US2898493A - Method and apparatus for controlling electron beams - Google Patents

Description

Aug. 4, 1959 e. A. BURDICK METHOD AND APPARATUS FOR CONTROLLING ELECTRON BEAMS Filed May 31, 1955 FIGJ.

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United States atent @flice METHOD AND APPARATUS FOR CONTROLLING ELECTRON BEAMS Glen A. Bur-dick, Waterloo, N .Y., assignor, by mesne assignments, to Sylvania Electric Products Inc., ton, Del., a corporation of Delaware Application May 31, 1956, Serial No. 588,443 4 Claims. (Cl. 313-77) This invention relates to electrical apparatus and more particularly to devices used in television apparatus for the reproduction of color images.

Image reproduction devices such as picture tubes used in color television receivers generally have a viewing panel or screen comprising groups of red, green and blue color emitting fluorescent material configurations of dots, bars or stripes. In multiple gun type picture tubes, these configurations are arranged so that they will be excited individually upon impingement of electrons emitting from the appropriate electron gun during tube operation. Generally, a grid or mask is positioned intermediate the gun and screen for either deflection or shading of the electron \beam so that it will strike the correct fluorescent material configuration. In order to assure proper excitation of the fluorescent materials and obtain color purity by minimizing color fringes, it is essential that the three beams will converge at the grid or mask position for all deflection angles.

Numerous methods have been prroposed for attaining the proper convergence necessary for the reproduction of a color image having good color purity and resolution. One such method utilizes a gun assembly having the electron guns positioned so that their axes will intersect at the proper static convergence point in conjunction with a magnetic beam convergence assembly positioned on the picture tube neck exterior and energized for dynamic operation in accordance with thebeam position at a given instant. This assembly is provided 'with adjustments which allow compensation for errors in beam alignment as well as with dynamic individual radial positioning controls for the electron beams. In addition to the mechanical gun alignment and radial convergence assembly, a purity magnet is often used to create a magnetic field which can jointly move all three beams transversely of the tube neck axis. Rotation of the magnet around the tube neck causes the field to exert a force in any desired transverse direction.

The aforementioned means for providing control over the multiple beams employed in the tube for the purpose of attaining the desired convergence characteristics have generally proved to be unsatisfactory since they are only effective on tubes which have been constructed with extreme accuracy and with parts having very close tolerances. When picture tubes'are made on a high pro duction scale, it is difficult to maintain the critical fabrication conditions necessary for making the tubes with satisfactory convergence, color purity, and resolution characteristics.

Accordingly, it is an object of the invention to reduce the aforementioned difiiculties and to provide a convenient method for altering or controlling the paths of the electron beams in a color picture tube to attain highly satisfactory picture tube reproduction characteristics.

A further object is to provide an image reproduction device assembly formed to control the electron beam or Wilming- 2,898,493 Fatented Aug. 4, 1959 beams employed in the device so that they may be moved radially or tangentially of the normal path of electron travel A further object is to provide an image reproduction device assembly formed to control the electron beam or beams employed in the device so that they may be moved radially, transversely, or tangentially 'of the normal path of electron travel.

A still further object is the provision of a magnet assembly constructed to exert forces on electron beams so that they may be moved tangentially of their normal path.

The foregoing objects are achieved in one aspect of the invention by the provision of an electron beam po sitioning magnet assembly adapted to be mounted upon the exterior surface of the picture tube neck. Several field adjustable magnets are employed on the assembly when it is used with a multiple gun type tube so that the produced fields can exert individual tangential forcesupon the beams. The combination of this beam positioning magnet assembly and a radial convergence device gives optimum control over the beams, and allows for a decrease in picture tube rejects without degradation of picture quality. The individual electron beams are acted upon individually and sequentially by the beam posi tioning assembly and convergence device as the electrons'proceed'from the cathode to the screen of the picture tube.

For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a plan view of a color picture tube and its associated components;

Fig. 2 is a diagram showing the devices which produce, control and converge the electron beams;

' Fig. 3 shows the effects of a radial dynamic convergence device on the electron beams;

Fig. 4 shows the effects of a purity magnet structure of the electron beam; and

Fig. 5 shows the effects of beam positioning magnets on the electron beams.

Referring to Fig. 1, a cathode ray tube 11 of the type employed in color television receiving apparatus is shown comprising a face plate 13, funnel 15, and neck portion 17 terminated with an electrical connector base 19. For purposes of illustration, tube 11 has been shown in the drawings as a round spherical-faced tri-gun tube of the aperture mask type. Mounted upon neck 17 adjacent funnel 15 are the deflection coils 21 which are formed and energized to impart the scanning motion to the electron beams. Positioned behind the deflection coils on the neck exterior is the dynamic convergence device 23 which is electrically connected to the scan circuits of the receiver so that proper convergence fields will cause the three spaced electron beams to converge at the correct position for any given scanning angle. Behind the dynamic convergence device 23 is a purity magnet structure 25' which operates on the beams jointly to cause transverse positioning of the beam group within the neck portion 17. Also mounted on the neck and placed intermediate magnet 25 and base 19 is a beam positioning assembly 27 which effectively provides individual tangential movement of the beams in a manner to be hereinafter described.

