US2672574A

US2672574A - Magnetic beam controlling system

Info

Publication number: US2672574A
Application number: US277490A
Authority: US
Inventors: John E Evans
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1952-03-19
Filing date: 1952-03-19
Publication date: 1954-03-16
Anticipated expiration: 1971-03-16

Description

J. E. EVANS 2,672,574

MAGNETIC BEAM CONTROLLING SYSTEM 5 Sheets-Sheet l March 16, 1954 Filed March 19, 1952 ORNEY Mm. nnl N Q @Q2/Zw@ I. al fr 5 Sheets-Shee 2 kg w INVENTO R Jahr/Eiken? B ATTO RN EY J. E. EVANS MAGNETIC BEAM CONTROLLING SYSTEM y March 16, 1954 Filed March 19. 1952 March 16, 1954 J. E. EVANS MAGNETIC BEAM CONTROLLING SYSTEM' 5 Sheets-Sheet I5 Filed March 19, 1952 IKNVENTOR E-Evanf ATroRNEY March 16, 1954 E EVANS 2,672,574l

' MAGNETIC BEAM CONTROLLING SYSTEM Filed March 19, 195g.` 5 Sheets-Sheet 4 Fgfa INVENTOR ATTORNEY March 16, 1954 J, E EVANS MAGNETIC BEAM CONTROLLING SYSTEM Filed March 19, 1952 5 Sheets-Sheet 5 ,ffl/IVA ail? ATTORNEY Patented Mar. 16, 1954 MAGNETIC BEAM CONTROLLING SYSTEM John E. Evans, Blawenburg, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 19, 1952, Serial No. 277,490

16 Claims.

This invention relates to systems for controlling the electron beams of cathode ray tubes. It pertains particularly to the control of a plurality of electron beam components used in televisionkinescopes so as to effect substantial convergence of the components at all points of a raster scanned in a predetermined plane.

One type of cathode ray tube in which there ls encountered the problem of maintaining substantial convergence of a plurality of beam components in the plane of a target electrode is a color kinescope such as that disclosed in a paper by H. B. Law titled A Three-Gun Shadow-Mask Color Kinescope published in the Proceedings of the IRE, vol. 39, No. 10, October 1951, at page 1186. Such a tube has a luminescent screen consisting of a multiplicity of phosphor areas of sub-elemental dimensions. Diierent ones of the phosphor areas are capable of producing light of the component image colors when excited by electron beam energy. In this tube, the different light-producing phosphor areas are excited respectively by a plurality of electron beams, or by a plurality of components of a single beam, approaching the screen from different angles through an apertured masking electrode. Color selection is secured by the angle at which the electron beam components approach the screen. A tube of the kind described forms the subject matter of acopending U. S. application of Alfred C. Schroeder, Serial No. 730,637, led February 24, 1947, and titled Picture Reproducing Apparatus, now Patent No. 2,595,548, granted May 6, 1952.

The expression "electron beam components as used in this specification and claims will be understood to denote the phosphor exciting electronic energy produced either by a single or by a plurality of electron guns. This energy may be continuous or pulsating as reouired Without departing from the scope of the invention. An example of color kinescope in which different components of a single electron beam are used to excite a phosphor screen of the kind described is disclosed in a paper by R. R. Law titled A One-Gun Shadow-Mask Color Kinescope published in the Proceedings of the vol. 39, No. 10, October 1951, at page 1194. Such a tube forms the subiect matter of a copending U S. application of Russell R. Iaw, Ferial No. 165.552. led June 1, 1950, and titled Color Television.

'Ihe successful operation of a multi-color kinescope of the type referred to reduires that the plurality of electron beam components be made to converge substantially in the plane of the masking electrode at all points in the scanned raster. In View of the fact that the different points of the target electrode are at diierent distances from the point or region of the electron beam deection, it is necessary to provide a fieldproducing means Which is variably energized to produce the desired dynamic convergence control. One such electron beam control system is disclosed in a paper by Albert W. Friend titled Deiiection and Convergence in Color Kine-I scopes published in the Proceedings of the IRE, v01. 39, No. 10, October 1951, at page 1249. Such a system forms the subject matter of a cepending U. S. application of Albert W. Friend, Serial No. 164,444, filed May 26, 1950, and titled Electron Beam Control System. In the Friend system, electron-optical apparatus is energized both statically and dynamically to produce the desired result. By means including the static energization of the optical apparatus, the Friend system effects initia1 convergence of the electron beam components substantially at the center of the raster to be scanned. The dynamic energization of the electron-optical apparatus is effected as functions of both the horizontal and vertical beam deflection. Essentially these functions are parabolic. In the Friend and other systems previously employed, comparatively complicated apparatus has been required to effect the desired results.

It is an object of the present invention to provide an improved and simplified electron beam control system for multi-beam kinescopes.

Another object of the invention is to provide an improved electron beam convergence system, whereby to effect accurate registration of substantially all parts of a plurality of images produced by the beams.

A further object of the invention is to provide novel electromagnetic apparatus which may be energized in a unioue manner to effect substantial convergence of a plurality of electron beam components in all parts of a raster scanned thereby.

