US3868532A

US3868532A - Shadow mask and overscan shield assembly

Info

Publication number: US3868532A
Application number: US395893A
Authority: US
Inventors: Lean Gerald K Mac; Thomas C Minzenberger
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1971-12-02
Filing date: 1973-09-10
Publication date: 1975-02-25
Anticipated expiration: 1992-02-25

Abstract

An improved shadow mask and overscan shield assembly for a color cathode ray tube has a metallic generally rectangular shaped mask supporting frame having a peripherally continuous substantially constant cross-section. The frame has a ring portion extending transversely with respect to the cathode ray tube center axis and a flange portion substantially parallel to the axis. A spherically curved color selection mask having an extended skirt of varying width is secured to the flange portion of the frame. An electron shield secured to the ring portion of the frame has a curved outwardly extending portion which bridges the gap between the frame and the inner wall of the color cathode ray tube envelope to shield the screen from impingement by electrons deflected from the side walls of the envelope and also has an inwardly extending portion of curviform rectangular outline to define the electron beam scansion limits of the screen.

Description

Unite .1%.

Mac Lean et a1.

States atent [1'91 [451 Feb. 25, 1975 SHADOW MASK AND OVERSCAN SHIELD ASSEMBLY [75] Inventors: Gerald K. Mac Lean, Hoffman Estates; Thomas C. Minzenberger, Lake Bluff, both of 111.

[73] Assignee: Zenith Radio Corporation, Chicago,

[22] Filed: Sept. 10, 1973 [21] App]. No.: 395,893

Related US. Application Data [63] Continuation of Ser, No. 204,241, Dec. 2, 1971,

abandoned.

[52] US Cl. 313/407, 313/408 [51] Int. Cl. H01j 29/06, l-l0lj 29/08, l-lOlj 31/20 [58] Field of Search 313/855 [56] References Cited UNITED STATES PATENTS 3,349,272 10/1967 Bathelt et al. 313/85 S 3,404,303 10/1968 Levin 313/85 5 3,454,813 7/1969 Lewinson 313/85 S 3,473,065 10/1969 Schwartz et al. 313/85 S 3,506,867 4/1970 Kraner l 313/85 S 3,585,431 6/1971 Long 313/85 S J. OConnor; Nicholas A. Camasto [57] ABSTRACT An improved shadow mask and overscan shield assembly for a color cathode ray tube has a metallic generally rectangular shaped mask supporting frame having a peripherally continuous substantially constant crosssection. The frame has a ring portion extending transversely with respect to the cathode ray tube center axis and a flange portion substantially parallel to the axis. A spherically curved color selection mask having an extended skirt of varying width is secured to the flange portion of the frame. An electron shield secured to the ring portion of the frame has a curved outwardly extending portion which bridges the gap between the frame and the inner wall of the color cathode ray tube envelope to shield the screen from impingement by electrons deflected from the side walls of the envelope and also has an inwardly extending portion of curviform rectangular outline to define the electron beam scansion limits of the screen.

1 Claim, 4 Drawing Figures RELATED APPLICATION This application is a continuation of application Ser. No. 204,241, filed Dec. 2, 1971, and now abandoned.

BACKGROUND OF THE INVENTION The invention pertains to picture tubes of the type used in television receivers, and more particularly to an improved shadow mask and overscan shield assembly for color television picture tubes.

In color picture tubes of the kind with which the invention is concerned, it is common to provide an evacuated envelope of glass comprising a screen panel section sealed to a mating funnel section. At one end of the funnel there is a neck which houses an electrode arrangement forming one or more electron guns for projecting a stream or streams of electrons toward the screen positioned at the other end. As in the case of a black-and-white picture tube, the energy of the electrons approaching the screen is converted into light by a suitable phosphor, which may be coated on the inside surface of the screen. The color tube, in one practical form of embodiment, utilizes a phosphor screen which is differentiated from point-to-point in that different adjacent elemental areas of the screen are of different phosphor materials to produce light of different colors. A parallax barrier, formed usually of very thin metal capable of interrupting the electron stream, is disposed adjacent the phosphor screen on the gun side, and this barrier is perforated with a large number of apertures geometrically related to the elemental phosphor areas producing the different colors oflight. The geometrical relationship is such that by controlling the beam direction, phosphor areas of different color-producing quality can be selectively energized to produce a visible picture corresponding faithfully to the composition of the original scene.

