US2881342A - Deflection apparatus - Google Patents

Description

April 7, 1959 A. c. STOCKER 2,881,342

DEFLECTION APPARATUS Original Fild May 15. 1953 2 Sheets-Sheet 1 INVENTOR.

Arf/zur C Smoker ATTORNEY United States Patent "ice DEFLECTION APPARATUS Arthur C. Stocker, Collingswood, NJ., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Continuation of application Serial No. 355,286, May 15, 3237.6 This application September 23, 1957, Serial No.

17 Claims. (Cl. 313-76) The present invention relates to new and improved electromagnetic apparatus for effecting deflection of an electron beam in a predetermined pattern and, more particularly, to such apparatus which provides improved field uniformity over that obtainable with heretofore known devices. This is a continuation of my copending application Serial No. 355,286, filed May 15, 1953, now abandoned, for Deflection Apparatus.

Electromagnetic deflection for cathode ray tubes has found widespread use in television apparatus and the like, wherein a beam is caused to scan a generally rectangular raster, for example. In this branch of the electronic art, it is well known that means are provided for focusing the electron beam or beams within a tube to a fine, circular cross section, pencil form. Electromagnetic deflection has, however, been found to cause certain defocusing of the electron beam by virtue of the flux leakage from the end windings of the deflection coils, which produces undesired magnetic field gradients.

Since the current supplied to the deflection coils varies in accordance with the desired pattern of scanning, this end turn flux or fringe flux as it is sometimes termed,

produces a variable defocusing effect on the electron beam and thus causes the beam to manifest different degrees of focus for various scanning positions, in addition to the non-uniform deflection resulting from the end flux.

It is, therefore, a primary object of the present invention to provide means for preventing or substantially reducing the adverse effects produced by the end turns of electromagnetic deflection coils.

Another and more specific object of the invention is to provide means which, while structurally simple and inexpensive to manufacture, will substantially prevent the introduction of magnetic field gradients into the main deflection field as a result of the deflection coils end loops.

Still another object of the present invention is the provision of means which may be employed in conjunction with existing cathode ray beam deflection yokes to reduce substantially any beam defocusing effects resulting from the inherent yoke flux leakage characteristics associated with the end turns.

By way of approximation, an electromagnetic deflection field is ordinarily described as being constant within two limiting planes and zero elesewhere. This condition, however, is not true, since, while it is possible to achieve constant flux density over a relatively small area compared to the total area of a field, the balance of the area comprises a fringe field and is characterized by a gradual decline to zero intensity. It has been known that the addition of a cylinder or core of ferro-magnetic material or the like outside the deflection yoke windings shortens the total length of the flux air path while making no appreciable change in the location of the magnetic field within the cathode ray tube. The field from the end turns, on the other hand, poses a more diflicult problem, since these turns are curved, such that 2,881,342 Patented Apr. 7, 1959 the field therefrom is constantly changing in direction, as will be appreciated.

According to the present invention, the core or sleeve of magnetic material is formed at its end and on its outer surface with a pocket-like passage for the reception of the end turns, such that an air gap for their flux is confined to the pocket which may be considered as remote from the electron beam path. In one embodiment, the sleeve is provided with a radial flange having an axial, rearwardly extending flange, which flanges define the pocket between themselves and the portion of the sleeve over which the latter flange extends. A second embodiment includes two spaced radial flanges which define a channel-like, annular passage or pocket.

Thus, it is a further object of the present invention to provide means, as described, comprising a magnetic core having a pocket or passage defined by a flange on'its exterior surface.

Another specific object is to provide means, as set forth, comprising a magnetic core sleeve having two spaced, radial flanges which define a narrow passage for the reception of the end turns of a deflection yoke.

It is a still further object of the present invention to provide means, as described, comprising a retroflexed extension of the conventional magnetic core for shielding an electron beam within a cathode ray tube from the field resulting from the end turns of a deflection yoke.

