Patent GB-377175-A (GB)
Title: Improvements in or relating to methods and apparatus for the transmission of pictures
IPC: H04N3/32
Filed: 1931-02-19
Abstract: 377,175. Television and copying- telegraphy. THUN, R., 57, Waldstrase, Schoneiche, Post Fichtenau, Germany. Feb. 19, 1931, No. 5325. Convention date, Feb. 20, 1930. Addition to 355,319. [Class 40 (iii).] The system described in parent Specification relates to a method and means for picture transmission in which a scanning beam is moved across the picture with a velocity which is varied automatically in accordance with the fineness of structure of the portion of the picture being scanned at any instant. According to the present invention the system of the parent Specification is modified by the incorporation of means which are effective when the scanning beam has reached the end of a line to return the beam to the beginning of the line and to effect the movement of the member carrying the picture or the displacement of the scanning beam for the transmission of the subsequent line on the picture. The scanning beam emanating from a light source 4 is reflected from the mirror 6 of an oscillograph 6a, 6b to scan the picture or film 2a carried on sprockets 2 driven by a flexible coupling or slip clutch from a motor 10. The light-beam impinging on a photo-electric cell 8 is varied in intensity by the structure of the film, and the voltage variations are impressed on a condenser 30, and on an amplifier valve 32, in whose output circuit is an amplifier 13, whose output circuit is connected to a further amplifier 39 leading to the line, to a coil 6a of the oscillograph and to a controlling coil 12a of an electromagnetic device operating a ratchet and pawl mechanism effecting the stepping forward of the shaft carrying the film sprockets. During the scanning of a line the condenser 30 is charged from a battery 31 under control of the photo-electric cell 8, and at the end of a line the voltage and current are arranged to be of such a value as to effect the energization of the ratchet-control coil 12a which releases the shaft 3 for a slight rotation so that over a contact device the discharge of the condenser 30 is effected and oscillograph mirror 6 is rapidly returned to the position in which the light beam is at the beginning of a fresh line. To prevent the ratchet pawl from returning to arrest the shaft 3 before it has advanced one tooth, a temporary holding circuit is maintained through the coil 12a by the discharge of a condenser 12d. The strong impulse for the operation of the coil 12a may be obtained by allowing the light beam to impinge on a narrow band on the film 2a which is either much darker or much lighter than the darkest or lightest portions of the film. Alternatively, Fig. 3, the control may be effected by allowing a beam from a subsidiary source 4a to impinge on an additional photoelectric cell 8a when the scanning beam from the light-source 4 has reached the end of a picture line. At the receiving end, the varying voltages are applied to an amplifier 28 and to the control coil 19a of a mirror oscillograph, from the mirror 19 of which a light beam from a source 19c is reflected to a mirror 53 and to a screen .53a where the picture is reproduced by the variable velocity of the beam from a constant light source. To produce the line spacing, the mirror 53 is continuously changed in inclination at the end of each line by a cam 20 on the shaft 24 which is stepped forward at the end of each line by the energization of a ratchet-control coil 27a effecting at contact 125, the discharge of the condenser 27d and the return of the oscillograph mirror. The picture may additionally be reproduced on a sensitized film 201 carried on sprockets 200 on the shaft 24 and mounted behind a slotted diaphragm 203 across which the lightbeam is moved by the oscillograph mirror 19. The ratchet control member of the receiving end is shown in Figs. 5, 7. The electromagnet is provided with a biasing winding 27b and an operating winding 27a by which an armature 27, formed with a tapered end, is actuated to control a ratchet wheel 26. A cam 20 on the shaft 24 controls through an abutment member 52b, which is adjustable at 52c, a member 52 carrying the mirror 53 and effecting by altering the inclination of the mirror at the end of each line, the second component of scanning when the image is reproduced on a screen. A step 20a on the cam 20 returns the mirror to a position to produce the first line of the succeeding picture. Modification of the system using cathode rays. In the system illustrated in Fig. 15, the scanning is effected by a cathodic beam of constant intensity which is displaced at the end of each line to effect the scanning of the subsequent line and after the scanning or reproduction .of a number of lines is returned to its original position. The scanning apparatus comprises a Braun tube 71 having pairs of plates 70, 72 which effect the movement of the cathode beam along the lines and transversely of the lines, respectively. The feeding of the lines is effected by a condenser 3<1> which is charged by equal increments at the end of the scanning of each line and during the return movement of the beam of cathode rays. At the end of a number of lines corresponding to the complete picture, the glow discharge tube 74 operates to pass current and to discharge the condenser 3<1> so that the plates 72 restore the scanning beam to its original position. The movement of the scanning beam is obtained by the action of the condenser 30 in conjunction with the glow-discharge tube 91 through which the condenser 30 is short circuited at the end of a line and with the photoelectric cell 8 which is illuminated through the film 2a from a fluorescent screen 71a exposed to a cathode beam of constant intensity but of varying velocity. At the receiving end the image is viewed on a fluorescent screen 78a subjected to a cathodic beam of varying velocity and displaced in line-by-line manner by the operation of the condenser 24<1> in conjunction with the glow-discharge tube 82. Construction of oscillograph. The oscillograph controlling the mirror 19 at the receiving end comprises an iron yoke 19f with a core 19e on which are mounted control and biasing windings 19a, 19b respectively. A spring member 60 secured to the yoke 19f is tapered towards the free end at which the mirror 19 is attached, and is restrained by damping means 62, mounted on a holder 61. Cooperating with the moving spring member 60 is a member 58, normally fixed, but carried on an adjustable supporting member 63. The mirror 19 is mounted on knife-edges formed on the members 60, 58 and is held against lateral movement by adhesive supports 57. Spring extensions 59a, 59b formed on a retaining member 59 secured to the member 58 maintain the mirror 19 against the operating knifeedges. A projection 60b on the spring 60 limits the outward movement of the member 60 by engagement with a shoulder associated with a notch 60c formed in the member 58. The range of movement of the mirror is adjusted by movement of the member 63 by means of a thumb screw 65. The Specification as open to inspection under Sect. 91 (3) (a) states that the apparatus may be utilized for the transmission and reception of coloured or stereoscopic pictures. This subject-matter does not appear in the Specification as accepted.