IMAGE DISPLAY APPARATUS

Abstract: An image display apparatus for displaying images on a fluorescent screen (5) comprises plural linear cathodes (1), an electron beam extraction electrode (2) with plural apertures and vertical deflection electrodes (3a, 3b, 3c, 3d) which are formed by segments, and the respective segments of the vertical deflection electrodes (3a, 3b, 3c, 3d) have various shapes and deflection voltages applied to the respective segments can be varied, whereby distortion of the displayed images on the fluorescent screen (5) is corrected.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT 1. FIELD OF THE INVENTION The present invention relates generally to an image display apparatus, and more particularly to an image display apparatus having plural linear cathodes wherefrom multi-electron beams are emitted and are deflected by electrostatic vertical deflection electrodes. 2. DESCRIPTION OF THE RELATED ART The above-mentioned image display apparatus in the prior art is shown in FIG. 7 and FIG. 8. Linear cathodes 1 are disposed parallelly to each other in one end portion of a vacuum enclosure 10 as shown in FIG. 7. A repeller 25 for reflecting electrons emitted from the linear cathodes 1 are disposed between the linear cathodes 1 and a back end of the vacuum enclosure 10. A fluorescent screen 5 is disposed in the opposite end portion of the vacuum enclosure 10. The fluorescent screen 5 has an anode 6 on its inside surface. An electron beam extraction electrode 2, which is a planer metal plate and has a number of apertures 8 lined up in plural rows, each disposed in front of and adjacent to the linear cathode 1, is provided between the linear cathode 1 and the fluorescent screen 5. Vertical deflection electrodes 13 and 14 are formed by, for example, metalizing process on surfaces of substrates 30 made of insulation material, and are disposed between the fluorescent screen 5 and the electron beam extraction electrodes 2, in a manner parallel to the linear cathode 1 and perpendicuclar to the electron beam extraction electrode 2. The electron beams 4, ... emitted from the cathode 1 pass the apertures 8, and travel between the vertical deflection electrodes 13 and 14, and finally reach to the fluorescent screen 5. The electron beams 4, ... are deflected by an electrostatic field which is formed by the vertical deflection electrodes 13 and 14, which is formed by the deflection voltage applied thereto. Horizontal deflection electrodes and acceleration electrodes are disposed between the vertical deflection electrodes 13, 14 and the fluorescent screen 5 in a portion shown by a chain line 20 in Fig. 8. However detailed construction is not shown in the drawing because those constructions are not important to the present invention. Theoretically, an image of a horizontal line on the fluorescent screen 5 made by the electron beams 4, ... are expected to form a linear line. However, by some reasons that the vertical deflection electrodes warp, there is voltage drop along the length of the linear cathodes 1, ... the electron beams 4, ... are not uniformly deflected. As a result, the images on the fluorescent screen 5 are distorted. Mechanical correction of the warped vertical deflection electrodes are difficult, since the warp of the vertical deflection electrodes is found after the assembly of components and subsequent sealing off of the image display apparatus in the vacuum enclosure 10. Hence, a yield rate in fabrication has been poor. OBJECT AND SUMMARY OF THE INVENTION An object of the present invention is to provide an image display apparatus wherein a distortion of images which is formed on a fluorescent screen can be corrected by variation of voltage to be applied to respective vertical deflection electrodes which are divided into plural segments. An image display apparatus in accordance with the present invention comprises: linear cathodes for emitting electron beams, an electron beam extraction electrode having apertures for extracting electron beams and disposed parallelly to the linear cathodes, a fluorescent screen disposed parallelly to the electron beam extraction electrode, and electrostatic deflection electrodes which is disposed between the electron beam extraction electrode and the fluorescent screen, and each is divided into at least two pieces of at least a piece disposed nearer to the electron beam extraction electrodes and another piece disposed nearer to the fluorescent screen. Electrostatic fields are formed by the divided vertical deflection electrodes are formed by impressing different voltages to respective segments of the deflection electrodes. Correction of the distorted images due to the distortion of the deflection electrodes can be made for wide extent by selecting the division ratio and the voltage to be applied to the respective segments of the vertical deflection electrodes. