This type the 45AX FST TUBE BY PHILIPS WAS WIDELY USED AROUND THE WORLD and fabricated form more than 22 YEARS.
Picture display system including a deflection unit with a double saddle coil system
PHILIPS 45AX SYSTEM
1. A picture display system including a colour display tube having a neck accommodating an electron gun assembly for generating three electron beams, and an electromagnetic deflection unit surrounding the paths of the electron beams which have left the electron assembly, said deflection unit comprising
a field deflection coil of the saddle type having a front and a rear end for deflecting electron beams generated in the display tube in a vertical direction;
a line deflection coil of the saddle type likewise having a front and a rear end for deflecting electron beams generated in the display tube in a horizontal direction, and a yoke ring of ferromagnetic material surrounding the two deflection coils and having front and rear end faces extending transversely to the tube axis, the electron beam traversing the coils in the direction from the rear to the front ends when the deflection unit is arranged on a display tube, characterized in that the deflection unit also has first and second magnetically permeable portions arranged symmetrically with respect to the plane of symmetry of the field deflection coil on either side of the tube axis, each magnetically permeble portion having a first end located opposite the rear end face of the yoke ring and a second end located at the neck of the display tube in the proximity of the location where the electron beams leave the electron gun assembly, the length of the first and second magnetically permeable portions and their distance to the yoke ring being dimensioned for providing a self-convergent picture display system.
3. A picture display system as claimed in claim 1 characterized in that the field deflection coil and the line deflection coil are directly wound on a support.
4. Apparatus for adapting a self-convergent deflection unit of the type mountable on the neck of a display tube and including a saddle type field deflection coil screen end and a gun end extending away from said tube in a plane disposed at an angle to a tube axis, and a yoke ring having a screen end and a gun end, for use with display tubes having different screen formats comprising:
format adjustment means disposed adjacent to the gun end of the yoke ring for coupling flux from the yoke ring to the neck of the tube to supplement the field produced by the vertical deflection coil to uniformly increase the vertical deflection field to produce a raster having a different format from the raster produced by said deflection unit alone.
6. The apparatus of claim 5 wherein each of said first and second magnetically permeablel members comprises a first end located opposite a gun end face of the yoke ring, and a second end located at the neck of the display tube adjacent the location where the electron beams leave the electron gun assembly.
7. The apparatus of claim 6 wherein said first end comprises a portion of said permeable member disposed parallel to the neck of the displaya tube and said second end comprises a portion of said magnetically permeable member located perpepndicular to the neck of the display tube.
8. The apparatus of claim 7 wherein said second endsn of said magnetically permeable members have inwardly extending arms subending a first angle.
9. The appaaratus of claim 8 wherein said angle is large so that the supplemental field has a positive sixpole component.
11. Apparatus for adapting a self-convergent deflection unit of the type used on the neck of a display tube having an electron gun disposed in a neck of said tube, said deflection unit including a field deflection coil of the saddle type having a rear end portion disposed at an angle to the axis of said tube, comprising means disposed adjacent to said neck between said electron gun and said deflection unit, and coupled to said deflection unit for changing the distance between the line and field deflection points for causing said deflection unit to produce a different screen format.
SUMMARY OF THE INVENTION The deflection unit has first and second magnetically permeable portions arranged symmetrically with respect to the plane of symmetry of the field deflection coil on either side of the tube axis, each magnetically permeable portion having a first end located opposite the rear end face of othe yoke ring and a second end located at the neck of the display tube in the proximity of the location where the electron beams leave the electron gun assembly. The length of the first and second magnetically permeable portions and their distance to the yoke ring are dimensioned for providing a self-convergent picture display system. The invention is based on the recognition that the first ends of the magnetically permeable portions draw a field deflection flux flux which is taken up is adjusted by means of the distance between the first ends and the yoke ring, and the length of the magnetically permeable portions determines how far the vertical deflection field is extended to the rear. A practical embodiment of the picture display system according to the invention is characterized in that regions of the rear end of the yoke ring located on either side of the plane of symmetry of the line deflection coil are left free by the rear end of the field deflection coil and in that the first ends of the magnetically permeable portions are located opposite said regions. The invention can particularly be used to advanatage if the field deflection coil and the line deflection coil are directly wound on a support. The invention also relates to an electromagnetic deflection unit suitable for use in a picture display system as described hereinbefore. For use in a display tube having a larger screen format than the display tube for which it is designed, the invention provides the possibility of moving apart the deflection points of the horizontal deflection field and the vertical deflection field generated by a given deflection unit having saddle coils and of moving them towards each other for use in a display tube having a smaller screen format. The great advantage of the invention is that only a modification of the length of the magnetically permeable portions (providing or omitting them, respectively) is required to adapt a deflection unit to different screen formats of a display tube family.
