Cathode ray tube

Abstract: A cathode ray tube includes a vacuum envelope (23) having a substantially rectangular panel (20), a funnel (21) formed contiguous to the panel, and a cylindrical neck (22) formed contiguous to a small-diameter end portion of the funnel, an electron gun assembly (47) disposed in the neck to generate electron beams, a substantially rectangular phosphor screen (44) arranged on an inner surface of the panel on a funnel side to generate luminescence upon impingement of the electron beams, and a deflection yoke (48) mounted on an outer side of the funnel near a neck side over a predetermined range (24) along a first axis parallel to a normal to the phosphor screen, to generate a magnetic field in the funnel, deflect the electron beams along second and third axes perpendicularly intersecting the first axis and perpendicularly intersecting each other, and scan the phosphor screen. Within the predetermined range of the funnel, of inner and outer shapes of the funnel, at least the inner shape from the neck side toward the panel side is formed to have a section which is gradually deformed from a circular shape to a non-circular shape having a maximum diameter along a direction other than the second and third axes. The predetermined range of the funnel includes a region where, on an orthogonal coordinate system having the first axis as the origin and the second and third axes as coordinate axes, an angle between the second axis and a straight line connecting the origin and a position where the diameter becomes the maximum is different from an angle between a diagonal axis of the panel and the second axis depending on a position within the predetermined range along the first axis.

Description: The present invention relates to a cathode ray tube, e.g., a color picture tube, and more particularly, to a cathode ray tube capable of effectively decreasing the consumption power of the deflection yoke and the leakage magnetic field generated by the deflection yoke. FIG. 1A shows a color picture tube as an example of a conventional cathode ray tube. This color picture tube has a vacuum envelope. The vacuum envelope is formed with a substantially rectangular glass panel 1, a glass funnel 2 formed contiguous to the panel 1, and a cylindrical glass neck 3 formed contiguous to the small-diameter end portion of the funnel 2. As shown in FIG. 1B, a substantially rectangular phosphor screen 4 including three dot-like or stripe-like color phosphor layers respectively emitting blue, green, and red light is formed on the inner surface of the panel 1. An electron gun assembly 7 for emitting three electron beams 6 is arranged in the neck 3. This electron gun assembly 7 is an in-line electron gun assembly that emits the three electron beams 6 arranged in a line on the same horizontal plane. A deflection yoke 8 is mounted on the outer side of the funnel 2 near the neck 3 side. The deflection yoke 8 generates a pincushion type horizontal deflection field and a barrel type vertical deflection field. The three electron beams 6 arranged in a line and emitted from the electron gun assembly 7 are deflected by the horizontal and vertical deflection fields generated by the deflection yoke 8 in a horizontal direction H and a vertical direction V. Hence, when they reach the phosphor screen 4 through a shadow mask, the three electron beams 6 arranged in a line converge on the entire portion of the phosphor screen 4, i.e., on the entire screen surface without requiring an extra correction unit, and horizontally and vertically scan the phosphor screen 4, thereby displaying a color image. A color picture tube having this structure is called a self convergence in-line color picture tube and is widely in use. In such a cathode ray tube, e.g., a color picture tube, it is important to decrease the consumption power of the deflection yoke 8 which is the maximum power consumption source. More specifically, in order to improve the screen luminance, the anode voltage for finally accelerating the electron beams must be increased. In order to cope with OA equipments, e.g., a HDTV or a High-Definition TV and a PC or a Personal Computer, the deflection frequency must be increased. An increase in anode voltage and an increase in deflection frequency cause an increase in deflection power, i.e., an increase in consumption power of the deflection yoke. In particular, when the electron beams are deflected with a high frequency, the deflection field tends to leak to the outside of the cathode ray tube. For this reason, for a PC in which the operator sits close to the cathode ray tube, regulations against the leakage magnetic field are strict. In order to decrease the leakage magnetic field, conventionally, a method of adding a compensation coil is generally employed. When, however, a compensation coil is added, the consumption power of the PC increases accordingly. Therefore, in order to decrease the deflection power and the leakage magnetic field, it is preferable to decrease the neck diameter of the cathode ray tube and the outer diameter of the funnel near the neck side on which the deflection yoke is mounted, so that the deflection field efficiently acts on the electron beams. In the cathode ray tube, when an electron beam is deflected in a direction along the maximum size of the screen, i.e., along the diagonal direction, the deflection angle of the electron beam, i.e., the angle the trace of the deflected electron beam makes with the Z axis becomes large. When the deflection angle of the electron beam increases, the electron beam passes closely to the inner surface of the funnel near the neck side on which the deflection yoke is mounted. For this reason, if the neck diameter and the outer diameter of the funnel near the neck side are simply decreased, the outer electron beam 6 bombards the inner wall of the funnel 2 near the neck 3 side, as shown in FIG. 1A. A portion 10 where the electron beam 6 does not reach is thus formed on the phosphor screen 4, as shown in FIG. 1B. Therefore, in the conventional cathode ray tube, the neck diameter and