IL31691A - Deflection yoke for cathode ray tube - Google Patents

Description

ηηιηρ *∞*¾g&Mftflpo W m¾npm map n»on n*?ir DEFLECTION YOKE FOR CATHODE RAY TUBE ABSTRACT OF DISCLOSURE · ■ .

A magnetic deflection system for a cathode ray tube employs opposed pairs of single layer spiral windings whose forward ends flare to develop deflection fields which remain perpendicular to the electron beam as it is deflected in the tube. A conforming sleeve of high magnetic permeability material surrounds the windings to provide a high reluctance path for leakage fields in the system, but a low reluctance path for the deflection field developed thereby. The forward winding ends are distributed to yield a pincushion correction, and the rear winding ends, are arranged to improve deflection linearity. 5his-appiieafei©!*-is-a-e<>ftfei»i^fe:H»»- i -pswtt -©.£-ray--appending-applieafeieft-Sej?iai-N©r-5θ3r&^Qr-filed-O -tdke*.-23-n .

The invention relates to an electromagnet whose con-struction and geometry achieve efficient, generation of a strong magnetic field and precise control over, the shape of that field. It also relates to a cathode ray tube, assembly incorporating the magnet as a beam 'deflection element. More particularly, the invention makes possible a magnetic deflection yoke of high performance and it will be described with specific reference to such a device.

A magnetic deflection yoke comprises a system of magnetic poles arranged on the neck of a cathode ray tube. The poles are used to controlledly bend the electron beam forme the tube in one direction or another from its straight line so that the beam strikes selected points on the tube face t provide visual indications thereon. . By suitably varying th magnetic fields, the electron beam can be made to sweep up down and back and forth across the face of the tube. Then, simultaneously modulating the intensity of the beam, a visu presentation or picture can be formed on the face of the tu A common use of this type of tube is in the conventional ho hold television receiver.

Deflection yokes are usually in the form of gener saddle shaped windings arranged around the neck of the cath ray tube. In a yoke capable of two-direction beam deflecti such as used on a television receiving tube, there are two of windings. The windings of. each pair are located on oppo sides of the tube neck, and the winding pairs are displaced around the tube. When energized, the two pairs of windings duce orthogonal magnetic fields through the neck of the cat ray tube. These fields are also perpendicular to the path the undeflected electron beam generated in the tube. By ap priately varying the currents in the. winding pairs, the dir and magnitude of the magnetic fields can be varied to defle the electron beam to give the proper pattern on the tube fa Prior beam deflection yokes usually include also a jacket o sleeve of low reluctance material such as ferrite fitted sn around the windings to help constrain the magnetic field an Only the component of the magnetic field that is perpendicular to the electron beam contributes to beam deflection. Therefore, the prior yokes whose fields are perpendicular to the undeflected beam can utilize a maximum amount of the available energy for beam deflection only so long as the' beam is essentially undeflected. As the beam deviates from its straight line path, the field component that is perpendicular to the beam becomes smaller and the effectiveness of the field decreases accordingly. At the same time the field component that is parallel to the deflected beam increases. This latter longitudinal component tends to shorten the focal length of the beam and cause defocusing of the spot on the tube face.

The defocusing effect is particularly prevalent at the two ends of the yoke. At those points, non-uniform fringe fields bow out from the ends of the yoke to provide substantial longitudinal field components unless steps are taken to prevent this . . . . . . .

The fringe field at the screen end of the yoke tends to produce flux lines which intercept the electron beam at widely different angles depending upon the degree and direction of beam deflection. Accordingly, the amount of the available energy contributing to beam deflection varies substantially -depending upon the degree of beam deflection. Even more importantly, as the electron beam bends to larger angles, the beam is defocused by different amounts. These effects are compounded by the fact that the beam has a finite cross section. Therefore, - BBCS^M.TP 84-116D the degree of deflection and defocus of different parts of the beam is not the same. The net result' is that the . spot on the tube face is not only defocused as it moves out from the center of the screen but also the spot symmetry is altered from the desired round shape.

The fringe field at the gun end of the yoke also cause premature beam deflection, which in turn requires that the yoke be made shorter to prevent the beam from hitting the unflared neck of the tube. Moreover, the outwardly bowed fringe field may be intercepted by the metallic parts of the electron gun in/ the tube. Eddy currents thus induced in those parts by the high frequency magnetic field components cause distortion of the pat¬ tern on the tube face. This eddy current distortion is frequency, dependent. It is especially troublesome in information display systems where it is desired to trace patterns on the tube face at very high speeds.

Attempts have been; made to overcome the aforementioned problems by the ob ious expedient of moving the end or cross¬ over segments : of the_ windings which give rise to the fringe : fields as far away as possible from the electron beam. Thus, ' · ·. ί· the opposite ends of the windings have been flared out, away from the neck of the cathode ray tube. Further, at the gun!end of the yoke, a fringe ring of lov; reluctance material has been . spaced from the end of the yoke to "short circuit" the remainder of the fringe field there.

While these steps have alleviated the problem somewhat, ■ ' ' i ■ · V-there have still remained appreciable fringe fields, particularl at the screen end of the yoke. More importantly, the steps taken to solve the fringe field problem have materially increased the overall inductance of the yoke without a concomitant increase in the usable magnetic flux. The fringe ring alone increases the inductance by almost 30% and the flaring out of the v/inding . segments increases the overall inductance even further. Bearing in mind that the frequency response of the yoke is limited by its self-resonant frequency and that this in turn is inversely proportional to the product of its overall inductance and capacitance, resort to the aforementioned practices places a serious limitation o the frequency response of. the yokes.

