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 doming and low/high temperature characteristics, the elastic support member has a bimetallic structure made of two kinds of materials a (hatched portion) and xcex2 (not-hatched portion) having different thermal expansion coefficients. The bimetallic effect of the elastic support member 59 is not, however, displayed unless the temperature of the elastic support member 59 itself changes. Therefore, there is a problem of a slow response to a change in environment or a sudden rise in temperature of the shadow mask. Since the temperature change amount of the elastic support member 59 is small, a large correction amount cannot be set. Consequently, there is another problem that a material of the shadow mask having a thermal expansion coefficient largely different from that of the material of the panel cannot be used.
In the frame structure, since corners 74 of the frame 58 are not supported, vibration easily occurs. Moreover, since the elastic support member of the TCM type has no damper effect, once vibration occurs, it is not attenuated easily. As a result, the shadow mask also vibrates, thereby causing a problem that an adverse influence such as a color shift is exerted on the picture quality.
FIG. 5A shows a frame structure of another conventional technique. As shown in FIG. 5, stud pins 71 are provided on the inner walls at the opposite corners of a panel 70. Each of elastic support members 72 has a catching portion 72(a) to be caught by the stud pin 71, a fixed portion 72(b) fixed to a frame, and a V-shaped connecting portion 72(c) for connecting the catching portion 72(a) and the fixed portion 72(b). The connecting portion 72(c) is attached to the phosphor screen side. However, the configuration has the following problems.
(1) The clearance between the panel 70 and the frame 73 is narrow since the elastic support members 72 are disposed at the opposite corners of the panel 70, so that the assembling is difficult. It is not easy to assemble the frame 73 to the panel 70, and reduction in yield due to damage in the elastic support member 72, the stud pin 71, and the panel 70 is a problem.
(2) Since the elastic support members 72 are disposed at the opposite corners of the panel 70, the elastic support member 72 cannot be widened. Consequently, the impact resistance is poor.
The present invention is intended to solve the conventional problems mentioned above and provide a color picture tube that is resistant to external vibration and is excellent in terms of doming and low/high temperature characteristics and impact resistance, and has a suitable configuration for easy assembling, and an image display apparatus using the color picture tube.
The first aspect of the present invention is a cathode ray tube comprising, at least, a panel having a phosphor screen formed thereon, a shadow mask having a plurality of electron beam-passing portions, and a frame across which the shadow mask is stretched in a state where a tensile force is applied thereto, the frame being securely attached to the panel by an elastic support member while the phosphor screen is opposed to the shadow mask, wherein the elastic support member is located substantially in the middle portion of a frame portion and the shadow mask is configured such that the tension in the middle portion of the shadow mask is larger than the tension at the edge portions of the shadow mask.
In the configuration described above, since the elastic support member is located substantially in the middle portion of the frame portion, the assembly and frame support may be improved, and since the tension in the middle portion of the shadow mask is larger than the tension at the edge portions of the shadow mask, the vibration attenuating effect of the elastic support member may be found not only at the edge portions of the shadow mask but also at the middle portion of the shadow mask.
The second aspect of the present invention is a cathode ray tube comprising, at least, a panel having a phosphor screen formed thereon, a shadow mask having a plurality of electron beam-passing portions, and a frame across which the shadow mask is stretched in a state where a tensile force is applied thereto, the frame being securely attached to the panel by an elastic support member while the phosphor screen is opposed to the shadow mask, wherein the elastic support member is fixed to an elastic support member-holding plate located substantially in the middle of the frame portion and the shadow mask is configured such that the tension in the middle portion of the shadow mask is larger than the tension at the edge portions of the shadow mask.
In the configuration described above, since the elastic support member is fixed to the elastic support member-holding plate located substantially in the middle of each frame portion, the elastic support members are located in the same plane by adjusting the extension direction of the elastic support member-holding plate even when the frame portions are not in the same plane, and therefore the effects of the first aspect of the present invention are demonstrated further.
In these first and second aspects of the present invention described above, the elastic support member desirably comprises a fixed portion to be fixed to the frame, a matching portion to be matched to a stud pin provided on the inside of the panel side wall, and a connecting portion for connecting the matching portion and the fixed portion. The connecting portion preferably has an approximately V-shaped configuration. With this configuration, better doming and low/high temperature characteristics may be obtained.
In this configuration, the fixed portion of the elastic support member preferably has an area of at least 5 cm2. This is because when the area of the fixed portion is made large, a force applied to the frame is dispersed, and this prevents the tension distribution pattern of the shadow mask from varying due to the frame deformation. To increase the effect described above, the ratio of the area of the fixed portion of the elastic support member to the area of the frame portion to which the elastic support member is fixed is preferably at least greater than {fraction (1/25)}.
Furthermore, the elastic support member desirably includes a vibration suppressing structure, because the vibration of the frame is transmitted to the shadow mask even when the vibration of the shadow mask is attenuated unless the vibration of the frame is attenuated.
