GB Patent 442666 - Improvements in or relating to television

Description

l?hird Edit ionm

a ESER Vr COF,,

l'hird Edition PATENT SPECIFICATION

Application Date: May 12, 1934 No: 14422/ 34 442,666 Enl ll u Complete Specification Left: April 11, 1935.

\ Complete Specification Accepted: Feb 12,1936.

PROVISIONAL SPECIFICATION.

Improvements in or relating to Television.

We, HRAls GERHARD' LUBSZYNSI,, of present invention there is provided apparGerman natiohality, of 36,-Cherry Grove, atus for transmitting images of an object 55 West Drayton Road, Elillingdon, Middle to a distance comprising an optical lens -sex, and SIDNEY RODDA, a British Sub '-stem fbr focusing an image of the object ject, of 170 ', Ladysmith -oad, Enfield, to be transmitted upon a photo-eleetrically

Middlesex, do hereby declare the fiature active screen mieans for accelerating the of this invention to be as follows:' electrons emitted froni said screen towards 60 The present invention 'relates to 'im a mosaic electrode of relatively insulated provements in television and is more par elements to such an extent as to cause a ticiitarly concerned with a method 'of secondary,emission of electrobs from said transmitting which involves the use of a elemients, and means for scanning said elecathode ray tube ienits with a primary beam of electrons 65.

According to the present invention there; such as a cahode ray.

is provided a method of transmitting The present invention may be carried images of an object to a distance wherein out in the following way:

an optical image of the object to be trans Television transmitting apparatus cornmmitted is projected upon a photo-elec prises a cathode ray tube having a cathode 70 trically active screen, photo-electrons gun of any suitable kind for generating a emitted �rom said photo-electrically active fne or focusedf primary beam of eleerons screen are accelerated towards-and focused 'and ' means -for deflbting the primary upon' a mosaic electrode of relatively' if beam so as to scan a mosaic electrode dissulated elements by nieans of an electron posed within the tube at an acute angle to 75 lens and said mosaic electrode is scanned the mean direction of the primary beam,; by a primary be'am of electrons such as a The mosaic electirode comprises a multi2 cathode ray plicity of elements which are insulated Aecording to a fufthr:feature of the from one another and from a eommon present invention there is' provided:' a conductive plate which will be called a 80 method of transmitting images of an oh " -signal '-' late 'The elements imaf be of ject to a distance wherein an optical image aluminium for example, and may be disof the object to be transmitted is projected posed 'upon a mica sheet which in turn is upon a photo-electrically active screen, disposed upon an aluminium " signal photo-electrons emitted from said photo plate The signal plate is connected to 85 electrically active screen,are accelerated earth through a resistance towards a mosaic electrode of relatively -Also disposed Within the tube, in a insulated elements to such an extent as plane substantially parallel to the plane to cause a secondary emission of electrons of the 'nmosaic' electrode, is a photo-elecfrom said eleme nts, and said mosaic dlee trieaaly aebive screen of non-mosaio 90 trode is scanned by a primary beam of charaeter; it may be, for example, a wire electrons such as a cathode ray mesh covered on both sides with photoAeording to another feature of the electrically active material The mosaic present invention there is provided apiar electrode is disposed so that the elements atus for transmitting images of an object may be scanned by the cathode ray and 95 to a distance, comprising an optical lens so that the elements face towards the system for projecting an optical image of photo-electrically active screen.

the object to be transmitted upon a photo Between the photo-electrically active electrically active screen, an electron lens screen and the mosaic electrode is dissystem for accelerating towards and focus posed a magnetio or electro-static electron 100 ing upon-a mosaic electrode of relatively lens, of large aperture 'designed to form insulated elements, electrons -emitted from an electron image:'of the screen upon the said photo-electrically active screen and mosaic electrode The electron lens mayv means for scanning -said mosaic electrode comprise, for 'example, two short-conduewith a beam of elections tive cylinders both maintained at positive 105 Ac ording to -another feature of the but different potentials relative to that of the screen.

Between the electron lens and the mosaic electrode is disposed an electrode in the form of a ring or a wire mesh which is adapted to collect, a secondary emission of electrons which occurs from the elements of the mosaic electrode during the operation of the tube This electrode is held at a-high positive potential relative to the photo-electric surface An optical lens system is provided outside the tube for focusing an optical image of the object to be transmitted upon one or other side of the photo-electrically active screen.

