AMENDED SPECIFICATION

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Reprinted as amended under Section 8 of the Patents and Designs Acts, 1907 to 1938

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482,195

PATENT SPECIFICATION

Application Date: Sept. 21, 1936. No. 25574/36

Complete Specification Left: July 24, 1937.

Complete Specification Accepted: March 21, 1938.

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PROVISIONAL SPECIFICATION

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

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

This invention relates to electromagnetic deflecting coils for cathode-ray tubes and has particular reference to the deflecting coils for cathode ray tubes used in television and similar systems, or for measuring purposes.

A cathode ray tube is usually provided with either electrostatic or electromagnetic means for deflecting the cathode ray and causing it to trace out a desired path on a fluorescent or other screen associated with the tube. In the case of electromagnetic means, two coils or two pairs of coils are arranged to produce deflection of the cathode ray in two directions at right angles to each other. Currents of sawtooth wave form, one having a frequency corresponding to the line scanning frequency and another corresponding to the framing frequency are passed through the coils and the picture field or raster is thus built up on the tube screen.

The object of the present invention is to provide compactness of construction in the coil system of a cathode ray tube and to effect economy in the provision of coils.

According to the present invention a single coil system is used to effect both horizontal and vertical deflection of a cathode ray or similar scanning beam. The current wave forms corresponding to the desired line and frame deflections in the case of a cathode ray tube used for television reception are passed through a single coil system.

In order that the nature of the invention may be more clearly understood one form of the coil system arranged in accordance with the invention will now be described by way of example with reference to the drawing, a ray deflecting coil system is shown diagrammatically, eight similar coils being connected together in a manner generally similar to that of a polyphase winding of a two-pole electric motor. The circles 1 and 11 represent the wires of a coil seen looking along the axis of a cathode ray tube. The line joining 1 and 11 represents the ends of the coil which is drawn for simplicity as crossing straight through the cathode ray tube. In practice the ends of the coils must be passed round the tube outside the glass envelope. One side of the coil is made shorter than the other, the coil when laid flat being trapezoidal in form. The end turns are turned radially out from the short side of the coil and return round the cathode ray tube to the long side.

The coil ends are brought out on one side of each coil as indicated at the circles, 1, 2 …8. The other sides of the coils represented by the circles 11, 21 … 81 receive current through the end turns. The wire entering centrally into the circle representing the coil, passes vertically through the plane of the paper and is bent round the tube at the end of the coil, returning through the plane of the paper to a corresponding circle on the outer side of the coil.

It will be seen from the drawing that the pitch of each coil is just short of 180°, the mean pitch in the particular example shown being 157.5°. Tappings TL are taken at diametrically opposite points for the introduction of one of the scanning currents and the other scanning currents are introduced at the tappings TF at right angles. Assuming that each coil section has an integral number of turns the bridging connections C from one coil to another will all be disposed at one end of the coil system and in the case shown, in which it is assumed that the bridging connections are all at the end of the coil remote from the observer, the wire of the coil at the conclusion of coils 4, 1, 2 and 3 must then pass immediately over the tube as shown by the full lines and the dotted lines crossing the circles 1, 2, 3 and 4.

Assuming that one scanning current enters and leaves as shown by the arrows, the currents in the coil sides will be a indicated by the crosses and dots. The crosses represent current leaving the observer and the dots current coming towards the observer. It will be seen that in all coils on the right between 51 and 4 inclusive, the currents are leaving the observer and in the case of the remaining eight coils the current is coming towards the observer. Thus, a magnetic field will be produced along the direction of the diameter passing between 11 4 on one side and 8, 51 on the other. Similarly currents introduced at the other two tapping points will produce a magnetic field at right angles.

The coil system is provided with a magnetic coil not shown in the drawing, but which is in the form of iron wire wound around the outside of the coils. If a uniform magnetic coil is used, however, the coil arrangement described will not produce uniform magnetic flux in the space desired, the particular current distribution shown producing too strong a field in the centre of the space. One way of obviating this difficulty is to shape the iron core so as to be more remote from the coil sides 8, 51, 4 and 11 than it is from the other coil sides, and in this case there would be a reduction of the central flux. Also in the case of the flux set up by the second scanning current, the iron core must be removed from the neighbourhood of coils 2, 71 31 and 6. This latter adjustment would not seriously affect the flux for the scanning direction marked on the drawing. The suggested formation of the iron core would result in its having an approximately square shape and this could be produced by placing pieces of padding over the coils at appropriate places before winding on an iron wire coil. The pieces of padding may usefully serve as blocks for terminals connected to the coils.

An alternative method of producing uniformity of flux lies in altering the pitch of the coils. Thus in the example described reduction of coil pitch from 157.5° to 112° would result in the following sequence of current production in the coils:-

x x x x x x . x …… x

Such an arrangement would tend to produce a more uniform field than that shown in the arrangement illustrated in the drawing although the scanning efficiency would be lower. On the other hand, the arrangement described might in practice be found to effect slight over correction for the arrangement shown in the drawing. If twelve coils instead of eight were employed, the coil pitch corresponding to the arrangement shown in the drawing would be 165° whereas in the case of an improved arrangement giving a more uniform field, the coil pitch would be 135°. It is of course clear that the method may be applied for any number of coils.