The electron beam convergence system, in accordance with the present invention, is primarily for use in connection with a cathode ray imagereproducing tube wherein a plurality of electron beam components, which traverse predeflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically to scan a raster in a predetermined plane. The beam convergence system comprises a double magnetic lens and individual field-producing means respectively functioning to inuence the electron beams. The lens is located adjacent to the'predeflection paths of the beams. Also, there is provided means controllable to selectively vary the individual beam-influencing fields produced by the magnetic lens so as to direct the beams relative to one another and to the longitudinal axis of the kinescope that there is effected substantial convergence of the beams at all points of the scanned raster. The means by which the individual beam-inuencing fields are selectively varied may be either mechanical or electrical. In the case of the mechanical control means the different beam-influencing fields are shaped and maintained substantially constant for a'll angles of deflection of the electron beams. .In the case of the electrical control means, a dynamic variation may be effected for different angular deflections of the beams. Furthermore, in the electrical form of control means, a unidirectional excitation of substantially constant magnitude may be employed to effect a predetermined orientation of the beams relative to one another and to the longitudinal tube axis, which orientation is Vmaintained substantially constant for all angular deflections of beams.

In accordance with another form of the invention, the predeflection orientation of the beams .relative to one another and to the longitudinal tube axis is effected by a beam alignment magnetic structure which preferably is electrically controlled and is located adjacent to the elecl tron beam'paths ahead of the region in which they are subjected to the convergence control.

In accordance with another feature of the invention, the energy for the excitation of the dynamic beam convergence apparatus is derived s directly from the horizontal and vertical deilection waves impressed upon the electromagnetic yoke by which the angular deiiection of the beams is effected. The energy so derived is shaped suitably by comparatively simple apparatus and impressed upon the electromagnetic beam convergence apparatus.

The novel features that are considered characteristic of this invention are set forth with particularityin the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof will best be understood from the following description when read in connection with the accompanying drawings. u

In the drawings:

Figurel is a view showingthev general arrangement of image-reproducing apparatus embodying 'one form of an electron .beam convergence systemin accordance with this invention;

Figure'2 is a circuit diagram showing one form of control apparatus which 'may be employed for the energization of the beam convergence systemshown in Figure l;

Figure 3 is another circuit diagram showing the structural arrangement of one of the components of the beam alignment apparatus used in one form of the beam convergence system in accordance withthe present invention such as that shown in Figure 1 Figures 4, 5, and 6 are diagrams showing different typical results of the operation of the beam convergence system o'f Figure 1;

Figure 7 shows a representative form of a horizontal wave-shaping network;

Figure 8 shows a representative form of vertical wave-shaping network;

Figure 9 illustrates an alternative type of hori- Zontal wave-shaping network;

Figure 10 shows an arrangement of electroand a focussing electrode.

magnetic field-producing apparatus which may be energized both statically anddynamically in such a manner as to produce beam alignment and dynamic beam convergence;

Figures 11 and 12 illustrate the structural arrangement of a lbeam convergence apparatus in which the held-shaping is effected by mechanical means, Figurev 12 being a sectional view taken on the line |2-l2 of Figure 11; and,

Figures 13, 14 and 15 are diagrams showing typical operations of the apparatus of Figures 11 Vand 12.

Reference rst will be made to Figure 1 of the drawings for a brief `description of a representative form of image-reproducing apparatus in which the electron beam convergence system in accordance with this invention may be embodied. The system includes a tri-color kinescope 2| which may be of the same general type as that disclosed in the H. B. Law paper previously referred to. It will be understood, however, :that the kinescope alternatively may be of other types such as that shown in the R. R. Law paper. In either case, however, the kinescope preferably has a substantially flat luminescent screen 22 provided with a multiplicity of small phosphor areas arranged in groups and capable respectively of producing light of the different primary colors in which the image isv to be reproduced when excited by an electron beam. In back of, and space-d from the screen 22 there is an apertured masking electrode 23 having'an aperture for and in alignment with each'group of phosphor areas of the screen 22. In the particular tube illustrated, the kinescope also has a plurality of electron guns, equal in number to the number of primary colors in which the image is to be reproduced. Each of these guns may be conventional, consisting of a cathode, a control grid Since the three-guns are identical, the different parts thereof will be referred to collectively as the cathodes 24, the control grids 25, and the focussing electrodes 26. The three electron guns produce beams represented at 21, 28 and 29 by which to energize,

respectively, the green, red and blue phosphor areas of the screen 22. When these electron beams are properly converged in the plane of the masking electrode 23 they passthrough the apertures thereof from different directions and impinge upon different phosphor areas of the various groups so as to produce green, red and blue light. It is to be noted that thesize ofthe phosphor area-s, the angles between the beams and the spacing of the mask 23 from the screen 22 as compared with the length of the tube are exaggerated for better illustration of the operation of the kinescope.

The electron-optical apparatus of the kinescope 2i also includes a beam-accelerating electrode consisting, in the present instance, of a conductive wall coating 30 formed on the inner surface of the tubular glass neck `3| of the knescope ex tending from the region adjacent to the outer end of the focussing electrodes 26 to the conical section 32 of the tube which in this case is metallic. Suitableelectrical connection is made at the junction of the wall` coating .with the metal cone32. Preferably, thetargetelectrode structure, including the masking electrode 23 and the.

luminescent screen 22 which for this purpose may be metallized, is electrically connected to the metal cone 32 by suitablemeans (not shown). Metallization of a luminescent screen of the character described maybe4 effected,4 in the-.man-

ner disclosed in a paper by D. W. Epstein and L. Pensak titled Improved Cathode-Ray Tubes with Metal-Backed Luminescent Screens published in the RCA Review, vol. VII, March 1946, at pages 5 to 10.

