoke
2
that is adapted to surround the outer peripheral surface of the neck portion and deflect the electron beams.
Now, an explanation of the construction and operation of each part provided in the general flat cathode ray tube will be discussed.
First, the electron gun
1
is composed of: a cathode that is made of a metal such as a carbonate, nickel and so on, for producing electrons; a heater that supplies a thermal energy to thereby lower the thermal energy of the carbonate of the cathode, with a result that the electron emission can be well carried out; a G
1
electrode that determines a beam spot size when the electron beams are focused on a screen; a G
2
electrode that regulates a voltage for drawing the electrons crowded in a cloud pattern around the cathode; a pre-focusing electrode that performs a pre-focusing for a bundle of electron beams emitted extensively from the cathode; a focusing electrode that serves as a main lens for enabling the electron beams to be focused on the screen in an accurate manner; and an accelerating electrode that accelerates the electrons such that the motion energy of the electrons can be great, thereby making the screen brighten.
The deflection yoke
2
is composed of: horizontal and vertical coils that are adapted to deflect the electron beams of the R, G and B colors horizontally and vertically; a ferrite core that is adapted to increase the efficiency of the magnetic force produced in the each coil and make the magnetic field positioned in the inside of the deflection yoke to thereby prevent the magnetic field from leaking; and a circuit terminal that is adapted to carry out a fine convergence for the three electron beams that have not been converged on the coils.
The panel glass
3
has thickness and curvature of a predetermined value or more, in order to have a vacuum intensity resistant to an atmospheric pressure, since the tube has an internal pressure of 10-7 torr approximating the vacuum state.
Additionally, the panel glass
3
is provided with R. G and B fluorescent materials and a black matrix (BM) which are spread on the internal surface thereof, for the purpose of visibly displaying desired information. An aluminum film is also formed on the fluorescent materials in a vacuum-evaporation manner for the purpose of enhancing the light emitting efficiency of the fluorescent materials and maintaining the voltage within the tube at a predetermined level. The funnel glass
4
into the neck portion of which the electron gun
1
is inserted and on the outer peripheral surface of the neck portion of which the deflection yoke
2
is inserted is spread with graphite as a conductive material on the internal surface thereof, such that the electrons are not affected by the external electric field. Therefore, the interior of the tube is made of a complete conduction film, thereby making the electric field thereof ‘0’.
The shadow mask
5
forms the plurality of apertures
7
function to discriminate R. G and B fluorescent material light emitting electron beams that are scanned by as high as twice that of a horizontal pitch Hp of a general mask and land the resulting electron beams at a predetermined position on the screen.
The magnetic shield
6
is of a magnetic material which draws the magnetic field flowing to the interior of the tube and flows it through the shield, in order to prevent the paths of the electron beams from being changed due to the variation of the magnetic field.
In the general flat cathode ray tube under the above construction, on the other hand, the electron beams are scanned from left to right and from top and to bottom, sequentially, and the vertical pitch of the electron beams scanned horizontally and the vertical pitch (i.e., the pitch on the vertical arrangement) of the apertures
7
formed on the shadow mask
5
are interacted to necessarily cause the phenomena of moire forming wave patterns, which results in the deterioration of a quality of screen and the reduction of reliability of the product.
Therefore, the s
Birch & Stewart Kolasch & Birch, LLP
Gemmell Elizabeth
Kim Robert H.
LG Electronics Inc.
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