METHOD OF MANUFACTURING A CATHODE RAY TUBE

Abstract: A method of manufacturing a cathode ray tube, which tube comprises an envelope part (1) having a longitudinal axis (9) and a gun assembly (5) which is assembled on a mounting (15) and has a longitudinal axis (22), in which a. the envelope part is fixed in a given position in an assembly device (14) b. the orientation of the gun assembly (5) is adjusted, c. the gun assembly (5) is fixed in the adjusted orientation, d. the gun assembly (5) is inserted into the neck (4) of the envelope part (1), the said axes (9, 22) substantially coinciding, and e. the mounting (15) is sealed to the neck (4) of the envelope part (1). The orientation of the gun assembly (5) (according to step c) is fixed by means of a clamping device which clamps at least three connection pins (17) which are connected to the gun assembly (5).

Description: The invention relates to a method of manufacturing a cathode ray tube, which tube comprises an envelope part having a longitudinal axis and a gun assembly having a longitudinal axis which gun assembly is assembled on a mounting, in which a. the envelope part is fixed in an assembly device in a given position, b. the orientation of the gun assembly is adjusted, c. the gun assembly is fixed in the adjusted orientation, d. the gun assembly is inserted into a neck of the envelope part, the said axes substantially coinciding, and e. the mounting is sealed to the neck of the envelope part. The cathode ray tube may be, for example a television camera tube or a display tube. Display tubes have a wide field of application. They may be used, for example as a projection television tube, an oscilloscope tube, a colour display tube and a DGD ( d ata g raphic d isplay) tube. All these types of tube comprise a gun assembly to generate at least one electron beam. Said electron beam must enter the deflection fields in a particular manner and land at a particular place on a target, for example a display screen. Therefore a very accurate assembly of the gun assembly in the envelope during the manufacture of the tube is necessary. A method as described hereinbefore is known from DE-A 2,706,420. The adjusted gun assembly orientation is fixed in said method in that an exhaust tube provided on the mounting is clamped. When the gun assembly is inserted into the neck, stresses may be built up in the gun assembly. Moreover, stresses may arise in the gun assembly during the mounting of the gun assembly on the mounting. Stresses also arise in the mounting notably at the area of the connection of the gun assembly to the mounting. During sealing of the mounting to the neck of the envelope part, the mounting is softened by heating. As a result of this the connection of the gun assembly to the mounting becomes less stable through the action of the said stresses and variations in the shape and movement of the gun assembly can occur. The adjusted orientation of the gun assembly consequently loses the desired accuracy. It is therefore the object of the invention to provide a method of manufacturing a cathode ray tube in which the adjusted orientation of the gun assembly during sealing is maintained. A method of the kind mentioned in the opening paragraph is for that purpose characterized according to the invention in that the fixing according to step c is achieved by clamping at least three connection pins, which are connected to the gun assembly, by means of a clamping device. The connection pins are connected to the gun assembly in a sufficiently rigid manner. When these connection pins are clamped following orientation of the gun assembly, substantially no shape variations or movements of the gun assembly occur during the sealing so that the gun assembly remains oriented. An embodiment of the method in accordance with the invention is characterized in that the adjustment of the orientation of the gun assembly is carried out with respect to the axis of the envelope part and the fixing of the adjusted orientation of the gun assembly according to step c is done by a clamping device which is integrated with the assembly device and which clamps at least three of the connection pins connected to the gun assembly. The place and/or angle orientation of the gun assembly may be adjusted outside the assembly device with respect to a first holder and the gun assembly may then be fixed in said position. When the assembly is to be introduced into the neck of the envelope part, the clamping device and the gun assembly must be transferred to the assembly device in which the envelope part is fixed in a given position. A second holder which as regards the adjustment of the orientation is substantially identical to the first holder then is necessary in the assembly device which positions the clamping device and the gun assembly in the fixed orientation in the assembly device, after which the gun assembly is inserted into the neck of the envelope part, the axis of the gun assembly substantially coinciding with the axis of the envelope part. However, when the adjustment of the orientation of the gun assembly is done with respect to the axis of the envelope part and the fixing of the adjusted orientation of the gun assembly is done by a clamping device which is integrated with the assembly device, an extra holder is not necessary. A few embodiments of the invention will now be described with reference to the accompanying drawings in which Figure 1 is a diagrammatic longitudinal sectional view of a cathode ray tube, Figures 2 a and 2 b show diagrammatically the assembly according to an embodiment of a method according to the invention with reference to a longitudinal sectional view of the tube not yet assembled. Figure 3 shows the integrated assembly according to a further embodiment of a method in accordance with the invention with reference to a longitudinal sectional view of