Patent Publication Number: US-6342760-B1

Title: Color cathode ray tube having reinforcing band arranged in a particular position relative to the position of stud pin

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a color cathode ray tube provided with a reinforcing band for preventing implosion of a vacuum envelope. 
     In general, a color cathode ray tube is provided with a vacuum envelope of glass. The vacuum envelope comprises a substantially rectangular panel, which includes an effective portion and a skirt portion provided on the peripheral portion of an effective portion, and a funnel attached to an end face of the skirt portion as a sealed edge. A phosphor screen is formed on the inner surface of the effective portion of the panel. The screen is composed of three color phosphor layers that glow blue, green, and red, individually. 
     A substantially rectangular shadow mask is opposed to the inside of the phosphor screen. The shadow mask includes a substantially rectangular mask body and a substantially rectangular mask frame attached to the peripheral portion of the mask body. A large number of electron beam passage apertures are formed in an effective surface of the mask body that faces the phosphor screen. The shadow mask is supported by means of a mask supporting mechanism, which has stud pins and elastic support members. The stud pins are provided the skirt portion of the panel. The support members are fixed to the mask frame and engage their corresponding stud pins. 
     An electron gun for emitting three electron beams is disposed in a neck of the funnel. In the color cathode ray tube, the three electron beams emitted from the electron gun are deflected by means of a deflector, that is mounted on the outer surface of the funnel, so as to horizontally and vertically scan the phosphor screen through the shadow mask, thereby displaying a color image. 
     A reinforcing band is attached to the outer periphery of the skirt portion of the panel. The band constricts the skirt portion to apply compressive stress to it, in order to prevent implosion of the vacuum envelope. A practical example of the reinforcing band is of a shrunk-on type in which a previously looped band is expanded by heating and attached to the periphery of a skirt portion of a panel, and thereafter, the outer periphery of the skirt portion is shrunk to be constricted by cooling. Another example is of a type such that a belt-shaped band is wound around the outer periphery of a skirt portion of a panel and expanded by heating. Thereafter, in this case, the band is looped by welding its lap portions under tensile stress, and the skirt portion is shrunk to be constricted by cooling. 
     In the conventional color cathode ray tube, moreover, the reinforcing band is situated so as to overlap or externally surround the stud pins that support the shadow mask. 
     If the reinforcing band is located in this manner, however, the compressive stress that acts on the skirt portion of the panel varies depending on the circumferential position of the skirt portion. In particular, the compressive stress that acts in the diagonal direction of the panel at each corner of the skirt portion increases and indirectly influences the shadow mask that is supported inside the panel. 
     Usually, the outer peripheral length of the skirt portion of the panel and the inner peripheral length of the reinforcing band are subject to manufacturing errors, and temperature conditions for the thermal expansion of the band are subject to variations. Accordingly, the compressive stress from the reinforcing band that acts on each corner of the skirt portion in the diagonal direction of the panel fluctuates, so that beam landing on the three color phosphor layers is subject to variations. 
     In general, a color cathode ray tube that is fitted with the reinforcing band is attached to the housing of a TV set by means of lugs that are provided on the band. If the reinforcing band is situated overlapping the stud pins that support the shadow mask, therefore, voice vibrations from a loudspeaker of the TV set are transmitted to the shadow mask through the reinforcing band, stud pins, and elastic support members in engagement with the pins. The resulting resonance (microphonic vibration) of the shadow mask causes image disturbance. 
     In a color cathode ray tube that is provided with a flat panel having a flat or slightly curved effective portion, on the other hand, the curvature of the shadow mask is reduced corresponding to the effective portion, so that the strength of the mask is lowered. If only a small external force acts on the tube, therefore, the shadow mask is influenced considerably. Thus, the aforementioned problems are more serious to the color cathode ray tube of this type than to the conventional one. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has been contrived in consideration of these circumstances, and its object is to provide a color cathode ray tube, in which variations in beam landing attributable to variations in the compressive stress of a reinforcing band and image disturbance caused by resonance of a shadow mask can be reduced. 
     In order to achieve the above object, a color cathode ray tube according to the present invention comprises: a vacuum envelope having a panel, including a substantially rectangular effective portion and a skirt portion provided on the peripheral portion of the effective portion, and a funnel joined to an end edge of the skirt portion; a shadow mask including a substantially rectangular mask body and a substantially rectangular mask frame attached to the peripheral portion of the mask body, the mask body having an effective surface opposed to a phosphor screen on the inner surface of the effective portion and a large number of electron beam passage apertures formed in the effective surface; a mask supporting mechanism supporting the shadow mask and including stud pins arranged on the skirt portion and elastic support members fixed to the mask frame and engaging the stud pins, individually; and a reinforcing band constricting the outer periphery of the skirt portion. 
