US3308328A

US3308328A - Magnetic apparatus for converging the beams of a plural gun cathode ray tube

Info

Publication number: US3308328A
Application number: US401043A
Authority: US
Inventors: John L Rennick
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1964-10-02
Filing date: 1964-10-02
Publication date: 1967-03-07
Anticipated expiration: 1984-03-07
Also published as: FR1073898A; GB1073898A; DE1487215B2; DE1487215A1; NL6512764A; ES318075A1

Description

} FIG.1'

March 7, 1967 J, 1 3,308,328

MAGNETIC APPARATUS FOR CONVERGING THE BEAMS OF A PLURAL GUN CATHODE RAY TUBE Filed Oct. 2, 1964 2 Sheets-Sheet l PRIOR ART INVENTQR.

March 7, 1967 J. L. RENNICK MAGNETIC APPARATUS FOR CONVERGING THE BEAMS OF A PLURAL GUN CATHODE RAY TUBE 2 Sheets-Sheet 2 Filed Oct. 2, 1964 Jo 71?? L. 75 61 BY dzi%y.

United States Patent MAGNETIC APPARATUS FOR CONVERGING THE lggAgIS OF A PLURAL GUN CATHODE RAY John L. Rennick, Elmwood Park, Ill., assignor to Zenith Radio Corporation, Chicago, 11]., a corporation of Delaware Filed Oct. 2, 1964, Ser. No. 401,043 9 Claims. (Cl. 31377) This invention relates in general to an electron beam control system and more particularly to apparatus for converging a plurality of beams in a cathode-ray tube image repro-ducer.

The cathode-ray tube conventionally employed in a color television receiver constitutes one type of image reproducer 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 in the manner of a col-or 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 in the plane of the screen. Generally, the beams are converged prior to 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 the center of the screen and a second to insure convergence of the beams at the extremities of their sweeps during scansion, i.e., dynamic convergence.

A conventional static convergence arrangement includes three adjustable magnets mounted upon the neck of the tube and individually disposed in radical alignment with an assigned one of the three beams. The fields of the magnets are so oriented with respect to the beam paths that, upon adjustment, each magnet efiects a radial displacement of its assigned electron beam, that is, a displacement either toward or away from the tube axis. In theory, it should be possible to converge the three beams at a point in the plane of the screen by adjusting these magnets. However, it is most frequently the case that, while any two of the beams can be radically displaced to intersect in the plane of the mask, invariably the third beam cannot be positioned to the point where the other two beams intersect. This is attributable, in part, to variations in the physical dimensions of the gun electrodes as well as to deviations in the geometry of the gun structures introduced during the tube assembly process.

In order to complete static convergence the prior art employs an auxiliary magnet which is mounted upon the neck of the tube adjacent the blue gun, the uppermost gun of the delta array. For purposes of standardization, the industry has arbitrarily selected this upper gun as the energizing means for the blue phosphor dots. Accordingly, this auxiliary magnet is designated the blue lateral convergence magnet and its magnetic field is so oriented relative to the path of the blue beam that it effects a lateral displacement of that beam relative to the tube axis. This magnetic field, however,'may also effect undesirable displacements of the red and green beams and the orientation of the field relative to these two beams is such that they are displaced in opposite directions. Where this spreading of the beams is encountered, a readjustment of the radial convergence magnets is necessary followed, in turn, by readjustment of the blue lateral magnet. This procedure is repeated until an acceptable convergence compromise is achieved. However, in spite of repeated adjustments, it is not always possible to establish acceptable convergence.

It is, therefore, a principal object of the invention to provide an improved electron beam convergence apparatus.

It is a specific object of the invention to provide an improved blue lateral convergence apparatus for a tricolor cathode-ray tube.

It is also an object of the invention to provide a blue lateral convergence apparatus which overcomes deficiencies of prior art apparatus.

