US3555473A - Convergence apparatus - Google Patents

Abstract

AN ELECTRON BEAM CONVERGENCE APPARATUS FOR A MULTIBEAM COLOR REPRODUCING CATHODE-RAY TUBE WHICH HAS POLE PIECE PAIRS INDIVIDUALLY FLAKING THE PATH OF AT LEAST TWO OF THE THREE BEAMS, INCLUDES A CORE OF MAGNETIC MATERIAL HAVING A PAIR OF SPACED LEGS EACH OF WHICH IS SUPPORTED ADJACENT AN ASSIGNED POLE PIECE. A PERMANENT MAGNET IS MAGNETICALLY COUPLED TO THE CORE FOR SIMULTANEOUSLY AND SYMMETRICALLY SUBJECTING THE TWO ELECTRON BEAMS TO EQUAL AND OPPOSITE HORIZONTAL STATIC CONVERGENCE DEFLECTION FIELD COMPONENTS. AN ADDITIONAL MAGNET, WHICH IS MAGNETICALLY ISOLATED FROM THE CORE, IS PROVIDED FOR SIMULTANEOUSLY AND SYMMETRICALLY SUBJECTING THE TWO BEAMS TO EQUAL AND OPPOSITE VERTICAL STATIC CONVERGENCE DEFLECTION FIELD COMPONENTS, BUT WITHOUT AFFECTING THE HORIZONTAL COMPONENTS.

Description

Jan.12, 1971 RQmLEWICZ ETAL 3,555,473

CONVERGENCE APPARATUS Filed July 7, 1969 2 SheetsSheet l I C\JLO T \NN \nvenTors Rqyrnond C.F| lewlcz vlcfor J. Kor on I Attorney Jan. 1 1971 R. c. FiGLEWlCZ ETAL 3 CONVERGENCE APPARATUS 2 Sheets-Sheet 2 Filed July '7, 1969 Red Beam Inventors Raymond C. FI lewicz Victor J. Kar mon Attorney 3,555,473 CONVERGENCE APPARATUS Raymond C. Figlewicz, Park Ridge, and Victor J.

Karhan, Glenview, IlL, assignors to Zenith Radio Corporation, Chicago, 111., a corporation of Delaware Filed July 7, 1969, Ser. No. 839,491 Int. Cl. H01f 1/00 US. Cl. 335212 4 Claims ABSTRACT OF THE DISCLOSURE An electron beam convergence apparatus for a multibeam color reproducing cathode-ray tube which has pole piece pairs individually flanking the ath of at least two of the three beams, includes a core of magnetic material having a pair of spaced legs each of which is supported adjacent an assigned pole piece. A permanent magnet is magnetically coupled to the core for simultaneously and symmetrically subjecting the two electron beams to equal and opposite horizontal static convergence deflection field components. An additional magnet, which is magnetically isolated from the core, is provided for simultaneously and symmetrically subjecting the two beams to equal and opposite vertical static convergence deflection field components, but without affecting the horizontal components.

BACKGROUND OF THE INVENTION The subject invention relates, in general, to color television but more particularly to convergence apparatus for use with color reproducing cathode-ray tubes.

The tri-bearn cathode-ray tube employed in conventional color television receivers constitutes one type of cathode-ray tube for which the invention has particular utility. Such a tube comprises three electron beam guns disposed in a delta array, a shadow or aperture mask and a screen formed of triads of red, green and blue phosphor dots. The shadow mask functions as a color selector in that it insures that each beam impinges only upon color dots of an assigned hue. To achieve color fidelity in such a system however, it is imperative that the three beams converge at or near the plane of the screen. Generally, convergence correction of the beams is applied prior to scanning deflection and for this purpose two distinct beam convergence arrangements are employed; one to effect an initial or static convergence of the three beams at or near the center of the screen and a second arrangement to insure convergence of the beams at the extremities of their sweeps during scansion, that is dynamic convergence.

