US2763804A - Cathode ray tube device - Google Patents

Description

A. M. MORRELL JNVENTOR. Enma-m M. Mm'fmu.

Sep. 18, 1956 nite rates Patent O M CATHDE RAY TUBE DEVICE Albert M. Morrell, East Petersburg, Pa., assiguor to Radio Corporation of America, a corporation of Delaware Application December 1, 1953, Serial No. 395,371

Ciaims. (Cl. 313-70) This invention relates to systems for controlling the electron beams of cathode ray tubes and, particularly, to systems in which a plurality of beams is dellec'ted by a common deflection apparatus,

One type of cathode ray tube with which the present invention may be successfully employed is a color kinescope of the type having a luminescent screen as part of a target electrode in which different phosphor areas produce differently colored light when excited by electron beam components impinging upon it from different angles, the angle of impingement determining the particular color of the light produced by the phosphor areas.

It is necessary for the satisfactory operation of such kinescopes to effect substantial convergence of the different electron beam components at all points of the raster scanned thereby in the plane of the target electrode.

More particularly, it will be understood that the term ferent positions thereof. Accordingly, the apparatus by which a plurality of such electron beam components is produced may include on the one hand, three electron guns or, on the other hand, a single electron gun, to-

gether with the auxiliary apparatus by which the spinning motion is imparted to the beam.

` One particular beam convergence apparatus with which this invention may be advantageously employed includes for each beam component a pair of pole pieces located Ainternally of the kinescope envelope. It has been found that magnetic flux leaking from the deilection yoke traverses the various pairs of pole pieces differently, thereby tending to cause a misconvergence of the beam components.

It, therefore, is an object of the present invention to prevent leakage liux from a raster-scanning dellection yoke from affecting beam-convergence apparatus in a manner to cause misconvergence of a plurality of beam components.

Another object of the invention is to shield a plurality of individual beam-convergence electromagnets located in a predeflection region of a plurality of beam components from a raster-scanning deflection yoke.

In accordance with the copending application of H. L. Goodrich, S. N. 356,620, filed May 22, 1953, and now Patent No. 2,677,779, multi-beam cathode ray tube apparatus, having a plurality of beam convergence electromagnets located in a predeection region of the beams, is provided with a magnetic shield located between the beam, deflection apparatus and the beam convergence ap- 2,763,804 Patented Sept. 18, 1956 a disc of high-permeability material such as ferrite. The present invention, on the other hand, and in recognition of the fact that the horizontal frequency deflection iield is capable of producing extremely deleterious elects upon beam-convergence apparatus of that type, provides a shield designed specifically for shielding against the flux produced by the high frequency deflection coils. Moreover, the shield of the present invention is particularly advantageous in that it has not undesirable distorting effect upon the deflection yoke field.

Additional objects and advantages of the present in vention will become apparent to persons skilled in the art from a study of the following detailed description of the accompanying drawing, in which:

Figure 1 is a view showing the general arrangement of image-reproducing apparatus embodying an electron beam convergence system and including shielding means in accordance with this invention;

Figure 2 is a transverse cross-sectional view taken generally on the line 2-2 of Figure 1 and showing the arrangement of the beam convergence electromagnets illustrated in Figure l; and

Figure 3 is another transverse cross-sectional View taken generally along the line 3-3 of Figure 1 and showing a form of shielding apparatus in accordance with the invention.

Reference rst will be made to Figure Il for a general description of an illustrative embodiment of electron beam convergence system in connection with which the present invention finds particular application. The system includes a tri-color kinescope 11 which has a luminescent screen 12 provided with a multiplicity of small phosphor areas arranged in groups and capable respectively of producing light of the diiiierent primary colors in which the image is to be reproduced when excited by an electron beam. In back of and spaced from the screen 12 there is an apertured masking electrode 13 having an aperture for and in alignment with each group of phosphor areas of the screen 12.

