US2568456A

US2568456A - Electromagnetic deflection yoke structure

Info

Publication number: US2568456A
Application number: US131364A
Authority: US
Inventors: Luiz G Malheiros
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1949-12-06
Filing date: 1949-12-06
Publication date: 1951-09-18
Anticipated expiration: 1968-09-18

Description

p 18, 1951 L. G. MALHEIROS 2,568,456

ELECTROMAGNETIC DEFLECTION. YOKE STRUCTURE Filed Dec. 6, 1949 2 Sheets-Sheet l T0 HORIZONTAL SWEEP SOURCE T0 VERTICAL SWEEP SOURCE Inventor:

Luiz G. Malheiros,

His Attorneg.

p 1951 L. G. MALHEIROS 2,568,456

ELECTROMAGNETIC DEFLECTION YOKE STRUCTURE Filed Dec. 6, 1949 2 Sheets-Sheet 2 Inventor:

Luiz G. Malheiros,

mbm

His Attorneg.

Patented Sept. 18, 1951 ELECTROMAGNETIC DEFLECTION YOKE STRUCTURE Lulz G. Malheiros, Syracuse, N. Y., assignor to General Electric Company, a corp r -tion of New York Application December 8, 1949, Serial No. 131,364

6 Claims. (CL 313-73) My invention relates to a deflecting yoke structure particularly adapted for use with television picture pick-up tubes employing electromagnetic deflecting circuits.

In structures of this type, it is now common practice to employ a common magnetic core structure, arranged to surround the neck of a television picture tube, on which are wound a first pair of horizontal deflecting coils and a second pair of transverse, vertical deflecting coils. As is well-known to the art, the coils of each pair are connected in series-opposing relation and are adapted to be energized by horizontal and vertical sawtooth current waves of the proper amplitude and frequencies to cause the cathode ray to scan a generally rectangular pattern, or raster.

One specific form of magnetic yoke structure of this type utilizes a square laminated core with the pairs of transverse deflecting coils wound on opposite legs. This form of structure is particularly useful for television picture pick-up tubes of the transmitting type, such as iconoscopes. Ordinarily, the coils in each pair are arranged to extend along substantially the entire lengths of the supporting legs in order to produce a substantially uniform magnetic field across the gap between opposite legs. However, when employing tubes having substantially flat targets, it is often necessary to modify the magnetic field distribution to correct for distortion due to the so-called "pin-cushion effect." Otherwise, this distortion appears on the reproduced image as "barrelling. To correct for this distortion, the vertical deflecting field must be made weaker at the corners of the yoke; that is, the field distribution must be pincushion-shaped. This can be accomplished by shortening the deflecting coils. In the case of pick-up tubes such as the iconoscope, the vertical coils need to be shortened. This is because in the process of modulation of the horizontal deflection current, necessary for keystone correction, the modulating wave can be easily shaped to correct the curvature of the vertical edges. However, this in turn introduces difliculties in centering the coils symmetrically on the core. Any lack of symmetry in the magnetic flelds results in undesirable magnetic coupling between the horizontal and vertical sweep coils, distorting the scanning raster. on the other hand, even though the yoke structure is carefully tested and accurately aligned during manufacture for zero cross-coupling between coils, there is still no assurance that the resulting magnetic flelds will be symmetrical.

These effects make the proper neutralization and alignment of the deflecting structure very difllcult prior to actual operation with the associated picture tube. Even though the design of the core and coils has been such that the individual sides of the scanning raster are substantially straight, it is usual to find that the pattern is a non-rectangular parallelogram or trapezoid.

It is accordingly a primary object of my invention to provide an improved deflecting yoke structure for television picture tubes which can readily be adjusted under actual conditions of operation to provide a symmetrical scanning pattern or raster.

Another object of my invention is to provide an improved electromagnetic deflecting yoke structure which is simple and economical to manufacture, and which may very quickly be adjusted under operating conditions to eliminate distortion effects due to manufacturing variations in the construction of the core, coils and associated shielding structure.