In accordance with the invention, in an electron beam convergence apparatus for a cathode-ray tube having means for developing a plurality of electron beams, a magnetic arrangement for controlling the lateral position of a particular one of the beams comprises means, including a first magnet polarized in a first orientation relative to the principal axis of the tube, for predominantly effecting a desired lateral displacement of one of the beams relative to its undisplaced path. This magnet has a magnetic field component transverse to the path of said one beam which, in addition to-effecting purposeful displacement of the one beam, secondarily effects undesired displacements of other beams. The beam converges apparatus further comprises means, including a pair of additional magnets disposed in juxtaposition to but on opposite sides of the first magnet, which pair of magnets are polarized in a different orientation relative to the principal axis of the tube. These additional magnets have magnetic field components transverse to the paths of the other beams so as to predominantly effect compensating displacements of these other beams to substantially neutralize their undesired displacements due to the field of the first magnet without effecting substantial displacement of said one beam.

- The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The organization and manner of operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in the several figures of which like reference numerals indentify like elements, and in which:

FIGURE 1 is a schematic representation of a prior art beam convergence magnet and its field pattern;

- FIGURE 2 is a fragmentary side view, party in section, of a tri-color cathode-ray tube employing the subject invention;

FIGURES 3 and 4 are sectional views taken along lines 33 and 44 respectively of FIGURE 2;

FIGURE 5 is a schematic representation of the resultant magnetic field established by the convergence apparatus of FIGURE 3;

FIGURE 6 shows an alternate embodiment of the invention; and

FIGURE 7 is a schematic representation of the magnetic field pattern of the convergence apparatus of FIG- URE 6.

Before proceeding to a description of the invention, the prior art blue lateral magnet M shown in FIGURE 1, together with its field pattern, will be considered briefly. In addition to the magnet and its field, FIGURE 1 shows the neck portion of a tri-color cathode-ray tube in crosssection. Three electron beams are represented by small circles symmetrically disposed about the axis of the tube in a delta array and identified by the letters R, G and B. The flux field for magnet M is represented, of course, by the pattern-of dashed lines converging at the south pole of the magnet and the direction of these flux lines is indicated by arrow heads. Magnet M is conventionally mounted upon the neck of the tube by a support member (not shown) of magnetic material which serves as an external pole piece for the magnet. It is also conventional practice to employ an internal pole piece (not shown) in order to achieve a desired field pattern. However, since the field pattern of even a simple bi-polar magnet in the presence of magnetic material is very complex, the field shown in FIGURE 1 ignores the influence of pole pieces in order to simplify this presentation. Moreover, it has been found that data obtained from experiments investigating the influence of magnets, with and without pole pieces, upon electron beams can be interpreted, insofar as the design of convergence apparatus is concerned, with reference to simplified field patterns.

It is a fundamental principle of electron optics that an electron beam upon entering a magnetic field is deflected in a direction normal to the direction of the flux lines and in an amount determined by the velocity of the beam and the strength of the field. Accordingly, as shown by its accompanying vector, the blue beam B in FIGURE 1 is displaced laterally to the left, in other words, the X direction viewing the tube axis as the center of a cartesian coordinate system. The red and blue beams also tend to be displaced by the magnetic field in the direction indicated by their associated vectors, that is, normal to the direction of the field flux in their immediate vicinities. Upon resolving the displacement vectors of the red and green beams into their coordinate components, it becomes apparent that, in addition to displacements in the -X direction, the red beam experiences a +Y displacement and the green beam a Y displacement. Accordingly, while the prior art blue lateral magnet does effect lateral displacement of the blue beam, it also induces an undesirable spreading of the red and green beams. The foregoing analysis, of course, is equally applicable to the situation in which the magnetic flux field is reversed so that the blue beam is laterally displaced to the right, the +X direction. In that case, the red and green beams are again subjected to a vertical spreading relative to one another. The blue lateral magnet arrangement of the present invention'obviates this spreading while still establishing the desired condition of convergence.

Referring now to FIGURE 2, the tri-beam color reproducing cathode-ray tube there represented comprises a neck portion 11 and a funnel or cone section 12 which is terminated by a display panel 13. A fluorescent screen 14 composed of a myriad of phosphor dots is disposed upon the inner surface of panel 13. The color dots are arranged in groups of three, or triads, each including a red, a green and a blue phosphor dot. A shadow-mask 15, having a multitude of apertures, is fixed in overlying relation to screen 14 and is so indexed with respect thereto as to register an aperture with each color triad.