Still another object hereof is to provide means, as described, for confining the air gap of the end turns flux to the core sleeve of a deflection yoke.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 illustrates, by way of side elevation, a pair of deflection coils of conventional design located on the neck of a cathode ray tube;

Fig. 2 is a vertical section taken along line 2-2 of Fig. 1; v

Fig. 3 is a view similar to that of Fig. 2 showing, in addition, a sleeve or core of magnetic material surrounding the assembly;

Figs. 4 and 5 are views similar to those of Figs. 1 and 2, respectively, which are employed in the following discussion;

Fig. 6 illustrates a coil winding and several flux paths associated therewith;

Fig. 7 is a view similar to that of Fig. 6 in which one of the flux paths is through a ring of magnetic material;

Fig. 8 illustrates a generalized aspect of the present invention;

Fig. 9 is an isometric view, with a portion broken away, of one embodiment of the invention;

Fig. 9a is an end view of the device of Fig. 9 taken generally in the direction of arrow A;

Fig. 10 is a vertical, sectional view of the device of Fig. 9 along line 1010';

Fig. 10a illustrates an additional member which may be employed as an adjunct to the structure of Figs. 9, 9a and 10; and

Fig. 11 is a view similar to that of Fig. 10, with portions broken away, illustrating another form of the invention.

Referring to the drawings and, particularly, to Fig. 1 thereof, reference numeral 10 indicates generally a portion of a cathode ray tube such as a kinescope" having a flared portion 12 and a cylindrical neck 14. One set of windings, which would, in accordance with their loca tion in the drawing, produce horizontal deflection is shown at 16, these windings comprising specifically sidewires 18 and end turns 20. For purposes of simplicity,

assuage r the efiects of the respective side and end windings will I 'be described herein separately. Thus, for example, the field produced by the straight side wires 18 (shown shaded in Fig. 1) is illustrated diagrammatically in Fig. 2, the flux lines being indicated by reference numeral 22. Merely in the interest of completeness of description, the flux lines 22 are shown as approximately straight in the center of the tube neck 14 but curved near the windings 18, although this latter feature is not involved in the present invention.

As has been stated, it has been found by prior investigators that the addition of a core of ferro-magnetic material outside the windings and surrounding the same decreases the total length of the flux path in air. Such a core is illustrated at 24 in Fig. 3 and may, as shown, comprise simply a cylindrical sleeve disposed around the windings 18 and tube neck 14.

As mentioned briefly supra, the magnetic field from the end turns introduces a vexatious problem, since the wires constituting these turns are constantly changing in direction, with the result that their field also changes in direction. This effect is illustrated in Figs. 4 and 5 wherein, for purposes of emphasis, the end turns 20 are shaded. Since, as will appear, the electron beam within a tube of this type is never far from the tubes axis as it enters the deflection field, the effects of the end turns of the entering end of the yoke are not considered here. Where deemed necessary, however, the entering-end end turns may be treated in the same manner as that to be described with respect to the exit-end end turns.

Assuming the flow of current in the coils of Fig. 4 to be in the direction of the arrows 26, the magnetic field surrounding the end turns 20 will be in the direction indicated by the arrows 28. From the foregoing it may be seen that, if an electron beam within tube is scanned in a rectangular pattern (through the addition of vertical deflection coils disposed at right angles to the horizontal coils illustrated in the drawing) as in television practice, the field from the end turns will affect the four corners of the raster differently. This is illustrated in Fig. 5 wherein the dotted rectangle 30 denotes the raster and the arrows 28 represent the magnetic forces acting upon the electron beam when in its various positions within the rectangular area 30. Moreover, persons skilled in the art will recognize the fact that the flux from the end turns has a strong component parallel to the direction of the beam at maximum deflection, which component causes a defocusing action opposite in sense at the two extremes of deflection. This latter fact may be seen from the relationship of the electron beam 32 in Fig. 4 and the flux line 28. When the beam 32 is deflected in the opposite direction, it is acted upon by the flux line 28 surrounding the other end turn 20, and in an opposite sense.

