Patent Grant
6987350
This application claims priority to and the benefit of Korean Patent Application No. 2002-47554 filed on Aug. 12, 2002 and Korean Patent Application No. 2003-31666 filed on May 19, 2003, the entire disclosures of which are incorporated herein by reference.
(a) Field of the Invention
The present invention relates to an inner shield for a color cathode ray tube, and more particularly, to an inner shield for a color cathode ray tube that effectively blocks external magnetic fields such as the earth's magnetic field to thereby minimize mis-landing of electron beams caused by fluctuations in the external magnetic fields. The present invention also relates to a cathode ray tube including the inner shield.
(b) Description of the Related Art
A color cathode ray tube (CRT) is a display device in which a phosphor screen is scanned by three electron beams emitted from an electron gun to realize specific images. A path of the three electron beams is altered by the earth's magnetic field, which is created by the earth's north and south magnetic poles, to thereby negatively affect purity, raster position, and convergence characteristics of the CRT.
The earth's magnetic field includes a vertical component that is vertical with respect to the earth's surface (earth's vertical magnetic field), and a horizontal component that is horizontal to the earth's surface (earth's horizontal magnetic field). Movement of the electron beams by the earth's horizontal magnetic field may be divided into North-South (N-S) electron beams movement and East-West (E-W) electron beams movement, depending on the direction of the CRT.
That is, with reference to
Forces received by the electron beams caused by the earth's magnetic field include a horizontal component and a vertical component. It is mostly the horizontal component that affects picture characteristics of the CRT. This is because with the shadow mask having elongated vertical slots used mainly in consumer CRTs(also referred to as color picture tube) and the shadow mask having dot-shaped holes used mainly in commercial CRTs(also referred to as color display tube), the horizontal component that moves the electron beams in the horizontal direction (x-axis direction) moves the electron beams away from their designated slots or holes.
Therefore, an inner shield is mounted within the CRT to minimize movement of the electron beams caused by the influence of the earth's magnetic field. A conventional inner shield is shown in
An inner shield 100 causes offset or reinforcing interference with the earth's magnetic field in areas surrounding the path of the electron beams to thereby vary distribution of the earth's magnetic field (in these areas) in directions that minimize changes in the landing of the electron beams. The inner shield 100 is mounted to a mask frame (not shown) and surrounds a path of the electron beams within a funnel (not shown) of the CRT. The inner shield 100 includes an electron gun opening 102 and a screen opening 104 through which the electron beams pass, and a pair of long sections 106 and a pair of short sections 108. The long sections 106 and the short sections 108 are interconnected to form the electron gun opening 102 and the screen opening 104.
Formed at the end of each of the short sections 108 forming the electron gun opening 102, is a V-shaped cutaway section 110 for minimizing N-S electron beams movement. A depth h of the V-shaped cutaway sections 110, which is measured from an apex of the V-shaped cutaway sections 110 to imaginary lines formed flush with edges of the long sections 106 forming the electron gun opening 102, is inversely proportional to an amount of N-S electron beams movement and directly proportional to an amount of E-W electron beams movement. That is, the greater the depth h of the V-shaped cutaway sections 110, the greater the reduction in the amount of N-S electron beams movement and the greater the increase in the amount of E-W electron beams movement.
As a result of this adverse affect on E-W electron beams movement while favorably affecting N-S electron beams movement, the depth h of the V-shaped cutaway sections 110 is limited to a predetermined range. This means that N-S electron beams movement may be controlled only up to a point.
With reference to
Screen margin refers to the amount of margin that exists before the electron beams land on adjacent phosphors of another color when landing errors occur. Screen margin is affected by such factors as pitch, phosphor width, electron beam size (mask hole size), landing errors, and phosphor arrangement errors.
In a CRT where the mask and screen are formed in a globe-like shape about a line passing through a tube axis of the electron gun, deviation in the emission angle of the electron beams results in identical amounts of deviation over the entire area of the screen. However, in a CRT where the mask and screen are formed in a flat configuration, the amount of deviation on the screen is not identical over the entire area of the screen. That is, for a flat screen, the same deviation in the emission angle of the electron beams translates into larger amounts of deviation on the screen at peripheral areas thereof. It is for this reason that there is an insufficient screen margin in the area {circle around (4)} as described above.