In prior art tubes having a spherically shaped shadow mask, the leading edge of the support frame is contoured in a fashion corresponding to its intersection with the spherical mask. Thus it is of scalloped configuration, being wider in the center portions of each side and narrower at the corners. The prior art supporting frame also has a ring portion perpendicular to the flange which determines the extent to which the tube screen is scanned by the electron beam or beams and also is of non-constant dimension. It is dimensioned in such a way that its opening resembles an hour-glass configuration to prevent electrons from striking the supporting frame flange and indiscriminately impringing upon the screen. This function performed by the supporting frame ring is commonly known as the rear window function.

The prior art shadow mask assembly also has an electron shield secured to the ring portion of the supporting frame. The supporting frame is secured to the inner walls of the screen section of the cathode ray tube but is spaced apart therefrom. The electron shield is provided to bridge the gap between the inner wall of the envelope and the outer dimension of the intermediate support frame. The electron shield is normally of a very thin metal, such as cold rolled steel foil.

While the prior art shadow mask assembly, as previously described, has been generally effective, it has had the fault of being relatively heavy, adding excessive weight to the picture tube. Excessive tub'e weight creates handling difficulties during the transit of these cathode ray tubes, even though the tubes may be packaged in protective cartons. It has been found that even small reductions in cathode ray tube weight results in substantially less breakage.

Also, since the skirt portion of the mask is relatively narrow in dimension, any weld placed along this skirt "portion to secure the mask to its supporting frame transmits a stress in the direction of the mask causing mask deformations in the peripheral areas of the mask. This causes degradation of the tube performance which is especially noticeable in the purity of the displayed image.

Accordingly, it is an object of the present invention to provide an improved shadow mask assembly for a color cathode ray tube.

It is a further object of the invention to provide a shadow mask assembly for a color cathode ray tube which is lighter in weight than prior structures.

It is a more specific object of the invention to provide a shadow mask assembly where the welding stresses applied to the mask are diminished so that improved color purity may be obtained in a tube incorporating such an assembly.

SUMMARY OF THE INVENTION The invention provides an improved shadow mask and overscan shield assembly for a color cathode ray tube of the type having a glass envelope comprising a curved generally rectangular image screen panel section and a mating funnel and neck section thereto, an interlaced pattern of different phosphors disposed on the curved screen surface, and electron gun means for developing at least one electron beam for generating a raster upon the screen. The improved shadow mask assembly has a metal generally rectangular-shaped mask supporting frame having a peripherally continuous substantially constant cross-section and symmetrically disposed about the central axis of the envelope. The frame has a ring portion extending transversely with respect to the axis and a flange portion substantially parallel to the axis, the frame being attached to the inner wall of the envelope but spaced therefrom. The leading edge of the flange portion is spaced from the screen surface and disposed in a single flat plane perpendicular to the tube axis. A metal shadow mask, of thinner metal stock than the frame, has a multi-apertured parallax barrier with a curvature generally conforming to that of the curved screen surface and with its apertures in spaced predetermined registration with the phosphor pattern and having an integral skirt extending from the parallax barrier parallel to the tube axis into surface contact with the flange portion of the frame and secured thereto. A metal foil electron shield secured to the ring portion of the frame has a curved outwardly extending portion which bridges the gap between the frame and the inner wall of the envelope and a second portion extending inwardly from the frame toward the tube axis to constitute a curviform rectangular rear window with inwardly curved sides for intercepting overscan electrons and preventing their impingement upon the flange portion of the frame, the shadow mask skirt, or the inner side walls of the envelope.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are be- FIG. 1 is a side view, partly in section, of a shadow mask type of color cathode ray tube embodying a shadow mask assembly constructed in accordance with the invention;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary cross-sectional view, partially cut away, taken along line 3-3 of FIG. 2; and

FIG. 4 is a fragmentary cross-sectional view, partially cut away, taken along line 4-4 of FIG. 3.

Referring now more particularly to FIG. 1, the color cathode ray tube there represented has an envelope comprising a curved generally rectangular image screen panel section and a funnel and neck section 11. Envelope sections 10 and 11 are matched as to configuration and dimension and integrated by the usual frit seal 12. The curved screen surface of panel 10 bears an interlaced pattern 13 of different phosphors, as for example a multiplicity of dot triads. Each triad consists of a dot of red phosphor, one of blue and one of green. Customarily the phosphor screen is backed by a layer of conductive light reflecting material, such as aluminum, of such thickness as to be readily penetrated by the electrons of the electron beams of the tube. For convenience, the aluminized layer has not been detailed in the drawing.