Neck portion 11 includes three

electron gun structures

20R, 20G and 20B, only two of which show in FIGURE 2, for developing the electron beams R, G and B which excite the red, green and blue phosphor dots, respectively, of screen 14. In order not to burden the description unnecessarily, only blue gun 20B will be detailed, it being understood that guns 20R and 206 are identical to the blue gun. In addition to a cathode (not shown) gun 20B includes a control electrode 22, a first accelerating electrode 23, a focusing electrode 24 and a second accelerating electrode 25, all of which electrodes are formed of a conductive non-magnetic material.

The three guns are symmetrically disposed in a delta array about the principal axis of the tube by a support arrangement comprising a plurality of saddle-

shaped straps

26, 26 and a trio of elongated rods 27 of insulating material. As seen in FIGURES 2 and 3, this delta gun array is achieved by welding the electrodes to the saddle portions of assigned straps and then embedding the extremities of the straps in rods 27. This gun structure,

which is typical for a tri-color cathode-ray tube, is conventionally provided with internal pole pieces for shaping the flux field of the blue lateral magnet. To this end, straps 26' which support focusing. electrodes 24 are formed of a magnetic material to constitute pole pieces,

see FIGURE 3. Straps 26 of the other electrodes, on the other hand, are formed of a non-magnetic material. As will be shown, the inventive convergence apparatus can be employed with this gun arrangement as well as with a gun structure devoid of pole pieces. It is common practice to cant the electron guns to achieve a measure of mechanical convergence, that is to say, the guns develop electron beams which traverse undeflected and converging paths leading to screen 14. The convergence is not, however, completely attained from the geometry of the structure.

A deflection yoke 30 is mounted upon the neck of the tube in an abutting relation with cone 12 and a radial convergence assembly is mounted adjacent yoke 30. It comprises -a dynamic convergence system 31 and a static convergence system 32. The form that these convergence systems take is of no consequence insofar as the subject invention is concerned. A representative prior art dynamic convergence system is disclosed in Patent 3,141,109, issued to James F. Chandler. In this regard it is sulficient to note that system 31 is a tripartite structure comprising a plurality of coils which, when energized, apply magnetic fields to a like plurality of associated pole piece pairs 34r, 34g and 34b. These pole pieces are afifixed to a shield clyinder 29 carried at the forward end of the gun structure and are situated immediately beneath their assigned coils. As shown in FIGURE 4,

pole pieces

341', 34g and 34b are disposed in axial alignment with the red, green and blue guns, respectively, with each pair disposed on opposite sides of the undeflected path of its.

assigned beam in order to direct components of the convergence fields transverse to the path of the beams.

The static radial convergence system 32 is also conventional and comprises a series of cylindrically shaped permanent magnets 351, 35g and 3512 which are symmetrically positioned about the neck of the tube in a confronting relation to the extension 34r, 34'g and 34'b of pole piece pairs 341- 34g and 34b, respectively; see

FIGURE 4. The magnets, which are polarized along their central axes, are supported on adjustable racks 36 for radial movement in respect to pole piece extensions 34'), 34g and 34b. Each magnet, together with its associated pole pieces, establishes a magnetic field having components transversely oriented relative to the path of an assigned electron beam so as to effect radial displacement of that beam with respect to the tube axis.

In accordance with the invention, and as best seen in FIGURE 3, an improved lateral convergence apparatus 40 is mounted upon the neck of the tube, preferably, directly over the blue gun. Structurally, it comprises a ferrite rod 41 and a mounting arrangement for the rod which includes a U-shaped bracket 42 having integral arcuate legs 43 that embrace the neck of the tube. In this embodiment of the invention bracket 42 is formed of magnetic material so as to constitute legs 43 external pole pieces for ferrite rod 41. Rod 41 is rotatably supported by the end walls of bracket 42 and captivated therein by a slotted brass sleeve 44 which also serves as a grip or control for manually adjusting rod 41 rotationally within its holder. A leaf spring 45 serves as a biasing means to retain rod 41 at a desired setting. A tension spring 46 of non-magnetic material spans legs 43 to adjustably secure the bracket and rod at a desired location upon the neck of the tube.

Referring now to FIGURE 5, the ferrite rod 41 includes a first or central magnet portion 48 polarized across a diameter of the rod in a first orientation relative to the principal axis of the tube so as to have a magnetic field component transverse to the path of the blue beam, as well as to the paths of the red and green beams. Rod 41 further includes a pair of

additional magnet portions

49, 50 which are disposed adjacent to but on opposite sides of magnet portion 48.