In accordance with the present invention, means are provided for eliminating the undesirable defocusing efiect of the end turns by shielding the beam from their field in a new and improved manner. By way of background, it should be noted that, in general, a source of field cannot be shielded except by the use of a shield which is of such thickness that it cannot be penetrated by the field. Moreover, it is known that thickness of the shield required is inversely proportional to the frequency of the field sought to be shielded. Since the frequencies involved in deflection as in television are relatively low, the thickness of a shield according to prior art thinking would necessarily approach infinity which is, of course, quite impracticable. As an aid in understanding the principles of the present invention, Fig. 6 illustrates at 34 a deflection winding, for example, consisting of N conductors carrying current (into the paper) of I amperes per conductor, such that the magneto-motive force produced thereby is NI ampere turns, which force acts around every closed path surrounding the coil, including a path X which is is proximity to the coil and a more remote path Y. It will be understood that the path X has a force of NI ampere turns which produces a magnetic flux equal to this value divided by the reluctance of the path. In a similar manner, the remote path Y has a force of NI ampere turns which produces a flux of this same value divided by the reluctance of its path. By virtue of the fact that flux density is, in general, inversely proportional to the reluctance of the flux path, the flux of path Y is substantially less than that of path X. It is, moreover, important to note that the presence of the flux in path X is without effect on the flux in path Y, in view of the fact that each incremental unit of length of path X has a reluctance proportional to its length, such that the passage of flux results in a drop in magneto-motive force which may be thought of as analogous to the voltage drop in a resistance and which is identical to the magneto-motive force acting along that length to produce the flux. The relationship between magneto-motive force and flux density is illustrated diagrammatically in Fig. 7 wherein flux path X from the conductors 34 is within a ferromagnetic material, while path ?Y is again in air. Although the low reluctance of path X' results in a great increase in the flux density of that path, the fact that each incremental unit of length of path X has a reluctance proportional to its length and since that reluctance multiplied by the flux flowing in the path causes an incremental magneto-motive force, the integrated magneto-motive force is equal to NI, just as was the case in the air path X of Fig. 6. This indicates the fact that the attempted shielding by means of the magnetic material for path X makes no difference in the magnetic-motive force for that path in air.

Despite the foregoing, it has been found by the present applicant that it is, nevertheless, possible to shield at small area in proximity to the magnetic material of a core such as that indicated at 24 in Fig. 3. The basis for this last statement may be more readily understood from an inspection of Fig. 8. Assuming in that showing that a region K is to be shielded" from the effects of the field produced by current flowing through conductors 34, the desired result is realized by introducing an air gap G at a point remote from the region K, the air gap being afforded between the open sides of a magnetic annulus 36 surrounding the conductors. That is to say, the high reluctance of the air gap G is a limiting factor as to the flux flowing in the member 36 to the extent that the value of such flux is substantially less than that which would have occurred with a continuous shield, such,-for example, as that of Fig. 7 (path X The greatly reduced flux results in a similarly reduced product of flux and incremental reluctance per unit length of the magnetic member. Hence, the magneto-motive force between any two points on the surface of member 36 near the critical area K" is much less than in the case of a continuous shield, with the end result that the flux in area K is also much smaller.

With the foregoing background material in mind, it will be seen that Fig. 9 illustrates a device, in accordance with the principles of the present invention, which efiectively protects the electron beam in a cathode ray tube from the magnetic field produced by the end turns of the defiection coils. In the interest of simplicity, the tube is omitted from this figure and only one coil which may, for example, comprise the horizontal deflection means for a television application, is shown, the side windings being indicated at 18 and the end turns at 20. Surrounding. the side windings is a cylinder or core 38 of ferro-magnetic material, for example, which is well known in the art as a means for affording a shorter external path for the primary flux (i.e., the flux resulting from the side windings). The core of Fig. 9, however, is provided with radial flanges 40 having axial extensions or flanges 42 which overlie a portion of the core sleeve 38. The flanges 40 are interrupted or slotted as at 44 to accommodate the-end turns 20 whichpass through the openings 'and around the core 38 adjacent but behind the flanges '40,'such that the axial flanges 42 overlie the end turns.