the outer diameter of the funnel near the neck side cannot be simply decreased. Accordingly, it is difficult to decrease the deflection power and the leakage magnetic field. If the electron beams 6 continue to bombard the inner wall of the funnel 2 near the neck 3 side, the temperature of this portion rises to melt the glass. Then, a portion of the inner wall of the funnel becomes thin, and the funnel may break from this portion. In order to solve these problems, Jpn. Pat. Appln. KOKOKU Publication No. 48-34349 discloses a cathode ray tube 12 as shown in FIG. 2A. This tube is developed based on the fact that when drawing a rectangular raster on a phosphor screen, a passing region which is defined by the trace of an electron beam passing inside the funnel near the neck side on which the deflection yoke is mounted also becomes substantially rectangular. More specifically, in this cathode ray tube 12, as shown in FIGS. 2B to 2F showing the sections of the cathode ray tube 12 taken along the lines IIB-IIB to IIF-IIF, respectively, the section of a funnel 2 near the neck 3 side toward the panel 1 side, on which the deflection yoke is mounted, gradually changes from a circular shape to a substantially rectangular shape through an elliptic shape. In a cathode ray tube whose funnel near the neck side on which a deflection yoke is mounted is formed with sections as shown in FIGS. 2B to 2F, the inner diameter of the corner portion, i.e., a portion near the diagonal axis (D axis), where the electron beams tend to land, becomes large, as shown in FIG. 3, as compared to that in a cathode ray tube whose funnel 2 near the neck side remains circular. This prevents the electron beams from impinging on the inner wall of the funnel. In the cathode ray tube having a structure as shown in FIGS. 2B to 2F, its inner diameter near the major axis, i.e., the horizontal axis (H axis), and its inner diameter near the minor axis, i.e., the vertical axis (V axis), become shorter than in the cathode ray tube whose funnel 2 near the neck side remains circular. This aims at setting the horizontal deflection coil and the vertical deflection coil of the deflection yoke to be closer to the passing region of the electron beams in order to efficiently deflect the electron beams, thereby decreasing the deflection power. In this cathode ray tube, however, when the section of the funnel near the neck side on which the deflection yoke is mounted becomes closer to a rectangle, the atmospheric pressure resistance decrease, and safety is impaired. Therefore, in practice, the shape of the funnel near the neck side must be appropriately rounded, and the deflection power and the leakage magnetic field cannot thus be decreased sufficiently. As described above, it is very difficult to realize a decrease in deflection power and leakage magnetic field of a cathode ray tube while satisfying demands for a higher luminance and a higher frequency required by a display equipment, e.g., a HDTV and a PC. Conventionally, in a structure proposed to reduce the deflection power of a cathode ray tube, the shape of a funnel near the heck side toward the panel sides, on which a deflection yoke is mounted, gradually changes from a circular shape to a substantially rectangular shape through an elliptic shape. When however, the section of the funnel near the neck side becomes closer to a rectangle in this manner, the atmospheric pressure resistance suffers, impairing the safety. Therefore, in practice, the shape of the funnel near the neck side must be appropriately rounded, and the deflection power cannot thus be decreased sufficiently. Also, at the time the above-mentioned reference was published, the simulation techniques for designing the shape of the envelope of the cathode ray tube were not mature yet, and electron beam trace analysis and deflection field analysis as accurate as those nowadays done could not be performed. Therefore, a funnel that could decrease the deflection power and the leakage magnetic field while maintaining the atmospheric pressure resistance could not be designed. US-A-3 720 345 discloses a CRT where the yoke rear is conical or flattened at the upper side of the CRT only so that the maximum diameter coincides with the diagonal axis of the tube. US-A-3 591 035 discloses a CRT in which certain parts of the cross sections of the funnel have oblate or flattened configurations with substantially straight-line opposed sides. Accordingly, the points of maximum diameter in the respective sections along the tube axis in these portions coincide with the vertical axis. JP-A-8 007 792 discloses a CRT in which certain parts of the cross sections of the funnel are formed to be elliptical. The points of maximum diameter in the respective sections coincide with the horizontal axis. US-A-5 258 688 discloses a CRT having flat face panels and concave diagonal wall sections for reducing discontinuity stresses between the face panel and the funnel in the evacuated CRT envelope. This document is not specifically directed to the contour of the funnel in the vicinity of the neck side where the deflection yoke is mounted. It is the object of the present invention to provide a cathode ray tube capable of reducing the deflection power and the leakage magnetic field and preventing a decrease in atmospheric pressure resistance while satisfying demands for a higher luminance and a higher frequency. According to the present invention, there is provided a cathode ray tube comprising the features of claim 1. Preferreed embodiments are defined in the dependent claims. With the cathode ray tube according to the present invention, since the outer or inner shape of the funnel within the predetermined range is formed to have a structure as described above, the deflection yoke to be mounted over the predetermined range of the funnel can be made compact while satisfying demands for a higher luminance and a higher frequency. Also, this deflection yoke can be arranged close to the electron beam passing region. As a result, a deflection power corresponding to the power consumption of the