Improved method of assembling an electron gun component

Abstract: A method of manufacturing an electron gun component, in which the electrodes are positioned in a jig by means of positioning means which are located at the edge of the electrodes. The method does not use pins to position the electrodes. In an exemplary embodiment, said electrodes are stacked in the jig with clearance. The positioning means are located at the vertices of a polygon which comprise the apertures in the electrodes. If an electrode is tubular in shape, the positioning means and the apertures in the electrode are preferably located in one plane.

Description: The invention relates to a method of manufacturing an electron gun component which electron gun component comprises at least two electrodes each electrode having at least one aperture for passing of an electron beam , in which method the at least two electrodes are stacked in a jig and the at least two electrodes are interconnected, the at least two electrodes having electrode locations and the jig having corresponding jig locations. Electron guns are used, inter alia , in display tubes for colour display devices, projection display devices and data display devices. Within the framework of the present application "locations" is to be understood as described in Chambers dictionary of Science and Technology, reprint of 1984, page 700, word "location", last sentence, i.e. a "geometrical feature by which one article may be correctly positioned with a corresponding feature in another (article)". A method of the type described in the opening paragraph is known from the abstract in the English language of Japanese Patent Application JP-A 56-54739, published in Patents abstracts of Japan vol. 5. No. 117, (E-67), (789), 28 July 1981. In said Application a description is given of a method of manufacturing an in-line electron gun. The electrodes have one central aperture and two outer apertures. The jig comprises a pin on which the electrodes are stacked, said pin penetrating the central aperture, and two fixed and two movable jaws. Said cavities jaws with the positioning means and the pin to position the electrodes. Each electrode comprises a projection on either side of the in-line plane which extends away from said plane. After the electrodes of an electron gun have been positioned in a jig, the electrodes are interconnected which is normally carried out by pressing a rod of ceramic glass which is heated to the flow temperature onto the projections, said rod interconnecting the electrodes after it has cooled. It has been found that the edges of the central aperture may be damaged which leads to failure of the electron gun, and that an electrode sometimes sticks to the pin so that it is difficult to remove the electron gun component from the pin. One of the objects of the invention is to provide a method by means of which a reduction of the above problems is achieved. To this end a method of the type as described in the opening paragraph is characterized in that the at least two electrodes are stacked in the jig with a clearance, none of the said apertures being penetrated by a pin, whereafter the at least two electrodes are interconnected and that during interconnection of the at least two electrodes said electrodes thermally expand whereby by means of the cooperating electrode and jig locations the positions of the at least two electrodes are determined. As no aperture is penetrated by a pin, no aperture can be damaged by the pin or stick thereto. The method according to the invention can be used for the manufacture of a component for an electron gun for generating one electron beam. Such electron guns are suitable for, for example, a monochrome display tube or a projection display tube. The method according to the invention can also be used for the manufacture of a component for an electron gun which, in operation, generates several, for example three, electron beams. Examples of such electron guns are the so-called delta and in-line electron guns. According to the invention, the at least two electrodes are stacked in the jig with a clearance such that during interconnecting the at least two electrodes thermally expand whereby the electrode and jig locations cooperate with each other. In the method according to the invention, the electrodes, when in the "cold" state, are stacked in the jig with clearance. During interconnecting, which is carried out, for example, by providing a connection member, for example a glass rod or a solder joint, which can be softened by heat, the temperature of the electrodes increases. The clearance is selected such that it disappears, at least substantially, when the electrodes are heated-up. Consequently in the "cold" state the electrode location and the jig locations do not lie against each other. In the hot" state, the electrodes with the electrode locations at least substantially lie against the locations of the jig. In the known method, the electrode, when in the "cold" state, is clamped between the movable and the fixed jaws and on the central pin. The electrode expands when it is heated by the connection member. As some