The operation of the tube is as follows:Electrons are emitted from the various points of the photo-electrically active screen to an extent proportional to the intensity of the light falling on this screen from the object The two cylinders forming the electron lens are given such shapes and potentials, relative to the photo-electric screen, that tlie photo-electrons emitted from any one point of the photoelectric screen are accelerated towards a'nd brought to a focus upon a corresponding point on the mosaic electrode.

The velocity of the electrons arriving at the mosaic electrode is sufficient to produce, from each element of the mosaic electrode, a secondary emission of electrons of intensity proportional to the intensity of the photo-electrons incident on the element In front of the mosaic electrode there is arranged a wire mesh or ring electrode, which is held at a positive potential relative to the photo-41 ecric surface The potential of each element of the mosaic will then adjust itself so that the number of secondary electrons leaving the element is equal to the number of primaries which impinge upon it Thus the potential of each element on the mosaic will reach-a value which is dependent on the numberof primaries, i e on the amount of light falling on the corresponding spot of the photo-electric screen.

Each element of the mosaic electrode forms a small condenser with the common signal plate, and in between successive scans each of these small condensers is charged positively, as described above, to an extent proportional to the intensity of the photo-current striking the element.

When the scanning beam strikes an element, however, that element receives a negative charge from the beam and the condenser is discharged The \discharge current is proportional to the positive charge which the condenser acquired since the last scan and this is proportional to the intensity of the photo-current striking the element of the condenser which in 65 turn is proportional to the light intensity of a corresponding point in the object.

Thus as the scanning beam sweeps over the multiplicity of elements, there are developed across the resistance in the lead 70 to the signal plate voltages which are proportional to the light intensity of corresponding points in the object These "picture " signals are amplified and transmitted in any known or suitable 75 manner.

In the embodiment of the invention described above the cathode ray and the photo-electrons are incident upon the same face of the mosaic electrode The photo 80 electric screen and the electron lens must therefore be disposed at some distance from the mosaio electrode in order that they may' not obstruct the cathode ray.

Systems are known, however, in which an 85 optical image is projected upon one sideof a mosaic electrode, and this electrode is scanned upon the opposite side The present invention may be applied to such a system in the following way: 90 The mosaic electrode consists of econ-' ductive elements studded in a conductive plate and insulated therefrom, each element extending right through the plate 6nd the plate being connected to earth 95 through a resistance Each element is brought to a dixed potential at each scan and acquires a positive charge, of value proportional 'to the light falling upon it, in between successive scans The aceeler 100 ation of the scanning beam towards an element, and therefore the current flowing to the conductive, plate, is proportional to the potential of the element at the'instant of scanning and' thus as each element is 105 scanned in turn, picture signals are generated across the resistance in the lead to the conductive plate In this case the electron lens may, if desired, be dis pensed with and the photo-electric screen 110 brought up very close to 'the mosaic elec trode, with a plane mesh electrode held at a positive potential in between,' in order to accelerate the photo-electrons' uniformly in their path, so as to produce as 115 many secondary electrons as possible.

Dated this 12th -day of May, 1934.

REDDIE & GROSE, Agents for the Applicants, 6, Bream's Buildings, London, E C 4.

442,666 442,666 COMPLETE SPECOIFICATION.

Improvements in or relating to Television.

We, H Iqs GERHALD LUBSZYNSKI, of German nationality, of 36, Cherry Grove, West Drayton Road, Hillingdon, Middlesex, and Si D Nmy RODDA, a British Subject, of 170, Ladysmith Road, Enfield,

Middlesex, 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 improvements in television and is more particularly concerned' with a method of transmitting which involves the use of a cathode ray tube ' A Mnethod of transmitting images of an object to a' distance has already been proposed, in which an optical image of an object to be transmitted is projected upon a photo-electrically active screen, photoelectrons emitted fromn said screen being accelerated towards a mosaic electrode, placed near the screen but spaced from it, and consisting of conducting elements projecting through and insulated from a metal plate, the acceleration being produced by a potential difference set up between' the screen and the plate The mosaic screen is scanned by a beam of electrons In this method, however, the photo-electric screen and the mosaic electrode are close together and no means are employed for focusing the, electrons emitted from the photo-electric screen on to the mosaic 'tleetrode With this arrangement, in order to form a sufficiently sharply defined electron image on the mosaic electrode, it is necessary to make the distance between the photoelectric screen and the mosaic electrode short enough to prevent excessive spreading of the electrons in their passage from the screen to the mosaic electrode.

