US2875374A - Electron beam convergence apparatus - Google Patents

Description

Feb. 24, 1959 J. c. COOPER ET AL 2,875,374 ELECTRON BEAM CONVERGENCE APPARATUS Filed oct. so, 195e 2 Sheetsfsheet l INVENTORS Jur-m E. EDDPER By Baas W. HAEMANN Feb 24, 1959 J. c. COOPER ET AL 2,875,374

ELECTRON BEAM CONVERGENCE APPARATUS Im-m E. EUDPER BY B @BWM-Imi v individually moved radially to its desired position. .will be appreciated that, in a three-beam kinescope of United States Patent 2,875,374 ELECTRON BEAM CoNvEnGiNcn APPARATUS john C. ICooper, Lititz, and Robert W.V Hagniann, Lancaster, Pa., assiguors to Radio Corporatin of America, a corporation of Delaware Application October 30, 1956, Serial No. 619,197

7 Claims. (C1. 315-13) -scope, by Seelen et al., published in the RCA Review for March 1955, at page 122. Such a tube has a 1uminescent screen as part of a target electrode structure and in which different phosphor areas produce differently colored light when excited by electron beam components impinging upon the target structure from different angles, the angle of impingement determining the particular color of the light produced by the phosphor areas.

It is necessary for the satisfactory operation of such kinescopes to effect substantial convergence of the different electron beams at all points of the raster scanned thereby at the target electrode structure. In general, the matter of beam convergence is discussed in an article entitled Deflection and Convergence in Color Kinescopes by A. W. Friend, Proceedings of the IRE, October 1951, at page 1249. One type of apparatus for controlling the convergence of a plurality of electron vbeams at a target electrode structure and with which the present invention is particularly concerned comprises, in general, individual electromagnetic means located re'- 'spectively adjacent to the predellection paths of the respective beams and of such character as to be energizable from the beam deflection circuits in a manner to effect the desired beam convergence.

A particular electromagnetic beam convergence means to which this invention pertains includes, for each beam, a pair of pole pieces located internally of the kinescope envelope. The internally located pole pieces are energized by magnetic apparatus located externally of the kinescope and associated, respectively, with the different "pairs ,of pole pieces. quire, in general, energization both statically and dynamically,.the latter energization being in accordance with a function of the angles through which the electron beams The convergence 4pole `pieces reare deflected.

Prior arrangements for effecting static convergence ofk 'a plurality of beam components have included means for separately energizing each convergence structure with an adjustable direct current energy so that, in order to converge a plurality of beams at the center of the target electrode or other selected point, each beam must be It the type described, this procedure, which may be termed a radial convergence, is time-consuming and requires painstaking care, since three separate controls must be adjusted.

It is, therefore, an object of the invention to provide -new andI improved apparatus for effecting convergence '2 of a plurality of electron beam components in a multiple beam kinescope. i

Another object of the invention is to provide improved apparatus for statically energizing the several structures under the control of which several electron beam components are converged at substantially the target electrode structure of a color kinescope.

In accordance with an illustrative embodiment of the present invention as it may be applied to a color kinescope of the type set forth, static convergence of three electron beams is effected by the application of suitable direct current energy to two of the beam converging structures via dual beam control means which kare so arranged that the two beams controlled thereby may be moved simultaneously toward each other until converged, the relative amplitudes of the static energy applied to them being controlled. The third beam controlling structure is adjustably energized from a separate source which may then be employed to move that beam into convergence with the two first-named beams. As will appear more fully hereinafter, the movement of the beams in accordance with the invention is in the nature of a rectangular coordinate movement.

By virtue of the rectangular coordinate nature of the present apparatus, the time required for effecting static convergence of a multi-beam kinescope is greatly reduced and the procedure itself is simplified over prior art arrangements. I

According to another aspect of the presentinvention, means are provided for cross-feeding certain of the convergence energy employed in moving the third-recited beam to the structures which control the first two beams, whereby adjustment of the third beam does not necessitate readjustment of the dual beam controls.

Additional objects and advantages of the present invention will become apparent to those skilled inthe art from a study of the following detailed descriptionrof the accompanying drawing, in which:

Figure l illustrates a cathode ray tube convergence system in connection with which thepresent invention is to be described;

Figure 2 is a vertical sectional view takenalong lin'e 2-,2 of Figure 1; and

Figures 3 and 4 arey schematic diagrams of circuits fo energizing the convergence magnets of Figures 1 and 2.

