US3004188A

US3004188A - Cathode-ray tube deflection structure

Info

Publication number: US3004188A
Application number: US753762A
Authority: US
Inventors: Jack Van Hutten
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1958-08-07
Filing date: 1958-08-07
Publication date: 1961-10-10
Anticipated expiration: 1978-10-10

Description

J. VAN HUTTEN 3,004,188

CATHODE-RAY TUBE DEFLECTION STRUCTURE Filed Aug. 7, 1958 Ha. F12

VERTICAL A IS Oct. 10, 1961 VERTICAL DEFLECTION FIELD HOR IZONTA L AXIS ORIZONTAL DEFFLIECTION ELD T0 HORIZONTAL DEFLECTION COILS, HIGH VOLTAGE RECTIFIER, DAMPER SYSTEM TUBE, AND B "BOOST" SUPPLY.

dfigm I/VVENTOR TRANSFORMER 1762616 Van QKuzien A TTOR/VE'Y 3,004,188 CATHODE-RAY TUBE DEFLECTI ON STRUCTURE Jack van Hutten, Villa Park, 111., assignor to Zenith Radio Corporation, a corporation of Delaware Filed Aug. 7, 1958, Ser. No. 753,762 Claims. (Cl. 315-27) This invention is directed to means for efl'ecting deflection of the electron stream in a cathode-ray tube by producing an electromagnetic field or fields and more particularly to means for regulating such electromagnetic fields.

It is common practice to use a yoke structure including separate horizontal and vertical deflection coils to effect proper scansion of the electron beam in the image reproducer of a television receiver. Such a yoke structure conventionally includes a bore section for receiving the neck portion of the cathode-ray tube, horizontal and vertical deflection coils supported on either side of a separator element, and a magnetic core encircling the yoke structure externally of the deflection coils. In response to application of the correct signals to the deflection coils, the electron beam is caused to move in a regulated pattern over the screen of a cathode-ray tube in order that intensity-modulation of the beam may reproduce the desired video intelligence at predetermined points.

A phenomenon frequently produced by such electromagnetic deflection systems is an undesirable stretch eifect in the presentation at the left-hand side of the screen, as viewed from the surface of the image screen remote from the electron gun. Such an effect is produced, for example, when the sawtooth waveform of the horizontal deflection current is distorted in a manner to accelerate the sweep at the left side of the image screen. Accordingly, it is desirable to provide some method of compensating for this unwanted stretch efiect.

One known method of correcting for the horizontal stretch effect is to use a cylindrical sleeve-like element of brass or another suitable conductive material, positioned to slide on the tube neck and enter the bore of the yoke structure. The relatively slow alternations of the vertical deflection field do not induce a signal of practical significance in the conductive sleeve. The rapidly varying horizontal deflection field induces circulating eddy currents in the sleeve when it is positioned at least partially within the yoke; the induced currents create fields opposing the horizontal field. By regulating the position of the sleeve the level of the induced eddy currents, and hence the magnitude of the horizontal stretch compensation, is also regulated. Actually the sleeve afiects the entire horizontal flux pattern, and thus is suitable for use as a width control for the horizontal sweep circuit of a television receiver.

Recent trends in yoke design and construction have produced yokes with little or no open space between the tube neck and yoke itself, leaving no room for the sleeve. .Additionally the increasing use of wide-deflection-angle tubes such as the 90 and 110 tubes, and the reduction in tube length to produce cathode-ray tubes with a shorter front-to-back or screen-to-base dimension, have resulted in yoke-andtube configurations not compatible with the sleeve corrector.

It is therefore an object of this invention to provide a compensating structure for regulating the horizontal deflection field strength, which structure need not be positioned within the bore of the yoke structure to achieve satisfactory operation.

It is another object of the invention to provide such a compensating structure which affects only the horizontal deflection field and does not aflect the vertical deflection field.

It is a further object of the invention to provide such a compensating arrangement in which the level of the correction is readily adjustable.

It is an additional object of the invention to provide such a correction structure which affects only a limited portion of the horizontal deflection field.

