Electron beam generation apparatus

Abstract: In an electron beam generation apparatus for a flat type cathode ray tube, line cathodes (17a, ...) are stretched in an arc shaped form being held by plural cathode position defining means (24, ...) disposed along the line cathode in forward convex arc form to protrude most at center and less towards both ends; and electron-beam take-out electrode means (11) in front side of the line cathode and back electrode in back side of said line cathode are also formed arc shaped.

Description: The present invention relates to electron beam generation apparatus according to the first part of claim 1, and more particularly the present invention relates to an electron beam generation apparatus suitable for line cathodes to be used for flat type cathode ray tube. Such an apparatus is known from Patent Abstracts of Japan, unexamined applications, E-field, Vol 8, No. 277, The Patent Office Japanese Government, page 81, E 285 & Kokai-no 59-146139. Electron beam generation apparatus for flat cathode ray tube are being developed for use in television receiver, computer terminal display apparatus, or the like flat shape display apparatus. Hitherto, the electron beam generation apparatus for such flat cathode ray tube is configurated as shown in FIG.13. In the configuration of FIG.13, a line-shaped cathode 17a, 17b, ... is stretched between a pair of holders 19₁ and 19₂, which are provided with a predetermined distance therebetween, with an appropriate tension. In the known flat shape cathode ray tube, a back electrode 10 and electron beam take-out electrode 13a having many electron passing apertures 12 are provided with parallel row of the line-shaped cathodes 10 therebetween. And such row of the line-shaped cathodes 17a, 17b, ... are provided in a direction perpendicular to sheet of FIG.13. The operation of the above-mentioned conventional electron beam generation apparatus is that, by impressing appropriate potential to the electron beam take-out electrode 13a, thermo-electrons emitted from the line-shaped cathode which is heated by current therethrough is taken-out, and the beam is emitted through the electron passing apertures 13a forwards. The above-mentioned configuration has been applied in the conventional flat type cathode ray tube as shown in FIG.14 which is a horizontal sectional view and FIG.15 which is a vertical sectional view taken by Z-Z sectional plane of FIG.15. In FIG.14 and FIG.15, in a vacuum casing 4 consisting of a face plate 1, side plates 2, 2 and back plate 3, a set of electron beam generation apparatus 5 is contained. The electron beam generation apparatus 5 comprises from the front side to back side, horizontal deflection electrodes 6₁, 6₂, ..., 6₇, electron beam take-out electrodes 11, row of vertical line-shaped cathodes 9a, 9b, ..., 9f and a back electrode 10. A phosphor screen 7 is provided on the inner wall of the face plate 1. Insulative supporting pins 8, 8, ..., 8 are provided projecting from respective horizontal deflection electrodes 6₁, 6₂, ..., 6₇ and touching the inside wall of the face plate 1. When the inside space of the vacuum casing 4 is evacuated, the back plate 3 is stressed towards the face plate 1 by means of large atmospheric pressure between the face plate 1 and the back plate 3, and the pressing force of the back plate 3 is supported by the touchings of the supporting pins 8, 8, ..., on the inside face of the face plate 1. The electron beam take-out electrodes 11 comprise plural electrodes 13a, 13b and 13c respectively having beam, passing apertures and isolated with insulation spacers 14 and 14 therebetween. As shown in FIG.15, the line-shaped cathodes 9a, 9b, ..., 9f are given appropriated tension by wire strings 15a and 15b. The electron beam take-out electrodes 11 are held on the back electrode 10 with insulation spacers 16, 16, ... therebetween. The electron beams radiated from the line cathodes 9a, 9b, ..., 9f are taken out forwards through apertures 12, 12, ..., of the electron beam take-out electrodes 11, and deflected by the horizontal electrodes 6₁, 6₂, ..., 6₇ and strike the phosphor screen 7, thereby to emit light. In the conventional configuration as shown in FIG.13 through FIG.15, when the lengths of the line-shaped cathode electrodes 17a, 17b, ... or 9a, 9b, ... are of a certain lengths, the line cathodes make vibrations by means of small mechanical shock