US3525892A - Asymmetric pole pieces for color kinescope convergence cage - Google Patents

Description

Aug. 25, 1970 JAVORIK ET AL ASYMMETRIC POLE! PIECES FOR COLOR KINESCOPE CONVERGENCE CAGE Filed 001;. 22, 1968 United States Patent 3,525,892 ASYMMETRIC POLE PIECES FOR COLOR KINESCOPE CONVERGENCE CAGE Laszlo Javorik, Chicago, George A. Rokos, Westchester,

and Benjamin L. Gelfand, Chicago, Ill., assignors to National Video Corporation, Chicago, Ill., a corporation of Illinois Filed Oct. 22, 1968, Ser. No. 769,513 Int. Cl. Hlllj 29/54, 29/72 US. Cl. 313-77 3 Claims ABSTRACT OF THE DISCLOSURE The two lower side pole pieces in the magnetic con- Vergence cage of a three-beam gun for a color kinescope of the shadow mask type are modified to provide asymmetric deflection loci. The deflection loci for the two side beams are directed above the axis of the convergence cage and thus correct for errors in vertical displacement of the converged beams due to the unequal vertical location of the beams relative to the axis of the convergence cage.

BACKGROUND AND SUMMARY The present invention relates to multiple-beam color kinescopes of the shadow mask variety; and more particularly, it relates to an improved magnetic convergence cage for a color kinescope.

A conventional color kinescope of the shadow mask type has a glass neck portion at one end, a faceplate (on which is formed an enlarged viewing screen) at the other end, and a funnel-shaped portion joining the constricted neck portion with the faceplate panel. Three guns (i.e. sources of electron beams) are arranged in delta array in the constricted neck portion of the tubethat is, in cross section, the centers of the three beams define an equilateral triangle and the center of the triangle is coincident with the axis of the constricted neck portion of the tube. Each electron beam is modulated with a video signal representative of a different primary color in the image being reproduced.

An apertured shadow mask is mounted within the tube envelope adjacent the viewing screen; and each aperture in the shadow mask is associated with a triad of the mosaic of color-producing phosphor dots deposited on the interior of the faceplate panel which comprises the viewing screen. Each of the phosphor dots of a triad produces a different primary color (for example, red, green, and blue); and each dot is, in turn, energized by that electron beam which is modulated by the video signal representative of the color component reproducible by that dot. Color separation is attained by converging the three beams at the shadow mask so that as the beams pass through an aperture, they cross and strike only their associated color-producing phosphor dots. The triads of the phosphor mosaic are interlaced so that the three images appear as one to the eye.

A conventional dynamic convergence cage for converging the beams has a circular plate mounted to the final electrode of each of the three electron beam guns; and this plate defines three equally-angularly spaced apertures through which the three separated electron beams flow. A cylindrical flange or wall member extends downstream (i.e. toward the viewing screen) from, and is integral with, the circular plate; and there are two elongated slots extending axially of the cylindrical wall member for each of the beams passing through the cage.

A magnetic pole piece is fitted into each of the slots so that a pair of magnetic pole pieces is associated with P CC each of the beams. Each of the pole pieces has a recep tion portion which generally conforms to the shape of the cylindrical wall member and is located externally thereof for receiving the dynamic convergence signal from a magnetic deflection coil. Each pole piece then extends interior of the cage and provides a pole face adjacent its associated electron beam. The pair of pole faces for each beam are located on opposite sides of the beam; and they cooperate to establish a magnetic field transverse of their associated electron beam for deflecting the same radially inward of the cylindrical wall of the cage toward its axisthus, conventional deflection loci are symmetrical relative to the axis of the convergence cage.

In conventional magnetic deflection schemes for dynamic convergence, a separate convergence coil is supplied exterior of the constricted neck portion of the tube for energizing each of the pairs of pole pieces. These deflection coils are normally spaced at angular degrees about the constricted neck portion of the tube; and each pair of pole pieces, when energized by its associated deflection coil sets up a center line of deflection force for its beam. All three of these deflection lines normally coincide with the axis of the convergence cage-- that is, the center of deflection is a point at center of equilaterial triangle defined by the beams.