A conventional yoke structure includes a first set of deflection coils for producing a first deflection field, a second set of deflection coils for producing a second deflection field perpendicular to the first #field, and a core member disposed concentrically with the deflection coils. In accordance with the invention, a conductive loop is provided encircling the core and positioned asymmetrically of the first set of coils to intercept the lines of force of the first field to develop a third field for asymmetrically modifying the first field. Additionally, an impedance is included in the conductive loop for regulating the intensity of the third field and its modifying eflect.

The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a side view illustrating an embodiment of the invention in combination with a conventional core structure; 7

FIGURE 2 is a schematic representation useful in understanding the operation of the invention;

FIGURE 3 is a schematic illustration of another embodiment of the inventive teaching;

FIGURES 4a and 4b are graphical representations useful in understanding the operation of the embodiment shown in FIGURE 3; and

FIGURE 5 is a partial schematic diagram portraying yet another embodiment of the invention.

The conventional yoke structure 10 depicted in the embodiment of FIGURE 1 includes a separator element '11 disposed between the vertical deflection coils 12 and the horizontal deflection coils 13. Small magnets 14 are affixed to separator 11 at predetermined positions to compensate for the pin-cushion distortion frequently produced by conventional yoke structures. A magnetic core 15 of ferrite or a similar material is disposed outwardly of and concentrically With respect to the deflection coils. Conventionally core 15 may be constructed in two semicircular pieces or produced in a single piece and then split for simplicity of mounting in the desired arrangement. After mounting, the two halves of core 15 are maintained in position by a clamp 16.

The rear portion of separator 11 is flared outwardly and terminated in a hollow cylindrical section 17; a semicircular indentation (not shown) is included in an edge of section 17. A similar indentation (not shown) is provided in a corresponding surface of the rear closure member 18, so that an aperture is formed to provide access for the leads 20 when member 18 is positioned in engagement with section 17. The leads 20 are connected to the horizontal and vertical deflection coils within the space provided by the rear closure member 18 and cylindrical section 17; conventionally, certain resistor and capacitor elements (not shown) utilized in the deflection circuits are also housed in this space and connected to the deflection coils.

The

adjustment tabs

21 and 22 are connected to annular magnetic elements (not shown) at the rear of yoke are indicated by the horizontal vectors.

direction, such as a diode, metal oxide rectifier, etc. shown in FIGURE 3, conductive loop 35 comprises a ribbon element 36 of severalturns, a'variable resistor provide a centering correction for the electron beam in well known manner. A plurality of resilient fingers 23 are positioned for mating engagement with the neck of a cathode-ray tube when the yoke is mounted thereon, to maintain the yoke in its proper position on the tube neck. Yoke is generally symmetrical about axis 19, which is concentric with the bore of the yoke Structure.

In accordance with the invention, a conductive loop 25 is positioned to encircle a section of core 15. To clearly illustrate the invention, loop 25 has been depicted as tilted slightly from a preferred positionyhowever, its position for optimum performance will be made clear in the subsequent explanation. Loop 25 is comprised of a conductive ribbon 26 of brass or other suitable material which substantially encircles a section of core 15. An inductor 2L7, Wound on a coil form 28, is connected in series with the ribbon 26. The efiective value of inductor 27 is regulated by adjusting the position of the slug 30 within coil form 28; slug 30 may be of ferrite, powdered iron, etc.

'The operation of the invention will be explained in connection with FIGURE 2. The horizontal deflection coils, in response to the application of suitable signals, produce an alternating electromagnetic deflection field perpendicular to the horizontal axis of the yoke structure; the strength and direction of this field at a given time are indicated by the vertical vectors in FIGURE 2. The vertical deflection coils produce an alternating field normal to the first field, the instantaneous values of which In accordance with the invention, the ribbon portion 26 of the conductive loop 25 is positioned approximately in the horizontal reference plane to intercept the lines of force of the first, or horizontal deflection, field but ribbon 26 is parallel to the second, or vertical deflection, fieldand thus is not affected by alternations of the vertical field flux. The horizontal reference plane is a plane in which axis in FIGURE 1. The horizontal deflection coils are disposed symmetrically with respect to this plane; that is,

one horizontal coil is positioned above the horizontal reference plane, and the other coil is oriented similarly relative to, but positioned below, the same plane. Axis 19 also lies in the verticalr'eierence plane, which is perpendicular to the horizontal reference plane.