deflection yoke, and a leakage magnetic field from the deflection yoke can be decreased. With this structure, a cathode ray tube having a sufficiently large atmospheric pressure resistance can be provided. This invention can be more fully understood form the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1A is a sectional view showing a conventional cathode ray tube; FIG. 1B is a front view of the cathode ray tube shown in FIG. 1A; FIG. 2A is a side view of the conventional cathode ray tube; FIGS. 2B to 2F are sectional views taken along the lines IIB-IIB to IIF-IIF, respectively, of FIG. 2A; FIG. 3 is a view for explaining an electron beam passing region obtained when a funnel near the neck side on which a deflection yoke is mounted is substantially rectangular; FIG. 4 is a view schematically showing the structure of a cathode ray tube, i.e., a color picture tube, according to an embodiment of the present invention; FIG. 5 is a view showing a vacuum envelope applied to a color picture tube according to the first embodiment of the present invention; FIG. 6 is a graph showing the trace of the ridge of an intermediate funnel region extending from the neck to the panel of the vacuum envelope shown in FIG. 5; FIG. 7 is a graph for explaining the relationship between the shape of the intermediate funnel region and the electron beam passing region of the conventional cathode ray tube; FIG. 8 is a graph for explaining the relationship between the shape of the intermediate funnel region and the electron beam passing region of the color picture tube of the first embodiment shown in FIG. 5; FIG. 9 is a table showing the maximum and minimum values of '(z) of nine types of cathode ray tubes CDT-A to CDT-I having different conditions; FIG. 10 is a view showing a vacuum envelope applied to a color picture tube according to the second embodiment of the present invention; FIG. 11 is a graph showing the trace of the ridge of an intermediate funnel region extending from the neck to the panel of the vacuum envelope shown in FIG. 10; FIG. 12 is a graph for explaining the atmospheric pressure resistance of the vacuum envelope of the second embodiment shown in FIG. 10; FIG. 13 is a view showing a vacuum envelope applied to a color picture tube according to the third embodiment of the present invention; FIG. 14 is a graph showing the trace of the ridge of an intermediate funnel region extending from the neck to the panel of the vacuum envelope shown in FIG. 13; FIG. 15 is a view showing a vacuum envelope applied to a color picture tube according to the fourth embodiment of the present invention; and FIG. 16 is a graph showing the trace of the ridge of an intermediate funnel region extending from the neck to the panel of the vacuum envelope shown in FIG. 15. A color picture tube according to an embodiment of the present invention as an example of a cathode ray tube will be described with reference to the accompanying drawing. As shown in FIG. 4, this color picture tube has a vacuum envelope 23. The vacuum envelope 23 is formed with a substantially rectangular glass panel 20, a glass funnel 21 formed contiguous to the panel 20, and a cylindrical glass neck 22 formed contiguous to the small-diameter end portion of the funnel 21. A substantially rectangular phosphor screen 44 including three dot-like or stripe-like color phosphor layers respectively emitting blue, green, and red light is formed on the inner surface of the panel 20. A shadow mask 45 having a large number of electron beam apertures is arranged inside the phosphor screen 44 to oppose it, i.e., on the neck side of the phosphor screen 44. An electron gun assembly 47 for emitting three electron beams 46 is disposed in the neck 22. This electron gun assembly 47 is an in-line electron gun assembly that emits the three electron beams 46 arranged in a line on the same horizontal plane. A deflection yoke 48 is mounted on the funnel 21 near the neck 22 side, i.e., on the outer side of an intermediate funnel region 24 of the funnel 21. The deflection yoke 48 generates a pincushion type horizontal deflection field and a barrel type vertical deflection field. The three electron beams 46 emitted from the electron gun assembly 47 are deflected by the horizontal deflection field generated by the deflection yoke 48 in the major axis direction, i.e., the horizontal axis (H axis) direction. Also, these three electron beams 46 are deflected by the vertical deflection field generated by the deflection yoke 48 in the minor axis direction, i.e., the vertical axis (V axis) direction. Hence, when the three electron beams 46 arranged in a line and emitted from the electron gun assembly 47 reach the phosphor screen 44 through the shadow mask 45, they horizontally and vertically scan the entire portion of the phosphor screen 44, i.e., the entire screen, thereby displaying a color image. A color picture tube having this structure is called a self convergence in-line color picture tube as the three electron beams 46 arranged in a line converge on the entire surface of the screen without requiring an extra correction unit. FIG. 5 shows the structure of a vacuum envelope 23 according to the first embodiment. The vacuum envelope 23 according to the first embodiment has a panel 20 formed such that a phosphor screen having an aspect ratio, i.e., the ratio of the length along the H axis and the length along the V axis, of 4 : 3 can be disposed on it. More specifically, assuming that the tube axis direction of the vacuum envelope 23, i.e., the direction along which the electron beams are emitted, is defined as the Z axis, the section of the panel 20 perpendicularly intersecting the Z axis has a substantially rectangular shape defined by the long sides of the panel substantially parallel to the major axis and the short sides of the panel substantially parallel to the minor axis. The ratio of the long sides to the short sides of this panel 20 is substantially equal to the aspect ratio of the phosphor screen, which is substantially 4 : 3. The section of a neck 22 perpendicularly intersecting the Z axis has