US2950407A

US2950407A - Electric beam controlling apparatus

Info

Publication number: US2950407A
Application number: US629870A
Authority: US
Inventors: William H Barkow; Martin W Schmutz
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1956-12-21
Filing date: 1956-12-21
Publication date: 1960-08-23
Anticipated expiration: 1977-08-23

Description

Aug. '23, 1960 w. H. BARKOW ETAL 2,950,407

ELECTRIC BEAM CONTROLLING APPARATUS Filed De c 21, 1956 2Sheets-Sheet 1 1! TTOR NE Y Aug. 23, 1960 w. H. BARKOW ETAL 2,950,407

ELECTRIC BEAM CONTROLLING APPARATUS Filed Dec. 21, 1956 2 Sheets-Sheet 2 IN V EN T 0R5 nited 2,950,407 ELECTRIC BEAM CONTROLLING APPARATUS Filed Dec. 21, 1956, Ser- No. 629,870

15 Claims. ((31. 313-70) This application is a continuation-in-part of application Serial No. 405,175, filed January 20, 1954, now forfeited.

The present invention relates to new and improved cathode ray image reproduction apparatus and, more particularly, although not necessarily exclusively, to beam controlling apparatus for use with multiple gun kinescopes of the variety employed in color television receivers.

While the invention will be described herein in connection with a three-beam color kinescope of the shadow mask type, such as is described in an article entitled A Three-Gun Shadow-Mask Color Kinescope by H. B. Law in the Proceedings of the IRE, October 1951, its applicability to other types of image reproducers should be borne in mind.

In the three-beam shadow-mask color kinescope described in the cited article, three electron beams are employed, one for each selected component color. The beams strike a phosphor screen composed of a regular array of red, green and blue light emitting phosphor dots. Between the electron gun position and the phosphor screen there is placed a thin perforated metal sheet which masks the electron beams. The phosphor screen is made up of closely spaced trios of phosphor dots on a glass plate, each trio consisting of red, green and blue luminescing dots, with the centers of the dots lying at the corners of an equilateral triangle. The trios themselves lie at the corners of a still larger equilateral triangle. Associated with each of the phosphor trios is a hole or aperture in the shadow mask, such holes also being located at the corners of an equilateral triangle. The three beams, located 120 apart about the longitudinal axis of the tube are converged to a point on the mask by an electron lens system. The electron beam which is to con tribute the red portions of the picture is prevented by the mask from striking those areas on the screen containing blue and green light-emitting phosphors. Similarly, the green and blue beams are permitted to strike only the green and blue phosphor dots, respectively.

The fabrication of the phosphor screen of the three beam shadow mask tube includes the coating of a glass plate used as the screen support with a film of photosensitive phosphor material. The apertured mask is mounted adjacent to the coated plate in the same position that it will occupy in the completed tube. The photosensitive film is exposed through the mask to a point light source placed at a point simulating a color center of the completed tube. The color centers of a three beam tube are those three points within the tube from which the three electron beams, at any one time, appear to emanate, after the beams have been deflected by the scanning yoke. After exposure, the unexposed portions of the phosphor film are removed and a second photosensitive phosphor film is applied to the glass plate surface and the plate again exposed to the point light source placed at a second color center. Again the unexposed phosphor film areas are removed from the glass plate and a third film is applied to the plate and exposed from the third color cen- States Fatcnt O ice ter. Again after removing the unexposed portion of the third film, there remains on the glass plate three dot patterns, each of a dilferent light emitting phosphor material.

The electron gun assembly and the phosphor screen are fabricated independently and only in the final assembly of the color tube parts within the envelope are they brought into an operative relationship. Since the screen was formed from accurately determined simulated color centers, it is necessary in the operation of the completed tube to insure that the three electron beams of the gun assembly will have color centers coinciding with the simulated centers used to form the phosphor screen. Because of the manufacturing tolerances obtained by mass production techniques in fabricating the electron gun, it has been found necessary to provide corrective means to insure that the color centers of the electron beams of each tube will substantially coincide with the simulated color centers used to form the screen of the tube. Such corrective means have been found necessary in most vcases to provide color purity of the picture formed on the tube screen during tube operation.