In a, known television transmitting tube an optical image of an object is formed on a photo-sensitive cathode, an electron image is formed from this cathode in the neighbourhood of a scanning aperture located at some distance from the cathode and this' electron' image is swept over the scanning aperture in such a way that each part of the electron image becomnes operative on the aperture in turn The electrons passing through the aperture are utilised to provide picture signals for transmission In this known tube an electron lens system in the form of a solenoid extending over the whole space between the cathode and the plane of the scahning aperture is provided to form the electron image It is well known that both solenoids extending around the whole space between object and image and also coils extending around only a small part of the' space act as electron lenses They act somewhat 65 differently because the former gives a parallel field and the latter a curved field.

The short coil more closely resembles in its -operation, an optical lens system.

It has also been proposed to use an elec 70 tron lens system to formn an electron image upon the fluorescent screen of a receiving tube from electrons passing through an electron-permeable anode In this case also the electron lens system is in the 75 form of a solenoid extending over substantially the whole space between the anode and the fluorescent screen.

The present invention is distinguished from the last two above mentioned known 80 arrangements in that it is concerned solely with transmitting tubes embodying screens of the mosaic type in which the electron emission produced by the light from the object acts cumulatively to vary 85 the charge upon the elements of the se.een and is therefore effective continuously exdept for the instants at- which the scanning spot is-operative to restore the charges to their datum, level 90 The present invention provides a method of transmitting images of aa object to a distance wherein an optical image of the object to be transmitted is projected' upon a photo-electrically aetive 95 screen, photo-electrons emitted from said photo-electrically active screen are accelerated towards a mosaic electrode of mutually insulated elements spaced apart from said screen and are focused upon the 100 electrode to form an electron image thereon by inmeans of an electrostatic or electromagnetic electron lens system and said mosaic electrode is scanned by a primary beam of electrons such as a cathode ray 105 The-velocity of the photo-electrons on impact with the elements of said mosaice may be such that there are emitted from said screen secondary electrons greater in number than the incident photb-electrons, 110 whereby each element acquires a positive charge in the intervals between scans.

The present invention also provides apparatus for transmitting images of an object to a distance said apparatus corn 115 prising an optical system for projecting an image bf the object upon a photoelectrically active screen, a mosaic electrode comprising mutually insulatqd elements this electrode being spaced apart 12 Q from said screen and being arranged with trically active screen 7 of non-mosaic the screen within an evacuated envelope, character; it may be,'for example, a coatfocusing means for causing the electrons ing, on the side of the glass wall facing emitted from said screen to form an elee- 'the mosaic electrode 4, of silver having 6 tron'image upon said mosaic electrode, a silver oxide surface on which is demeans for developing a beam of electrons posited a layer of caesium This coating and means whereby said -beam of electrons is so thin as to be semi-transparent The can be caused'to scan said mosaic elec mosaic electrode 4 is disposed so that the trode elements 5 may be scanned by the cathode The beam of electrons may be caused ray and so that the elements 5 face toto scan the mosaic'eleetrbde on either side wards the photo-electrically active screen thereof In the case where the beam of 7.

electrons scans the mosaic electrode on the Surrounding a small part of the space side thereof facing said photo-electrically between the photo-electrically active active screen, the mosaic electrode al screen and the mosaic electrode is disposed though usually comprising a multiplicity a coil 8 constituting when suitably ener-of discrete elements insulated from one gised a magnetic electron leans of large another, may take the form of a sheet of aperture designed to form an electron material of high transverse resistance, image of the screen upon the mosaic'elecsuch as a sheet of mica, the sheet being trode.