A conventional static convergence arrangement includes three adjustable magnets mounted upon the neck of the tube and individually disposed in radial alignment with an assigned one of the three beams. The fields of the magnets are so oriented with respect to the beam path that, upon adjustment, each magnet eifects a radial displacement of its assigned electron beam, that is, a displacement either toward or away from the tube axis. This orientation of the fields is established by a magnetic circuit disposed within the next section of the tube. One such circuit is provided for each beam and typically takes the form of a pair of elongated pole pieces which flank the path of their assigned electron beam to direct the field of the magnet across the path of the beam.

Dynamic convergence is attained by resort to electromagnetic apparatus, one for each of the three beams, which also directs magnetic flux into the internal pole pieces. Individual electromagnets are energized by correction signals derived from the horizontal and vertical deflection circuits. The electromagnetic apparatus, as well as the permanent magnets, are commonly mounted on a United States Patent O "ice the cost and complexity of the circuits required to derive the correction signals for such apparatus, it is obvious that prior art convergence apparatus constitutes a significant factor in the cost of a color television receiver.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of the invention to provide an improved convergence assembly for a color reproducing cathode-ray tube.

It is also an object of the invention to provide an easily adjustable convergence apparatus for achieving static beam convergence in a delta gun color reproducing cathode-ray tube.

It is a specific object of the invention to provide a static convergence apparatus for a delta gun cathode-ray tube which effects significant economies over prior art convergence apparatus.

In accordance with the invention an electron beam convergence apparatus for a multi-beam cathode-ray tube having pole piece pairs individually flanking the paths of at least two of the electron beams comprises a dynamic convergence unit that includes a core of magnetic material. A pair of coils are wound on respective spaced apart legs of the core which are adapted to be supported adjacent an assigned pole piece pair in a magnetic flux coupling relation therewith. Means, consisting essentially of a single permanent magnet magnetically coupled to the core, is provided for simultaneously and symmetrically subjecting the two electron beams to equal and opposite horizontal static convergence magnetic deflection field components in response to a continuous simple movement of the magnet. Additional means, consisting essentially of a separate permanent magnet device magnetically isolated from the core, is provided for simultaneously and symmetrically subjecting the two electron beams to equal and opposite vertical static convergence magnetic deflection field components, but without affecting the horizontal components, in response to a continuous simple movement of the separate magnet device.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof may best be understood, however, by reference to the following description taken in conjunc tion with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIG. 1 is an elevational view, partly in section, of the inventive convergence apparatus positioned upon the neck of a tri-beam cathode-ray tube.

FIG. 2 is a side view of the convergence apparatus shown in FIG. 1;

FIG. 3 is a fragmentary view of the convergence apparatus of FIG. 1 and includes a schematic representation of the horizontal static convergence magnetic field pattern developed by one portion of that apparatus;

FIGS. 3A and 3B are vector diagrams helpful in an understanding of the magnetic field patterns developed by the apparatus of FIG. 3; and

FIG. 4 is a schematic representation of the vertical static convergence magnetic field pattern developed by another portion of the convergence apparatus of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT The convergence apparatus 10 depicted in FIGS. 1 and 2 embodies a form of the invention and, as there shown, is mounted upon the neck 11 of a tri-beam cathode-ray tube of the type employed in a conventional color television receiver. The depicted orientation of the electron gun structure is as it appears when viewed from the display screen looking back toward the beam sources. The gun structure comprises a trio of electron guns G, R, B which are symmetrically disposed about the longitudinal axis of the tube in the manner shown to develop the commonly designated green, red and blue electron beams, respectively. Supported within the neck portion of the tube and extending radially from the tube axis are pairs of metallic pole pieces 12, 13 and 14. These pole pieces, which are spaced about the tube axis on 120 centers, present selected ones of their outer faces 1211-1212, 13a13b and 14aa-14b, see FIG. 3 for these details, to electromagnetic devices which are included in convergence apparatus and which will be more fully described below. The inner faces 12c-12d, 13c-13d and 14c-14d of these pole pieces, on the other hand, flank and paths of the green, red and blue electron beams. A Y-shaped magnetic shield 15 is interposed between the internal pole pieces to prevent interaction of the magnetic fields developed across the pole piece pairs.