The described electrode structure of the kinescope may be energized in a conventional manner such as that illustrated. The source of energy is represented by a battery 33 across the terminals of which there is connected a voltage divider 34. rThe cathodes 24 are connected to the grounded point of the voltage divider and the control grids 25 are connected to a point which is somewhat negative relative'to ground. Similarly, the focussing electrodes 26 are connected to a point on the voltage divider which may conventionally be at a potential of approximately 3000 volts positive relative to the grounded cathodes. Also the beam-accelerating anode,

including the wall coating 30 and the metal cone 1 32, is connected to the voltage divider 34 at a point which may conventionally be approximately 18,000 volts positive relative to the grounded cathodes.

The electron beams represented at 21, 28 and 29 are modulated suitably in intensity under the control of color-representative video signals derived from a source 35. It will be understood that the video signal source is represented herein entirely diagrammatically since it does not form an essential part of the present invention. The signal source 35 usually will be part of a signal receiver and may be understood to include a signal detector, or equivalent device, together with one or more stages of video signal amplification. Alternatively, the video signal source may be a color television camera in the event that the kinescope 2| is employed as a monitor. for example. Also it will be understood that the illustrated connection of the video signal source 35 to the electron guns of the kinescope 2| is merely diagrammatic and accordingly these connections may or may not be made directly to the cathodes 24. Instead, it will be understood that they may be made to the grids 25 or, in accordance with some modes of operation of color image-reproducing apparatus, the video signal source may be connected both to the cathodes and to the control grids of the electron guns.

Also associated with the color kinescope 2| is a deflection yoke 36 which may be entirely conventional including two pairs of suitably placed coils electrically connected together in such a manner that, when properly energized, electromagnetic elds are produced whereby to effect both horizontal and vertical angular deflections of the electron beams so as to scan the usual rectangular raster. Energization of the deilection coils comprising the yoke 3B may be effected by conventional vertical and horizontal deilection wave generators 31 and 38, respectively. It will be understood that this apparatus which may be the same as or similar to that disclosed in a paper by Antony Wright titled Television Receivers published in the RCA Review of March A1947 at page '7. Such apparatus wil1 be under- Stood to function suitably to produce s"bstan tially sawtooth energy at both horizontal and vertical deflection frecuencies so that the elds produced by the yoke 30 are varied in a substantially sawtooth manner.

: The present invention which is employed with apparatus of the character described in its present form includes a double magnetic lens 39 mounted around the neck 3| of the kinescope 2| in the region between the focussing electrodes 26 and the deflection yoke 3G. The structure of one form of double magnetic lens in accordance with this invention will be described subsequently. For present purposes, however, it will be understood that the lens 39 is a structure having three salient pole pieces located respectively adjacent to the paths followed by the electron beams emanating from the respective focussing electrodes 2t. In such a case, each of the beams is subject to individual control by the salient pole pieces of the lens 39 which is adjacent thereto. Means also to be described are provided for selectively energizing the diierent salient pole pieces whereby to selectively inuence thel dilerent beams.

The selective energization of the pole pieces of the lens 39 is effected by dynamic convergencecontrol apparatus 4|, a representative form of' which will be described subsequently. In general, the dynamic convergence control apparatus derives energy from either the horizontal deection circuit or from both the horizontal and vertical deflection circuits as indicated to produce three substantially independent waves to energize respectively salient pole pieces of the lens 39.

It is to be understood that lens 39 is of the double magnetic type and is arranged so that the two elements thereof produce elds tending to aiTect the electron beams in opposite senses. A magnetic field, by reason of the axial character thereof, produces a spiral movement of electrons generally in the same longitudinal direction as the eld. In the present instance, the effect of a single magnetic lens upon the three axially spaced electron beams is to rotate the beams about the longitudinal axis of the tube. Since the color selection is dependent upon the particular angle of approach of an electron beam to the luminescent screen, it will be seen that the rotation of the beams about the tube axis changes this angle of approach and, therefore, is likely to produce incorrect colors. Hence, the lens 39 is provided with another element of a substantially identical character as the first element so as to produce a rotational effect upon the beams which is equal and opposite to that produced by the first element. Hence, so far as the rotational eiect produced by the double magnetic lens 3S upon the electron beams is concerned, one lens element counteracts the other thereby producing a net beam rotational eiect of zero. l

In the form of the invention illustrated in Figure 1, the apparatus also includes a beam alignment magnet 42. The structure of this apparatus component will be described in greater detail subsequently. Briefly, it functions to produce in the vicinity of each of the electron beams a magnetic field extending longitudinally of the tube and of such a character that the individual beams may be oriented relative to one another and to the axis of the tube suitably so that, so far as the deilection apparatus is concerned, they appear to originate at points symmetrically disposed relative to the tube axis. The bef/malignment magnet 42 consists of individual electromagnets which may be selectively energized to move their associated beams rela-tive to one another and to the tube axis to effect the desired alignment thereof. The beam alignment magnet 42 may be energized by unidirectional energy derived from a beam alignment control 43. This apparatus may consist essentially of a power sup- 131V of.' unidirectional energy togethery with.V suitable; individual control, apparatus byy means; of; which the; individual' parts of: the beam alignment. magnet; 42; may be.y variablyenergized; A representative form of beam alignment control appa- Ratus will be. described Subsequently'.`

Reference now will be made to Figure 210i' the drawings fori a,des,criptionv of-one-form oifdynamicr beam convergence control apparatus. The double magnetic: lens 39Y which is mounted around the neck-1.3!; ofi the. lrinescope.y comprises three, salient` pole pieces-- M, la and' 43;' disposed respectively adjacent; to the paths traversed by the electron bBamSZL 2.8 and 23.-. rihe polepieces 44; 4t andv 46; are provided respectively with windings-t1, 48= and 49., it will: be understood that; these; windings are placed around the central legs; ofthe double magnetic lens corefstructure. As a result, the: core structure; is energized' in such a mannen that as. viewed: in Eigure 1, the central legsl` of each ofthe pole pieces have one magnetic" polarity suchy as'lthat corresponding to a south pole, for example, while the outer. legs 52 and:v '53 have oppositepolarity suchas north poles.