In one embodiment, the present invention provides an inner shield for a color cathode ray tube that effectively reduces N-S electron beams movement, while at the same time preventing increases in the amount of E-W electron beams movement. The present invention also provides a cathode ray tube having the inner shield.
An inner shield for a cathode ray tube includes a screen opening and an electron gun opening through which electron beams pass, and a main body including a pair of long sections and a pair of short sections interconnected to form the screen opening and the electron gun opening. Each of the short sections includes a cutaway section having a pair of first cutaway sections formed starting from the electron gun opening and extending at a predetermined angle for a predetermined distance toward the screen opening, and a second cutaway section formed starting from where the first cutaway sections end and extending inwardly toward the screen opening, the second cutaway section being formed to extend past imaginary lines formed from where the first cutaway sections end to a furthermost inward point of the second cutaway section, that is, the point of the second cutaway section closest to the screen opening.
In one exemplary embodiment, the second cutaway section is formed as a circular arc or in substantially a circular arc configuration. In this case, if the second cutaway section is extended using imaginary lines to complete the circle started by its circular arc shape, a center of this circle is closer to or alternatively, farther from the screen opening than an imaginary line formed by connecting two points of the first cutaway sections where each of the first cutaway sections start in the electron gun opening.
In another exemplary embodiment, the second cutaway section is formed as a predetermined section of an ellipse or in substantially an elliptical form (ellipse). In this case, if the second cutaway section is extended using imaginary lines to complete the ellipse, a center of this ellipse is closer to or alternatively, farther from the screen opening than an imaginary line formed by connecting two points of the first cutaway sections where each of the first cutaway sections start in the electron gun opening.
In another exemplary embodiment, if an imaginary line is drawn between two points where the first cutaway sections end, the second cutaway section is formed as a trapezoid with the imaginary line forming the base of the trapezoid.
In the case of a consumer CRT(also referred to as color picture tube) having a slot-type phosphor pattern, the present invention is configured with a depth of the cutaway sections being 50% or less of a height of the inner shield, preferably between 44 and 48% of the height of the inner shield. Here, the height of the inner shield is measured as a length between the electron gun opening and the screen opening, and the depth of the cutaway sections is measured in the same direction. Such a configuration ensures that E-W electron beams movement does not abruptly increase.
In the case of a commercial CRT(also referred to as color display tube) having a dot-type phosphor pattern, the present invention is configured with the depth of the cutaway sections being equal or greater than 50% of the height of the inner shield.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and together with the description, serve to explain the principles of the invention.
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
With reference to the drawing, a cathode ray tube (CRT) 10 according to an embodiment of the present invention includes a face panel 12, a neck 16, and a funnel 14 interconnecting the face panel 12 and the neck 15. The face panel 12, neck 16, and funnel 14 form a tube assembly 18, an inside of which is maintained in a high vacuum state.
A phosphor screen 12′ is formed on an inner surface of the face panel 12. The phosphor screen 12′ is realized through a plurality of red, green, and blue phosphors. An electron gun 20 that emits electron beams toward the phosphor screen 12′ is mounted within the neck 16. Also, a deflection yoke (not shown) is mounted to an outer circumference of the funnel 14. The deflection yoke generates a deflection magnetic field for deflecting the electron beams emitted from the electron gun 20.
A shadow mask 24 having a plurality of electron beam apertures 22 formed therein is suspended at a predetermined distance from the phosphor screen 12′ of the face panel 12 by a mask frame 16. One end of a magnetic blocking device, that is, an inner shield 28, is mounted to the mask frame 26. The inner shield 28 encompasses a section of the path of the electron beams.
In the CRT 10 structured as in the above, electron beams (not shown) corresponding to picture signals emitted from the electron gun 20 are deflected by the magnetic field generated by the deflection yoke and pass through the electron beam apertures 22 of the shadow mask 24 to undergo color separation and thereby land on designated phosphors of the phosphor screen 12′.
