US2923844A - Cathode ray tube structure including convergence system - Google Patents

Description

Feb. 2, 1960 E. GUNDERT 2,923,844

CATHODE RAY TUBE STRUCTURE INCLUDING CONVERGENCE SYSTEM Filed Jan. 11, 1957 2 SheetsSheet 1 lNvENToR:

EBERHARD GUNDERT,

Fb. 2, 1960 E. GUNDERT 2,923,844

CATHODE RAY TUBE STRUCTURE INCLUDING CONVERGENCE SYSTEM Filed Jan. ll, 195'? 2 Sheets-Sheet 2 INVENTORI EBERHARD GUNDEIRT,

United States Patent CATHODE RAY TUBE STRUCTURE INCLUDING CONVERGENCE SYSTEM Eberhard Gundert, Ulm (Danube), Germany, assignor to General Electric Company, a corporation of New York Application January 11, 1957, Serial No. 633,568 Claims priority, application Germany February 4, 1956 1 Claim. (Cl. 313-70) My invention relates to cathode ray tubes and pertains more particularly to a new and improved cathode ray tube structure including new and improved means adapted for effecting convergence of electron beam components therein.

Color cathode ray tubes to which the present invention is particularly, although not exclusively, applicable generally include a luminescent screen comprising part of a target electrode structure in which different phosphor areas produce differently colored light when excited by electron beam components impinging thereupon, means for producing and directing a plurality of electron beam components toward the target electrode and means for deecting the beam components thereby to scan a raster at the target electrode. ln such tubes it is generally necessary to provide means for effecting substantial convergence of the dierent electron beam components at the target electrode structure, thereby to provide desired image rendition and color fidelity. Heretofore, various means have been resorted to in attempts to accomplish satisfactory beam convergence. However, many have been found generally unsatisfactory in that they resulted in complicated and expensive tube constructions, required considerable complicated control equipment, or -had undesired effects on the operation of other tube components. Accordingly, the primary object of the present invention is to provide a new and improved cathode ray tube structure including new and improved electron-beam deiiecting means.

Another object of the present invention is to provide a new and improved color cathode ray tube structure including new and improved means for effecting convergence of beam components therein.

Another object of the present invention is to provide a new and improved arrangement for magnetically effecting beam convergence.

Still another object of the present invention is to provide a new and improved beam-convergence arrangement which is simple and less expensive in construction, provides improved color quality and is operable with a minimum of control equipment.

Fur-ther objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the obiects of my invention, I provide a cathode ray tube including an envelope containing a target electrode structure, and means for producing and directing several electron beam components toward the target electrode structure. Straddling each of the outer ones of the beam components is a spaced pair of magnetic pole pieces and straddling an intermediate beam component is a similar pair of pole pieces extending transverse to and through the planes of the others. Means are provided for establishing predetermined magnetic fields between the pole pieces to align substantially coplanarly the -associated lbeam components.

Other magnetic means is i 2,923,84f-i Fatented Feb. 2, 1960 provided for rotating the beam components about an axis of the tube for thus effecting direction of the beam components toward the target electrode in a predetermined plane. By means of the pole pieces the beam components are converged in the predetermined plane and at the target electrode. The pole pieces comprising each pair may be unequally spaced radially throughout the lengths thereof to effect a predetermined desired field distribution therebetween.

For a better understanding of my invention, reference may be, had to the accompanying drawing in which:

Figure l is a schematic fragmentary illustration of one embodiment of the present invention;

Figure 2 is a sectional view taken along the line 2 2 in Figure l and looking in the direction of the arrows;

Figure 3 is a diagrammatic illustration of convergence effects attainable with the present invention;

Figure 4 isanother diagrammatic illustration of other convergence effects attainable with the present invention.

Referring to Figure l, there is shown a color cathode ray tube structure generally designated 1 including an envelope 2 having a cylindrical neck portion 3, a transparent viewing end or face plate portion 4 and a substantially conical transitional portion 5.

Located at the viewing end of the envelope 2 is a target electrode structure generally designated 6. The structure 6 includes the face plate portion 4 of the envelope, a phosphorescent material coating or screen 7 on the inner surface of the face plate portion 4, which screen preferably comprises phosphors capable of producing light of different colors in response to any impingement thereon by charged particles or electrons. The screen 7 preferably comprises red, green and blue light-producing phosphors deposited or arranged on the inner surface of the face plate in repeated triades of vertical red, green and blue phosphor stripes, in the manner illustrated exaggeratedly in Figure l at R, G and B.