In some tubes used for color television or for other purposes, only a single beam may be used. The operation of such tubes may require that the beam be sequentially deflected oft the gun axis in difierent directions to effectively produce three beam portions approaching the tube target from ofi-axis positions to which the beam was deflected. For color television it is again important that the beam portions pm through their proper color center-s.

It is therefore an object of the present invention, to provide new and simplified means for providing color purity in a cathode ray tube used for viewing a color image.

A further object of the present invention is the provision of means for affording color purification in a color cathode ray tube in a novel and simple manner.

It is another object of this invention to provide color purity in a plural beam cathode ray tube by novel means for correctly positioning the color centers of the beams.

The present invention is a device for obtaining color purity in a plural beam color tube. The device includes three metal rings, each of which is rotatable about the axis of the cathode ray tube. Two of the rings are magnets and the third ring is a washer of high permeability material. The assembled rings are supported coaxially on the axis of the neck. The relative positions of the magnet rings determine the direction and value of the resulting magnetic flux, which is used to position the sever-al beams of the tube so that they pass through the proper color centers in the deflection region of the tube.

Additional objects and advantages of the present invention will become apparent from a study of the following detailed description of the accompanying drawings, in which:

Figure 1 is an elevational view, partially in section, of a tri-gun shadow mask color kinescope in association with apparatus embodying the principles of the present invention;

Figure 2 is a vertical sectional view along line 2-2 of Figure 1, with parts removed in the interest of simplicity;

Figure 3 is an exploded view of one form of the invention, and

Figure 4 is an exploded view of another form of the invention;

Figures 5 and 6 are partial sectional views of alternative arrangements of the structures of Figures 1-3.

Referring to the drawing, there is illustrated in Figure l a tricolor kinescope 10 of the type described in the above mentioned Law article, which kinescope includes triangle. I v are 'show'n,cbut it will be understood that each of the in the'vicinity of the target structure.

' the electron beamsi beain alignment of beam positioning apparatuscomprises threeper-manent magnets 'such as the one shown at 34.1 Each of the magnets 34 is or may be in the form I which are described in detail in the article. Three electron guns are located within the neck portion 16 of the kinescope and are arranged at -the apices ,of an equilateral In the drawin'g, only two of the three guns guns includes an indirectly heated cathode 18 enclosed within a cylinder 20 (closed at the target end by an 'aperture'd disc) which cylinder serves as the control grid. 'Each gun-further includes an accelerating cylinder 22,

having'an apertured endplate at its target end and a second or beam focusingaccelerating cylinder 24, which includes alimiting aperture disc 26. The kinescope is.

also provided with a substantially cylindrical accelerati-ng convergence electrode 28, which is common to and surrounds the paths of all three guns. Another important part of the electronsystem of the kinescope is the final or' beam-accelerating "electrode 30, which is illustrated 'herein as a conductive wall coating, formed on the inner surface of thekinescope and which extends from the 'neck'thereof in the vicinity of the convergence electrode 28' along the flared bulb envelope portion to a region Respective electron lenses formed between the individual beam-focusing electrodes 24 and'the common con- "vergeace electrode 28,whe'n all are suitably energized,

function toeffect independent focusing of the individual electron beams so that they may have minimum spot sizes mask-14. a conventional manner, the kinescope 10 is further provided with a deflection yoke 32 seated on 4 the tube neck, as showrnfor effecting the desired raster scanning deflection of the beams and which may comprise the usu-alarrangement of horizontal and vertical deflection windings assembled so that the yoke is substanti-ally anastig'matic.

' ;Als"oill'ustrated inthe. interest of completeness of description are means for efiecting rotatable positioning of Briefly, such means, known as of a magnetized threaded bolt, held in spaced relation ship 120 apart about the'lohgitudinal axis of the tube),

as-by means of ;a cylindricaljnember 36 secured rigidly to thetube neck through the agency of a clamp member 38 and struts 40.- The cylindrical member 36 may be i formed of high permeability material in order that it may serve additionally as shielding'means. Thus, it will be understood that each of the. magnets 34 may be adjustably-positioned with respect to a different one of the "electron beams in such manner as to effect what amounts to arotational alignment or radialpositioning of the beam, in orderthat the beam is initially directed toward its properlposition atthe' shadow mask 14.

The electron gun structure of the color tube may consifst'of several electron guns or a single common gun' structure for producing three electron beams angularly spaced 120 about the axis of the tube neck.

