US3313970A - Flat cathode ray tube traversed by tunnel containing magnetic deflector - Google Patents

Description

ULFHYUH HUM/EM 313-+22w OR 393139970 SR April 11, 1967 w. R. AIKEN 3,

FLAT CATHODE RAY TUBE TRAVERSED BY TUNNEL CONTAINING MAGNETIC DEFLECTOR Flled June 29, 1964 3 Sheets-Sheet 1 INVENTOR.

WILLIAM R. AIKEN Apnl 11', 1967 w. R- AIKEN 3,313,970

FLAT CATHODE RAY TUBE TRAVERSED BY TUNNEL CONTAINING MAGNETIC DEFLECTOR Filed June 29, 1964 3 Sheets-Sheet 2 4 W 4 3104 5 4O /30b 22 0 o 29b Apnl 11, 1967 AIKEN 3,313,970

FLAT CATHODE RAY TUBE TRAVERSED BY TUNNEL CONTAINING MAGNETIC DEFLECTOR Filed June 29, 1964 3 Sheets-Sheet 3 United States Patent FLAT CATHODE RAY TUBE TRAVERSED BY TUNNEL CONTG MAGNETIC DE- FLECTOR William R. Aiken, 10410 Magdalena Ave., Los Altos Hills, Calif. 94022 Filed June 29, 1964, Ser. No. 378,540 6 Claims. ,(Cl. 31379) The present invention relates to the flat cathode ray tubes known as the Kaiser-Aiken type cathode ray tubes.

In tubes of this type the electron beam is usually delivered into the tube along a marginal edge thereof and a first set of electrostatic beam-bending electrodes in combination with beam-accelerating and refocussing electrodes in an area above said beam-bending electrodes is employed to deflect the beam within a plane parallel to the target surface of the tube through an angle of ap proximately 90. In addition, a second set of electrostatic beam-bending electrodes is employed to bend the beam into a course approximately perpendicular to the target plane for impingement upon the target surface. In view of the high velocity of the electron beam as it leaves the beam emitting device, the initial bending forces provided by said first set of beam-bending electrodes may be less than required to bend the beam through a full 90. This causes the raster produced upon the target surface by the twice-bent beam, to be canted slightly with regard to the vertical. In my US. Patent No. 2,937,315 I have described a magnetic device for straightening the raster produced upon the screens of cathode ray tubes of the type here under consideration. This device comprises a pair of magnet bars located adjacent to the front and rear faces of the tube envelope to establish a force field that passes through the envelope and imparts to the upwardly deflected electron beam an additional bending moment that straightens the raster upon the screen of the tube.

The diffieulty with magnetic raster-straightening devices of the type described, is that the field established between the magnetic bars is not uniform, and the force lines of said field are parallel only in the immediate vicinity of a vertical center plane which divides the space between the magnetic bars into symmetrical halves. At either side of said plane of symmetry, the force lines above and below said plane arch upwardly and downwardly, respectively. In flat tubes of the type here under consideration the electron beam is usually swept upwardly in a vertical plane that lies closer to the side of the envelope where the secondary deflection devices are located than to the target side of the envelope where the phosphor screen is located. As a result thereof, when using a magnetic raster-straightening device of the type described the electron beam is mostly acted upon by arched diverging portions, rather than straight and parallel portions of the force lines set up by the magnetic bars and is, therefore, bent to different degrees and in different directions in different regions of the envelope. This results in a defocussing of the beam in a plane parallel to the screen, and this defocussing of the beam is the more pronounced the higher is the level at which the beam is bent into impingement with the phosphor screen of the tube by the secondary deflection electrodes.

An answer to the problem may be to space the magnetic bar on the rear wall of the envelope from the outer surface of the rear wall so that the plane of symmetry of the force field established by the magnetic bars may coincide with the plane into which the electron beam is deflected by the primary beam deflection electrodes. Such an arrangement, however, would detract from the main advantage of the flat tubes, i.e., their compactness,

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and would significantly increase the power requirements for the magnetic structures.