For additional objects and advantages, and for a better understanding of the invention, attention is now directed to the following description and accompanying drawing... The features of the invention believed to be novel are particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is a perspective view of a television picture pick-up tube of the iconoscope type equipped with a rectangular electromagnetic deflecting yoke structure embodying my invention;

Fig. 2 is a front elevation view of the yoke structure of Fig. 1, with the shielding cover removed;

Fig. 3 is a section view of the yoke structure of Fig. 1, looking upward along the section line 33 in Fig. 2;

Fig. 4 is a group of schematic diagrams which will be referred to in discussing diiferent types of distortions in the scanning raster and methods of eliminating them;

Fig. 5 is a front elevation view of a modified yoke structure embodying the invention;

Fig. 6 is a partially-exploded perspective view of still another form of yoke structure embodying the invention; and

Fig. '7 is a cross-sectional view through the assembled yoke structure of Fig. 6.

As shown in Fig. 1, the magnetic deflecting system is contained in a shielding enclosure comprising a casing l and a cover 2 with a central aperture arranged to fit over the neck of a television picture signal tube I, illustrated as an iconoscope. A suitable flange plate t may be provided for mounting the yoke structure. The connecting leads to the horizontal and vertical sweep coils are conventionally represented as being brought out within a shielded cable 5, one pair of leads 6 being connected to a suitable horizontal sweep source and the other pair of leads T being connected to a suitable vertical sweep source, not shown.

The iconoscope tube 3 has been conventionally represented in Fig. 1 as comprising an electron gun structure 8 for projecting a cathode ray 9 against a sensitive target Hl within the tube. The tube may also have additional electroma netic or electrostatic structures associated therewith for centering and focusing the electron beam. However, these elements, and also the circuits for energizing the internal tube elements have been omitted, since they may be conventional and form no part of the present invention. While the tube 3 has been represented as a television pick-up tube of the iconoscope type, it will be understood that my invention is applicable to other types of television picture tubes, such a; image orthicons, monoscopes, etc.

As best seen in Fig. 2, the yoke structure comprises a closed, laminated, magnetic core I6 of substantially square shape. The laminations are secured together at the four corners by means of bolts l1 and nuts l8. As shown in Fig. 3, these bolts and nuts also secure the core l6, casing I and mounting plate 4 together; and the cover 2 is also removably secured to the adjacent ends of bolts I! by means of four cap screws l9.

Referring again to Fig. 2, the horizontal deflecting coils 20 are preferably arranged to surround substantially the full axial length of the two vertical legs of the core, as shown. As is well known to the art, they are connected in series-opposing relation from the source of horizontal sweep currents to produce a horizontal magnetic field pattern across the central aperture surrounding the neck of the tube. The shielding casing l and cover 2 are preferably made of nonmagnetic metal, to reduce the magnetic field on the outside of the core, thus improving the deflection eificiency. A cylindrical wire mesh shield 2| is also conventionally represented as surrounding the neck of the tube 3. This is electrically connected to the casing I and thus forms an electrostatic shield to reduce interference due to electrical disturbances.

The vertical deflecting coils 22 surround the horizontal legs of the rectangular core, but it will be seen that they differ from the horizontal deflecting coils in that each coil 22 has an axial length only approximately half that of the leg on which it is mounted. As in the case of the horizontal deflectin coils, the vertical deflecting coils are also connected in series-opposing relation to produce a vertical magnetic field across the neck of the tube. However, in both cases the internal wiring connections between coils of the yoke structure have been omitted from Figs. 2 and 3 to simplify the drawings. As previously mentioned, the vertical magnetic deflecting fleld may be made somewhat non-linear at the edges in order to correct for the distortion effects otherwise caused by the use of a flat surface for target area Hi.

In accordance with my invention, each of the vertical deflecting coils 22 is axially adjustable along the length of the core leg on which it is mounted. This is accomplished by securing each of the coils 22 to a U-shaped bracket 23. Also secured to each bracket 23 is a threaded lead screw 24 extendin through the side of casing I. The screws 24 are threaded into thumb nuts 25. As best seen in Fig. 3, each of the thumb nuts 25 has a shank 26 extending through a hole in the casing l and terminating in an internal flange 271. Thus, the thumb nuts 25 are rotatably secured to casing l and, as each nut is turned, its associated lead screw 24 and coil 22 are moved along the supporting leg of core l6.