of the jaws can be moved and forces are exerted on the electrodes when the connection member is provided, the central aperture may be displaced however and/or insecurities in accuracies positioning of the electrodes may occur or an electrode may stick to the pin, as will be explained hereinbelow. Preferably, the at least two electrodes are positioned by means of electrode locations which are located at least substantially at the vertices or the sides of a polygon comprising the centroid of all apertures. When the electrode locations are located at least substantially at the vertices of a polygon which comprises the centroid of all apertures, it is possible to position the electrode with a high degree of accuracy. Regarding the accuracy with which the electrodes are positioned, it is to be noted that it has been found in practice that a thin central pin, i.e., a pin having a cross-section in the order of 1 mm or smaller, does not determine the position of the electrodes but is bent such that it follows the apertures in the electrodes. Consequently, the method can be used very suitably if at least the central apertures in the at least two electrodes have a diameter of 1 mm or smaller. Preferably, the at least two electrodes are the electrodes which can be located nearest to the cathode. In general, these electrodes have the smallest apertures. There is a great chance that an aperture or pin becomes damaged. A further preferred embodiment of the method according to the invention is characterized in that none of the apertures of a number of successive electrodes are penetrated by a pin, preferably, none of the apertures of all electrodes are penetrated by a pin. In this case, one jig can be used for many electron-gun constructions, and the chance of an electron gun sticking to a pin is absent. Preferably, the position of the electrodes is checked while the electron gun component is located in the jig. This saves time and precludes a sub-standard electron gun from continuing in the production line. An embodiment of the invention is characterized in that the electrodes are separated by spacers. Preferably, at least one of the electrodes is provided with at least one electric connection, while the electron gun is located in the jig. This is time-saving. The invention also relates to an electron gun component manufactured according to the above method. The component may be, for example, a composite electrode or an assembly of electrodes or an entire electron gun. The invention also relates to an electron gun component comprising at least at least two electrodes, each having at least one aperture and electrode locations. According to the invention, the component of this type is characterized in that at least one of the at least two electrodes comprises a plate shaped portion which is secured to a cylindrical portion, the plate shape portion comprising at least one aperture and electrode locations extending at least substantially in one plane, the electrode locations being located at least substantially at the vertices or sides of a polygon which comprises the centroid of the aperture(s) in the plate shaped portion. Such an component can be used advantageously in the above described method. The position of the at least one aperture is determined more accurately when the apertures (or apertures) and the electrode locations extends substantially in one plane, then when the aperture(s) and the electrode locations extend in different planes. By forming the electrode locations and the at least one aperture in a plate-shaped portion of the electrode a high degree of accuracy can be obtained in a simple manner. In an embodiment the at least one of the at least two electrodes comprises two plate shaped portions, one at each side of the cylindrical portion. The electron gun component may be, for example, a composite electrode, an assembly of electrodes or an entire electron gun. The invention also relates to a cathode ray tube comprising an electron gun according to the invention. The invention will be explained in greater detail by means of a few exemplary embodiments and with reference to the accompanying drawings, in which, Fig. 1 is a sectional view of a cathode ray tube which comprises an electron gun manufactured according to the inventive method, Fig. 2 is a sectional view of an in-line electron gun, Fig. 3 is a top view of an electrode of an in-line electron gun according to the present state of the art, Fig. 4a and 4b are top views of an electrode showing how an electrode is positioned in the known method, Fig. 5 is a top view of an electrode showing a problem which occurs in the known method, Figs. 6a to 6d are top views of electrodes 70 of an electron gun according to the invention, Fig. 7 is a sectional view of an electrode 70 and parts 81 and 82 of a jig, Fig. 8 is a partly perspective elevational view of a jig 100, Fig. 9 is a sectional view of an electron gun manufactured according to the inventive method, Figs. 10a and 10b are sectional views of two electrodes of an electron gun according to the invention, Fig. 10c is a further example of an electrode of an electron gun according to