JPH054777B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic deflection device for color television, and more particularly to a deflection device consisting of a combination of a self-focusing deflection yoke and a magnetic permeability correction device.

The picture tube of a color television produces three electron beams that illuminate each color's light-emitting phosphor elements on the display surface. A deflection yoke attached to the picture tube generates a time-varying magnetic field in the vicinity of the electron beam, causing it to scan the display surface horizontally and vertically to form a raster. It is desirable that each beam illuminate only those phosphor elements that emit light of a specified specific color, and the degree to which this is achieved determines the color purity of the raster. and that each beam impinges on the display surface in close proximity to each other at all points on the display surface;
That is, it is important that the beam be concentrated on the display surface.

Most color picture tubes produce one of two types of electron beams: one is a triangular or delta beam, and the other is a horizontal line. Picture tubes with delta-type electron guns require a dynamic concentration circuit to concentrate the beam during deflection, but in-line picture tubes can cover the entire display surface without a dynamic concentration circuit due to the structure of the deflection yoke. The electron beam can be substantially focused over the entire area.

This self-focusing yoke for in-line picture tubes concentrates the electron beam by the nature of the non-uniform magnetic field generated by the special shape of the deflection coil. It is well known that in order to achieve beam concentration, it is necessary to form a net pincushion-shaped magnetic field by means of horizontal deflection coils and a net barrel-shaped magnetic field by means of vertical deflection coils, and also to obtain the necessary non-uniform magnetic field. It is also known how to wind a deflection yoke coil to obtain the following.

The deflection yoke has a toroidal coil, a saddle coil, or a combination of both coils wound around a magnetically permeable magnetic core. A typical yoke has a saddle-shaped horizontal coil and a toroid-shaped vertical coil, but both saddle-shaped coils and toroid-shaped coils generate external magnetic fields on both sides and rear of the yoke in addition to the main deflection magnetic field generated inside the yoke. . However, the external magnetic field generated behind the yoke by the toroidal coil is five times larger than the external magnetic field generated by the saddle-shaped coil, and because such an external magnetic field exists behind the yoke, the beam within the focus area of the electron gun assembly of the picture tube is may cause adverse effects. For example, the deflection of the beam may begin too early, thereby causing significant defocusing of the beam at certain locations on the display surface. This external magnetic field has the greatest negative effect on yokes with toroid-shaped vertical coils and saddle-shaped horizontal coils.

There is one problem with self-centering yokes. A barrel-shaped vertical magnetic field is required to focus the electron beam, but the barrel-shaped field deflects the outer beams more than the center beam, so that the raster height of the center beam is lower than the raster height of the outer beams. Causes vertical coma distortion. It is known that this vertical coma distortion error has the highest sensitivity to the non-uniformity of the magnetic field at the beam entrance end, that is, the rear end of the yoke. Therefore, the barrel-shaped external magnetic field from the vertical deflection coil contributes significantly to the vertical coma distortion error.

One solution to the problem of beam misfocusing due to external deflecting magnetic fields is to configure a portion of the electron gun assembly of magnetic material to expel the external magnetic field from the focus area of the electron gun. This method may actually distort the shape of the external magnetic field to the point where degradation of beam concentration occurs. U.S. Pat. No. 3,430,169 discloses fitting a magnetically permeable ring around the neck of an electron gun's tube focus zone to "short-circuit" the external magnetic field. This "short circuit" may undesirably weaken the deflection field, resulting in poor beam scanning and requiring increased deflection power.

In accordance with a preferred embodiment of the invention, self-focusing deflection yokes for use in picture tubes producing three horizontal in-line electron beams are separated from each other by plastic insulators that produce non-uniform magnetic fields for beam deflection. Has horizontal and vertical deflection coils
These coils generate the main deflection field and the external field. The external magnetic field has a barrel-shaped magnetic field component formed behind the yoke near the electron gun assembly.

The device of the invention includes a compensator located within the external magnetic field as described above and spaced longitudinally of the tube from the rear flange of the plastic insulator separating both the horizontal and vertical deflection coils. It consists of a magnetically permeable ring positioned above the focusing area of the electron gun assembly. This magnetically permeable annulus has a gap (slit) corresponding to a small portion of the diameter of the annulus pointing in the direction of the vertical deflection axis of the yoke, which suppresses the magnetic flux flowing through the annulus. By weakening the intensity of the external magnetic field in the focusing region, coma distortion can be reduced while maintaining the barrel shape of the external magnetic field.

1 and 2 illustrate a color television display system including a picture tube 10 having a neck portion 11, a funnel portion 12, and a fluorescent display screen (not shown) at the end opposite the neck portion 11. An electron gun assembly 13 is located inside the network portion 11, and generates, accelerates, and focuses three electron beams. In the display system shown in FIG. 1, three electron beams are arranged in a horizontal line. A deflection yoke 14 is provided in the region where the neck portion 11 and the funnel portion 12 of the picture tube 10 are connected.
installed. The deflection yoke 14 has a pair of horizontal deflection coils (not shown) wound in a saddle shape around a magnetically permeable magnetic core 16 and a pair of vertical deflection coils (FIG. 2) wound in a toroid shape. However, each horizontal and vertical coil is separated by a plastic insulator 17. A mounting plate 18 may be used to facilitate fixing the yoke 14 to the picture tube 10 after the yoke is properly positioned.

FIG. 1 shows the yoke 14 as represented by magnetic field lines 20.
The external magnetic field produced by the vertical deflection coil 15 of FIG. As shown, the external magnetic field exists in a region occupied by a portion of the electron gun assembly pair 13, and may give a slight deflection to the beam within the electron gun assembly, resulting in poor beam focusing. This problem is exacerbated in the generally preferred short length picture tubes because the electron gun assembly is so close to the rear end of the deflection yoke that it is within the external magnetic field of the yoke.