The spring constant of the elastic support member may be altered relatively easily without changing the size of the elastic support member by is forming an opening in the connecting portion of the elastic support member and adjusting the size of the opening.
The force applied to the frame portion by the elastic support member is preferably in the range of 1 kgf to 8 kgf and the spring constant of the elastic support member is preferably in the range of 0.1 kgf/mm to 2.5 kgf/mm.
The stretched shadow mask is provided with a damper for attenuating the vibration and has a tension distribution such that the tension is largest in the middle portion of the shadow mask and decreases gradually toward the edge portions to ensure that the vibration may be attenuated in the entire shadow mask. In order to extend the attenuating effect of the damper to the entire shadow mask, it is preferable that the tension distribution satisfy the relationships T1xe2x89xa7T2xe2x89xa7T3 and T1xe2x89xa71.1xc3x97T3, where the tension of the shadow mask middle portion is T1, the tension of the shadow mask edge portions is T3, and the tension of the intermediate portions between the middle and the edge portions is T2.
Preferably, the damper has a structure that is freely movable with no portion thereof fixed to the shadow mask in order to improve the attenuating effect.
Specifically, the damper is preferably so constructed as to be inserted into an opening formed in the shadow mask and is preferably a wire-like member or a ring-like member.
As the material for the shadow mask, Fexe2x80x94Ni alloy is preferable since its creeping rate is small even when heated to higher temperatures.
The third aspect of the present invention is a cathode ray tube comprising, at least, a panel having a phosphor screen formed thereon, a mask having a plurality of electron beam-passing portions, and a frame on which the mask is held, the frame being securely attached to the panel by a plurality of elastic support members while the phosphor screen is opposed to the mask, wherein the plurality of elastic support members are such that at least two elastic support members having substantially different spring constants are combined.
In the composition described above, when the plurality of elastic support members are such that at least two elastic support members having substantially different spring constants are combined, single vibration mode, in which the vibration is easily suppressed, predominates, and therefore the vibration of the frame may be suppressed.
In this third aspect of the present invention described above, desirably, each of the elastic support members is located substantially in the middle of a frame portion to suppress the vibration of the mask.
To obtain better doming and low/high temperature characteristics, desirably, the elastic support member comprises a fixed portion to be fixed to the frame, a matching portion to be matched to a stud pin provided on the inside of the panel side wall, and a connecting portion for connecting the matching portion and the fixed portion. The connecting portion preferably has an approximately V-shaped configuration.
Of the elastic support members, opposing elastic support members desirably have the same spring constant in order to increase the intensity of single vibration further.
The fixed portion of the elastic support member preferably has an area of at least 5 cm2. This is because when the area of the fixed portion is made large, the force applied to the frame is dispersed, and this prevents the tension distribution pattern of the shadow mask from varying due to the frame deformation. To increase this effect described above, the ratio of the area of the fixed portion of the elastic support member to the area of the frame portion to which the elastic support member is fixed is preferably at least greater than {fraction (1/25)}.
The elastic support member desirably includes a vibration suppressing structure, because the vibration of the frame is transmitted to the shadow mask even when the vibration of the shadow mask is attenuated unless the vibration of the frame is attenuated.
The spring constant of the elastic support member may be altered relatively easily without changing the size of the elastic support member by forming an opening in the connecting portion of the elastic support member and adjusting the size of the opening.
The force applied to the frame portion by the elastic support member is preferably in the range of 1 kgf to 8 kgf and the spring constant of the elastic support member is preferably in the range of 0.1 kgf/mm to 2.5 kgf/mm.
Preferably, the mask is stretched across the frame in a state where a tensile force is applied thereto, and more preferably, the tension in the middle portion is larger than the tension at the edge portions in the tension distribution of the mask. The reason for this is that the stretched shadow mask is provided with a damper for attenuating the vibration and has the tension distribution in which the tension is largest in the middle portion of the shadow mask and decreases gradually toward the edge portions to ensure that the vibration may be attenuated in the entire shadow mask. In order to extend the attenuating effect of the damper to the entire shadow mask, it is more preferable that the tension distribution satisfy the relationships T1xe2x89xa7T2xe2x89xa7T3 and T1xe2x89xa71.1xc3x97T3, where the tension of the shadow mask middle portion is T1, the tension of the shadow mask edge portion is T3, and the tension of the intermediate portions between the middle and the edge portions is T2.
Preferably, the damper has a structure which is freely movable with no portion thereof fixed to the shadow mask in order to increase the attenuating effect.
Specifically, the damper is preferably so constructed as to be inserted into an opening formed in the shadow mask and is preferably a wire-like member or a ring-like member.
As the material for the shadow mask, Fexe2x80x94Ni alloy is preferable since its creeping rate is small even when heated to higher temperatures.
Furthermore, the first, second, and third aspects of the present invention described above may be applied not only to the foregoing cathode ray tube but also to a general image display apparatus such as a television set which includes an electron beam controlling circuit, a cabinet, and the like in addition to the cathode ray tube.