or small electric field interaction, thereby making a simple harmonic chordal motion. When the chordal harmonic motion occurs, the emission current from the cathode changes, and therefore fluctuation of brightness on the display screen of TV picture or computer display occurs. Furthermore, when the cathodes, making the chordal harmonic motion, touch the electron beam take-out electrodes 13a of FIG.13 or 11 of FIG.14, large short-circuit current flow through the cathode electrodes 17a, 17b, ... or 9a, 9b, ..., and the line cathodes break. In order to improve the above-mentioned shortcomings, an improvement is made that as shown in FIG.16, several protrusions 105₁, 105₂ and 105₃ are provided on the back electrode 10 so as to touch the line-shaped cathode, thereby to suppress the simple harmonic chordal motion. However, it is difficult to make the heights 1₁, 1₂, and 1₃ of the protrusions 105₁, 105₂ and 105₃ make uniform so as to touch the line-shaped cathode 17a, 17b, ... uniformly; and in such case the suppressing of the simple harmonic motion can not be attained sufficiently. The purpose of the present invention is to provide an improved electron beam generation apparatus which is capable of displaying stable picture without making undesirable effect of simple harmonic chordal motion of the line-shaped cathodes. The electron beam generation apparatus in accordance with the present invention comprises the features as described in claim 1. While the novel features and particular embodiments of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. FIG.1 is a sectional side view of an electron beam generation apparatus embodying the present invention. FIG.2 is a rear view of the electron beam generation apparatus of FIG.1 taken at the sectional plane X-X. FIG.3 is a sectional plan view showing a flat type cathode ray tube embodying the electron beam generation apparatus in accordance with the present invention. FIG.4 is a sectional side view of flat type cathode ray tube of FIG.3 taken at the sectional plane H-H. In FIG.3 and FIG.4, the front and back direction of the flat type cathode ray tube are shown prolonged for easy illustration. FIG.5 is a perspective view showing vibration prevention device 20 of the embodiment of FIG.3. FIG.6 is an enlarged partial sectional view of a part of the vibration prevention device 20 of FIG.5. FIG.7 is a perspective view of an electron beam take-out electrode 13a, 13b, 13c of the embodiment of FIG.3. FIG.8 is a perspective view and insulative spacer 14 of the embodiment of FIG.3. FIG.9 is an enlarged perspective view of a holding member 27 shown in FIG.4. FIG.10 is an enlarged side view of a modified embodiment of the insulation spacer 14. FIG.11 and FIG.12 are sectional side views of one embodiment of a combination of back electrode 30 and vibration prevention device 31 or 32. FIG.13 is the sectional side view of one unit of the conventional electron beam generation apparatus. FIG.14 is a sectional plan view of the conventional flat type cathode ray tube using the electron beam generation apparatus shown in FIG.13. FIG.15 is the sectional side view of the conventional flat type cathode ray tube of FIG.14 taken at sectional plane Z-Z. In FIG.14 and FIG.15, the front and back direction of the flat type cathode ray tube are shown prolonged for easy illustration. FIG.16 is the sectional side view of the modified conventional electron beam generation apparatus. In the electron beam generation apparatus in accordance with the present invention; line-shaped cathodes are stretched in parallel row between a back electrode and an electron beam take-out electrode having many electron beam passing apertures, in an evacuated casing; the back electrode is bent by atmospheric pressure toward the face plate, so that supporting members are pressed onto the inner wall of the face plate 1, and that each line-shaped cathodes are held by plural cathode position defining member, such as cathode vibration stoppers, which are provided along the cathode with certain intervals and is disposed to form an arc shape by the bending of the back plate 10; and holding members formed in centre-thin and end-thick bars are provided in forward side of the electron-beam take-out electrode, so that the supporting member flatly abut the inner wall of the face plate. According to the constitution of the present invention, by means of the plural position