Reference will first be, made to Figure l of the drawing for a general description of an illustrative embodiment ofan electron beam convergence system in accordance with the present invention. The system includes a color kinescope 11 which may be of the same general type as that disclosed in the Seelen et al. article referred to above. The kinescope has aluminescent screen 12 provided with a multiplicity of small phosphor areas arrangedin groups, the areas of each group being capable respectively of producing light of different component colors in which the image is to be reproduced in response to electron impingement. In back of and spaced from the screen 12 is an apertured masking electrode 13 having an aperture for and in substantial alignment with each group of phosphor areas of' the screen 12. It will be noted that both the luminescent screen and the masking electrode have generally spherical surfaces which are substantially concentric. It is to be understood, however, that the present invention is equally applicable to other forms of target electrode configuration.

In the particular case illustrated, the kinescope also has a plurality of electrony guns, equal in number to the number of component colors in which the image is to be reproduced. Each of these guns may be conventional, consisting of a cathode, a control grid and a focusing electrode. v.Since the three guns are identical, the dit`- 3' ferent parts thereof will be referred to collectively as the cathodes 14, the control grids 15, and the focusing electrodes 16. The three electron guns produce schematically represented electron beams'i, 18 and 19 by which to energize, respectively, the blue, red and green phosphor areas of the screen 12. When these electron beams are properly converged at the target electrode structure including the screen 12 and the masking electroder13, they pass through the apertures of the masking electrode from different `directions and impinge upon different phosphor areas of the various groups so as to produce blue, red and green light. It is to be noted that the size of the phosphor areas, the angles between `electrode structure, including the masking electrode 13 and the luminescent screen 12, which for this purpose may be metallized, is electrically connected to the wall coating 20 by suitable conventional means (not shown). Metallization of a luminescent screen of the character described Amay be etected in the manner disclosed in a paper by D. W. Epstein and L. Pensak entitled Improved Cathode Ray Tubes with Metal-Backed Luminescent Screens published in the RCA Review, vol. VII, March 1946, at pages 5-l0.

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 23 across the terminals of which there is connected a voltage divider 24. The cathodes 14 are connected to the grounded point of the voltage divider andthe control grids 15 are connected to a point which is somewhat negative relative to ground. Similarly, the focusing electrodes 16 are connected to a point on the voltage divider which may conventionally be at a potential of approximately 4,000 volts positive relative to the grounded cathodes. Also, the beam-accelerating anode, including the wall `coating 20, is connected to the voltage divider 24 at a ,point which may conventionally be approximately 25,600

volts positive relative to the grounded cathodes.

The electron beams 17, 1S and 19 are modulated suitf ably `in intensity underthe control of color-representative -video Asignals derived from a source Z5. Itwill be understood that the video signal source is represented herein ,entirely diagrammatically since'it does not per se form part of Ithe present invention. The signal source 25 usually `will be Apart 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 11 is employed as a monitor, for example. Also, it will be understood that the illustrated connection of the video signal source 25 to the electron guns of the kinescope 11 is merely diagrammatic and accordingly these connections may or may not be made directly to the cathodes 14. Instead, itwill be understood, that they may be made to the grids 15 or, in accordance with other modes of operation ot' 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 11 is a deflection yoke 26 which may be entirely conventional including two pairs of suitably placed coils electrically connected together in such a manner that, when properly energized, electromagnetic lields are produced, whereby to elect both horizontal and vertical angular deflections of the electron beams so as to scan the usual rectangular raster at the target electrode structure. Energization of the dellection coils comprising the yoke 26 may be eiected by conventional vertical and horizontal deflection wave generators 27 and 28, respectively. Such apparatus will be understood to function suitably to produce substantially sawtooth wave energy at both horizontal and vertical dellection frequencies so that the fields produced by the yoke 26 are varied in a substantially sawtooth manner.

The beam convergence system with which the present invention is to be illustrated also includes a plurality of electromagnetic held-producing elements such as the electromagnets 29, 30 and 31 (see also Figure 2) mounted around the neck 21 of the color kinescope adjacent to the predellection paths of the electron beams. It is to be understood that the precise location of these magnets is not necessarily indicated in Figure 1. Instead, it is to be understood that each of these magnets is located relative to one of the electron beams so as to inuencc its associated beam to the virtual exclusion of the others, Furthermore, it is to he understood that these magnets are of a character which, when suitably energized, produce respective fields which are transverse to the associated beam paths and in directions to move the associated beams radially relative to the longitudinal axis of the kinescope 11.