FIG. 2 is a rear view of the yoke. The magnetic field lines 20 of the external magnetic field are barrel-shaped and represent the external magnetic field of the vertical deflection coil. This barrel shape of the magnetic field is the result of expansion of the magnetic field due to mutual repulsion of magnetic field lines between the concentrated ends of the magnetic field. Since the toroidal external vertical magnetic field is five times larger than the saddle-shaped external horizontal magnetic field, the external vertical magnetic field has a much greater effect on the electron beam than the external horizontal magnetic field. Although the external magnetic field of the saddle horizontal coil is not insignificant overall, its effect on the beam is not. Therefore, only the external perpendicular magnetic field is shown in FIG.

The external perpendicular magnetic field shown in FIG. 2 affects the focusing of the electron beam and can also cause problems due to non-uniformity in the shape of the magnetic field. The barrel-shaped external vertical magnetic field exerts a greater deflection force on the outer beams 21, 22 than on the central beam 23 because the magnetic field lines 20 are least concentrated along the vertical axis passing through the neck of the picture tube. This larger vertical deflection for the outer beams 21, 22 than for the central beam 23 results in vertical coma distortion, ie, distortion in the form of a raster of the central beam having a smaller height than that of the outer beam.

3 and 4 show a color television display system including a picture tube 110 and a deflection yoke 114, similar to FIG. 1. Here, a toroidal vertical deflection coil 115 and a plastic insulator 117 are shown.
It is shown. As can be seen from FIG. 3, the insulator 117 has a front flange and a rear flange formed in front (on the screen side) and behind (on the electron gun side) of the deflection yoke 114, respectively. A correction device 24 is attached to the neck of the picture tube near the focusing area of the electron gun pair. The compensator 24 is made of a magnetically permeable material and presents a path of lower reluctance to the magnetic flux than air. Therefore, a portion of the magnetic flux 120 from the external deflection field is shunted to the correction device 24 as shown in FIG. 3, and the effect of this shunted magnetic flux reduces the density of the remaining magnetic flux within the tube neck. As a result of this reduction in magnetic flux density, the interaction between the external magnetic field and the electron beam is reduced, and therefore coma distortion is also reduced. Coma distortion is also reduced by the action of the permeability correction device, which compresses the profile of the external magnetic field, particularly above and below the tube neck, and flattens the magnetic field lines within the neck slightly. This flattening reduces the barrel shape of the magnetic field and reduces coma distortion.

The correction device 24 consists of a pair of semicircular rings 25 and 26 separated by cuts 27 and 28 on both sides in the vertical deflection axis direction, and the separation interval, that is, the width of the cut, surrounds the picture tube neck. This is a small portion of the diameter of the annulus, but it is important for the following reasons. This division of the ring creates an interruption in the low reluctance magnetic path of both halves 25 and 26 of the corrector, and the magnetic reluctance of the entire magnetic path increases slightly. The annular case reduces the magnetic flux that is shunted through it. Although it is desirable to remove external magnetic fields from the beam focus area, external deflection fields at other locations assist in deflecting the beam, thereby reducing the deflection and power required by the main deflection field. When the corrector 24 is a complete ring, a significant amount of the desired external magnetic field is shunted into the corrector 24 resulting in a reduction in beam scan width, requiring deflection power and an increase to compensate. The separation of the two halves 25, 26 diverts sufficient magnetic flux from the external magnetic field to the corrector 24 to improve beam focusing and reduce coma distortion, but avoids unnecessary flux diversion causing an undesirable reduction in scanning. It can be prevented.

The cut in the ring is disposed along the vertical axis of the picture tube and is adapted to form an interruption in the magnetic flux path of the vertical magnetic field. This orientation is due to the difference in horizontal and vertical external magnetic fields as described above. If both half rings are not cut, they will slightly suppress (deenergize) the flow of horizontal magnetic flux that goes around the correction device 24.

Note that the ring body having the above-mentioned cut (interval part) does not change the barrel shape of the external magnetic field and maintains it as it is.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional plan view of a color television display system showing the positional relationship between the external magnetic field of the deflection yoke and the electron gun assembly of the picture tube, and Figure 2 is a cross-sectional plan view of the display system of Figure 1 showing the external magnetic field of the vertical coil. Cross-sectional rear view, 3rd
4 is a plan view of a color television display system showing a correction device according to the present invention, and FIG. 4 is a sectional view of the display system of FIG. 3 showing the characteristics of the correction device. 10...Picture tube, 14...Deflection yoke, 15...
...Vertical deflection coil, 20... External magnetic field, 24...
Magnetically permeable ring (correction device), 27, 28... cut.

Claims (1)

[Claims] 1. There is a device for use with a picture tube equipped with an electron gun structure that generates three horizontal in-line electron beams, and a non-uniform magnetic field for deflecting and concentrating the three beams. consisting of a self-concentrating deflection yoke with horizontal and vertical deflection coils separated from each other by plastic insulators, in combination with a compensator, to generate; and a barrel-shaped external magnetic field behind the yoke, which, if no corrective action is applied, will cause the three beams to be unequally deflected, resulting in a vertical coma distortion error between the rasters scanned by each beam. and the correction device is arranged to be located within the external magnetic field and spaced longitudinally from the rear flange of the insulator and above the focal region of the electron gun assembly. It consists of a magnetically permeable annulus having a diameter corresponding to a small portion of the annulus and oriented in the direction of a vertical axis, which suppresses the flow of magnetic flux through the annulus and concentrates the above-mentioned focusing area. A magnetic deflection device for reducing the coma distortion while maintaining the barrel shape of the external magnetic field by weakening the strength of the external magnetic field.