defining means disposed at predetermined position along the line cathodes to shape it forward convex to protrude most at centre and less toward both ends, the lined-shaped cathode electrodes are stretched in the arc shaped form which is forward convex to protrude most at center and less toward both ends. Therefore, all of the position defining means certainly contact the line-shaped cathode thereby to make the contact points at nodes of vibration of the line-shaped cathodes, and hence frequency of natural vibration becomes high and amplitude of vibration becomes small, and attenuation of vibration of the line-shaped cathode becomes short. Thus, reliability of breaking of the line-shaped cathode in minimized and reliability is greatly improved. Furthermore, since the arc shape of the line cathode is accurately formed, by shaping the back side surface of the electron beam take out electrode accurately to maintain the gap against the line-shaped cathode uniform, amount of electron beam take-out becomes uniform along the length of the line-shaped cathodes. Accordingly, both owing to the minimizating of vibration and the above-mentioned uniformity of amount of electron beam, inuniformity of brightness on the screen is greatly reduced and picture of good brightness uniformity is obtainable. Detailed preferred embodiments of the present invention is described with reference to FIG.1 through FIG.12. FIG.1 and FIG.2 show sectional side view and sectional rear view of electron beam generation apparatus in accordance with the present invention. In the configuration of FIG.1, a line-shaped cathode 17a, 17b, ... is stretched with an appropriate tension between a pair of holders 19₁ and 19₂, which are provided with a predetermined distance therebetween, being held by plural cathode position defining member 24₁, 24₂, 24₃ ... 24₇, which are made of quartz rods and held on a vibration preventing member 20. In the known flat shape cathode ray tube, a back electrode (not shown) and electron beam take-out electrode 13a having many electron passing apertures 12 are provided with vertical parallel row of the line-shaped cathodes 17a, 17b, ... therebetween. And vertical parallel row of the line-shaped cathodes 17a, 17b, ... are provided in a direction perpendicular to sheet of FIG.1. The cathode position defining members 24₁ ... 24₇ are disposed convex in arc shape toward the face plate, that is protruding at the center parts most and at both end parts less between the pair of cathode holders 19₁ and 19₁. The back electrode (not shown) and the electron beam take-out electrode 13a are also formed in the similar curved form so that the gap from the line-shaped cathode 17a, 17b, ... to the back electrode and the electron beam take-out electrode 13a are uniform along the length of the line-shaped cathode 17a, 17b, .... When the back electrode, the electron beam take-out electrode 13a and the vibration preventing member 20 are assembled with right positional relation, the cathode position defining members 24₁, 24₂, 24₃ ... are disposed uniformly between the pair of holders 19₁ and 19₂, and the line-shaped cathode is pushed forward by the cathode position defining members 24₁ through 24₇ making near arc shape, in a manner to be pushed forward most at the center. And by disposing the position of the cathode position defining members 24₁ through 24₇ in arc shape, all the cathode position defining members 24₁ through 24₇ firmly pushes the cathode 17a, 17b .... As a result of such configuration, the points of touching of the cathode position defining members 24₁ through 24₇ to the line-shaped cathode 17a, 17b, ... becomes nodes of the vibration of the line-shaped cathode 17a, 17b, .... Because the distance between the nodes are short, natural vibration frequency of the cathode rises high and its amplitude of vibration becomes very small. And thereby the undesirable vibration of the line-shaped cathode becomes negligibly small in comparison with the conventional line-shaped cathode. Furthermore the vibration is attenuated in at very short time and there is almost no fear of short-circuiting of the cathode by excessive vibration and touching to other electrode. And thus, reliability is much improved. Furthermore, since gap between the line-shaped cathode and the electron beam take-out electrode is uniform all along the length of the line-shaped cathode 17a, 17b, ..., the amount of electron beams taken-out through the apertures 12 becomes uniform along the length of the line-shaped cathode 17a, 17b, ..., thereby making brightness of phosphor screen uniform. FIG.3 through FIG.12 show a preferred embodiment of a flat type cathode ray tube wherein the electron beam generation apparatus of the present invention is used. In FIG.3, the line-shaped cathodes 17a, 17b, 17c, 17d are stretched substantially in vertical direction making an arc shape being pushed by cathode position defining members 23₁, 23₂, 23₃, 23₄ ... 