Bever-ting nowA tio-Figure 2, the magnetic lens windings are energized individually as functionsVv o f either the horizontalA deflection frequencyor. the horizontal and vertical deection frequencies combined'. Energy at the horizontal deiection frequency is derived as-shown inv Figure 1 from 1 the circuits; leading to thehorizontal coils ci the deection yoke 36'. Since this' energy is essentialiy current having a substantially sawtocth waveform and voltagehavinga substantially rec-V tangularwaveform, it is impressed upon a hori zontal wave-shaping network EAT for convers? on into a-.waveforrni suitable to control the converg ence-apparatus: As previously indicated', such ai waveform is substantially parabolic. Acc-ord-` ingly; it willlbeunderstoodr that the wave-shap ing networkfi, representative,-examples `of which willfbefreferredtosubsequently; functions to perform.l the;v desired waveshaping'. The substantially:parabolicaliyshapedfwave derived from the network 54. is impressed; by a coupling circuit including av capacitor 55', uponV the control grid of an electron tube 56; Thise tube performs some degree.` of;v ampliiicationv of` the parabolically shaped wave; but servesl primarily as an impede ance.inverter.

I- n theioutput circuit Vof thetube tfisthe primary winding 510i a transformer which also includes. a ferr-.ite core dr and three; secondary windings El, 62 and 63. The primary winding 5-1. forexample; mayY consistV of: 40G turns of No.- 4'1 wire and each oi the secondary windings maywconsist of 200 turns of? No. 38 wire: The primary winding'S-i also is tuned byl a shunt' capacitorY 611 fory resonance substantially at the horizontal, deection frequency;

The termina-ls ofthe secondary'windings 5i', 52 andGS-are connectedA respectively to tile-resistive elementsof control poten'tiometers'; tei-and (il'll. 'Ihe windings 4l, tand 49' ofthev doublemagnetic lensl 39are connected' respectivelybetween the sliding contactsY of potentiorneters` 6BA and BTI-and the; center taps of the Aassociated secondi# ary' windings 6l, 52 and. By: thisfmeans, the magnitude and polarity of the elds'produced bythe different pole pieces fifi; e5 and d'of: the double` magnetic lens may be varied independ# entlyof one another:

If it is also desired to vary-the eldsproduced bythe doubleymagnetic'lensr 39: as functionsy of the, verticaleleetronrbeann deflection.. therel also may be included' a vertical` wavershaping network (i8, representative; details:Y of one; form of which will` be disclosed subsequently'. It, is connected to the vertical'` deflection circuit and functions to convert the vertical deflection energy to: a substantially parabolic form. The. parabolic vertical energy derived from the network 68- isiin--Y pressed by a coupling inciuding a capacitor 69: and a grid resistor, 'H upon the control grid oi'v an electron tube; '12. This? tube also functions as an amplier as well as any impedance, inverter. The primary winding 13 of' an output transformerV 'iii iscoupled in the anode'r circuit of the tube 12. Thistransformer may be. somewhat conventional, as, for example, a commercially available component identified. as` UTC-A18. The primary winding 'i3A may betuned for resonance substanY tially at the; vertical deiecting frequency by a. shunt connected capacitor 15. The secondary winding 'ie of the vertical output transformer has a grounded center tap and the, terminals connected toV the resistive element of a. potenA tiometer l1; The. adjustable contact of this' potentiometer is coupled as shown to the control; grid circuit of tubef previouslyreferred to;

By the described means, a component of the vertical parabolically shapedenergy derivedfrom the potentiometer Ti is combined'inuthe-inputcir* cuit oi the tube- 5G with the horizontal parabolic; wave energy. 1t has beenvfoundpractieefthat; in most cases, only acomparatively small com-- ponent of the vertical energy isy required, and in; many cases, may be entirely omitted Without notice-ably afkeer-ingv the performanceof the appa.-` ratus. it will also be noted that the resistive portion of the potentiometer?? serves as agrid resistor for` the tube 56. It will be` understood:v thatin cases where-no energy. is to be supplied for dynamic electron beam convergence control atthe vertical deflection frequency the apparauius just described: may be omitted, in which case ai suitablek gridl resistor for the tube 58 may1 be; supplied4 to replace the potentiometer Tl.

