483,650

PATENT SPECIFICATION

Application Date: Oct. 20, 1936. No. 28516/36.

Complete Specification Left: Sept. 20, 1937.

Complete Specification Accepted: April 20, 1938.

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PROVISIONAL SPECIFICATION

Improvements in or relating to Electromagnetic Deflecting Coils for Cathode Ray Tubes

I, ALAN DOWER BLUMLEIN, a British subject, of 32, Audley Road, Ealing, London, W.5, do hereby declare the nature of this invention to be as follows:-

The present invention relates to deflecting means of the electromagnetic type for cathode ray tubes. Cathode ray rubes are used for television and also as oscillographs for the study of wave forms of applied variations and in both cases it is usually desired to trace upon the screen a figure which is as nearly as possible a graph, in rectangular co-ordinates, of two independent sets of current values. For the sake of convenience the case usually met with in television will be discussed in detail and it will be understood that the invention is applicable in other cases also.

In television the ray is usually deflected by currents of saw-tooth save form and constant amplitude, one of high frequency (strip or line frequency) and the other of low frequency (frame or picture frequency). Each cycle of the saw-tooth wave forms consists of a scanning stroke followed by a relatively rapid return stroke. It is usually desired that the area over which the ray is swept should be of rectangular form.

The object of the present invention is to provide a cheap and efficient electromagnetic coil deflection system for a cathode ray tube.

According to the present invention electromagnetic coils providing deflecting forces for the electron beam of a cathode ray tube in two mutually perpendicular directions are arranged at substantially equal distances from the axis of the cathode ray tube, the effective conductors of the coils lying substantially longitudinally with respect to the tube axis. Thus the separate coils providing the line and frame deflecting forces are arranged to lie side by side at the surface of the cathode ray tube instead of one set of coils lying on top of the other set. In order to assist assembly of the separate coils one set is made shorter than the other.

The nature of the invention will be more clearly understood from the following description of one example of a coil system arranged in accordance with the invention and illustrated in the accompanying drawing which shows a section of such a coil system.

Referring to the drawing, four coils are shown, 1, 11 being one coil, 2, 21 a second, 3, 31 a third and 4, 41 a fourth coil. The coils 1 and 2 together form the line scanning coils and 3 and 4 the frame scanning coils, and it will be seen that the coils form a circle of constant mean diameter, such an arrangement occupying relatively small space when assembled.

Considering the case of a single coil, for example 1, 11, the turns may be regarded as passing through the plane of the paper away from the section 1 then extending longitudinally of the tube around which they are bent before returning longitudinally of the tube and again passing through the plane of the paper at the section 11.

One pair of coils is made longer than the other pair in order to permit the two pairs to lie edge to edge in the manner shown in the section drawing. Conveniently the wound coils are assembled apart from the tube upon which they are slid when assembled. A winding of iron wire may be provided to constitute magnetic yoke.

The magnetic field set up in the space bounded by the coils is not of uniform flux density or pattern, and a field pattern is produced which is useful for the purpose of correcting a distortion of the scanned patch or raster on the screen of the tube known as pincushion distortion. This distortion is due to the fact that, a system of uniform deflecting fields provided by currents of sawtooth wave form does not scan a square on a flat screen or in general on a curved screen which has a radius of curvature different from the distance of the screen from the centre region of the deflecting fields. Thus the lines of force tend to assume pincushion pattern and the electron beam is caused to traverse a barrel-shaped pattern which compensates for the pincushion distortion. The anti-pincushion effect may, if desired, be made more intense by a suitable distribution of the turns in the separate coils. Thus by using a greater number of turns in any region the field in that region will be intensified and such distribution of turns may be done while retaining the essential features of the invention, namely arranging both frame and line of deflecting coils to lie side by side.

Dated this 19th day of October, 1936.

F. W. CACKETT,

Chartered Patent Agent.

COMPLETE SPECIFICATION

Improvements in or relating to Electromagnetic Deflecting Coils for Cathode Ray Tubes

I, ALAN DOWER BLUMLEIN, a British Subject, of 32, Audley Road, Ealing, London, W.5, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

The present invention relates to deflecting means of the electromagnetic type for cathode ray tubes. Cathode ray rubes are used for television and also as oscillographs for the study of wave forms of applied variations and in both cases it is usually desired to trace upon the screen a figure which is as nearly as possible a graph, in rectangular co-ordinates, of two independent sets of current values. For the sake of convenience the case usually met with in television will be discussed in detail and it will be understood that the invention is applicable in other cases also.

In television the ray is usually deflected by currents of saw-tooth wave form and constant amplitude, one of high frequency (strip or line frequency) and the other of low frequency (frame or picture frequency). Each cycle of the saw-tooth wave forms consists of a scanning stroke followed by a relatively rapid return stroke. It is usually desired that the area over which the ray is swept should be of rectangular form.