1. A method of manufacturing a color display tube in which magnetic poles are provided in or around the neck of said tube and around the paths of the electron beams, which poles generate a permanent static multipole magnetic field for the correction of errors in convergence, color purity and frame of the display tube, which magnetic poles are formed by the magnetisation of a configuration of magnetisable material provided around the paths of the electron beams, the method comprising energizing a magnetisation device with a combination of direct currents with which a static multipole magnetic field is generated, and superimposing a decaying alternating magnetic field over said static multipole magnetic field which initially drives said magnetisable material into saturation on either side of the hysteresis curve thereof, said decaying alternating magnetic field being generated by a decaying alternating current. 2. The method as claimed in claim 1, 6 or 7, wherein the decaying alternating magnetic field is generated by means of a separate system of coils in the magnetisation device. 3. The method as claimed in claim 2, wherein the decaying alternating magnetic field varies its direction continuously. 4. The method as claimed in claim 3 wherein the frequency of the decaying alternating current is approximately the standard line frequency. 5. A colour display tube manufactured by means of the method as claimed in claim 4. 6. The method as claimed in claim 1 which further comprises erasing any residual magnetism in said configuration, prior to said magnetisation, with an alternating magnetic field. 7. The method as claimed in claim 6 which further comprises correcting the errors in convergence, color purity and frame of the display picture with a combination of direct currents applied to said magnetisation device and then reversing said direct currents while increasing the magnitudes thereof and applying these adjusted direct currents to said magnetisation device for the magnetisation of said configuration.
The invention relates to a method of manufacturing a color display tube in which magnetic poles are provided in or around the neck of the envelope and around the paths of the electron beams, which poles generate a permanent multipole magnetic field for the correction of the occurring errors in convergence, color purity and frame of the color display tube, which magnetic poles are formed by the magnetisation of a configuration of magnetisable material provided around the paths of the electron beams, which configuration is magnetized by energising a magnetising device with a combination of currents with which a static multipole magnetic field is generated.
The invention also relates to a color display tube manufactured according to said method.
In a color display tube of the "delta" type, three electron guns are accommodated in the neck of the tube in a triangular arrangement. The points of intersection of the axes of the guns with a plane perpendicular to the tube axis constitute the corner points of an equilateral triangle.
In a color display tube of the "in-line" type three electron guns are arranged in the tube neck in such manner that the axes of the three guns are situated mainly in one plane while the axis of the central electron gun coincides substantially with the axis of the display tube. The two outermost electron guns are situated symmetrically with respect to the central gun. As long as the electron beams generated by the electron guns are not deflected, the three electron beams, both in tubes of the "delta" type and of the "in-line" type, must coincide in the center of the display screen (static convergence). Because, however, as a result of defects in the manufacture of the display tube, for example, the electron guns are not sealed quite symmetrically with respect to the tube axis, deviations of the frame shape, the color purity and the static convergence occur. It should be possible to correct said deviations.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a method with which a combined multipole can be obtained by one total magnetisation.