Reference now-willv be made to Figure 3% of the drawings for a description of the typezo beam* alignment magnet 42 used` inthe illustrative embodiment of theV inventionv shown in- Figure 1. It"- includes' a plurality ofA substantially. wesliaped:

pole pieces disposed in the` generali manner indn cated in Figure 1 so that the two legs thereof are spaced longitudinally along the axis ofthe kinescope. As in the case ofu the. double.: magnetic lens 3&1,Y there prefera'blyfareV provided as many pole-pieces aslthererare electron beams. Accordingiy,in the: present illustrative embodiment ofthe; invention utilizing three electron beams,l there are provided three beam alignment pole pieces Sl, 82 and 83? disposed` about thefneck` 3f of;y the kinescope so asf to be' respectively adjacent the electron beams 2T, 2t and 29`. The pole pieces may be mechanically supported in any suitable manner such as being mounted'in a cornmon retaining ring 811" which preferably is made of a non-magnetic material. Also', in a convenient place such as on one ofv the legs'ofthe pole pieces l, 32and33 there are mountedi energizing coils 85, 86`and'8'1 respectively. Eachofthese coils/is provided with two` end terminals anda center tap;

The coils 86 and 8T are connected respectively to control potentiometers 8,8, 89 and'. 9'02 As indicated, the terminalsofeach' of the coils are connected to the respective terminals of the resistive elements of the potentiometers andthe centerftaps` of thef-coilsare connectedtothemova `kinescope axis.

*9 able contacts of the associated potentiometers. The terminals of the potentiometers are connected to the respective terminals of a source of unidirectional energy such as indicated by the battery 92.

It may be seen that, by means of the described apparatus there may be produced in the vicinity of each of the

electron beams

2l, 23 and 29 mag- 'neti'c elds of such character that the individual beams may be positioned relative to one another and to the longitudinal axis of the tube substantially in any desired way. The strength of the magnetic fields as well as the polarity thereof may be controlled by suitable adjustment of the control potentiometers.

It has been found advantageous, in the operation of apparatus embodying the present invention, to initially align the beams by means of apparatus such as that shown in Figure 3 so that beam convergence is effected at the corners of the raster instead of at the center thereof as usually practiced heretofore. The advantage of such a procedure is that the corner convergence iseffected by unidirectional energy so that the dynamic energization of the beam convergence apparatus needs to be sufficient only to modify the relative beam positions as they are deflected back toward the center of the raster. In effect, this is accomplished by applying the dynamic energization in opposition to the unidirectional energization. The result of this method of operation is that, where beam convergence is the most difficult, it is produced by unidirectional energization of the apparatus which ordinarily is maintained static or constant in magnitude, whereas in prior art modes of operation this additional energization had to be supplied dynamically.

Figure 4 represents the usually desired alignmentY of the electron beams, if it is considered that the center of the concentric circles shown in this figure coincides with the longitudinal axis of the kinescope. It is seen that the three electron beams are symmetrically disposed relative to the tube axis, both angularly and radially.

Figure 5 represents a condition where the

beams

28 and 29 are positioned angularlyas desired, but the beam 2l is radially displaced from the desired position. Its angular relationship to the other two beams is assumed to be correct.

Accordingly, in the control of the beam alignment n nanother possible arrangement of the

electron beams

2l, 28 and 29 as they emerge from the apparatus producing them, it is assumed in this instance that the beam 21 is positioned as desired. It is further assumed that all three of the beams vare angularly positioned relative'to one another in the desired manner. However, the beam -28 is located closer to the axis thanthe beam 21 and the beam 29 is located even closer to the Accordingly, the winding 86 is required to be energized by a suitable adjustment of the associated potentiometer 89 so that the magnetic 'field produced rby the pole piece 82 is of a suitable polarity and strength to move the beam 28 away from the kinescope axis so that its radial displacement therefrom is equal to that ofhthebeam 2l. Similarly thepotentiorneter 90 needs@ be. adjusted-SQ that thaenersization 0f the coil 81 is suitable to effect the production by the pole piece 83 of a magnetic eldhaving substantially the same polarity as that produced by the pole piece 82. However, in this case, the strength of the eld produced by the pole piece 83 is required to be substantially twice that of the field produced by the pole piece t2. By such adjustment of the apparatus shown in Figure 3, the

electron beams

2l, 23 and 29 may be aligned substantially in any desired manner.

A brief reference now will be made to Figures 7, 8 and 9 for a consideration of representative types of wave-shaping networks suitable for use as the networks 5d and 58 of Figure 2. Typical valves of the components are indicated and with which the networks have been successfully operated. Figure 7 discloses an LC type of wave-shaping network which has been found suitable for use as the horizontal wave-shaping network 54. Figure 8 illustrates an RC type of wave-shaping network which has been found suitable for use as the vertical wave-shaping network 68. It is to be understood that the present invention is not necessarily limited to any particular types of waveshaping networks. Those skilled in the art are familiar with various other forms of networks which may be employed at both the horizontal and vertical deflection frequencies for the conversion of substantially rectangular wave energy to waves having approximately parabolic forms. Figure 9, for example, shows an RC type of waveshaping network which may be used as a horizontal wave shaping network 54' as an alternative to that shown in Figure 7.

As previously indicated it is not essential in all cases to eiect beam alignment and dynamic beam convergence by separate devices. Reference will now be made to Figure l0,of the drawings for a description of a single apparatus which may be operated in such a manner as to eiect both beam alignment vand dynamic beam oonvergence. The apparatus includes an electromagnetic yoke 93 which, in the case of a three electron beam kinescope, has three salient pole pieces Q4, 95 and 96 positioned respectively adjacent to the

electron beams

2l, 28 and 29. The pole pieces 94, 95 and 96 are provided respectively with energizing windings 91, 98 and 99. Each of these windings is center-tapped and grounde at these points as indicated.

