Patent Publication Number: US-6211609-B1

Title: Corner spring for color cathode ray tube

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a color cathode-ray tube (hereinafter referred to as “CRT”). More particularly, it relates to a design compensation volume setup of a corner spring for supporting a mask structure within a panel. 
     2. Discussion of Related Art 
     As shown in FIG. 1, a conventional CRT includes a panel  2  mounted in front thereof; a funnel  7  mounted at the back of the panel  2  in order to maintain a vacuum; a neck  10  extending from the back of the funnel  7 ; an electron gun  8  within the neck  10 , for emitting R, G, and B electron beams; a phosphor screen  3  applied to the inner surface of the panel  2 , including phosphor layer for producing red, green, and blue lights in accordance with landing of electron beams; and a shadow mask structure  6  consisting of a rectangular shadow mask  4  where a plurality of electron beam apertures (not shown) are formed for color selection, and a frame  5  for fixing the shadow mask  4 . 
     The frame  5  is supported by a corner spring  11  connected to a stud pin  12  toward the panel  2 . As shown in FIG. 2, the corner spring  11  disclosed in U.S. Pat. No. 4,827,180 is constructed of a first arm  27  having a stud pin hole, and a second arm  29  connected to the frame  5 , the first and second arms being welded to each other. The two, respective arms make a specific angle (θ 1 ,θ 2 ) with a central axis  1  of welding portion. 
     Reference numeral  9  is indicative of a deflection yoke for deflecting the electron beams. 
     In the conventional CRT, the electron beams emitted from the electron gun  8  are deflected by the deflection yoke  9 , before passing through the apertures of the shadow mask  4  and scanning the phosphor screen, to thereby display an image. 
     The internal parts are located like a dotted line of FIG. 3 prior to operation of the CRT, but move like a solid line when the temperature rises due to heat expansion. 
     The mask apertures formed on the shadow mask  4  move toward P′ from P, and the corner spring  11  serves to allow the mask apertures to move to a phosphorescent screen, heading for the position of Q. 
     That is, in this case, the V-shaped corner spring  11  is pressed to make the first and second arms  27  and  29  closer to each other. The second arm  29  is welded to the frame  5 , and θ 1  and θ 2  of FIG. 2 is differently changed, in such a way that the position of the corner spring  11  is varied outside. 
     The color CRT has been developed in recent years, having the shadow mask made of the material of low coefficient of expansion such as Invar alloy, namely 36% nickel-iron alloy with coefficient of expansion of about 1.2×10 −6 /° C., and the mask frame made of iron. 
     The shadow mask made of Invar alloy with very low coefficient of expansion, does not expand with heat, and the mask frame expands around with heat during operation of the CRT. 
     The typical corner spring for compensating the mislanding by angle (θ 1 ,θ 2 ) of spring results in inaccurate electron beam landing. The reason why the electron beams land inaccurately is as follows. 
     When the temperature rises in the CRT the shadow mask does not efficiently expand with heat. The mask frame is made of iron with coefficient of expansion (about 1.2×10 −5 /° C. at room temperature) about ten times as high as 36% nickel-iron alloy. In this connection, the mask frame expands with heat. 
     Consequently, the corner spring allows the shadow mask move toward the screen. A passage that the electron beams pass through the mask apertures is altered, which causes the electron beams to inaccurately land on the phosphor element, thereby resulting in degradation of color purity. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a corner spring for color CRT that substantially obviates one or more of the problems, limitations, and disadvantages of the related art. 
     An objective of the present invention is to provide a corner spring whose movable piece&#39;s length L is optimized to prevent the mislanding caused by heat expansion, to thereby enhance the color purity of a CRT. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned through practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure, particularly as detailed in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the length L of slope of a first arm is represented as 1.08S≦L≦1.75S to the distance S from a center of a stud pin coupling portion  113  to a frame contacting portion that is an end of a frame welding portion  123  of a second arm, and the distance H between a welding portion  103  where the first and second arms are welded to each other and the frame welding portion  123  of the second arm is expressed as H &lt;0.668S. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention that together with the description explain the principles of the invention: 
     In the drawings: 
     FIG. 1 is a cross-section of part of a conventional CRT; 
     FIG. 2 is an enlarged cross-section of corner spring of the CRT; 
     FIG. 3 shows a changed state of the conventional corner spring; and 
     FIG. 4 depicts in detail the structure of a corner spring of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     With reference to FIG. 4, a corner spring for color CRT includes a first arm  101  where a coupling hole is formed to mate with a stud pin inside the panel, and a second arm  102  coupled with an outer face of the frame for supporting the shadow mask, the first arm  101  having a first coupling portion  111  to match with the second arm, a first slope  112  which is bent, making an obtuse angle with the coupling portion, and a stud pin coupling portion  113  which is bent, extending from the slope, with a spring hole  100  to receive the stud pin, and the second arm  102  having a second coupling portion  121  to match with the first arm, a second slope  122  which is bent, making an obtuse angle with the coupling portion, and a frame welding portion  123  which is bent, extending from the slope to be welded to the frame. The length L of slope of the first arm is represented as 1.08S &lt;L&lt;1.75S to the distance S from a center of the stud pin coupling portion  113  to a frame contacting portion that is an end of a frame welding portion  123  of the second arm, and the distance H between a welding portion  103  where the first and second arms are welded to each other and the frame welding portion  123  of the second arm is expressed as H&lt;0.668S. 
     At the time of design compensation volume setup of corner spring, the length L of the first slope and the height H of the welding portion are constructed adequately. In case of reducing the first slope in length L and making coefficient of expansion high, a force applied to the stud pin is increased. Therefore, two of four corner springs mates with two stud pins, but it is hard to manually attach two remaining corner springs because of extremely high, mechanical strength of spring. In case of increasing the first slope in length L, when an impact is applied, the corner spring arranged within the panel may be detached from the stud pin, and apparatus interference may occur within the panel, to cause scratch and bad parts. 
     The welding portion of the second arm, that decreases in height H, may result in over compensation. The compensation volume exceeds a certain range, to apply an interference to panel stud pin at the time of mounting/detaching the mask structure. 
     In this connection, the length L of the first slope lies in 12≦L ≦23 mm(1.08S&lt;L&lt;1.75S), to prevent the spring from being detached due to external impact. Therefore, the spring can be easily mounted on/detached from the stud pin manually. In addition, the height H of the welding portion of the second arm exceeds the range of H≦8.0 mm(H≦0.668S), which applies an interference to the stud pin when mounting/detaching the mask structure. The design of corner spring is to be made, depending on the L and H. 
     As described above, the corner spring of the present invention has a construction that allows adequate compensation volume. Thus, the mounting/detaching operation of the mask structure is effectively performed as compared to prior art, to thereby increase productivity of goods. The expansion of CRT mask by heat is adequately compensated to greatly alleviate purity drift volume, thereby producing an excellent image. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in a corner spring for color CRT of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention that come within the scope of the appended claims and their equivalents.