As a direct result of the redirecting and shunting of the fringe field,, the efficiency of these prior yokes has suffered even more because a very substantial part of the magnetic energy in the magnetic field is not utilized fo beam deflection. Field utilization efficiency of only 50% is quite common. This, coupled with the fact that the ferrite jacket itself gives rise ' to substantial hysteresis losses, re.sults.in an unduly large electric current requirement for maintenance of the proper deflecting fields.

Many of the prior systems are further disadvantaged because they require a separate device for correcting pincushion type distortion. This increases even more their cost and complexity. Still others are not accurate enough to be employed in applications requiring extremely precise deflection.

Accordingly, this ..invention' aims to provide a magnetic deflection system having materially reduced energy re- quirements.

A still further object of this invention is to provide a magnetic deflection system having a Relatively high resonant frequency.

Another object of this invention is to provide an efficient magnetic deflection system particularly suited as a yoke for a cathode ray tube capable of producing beam deflection of improved linearity.

Still another object of this invention is to provide an efficient magnetic deflection system particularly suited as a yoke for a cathode ray tube v/hich minimizes defocusing out to larger deflection angles even v/ith a flat tube face.

A . further object of the invention is to provide a magnetic deflection system which dynamically..corrects pincushion distortion without at the same time defocusing or otherwise'; i distorting the electron beam. L Another object of ..the invention is to provide a mag-netic deflection yoke characterized by low distortion, aberra¬ tion and defocusing at the ends of the yoke even when the de¬ flection windings are formed using printed circuit techniques.

Another object of the invention is to provide a mag¬ netic deflection .system which is reiatively inexpensive to make.

A further object of the invention is to provide a ' "BfifcjS.MTP '84-116D . -· ■The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following de- " tailed description take.n in connection with the accompanying drawings, in which: FIG. 1 is an exploded perspective view of a magnetic deflection yoke embodying the principles of my invention; FIG. 2 is an axial section of the magnetic deflection yoke shown in FIG. 1, showing its spatial relationship to a cathode ray tube on which it- is mounted; FIG. 3 is an axial section of one of the winding forms shown in FIGS . 1 and 2 ; FIG. 4 is a perspective vie illustrating schematically the deflection windings and their connections; FIG. 5 illustrates the horizontal field distribution near the front of the yoke; FIG. 6 illustrates the horizontal field distribution near the middle of the yoke; FIG. 7A illustrates a rectangular grid traced on a cathode ray tube undergoing pincushion distortion; FIG. 7B is a schematic representation of a cathode ray tube employing a deflection yoke made in accordance with · · ■ ■ · β-2'077Α BBCSV: TP ■84-1-16D FIG . 8 is a perspective view of a modified deflection section which effects very precise deflection and aLso corrects pincushion distortion; and FIGS. 9A to 9D illustrate the operation of a deflectio yoke employing deflection sections of the FIG. 8 type.

Generally, my improved low energy magnetic deflection^ yoke has materially reduced energy requirements because it uses a maximum amount of its magnetic field for beam deflection.

A low reluctance path in the form of a ferrite sleeve is provided around the outside of the windings to shape the magnetic fields and to increase the flux density through the cathode iray tube. Unconventionally,; however, the sleeve is separated from the windings by an intervening space having a very high reluctance. This serves to materially reduce hyster¬ esis losses in the yoke without appreciably reducing the effi¬ ciency thereof. It also effects a substantial reduction in the non-beam deflecting "leakage" field developed by the windings.

The sleeve itself is shaped to cooperate with the windings in shaping the magnetic fields especially at the ends ' of the yoke. Thus, at the forward or screen end of the yoke, it- projects ut beyond the forward ends of the deflection wind- ings. Instead of attempting to eliminate the effects of the fringe field on the beam at the forward end of the yoke, as was the prior practice, I have flared the winding and sleeve to. redistribute and shape this field, giving' it a curvature that D-207 A BBCSi TP . 84-116D renders it generally perpendicular to the beam over(the entire range of beam deflection. The formation and utilization of the , fringe field at the forward end of the yoke greatly improves th efficiency of the yoke in that a maximum amount of the magnetic energy is utilized to deflect the electron beam.

In addition, the aforesaid shaping of the fringe fiel at the forv/ard end of the yoke reduces defocusing to a minimum.

At all beam deflection angles, the magnetic flux lines of the' fringe field intercept the beam at substantially right angles.

Thus the component of the flux which is parallel to the beam an causes defocusing is minimized.

At the rear or gun end of the yoke, the sleeve projec axially beyond the rear ends of the deflection windings, making the net flux there also perpendicular to the electron beam, whi is always undeflected at that point. The total length of the field is shortened. Accordingly, there is less tendency for th beam to deflect prematurely » Finally, my improved deflection yoke has materially less built-in inductance and capacitance. than prior comparable yokes . Consequently, it is faster and ca operate at higher . frequencies than those yokes. \: Referring more specifically to FIG. 1 of the drawings i the yoke comprises a vertical beam deflection section indicated generally at 10 and a horizontal beam deflection section indica ted generally' t 12. Sections 10 and 12 are nested coaxially inside a jacket 'indicated generally at 14 comprising a high per meability material such as a ferrite. A terminal ring 18 is D-2O77A / BBCSiMTP secured to jacket 14 to make electrical connections to the de- flection sections 10 and 12· The assembled yoke is adapted to be slid over the end of a cathode, ray tube and positioned on the neck of the tube (FIG. 2) . .