The phosphor screen 12 of the shadow-mask color tube is normally 'tabricatcdby coating a glass plate 13 with "a:photosensitive'phosphor film. The glas's plate may be a separate plate mounted within the tube envelope, 'or

' may be the faceplate of tube envelope. The apertured mask 14 is mountedin a predetermined spaced relation;

ship to the glass plate; The photosensitive phosphor film isexposed to a pointlight'source positioned so that lightpas sing throughthe apertured mask will strike the photo-sensitive film in areas to which the electron beams willbe directed in the finished tube. The positioning of thelightsource is, thus, critical and is at points spaced 'from'the mask corresponding to the three color centers y and the projection of the beam path after deflection.

Thus,.the three color centers are within the tube neck portion enclosed by the deflection yoke. Because the alignment of the tube gun structure withjthe tube neck provides three beams angularly spaced about the tube axis, the three color centers also have the same angular spacing. V a V The phosphor screen is fabricated by placing the exposing light source at a first point, corresponding to a first color center, to expose the phosphor screen through the apertured mask in dot areas to be struck by one of the electron beams in the finished tube. .The unexposed phosphor film is removed and a second photosensitive film of a different color luminescent phosphor is coated over the glass plate The light source ismoved to a second pointgcorresponding to a second color center and the phosphor film exposed to form a second set of tofo'rm the respective screens. This'results in the electron beam of a particular tube following paths difierent from those of the light used to produce the phosphor dot patterns of the screen. Thebeams, then, will.strike phosphor areas other than those forwhich they are intended and will produce colon'dilution. It is necessary,

in tubes of this type, to provide corrective means to ensure that theelectronlbeams of each tube will have color centers substantially coinciding with the simulated centers used to form the screen of the tube, in order to provide color purity of thepicture. Y I

' In accordance with the invention, there is provided means for shifting the three beams, of the tube of Figure l,-as a group with respect to the tube axis. Such shifting isrin'addition to the alignment function performed by the' positioning magnets '34; lnaccordanc'e with a lepecific embodiment of thepresent invention such shifting forcolor purificationfis accomplished through the agency 7 0 of the'apparatus indicated generally by reference numeral 44-. As shown in Figure l, the color purity apparatus 44' comprism a pair of ring or annular permanent magnet elements or'members 4'6 and and'an annular shunting elementorwasher memberefi of material; which has-high permeability at low flux densities, but, which saturates'rapidly for greater flux densities. The two ring magnet elements "46 ands? and shunting member 50 are of equal inner diameter andare' supported coaxially with l respecfltothe neck of the kines cope 1G by means of a non-magnetic holder 52. Shunting member 50 is thinner "than magnetelements 46 and 48. 5

Insofar as the specific material of which the washer' member 50 is formed is concerned, the specifications set forth abovetherefor describe the particulari'p'roperties.

"One 'well known material which may be employed is that manufactured and '{sold bylthe Allegheny Ludlum Steel Corpora'tion under the registered trademark Mu metal, which comprises a nickel copper-iron alloy having high-permeability at low 'fiux' densities. A typical compositionof Mumet'al is7-7';2 percent nickel, 4.8 percent copper, -1 .'5 percent chromium and theb'alance iron. Each o'f the ring magnets i-G and 47 is provided with 7 radial extensions -or tabs A6 and 48, respectively, for ease of manipulation. "Moreover, the tabs 16' and 48' may be bent out of the planes ofthe r'r'iagnets'themselves in-order to facilitate 'grasping of the tabs.' The m-agnets are, perhaps, better seen in the view of Figure 2 in their relationship to both the cathode ray tube neck 16 and the holder 52.

The holder 52 comprises a strip of insulating material such as nylon formed into an equilateral triangle with its overlapping ends heat-sealed as at 54. Each apex of the triangular nylon holder is provided with a slot, as shown in Figure 3, which slots are indicated at 56. The depth of the slots 56 is so chosen that the

ring magnet elements

46 and 48 and the Mumetal shunting washer member 50 are held within the-slots coaxially with the center of the triangle. The width of each of the slots 56 should be no greater than is necessary to accommodate the ring magnets and washer with a slightly frictional fit. ber 52 should be such that the holder fits snugly about the kinescope neck 16. Since the nylon material is somewhat flexible, the holder may be slightly smaller than the tube neck so that its sides bow to accommodate the tube, whereby a tight fit is afforded. By virtue of the triangular shape of the holder 52, the magnetic holder is self-centering with respect to the neck of the kinescope 10. That is to say, since the holder contacts the tube neck at three equally spaced points, the ring magnets and washer may be automatically centered about the longitudinal axis 16' of the tube (represented by the cross mark in Figure 2). With the nylon holder 52, no metal contacts the tube neck. This eliminates possible scratching of the glass neck. Also, the nylon holder provides a better bearing surface against the glass.

