Source: {"pile_set_name": "USPTO Backgrounds"}

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.
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 compensated even if a tensile force is applied to the shadow mask 55. When the shadow mask 55 expands relatively, the displacements between the shadow mask 55 and the inner face of the panel 52 on which the phosphor screen 54 is formed has to be compensated by shortening the distance between the shadow mask 55 and the inner face of the panel 5. On the contrary, when the panel 52 expands, it is necessary to widen the distance between the shadow mask 55 and the panel 52. In this manner, the elastic support member 59 has to have the function of displacing the position of the shadow mask 55 in accordance with the temperature difference between the panel 52 and the shadow mask 55.
At the time of carrying the color picture tube, there is a case such that the color picture tube is subjected to an impact that cannot be imagined in a normal use state due to an unexpected event (such as collapse of a cargo). When the shadow mask 55 is displaced due to plastic deformation of the elastic support member 59 or buckling of the matching portion by the impact, the positional alignment relationship between the shadow mask 55 and the panel 52 is displaced. The elastic support member 59 therefore has to be strong enough not to cause a displacement in the shadow mask 55 even when a specific impact (acceleration) is applied.
The structure including the frame, the shadow mask, and the elastic support member (hereinbelow, called a frame structure) is desired to have overall excellent characteristics with respect to the suppression of the vibration of the shadow mask, doming and low/high temperature characteristics and impact resistance.
An example of the conventional frame structure will be described hereinbelow. FIG. 4A is an entire view showing a state where a frame 58 is disposed in the panel 62 with strip-shaped elastic support members 59. FIG. 4B is an enlarged view of the strip-shaped elastic support member 59. The strip-shaped elastic support member 59 has a catching portion 60(a) to be caught by a stud pin 63 of the panel 62, a fixed portion 60(b) to be fixed to the frame, and a connecting portion 60(c) for connecting the catching portion 60(a) and the fixed portion 60(b). Such a strip-shaped elastic support member is called a TCM type and has a characteristic of excellent impact resistance. As a countermeasure against