In the particular tube illustrated, the kinescope also has a plurality of electron guns, equal in number to the number of primary colors in which the image is to be reproduced. Each of these guns may be conventional, lconsisting of a cathode, a control grid, an accelerating grid and a focusing electrode. Since the three-guns are identical, the different parts thereof will be referred to collectively as the cathodes 14', the control grids 14, accelerating grids 15, and the focusing electrodes 16. The three electron guns produce schematically represented beams 17, 18 and 19 by which to energize, respectively, the blue', red and green phosphor areas of the screen 12. When these electron beams are properly converged in the plane of the masking electrode 13, they pass through the apertures thereof from different directions and impinge upon different phosphor areas of the various groups so as to produce blue, red and green light. it is to be noted that the size of the phosphor areas, the angles between the beams and the spacing of the mask 13 from the screen 12 as compared with the length of the tube are exaggerated for better illustration of the operation of the kinescope.

The electron-optical apparatus of the kinescope 11 also includes a beam-accelerating electrode consisting, in the present instance, of a conductive wall coating 20 formed on the inner surface of the tubular glass neck 21 of the kinescope extending from the region adjacent to the outer end of the electrodes 16 to the conical section 22 of the tube which in this case is metallic. Suitable electrical connection (not shown) is made at the junction of the wall coating with the metal cone 22. A cylinder 20' electrically connected to the wall coating 20 also serves in the focusing of the several beams. Preferably, the target electrode. structure, including the masking electrode 13 and the luminescent screen 12 which for this purpose may be metallized, is electrically connected to the metal cone 22 by suitable mea-ns (not shown).

The described electrode structure of the kinescope may be energized in a conventional manner such asthat illustrated. The source of energy is represented by a battery 23 across the terminals of which there is connected a voltage divider 24. The cathodes 14' are connected to the grounded point of the voltage divider and the control grids 14 areconnected to a point which is somewhat negative relative to ground. The accelerating grids 15 are supplied with a potential of, for example, V200volts. Similarly, the focusing electrodes 16 are connected to a point on the voltage divider which may conventionally be at a potential of approximately 8000 volts positive relative lto the grounded cathodes. Also the beam-accelerating anode, including the wall coating 20 and metal cone 22, is connected to the voltage divider 24 at a point which may conventionally be approximately 27,000 volts positive relative to the grounded cathodes.

'Ehe electron beams 17, 18 and 19 are modulated suitably in intensity under the control of color-representative video. signals derived from a source 25. It will be understood that the video signal source is represented herein entirely diagrammatically since it does not form an essential part of the present invention. The signal source 25 usually will be part of a signal receiver and may be understood to include a signal detector, or equivalent device, together with one or more stages of video signal amplification. Alternatively, the video signal source may be` acolor television camera in the event that the kinescope 11 is employed as a monitor, for example. Also, it will be understood that the illustrated connection of the video signal source 25 to the electron guns of the kinescope 11 is merely diagrammatic and accordingly these connections may or may not be made directly to the cathodes 14. instead, it will be understood, that they may be made to they grids i4 or, in accordance with modesl of operation of color image-reproducing apparatus, the video signal source may be connected both to the cathodes and to the control grids of the electron guns.

Also associated with the color kinescope 11 is a dcilection yoke 26 which may be entirely conventional including two pairs of' suitably placed coils electrically connected together in such a manner that, when properly energized, electromagnetic elds are produced, whereby to effect both horizontal and vertical angular detiections of the electron beams so as to scan the usual rectangular raster. Encrgization of the deflection coils comprising the yoke 26 may be effected by conventional vertical and horizontal deflection Vwave generators 27 and 28, respectively. Such apparatus will be understood to function suitably to produce substantially sawtootli energy at both horizontal and vertical deflection frequencies so that the fields produced by the yoke 26 are varied in a substantially sawtooth manner.

IThe beam convergence control system also includes a plurality of electromagnetic fieldl producing elements such as the magnets 29 and 30 mounted around the neck 21 of the color kinescope adjacent to the predeflection paths of the electron beam components. It is to be understood that the precise location of these magnets is not necessarily indicated in this figure. Instead, as will appear in greater detail from a subsequent portion of the specification, it is to be understood that each of these magnets i s -locatedrelative to one of the electron beam components so as to influence its associated beam component to the substantial exclusion of the others. Furthermore, it is to b c understood that these magnets are of a character which, when suitably energized, produce respective elds which are transverse to the associated beam paths.

Each of these convergence electromagnets includes a pair of spaced pole pieces and at least one, energizing 4 winding. Preferably two windings are provided for each of the electromagnets for separate energization. These features will be described subsequently in greater detail.

