COLOR CATHODE RAY TUBE COMPRISING AN ELECTRON GUN HAVING A FOLDED TUBULAR PART

Abstract: A color cathode ray tube comprises an in-line electron gun. Said electron gun includes at least a tubular part which is composed of two (or more) folded portions which are secured to each other.

Description: COLOR CATHODE RAY TUBE COMPRISING AN ELECTRON GUN HAVING A FOLDED TUBULAR PART The invention relates to a color cathode ray tube comprising an in-line electron gun having at least one electrode which includes a substantially flat grid with apertures for allowing passage of electron beams, and a tubular part which is connected to said flat grid. Such color cathode ray tubes are known and are used, inter alia, in display devices such as color television receivers and color monitors for computers. When such color cathode ray tubes are in operation, three electron beams are generated by an in-line electron gun. Said electron beams are accelerated and focused by means of electrodes. Some of the electrodes, particularly diose which are at a relatively high voltage, are provided with more or less tubular parts which extend substantially parallel to the electron beams. One of the functions of these tubular parts is to shield the electron beams from external electric and/or magnetic fields. For the known color cathode ray tubes, these parts are made by means of a deep drawing process, in which said part and the flat grid are made in a single piece, or said part consists of a piece of deep-drawn tube in which the flat grid has been welded. However, ever higher demands are imposed on the accuracy with which the various parts of an electron gun are manufactured. Moreover, in the case of color cathode ray tubes, the high-voltage sensitivity is a constantly recurring problem. It is an object of the invention to provide a color cathode ray tube of the type mentioned in the opening paragraph, in which one or both of the above-mentioned problems are alleviated. To this end, the color cathode ray tube in accordance with the invention is characterized in that the tubular part is composed of a number, preferably two, folded portions which extend parallel to the electron beams and which are interconnected. Such folded portions can be made of plates without subjecting the material of the plates to a deep drawing operation. Deep drawing is a process in which a lubricant must necessarily be used. Even after a thorough cleaning operation, the lubricant leaves some residue, which may have a negative effect on the high-voltage behavior of the cathode ray tube. A cleaner electrode, i.e. an electrode having a better high-voltage resistance, can be obtained by using parts which are folded and subsequently interconnected. In addition, deep drawing is a process which yields a product which is inaccurate to some extent. This can be attributed to the fact that the deep-drawn part always springs back after the deep drawing operation. This phenomenon does not occur if folded plates are used. Consequently, the tubular part has a greater flatness and dimensional accuracy than deep-drawn parts. The folded portions are preferably similar in form. As a result, the electron gun is simplified, which leads to lower costs. Preferably, each of the folded portions comprises a projection, which projections are interconnected, and the tubular part formed by the plate-shaped portions is connected to supports of the electron gun via said projections. The in-line electron gun comprises supports, generally made of glass, to which the various electrodes are secured. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawings: Fig. 1 is a cathode ray tube; Fig. 2 is an electron gun; Figs. 3A to 3C show a part of an electron gun in a cathode ray tube in accordance with d e invention; Figs. 4A, 4B, 5 A, 5B and 6 show further examples of a part of an electron gun for a cathode ray tube in accordance with the invention. The Figures are not drawn to scale. In general, like reference numerals refer to like parts. Color cathode ray tube 1 (Fig. 1) comprises an evacuated envelope 2 having a display window 3, a cone portion 4 and a neck 5. In the neck 5 there is provided an electron gun 6 for generating three electron beams 7, 8 and 9. A display screen 10 is situated on the inside of the display window 3. The display screen 10 comprises a pattern of phosphor elements luminescing in red, green and blue. On their way to the display screen, the electron beams 7, 8 and 9 are deflected across the display screen 10 by means of a deflection unit 11 and pass through a shadow mask 12 which is arranged in front of the display window 3 and which comprises a thin plate with apertures 13. The three electron beams 7, 8 and 9 pass through the apertures 13 of the shadow mask at a small angle with respect to each other and, consequently, each electron beam impinges on phosphor elements of only one color. Fig. 2 is a partly perspective view of an electron gun 6. Said electron gun 6 comprises a common control electrode 21, also referred to as G, electrode, in which three cathodes 21 , 22 and 23 are secured. The G, electrode is secured to supports 26 by means of connecting elements 25. These supports are made of glass and are also referred to as "beading rods". In this example, the electron gun 6 further includes a common plate-shaped electrode 27, also referred to as G 2 electrode, and the common electrodes 29 and 31 which are also secured to the supports