     The reinforcing band is arranged so as to fulfill a relation, b≧2.0a, where a is the distance between first and second planes along a tube axis passing through the center of the effective portion of the panel, the first plane being in contact with the end edge of the skirt portion and extending perpendicular to the tube axis, the second plane containing the central axis of each of the stud pins and extending perpendicular to the tube axis, and b is the distance between the first plane and a third plane along the tube axis, the third plane being in contact with a side edge of the reinforcing band on the side remoter from the phosphor screen and extending perpendicular to the tube axis. 
     If the position of the reinforcing band relative to each stud pin is regulated in this manner, the reinforcing band, which constricts the skirt portion of the panel, never overlaps the stud pins that support the shadow mask, so that it never directly constricts those portions on which the stud pins are arranged. Accordingly, the shadow mask can be less influenced by compressive stress that acts on the skirt portion as the skirt portion is constricted by the reinforcing band. Thus, deviations in beam landing, which is attributable to variations in the compressive stress, can be lessened. 
     In the case where the color cathode ray tube is incorporated in a TV set, moreover, voice vibrations transmitted from a loudspeaker to the shadow mask can be attenuated to lower the possibility of resonance of the mask. Since no substantial load from the reinforcing band acts on those portions of the panel which are lowered in strength due to the presence of the stud pins, furthermore, the implosion-proof characteristic of the vacuum envelope can be improved. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIGS. 1 to  3  show a color cathode ray tube according to an embodiment of the present invention, in which: 
     FIG. 1 is a plan view, partially in section, showing the color cathode ray tube; 
     FIG. 2 is a sectional view of a panel of the color cathode ray tube taken along line II—II of FIG. 1; and 
     FIG. 3 is a sectional view showing the relative positions of a reinforcing band and a mask supporting mechanism. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A color cathode ray tube according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 
     As shown in FIGS. 1 and 2, the color cathode ray tube comprises a vacuum envelope  10  of glass. The vacuum envelope  10  comprises a substantially rectangular panel, which includes a substantially rectangular effective portion  20  and a skirt portion  21  provided on the peripheral portion of the effective portion, and a funnel  24  joined to an end face  23  of the skirt portion as a sealed edge. The effective portion  20  is substantially flat, and its outer surface is composed of a flat surface or a curved surface that has a radius of curvature of 10,000 mm or more. 
     A phosphor screen  27  is formed on the inner surface of the effective portion  20  of the panel  22 . The screen  27  includes three color phosphor layers that glow blue, green, and red, individually. A substantially rectangular shadow mask  28  is opposed to the inside of the screen  27 . The shadow mask  28  includes a substantially rectangular mask body  29  and a substantially rectangular mask frame  30  attached to the peripheral portion of the mask body. A large number of electron beam passage apertures are formed in an effective surface of the mask body  29  that faces the phosphor screen  27 . 
     As shown in FIGS. 1 to  3 , the shadow mask  28  is supported on the inside of the panel  22  by means of a mask supporting mechanism. The supporting mechanism includes stud pins  31  and elastic support members  32 . The stud pins  31  are arranged individually at the four corners of the skirt portion  21  of the panel  22 . The support members  32  are fixed individually to the four corners of the outer surface of the mask frame  30  and engage their corresponding stud pins  31 . 
     As shown in FIG. 1, a neck  34  is joined to the small-diameter-side end of the funnel  24 , and an electron gun  36  for emitting three electron beams  35 R,  35 B and  35 G is disposed in the neck. The gun  36  is located substantially coaxially with a tube axis Z that passes through the center of the effective portion  20  of the panel  22 . 
     In the color cathode ray tube, the three electron beams  35 R,  35 B and  35 B are deflected by a magnetic field generated from a deflector  37  that is attached to the outside of the funnel  24 . In this state, a color image is displayed as the phosphor screen  27  is scanned horizontally and vertically through the shadow mask  28 . 
     As shown in FIGS. 1 to  3 , a reinforcing band  25  is attached to the outer periphery of the skirt portion  21  of the panel  22 . The band  25  constricts the skirt portion  21  to apply compressive stress to it, in order to prevent implosion of the vacuum envelope  10 . The reinforcing band  25 , which is a rectangular structure substantially coaxial with the tube axis Z, extends throughout the circumference of the skirt portion  21 . Further, lugs  38  are fixed to the respective outer surfaces of the four corners of the band  25 , individually. The color cathode ray tube is attached to the housing of a TV set by means of the lugs  38 . 
     In this color cathode ray tube, the reinforcing band  25  on the outer periphery of the skirt portion  21  is situated in a position shifted from the stud pins  31  toward the phosphor screen  27  along the tube axis Z lest it overlap the pins  31 . 
     More specifically, as shown in FIG. 3, the reinforcing band  25  is provided on the outer periphery of the skirt portion  21  of the panel  22  so as to fulfill the following relation: 
     