Before describing the details of the convergence system, a brief description will be given of the general manner in which the apparatus functions to produce the desired results. The convergence magnets such as 29 and 3f) are energized by substantially unidirectional energy no as to effect an initial convergence of the electron beam ,:ornponents substantially in the plane of the apertured masking electrode 13. In order to do this, the unidirectional energization of these magnets is effected in such a way that the magnets may be individually energized in different magnitudes. In effecting this initial beam convergence, it is to be understood that the beam may be in any desired one of their different deflected positions. For example, they may be initially converged at the center of the raster to be scanned. Alternatively they may be initially converged at one corner of the raster.

The convergence control magnets such as 29 and 30 also arel dynamically energized by the control wave energy derived from a suitable generator (not shown in FigureA 1) so as tok effect a variation in the magnitude of the transverse fields produced respectively thereby. These field strength variations are in` accordance with a predetermined function of the beam deflection. Variations in thc strength of the fields produced by the convergence mag-y nets such as 29 and 30 effect corresponding variations in the paths of the electron beam components relative to the longitudinal axis of the tube. Hence, suitable variations are made in the convergence angles between the various beam components so as to produce the desired convergence or" they beam components substantially in the plane of the masking electrode 13.

For a further description of this type of beam convergence apparatus, reference now will be made to Figure 2 of the drawings. This figure shows rnore clearly the relative positions of the convergence magnets, such as 29 and 30 and, additionally, 31, relative to one another and to the electron beams with which they are respectively associated. Inasmuch as all of these magnets are substantially the same, only one of them will be described in detail. The convergence magnet 29, which is associated with the blue electron beam 17, is provided with a core having a body portion 32 and two external pole pieces 33 and 34. These pole pieces are mounted ,so as to be in close association with the tube neck 2,1.

Also, as indicated in Figure 1, the pole pieces extend for some distance longitudinally of the tube substantially as indicated. The magnet also is provided with an energizing coil structure 3S mounted upon the body portion 32. The energizing coil 35 preferably is provided with two windings, one for static energization and the other for dynamic energization in a manner in the above-cited Goodrich Patent 2,677,779. The convergence magnet 29 produces a field which, in the vicinity'of the electron beam 17, is substantially transverse to the axis of the kinescope. By means of such a field, the electron beam 17 may be moved toward or away from the longitudinal tube axis. The direction and magnitude of such a beam movement is controlled by the energization of the magnet by means including the coil 35.

In Figure 2, it also is illustrated that for each of the magnets there are provided on the inside of the tube neck 2,1` extended pole pieces so as to increase the effectiveness of these magnets.y The magnet 29, for example, is provided with a pair of inwardly extending pole pieces 36 and 37, associated respectively with the external pole pieces 33l and 34. By such means, it is seen that the re.

Vluctance of the magnetic circuit is considerably decreased,

and also the flux distribution of the field produced between the internal pole pieces 36 and 37 is considerably improved.

With beam convergence control apparatus of this general character, itrmayy be seen fromV a further considera- Y INK,

tion of Figure 2 that such apparatus is adversely effected by both horizontal and vertical deflection flux from the deliection yoke. Leakage deflection flux of a character to deflect the electron beam components 17, 18 and 19 to the left as viewed in the drawing is indicated by the broken lines 38. With respect to the internal pole pieces 36 and 37 associated with the electromagnet 29, no adverse effects of the leakage deliection flux are produced. However, it is seen that the leakage deflection flux 38 passes between the internal pole pieces 39 and 40 `of the electromagnet 3h substantially at right angles to these pole pieces since this is the path of lowest reluctance. Similarly, the leakage deflection flux 38 passes between the internal pole pieces 41 and 42 of the electromagnet 3l at right angles to these pole pieces. As a result, it may be seen that when the beams are being deflected to the left, the red beam 18 will be moved to a higher position than it would have in the absence of the leakage fiuX from the deflection yoke, as indicated by the arrow. Similarly, the green beam 19 will have a lower than normal position when beam deflection is toward the left. Conversely, when beam defiection by the yoke is toward the right, as viewed in Figure 2, the leakage flux 38 will be in the opposite direction, thereby tending to move the red beam downwardly and the green beam upwardly. Consequently, there is effected a misconvergence of the electron beam components as a result of the leakage fiux from the deflection yoke traversing the internal pole pieces of certain of the convergence electromagnets.