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a persepective view of an image display apparatus of an embodiment in accordance with the present invention. FIG. 2 is a cross-sectional view of the embodiment of FIG. 1. FIG. 3(a), FIG. 3(b) and FIG. 3(c) are cross-sectional views for showing principle of deflection of an electron beam. FIG. 4 is a plane view of rectangular vertical deflection electrodes for showing principle of the present invention. FIG. 5(a) and FIG. 5(b) are plane views of vertical deflection electrodes embodying the present invention. FIG. 6(a) and FIG. 6(b) are illustration of images to be represented on a straight line by the electron beams on a fluorescent screen 5. FIG. 7 is the persepective view of the image display apparatus in the prior art. FIG. 8 is the cross-sectional view of the image display apparatus of FIG. 7. DESCRIPTION OF THE PREFEERED EMBODIMENT An embodiment of an image display apparatus in accordance with the present invention is shown in FIG. 1 and FIG. 2. Linear cathodes 1 are disposed in one end portion of a vacuum enclosure 10 as shown in FIG. 2. Although two linear cathodes are shown in FIG. 1 and FIG. 7, plural linear cathodes, for example 15--60, are used in the practical image display apparatus in accordance with the present invention. A repeller 25 for reflecting electrons emitted from the linear cathodes 1 is disposed between the linear cathodes 1 and a back end of the vacuum enclosure 10. A fluorescent screen 5 is disposed in the opposite end portion of a vacuum enclosure 10. The fluorescent screen 5 has an anode 6 on its inside surface. An electron beam extraction electrode 2, which is a planer metal plate and has a number of apertures 8 lined up in plural rows, each disposed in front of and adjacent to the linear cathode 1, is provided between the linear cathode 1 and the fluorescent screen 5. Vertical deflection electrodes 3a, 3b, 3c and 3d are formed by, for example, metalizing process on surfaces of substrates 30 made of insulation material, and are disposed between the fluorescent screen 5 and the electron beam extraction electrode 2, in a manner parallel to the cathode 1 and perpendicular to the electron beam extraction electrode 2. A pair of vertical deflection electrodes 3a and 3c are disposed nearer to the electron extraction electrodes 2 on both sides of each electron beam path passing through the apertures 8. Another pair of vertical deflection electrodes 3b and 3d are disposed nearer to the fluorescent screen 5 on both sides of each electron beam path passing through the apertures 8. The electron beams 4, ... from the cathode 1 pass the apertures 8, and travel between the vertical deflection electrodes 3a, 3b and the vertical deflection electrodes 3c, 3d, and finally reach to the fluorescent screen 5. The electron beams 4, ... are deflected by an electrostatic field which is formed by the vertical deflection electrodes 3a, 3b, 3c and 3d, which is formed by the deflection voltages applied across the linear cathode 1 and the respective vertical deflection electrodes 3a, 3b, 3c and 3d. Four power sources of different voltages for the vertical deflection electrodes 3a, 3b, 3c and 3d are provided (not shown in Fig. 1 and 2), so that respective vertical deflection electrodes can be impressed with different voltages each other. First, principle of the present invention is elucidated with reference to FIG. 3(a), FIG. 3(b), FIG. 3(c) and FIG. 4. The electrons emitted from the linear cathode 1 pass through the plural apertures 8 of the electron beam extraction electrode 2, and rows of electron beams 4, ... are formed. When the electron beams come out of the apertures, at first, they are deflected by an electric field formed by the vertical deflection electrode 3a and 3c. Subsequently, the electron beams are deflected by an electric field formed by the vertical deflection electrode 3b and 3d. For example, in case that rectangular vertical deflection electrodes 3a, 3c, 3b and 3d as shown in FIG. 4 are