US3596126A - Cathode-ray tube with parallel slit grid structure adjacent color display screen - Google Patents

Abstract

A color picture tube or other cathode-ray tubes in which a plurality of electron beams emanating from one or more cathodes are made to converge substantially at the optical center of an electrostatic focusing lens which focuses the beams on an electron receiving screen. When beams are focused on the electron receiving screen are all to converge at a common point on such screen an electrostatic or magnetic deflection device acts on those beams which diverge after passing through the lenslike focusing system. A grid is positioned adjacent the electron receiving screen of the tube in order to sharply focus the electron beams on the electron receiving screen. The support for the grid structure is stressed to compensate for any expansion of the grid wires due to heating. The support has a pair of opposed parallel arms with the grid wires attached to and extending transversely between the arms and a pair of braces supporting the arms at the bessel point, the braces being stressed in a direction substantially parallel to the direction of the grid wires so that as the grid wires expand due to heat, the braces will expand a corresponding amount to maintain a substantially constant tension on the grid wires.

Description

United States Patent [72] inventors Susulnu Yoahida;

Aldo Ohgoshl, Tokyo; Senrl Miyanlta, Kanagawa-lten; Yoshlllaru Katagiri, Tokyo, all of, Japan [21] Appl. No. 829,295

[22] Filed June 2, 1969 [45] Patented July 27, 1971 [73] Assignee Sony Corporation Tokyo, Japan [32] Priority Jan. 14, 1967, Mar. 22, 1967 [31 42/2629 and 42/ 17856 Continuation-impart of application Ser. No. 697,414, Jan. 12, 1968, now Patent No. 3,448,316, dated June 3, 1969.

[54] CATHODE-RAY TUBE WITH PARALLEL SLl'l GRID STRUCTURE ADJACENT COLOR DISPLAY SCREEN 2 Claims, 3 Drawing Figs.

[52] U.S.Cl 313/86,

[51] int. Cl '.1401) 29/56,

i-iOij 29/80, HOIj 29/06 [50] Field of Search 313/92 PD, 85,69 C, 70 C, 92 8, 86

[56] References Cited UNITED STATES PATENTS 2,777,088 1/1957 Laffcrty 313/92 PDF X 2,832,911 4/1659 Van Velzer............ 313/ 85 x 2,862,107 11/1958 Cummings.................... 3| 3/85 X 3,462,638 8/1969 Tetsuo et al. 313/70 C X FOREIGN PATENTS 1,071,963 6/1967 Great Britain 313/85 Primary Examiner-Robert Segal Attorneys-Albert C. Johnston, Robert E. lsner, Lewis H.

Ealinger and Alvin Sinderbrand ABSTRACT: A color picture tube or other cathode-ray tubes in which a plurality of electron beams emanating from one or more cathodes are made to converge substantially at the optical center of an electrostatic focusing lens which focuses the beams on an electron receiving screen. When beams are focused on the electron receiving screen are all to converge at a common point on such screen an electrostatic or magnetic deflection device acts on those beams which diverge after passing through the lenslike focusing system. A grid is positioned adjacent the electron receiving screen of the tube in order to sharply focus the electron beams on the electron receiving screen. The support for the grid structure is stressed to compensate for any expansion of the grid wires due to heat ing. The support has a pair of opposed parallel arms with the grid wires attached to and extending transversely between the arms and a pair of braces supporting the arms at the bessel point, the braces being stressed in a direction substantially parallel to the direction of the grid wires so that as the grid wires expand due to heat, the braces will expand a corresponding amount to maintain a substantially constant tension on the grid wires.

PATENTEU JULZT IBYI 4 mv- TORS SUSUMU YOSHIDA AKIO OHGOSHI SENR! MIYAOKA VOSHIHARU KATAGIRI iwe CATHODE-RAY TUBE WI'I'II PARALLEL SLI'I GRID STRUCTURE ADJACENT COLOR DISPLAY SCREEN This application is a continuation-in-part application of our copending application Ser. No. 697,414, filed Jan. 12, 1968 and issuing June 3,1969 as US. Pat. No. 3,448,3 I 6.

This invention generally relates to cathode-ray tubes and is particularly directed to improvements in color cathode-ray tubes of the type in which a single electron gun is provided for emitting a plurality of electron beams in order to produce a color picture such for example as in color television receivers.