23₇. And both ends of the line-shaped cathode are held by a pair of springs 18a, 18b. A pair of cathode holders 19a and 19b are provided to touch the electron beam take-out electrode 11. Between most back side electrode 13a of the electron beam take-out electrode 11 and a back electrode 10, plural vibration prevention members 20, 20 ... are provided. As shown in FIG.5, the vibration prevention member 20 is made by laminating a pair of insulation sheets 22a and 22b respectively having vertically oblong windows 21a, 21b, 21c and 21d, wherein a plurality of the cathode position defining rods 24 are held by inserting their base parts between the pair of the holding sheets 22a and 22b. The enlarged sectional configuration of one part of the holding of the cathode position defining rod 24 between the holding sheets 22a and 22b is shown in FIG.6. The vibration prevention member 20 is insulated from the back electrode 10 by insertion of appropriate known insulation means therebetween. The electron beam take-out electrode 11 is constituted by laminating several (three, in this embodiment) metal sheet electrode 13a, 13b, 13c shown in FIG.7, each having a number of electron beam passing apertures 12 with insulation spacers 14 shown in FIG.8 therebetween. The insulation spacers 14 has vertically oblong windows 25a, 25b, 25c, 25d. On the front side face of the electron beam take-out electrodes 11, a group of horizontal deflection electrodes 6₁, 6₂, 6₃, 6₄, 6₅ are fixed with spacers 27a, 27b, 27c, 27d, 27e, having curved faces, in-between. Until the inside space of the casing 4 is evacuated, the vibration prevention member 20, the electrode metal sheets 13a, 13b, 13c and the insulation spacers 14, 14 are, as shown in FIG.5, FIG.7 and FIG.8, of flat shapes. However, when the inside space is evacuated after installation of these components in the casing 4, the back face 3 of the casing 4 is stressed toward inside of the casing 4 by a great atmospheric pressure, and the back electrode 10 is bent inside. Therefore, as shown in FIG.4 the back electrode 10 is bent toward the face plate 1 and hence the line-shaped cathode 19a is also bent, and further, the electron beam take-out electrodes 11 and the rear face 26 of the holding sheets 27 are also bent to front side, and the front side faces of the holding sheet 27 become flat and contact the rear ends of horizontal deflection electrodes 6₁ ... 6₅. Therefore, atmospheric pressure on the back plate 3 is transmitted to the horizontal deflection electrodes 6₁ ... 6₅ and to inside wall of the face plate 1 through needle shaped supporting pins 8, 8, .... Thus the cathode position defining members 23₁ through 23₇ and hence the line-shaped cathodes 17a, 17b ... are bent in arc shape to front side. In the flat type cathode ray tube configurated as above, when the line-shaped cathode electrodes 17a, 17b, 17c ... are heated and a predetermined potentials are impressed on respective electrodes, electrons are emitted from the line-shaped cathode electrodes 17a, ... and taken-out by the electron beam take-out electrodes 11, and after deflection by the horizontal deflection electrodes 6₁, 6₂ ... and by vertical deflection electrodes (not shown), the electron beams strike the phosphor screen 7 on the inner wall of the face plate 1 and emit light. Since the vibration prevention member 20 hold the cantilever shaped cathode position defining pins 23₁, 23₂ ..., the rod shaped cathode position defining pins can easily be bent by tension of the line cathode. And therefore, even though there may be some positional error in fixing of the cathode position defining pins the line-shaped cathodes 17a, 17b, ... all contact the cathode position defining pins 23₁, 23₂ ..., and hence, intended vibration prevention is attainable. Furthermore, since the rods of the cathode position defining pins are fixed in cantilever