According to the invention, a method, of the kind described in the first paragraph with which this is possible, is characterized in that the magnetisation is effected by means of a decaying alternating magnetic field which initially drives the magnetisable material on either side of the hysteresis curve into saturation. After the decay of the alternating magnetic field, a hard magnetisation remains in the material of the configuration which neutralizes the externally applied magnetic field and is, hence, directed oppositely thereto. After switching off the externally applied magnetic field, a magnetic multipole field remains as a result of the configuration magnetized as a multipole. The desired magnetisation may be determined in a number of manners. By observing and/or measuring the deviations in the frame shape, color purity and convergence, the desired multipole can be determined experimentally and the correction may be carried out by magnetisation of the configuration. If small deviations are then still found, the method is repeated once or several times with corrected currents. In this manner, by repeating the method according to the invention, it is possible to produce a complete correction of the errors in frame, color purity and convergence. Preceding the magnetisation, residual magnetism, if any, in the configuration is preferably erased by means of a magnetic field.
The method is preferably carried out by determining the required correction field prior to the magnetisation and, after the erasing of the residual magnetism, by correcting the errors in the convergence, the color purity and the frame of the displayed picture by means of a combination of currents through the magnetising device, after which the magnetisation is produced by reversing the direction of the combination of currents, increasing the current strength and simultaneously producing the said decaying alternating magnetic field.
The correction field, obtained with the magnetizing device and measured along the axis of the electron beams, is generally longer than the multipole correction field generated by the configuration. So the correction of the deviations will have to be carried out over a shorter distance along the axis of the tube, which is possible only with a stronger field. During the magnetisation, a combination of currents, which in strength and direction is in the proportion of m:1 to the combination of currents which is necessary to generate a correction multipole field with the device, where m is, for example, -3, should flow through the magnetisation device. The value of m depends on the ratio between the length of the correction multipole field, generated by the magnetizing device, to the effective field length of the magnetized configuration. This depends upon a number of factors, for example, the diameter of the neck, the kind of material, the shape and the place of the configuration, etc., and can be established experimentally. If it proves, upon checking, that the corrections with the magnetized configuration are too large or too small, the magnetisation process can be repeated with varied magnetisation currents.
The decaying alternating magnetic field can be generated by superimposing a decaying alternating current on the combination of currents through the magnetisation device (for example, a device as disclosed in Netherlands Pat. application No. 7,503,830 laid open to public inspection). The decaying alternating magnetic field is preferably generated in the magnetisation device by means of a separate system of coils. In order to obtain a substantially equal influence of all parts of the configuration by the decaying alternating field, it is recommendable not only to cause the alternating field to decay but also to cause it to vary its direction continuously. The system of coils therefore consists preferably of at least two coils and the decaying alternating currents through the coils are shifted in phase with respect to each other. Standard line frequency (50 or 60 Hz) has proven to give good results. The phase shift, when using coils or coil pairs, the axes of which enclose angles of 120° with each other, can simply be obtained from a three-phase line.
DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with reference to a drawing, in which
FIG. 1 is a diagrammatic sectional view of a known color display tube of the "in-line" type having an external static convergence unit,
FIG. 2 shows the pinion transmission used therein,
FIGS. 3 and 4 are two diagrammatic perpendicular cross-sectional views of the color display tube with a ring, which has not yet been magnetized, and in which the outermost electron beams do not converge satisfactorily,
FIGS. 5 and 6 are two diagrammatic perpendicular sectional views of a color display tube in which convergence by means of the magnetisation device has been obtained,
FIGS. 7 and 8 show the magnetisation of a ring arranged in the system of electron guns,
FIGS. 9 and 10 show two diagrammatic perpendicular sectional views of a color display tube with a magnetized ring with which the convergence error, as shown in FIG. 4, is removed,
FIGS. 11 and 12 show two types of devices suitable for magnetisation according to the invention, and
FIGS. 13 to 18 show parts of another type of magnetisation unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a diagrammatic sectional view of a known color display tube of the "in-line" type. Three electron guns 5, 6 and 7, generating the electron beams 8, 9 and 10, respectively, are accommodated in the neck 4 of a glass envelope 1 which is composed of a display window 2, a funnel-shaped part 3 and a neck 4. The axes of the electron guns 5, 6 and 7 are situated in one plane, the plane of the drawing. The axis of the central electron gun 6 coincides substantially with the tube axis 11. The three electron guns are seated in a sleeve 16 which is situated coaxially in the neck 4. The display window 2 has on the inner surface thereof a large number of triplets of phosphor lines. Each triplet comprises a line of a phosphor luminescing green, a line of a phosphor luminescing blue, and a line of a phosphor luminescing red. All of the triplets together constitute a display screen 12. The phosphor lines are normal to the plane of the drawing. A shadow mask 12, in which a very large number of elongate apertures 14 are provided through which the electron beams 8, 9 and 10 pass, is arranged in front of the display screen 12. The electron beams 8, 9 and 10 are deflected in the horizontal direction (in the plane of the drawing) and in the vertical direction (at right angles thereto) by a system 15 of deflection coils. The three electron guns 5, 6 and 7 are assembled so that the axes thereof enclose a small angle with respect to each other. As a result of this, the generated electron beams 8, 9 and 10 pass through each of the apertures 14 at said angle, the so-called color selection angle, and each impinge only upon phosphor lines of one color.