The problems briefly outlined above in employing magnetic structures for straightening the raster of flat cathode ray tubes of the type here under consideration, are greatly aggravated in tubes designed to produce multicolor pictures, such as the tubes which employ a pair of synchronized electron emitting devices arranged to produce two registering rasters upon phosphor screens that are applied to opposite sides of an intermediately positioned transparent target. In tubes of this type, the vertical planes into which the two electron beams are deflected by the primary deflection devices would inherently intersect portions of the magnetic field established between the bars of a conventionally located magnetic straightening structure, that are removed from the plane of symmetry of the field and wherein the force lines are curved and diverge from each other.

The present invention aims to produce an improved arrangement for straightening the raster produced upon the phosphor screen of a flat cathode ray tube of the type referred to, without introducing any significant defocussing of the beam as it is directed against the phosphor screen.

More particularly the present invention aims to provide a simple and elfective arrangement for straightening two registering rasters that are produced upon opposite sides of a target plate to which different phosphors are applied.

In the accompanying drawings FIGURE 1 is a fragmentary perspective of a flat twocolor cathode ray tube embodying the invention;

FIGURE 2 is a perspective of the envelope of said tube;

FIGURE 3 is a horizontal section through the same tube taken along line 33 of FIGURE 4 and viewed in the direction of the arrows associated with said line;

FIGURE 4 is a vertical cross section through said tube taken along line 4-4 of FIGURE 3 and viewed in the direction of the arrows associated with said line;

FIGURE 5 is a cross section, similar to FIGURE 4, of a modified embodiment of the invention;

FIGURE 6 is a horizontal section through the embodiment illustrated in FIGURE 5 taken along line 6-6 of FIGURE 6 and viewed in the direction of the arrows associated with said lines; and

FIGURE 7 is a cross section, similar to FIGURES 4 and 5, of yet another embodiment of the invention.

The embodiment of the invention illustrated in FIG- URES 1, 2, 3 and 4 comprises an envelope 10 which may be of glass and which may be composed of two symmetrically shaped sections in the forms of shallow rectangular trays and that are suitably fused together along their contacting edges (FIGURE 1). The envelope has two parallel flat side walls 12a and 12b, and suitably mounted within said envelope in the plane of symmetry of its two sections is a transparent plate 18 which may likewise be of glass. Applied to the opposite faces of said plate are layers of different type of phosphor 20a and 20]) that generate light of different color in response to impingement by electrons. adjacent the side walls thereof are relatively narrow channels 24a and 24b, respectively, of rectangular cross section that extend parallel to the bottom edges of the phosphor screens 20a and 20b (FIGURE 4). In alignment with said channels the end wall 25 of the envelope 10 is provided with openings 26a and 26b (FIGURE 2) into which are fused in an air tight manner the sockets 28a and 2812, respectively (FIGURE 1), of two electron beam generating devices. Located in the channels 24a and 24b are horizontal rows of adj acently positioned U-shaped deflection members 29a and 29b, respectively, which may be formed by metal strips or by coatings of conductive Formed in the bottom of the envelope paint upon the floor and side walls of the channels 24a and 24b and which constitute the primary deflection ele ments. Above the side bars of the U-shaped deflection elements 29a, 29b, the side walls of the channels 240 and 24b form pairs of inwardly projecting shoulders and upon said shoulders are supported pairs of longitudinally extending electrodes 30a and 30b that are coextensive in length with the horizontal rows of deflection elements 29a and 2%. Initially, a positive potential relative to the electron emitting electrode of the electron beam producing devices may be applied from a suitable source to all the horizontal deflection members 290 and 29b and to the electrode pairs 30a and 30b to produce a fieldfree region along which the electron beams may travel without interference in a straight line. During performance of the cathode ray tube, reduced, i.e. relatively negative potentials are successively applied to the deflection members 2911 and 2% starting, for instance, with the horizontal deflection members most remote from the electron emitting evices. These reduced potentials block travel of the electron in its initial direction to and beyond the members to which they are applied, and thus enable the pairs of positively charged electrodes 30a and 30b to accelerate the beams in an upward direction through the space between the individual electrodes of each pair in planes parallel and adjacent to the side walls of the envelope 10, at points that lie progressively closer to the points of origin of said beams. Arrangements for sweeping the electron beam of a flat cathode ray tube in this manner successively into and across a plane parallel to its side walls and its phosphor target in a direction substantially perpendicular to its initial course are described in my US. Patents Nos. 2,864,970 and 2,928,014, to which reference is made for details.