Existing color picture tubes are usually of the multigun type and include three independent electron guns emitting respective electron beams which are modulated by corresponding color signals and acted upon by a grid system so as to be focused on a collector or electron receiving screen which may be simply a phosphor or luminescence screen or a phosphorus screen with a perforated electrode or shadow mask in front thereof. The three electron guns have to be aligned with respect to each other so that the emitted electron beams converge at the electron receiving screen. Such color picture tubes of the multigun type are disadvantageous in that it is difficult to obtain and maintain the precise alignment of the three electron guns required for the convergence of their beams on the electron receiving screen and any misconvergence of the beams causes deterioration of the quality and resolution of the color picture that results.

In an attempt to avoid the above-mentioned disadvantages and limitations of the existing color picture tubes of the multigun type, it has been proposed to provide a color picture tube of the single gun plural beam type in which a single electron gun emits three beams from either three respective cathodes or a single cathode and the three electron beams are passed through a lenslike focusing system so as to converge at the electron receiving screen. However, in the tubes of the single gun plural beam type heretofore proposed. no more than one of the electron beams passes through the lenslike focusing system at the optical axis of the latter and the beams that pass through the focusing system at a distance from the optical axis are subject to coma and spherical aberration. By reason of such coma and spherical aberration and the consequent deterioration of the quality of the color picture that results, color picture tubes of the single gun plural beam type have not enjoyed any widespread use.

In my copending patent application filed Jan. I2, 1968, and bearing U.S. Pat. No. 3,448,3l6 entitled CATHODE-RAY TUBE, there is described a cathode-ray tube adapted for use in a color television receiver and which is provided with a single electron gun. This gun includes a cathode structure that emits electrons which are formed into a plurality of electron beams and such beams are made to converge substantially at the optical center of a lenslike electrostatic focusing lens which is common to all the beams and focuses the beams on the electron receiving screen whereby the introduction of spherical aberration is diminished.

In cases where the electron beams are emitted parallel to each other, the convergence of the beams at the optical center of the lenslike focusing means is effected by an auxiliary electrostatic lens located between the grid structure which forms the electron beams and the focusing lens. When it is desired that the beams focused on the electron receiving screen be converged at a common point on the screen the beams which diverge from the focusing lens are acted upon by either electrostatic or magnetic deflection means located between the focusing lens and the screen.

As is well known in the prior art, color cathode-ray tubes employ, for electron beam postdeflection and focusing, a grid structure such that a plurality of parallel grid wires are stretched across a parallelograrnic frame between a pair of opposed sides. Such a grid structure is produced in the following manner. A plurality of parallel grid wires are stretched on a master frame under predetermined taut conditions and a grid frame is put on the grid wires from inside of the master frame.

The grid wires are then fixed to a pair of opposed supports of the grid frame and are thereafter severed along the margins of the grid frame. In this case, the grid frame is prcstressed inwardly by a turnbuckle to apply a maximum tension to the grid wires secured to the central portion of the opposed supports of the grid frame and a smaller tension to those fixed to end portions of the supports, ensuring that all the grid wires are subjected to substantially uniform tension by the restoring force of the prcstressed grid frame after disassembling it from the master frame.

Such a grid structure may be regarded as one where a plurality of grid wires are stretched at substantially uniform ten sion on a parallelogramic frame prcstressed in a manner to be displaced the most at the center of the frame. When a predetermined positive potential is applied to such a grid structure and electron beams are emitted from the electron gun of a cathode-ray tube toward the fluorescent screen thereof, electron beams of several to lO-odd percent strike against the grid wires and are discharged therethrough to thereby heat the grid wires. As a result of this, the temperature of the grid wires is raised several-l0" and the wires expand. An examination of the expanded grid wires shows that since the displacement of the frame is greatest at the center thereof, elongation of the grid wires of that portion due to the thermal expansion is cancelled by the restoring force of the prcstressed frame as if the grid wires had not been elongated. Accordingly, the grid wires are still subjected to substantially the same original tension, and hence do not sag. The elongation of the grid wires lying on both sides of the central grid wires cannot be absorbed with the displacement of the frame at those particular portions, since the displacement is basically small. Consequently, when the elongation of the grid wires exceeds the displacement of the frame, the grid wires are likely to sag. Even if the grid wires do not sag, they are not pulled at a predetermined tension and are readily vibrated at great amplitude to lower the picture quality of the reproduced picture when subjected to accidental small shocks.

The above can be easily understood from the fact that when all the grid wires have substantially the same length, the amount of restoration of the frame on both sides of the center thereof is smaller than that of the central portion.

This defect is remarkable especially in the grid structure of a color cathode-ray tube of the type where a plurality of ribbonlike grid elements are stretched in parallel with phosphor strips and function as a kind of shadow mask. In this type of structure three electron beams are impinged upon three different color emissive phosphor strips through slits defined between adjacent grid elements.

