Abstract:
In a cathode ray tube panel, contour lines of uniform thickness are continuous, closed loops without discontinuities at the periphery of the screen providing a natural picture throughout the panel. Hence, a distorted picture rarely occurs at the periphery of the panel.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cathode ray tube, and more particularly to an improvement in the panel of a cathode ray tube. 
     Generally, a cathode ray tube has such elements as a neck, a funnel, and a panel. In such a cathode ray tube, an assembled electron gun is installed in a predetermined position in the neck, and a phosphor screen is formed on the inner surface of the panel. A shadow mask is installed inside the cathode ray tube and spaced apart from the phosphor screen at a predetermined distance. In a cathode ray tube constructed as above, the inside pressure of the tube is at a high vacuum, approximately 10 -6  to 10 -7  mmHg, so as to easily emit an electron beam and allow it to proceed away from the electron gun. 
     By forming the tube in a high vacuum state, the exterior of the tube is under great atmospheric pressure. Accordingly, as illustrated in FIG. 1, due to the structural characteristic of the circumference of the tube, a location 1b on the funnel as well as a location la on the panel are subjected to compressive stress. A periphery location 1c on the funnel and panel is subjected to tensile stress, which weakens the structural aspects of location 1c. Therefore, when a highly evacuated cathode ray tube implodes, there is dangerous flying glass at its periphery. Hence, a safe tube should be manufactured by reinforcing the structurally weak portions. For this purpose, a tension band is conventionally employed to reinforce the periphery of the funnel and panel. Also, the periphery of the panel is made to be relatively thicker than the center of the panel. 
     However, since the panel of a cathode ray tube is substantially rectangular in shape and due to the structural characteristics of a cathode ray tube, the deforming force caused by atmospheric pressure becomes greatest along the edges of the shorter axis of the panel, the least along its diagonal, and the mean along its longer axis. Based upon consideration of the above-described matters, the panel is formed to vary in thickness. That is, the panel is the thinnest along the diagonal line of the panel, and is the thickest along the edges of the shorter axis. 
     Therefore, contour lines 2 drawn along the same thickness, as illustrated in FIG. 2, of a panel 1 constructed as above, have discontinuous points at periphery 3 of a screen. As a result, a problem occurs wherein the picture is distorted at the screen&#39;s periphery due to the discontinuity of contour lines 2 at periphery 3. 
     SUMMARY OF THE INVENTION 
     The present invention provides a cathode ray tube, wherein the above-described problem is solved. 
     Accordingly, it is the object of the present invention to provide a cathode ray tube employing a panel whose structure is improved to decrease distortion of a picture at the periphery of the panel. 
     To achieve the above and other objects of the present invention, there is provided a cathode ray tube comprising a phosphor screen on the inner surface of a curved rectangular panel whose central axis is perpendicular to the center of the phosphor screen, substantially having a predetermined ratio between the longer and shorter lengths, provided that, when a plane in contact with the center of the panel is defined as a tangent plane, the longer axis of the panel which extends in the horizontal direction of the tangent plane is designated as the X-axis, the shorter axis which extends in the vertical direction is designated as the Y-axis, an axis perpendicular to the tangent plane passing through the center of the panel is designated as the Z-axis, and arbitrary points on each of the X-axis and Y-axis are designated as arbitrary points a and b having the same ratio as the predetermined ratio between the longer and shorter lengths of the panel, wherein 
     the thickness of the panel along a line through the arbitrary point a of the X-axis drawn perpendicular to the tangent plane is the same as the thickness of the panel along a line through the arbitrary point b of the Y-axis drawn perpendicular to the tangent plane, and contour lines are positioned within a triangular region formed by a straight line of X coordinates at X=a, a straight line of Y coordinates at Y=b, and a line connecting the arbitrary points a and b, or placed on a line obtained by connecting the straight line of X coordinates at X=a and the straight line of Y coordinates at Y=b, or the straight line which connects the arbitrary points a and b, thereby eliminating discontinuous points of the contour lines throughout a screen. 
     According to the present invention, the contour lines of the panel&#39;s thickness form closed loops throughout the screen of the panel. Therefore, a distorted picture rarely occurs at the periphery of the screen. 
     Preferably, the interval between adjacent contour lines is uniform throughout the whole region of the picture, thereby providing a natural picture throughout the screen. 
     By improving the shape of the contour lines of the panel&#39;s thickness, the present invention provides a cathode ray tube wherein a picture is rarely distorted. As a result, the present invention enhances the value of the end product. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features, aspects and advantages of the present invention will become more apparent when taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a schematic view showing the atmospheric pressure applied to the circumference of a conventional cathode ray tube; 
     FIG. 2 is a schematic view of the panel of the conventional cathode ray tube, in which contour lines are illustrated; 
     FIG. 3 is a sectioned view used for illustrating the panel of a cathode ray tube according to the present invention; 
     FIG. 4 is a schematic view for illustrating the panel of the cathode ray tube according to the present invention; and 
     FIG. 5 is a schematic view of the panel of the cathode ray tube according to the present invention, in which contour lines are shown. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3 shows an extracted quadrant of a panel 10 according to the present invention, and FIG. 4 shows the entire surface of panel 10. Panel 10 of a cathode ray tube according to the present invention is formed to have a predetermined curvature and a predetermined ratio between long and short sides, e.g., the ratio between the length of the long side and the length of the short side is 4:3. 
     To begin with, a plane in contact with the center of panel 10 is a tangent plane 11. With respect to panel 10, the longer axis of tangent plane 11 is designated as the X-axis, its shorter axis is designated as the Y-axis, and the perpendicular axis passing through center of the panel and perpendicular to the tangent plane is the Z-axis. Also, arbitrary points a and b of the X and Y axes, respectively, are located at points having the same relative ratio as the sides of panel 10. In other words, arbitrary points a and b are designated on the X-Y axis by the relationship that X&#39;:Y&#39;=a:b, where X&#39; is the length of the panel&#39;s longer side and Y&#39; is the short side&#39;s length. 
     As shown in FIG. 3, in the present invention, a thickness T 1  of panel 10 at an arbitrary point a on the X-axis along a line drawn perpendicular to tangent plane 11 is the same as a thickness T 2  of the panel at an arbitrary point b on the Y-axis along a line drawn perpendicular to the tangent plane 11. Further, a contour line 12 drawn through both points is located within a portion (marked by oblique lines) defined by a triangle formed by a straight line of X coordinates at X=a, a straight line of Y coordinates at Y=b, and a line connecting points a and b. Here, contour line 12 can also be placed on a line connecting arbitrary points a and b, or on a line obtained by connecting the straight line of X coordinates at X=a and the straight line of Y coordinates at Y=b. 
     FIG. 4 illustrates the continuation of contour line 12 drawn by carrying out the foregoing method throughout all four quadrants of the panel. FIG. 5 shows multiple contour lines 12 throughout the panel, having predetermined intervals between each contour line. 
     As illustrated in FIG. 5, in the cathode ray tube according to the present invention, contour lines 12 of panel 10 are drawn as closed loops without discontinuous points at the periphery of a picture 13 of panel 10. Therefore, while a picture is distorted at the periphery of a screen of a conventional panel due to the discontinuous contour lines, such distortion rarely occurs in the cathode ray tube according to the present invention. Further, the present invention provides a cathode ray tube which can realize a natural picture throughout the screen by maintaining a constant interval between contour lines.