Patent GB-274870-A (GB)
Title: Improved picture telegraph system and transmission scanning arrangements therefor
IPC: H04N1/04
Filed: 1927-07-19
Abstract: 274,870. Siemens & Halske Akt.- Ges. July 20, 1926, [Convention date]. copying-telegraphs.-In an exploring arrangement for copying-telegraph transmission, having a picture carrier movable in relation to a rotating optical system, the light-sensitive cell rotates with the optical system. Figs. 1<a> and 1<b> show one arrangement for exploring simultaneously two pictures or sets of pictures each mounted on a band a which during the exploration is unwound from a drum h and rewound on a drum i. Each band passes between an outer pair of rings f and an inner pair of rings g, each ring being concentric with a hollow rotary spindle k carrying a mirror e, a lens b, and a photoelectric cell c. Light directed through the spindle is reflected by the mirror e and directed by the lens b on to the curved portions of the bands a, and the light reflected from the bands is incident on the cell c. Alternatively, the light source, the optical system, and the photoelectric cell may rotate around the picture carrier. Figs. 2<a> and 2<b> show an arrangement for exploring simultaneously the pictures on four bands a without curving the bands. The bands move radially in one plane towards an axis k, and each is turned at right-angles before reaching the axis. The light, directed axially, is reflected at right-angles by a mirror i to a mirror h reflecting through a lens b on to a band a and the light reflected by the bands is incident on a photoelectric cell c as the mirrors hand i, lens b, and cell c rotate together about the axis k. Fig. 3<a> shows an arrangement for exploring a single band a by a pencil of light traversing the band twice during each rotation of the optical system and the cell c. The receiving arrangements are similar, the photoelectric cell being omitted, and the pictures reproduced on lightsensitive bands. These, after exposure, may pass through developing, rinsing, and fixing baths in the receiver or in a separate dark room. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the following subject-matter. (1) To enable the whole time of rotation of the members h, b, and c, Figs. 2a, 2b, and 3<a> to be utilized, a system of mirrors may be employed such that when a pencil of light from one mirror reaches the edge of a band a, a pencil from another mirror is substituted for it. (2) A reciprocating movement of the exploring pencil may be used instead of the movement of rotation. (3) In all cases the movements of the exploring device and of the band or bands a may be interchanged. (4) More uniform exploration of the bands a at all parts of the exploring cycle may be obtained, e.g. in the arrangements described with reference to Figs. 2<a>, 2<b>, and 3a, by the use of optical wedges or shutter devices in the exploring pencil of light. (5) Various methods are described for minimizing the effects of non-uniform exploration of a band a. These include the superposition on the picture transmission current of a compensation current varying synchronously with the exploring movements, the application of such a compensation current to the magnetic field of the string galvanometer or to the Kerr cell employed for the photographic reproduction, and the variations of the intensity of the light source at the transmitting or the receiving station synchronously with the exploring movements. (6) The reproduction of the pictures may be effected electrochemically. This subject-matter does not appear in the Specification as accepted.