Above the hereinbefore described inwardly projecting shoulders, the sides of channel 24a and 24b carry additional superposed pairs of electrodes 31a, 32a and 31b, 32b, respectively (FIGURES 1 and 4), and during performance of the tube suitable potentials are applied to these electrodes to refocus the deflected electron beams in two successive stages.

As best shown in FIGURE 4, the arrangement is such that the upwardly deflected electron beams extend in planes that lie closely adjacent to the inner surfaces of the side walls 12a and 12b of the envelope 10, and in any case closer to said side walls than to the phosphor screens upon the centrally located target plate 18; and provided upon the inner faces of said side walls are arrays of vertically superposed, longitudinally extending, deflection electrodes 34a and 34b that are preferably formed by layers of a transparent conductive varnish. Initially high positive potentials are applied to the layers of phosphor 20a and 2012 upon the opposite faces of the target plate 18 and to all the superposed vertical deflection electrodes 34a and 34b so that a field-free region is formed between the layers of phosphor and the oppositely located deflection electrodes, into which region the upwardly deflected electron beam may travel without interference. As likewise explained in detail in the hereinbefore mentioned US. Patents Nos. 2,864,970 and 2,928,014, and also in my US. Patent No. 2,904,722, during practical performance of the cathode ray tube, a voltage generating arrangement controlled by a sync detection stage associated with the receiver, is arranged to apply a negative voltage first to the uppermost vertical deflection electrodes and successively to lower ones of said deflection electrodes for the time required by the horizontal deflection elements to deflect the initial beams successively in upward direction from one end to the other end of the tube. Hence, the upwardly deflected beams are deflected into impingement with the positively charged layers of phosphor along successively lower levels and in this manner scan the phosphor layers on the target from one side to the other and from top to bottom. It will be understood by those skilled in the art that the described deflection process may be arranged to occur in the opposite direction, i.e., the poten tials applied to the horizontal deflection electrodes may be such that the upward deflection of the beams proceeds from the horizontal deflection electrodes nearest to the points of origin of the electron beams toward the deflection electrodes most remote from said points of origin, and the nature and order of application of the potentials sequentially applied to the vertical deflection electrodes may be such that the upwardly directed beams are first deflected into impingement with their respective phoshor screens at their lowest levels and are then deflected at successively higher levels.

As pointed out initially, the electrostatic deflecting force set up by the horizontal deflection electrodes 29 is usually insufficient to deflect the initial beams upwardly by a full angle of due to the high initial velocity of the electron beams, and the rasters appearing on the phosphor layers of the cathode ray tube may therefore be canted. Auxiliary deflection means in the form of magnetic bars located adjacent to the front and rear surfaces of the tube at the level of its accelerating and focusing electrodes 30, 31 and 32 are therefore necessary to bend the initial beams by a full angle of 90 in an upward direction and thus straighten the rasters appearing on the phosphor screens 20a and 20b of the tube. In order to subject the upwardly deflected electron beams to the full force of the deflection fields set up by the vertical deflection electrodes, and to provide sufficient space for the beams to bend into horizontal paths before impinging upon the phosphor screens, it is desirable to place the vertical planes into which the initial beams are deflected as close as possible to the vertical deflection electrodes and in any case closer to said electrodes than to the planes of the phosphor layers (FIGURE 4). Unfortunately, this places the upwardly deflected electrode beams into highly arched areas of the magnetic deflection field set up by and between the bars of the magnetic raster straightening structure and this is liable to defocus the beams and distort the raster appearing upon said layers in an unsightly manner.