A display tube has
a good static convergence if the three electron beams, when they are not being deflected, intersect each other substantially in the center of the display screen. It has been found, however, that the static convergence often is not good, no more than the frame shape and the color purity, which may be the result of an insufficiently accurate assembly of the guns, and/or sealing of the electron guns, in the tube neck. In order to produce the static convergence, so far, externally adjustable correction units have been added to the tube. They consist of a number of pairs of multipoles consisting of magnetic rings, for example four two-poles (two horizontal and two vertical), two four-poles and two six-poles. The rings of each pair are coupled together by means of a pinion transmission (see FIG. 2), with which the rings are rotatable with respect to each other to an equal extent. By rotating the rings with respect to each other and/or together, the strength and/or direction of the two-, four- or six-pole field is adjusted. It will be obvious that the control of a display tube with such a device is complicated and time-consuming. Moreover, such a correction unit is material-consuming since, for a combination of multipoles, at least eight rings are necessary which have to be provided around the neck so as to be rotatable with respect to each other.
In the Netherlands Pat. application No. 7,503,830, laid open to public inspection, the complicated correction unit has, therefore, been replaced by one or more magnetized rings, which rings are situated in or around the tube neck or in or around the electron guns.
However, it has proved difficult with the magnetising methods known so far to provide a combination of multipoles in the ring by magnetisation.
The method according to the invention provides a solution.
For clarity, identical components in the following figures will be referred to by the same reference numerals as in FIG. 1.
FIG. 3 is a diagrammatic sectional view of a display tube in which the electron beams do not converge in the horizontal direction. As is known, the outermost electron beams can be deflected more or less in the opposite direction by means of a four-pole, for example, towards the central beam or away therefrom. It is also possible to move the beams upwards and downwards. By means of a six-pole the beams can be deflected more or less in the same direction. For simplicity, the invention will be described with reference to a display tube which requires only a four-pole correction. The convergence errors in the horizontal direction of the electron beams 8 and 10 are in this case equally large but opposite.
FIG. 4 is a sectional view of FIG. 3. On the bottom of sleeve 16, a ring 18 is provided of an alloy of Fe, Co, V and Cr (known as Vicalloy) which can be readily magnetized. It will be obvious that the ring may alternatively be provided in other places around the guns or in or around the tube neck. Instead of a ring it is alternatively possible to use a ribbon or a configuration of rods or blocks of magnetisable material.
In FIG. 5 a device 19 for generating a controllable multipole magnetic field is provided around the neck 4 and the ring 18 according to the method of the invention. 2-, 4- or 6-poles and combinations thereof can be generated by means of the device 19. For the tube shown in FIG. 3, only a four-pole correction is necessary. The coils of the device 19, which device will be described in detail hereinafter, are in this case energized as four-poles until the point of intersection S of the three electron beams 8, 9 and 10, which in FIG. 3 was situated outside the tube 1, lies on the display screen 12. The current I through the coils of the device originates from a direct current source B which supplies a current -mI 1 (m being an experimentally determined constant >1) to the coils via a current divider and commutator A. The current can be adjusted per coil so as to generate the desired multipole. In this phase of the method, an alternating current source C does not yet supply current (i=0).