Each of the

ring magnets

46 and 48 is magnetized along a diameter, as shown for example, by the north and south pole designations N and S and the arrows, shown in Figure 3. Thus, it will be understood that, when the tabs of the two

magnets

46 and 48 are together with the magnetic fields in alignment, the combined magnetic field across the diameters of the two magnets is at its maximum value. When one of the magnets is rotated 180 about an axis normal to its plane, the resultant magnetic field will be at its minimum value.

There have been previous proposals for permanent magnet centering devices, such as have been suggested for use with single beam kinescopes, which bear a general resemblance to the ring magnets forming a part of the present invention. These devices include only a pair of magnet rings, magnetized across their diameters. Such prior art devices act upon a single beam, the cross-sectional diameter which may be of the order of 100 mils. When the two magnets of these prior devices are rotated so as to oppose each other, the magnet fiux field at their centers is sufliciently zero so that the beam is unaffected. However, the flux field, as measured from the center radially outwardly to the rings, has a gradually increasing, finite value. Such a zero field is not sufiicient for use in the present type of arrangement, wherein three beams are spaced a substantial distance from the central axis of the tube, such that the beams are for example, located perhaps /2" from each other. This latter arrangement is illustrated in Figure 2, wherein the beams produced by the electron guns of kinescope 10 are shown at 60, 62 and 64. Moreover, it has been found that such a gradually increasing field, supplied by these prior art structures, is not suificiently uniform for all points on concentric circles about the tube axis. Thus, each of the three beams of the color tube would be subjected to a magnetic field different from that acting upon each of the other beams. With such a magnetic environment, undesirable mispositioning and distortion of the beams are necessary results which are obviated by means of the present invention.

More specifically, in accordance with the invention the Mumetal washer 50, having a high permeability at low flux densities, serves as a shunt or short circuit for the weak field which is present when the two

ring magnets

46 and 48 are diametrically opposed. That is to say,

The internal dimensions of the triangular memthe fiu'x lines, which are present, travel short-circuit-wise through the washer and are prevented from passing through the neck of the kinescope, where their influence is undesired. Since the Mumetal washer saturates readily, the stronger magnetic fields, which are produced when the magnets are not opposed are permitted to pass through the tube to effect the color purification desired.

The magnetic field required for beam correction by the

magnets

46 and 48 is relatively small. The maximum field at the center of the two magnet rings is in the order of 9 gauss. When the

rings

46 and 48 are turned so that their fields mutually buck-out, or oppose each other, the minimum field at the center of the rings is in the order of 0.1 gauss. Since this is a very weak field, its action on the electron beams is effectively zero. Without the shunting ring 50, however, it would be quite impossible to obtain as low a field as 0.1 gauss within the magnet rings.

What has been described above are magnet rings, which are being used successfully in accordance with the invention, with color tubes of the type described. Each alone produces a field across its center in the order of 4 to 5 gausses. Each magnet of the assembly 44 is magnetized uniformly. It has been found desirable that the magnet rings 46 and 48 be of the same shape and size so that the fields of the magnets will more effectively buck-out when the magnets are turned to oppose each other. High quality metal is preferred, since non-uniformity in the metal of the magnet results in non-uniformity of the field of the magnet and thus, hinders the bucking-out of one field by the other. The

magnets

46 and 48 are thus matched as closely as possible. Differences caused by mismatching of a pair of magnets due to production tolerances are compensated for by the shunt washer 50, when the magnets are positioned in the range of adjustment for a minimum field. The magnet rings are easily magnetized in a manner similar to that used for magnetizing speaker magnets. The procedure is that of placing the rings in a high density unidirectional magnetic field, until the desired magnetism is estabilshed across each ring.

