US2455977A

US2455977A - Magnetic lens for correcting scanning defects

Info

Publication number: US2455977A
Application number: US719428A
Authority: US
Inventors: Carlo V Bocciarelli
Original assignee: Philco Ford Corp
Current assignee: Space Systems Loral LLC
Priority date: 1946-12-31
Filing date: 1946-12-31
Publication date: 1948-12-14
Anticipated expiration: 1965-12-14

Description

Dec.` 14, 1948. c'. v. BocclARELLl 2,455,977

MAGNETIC -LENS-FOR CORRECTING SCANNING DEFECTS pff-L Ec 770,4/ GEA/52,0 Tae:

\ CQMDEA/s/QT/ou MEGA/5 l INVENTOR.

ATTORNEYS CARLO Il BOCC/ARELL/ Dec. 14, 1948. c. v. BocclARELLl 2,455,977

MAGNETIC LENS FOR CORRECTING SCANNING DEFECTS Filed Dec. l31, 194e 2 sheets-.sheet 2 INVENTOR.

CARL l( BOCC/ARE'LL/ ATTORNEYS Patented Dec. 14, 1948 PATENT" QFFlCE v o n j 2355.917# y MAGNETIc lENs ron,oommo'iINc.` @.SCNNING DEFEQTS'- (#'Jarl'c'l Bocciarelli; Oxford, Pa.,L assigner.:4 'to' Philco; Corporation, acorporation of Pennsyl- Applica-tion ncenlierlsl, m46,- serialrNa; 7191,428A

on the` screen` traces;V a: substantially' rectangular raster of horizontal lines. `Simultaneously.;j'the fie-claims.. (o1. 25o- 157), y

electr-'Orr bcamai'sl intensity modulated withfal video sign-afl"` representing'the instantaneous lightsl and shadesA of' i the transmitted' picture; whereby'. the combined sweep' and intensity' modulation. provide the. fina'l` image1` upon` the.1 fluorescenti" screen.

Electrostatic' and: electromagnetic. `deflection systems: for cathode ray tubes' are fboth: in. `wide use. in television' receivers; and eachzhas'its' ad'- vantages and'. problems; frsftheiA present invention hasl particular advantage Awhen `associated Awith magnetic receiver' deflection: means; a;.`r' `rief'` discussion: of the `general: features fthereofr. isr given in the: following. i.'

For magnetic4 deection, afyokefhavingLtwo sets of orthogonally disposed coils is positionedV around the neck of` the cathode ray tube between `the electron guniand the iluorescentsscreen,v In order to obtain al uniform rectangular raster, it is required that these coils provide two magnetic fields which vary in' a saw-tooth manner with respect to time and which 'are related in frequency. -f

In present da-y commercial l'practice the horizontal and vertical sweepifrequencies are 15,750 and 60 cycles per secondi respectively,'for` interlaced scanning of' 30 frames per second. In colorl'telejvision, and high d'e'nition'black-and-'white television still higher frequencies may be employed.

In order` to obtain a magnetic eld" which has a saw-tooth time variation",` it' is required'that the deflection coil be energized with a sait/#tooth of current. Asa deection coil includes resistive and inductive components, the `voltage wave-form which must be applied is complexinffnaturefand particulary care must be taken" in deflectiongem era-tor design'. "f'

The power requirements of a magneti'crdeflection generatory are a function fo theLE Reflection circuit resistance. and` the :magnitude-of the-currentirequired: tofprovidezthe desired sweepflength'. In generaL. thefpowern capacity of a deection generatorwmustrbef fairly' highA while the waveform. ofthe output must be heldI to close tol'- erances.

A deviation? from linearity in the saw-tooth of current ordinarily'results in a. corresponding deviationi in the linearity'of' the image! reproduced. As a representativeexample', consider a television receiver wherein thea horizontal sweep generator provides an output. current' which increases ex- 'ponentiallyfwitl'r time; that is, the time rate of Achanger of 'current'decreases. throughout the' trace period from an initial. maximum. This. is rep.-

reserrtativef of' the. usual? case., WhenA energized by a.non;.linearf saw-tooth signalf of this type, thecathoderayitube image exhibits'y a distortion characterizediby'initial expansionv and nal` compression, i. e., by an expansion at one side thereof and au compression at the other side thereof; hence equal time intervals are not represented ."ny:.equa'l'distances=` across` the fluorescent screen.