Each of these convergence electromagnets includes a generally U-shaped pole piece or core member and a pair of energizing windings. Two windings are or may b e provided for each of the clectromagnets for separate energization, as will be `described subsequently in greater detail.

Before describing the details of the particular beam convergence system in accordance with the present invention, a brief description Will be given of the general manner in which the apparatus functions to produce the Vesired results. The convergence magnets 29, 30 and 31 are energized, in one embodiment, by substantially unidirectional energyso as to effect an initial `convergence `of the electron beams substantially at the target electrode structure including the screen 12 and the aperturcd masking electrode 13. In order to do this, prior art systems have involved the separate unidirectional energization of these magnets in such manner that the magnets are indi vidually energized in different magnitudes. The present invention, on the other hand, affords a simpler convergence system employing whathas been termed herein a dual control system to be described in detail hereinafter. In effecting this initial `beam convergence; it is to be understood that, las in the case of prior art systems, the beams may be in any `desired one of their different deflected positions` For example, they may be initially converged atthe center of the raster to bescanned. Alternatively, they may be initially converged at one corner ofthe raster.

The convergence magnets 29, 30 and 31 are also dynamically energized by the control wave energy derived from suitable generators (shown in, and described subsequently with reference to, Figures 3 and 4) so as to eliect a variation in the magnitude of the transverse fields produced respectively thereby. These field strength variations are in accordance with a predetermined function (usually approximately parabolic) of the angular beam detlection. Variations in the strength of the elds produced by the convergence magnets effect corresponding variations in the paths of the electron beam components relative to the longitudinal axis of the tube. Hence, suitable variations `are made in `the convergence angles between the various beam components so as to produce the desired convergence of the beam components substantially at the target electrode structure including the screen 12 and the masking electrode 13.

For a further description of this type of beam convergence apparatus, reference lwill now be `made to AFigure 2 of the drawings. Thisgurefshows more clearly theA positions of the convergence magnets 29, 30 and 31 relative to one another and to the electron beams with which they are respectively associated. Inasmuch as all of these magnets are substantially the same, only one of them will be described in detail. The convergence mag- .net r29, which is associated with the blue electron beam 17, is provided with a core having two external pole pieces which are mounted so as to be in close association with the tube neck 21. The magnets may be mounted around the neck of the kinescope by any suitable means `such as holders of insulating material which are springlthe internal pole pieces 37 and 38 is considerably improved. l

Thus, the convergence magnet 29 effectively produces a field which, in the vicinity` of the electron beam 17,

'is substantially transverse to the axis of the kinescope.

By means of such a field, the electron beam 1.7 may be moved radially toward or away from the longitudinal tube axis, the direction and magnitude of such a beam movement being controlled by the energization of the magnet. The convergence magnets 30 and 31, respectively, control the electron beams 18 and 19 in a substantially similar manner.

The magnet 29 comprises a generallyU-shaped pole piece 40 of ferrite or other suitable magnetic core material, the extremities of the legs of the U being located adjacent to the internally located pole pieces 37 and 38.

Electromagnetic coils 41 and 42 for energizing the magnet 29v with a suitable waveform of television vertical or 'iield frequency are wound about the legs of the U near the bight thereof (i. e., remote from the extremities of the legs of the U). Electromagnetic coils 43 and 44 are also wound about the legs of the U-shaped pole piece 40 adjacent their extremities. These latter coils are adapted for energization with horizontal deflection frequency energy of suitable wave shape. It will further be seen that the magnet 30 comprises a U-shaped core member 40', vertical frequency exciter coils 41 and 42 and .horizontal frequency exciter coils 43 and 44. Similarly,

the magnet 31 includes a U-shaped pole piece 40, verticalexciter coils 41 and 42" and horizontal exciter y coils 43" and 44".