'Iherelationship of the windings and the core is perhaps more readily understood from the end elevational view of Fig. 9a, which is taken in the direction of arrow A of Fig. 9. In Fig. 9a, the neck of a cathode ray tube 14 is also shown, in order to complete the picture, with the windings 20 emerging from inside the core 38 radially for a short distance and then passing behind the flanges 40.

Fig. 10 is a sectional view of the same structure and further shows the manner in which the core is or may be slotted at 44 to permit the windings to be wrapped around the sleeve 38 at their front ends. Thus, it will be seen that when a current flows through the coils (including the side windings 18 and end turns 20), the flux from the side windings 18 is, just as in the prior art, permitted to act upon an electron beam produced by a suitable source indicated diagrammatically at 50. The magnetic field produced by the end turns 20, however, is effectively prevented from acting upon such electron beam by means of the radial flanges 40 and their axial extensions 42 overlying the sleeve 38. That is to say, the action of flanges 40 and 42 is similar to that of the diagrammatic structure of Fig. 8 described above, in that an air gap is formed at G which greatly increases the reluctance of the endturns flux path to reduce the density of such flux and thereby decreases substantially the magneto-motive force between any two points on the surface of the flange 40 near the electron beam. Hence, the flux in the latter area is much less than it would have been in the absence of the flanges 40 and 42.

Although the present invention has been illustrated in a simple form showing only one set of coils and, thererfore, a single pair of slots 44, it will be appreciated that a second pair of coils (viz., the vertical deflection coils) may be wound about the core in substantially the same manner as the foregoing, with the end turns behind the flanges 40, this being accommodated by an additional pair of slots at right angles to the first pair. By forming the slots as small as possible, the portions of the end turns which are not covered may be maintained at a minimum so that their field which might escape to the region traversed by the electron beam is also sufliciently small as to have little undesirable effect upon the beam. Where necessitated by strict operational requirements, the slots may be covered, after the coils have been wound about the core, as described, by filler plugs of magnetic material held in place by any suitable means. One such filler plug is illustrated in Fig. 10a at 52, in relation to a slot 44 and its securing means may be in the form of clips 54 adapted to engage the flange 42 adjacent the sides of the slot.

Fig. 11 illustrates, by way of a vertical, sectional view similar to that of Fig. 10, another embodiment of the present invention which includes a sleeve 38 and a radial flange 40 of magnetic material. The sleeve 38 is again notched or slotted at 44 to accommodate the end turns 20 of, the coil which further comprises the side windings 18. In this case, however, the radial flange 40 is not retroflexed as in the structure of Figs. 9 and 10. Instead, an annular pocket or passage 45 is defined between the radial flange 40 and an additional annular flange 47 which is spaced from the flange 40 a distance sufiicient to accommodate the end turns 20. Flange 47, which is also of magnetic material, may, by way of illustration, constitute a portion of the supporting means or mounting for the yoke. Alternatively, the flange 47 may be a separate member secured to the sleeve 38 during assembly. In either event, according to the operation of the structure of Fig. 11, flux from the end turns 20 will travel through the'radial flange 40, a portion of the sleeve 38, flange 47 and an air gap, 6', indicated by the dotted lines. Since the air gap is remote from the neck of the cathode ray tube which is, of course, disposed within the sleeve 38, the flux traversing such path will not have deleterious eflects upon an electron beam within the tube. Additional changes and modifications within the scope of the invention will further suggest themselves to persons skilled in the art and, for that reason, the foregoing embodiment is not to be considered as limiting.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An electromagnetic deflection yoke for a cathode ray device, which comprises a core of magnetic material having a radial flange portion, said radial portion having an axial portion overlying a part of said core.