covered on the side thereof remote from Between the electron lens 8 and the the photo-electrically active screen by a mosaic -electrode 4 is disposed an electrode conductive backing, e g a metallic plate, 9 in the orm of a cylinder of conductin;g forming a " signal plate ", a term to be material placed co-axially with the tube, hereinafter defined and explained The the purpose of which is to accelerate the teim " mnosaic electrode "where used with photo-electrons from the sereen 7 and to reference to apparatus in:which this elec collect a secondary emission of electrons trode is scanned on the side facing the which occurs from the elements of the photo-electrically active sereen is intended mosaic electrode during the operation of to include sheets of material such as the tube This electrode is held at a mica with a suitably high transverse re suitable positive potential relatively to sistance, such sheets, in effect, compris the screen 7 An optical lens system shown ing a multiplicity of mutually insulated diagrammatically at 10 is provided outelements side -the tube 1 for focusing an optical Other features of the invention will image of the object to be transmitted upappear from the following description on the side of the photo-electrically active and the appended claims screen 7 remote from the mosaic electrode The invention will be described with 4 " reference to the accompanying drawing The operation of bthe tube is as in which are, shown diagrammatically by follows: way of example two embodiments of the-: ''Electrons are emitted from the various present invention points of the photo-electrically active Referring to Fig 1, television trains screen 7 to an extent proportional to the mitting apparatus comprises a cathode ray intensity of the light falling on this tube 1 having a cathode gun 2 of any suit screen from the object The electrode 9 able kind -for generating a fine or focused accelerates these photo-electrons towards :: primary beam of electrons 8 and means the mosaic electrode 4, and the magnetic (not shown) for deflecting the primary electron lens system 8 produces a magnetic beam so that it can scan a mosaic electrode field whicdhhas the effect of focusing the

4 disposed within the tube at an acute _phto-electrons emitted from,any one angle to the -mean direction of the pri point of the photo-electric screen 7 upon marv beam 3 'a corresponding point on the mosaic elccThe mosaic electrode 4 comprises a trode 4:

multiplicity of 'elements -5 which are in Secondary electrons emitted from the 6,5 sulated from one anothey and from a bombarded surfaces of the mosaic elecommon, conductive plate 6 which will ments 5 are collected by the -electrode 9 be called a" signal "plate The elements and:the potential of each of the 'lements may be of silver, for -example, and may 5 will change in accordance with the numbe disposed upon a mica sheet which in ber of photo-electrons reaching it and turn is disposed upon an aluminium hence in accordance with the brightness "signal " plate The signal plate maydbe of illumination of the corresponding point connected to earth through a resistance on the screen 7 If the number of seconAlso disposed within the tube, in 'a dary electrons emitted exceeds the numplane substantially parallel to the plane her of primary photo-electrons arriving of the' mosaic electrode 4, is a photo-elec the element will become more positive 9 O 13,0 G 4 'n'663 not the signal plate.

In the embodiment of the invention described above the cathode ray and' the photo-electroas are ineident' upon the same face of the mosaic electrode The 70 photo-electric screen and the electron lens must therefore be disposed at some distance from the mosaic electrode in order that they may not obstruct the cathode ray Systems are kniown, however, in 75 which an optical image is projected upon one side of a mosaic electrode, and this electrode is scanned upon the opposite.

side The present' invention may be applied to such a system with apparatus 80 arranged as shown diagrammatically in Fig 2.

In the arrangement of Fig 2, the cathode ray gun 2 and the photo-eleetrically active screen 7 are on opposite 85 sides of -the nfmsaic electrode 13, which in this case consists of conductive elements 14 studded in a 'conductive signal plate and insulated therefrom, each element extending right through the plate, and 90 the plate being connected to -earth through a resistance 11 Thus +,he mosaic electrode 18 may take the form in which the signal plate is constituted by a 'wire mesh having its wires coated with glass and having the 95 conductive elements 14 in the form of conducting rivets located in the interstices of the mesh In making such a screen, one set of wires coated with glass iay be laid parallel to one another in the grooves 100 of a suitable mould,, and a second set may be laid above the -first set 'and at right angles thereto A second grooved mould plate is laid above the upper set of glass coated wires with these wires in the 105 grooves and by heat and pressure the two sets of coated wires are caused to weld together so that the upper and lower faces of the screen so formed are substantially flat, The rivets may be formed in the in 110 terstices of the mesh by plating or otherwise, but the process of making the screen forms no part of the present invention.

