Patent GB-485622-A (GB)
Title: Method and apparatus for television scanning
IPC: H04N3/08
Filed: 1936-11-18
Abstract: 485,622. Television. CLOTHIER, S. L., and HOGENCAMP, H. C. Nov. 18, 1936, No. 31652. Convention date, Nov. 18, 1935. [Class 40 (iii)] A method of television reception, in which a beam of modulated light issuing from an aperture is projected for line scanning on to mirrors tangentially disposed on a rotating disc, and thence on to an oscillatory mirror for frame scanning, is characterized by the production of an image in space of the illuminated aperture, between the rotating disc and a screen, and the formation from the said image of an image on the screen. The invention is also applicable to transmission, with substitution of an illuminated object for the screen, and a photoelectric cell for the light modulator, the path of the light beam being reversed in this case. The Figures show a receiver in which a beam passing through a light-modulator L (controlled by the received impulses, e.g. through a Kerr cell), and through an aperture 16, is caused to scan a screen S by the action of a high-speed disc D carrying on its periphery a large number of mirror elements, and a vibratory mirror N. The disc may have its edge formed into reflecting surfaces, there being at least 90, and preferably 360 such surfaces, or separate mirrors may be attached thereto. It is driven by a synchronous motor 22, synchronized with the transmitter. The oscillatory mirror M is actuated by a cam C in conjunction with a spring T. The cam is driven by a motor 39, which is preferably synchronized either mechanically or electrically with the motor 32. The lens system 17 employed with the light-modulator L is adapted to form an image of the aperture 16 in a plane between the disc D and the screen S, and a lens 53 forms upon the screen an image of the image in space. The image so formed on the screen represents a single elemental area of the received picture. Various adjusting means are provided. For example, worm and wheel gearing 25 may be employed for adjusting the position of the motor field, or the whole motor may be rotatable on its cradle 27 or movable vertically : the motor 39 may have a similarly adjustable field, and it may be slidable on guide rails 41 : the frame 32 in which the mirror M is mounted may be adjustable vertically: an arm, adjustably secured on the shaft of the mirror M carries a sleeve 45 for variably positioning a roller 44 engaging the cam C by which the mirror is vibrated. Instead of using a cam as shown to produce a uniform scanning motion of the mirror in one direction followed by a quick return motion, a twin spiral cam may be provided, to produce uniform scanning movements in both directions. Alternatively, the cam may be otherwise formed, to produce irregular scanning movements, which must correspond to scanning movements produced at the transmitter. Instead of operating the mirror by a cam, an oscillograph may be used, operated by saw-toothed electrical oscillations. To enable the screen S to be placed closer to the mirror M, the angles of divergence of the reflected beam may be increased by making the mirror slightly convex. The Specification as open to inspection under Sect. 91 also describes the use of a slowly rotating mirror drum in place of the vibrating mirror. This subject-matter does not appear in the Specification as accepted.