Since the top beam is situated directly over the center, the deflection force exerted on the top beam is vertically downward. The other two beams, being located beneath and to the sides of the axis of the convergence cage, are deflected toward the axis at angles of 30 from the horizontal. Hence, for the same deflection force exerted on each of the beams, the vertically downward deflection (that is, the vertical component of deflection only) of the top beam will be much greater than the corresponding vertical component of the deflection of the side beams. Thus, in order to converge, the top beam experiences a much greater vertical displacement component relative to the center of deflection than to the side beams. A balanced correction is made diflicult by this greater vertical component of deflection in the top beam.

According to the arrangement of the present invention, the two side beams are caused to be deflected upwardly at a greater angle relative to the horizontal (for example, at a 60 angle) so that the upward deflection of these beams more nearly equals the downward deflection of the top beam. Reference will sometimes be made herein to the deflection locus of the beams, and this refers to the straight-line direction in which the beams are forced in a plane perpendicular to the flow of electrons by the convergence cage. Thus, according to the present invention, the center lines of the deflection force for the side beams no longer meet at the axis of the cylindrical wall of the convergence cage; rather, they meet at a point above the axis of the cylindrical cage wall so that the vertically upward deflection of the side beams is more nearly equal to the vertically downward deflection of the top beam. In other words, the center of deflection is translated directly upward, and the pole piece arrangement becomes asymmetric relative to the axis of the cage.

This result is accomplished without changing the equilateral triangle array of the three beams and without changing the angular disposition of the magnetic deflection coils exterior of the constricted neck portion of the tube.

Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.

3 THE DRAWING FIG. 1 is a partially cut-away view of the electron beam guns in the constricted neck portion of a color kinescope incorporating the present invention;

FIG. 2 is a transverse cross section view taken through the sight line 22 of FIG. 1;

FIG. 3 is an enlarged detail cross section view of the improved convergence cage of the kinescope of FIG. 2; and

FIGS. 4-5 are enlarged perspective views of separate pole pieces incorporated in the convergence cage of the kinescope of FIG. 2.

DETAILED DESCRIPTION Referring now to FIG. 1, a glass envelope of the constricted neck portion of a color kinescope of the shadow mask type is generally designated by reference numeral 10. At the base (or upstream end) of the neck (that is, the left-hand end as viewed in FIG. 1), a plurality of terminal pins 11 are fed through the glass envelope 10 for coupling suitable filament and grid voltages to the various electrodes, presently to be described.

These are three separate sources of electron beams, commonly referred to as guns in the constricted neck portion of the tube envelope; and the three beams flow parallel to the axis of the neck. In cross section, the centers of the three beams define an equilateral triangle, the center of which is coincident with the axis of the neck. Although not illustrated in the drawing, a funnel portion of the tube envelope is formed integrally with the neck portion and extends outwardly thereof. A faceplate panel is joined at the enlarged end of the funnel; and a conventional apertured shadow mask is mounted inwardly of the faceplate panel. These elements are not illustrated since they are conventional, and the present invention may be fully understood by persons of ordinary skill in this art without describing such elements in further detail.

Each of the three electron guns, arranged in delta array, is substantially identical to the others; and therefore, only one of the guns will be described in greater detail here. Referring to FIG. 1 and in particular to the lower left hand gun as seen in FIG. 2, a first cylindrical grid 12, commonly referred to as grid I or the control grid, is mounted about a conventional cathode assembly (not shown) which is mechanically supported within, but electrically isolated from, the conductive electrode 12. Proceeding downstream of the beam from the control grid 12, there are three other electrodes arranged in order and generally designated by reference numerals 13, 14, and 15 respectively. These three grids are commonly referred to as the screen grid, the focus electrode, and the anode. Each of the electrodes 12-15 associated with one of the electron guns is located coaxially with respect to the beam it generates; and the center of each defines an aperture to permit unrestricted passage of the electron beam.

As is also conventional, the three guns are rigidly mounted as a unit by means of supporting straps, the ends of which are secured in elongated glass beads such as the one shown at 16. Each strap has one end mounted in a bead, then is formed into a circular portion which is welded to an associated cylindrical electrode, and has its second end mounted in a second bead spaced about the interior of the neck portion. Thus, all three guns form a rigid structure supported within the constricted neck portion 10 of the tube envelope by three glass supporting rods or beads.