In accordance with the above-cited Goodrich Patent 2,677,779, there is provided means for preventing the leakage flux from the deflection yoke from adversely affecting the individual beam convergence electromagnets in the manner described. By referring again to Figure l l and also to Figure 3 of the drawings, this apparatus comprises a magnetic shield located between the defiec tion yoke 26 and the convergence electromagnets, such as 29 and 3d. The magnetic shield includes a disk-like shielding member of magnetic material located eX- v ternally of the tube. The shielding member 45 has a centrally located aperture of proper diameter to enable it to be suitably mounted in close proximity to the outside of the tube neck 2li. The outside diameter of the magnetic shielding member 45 is made sufficient to effect the desired shielding. The thickness of the member 45 i should be sufficient to provide the necessary mechanical strength. Also, it may be arranged so as to enable a sliding adjustment thereof for varying the effectiveness of the shield. Also, in accordance with the invention, the magnetic shield may include a plurality of members such as 45.

The present invention, in recognition of the fact that a magnetic shunt of ferrite or other high-permeability material produces an undesired distortion in the deflection field by virtue of its tending to short circuit the eld across the rear windings, thereby shifting the center of deflection, provides additional shielding means. More specifically, the present invention affords means for shielding against the high frequency, horizontal defiection field, which means have no distorting effect thereupon. Since conventional horizontal and vertical deflection rates are of the order lof 15.75 kilocycles and 60 cycles, respectively, applicant herein has found that an effective shielding which is frequency selective may take the simple form of a disk of copper or other nonmagnetic material having high electrical conductivity placed between the deflection yoke and the apparatus to be shielded (i. e., the beamconvergence magnets). Thus, there is illustrated in Figure l and Figure 3, a disk 48 having an outer diameter which is preferably greater than that of the magnetic disk 45, for reasons which will become apparent. Disk 48 has, as shown, a central aperture of such size as to accommodate the neck 21 of the kinescope and is located between the defiection yoke 26 and the magnetic disk 45. As in the case of the magnetic disk, copper disk 48 should be of sufficient thickness to possess the necessary mechanical strength and may be arranged to enable a sliding adjustment thereof. While the spacing of disk 48 from yoke 26 is not critical, it must be located between the yoke and the magnetic disk 45.

Before describing the action of the disk-s 45 and 48 in preventing leakage flux from interfering with the proper `operation of the beam convergence apparatus, certain facts should be noted. As is well known, a magnetic field will induce eddy currents in a member of electrically conductive material which, in turn, will produce a reverse magnetic field (Lenzs law); that is, these currents are always in such a direction as to oppose the motion or field producing them. Since the production of eddy curtrents is a function of the frequency of the inducing field, it will be apparent that the disk 48 will be far more affected, insofar as eddy currents are concerned, by the horizontal deflection field than by the vertical field. Thus, it will be apparent that the copper disk 48 will be more edective as a shield against the higher frequency field.

The leakage flux from the defiection yoke 26, in the absence of the shielding means, is indicated in Figure l, as following generally the path 46. It is seen thatthis path links the electromagnetic convergence apparatus and produces the deleterious effects previously described. By virtue of the invention, however, the horizontal frequency leakage flux is effectively shielded and confined to the region bounded by disk 48. Specifically, the horizontal flux traveling along the path shown by dotted line 49 will induce eddy currents in disk 48, which currents will produce a reverse magnetic field to cancel the leakage field. Moreover, while the horizontal field is thus prevented from reaching the convergence apparatus, it is not di-storted as in the case of a magnetic shunt. This feature is of real importance, since the configuration of the horizontal deflection field is quite critical in a tube of the type in question.

By means of the magnetic shunt 45, the lower frequency leakage flux from the vertical deflection field is confined substantially to the path indicated by the broken line 47. In this case, it is seen that the vertical field flux, which is not appreciably affected by the copper shield 48, is shunted into a path which is harmless, so far as the beam convergence apparatus is concerned. Since, as has been stated, the shield 48 effectively prevents the passage of horizontal defiection flux, the magnetic disk 45 can have no distorting effect thereupon.

While the disk 48 has been described as copper, it should be borne in mind that any high conductivity, non-magnetic material may be used, such, for example, as aluminum, silver and the like.