In order to effect both beam alignment and dynamic beam convergence by this apparatus the windings are energized both by unidirectional and dynamic components. The unidirectional energization of these windings is effected by control apparatus connected to a source of unidirectional energy such as represented by a battery lill. For this control of the windings el, 98 and S9,the terminals of the energy source l0! are connected respectively to the terminals of the resistive elements of pctentiometers |02, 03 and H315. The mid-points of these resistive ele- -ments are grounded as shown. The movable contacts of the control potentiorneters H22, |03 and it@ are connected through parallel resonant .LC networks I05,- Hit and "lill respectivelyto one terminal of each of the windings 91, 98- and te respectively. The parallel resonant circuits are tuned to prevent the feedback of energy from the electromagnet windings at the ,horizontal deflection frequency. o

The dynamic energization of the electromagnet windings may be eifected by apparatus including a transformer Ei which Amay be the same as .that shownwanddescribed` in connection with Figure f2. The primary win-ding 51 :is :coupled vby the :described means .to the -deection circuits. The Vindividual `secondary windings 16|., .2 .and 163 are center .tapped and provided .respectively with .control potentiometers 65, E6 and the previously 1described:embodirnent of the invention. In this .case as vin the apparatus .of 'Fig-ure '2, the center taps yof the .secondary vwindings el, `82 .and 6@ :are .connected respectively to one terminal of the windings 91, Slt .and S9. The adjustable contacts of the potentiometers l(-25, @36 :and .El are coupled respectively by capacitors 108, |08 and 1 ill vto 4the 'other termina-ls -cf `the windings 97, e8 and 93 respectively. `These .capacitors serve as vblocking capacitors to prevent the unidirectional energy .derived from the source lili from mixing with `the dynamic `energy derived from `the transformer 53.

The operation of this unitary apparatus is substantially the same as the independent operation of the separate devices previously described. The .unidirectional vcomponents of energy supplied to :the windings in accordance with the adjustments of the potentiometers :m2, yl-i'lB Iand 104 produce fields by which the `individual elec- -tron beams v2l, 28 and 2'9 are separately inluenced for positioning them suitably with respect to one Yanother vand to the longitudinal axis ofthe kinescope in the :desired manner. As inthe previously describedapparatus, the polarity and `magnitude of each o-f the fields produced -by Athe unidirectional energizing apparatus .may fbe independently adjusted to lproduce the desired beam alignment, either at the center of the raster or .at the corners thereof as Vpreviously described. The dynamic energization of the windings 97, 98 Vand 29 is substantially similar `to that described inconnection with Figure Reference now will 4be made to Figures ll 4and l2 yof the drawings for a description of a :type of beam vconvergence :apparatus in :which the necessary field-shaping is eiected by mechanical means. Such apparatus may be employed ad vantageously in cases where-dynamic 4beam condvergence is unnecessary or not desired. This -way toward the center of vthe device and lforms one of the pole pieces which in the lpresent instance will be assumed to be a south pole. One `end of ,the device `is formed of a plate l l'5 having a configuration 'which is generally disc. like and an inwardly extending hub portion H5' forming one of the outer pole pieces which in lthe assumed case is a north pole. The plate H5 is substantially unbroken `throughout the entire l360" thereof. The other end plate of the double magnetic lens Vis formed of three segvments Hl, .H8 and H. In this 4instance the segments are approximately 120 in extent being separated from one another as shown in 'Figure ll sufliciently to provide for the creation .of three independently adjustable portions of the nel-d produced by the device. The segmented plates Hl, H3 and H9 are also provided with respective inwardly extending hub portions such as l2| on `the segment IH and `|22 4on vthe segs ment 17138. Eachso these segmented hubsfcrms yanother north 4pole of the `double magnetic lens. The outer plates il II5, yHl, H8 and II'S are :attached to Vthezannular `pole piece H3 :by suitable means such as a plurality of screws 123,.

:plurality of adjustable `held-varying 'ele- ;ments such as screws 424 are threaded into the -hub portions of the two 'outer pole pieces H5, H1., H8 and HS.. Briey, these Ascrews :are ci soft iron -so Athat the introduction thereof tin-to -the gap A'produced between the .pole pieces effects a distortion ofthe field produced inthis gap.

The `magnetic structure formed substantial?,Y .in the manner described may :be either -of the permanent magnet or of .the electromagnet type. In Vthe latter case, a 4coil 125 .may be mounted inthe spaces provided rbetween the cuter Imud inner lpole pieces substantially as indicated Figure A12. In this case, the pele pieces preferably are .formed of `soft iron materials. ln lthe fcase fnf .a permanent magneticwdevice, the pole -pieces themselves will be -`the vpermanent magnets.

By adiusting the screws 24 .so that they exitend Ato suitable points `in .the magnetic eldjprc- :duced by the outer land inner .pole pieces, `the shape oi the resultant field `may be controlled insuch amanner as to eect the desired orientation `of the electron beams of the ikinescope.

'The .apparatus 'of `figures l1 Land l2 uis made `in .such :form that lit `envelopes, the .neck portion nf the kinescope so that the electron beams are 'subjected to the i-nluence of the iield produced `by the apparatus.

Reference .is made to Figures 13, 14 and .15 for typical examples `of the :marmer in which fthe .apparatus of Figures 11 -and l2 operates. -Ln Figure 13, `for example, Lwhere 4the elec-tron `beams 2.7i, 28 and '29 are in the positions shown, the angular relationship between them is as desired. Also the radial positions of the beams 225 `and .28 Yrare satisfactory. The radial position of' the beam 29, however, is closer to the axis oT the kinescope vthan desired. Accordingly, the adjustment of the screws, Hill of the apparatus cf`Figu1-es 1l .E and 12 should be such as to alter the -fe'ld in the vicinity of the beam suitably 4from that'in the .vicinity of beams 2l and 28 to effect a movement of `the beam 29 radially outward to the same distance as that at which the beams El and 2B are located from the center.