Circuitry for energizing the horizontal frequency exciter coils of the magnets 29, 30 and 31 is illustrated in Figure 3 of the drawing wherein reference numerals identical to those employed in Figure 2 designate the same parts. A positive-goingpulse 45 of generally rectangular wave shape is applied to the input terminal 46 of the blue horizontal convergence circuitry. Pulses such as the one represented by reference numeral .45

`may bederived by connecting the terminal 46 directly to a suitable point in the horizontal deflection wave generator 28 such, for example, as the usual horizontal output transformer found in conventional television receivers. The pulse 45 may be of 50 volts amplitude, peak to peak,

. and is integrated into a generally sawtooth waveshape 48 by the variable inductance 47 connected to the input terminal 46. A shunt path comprising a capacitor 49 .and the parallel combination of a variable inductance 50 Y and resistor 51 serves to shape the wave form 48 further toward a parabolic voltage wave form as indicated at 52. This wave form, when passed through the coils 43 and 44, connected in series-aiding relationship, produces a generally parabolic current waveform 53 in the coils for Asawtooth voltage waveform .for the rproducing the required parabolically varying magnetic field between the pole pieces 37 'and 38 of the kinescope.y

The amplitude of the convergence waveform flowing through the coils 43 and 44 is controlled by the variable series inductance 47, while its tilt or phase (i. e., shift in the minimum amplitude point of the parabolic Wave toward the beginning or end of the wave) is controlled `by the Variable inductance 50. It is to be noted that 'the waveshaping function is performed, in part, by the suitable point on the horizontal output transformer. The

input pulse 45' is applied via a red-green horizontal amplitude control inductance 47 to the center tap of an inductance 56 which controls thev relative amplitude of the sawtooth wave (produced by the integrating action of the inductance 47') applied to the red and green convergence magnets, respectively. The tilt of the Vparabolic currents applied to the convergence windings is controlled by a resistor 54 designated Red-green Horiz. Tilt while the amount of tilting imparted to the two waves is controlled by the Red-green Tilt Balance potentiometer 55.

Figure 4 illustrates circuitry in accordance with a specific form of the invention for energizing the Vertical frequency exciter coils such as the coils 41 and 42 of 4the magnet 29. In Figure 4, there is shown a conven- 35' tional vertical deflection output stage including a vertical deflection wave amplifier 56 whose anode is connected to oneend of theV primary winding 57 of a deflection 'output transformer 58. The other end of the primary winding 56'is connected to a source of positive operating potentialt-j-B) indicated at the terminal 59. The screen grid electrode 60 of the amplifier 54 is connected vto a source of positive Voltage, as indicated. The suppressor grid electrode 61 of the amplifier is conventionally connected to the cathode 62 which, in turn, is connected to a point of reference potential (e. g., ground) through a resistor 63. The amplifier 54 is adapted toreceive at its control grid input terminal 64 a conventionall spiked sawtooth voltage wave of vertical deiiection frequency from a suitable source such as the usual vertical deflection oscillator. The transformer 58 includes a secondary winding 65 connected to the vertical deflection coils of the yoke 26 for applying vertical deflection frequency energy to the latter. l Y

Energization of the vertical frequency exciter coils of the convergence magnets is effected in the following manner: a sawtooth voltage wave shaped generally as indicated by the waveform 66 is derived from the cathode ,62 of the vertical deection output amplier. This volt- :age wave, peaked somewhat as shown, is present across the resistor 63 and also across each of a pair of potentiometers 67 and 68, so that a parabolic current wave is automatically applied to the vertical frequency exciter coils such as the coils 41 and 42 of the magnet 29. Thus, a controllable amount of the voltage wave 66 appearing across the resistor 63 is applied Via the adjustable tap 71 to one end of the coil I1- 42, as illustrated. Similarly, an adjustable tap 72 on the potentiometer 67 applies an adjustable amount of the sawtooth voltage wave to the winding 41-42 of the magnet 30. A similar connection is made from the potentiometer 68 via a tap to the winding 417-42" of the magnet 31.

The vertical frequency convergence circuitry further includes a winding 74 von the transformer 58 in which there is induced a voltage wave such as that indicated at 75, which voltage wave is in the nature of a peaked j t 7 sawtooth wave for controlling `the tilt of the parabolic waveform to be produced in the coils 41--42 of the magnet 29. The amplitude of the tilt voltage applied to these coils is controlled by the potentiometer 76 whose movable contact 76' is connected to the coils 41-42. Thus, by adjustment of the tap 71 and the contact 76', the amplitude and tilt of the voltage waveform applied to the coils 41-42 may be controlled. The composite voltage waveform resulting from the combination of the waves 66 and 75 is integrated by the inductance of the coils 41--42 to produce therein the generally parabolic current Wave 77.

