Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
2002-03-07
2004-07-13
Lee, Wilson (Department: 2821)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S407000
Reexamination Certificate
active
06762546
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a cathode ray tube (hereinbelow, called a color picture tube in the specification) and an image display apparatus using the same. More particularly, the invention relates to a color picture tube which is characterized by an elastic support member used to support a frame across which a mask is stretched in a state where a tensile force is applied thereto and to an image display apparatus using the same.
BACKGROUND ART
A color picture tube has, as shown in
FIG. 1
, a structure including an envelope constructed by a panel
52
and a funnel
53
joined to the panel
52
. In the periphery of the panel
52
, a side wall
51
is formed. A phosphor screen
54
having three colors of R, G, and B is formed on the inner face of the panel effective portion. A shadow mask
55
in which a number of electron beam-passing apertures are formed is disposed so as to face the phosphor screen
54
. The funnel
53
has a neck
56
in which an electron gun
57
for emitting three electron beams is disposed. By deflecting the three electron beams by a magnetic field generated by a deflection yoke
80
attached on the outside of the funnel
53
, and by horizontally and vertically scanning the phosphor screen
54
via the shadow mask
55
, a color image is displayed.
From the viewpoint of a smaller amount of entering external light and good looking, the panel of a recent color picture tube is being flattened and the shadow mask
55
is being accordingly flattened. When the shadow mask
55
is flattened, the plane of the shadow mask
55
cannot be maintained only by supporting the body of the shadow mask
55
by a frame
58
. When the shadow mask
55
is simply supported only by the frame
58
, the shadow mask
55
easily vibrates by external vibration, so that an adverse influence is exerted on a display image of the color picture tube. Consequently, the shadow mask
55
is stretched across the frame
58
in a state where a tensile force is applied thereto.
In a doming phenomenon that the surface of the shadow mask
55
is thermally deformed by collision of electron beams with the shadow mask
55
, when the shadow mask
55
is flattened, a displacement amount of the electron beam becomes large especially around both the left and right edge faces of the screen. In order to absorb the thermal expansion caused by the collision of electron beams, a practically maximum tension close to the elastic limit is applied to the shadow mask
55
.
In order to display an accurate color image on the phosphor screen
54
in such a color picture tube, it is necessary to hold the shadow mask
55
in a predetermined alignment relationship to three-color phosphor layers constructing the phosphor screen
54
. One of the factors that deteriorate the alignment relationship between the shadow mask
55
and the phosphor screen
54
is vibration of the shadow mask
55
. Although a tensile force is applied to the shadow mask
55
as described above, it is difficult to completely suppress the vibration of the shadow mask
55
only by the tensile force. The vibration of the shadow mask
55
occurs when external vibration or impact (for example, the vibration of a loudspeaker disposed on a side of the panel
52
) is transmitted from the panel
52
via an elastic support member
59
and the frame
58
to the shadow mask
55
. When the shadow mask
55
vibrates, the distance between the shadow mask
55
and the phosphor screen
54
changes, and thereby a landing displacement of the electron beam occurs. It is consequently desired that the vibration of the shadow mask
55
be attenuated as much as possible in a short time.
In order to suppress the vibration of the shadow mask
55
, it is necessary to suppress the vibration of the shadow mask
55
itself and the vibration of the frame
58
.
As a method of suppressing the vibration of the shadow mask
55
itself, a case where a damper is provided on an edge face of the shadow mask
55
has been reported.
FIG. 2
shows an example of the damper. This damper
61
has a structure obtained by bending the ends of a wire. The damper
61
is provided by passing the bent portions into openings
62
in the shadow mask
55
. The size of the opening
62
in the shadow mask
55
is set so that the damper
61
can freely vibrate. When the shadow mask
55
vibrates, a part of the energy for vibrating the shadow mask
55
is used to vibrate the damper
61
, so that the vibration of the shadow mask
55
is attenuated. Even the structure in which such dampers
61
are provided is insufficient to demonstrate a vibration attenuating effect over the entire shadow mask
55
.
On the other hand, in order to suppress the vibration of the frame
58
, it is necessary to add a function such that the vibration can be absorbed by converting the vibration energy of the frame
58
to, for example, thermal energy (hereinbelow, called a damper function). As is disclosed in Japanese Unexamined Patent Publication No. 9-293459, a conventional method in which a sliding portion is provided with the elastic support member
59
itself so as to suppress the vibration of the frame
58
by the generated friction has been reported.
FIGS. 3A and 3B
show the structure of the elastic support member disclosed in Japanese Unexamined Patent Publication No. 9-293459.
FIG. 3A
is a front view and
FIG. 3B
is a side view. The structure has a matching portion
65
having a matching opening
64
to be matched to a stud pin
63
, a fixed portion
66
to be fixed to the frame
58
, and connecting portions
67
for connecting the matching portion
65
and the fixed portion
66
. The connecting portions
67
are joined together by welding in their mid-portions so as to form a V shape. The fixed portion
66
has a blade
68
that is inserted into an opening
69
formed in the matching portion
65
. When the elastic support member expands and contracts in the directions indicated by the two-headed arrow as the frame vibrates, the blade
68
slides in the opening
69
, thereby obtaining a damper function. However, such an elastic support member has a complicated structure and is not easily produced. Due to a problem of a high cost, it is difficult to actually adopt the elastic support member.
In addition, the shadow mask
55
has to be attached and detached a plurality of times during a process of forming the phosphor screen
54
by a photo printing method using the shadow mask
55
as a photo mask. Consequently, the elastic support member
59
for holding the frame
58
across which the shadow mask
55
is stretched in a state where a tensile force is applied thereto has to be easily attached and detached in the same position with excellent reproducibility.
Further, in addition to the suppression of the vibration, the elastic support member
59
is required to have the following characteristics:
(1) improvements in terms of doming characteristic and low/high temperature characteristic; and
(2) assurance of impact resistance.
Doming characteristic (phenomenon) of (1) is a phenomenon such that the temperature of the shadow mask
55
rises due to the collision of electron beams as described above, creating a temperature difference between the shadow mask
55
and the panel
52
(usually made of glass), and therefore the predetermined alignment relationship deteriorates due to a thermal expansion coefficient difference between the material of the shadow mask
55
and that of the panel
52
. Low/high temperature characteristic is similar to doming characteristic and is a phenomenon such that a positional alignment relationship between the shadow mask
55
and the panel is displaced due to the temperature difference between the shadow mask
55
and the panel
52
caused by the ambient temperature of the panel
52
. Both of the characteristics are phenomena that the positional alignment relationship between the shadow mask
55
and the panel
52
is displaced due to the temperature difference between them. The phenomena cause a color shift and color unevenness. The displacements cannot be completely
Akiyama Koji
Kurokawa Hideo
Nakatani Toshifumi
Ohki Shigeru
Suzuki Hideo
Lee Wilson
Parkhurst & Wendel L.L.P.
Tran Chuc
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