A grid structure such as described above has been proposed in an attempt to increase the electron beam transmission factor of the so-called shadow mask in which a plate having bored therethrough a plurality of apertures is used as a mask for the electron beam. In such a grid structure, however, the grid elements are secured only at both ends to the frame, so that the grid elements heated by electron beams striking thereon radiate heat mainly through the ends fixed to the frame. Further, the transmission factor of the electron beam through such a grid is lO-odd to 20-odd percent and the temperature of the grid elements rises up to I00 C. to C. Consequently this type of grid structure encounters the same problems as in the Chromatron (Registered Trademark) type color cathode-ray tube.

In addition to the sag of the grid elements, nonuniformity in the tension applied to the grid elements raises another problem in such a grid structure as mentioned above. Even slight nonuniformity in the tension causes the grid elements to twist and the space between adjacent grid elements becomes wider in a direction normal to the incident direction of the electron beam, although the pitch of the grid elements remains unchanged. As a result of this, there is the possibility that the electron beam strikes on a phosphor strip other than a predetermined one, especially a phosphor strip adjacent the predetermined one to cause unnecessary color emission.

Therefore, the nonuniforrnity in the tension applied to the grid elements should be avoided.

Accordingly, it is an object of this invention to provide a cathode-ray tube of the single gun, plural beam type which is free of the above-mentioned disadvantages characteristics of tubes of that type as previously proposed and which is particularly suited to serve as a color picture tube for producing color pictures of high resolution and brightness.

Another object of this invention is to provide a cathode-ray tube particularly a color picture tube which is of the single gun, plural beam type and can be relatively easily manufactured even when miniaturized to a considerable degree.

A further object of this invention is to provide a cathode-ray tube in which a grid structure is provided such that the grid elements are always subjected to a predetermined tension and do not sag during operation though heated by electron beams.

Yet another object of this invention is to provide a grid structure for shadow mask type color cathode-ray tubes in which the grid elements heated by electron beams do not sag during operation to thereby insure uniformity in the spacing between adjacent grid elements and hence prevent unnecessary bombardment of the phosphorus strips by the electron beam.

A still further object of this invention is to provide the cathode-ray tube with a grid structure which is constructed such that the grid elements are protected from shocks applied from the outside and caused by electron beam bombardment.

The above and further objects, features and advantages of the present invention will appear from the following detailed description of a preferred embodiment of the invention which is to be read in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic view illustrating the optical equivalent of a single gun, plural beam system in which the beams are converged to substantially the optical center of an electrostatic focusing lens;

FIG. 2 is a plan view showing one example of a grid structure for color cathode-ray tubes produced according to this invention; and

FIG. 3 is a side view of the grid structure illustrated in FIG. 2.

Referring now to the figures there is illustrated in FIG. I the optical equivalent of a cathode-ray tube having a single electron gun that generates a plurality of electron beams that are converged to substantially the optical center of a focusing lens. The single electron gun A includes equivalent beam generating sources K,, K, and K, which are located on a straight line in a plane substantially perpendicular to the axis of the electron gun and spaced apart from each other by a distance d,. These beam generating sources K,, K,, and K, have been converged to an area of minimum cross section by means not illustrated such that the area of minimum cross section of each of the beams is at the position designated K,, K, and K, The beam generating sources emit three electron beams 3,, B, and 8,, respectively, which are refracted by means of a common auxiliary lens L so as to be converged substantially at the optical center of a main focusing lens L. Thus, the three 8,, B, and B, are made to cross each other at substantially the optical center of the main focusing lens L and then to emerge from the focusing lens L in divergent directions. Subsequently the beams B, and B, which diverge from the optical axis and from the beam B, lying on such axis are deflected toward the center beam B, by means of convergence deflectors F, and F, provided between the electron receiving screen S and the main lens L and spaced from the latter by a distance 1 so that the three beam spots 8,, B and B, on the screen are converged or superimposed on each other.

With the arrangements shown in FIG. I therefor very small beam spots can be obtained since all three beams 13,, B, and B, pass through the center of the main focusing lens L and thus the focused beam spots are prevented from being blurred due to various spherical aberrations. Consequently a picture with a high resolution can be produced. Furthermore, utilization of the deflectors F, and F advantageously facilitates the dynamic convergence correction with respect to the three beams.

It is to be understood that although FIG. 1 illustrates the beam generating sources K,, K, and K, as lying in a straight line and the electron beams being refracted by means of a common auxiliary lens L so as to be converged substantially at the optical center of the main focusing lens L the same thing can be accomplished by arranging the beam generating sources I(,, K, and K, on a arcuate surface. In this respect FIG. I is merely illustrative and not in any way meant to limit the scope of this invention.