Convergence apparatus 10 is a two piece construction comprising two substantially identical oppositely disposed housings or lobes 16, 17 which are mounted upon an elongated frame 24 that is apertured to receive tube neck 11. As best seen in FIG, 1, each of lobes 16, 17 includes an inner arcuate wall section having a curvature that conforms to the outside wall of tube neck 11. A compressible spring-like clamp 18, fitted with an adjusting screw 19, secures apparatus 10 at a desired location upon the neck, that is with lobe 16 positioned over electron guns G, R and with lobe 17 centered directly over electron gun B.

Each of lobes 16, 17 comprises identical structure for dynamically converging the beams they confront, therefore discussion will be confined mainly to a consideration of lobe 16, the internal construction of which is detailed for this purpose. Accordingly, and as shown in FIG. 1, lobe 16 houses an electromagnetic device 20 comprising a U-shaped core 21 of magnetic material having a pair of spaced apart parallel legs 22, 23. Core 21 is preferably constituted of a high permeability material such as ferrite, although other high permeability materials are also suitable. The upper ends of core legs 22 23 are disposed in an abutting relation while the free extremities of the legs are canted to accommodate the curvature of neck 11 of the cathode-ray tube and are supported in a confronting relation to respective outer pole faces 12a, 13a associated with the green and red beams, see FIG. 3. A pair of pole shoes 25, 25 which preferably adopt the construction of the shoes described in Pat. No. 3,354,337 which issued on Nov. 21, 1967 to Raymond F. DeBoth and is assigned to the present assignee, are positioned between the extremities of legs 22, 23 and pole faces 12a, 13a.

A pair of horizontal convergence windings 26 are mounted upon and individually encompass one of leg sections 22, 23. A pair of vertical convergence windings 27 are also mounted upon legs 22, 23 over horizontal windings 26. The free ends of windings 26 and 27 are returned, respectively, to the horizontal and vertical deflection systems of the receiver proper, not shown, for energization by correction signals derived from the deflection circuits.

In accordance with the invention convergence apparatus 10 is provided with means for simultaneously and symmetrically subjecting the green and red electron beams to equal and opposite horizontal static convergence magnetic deflection field components in response to a continuous simple movement of a magnet. More particularly, lobe 16 of apparatus 10 includes a disc type permanent magnet 30 which is supported atop magnetic core 21 to bridge the area where core legs 22, 23 abut. An upper wall 31 of the housing 16 -is bowed downward to resiliently engage one side of magnet 30 and retain it in a selected position. Secured in this fashion magnet 30 is rotatable 360, or more, to provide a magnetic field of desired intensity and polarity for application to core 21.

Supported adjacent lobe 16 is another magnetic field source consisting essentially of a separate permanent magnet device magnetically isolated from core 21 for simultaneously and symmetrically subjecting the green and red electron beams to equal and opposite vertical static convergence magnetic deflection field components, but without affecting the horizontal components developed by magnet 30, in response to a simple movement of the magnet device. More particularly, and as best seen in FIG. 2, a rod shaped magnet device 32 is rotatably supported over electron guns G, R by a bracket 37, but at a distance sufliciently removed from pole piece pairs 12 and 13 as to not influence the magnetic field translated by those pole pieces. Preferably, as shown in FIG. 4, magnet '32 is formed of a ferrite rod comprising a plurality of magnets including a central magnet portion 33 which is magnetized across a diameter of the rod in a first orientation. Magnet portion 33 is flanked by a pair of additional magnets 34, 35 which are also magnetized across a diameter of the rod but in a different orientation relative to the principal axis of the tube, specifically, the polarity of magnets 34, 35 differs from that of magnet 33 by 180. Magnets 33, 34, and 35 produce magnetic fields having transverse components which are oppositely directed across the paths of the green and red beams, respectively. As shown in FIG. 4, the transverse magnetic field components developed by rod magnet 32 are established across the paths of the red and green beams. The ends of magnet '32 are fitted with finger grips 36 to facilitate adjustment of the magnet.