by means of connecting elements. In this Figure, the electrodes 29 and 31 are manufactured from deep-drawn parts. An electrode of an electron gun for a caϋ ode ray tube in accordance with the invention is shown in a side view, plan view and in the unfolded state in Figs. 3A, 3B and 3C, respectively. The electrode comprises two plate-shaped grids 31 and 32 between which a tubular part 33 is situated. Said tubular part includes two portions 33A and 33B. One of said portions is shown in the unfolded state in Fig. 3C. Said portion comprises the flat members 41, 42, 43, 44 and 45, of which the members 41 and 45 are provided with projections 46. Further, the folding lines 47, 48, 49 and 50 are shown. Such a portion can be manufactured very accurately without subjecting material to a deep drawing process, for example, by means of punching. Preferably, the folding lines are made, for example by punching or notching, in the flat part. Both portions 33A and 33B are subsequently folded and welded together by means of the members 45. The plate-shaped grids are secured thereto, for example by means of welding. The upper edge of the portions 33 A and 33B can be made very accurately, so that the position of the electrode 33 can be determined more accurately than in the case of a deep-drawn electrode. An example of a preferred embodiment of an electrode for an electron gun in accordance with the invention is shown in a plan view and in the unfolded state in Figs. 4 A and 4B, respectively. In this example, the grid 31 and the portions 33 A and 33B are manufactured from a single piece of folded material 51. This is a preferred embodiment because the number of separate parts necessary for the manufacture of an electron gun is reduced by one. Thus, within the scope of the invention, the folded portions may be interconnected. A further example of a preferred embodiment of an electrode for an electron gun in accordance with the invention is shown in a plan view and in the unfolded state in Figs. 5A and 5B, respectively. In diis example, the grids 31 and 32 and the portions 33A and 33B are manufactured from a single piece of folded material 52. This is another preferred embodiment because the number of separate parts necessary for the manufacture of an electron gun has been reduced further. All embodiments (Figs. 3A to 3C, 4A, 4B, 5A, 5B) also have the advantage that an electrode comprising a tubular part can be made in the form of a strip. For example, die electrode shown in Fig. 4B can form part of a strip in which many of such electrodes are made, for example, by punching or laser cutting. Such a strip can be wound on a reel and, in the manufacturing process, supplied to a machine which removes the electrode from the strip, folds the electrode and secures it by welding. This has the advantage that, prior to their manufacture, the electrodes occupy very little space. The advantage of folding over bending or drawing is that a lubricant can be dispensed with and less plastic or elastic deformation occurs. It will be obvious that within the scope of the invention many variations are possible. For example, Fig. 6 is a plan view of a very simple embodiment of the invention, in which a tubular part is made from two portions 61 A and 61B which axe welded together at points 62. The invention is particularly advantageous if me folded portions are made from a material which cannot be deep-drawn, or only with difficulty such as some NiFe compounds. Such compounds have a very low coefficient of thermal expansion, which is very favorable. These materials can be folded, but they cannot be deep-drawn or bent, or only with great difficulty. In summary, the invention relates to a color cathode ray tube comprising an in-line electron gun. Said electron gun includes at least a tubular part which is composed of two (or more) folded portions which are secured to each odier. The folded portions are preferably folded along folding lines, that is lines along which the material has been weakened, for example by notching.

Claims: CLAIMS: 1. A color cathode ray tube comprising an in-line electron gun having means for generating three coplanar electron beams and at least one electrode which includes a substantially flat grid wim apertures for allowing passage of the electron beams, and a tubular part which is connected to said flat grid, characterized in that the tubular part is composed of a number, preferably two, folded portions which extend parallel to the electron beams and which are interconnected. 2. A color cadiode ray tube as claimed in Claim 1 , characterized in that the folded portions are similar in form. 3. A color cathode ray tube as claimed in Claim 1 or 2, characterized in that the flat grid and the portions are manufactured from a single piece of folded material. 4. A color cadiode ray tube as claimed in Claim 3, characterized in that two flat grids and the folded portions are manufactured from a single piece of folded material. 5. A color cathode ray tube as claimed in any one of the preceding Claims, characterized in that the folded portions are made of materials having a low coefficient of thermal expansion. 6. An electron gun suitable for use in a color cadiode ray tube as claimed in any one of the preceding Claims.

Inventors: VAN ECK ARNOLDUS HUBERTUS MARI, VAN ECK, ARNOLDUS, HUBERTUS, MARIA
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1996
Main classification: H01J29
IPC codes: H01J29