MXPA00000921A - Deflection yoke for a cathode-ray tube with both improved geometry and convergence - Google Patents

Abstract

A deflection yoke mounted on a neck of a cathode-ray tube includes a pair of horizontal deflection coils, a pair of vertical deflection coils and a core (20) of a ferromagnetic material. The core has magnetic reluctance, in a front region, close to a screen end of the tube, that is greater along the vertical direction than along the horizontal direction. In one embodiment of the invention this feature is achieved by making recesses (24) at the intersection of a flared front part (21) of the core with the horizontal plane of symmetry XZ. In another embodiment of the invention, the thickness (e) of the core varies.

Description

Deflection yoke for a cathodic ray tube with improved geometry and convergence The invention generally relates to a deflection yoke for a color cathode ray tube. A deflection yoke includes a pair of vertical deflection coils, a pair of horizontal deflection coils in the shape of a saddle and a ring of ferromagnetic material surrounding the deflection coils to concentrate the deflection fields in the appropriate region. A cathode ray tube that is intended to generate color images generally includes an electron gun that emits three coplanar electron beams, each beam is intended to excite a luminescent substance of a defined primary color (red, green or blue) in the screen of the tube. The electron beams scan the tube screen under the influence of the deflection fields created by the horizontal and vertical deflection coils of the deflection yoke attached to the neck of the tube. The three beams generated by the electron gun must always converge on the tube screen, otherwise a so-called convergence error is introduced that falsifies, in particular, the delivery of the colors. To make the three coplanar converge, it is known to use the so-called self-convergent astigmatic deflection fields; In a self-converging deflection coil, the field strength or flow lines that are produced by the horizontal deflection winding are generally in the form of a pincushion in the region of a portion of the coil that is located approximately at the front of the coil. last on the side facing the tube screen. Additionally, under the action of the vertical and horizontal deflection fields, the volume explored by the electron beams is a pyramid whose tip coincides with the deflection center of the deflection yoke and whose intersection with a non-spherical screen surface exhibits a defect geometric called pincushion distortion. This geometric distortion of the image increases as the radius of curvature of the tube screen increases. The self-converging deflection yokes generate astigmatic deflection fields that make it possible to modify the North / South and East / West geometry of the image and, in particular, partially correct the North / South pincushion distortion. The correction of the convergence of the electron beams and the North / South geometry of the image on the screen, by means of a particular configuration of the conductors forming the deflection coils, has been difficult to achieve without additional components, such as parts of metal or permanent magnets. The additional components are placed to produce the local modification of the deflection fields. These additional components can be expensive and can cause overheating problems associated with the operating frequency, particularly when used to modify the horizontal deflection field, since the current tendency is to increase said frequency up to 32 kHz or even 64 kHz. Additionally, these problems of image geometry and convergence are associated with the planarity of the screen and increase with the radius of curvature of the aforementioned screen, the conventional cathode ray tubes that were manufactured a few years ago, generally have a radius of curvature A. When the screen has a relatively large radius of curvature, greater than 1 R, such as 1.5 R or more, for example, it becomes much more difficult to solve the aforementioned problems simply by fields generated by the deflection coils. The published European Patent Application EP 701, 267 discloses a means to control the North / South geometry of the image created by the deflection yoke on the screen surface, as well as the convergence of the beams, using a ring or core of material ferromagnetic to concentrate the deflection fields. Part of the nucleus, the one closest to the screen of the tube, is configured in such a way that the regions closest to the vertical axis of symmetry have a greater magnetic reluctance than the regions closest to the horizontal axis of symmetry. However, this configuration may require the use of an additional field former for local defect correction. It may be desirable to employ in a deflection yoke for a color cathode ray tube a magnetic core having a geometry that makes it possible to correct the convergence and geometric errors without the use of additional field formers. In accordance with one aspect of the invention, a deflection yoke includes a pair of horizontal deflection coils and a pair of vertical deflection coils. A roughly frustoconical ferromagnetic core is placed, at least partially, on the deflection coils. The nucleus has a vertical plane of symmetry, YZ, and a horizontal plane of symmetry, XZ. The magnetic reluctance of the nucleus, in its frontal part, in the vicinity of the horizontal plane of symmetry, is greater than in the vicinity of the vertical plane of symmetry. IN THE DIAMETERS: Figure 1 shows a cathode ray tube equipped with a deflection yoke of the prior art to deflect the electron beams; Figure 2 shows a ring or core made of ferromagnetic material according to the prior art; Figure 3 shows another embodiment of a ferromagnetic ring according to the prior art; Figure 4 illustrates a perspective view of a ring according to the invention; and Figure 5 illustrates a perspective view of a ring in accordance with another embodiment of the invention. As illustrated in Figure 1, a self-converging color deployment device comprises a cathode ray tube (CRT) 50 provided with a vacuum glass envelope 6 and a matrix of luminescent substance elements representing three colors arranged in one end of the enclosure forming a deployment screen 9. A set of three on-line electron guns 7 is disposed at a second end of the enclosure. The set of electron guns is arranged to produce three electron beams 12 which are aligned horizontally to excite the corresponding various elements of colored luminescent substances. The electron beams scan the entire surface of the screen by means of a deflection yoke 1, placed on a neck 8 of the cathode ray tube 50. The deflection yoke 1 includes a pair of horizontal deflection coils 3, a pair of coils of vertical deflections 4, separated between them by a separator 2 and a ferromagnetic core 10 that is intended to concentrate the field where it is intended to act. A conventional deflection yoke for a cathode ray tube of the self-convergent type causes the electron beams to converge on a screen panel of the cathode ray tube by non-uniform magnetic deflection fields. In the deflection yoke, the horizontal deflection field has a pincushion intensity distribution and the vertical deflection field has a barrel-shaped intensity distribution. The intensity distribution of the horizontal field provides a partial correction of the North / South geometric distortion of the image. However, this non-uniform field can cause a so-called gull wing distortion of the horizontal edges of the image on the screen. This distortion is due to the harmonic components of the fifth order and higher order of the series decomposition of the deflection field. A deflection yoke according to the prior art includes a core or ring of ferromagnetic material, as shown in Figure 2. This ring is generally symmetrical with respect to a Z axis and has a back 13 or internal diameter d. It has a flared part 12 that ends in a front surface 1 1 contained in a plane perpendicular to the Z axis. The internal diameter of the front part is D. The thickness "e" of the ring, measured in a section perpendicular to its surface, is approximately constant. According to a prior art, illustrated in Figure 3, the ring or core may have in a front part grooves 14 which are arranged symmetrically with respect to the plane XZ and are in the vicinity of the intersection with the plane YZ. These grooves locally alter the magnetic reluctance of the ring and alter the distribution of the force lines of the deflection coils. This configuration can improve the North / South geometry of the image as well as minimize seagull wing distortions. It can also improve the situation with respect to the convergence of the electron beams along the X and Y axes of the screen. However, the convergence situation in intermediate positions can be greatly degraded, particularly in the corners of the image.

