US2830212A - Electromagnetic deflecting means - Google Patents

Description

April 8, 1958 J, HANLET 2,830,21

I ELECTROMAGNETIC DEFLECTING MEANS Filed Jan. 6 1955 o. L ..9 Jr

A I B C 24 n 22g es an L322 g;

a INVENTOR.

Fl JAc uEs MARIE NoL HANLET BYMW ATMh/VEY ELECTROMAGNETIC DEFLECTING MEANS Jacques Marie Noel Hanlet, Paris, France, assignor to J. Visseaux S. A., Paris, France Application January 6, 1955, Serial No. 480,098 Claims priority, application France January 15, 1954 6 Claims. (Cl. 313-76) The present invention relates to improvements in electromagnetic deflecting means for controlling the deflection in at least one direction of the electron beam of a cathode ray tube.

A conventional type of electromagnetic deflector comprises two conductor coils serially interconnected and having the same number of turns. These coils are so shaped as to be applied upon opposite sides of the neck of a cathode ray tube, thereby determining within such neck a cylindrical deflecting space, the base of which is defined by the inner diameter of the coil assembly and the length of which is defined by the length of this assembly. The assembly is symmetrical with respect to the electron beam. It determines the deflection plane within which this electron beam is deflected from its rest position in a perpendicular direction depending upon the direction and value of the electrical current passing through the winding and the corresponding distribution of the magnetic field produced by this current.

conventionally also the electron beam is focused upon the screen of the cathode ray tube in its rest or center position. In this position the spot produced by the beam has its highest fineness. When the beam is deflected, the distance between the mid-point of the deflecting space and the spot on the screen varies if the screen is not of hemispherical shape. At present, the shape of a screen, whether fluorescent or electrostatic, is usually hemispherical, tending to become substantially flat for the screen of an oscilloscopic or picture reproducing tube, and plane for a picture analyser tube, an information storage tube and the like. Consequently, in such aspherical tube screens the focusing of the spot of the electron beam is not preserved as the beam is deflected, and the defocusing becomes greater as the deflection of the electron beam increases.

An object of the invention is to provide an improved structure of an electromagnetic deflecting means by which this drawback is substantially eliminated.

. A further object of the invention is to provide electromagnetic deflecting means which in addition to the elimination of the above mentioned drawback, reduces the well-known edge effect and increases overall efficiency.

The invention more specifically relates to so-called printed deflecting means, viz. a deflector winding for a cathode ray tube which comprises a pair of coils each covering substantially an angle of 180 degrees of the cylindrical structure thus defined. Each printed deflecting means is obtained from piling up or superimposing a number of insulating sheets each bearing a pair of solenoidal spirals of printed rectangular conductor turns. These sheets are insulated from each other, but the spiralled solenoids are serially electrically interconnected. Methods for making such windings are known, as will be pointed out further below. In the following, such a printed electrical deflector winding will be called a printed winding of the kind specified.

According to the invention, in the printed solenoids widths of the longitudinal sides of the turns are varied atent O F'ic6 in the one half of the circumference covered by this solenoid. This variation, which also corresponds to a variation in the distribution of these sides in this half of the circumference covered by the solenoid, is proportional to the variation of a predetermined trigonometrical function of the deflection angle of the beam. At the same time the lengths of these sides are also varied in accordance with the same distribution law, so that the magnetic field created within the cylindrical space of the deflector winding will present a distribution of intensity which will vary in both longitudinal and transversal directions in each plane parallel to the deflection plane of the beam, according to the square of the value of this trigonometrical function.

According to the invention, further, in such a structure, each one of the printed solenoids of the deflector winding has arcuate sides so changing in width that irrespective of the position of these sides, the same uniform value of potential drop is caused to occur between the ends of the longitudinal sides interconnecting these arcuate sides.

These and other features of the invention as well as the realizations and advantages thereof, will be more fully explained in the detailed description of the accompanying drawings, wherein:

Fig. 1 shows a side view of a cathode-ray tube, and Fig. 1A represents the geometrical distortion occurring on the screen of this tube as a function of the deflection angle of the electron beam;

Fig. 2 shows the distribution of the magnetic field created within the neck of the tube by a single deflection winding of uniform coiling rate;

Figs. 3 and 4 show different distributions of the same magnetic field for different rates of distribution of the turns of this winding;

Fig. 5 in a simplified perspective view and Fig. 6 in a further perspective view, respectively, represent deflector windings applied to the neck of a cathode ray tube;

Fig. 7 illustrates a flatdevelopment of a sheet bearing printed solenoids in accordance with the invention, forming part of a complete deflector winding extending through a pile of such sheets which are electrically interconnected.

Figs. 8A and B represent schematically the two types of sheets included in such a pile, and Fig. represents a cross-section through the pile itself.

Referring to Fig. l, a cathode ray tube is shown at 1 provided with a cylindrical portion or neck 2 and a screen surface 3. The electron beam to be deflected is generated by an electron gun 4 focused by means of a focusing coil 5 surrounding neck 2 of the tube and controlled for deflection by means of a deflector arrangement 6 also placed around a further portion of neck 2 of the cathode ray tube. The deflection itself will be considered from point 7 which is the center of deflection and midpoint of the cylindrical space defined by deflector arrangement 6.