In accordance with the invention I provide the envelope of cathode ray tubes of the type referred to at the level of the accelerating and refocussing electrodes with a tunnel or tunnels extending longitudinally through the tube from end face to end face (FIGURE 2) for the reception of one or more of the field-establishing bars of the magnetic raster straightening structures. In this manner it is possible to locate the bars of a magnetic raster straightening structure in such a manner that the vertical plane of symmetry of the magnetic field established by and between said bars extends closely adjacent to the vertical beam deflection electrodes. As a result thereof the beam is subjected to regions of the magnetic field wherein the force lines extend substantially parallel to each other and perpendicular to the plane into which the electron beam is deflected by the horizontal deflection elements. While the tunnels may be made from glass and may in fact form an integral part of the envelope, they may also be made from other non-magnetic materials, such as nonmagnetic metals. Thus, tubes of non-magnetic stainless steel may be arranged to extend between suitable apertures in the end walls of the envelope and may be fused to said end walls along the edges of said apertures.

For the magnetic bars I prefer to use a material known as magnetic rubber which is a synthetic or natural rubber compound into which a large percentage, by weight, of particles of a magnetizable material have been worked. Upon energization bars made from magnetic rubber of this kind produce a highly uniform field, and bars made from this material may readily be trimmed to influence the configuration and intensity of the field produced by and between them. As an alternative, bars of ceramic magnetic materials may be arranged at the proper places in the interior of the envelope.

The envelope 10 illustrated in FIGURE 2 has a centrally located tubular tunnel 36 which extends above and intermediately of the openings 26a and 26b for the sockets 28a and 28b, respectively, of the electron emitting devices longitudinally from end face to end face of said envelope. In the assembled tube a bar 40 of magnetic rubber is received within the tunnel 36 and two additional bars 42a and 42b of magnetic rubber are located at either side of the envelope adjacent the outer surfaces thereof as shown in FIGURES 1, 3 and 4, where they maybe held in any suitable manner, such as by means of cement. By properly orienting the magnetic bars 40, 42a and 42b relative to each other so that the outer bars present areas of opposite polarity to the oppositely located areas of the center bar 40, it is possible to establish separate magnetic fields for the electron beams generated by the two electron beam emitting devices comprised in the tube and to center said fields with respect to the vertical planes into which the electron beams are deflected by the two sets of horizontal deflection members 29a and 29b. Thus, with an envelope constructed in accordance with my invention, it is possible to put a magnetic structure effectively into the interior, and in fact into the very center of a cathode ray tube without risking impairment of its magnetic properties during assembly of the tube when the envelope is subjected to elevated temperatures as its halves are fused together and as its interior is evacuated.

FIGURES 5 and 6 illustrate another embodiment of the invention designed to produce a two-color picture. In said embodiment the envelope 50 has formed therein a longitudinal tunnel 52 of elliptic cross section that is located below the target plate 54 which carries the different phosphor layers 56a and 56b. Received within the tunnel 52 are two separate magnetic bars 58a and 58b, respectively, which cooperate with external magnet bars 60a and 60b located closely adjacent to the outer surfaces of the envelope to establish two separate auxiliary deflection fields whose planes of symmetry coincide with the upwardly directed deflection planes of the electron beams generated by the two electron beam emitting devices comprised in the tube. To hold the bars 58a, 60a and 58b, 60b in their proper position relative to each other and to provide a magnetic return path, circumferential straps or bands of steel 62a and 62b, respectively, may be provided which embrace the outer surfaces of the external bars and the centrally located faces of the internal bars, as shown in both FIGURES 5 and 6.

FIGURE 7 illustrates the manner in which the principles of the invention may be applied to flat cathode ray tubes employing but a single electron beam emitting device and a single phosphor screen 63 that is applied to the inner surface of the transparent picture area 64 of one of the side walls of the tube envelope 66. The envelope has but a single tunnel 68 that extends longitudinally through the envelope from end face to end face thereof. The center axis of said tunnel 68 and hence the center axis of the magnetic bar 70 received within said tunnel is spaced from the vertical plane 71 into which the electron beam is deflected upwardly by the horizontal deflection electrodes 72 by substantially the same distance by which the center axis of the exteriorly located outer magnet bar 74 is spaced from the deflection plane of the electron beam.

While I have explained my invention with the aid of certain preferred embodiments thereof, it will be understood that the invention is not limited to the specific constructional details shown and described by way of example, which may be departed from, without departing from.

the scope and spirit of the invention.