'In' practical. television systems, it is often difcult to obtain a; linear-sawtooth current variation of sucient magnitude and power to provide a sweepl for a' l'argccathode` ray tube, particularly in the` case of the high frequency horizontal sweep, .without excessive circuit complication. y

`may beV employed but the costof a construction of thistype is very high.

' The present. invention contemplates, and has asaprimary object, the provision. of means for compensating. an image system whereby a` uni.-

formnlineai. image is obtained in a cathode ray tube utilizing non-lineardeiiection means.

'Another object` of this invention is to provide a; cathodefray'imaget system with fixed magnetic means-Fior' minimizing image distortion resulting from anon-linear sweep.

Ai further' object! of this' inventiony isr to provide meanseorestablisliing acorrective magnetic eld These and other objects of the present inven- .Y

tion will now become apparent from the following specification taken in connection with the accompanying drawings in which:

Figure 1 is a top view of a cathode ray tube showing various components thereof asused in an image system;

Figure 2 is a graphical representation of anonlnear saw-tooth wave-form which may be applied to thehorizo'ntal deflection circuit of the -cathode ray tube shown in Figure 1;,l

Figure 3 is a front View of the fluorescent screen of the cathode ray tube of Figureland illustrates a distorted image thereon;

Figure 4 is a front Viewof one embodiment of a magnetic compensation system;

Figure 5 is a front viewof another embodiment of a magnetic compensation system; and

Figure 6 is a top cross-sectional view of the magnetic system shown in Figure'5.

With reference now to the drawings, vand more particularly Figure 1, there is shownk the essential components of a television or like image system utilizing a cathode ray tube I I. Cathode ray tube I I comprises a glass envelope having Ia face I2, the inside of which is coated with a phosphor capable of generating light upon the impact of an electron beam.

Within the neck of 'cathode ray tube II, and above tube base I3, is an electron gun I4 which when suitably energized from arrconventional power source (not shown) provides an :electron beam I5 focused to asharply defined point I6 on ilu-crescent screen I2.

The luminous intensity of the point of impact I6 upon 4iluorescent screen I2 is controlled by intensity modulating electron beam I5 from a video signal source I'I suitably connected to electron gun I4. The particular nature of the video sign-a1 'is not important to an understanding of thepresent invention. s l

A magnetic deflection yoke, schematically represented at 2| in Figure 1, is disposed about'the neck of the cathode ray tube I I between the electron gun I4 and fluorescent screen I2. This deection yoke comprisesr a pair of coils having orthogonally oriented axes, which coils -areenergized from horizontal and

vertical deflection generators

22 and 23 respectively. When Vthus energized, the electron beam. I5 is swept horizontally and vertically to produce a rectangularl raster of light on screen I2 of cathode rat tube.

In Figure 2 there is illustrated a current-time Wave-form 3| which is generally saw-tooth in shape and if of suitable frequency maybe applied to the horizontal deflection coil of yoke 2| (Figure 1). The saw-tooth of current 3| of Figure'2 illustrates ya common distortion encountered in television vhorizontal deection generators. Here the ycurrent rise is exponential so that the time rate of current ris-e diminishes with time, progressively flattening the Icurve asshown.