Usually the focusing of the electron beam causes the spot produced at the center 8 of screen 3 to be of maximum fineness and of circular shape. If the screen were of hemispherical shape, as indicated by dotted line 25, the electron beam when deflected from its rest position by any angle 0 between 0 and a maximum value 0 would remain focused on the screen, provided that the magnetic deflecting field is uniformly distributed within the deflecting space or any cross-section thereof as shown in Fig. 2. Obviously, the showings of Figs. 2, 3 and 4 are concerned with the deflection of an electron beam in one direction and a single symmetrical deflector winding only. Such a uniform field is generated by a winding consisting of a pair of coils 12 and 13, each covering an angle of substantially Neglecting first the distortion introduced by the well-known edge effect at each end of deflector 6, the geometrical configuration of the picture of the spot upon the hemispherical screen 25 will be perfect. Obviously the length of travel of the beam from center point '7 to any point of screen 25 remains constant. For instance, distance 7-11 is equal to distance 7-8, and so forth.

However the curvature of an actual screen such as shown at 3 of a conventional cathode ray tube is not constant and consequently for a deflection angle of 6, distances 7-9 is not equal to distance 7-3. In the illustrated example, the difference between such values will be greatest when 6:6 For a two-direction deflection, therefore, the geometrical configuration of the image on screen 3 will be such as shown in Fig. 1A. The distortion is increased when screen 3 is replaced by a flat screen such as shown at 26 because in this case for the same angle 6, distance 7-H) will be greater than distance 7-9.

From another point of view, it is apparent that for any condition of the electron beam other than its rest position, the shape of the spot formed upon screen IE will not be circular but elliptical and the more distorted, the greater its deflection from rest position.

In order to establish a good condition of complete anastigmatism and focusing, a systematic corrective distortion of the magnetic field is provided wtihin the deflection space. Such distortion is obtained from a special distribution of the wire turns of the deflecting coils. This distribution follows a law related to the angular deviation imparted to the beam on either side of the deflection plane, and which is obviously symmetrical with respect to this plane. Actually such a law can be determined as a trigonometrical function of this deviation, for instance the sine or cosine of angle 0. In the crosssectional views of Figs. 3 and 4, this distribution of turns is made proportional to sine and corresponds to the very shape of screen 3, viz. a portion of a paraboloid osculating the sphere of radius 7-3. A distribution law according to the cosine of the angle 0 would correspond to a flat screen such as shown at 2.6. Other distribution laws can be provided in accordance with an analysis of the geometrical configuration of the cathode ray tube for other shape of screen.

Any law of distribution of the magnetic field in any cross-section of the deflecting space can be obtained from a corresponding law of distribution of the rectilinear portions of the wire turns forming the deflecting coils which are parallel to the axis of this space. For instance, the turns can be so placed as indicated in Fig.3 that coils 14 and 15 present each a variation in thicknes, e. g. a variation of the number of conductors in any plane parallel to the deflecting plane. In the example of Fig. 4, the number of turns in peripheral elements of the circumference can be varied in proportion to the value of the trigonometrical function in these portions. Each coil of Fig. 4, for instance, consists of a first set 16 of tightly wound wires, a looser set 17 and finally a set of wires 18 which is still more loosely wound, altogether covering a quarter of circumference. In the manufacture of such electrical coils, first, flat windings are made with progressively increasing wire diameters, then the sets of wires are interconnected and finally the coil is arcuated to its final shape.

In addition to these features, a deflector winding according to the invention will present at least one further feature, viz. a corresponding variation in the lengths of the longitudinal sides of the wire turns.

Fig. shows a simplified representation of a deflector winding around the neck of a cathode-ray tube. It will be seen that this winding includes at least one pair of solenoids bent around this neck; each solenoid covers 180. These solenoids are so serially connected through a portion 27 of a longitudinal wire turn that their parallel sides generate the useful components of the magnetic deflecting field. Their bent sides are not useful and even generate stray or parasitic components in such a field. The effect of these parasitic components appears mainly at both ends of the winding and is known as the edge effect of a cylindrical deflector winding.

Fig. 6 shows another representation of one of these coils, modified in accordance with the invention. On one side of Fig. 6 the deflection is indicated on an arbitrary scale. The longitudinal parts of the wire turns are distributed along the half-cylindrical surface according to a trigonometrical law; the relative lengths of these parts are also varied in accordance with this law.

