US3506867A

US3506867A - Cathode ray tube with electron shield hingedly mounted on shadow mask frame

Info

Publication number: US3506867A
Application number: US737968A
Authority: US
Inventors: James L Kraner
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1968-06-18
Filing date: 1968-06-18
Publication date: 1970-04-14
Anticipated expiration: 1987-04-14

Description

Apnl 14, 1970 .KRANER 3,506,867

CATHODE RAY TUB ELECTRON SHIELD HINGEDLY MOUNTED ON ADOW MASK FRAME Filed me 18, 1968 '5,7,,F1G:l,,,....

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Inventor James L. Kroner Ahorn y United States Patent O US. Cl. 31385 8 Claims ABSTRACT OF THE DISCLOSURE An electron shield for a shadow mask type of color tube bridges the space between the mask frame and the tube envelope. The cross-section of the shield has a L shaped portion located in the space between the frame and the envelope with its bowed part toward the screen and with its bight dimension less than the spacing of the frame to the envelope. The stem of the J-shaped portion has a mounting portion connected thereto and defines therewith a hinge. The mounting portion is welded to the mask frame and the dimensioning is such that the hinge is spaced away from the frame both in the direction of the gun and in the direction of the envelope.

BACKGROUND OF THE INVENTION The present invention is directed to an improved electron shield for a color cathode-ray tube which features the use of a color selection electrode, such as a shadow mask.

It is 'well known that the forming of the phosphor screen of such a tube, which in the usual case is an interlaced pattern of three different phosphor materials, requires a great many process steps for some of which it is necessary that the shadow mask be in position adjacent the faceplate whereas for others the mask is removed. To permit such process steps to be conducted, the envelope of the tube is constructed of a funnel section and a cap or faceplate panel section which is comprised of an image screen surrounded by a shallow peripheral flange. Studs projecting inwardly from the flange releasably receive mounting springs secured to the frame of the shadow mask and this frame has smaller overall dimensions than the faceplate panel. Accordingly, the mask may readily be installed and removed from the panel as required in carrying out the process step through which the screen is deposited. The panel is then united with the funnel section of the envelope and the remaining steps are carried out to complete the tube.

From what has been said it is clear that a space surrounds the frame of the shadow mask, representing the separation of that structure from the envelope. Since it is common practice in the operation of a television receiver to overscan the screen, this space gives access of electrons to the screen which is undesirable; by distinct preference electrons should reach the screen only through the shadow mask or color selection electrode because only in this fashion is color purity obtained. Thus, it will be understood that electron reaching the screen through the space between the frame of the shadow mask and the tube envelope result in spurious excitation of the peripheral portions of the screen and lead to degradation of color fidelity.

To overcome this difiiculty, it has been proposed heretofore that a shield bridge the space between the frame of the shadow mask and the adjacent internal walls of the envelope. Usually the shield is formed of metal, such as relatively thin steel, but the arrangements previously adopted have been subject to one operating defect in ice particular. Notably, the shield structure is such that, when the frame expands as the tube attains its operating temperature, the shield is caused to be driven against the envelope. Frequently, the free end of the shield either digs into the frit by means of which the faceplate panel and funnel are united or chips off flakes of the aluminized layer normally applied to the screen and frequently overlapping the flange of the screen panel. Such particles may result in short circuits within the electron gun and destroy the tube.

This problem is readily understood when it is appreciated that the prior shield structure was J-shaped in cross section and was wedged between the mask frame and the contiguous internal wall of the envelope. Heating of the frame, which results in expansion in a direction transverse to the tube axis, creates a torque against the shield, driving it away from the frame and into the envelope, that is to say, into the frit seal or the aluminum layer.

Accordingly, it is an object of the invention to provide an electron shield for a color cathode-ray tube which avoids or minimizes the aforementioned difliculty of prior shield structures.

It is a specific object of the invention to provide an improved electron shield for a shadow mask type of three gun cathode-ray tube.