the invention, Fig. 11 is a top view of a further jig which can suitably be used in the method according to the invention. The Figures are diagrammatic representations and are not drawn to scale, corresponding parts in the different embodiments generally bearing the same reference numerals. Fig. 1 is a sectional view of a cathode-ray tube comprising an electron gun manufactured according to the invention. In a glass envelope 1 which comprises a display window 2, a cone 3 and a neck 4, an in-line electron gun 5 is arranged in said neck 4, which electron gun generates three electron beams 6, 7 and 8 whose axes are located in the plane of the drawing. In the undeflected state, the axis of the central electron beam 7 coincides with the tube axis 9. The display window 2 is provided on the inside with a large number of triads of phosphor elements. Said elements may consist of, for example, lines or dots. In the present case, the cathode-ray tube comprises linear elements. Each triad comprises a line containing a phosphor luminescing in green, a line containing a phosphor luminescing in blue and a line containing a phosphor luminescing in red. Said phosphor lines extend perpendicularly to the plane of the drawing. In front of the display screen a shadow mask 11 is positioned in which a large number of elongated apertures 12 are formed through which the electron beams 6, 7 and 8 pass. The three electron beams which are located in one plane, the in-line plane, are deflected by a deflection-coil system 13. Figure 2 is a partly sectional view of an in-line electron gun. The in-line electron gun comprises a cup-shaped electrode 20 in which three cathodes 21, 22 and 23 are located, and a common plate-shaped screen grid 24. The three electron beams are focused by means of common electrode systems 25 (G3) and 26(G4). Electrode system 25 comprises two cup-shaped parts the open end portions of which face each other, a first electrode 27 and a second electrode 28. The main lens is formed between the first electrode system 25 and the second electrode system 26 and may be of a conventional type or of, for example, the polygon type. Electrode 26 comprises a cup-shaped part 29 and a centring sleeve 30 the bottom of which contains apertures 31 through which the electron beams pass. Electrode 25 comprises an outer edge 32 which extends towards the electrode 26, and electrode 26 comprises an outer edge 33 which extends towards the electrode 25. Apertures 38, 39 and 40 are formed in the recessed part 34 which extends transversely to the axes 35, 36 and 37 of the electron beams 6, 7 and 8. Apertures 42, 43 and 44 are formed in the recessed part 41 which extends mainly transversely to the axis 36 of the central electron beam. The recessed parts 34 and 41 are integral with the parts 28 and 29, respectively. In the first electrode system, an astigmatic element is formed by means of an auxiliary electrode G AST which is provided separately at some distance from the main lens as a flat plate having elongated apertures 45, 46 and 47. Said apertures may be, for example, rectangular, oval or diamond-shaped. The auxiliary electrode is coupled to electrode 27 and comprises means for supplying a constant voltage V foc . G3 also comprises means for supplying a control voltage V foc +Vc to electrode 28. It is very important that the electrodes are accurately positioned relative to each other and that the edges of the apertures are undamaged, otherwise this may influence the electric fields between the electrodes. Not all apertures in the electrodes are in line, some apertures are square or oval. For example, the outer apertures 31 are not in line with the apertures 44 and 42, the apertures 45, 46 and 47 are not round but elongated, as described above. So far, in the assembly of the electron gun the various electrodes were threaded on pins. It will be obvious that an electron gun as shown in Fig. 2 requires pins having a very complex shape. Fig. 3 is a top view of an electrode 50 known from JP-A 56-54739. Said electrode comprises three apertures 51, 52 and 53. Said electrode 50 further comprises two projections 54 and 55, and positioning faces 56. Fig. 4a is a top view of the manner in which the electrode 50 is positioned according to the state of the art. The electrodes 50 are stacked on a pin 60. The positioning faces 56 cooperate with four jaws 61, 62, 63 and 64. Two of these jaws (62 and 63) are fixed and two (61 and 64) are movable. This enables the electrode to be clamped. Subsequently, the electrodes are interconnected which is normally carried out by pressing a few rods 65 and 66 of ceramic glass, which have been heated to the flow temperature, against the projections 54 and 55. After the rods have cooled, the electrodes are interconnected by the glass rod. Fig. 4b again shows, in detail, the manner in which the electrode 50 is positioned. The jaws 61 and 64 are movable and exert a force F on the electrode, thereby urging the electrode against the jaws 63 and 62. However, it has been found that there is a chance that the central pin causes damage to the edges of the central aperture 51 or that the electrode is