The vertical deflection section 10 comprises a bell- shaped form 19 made of an insulating material such as transparen styrene , for example. As best seen in FIG. 3, form 19 has a generally cylindrical rear tube 20 integral with a forward flare 22 whose shape will bo dealt with more particularly later. The outside, surface of the flare 22 is recessed to form a circumferential band 24. The rear end of tube 20 is similarly recessed, forming a circumferential band 28. Circumferential ribs 26 and at the ends of the form 19 and a circumferential band 27 alon the central portion thereof bound the recessed bands 24 and 28.

Returning to FIG. 1, a pair of substantially identical diametrically opposed windings 34 and 36 are arranged around the outsid of form 10 at opposite "sides" in a Helmholtz type coil arrangement. Each winding · forms a rectangular spiral arranged lengthv/ise on. and. flat against the form 10. Thus, the winding 34, for example, has lengthwise segments 34a which are seated in successive pairs of slots 37. distributed around the tube 20 in - ! a fashion to be described presently. Its front and rear end: crossover segments 34b and 34c, respectively, extend arcuately around the form 10 in single layer fashion in the recessed bands 24 and 28, respectively. In the illustrated embodiment, each winding has eleven turns (FIG. 4) .

Mathematically, the slots 37, and hence the winding segments 34a, are distributed with respect to the center of the winding 34 in accordance with a sine function. In other"' words, proceeding out on each side from the longitudinal center line o the winding (corresponding to an angle of 0°) , the distance to each successive winding segment 34a corresponds approximately t a point on the sine curve. Proceeding from the center line, th successive segments 34a are "spaced closer and closer together, The distribution of the longitudinal winding segments is described mathematically as follows: .©η=είη~ f(2n-l) - (n-1) (dfrk) | (1) N L Where:.

N is the number of turns in the winding d is the width of the conductor (the diameter of round wire) L is the length of the winding measured between the two endmost crossover, segments and following the curvature of the winding k is the spacing between the conductors of adjacent •crossover segments Θη is the angular position of the nth -longitudinal segment of the winding from the reference plane which is a plane passing through the center of .the innermost winding loops and the longitudinal . a'xis of the form 19 . ... . } _ n is the longitudinal winding segment whose angular position is being calculated ί The second winding 36, which. is arranged symmetricall in relation to the winding 34, has longitudinal segments 36a an crossover segments 35b and 36c, arranged in the same manner as thei ' counterparts in the winding 34. Each of the windings ex-, tends approximately halfway around the form 10. Leads to the D--2Q77A 84-116D windings 34 and 36, which are connected 'in series, extend throu slots 39 in rib 30. When current is supplied to the windings, horizontally directed magnetic field is produced within the for 19 between the two windings 34 and 36. The aforementioned distribution of the lengthwise."winding segments 34a and 36a and th forward ends of the windings 34 and 36, which are flared in con formance with flare 22 of form 19, shape the magnetic field pro duced in the yoke in a fashion that will be described more particularly later.

The horizontal deflection section 12 is the same as vertical deflection section 10 except that its diameter is some what larger so that section- 10 can nest snugly within it. Thus section 12 comprises an insulating bell-shaped form 40 having a generally cylindrical tube 41..integral with a flare 42. As before, the flare 42 has a recessed circumferential band 44 around its exterior and the tube 41 has a similar band 48. The bands are defined by ribs 46 and 49 and a centrally disposed raised band 47.

A pair of upper and lower deflection windings 50 and ! 52, respectively, are arranged on opposite sides of form 40·;: forming another Holmholt2 type coil. As with the section 10 windings, the windings '50 and 52 are wound in spiral fashion flat against the outside of form 40. Thus, the lengthwise segments 50a and 52a are seated in lbngitudinal slots 54 in the band 47 in accordance v/ith the sine function described above.

The front and rear winding crossover segments 50b, 52b and 50c, P-2077A BBCStMTP 84-116D 52c extend arcuately around form 40 in the recessed bands 44 and 48, respectively, just as described above in connection with section 10. Leads from the windings 50 and 52 extend through slots 58 in. the rib 49.

If desired, the deflection systems 10 and 12 can be made very easily and inexpensively by using conventional etched circuit techniques. The deflection windings are then formed fro thin conductive films bonded to the plastic forms. Using these same techniques, it is even feasible to apply both the vertical and horizontal deflection windings to a single form further simplifying the yoke. In this event, the vertical deflection windings might be "formed" on the inside surface of the single form and the horizontal deflection windings applied to the out¬ side surface. Of course, the windings would still be shaped and oriented as described above.

When energized, the windings 50 and 52 produce a stron magnetic field through the center of the form 40 vertically be¬ tween the windings. _ Here again, the winding distribution and the flared forward ends of the windings shape the magnetic field as will be described later.

Still referring to FIG. 1, the deflection sections 10 and 12 are adapted to be nested inside the jacket 14. Jacket 14 includes a loose sleeve 64 fabricated from a high permeability material such as a ferrite. ..Sleeve 64 provides a low reluctance return path for the magnetic fields, extending across the in D-2077A ,BBCS:MTP , 84-116D and 12. Also, it is appreciably longer than deflection sections 10 and 12 for reasons that will become apparent. Actuall for facilitating its fabrication, sleeve 64 is made up of a < series of four ring-like sections 64a-64d. Of course, the sleeve 64 may just as well comprise a single ferrite piece.

A cylindrical axial passage 66, whose diameter is appreciably larger than- the outside diameter of the deflection section 12, extends through sleeve 64. A tubular cylindrical spacer 70 is snugly fitted within passage 66. For ease of illustration, spacer 70 is shown displaced rearwardly somewhat in FIG. 1. In use, it extends through rings 64b-64d and its end 70a (FIG. 2) protrudes an appreciable distance out the rear of sleeve 64. The inside . diameter of spacer 70 is only slightly greater than the outside diameter of tube 41 of deflection section 12 so that %<;hen sections 10 and 12 are nested in jacket 14, tube 41 is snugly accommodated within sleeve 64. The space 70 is fabricated of a material, such as plastic, having a very low magnetic permeability as compared with the ferrite sleeve.