the tube not yet assembled, Figure 4 is a diagrammatic elevation of an adjustment of the orientation of the gun assembly, Figures 5 a and 5 b are diagrammatic sectional views of the principle of clamping three connection pins, Figure 6 a is a diagrammatic elevation of a sealing pin with an integrated clamping device, Figure 6 b is a diagrammatic sectional view of a sealing pin taken on the line 6 b -6 b of figure 6 a , and Figure 7 is a diagrammatic longitudinal sectional view of a tube assembled according to a method of the invention. The cathode ray tube shown in Figure 1 is a colour display tube of the in-line type. An integrated electron gun assembly 5 is provided in the neck 4 of a glass envelope 1 which is composed of a display window 2, a cone 3 and the said neck 4, which assembly generates three electron beams 6, 7 and 8 which before deflection are situated with their axes in one plane. The axis of the central electron beam 7 coincides with the tube's longitudinal axis 9. The display window 2 comprises on its inside a large number of triplets of phosphor elements. The elements may consist of lines or dots. Each triplet comprises an element consisting of a blue-luminescing phosphor, an element consisting of a green-luminescing phosphor, and an element consisting of a red-luminescing phosphor. All triplets together constitute the display screen 10. The phosphor lines are substantially perpendicular to the said plane through the beam axes. In front of the display screen a shadow mask 11 is positioned in which a very large number of apertures 12 is provided through which the electron beams 6, 7 and 8 pass. The electron beams 6, 7 and 8 are deflected in a horizontal direction (in the plane of the drawing) and in a vertical direction (perpendicular to the plane of drawing) by the system of deflection coils 13. The three electron guns are assembled so that their axes enclose a small angle with each other. The generated electron beams 6, 7 and 8 as a result of this pass through the apertures 12 at said angle, the so-called colour selection angle, and each impinges only on phosphor elements of one colour. A display tube has a good static conversion when the three electron beams, when they are not deflected, intersect each other substantially in the centre of the display screen. However, it has been found that the static convergence, and likewise the frame shape and the colour purity, often is not good, which may be the result of an insufficiently accurate gun assembly and/or sealing of the electron guns in the tube neck. The adjustment of the orientation of the gun assembly and the fixing of the gun assembly in the adjusted orientation may be done outside the assembly device in which the envelope part is fixed in a given position. When the gun assembly is to be inserted into the neck of the envelope part, the gun assembly and a clamping device therefor should be placed in the assembly device while being positioned in such a manner that upon inserting the gun assembly into the neck of the envelope part, the axes of the gun assembly and the envelope part substantially coincide. A possibility herefor is to adjust the orientation of the gun assembly 5 which is placed, for example, on a sealing pin 19, outside the assembly device with respect to a first holder 39 and by fixing the clamping device in the adjusted orientation with respect to the first holder 39, as is shown diagrammatically in Figure 2a. The clamping device, which is not shown, may be present, for example, in the sealing pin 19. By transferring the gun assembly 5 and the clamping device of the first holder to a holder 40 in the assembly device 14, which second holder is substantially identical to the first holder 39, the gun assembly may be provided in the neck 4 of the envelope part 1, provided the second holder is positioned accurately in the assembly device 14 as is shown diagrammatically in Figure 2b, the axis of the gun assembly coinciding substantially with the axis 9 of the envelope part. The holder 39, 40 comprise, for example, centring rings 41, 43 for centring the sealing pin 19 on the holders 39, 40. By adjusting the place and/or angle orientation of the gun assembly with respect to the axis of the envelope part by means of a positioning device which is integrated in the assembly device and then fixing said adjusted orientation within the assembly device, holders need not be used. An embodiment of the method in accordance with the invention will now be described in greater detail with reference to Figure 3. The envelope 1 is fixed in an assembly device 14 in a given position. This is shown diagrammatically by means of the positioning cams 42. The gun assembly 5 comprises electrodes which are connected together by means of glass rods. The gun assembly 5 is assembled on a glass plate 15, also termed mounting, by means of connection wires 16 which are connected to the connection pins 17 which are sealed in the mounting 15. Furthermore a glass tube, the exhaust tube 18, is connected to the mounting 15. The gun assembly 5 is placed with the pins 17 in a sealing pin 19 shown diagrammatically, which sealing pin 19 forms part of the assembly device 14. The orientation of the gun assembly 5 consisting of the electrodes and the mounting 15 with the 6 exhaust tube 18 is now adjusted at some distance from the neck end 20 by means of a positioning device 21 integrated with the assembly device in such a manner that the axis of the gun assembly 22 coincides substantially with the axis 9 of the envelope 1. The adjustment of the orientation of the gun assembly 5 occurs in that the positioning device 21 directly engages electrodes of the gun assembly 5, which electrodes of the gun assembly 5 are connected together, for example, by means of glass rods 24, as shown in Figure 4. It has been found in practice that the adjustment of the orientation