a circular shape. Regarding an intermediate funnel region 24 of a funnel 21 connecting the panel 20 and the neck 22, its section perpendicularly intersecting the Z axis changes along the Z axis. This intermediate funnel region 24 includes a region on which the deflection yoke is to be mounted. The section of the intermediate funnel region 24 from the neck 22 side to the panel 20 side along the Z axis gradually changes from a circular shape similar to that of the neck 22 to a non-circular shape having the maximum diameter along a direction other than the major and minor axes of the panel 20. In other words, at the panel 20 side, the section of the intermediate funnel region 24 has a rectangular shape similar to a substantially rectangular shape defined by the long sides substantially parallel to the major axis of the panel and the short sides substantially parallel to the minor axis of the panel. When the section of the intermediate funnel region 24 is rectangular, the direction of the maximum dimension other than the major and minor axes is parallel to the diagonal direction of the panel 20, i.e., the diagonal axis (D axis). FIG. 6 shows in a solid line the trace of the ridge of the intermediate funnel region 24 extending from the neck 22 to the panel 20. As shown in FIG. 6, of the inner and outer shapes of the section of the intermediate funnel region 24, at least the inner shape from the neck 22 side to the panel 20 side is similar to a passing region 26 of the three electron beams that pass inside the intermediate funnel region 24, and is gradually deformed from a circular shape to a non-circular shape having its maximum diameter along a direction other than the major and minor axes of the panel 20, i.e., to a rectangular shape. The passing region 26 of the three electron beams is rectangular shape which is similar to a pincushion shape. In addition, the section of the intermediate funnel region 24 is formed such that, on an H-V orthogonal coordinate system having a point O along the tube axis or the Z axis as the origin, the major axis or the horizontal axis as the H axis, and the minor axis or the vertical axis as the V axis, an angle between the H axis and a straight line connecting the origin O and an arbitrary point on a solid line R1 changes depending on a position along the tube axis. The arbitrary point on the solid line R1 corresponds to a position where the diameter becomes the maximum at an arbitrary position along the tube axis. In FIG. 6, only the first quadrant of the H-V orthogonal coordinate system is shown. In the following H-V orthogonal coordinate system as well, only the first quadrant is shown. In other words, the intermediate funnel region 24 is formed such that, assuming that the angle between the H axis and the straight line connecting the origin O and the arbitrary point on the solid line R1 representing the trace of the ridge of the intermediate funnel region 24 is defined as , this  satisfies the following relation: tan  > 3/4 with respect to the ratio of 3/4 of the length of the phosphor screen along the vertical axis to the length of the same along the horizontal axis. In the conventional cathode ray tube 12 shown in FIGS. 2A to 2F, the passing region of the electron beam 6 of the funnel near the neck side as shown in FIG. 2D was supposed to form a rectangular shape having as the corner portion the passing position of the electron beam 6 that reaches the corner portion of a screen 27. More specifically, on the H-V orthogonal coordinate system having the point O along the tube axis as the origin, the major axis of the screen as the H axis, and the minor axis of the screen as the V axis, the angle  between the horizontal axis and the orthogonal axis serving as the maximum outer diameter of the section, i.e., the D axis was set to satisfy: tan  = N/M with respect to the aspect ratio of M : N of the phosphor screen. However, when the trace of the three electron beams emitted from the in-line electron gun assembly and arranged in a line along the H axis, and the deflection field generated by the deflection yoke were analyzed, a trace 28 of an electron beam in the intermediate funnel region 24 was not parallel to the D axis, and the passing region 26 of this electron beam was distorted to have a pincushion shape, as shown in FIG. 8. In general, when the horizontal and vertical deflection fields generated by the deflection yoke have a pincushion shape and a barrel shape, respectively, the center of the vertical deflection field is on the neck side of the center of the horizontal deflection field. Therefore, the electron beam that reaches the corner portion of the screen is deflected relatively strongly along the vertical direction on the neck side, and is then gradually deflected along both the horizontal and vertical directions as it is closer to the panel. As a result, the electron beam reaches the diagonal axis of the screen while drawing the trace 28 as shown in FIG. 8 and forms a passing region 26 distorted into a pincushion shape. When utilizing an in-line electron gun assembly, the corner portion of the passing region 26 is located on a trace along which a side beam among the three electron beams arranged in a line reaches the corner portion of the screen. Therefore, in a color picture tube whose phosphor screen has an aspect ratio of 4 : 3, assuming that the angle between the H axis and a straight line connecting the origin O and an arbitrary position P on the trace 28 of the side beam reaching the corner portion of the screen 27 on the H-V orthogonal coordinate system is defined as '(z), this '(z) sharply increases from zero at the neck-side end portion of the intermediate funnel region 24, as shown in FIG. 8. Inside a portion on which the deflection yoke is to be mounted, '(z) exceeds an angle between the H axis and the diagonal axis of the phosphor screen or the D axis, i.e., tan -1 (3/4) = 36.87° This '(z) changes to gradually decrease from a portion near the phosphor screen near the end portion side on which the deflection yoke is to be mounted, and reaches the corner portion of the screen. The maximum and minimum values of '(z) change depending on the various conditions, e.g., the structure of the cathode ray tube, the neck diameter, the deflection angle, the characteristics of the deflection field, and the like. For example, the larger the deflection magnetic field characteristics, i.e., the non-uniformity of the deflection field and the larger the difference between the center of the vertical deflection field and the center of the horizontal deflection field, the larger the maximum value of '(z). In some 110° deflection tube whose phosphor screen has an aspect ratio of 4 : 3, the maximum value of '(z) is about 41°. FIG. 9 shows the minimum and maximum values of '(z) of nine types of cathode ray tubes CDT-A to CDT-I having different conditions. 