The inside forward edge 71 of ring 64a is beveled to conform to the flare 42 of deflection section 12 and for other reasons that will become apparent later.

The terminal ring 18 comprises simply an insulating ring 80 for securing by screws 82 to the end of spacer 70. . The ring 80 carries terminals 84 for the deflection" windings 34, 36, 50 and 52.

D-207.7A BBCS- TP 84-116D FIG* 2 illustrates the assembled yoke, v/ith the deflec tion section 10 snugly nested coaxially inside deflection sec- tion 12 and the section 12 within the jacket 14. The components of the yoke may be bonded in place with a suitable resin. The yoke is fitted oh the neck 100 of a cathode ray tube 98. Since the sections 10 and 12 are coextensive, their corresponding forward ribs 26 and 46 and rear ribs 30 and 49 are adjacent to one another. The flare 42 of section 12 seats against the beveled edge 71 of sleeve 64. The flare 22 of section 10 seats against the flared surface 101 of the cathode ray tube 98. The two deflection sections 10 and 12 are oriented about their common longitudinal axis so that their deflection windings are angularl displaced 90° from one another .

As mentioned previously, the sleeve 64 is appreciably longer than the deflection sections 10 and 12. As seen from FIG. 2, the beveled forward -edge 71 of .sleeve ring 64a extends . forwardly beyond the ribs 26 and 46 of deflection sections 10 an 12, forming there an annular beveled overhang 90. The rear end of the sleeve ring 64d also extends out beyond the rear ribs 30 and 49 of sections 10 and 12, respectively, forming there also an annular overhang 92. i " I Finally, insulating ring SO is secured to the rear, end 70a of spacer 70 by means of the screws 82.

FIG. 4 illustrates the relationship and connections between the four windings of the yoke. The numerals on the terminals at the ends of the windings correspond to those on the When the cathode ray tube 98 is energized,, it generat an electron beam which in the absence of outside forces follows a straight line path and strikes the tube face 102 at the point A on the longitudinal axis of the deflection system. When the vertical defleqtion windings 34 and 36 are energized, they generate a magnetic field whose flux lines, indicated at 106 in FIG. 2, are generally horizontal (i.e. parallel to. the drawing) The field tends to deflect the electron beam 104 vertically (i.e. into or out of the plane of the drawing) . The energized horizontal deflection windings 50 and 52 generate a magnetic field whose flux lines (not. shown) are generally vertical (i.e. perpendicular to the plane. of the drawing) . This vertical fiel accomplishes horizontal beam deflection.

Thus, viewing the. tube from the front, current of a certain magnitude in one direction deflects the beam 104 to the left, where it strikes the tube face 102 at point B. Current of a lesser magnitude in the opposite direction deflects the i beam 104 a smaller distance to the right of point A, where i strikes the' t,ube face at point C. In actual practice, the two i deflection sections 10 and 12 can be operated together to deflect the beam 104 to any point on the tube face 102. The-. ! deflection winding segments, distributed as aforesaid and surrounded by the ferrite sleeve 64, produce strong magnetic field across the tube neck 100 in, the inte ior of the yoke.

The fringe field at the forward end of the yoke, instead of being largel diverted from the interior of the tube a D-2077A :ϊ·.ΐ'Ρ 84-116D thus converted to a useless "leakage field", as was' the prior practice, is actually shaped so that it can be utilized to a maximum extent to help deflect the beam 104 and to minimize dev focusing. The gradually flared, different length, forward winding crossover segments 34b, 36b, 50b and 52b, each seated in single layer fashion inside the correspondingly beveled ferrite ring 64a, shape the vertical and horizontal magnetic deflection fields at the forward. end of the yoke so that their flux lines are substantiall transverse to the beam 104 no matter how the beam is deflected.. For very precise shaping of the fields to obtain the best possible results, the aforesaid flai . angle might have to depend somewhat on the speed of the electron generated in the tube 98. However, for the most standard tubes, a standard flare angle of about 45° can be used with execellent results. The beveled t overhang 90 at the very front of the yoke cooperates with the winding arrangement by "short circuiting" the very forward magnetic field components, with the net effect of flattening the bowing fields somewhat and thereby helping to properly shape them. . i Thus, as readily seen from FIG. 2, whether the electro beam 104 is deflected to strike the tube face 102 at points A , B or C, the curved horizontal flux lines 106a intercept the beam .104 substantially at right angles regardless of the horizontal deflection. Thus .vertical deflection is relatively independent of the horizontal position of the beam. Furthermore, since only the beam produces vertical beam deflection, it is quite apparen that a maximum amount of the magnetic field generated by the windings, even at the very front of. the yo!ce,'can contribute , to vertical beam deflection. The efficiency of the yoke is thus materially increased. Magnetic energy that was formerly wasted is now utilized to a maximum extent, resulting in reduced energ requirements for the' yoke.

- The same condition holds true in the case of the vertical deflection field. It is shaped as aforesaid so that it intercepts the electron beam 104 transversely no matter how the beam is deflected vertically. Therefore, the outwardly bowing vertical field can be used to a maximum degree to help deflect the beam 104. horizontally.