Formed over the screen '7 is an electron permeable conductive layer 8 which can comprise aluminum or any other suitable conductive material and constitutes what shall hereinafter be referred to as the first electrode in the target electrode structure 6. Also included in the target electrode structure 6 and provided for cooperating with the first electrode S is a second electrode in the form of a grille generally designated it). The grille 10 cornprises a plurality of closely spaced wires 11 extending substantially parallel to each other and to the stripes of phosphorescent material comprising the screen 7. The size .and spacing of the grille wires 11 are also illustrated exaggeratedly in the drawing.

By means not shown, the second electrode 10 is supported for conforming substantially to the curvature of the face plate 4 so as to provide substantially uniform spacing between the first and second electrode 8 and 10, respectively, across the target electrode. In the justdescribed target electrode structure the rst electrode 8 is adapted for being maintained at a potential higher than that of the second electrode 10, thereby to set up and maintain a predetermined electric field in the inter-electrode region defined by the electrodes. By virtue of its construction, the second electrode 1t) is permeable to charged particles or electrons directed toward the screen. Thus, during the operation of the tube 1, electron beams or beam components directed toward the electrode by beam producing means, which will be described hereinafter, are admitted into the inter-electrode region through the spaces between the wires 11 and travel through this region for striking or impingng upon the phosphorescent material screen 7. in the inter-electrode region the higher potential of the conductive layer or first electrode 8 is effective for attracting and thereby accelerating the movement of the electrons comprising the beam components toward the screen thereby to lincrease the striking force of ythe electrons on the screen whereby color brightness is increased. Additionally, the second electrode serves properly to focus the electron beam components entering the inter-electrode region and to direct them onto the phosphor stripes in a predetermined desired manner.

Provided for producing the electron beams or beam components for impinging on the screen and located in the neck portion 3 of the tube envelope is a plurality of electron beam or beam component producing means or guns 12. The guns 12 are equal in number to the number of primary colors in which an image is to be reproduced on the screen 6; and, therefore, in the illustrated embodiment three guns are provided. Each of the guns 12 may be of the conventional type, consisting of a cathode, a control grid, one or more accelerating electrodes, and a focusing electrode, none of which component elements need be specifically illustrated or described. The three guns 12 are suitably connected through an insulative tube base 13 to a conventional video signal source generally designated 14; and, in accordance' with color intelligence received from the source 14, the guns 12 produce and direct toward the target electrode 6 schematically-represented beam components 15, 16 and 17.

It will be seen that, while I have shown and described the beam component producing means as constituting a plurality of individual electron gun structures, any means may be employed for producing and directing toward the target electrode a plurality of beam components which should be understood herein to denote individual electron beams formed by separate means or separate portions of a stream of electrons emanating from a single means.

By means of horizontal and vertical deflection coils schematically illustrated and designated 20 and 21, respectively, the beam components emanating from the guns 12 are deflected in both horizontal and vertical planes of deflection, thereby to scan a raster at the target electrode structure 6. The operation of the horizontal and vertical deflection coils is controlled by conventional horizontal and vertical dellection signal generators, the construction and operation of which are well-known in the art and, therefore, are not shown or described. Additionally, the scanning operation can be conventional and will not be described hereinafter.

During assembly of the above-described tube structure, and as seen in Figures l and 2, the guns 12 are physically aligned for being substantially parallel to each other and for directing the beam components 15-17 toward the target electrode in substantially the same horizontal plane.

In order to obtain the necessary convergence of the beam components 15-17 at the target electrode, and as perhaps better seen in Figure 2, I have provided beam component convergence means which includes two pairs of vertically spaced elongated plates or pole pieces and '26. The pole pieces 2S and 26 extend transverse to the longitudinal axis of the tube 1 and are disposed for straddling each of the outer beam components 1S and 17 adjacent the exit ends of the corresponding electron guns 12. Also included in the convergence means is a pair of similar but longer pole pieces 27 straddling the inner beam component 16 and preferably extending substantially perpendicular to the pairs of pole pieces 25 and'26. While the pole pieces 27 preferably extend perpendicular to the pole pieces 25 and 26 in the presently disclosed embodiment, it will be seen from the following that it is sutiicient if the pole pieces 27 extend transversely to and through the planes of the pole pieces 25 and 26.