The object of the present invention is to provide a cheap and efficient electromagnetic control system for use in obtaining the desired deflection of the electron beam in a cathode ray tube.

According to the present invention an electromagnetic system for providing deflecting forces for the electron beam of a cathode ray tube in two mutually perpendicular direction consists of at least two pairs of coils arranged so that two sides of each coil, when the coils are assembled upon a cathode ray tube lie on the surface of the tube and longitudinally with respect to the axis thereof, the coil conductors causing deflection of the beam in one of said directions being arranged in opposite quadrants and the coil conductors causing deflection of the beam in the other of said directions being arranged in the remaining opposite quadrants, the effective conductors of the coils occupying substantially all the available space between two cylindrical surfaces co-axial with the cathode ray tube. The pair or pairs of coils effecting deflection of the electron beam in one of said directions is shorter in length than the other pair or pairs.

In order that the invention may be more clearly understood and readily carried into effect, a coil system designed in accordance therewith will not be described by way of example with reference to the drawing left with the Provisional Specification and to the drawing accompanying the present Specification, which, for the sake of convenience, will be referred to as Fig. 2.

Referring to the drawings, four coils are shown, 1, 11 being one coil, 2, 21 a second, 3, 31 a third, and 4, 41 fourth coil. The coils 1 and 2 together form the line scanning coils and 3 and 4 the frame scanning coils, and it will be seen that the coils form a circle of constant mean diameter, such an arrangement occupying relatively small space when assembled. The line deflecting coils 1 and 2 are arranged in opposite quadrants of the circle formed by the coil cross-sections and the coils 3 and 4 occupy the remaining opposite quadrants. The conductors contained in the ends of each coil requires to be disposed as shown in Fig. 2 for example, such a manner that the field due to them will not affect adversely the deflecting magnetic field and are conveniently bent to stand away radially from the surface of the tube. It will further be seen from the drawing that with the Provisional Specification that the cross-sections of the sides of the coils which lie along the surface of the cathode ray tube occupy substantially all the available space contained within the concentric circles constituted by the inner and outer surfaces of the coil sides.

Considering the case of a single coil, for example 1, 11 in the drawing left with the Provisional Specification, the turns may be regarded as passing through the plane of the paper away from the section 1 then extending longitudinally of the tube around which they are bent before returning longitudinally of the tube and again passed through the plane of the paper at the section 11.

One pair of coils is made longer than the other pair in order to permit the two pairs to lie edge to edge in the manner shown in the section drawing accompanying the Provisional Specification and more clearly in Fig. 2. Conveniently the wound coils are assembled apart from the tube upon which they are slid when assembled. A winding of iron wire may be provided to constitute a magnetic yoke.

The magnetic field set up in the space bounded by the coils is not of uniform flux density or pattern, and a field pattern is produced which is useful for the purpose of correcting a distortion of the scanned patch or raster on the screen of the tube known as pincushion distortion. This distortion is due to the fact that, a system of uniform deflecting fields provided by currents of saw-tooth wave form does not scan a square on a flat screen or in general on a curved screen which has a radius of curvature different from the distance of the screen from the centre region of the deflecting fields. Thus the lines of force tend to assume pincushion pattern and the electron beam is caused to traverse a barrel-shaped pattern which compensates for the pincushion distortion. The anti-pincushion effect may, if desired, be made more intense by a suitable distribution of the turns in the separate coils. Thus by using greater number of turns in any region the field in that region may be intensified and such distribution of turns may be done while retaining the essential features of the invention, namely arranging both frame and line deflecting coils to lie side by side.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

  1. An electromagnetic system for providing deflecting forces for the electron beam of a cathode ray tube in two mutually perpendicular directions, consisting of at least two pairs of coils arranged so that two sides of each coil, when the coils are assembled upon a cathode ray tube lie on the surface of the tube and longitudinally with respect to the axis thereof, the coil conductors causing deflection of the beam in one of said directions being arranged in opposite quadrants and the coil conductors causing defection of the beam in the other of said directions being arranged in the remaining opposite quadrants, the effective conductors of the coils occupying substantially all the available space between two cylindrical surfaces co-axial with the cathode ray tube.
  2. An electromagnetic system according to claim 1 wherein the pair or pairs of coils effecting deflection of the electron beam in one of said directions is shorter in length then the other pair or pairs, in order to permit assembly of the coils in such a manner that they lie edge to edge longitudinally with respect to the tube axis.
  3. An electromagnetic coil deflecting system for a cathode ray tube substantially as described with reference to the drawings accompanying the Provisional and Complete Specifications.

Dated this 20th day of September, 1937.

F. W. CACKETT,

Chartered Patent Agent.

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Leamington Spa: Printed for His Majesty’s Stationery Office, by the Courier Press. - 1938