type configuration, there is no fear of breaking by thermal expansion during manufacturing of the vibration prevention member 20. When quartz glass rods are used as material of the cathode position defining pins of small thermal conduction, heat of the line-shaped cathode electrodes 17a, 17b ... are not lost therethrough, and an intended cathode temperature is attainable. In modified examples, the vibration prevention member can be made in an integral configuration by using an insulative and heat resistive material. Furthermore, the vibration prevention member 20 can be made by using metal sheets 13a, 13b, 13c coated by heat resistive insulation film thereon. Apart from the above-mentioned embodiment wherein the insulating supporting pins 8, 8 ... are impressed on the inner all of the face plate 1 through the horizontal deflection electrodes 6₁, 6₂ ... via holding members 27a, 27b ... having arc shape curved surface 26 on one side thereof, the holding members 27a, 27b ... may have arc shaped concave face on both side. Furthermore, still modified embodiment can be made such that the holding members 27a, 27b ... are formed in straight oblong rectangle of uniform thickness instead of having curved concave face(s), and a curved concave face as shown in FIG.10 is formed in shapes of insulation spacers 14, 14 which is to be provided between the electron beam take-out electrodes 13a, 13b, 13c. Such insulative spacers 14, 14 are made by sandwiching a core metal sheet 28 by a pair of insulative sheet having tapered thickness thinner at the center part and thicker at both end parts thereby to make curved surfaces. Such insulative material can be made by coating an insulative resin of such tapered thickness on both faces of the core metal sheet 28. By using such spacer 14 having concave curved surfaces disposed between the plural metal electrodes of the electron beam take-out electrodes 11, when the back plate 3 of the casing 4 is pressed to concave shape thereby forming the back electrode 10 in concave curved shape, the front side surface of the electrode metal sheet 13a which is facing the line-shaped cathode 17a, 17b ... can be curved forwards, so that gap between the line-shaped cathode 17a, 17b ... and back side face of the electron beam take-out electrode 13a is made substantially uniform all along each line-shaped cathodes 17a, 17b .... Apart from the above-mentioned embodiments shown in FIG.1 through FIG.10 wherein the back electrode 10 and the vibration prevention member 20 are made as individual members, these members can be made integrally. In the embodiment of FIG.11, in the front side surface of a substrate of back electrode substrate 30 a number of protrusions 31 made of insulative and of small thermal conductivity are provided in parallel horizontal lines, and the parallel horizontal protrusions 31 are used as the cathode position defining member 17a, 17b .... As the material for the protrusions 31, solder glass can be used. Though conductive film of the back electrode 10 is not shown in these figures, the back electrode is formed by known method on the surface of the back electrode substrate 30 at the position between appropriate two protrusions 31. FIG.12 shows another example of the back electrode substrate 30 and the cathode position defining members in integral configuration. In this example of FIG.12, the front side surface of the back electrode substrate 30 is etched so as to make parallel horizontal grooves 33, hence make parallel horizontal protrusions relatively, and the parallel horizontal protrusions 32 are used as the cathode position defining members 17a, 17b .... The back electrode are formed in a suitable place between the protrusions 32. As material of the back electrode substrate 30, glass of high melting point or ceramic are used. In the above-mentioned modified embodiments of FIG.11 and FIG.12, by integrally making the back electrode 10 and the cathode position defining members 31 or 32, number of components can be reduced and the vertical pitch between the parallel horizontal cathode position defining member 17a, 17b ... can be made very short thereby satisfactorily reducing the vibration of the line-shaped cathode. Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been changed in the details of construction and the combination and arrangement of parts may be resorted to without departing from the scope of the claims.