'min represents an angle between the H axis and the straight line connecting the origin O and a position of the end portion of the intermediate funnel region near the neck side where the side beam passes. 'max represents the maximum value of an angle between the H axis and the straight line connecting the origin O and a position in the intermediate funnel region where the side beam passes. As shown in FIG. 9, in all the nine tube types, the end portions of the funnel intermediate portions near the neck sides are formed such that ' is equal to -20° or more, and the funnel intermediate portion is formed such that the maximum value of ' is equal to  + 10° or less. In other words, assuming that the arc tangent of the aspect ratio of the phosphor screen is defined as ϕ, the intermediate funnel region is formed such that ' falls within the range of ϕ-20° ≦ ' ≦ ϕ + 10° The color picture tube described above according to the first embodiment is designed based on the result obtained through simulation analysis of the electron beam trace and the deflection field generated by the deflection yoke. More specifically, of the inner and outer shapes of the section of the intermediate funnel region 24 including a region on which the deflection yoke is to be mounted, at least the inner shape from the neck 22 side to the panel 20 side is similar to the passing region 26 of the electron beam that passes inside the intermediate funnel region 24, and is gradually deformed from a circular shape to a non-circular shape having its maximum diameter along a direction other than the major and minor axes of the panel 20, i.e., to a rectangular shape. The trace of the maximum diameter corresponds to the side beam pointing in the direction of the corner portion of the screen. The section of the intermediate funnel region 24 is formed such that, on the H-V orthogonal coordinate system, the angle between the H axis and the straight line connecting the origin O and an arbitrary point on the trace 28 of the side beam changes depending on a position along the Z axis. Preferably, assuming that the aspect ratio of the phosphor screen is M : N, the angle  between the H axis and the straight line connecting the origin O and the arbitrary point on the trace of the side beam is set to satisfy: tan  > N/M When the funnel 21 is formed in this manner, the deflection yoke mounted on the outer side of the intermediate funnel region 24 can be formed compact while avoiding impingement of the electron beams on the funnel 21 along the diagonal axis. Also, the deflection yoke can be mounted to be close to the passing region where the electron beam passes. As a result, the deflection power and the leakage magnetic field can be reduced while satisfying demands for a higher luminance and a higher deflection frequency. As described above, the angle  between the horizontal axis of the orthogonal coordinate system and the arbitrary position on the maximum diameter in the intermediate funnel region on which the deflection yoke is mounted should be changed in accordance with the trace of the electron beam that reaches the corner portion of the screen. The structure of a vacuum envelope 223 according to the second embodiment will be described. FIG. 10 shows a color picture tube having the vacuum envelope 223 according to the second embodiment. This color picture tube is horizontally elongated and has a phosphor screen having an aspect ratio of 16 : 9. This vacuum envelope 223 has a panel 220, a neck 222, and a funnel 221. The ratio of the long side to the short side of the panel 220 is 16 : 9, which is substantially equal to the aspect ratio of the phosphor screen. A section of the neck 222 perpendicularly intersecting the Z axis is circular. The funnel 221 connects the panel 220 and the neck 222. The remaining arrangement of this color picture tube is the same as that of the color picture tube of the first embodiment, and a detailed description thereof will therefore be omitted. A section of a region of the funnel 221 on which a deflection yoke is to be mounted, i.e., a section of an intermediate funnel region 224 which perpendicularly intersects the Z axis changes along the Z axis. In the same manner as in the first embodiment, the section of this intermediate funnel region 224 from the neck 222 side to the panel 220 side along the Z axis gradually changes from a circular shape similar to that of the neck 222 to a non-circular shape having the maximum diameter along a direction other than the major and minor axes of the panel 220. FIG. 11 shows in a solid line the trace of the ridge of the intermediate funnel region 224 extending from the neck 222 to the panel 220. As shown in FIG. 11, of the inner and outer shapes of the section of the intermediate funnel region 224, at least the inner shape from the neck 22 side to the panel 20 side is similar to a passing region 226 of the three electron beams that pass inside the intermediate funnel region 224, and is gradually deformed from a circular shape to a non-circular shape having its maximum diameter along a direction other than the major and minor axes of the panel 220, i.e., to a rectangular shape. The passing region 226 is substantially equal to a pincushion shape. In addition, the section of the intermediate funnel region 224 is formed such