The size of the magnets, as well as of the shunt washer ring 50 is not critical. However, dimensions are minimized to provide a device of lowest cost which will provide the desired results. It is preferable that the shunt ring he of a material which will saturate above low field strengths. The washer 50 of mu-metal is thick enough to function as a magnetic shunt element yet thin enough to saturate in the desired manner. The magnets are designed to provide the desired range of field strengths across their diameters. Stronger magnets can be used, but this would require a thicker shunt ring with a resulting increase in cost of materials. The

magnets

46 and 48 may be made of appropriate magnetic material. However, it has been found that spring steel has proved to be a less expensive material, and is sutficient for the purpose described.

It is possible that other shapes of the rings 46, 4S and 59 may 'be used. For example, washer 50 could consist of a tubular ring encircling

tubular magnets

46 and 48. This, however, would be a more expensive design.

The shape of

magnets

46 and 48, as shown in Figure 3, need not be limiting. However, the design of the magnets, as shown, appears to provide the optimum effects desired. The

magnets

46 and 48 may be segments of rings mounted in an insulating holder. The arcuate or ring-shape of

magnets

46 and 48 and shunting ring 50 appear to be an optimurn configuration. The arcuate ring shape provides greater uniformity of the magnetic field and is easily duplicated from magnet to magnet in production, which results in optimum bucking effects between opposed magnets. Furthermorqthe arcuate shape provides a consistently good centering of,

beam gun.

Jenny. the beam at the color centers is also important; The

assembly and shows the shunting ring 56 on one side of the magnet rings 46 and 48. cordance with the invention thatring 50 need not be "sandwiched between'the magnet rings 46 and 48, but

can be positioned on either side of the magnet rings to a provide the desired shunting efiect. The assembly shown in Figure 4 includes a nylon triangular support structure '52" having supporting notches 56 corresponding 'to notches 56 of the structure of Figure'3. Fastened along each side of the triangular support rod 52' is a spring wire 70,.Which is threaded through apertures 72 at the corners of the triangular support. Wires 70 add a cer tain resilience to the nylon support and help to hold it securely to the round neck of the tube, when the magrings 46 and 48 which are positioned next to each other. This is the same arrangement shown in Figure 4. If desirable anon-magnetic ring 51 such as brass, fiberboard'or the like may be assembled on support 52 with 'rings 46, 48 and .50, to add lateral support to the thin washer 50. Figure 6 shows an arrangement of two shunting washers 50 and 50', one on either side of the It was found, in ac two adjacent magnet rings 46 and 48 for the purpose of producing a more symmetrical field produced by the structure of Figure 4. This arrangement is feasible, if

the two washers 50 and 50' will both saturate at the low field density present when magnets 46 and 4-8 are aiding each other. It is also possible to use a third shunt 'washer between'magnets 46 and 48 in the arrangement of Figure 6. Again all'the shunt washers should saturate at the low flux density in accordance properties may be employed. Additionally, any other non-magnetic material having the requisite mechanical strength and flexibility may be substituted for the nylon described above as the material of which the triangular holder 52 is fashioned.

The position of the novel beam alignment device 44 on the tube neck need not belimited to the position shown in Figure 1. On some successfully operated tubes the assembly 44 is positioned adjacent to the focus lens between electrodes 26 and 28. However, the device can be used anywhere on the tubeflfrom the gun cathode position to the apertured mask 14, to provide color purity.

The use of the alignment device 44 has been described specifically with respect to a three bearntubev However, some color television picture tubes utilize a single 7 The single-beam is sequentially directed along aplurality of beam path which approach the target of the tube from different directions. A tube of this type is disclosed in U.S. .Patent 2,581,487 .to-D. A. In single beam multi-path tubes, alignment of above described alignment device 44 can also be used with'single beam tubes :of this type in the manner detheir diameters; means for supporting said magnets co-' axially with and forrotation about the neck of a cathode ray tube; and an annular member disposed between ,8 said magnets; said annular, member being of high permeability at low flux densities. a V

2. The invention as defined by claim l'wherein said annularmembe'r comprises an iron alloy washen 3 Electron beam controlling apparatuscomprising a pair of annular permanent magnets, each magnetized along its diameterya washer of high permeability; and means'for supporting said magnets and washercoaxiallytwith and for rotation about the neck of a. cathode ray tube, said means comprising a triangular member of non-magnetic material whose internal dimensions are sufiicient to accommodate tightly the neck of a cathode ray tube, said triangular member having means on its apices for holding said magnets in axial alignment with each other.