Magnets

49, 50 are also polarized across a diameter of the rod but in a different orientation relative to the principal axis of the tube, specifically, displaced 180 relative to the orientation of magnet 48.

Magnets

49, 50 have magnetic field components transverse to the paths of the red and green beams and also to the blue beam. Preferably,

magnets

48, 49 and 50 have substantially equal lengths and equal field strengths. They may be formed by selectively magnetizing a single ferrite rod or may be prepared individually and integrated into a single cylindrical structure. It is recognized, of course, that magnets having relative polarizations other than 180 will produce a resultant field different from that shown in FIGURE 5. This in turn, would alter the compensating affect of

magnets

49, 50 upon the red and green beams and while it is preferred that the strengths of the three magnets be the same, they may be tailored or varied to develop a resultant magnetic field of a desired configuration and strength.

To achieve static convergence of the color tube, the antenna terminals of the receiver including the tube with blue lateral 40 in place are coupled to the output of a cross-hatch signal generator. Thus energized, the tube develops a raster comprised of red, green and blue patterns of intersecting lines or bars. Initially, the red and green beams are radially converged by moving magnets 35r and 35g inward or outward as required. Red and green convergence is manifested when the central portions of the bar patterns associated with these two beams are superimposed. The blue beam is then brought as near to convergence with the red and green beams as possible by radially adjusting magnet 35b.

If convergence is not entirely correct, observation of the screen reveals not only the sense of the correction but also the degree required by manipulation of the blue lateral magnet 40. Since the magnets thereof are magnetized along a diameter, rotation of rod 41 varies the strength of the blue lateral field and additionally the direction of that field changes with rotation, reversing itself after rotational displacement of 180 from a reference position. Accordingly if correction be required, rod 41 is rotated displacing the blue bearnlaterally until its bar pattern merges with the previously converged red and green patterns. Proper convergence is achieved when the raster appearing at the center of the screen is formed of a single pattern of intersecting white lines, since white is the color sum of red, green and blue.

In achieving blue lateral correction magnet 48 exerts its dominant influence on the blue beam because of its proximity thereto. Moreover, as is true of prior art devices, magnet 48 also effects undesired displacement of both the red and green beams. In accordance with the invention, these undesired displacements are neutralized by the field contributions of flanking

magnets

49, 50. This phenomena is best understood by referring to the field pattern of FIGURE 5 which comprises superpositioned portions of the fields of

magnets

48, 49 and 50 and by separately considering the influence of each magnet upon each of the three beams. Accordingly, as indicated by vector V-48-b, the upwardly directed flux field of magnet 48 displaces the blue beam laterally to the left. The undesired displacements of the red and green beams are indicated by the vectors V-48r and V-48g.

The influence of magnet 49 upon the red beam is to displace it to the right shown as by the vector V-49r. The forces it exerts on the green and blue beams are indicated by the obliquely directed vectors V-49g and V-49b. Note that its effect upon the green beam is to substantially counteract the undesired displacement of that beam caused by magnet 48.

Magnet 50 displaces thegreen beam to the right and substantially cancels the undesired displacement of the red beam caused by magnet 48. The field of magnet 50 also neutralizes any oblique displacement of the blue beam caused by magnet 49. Vectors V-50g, V-50r and V-50b represent the field components attributable to magnet 50.

Accordingly, the result achieved by this combination of fields is threefold, first a desired lateral displacement of the blue beam to the left or right by magnet 48; secondly, cancellation of the spreading of the red and green beams due to the field of magnet 48 by the counter-fields of

magnets

49, 50; and finally, a desired displacement of the red and green beams in a direction which serves to complement convergence with the blue beam. In particular, the illustrative example was predicated on the need of a shift of the blue beam to the left and it has been demonstrated that the red and green beams have been shifted to the right to complement the displacement of the blue beam.