Dynamic convergence device 23 may employ electromagnets excited by an alternating current derived from the scan circuit, with or without the addition of a direct current correction or permanent magnet for altering the level of the field strength. Magnet structure 25 and beam positioning assembly 27 have been shown generally as permanent magnets. However, electro-magnets may be used with or without direct current correction or dynamic energization.

Fig. 2 shows diagrammatically the electron gun assembly components for a multiple gun type picture tube and the associated structures which provide the proper convergence for the electron beams 28. The drawing is intended to illustrate an aperture mask tube, although it is to be understood that the aspect of the invention recited herein is not restricted to this particular structure. For instance, it is equally applicable to any multiple gun type tube wherein convergence is necessary for the reproduction of a satisfactory image.

Two electron guns 29 have been shown for purposes of simplicity in Fig. 2 since the convergence principles utilized in the structures shown therein are similar for any two of the group of three electron guns illustrated elsewhere in the drawings. As seen more clearly in Fig. 3 through 5 inclusive, the tri-gun shadow mask type tube employs three electron guns arranged equi-distant from one another and 120 apart.

A typical picture tube electron gun structure provides the source, acceleration, modulation and focusing for an electron beam. In a tri-color tube of the type described herein, it is additionally necessary to move individual beams such as is indicated by the numeral 28 in a manner so that they will converge at the aperture mask 31. When this convergence position is correct, the beams will cross one another and impinge upon appropriate fluorescent configurations 33 formed on the internal surface of the picture tube face plate 35. The beam positions shown in Fig. 2 are those existing during a period of static convergence, or at the'instant the horizontal and vertical scanning movement has reached a position coincident with the longitudinal axis of the ,tube.

The gun structures 29 comprise a cathode 37, shown displaced from a first or control grid 39 for clarity, a second or accelerating grid 41, a third or pre-focusing grid 43, and a fourth or final focusing grid 45. The electron guns are tilted relative to one another so that they will have a normal tendency to converge at the static position as shown. Spaced from gun structures 29 and disposed in proper relationships with their associated grids or electrodes are the dynamic convergence assembly 23, purity magnet 25, and beam positioning magnet 27. In addition to the electrodes so far described, the gun structures 29 are terminated in the internal dynamic convergence pole pieces 47'. These poles provide the internal flux path for the magnetic field applied by the exteriorly mounted dynamic convergence device 23.

Although beam positioning magnet assembly 27 is shown near the leading edge of grid 43, it is to be understood that this location is somewhat arbitrary, since the position depends on the number of grids used, the length of the grids, the potential on the grids, the position of the guns relative to one another, the strength of the magnets employed, the diameter and the thickness of the glass neck portion, etc.

Figs. 3 to 5 inclusive illustrate the manner in which purity magnet structure. 25, convergence device 23, and assembly 27 operate on the electron beams to alter their paths. Fig. 3 specifically shows the radial force exerted on the electron beams 28 by. the dynamic convergence device 23. These beams emerge from approximately the centers of their respective symmetrically arranged electron guns 29. As the beams enter the region of their associated convergence device pole pieces 47, the magnetic field existing between these pole pieces causes the beams 28- to be moved radially withrespect to the axis of the neck portion 17 as indicated by the arrows. Since the individual magnetsof device 23 are independently energized,

.each magnet associated beam 28 may be individually controlled as to its radial position over the entire scanning raster. The polarlty of the magnetic field determines whether the beams will be moved radially toward or away from one another.

Fig. 4 illustrates one embodiment of the purity magnet structure 25 adapted to be used if desired, with the other beam controlling devices herein described. The magnet generally comprises one or more washer-like magnetic pieces formed to surround neck portion 17 of tube 11. A magnetic field exists in the region of the electrodes of guns 29 at this position to exert a transverse force on beams 28 as indicated by the arrows. The force acts equally in magnitude and direction on all three beams. Axial rotation of purity magnet 25 will change the direction of the force. Shunting means may be employed with the magnet if desired to control the magnitude of the field.

Fig. 5 illustrates one embodiment of a beam positioning magnet assembly 27 which comprises a hoop 49 of resilient material such as cold rolled steel or a section cut from a plastic extrusion provided with support positions or indentions 51 formed to contact the exterior surface of neck 17'. If desired, instead of using indentions 51, the hoop may be provided with threadably attached non-magnetized screws which extend therefrom to a position whereat they will be in' contact with the exterior surface of the neck to provide at least a three point support for the hoop. Three magnets 53 are mounted on hoop 4-9. inalignment with their respective electron guns 29. The field exerted by each of these magnets provides a tangential force on the individual beam with which it is aligned as shown by the arrows in Fig 5. Preferably, magnets 53 are made with an. adjustable core 55 so that the magnitude of the field can be determined separately for each electron beam 28. To provide for adjustment, magnet core 55 may be constructed with screw threads or with a surface adapted to slide transversely toward the tube neck.