Actually, the shaped flare at the forward end of the yoke affects the field back in the cylindrical portion of the yoke. The field there tends to bow forwardly, though to a lesser degree, with increasing distance from the flare. Thus, b the time the electron beam is deflected appreciably, it encounters the curved field whose flux lines are substantially per-pendicular to the beam. j ■ For certain applications, it may be desirable to ex-tend the flare back so that it constitutes the major or entire portion of the yoke. For example, for short yokes having a very vide angle deflection capability, the yoke is preferably con-tinuously flared or trumpet shaped. This construction insures that the magnetic flux lines all along the yoke intercept the The modification to the sine distribution compensates for this. It produces a magnetic field in the cylindrical por- tion of the deflection section whose flux lines bow out slightl from the ©n reference plane, the bowing being more pronounced a the distance from said plane increases..

For example,. FIG. 6 shows the field distribution near the middle of the vertical deflection section 10. The flux lin are substantially horizontal at the middle of the section where Θη = 0. As &n increases, however, the flux lines become bowed out to a greater degree. With the density of the flux increasi with distance from the tube axis-, the deflection per unit of winding current also increases with the distance from the axis.

This increase is arranged to compensate for the decrease in the forward fringe field, thereby providing a relatively linear ove all deflection characteristic.

The same situation prevails in the horizontal deflection section 12. The field in the cylindrical part of the sec- i tion is bowedJ out sideways to compensate for the inward bowing of the flux in the region of the flare due to the crossover seg ' ' · i ments 50b and 52b. The effects of these bowed fields on deflec tion linearity are compensated by the configuration in the^cyl- i indrical part of the yoke. ' Referring again to FIG. 2, the aforesaid shaping of the fringe fields at the forward end ι of the yoke has been found to reduce the defocusing of the electron beam 104 particularly when the beam undergoes fairly large angle deflection. This is due' also to the fact that the beam 104 intercepts the magnetic flux lines transversely. Thus the component of the magnetic field which is parallel to the beam and which tends to shorten the focal length is minimized. Also, even though the beam has a finite cross-section, both edges of the beam arrive at a given flux line in the field at the same time. This is in contradistinction to the situation that prevails when the beam approaches at an angle other than .90° v/here the degree of deflection differ slightly at the opposite edges of the beam.

At the rear end of the yoke, the fringe fields tending to bow out the rear of the yoke toward the gun end 96 of the cathode ray tube follow the low reluctance path afforded by the circumf rential portion 92 of the ferrite sleeve 64 which overhangs the rear ends of. the vertical and horizontal deflection windings. Thus, the fringing flux lines are short circuited by the ferrite overhang 92 so that the net field there tends to be straightened out. The field. is not intercepted by the conductiv components of the electron gun and there is less likelihood of the electron beam 104 being deflected prematurely.

Still referring to FIG. 2, the separation between the sleeve 64 and. the cylindrical portions of deflection sections 10 and 12 afforded by the low permeability spacer 70 sets up a high reluctance barrier to the leakage magnetic flux from individual winding turns that formerly tended to directly encircle the turns by way of the ferrite sleeve rather than bridge the cathod ray tube 98. This, in turn, increases the efficiency of the yok Referring'' now to FIGS. 7A and 7B, a preferred embodi- / ment of my deflection system also corrects pincushion-type dis-. tortion without any material sacrifice in the 'desirable yoke . characteristics described above. Pincushion distortion as depicted in FIG . 7A arises because of the, difference in the. radii of curvature of the cathode ray tube screen and the electron beam scan.

More particularly, FIG. 7B shows a cathode ray tube 1 v/hich generates an electron beam.122 impinging on a screen 120a The beam is focused by a conventional magnetic lens so that its cross-section decreases as it approaches the screen. A deflec¬ tion yoke 124 on the neck of the cathode ray tube controlledly deflects beam 122 so that it strikes the screen at the desired points thereon. Beam 122 is deflected about a theoretical cent of deflection near the middle of yoke 124. It can be deflected vertically as shown in FIG. 7B, to sweep out a vertical arc in- dicated at 126 whose radius -of curvature is the distance betwee arc 126 and the center of deflection inside yoke 124. It can also be deflected horizontally so as to sweep out the same sort ' · " . ■ ■ · i of arc in a horizontal plane.

" ( If the tube screen 120a coincided with arc 126 (and also v/ith the swept arc in the horizontal plane) , a grid •'patter swept out by beam 122 v/ould appear perfectly rectangular since the sine of the angle of deflection of the beam is proportional to the current in the yoke 124. However, due to the difference in the. adii of curvature of the beam scan and screen 120a, the D-2-077A BfeCS-ίΊΤΡ even more difficult to obtain uniformity, in such adjustment from .one unit to the next when they are produced in numbers. Moreover, it is extremely difficult if not impossible, to find an adjustment of the static lens which will correct the pincushion distortion and yet maintain an even spacing between the lines of a grid-type pattern. That is, the static lens can straighten out the vertical and horizontal lines in the grid pattern shown in FIG. 7A. However, because it is a static correction, it does not restore the uniform spacing, of the grid lines. Finally, it also may introduce other distortions. Therefore,, it cannot be used in applications requiring the highest precision.

FIG. 8 illustrates a vertical deflection section 130 of a deflection systera having capacity for correcting pincushion distortion while still obtaining linear beam deflection and lov; beam distortion/aberration and defocusing. For clarity, we hav only shown a few winding turns and have exaggerated- the spacing between them.' — The associated horizontal deflection section is like vertical section 130" and will not be described in detail. It bears the same relationship to section 130 that deflection sec- \ tion 12 bears to section 10 in FIG. 1. That is, the two deflec- ί tion sections are nested together and oriented at right angles to one another as fully described above. Also, the two deflection sections in this embodiment of the invention are themselves nested inside a ferrite jacket similar to jacket 14 in FIG. 1.