While the superposed field pattern of FIGURE 5 does not take into consideration the influence of the internal pole pieces of the gun or the external pole pieces of bracket 42, the explanation is valid in view of substantially identical convergence results achieved with a threesixteenths inch diameter ferrite rod one and one-eighths inches long and alternately magnetized in the manner shown at three spaced regions of equal length therealong. This rod was inserted in a prior art holder of the type shown in FIGURE 3 and then employed to converge a 25GP22 cathode-ray color tube of the type shown in FIGURE 2.

The convergence apparatus 60 shown in FIGURE 6 constitutes an alternate embodiment of the invention comprising a ferrite rod 61 and a mounting arrangement for the rod in the form of a U-shaped bracket 62 having integral legs 63 which embrace the neck of the tube. As in the principal embodiment, apparatus 60 is mounted directly over the blue beam focusing electrode 24. In this embodiment neither internal nor external pole pices are required and all the support straps 26 employed in the gun structure are formed of a non-magnetic material as is bracket 62. In all other respects the gun structure of FIGURE 6 is identical to that shown in FIGURES 2 and 3. Moreover, as in the principal embodiment, ferrite rod 61 is rotatably supported by the end walls of a bracket 62 and is captivated therein by a brass sleeve 64. The leaf spring 65 constitutes a biasing means to retain rod 61 at a desired setting. The bracket and rod are adjustably secured upon the neck of the tube by a tension spring 66 which spans bracket legs 63.

Referring now specifically to ferrite rod 61, this element comprises a first magnet portion 68 which is polarized across a diameter of the rod with a first orientation relative to the principal axis of the tube. As graphically illustrated in the field plot of FIGURE 7, magnet 68 has a magnetic field component transverse to the path of the blue beam. Rod 61 includes a pair of

additional magnet portions

69, 70 which are disposed adjacent to but on opposite sides of magnet 68.

Magnets

69 and 70 are likewise polarized across a diameter but in a different orientation relative to the principal axis of the tube, specifically, displaced relative to the orientation of magnet 68. These magnets have field components directed traverse to the paths of the beam. Rod 61 further includes another pair of

magnet portions

71, 72 which are disposed adjacent to

magnets

69 and 70, respectively.

Magnets

71, 72 are also polarized across a diameter of rod 61 in substantially the same orientation as magnet 68. Preferably, magnets 68-72 have approximately the same length and field strengths.

The operation of convergence apparatus 60 to attain blue lateral convergence is identical to that described for convergence apparatus 40. However, the manner in which the resultant field of apparatus 60 achieves such convergence is explainable without separately considering the effect of each magnet upon each beam as undertaken for apparatus 40. This is possible since the convergence apparatus of FIGURE 6 is not associated with internal or external pole pieces; thus a plot of the resultant field of multiple magnet rod 61 is practically reliable. FIGURE 7 is a plot of the resultant field of a three-sixteenths inch diameter ferrite rod measuring two inches in length and alternately magnetized along its length to have five magnet portions. A five magnet ferrite rod constructed in this fashion was inserted in a nonmagnetic holder and employed to converge a 25AP22 cathode-ray tube, a type of color tube which does not employ internal pole pieces.

As indicated in the plot of FIGURE 7, lateral displacement of the blue beam is due principally to the flux field beneath magnet 68. The field contributions of the other magnets, on the other hand, serve to substantially eliminate any spreading of the red and green beams due to the field of magnet 68. This phenomenon is best understood by considering the distribution of the field forces, particularly those areas of the field wherein the force upon an incident electron beam has either a zero horizontal or a zero vertical component. Specifically, and again assuming that the axis of the tube is coincident with the center of a cartesian coordinate system, the solid line curves H connect those points in the field where the resultant flux is parallel to the abscissa so that the horizontal component of electron beam displacement is zero. In other words, a beam piercing the field at any point along curve I-I would be displaced vertically only. The curve H on the other hand, is a plot of those points in the field Where the flux is parallel to the ordinate of the assumed cartesian system so that the vertical component of beam displacement is zero. Thus, a beam entering the field anywhere along the line H would be horizontally displaced. only.

Consider now the positions occupied by the three beams. The blue beam lies in an area of concentrated flux density and is subjected to a lateral displacing force indicated by the vector V-68. The red and green beams are situated near the intersections of the H and. H curves, points at which the resultant field would produce zero displacement of an electron beam. Clearly then, the resultant field of the five magnet ferrite rod is so configured as to effect a desired lateral displacement of the blue beam while producing little if any displacement of the red and green beams.