Assume now that the horizontal and vertical deflecting coils are properly energized with synchronized, sawtooth deflectin currents such as are commonly employed in present day television scanning. It is desired that the scanning pattern or raster producted on the sensitive target area of the tube be exactly rectangular. However, even with proper keystone correction of the horizontal sawtooth deflecting currents, it will ordinarily be found that the raster has a non-rectangular, distorted shape. This may be due to the effects of manufacturing tolerances in winding the coils or lack of symmetry in their placement, or both. Some typical forms of unsymmetrical magnetic field distribution are shown in diagrams (A) and (B) of Fig. 4, and the resultant scanning rasters are shown in diagrams (A') and (B') respectively. (The distortions are somewhat exaggerated for purposes of illustration.) It will be seen that diagrams (A) and (A') represent a parallelogram form of distortion while diagrams (B) and (B') represent a trapezoidal form of distortion.

In accordance with my invention, either of these types of distortion may easily be eliminated by individual adjustments of the vertical deflecting coils 22 to adjust their magnetic axes with respect to the axes of coils 20. For example, as viewed in Fig. 4, the magnetic field distortion in diagram (A) is corrected by moving the upper coil 22 to the right and the lower coil 22 to the left. To correct the distortion of diagram (B), both coils 22 are moved to the left.

Diagrams (C) and (0') show the ideal field distribution (excluding the keystone correction) and the resultant scanning raster for the iconoscope type of picture tube. As previously explained, the magnetic field distribution is purposely made weaker at the corners for correction of the pincushion" distortion which otherwise results from scanning a flat target.

I have found by actual practice that it is a very simple matter to adjust the coils 22 so that the scanning raster may be made rectangular under all ordinary conditions encountered in operation.

While my invention has thus far been described in connection with a square yoke structure, it will be appreciated that the same principles may readily be applied to a toroidal yoke structure, such as is represented in Fig. 5. In this figure, elements having functions corresponding to those of the elements of the structure previously described have been assigned the same reference numerals with the subscript a added, to facilitate comparison. In this construction, the horizontal deflecting coils 20a are arranged to surround diametrically opposite sides of the annular, laminated core I Get and have shapes conforming to the curvature thereof. Each of the coils 20a also subtends substantially a full quadrant at the axis of the core, in substantially the same manner as the coils 20 in Fig. 2. The vertical deflecting coils 22a each subtend approximately only half this angle and similarly conform to the curaacacco vature of the core. Any suitable mechanism is then provided for rocking the coils 22a to any desired angular position within their respective quadrants, therebyto vary their magnetic axes. As shown in Fig. 6, each coil has a curved rack ll secured thereto by means of clamping straps ll. The curved rack 40 is then actuated by means of a worm gear 42 which may be turned by operating a knurled knob 43 secured to a tangential shaft extending from the gear 42.

Figs. 6 and 7 show another application of my invention toan annular yoke structure. In these figures, elements having functions corresponding to those of the structures previously described have been assigned the same reference numerals with the subscript b added, to facilitate comparison. This yoke structure employs a wellknown coaxial construction of the horizontal and vertical deflecting coils in which all of the turns of each pair of deflecting coils are arranged in a single layer on the surface of a cylinder. Thus, each of the horizontal deflecting coils 20b is formed of a plurality of rectangular loops of increasing size arranged on the surface of an insulating cylinder 50. As is best seen in Fig. 7, the outer turns of these coils subtend nearly 180 on the right and left halves of the cylinder 50, respectively.

Another concentric insulating cylinder is fitted over the horizontal deflecting coils and serves as a support for a similar pair of vertical deflecting coils 221), which subtend nearly 180 on the top and bottom halves of cylinder 5|, respectiveb'. The deflecting system is enclosed within a suitable cylindrical casing lb provided with an annular cover 2b surrounding the neck of the cathode ray tube.

Since each of the vertical deflecting coils 22b in Figs. 7 and 8 subtends nearly 180, it is obviously impractical to rock or oscillate the entire coil to correct for the types of distortion previously discussed. In accordance with my invention, the magnetic axis of each coil may be adjusted by making only the inner turn 52 of each vertical deflecting coil movable with respect to the other turns. Thus, this turn 52 is shown as being separately supported on a curved insulating strip 53 which is slidable over the surface of insulating cylinder 5|. Angular movement of the pairs of strips 53 and turns 52 is accomplished by means of rack and worm assemblies very similar to those previously described in connection with the modification of Fig. 4. Each assembly comprises a rack 40b, secured to the turn 52 and strip 53, which engages a worm gear 42b. The shaft 54 carrying worm gear 421) is supported within an arcuate slot 55 in the casing 10b, by means of apair of trunnions 56 secured thereto. In this manner, arcuate movement of the single turn 52 may be accomplished, within limits of movement determined by the next turn 51 lying outside turn 52. This shifts the mean axis of the magnetic field produced by the entire coil, so that the axis of symmetry of the magnetic field between coils 22b, and the magnetic coupling with the coils 201:, are effectively adjusted in a manner substantially the same as previously described.