In the above process, a path of the electron beams is varied by influence of external magnetic fields. A horizontal force Fx and a vertical force Fy acting on each of the electron beams may be respectively expressed as:
Fx=−e(VyBz−VzBy)
Fy=−e(VxBz−VzBx), [equation 1]
where e is the electric charge in coulombs (C); Vx, Vy, and Vz are velocities (m/s) of the electron beams in a horizontal direction (x-axis), a vertical direction (y-axis), and a tube axis direction (z-axis) of the CRT 10; respectively. Bx, By, and Bz are strengths (T) of the components of the earth's magnetic field in the horizontal direction (x-axis), vertical direction (y-axis), and the tube axis direction (z-axis) of the CRT 10 respectively.
As is evident from equation 1, the force Fx acting on each of the electron beams in the horizontal direction is determined by the strengths of the earth's magnetic field in the peripheries of each of the electron beams, if the electron beam velocities are constant. That is, the force Fx is proportional to the difference between Bz and By. Similarly, the force Fy acting on the electron beams in the vertical direction is proportional to the difference between Bz and Bx, when it is assumed that the electron beam velocities are constant.
Therefore, it is clear that in order to reduce movement of the electron beams caused by external magnetic fields, the component Bz that is parallel to the tube axis (z-axis) of the CRT 10 must be induced toward the component Bx or the component By. The inner shield of the present invention varies the distribution of magnetic fields using a structure described below such that N-S electron beams movement of the electron beams is minimized. In the embodiments described below, the inner shield is by way of example, approximately 184 mm in length and approximately 161 mm in height.
An inner shield 28 of the first embodiment of the present invention includes a pair of long sections 30 provided opposing one another in a vertical direction (y-axis direction), and a pair of short sections 32 provided opposing one another in a horizontal direction (x-axis direction). The long sections 30 and the short sections 32 are interconnected to encompass a section of the path of the electron beams emitted from the electron gun 20.
Flanges 34 are formed along edges of the long sections 30 closest to the phosphor screen 12′ of the face panel 12 when the inner shield 28 is mounted within the CRT 10. The flanges 34 are connected to the mask frame 26 to thereby realize the mounting of the inner shield 28 within the tube assembly 18 of the CRT 10. An electron gun opening 36 and a screen opening 38 are defined by the long sections 30 and the short sections 32, and are formed at opposite ends of the inner shield 28. That is, the inner shield 28 is mounted such that the screen opening 38 is adjacent to the shadow mask 24, and the electron gun opening 36 is closest to the electron gun 20.
Further, cutaway sections 40 are formed at the ends of the short sections 32 forming the electron gun opening 36. The cutaway sections 40 act to minimize N-S electron beams movement of the electron beams. Each of the cutaway sections 40 includes two first cutaway sections 42 that are formed each starting from the electron gun opening 36 and extending at a predetermined angle for a predetermined distance toward the screen opening 38, and a second cutaway section 44 formed starting from where each of the first cutaway sections 42 ends and extending in a predetermined circular arc shape for a predetermined distance toward the screen opening 38. As shown in
If the second cutaway section 44 is extended using imaginary lines to complete the circle started by its circular arc shape as shown in
A height H of the inner shield 28 (i.e., a distance from the screen opening 38 to the electron gun opening 36) for use in a 34-inch CRT is approximately 161 mm. Therefore, the cutaway sections 40 structured in this manner have a depth D that is approximately 46% of the height H of the inner shield 28.
Results of measuring the horizontal force Fx acting on the electron beams by external magnetic fields while the electron beams emitted from the electron gun 20 are moving in the area {circle around (4)} of
The eclipse appearing in
Amounts of N-S movement and of E-W movement of the electron beams at each area of measurement ({circle around (1)}˜{circle around (5)}) of
As shown in Table 1, the inner shield 28 of the first embodiment of the present invention significantly reduces N-S movement of the electron beams over the conventional inner shield with the V-shaped cutaway sections of the same depth D as the cutaway sections of the present invention.