SUMMARY OF THE INVENTION An electron shield embodying the invention bridges the space between the frame of the color selection electrode and the tube envelope. The shield is impervious to electrons and in cross-section has a configuration comprising a J-shaped portion bowed toward the phosphor screen with a bight dimension less than the spacing between the frame and the envelope. 'One end of the J-shaped portion is free but the other or stem connects with a mounting portion and together they define a hinge. The mounting portion is secured to the frame of the color selection electrode with the J-shaped portion of the shield disposed in the space to be bridged but out of contact with the electrode frame and further with the hinge not only spaced from this frame but extending in the direction of the tube base or gun mount.

BRIEF DESCRIPTION OF THE DRAWING The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a cross-sectional view of a shadow mask type of color cathode-ray tube in which an electron shield embodying the invention has been installed;

FIGURE 2 is an enlarged fragmentary view of the color tube showing in greater detail the cross-sectional configuration of the electron shield.

Referring now more particularly to FIGURE 1, the color cathode-ray tube there represented has an envelope comprising essentially of a faceplate panel 10 and a funnel section 11. It is of no particular moment whether the tube be round or rectangular although, of course, envelope sections 10 and 11 must be matched as to configuration and dimensions in order that they may be integrated by the usual frit seal 12. The faceplate panel bears an interlaced pattern 13 of different kinds of phosphor materials, the more popular pattern being a multiplicity of so-called 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 and 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 in block diagram 15 because it is of no particular concern to the present invention. Suffice it to say that the gun mount is an assembly or delta array of three electron guns which, when energized, develop three electron beams for scanning phosphor screen 13.

In order to obtain color selections, a color-selection electrode 16, which for the case under consideration is an apertured shadow mask, is disposed across the beam paths 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 issued from gun mount 15 to see or impinge solely upon an assigned one of the different color phosphor materials of screen 13. Frequently this is referred to as defining red, blue, and green guns by which it is seen that each such gun energizes only the assigned color phosphor component of the screen. The color-selection electrode is supported in position by a structural frame 17 which has one portion disposed parallel to the longitudinal axis of the tube and another flat portion 17a disposed transversely of the tube axis. The mask frame 17 is removably secured within the tube envelope by studs projecting inwardly from the envelope to receive a plurality of mounting springs carried on the periphery of mask frame 17. One such stud 18 is shown in the drawing along with one of the mounting springs 19 but again all of this structure is well known.

As thus far described, there is nothing unique or unusual in the color tube of FIGURE 1. It is the usual shadow mask device in which three electron beams, controlled by both chrominance and luminance information, are caused to scan the image screen 13 through the apertures of shadow mask 16. Through the assignment of the three beams with the three phosphor components of the screen, an image is reproduced in natural color. Clearly if in the scanning process the beams pass beyond the confines of mask 17, electrons may enter the space 20 between the mask frame and the envelope and cause spurious excitation of the screen as related above. This is avoided by an improved electron shield 21 arranged to bridge space 20 and preclude electron access to screen 13 through that space.

The details of the shield are best understood with reference to the enlarged view of FIGURE 2. The shield is impervious to electrons being formed, for example, of stainless steel of a thickness of approximately 3 mills. In cross-section the shield has a configuration comprising a J-shaped portion 21a bowed in the direction of screen 13 and with a bight dimension d that is less than spacing 20. End 21b of the I-shaped portion is free but the other end or stem 21c thereof is extended and has a mounting portion 21d connected to it to define therewith a hinge or pivot 21e. The mounting portion 21d is secured to the flat portion 17a of the frame by welding with matters arranged by dimensioning of the shield so that the J-shaped portion 21a is not only disposed in space 20 but is out of contact with frame 17. Further, the hinge 21e is spaced from frame 17 and extends in the direction of gun mount 15. It will be observed that the contact point 21 of the shield with the envelope occurs in a plane that is disposed to the screen side of hinge 21a and preferably it is substantially in the plane of frame portion 17a. Notice further that free end 2111 is formed away from contact point 21 toward the longitudinal axis of the tube and terminates on the screen side of hinge 21a. Additionally with the described structure the entirety of the shield is spaced from the plane of mounting studs 18 in the direction of gun mount 15 to avoid the objectionable problem of distortion where the shield, as in prior arrangements, overlaps these mounting studs. In short, the studs do not destroy the desired J-shaped configuration of the shield.