The circuits for energizing the exciter coils of the magnets and 31 with vertical deliection frequency convergence waves are similar to that described in connection with the magnet 29. One difference, however, is that, while the tilt waveform 75 provided by the winding 74 is adjustable only as to magnitude, the tilt waveforms provided by the winding 85 across the potentiometers 86 and 87 for use in the magnets 30 and 31, respectively, are adjustable both as to amplitude and polarity. That is to say, the winding 8S on the transformer 58 is center tapped. Thus, there appear at apposite ends of the vertical green tilt potentiometer 86 and the vertical red tilt` potentiometer 87 oppositely polarized waveforms corresponding in shape to the waveform 75 which appears across the potentiometer 76. It will be recognized7 therefore, that each of the magnets 30 and 31 will receive both the sawtooth and tilt waves of adjustable ampli- ,tude and phase.

In accordance with the present invention, static convergence of the beams 17, 18 and 19 is effected through direct current energization of the magnets 29, 30 and 31.

Specifically, the present invention provides means for ap-j plying variable direct current energy to the vertical frequency exciter coils of the convergence magnets. While such arrangements have been employed in the past, prior `systems have involved separate energization of each of the magnets, so that each of the several electron beams could be moved radially inwardly or outwardly with respect to the longitudinal axis of the tube and independently of each of the other beams. According to the present invention, on the other hand, and as has been stated generally above, static convergence of the..

electron beams is so controlled that the convergence may be likened to a rectangular coordinate system. The manner in which this novel system of convergence may be realized and specific apparatus for performing this function will become apparent from the remaining circuitry of Figure 4.

In Figure 4, there is illustrated the horizontal deflection output amplifier stage which includes an amplifier tube 90 whose anode 91 is, as shown, adapted for connection to a suitable point on the horizontal deflection output transformer. The control grid input terminal 92 of the amplifier receives a conventional sawtoothV wave of horizontal deflection frequency, while the cathode 93 of the amplifier is connected through series (e. g., ground). The potentiometers 94 and 95 are bypassed by a large capacitor 96, so that there is present across the potentiometers 94 and 95 a direct current voltage produced by anode-cathode current flow through .potentiometers 94 and 95 to a point of fixed potential the ampliiier tube 90. The potentiometer 95 includes a..

slider tap 97 which is connected to that end of the coils 41-42 of the magnet 31 which is remote from the end connected to the potentiometer 68 and constitutes means for causing direct current static convergence `energy to ow through the coils 41"-42".

Connected across the potentiometer 95 is a potentiometer 93 whose slider tap 99 is ganged to the tap 97 2in such manner that the two taps are moved in the same ldirection through a single control. As will be noted from Figure `4, movement of the taps 97 and 99 in a given direction produces equal amounts of voltage ltive, while the voltage at the tap 99 will become more positive by the same amount. The tap A99 is connected to the coils 41-42 at the end remote from the end connected to the potentiometer 67 and serves to cause direct current static convergence energy to flow through the magnet 30. For simplicity of terminology, the potentiometers 95 and 98 will be termed herein the redgreen vertical static convergence control. The reason for this designation is that, by adjustment of the taps 97 and 99, the red and green electron beams 18 and 19, respectively, may be moved simultaneously with` respect to the longitudinal axis of the tube along radii thereof and in opposite directions with respect to the axis. That is, if the taps 97 and 99 are adjusted in such direction as to move the beam 18 toward the axis of the tube by a given amount, the beam 19 will be moved away from the axis of the tube by the same amount. When the tube face is viewed, it appears that the vertical spacing between the spots produced by the beams 18 and 19 is changed. Actually, although each of the beams 18 and 19 is moved only along a radius of the tube, the vertical component of such beam movement does indeed produce a change in the vertical spacing between the spots produced thereby. It is this simultaneous movement of the two beams 18 and 19 which is termed hereinabove as a `dual control.

Also connected across the potentiometers 95 and 98 `is apotentiometer 100 which will be termed herein the ,.red-green horizontal static convergence control. The

adjustable slider tap 101 of the potentiometer 100 is connected to the center tap 85 of the winding 85 of the transformer 58. It will, therefore, be appreciated that, by virtue of the connection `from the potentiometer 100 to the center tap 85, a direct current voltage is produced across the potentiometers 86 and 87 from which the tilt waveforms are applied to the magnets 30 and 31. Move- `ment of the slider tap 101 on the potentiometer 100 af- `such simultaneous movement of the beams 18 and 19 has the effect of altering the horizontal separation of the beam spots, such horizontal separation being a func- `tion of the horizontal component of the radial movement of the beams. Hence, it will be recognized that, while the potentiometers 95 and 98 control the vertical spacing between the beam spots produced by` the bearns 18 and 19, the horizontal separation between the same spots i's controlled by the potentiometer 100, so that the spots produced by the beams 18 and 19 may be readily converged at the screen.