As explained in copending Pat. application Ser. No. 790,350, filed Jan. l0, I969, entitled GRID STRUCTURE FOR COLOR PICTURE TUBES and assigned to the same assignee as this patent application, a grid structure is positioned adjacent the electron receiving screen and therefor between the electron gun and the electron receiving screen. The construction of this grid structure is illustrated in FIGS. 2 and 3.

As clearly shown in the figures, the grid structure of this invention comprises a frame of a predetermined configuration which consists of bar supports 4 and 4' and a pair of substantially C-shaped resilient supports 5 and 5 supporting the bar supports 4 and 4' at locations spaced inwardly from the ends thereof, and more particularly at or in the vicinity of the Bessel points 8,, B, and B,,', B, thereof, and a plurality of ribbon-shaped grid elements of, for example, stainless steel are stretched between the bar supports 4 and 4' at a predetermined pitch under predetermined distribution of tension. Reference numeral 7 indicates generally the grid structure.

The bar supports 4 and 4' may be formed of a metal such as iron, stainless steel or the like and in the illustrated example the bar supports 4 and 4 are square in cross section and are bent to conform to the panel to which the grid structure will be attached. The resilient supports 5 and 5' may be formed of a metal such as iron, stainless steel or the like and are substan tially C-shaped so as not to disturb the irradiation of the phosphor screen by the electron beam emitted from the electron gun of a cathode-ray tube. It is a matter of course that the supports 5 and 5' may be configured at will so long as they do not disturb the electron beam directed to the fluorescent screen of the cathode-ray tube. The grid elements 6 may also be formed of a metal such as iron, stainless steel or the like.

With such an arrangement, since the pair of bar supports 4 and 4' constituting one portion of the frame are jointed to the resilient supports 5 and 5' as a unitary structure at or in the vicinity of the Bessel points 8, B, and B and B,,', the bar supports 4 and 4' may be regarded as a rigid body with respect to the load caused by the tension of the grid elements. The term Bessel points," as used herein, has its accepted meaning and refers to those points along each of bar supports 4 and 4' spaced inwardly from the ends of the bar supports by a distance equal to about 0.2232 X the length of the bar support so that, when the latter is loaded substantially equally along its length, as by the tension in grid elements 6, and supported at the Bessel points, as by the supports 5 and 5', the deflections of each of bar supports 4 and 4' at the ends thereof will be equal to the deflection at the center and the deflections at the ends and center will be minimized. Accordingly, when the grid elements 6 that are stretched between the bar supports 4 and 4' uniformly at a predetermined tension expand by heat resulting from the electron beam bombardment thereon, the bar supports 4 and 4' are pulled outwards by the resilient supports 5 and 5' in a parallel relationship by a distance corresponding to the length of the grid elements which have been extended by the thermal expansion. Consequently, although the ab solute value of the tension is different from the initial one, the initial distribution of the tension over the entire grid elements remains unchanged.

The foregoing description has been made in connection with a grid structure in which the grid elements are of substantially the same length at the both end portions and central portion of the bar supports and hence they are expanded substantially equally due to thermal expansion. According to our experiments on a grid structure in which the bar supports of square cross section were made of stainless steel and had a size of about It) mm. XIO mm. X240 mm. and 400 grid elements 0.5 mm. wide, 0.I mm. thick and about I80 mm. long (the length of the grid elements on the end portions of the bar supports were I75 mm. and that of the elements of the central portion: 185 mm.) were stretched between the bar supports at a tension of about 350 g. for each grid element, it has been ascertained that although the grid elements were heated by electron beams and extended due to thermal expansion during operation, accidents such as vibration of the grid elements due to nonuniformity of the tension or color contamination due to irregularity of the space between adjacent grid elements were not caused. Further, it has been found that the deviation from the initial distribution of the tension of the grid elements caused by the thennal expansion thereof resulting from the collision of the electron beam therewith were compensated for by the stretch or shrinkage of the grid elements or slight restoring force of the bar supports.

In addition, it has also been found that if the deviation of the length of the grid elements is in a range of percent relative to its mean value, the length of the grid elements extended by the thermal expansion is extremely short and the initial distribution of the tension of the grid elements is maintained during operation by the stretch and shrinkage of the grid elements or by compensation due to the restoring force of the bar supports.

