US2728027A - Cathode ray deflection systems - Google Patents

Description

DC 20, 1955 w. E. Scum., JR

n CATHODE RAY DEF'LECTION SYSTEMS Filed` Aug. 12, 1952 INI/ENTOR.

ATTORNEY United States Patent O CATHODE RAY DEFLECTION SYSTEMS William E. Scull, Jr., Haddoneld, N.

J., assignor to Radio Corporation of America,

This invention relates to` cathode ray tube devices and systems, and more particularly, to cathode ray'beam dellection systems and methods for use with or in cathode raytube devices and systems, such as television receivers and the like.

In the use of cathode ray tubes for certain purposes, such as television, there has been an ever increasing desire for wider angles of beam deflection to facilitate the design of kinescopes with larger screens without increasing other critical tube dimensions to unwieldy proportions. In conventional deilection systems, a limiting factor on the magnitude of deilection angle obtainable has been the Width of the neck aperture of the tube, since the deilected beam must clear the corners at the junction of the neck and llared portions of the tube. One approach to the problem of obtaining wider deflection angles for a given order of neck aperture Width has been to cut down the length of the deilection yoke to encompass a very short distance along the beam path as closely adjacent to the corners as possible. A serious disadvantage to this approach is that deflection eilciency is considerably reduced by such a decrease in the yokes operating length, and considerably more power is needed to achieve the desired dellection. Also, deilection linearity tends to be adversely affected as the yoke length is decreased. j

In accordance with the present invention, extremely wide deflection angles may be `obtained for a given order of neck aperture width without decreasing deflection elllciency and, in some cases, accompanied `by increased deilection efficiency.` The present invention rather'` than shortening the deflection yoke from conventional length permits an increase in dellection yoke length to obtain a more ecient yoke requiring less driving power. The essence of the present invention, whereby a more eilicient wide-angle deflection system is achieved, lies in the` provision for preliminary deilection of the electron beam between the electron gun and the main deflection yoke in a sense synchronously opposite to the main scanning deflection of the beam. p l i The effect of the reverse sense preliminary deilection is a substantial increase in the effective neck aperture width, with consequent assurance of beam clearance of corners over an exceptionally widerange of deection angles. If the present invention-is applied to conventional cathode ray tube devices ofthe present day, whereby the extremes `of the thus available deflection angle range are not utilized, the invention nevertheless provides considerable leeway for redesign of dellection yokes to longer, more eilcient, lengths. Also, the present invention will provide considerable leeway in thefheretofore exceptionally critical adjustments of the positions of various components, such as the focusing coil,` scanningvdeilection yoke, ion trap, etc. on the neck of conventional tubes.

Accordingly, a primary object of thepresent invention is to provide an improved cathode ray beam dellection system.

Another object of the present invention is to provide an eilicient wide-angle electron beam deection system.V

A further object of the present invention is to increase the eiective neck aperture width for the scanning beam in cathode ray tube apparatus, such as television receivers and the like.

An additional object of the present invention is to provide a cathode ray tube device with an improved beam detlection system whereby exceptionally large angles of deflection may be satisfactorily obtained.

Another object of the present invention is to improve the deflection eiliciency in cathode ray tube apparatus, such as television receivers and the like.

A further object of the present invention is to provide an improved cathode ray beam deflection system whereby beam clearance of the tube neck corners is assured over a wide range of dellection angles, and whereby positional adjustment of components on the tube neck is rendered less critical. v l

An additional object of the present invention is to provide an elllcient method of deflecting cathode ray beams over a wide range of deflection angles.

` Other and incidental objects of the present invention will be apparent to those skilled in the art from a reading of the following description and an inspection of the accompanying drawing which illustrates an embodiment of the present invention in which an auxiliary predellection yoke, preceding the main deflection yoke in position along the cathode ray beam path, is adapted to impart a preliminary deflection to the beam in a sense synchronously opposite to that imparted bythe main deflection yoke.

In the accompanying drawing there is shown a partially sectional view of a cathode ray tube 10 of conventional type. The tube 10 includes a neck portion 11 integral with or joined to a flared portion 13 which terminates in a target 15 which may comprise a phosphor screen of a well-known function. -The periphery of the junction of the neck and ilared portions of the tube presents theeffect of corners 17 in the sectional plane illustrated.

An electron beam source 2, 3, 4, is positioned at the remote end of the neck section 11 to provide a beam of electrons which may be deflected to trace suitable scanning rasters on the target 15. The electron beamsource may be in the well-known form of an electron gun, which may include a cathode 2, a beam intensity control electrode 3, and a lirst anode 4, in cooperation With a second anode 5 (shown las a conductive coating on the innersurface of the neck portion 11 and extending into the ilared portion 13 to a limit adjacent the screen 15). The several electrodes described are, during tube operation, connected to a source of D. C. potential, which may bea voltage divider 6 connected between the positive and negative terminals of a battery 7.