In accordance with one aspect of the invention, a ring or core 20 of Figure 4, for example, of ferromagnetic material, is used to concentrate the deflection fields of the electron beams. The core 20 is placed, at least partially, above the deflection coils. The core 20 has a vertical plane of symmetry, YZ, and a horizontal plane of symmetry, XZ. The magnetic reluctance that is, in the frontal region of the core 20, in a neighborhood of the intersection with the horizontal plane of symmetry, XZ, is greater than in the region of the core 20 located in the vicinity of the intersection with the vertical plane of symmetry, YZ. A region located in the vicinity of the intersection with a given symmetry plane, horizontal or vertical, is defined as a region surrounded by a radial opening angle of 45 ° on either side of the given plane of symmetry. The core 20 can be used in a configuration similar to that of Figure 1, instead of the core 10. The front region of the core 20 of Figure 4 is located near the screen end of the cathode ray tube 50. In accordance with the embodiment of the invention, illustrated in Figure 4, the ring or core 20 is formed of a body having an approximately constant "e" thickness or the like and having an approximately frusto-conical shape. The core 20 has a front part 21 of internal diameter D, a rear part 23 of internal diameter d and a flared part 22. A pair of cuts, which lie symmetrically with respect to the plane YZ, are formed on the front of the ring, in intersecting with the XZ plane, to create a pair of semicircular grooves 24. A cutting plane 25 can preferably be selected parallel to the Z axis. In this way, the thickness of the ring 20 around the intersection of the front of the ring with the XZ plane varies gradually from the aforementioned "e" value to zero, thus allowing the value of the reluctance in the region of the slots 24 to increase gradually. This gradual change may be preferable, to improve the convergence and geometrical parameters, to an abrupt change of a thickness equal to "e" at zero thickness. In contrast to the gradual change, an abrupt change would occur from a groove cut whose side walls are contained in planes perpendicular to the Z axis. Additionally, this gradual change can be altered as required, depending on the desirable degree of correction that is left. to carry out. To achieve this, the cutting plane can be modified to form a nonzero angle with the Z axis. Tables 1 and 2 below show the measured results obtained from a deflection yoke of the saddle / saddle type for a cathode ray tube. of type A68SF that has a screen with a diagonal of 68 cm and a radius of curvature greater than 1 .5R. The deflection yoke includes the ring or core 20 of Figure 4 made of ferromagnetic material that extends in the direction of the Z axis by a length of 50 mm. The core 20 has a flared portion 22 having a length of 38 mm, a rear diameter "d" of 50 mm and a front diameter D of 105 mm.