Lobe 17 of convergence apparatus 10 includes an electromagnetic apparatus 42 which affords dynamic convergence of the blue beam. The construction of apparatus 42 is substantially the same as that of previously described apparatus 20 in that it comprises a magnetic core and pairs of horizontal and vertical convergence windings. Lobe 17 also includes a static convergence magnet 43 for radially displacing the blue beam and a blue lateral static convergence magnet 44 which is rotatably support ed upon bracket 45. Magnet 44 is also provided with finger grips 46. Magnet 43 can be of the same construction as magnet 30 of lobe 16 while blue lateral convergence magnet 44 preferably adopts the construction of the blue lateral magnet disclosed and claimed in Pat. 3,308,- 328 which issued to John L. Rennick on Mar. 7, 1967 and is assigned to the same assignee as the subject invention.

Circuitry for deriving the correction signals for application to the horizontal and vertical dynamic convergence coils of lobes 16 and 17 can be of the type conventionally employed in prior art television receivers as, for example, the circuitry utilized in chassis 14A9C51, a color television receiver manufactured by Zenith Radio Corporation and described in Zenith Service Manual CM115, published in February 1969.

In operation, the derivation of equal and opposite horizontal static convergence magnetic deflection field components for the green and red beams is now considered with reference to FIG. 3. For purposes of illustration, permanent magnet 30 is oriented to provide a magnetic field which produces a principal flux component P that flows from the 'North pole of the magnet down leg 22 of the core, through pole shoe 25 through a non-magnetic gap which includes the wall of the tube neck 11 into outer pole face 12a of pole pair 12 and thence to inner pole face where it confronts its companion pole piece 12d. Magnet 30 also produces, at the lower extremity of core leg 22, a fringing fiux component F which emanates from the free end of core leg 22, as well as from pole shoe 25, to traverse the space between pole pieces 12a,

12b. The direction of principal flux component P, absent any influence by fringing fiux F, would be directly across inner pole faces 12c, 12d, while the direction of fringing flux F, similarly uninfluenced, would be parallel to the central portions of pole pieces 12. The interaction of the principal flux component and the fringing flux component, however, causes a resultant flux H, which is vertically oriented relative to the axis of the green electron beam, to be established across the path of that beam. The derivation of this resultant flux is best understood by reference to the vector diagram of FIG 3A. The effect of this resultant magnetic field H upon the green beam is such as to displace the beam laterally, that is, in a horizontal direction. Assuming that the source of the beam is behind the plane of the drawing so that the beam is directed toward the person viewing the drawing, and the resultant flux field is directed downwardly, then the green electron beam will be displaced to the left as indicated by the arrow.

The principal flux path is completed through a central portion of shield as indicated by the arrows and establishes a principal flux component P at pole piece 13d adjacent the red beam. Shield 15 also completes the path for the fringing flux component P which traverses the space between pole pieces 13a and 13b and combines with the principal flux components P. These principal and fringing flux components combine to produce a second resultant flux H across the path of the red electron beam, see FIG. 3B. This resultant flux is also vertically oriented, but is directed upwardly, as viewed in FIG. 3, to displace the red electron beam to the right, or in the opposite direction with respect to that in which the green electron beam was displaced. The principal and fringing flux components P, F are returned to the South pole of magnet 30 through pole shoe and leg 23 of core 21.

It is noted therefore that a means consisting essentially of magnet 30, in conjunction with magnetic core 21, produces magnetic field components which simultaneously and symmetrically subject the green and red electron beams to equal and opposite horizontal displacements. To achieve convergence of the red and green beams in an actual color television receiver embodying the invention, a generator is coupled to the signal circuits of the receiver to develop, in known fashion, a cross-hatch pattern on the viewing screen of the receiver. This pattern comprises a series of green, red and blue horizontal lines and an intersecting series of green, red and blue vertical lines. Disc magnet is then rotated to horizontally displace the green and red lines until they are observed to converge. This coincidence is visually indicated by a yellow pattern of vertical lines on the screen, which hue, of course, is the color addition of red and green.