The third beam, namely, the blue beam 17, is controlled, insofar as static convergence is concerned, by

i means of a blue vertical static convergence potentiometer 102 whose slider tap 103 is connected via a resistor 104 and a lead 105 to that end of the coils 41--42 remote from the end connected to the potentiometer 76. The potentiometer 102 is, further, center-tapped, the center tap 106 being directly connected to one end of the potentiometer 76. It will be apparent, therefore, that opposite polarities of direct current voltage may be ,applied to the coils 41--42 by movement of the tap 103 `from one side to the other of the center tap 106 of the `potentiometer 102, so that the beam 17 may be moved toward or away from the axis of the lube` along la radius thereof. By virtue of such movement of the "horizontal line as that on which the earlier converged beams 18 and 19 lie. Assuming that the three guns are yperfectly located at the apices of an equilateral triangle such that the beams are movable exactly along radii of the tube, the described movement of the beam 17 would bring the spot produced by that beam into coincidence With the spots of the beams 18 and v19. Actually, however, and in order to correct for de- `partures from such perfect construction, conventional convergence systems further include an element for controlling the lateral positioning of one of the electron vbeams such, for example, as the blue beam 17. An example of such an element is given in an article by M. J.

rObert entitled Deflection and Convergence ofthe 21 yColor Kinescope which appeared in the same issue of the RCA Review as the Seelen et al. article. of blue positioning correcting means shown in the The form Obert article is a permanent magnet adjustable as to fdirection and strength. In accordance with the present apparatus, the blue beam positioning means takes the 'form of an electromagnet 108 of suitable configuration represented diagrammatically in Figure 1; The electrojmagnet 108 may include a core member (not shown) associated with the tube for producing lateral shifting of the beam 17 when energized by suitable direct current.

vThis energization is afforded by the circuitry of Figure 4 which also includes the potentiometer 94, mentioned above, in series with the static convergence potentiom- 'eters 95 and 98. The electromagnetic winding of the magnet 108 is connected to the potentiometer 94, as shown, in such manner that a direct current of reversible direction and variable amplitude may be caused to ow through the winding. In this manner, the blue beam 17 f may be brought into convergence with the other two 'beams.

It has been found that, once the red and green beams of the kinescope have been properly converged in ac- :cordance with the procedure set forth above, adjustment -of the blue beam controlling magnet 29 through the 'agency of the potentiometer 106 produces an interaction with the red and green beam convergence magnets 30 and 31. Such interaction is undesirable, since it 'changes the static convergence fields of the earlier ad- -justed beams. aspect of the present invention, means are provided for Hence, in accordance with a further substantially eliminating the undesirable elect of the *blue beam controlling magnet 29 upon the red and green beam controlling magnets 30 and 31. Such means may -take the simple form of a circuit connection indicated as a resistor 110 for applying from the blue'beam vertical `static convergence controlling potentiometer 102 to 'the red and green convergence magnets energy of the samemagnitude as that applied to the blue magnet 29 "but of such sense as to buck the elect of the magnet 29 upon the magnets 30 and 31. That is, the resistor 110 is connected from the slider tap 103 on the potentiometer 102 to the center tap 85' of the transformer winding 8S.

Thus, in addition to the direct current energy applied to thered and green convergence magnets via the center tap connection to the potentiometer 100, there is applied Y the further direct current from the potentiometer '102 which adds algebraically to the first-named direct current energy and in such manner as to compensate for any undesirable interaction between the blue convergence magnet eld and that of the red and green convergence I magnets.