The invention thus employs, in either embodiment, a plurality of magnets so disposed that adjacent ones have oppositely polarized fields. Insofar as the principal embodiment of FIGURE 3 is concerned, it has been determined that the three magnet convergence device 40 performs excellently with a conventional tri-beam color tube having internal pole pieces. This device also will achieve an acceptable degree of convergence of a cathode-ray tube without internal pole pieces. On the other hand, the five magnet convergence apparatus 60 of FIGURE 6 may be used to converge a cathode-ray tube having internal pole pieces, but is more particularly suited for use with a tube devoid of pole pieces. While the magnets constituting

convergence apparatus

40 and 60 have been disclosed as permanent magnets, it is appreciated that electro-magnet devices may be employed with equally acceptable results.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

a 1. In an electron beam convergence apparatus for a cathode-ray tube, which includes means for developing a plurality of electron beams, a magnetic arrangement for controlling the lateral position of a particular one of said beams, comprising:

means, including a first magnet polarized in a first orientation relative to the principal axis of said tube to have a magnetic field component transverse to the path of said one of said beams, for predominantly effecting a desired lateral displacement of said one beam relative to its undisplaced path while secondarily effecting undesired displacements of others of said beams;

and means, including a pair of additional magnets disposed in juxtaposition to butt on opposite sides of said first magnet and polarized in a different orientation relative to said principal axis to have magnetic field components transverse to the paths of said other beams, for predominantly effecting compensating displacements of said other beams to substantially neutralize the undesired displacements thereof due to the field of said first magnet without effectingsubstantial displacement of said one beam.

2. In an electron beam convergence apparatus for a cathode-ray tube, which includes means for developing a plurality of electron beams, a magnetic arrangement for controlling the lateral position of a particular one of said beams, comprising:

and means, including a pair of additional magnets disposed in juxtaposition to butt on opposite sides of said first magnet and oppositely polarized relative to said first magnet to have magnetic field components transverse to the paths of said beams, for predominantly effecting compensating displacements of said other beams to substantially neutralize the undesired displacements thereof due to the field of said first magnet without effecting substantial displacement of said one beam.

3. In an electron beam convergence apparatus for a cathode-ray tube, which includes means for developing a plurality of electron beams, a magnetic arrangement for controlling the lateral position of a particular one of said beams, comprising:

means, including a pair of additional magnets disposed in juxtaposition to butt on opposite sides of said first magnet and polarized in a different orientation relative to said principal axis to have magnetic field components transverse to the paths of said other beams, for predominantly effecting compensating displacements of said other beams to substantially neutralize the undesired displacements thereof due to the field of said first magnet while effecting substantial displacement of said one beam;

and means for changing the orientations of said transverse field components relative to said principal axis of said tube to adjust the displacements of said beams.

4. An electron beam convergence apparatus for a cathode-ray tube having a neck portion which includes means for developing a plurality of electron beams, comprising:

a ferrite rod comprising a first magnet portion polarized in a first orientation relative to the principal axis of said tube to have a magnetic field component transverse to the path of one of said beams for effecting a desired lateral displacement of said one beam relative to its undisplaced path and tending to effect undesired displacements of others of said beams;

said rod further including a pair of additional magnet portions disposed adjacent to but on opposite sides of said first magnet portion and polarized in a different orientation relative to said principal axis to have magnetic field components transverse to the paths of said other beams for effecting compensating displacements of said other beams to substantially neutralize the undesired displacements due to the field of said first magnet portion;

and means for supporting said rod upon said neck portion of said tube with said first magnet portion disposed adjacent the path of said one beam.

