US2879435A

US2879435A - Cathode-ray tube

Info

Publication number: US2879435A
Application number: US606001A
Authority: US
Inventors: Sanford Emil
Original assignee: Allen B du Mont Laboratories Inc
Current assignee: Allen B du Mont Laboratories Inc
Priority date: 1956-08-24
Filing date: 1956-08-24
Publication date: 1959-03-24
Anticipated expiration: 1976-03-24

Description

E. SANFORD CATHoDE-RAY' TUBE March 24, 1959 g-Filed Aug. 24, 1956 3 sheet-sheet 1 INVENTOR. EMIL SAN/:URD

ATTORNEYS March 24, 1959 E. SANFORD cATHoDE--RAY TUBE :Filed Aug. 24. 1956 INVENTOR. .EM/L SANFORD BYE f'a'ivfy/ ATTORNEYS- I March 24, 1959 Filed Aug. 24, 1956 E. SANFORD CATHODE-RAY TUBE Fig. 6

3 Sheets-Sheet 3 INVENTOR.

sfu/L SANFORD ATTORNEYS 2,879,435 Patented Mar. 24, 119,59

ICC

Laboratories, Inc., Clifton, NJ., a corporation -o'f rDelaware `Application August 24, 1956, Serial No. 606,001

-6 Claims. (Cl. 315-1) 'This invention relates to cathode-tray tubes, fand fin particular to cathode-ray tubes ladapted ffor ycolor presentaticn.

'The usual cathode-ray tube 4has on "the inner surface on its faceplate, a ysubstantially continuous uorescent screen which emits light from any portion which .is struck by an electron beam. Cathode-ray tubesr adapted to produce color presentations have, instead of a continuousuorescent screen, discrete -areas each 'of which emits light of a particular color. Thus, vred light is emitted When a red electron beam strikes .a red-light-emittingarea (which may be va red dot, "f1-ed stripe, vor 4other geometrical configuration). In order `to prevent excitation or other areas 'by the red electron beam, a foram'inous mask is utilized. 'It is positioned so 'that {the red electron beam passes through 'the apertures -a't a given angle to strike the red dots,'the other light-emitting areas being meanwhile masked from the red Abeam by the solid 'portions of the mask. In Ava similar manner, a blue electron gun produces a blue Aelectron beam which passes through the lmaskapertures at `a slightly different angle to strike only phosphors nwhich Iemit f'blue ligh't. Green light is lemitted in ya ksimilar manner.

ln orderto produce light from areas remote from Vthe center of the tubes faceplate, the, deection coil Iis ener g'ized.- The electron beam paths are 4gradually ycurved 5 thereby, but ltheyact as though they weresharplybentea't points known as color centers which 'occu'rat the intersections of the various undeected electron y:beam paths and aihypo'thetical deect'ion planejthus there iisared, a'green, "and ablueco'lor-center. It will jbe `understood that aline drawn from any fcolor-center 'through any aperture should tpass through a phosphor jdot which emits light whose color corresponds to lthat particular Ycolor center. .Displacement .of .either the color-center, the mask (and =its apertures), or 'the phosphor `areas would cause an electron beam -to vexcite .other color emitting areas, producing a condition knownas .fcolcr fimpurity. x In the finally-assembled tube tthe aperture mask firequently :shifts from itsr ideal position-these shifts 'being caused:l by mechanical shock, non-uniformr heating vand contraction -of the mask, and numerous-other conditions. Ideally, fas .previously stated, any ,Kline/drawn .from fatty color dot through any aperture fshouldvpass tthrough a corresponding color-center. In the case of misalignment due to shifting of the mask, this line does not pass through the true color-center, but misses it to produce a displaced or quasi-color-center in the deection plane. Since the `spacing between the phosphor screen and the foraminous mask is very small, any slight shift of the mask produces an appreciably displaced quasi-colorcenter. Cases of extreme mask-shifts may produce a quasi-color-center which is actually outside of the tube. In prior-art tubes when mask-shift or misplacement of the electron guns prevented coincidence of the true and quasi-color-centers, a color coil was mounted around deflection coil, in order to curve the electron beam paths 4sothat they did pass through their respective 'quasi-color centers. `When the quasi-color-center was outside ofthe tube this adjustment was lphysically impossible, and when the -quasi-color-center was close vto the inner surface of the neck of the tube, normal delection would cause lthe electron beam to strike the wall `ot" the tube, producing a condition known as Aneck shadow. An additional objection to the prior art-color coil was that its magnetic eld tended to distort the electron beams cross-section, and also tended to interfere with `normal deflection.