If a horizontal sweep current wave-form as shown vin Figure 2 is applied by deflection genera- I sweep current 3|.

tor 22 to cathode ray tube I I (Figure 1) the luminous raster produced upon iiuorescent screen I2 will be characterized by a distortion which is illustrated in Figure 3. With reference to Figure 3, there is shown the fluorescent face I2 of cathode ray tube I I and a representative image raster 32 of substantially rectangular form as is conventional in `commercial television practice. The raster 32 is composed of a plurality of horizontal luminous lines, such as line 33, which are formed by deection of electron beam I5 under the inuence of In Figure 3 the raster 32 has been divided by a plurality of vertical lines 34 which, represent equal sweep time lintervals by the spacing therebetween. A grid of vertical lines 34 may be formed upon screen |2 if the video signal source I'I of Figure 1 provides a succession of sharp pulses equally spaced in time, the number of pulses occurring during each horizontal sweep cycle being a, xed, predetermined number.

` If the sweep current 3| (Figure 2) were uniormly linear for `the entire s weep cycle, then the individual lines 31 produced by the modulating pulses would be equally spaced across the face of the fluorescent screen. However, for a' current wave-form 3|, as shown, as the time rate of change of current falls olf, the time rate of change of displacement correspondingly falls off, so that a series of pulses as mentioned above produce a grid of Vertical lines 34 as shown in Figure 3, wherein the lines are progressively crowded toward the right. If instead of a pulsed video signal, conventional television picture signals were employed, the picture on screen I2 would exhibit a progressive compression from left to right as vi-ewed in Figure 3.

I In accord-ance with the principles ofthe present invention, linearization of the image is obtained without change in the deflection generators, and without adjustment yof the sweep current waveform 3|. As is schematically indicated in Figure 1, compensation means 4| are provided between the deflection yoke 2| and the uorescent screen, which means are capable of introducinga predetermined deection lto the electron beaml I6 at each point in its sweep pattern, whereby the combined'effect of the` non-linear sweep and they compensating means produce an over-al1 raster which is Well within commercial tolerances when considered from the standpoint of distortion.

Although the compensating means 4l .are shown positioned about the neck of tube I it will become apparent that these means may be posi- `tioned at any point between the electron gun and the fluorescent screen.

Before considering specific embodiments of sweep compensating means, the general requirements thereof will be dis-cussed. In order to correct the distortion of the raster indicated in Figure 3, it'is necessary to contract the image horizontally at the left and correspondingly expand the image at the right. In Figure 4 there is illustrated means for accomplishing a correction of this kgeneral nature through the use of a Xed magnetic field, which may for simplicity of construction throughout be established by permanent magnets. As shown in Figure 4, a pair of

magnets

42 and 43 are disposed about the neck of cathode ray tube II described in connection with Figure 1. The electron beam of thetube is schematically shown by broken line I5 directed toward the tube fluorescent screen.

Magnets

42 and 43 comprise rectangular

magnetic cores

44 and 45 respectively about which arewound lfield coils 46 and III,- energized from. suitable direct current musicas deviation off electron beam I5 as it,y is" swept-` throughthis -iielda` variescontinuously, beinggapicture'I and-minimum^ near the centen.. so that lineariz-ation-ofthespacingbetween-verticalflines 34 as shown in-the'-raster oIEIQ v3 is obtained; The magneticiieldvisi-rionlinr-1^ to the axisoitube I l and y varies in" intensita;t4 'in a horizontal line normar' to theelectron beamv I5; Ay sufficient degreeof lineemit.'ation',` fori c'ertainecommercial purposesmaysometimesi-b're accomplished through theuse of only one -ofthe'magnets 42e-43- shown ingigurev. n l, Y VBy,suitablyalteringe the strength of the currentsin'coilsell; and' 41,1 Vanyijegree otcompensation maybeobtainelieand` de sirdir any. reason the distortiorl shown Fiure mayberef' Y lines may crowded at thelefteandexpanded` at the" righ In 'picture systems; df" course' is? df no y dan Magnet cores 4F and'B maybe, replaced'b 'permanent rr'iag'e'ts' having? the rduii'e'd s'tr'stl: iii which case the requiredVV compensation ,may be` obtainedI r" of power( meededen e about. tliecko c' th Gebieden@ t. m

and 112' extend einer @bei mi de ity" ist essen: rsa1 corresponding S tese-s ess "e einem' sj' ,t Hiiiztiitertmpcnentsefmedew-movements e clarity.l v