After the vertical green and red lines have been converged, magnet device 32 is then adjusted to secure a vertical displacement of the green and red horizontal lines. More particularly, and as shown in FIG. 4, the particular arrangement of magnets 33 and 34 is seen to establish a magnetic deflection field having flux components which traverse the path of the green beam from left to right, while magnets 33 and 35 establish a magnetic deflection field having flux components which traverse the path of the red beam from right to left. This arrangement of magnet device 32 is thus seen to establish resultant magnetic fields which simultaneously and symmetrically subject the green and red electron beams to equal and opposite vertical displacements. Accordingly, desired vertical displacements of the green and red horizontal lines are secured by rotating magnet 32 to adjust the intensity, as well as the sense orientation, of the deflection components. Moreover, these magnetic field components of magnet 32 do not afiect the field components of magnet 30 since, as observed in FIG. 2, magnet 32 is supported a distance sufficiently removed from electromagnetic device 20 as to be magnetically isolated from magnetic core 21, as well as from the convergence pole pieces. Magnet 32 thus efiects equal and opposite vertical displacements of the green and red horizontal lines to achieve, in cooperation with magnet 30, a complete convergence of the horizontal and vertical green and red lines. Because the lateral and vertical components of magnets 30 and 32 are directly and separatel adjustable, and because each magnet simultaneously and symmetrically adjusts corresponding components for two beams, the static convergence process is greatly simplified and expedited.

At this juncture the cross-hatch pattern comprises a series of horizontal and vertical yellow (the sum of green and red) lines and a series of horizontal and vertical blue lines. Static convergence is then completed by rotating magnet 44 to laterally displace the vertical blue lines until they converge with the vertical yellow (green and red) lines. (This blue lateral convergence is achieved in the manner described in the aforementioned Rennick patent.) Finally, disc magnet 43 is rotated to adjust the magnitude and polarity of flux lines established across pole faces 14c, 14d which field serves to vertically displace the horizontal blue lines and thereby achieve total static convergence of the green, red and blue lines, which convergence is manifested by a pattern of white intersecting horizontal and vertical lines.

Insofar as dynamic convergence of the beams is concerned, the correction signals applied to electromagnetic devices 20, 42 serve to establish magnetic flux components in their cores, and across pole piece pairs 12, 13 and 14, similar to the magnetic field components es tablished by static convergence magnets 30, 43 in that they are also constituted of principal and fringing components. A difference, however, resides in the fact that the strengths of the magnetic flux components utilized in dynamic convergence vary in time in accordance with the applied correction signals so that proper convergence is achieved irrespective of the location of the beams during scansion.

An electron beam convergence apparatus embodying the teaching of the ubject invention has been constructed and successfully operated with a 14" color reproducing cathode-ray tube, specifically, a 15ACP22 tube. In this particular application the disc type permanent magnets 30 and 43 comprised five-eighths 4;) inch diameter discs of one-eighth A5) inch thickness. Disc 30, specifically, is magnetized to register :4 gauss, when rotated through its range, on a Bell Model 640 gauss meter when its probe is located at either the red or green beam center. Magnet device 32 comprised a rod having a diameter of approximately one quarter inch and a length of about two inches and is magnetized so that magnet portion 33 registers approximately 1.5 gauss on the gauss meter when its probe is located approximately one-half inch below magnet 33 while each of magnets 34 and 35 registers approximately 8 gauss on the meter when the probe is spaced one-half inch away from them. The foregoing illustrative figures are given merely by way of illustration and in no sense by way of limitation. It is recognized that, depending upon the particular cathoderay tube to which the invention is applied, magnets having field strengths different than the recited examples may be indicated. By the same token, depending upon the spacing of the electron beams, the type of tube, etc., the field strengths of magnets 34 and 35 relative to magnet 33 may also differ.