"It is the principal object of my linvention to provide an vimproved cathode-ray tube for color presentation.

It is another object of my invention to provide an imJ proved color purity-coil `arrangement vfor cathode-'ray tubes.

These objects "and others will `be realized from the vfollowing specification, `taken yin conjunction with the drawings, of which: y

Fig. 1 isa cutaway fragmentaryview of a cathode-ray the neck of the tube between the gun structure and the Fig. '2 is an enlarged fragmentary 'view of the relation between the mask, screen, and electron beam paths;

Fig. 3 *shows a diagrammatic cutaway view of a cathode-ray-tube utilizing my invention; and v AFigs. 4, 5 and `6 illustrate various embodiments o'f my invention andthe ,operation thereof.

For lconvenience of illustration, the following discussion will 'be directed Ito a three-gun tube used for color television. However, 'the disclosed principles also `apply to tubes having other purposes-such .as radar presentations in color; to tubes utilizing gun-structures having more or less than three guns; and to certain types Aof tubes 'wherein 'the phcsphors are deposited rin stripes rather vthan dots.

'Referring .nowto Fig. 1, there 'is illustrated in .cutaway form a tube v'10 vhaving a cylindrical neck portion 12, a funnel-shapedportion 14 which joins neck portion '12 .at a reference plane,.and `a faceplate 16. Within theneck portionjlZ is' an electron ,gun assembly designated .as .1S- the sub-references '1811, 1871 and 18g, indicating the association of particular guns with the Iproduction of red, blue, `vand green light. Ideally, these electron guns ,emit electrons which 'form `axially-j iositioned beams vdesignated as 2dr, ,"20b and 20g, which are "focussed .and directed through the apertures of va foraminousmask `22 'to strike lighbemitting Aareas 231', j23jb and 23g as -shown -in the ','fragmentany view ol' Fig. 2. A -deiiection yoke 24 is `mounted on the neck of the tube in`F ig. l, .and the hypothetical .deflection plane is indicated by vdottedlline 26. The intersections of the .various idealized ,electron beam' paths `2.0, and .the deflection ,plane 26 produce 'the previously described color centers which are designated 281', 28h, and {28,g.

i The previous discussion has been for `the idealalignment in which .the ,electronheams .etect'ivelypass through their true color-centers, ,traverse -the mask-apertures, ,and strike Ithe yproper 'color-emitting (areas.

Figure Sfillus'trates .the condition whenioramincusmask 22 has been shifted upwards. .lnthiscase ,dashedflines 30r, 30h, and 30g, drawiiromareas 23r, 23h, and`23g through an aperture produce quasi-color-

centers

32r, 3217, and 32g, which are shown exaggeratedly displaced for illustrative purposes, although this condition is frequently met in actual tube construction, and results in an unuseable tube.

Prior-art color coils attempted to cause the electrons to actually pass through their quasi-colcr-centers as shown by the dotted paths, in some cases a physical impossibility.

My invention provides a collar-like color-purity device 32 which is mounted around the funnel-shaped portion of the tube between the deflection yoke 24 and the faceplate 16. An electron beam such as 20r is deflected in the normal manner by yokei24 and starts to follow the same path as shown in Fig. 1, by the solid lines. However, due to mask-shift its original path would now cause it to miss the aperture and strike the solid portion of foraminous mask 22. My invention provides a magnetic field transverse to the tube axis. This field causes each electron beam to be upwardly displaced a slight amount to compensate for mask-shift, and the beams therefore pass through the mask aperture to strike their correct color-emitting area.

Due to my invention the electron beams actually pass through their true colorcenters, thus permitting proper deflection by yoke 24, but appear to come from their quasicolorcenters as required by the relative positions of the mask and Vphosphor areas.