It, therefore, is seen from the foregoing description of an illustrative embodiment of the present invention that the leakage fiux from a raster-scanning deflection yoke is prevented from reaching the region in which individual electromagnets are employed to effect static as well as dynamic convergence of a plurality of electron beam components in the plane of a target electrode. The shield, in accordance with the invention and by means of which the leakage ux is prevented from reaching the pole pieces, comprises one disk of non-magnetic material of high electrical conductivity and one of magnetic material, which are located perpendicular to the neck of the cathode ray tube and in the order named between its defiection yoke and convergence apparatus. It is to be noted that the shielding apparatus may be of a fixed or adjustable type as desired.

The nature of the invention, having been set forth in the foregoing description of an illustrative embodiment thereof, its scope is pointed out in the appended claims.

I claim:

l. ln a cathode ray tube image reproducing system, wherein an electron beam component which, after traver-sing a predeflection region is angularly deflected both horizontally land vertically lat substantially different rates b y electromagnetic beam deection apparatus to scan a rectangular raster; apparatus located between `said p-redeection region andV said electromagneticV apparatus for excluding deflection ilux from said region, which com prises; a disk-like member of non-magnetic material having high electrical conductivity mounted externally of said tube and having a central aperture of suitable dimensions to accommodate said tube; and a second disk-like member of magnetic material mounted externally of said tube and having a central aperture of suitable dimensions to accommodate said tube, said second disk-like member being located on the side of said iirst member remote from Said beam deectioa apparatus- The invention as' defined by daim. 1 wherein Said first-named disk-like member is of greater external dimensions radially of said tube than said second member. 3. Inl a cathode ray tube image reproducing system, wherein ian electro-n beam component which, after traversingv a` pre-deection region is angularly deflected both horizontally and vertically at substantially different rates by electromagnetic beamr deflection apparatus to scan a rectangular riester; apparatus located between said predetiection region and said electromagnetic apparatus for excluding deflection flux from said region, which comprises :f a disk-like member of non-magnetic material having high electrical conductivity mounted externally of said tube land having la central aperture of suitable dimensions to accommodate said tube; and a second disklike member of magnetic4 material mounted externally of said tube and having a central aperture of suitable dimensions t accommodate said tube, said second disk-like member being spaced from and located on the side of said first member `remote from said beam deection apparatus. 4. in a cathode ray tube image-reproducing system wherein a plurality of electron beam components, which traverse pre-.deflection paths that are spaced respectively about the longitudinal axis `of the tube, are angularly deilected both horizontally and vertically at high and low frequencies, respectively, by electromagnetic beam d election apparatus to scan a raster in a predetermined plane, electron beam CODVergence apparatus comprising, a plurality of electromagnets respectively mounted adjacent to said pre-deection beam paths and energizable to produceV respective fields transverse to said beam paths, each of said electromagnets having a core including a body portion located externally of said tube and a pair of pole pieces located internally of said tube and respectively extending from points adjacent to opposite ends of said body portion into the region of said associated beam component; a non-magnetic shield of electrically conductive material located between said deflection apparatus and said convergence electromagnets to exclude high frequency delection ilux from said electromagnets; and a shield member of high permeability magnetic material located between said non-magnetic shield and said convergence electromragnets.

5.. Electron beam convergence apparatus as defined in claim 4, wherein, said non-magnetic shield and said shield member of magnetic material comprise disk-like members.

6. Electron beam convergence apparatus as defined in claim 5 wherein, said disk-like member of non-.magnetic material is of greater dimension radially of said tube than said magnetic member.

7. A shielding device for use with a cathode ray tube having an envelope, a deflection yoke mounted on a neck portion of said envelope and structure within said neck portion for providing predeflection control of an electron b eam of s aid tube, said shielding device comprising, a rst shield element of non-magnetic material having high electrical :conductivity [and adapted `to be mounted on said envelope neck portion between said deflection yoke and said beam control structure, and a second shield element of magnetically permeable material adjacent to lirst shield elementy and adapted to be mounted on said envelope neck portion between said rst shield element and said beam lconverger-me structure.

8.` The invention of claim 7 wherein said non-magnetic material of said rst shield element consists of one of the metals selected from the group comprising copper, aluminum and silver.

References Cited in the le of this patent UNITED STATES PATENTS

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