that, on an H-V orthogonal coordinate system, an angle between H axis and a straight line connecting an origin O and an arbitrary point on a solid line R2 changes depending on a position along the Z axis. The arbitrary point on the solid line R2 corresponds to a position where the diameter becomes the maximum at an arbitrary position along the Z axis. In particular, in this second embodiment, assuming that the angle between H axis and the straight line connecting the origin O and the arbitrary point on the solid line R2 is defined as ,  is set larger than the that of the first embodiment with respect to the aspect ratio of the phosphor screen. This is because, in the horizontally elongated color picture tube whose phosphor screen has an aspect ratio of 16 : 9, if the section of the intermediate funnel region 224 on which the deflection yoke is mounted has a non-circular shape having the maximum diameter along a direction other than the major and minor axes of the panel 220, the way of setting the angle  influences the atmospheric pressure resistance of the vacuum envelope 223. More specifically, in the horizontally elongated color picture tube whose phosphor screen has an aspect ratio (M : N) of 4 : 3 or 16 : 9, if the angle  in the intermediate funnel region is set equal to an angle 1 between the H axis and the diagonal axis of the screen, as indicated by a broken line in FIG. 12, to satisfy tan 1 = N/M then the atmospheric pressure resistance of the long side of the intermediate funnel region 224 at the substantially intermediate position, i.e., of a side wall 229a near the V axis is degraded extremely. For this reason, the side wall 229a near the long side of such a funnel must be rounded to a certain degree such that its diameter is large near the V axis. As a result, the diameter of the intermediate funnel region 224 becomes large, and the diameter of the deflection yoke near the V axis cannot be sufficiently decreased. In contrast to this, if the angle  of the intermediate funnel region 224 is set equal to an angle 2 between the H axis and the diagonal axis of a rectangle obtained by decreasing the length along the H axis and increasing the length along the V axis of a rectangle having an aspect ratio M : N, such that it satisfies tan 2 > N/M then the section of the intermediate funnel region 224 becomes close to a square, and the atmospheric pressure resistance of a side wall 229b near the V axis can be increased. More specifically, the closer 2 is 45°, the larger the atmospheric pressure resistance becomes, and the smaller the outer shape along the H or V axis becomes. Hence, the diameter of the deflection yoke can also be decreased. In the horizontally elongated color picture tube whose phosphor screen has an aspect ratio of 16 : 9, in the intermediate funnel region 224, the angle between the H axis and the straight line connecting the origin O and an arbitrary point on the trace of an electron beam reaching the corner portion of the screen tends to be larger than the angle between the diagonal axis of the screen and the horizontal axis. Therefore, if the intermediate funnel region is designed such that the angle  between the H axis and the straight line connecting the origin O and the position of the intermediate funnel region 224 where the diameter becomes the maximum becomes larger than the angle between the diagonal axis of the screen and the horizontal axis, the electron beam is prevented from impinging on the inner surface of the intermediate funnel region, and the high atmospheric pressure resistance of the vacuum envelope 223 can be firmly maintained, thereby improving the performance of the color picture tube. Hence, when the funnel 221 is formed as described above, the deflection yoke to be mounted on the outer side of the intermediate funnel region 224 can be made compact, and this deflection yoke can be mounted close to the electron beam passing region. As a result, the deflection power and the leakage magnetic field can be reduced while satisfying demands for a higher luminance and a higher deflection frequency, and a degradation in atmospheric pressure resistance of the vacuum envelope can be avoided. The structure of a vacuum envelope 323 according to the third embodiment will be described. FIG. 13 shows a color picture tube having the vacuum envelope 323 according to the third embodiment. This color picture tube is vertically elongated and has a phosphor screen having an aspect ratio of 9 : 16. This vacuum envelope 323 has a panel 320, a neck 322, and a funnel 321. The ratio of the long side to the short side of the panel 320 is 9 : 16, which is substantially equal to the aspect ratio of the phosphor screen. A section of the neck 322 perpendicularly intersecting the Z axis is circular. The funnel 321 connects the panel 320 and the neck 322. The remaining arrangement of this color picture tube is the same as that of the color picture tube of the first embodiment and a detailed description thereof will therefore be omitted. A section of a region of the funnel 321 on which a deflection yoke is to be mounted, i.e., a section of an intermediate funnel region 324 which perpendicularly intersects the Z axis changes along the Z axis. In the same manner as in the first embodiment, the section of this intermediate funnel region 324 from the neck 322 side to the panel 320 side along the Z axis gradually changes from a circular shape similar to that of the neck 322 to a non-circular shape having the maximum diameter along a direction other than the major and minor axes of the panel 320. FIG. 14 shows in a solid line the trace of the ridge of the intermediate funnel region 324 extending from the neck 322 to the panel 320. As shown in FIG. 14, of the inner and outer shapes of the section of the intermediate funnel region 324, at least the inner shape from the neck 322 side to the panel 320 side is similar to a passing region 326 of the three electron beams that pass inside the intermediate funnel region 324, and is gradually deformed from a circular shape to a non-circular shape having its maximum