used, when a voltage applied to the vertical deflection electrodes 3a is higher than that applied to the electrodes 3b, 3c and 3d, and the vertical deflection electrodes 3a and 3c are wider than the vertical deflection electrode 3b and 3d as shown in FIG. 3(a), the electron beam 4 is widely deflected as shown by large deflection valve y₁. When the vertical deflection electrodes 3a, 3c, 3b and 3d have equall widths as shown in FIG. 3(b), the electron beam 4 is deflected in a medium extent as shown by a medium deflection value y₂. When the vertical deflection electrodes 3b and 3d are wider than the vertical deflection electrodes 3a and 3c, the electron beam 4 is deflected in a smallest extent as shown by a small deflection valve y₃. Plane-views of vertical deflection electrodes of embodiments in accordance with the present invention are shown in FIG. 5(a) and FIG. 5(b). The vertical deflection electrodes 3a and 3b are formed to concave and a convex shapes respectively, as shown in FIG. 5(a). In the embodiment, when a voltage applied to the vertical deflection electrode 3a is lower than that applied to the vertical deflection electrode 3b, the electron beams which pass the central portion B of the vertical deflection electrode 3a and 3b are more deflected than the electron beams which pass the end portions A and C. When an image for a straight horizontal line produced by spots made by the electron beams on the fluorescent screen 5 is not linear but is a curve as shown by black dots 27 in FIG. 6(a) due to inclination of the initial speeds of the electron beams along the positions of the linear cathode, use of the vertical deflection electrodes 3a and 3b as shown in FIG. 5(a) are recommendable. A deflection voltage (negative) which is larger than that of the vertical deflection electrode 3a is applied to the vertical deflection electrode 3b. Hence, the electron beams passing the central portion B of the vertical deflection electrodes 3a and 3b are deflected more than those passing the end portions A and B. As a result, the distortion from the straight line of the images on the fluorescent screen 5 is corrected to straight line as shown by small circles 26 in FIG. 6(a). When an image for a straight horizontal line produced by spots made by the electron beams on the fluorescent screen 5 inclines to the straight horizontal line as shown by black dots 27 in FIG. 6(b), use of the vertical deflection electrodes 3a and 3b as shown in FIG. 5(b) are recommendable. A deflection voltage (negative) which is larger than that of the vertical deflection electrode 3a is applied to the vertical deflection electrode 3b. Hence, the electron beams passing the left portion D of the vertical deflection electrodes 3a and 3b are deflected more than those passing the right portion E. As a result, the distortion from the straight line of the images on the fluorescent screen 5 is corrected to straight line as shown by small circles 26 in FIG. 6(b).

Claims: 1. An image display apparatus comprising: linear cathodes (1) for emitting electron beams, an electron beam extraction electrode (2) having apertures (8) for extracting electron beams and disposed parallelly to said linear cathodes (1), a fluorescent screen (5) disposed parallelly to said electron beam extraction electrode (2), and electrostatic deflection electrodes (3a, 3b, 3c, 3d) which is disposed between said electron beam extraction electrode (2) and said fluorescent screen (5), and each is divided into at least two pieces of at least a piece disposed nearer to the electron beam extraction electrode (2) and another piece disposed nearer to the fluorescent screen(5). 2. An image display apparatus in accordance with claim 1, wherein difference voltages are applied to said respective electostatic deflection electrodes (3a, 3b, 3c, 3d). 3. An image display apparatus in accordance with claim 1, wherein a shape of said electrostatic deflection electrode (3a, 3b, 3c, 3d) is concave. 4. An image display apparatus in accordance with claim 1, wherein a shape of said electrostatic deflection electrode (3a, 3b, 3c, 3d) is convex. 5. An image display apparatus in accordance with claim 1, wherein said electrostatic deflection electrodes (3a, 3b, 3c, 3d) have linearly changing widths from one end to another end.

Inventors: MORIYAMA, YUICHI, SEKIHARA, TOSHINOBU
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1986
Main classification: H01J31
IPC codes: H01J31, H01J29