It will thus be seen that I have provided a simple mechanical means for independently adjusting the positions of each of the vertical sweep coils in order to adjust its magnetic coupling with the fixed coils of the horizontal sweep coils and also the symmetry of the magnetic fields.

While specific embodiments have been shown and described, it will of course be understood that various other modifications may be made without departing from the invention. The appended claims are therefore intended to cover any such modifications within the true spirit and scope of the invention.

I claim:

1. An electromagnetic deflecting yoke struc-' 2. An electromagnetic deflecting yoke structure for a television picture tube comprising a laminated magnetic core structure in the form of a closed ,loop having a central opening adapted to surround the neck of such tube, two pairs of coordinate ra deflection coils linking said loop, said pairs being adapted to be energized to produce transverse magnetic deflecting fields, the coils of a first pair surrounding diametrically opposite sides of said loop, the coils of the second pair surrounding intermediate portions of said loop, and means for independently adjusting the magnetic coupling between either coil of said second pair and the coils of said first pair.

3. An electromagnetic deflecting yoke structure for a televislompicture tube comprising a rectangular laminated magnetic core adapted to surround the neck of such tube, a first pair of deflecting coils surrounding opposite sides of said core, said coils being adapted to be energized to produce a first magnetic deflecting field across the gap between said sides, a second pair of deflecting coils surrounding the other two sides of said core and adapted to be similarly energized to produce a second, substantially transverse, magnetic deflecting field, and means for independently adjusting the axial position of each coil of said second pair along its respective side, thereby to adjust its magnetic coupling with the coils of said first pair and the symmetry of its deflecting field.

4. An electromagnetic deflecting yoke structure for a television picture tube comprising a square, laminated, magnetic core adapted to surround the neck of such tube, a first pair of substantially identical deflecting coils surrounding opposite legs of said core and each extending axially substantially the full length of its supporting leg, a second pair of substantially identical deflecting coils surrounding the remaining legs of said core and each having a length substantially shorter than the length of its supporting leg, the coils in each pair being adapted to be energized by horizontal and vertical sawtooth deflecting waves respectively, and means for independently adjusting the axial position of each coil in said second pair along the length of its supporting leg, whereby dissymmetry in the scanning pattern may be substantially eliminated.

5. An electromagnetic deflecting yoke structure for a television picture'tube comprising a toroidal laminated core adapted to surround the neck of such tube, a first pair of fixed ray de- 7 fiecting coils surrounding diametrically opposite sides of said core and conforming to the curvature thereof, said coils each subtending approximately a full quadrant at the axis of said core, a second pair of coordinate ray deflecting coils wound around the intermediate portions of said core and similarly conforming to the curvature thereof, said second coils each subtending substantially less than a quadrant at the axis and being arranged for sliding movement along said portions, each of said pairs of coils being adapted to be energized by coordinate ray-deflecting waves, and mechanical adjusting means for independently adjusting the angular positions of each coil of said second pair to adjust its magnetic coupling with the fixed coils of said first pair and the symmetry of he magnetic field between said adjustable coils.

6. An electromagnetic deflecting yoke structure for a television picture tube comprising a cylindrical coil support adapted to surround the neck of such tube, an inner pair of multi-turn single-layer deflecting coils lying on the surface of said support with their magnetic axes aligned generally on a transverse diameter through said support, an outer pair of multi-turn, single-layer deflecting coils lying on a cylindrical surface coaxial with said support with their magnetic axes aligned generally on a second, mutually-per pendicular transverse diameter through said support, said pairs of coils being adapted to be energized by coordinate ray-deflecting waves, and mechanical means for independently adjusting the angular position of the magnetic axis of each coil of said outer pair with respect to the magnetic axes of said inner pair, said means comprising an inner section of each outer coil Which is angularl movable with respect to the remainder of said coil.

LUIZ G. MALI-IEIROS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Gethmann June 8, 1948