I t will be appreciated that the particular conguration of elements which constitute the electron gun in the accompanying drawing is illustrative only, and that the electron beam source in the present invention may take any of a variety of vforms known to the art. Electron guns are discussed in detail in an article entitled Factors governing performance of electron guns in television 'cathode-ray tubes, by R. R. Law beginning on page 103 of the Proceedings of the Institute of Radio Engineers for February 1942, and in an article entitled Improved electron gun for cathode-ray tubes, by `L.,E. Swedlund, appearing in Electronics for March 1945.

A main deilection yoke 2l, which lis mounted in a conventional' manner on the tube neck 11 closely adjacent to the junction of the neck and llared portions, includes suitable horizontal and vertical deilecting means, such as deilection coils'. An auxiliarydeilection yoke 23, also including horizontal and vertical deilecting means such asA deflection coils, which may be similarin structurc to the'man deflection yoke assembly but'is preferably smaller in size, is similarly mounted on the tube neck 11 in a position spaced from and preceding the main deflection yoke 21.

,Deflecting waves ofline frequency, developed by the horizontal deflection generator 25, energize vthe respective nhorizontal deecting vmeans of the main and auxiliary deflection yokes. The energizations are so related as to synchronously impart deflections in mutually opposite senses; that is, as energization of the vhorizontal deflecting means of the auxiliary deflection yoke 23 imparts deflection to an-electron beam passing through the tube neck in one-direction, the synchronous energization of the horizontal deflecting means of the main deflection yoke 21 imparts deflection to the electron beam in the opposite direction.

vDe'flecting waves of field frequency, developed by the vertical deflection generator 27, energize the respective vertical deflecting means of the main and auxiliary deflection yokes 21 and 23, respectively. Again, the energ'izations are so related as to synchronously impart deflections in mutually opposite senses; that is, as energization of the vertical deflecting means of the auxiliary deflection yoke 23 imports deflection to the electron beam in one direction, the synchronous energization of the vertical deflecting means of the main deflection yoke 21 imparts deflection to the electron beam in the opposite direction.

It will be appreciated that the net effect of conjoint energizations of the vertical and horizontal deflecting means will again be impartation of deflections by the two energized yokes 21 and v23 in mutually opposite senses; that is, as conjoint energizations of the horizontal and vertical deflecting means of the auxiliary deflection yoke 23 impart a net deflection to the electron beam in one direction, the respectively synchronous energizations of the horizontal and vertical deflecting means of the main deflection yoke 21 impart a net deflection to the electron beam in the opposite direction.

Thus, for example, when the electron beam is being deflected by the main deflection yoke 21 to strike a point in the upper right hand segment of the screen 15, the preliminary deflection imparted by the auxiliary deflection yoke 23 is causing the beam to enter the operating region of the main deflection yoke 21 at a point in the lower left hand segment of the tube neck cross-section. Similarly, when the electron beam is being deflected by the main deflection yoke 21 to strike a point in the lower left hand segment of the screen 15, the preliminary deflection imparted by the auxiliary deflection yoke 23 is causing the beam to enter the operating region of the main deflection yoke 21 at a point in the upper right hand segment of the tube neck cross-section. The entire width of the tube neck is thus available for sweeping the electron .beam to these deflection extremities, as contrasted to half the neck width which is the width `available for extremes of beam sweep when the beam conventionally enters the deflection yoke region at a point on the tube neck axis. `It is therefore seen that the effective width of a tube neck aperture for deflection purposes is substantially increased by the use of the predeflection principles of the present invention.

Only a small degree of preliminary deflection need be imparted to effect a maximum displacement from the tubeneck axis of the point of entry of the electron beam into the main Vdeflection region, particularly if there is some spacing between the positions of the auxiliary and main yokes 23 and 21 along the beam path.