The variations of the horizontal field strength induce a'signal in the conductive loop 25 which develops a third field; this third field opposes, and thus modifies, the first or horizontal deflection field in accordance with well known electrical laws. It is evident that the horizontal deflection field is modified in relation to the strength of the opposing field created by current flow through the conductive ribbon Z6 and inductor 27 of loop 25. The

intensity of the modifying field depends upon the level of the current flowing in conductive loop 25, which is regulated by adjusting slug 343 within inductor 27. Such a structure has been found to compensate for the horizontal stretch effect and to leave the vertical deflection field substantially unafiected.

The eifect of the conductive loop 25 of FIGURES l flux by inserting a rectifier element in the conductive loop. The rectifier element may be any conventional unit which is eflective to pass current flow in one direction and'op-pose or prevent current'flow in the opposite As or potentiometer 37 and a rectifier'38, all connected in series. The horizontal deflection field induces a signal of sawtooth waveform, depicted as thesolid line curve 49 in FIGURE 4a, in loop 35. The broken line 41 is a reference axis indicating zero current flow in loop 35; thus, each intersection of curves 4t) and 41 indicates a reversal of the direction of current flow in loop 35, corresponding to a reversal of the direction of the horizontal deflection field. The portion of curve 40 below axis 41 represents current flow over a particular range, i.e., the current induced in loop by that portion of the horizontal deflection flux which causes movement of the electron beam from the left-hand side to the center or" the screen.

In accordance with a feature of the invention, rectifier 35 is connected in loop 35 to block current flow over the range indicated by the upper portion of curve hence no field is created to oppose that part of the horizontal deflection flux which causes electron beam movement from the center to the right-hand side of the screen. Instead the current flow is limited to one direction by rectifier 38, permitting a current flow in loop 35 such as that depicted by curve 42 in FIGURE 4b. Accordingly loop 35 provides a variable compensating field, the magnitude of which is adjustable by varying the position of movable armS? of potentiometer 37, opposing only that portion of the horizontal deflection field in which the undesirable stretch eflec't is sometimes manifested. Because loop 35 does not produce a field opposing the remainder of the horizontal deflectionfield, this embodiment is more emcient than the construction illustrated in FIGURES 1 and 2.

In the embodiment of FIGURES land 2, a single turn of ribbon conductor 26 around core 15 has been found toprovide ample induced signal in'loop 25. A lesser signal is induced in loop 35 because one-half of the horizontal field flux does not induce any signal in the loop, and that part of the horizontal signal which does 'cut the turns of ribbon conductor 36 never changes direction. Accordingly it is preferred to use three or four turns of the conductor about core 15 in any embodiment which provides unidirectional current flow through the conductive loop; such a construction has been found quite satisfactory.

Another conductive loop 45, comprising a ribbon element 46 and an inductor 4-7, is shown positioned diametrically opposite loop 35 in FIGURE 3. The conductive loop 45 functions in exactly the same manner as does the embodiment of the invention described above and shown in FIGURES 1 and 2, except that conductive loop 45, because of its position, has its principaletfect upon a diflerent portion of the horizontal deflection field. .It is apparent from FIGURE 3 that the compensation or regulation efiected by loop 45 occurs at the right-hand side of the viewing screen. This orientation of the conductive'loop circuit has been found eminently suitable to regulate the horizontal width of the pattern on the screen of a cathode-ray tube. If desired, loop 45 can "be replaced by a unidirectional current loop, such as loop 35.

It is evident that conductive loop 45 can only afford width regulation by diminishing the field strength from a maximum value in a given area; thus the width regulation can only be accomplished by reducing the horizontal dimension of the displayed picture from a maximum length. In some instances it may be desired to provide width control by increming the horizontal dimension of the picture beyond the maximum length obtainable with conventional deflection circuitry. Such an ex-,

tension is made possible by the embodiment of the in: vention shown in FIGURE 5. As there shown, a conductive loop circuit 55 includes a ribbon element-5o, a variable inductor 57, and another Winding or loop 58, all connected in series. Winding 58, which may be only a single turn, is positioned adjacent to or encircling a portion of the core 60 of the horizontal output transformer 61. Because the horizontal output transformer'is connected between the horizontal deflection system 62 and the horizontal deflection coils, it is evident that the flux induced in winding 58 provides an auxiliary modifying field to augment or reinforce the flux circulatingin core 15 by reason of the field'created'by the horizontal deflection coils. By adjusting the effective inductance of inductor 57, the amplitude of the reinforcing flux provided by the auxiliary modifying field is regulated and hence the degree of extension of the picture along the horizontal axis is controlled.