' magnetized along its diameter; an annular washer of high permeability material disposed between said magnets, said washer and said magnets having substantially equal internal diameters greater than the external diameter of the neck of such cathode ray tube; and means including a holder for maintaining said magnets and said washer in axial alignment With each other and coaxially with such tube.

5. The invention as defined by claim 4 wherein said washer of high permeability is readily saturated by a relatively strong magnetic field.

6. In combination with a cathode ray color image reproducing tube having a neck portion, a target area and means within said neck portion for directing a plurality of electron beams along spaced paths toward said target, beam controlling apparatus for 'adjustably positioning said beams with respect to the .axis of said tube, which comprises: a pair of annular magnets, each permanently magnetized along its diameter; an annular washer having high permeability to relatively low flux densities, said washer being disposed coaxially with and betweensaid magnets; and means for supporting said washer and 'magnets around and coaxially with said tube neck and of electron beams along spaced paths toward said target and beam alignment means for providing each such beam with a predetermined location relative to another of such beams, electron beam controlling apparatus disposed. between said beam alignment means and said target area for adjustably positioning said beams with respect to the axis of said tube, which comprises: a pair of annular permanent magnets, each magnetized along its diameter;

means for supporting said magnets coaxially with and for rotation about the axis of said tube; and anannular Washer member disposed between and substantially coaxially with said magnets, said Washer being of material having high permeability at low flux densities whereby to provide a zero field strength within said tube when said magnets are arranged with their opposite poles in substantial juxtaposition.

9. A magnet device for a cathode ray tube, said magnet device comprising a plurality of annular elements, means coaxially mounting said elements adjacent to' each other, at least two of said annular elements including a magnet, another one of said annular elements being of material having a high magnetic permeability at low magnetic flux densities a 10. A magnet device for a cathode ray tube, said magnet device comprising a plurality of annular elements,

means coaxially mounting said elements adjacent to each other, at least two of said annularelements being diametrically magnetized to provide a magnetic field across each of said two annular elements, another one of said annular elements being of material having a high magnetic permeability at 10W magnetic flux densities.

11. A magnet device for a cathode ray tube, said magnet device comprising a plurality of rings, means coaxially mounting said rings adjacent to each other, at least two or" said rings having magnetized portions positioned to provide a magnetic flux diametrically across each of said tWo rings, another one of said rings being of material having high magnetic permeability at low magnetic flux densities.

12. A magnet device for a cathode ray tube, said magnet device comprising a plurality of rings, a mount structure supporting said rings in contact with each other and for rotational movement about a common axis through the center of said rings, at least two of said rings being magnetized along their respective diameters, a magnetically permeable element mounted adjacent to said rings, said permeable element being of a material having the property of high magnetic permeability at low magnetic flux densities, said permeable element being formed of material which saturates rapidly at greater flux densities.

13. Electron beam controlling apparatus comprising a pair of annular permanent magnets magnetized along their diameters, means supporting said magnets for rotation about a common axis through their centers, and an annular member coaxially mounted in contact with one of said annular magnets, said annular member being of material having high permeability at low flux densities.

14. A color purity magnet device for use With a plural beam cathode ray tube, said magnet device comprising a pair of annular permanent magnets, means mounting said magnets adjacent to each other on a common axis, and a shunting element of a material having high magnetic permeability at low flux densities supported by said mounting means adjacent to said magnets.

15. An electron discharge device comprising a tubular envelope portion, an electron gun structure within said envelope for providing a plurality of beams spaced from the axis of said envelope portion, a pair of permanent magnets magnetized along their diameters, means supporting said magnets on said tubular envelope portion for a rotation about said axis, and an annular member coavially mounted With said magnets, said annular memoer being of material having high permeability at low flux densities.

References fitted in the file of this patent UNITED ST TES PATENTS 2,544,898 Obszarny Mar. 14, 1951 2,568,668 Steers Sept. 18, 1951 2,653,262 Bowman Sept. 22, 1953 2,854,598 Baermann Sept. 30, 1958 FOREIGN PATENTS 501,931 Great Britain Mar. 8, 1939