Table 1 provides the results of measurements of the convergence and geometric parameters in the following three successive situations: 1. A situation mentioned in Table 1 as the "initial situation", in which a ring of the prior art of Figure 2 does not have a groove in the front and its thickness "e" is approximately constant; 2. A situation in which the ring or core 20 of Figure 4, according to the invention, has, at the front, grooves having a maximum depth P equal to 13 mm at the intersection with the horizontal plane XZ; and 3. A situation in which the core of the pair of Figure 3 has, at the front, the same grooves but they are at the intersection with the vertical plane YZ. The measured parameters are given as percentage errors. Errors in the North / South geometry are measured at the extreme horizontal edges of the image (N / S end) and halfway between the center of the image and the extreme edges (internal N / S). Gull wing distortion errors are measured at four points in a quadrant of the screen: - on the horizontal outer edge of the image: a 1/3 of the Y axis, 2/3 of the corner (external 1/4 GW) to 2/3 of the Y axis, 1/3 of the corner (1/8 external GW); and - along the horizontal line that is halfway between the X axis and the upper edge of the image on the screen: Horizontal convergence errors are measured at the edges of the image at 6 o'clock / 12 o'clock (6-12 OC), at 3 o'clock / 9 o'clock (3-9 OC), along the direction of the diagonal (corner OC) and along the direction between the diagonal and 6 o'clock / 12 o'clock (1/2 H OC). TABLE 1 The results of these measurements show the manner in which the configuration according to the invention leads to an improved overall situation with respect to the configuration described in European Application E P 701, 267. Although the convergence situation is improved, both in the configuration suggested by the prior art, and in accordance with the invention, the results show that the configuration according to the prior art significantly degrades the convergence situation in the corners. and between the corners and 6 o'clock / 12 o'clock. In particular, the fact of having convergence errors (6- 12 OC), (3-9 OC) and (esqui na OC), (1 / 2H OC) of opposite signs means that it might not be impossible to take these errors to values acceptable when altering the deflection coils. In this case it may be necessary to use additional field trainers to correct these errors. On the other hand, in the case of the invention, Table 1 shows an improvement in the geometric error. Ideally, the geometric error should be carried out at - 1%, which corresponds to see without any apparent defect at a distance of the screen equal to 5 times the height of the image. An improvement in the gull wing is also obtained. The convergence situation can be optimized by means of simple and known alterations of the deflection coils since the measured convergence errors are all of the same sign. According to another embodiment of the invention, which is illustrated in Figure 5, the grooves are located not only at the intersection of the front of the ring with the XZ plane but also at the intersection with the YZ plane. In this case, the results obtained with respect to the geometric and convergence parameters are given in Table2. The initial situation, in which the deflection yoke is equipped with a ring that has approximately a constant thickness and whose front part has a uniform reluctance, is compared with the same deflection yoke whose ferromagnetic ring has, in its front part, grooves 24 Depth Px and 24 'Depth Py. From Table 2 it can be seen that the most favorable configuration is that in which Px is greater than Py. This favorable configuration that causes the magnetic reluctance of the ring to remain, is in its frontal part that is in a region in the vicinity of the intersection with the horizontal plane of symmetry, greater than in the part that is in the vicinity of the intersection with the vertical plane of symmetry. In this case, all geometric and convergence parameters are improved. On the other hand, the case in which Py is greater than Px causes at least one of the four convergence errors 6-12 OC, 3-9 OC and OC corner, 1 / 2H OC, to be of opposite sign with respect to to at least one of the other three. Inconveniently, the opposite sign situation may not be possible to correct without an additional field trainer.