As seen in Figure 2, the pole pieces 25-27 are mounted in the neck 3 of the tube envelope 2 on a transversely extending diaphragm 3a in any suitable manner whereby they are maintained at the same potential as the diaphragm and the exit ends of the guns 12. For example, each of the pole pieces may be formed @with an ear spetwelded to the diaphragm, in the manner illustrated in Figure 2. For simplilication of illustration, the diaphragm 3a has not been shown in Figure l.

The above-mentioned convergence of the components 15-17 at the target electrode is accomplished by magnetic deflection and to this end the pairs of pole pieces 25- 27 are formed of any suitable soft-magnetic material, such as soft iron.

Additionally, the individual pole pieces of each pair thereof include arcuate portions 28 disposed in close proximity and conforming substantially to the internal surface of the neck of the tube. Still further, the pole pieces of each pair are mutually inclined or unequally spaced radially or outwardly throuhgout their lengths with the innermost edges of each pair being most closely spaced. The purpose for this will be brought out in detail hereinafter.

Thus, each spaced pair of pole pieces 25-27 is adapted for cooperating with a corresponding one of three electromagnets StL-32. The electromagnets 311-32 are disposed externally of the tube neck and are spaced 90 apart thereabout for thus locating each in close proximity to its associated pair of pole pieces. Each of the electromagnets includes a substantially U-shaped softmagnetic material core 33 which may be formed of ferrite or the like. The cores 33 are adapted each for carrying a coil or winding 34 on the center portion thereof. Additionally, as shown in Figure 2, the cores 33 include upper and lower leg portions, the ends of which constitute external magnetic pole pieces which are shaped for conforming substantially to the external surface of the tube neck and are disposed for cooperating magnetically with a corresponding pair of the plates 25-27 to estab` lish magnet elds therebetween. The conformance of the ends of the core leg portions and the arcuate portions 28 of the internal pole pieces 25-27 afford better coupling therebetween and thus the establishment of fields Y of greater strength between the pole pieces for a given energizing current. Additionally, the mutual inclination of the pole pieces of each pair enables wider spacing of the legs of the cores. This, minimizes the concentration of magnetic lields between the outer ends of the pole pieces for thus affording a predetermined more uniform field distribution between the pole pieces of each pair and resultant more uniform beam-deflection effects.

The coils of the electromagnets 311-32 are suitably electrically connected to adjustable electromagnetic convergence control sources generally designated 35-37, respectively in Figure l. These adjustable control sources may be any suitable arrangement adapted for independently, variably energizing each of the electromagnets 30-32 through its respective coil and in accordance with a preselected polarity. When the magnets 311-32 are thus energized magnetic fields at the pole pieces thereof are caused to couple through the tube envelopes to the spaced internal pole pieces for establishing transverse magnetic elds between each pair thereof, whereby the outer beams 15 and 17 can be caused to be deflected or shifted horizontally in either direction and the inner beam 16 can be deflected or shifted vertically in either direction in Figure 1.

As seen in Figure l, the control sources 35 and 36 may be both static and dynamic. That is, each ofthese sources may b'e adapted for energizing the related coils of the magnets 3i) and 31 with a predetermined DIC. current in order thereby to correct for static misconvergence, or misconvergence due generally to gun misalignment; and, additionally, the sources may be such as to energize the magnets 3@ and 31 with an A.C. signal of a predetermined parabolic wave form, thereby to correct for dynamic misconvergence, or misconvergence generally encountered as a result of scanning. lt will be evident from the foregoing that, for the purpose of effecting dynamic convergence, the sources 35 and 36 can be associated with the scanning means including the deflection coils 20 and 21.

Also included in the convergence system is an electromagnetic convergence coil or yoke 40. The coil 40 is mounted concentrically on the neck of the tube envelope immediately adjacent the pole pieces 25-27. As illustrated in Figure l, the coil 40 is preferably disposed between the internal pole pieces and the target electrode. However, it will be clear from the following that in some forms of the present invention the coil 40 may be located on the gun side of the internal pole pieces.

Additionally, the coil 40 is suitably electrically connected to a control source generally designated 41. The control source 41 may be of any suitable generally available type adapted for adjustably controlling the energization of the electromagnetic coil 40 to produce a magnetic field of adjustable intensity and polarity. As is well known to those skilled in the art, the shape of such a magnetic field is generally toroidal, with the lines of force extending generally axially through the tube neck and flaring outwardly from the neck axis on both sides of the coil 40. As is also well known, the effect of such a magnetic field on an electron beam travelling down the neck of the tube generally parallel to the neck axis 'but radially displaced therefrom is to converge the beam toward the neck axis by a somewhat helical or spiral deflection of the beam. Thus, in accordance with the energization of the coil 40 the beam components 15-17 may be deflected so as to effect a rotational movement of the beam components about the longitudinal axis of the tube. The purpose for this feature will be brought out in detail hereinafter.