Therefore, in all respects except as described . specifically be- Section 130 comprises an insulating, bell-shaped form 132 having a generally cylindrical rear tube 134 and an integral forward flare 136 whose shape will be described in more detail later. In other respects, form 132 is the same as form 19 in FIG. 1.

A pair of substantially identical, diametrically opposed windings 138 and 140 are arranged about the outside of form 132 in a Helmholtz'-type coil arrangement. In use, section 130 is oriented so that windings 138 and 140 generate a generall horizontal magnetic field inside form 132. This horizontal fiel produces vertical beam deflection as described above in connection with FIGS. 1-6. ' - Each v/inding 138 and 140 forms a generally rectangular spiral arranged lengthwise on form 132. In the deflection section illustrated specifically in FIG. 8, each winding 138 and 140 has four turns. The longitudinal' winding segments 138a and 140a of these windings are distributed about the circumference o form 132 in the same manner as are longitudinal segments 34a and 36a of deflection section 10 in FIG. 1. Also, the front winding crossover segments 138b and 140b of the two windings extend cir-cumferentially in a single layer about flare 136, while the rear crossover segments 138c and 140c extend generally circumferen-tially about the rear end of tube 134.

The longitudinal v/inding segments 138a and 140a are distributed about the circumference of tube 134 in accordance with a sine function to produce a uniform magnetic .deflection D-2077A BBCSiMTP 84-116D Still, referring to FIG. 8, the forward winding crossover segments 138b are distributed on flare 136 so that, proceeding forwardly, they are spaced progressively farther apart. along the surface of the flare. More particularly, in the illustrated embodiment, the spacing between successive pair's of crossover segments increases linearly. In a typical example, the spacing between the two innermost segments 138b is 0.05 inch, the spacing between the next two segments is 0.10 inch, and the spacing between the third and fourth segments is .150 inch. Flare 136 is made long enough to accomodate the desired number of crossover segments.

' The winding crossover segments 140b have the same distribution as segments 138b..: A deflection system has also been constructed wherein the crossover segments 138b and 140b are, distributed in accordance with a power function, e. g. a square function. In this embodiment, the successive segments are spaced farther apart than is the case with the linear distribution. Consequently this distribution requires a longer flare 136 to accomodate the same number of wires.

Referring now to FIGS. 8 and 9A-9D, the two windings 138 and 140 in vertical deflection section 10, when energized, produce a generally horizontal magnetic field which deflects the electron beam 122 (FIG. 7B) vertically as mentioned previously; and the deflection field is substantially uniform in tube 134. However, as the beam progresses toward the front section 130", and moves off the yoke axis, it encounters the crossover segments 138b and 140b which produce a nonlinear field distribution inside flare 136 which dynamically corrects pincushioning.

FIGS. 9A-9D illustrate the field distribution inside form 132 at the correspondingly lettered location along the longitudinal ■ axis of section 130 in. FIG. 8. The solid^ lines represent the field produced by vertical deflection section 130 The dotted lines represent the field developed by a similar horizontal deflection section (not shown) . Actually, the field and the flare also bow forwardly as shown in FIG. 2. However, for ease of illustration, we have shown them in FIGS . 9A to 9D with no forward bow.

FIG. 9A shows that at point A in the cylindrical portion of deflection section 13,0, i.e. within tube 134, electron beam' 122 coincides essentially with the longitudinal axis of section 130 and- its diameter is relatively large at this point.

Also, the vertical and horizontal deflection fields here are very linear and uniform as illustrated by the substantially rectangular flux pattern. This is essential because the beam 122 diameter is a relatively large fraction of the diameter of the deflection . field, or more' specifically, both the beam ' " ' i diameter and the intensity of the deflection field are rela- : tively large. ' Thus, even a small percentage distortion in the field here will result in a relatively large difference in the i field strength and/or direction from one side of the beam 122 to the other. Electrons from one part of the beam would there¬ fore be deflected quite dif erently from those in another part thereof, resulting, in defocusing and image distortion. 1 BBCS :ΜΤΡ 84-ll'6D The deflection fields produced by the vertical and horizontal deflection sections now move beam 122 off the longitudinal axis of the yoke in the direction of the final deflection position. Also, the cross section of the electron beam 122 gradually becomes progressively smaller due to the fact that ■ the beam is focused by a focusing coil as noted above.

FIG. 9B is representative of the deflection fields at point B just beyond the first pair of crossover segments 138b and 140b. This pair of current-carrying wires extending around the circumference of flare 136 causes the deflection fields to have the requisite nonuniformity to correct pincushioning with .the illustrated beam deviation from the yoke axis. However, the field nonuniformity still produces very little distortion of beam 122 because, the deflection field is growing larger in cross section and therefore less intense, while at the same time the beam 122 cross section is growing smaller. . Conse- quently, even with a relatively large percentage nonuniformity in'the field, the absolute amount of field variation across the electron beam 122 is small and there is minimal defocusing of the beam. . 1. 1.

This process continues so that while the correcting field nonuniformity becomes progressively greater as beam 122 moves toward the screen, the field intensity and beam diameter .v decrease concomitantly. For example, FIG..9C shows the' deflection fields at point C just beyond the third pair of crossover segments 138b and 140b. The three pairs of circumferential winding segments cause a relatively large nonuni-formity in the fields illustrated by the inwardly bowing. magnetic'1 flux lines. This large nonuniformity is required to obtain the requisite pincushion correction because the beam is now relatively far away from the yoke axis. However, again the field intensity and beam diameter are much less than at points A and B. Consequently, the nonuniform field still causes relatively little spot distortion and defocusing. •i Progressing along the longitudinal axis of section 130, the deflection fields become even more nonuniform and larger as we proceed to point D at the forward end of the yoke in order to apply the requisite correction to the beam which is now a maximum distance away from the yoke axis. By the same time, however, the field intensity and cross section of beam 122 are still smaller so that there is little difference in field intensity and direction across the beam. Therefore, even at this point, the nonuniform fields do. not distort or defocus beam 122 to any appreciable extent.