TAB LA 2 In another embodiment, shown partially in a line interrupted in Figure 4, a magnetic reluctance is obtained according to the invention, on the front of the ferromagnetic ring, not creating grooves, but locally altering the thickness of the ring get an "e" thickness. Thus, by having a smaller thickness at the intersection of the front part of the ring with the horizontal plane xz than at the intersection of the front part with the vertical plane it is possible to obtain the reluctance characteristics according to the invention. The invention is not limited to deflection devices for color cathode ray tubes; its action on the geometry of the image allows the incorporation of a ring of ferromagnetic material according to the invention in a deflection yoke which is intended to equip a monochromatic cathode ray tube.

Claims (6)

1. CLAIMS 1. A deflection yoke for a cathode ray tube, comprising: a horizontal deflection coil to produce a vertical deflection field; and a core made of magnetic material placed in a flow path of at least one of said deflection fields in the vicinity of at least one of said deflection coils, such core has a magnetic reluctance, in a first portion of such a core disposed in a frontal region of such a core that includes a horizontal plane of symmetry, which is greater than in a second portion of said core disposed in such frontal region of said core that includes a vertical plane of symmetry. A deflection yoke according to claim 1, wherein a core thickness in said first portion is smaller than in said second portion. A deflection yoke according to claim 1, wherein a pair of grooves, symmetrical with respect to the vertical plane of symmetry, are formed in said frontal region of said core at the intersection with the horizontal plane of symmetry. A deflection yoke according to claim 1, wherein said core includes a pair of grooves symmetrical with respect to the horizontal plane of symmetry and located, in the frontal region of said core, at the intersection with the vertical plane of symmetry . 5. Deflection yoke according to claim 4, wherein a plane of cut of said pair of symmetrical grooves is placed with one of the vertical plane of symmetry and the horizontal plane of symmetry. 6. Deflection yoke according to claim 1, wherein said core includes a pair of grooves having a semicircular shape. RESU MEN A deflection yoke mounted on a neck of a cathode ray tube includes a pair of horizontal deflection coils, a pair of vertical deflection coils and a core (20) of a ferromagnetic material. The core has magnetic reluctance, in a frontal region, near one end of the tube screen, which is greater along the vertical direction than along the horizontal direction. In one embodiment of the invention this feature is achieved by making grooves (24) at the intersection of a front flared part (21) of the core with the horizontal plane of symmetry XZ. In another embodiment of the invention, the thickness (e) of the core varies.