FIG. 6 is a perpendicular sectional view of FIG. 5. The current I 1 is a measure of the strength of the required correction field. The correction field of the multipole of the device 19 extends over a larger length of the electron paths than the magnetic field generated later by the magnetized ring. Therefore the field of the ring is to be m-times stronger.
FIG. 7 shows the step of the method in which the ring 18 is magnetized as a four-pole. As follows from the above, in this preferred embodiment of the method, the current through the coils of the device must be -mI 1 during the magnetisation, so must traverse in the reverse direction and be m-times as large as the current through the coils during the correction. Moreover, the alternating current source C supplies a decaying alternating current (i=i 1 >0) to the device 19, with which current the decaying alternating field is generated. When the alternating current is switched on, it must be so large that the ring 18 is fully magnetized on either side of the hysteresis curve. When the alternating field has decayed, the ring 18 is magnetized, in this case as a four-pole. It is, of course, alternatively possible to magnetise the ring 18 as a six-pole or as a two-pole or to provide combinations of said multipoles in the ring 18 and to correct therewith other convergence errors or color purity and frame errors. It is also possible to use said corrections in color display tubes of the "delta" type.
FIG. 9 shows the display tube 1 shown in FIG. 3, but in this case provided with a ring 18 magnetized according to the method of the invention as shown in FIGS. 5 and 7. The convergence correction takes place only by the magnetized ring 18 present in sleeve 16. The provision of the required multipole takes place at the display tube 1 factory and complicated adjustments and adjustable convergence units (FIG. 2) may be omitted.
FIG. 10 is a cross-sectional view perpendicular to FIG. 9. FIG. 11 shows a magnetisation device 19 comprising eight coils 20 with which the convergence (see FIG. 5) and the magnetisation (see FIG. 7) are carried out. For generating the decaying alternating magnetic field, two pairs of coils 21 and 22, extending in this case at right angles to each other, are incorporated in the device 19. The current i a through the pair of coils 21 is shifted in phase through 90° with respect to the current i b through the other pair of coils 22, so that the decaying alternating magnetic field changes its direction during the decay and is a field circulating through the ring 18. FIG. 12 shows a magnetisation device known from Netherlands Pat. application No. 7,503,830 laid open to public inspection. In this case, the decaying alternating current may be superimposed on the direct current through the coils 23 so that extra coils are not necessary in the device. The coils 23 are wound around a yoke 24.
The magnetisation device 19 may alternatively be composed of a combination of electrical conductors and coils, as is shown diagrammatically in FIGS. 13 to 18.
FIG. 13 is a sectional view of the neck 4 of a display tube 1 at the area of a ring 18 to be magnetised. A two-pole field for corrections in the horizontal direction is generated in this case by causing currents to flow through the conductors 25, 26, 27 and 28 in the direction as shown in the figure. Said conductors may be single wires or wire bundles forming part of one or more coils or turns, and extending parallel to the tube axis at the area of the ring 18.
FIG. 14 shows how, in an analogous manner, a four-pole field for corrections of the outermost beams 8 and 10 in the horizontal direction can be generated by electrical conductors 29, 30, 31 and 32. A four-pole field for corrections of the outermost beams 8 and 10 in the vertical direction is substantially the same. However, the system of conductors 29, 30, 31 and 32 is rotated through 45° with respect to the neck 4 and the axis of the tube 1.
FIG. 15 shows, in an analogous manner, a six-pole for corrections in the horizontal direction with conductors 33 to 38. By means of a combination of conductors (wires or wire bundles) with which 2-, 4- and 6-poles can be generated, all combinations of two-, four- and six-pole fields with the desired strength can be obtained by variations of the currents through said conductors 33 to 38.
The decaying alternating magnetic field in a magnetisation unit with conductors as shown in FIGS. 13, 14 and 15 can be obtained by means of coils positioned symmetrically around the neck 4 and the conductors as shown in FIGS. 16 and 17 or 18. By energizing the coils 39 and 40, shown in FIG. 16, with a decaying alternating current, a decaying alternating magnetic field is generated. A better influencing of the ring 18 by the decaying alternating field is obtained when a system of coils having coils 41 and 42 in FIG. 17 is provided which is rotated 90° with respect to the coils 39. In this case, 40 and the decaying alternating current through the coils 41 and 42 should then preferably be shifted 90° in phase with respect to the decaying alternating current through the coils 39 and 40.