All three beams, after exiting from the accelerating anodes 15, are fed into a convergence cage which includes a cup-shaped member generally designated 18 and including a circular plate 19 (see FIGS. 2 and 3) adjacent the anodes 15, and a cylindrical side wall 20 integral with and extending downstream from the plate 19. The con- 4 vergence cage 18 is at the same electrical potential as the anode 15.

Referring now to FIGS. 2 and 3, three apertures permitting passage of the three beams are provided in the circular plate 19; and these three apertures are designated respectively by reference numerals 21, 22, and 23. As mentioned, the electron beams are arranged in delta array; and so the centers of the apertures 21-23 define an equilateral triangle having its center at the axis of the cylindrical side wall 20. The convergence cage, in end view, is divided into three equal wedge segments by a Y-shaped separator 26.

Three magnetic deflection coils designated respectively 28, 29 and 30 in FIG. 2 are mounted exterior of the constricted neck 10 adjacent the convergence pole pieces of the three beams respectively. As seen in FIG. 2, the magnetic deflection coils 2830 have one pole face respectively on each side of radial lines passing through the apertures 2123. These deflection coils are energized by dynamic convergence signals which are generated according to known technique as the three beams scan a raster on the image screen. Heretofore, the deflection locus of each of the beams was symmetrically toward the axis of cage.

Further details concerning the structure and operation of convergence pole pieces in color kinescopes may be obtained from the co-pending, co-owned application of Javorik et al., for Improved Convergence 'Cage for Color Kinescope, Ser. No. 722,581, filed Apr. 19, 1968.

The cylindrical wall member 20 is provided with a plurality of elongated slots extending parallel to its axis for receiving the convergence pole pieces; and there are two such pole pieces associated with each of the beam apertures 21-23.

Received in each of the slots 31 in the cylindrical wall 20 1s a magnetic pole piece. The two pole pieces associated with the aperture 21 are generally designated 33 and 34 in FIG. 3. Each of the pole pieces 33 and 34 is similar; and they are symmetrical about a vertical radial line passing through the axis of the cylindrical wall 20. The pole piece 33 has a reception portion 35 welded to the exterior surface of the wall member 20 and extending beneath one of the poles of the deflection coil 28 and a lower, detented pole face 36 extending to the left side of the aperture 21. Similarly, the pole piece 34 has a reception portion 38 lying beneath the other pole of the deflection coil 28 and a pole face 39 lying adjacent the beam passing through the aperture 21.

The pole faces 36 and 39 of the pole pieces 33 and 34 face each other; and it is across these opposing pole faces that the magnetic field is generated to deflect the beam passing through the top aperture 21 in a downward directron relative to the center of the three beams. The line of magnetic deflection force exerted by the magnetic field generated across the pole faces 36 and 39 is illustrated by the chain line 40 in FIG. 3.

The pole pieces deflecting the electron beam passing through the aperture 22 are generally designated by reference numerals 41 and 42. The pole piece 41 is provided with a reception portion 43 welded to the exterior surface of the cylindrical wall 20; and it includes a pole face portion 44 which is again provided with a detent, although these are not necessary for operation. Similarly, the pole piece 42 has a reception portion 45 and a pole face 46. The reception portions 43 and 45 of the pole pieces 41 and 42 receive the magnetic field generated by the deflection coil 29 and generate a magnetic deflection force across the pole faces 44 and 46; however, in this case, the pole faces 44 and 46 are arranged so that the center line (deflection locus) along which the magnetic deflection force is exerted displaces the center of the beam flowing through the aperture 22 along the chain line 49. It will be appreciated that the deflection locus does not force the electron beam passing through the aperture 22 directly toward the axis of the cylindrical wall 20, but along a locus inclined slightly above it. In a preferred embodiment, the deflection lines of the two lower convergence pole pieces form a 30 angle on either side of a vertical line which lies along the deflection locus of the upper convergence pole piece.