5. An electron beam convergence apparatus for a cathode-ray tube having a neck portion which includes means for developing a plurality of electron beams, comprising:

a ferrite rod comprising a first magnet portion polarized in a first orientation relative to the principal axis of said tube to have a magnetic field component transverse to the path of one of said beams for effecting a desired lateral displacement of said one beam relative to its undisplaced path and tending to efiect undesired displacements of others of said beams;

said rod further including a pair of additional magnet portions having the same cross section as said first magnet portion and supported in coaxial alignment therewith but on opposite sides thereof,

said pair of additional magnet portions disposed adjacent to but on opposite sides of said first magnet portion and polarized in a diiferent orientation relative to said principal axis to have magnetic field components transverse to the paths of said other beams for effecting compensating displacements of said other beams to substantially neutralize the undesired displacements due to the field of said first magnet;

' 6. An electron beam convergence apparatus for a cathode-ray tube having a delta electron gun arrangement for developing three electron beams comprising:

a coaxial array of an odd number of magnets; and means for mounting said array transversely of the paths of said beams with the central one of said magnets disposed over the path of a particular one of said beams,

said magnets being polarized so that the polarity of each of said magnets is opposite that of its neighbors in said array.

7. An electron beam convergence apparatus for a cathode-ray tube having a delta electron gun arrangement for developing three electron beams comprising:

said magnets having equal axial lengths and equal field strengths and being polarized so that the polarity of each of said magnets is opposite that of its neighbors in said array.

8. An electron beam convergence apparatus for a cathode-ray tube having a delta electron gun arrangement for developing three electron beams comprising:

a coaxial array of an odd number of magnets; and means for mounting said array transversely of the paths of said beams With the central one of said magnets disposed over the path of a particular one of said beams and equidistant from the paths of the other two of said beams,

9. An electron beam convergence apparatus for a cathode-ray tube which includes means for developing a plurality of electron beams, comprising:

means including a first magnet polarized in a first orientation relative to the principal axis of said tube to have a magnetic field component transverse to the path of one of said beams for elfecting a desired lateral displacement of said one beam relative to its undisplaced path and tending to eflfect undesired displacements of others of said beams;

and means including a pair of additional magnets disposed adjacent to and on opposite sides of said first magnet and polarized in a different orientation relative to said principal axis and a pair of auxiliary magnets disposed on opposite sides of said additional magnets and polarized in the same orientation as said first magnet,

said additional and said auxiliary magnets having magnetic field components transverse to the paths of said other beams for elfecting compensating displacements of said other beams to substantially neutralize the undesired displacements due to the field of said first magnet.

References Cited by the Examiner UNITED STATES PATENTS 6/1960 Reiches 3l377 7/1960 Taylor 3l377 References Cited by the Applicant UNITED STATES PATENTS JAMES W. LAWRENCE, Primary Examiner.

V. LAFRANCHI, Assistant Examiner.

Claims

1. IN AN ELECTRON BEAM CONVERGENCE APPARATUS FOR A CATHODE-RAY TUBE WHICH INCLUDES MEANS FOR DEVELOPING A PLURALITY OF ELECTRON BEAMS, A MAGNETIC ARRANGEMENT FOR CONTROLLING THE LATERAL POSITION OF A PARTICULAR ONE OF SAID BEAMS, COMPRISING: MEANS, INCLUDING A FIRST MAGNET POLARIZED IN A FIRST ORIENTATION RELATIVE TO THE PRINCIPAL AXIS OF SAID TUBE TO HAVE A MAGNETIC FIELD COMPONENT TRANSVERSE TO THE PATH OF SAID ONE OF SAID BEAMS, FOR PREDOMINANTLY EFFECTING A DESIRED LATERAL DISPLACEMENT OF SAID ONE BEAM RELATIVE TO ITS UNDISPLACED PATH WHILE SECONDARILY EFFECTING UNDESIRED DISPLACEMENTS OF OTHERS OF SAID BEAMS; AND MEANS, INCLUDING A PAIR OF ADDITIONAL MAGNETS DISPOSED IN JUXTAPOSITION TO BUTT ON OPPOSITE SIDES OF SAID FIRST MAGNET AND POLARIZED IN A DIFFERENT ORIENTATION RELATIVE TO SAID PRINCIPAL AXIS TO HAVE MAGNETIC FIELD COMPONENTS TRANSVERSE TO THE PATHS OF SAID OTHER BEAMS, FOR PREDOMINANTLY EFFECTING COMPENSATING DISPLACEMENTS OF SAID OTHER BEAMS TO SUBSTANTIALLY NEUTRALIZE THE UNDESIRED DISPLACEMENTS THEREOF DUE TO THE FIELD OF SAID FIRST MAGNET WITHOUT EFFECTING SUBSTANTIAL DISPLACEMENT OF SAID ONE BEAM.