In this fashion, the progressively changing field nonuniformities created by the flared, distributed crossover segments 138b and 140b achieve a dynamic pincushioning ..correction while still causing minimum beam distortion. This is because as the field nonuniformity increases, the product of field intensity and cross section decreases at an even faster rate so that the nonlinear fields have minimum tendency to distort and defocus the beam.

It is important to emphasize at this point that the present yoke produces a pincushion correction which. is dynamic rather than static. That is, the nonuniform correcting fields - to which beam 122 is subjected change progressively as the beam passes out through flare 136.' The advantage of this dynamic correction over the standard static magnetic lens correction is that the former not only corrects pincushioning, but does so without causing any change in ' the line spacing of the ideal rectangular grid pattern such as occurs ;Ln a conventional ■system employing a fixed magnetic correction lens.

As best seen in FIG. 1,. when the windings .are .'flared as are those in deflection section 12, for example, the longi¬ tudinal winding, segments 50a1, 52a, grow further apart as they progress up flare 42 due to the curvature of the flare. I ., have found that a pincushioning correction can be obtained by properly distributing the wires in the windings as they progre up the flare.

For example, when the longitudinal segments in each winding are positioned at a uniform distance from' one another as they progress up flare 44, instead of at constant angle from the center of section 12, a nonuniform field is developed at the flare end which suffices to correct pincushioning. Thi corrective wire distributio can be used instead of the technique described in connection with FIG.^ 8. Alternatively, it may be used along with the FIG. 8 construction to obtain an ; additional pincushion correction. · i In addition to eliminating the usual' static pin- ' ' ' . cushion correction lens, the present yoke construction also;. i somewhat improves deflection efficiency. This is because the i crossover segments 138b and 140b are spaced progressively t further apart. This reduces' the overall capacitance of the yoke, even though there may be more inding turns in the present construction than in. a comparable conventional yoke.

Further, the present construction eliminates the difficult BBCS:JPL 84-116D •1 In actual practice ,· this distribution is governed by a set of equations whose derivation assumes that the number of field generating winding turns remains constant all along tube 134. However, progressing toward the rear of tube 134, to point 1, we go beyond the innermost crossover winding segment; hence there are two less winding turns (i.e. one on each side of tube 134). Consequently, \ the radial distribution of winding segments 138a, 140a as- determined by the original set of equations does not produce a perfectly uniform field in this region.

In progressing from point 1 to point m, another cross- oyer segment is passed and again there are two less winding turns. Consequently, in the region between the two outermost crossover segments, the field nonuniformity becomes even more pronounced.

We have shown only a few winding turns in section 130, However, it will be appreciated that with a deflection section having many turns, the field nonuniformity at the rear end thereof might be further aggravated and give rise to consider¬ able beam distortion and aberration.

A yoke employing deflection sections made in accordance with FIG. 8 corrects .these field . nonuniformities at the rear end of the yoke by shaping the crossover segments (e.g. at 1 and m) .

More, particularly, I alter the angular distribution on tuba 134 of the longitudinal, winding r.c'gmcntG 13On, 1 On in the regions between the successive crossover segments 138c, 140c, to compensate for the decreased number of winding turns in those regions- For example, for the regions containing -points 1 and m, the basic distribution equations are changed to correct for the reduced number of turns there. That is, N in Equation 1 decreases by two in each case.. These corrected equations then define a new winding segment distribution for these regions which will produce -a uniform field there.

As seen from FIG. 8, the distribution corrections manifest themselves as rounded corners 150 on the turns of winding 138 and similar rounded corners ; 152 on winding 140 at the rear end of section 130. Ideally, each corner is made up of one or more short wire segments 150a, 152a representing the angular redistribution required in successive regions to correct for smaller number of winding turns. These segments are quite noticeable in FIG. 8 because only a few winding turns are shown and their spacing is exaggerated.. It is seen that ideally each segment- begins and ends .off the end' of a crossover segment. In 'actual practice, however, where a number of relatively closely spaced turns are used, the corners 150, 152 would appear more gradually rounded.

'D-2077A BBCS.-MTP 84-116D This same correction can be. made at the flare end of a yoke such as shown in FIG. 1 to further improve its performance. In this case, an electron beam at any position in the yoke, including both crossover regions thereof, encounters a very uniform field. . This correction will ordinarily not be made in the flare end of deflection, sections of the FIG. 8 type because the redistribution of the segments as just described is not fully compatible with the winding distribution required in the flare to correct for pincushioning A yoke made in accordance with FIG. 8 is further advantaged in that the separation between the crossover segments lowers the capacitance between the winding turns. This raises the resonant frequency of the yoke and increases its speed of response. Without the aforesaid angular distribution of the windings' at the crossovers, it has not been practical until now to separate the winding segments and still obtain a high performance yoke. . ..

. Relative to the center of the conductors, one can derive a conductor distribution independent of the factors d, k and L· of Equation (1). Such a distribution may be represented as follows: -I X . . . Θ - tan (2) where 2n X - 1- 20 N+l (3) and Y=\/l-X (4) I Expressions (2), (3) and (4) .also- certain ambiguities that may sometimes result from the. use of Equation (1). However, it should be noted that, like Equation (1), they provide a sinusoidal distribution. In fact, although Expression (2) is in terms of the tangent, a simple trigonometric substition yields the equivalent ' sin function, 0n = sin"1 (!-¾-) : (5) While I have described an improved magnetic deflection system capable of two-direction deflection, it will be apparent that the invention is also effective in applications where only single-direction deflection is required, in this event, a yoke comprising only one of the aforementioned?! deflection sections can be used. Also, in some applications : it may only be necessary to provide high grequency deflection- in only one direction, say the horizontal directio ..Here , a yoke comprising the deflection section 12 combined with a conventional lower speed vertical deflection section may accomplish the desired result.