Turning now to the pole pieces associated with aperture 23, reference numerals 50 and 51 generally designate these pole pieces. The pole piece 50 forms a mirror image of the previously-described pole piece 41; and it includes a reception portion 52 and a pole face 53. Similarly, the pole piece 51 is a mirror image of the previously-described pole piece 42, and it includes a reception portion 55 and a pole face 56. The reception portions 52 and 55 receive the magnetic field generated by the deflection coil 30; and the pole faces 53 and 56 cooperate to deflect the beam passing through the aperture 23 along a locus indicated by the chain line 57. If extended, the deflection loci 49 and 57 for the lower side beams would intersect at a point above the axis of the cylindrical wall 20 of the convergence cage. For this reason, the cage is sometimes referred to as asymmetric.

Turning now to FIG. 4, the configuration of the pole pieces 42 and 51 is seen in perspective view; and it will be appreciated that the same configuration is interchangeable for each of these poles by turning the member endon-end. In FIG. 4, the reception portion of the pole piece is designated 60; and the pole face is generally designated til. FIG. shows a similar view of a pole piece which may interchangeably be used for either of the previously-described pole pieces 43 or 52 by, again, turning it end-on-end. In FIG. 5, the reception portion is generally designated 62, and the pole face which extends adjacent the beam aperture in the plate 19 is generally designated by reference numeral 64.

With the pole piece thus arranged, it can be seen that the deflection locus for the beam passing through the top aperture 21 remains directly downwardthat is, toward the axis of the cylindrical wall At the same time, the deflection loci defined by the pole faces for the beams passing through the lower side of the aperture are more steeply inclined upwardly than heretofore; and they meet at a point above the axis of the cylindrical wall 20 to cause the vertically upward deflections of the side beams to be more nearly equal to the vertically downward deflection of the top beam-thus reducing the vertical displacement error caused in converging the blue (top) beam at the shadow mask or on the viewing screen.

Having thus described in detail a preferred embodiment of the improved convergence cage, persons skilled in the art will readily conceive of variations in pole piece configurations which may be substituted for the particular ones described and yet which practice the inventive principle; and it is, therefore, intended that all such modifications and substitutions be covered as they are embraced within the spirit and scope of the appended claims.

We claim:

It. in a three-beam color kinescope having a shadow mask adjacent a mosaic of phosphor dots on the viewing screen and a magnetic deflection coil for dynamically converging each of said beams, an improved convergence cage comprising: a cylindrical wall member in the constricted neck of said kinescope and defining a pair of elongated slots for each beam, each pair of slots lying adjacent a pole of its associated magnetic deflection coil; a circular plate member integral with the upstream edge of said cylindrical wall member and defining an aperture for the passage of each of said beams, the centers of said apertures disposed at equal angular increments about the axis of said wall member, and a center of one of said apertures lying directly above said axis, the other centers of said apertures lying beneath and to the respective sides of said axis; a first pair of magnetic pole pieces received in a first pair of slots of said cylindrical wall member and including opposing pole face members on opposite sides of said top aperture, said pole faces of said first pair of pole pieces defining a deflection locus extending along a line from the center of said top aperture through the axis of said cylindrical wall member; a second pair of magnetic pole pieces received in a second pair of said slots and includin pole faces extending on either side of a second beam passing through a second of said apertures, said second pair of pole faces acting to define a deflection locus for said second beam extending from the center of said second aperture to about the center of said top aperture: and a third pair of pole pieces received in said third pair of slots and providing a pair of pole faces on either side of said third aperture, said third pair of pole pieces cooperating to define a deflection locus for said third beam along a line extending from the center of said second aperture to about the center of said top aperture.

2. The convergence cage of claim 1 wherein said wall member defines a slot extending generally axially thereof for receiving an associated pole piece, the reception portions of each of said pole pieces generally conforming to and welded to the exterior surface of said convergence cage, said deflection coils being spaced at 120 separations about said constricted neck portions.

3. The convergence cage of claim 2 wherein the extensions of the deflection loci defined by said pole pieces associated with said side beams intersect at an axial extension of the center of said top aperture and thereby form an angle of References Cited UNITED STATES PATENTS 2,847,598 8/ 1958 Hughes.

FOREIGN PATENTS 259,640 1/1968 Austria.

ROBERT SEGAL, Primary Examiner US. Cl. X.R. 313-

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