I claim:

1. A cathode ray tube comprising an envelope having relatively spaced side walls and a picture area, end walls extending between the end edges of said side walls and defining an evacuated space with said side walls, and a tunnel in communication with the outside atmosphere extending between opposite end walls at a level below said picture area; electrostatic means within said evacuated space below said picture area for deflecting an electron beam upwardly into a plane parallel and adjacent to the inner surface of a side wall, and means passing through said tunnel and externally adjacent to the outer surface of a side wall for establishing a magnetic field passing through said evacuated space.

2. A cathode ray tube according to claim 1 wherein said magnetic field establishing means are bars of magnetic rubber.

3. A two-color cathode ray tube comprising an envelope having relatively spaced, substantially flat side walls, a transparent target plate arranged in the space between said side walls and carrying different phosphor layers upon opposite sides thereof, end walls extending between the end edges of, and defining an evacuated space with said side walls and a tunnel in communication with the outside atmosphere extending between opposite ones of said end walls at a level below said phosphor layers; electrostatic means within said evacuated space at either side and below said target plate for deflecting electron beams upwardly into planes parallel and adjacent to the inner surfaces of said side walls, and means passing through said tunnel and externally adjacent to the outer surfaces of said side walls for establishing magnetic fields passing through said evacuated space with their planes of symmetry coincident with said electron beam deflection planes to accentuate the deflection of the electron beams.

4. A cathode ray tube according to claim 3 wherein said magnetic field establishing means are bars of magnetic rubber.

5. A cathode ray tube comprising an envelope having relatively spaced substantially flat side walls and end walls extending between said side walls and adapted to define with said side walls an evacuated space, a target plate mounted within said evacuated space in a position substantially parallel to said side walls, electrostatic means within said evacuated space at either side and below said target plate for deflecting electron beams upwardly into planes parallel and adjacent to the inner surfaces of said side walls, a magnetic bar arranged within said evacuated space below said target plate intermediately of and parallel to said side walls, and magnetic bars arranged exteriorly adjacent to said side Walls to establish magnetic fields passing through said evacuated space.

6. A cathode ray tube comprising an envelope having relatively spaced side Walls and a picture area, end Walls extending between said side walls and defining an evacuated space with said side walls, and a tunnel in communication with the outside atmosphere extending between said end walls at a level below said picture area; electrostatic means within said evacuated space for deflecting an electron beam upwardly into a plane parallel and adjacent to the inner surface of one of said side walls, and magnetic means passing through said tunnel for establishing a magnetic field extending into said evacuated space.

References Cited by the Examiner UNITED STATES PATENTS 2,795,731 6/1957 Aiken 313-92 2,850,669 9/1958 Geer 313-92 2,997,621 8/ 1961 Schlesinger 31392 FOREIGN PATENTS 608,711 3/ 1962 Belgium.

JAMES W. LAWRENCE, Primary Examiner.

R. SEGAL, Assistant Examiner.

Claims (1)

1. A CATHODE RAY TUBE COMPRISING AN ENVELOPE HAVING RELATIVELY SPACED SIDE WALLS AND A PICTURE AREA, END WALLS EXTENDING BETWEEN THE END EDGES OF SAID SIDE WALLS AND DEFINING AN EVACUATED SPACED WITH SAID SIDE WALLS, AND A TUNNEL IN COMMUNICATION WITH THE OUTSIDE ATMOSPHERE EXTENDING BETWEEN OPPOSITE END WALLS AT A LEVEL BELOW SAID PICTURE AREA; ELECTROSTATIC MEANS WITHIN SAID EVACUATED SPACE BELOW SAID PICTURE AREA FOR DEFLECTING AN ELECTRON BEAM UPWARDLY INTO A PLANE PARALLEL AND ADJACENT TO THE INNER SURFACE OF A SIDE WALL, AND MEANS PASSING THROUGH SAID TUNNEL AND EXTERNALLY ADJACENT TO THE OUTER SURFACE OF A SIDE WALL FOR ESTABLISHING A MAGNETIC FIELD PASSING THROUGH SAID EVACUATED SPACE.

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