clamped on the central pin. It is an object of the invention to provide a method in which this problem is obviated. To this end, the method according to the invention is characterized in that no central pin is used to position the electrode, but that it is positioned only by means of locations on or at the electrodes and locations on, in or at the jig. In the known method, problems arise, when the electrodes are interconnected in such a manner that heat is supplied to the electrodes, for example, when the electrodes are interconnected by means of a heated glass rod or a solder joint. Fig. 5 illustrates why problems occur. Since the central pin 60 and the jaws 63 and 64 are fixedly arranged, the electrode, which has expanded as a consequence of the rise in temperature, will rotate. It will be obvious that this is a problem because the position of the apertures changes. A further consequence of the rotation of the electrode is that the pin may damage the edges of the aperture. It may be possible to fixedly arrange jaws 63 and 64 and movably arrange jaws 61 and 62, so that tilting of the electrode is prevented. When the electrode is heated, however, another problem arises: the electrode 50 expands, but the distance between the jaws 63 and 64 and the central pin 60 does not change. Consequently, the electrode is deformed or the pin is pushed aside. The latter is more likely when the pin is thin. Also in this case the position of the apertures changes and the central aperture may be damaged by the pin. Regarding the accuracy with which the electrodes are positioned, it is to be noted that it has been found in practice that in the case of thin pins, i.e., for electrodes having very small apertures with a cross-section of 1 mm or smaller, the pins do not determine the position of the electrode, but are bent in such a manner that they follow the apertures in the electrode. In the case of such electrodes, the accuracy with which the electrode is positioned is determined by the accuracy with which the apertures are formed in the electrode. In the method according to the invention, the electrode locations and the jig locations cooperate only during interconnection. In the method according to the invention, the electrodes, when in the "cold" state, are stacked in the jig with clearance. During the provision of the connection member which can be softened by heat, said member being for example a glass rod or a solder joint, the temperature of the electrodes rises. The clearance is selected such that it disappears when the electrodes are heated up. Consequently, the electrode locations and the jig locations do not lie against each other in the "cold" state. In the "hot" state, the electrodes and the electrode locations at least substantially lie against the locations of the jig. Figs. 6a and 6b are top views of an electrode 70 which can suitably be used in an in-line electron gun component manufactured according to the inventive method. The electrode 70 comprises apertures 71, 72 and 73. Apertures of other electrodes are represented by reference numerals 74, 75 and 76. The Figures clearly show that the apertures 73 up to and including 76 are not all in line. The electrode 70 has projections 77 at its outer edge, through which the positioning faces 78 (Fig. 6b) or 78 and 79 (Fig. 6a) are formed. The positioning faces define a quadrangle R having vertices 80. The centroid of the apertures 71, 72 and 73 all lie within said quadrangle. Figs. 6c and 6d show further examples of electrodes which can suitably be used in an electron gun manufactured according to the inventive method. Fig. 6c shows an electrode having one aperture 72, electrode locations formed by reference faces 78 and 79, and securing members 85. Fig. 6d shows an electrode which can suitably be used for a delta electron gun manufactured according to the invention. This electrode contains three apertures 72 which are arranged in a triangle, electrode locations formed by reference faces 78 and 79 and securing members 85. Reference faces 78 and 79 define a polygon, in the present example a hexagon, within which the centroid of the apertures 72 are located. As the electrode locations define a polygon which comprises the centroid of all apertures, the position of the electrode can be determined by the positioning means with a high degree of accuracy. The accuracy with which apertures are positioned is determined by the accuracy with which the apertures in the electrode are formed and by the accuracy with which the electrode is positioned. On the assumption that all parts of the electrodes and the jig are manufactured with approximately equal accuracy, in the present examples, the last-mentioned accuracy is equal to or greater than the accuracy with which the apertures in the electrode are formed. Fig. 7 is a sectional view of electrode 70 and parts 81 and 82 of a jig. In this Figure, the electrode is connected to a glass rod 83 and provided with lugs 84. Said lugs can be used to form electric connections with the electrode. In the assembly operation, the glass rod is heated to the flow temperature and pressed against projections 85. The parts 