For: simplicity cf design and to: reduceV the sysh tempower requirements, coils 13 and 'M' maybeA dispeifised-Withi and-permanent magnets and pole pieces cf-suitable-formemployed. Inf-this-,man-nerairiinexpensive non-linear sweep may be usedi toy obtain' adistortionless image. As mentionedinconnection.witllI the embodiment of Figure 4,- kthe magneti-c'ifields of ma-'gnets 'H and 1-2\ of Figures 5 and 6 maybe adjusted so that the distortion shown-in'- Figure 3: is overcompensated and the compression and expansion arey on sides opposite,- thoseshown. This indicates that a Wide range` of distortionmay becompensated, although overcompensation'- itself is of no utility in television,y

unlesscertai-n effects are desired.

The lirlagnetic systems of Figures 4 throughg inclusive have been shown disposed about the tube-neck.- From the standpoint of equipment size,I this isadvantageous. However,` construction'of: the compensating means need notbe limitedetotlioser shown, and may be disposed whereve-r convenient between theelectron gunvandfthe iiuorescentscreen.

Asta resultof linearizationby the magnetic means shown inFigures-4, 5 and 6; the raster apnearing onthe tube face may become otherwise distorted.v One such distortion, known as shear,y results in the upper and lower boundaries of the raster S-I and` 82'respectively, in Figure 3, shiftingl sggtliat-tl/iey are-*no longer parallel to eachother.` Such'- shear may be compensated by suitably designed!- deiiectio-n yokes, but ordinarily this shear isneglfig-i'ble and need not be compensated.

IIn distortiomoi another form, the sides of the raster,- 83= and-84 in Figure 3, exhibit considerable curvature. Such curvature whenl significant may be compensated in various ways, for examplev by feed-ing. a suitable sinusoid'ally or parabolically varyingivoltage, readily obtained in al television circuit, to the cathode ray tube centering coils (not-'shown'fin the drawings) in proper phase;

in summary, the foregoing disclosure teaches an: imager system construction wherein; the time rate of displacement oi a fluorescent spot in a;

d cathode ray tube may be altered from the time rateiofchange cfa deflection current. A linear sweep maybe produced by utilizing a non-linear sweep current and afiXed compensating magnetici a field:

It willbe understood that compensation of the type described above may be utilized in connecv tionf with: cathode ray tubes other thanV thosek in television systems, and with other than magnetic deli-ectionl Thus;` sin-ce various modifications and extensions of the-principles 'of the present invention may become' evident to those skilled in theA art, it' is' preferred that the spirit and scope-ofthe inevention be dened solely bythe appended claims;

claim: f i. In an image system, a' cathode ray tube lfiav-Y ing means for generating a luminous spot; means" for'applying a sweep signal to said cathode ray' tube" fordefl'ecting said luminous spot, said sweep signal' having a substantially non-linear time variation, and an adjustable magnetic' means" for" stablshing a constant magnetic field through" said cathode ra'y tube, the orientation and' confi'guraucn of' eeidymagneue field being-arranged WhelebyiCombination' With Stf SWESY 7 said held provides substantially linear deflection of said luminous spot.

2. In an image system, a cathode ray tube, said tube including means for generating an electron beam, a fluorescent screen, means for impinging said electron beam upon said screen for providinga luminous spot, means for deflecting said electron beam, said last mentioned means being energized from a non-linear deecting signal source, and means for linearizing the deflection of said luminous spot comprising magnetic means for establishing a constant magnetic field through said cathode ray tube between said deecting means and said fluorescent screen.

3. In an image system, a cathode ray tube, said tube including means for generating an electron beam, a fluorescent screen, means for impinging said electron beam upon said screen for providing a luminous spot, means for defiecting said electron beam, said last mentioned means being energizedfrom a non-linear deflecting signal source, and means for linearizing the deflection of said luminous spot comprising magnetic means for establishing a constant magnetic field through said cathode ray tube between said delecting means and said fluorescent screen, said magnetic eldbein'g substantially normal to the axis of said cathode ray tube and of variable intensity in a direction normal thereto, said magnetic iield being of la configuration to act on said electron beam in combination with said deflecting means to provide substantially linear deflection of said beam.