If the guns 12 are accurately aligned in assembly the beam components 15-17 emanating therefrom will be directed toward the target in a Vhorizontal plane with the inner component substantially coaxial with the longitudinal axis of the tube, in the manner indicated diagrammatically in Figure 3. Thus, convergence of the three beam components at the target electrode can be accomplished simply by operating the D.C. or static feature of the control sources 35 and 36 for shifting or defiecting the outer components inwardly or outwardly relative `to the center component, as for example, to the positions 15a and 17a and until desired convergence is obtained. Subsequently, during operation of the tube and scanning of the beam components, the AJC. signals provided by the sources 35 and 36 will effect energization of the related magnets and pole pieces whereby dynamic convergence will be effected.

As a practical matter, however, and due, among other reasons, to difficulties in obtaining satisfactorily accurate gun alignment by known manufacturing and assembling methods, the guns are not generally effective for directing the beam components toward the target electrode in the manner indicated at 15-17 in Figure 3. Instead, and even after the guns are physically aligned as well as humanly possible, the components often emanate from the guns somewhat irregularly, such as in the manner illustrated exaggeratedly at 15-17 in Figure 4, resulting in the beam components impinging upon the screen 6 in different horizontal planes and thus causing misconvergence with resultant reduced and unsatisfactory image rendition and color fidelity. To overcome this condition the control source 37 can be operated for establishing a predetermined magnetic field between the pair of pole pieces 27 effective for defiecting the center component 16 upwardly to position 16a in Figure 4.

Then the control sources 35 and 36 can be operated for l establishing suitable static electromagnetic fields between the outer pairs of pole pieces 25 and 26 for deflecting .6 the outer beam components horizontally until they assume positions such as 15a and 17a and lie in a substantially common plane with the center beam, such as that indicated at 42 in Figure 4. In this plane, however, suitable convergence is not generally attainable and to overcome this the coil control source 41 can be operated for energizing the coil 40 sufciently to effect rotation of the outer beam components about the position 16a for causing them to assume the positions 15b-17h and to lie and be directed toward the target electrode in the same horizontal plane. Subsequently, the control sources 35 and 36 can be further operated for causing the outer beam components to converge satisfactorily on the inner component, as at the target electrode 6 and specifically in the plane of the grille iti) in the manner shown in Figure l.

The just-described convergence of the beam components is facilitated to a high degree by the above-referredto mutual outward inclination of `the pole pieces comprising the pairs 25-27. This inclination of the pole pieces results in a predetermined substantially uniform field distribution across the region between the poles and thus provides more uniform beam deflections for given changes in energization currents as eected by the conltrol sources 35-36.

While a specific embodiment of the invention has been shown and described, it is not desired that the invention be limited to the particular form shown and described, and itis intended by the appended claim to cover dl modifications within the spirit and scope of' the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

A cathode ray tube including an envelope, a target electrode, three substantially coplanar electron guns for directing three electron beam components toward said target electrode, and means for converging `said three beam components into equally spaced relation in a plane parallel to said electron guns comprising a pair of first magnetic pole piece straddling each of the outer ones of said beam components in said envelope, said first pole pieces being adapted for magnetic field displacement of said outer beam components in a plane parallel to the plane of said electron guns, a pair of second magnetic pole pieces straddling the inner one of said beam components, said second pole pieces being substantially perpendicular to said first pole pieces and being adapted for magnetic convergence of said inner beam component to a position midway between said outer beam components on the plane determined by the outer ones of said beam components, the pole pieces of each of said pairs of pole pieces including mutually inclined portions for generating a uniform magnetic field throughout the space between said mutually inclined portions, an electromagnetic coil surrounding the paths of said beam components and positioned to generate a magnetic field having an axis substantially parallel to the paths of said beam components for effecting rotational displacement of at least the outer ones of said beam components about the axis of said tube, and respective magnet means for establishing predetermined magnetic fields between said respective pairs of pole pieces.

References Cited in the le of this patent UNITED STATES PATENTS 2,587,074 Sziklai Feb. 26, 1952 2,752,520 Morrell June 26, 1956 2,769,110 Obert Oct. 30, 1956 2,807,737 Wright Sept. 24, 1957 2,849,647 Francken Aug. 26, 1958

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