The grid structure is assembled with the panel of a cathoderay tube in the following manner. Resilient pieces of a predetermined shape are secured to the resilient supports 5 and 5' and the bar support, for example, 4, each resilient piece having bored therethrough an aperture at the free end. It is preferred that an elongated hole extending in the direction of the grid elements be formed in at least one of the resilient pieces secured to the resilient supports. Projections are provided on the sides of the panel on the inside thereof and the projections are inserted into the apertures of the resilient pieces in assembling the grid structure with the panel. In this case the resilient pieces and the projections of the panel may be four respectively.

In the aberration of the cathode-ray tube of the present invention, appropriate voltages are applied to the grids of the electron gun. In this manner the beams 8,, B, and B, emanat ing from the cathodes K,, K, and K, are made to cross each other substantially at the optical center of the main focusing lens L. The beam: B, and B, emerge from the main focusing lens L along divergent paths. These three beams are acted upon by the convergence deflectors F and F, provided between the electron receiving screen S and the main lens L and spaced from the latter by a distance so that the three beam spots 8,, B, and B, are converged or superimposed on each other. A color screen 5 comprised of sets of red, green and blue phosphorous strips has positioned before it the aperture grill A of the present invention. The three beams 8,, B and B, are made to cross each other at the position of the aperture grill A, and thus to laiid on the corresponding phosphorous strips.

In the foregoing description the electron gun embodying this invention has been described as being applied specifically to colored picture tubes in which a single gun is employed to produce three electron beams which are intensity modulated with the usual red, green, and blue color signals. However, it is obvious that an electron gun in accordance with this invention can be used in any other cathode-ray tube requiring a plurality of beams which are to be focused at a common spot or at separated spots on an electron receiving screen.

Although illustrative embodiments of electron guns according to this invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications may be made therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.

What we drum is:

I. A cathode-ray tube comprising beam producing means for producing a plurality of electron beams, a screen having arrays of different color phosphors and being positioned to have said beams impinge on respective color phosphors of said arrays for exciting the same, means for causing said beams to intersect at a location in the tube between said beam producing means and said screen, whereby said beams diverge with respect to each other in traveling toward said screen from said location, focusing lens means for focusing all of said beams on said screen, said focusing lens means having an equivalent optical center and being positioned to dispose said optical center substantially at said location where the beams intersect, convergence deflection means positioned between said focusing lens means and said screen and operating on at least certain of said beams diverging with respect to each other to cause the beams to again intersect each other in a plane in advance of said screen, and a grid structure positioned in said plane in advance of said screen and having parallel slits through which said beams can pass for impingement on the respective phosphors of said arrays.

2. A cathode-ray tube according to claim 1, in which said grid structure includes a pair of opposed, spaced-apart sup port bars, a set of substantially parallel, spaced-apart elongated elements extending between said support bars and defining said slits between said elements, and a pair of braces extending between said support bars and being stressed in compression while said elements are stressed in tension so that, when said elements expand in response to heating thereof, said braces maintain said elements under tension.

Disclaimer 3,596,126.Swsumu Yoshz'da and Akz'o Ohgoshi, Tokyo, Semi Mz'yaolca, KamigaWa-ken, and Yoshz'ham Katagiri, Tokyo, J a an. OATHODE RAY TUBE WITH PARALLEL SLIT GRI TRUCTURE ADJ A- CENT COLOR DISPLAY SCREEN. Patent dated July 27, 1971. Disclaimer filed Apr. 7, 1972, by the assignee, Sony Corporation. Hereby disclaims the portion of the term of the patent subsequent to June 3, 1986.

[Oficial Gazette May 9, 1.972.]

Claims (2)

1. A cathode-ray tube comprising beam producing means for producing a plurality of electron beams, a screen having arrays of different color phosphors and being positioned to have said beams impinge on respective color phosphors of said arrays for exciting the same, means for causing said beams to intersect at a location in the tube between said beam producing means and said screen, whereby said beams diverge with respect to each other in traveling toward said screen from said location, focusing lens means for focusing all of said beams on said screen, said focusing lens means having an equivalent optical center and being positioned to dispose said optical center substantially at said location where the beams intersect, convergence deflection means positioned between said focusing lens means and said screen and operating on at least certain of said beams diverging with respect to each other to cause the beams to again intersect each other in a plane in advance of said screen, and a grid structure positioned in said plane in advance of said screen and having parallel slits through which said beams can pass for impingement on the respective phosphors of said arrays.

2. A cathode-ray tube according to claim 1, in which said grid structure includes a pair of opposed, spaced-apart support bars, a set of substantially parallel, spaced-apart elongated elements extending between said support bars and defining said slits between said elements, and a pair of braces extending between said support bars and being stressed in compression while said elements are stressed in tension so that, when said elements expand in response to heating thereof, said braces maintain said elements under tension.

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