       
         b≧2.0a, 
       
     
     where a is the distance from a point  39  at which a first plane P 1 , which is in contact with the end face  23  of the skirt portion  21  and extends perpendicular to the tube axis Z, crosses the axis Z to a point  41  at which a second plane P 2 , which contains the central axis of each stud pin  31  and extends perpendicular to the tube axis Z, crosses the axis Z, that is, the distance between the first and second planes P 1  and P 2  along the axis Z, and b is the distance from a point  43  at which a third plane P 3 , which is in contact with a side edge  42  of the reinforcing band  25  on the side (sealed-edge side) remoter from the phosphor screen  27  and extends perpendicular to the tube axis Z, crosses the axis Z to the point  39 , that is, the distance between the first and third planes P 1  and P 3  along the axis Z. 
     The table below shows the results of a test on the landing characteristic (landing stability) of electron beams and microphonic vibration characteristic of the shadow mask  28 , for three color cathode ray tubes with an aspect ratio of 16:9 and screen diagonal sizes of 66 cm, 76 cm, and 86 cm and a color picture tube with an aspect ratio of 4:3 and a screen diagonal size of 68 cm. In this test, the distances a and b were set at various values. In the table, ⊚, ◯, and Δ indicate the priority order of adequacy of the characteristics. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 
               
               
                   
               
               
                 Aspect 
                 Diagonal 
                 a 
                 b 
                 Relational 
                 Landing 
                 Microphonic 
               
               
                 ratio 
                 size (cm) 
                 (mm) 
                 (mm) 
                 expression 
                 stability 
                 vibration 
               
               
                   
               
             
            
               
                 16:9 
                 66 
                 20.0 
                 40 
                 b = 2.0a 
                 Δ 
                 Δ 
               
               
                   
                 76 
                 21.5 
                 43 
                 b = 2.0a 
                 Δ 
                 Δ 
               
               
                   
                 86 
                 20.0 
                 47 
                 b = 2.35a 
                 ◯ 
                 ◯ 
               
               
                  4:3 
                 68 
                 21.5 
                 57 
                 b = 2.65a 
                 ◯ 
                 ⊚ 
               
               
                   
               
            
           
         
       
     
     As seen from this table, the longer the distance (a−b) from each stud pin  31  to the opposite side edge  42  of the reinforcing band  25 , the higher the landing stability of the electron beams is. The longer the distance (a−b), moreover, the more difficult it is for microphonic vibration to occur. Very good results were obtained from the color cathode ray tube with the diagonal size of 68 cm. 
     The landing and microphonic vibration characteristics can be improved by adjusting the relative positions of each stud pin  31  and the opposite side edge  42  of the reinforcing band  25  so that the distance b is b≧2.0a, and preferably to b≧2.3a, without regard to the size of the color cathode ray tube. If the position of the reinforcing band  25  relative to each stud pin  31  is regulated in this manner, the band  25 , which constricts the skirt portion  21  of the panel  22 , never overlaps the stud pins  31  that support the shadow mask  28 , so that it never directly constricts those portions on which the pins  31  are arranged. Accordingly, the shadow mask  28  can be less influenced by the compressive stress that acts on the skirt portion  21  as the skirt portion is constricted by the reinforcing band  25 . Thus, if the compressive stress from the band  25  is subject to some variations, depending on the position of the skirt portion  21  or owing to manufacturing errors in the outer peripheral length of the skirt portion  21 , the inner peripheral length of the band  25 , etc., the influence of the variations in the compressive stress upon the shadow mask  28  is reduced, so that deviations in beam landing can be lessened. 
     In the case where the color cathode ray tube is incorporated in the TV set, moreover, voice vibrations transmitted from a loudspeaker to the shadow mask  28  can be attenuated to lower the possibility of resonance of the mask  28  for the same reason as aforesaid. Since no substantial load from the reinforcing band acts on those portions of the panel  22  which are lowered in strength due to the presence of the stud pins  31 , furthermore, the implosion-proof characteristic of the vacuum envelope can be improved. 
     It is to be understood that the present invention is not limited to the embodiment described above, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention. According to the above-described embodiment, for example, the supporting mechanism for the shadow mask has the stud pins arranged individually at the corners of the skirt portion and the elastic support members fixed individually to the corners of the mask frame. However, the present invention is also applicable to a color cathode ray tube in which a shadow mask is supported by means of stud pins arranged individually on the respective intermediate portions of the four sides of a substantially rectangular skirt portion and elastic support means fixed individually to the respective intermediate portions of the four sides of a substantially rectangular mask frame. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.