It willl also be noted that the larrangement of Figure 4 in which the vertical frequency convergence waves are This direct current voltage is,

of this direct current voltage from the convergence wave source to the magnets has vthe advantageous eiect of l the sum of the direct current components of the vertical and horizontal frequency waves) applied to the magnet. That is to say, it has been found that when the beams of a kinescope such as the type in question have been statically and dynamically converged, if the dynamic convergence energy is removed from the convergence magnets, the beams tend to be converged nearer the edges of the screen rather than at the center thereof. By virtue of the fact that the several vertical frequency convergence waves are derived from resistors in the cathode circuit of the vertical deection amplilier, each such wave applied to a convergence magnet is accompanied by direct current of equal magnitude but opposite sense from the direct current component of the convergence wave, whereby the direct current component of the wave is effectively compensated. In the illustrated circuit, the amplitude of vertical frequency convergence wave required for the blue beam may, in speciic'instances, be quite small. In such event, a separate source 'of direct current may be vprovided for the blue convergence winding to furnish the requisite amount of direct current compensation for that beam.

It will be recognized by those skilled in the art that the apparatus of the present invention lends itself to setting up the convergence in a three beam color kinescope with a cross-hatch pattern of horizontal and vertical bars. That is, video signals representative of such a pattern may be applied to the several beams such that, when the `rbeams are properly converged, the image produced on the kinescope screen is that of a black and white crosshatch pattern. A simple static convergence set-up procedure which may be followed when using such a crosshatch pattern is as follows:

(l) Adjust the red-green vertical static convergence control (potentiometers 95 and 98) until the associated red and green horizontal bars of the pattern are coincident. l

(2) Adjust-the lateral static convergence component via potentiometer 94 until a given blue vertical bar lies vmid-way between its associated red and green vertical bars.

use; of i the cross-connected potentiometers 95 and 98 whereby, through the agency of a single control, the direct current energy applied to the red magnet, for example, is increased as the direct current energy applied to the green magnet is decreased (and viceversa), a similar beam controlling action may be realized in other manners. vFor example, while the vertical frequency exciter coils of the magnets 29, 30 and 31 described herein are assumed to be wound in the same direction, and energized in the same direction, the windings ofthe coils 41-42 may be reversed with respect to the direction of winding of the coils 41"-42, in which case both of the two magnets could be energized from a single potentiometer, insofar as vertical static convergence is concerned, since the desired diierential movement of the red and green beams would be aorded from the single potentiometer. That is, assuming an increased direct current voltage is applied to the two magnets whose coils are oppositely wound, one of the beams would be moved toward the center or axis of the tube, while the'other l1 t t beam would be moved farther from the axis of the tube. A decrease in the direct current voltage applied to the magnets would, on the other hand, move the beams in the opposite directions. rangement is employed, however, the horizontal static `convergence control would involve the use of an arrangement such as the cross-connected potentiometers 9S and 98 for moving the red and green beams in the same direction with respect to the center of the tube (i. e., both moved toward the center or both moved away from the center). Also, this second arrangement would require the reversal of phase of the vertical frequency convergence and tilt waves applied to one of the magnets, so that the dynamic convergence action would remain in the proper sense.

Having thus described our invention, what We claim as new and desire to secure by Letters Patent is:

l. In a cathode ray tube image-reproducing system `wherein a plurality of electron-beam components, which traverse pre-deflection paths spaced respectively about the horizontal axis of the tube are angularly deflected by j horizontal and vertical beam deflection apparatus to scan a raster at a target electrode, the combination comprising; a plurality of beam convergence structures respectively mounted adjacent to such pre-deflection paths, each of said structures being arranged to effect radial movement of its associated beam component; a source of direct current static convergence energy; and adjustable `means including a potentiometer for applying energy from said source in inverse relationship to first and second ones of said structures, said adjustable means and said first yand second structures being operatively connected in such manner that, for a given adjustment thereof, the energy supplied to said iirst structure is decreased Awhile the energy supplied to said second structure is increased whereby the beaml component acted uponfby said iirst structure is moved away from the axis of said tube while the beam componentacted upon by said secondstructure is moved toward the axis of said tube, both of said movements being along radii of said tube.

2. In a cathode ray tube image-reproducing system wherein a plurality of electron beam components, which traverse pre-deflection paths spaced respectively about the horizontal axis of the tube are angularly deflected by horizontal and vertical beam deection apparatus to scan a raster at a target electrode, the combination comprising: a plurality of beam convergence ield producing structures respectively mounted adjacent to such pre-de ection paths, each of said structures being arranged to eiect radial movement of its associated beam component; a source of direct current static convergence energy;

. adjustable means forapplying energy from said source to first and second ones of said structures, said adjustable means and said irst and second structures being operatively connected in such manner that, for a given adjustment thereof, the field produced by said rst strucn,ture is varied in one sense so that the beam component j acted upon by said first structure is moved away from the axis of said tube while the field produced by said l second structure is varied in the opposite sense so that the beam component acted upon by said second structure is moved toward the axis of said tube, both of said movements being along radii of said tube; and means operatively connected to said first and second structures` for applying direct current energy to said structures in Where this latter type ofy arl the same sense and in such manner as to move the beam components controlled thereby in unison along said radii `and in the same direction with respect to the axis of said tube.