The angle x defined by mounting portion 21d and frame portion 17a is of the order of 35. A distinct advantage of the disclosed structure will be apparent from consideration of the consequence of movement of frame 17 as the tube achieves its elevated operating temperature. As the frame is brought to its stable operating temperature, it expands transversely and thus tends to move in the direction of the envelope. This applies a force which causes the bight portion 21a of the shield to rotate in a clockwise direction in FIGURE 2 about hinge 21e. In other words, it swings toward frame 17 which is opposite to the response experienced in prior structures as a consequence of frame expansion. This avoids any possible damage to the frit seal and precludes flaking of the aluminum coating which may be deposited on the flange of faceplate panel 10 during the aluminizing process. This same advantageous direction of shield deflection is encountered when it is necessary to load or unload frame 17 from the envelope during screening with attendant advantages of minimizing damage to the tube and frame structures. Of course, the shield may, if desired, be attached to frame 17 after the screening process has been completed. The bight portion 21a in conjunction with stem portion 21c and mounting portion 21d contributes mechanical rigidity to the shield, in a direction normal to the functional movement of bight position 21a, which is also desired.

Finally, since the shield is to protect the entire space around frame 17 few parts are required. If the tube is round, for example, two C shaped sections of the shield may suffice and for the case of a rectangular tube two L sections are suitable.

By way of further particularization of the illustrated embodiment, a shield constructed from a 25 inch rectangular tube in which spacing 20 was .385 inch had the following specification:

Material 3 mil stainless steel. Bight diameter d .250 inch.

Stem dimension e .125 inch.

Angle x 5730.

Dimension 1 .520 inch. Dimension g .060 inch.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a color cathode-ray tube of the type having an envelope terminated at one end in an image screen, an interlaced pattern of different kinds of phosphor materials disposed on said screen, an electron gun means for developing at least one electron beam to be scanned across said screen, and a structural frame attached to said envelope but spaced therefrom and supporting a colorselection electrode across the beam path of said tube between said screen and said gun means to determine the particular phosphor material impinged by said beam during the scanning of said screen, the improvement which comprises an electron shield bridging the space between said envelope and said frame to prevent electron access to said screen by way of said space, said shield being impervious to electrons and, in cross-section, having a configuration comprising a J-shaped portion bowed toward said screen with a bight dimension less than said spacing, being free at one end and having a mounting portion connected to and extending from the other end to define therewith a hinge, said mounting portion being secured to said frame with said J-shaped portion disposed in said space out of contact with said frame and with said hinge spaced from said frame and extending in the direction of said gun means.

2. An electron shield in accordance with claim 1 in which said frame supports said color-selection electrode on one face and on its opposite face has a flat portion disposed in a plane extending transversely of said beam path, and in which said mounting portion of said shield is affixed to said flat portion of said frame.

3. An electron shield in accordance with claim 2 in which said J-shaped portion contacts said envelope in a plane that is to the screen side of said hinge.

4. An electron shield in accordance with claim 3 in which said J-shaped portion contacts said envelope sub- 'stantially in the plane of said flat portion of said frame.

5. An electron shield in accordance with claim 4 in which said mounting portion, in extending to said hinge, defines with said flat portion of said frame an angle of approximately 35.

6. An electron shield in accordance With claim 4 in which said J-shaped portion is dimensioned so that said free end thereof deflects away from the contact plane of said shield with said envelope toward the longitudinal 6 axis of said tube and terminates on the screen side of said hinge.

7. An electron shield in accordance with claim 4 in which said envelope has internal studs to which said frame is attached and in which said shield is spaced from studs in the direction of said gun means.

8. An electron shield in accordance with claim 3 in which said hinge is spaced from said frame in the direction of said envelope.

References Cited UNITED STATES PATENTS 3,346,753 10/1967 Haas 313-92 3,377,493 4/1968 Levin et al. 31392 3,404,303 10/1968 Levin 31385 JAMES W. LAWRENCE, Primary Examiner V. LAFRANCHI, Assistant Examiner US. or. Xn. 34 s 240