4, vIn an image system, a cathode ray tube, said tubeincluding means for generating an electron beam, a iluorescent screen, means for impinging` said electron beam upon said screen for providing a luminous spot, means for dellecting said electron beam, said last mentioned means being energized from a non-linear deflecting signal source, and means for linearizing the deflection of said luminous spot comprising magnetic means for establishing a constant magnetic iield through saidcathode ray tube between said deecting means'and said fluorescent screen, said magnetic field'being substantially normal to the axis of said -cathode'ray tube and to the direction of deflection of said luminous spot.

5. yIn an image system, a cathode ray tube, said tube including means for generating an electron beam, a iuorescent screen, means for impinging said lelectron beam upon said screen for providing a luminous spot, means for deflecting said electron beam, said last mentioned means being energized from a non-linear deflecting signal source, and means for linearizing the deection of said luminous spot comprising magnetic means 'for establishing a magnetic eld through said cathode ray tube between said deflecting means and said fluorescent screen, said magnetic eld being sub-- stantially normal to the axis of said cathode ray tubezand to the direction of deflection of said luminous spot, said magnetic field being of substantially uniform density and voi" Variable extent axially of said tube.

6. A picture system comprising a cathode ray tube having means for generating and deecting a luminous spot, said deflecting means being energized from a deilection signal source, said signal source having an output non-linear with respect to time, and a constant compensation means betweensaid deflecting means and said luminous spot, whereby the deilection of vsaid luminous spot under the iniluence of said deflectingmeansand said compensation means is substantially linear with respect totime.

'7.vr A cathoderay tube vsweep, -systemfcompris ing in combination a'sweep signal generator, the output signal of said generator being saw-tooth in form and having'a non-lineartime Variation, deflectionA means'associated with said cathode ray tube and energized'by said-.non-linear sawtooth signal, and magnetic 'means for establishing a xed. magnetic eld of predetermined configuration 'adjustable `to Vary the field distribution through said cathoderay tube whereby said sweep system is substantially linearized.

8. A cathode ray tube deflection system comprising inv combination :a` deflection yyoke positioned about said cathode ray tube, a deflection signal source energizing said' deection yoke, said source providing 'a' saw-tooth deflection signal of non-lineartim'e variation, means for substantially compensating said non-linear deflection signal including an adjustable magnetic member for Vestablishing' a constant magnetic field through v'said cathode ray tube, said field being normal'to vthe axis ofsaid tube and varying in intensityfalongan `axis normal to said field and extending through said'tube-axis.

9. A cathode ray tube' deflection system comprising in combination a deflectionfyoke positioned about said'cathode ,ray tube, a d eection signal source energizingy "said deflection yoke, said'source providing-a saw-tooth deflection signal of non-linear time variation, means for substantially compensatingI said non-linear deflection signal including 'a"iria'gneticy member for establishing,y a magnetic eld through said cathode ray tube, vsaid field beingnormal to the axis of said tube aiidvarying inV intensity along an axis normal to said lfield and extending through saidtube axis, said magnetic member including arcuate pole pieces* dispo-sed about saidcathode 'ray tube and means for magnetizing said pole pieces. "l

10. A cathoderay tube deflection system comprising in .combination a deflection yoke vpositioned about said cathode ray tube, a deflection signalv source energizingwsaid deiiection yoke for sweepingltheflectron beam of said cathode ray tube, said sourcefpi'oviding a .saw-tooth sweep signal ofk non-'linear timevariation, the sweep of saidktube electron beamfunder,the` influence of said sweep` signahbeing correspondingly nonlinear, compensating means associated with said cathodey yray tube forsubstantially .linearizing said electronfv beammjsvveep,y said compensating means'including a lmagnetic member disposed about said cathode "ray, tube, said magnetic member having pole pieces extending therefrom and embracing said` cathode ray tube, said magnetic member andvpole pieces providing-a magnetic eldv extendingthrough said cathode ray tube normal to the axis thereofand normal to the direction of sweepof said electron beam under the influence of said ,sweep-signal, said magnetic -eld having an intensity variation parallel to saidv direction of sweep of said electron beam, said `electron beam beingv directed through said magnetic eld fwhereby. .the deviation. of said electron beamv in'transit through said magnetic eld is varied in raccordance with said intensity variation, said intensity variation being arranged toA substantially` linearize said electron beamsweep. .y .1 ff