81 and 82 are far removed from the glass rod 83, because they are located at the vertices of a polygon which comprises the aperture. Consequently, there is more space for the glass tube, which is advantageous. This results in the parts 81 and 82 being heated less than the jaws shown in Figs. 4a and 4b. In this manner, thermal stresses in the parts are reduced. The assembly process can be simplified because the melting-on of the glass rods and the formation of electric connections ( via lugs 84) can be carried out simultaneously or almost simultaneously. Also other parts, for example a centring sleeve, can be secured to the electron gun while the electron gun is still in the jig. Fig. 8 is a partly perspective elevational view of a jig 100. Said jig comprises a base plate 105 on which the fixed parts are secured. Said jig further comprises the movable parts 82 and an end plate 102. Beside the jig, two electrodes 70 and 110 are shown. They are stacked in the jig together with other electrodes, the distance between the electrodes being defined by spacers 120. The latter are removed after the electrodes are interconnected. While the electron gun or an electron gun component is still in the jig the relative positions of the apertures in the electrodes can be checked, for example, using a laser beam by means of which the contours of the apertures can be scanned. When the accuracy with which the electron gun is manufactured does not meet specific requirements, the electron gun can be removed from the production line immediately after it has been manufactured, thereby saving costs. The electrode locations and the jig are produced such that the electrodes fit in the jig with a small clearance in the order of, for example, 10 to 100 µm. Subsequently, a heated glass rod is pressed on the projections. As a consequence hereof, the electrodes expand and, in the heated state, the electrode locations cooperate with the jig locations. Dependent upon the shape and the material of the electrodes, the expansion of the various electrodes does not have to be equal, consequently the clearance of the various electrodes may vary in the cold state. Fig. 9 is a sectional view of an electron gun according to the invention during its manufacture. The electrodes are separated by spacers 120. For each electrode the electrode locations 77 are located in one plane with the apertures in the electrode. As the positioning means and the apertures are located in one plane, the position of said apertures is determined more accurately than in the case that the positioning means are located in a different plane. Figs. 10a and 10b are sectional views of electrodes which can suitably be used for an electron gun (or an electron gun component) manufactured according to the method. A tubular electrode 131 comprises a cylindrical portion a plate-shaped portion 133 with apertures 134, 135 and 136, and electrode locations 137 and 138, and a plate-shaped portion 139 having apertures 140, 141 and 142 and electrode locations 143 and 144. The cylindrical portion and the plate-shaped portions 133 and 139 are secured to each other by means of welding. A tubular electrode 151 comprises a cylindrical portion 152, a plate-shaped portion 153 having apertures 154, 155 and 156 and electrode locations 157 and 158, a collar-shaped portion 159 and a second plate-shaped portion 160 having apertures 161, 162 and 163 and electrode locations 164 and 165. The plate-shaped portion 153 is secured to the cylindrical portion 152 and the collar-shaped portion 159 by means of welds 166. The cylindrical portion 152 is secured to the plate-shaped portion 160 by means of welds 166. As the apertures and the electrode locations are located in one and the same plate-shaped portion, the apertures and the positioning means can be made to extend in one plane in a simple manner. This embodiment is preferred to an embodiment in which the apertures and electrode locations are positioned on different portions of the electrode, for example, a cylindrical portion 170 and a collar-shaped portion 171 and a portion 173 having apertures 174, 175 and 176 can form an entity which is provided on the outside with projections 177 on which the electrode locations 178 are provided, as is shown in Fig. 10c. With such an electrode it is more difficult to accurately position the apertures and the electrode locations relative to each other than with an electrode as shown in Fig. 10b. The cylindrical portions 132, 152, 170 may be of various shape or form, e.g. the cross-section may be circular triangular, quadrangular, or polygonal. It may have sharp or rounded corners. It may be provided with internal or external projections. It may change in diameter. Fig. 11 is a top view of a further embodiment of a jig which can suitably be used in the method according to the invention. The portions 81 of the jig differ from the portions 81 of the jig shown in Fig. 7. The electrode 70 comprises electrode locations 710 in the in-line plane. It has been found that when the electrode locations are located in the in-line plane an improved positioning of the electrode in the in-line plane is obtained.