In Figure le the positions fof the beams 21, 26 and 2e are such that the `beams 28 and '29 are at suitable radial distances from the axis `of thejtube but the beam 2l, however, is not sumciently spaced from the axis of the tube. If 'it is assumed that the beam 2l is correctly posi- 'tiene'd singularly, the beams 2B and A2!! are im- -properly positioned in this respect. Accordingly.. adjustment of the iield--shaping screws |24 is required to lee such that the beam 2l will be outwardly from the axis cf the tube. The elds produced by two'adjacent pole pieces of 'the apparatus is required to be such that both cf `them iniluence the beam 28 suitably to rotate it about the central axis sufciently to'place it in proper angular relationship to the beam 2l. Similarly, the eldrproduced by two ,other vadjacent segmented pole pieces is required lto be such that components of each influence the beam 2@ to rctate it so that lit occupies the desired angular relationship to the other two beams;

Figure -15 to which `reference now will lbe made shows another aspect of the relationship lof the electron beams to one another and to `the een trai axis ctihe--tube under other ccnditions.- I-f it be assumed that the three

electron beams

21, 28 and 29 are symmetrically located with respect to one another and to the axis of the tube, either as they issue from their respective electron guns or as a result of a suitable control of the magnetic lens apparatus such as that shown in Figures 11 and 12, for example, in which the adjusting screws |24 are manipulated to produce the described positioningr of the beams, then Figure illustrates the arrangement of the

beams

21, 28 and 29 under strong magnetic lens influence. If this inuence be uniformly decreased as, for example, by reducing the exciting current in the coil |25, then the electron beams will assume positions such as indicated at 2l', 2S and 29. Similarly, a further decrease of the magnetic lens effect will result in the further movement of the beams away from the central axis of the tube so that they take positions such as indicated at 21, 28" and 29".

It may be seen from the foregoing description of a number of illustrative embodiments of this invention that there is provided an improved and'considerably simplied system for effecting the desired electron beam control for multi-beam kinescopes whereby there is effected substantial convergence of the beams. In cases where the required beam convergence is to be effected substantially at all points of a target electrode in a raster of moderate dimensions, the beam control apparatus may provide satisfactory performance without any dynamic energization thereof. In such cases the initial beam convergence may be eected by suitable control of the different portions of a magnetic eld to which the beams are subjected, either by the introduction of held-distorting elements or by adjustment of the electromagnetic apparatus by which the elds are produced.

The invention further provides a control apparatus by which the beam-controlling elds may be varied as functions of the beam deflections. In accordance with the apparatus embodying the present invention, this dynamic control of the magnetic lens is effected by energy derived directly from the circuits energizing the deection yoke coils and utilized with a minimum of shaping or other control, thereby requiring aminimum of additional apparatus.

Furthermore, in accordance with this invention, there is provided apparatus by means of which a suitable control of the electron beam components may be eifected whereby to initially position the beam components relative to one another and also to the central axis of the kinescope to produce the desired effects, such as color selection in a colorkinescope, and subsequently to produce the desired beam convergence, not only at a predetermined point in the scanned raster, but at substantially all points therein by suitable dynamic control of the beam components.

In accordance with a further feature of the invention, the control of the electron beam components, whereby substantial convergence thereof in all points of a raster scanned in a plane of a target electrode, is effected in asimpler manner than heretofore by first producing beam convergence at a non-central point of the raster, such as at one corner thereof, and then subjecting the beams to a dynamic convergence control for all other points in the scanned raster as functions of the beam deflection, Still another feature of this invention is the provision of a unitary apparatus forming a magnetic lens which may yld be energized both statically and dynamically to effect both the functions of initial beam alignment and also the convergence of the beam components for all other deflected positions thereof. It will be appreciated that, by reason of provision of one or more of the features of the present invention, beam convergence both static and dynamic in a multi-beam kinescope is eifected in a more eflicient and more eiective manner than heretofore.

The nature of the invention is set forth in the foregoing description of a number of illustrative embodiments thereof. The scope of the invention is set forth in the appended claims.

What is claimed is:

1. In a cathode ray tube image-reproducing system wherein a plurality of electron beams, which traverse pre-deflection paths that are spaced respectivelyabout the longitudinal axis of the tube, are angularly deflected both horizontally and vertically to scan a raster in a predetermined plane, ,an electron beam convergence system comprising, a double magnetic lens having individual field-producing means respectively influencing said electron beams, said lens being located adjacent said pre-deflection paths of said beams, and means controllable to selectively vary the individual beam-influencing fields produced by said magnetic lens to direct said beams relative to one another and to said longitudinal tube axis so as to effect substantial convergence of said beams at all points of the scanned raster.

2. In a cathode ray tube image-reproducing system wherein -a plurality of electron beams, which traverse pre-deflection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deilected both horizontally and vertically to scan a raster in a predetermined plane, `an electron beam convergence system comprising, a double magnetic lens having individual field-producing pole pieces respectively positioned radially to influence said electron beams, said lens being located adjacent said pre-deection paths of said beams, and means Iassociated respectively with said pole pieces and controllable to selectively vary the individual beam-influencing fields produced by said magnetic lens to direct said beams relative to one another and to said longitudinal tube axis so as to effect substantial convergence of said beams at all points of the scanned raster.

