Patent GB-293093-A (GB)
Title: Apparatus for selecting the luminous points of an image for reproduction by television
IPC: H04N3/04
Filed: 1927-03-26
Abstract: 293,093. Brun, E. J., (known as Brun, S.). March 26, 1927. Television.-An exploring or reconstituting device for television comprises two coaxial discs 6, 8, rotated at slightly different speeds, the one provided with straight radial slots 6<1> and the other with straight slots 8<1>, Fig. 1, inclined at 30‹ to 45‹ to the radius. Synchronism is obtained by the use at each station of a centrifugally-controlled driving motor and a periodic braking and release of the driven mechanism under control of a local clock. The inner and outer shafts 4, 7 carrying the discs 6, 8 respectively are driven through gearing from the motor shaft 3 at a predetermined difference of speed corresponding to one revolution in each exploration of the image; 10, 11, or 12 images are explored per second according to the gearing adopted. To enable the width of the slots 6' and 8<1> to be .adjusted each disc may be constituted by two similar angularly adjustable superposed disc members. Carrier current for transmission. A screen of closely arranged fine wires, each wire extending radially of the axis of the discs, may be placed between the scene and the apparatus at the transmitting station to produce light-interruptions acting on the photoelectric cell to generate a carrier current. Transmission of colours. A number of red, yellow, and blue screens may be used to cover particular slots in the discs 6 and 8, the arrangement in this respect being precisely similar at the two stations, to enable colour television to be effected. Synchronizing arrangements. The motor shaft 3 at each station drives a countershaft 5 through gearing such that shaft 5 makes normally one revolution per image explored. The speed is controlled by a centrifugal governor on shaft 5 and a periodic light braking action is effected, under control of a clock 22, Fig. 9, by the engagement of a spring 16, Fig. 6, with a projection 15 on a disc 14 secured to to shaft 5. Vibration of the spring 16 is damped by a spring-pressed plate 19<c>. The clock closes once per second a contact in a circuit including a solenoid 21, Fig. 7, and a commutator switch 23, Fig. 5, carried by the shaft 5. When contact is closed by the switch simultaneously with the closure by the clock the solenoid 21 is energized to operate a lever 20 for turning the mounting 17 of the spring 16 about a pivot 19<a>, Fig. 6, thus removing the spring from the path of the projection 15 until the solenoid 21 is de-energized. The speed of the shaft 5 is thus controlled so that the projection 15 passes the spring 16 once per image. Synchronism as distinct from isochronism is attained by rotating the switch 23 at the receiving station until the image comes correctly into view. A shaft 11 carrying a dial 25 graduated in fractions of a second is driven from the shaft 5 through worm gearing such that its speed is one revolution per second when the shaft 5 makes one revolution per image. The shaft 11 carries also a cam 26 acting through a lever 27 to close at each revolution a contact 34, 35 for supplying impulses to drive a clock mechanism 28, Fig. 9, enabling the speed of the shaft 11 to be checked against the main clock 22.