of the gun assembly 5 occurs readily when the positioning device 21 engages two electrodes of the gun assembly 5 by means of prismatic tongs 23. During the adjustment of the orientation of the gun assembly 5 the holder 39 can move freely, for example by means of an air-cushion on which the holder 39 floats. When the orientation of the gun assembly 5 is adjusted the holder 39 is fixed in its position, for example by means of a vacuum-chuck. By clamping three of the connection pins 17 by means of a clamping device the adjusted orientation of the gun assembly is fixed. The positioning of the gun assembly 5, however, is not restricted to the adjustment method shown in Figure 4. It is also possible, for example, for the prismatic tongs 23 to engage two other electrodes or even only one electrode. Figure 5 a is a diagrammatic sectional view of the principle of clamping three connection pins. The three connection pins 25, 26 and 27 are provided against three engaging surfaces 28, 29 and 30. These three engaging surfaces 28, 29 and 30 form part of a first tongs portion. Clamping the connection pins 25, 26 and 27 is done in that a second tongs portion exerts pinching forces on the connection pins 25, 26 and 27. These pinching forces are substantially perpendicular to the engaging surfaces 28, 29 and 30 as is shown in Figure 5 a by arrows. The second tongs portion comprises, for example, three clamping surfaces 32, 33 and 34 as is shown diagrammatically in Figure 5 b . The two tongs portions together constitute the clamping device. The principle of clamping may be applied to three arbitrary connection pins. The principle of clamping can also be extended to more than three pins, although in that case an over-determination of the position of the gun assembly is obtained. It has been found in practice that the adjusted orientation of the gun assembly can simply be fixed by integrating the clamping device with the sealing pin 19 which forms part of the assembly device. Figures 6 a and 6 b show diagrammatically an example of a sealing pin 19 with integrated clamping device. Figure 6 a is a plan view of the sealing pin 19 having holes 35 for receiving connection pins. The sealing pin furthermore comprises three engaging surfaces 28, 29 and 30. The sealing pin 19 comprises a clamping device consisting of a cylinder 36 present within the sealing pin 19. The cylinder 36 has projections 37 and comprises three clamping surfaces 32, 33 and 34 which correspond to the engaging surfaces 28, 29 and 30. The cylinder 36 has been mounted in the sealing pin 19 so as to be rotatable via a spherical hinge 38 (see Figure 6 b ). When the gun assembly is placed in the sealing pin, the orientation of the gun assembly can be adjusted, by means of the positioning device, with respect to the axis of the envelope part and the connection pins can be clamped between the engaging and clamping surfaces by rotating the cylinder present in the sealing pins. Once the orientation of the gun assembly 5 has been fixed by the clamping device the gun assembly 5 is introduced into the neck of the envelope 2 in such a manner that the axis 22 of the gun assembly coincides substantially with the axis 9 of the envelope 1 as is shown diagrammatically in Figure 7. The mounting 15 is then sealed to the end 20 of the neck. Since the clamping device still clamps the connection pins 17 the softening of the mounting 15 has no influence on the orientation of the gun assembly 5. When the gun assembly 5 is connected in the neck 4 the clamping device is removed. After further treatments, if any, the assembled tube is evacuated via the end of the tube 18 after which this is sealed and partly removed. The method described provides a display tube in which the axis of the gun assembly coincides accurately with the axis of the envelope of the display tube. It will be obvious that the invention is not restricted to the embodiments described but that many variations are possible to those skilled in the art without departing from the scope of this invention.

Claims: A method of manufacturing a cathode ray tube, which tube comprises an envelope part having a longitudinal axis and a gun assembly having a longitudinal axis which gun assembly is assembled on a mounting, in which a. the envelope part is fixed in an assembly device in a given position, b. the orientation of the gun assembly is adjusted, c. the gun assembly is fixed in the adjusted orientation, d. the gun assembly is inserted into a neck of the envelope part, the said axes substantially coinciding, and e. the mounting is sealed to the neck of the envelope part, characterized in that the fixing according to step c is achieved by clamping at least three connection pins, which are connected to the gun assembly, by means of a clamping device. A method as claimed in Claim 1, characterized in that the clamping device which fixes the gun assembly in the adjusted orientation is positioned with respect to a first holder, after which the clamping device with the fixed gun assembly is transferred to a second holder which is substantially identical to the first holder and which is provided in the assembly device and the gun assembly is then inserted into the neck of the envelope part according to step d. A method as claimed in Claim 1, characterized in that the adjustment of the orientation of the gun assembly is carried out with respect to the axis of the envelope part and the fixing of the adjusted orientation of the gun assembly according to step c is carried out by a clamping device which is integrated with the assembly device and which clamps at least three of the connection pins connected to the gun assembly.

Inventors: VAN RENS, PIET CHRISTIAAN JOZEF, VERHAGEN, JOHANNES WILHELMUS HENRICUS, WEENING, RIENK
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1987
Main classification: H01J9
IPC codes: H01J9