The described convergence apparatus, in addition to greatly simplifying and expediting the task of converging the electron beams, also permits substantial cost savings to be realized. Specifically, a conventional prior art three-unit convergence apparatus commonly comprises twelve adjustable controls as opposed to the subject two unit convergence apparatus which requires but eight adjustable controls. In addition to this savings, the disclosed convergence apparatus, by eliminating one unit or lobe,

also dispenses with a magnetic core, a pair of horizontal convergence windings and a pair of vertical convergence windings. Further, insofar as ease of achieving static convergence of the green and red beams is concerned, it should be noted that in the conventional prior art three lobe convergence apparatus, each of the green and red beams is displaced radially, rather than in the distinct horizontal and vertical steps as herein taught. In the prior art practice there is no way, short of a cut-and-try procedure, to determine how far the green and red beams should be radially displaced to achieve convergence. This is because the initial radial displacement of the green beam, for example, must be an approximation since it is not known where the red beam will intersect the radial path of the green beam. The red beam is then radially displaced until it intersects the path of the green beam. Thereafter the green beam must be repositioned, then red, and so forth until a satisfactory result is obtained. This relatively complex prior art convergence procedure is in clear contrast to the simple and efficient manner of achieving convergence permitted by the subject invention.

In summary, the objectives of the invention are achieved for a multi-beam color reproducing cathode-ray tube by resort to a convergence unit which includes a core of magnetic material and a permanent magnet magnetically coupled thereto for simultaneously and symmetrically subjecting two of the electron beams to equal and opposite horizontal static convergence magnetic deflection field components to achieve lateral convergence of the green and red beams. Additionally, a separate permanent device, which is magnetically isolated from the magnetic core, is provided for simultaneously and symmetrically subjecting the green and red electron beams to equal and opposite vertical static convergence deflection field components in order to effect a vertical convergence of the red and green beams.

While a particular embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. An electron beam convergence apparatus for a multibeam cathode-ray tube having pole piece pairs individually flanking the paths of at least two of said electron beams, said apparatus comprising:

a dynamic convergence unit including a core of magnetic material having a pair of coils wound on respective spaced apart legs each adapted to be supported adjacent an assigned pole piece pair in magnetic flux coupling relation therewith;

means, consisting essentially of a single permanent magnet magnetically coupled to said core, for simultaneously and symmetrically subjecting said two electron beams to equal and opposite horizontal static convergence magnetic deflection field components in response to continuous simple movement of said magnet;

and means consisting essentially of a separate permanent magnet device magnetically isolated from said core for simultaneously and symmetrically subjecting said two electron beams to equal and opposite vertical static convergence magnetic deflection field components, without affecting said components, in response to continuous simple movement of said separate magnet device.

2. An electron beam convergence apparatus as set forth in claim 1 which further includes means for supporting said permanent magnet device for rotation about an axis normal to the path of said electron beams and at a location magnetically remote from said core and said pole piece pairs.

3 An electron beam convergence apparatus as set forth in claim 2 in which said permanent magnet device comprises a plurality of magnets including a central magnet portion and a pair of flanking magnet portions, and

in which said flanking magnet portions have a magnetic intensity in the order of siX times greater than the magnetic intensity of said central magnet.

4. An electron beam convergence appaartus as set forth in claim 1 in which one of said core legs is supported in a flux coupling relation to one pole piece of one of said pairs and the other of said core legs is supported in a flux coupling relation to one pole piece of the other of said pole piece pairs.

References Cited UNITED STATES PATENTS 2,975,314 3/1961 Clay et a1. 3l3-77 3,348,177 10/1967 Wood 31377X 3,454,807 7/1967 Egawa 3 l377 3,512,023 5/1970 Anthony 3l377 GEORGE HARRIS, Primary Examiner US. Cl. X.R.

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