Since mask-shift would produceY quasi-color-centers which are'all displaced the same amount in thesame direction, my color-purity device produces a magnetic field transverse to the tube axis, said field causing simultaneous movement of all three beams the same amount in the same direction to counteract mask-shift. If movement in another direction is desired, my color-purity device is rotated bodily, so that the effective north and south poles may be at any angle to the horizon.

Another advantage accrues'to my color-purity device in that it is remote from, and therefore does not effect, the deflection field orthe focusing electrodes-thus eliminating the adverse resultant prior-art effects on the beam.

The electroragnetic-embodiment has an additional advantage over the previous embodiment in that if there is an A.C. magnetic field from some other element, such as a transformer, my device may compensate for such an Veffect by the application thereto of an electrical signal having the proper phase, amplitude, and frequency.

Referring now to Fig. 4, there is illustrated the embodiment of my invention which utilizes permanent magnets. In this embodiment, the use of magnets 40 and pole pieces 42 provides a uniform magnetic field transverse to the tube axis. It is well known 'in the art that mag netic fields of suitable strength may be obtained by utilizing permanent magnets of the desired strength, or

r from each other, and all flow horizontally in a clockwise direction. Axial sections 38 thus effectively form a section of a coil which surrounds the tube in a horizontal plane. Current flowing through this coil produces the previously described uniform, magnetic. field which is transverse to the tube axis, as shown by the dotted lines. While Fig. 5 shows one complete loop, it is illustrative only, and a stronger field may be produced by inserting similar additional loops for the current to traverse before it returns to power source 34.'

Fig. 6 depicts the physical appearance of the electromagnetic embodiment of my invention. Current producing means encrgizesV a plurality of loops having their cancelling arcuate sectionsiadjacent. In order that the axial portions may be longer, and therefore more effective, the arcuate sections are spaced. A magnetic material similar to the pole pieces 42 of Fig. 4 is utilized to assure amore uniform magnetic field.

My invention has been described in terms of a foraminous mask and a dot pattern screen. Some types of color cathode-ray-tubes utilize phosphor stripes and grids. My invention may be utilized in these tubes in the same manner as hereinabove described, since there is an essential alignmentbetween the light emitting areas, the space between the grids, and respective color centers.

I have shown that my invention provides a color-purity device which has a much wider range of correction for misalignment, and in addition is positioned in such a manner that it `does not interfere with focusing, deflection, or beam-cross-sectlon.

Having described the principles of my invention and several embodiments thereof, I desire to be limited not by the specific description and explanations given, but rather by the following claims.

What ismclaimed is:

l. In a cathode ray tube having means for causing electron beam scansion, a device comprising: a collar-like configuration having an internal diameter greater than the outer neck diameter of said tube and adapted to encircle the bulb-like portion of said tube; means causing said electron beam tobe displaced the same amount in ,the same direction regardless of its instantaneous position infthe scansion pattern, said means comprising means to energize said collar-like configuration to produce a fixed strength, uniform, unidirectional, magnetic eld transverse to the axis of said tube.

l 2. The device of claim l wherein said energizing means comprises an electric current. i

. 3. The vdevice of claim 1 wherein said energizing means are permanent magnets.

4. The device of claim 3 including means comprising magnetic pole pieces to produce a more uniform magnetic field. p

5. The device of claim 1 wherein said collar-like configuration comprises coils of wire having arcuate portions and axial portions.

6. The device of claim 5 including current producing means for energizing said collar-like configuration, and wherein said coils of wire are wound in such a manner that the magnetic fields produced by said arcuate por tions are self cancelling while the magnetic fields produced by said axial portions are additive.

Referencec'Cited in the lc of this patent UNITED STATES PATENTS 2,459,732 Bradley Ian. 18, 1949 2,474,223 Chevigny June 28, 1949 2,513,221 Webb June 27, ,1950 2,541,446 p Trott Feb. 13, `1951 2,675,501 Friend Apr. 13, 1954 2,816,244 Hillegass Dec. 10, 1957 2,825,835 Heppner Mar. 4, 1958