Therefore, the auxiliary deflection yoke 23may be considerably shorter than the main deflection yoke 21 and may take only a small fractional portion of the energy outputs of the deflection generators 25 and 27. To achieve the vdesired reverse effect in the preliminary deflection, the auxiliary yoke-generator connections may be 'made in Aa manner reverse to that employed in making themain yoke-generator connections, or phase reversers may be included in the auxiliary yoke-generator connections, or the auxiliary yoke coils 23 may be oppositely wound as compared with the main yoke coils 2i. If the inter-yoke spacing and auxiliary yoke energization values are selected to effect the maximum entry point displacement for sweep extremes, exceptionally large deflection angles, extending well into the obtuse angle range, may be achieved without the beam striking the tube neck corners However, it will be appreciated that in many utilizations, such exceptionally large deflection angles will not be required. In these utilizations, particularly where conservation of component spacing and conservation of deflection energy are of importance, the inter-yoke spacing and auxiliary yoke energization values may be restricted to effect somewhat less than maximum entry point displacement for sweep extremes, and reasonably large deflection angles may still be achieved without the striking of tube neck cornersf To illustrate the effect on an electron beam of the reverse preliminary deflection, a pair of beam paths 33 and 35 have been shcwn in the accompanying drawing, one beam path 33 (shown by dot-and-dash lines) illustrating one path taken by a beam subject only to the deflection field of the main yoke 21, and the other beam path 35 (shown by dash lines) illustrating a path taken by a beam subject to the deflection field of the auxiliary yoke 23 as well as the deflection field of the main yoke 21. In both instances the electron beam emanating from the electron beam source 2, 3, 4, originally follows an axial path coincident with the tube axis 31.

For purpose of explanation, it will be assumedthat the illustrated beam paths lie in a horizontal sectional plane, and show the effects of an extreme of horizontal deflection only. However, it will be appreciated that the -explanation is equally applicable to vertical deflections due to vertical deflection energization only, or to diagonal or other deflections due to conjoint vertical and horizontal deflection energizations.

In conventional apparatus, the beam path 33 follows thettube axis 31 until reaching the main deflection region. Therein, under the influence of the main deflection field, it follows an arcuate path, the effective diameter of which is inversely proportional to the instantaneous strength of the transverse deflection field. Upon passing out of the deflection field region, an essentially straight line path is resumed terminating at a point 34 on the tube screen 15.

It is seen thatin the achievement of a deflection angle sufficiently large to permit the beam to reach point 34 on the screen, the conventional beam path 33 just barely clears the corner 17. Greater deflection angles, such as one sulciently large to permit the beam to reach point 36 on the screen 15, are not achievable using conventional deflection principles as the beam will strike the corner 17 enroute. VAlso if the main deflection yoke 21 was substantially lengthened to improve deflection efhciency, the ,masking eect of the corners 17 would restrict conventional deflection to maximum deflection angles even smaller than that necessary to reach point 34.

The more desirable performance achieved by utilizing the principles ofthe present invention is illustrated by the beam lpath 35. As the beam enters the field of the auxiliary deflection yoke 23 it is deflected from its axial path to follow an arcuate path (curving in a righthand direction in the illustrated instant of the deflection cycle). Upon leaving the auxiliary deflection field the beam continues in a straight line path, at an angle tothe tube axis, -until entering the main deflection field at vthe right-hand side of the illustrated section of the tube 'neck 11. Under the influence of the main deflection field, opposite in effect to the auxiliary deflection field, the beam follows an oppositely curved arcuate path. Upon passing out of the main deflection field, the beam continues ina straight line path terminating at point 36 at the extreme left end ofthe illustrated section of the screen Y15.

It is seen that this dellection extreme is achieved with considerable clearance of the corners 17. It will also be appreciated that much greater deection angles than that necessary to reach point 36 could be achieved in accordance with the inventions predeection principles without the problem of corner masking arising atall. Also, the main deection yoke 21 could be substantially lengthened to improve deflection eiciency, and' deection angles of a magnitude sucient to reach point 36 would still be easily attainable without fear of the interfering effect of corner shadows. Also, with such great leeway in beam clearance of the tube neck corners in all utilizations of the present invention (except perhaps those that might require exceptionally large obtuse angles of dellection) the positional adjustment of the tube neck of components such as deflection yokes, focusing coils, etc., is rendered much less critical if the cathode ray tube apparatus is adapted to employ the improvements embodied in the presentinvention.

While the foregoing explanation has only illustrated the elfect of the present invention on one extreme of deflection in a given plane, it will be appreciated by those skilled in the art that, with energization of the horizontal and vertical delecting means in the revealed manner, complete rasters of any desired type may be developed with the above-discussed freedom from corner masking problems and the accompanying elliciency advantages prevailing throughout the scanning cycles.

In another form of this invention, electrostatic deflecting means mounted inside the tube neck are employed to effect a similar solution to the corner masking problem. Main and auxiliary deflection plates (or electrostatic deflection yokes) are secured within the tube neck in positions along the beam path corresponding to those of the main and auxiliary deection yokes 21 and 23, in the illustrated embodiment. With energizations of the main and auxiliary deection plates so related as to produce mutually opposite deflection eifects as in the illustrated embodiment, deflection angles over an exceptionally wide range may be achieved with a high degree of deection eliciency.