The picture to be transmitted is imaged upon the photo-electrically sensitive 115 screen 7 by an optical system 10 The photo-electrons are accelerated by the electrode 9 which is maintained positive with respect to the screen 7 and are focused upon the mosaic electrode 13 by 120 a magnetic electron lens 8 An electrode 16, which may be constituted as in the case of electrode 9 by a conductive coating on the walls of the envelope 1, is provided around the space between the 125 electron;giun 2 and the mosaic electrode 18 The cathode ray beam 3 from the gun 2 is defiectedodo as to scan the mosaic electrode 13 by 'means of two pairs of eleciromagnetic deflecting coils placed at 130 and if the number of primary electrons exceeds the number of secondary electrons the element will become more negative.

Each element 5 of the mosaic electrode 4 forms a small condenser with the common signal plate 6, and in between successive scans each of these small condensers is charged, as described above, to an extent dependent upon the intensity of D O the photo-current striking the element.

The velocity of the scanning beam 3 is so adjusted in relation to the nature of the mosaic surface that the pptential of each element when scanned is changed to an equilibrium value If the effect of the photo-electrons is to -raise the potential of an element, the velocity of the scanning beam is so adjusted that the scanning beam reduces the potential of the element.

This adjustment can readily be made by trial in any particular' case The condenser formed between the element 5 and the signal plate 6 is thus discharged, and the discharge current is dependent upon the charge which the condenser acquired since the last scan This is in turn dependent upon the intensity of the photo-current striking the element 5 of the condenser which is furthermore dependent upon the li'ght intensity of a corresponding point in the object Thus as the seanningg beam sweeps over the multiplicity of elements 5, there are developed across the resistance 11 in the lead to the signal plate 6 voltages which are dependent upon the light intensity of correspohding points in the object These " picture" voltages are amplified for instantie by being applied to the grid and cathode of a valve 12, and are transmitted in any known or suitable manner.

Instead of the screen 7 being, as described, in the form of a continuous photo-eleatrieally sensitive coating, it may take the form of a photo-electric coating upon a wire mesh structure Where the photo-electric coating is of the continuous type it may be formed upon a part of the wall of the tuibe envelope If the /i O photo-sensitive coating and any backing laver which may be provided is sufficientlr transparent, the image may be thrown thereon as shown in Fig 1 Alternatively the image may be formed on the side of the screen 7, facing the mosaic electrode 4, particularly in cases where the' mosaic electrode 4 is in the form of d transparent sheet, such as a sheet of mica, when the optical image may be thrown on to the photo-electric screen 7 through the' mica sheet.

It will be noted that as the cathode ray B scans'the iosaic surface it strikes either the eondueting elements 5 or else the insulating material between elements, but 442,666 right angles One pair is shown diagrammatically at 18 and 181, and one coil of a second pair at 19.

In order that the magnetic deflecting fields shall not affect the focusing field due to the coil 8, a suitable screen indicated at 17 may be placed around the tube in order to screen thle two magnetic systems from one -,another Similar screening means may be provided in tubes in which electrostatic focusing or defiecing means are used If desired such means or a part thereof (whether they act as electrostatic or electromagnetie screens or as both) may be incorporated in the interior of the tube.

It may be assumed that the electrode 16 is maintained at zero or earth potential and that the cathode of tihe' electron gun 2 is at 1000 volts The surfaces of the mosaic elements 14 facing the gun and the voltages applied are assumed to be such that the ratio of secondary electrons leaving the mosaic electrode to primary electrons' reaching it from the gun is greater than unity and the elements 14 when scanned will take up an equilibrium potential near to zero volts ' Electrode 9 may be held at 50 volts positive to earth and the screen 7 may be 'held at 500 volts.

Considering any one element 14 just after it has been scanned, its potential is nearly zero and the primary photo-electrons reaching it from a, corresponding point on the screen 7 are arranged to release a greater number of' secondary electrons, substantially-all these secondary -electrons being collected on the electrode 9 The element will thus become' more positive at a rate dependent upon the brightness of the corresponding point on the screeh 7 ' When the ray next reaches the element the potential of the element will be reduced again to its equilibrium value near zero volts.