Hence, the inner shield 28 of the first embodiment of the present invention significantly reduces N-S movement of the electron beams while preventing an increase in E-W movement of the electron beams. Substantial reductions are realized particularly in areas {circle around (3)} and {circle around (4)} indicated in
In more detail, an inner shield 28a of the first modified example includes cutaway sections 40a that are formed at the ends of the short sections 32 forming the electron gun opening 36 as in the first embodiment. Each of the cutaway sections 40a includes two first cutaway sections 42a that are formed starting from the electron gun opening 36 and extending at a predetermined angle for a predetermined distance toward the screen opening 38, and a second cutaway section 44a formed starting from where the first cutaway sections 42a end and extending in a predetermined arc shape for a predetermined distance toward the screen opening 38.
If each of the second cutaway sections 44a is extended using imaginary lines to complete the circle started by its circular arc shape as shown in
An inner shield 28b of the second modified example includes cutaway sections 40b that are formed at the ends of the short sections 32 forming the electron gun opening 36 as in the first embodiment. Each of the cutaway sections 40b includes two first cutaway sections 42b that are formed starting from the electron gun opening 36 and extending at a predetermined angle for a predetermined distance toward the screen opening 38, and a second cutaway section 44b formed starting from where the first cutaway sections 42b end and extending in a predetermined circular arc shape for a predetermined distance toward the screen opening 38.
If each of the second cutaway sections 44b is extended using imaginary lines to complete the circle started by its circular arc shape as shown in
N-S movement and E-W movement test results for the first and second modified examples of
The inner shields 28 and 28a of the first embodiment and of the first modified example may be applied to both CPT(color picture tube)s and CDT(color display tube)s. This is because with these inner shields 28 and 28a, the depths D and D1 of the cutaway sections 40 and 40a are less than 50% of the heights H of the inner shields 28 and 28a, thereby preventing a reduction in picture quality caused by increases in E-W electron beam movement.
The CPTs mentioned above refer to CRTs having slot-shaped phosphors on the phosphor screen 12′ that experience a reduction in picture quality with increases in E-W electron beams movement. The CDTs refer to CRTs having dot-shaped phosphors on the phosphor screen 12 in which E-W electron beams movement is limited such that picture quality is not significantly affected by the E-W movement.
As described above, the depths D and D1 of the cutaway sections 40 and 40a are less than 50% of the inner shield heights H. Preferably, the depths D and D1 of the cutaway sections 40 and 40a are between 40% and 48% of the heights H of the inner shields 28 and 28a to thereby allow application of the inner shield to both CPTs and CDTs.
With respect to the second modified example of
An inner shield 28c of the second modified example includes cutaway sections 40c that are formed at the ends of the short sections 32 forming the electron gun opening 36 as in the first embodiment. Each of the cutaway sections 40c includes two first cutaway sections 42c that are formed starting from the electron gun opening 36 and extending at a predetermined angle for a predetermined distance toward the screen opening 38, and a second cutaway section 44c formed starting from where the first cutaway sections 42c end and extending in a predetermined circular arc shape for a predetermined distance toward the screen opening 38.
If each of the second cutaway section 44c is extended using imaginary lines to complete the circle started by its circular arc shape, as shown in
In the above examples, the second cutaway sections 44, 44a, 44b, and 44c are described as being formed in circular arc shapes. However, as long as the second cutaway section extends outside and encompass imaginary lines formed from where the first cutaway sections end to a furthermost inward point of the second cutaway sections, the second cutaway sections may be formed in a variety of different configurations. Examples of such different configurations are shown in
As shown in
If the second cutaway section 52 is extended using imaginary lines, as shown in
As shown in
If the second cutaway section 60 is extended using imaginary lines as shown in
As shown in
For each of the cutaway sections 64, if an imaginary line 69 is drawn between two points where the first cutaway sections 66 end (or where the second cutaway section 68 begins), the second cutaway section 68 is formed as a trapezoid with the imaginary line 69 forming the base of the trapezoid.
As described above, the inner shield of the present invention having first and second cutaway sections effectively reduces N-S movement of the electron beams at all areas of the screen and that are caused by external magnetic fields, while preventing an increase in E-W movement. Therefore, a reduction in purity, raster distortion, and convergence characteristic variations caused by external magnetic fields such as the earth's magnetic field are minimized.
Although embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2002-0047554 | Aug 2002 | KR | national |
| 10-2003-0031666 | May 2003 | KR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20010026119 | Murai et al. | Oct 2001 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20040080254 A1 | Apr 2004 | US |