It will be appreciated that the present invention is applicable to sundry types of cathode-ray tube apparatus, such as television receivers, television pick-up systems, Oscilloscopes, facsimile scanners, radar-display systems, etc., and will provide for elcient wide-angle beam deflection in various forms of cathode-ray tubes, such as kinescopes, iconoscopes, image orthicons, flying-spot" scanners, P. P. I. scopes, etc., with freedom from corner masking problems therein.

What I claim is:

l. In a cathode ray tube assembly including a cathode ray tube having a neck, and an electron gun located at one end of said neck, the combination of a main electromagnetic deflection yoke surrounding a region of said neck at the opposite end thereof, an auxiliary electromagnetic deflection yoke surrounding said neck at a position intermediate the location of said main deflection yoke and the location of said electron gun, said auxiliary deliection yoke being spaced from said main deection yoke by a distance along said neck comparable to the length of said region, and means for synchronously energizing both of said deflection yokes, the energization of said auxiliary deflection yoke regularly causing preliminary deflection of the electron beam from said electron gun in a direction opposite to the direction of beam deflection caused by energization of said main deflection yoke.

2. In cathode ray tube apparatus including a cathode ray tube comprising an electron beam source, an electron target, and an enclosed beam path between said source and said target, the combination including a main electromagnetic deflection yoke operating over one region of said beam path for impartingscanning deliections to said beam, an auxiliary electromagnetic deflection yoke preceding and appreciably spaced from said main deliection` yokes being so related that the direction of the displace-I ment imparted by saidV auxiliary deection yoke continually opposite to the direction of the dellection imparted by said main deection yoke whereby said main deection yoke is provided with an elective center of deliection locatedat a point in said beam path subsequent to said one region.

3. In cathode-ray tube apparatus including a cathoderay tube comprising an electron beam source, an electron target, and an enclosed beam path between said source and said target, said cathode-ray tube including a neck portion enclosing said electron beam source and a segment of said beam path, the combination comprising a main electromagnetic deflection yoke surrounding said neck and operating over a given region of said beam path for imparting scanning deflections to said beam, an auxiliary electromagnetic dellection yoke also surrounding said tube neck but spaced from said main deflection yoke for displacing the point of entry of said beam into said given region, the spacing between said auxiliary and main deection yoke being of appreciable length with respect to the length of said auxiliary deection yoke, and means for synchronously energizing both of said deflection yokes such that the direction of displacement imparted by said auxiliary dellection yoke is continually opposite to the direction imparted by said main dellection yoke.

4. In cathode-ray tube apparatus including a cathoderay tube comprising an electron beam source, a luminescent target, and an enclosed beam path between said source and said target, said cathode-ray tube including a neck portion enclosing said electron beam source and a segment of said beam path, the combination comprising a main electromagnetic dellection yoke surrounding said neck and operating over a given region of said beam path for imparting scanning deections to said beam, an auxiliary electro-magnetic dellection yoke also surrounding said tube neck but spaced from said main deflection yoke for displacing the point of entry of said beam into said given region, the spacing between said auxiliary and main deection yoke and said given region being of a length substantially greater than the length of said auxiliary dellection yoke, means'for energizing said main deflection yoke with scanning waves of predetermined amplitude and periodicity, and means for energizing said auxiliary deliection yoke in synchronism with the energization of said main deflection yoke but with scanning waves of reduced amplitude relative to said predetermined amplitude, the energizations of both of said deflection yokes being related such that the direction of displacement imparted by said auxiliary yoke is continuously opposite to the direction of the deilection imparted by said main yoke.

5. In a cathode-ray tube assembly including a cathoderay tube having a neck portion and a flared portion, and including an electron gun located at one end of said neck, and a luminescent target located in said flared tube portion, said neck providing an enclosure for the path of an electron beam generated by said electron gun and directed toward said target, the combination comprising a main electromagnetic deflection yoke surrounding said neck at the end thereof adjacent to said llared tube portion for imparting dellections to said beam over a given region of said beam path, an auxiliary electromagnetic dellection yoke surrounding said neck at a position intermediate the location of said main deflection yoke and the location of said electron gun for displacing the point of entry of said beam into said given region, said auxiliary deliection yoke being spaced from said main deflection yoke by a distance along said beam path comparable to the length of said given region, such spacing providing anessentially eld free region of said ybeam path inter# current waveforms of similar .periodicity but reduced am-y plitude relative to said predetermined amplitude, the erw ergizations of both said yokes being so related as to cause the direction of the displacement impartedl by said aux iliary yoke to be continually opposite to the direction of the deflection imparted by said main yoke.

References Citedin the le'of this patent UNITED STATES PATENTS Schlesinger Sept. 8, Iams Nov. 9, Truell July 4, Gabor Apr. 16, Hickok Sept. 17, Taylor Aug. 19, Goldberg Mar. 5,

FOREIGN PATENTS France Mar. 31,

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