At the other end, the tube has the usual base 14 which accommodates the necessary pins through which connections are conveniently made to the electrode systems of the tube. These systems comprise a gun mount shown schematically at 15, because the specific construction is of no particular concern to the present invention. Suffice it to say that the gun mount may be a conventional delta array of three electron guns which, when energized, develop three electron beams for scanning phosphor screen 13.

In order to obtain color selection, a multi-apertured parallax barrier 16, with a curvature generally conforming to that of the curved screen surface and with its apertures in spaced predetermined registration with the phosphor pattern, is disposed across the beam path of the tube between screen 13 and gun mount 15. Its function, as well understood in the art, is to achieve color selection by permitting each of the three beams issuing from the gun mount to see or impinge solely upon an assigned one of the different color phosphor materials of screen 13. Normally, assigned ones of the guns, which are conventionally designated as red, blue and green guns, energize only the assigned color phosphor component of the screen. The color-selection electrode is supported in position by mask supporting frame 17 which is also generally rectangular-shaped. The mask frame 17 is removably secured within the tube envelope by studs 18 projecting inwardly from the envelope to receive a plurality of mounlng springs 19 carried on the periphery of the mask frame 17.

The shadow mask and overscan shield assembly of the present invention comprises mask supporting frame 17 which has a peripherally continuous, substantially constant cross-section and is symmetrically disposed about the central axis 21 of the tube envelope. As best seen in FIG. 3, mask supporting frame 17 has a flange portion 17a which is substantially parallel to axis 21 and has a leading edge spaced from the curved screen surface of panel section 10 and disposed in a single flat plane perpendicular to axis 21. Frame 17 also has a ring portion 17b which extends inwardly from flange por tion 17a toward axis 21 and is preferably perpendicular to the tube axis. In the preferred construction shown in the drawings, the width of ring portion 17b is substantially equal to that of flange portion 17a.

Shadow mask 16, which is formed of much thinner metal stock than frame 17 (typically 6 mils sheet steel as compared with mils cold rolled steel for the frame), comprises a multi-apertured parallax barrier 16a and an integral skirt 16b extending from the para]- lax barrier parallel to tube axis 21 into surface contact with flange portion 17a of the frame, as is best shown in FIG. 3. Parallax barrier 17a has a curvature generally conforming with the curved screen surface and is disposed with its apertures in spaced, predetermined registration with the phosphor pattern of the image screen as is well understood in the art. Skirt 16b is secured, preferably by spot welding at spaced intervals as shown at 23 in FIG. 3, to flange portion 17a of frame 17.

Incorporated onto the flange portion of the shadow mask frame are resilient mounting springs 19 which secure the mask assembly within the envelope in substantially spaced parallel relation to the faceplate by engaging the mounting studs 18. Springs 19 are welded to frame 17 as shown at 26 in FIG. 4. A three-point arrangement has been illustrated in FIG. 1 with the mounting springs on opposing side portions of shadow mask support frame 17 and a mounting spring centrally located at the top of the frame. As can be seen in FIGS. 1, 3 and 4, the periphery of shadow mask support frame 17 is spaced apart from the inner wall of the faceplate panel section resulting in a space therebetween.

A metal foil electron shield member 20 is provided in surface contact with ring portion 17b of frame 17, and shield member 20 is secured to ring portion 17b, preferably by spot welding at spaced intervals, as shown at 22 in FIGS. 2 and 4. Shield member 20 has a curved, outwardly extending portion 20a which bridges the gap between frame 17 and the inner side walls of the tube envelope, in a manner which is well understood in the art and which for example may correspond to that described in detail in U.S. Pat. No. 3,506,867, issued by James Kraner and assigned to the same assignee as the present application. Shield member 20 may be formed of a stainless steel foil of 3 mils thickness.

Further in accordance with the invention, metal foil shield member 20 includes a second portion 20b which extends inwardly beyond the inner edge of ring portion 17b of frame 17 toward the tube axis 21 to constitute a curviform rectangular rear window with inwardly curved sides as best illustrated in FIG. 2. The inwardly extending portion 20b of shield member 20 intercepts overscanned electrons from the gun assembly and prevents them from impinging upon and scattering from the inner surface of flange portion 17a of the frame or upon skirt 16b of the shadow mask, while the curved outwardly extending portion 20a prevents overscanned electrons from passing between the shadow mask assembly and the envelope to the phosphor screen.