2. An electromagnetic deflection yoke for a cathode ray tube, which comprises an elongated core of magnetic material having an outwardly extending radial flange, said radial flange having an axial flange substantially coextensive therewith and partially overlying said elongated core.

3. A core for an electromagnetic deflection coil having side and end windings, which comprises: an elongated magnetic member adapted to cover such side winding, said elongated member having an end portion retroflexed so as to overlie such end winding, whereby to provide an air gap between said elongated member and the end of said retroflexed portion for flux produced by such end winding.

4. A magnetic core for an electromagnetic deflection coil having side and end windings, which comprises: an elongated member adapted to cover such side winding, said elongated member having an end portion retroflexed so as to overlie such end winding, whereby to provide a localized air gap between said elongated member and the end of said retroflexed portion for flux produced by said end winding.

5. A core for an electromagnetic deflection yoke which includes a conductor having side and end turns, which comprises: a magnetic member adapted to cover such side turns, said member having a radial, outwardly extending flange, said radial flange being turned rearwardly so as to overlie a section of said member, whereby to define an air gap between its edge and said member for flux produced by such end turns which are adapted to lie between said rearwardly turned portion and said member.

6. A core as defined by claim 5, wherein said flange is provided with an opening for accommodating such winding.

7. A core as defined by claim 5, wherein said member comprises a tubular sleeve adapted to surround a cathode ray beam path and wherein said flange is substantially coextensive with said sleeve, said flange having a slot therein through which such conductor is adapted to pass.

8. In an electromagnetic deflection yoke for a cathode ray tube which yoke includes a conductor having substantially straight side windings and a curved end turn, a core of magnetic material, which comprises: an elongated portion adapted to overlie said side windings, said elongated portion having a radially extending flange member, said radial flange being provided with an axial flange at its end remote from said elongated portion, said axial flange being generally concentric with and overlying a portion of said elongated portion whereby to receive, between itself and said elongated portion said end turn, said radial flange having an opening to permit winding of said conductor from inside said elongated member to the space between it and said axial flange.

9. In an electromagnetic deflection yoke for a cathode ray tube which yoke includes a conductor having substantially straight side windings and a curved end turn, a core of magnetic material which comprises: an elongated portion adapted to overlie said side windings, said elongated portion having a radially extending flange member substantially coextensive therewith, said radial aesnsaa flange being provided with an axial flange at its end remote from said elongated portion, said axial flange being generally concentric with and overlying a portion of said elongated portion whereby to receive between itself and said elongated portion said end turn, said radial flange having an opening to permit winding of said conductor from inside said elongated member to the space between it and said axial flange.

10. An electromagnetic deflection yoke for a cathode ray device, which comprises a coil having side and end conductors with corner connections therebetween, a hollow core of magnetic material surrounding said side conductors, said core having a radial flange portion on its exterior and magnetic means cooperating with said flange portion to form an annular passage exteriorly of said core and adjoining said core to receive said end conductor.

11. In combination, a core and a substantially rectangular electromagnetic deflection coil having side windings and end windings bent around said core, said core comprising: an elongated hollow magnetic member adapted to cover such side winding, said elongated member having means forming a channel around said core but within the axial dimension of said core adapted to receive such end winding, said channel defining an air gap for flux produced by such end winding, said core being provided with openings into said channel for passing corners of said deflection coil.

12. In combination, a core and a substantially rectangular electromagnetic deflection coil having side windings and end windings bent around Said core, which comprises: an elongated sleeve of magnetic material, said sleeve including a passage for such end windings around the outside of said sleeve, said passage affording a complete path including an air gap for'flux produced by such end windings, said air gap being located exteriorly of said sleeve but within its axial dimension, said core being provided with openings into said path for passing said deflection coil.