Fig. 7 shows a printed sheet for a deflector winding embodying the features of the present invention. At the bottom of Fig. 7 the same arbitrary scale is shown as in Fig. 6. This printed sheet is manufactured according to any well-known method of printing circuits. It consists of an insulating base sheet 20 upon which is printed an electrically conducting drawing shown in black. The rectilinear sides which are parallel to the longitudinal axis of the sheet when bent around a cylinder have widths and lengths which both vary according to the same law representing a trigonometrical function of deflection angle 6, shown on the arbitrary scale. Consequently the magnetic field distribution within the deflection space will vary in axial and radial directions according to the square of the value of this trigonometric function. This will result in a corrective distribution and also, principally due to the change in lengths of the longitudinal sides of the wire turns, in a higher efliciency of the deflector winding. in accordance with an additional feature, the transversal portions of the wire turns forming the bent portions of the deflector winding, are so changed in width from the edges to the center of the printed sheet that each of these bent portions cause the same drop of potential between any pair of connection points such as 1223-29. This has been found to enhance the overall efiiciency of the winding and especially to reduce the drawback of edge effects since the axial distribution of the magnetic field within the deflection space will be made more uniform.

Manufacture of a deflector winding according to the invention can proceed in the manner disclosed in my co-pending application Ser. No. 440,154. However it may also be processed as briefly stated in the present disclosure with reference to Fig. 8.

A number of printed sheets are made, according to Fig. 7 or any similar arrangement, or according to any law of distribution other than the sine law.

Furthermore, as shown in Fig. 8, two kinds of such printed sheets are prepared, one in accordance with scheme A, and the other in accordance with scheme B of Fig. 8.

Printed sheets may be prepared by metallizing an insulating sheet, photosensibilising the same, impressing thereon through optical means an image of the drawing to be printed, developing, fixing, washing and drying this print and then engraving the same so that the parts of the inetallized surface which have not been impressed are completely removed.

The remaining metal parts consisting for example of copper will reproduce the drawing. A suitable thickness for such an electrically conducting print is for instance of a millimeter and if required, this thickness may be obtained after a first engraving from a galvanic deposition of material.

After two series of printed sheets have been prepared, as above stated, they are piled up as shown at C in Fig. 3 and alternately interconnected by solder points such as shown at 24. It must be understood that either insulating sheets are interposed between the A and'B sheets or these same sheets A and B are provided with insulating films over their elective-conductingprints. The'interconnected terminals are shown at 22 and 23 in the A'and B views of Fig. 8. Each solder point may be produced by applying thereupon a mixture of rosin and stannic'powder and applying the end of a soldering iron to this mixture; the insulation is burned through and thereby the electrical connection is obtained.

I claim:

1. In an electromagnetic deflector device for a cathode ray tube having an aspherical screen, severalarrays of a number of superimposed layers of solenoidal spirals of rectangular turns of wire, said layers being insulated from each other and said spirals being serially electrically interconnected; and means for juxtaposing said arrays so as to form a cylindrical deflection space; each of said spirals having longitudinal sides extending parallel to the axis of said cylindrical deflector space and varying in both width and length while not varying in height from one end of the spiral to its center as a function of the deflection angle of the cathode ray from its rest position so as to compensate for defocusing due to the deviation of the screen from a spherical surface.

2. Deflector device according to claim 1 comprising two arrays of layers, each forming an arcuate coil and each extending substantially over an angle of 180 dedegrees of said cylindrical deflection space, and each layer consisting of a sheet bearing a pair of solenoidal spirals printed thereupon, the electrical conductors in said print being of uniform thickness but of varying Width.

3. Deflector device according to claim 1 wherein said screen is a paraboloid and cross section and length of said Wire turns are both varied in accordance with sine function of the deflection angle of the cathode ray from its rest position.

4. Deflector device according to claim 1 wherein said screen is flat and cross section and length of said wire turns are both varied in accordance with a cosine function of the deflection angle of the cathode ray from its rest position.

5. In an electromagnetic deflector device for a cathode ray tube having an aspherical screen, two arrays of a number of superimposed layers of solenoidal spirals of rectangular turns of wire, said layers being insulated from each other and said spirals being serially electrically interconnected; and means for arranging said arrays so as to form each one half of the circumference of a cylindrical deflection space; each of said spirals having longitudinal sides extending parallel to the axis of said cylindrical deflector space and increasing in width and decreasing in length while not varying in height from one end of the spiral to its center in accordance with a function of the deflection angle of the cathode ray from its rest position; said function depending upon the deviation of the screen from a spherical surface.

6. Deflector device according to claim 1 comprising two arrays of layers, each forming an arcuate coil and each extending substantially over an angle of 180 degrees of said cylindrical deflection space, and each layer consisting of a sheet bearing a pair of solenoidal spirals printed thereupon, the electrical conductors in said print being of uniform thickness but of varying width; and the arcuate sides of the rectangular turns being of a width such as to cause substantially the same drop of potential between their points of connection.

References Cited in the file of this patent UNITED STATES PATENTS 2,148,398 Bowman-Manifold et al. Feb. 21, 1939 2,237,651 Bruche Apr. 8, 1941 2,395,736 Grundmann Feb. 26, 1946 2,461,230 Obert Feb. 8, 1949 2,550,592 Pearce Apr. 24, 1951 2,722,621 Schenau Nov. 1, 1955 OTHER REFERENCES Tele-Tech and Electronic Industries, December 1954, pp. 82, 83, 140, 141, Martin Printed.

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