Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
1999-11-12
2002-11-19
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S406000
Reexamination Certificate
active
06483233
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color cathode-ray tube (CRT) and more particularly, to a color CRT having an expanded effective display area without increasing the size of the face panel, in which the space existing between the face panel and the shadow mask is effectively utilized by expanding the opening of the mask frame.
2. Description of the Prior Art
FIGS. 1 and 2
schematically show a part of a prior-art color CRT, in which a shadow mask assembly
101
is fixed to the inside of a face panel
105
made of glass. The panel
105
forms the front section of a vacuum envelope. A substantially rectangular phosphor screen
104
is formed on the inner surface of the panel
105
.
As shown in
FIGS. 1 and 2
, the shadow mask assembly
101
includes a frame
103
with a rectangular opening and a rectangular shadow mask
102
fixed to the frame
103
to close the opening. The frame
103
has a main part
103
b
and a flange
103
a
formed at the rear end of the part
103
b
. The main part
103
b
extends in parallel to the central longitudinal axis of the envelope and the flange
103
a
is perpendicular to the axis. Four spring or elastic members
106
, each of which is formed by an elongated metal piece bent to have a step-shaped cross-section, are respectively fixed by welding onto the outer surfaces of the main part
103
b
at its four sides.
The shadow mask
102
, which is formed by a thin, rectangular metal plate, has a lot of regularly-arranged small apertures
102
a
for color selection. The mask
102
has a skirt section
102
b
formed at the periphery. The skirt section
102
b
is fixed to the front end of the main part
103
b
of the frame
103
by welding so as to fit into the rectangular opening of the frame
103
. The section
102
b
is contacted with the inner surface of the main part
103
b.
The face panel
105
has a substantially rectangular main part and four side walls
105
a
connected to the periphery of the main part. Four stud pins
107
are respectively fixed to the inner surfaces of the four side walls
105
a.
The four spring members
106
fixed to the frame
103
are respectively engaged with the four stud pins
107
fixed to the face panel
105
, thereby fixing the shadow mask assembly
101
to the inside of the panel
105
so that the shadow mask
102
is apart from and opposite to the phosphor screen
104
. The engagement of the members
106
and the pins
107
is realized by hooking the end of each pin
107
with the hole of each spring
106
.
Although not shown, an inner shield is attached to the flange
103
a
of the frame
103
to suppress the effect of the geomagnetism.
The prior-art color CRT described above is termed the “mask-inner” type, because the skirt section
102
b
of the shadow mask
102
is inserted into the inside of the supporting frame
103
and fixed thereto.
Color CRTs have been often used as display devices for electronic terminal equipment such as personal computers. In recent years, in this case, larger display areas (i.e., larger screen size) tend to be desired to improve the visibility without reducing the amount of displayed information. Thus, the popular screen size has been increasing from 15 inches to 17, 19, or 21 inches.
However, as the screen size becomes larger, the size, weight, power consumption, and production cost of color CRTs will increase abruptly. Therefore, it is preferred to increase the effective display area as much as possible without enlarging the glass envelope. In other words, it is desired to use the display area as efficiently as possible.
From this point of view, as shown in
FIG. 2
, it is found that the above-described prior-art CRT has a comparatively large space S between the supporting frame
103
and the opposing sidewalls
105
a
of the face panel
105
. This space S is generated due to the thickness or height of the spring members
106
. Therefore, if the size of the face panel
105
is not changed, the maximum size of the rectangular opening of the frame
106
, which is entirely covered with the shadow mask
102
, is limited by the thickness or height of the spring members
106
. As a result, even if the space S remains unused, a larger shadow mask is unable to be applied to the face panel
105
. This means that the effective display area of the shadow mask
102
cannot be enlarged. In other words, the trajectory of electron beams emitted from the electron gun assembly provided in the neck of the vacuum envelope is unable to be bent in a wider range with respect to the central longitudinal axis of the envelope.
The space S may be narrowed by decreasing the thickness of the frame
103
and/or the thickness or height of the spring members
106
. However, this causes a disadvantage that the mechanical strength of the frame
103
and/or the members
106
is lowered, and at the same time, this is incapable of generating a satisfactory result.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention to provide a color CRT that expands the effective display area without increasing the size of a face panel.
Another object of the present invention to provide a color CRT that makes it possible to use a larger-sized shadow mask without increasing the size of a face panel.
Still another object of the present invention to provide a color CRT that increases the maximum angle of the electron-beam trajectory with respect to the central longitudinal axis of a vacuum envelope.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
A color CRT according to the present invention has a feature that a frame for supporting a shadow mask has a front end section bent outwardly with respect to the remainder, thereby decreasing the gap or space between the frame and opposing sidewalls of a face panel.
In other words, the color CRT according to the present invention is comprised of a vacuum envelope having a face panel, a funnel connected to the panel, and a neck connected to the funnel. The envelope has a central longitudinal axis approximatley pernendicular to the panel. The panel has side walls formed at a periphery of its main part to extend approximately in parallel to the central longitudinal axis. Engagig pins are fixed to inner surfaces of the side walls.
A phosphor screen is formed on an inner surface of the main part of the panel.
A shadow mask assembly includes a frame with an opening and a shadow mask fixed to the frame to close the opening. The frame has a front section, a rear section, and a middle section located between the front and rear sections. The front section and the rear section extend approximately in parallel to the central longitudinal axis of the envelope. The front section is shifted outwardly with respect to the rear section. A periphery of the mask is fixed to the front section. Elastic engaging members are fixed to an outer surface of the rear section,
The assembly is fixed to the panel by engaging respectively the engaging members of the frame with the engaging pins of the panel, thereby locating the mask apart from and opposed to the phosphor screen in the envelope.
With the color CRT according to the present invention, the frame in the shadow mask assembly has the front section extending approximately in parallel to the central longitudinal axis of the envelope, the rear section extending approximately in parallel to the central longitudinal axis of the envelope, and the middle section intervening between the front and rear sections. The front section is shifted outwardly with respect to the rear section. The periphery of the mask is fixed to the front section. Thus, the assembly is fixed to the panel by engaging respectively the engaging members of the frame with the engaging pins of the panel, thereby locating the mask apart from and opposed to the phosphor screen in the envelope.
Therefore, the shadow mask can be made larger in size without increasing the size of the face panel. In other words, the color CRT according t
Day Michael H.
McGinn & Gibb PLLC
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