Instead of using hoop 51', the support means for mag nets 53 could employ non magnetic support arms attached to or fabricated as a portion of the convergence device. 23 and be formed to extend rearwardly of the assembly in a spaced relationship with the tube neck. Magnets 53 could then be mounted on these arms in the appropriate position. If misalignment of the beams prove to be generally great enough to warrant the application of purity magnet 25 in addition to device 23 and assembly 27, the beam positioning magnets 53 may be mounted upon support arms extending from magnet 25.

As described heretofore, beam positioning assembly 27 may employ permanet magnets or electro-magnets and.

it may be electrically connected in the receiver for dynamic operation with or without direct current correction. In addition, although three individual beam magnets are preferred, two or more similar devices may perform satisfactorily. One such magnet is insufiicient since the tangential force exerted on one beam tends to separate the other two even when internal shielding is used with the electron gun mount. In efiect, the action of only one magnet necessitates a greater radial force by the convergence magnets to bring, these separated beams again into radial alignment, which in turn causes further tangential misalignment and so on ad infinitum.

The application of a beam positioning assembly such as the one described herein, when used in conjunction with a purity magnet and a convergence assembly, gives maximum, control over the electron beams utilized in a color television picture tube. These tubes may be economically fabricated on a production scale, and subsequently easily set up by means of these devices to reproduce pure color images. However, it is to be understood that if misalignment of the beams individually within each gun or the guns within the neck portion of the tube is not initially extreme in a transverse direction, the forces provided by convergence device 23 and beam positioning magnet assembly 27 will be suflicient to alter or control the beam positions, without necessitating the use of purity magnet 25. Referring to Figs. 3 and 5, it can be seen that a combination of individually adjustable radial and tangential forces provided by the magnets in device 23 and assembly 27 can produce any given resultant force for each beam within the limits of the magnetic fields contributed by these magnets. The need for mechanical converging alignment of the electron guns may also be relieved if the magnetic fields produced by device 23 and assembly 27 are made large enough in magnitude.

Although several embodiments ofthe invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. In a television receiving apparatus, the combination comprising a cathode ray tube having an envelope with a face panel and a neck portion, an image reproduction screen formed on the internal surface of said face panel, and three electron gun structures disposed in said neck portion with intersecting longitudinal axes each providing an electron beam directed to impinge upon said screen; and an electron beam positioning assembly formed to exert tangential forces on each of said beams, a color purity controlling magnetic structure formed to exert transverse forces on said beams, and a beam convergence device formed to exert radial forces on said beams, said assembly, structure and device being disposed on the external periphery of said neck portion in spaced rela tionship and arranged sequentially in the direction of electron travel.

2. A television receiving apparatus including a cathode ray tube having an envelope with a face panel and a neck portion, an image reproduction screen formed on the internal surface of said face panel, and a plurality of electron gun structures disposed in said neck portion providing electron beams directed to impinge upon said screen, in combination with an electron beam positioning assembly formed to exert tangential forces on each of said beams, a color purity controlling magnetic structure formed to exert transverse forces on said beams, and a beam convergence device formed to exert radial forces on said beams, said assembly, structure and device being disposed on the external periphery of said neck portion 6 in spaced relationship and arranged sequentially in the direction of electron travel.

3. A television receiving apparatus including a cathode ray tube having an envelope with a face panel and a neck portion, an image reproduction screen formed on the internal surface of said face panel, and a plurality of electron gun structures disposed in said neck portion providing electron beams directed to impinge upon said screen, in combination with an electron beam positioning assembly formed to exert tangential forces on each of said beams, and a beam convergence device formed to exert radial forces on said beams, said assembly and device being disposed on the external periphery of said neck portion in spaced relationship and arranged sequentially in the direction of electron travel.

4. A television receiving apparatus including a cathode ray tube having an envelope with a face panel and a neck portion, an image reproduction screen formed on the internal surface of said panel, and three electron gun structures disposed in said neck portion providing individual electron beams directed to impinge upon said screen, in combination with an electron beam positioning assembly formed to exert individual tangential forces on each of said beams, and a. beam convergence device formed to exert individual radial forces on each of said beams, said assembly and device being disposed on the external periphery of said neck portion in spaced relationship with one another and arranged sequentially in the direction of electron travel.

References Cited in the file of this patent UNITED STATES PATENTS 2,513,929 Gethmann July 4, 1950 2,541,446 Trott Feb. 13, 1951 2,574,039 Ingle Nov. 6, 1951 2,591,159 Kaluss Apr. 1, 1952 2,646,522 Shaw July 21, 1953 2,672,574 Evans Mar. 16, 1954 2,707,248 Goodrich Apr. 26, 1955 2,722,622 Adler Nov. 1, 1955 2,743,389 Giulfrida Apr. 24, 1956 2,766,393 Casey Oct. 9, 1956

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