While in the example described the coils have circular sides, such a shape is not essential and the coils may be wound on former design to give the coils a segmental shape so that they will fit neatly together and occupy a minimum amount of space. The coils may be shaped to fit cylindrical, conical or other shaped cathode ray tubes.

Dated this 19th day of September, 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, of 32 Audley Road, Ealing, London, W.5, a British subject, do hereby declare the nature of this invention and in what manner 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:-

This invention relates to electromagnetic deflecting coils for cathode ray tubes used in television and similar systems, or for measuring purposes.

A cathode ray tube is usually provided with either electrostatic or electromagnetic means for deflecting the cathode ray and causing it to trace out a desired path on a fluorescent or other screen associated with the tube. In the case of electromagnetic means, two coils or two pairs of coils are arranged to produce deflection of the cathode ray in two directions at right angles to each other. Currents of sawtooth wave form, one having

INSERT MISSING PAGE HERE

around the outside of the coils. If a uniform magnetic core is used, however, the coil arrangement described will not produce uniform magnetic flux in the space desired, the particular current distribution shown producing too strong a field in the centre of the space. One way of obviating this difficulty is to shape the iron core so as to be more remote from the coil sides 8, 51, 4 and 11 than it is from the other coil sides, and in this case there would be a reduction of the central flux. Also in the case of the flux set up by the second scanning current, the iron core must be removed from the neighbourhood of coils 2, 71, 31 and 6. This latter adjustment would not seriously effect the flux for the scanning direction marked on the drawing. The suggested formation of the iron core would result in its having an approximately square shape and this could be produced by placing pieces of padding over the coils at appropriate places before winding on an iron wire coil. The pieces of padding may usefully serve as blocks for terminals connected to the coils.

An alternative method of producing uniformity of flux lies in altering the pitch of the coils. Thus in the example described in reduction of coil pitch from 157.5 degs. to 112.5 degs. would result in the coil numbering shown in the drawing being altered to the sequence, reading in the clockwise direction from the coil 8

8, 61, 1, 71, 2, 81, 3, 11, 4, 21, 5, 31, 6, 41, 7, 51

. + + + + + + . + . . . . . . +

Such an arrangement would tend to produce a more uniform field than that shown in the arrangement illustrated in the drawing, although the scanning efficiency would be lower. On the other hand, the arrangement described might in practice be found to effect slight over correction for the arrangement shown in the drawing. If twelve coils instead of eight were employed, the coil pitch corresponding to the arrangement shown in the drawing would be 165 degs. whereas in the case of an improved arrangement giving a more uniform field, the coil pitch would be 135 degs. It is of course clear that the method may be applied for any number of coils.

While in the example described the coils have circular sides, such a shape is not essential and the coils may be wound on formers designed to give the coils a segmental shape so that they will fit neatly together and occupy a minimum amount of space. The coils may be shaped to fit cylindrical, conical or other shaped cathode ray tubes.

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. A single electromagnetic deflecting coil for a cathode ray tube consisting of a winding having those portions which are effective in deflecting when assembled on a cathode ray tube, extending substantially longitudinally with respect to the electron beam of the tube, the arrangement of the turns being such that horizontal and vertical deflecting fields are set up on the application of energising currents to tapping points in said coil so chosen that a current entering or leaving by one pair of tapping points produces a field at right angles to that produced by current entering or leaving the other pair of tapping points.
  2. A single electromagnetic deflecting coil for a cathode ray tube for use in a television system consisting of a winding having those portions which are effective in deflecting when assembled on a cathode ray tube, extending substantially longitudinally with respect to the electron beam of the tube, the arrangement of the turns being such that defecting forces corresponding to desired line and frame deflections are set up when currents of saw-tooth wave form of the frequency of said line and frame deflections respectively are applied to tapping points in said coil so chosen that a current entering or leaving by one pair of tapping points produces a field at right angles to that produced by current entering or leaving the other pair of tapping points.
  3. A coil according to Claim 1 or 2 provided with a magnetic flux distributing member formed so as to decrease the concentration of the magnetic flux in the central region of the field set up by said coil.
  4. A single electromagnetic coil according to Claim 1 or 2 wherein, in order to produce substantially uniform flux density, the distribution of the coil turns is arranged to be such that the current flowing in a particular coil side due to current controlling one direction of scan is opposite in direction to the flowing in the immediately adjacent coil sides and the current flowing in another coil side displaced from said particular coil side by 180° is also opposite in direction to that flowing in the coil sides immediately adjacent said other coil side.
  5. A single electromagnetic deflecting coil for a cathode ray tube substantially as described with reference to the drawing filed with the Provisional Specification.

Dated this 23rd day of July, 1937.

F. W. CACKETT,

Chartered Patent Agent.

Reference has been directed, in pursuance of Section 8, sub-section (2), of the Patents and Designs Acts, 1907 to 1938 to Specification No. 494,672.

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Leamington Spa: Printed for His Majesty’s Stationery Office, by the Courier Press. – 1939.