3. An electron beam convergence system as defined in claim 1 wherein, said magnetic lens comprises electromagnetic eld-producing means.

4. An electron beam convergence system as denned in claim 1 wherein, said magnetic lens comprises electro magnetic eld producing means, and includes additionally individual pol-e pieces having movable elements by which to provide individual elds shaped suitably to eect the desired direction of said beams.

5. An electron beam convergence system as dencd in claim 4 wherein, said field-shaping elements are threaded members adapted to be moved into and out of the respective air gaps of said double magnetic lens.

'6. An electron beam convergence system as defined in claim 1 wherein, said magnetic lens comprises a plurality of individual electromagnetic field-producing means including individual pole pieces having energizing windings located respectively thereon and energizable individually to provide individual fields shaped suitably to eiect the desired direction of said beams.

gera-uve '7; 'An electron beam convergence' system as de-g ned inclaim 6 wherein. said coils are variably energized as a function .of said angular beam deflection.

8. An electron beam convergence system as defined .in claim "l, and including additionally means including a source of uni-directional energy `to excite magnetic lens coils individually to effect a predetermined orientation of said beams relative to one another and to said longitudinal tube axis.

9. In a cathode ray tube image-reproducing system wherein a plurality of electronv beams, which traverse predelection paths that are spaced respectively about the longitudinal axis of the tube, are angularly deflected both horizontally and vertically to scan a raster in a predetermined plane, an electron beam convergence system comprising, an initial lbeam alignment coil array having individual fieldproducing elements located .respectively adjacent to sources of said electron beams, said individual elements being separately .controllable to eiect a predetermined orientation of said beams relative to one another and to said longitudinal tube axis, a double magnetic lens having individual held-producing means for influencing each of said electron beams, saidY lens being located adjacent the paths of saidV beams before entering the deflection region, and means controllable to selectively vary as a function of said angular beam deection the individual beam-influencing nelds produced by said magnetic lens to direct said beams relative to one another and to said longitudinal tube axis so as to eect substantial convergence of said beams at al1. points ofY the scanned raster.

10; In` a cathode ray tube .image-reproducing system wherein a plurality of electron. beams, which traverse pre-deilection paths that are spaced respectively about. the longitudinal axis of the tube, are angularly deilected both hori- Zonta-ily and vertically to scan a raster in a predetermined plane, 4an electron beam convergence system comprising, means energizable to effect a predetermined orientation of said beams relative to. one another and to said longitudinal tube axis, whereby to produce initial static convergence of said beams, means including a source unidirectional energy to energize said beamorienting means in a manner to effect said initial beam convergence at an eccentric point oi said raster, and means dynamically energizable to influence said beams so as to effect substantial convergence of said beams at all points of said raster.

ll. An electron beam convergence system as dened in claim 10 wherein, said said un-directional energization of said beam-orienting means is of such a character to eiect said initial beam convergence in a corner of said raster.

l2. An electron beam convergence system as donned in claim 10 wherein, said beam-orienting means and said beam convergence means include a common electromagnetic device .located adjacent to said pre-deflection beam paths.

13, an electron beam convergence system as donned in claim 12 wherein, said common electromagnetic device is provided with individual field-producing pole pieces respectively posi.- tioned to inuence individual ones of said beams.

le. An electron beam convergence system as denned in claim l0 wherein, said beam-orienting means and said beam convergence means include respective electromagnetic devices located at points spaced along the longitudinal tube axis adjacent to said pre-deflection beam paths.

l5. An electron beam convergence system as dened in claim 14 wherein, both of said electromagnetic devices are provided with individual `field-producing pole pieces respectively positioned to influence individual ones of said beams, and all of said pole pieces being independently energisable.

16. In an. image-reproducing system embodying avcolor lrinescope having a luminescent screen including a multiplicity of groups of phosphor areas capable respectively of producing differently colored light when electronically excited, a masking electrode located in a plane spaced from said luminescent screen and having an aperture for each of said groups of phosphor areas and in which means are provided for developing and directing electron beam components toward said 1uminescent screen through successive apertures of said masking electrode to selectively excite said different color producing phosphor areas, an electron beam convergence system comprising, deflection apparatus energizable to angularly deflect said beam components both horizontally and ver.. tically to scan a predetermined raster at said masking electrode, electromagnetic means lof cated adacent to said electron beam-developing means and having individual eld-producing pole pieces respectively positioned and energizable to eect a predetermined orientation of said beam components relative to one another and lto said longitudinal tube axis, means including a source of unidirectional energy to energize said beamorienting means in a manner to effect initial static convergence of said beam components at a .predetermined point of said raster, a double magnetic lens having individual field-producing pole pieces respectively positioned radially to inuence said electron beam components, said llens being located between said electron beam-devel oping means and said deflection apparatus, and means including windings for each of said pole pieces coupled to said deflection apparatus for energization and controllable to selectively vary the individual beam-influencing fields to effect dynamic convergence of said beams at all points of said scanned raster.

JOI-IN E. EVANS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,454,345 Rodenberg Nov. 23, 194B 2,454,378 Forque Nov. 23, 1948 2,457,175 Parker Dec. 2S, 1948 2,567,377 Holbrook Sept. ll, 1951 FOREIGN PATENTS Number Country Date 866,065 France June 6, 1941