Claims: An electron beam generation apparatus comprising: at least one line cathode (17a, 17b, ...) stretched between a pair of holding means (18a, 18b) for holding said at least one line cathode at both ends thereof; an electron beam take-out electrode (11) provided on a front side of and along said at least one line cathode with a predetermined gap therefrom, said electron beam take-out electrode having a plurality of apertures each for letting an electron beam pass therethrough; a back electrode (10) provided on a back side of and along said at least one line cathode with a predetermined gap therefrom, and plural cathode position defining means (24₁, ..., 23₁, ...) provided at predetermined positions along said at least one line cathode; characterized in that said cathode position defining means are disposed so that said at least one line cathode is shaped in a forward convex arc which protrudes at its center toward said electron beam take-out electrode. An electron beam generation apparatus in accordance with claim 1, wherein said plural cathode position defining means are held by a pair of holding sheets (22a, 22b) in a manner that a part of each of said cathode position defining means is sandwiched between said holding sheets with the other part extended into an oblong window formed in said holding sheets; and said holding sheets and said electron beam take-out electrode are laminated and pressed onto forward convex arc shaped surfaces of holding member, thereby forming forward convex arc shapes of said line cathodes and said electron beam take-out electrode. An electron beam generation appratus in accordance with claim 1 or 2, wherein said cathode position defining means are made of low thermal conduction substance. An electron beam generation appratus in accordance with one of the claims 1 to 3, wherein said cathode position defining means are cantilever pins held by a pair of holding sheets (22a, 22b) in a manner that a part of each of said cantilever pins is sandwiched between said holding sheets with the other part extended into an oblong window formed in said holding sheets. A flat type cathode ray tube including an electron beam generation appratus in accordance with claim 1, wherein said plural cathode position defining means (24₁, ..., 23₁, ...) is held by a pair of holding sheets (22a, 22b) in a manner that a part of each of said cathode position defining means is sandwiched between said holding sheets with the other part extended into an oblong window formed in said holding sheets, said cathode position defining means being pressed onto holding members having forward concave arc shaped surfaces, thereby to define forward convex arc shapes of said at least one line cathode and said electron beam take-out electrode; and further comprising a vacuum casing (4) for enclosing the above-mentioned components therein, said vacuum casing having a face plate (1) with a phosphor screen on the inside wall thereof and a back plate (3) against which said back electrode is held, said back plate being bendable in a forward convex manner when said vacuum casing is in an evacuated state, thereby forming said back electrode and said plural cathode position defining means into a forward convex arc shape in said evacuated state. A flat type cathode ray tube in accordance with claim 5, wherein said holding members have forward concave surface on back sides thereof for receiving said electron beam take-out electrode, and said holding sheets and said back electrode are bent into a forward convex arc shape by menas of atmospheric pressure on the back plate when said vacuum casing is in said evacuated state. A flat type cathode ray tube in accordance with claim 5 or 6, wherein said electron beam take-out electrode comprises metal electrode sheets and bar shaped insulation spacers which are inserted between said metal electrode sheets, said electron beam take-out electrode having a tapered thickness distribution so as to be thinner at its central part and thicker at respective end parts thereof. A flat type cathode ray tube in accordance with one of the claims 5 to 7, wherein said position defining means comprises a plurality of rod-shaped pins (24) which are held by said holding sheets. An electron beam generation apparatus in accordance with claim 5, wherein vibration prevention protrusions for serving as said cathode position defining means are formed into an integral body with said back electrode. An electron beam generation apparatus in accordance with claim 9, wherein surfaces of said protrusions are made of heat resistive insulative material.

Inventors: NAKATANI TOSHIFUMI, YAMAZAKI FUMIO, NAKATANI, TOSHIFUMI, YAMAZAKI, FUMIO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1987
Main classification: H01J29
IPC codes: H01J29, H01J31