. 11, A cathode ray 1tubedeilection system comprising in combination a deflection-yoke 'posi-- tioned-,about said, ,cathode ray tube,-,a deflection signal source energizing saidzdeflection yoke for Sweeping-iliefelsirogfbsem Ofi-,said 'cathode ray tube, said source providing a saw-tooth sweep signal of non-linear time variation, the sweep of said tube electron beam under the influence of said sweep signal lbeing correspondingly nonlinear, compensating means associated with said cathode ray tube for substantially linearizing Isaid electron beam sweep, said compensating means including a magnetic member disposed about said cathode ray tube, said magnetic member having pole pieces extending therefrom and embracing said cathode ray tube, said magnetic member and pole pieces providing a magnetic field extending through said cathode ray tube normal to the axis thereof and normal to the direction of sweep of said electron beam under the inuence of said sweep signal, said magnetic field being of substantially uniform density in a plane through the axis of said tube and parallel to said direction of said sweep, said field extending through an area of said plane of substantially triangular configuration, said electron beam being swept through the area of said field, said electron beam Ibeing deviated in traversing said eld, the extent of said deviation being a function oi the extent of said electron beam path through said area of said eld, said triangular eld area being disposed and arranged whereby said electron beam sweep is substantially linearized in transit therethrough.

12. A cathode ray tube deilection system comprising in combination av deflection yoke positioned about said cathode ray tube, a deflection signal source energizing said deflection yoke for sweeping the electron beam of said cathode ray tube, said source providing a saw-tooth sweep signal of non-linear time variation, the sweep of said tube electron beam under the influence of said sweep signal being correspondingly nonlinear, compensating means associated with said cathode ray tube for substantially linearizing ,said electron beam sweep, said compensating means including a, magnetic member disposed about said cathode ray tube, said magnetic member having pole pieces extending therefrom and embracing said cathode ray tube, said magnetic member and pole pieces providing a magnetic eld extending through said cathode ray tube normal to the axis thereof and normal to the direction of sweep of said electron beam under the iniiuence of said sweep signal, said magnetic iield being of substantially uniform density in a plane through the axis of said tube and parallel to said direction of said sweep, said eld extend, ing through an area of said plane of substantially triangular configuration, said electron beam being swept through the area of said eld, said electron beam being deviated in. traversing said eld, the extent lof said deviation 'being a function of the extent of said electron beam path through said area of said field, said triangular field area being disposed and arranged whereby said electron beam sweep is substantially linearized in transit therethrough, said pole pieces of said magnetic member being of substantially triangular crosssectional area, and means for substantially eliminating magnetic field components within said cathode ray tube parallel to said direction of said sweep.

13. In an image system, a cathode ray tube having means for generating a luminous spot, sweepI means having a predetermined time variation for causing motion of said luminous spot, said motion normally being non-linear with respect to time and a correction magnetic means acting directly in said deflected spot to effect linearity of motion thereto, said magnetic means being adjustable to vary the field distribution and to vary the eld strength.

CARLO V. BOCCIARELLI,

REFERENCES CITED The following references are of record in the nie of this patent:

UNITED STATES PATENTS Number Name Date 2,177,688 Cawein Oct, 31, 1939 2,239,865 Urtel Apr. 29, 1941 2,258,643 De Gier et al. Oct. 14, 1941 2,259,233 Tingley Oct. 14, 1941 2,264,567 Gunther Dec. 2, 1941 FOREIGN PATENTS Number Country Date 474,710 Great Britain Nov. 5, 1937