13. An electromagnetic deflection yoke which includes a conductor having side and end turns, and a core which comprises: a magnetic sleeve adapted to cover such side turns, said sleeve having a radial, outwardly extending flange member at its end, a second radial, outwardly extending member spaced a' relatively short distance from said first flange member back along said sleeve so as to form a channel for the reception of such end turns, thereby defining an air gap between said members for flux produced by such end turns, said sleeve being provided with openings into said channel to receive the corners of said conductor between said side and end turns.

14; An electromagnetic deflection yoke which comprises: a sleeve having a radial, outwardly extending" flange attached to its end and a second flange spaced a relatively short distance from and substantially parallel to said first flange back along said sleeve, said sleeve and flanges being of magnetic material, a deflection coil made up of side and end conductors, said coil being disposed with its Side conductors located inside said sleeve and with an end conductor located outside said sleeve but between said flanges, said sleeve being provided with two openings between said flanges to pass the corners of said deflection coil.

15L An electromagnetic deflection yoke which coin prises: an open ended cylindrical sleeve of magnetic material having a pair of spaced slotted openings in' an abutting and' extending'outwardly in a radial direction from said cylindrical sleeve and spaced ;a relatively short distance from and parallel to said first flange back along said sleeve, and a formed deflection coil having straight side portions extending along the inside of said sleeve and parallel to the axis thereof, said deflection coil also having arc-shaped end Portions equal in arcuate length to the distance between said slotted openings, at least one of said end portions lying around said sleeve between said flanges, said flanges enclosing said end portion on two sides thereof, said end portion being joined to said sidepportions by olfset joining portions of the coil petpendicular to both said straight side portions and said end portions and extending through said slotted openings.

16. An electromagnetic deflection yoke which coin prises: an open ended cylindrical sleeve of magnetic material having a first pair of spaced slotted openings in a first open end thereof, a second pair of spaced slotted openings in the second open end of said sleeve and oppositely disposed to said first pair of openings, 21 annular disk-shaped flange of magnetic material extend ing outwardly in a radial direction from said first open end of said cylindrical sleeve, a second annular disk shaped flange of magnetic material abutting and extend'f ing outwardly in a radial direction from said cylindrical sleeve and spaced a relatively short distance along said sleeve from and parallel to said first flange, a third an} nular disk-shaped flange of magnetic material extending outwardly in a radial direction from said second open end of said cylindrical sleeve, a fourth annular disk-shaped flange of magnetic material abutting and extending out wardly in a radial direction from said cylindrical sleeve and spaced a relatively short distance along said sleeve" from and parallel to said third flange, a formed deflection coil having two straight side portions extending along the inside of said sleeve parallel to the axis thereof, said side portions extending between said pairs of spaced slotted openings, said deflection coil also having arcv shaped end portions, said end portions lying around said sleeve in the space between said first and second flanges and between said third and fourth flanges, and said end portions being joined to said side portions by oifset joining portions perpendicular to both said straight side portions and said end portions at the points ofjuncture, said joining portions extending through said slotted open ings. 1 7

17. An electromagnetic deflection yoke which com prises: an open ended cylindrical sleeve of magnetic material having a pair of spaced slotted openings in an open end thereof, a first annular divided disk of magnetic material extending outwardly in a radial direction from said open end of said cylindrical sleeve and split adjacent said pair of slotted openings, at second annular disk of magnetic material abutting and extending outwardly in a! radial direction from said cylindrical'sleeve and spaced of said sleeve and parallel to the axis thereof, said tion coil also having arc-shaped end portions eqnal'in" arcuate length to the distance between said slottedopena ings, and one of said end portions lying around said sleeve between said flanges, said end portion being joined to said side portions by offset joining portions perpendicn' lar to both said straight side portions and said end pof tions and extending through said-slotted openings.

References Cited in thefile of this patent UNITED STATES PATENTS 2,677,779 Goodrich ,May 4, 1954"- 2,713,131 Urtel July 12,1955} 2,763,804 Morrell Sept. 18,-1956,"

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