diameter along a direction other than the major and minor axes of the panel 320, i.e., to a rectangular shape. The passing region 326 is substantially equal to a pincushion shape. In addition, the section of the intermediate funnel region 324 is formed such that, on an H-V orthogonal coordinate system, an angle between the H axis and a straight line connecting an origin O and an arbitrary point on a solid line R3 changes depending on a position along the Z axis. The arbitrary point on the solid line R3 corresponds to a position where the diameter becomes the maximum at an arbitrary position along the Z axis. In particular, in this third embodiment, assuming that the angle between the H axis and the straight line connecting the origin O and the arbitrary point on the solid line R3 is defined as ,  is set smaller than the angle between the diagonal axis of the screen and the H axis. More specifically,  is designed to satisfy the following relation: tan  < N/M with respect to the aspect ratio M : N of the phosphor screen. For example, if the aspect ratio of M : N is 9 : 16, as shown in FIG. 13,  is set to satisfy the following relation: tan  < 16/9 Even with this structure, effects such as a decrease in deflection power and leakage magnetic field, prevention of degradation of the atmospheric pressure resistance of the vacuum envelope, prevention of impingement of the electron beams on the inner surface of the funnel, and the like can be obtained, in the same manner as in the second embodiment described above. The structure of a vacuum envelope 423 according to the fourth embodiment will be described. FIG. 15 shows a color picture tube having the vacuum envelope 423 according to the fourth embodiment. This color picture tube is horizontally elongated and has a phosphor screen having an aspect ratio of 4 : 3. This vacuum envelope 423 has a panel 420, a neck 422, and a funnel 421. The ratio of the long side to the short side of the panel 420 is 4 : 3, which is substantially equal to the aspect ratio of the phosphor screen. A section of the neck 422 perpendicularly intersecting the Z axis is circular. The funnel 421 connects the panel 420 and the neck 422. The remaining arrangement of this color picture tube is the same as that of the color picture tube of the first embodiment and a detailed description thereof will therefore be omitted. A section of a region of the funnel 421 on which a deflection yoke is to be mounted, i.e., a section of an intermediate funnel region 424 which perpendicularly intersects the Z axis changes along the Z axis. In the same manner as in the first embodiment, the section of this intermediate funnel region 424 from the neck 422 side to the panel 420 side along the Z axis gradually changes from a circular shape similar to that of the neck 422 to a non-circular shape having the maximum diameter along a direction other than the major and minor axes of the panel 420. FIG. 16 shows in a solid line the trace of the ridge of the intermediate funnel region 424 extending from the neck 422 to the panel 420. As shown in FIG. 16, of the inner and outer shapes of the section of the intermediate funnel region 424, at least the inner shape from the neck 422 side to the panel 420 side is similar to a passing region 426 of the three electron beams that pass inside the intermediate funnel region 424, and is gradually deformed from a circular shape to a non-circular shape having its maximum diameter along a direction other than the major and minor axes of the panel 420, i.e., to a rectangular shape. The passing region 426 is substantially equal to a pincushion shape. In addition, the section of the intermediate funnel region 424 is formed such that, on an H-V orthogonal coordinate system, an angle between the H axis and a straight line connecting an origin O and an arbitrary point on a solid line R4 changes depending on a position along the Z axis. The arbitrary point on the solid line R4 corresponds to a position where the diameter becomes the maximum at an arbitrary position along the Z axis. In particular, in the funnel 421 of this fourth embodiment, assuming that the angle between the H axis and the straight line connecting the origin O and the arbitrary point on the solid line R4 is defined as , on the neck side,  is set larger than the angle between the diagonal axis of the screen and the H axis, and on the panel side,  is set substantially equal to the angle between the diagonal axis of the screen and the H axis. This is designed considering the leakage magnetic field generated by the horizontal deflection coil of the deflection yoke. When the inner shape of the intermediate funnel region 424 is formed as described above, the diameter of screen-side opening of the deflection yoke along the V axis is reduced, so that the leakage magnetic field from the horizontal deflection coil can be further decreased. Even with this structure, effects such as a decrease in deflection power and leakage magnetic field, prevention of degradation of the atmospheric pressure resistance of the vacuum envelope, prevention of impingement of the electron beams on the inner surface of the funnel, and the like can be obtained, in the same manner as in the third embodiment described above. In the embodiments described above, color picture tubes are described. However, the present invention can also be applied to a cathode ray tube other than a color picture tube. As has been described above, in this cathode ray tube, since the outer or inner shape of the intermediate funnel region is formed to have a structure as described above, the deflection yoke to be mounted on the intermediate funnel region can be made compact while satisfying demands for a higher luminance and a higher frequency. Also, this deflection yoke can be set close to the electron beam passing region. As a result, a cathode ray tube can be provided which can decrease a deflection power corresponding to the power consumption of the deflection yoke, and a leakage magnetic field from the deflection yoke, while having a sufficiently high atmospheric pressure resistance.