It is alternatively possible to generate the decaying alternating magnetic field with one or more systems of coils as shown in FIG. 18. The coils 43, 44 and 45 are situated symmetrically around the tube axis and are energized with decaying alternating currents which are shifted 120° in phase with respect to each other (for example from a three-phase line).
CRT TUBE PHILIPS 45AX TECHNOLOGY Method of manufacturing a static convergence unit, and a color display tube comprising a convergence unit manufactured according to the method, PHILIPS 45AX INTERNAL STATIC CONVERGENCE SYSTEM Application technology:
IMACO RING (Integrated Magnetic Auto Converging )
The method according to the invention consists in the determination of data of the convergence errors of a color display tube, data being derived from the said determinations for determining the polarity and the intensity of magnetic poles of a structure. The structure thus obtained generates a static, permanent, multipole magnetic field adapted to the convergence errors occurring, so that the errors are connected.
providing around the neck of the color display tube an auxiliary device for generating variable magnetic fields in the neck of the color display tube, activating the color display tube, adjusting the auxiliary device to produce a magnetic field for converging the electron beams, determining from data derived from the adjustment of the auxiliary device the extent and the direction of the convergence error of each electron beam, and using such data to determine the polarity and the intensity of magnetic poles of said magnetic convergence structure for generating a permanent multi-pole static magnetic field for the correction of the convergence errors occuring in the color display tube. 2. A method as claimed in claim 1, wherein the auxiliary device comprises an electromagnet convergence unit which comprises a number of coils, said generating step comprising passing electrical currents through said coils for generating a magnetic field required for the static convergence of the electron beams, and said determining step comprising using the values of the electrical currents for determining the permanent magnetic structure. 3. A method as claimed in claim 2, further comprising storing the data from the auxiliary device in a memory. 4. A method as claimed in claim 2, wherein said using step comprises controlling a magnetizing unit for magnetizing an annular magnetizable convergence structure. 5. A method as claimed in claim 2, further comprising converting the data into a code, and constructing said annular permanent magnetic convergence structure having a desired magnetic field strength from a set of previously magnetized structural parts. 6. A method as claimed in claim 1, further comprising forming the convergence structure from a magnetizable mass which is annularly arranged on at least one wall of the neck of the color display tube. 7. A method as claimed in claim 1, further comprising forming the convergence structure from a magnetizable ring which is arranged on the neck of the color display tube. 8. A method as claimed in claim 1, wherein the convergence structure comprises a non-magnetizable support and a number of permanent magnetic dipoles. 9. A method as claimed in claim 4, wherein said magnetizing step cofmprises polarizing the magnetizable material of the annular convergence structure at one location after the other by means of the magnetizing unit. 10. A method as claimed in claim 4, further comprising assemblying the auxiliary device and the magnetizing unit in one construction, and then enclosing a convergence structure to be magnetized with said magnetizing unit. 11. A method as claimed in claim 10, further comprising displacing said construction with respect to said tube after said determining step.
Color television display tube with coma correction ELECTRON GUN STRUCTURE PHILIPS CRT TUBE 45AX
A color television display tube including an electron gun system (5) in an evacuated envelope for generating three electron beams whose axes are co-planar. The beams converge on a display screen (10) provided on a wall of the envelope and are deflected in the operative display tube across the display screen into two orthogonal directions. The electron gun system (5) has correction elements for causing the rasters scanned on the display screen by the electron beams to coincide as much as possible. The correction elements include annular elements (34) of a material having a high magnetic permeability which are positioned around the two outer beams. In
addition a further correction element (38, 38", 38"') of a material having a high magnetic permeability is provided around the central beam in a position located further from the screen in order to correct field coma errors at the ends of the vertical axis and in the corners to an equal extent. The further element is preferably positioned in, or on the screen side of, the area of the focusing gap of the electron gun.