•Morever, as a general proposition, my system may be used. in conjunction with other types of particle generator to con- trollably' bend any particle beam having- a charge, e.g. a proton beam.

In summation, the deflectio system described above shapes the magnetic fields generated therein so that they are used to a maximum extent to deflect the beam. The overall yoke inductance is kept to a minimum so that, the yoke is capable of fast response. Moreover, the .deflection is ' accomplished in a highly uniform fashion, rendering a visual presentation which is marked by high linearity and sharpness even near - the edges of the tube face. With improved efficiencies made possible with my system, on the order of 75 percent, the energy requirements for the system are kept" to a minimum.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are · efficiently attained and, since certain changes may be made in the above construction without departing-; fzo-m the scope of -the invention, it is intended that all matter contained in the above description or shown in the accompanying', drawings shall' be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the' generic and specific features. of the invention herein described, and all statements of the scope of the invention,, which, as a matter of language,' might be said to fall in between them.

P.A. 31691/2 A magnetic deflection system comprisin A. a curved screen , B. means for directing a beam of charged particles along a path toward said screen, C. magnetic deflecting means positioned adjacent said path, said deflecting means . (1) producing a magnetic field which deflects said beam as said beam travels -- '- •from one end to the other of said- de- . fleeting means, and (2) including deflection windings positioned at opposite s des of said path, each of said windings having (a) segments extending generally in the direction of said path, and (b) forward crossover segments extending generally transverse to said path, said crossover segments being distributed in a longitudinal direction over an outwardly flared estension of a tube defined by said windings and being spaced progressively further in a direction outwardly along apart/on said flare so as to produce a nonlinear magnetic field whose flux lines bow in toward the longitudinal axis of said tube so that

Claims (2)

1. the nonlinear field corrects pincushion-type distortion of the pattern traced on said screen due to the difference in the radius of curvature of said screen and the radius of deflection of said beam* and 2. there is a minimum difference in the field across the beam cross section. · A magnetic deflection system as defined in claim 1 wherein said spacing between said crossover segments increases linearly in a direction outwardly along said flare* · A magnetic deflection system as defined in claim 1 wherein said spacing between said crossover segments increases in a direction outwardly along said flare in accordance with a power law. A magnetic deflection system as defined in claim 1. wherein said forward crossover segments are also distributed so that said, magnetic flux lines also bow out in the direction of said path, whereby said flux lines are generally perpendicular to the electron beam as it is deflected by said deflecting means toward said crossover segments of said winding P.A. 31691/2 5. · . . . . . j6l, A magnetic deflection system as defined in Claim 1, wherein the turns of each said winding have corners at the rear of said winding' hich are shaped so as to maintain a uniform field Jin the regi between said rear crossover segments. / -Ul- 5' A magnetic deflection system as defined in claim ftf w eicin each aciid winding has forward crossover segments which are distributed so that the magnetic flux lines also bow out in the .direction of said path, whereby said flux lines', are generally perpendicular-,- to the electron beam as it is deflected toward said forward crossover segments. 6 A magnetic deflection as' defined in claim wherein the corners of each said winding at the forward end thereof are shaped so as to maintain a uniform field in the region between said forward crossover segments. 7 A magnetic deflection system as defined in claim .. fi wherein said longitudinal winding segments are ■ distributed as follows: a = sin-^l- -2-—> (5) " N+l Where: 6nis the angular, position of the nth longitudinal segment of the winding from the reference plane which is a plane passing through the center of the . innermost winding loops and the longitudinal '■■ axis of the tubular form, N is- the number of turns in the winding, and . ,n is the longitudinal winding segment whose angular position is being measured, with enbeing recomputed at each rear crossover segment to account for the reduced value of N, said value being N-2n. ' -42- D-2077A, ¾BCS:AMS 8*4-116D . 9. ' . . . /|/0 A magnetic deflection system comprising Λ. means for directing" a ' beam of charged particles along a path, ': B. magnetic deflection., means positioned adjacent said path, said deflecting .means (1) producing a magnetic deflection field which deflects said beam as said beam travels from one end to the other of said deflecting means, and (2) including deflection windings positioned at 10 opposite sides of said path, each of said windings having . .-. (a) segments extending generally along said path, • J. and " ; (b) ' forward crossover segments extending 15 generally -transverse to said path , said crossover segments being distributed in ' a longitudinal direction over a outwardly - flared extension of a tube defined by said windings so as . to produce a non¬ 20 linear magnetic field whose flux lines bow in toward the longitudinal axis of said tube so that

1. the nonlinear field corrects pin- " cushion distortion, and 25

2. there is a minimum difference in the field across the beam cross section, JD-207 7& BBC.S': A S *8 -116ώ ' said crossover' segments also being, distributed so that said 'magnetic flux lines also bow out in' the direction of 30 said path, whereby said flux lines are. · generally perpendicular to the electron beam as it is deflected toward said forward crossover segments of said windings, each of said' windings also having rear 35 crossover segments distributed in a direction generally parallel to said path, and the turns of each said winding having corners at the rear of said winding which are shaped so as to maintain a uniform field in the 40 region between said rear crossover segments. COHEN ZEDEK & SP!SBACH