Claims: A method of manufacturing an electron gun component which electron gun component comprises at least two electrodes (70, 110, 131, 151, 170) each electrode having at least one aperture (71, 72, 73, 134, 135, 136, 140, 141, 142, 154, 155, 156, 161, 162, 163, 174, 175, 176) for passing of an electron beam (6, 7, 8), in which method the at least two electrodes are stacked in a jig (100) and the at least two electrodes are interconnected, the at least two electrodes having electrode locations (77, 78, 79, 137, 138, 143, 144, 157, 158, 164, 165, 178) and the jig having corresponding jig locations, characterized in that the at least two electrodes are stacked in the jig with a clearance, none of the said apertures being penetrated by a pin, whereafter the at least two electrodes are interconnected and that during interconnection of the at least two electrodes said electrodes thermally expand whereby by means of the cooperating electrode and jig locations the positions of the at least two electrodes are determined. A method as claimed in claim 1 characterized in that the electrodes are positioned by means of electrode locations which (77, 78, 79, 137, 138, 143, 144, 157, 158, 164, 165, 178) are located at least substantially at the vertices or sides of a polygon (R) which comprises the centroid of all apertures. A method as claimed in claim 1 or 2, characterized in that at least two electrodes are stacked which each have a central apertures having a diameter smaller than 1 mm. A method as claimed in claims 1, 2 or 3 characterized in that all electrodes comprised in the electron gun component are stacked in the jig, each electrode having at least one aperture for passing an electron beam, none of said apertures being penetrated by a pin, whereafter all electrodes are interconnected and that during interconnection the electrodes thermally expand whereby by means of the cooperating electrode and jig locations the positions of the electrodes are determined. A method as claimed in any of the preceding claims, characterized in that the positions of electrodes are checked while the electron gun component is located in the jig. A method as claimed in any of the preceding claims, characterized in that the electrodes are separated by spacers (120). A method as claimed in any one of the preceding claims, characterized in that at least one electric connection is formed at at least one electrode, while the electron gun component is located in the jig. An electron gun component which comprises at least two electrodes, each having at least one aperture and electrode locations, characterized in that at least one of the at least two electrodes (131, 151) comprises a plate shaped portion (133, 153) which is secured to a cylindrical portion (132, 152), the plate shape portion comprising at least one aperture (134, 135, 136; 154, 155, 156) and electrode locations (137, 138; 157, 158) extending at least substantially in one plane, the electrode locations being located at least substantially at the vertices or sides of a polygon which comprises the centroid of the aperture(s) in the plate shaped portion. An electron gun component as claimed in claim 8, characterized in that the at least one of the at least two electrodes comprises two plate shaped portions (133, 139; 153, 160), one at each side of the cylindrical portion, each plate shaped portion comprising at least one aperture (134, 135, 136, 140, 141, 142; 154, 155, 156, 161, 162, 163) and electrode locations (137, 138, 143, 144; 157, 158, 164, 165) extending at least substantially in one plane, the electrode locations being located at least substantially at the vertices or sides of a polygon which comprises the centroid of the aperture(s) in the plate shaped portion. An electron gun component as claimed in claims 8 or 9 characterized in that the electron gun component is an entire electron gun.

Inventors: VAN DER HEIJDEN GERRIT, VAN ECK ARNOLDUS HUBERTUS MARI, VAN DER HEIJDEN, GERRIT, VAN ECK, ARNOLDUS HUBERTUS MARIA
Applicants: PHILIPS ELECTRONICS NV, PHILIPS ELECTRONICS N.V.
Application year: 1989
Main classification: H01J9
IPC codes: H01J9