3. In a cathode ray tube image-reproducing system j wherein a plurality of electron beam components, which by horizontal and vertical beam deflection apparatus to scan a raster at a target electrode, the combination"` comprising: a plurality of beam convergence rtield producing structures respectively mounted adjacent yto such pre-detiection paths, each of said structures being arranged to eifeet radial movement of its associated beam component; a source of direct current static convergence energy; and adjustable means for applying energy from said source to rst and second ones of said structures to energize said iirst and `second structures in inverse relationship, said adjustable means being of fsuch character that, for a given adjustment thereof, the direct current energy applied to said first structure is increased While the direct current energy applied to said second structureis decreased. y.

` 4. In a cathode ray tube image-reproducing system wherein a plurality of electron beam components, which traverse pre-deflection paths spaced respectively yabout the horizontal axis of the tube are angularly deiiected` by horizontal and vertical beam deiection apparatus to scan a raster at a target electrode, the combination comprising: `a plurality of beam convergence eld producing structures respectively mounted adjacent to such pre-deflection paths, each of said structures being Iarrartrlged to effect radial movement of its associated beam component; a` source of direct current static convergence energy;

`adjustable means for applyingr energy from said -source to first `and second ones of said structures, said adjustable means `and said first and second `structures being operartively connected in such manner that, lfor a given ad- .ments being along radii `of said tube; adjustable means for applying direct current static convergence energy to a kthird one of said structures,y energization of said third structure having an interacting effect` upon the fields produced by said first and second structures; and means connected between said last-named means and said rst and second structures for applying to said irst and second structures direct current energy of such amplitude and sense as to compensate for the effect of said third structure upon the fields produced by said first and second structures.

5. In a cathode ray tube image-reproducing system wherein first, second and third electron beams, which `traverse pre-deflection paths spaced respectively about the horizontal axis of the tube are angularly deliected by horizontal and vertical beam deection apparatus to scan a raster at a target electrode, the combination comprising: rst, second and third beam convergence magnet structures respectively mounted adjacent to such pre-deection paths, each of said structures being arranged to eiect radial movement of its associated beam; a source of direct current static convergence energy; adjustable means for applying energy from said 'source to irst and second ones of said structures for causing each of said first and second structures to produce a magnetic field, said adjustable means and said irst and second structures being operatively connected in such manner that, for a given adjustment thereof, the beam acted upon bysaid tirst structure is moved away from the axis of said tube while the beam acted upon by said second structure is moved toward the axis of said tube, both of said movements lbeing along radii'of said tube; means for energizing said third magnet structure with direct current energy to cause it to produce a magnetic iield` for moving said third beam along a radius of such tube, there being undesirable interaction between said last-named lield and the elds produced by said rst and second structures; and mean-s operatively connected between said last-named energizing means and saidrst and second structures for applying to said first and second structures direct current energy of such 13 magnitude and sense as to counteract such undesirable interaction.

6. In a cathode ray tube image-reproducing system wherein a plurality of electron beam components, which traverse pre-deection paths spaced respectively about the vhorizontal axis of the tube, are angularly deflected by horizontal and vertical beam deection apparatus to scan a raster at a target electrode, the combination comprising: a plurality of beam convergence structures respectively mounted adjacent to such pre-deflection paths, each of said structures Ibeing arranged to effect radial movement of its associated beam component; a source of direct cur-r contact members being connected to said second structure, and means connecting said potentiometers to said source in opposite sense with respect to each other, such that, for a given adjustment of said contact members, the direct current energy applied to said rst structure is increased while the direct current energy applied to said second v structure is decreased.

7. The invention as defined by claim 6 including a third potentiometer connected across said source and having an adjustable output terminal, and means for applying energy from said terminal to said rst and second structures in the same sense.

References Cited in the le of this patent UNITED STATES PATENTS 2,707,248 Goodrich Apr. 26, 1955 27,742,589 Goodrich Apr. 17, 1956 2,743,389 Giuffrida Apr. 24, 1956

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