Claims: A cathode ray tube comprising: a vacuum envelope (23) having a substantially rectangular panel (20), a funnel (21) formed contiguous to said panel (20), and a cylindrical neck (22) formed contiguous to a small-diameter end portion of said funnel (21) ; an electron gun assembly (47) disposed in said neck (22) to generate electron beams (46); a substantially rectangular phosphor screen (44) arranged on an inner surface of said panel (20) on a funnel (21) side to generate luminescence upon impingement of the electron beams (46); and a deflection yoke (48) mounted on an outer side of said funnel (21) near a neck (22) side over a predetermined range (24) along a tube axis (Z) coincidental with the central axis of the cylindrical neck (22), to generate a magnetic field in said funnel. (21), deflect the electron beams (46) in a horizontal axis (H) direction perpendicularly intersecting the tube axis (Z) and a vertical axis (V) direction perpendicularly intersecting the tube axis (Z) and the horizontal axis (H), and scan said phosphor screen (44), wherein, within said predetermined range (24) of said funnel (21), of inner and outer shapes of said funnel (21), at least the inner shape is substantially similar to a shape of an electron beam passing region (26), in the vicinity of the neck (22) side, and is formed to have a section perpendicular to said tube axis (Z) at an arbitrary point (O) along the tube axis (Z) which section is gradually deformed from a circular shape to a noncircular shape having a maximum diameter along a direction other than that of the horizontal and vertical axes (H,V), and in which section the angle  between the horizontal axis (H) and a straight line connecting said point (O) on the tube axis (Z) with a point (P) where the diameter becomes maximum changes depending on the position along the tube axis (Z) and is different from an angle between the horizontal axis (H) and a diagonal axis of said panel (20). A tube according to claim 1; wherein, assuming that a ratio of a length of said phosphor screen (44) along the vertical axis (V) to a length of said phosphor screen (44) along the horizontal axis (H) is defined as N/M, the predetermined range (24) of said funnel (21) includes a region which is formed to satisfy the relation tan  ≠ N/M depending on the position along the tube axis (Z). A tube according to claim 2, wherein N/M ≠ 1 and tan  is closer to 1 than N/M. A tube according to claim 1, wherein, assuming that an arc tangent of a ratio of the length of said phosphor screen (44) along the vertical axis (V) to the length of said phosphor screen (44) along the horizontal axis (H) is defined as ϕ, and the angle between the horizontal axis (H) and a straight line connecting said point (O) on the tube axis (Z) with an arbitrary position on the trace (28) of the side beam reaching the corner portion of the screen (27) is defined as ', the predetermined range (24) of said funnel (21) includes a region which is formed to satisfy the relation: ϕ - 20° ≤ ' ≤ ϕ + 10° depending on the position along the tube axis (Z). A tube according to any one of claims 1 to 4, comprising as said electron gun assembly (47) an in-line electron gun assembly arranged in a line along a direction parallel to the horizontal axis (H) adapted to emit three electron beams (46), and as said deflection yoke (48) one which forms a pincushion type deflection field along the horizontal axis (H) direction and forms a barrel type deflection field along the vertical axis (V) direction to converge the three electron beams (46) emitted from said in-line electron gun assembly and arranged in a line over an entire portion of said phosphor screen (44). A tube according to claim 5, wherein the predetermined range (24) of said funnel (21) includes a region formed such that a trace (R1) along the tube axis (Z) of the point (P) where the diameter becomes the maximum becomes substantially parallel to a trace along which a side beam among the three electron beams (46) emitted from said in-line electron gun assembly reaches a corner of said phosphor screen (44).

Inventors: KAMOHARA EIJI, KOJIMA TADAHIRO, SANO YUUICHI, YOKOTA MASAHIRO, KAMOHARA, EIJI, KOJIMA, TADAHIRO, SANO, YUUICHI, YOKOTA, MASAHIRO
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1997
Main classification: H01J29
IPC codes: H01J29