The shadow mask and overscan shield assembly of the present invention provides distinct and important advantages with respect to prior art constructions. Firstly, the mask supporting frame 17 is of much simpler construction and lighter weight than the support frames of previously used shadow mask assemblies. Secondly, because the shadow mask skirt is welded to the supporting frame at locations which are removed from the curved parallax barrier portion of the mask, there is a greatly reduced likelihood of deforming the parallax barrier during assembly of the mask to the frame. Because of the greater simplicity in construction and the higher yield or lower reject rate attributable to the improved ease of assembling the mask to the frame without injury to or deformation of the apertured parallax barrier, the construction of the present invention is significantly more economical than previously used constructions. And these advantages are obtained without sacrificing structural strength or stability as compared with prior constructions using scalloped supporting frames of comparable cross-section in the corners but heavier on the sides.

While a particular embodiment of the invention has been shown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

We claim:

1. in a color television picture tube of the type having a glass envelope comprising a curved generally rectangular image screen panel section and a mating funnel and neck section sealed thereto, an interlaced pattern of different phosphors on the curved screen surface of said panel section, and electron gun means housed in said funnel and neck section for scanning the phosphors on said curved screen surface with electrons, an improved shadow mask and overscan shield assembly comprising:

a metal generally rectangular mask supporting frame having a peripherally continuous substantially constant cross-section and symmetrically disposed about the central axis of said envelope, said frame having a flange portion substantially parallel to said axis with a leading edge spaced from said screen surface and disposed in a single flat plane perpendicular to said axis and a ring portion, of a width substantially equal to that of said flange portion, extending inwardly from said flange portion toward said axis and substantially perpendicular thereto, and said frame being secured to said envelope with a space between said frame and the inner side walls of said envelope;

a metal shadow mask, of thinner metal stock than said frame, having a multi-apertured parallax barrier with a curvature generally conforming to that of said curved screen surface and with its apertures in spaced predetermined registration with said phosphor pattern and having an integral skirt extending from said parallax barrier parallel to said axis into surface contact with said flange portion of said frame and secured thereto;

and a metal foil electron shield member in surface contact with said ring portion of said frame and secured thereto, having a curved outwardly extending portion bridging the gap between said frame and said envelope side walls and a second portion extending inwardly from said frame toward said axis to constitute a curviform rectangular rear window with inwardly curved sides, for intercepting overscan electrons from said electron gun means and preventing their impingement upon the flange portion of the mask frame, the shadow mask skirt,

or the inner side walls of the envelope.

Claims

1. In a color television picture tube of the type having a glass envelope comprising a curved generally rectangular image screen panel section and a mating funnel and neck section sealed thereto, an interlaced pattern of different phosphors on the curved screen surface of said panel section, and electron gun means housed in said funnel and neck section for scanning the phosphors on said curved screen surface with electrons, an improved shadow mask and overscan shield assembly comprising: a metal generally rectangular mask supporting frame having a peripherally continuous substantially constant cross-section and symmetrically disposed about the central axis of said envelope, said frame having a flange portion substantially parallel to said axis with a leading edge spaced from said screen surface and disposed in a single flat plane perpendicular to said axis and a ring portion, of a width substantially equal to that of said flange portion, extending inwardly from said flange portion toward said axis and substantially perpendicular thereto, and said frame being secured to said envelope with a space between said frame and the inner side walls of said envelope; a metal shadow mask, of thinner metal stock than said frame, having a multi-apertured parallax barrier with a curvature generally conforming to that of said curved screen surface and with its apertures in spaced predetermined registration with said phosphor pattern and having an integral skirt extending from said parallax barrier parallel to said axis into surface contact with said flange portion of said frame and secured thereto; and a metal foil electron shield member in surface contact with said ring portion of said frame and secured thereto, having a curved outwardly extending portion bridging the gap between said frame and said envelope side walls and a second portion extending inwardly from said frame toward said axis to constitute a curviform rectangular rear window with inwardly curved sides, for intercepting overscan electrons from said electron gun means and preventing their impingement upon the flange portion of the mask frame, the shadow mask skirt, or the inner side walls of the envelope.