The velocity of the photo:electrons impingin g on the mosaic electrode is ' so great that the weak reverse eleetrostatie field between electrodes 9 and 13 will not appre'eiably distort the' photo-electron stream On the other hand the slow mova ing secondary electrons will substantially all be drawn on to the electrode 9.

One advantage of the arrangement just described is that a so-called double sided mosaic electrode can be used with the attendant advantage that both the optical axis of the system 10 and the electron gun axis can be arranged normal to the mosaic, electrode Furthermore the arrangement permits an amplified response to be dbtained because the ratio of secondary electrons to primary photo-electrons can be maintained greater than unity Having -now particularly described and ascertained the nature ot our said invention and in what manner tihe same is to be performed, we declare that what we claim is 70 1 A method of transmitting images of an object to a distance whereia an optical image of the object to ibe transmitted is projected upon a photo-electrically active' screen, photo-electrons emitted from said 75 photo-electrically active screen are accelerated towards a mosaic electrode of.

mutually insulated elenents spaced apart from said screen and are focused upon the electrode to form an electron image, there 80 on by means of an electron lens systenm, and said mosaic electrode is scanned by a primary beam of electrons such as a cathode ray.

2 A method according to claim 1, 85 wherein the velocity of said photo-electrons on impact with the elements of said mosaic screen is such that there are emitted from said screen secondary electrons greater in number than the incident 90 photo-electrons, whereby each element acquires a positive charge in the intervals between scans.

S A method accordine to either of the preceding claims, wherein said mosaic 95 electrode is scanned on the side remote from said photo-electrically active screen.

4 Apparatus 'for transmitting images of an object to a distance, said apparatus omprising an optical system for projecting an image of the object' upon a photoelectrically -active screen, a mosaic electrode comprising mutually insulated elements this electrode being spaced apart from said screen and being arranged with 105the screen within an evacuated envelope, focusing means for causing the, electrons emitted from said screen to form an electron image upon said mosaic electrode, means for developing a beam of electrons 110 and means whereby said beam of electrons can be caused to scan said mosaic elec, trode, Apparatus according to elaim 4, wherein said focusing means coniprise a 115 coil surrounding only a small-part of the spaoe between said screen and said mosaic electrode.

-6 Apparatus according to claim 4 or 5, wherein the scanning beam of electrons is 120 arranged to fall upon the side of said mosaic,electrode remote from said screen.

7 Apparatus according to any of claims' 4 to 6, wherein said photo-sensitive screen is at least partially transparent 125 8 Apparatus according to any of blaims 4 to 7, wherein an electrode is provided in the space between said screen and said mosaic electrode for 'collecting secondary 1 electrons emitted by said mosaic electrode 130 442,666 claims 4 to 11 wherein the focusing means for the photo-electrolns comprise means for developing an electrostatic or a magnetic 25 focusing field and wherein the deflecting means for the soanning beam of electrons comprise means for developing an electrostatie or a magnetic field under the, control of scanning oscillations, characterised by 30 the provision of a screen for screening the focusing means from the deflecting, means.

14 A method, of transmitting images of an object to a distance substantially as herein'described 35 Apparatus for transmitting images of an object to a distance substantially as herein described with reference to the accompanying drawing.

Dated this 1th day cf April, 1935.

REDDIE & GR 1 OSE, Agents for the Applicants, 6, Bream's Buildings, London, E C 4.

9 Apparatus according to any of claims 4 to 8, wherein the scanned surface of said mosaic electrode is composed of surfaces of mutually insulated conducting elements having insulating material extending over the space between them.

Apparatus according to' any of claims 4, 5, 7 or 8 wherein the mosaic electrode is in the form of a sheet, of material such as mnica having a high resistance in directions parallel to its surface.

11 Apparatus according 'to any of claims 4 to 10, wherein the photo-electrically active screen is provided with a continuous photo-eleetric coating.

-12 Apparatus according to any of claims 4 to 11, wherein said screen is in the fdrmn of an imperforate sheet of insulating 'material provided with a coating of photo-electrically sensitive material.

138 Apparatus according to' any of London: Printed for His Majesty's Stationery Office, by Charles & Read Ltd 1949.

442,666