The invention has been found simple to fabricate and economical in use. Its installation in conventional yoke structures is readily accomplished, because the two-part core assembly lends itself to the simple insertion of the conductive loop prior to securing core 15 in place by tightening clamp 16. The degree of correction of the horizontal field strength is readily variable, and the range over which the correction is efiected can be limited by utilizing the embodiment of FIGURE 3. The vertical deflection field is completely unaffected by such correction. Moreover, the invention has a Wider area of utility than prior art compensating circuits because it need not be inserted within the bore of the yoke structure.

While particular embodiments of the present invention have been shown and described, it is apparent that changes and modifications may be made therein without departing from the invention in its broader aspects. The aim of the appended claims, therefore, is to cover all such changes and modifications as fall within the true spirit and scope of the invention,

I claim:

1. In combination with a deflection yoke structure for a cathode-ray tube including a first set of deflection coils for producing a first deflection field, a second set of deflection coils for producing a second deflection field perpendicular to said first field, and a core member disposed concentrically with said deflection coils, the improvement which comprises a conductive loop encircling a section of said core and positioned asymmetrically of said first set of coils to intercept the lines of force of the first field to develop a third field for asymmetrically modifying said first field, and an impedance included in said conductive loop for regulating the intensity of said third field and its modifying effect.

2. In combination with a deflection yoke structure for a cathode-ray tube including a first set of deflection coils for producing a first deflection field, a second set of deflection coils for producing a second deflection field perpendicnlar to said first field, and a core member disposed concentrically with said deflection coils, the improvement which comprises a conductive loop, including a ribbon-like conductor and a variable inductor connected in series, encircling a section of said core and positioned asymmetrically of said first set of coils to intercept the lines of force of the first field to develop a third field for asymmetrically modifying said first field, adjustment of said variable inductor being efiective to regulate the intensity of said third field and its modifying eflect.

3. In combination with a deflection yoke structure for a cathode-ray tube including a first set of deflection coils symmen'ically positioned about a horizontal reference plane for producing a first deflection field, a second set of deflection coils symmetrically positioned about a vertiducing a second deflection field perpendicular to said 6 cal reference plane for producing a second deflection field perpendicular to said first field, and a core member disposed concentrically with said deflection coils, the improvement which comprises a conductive loop encircling a section of said core and positioned asymmetrically of said first set of coils approximately in said horizontal reference plane to intercept the lines of force of the first field to develop a third field for asymmetrically modifying said first field, and an impedance included in said conductive loop for regulating the intensity of said third field and its modifying effect.

4. In combination with a deflection yoke structure for a cathode-ray tube including a first set of deflection coils for producing a first deflection field, a second set of deflection coils for producing a second deflection field perpendicular to said first field, and a core member disposed concentrically with said deflection coils, the improvement which comprises a conductive loop encircling a section of said core and positioned asymmetrically of said first set of coils to intercept the lines of force of the first field to develop an induced signal and a third field for asymmetrically modifying said first field, a rectifier element included in said loop for limiting the modifying eflect of said third field to a particular amplitude range of said signal, and an impedance included in said conductive loop for regulating the intensity of said third field and its modifying eflect over said amplitude range.

5. In combination with a television receiver including a horizontal output transformer having a core element and a deflection yoke structure for a cathode-ray tube including a first set of deflection coils for producing a first deflection field, a second set of deflection coils for profirst field, and a core member disposed concentrically With said deflection coils, the improvement which comprises a conductive loop encircling a section of said core member and asymmetrically of said first set of coils positioned to intercept the lines of force of the first field to 7 develop a third field for asymmetrically modifying said first field, a winding positioned adjacent said core element and series-coupled in said conductive loop for developing an auxiliary modifying field to augment said first field, and an impedance included in said conductive loop for regulating the intensity of said third field, said auxiliary field and their modifying effects. 7

References Cited in the file of this patent UNITED STATES PATENTS