Patent GB-951469-A (GB)
Title: System for large-area display of two-colour information
IPC: G03G15/01
Filed: 1961-03-10
Abstract: 951,469. Television. STANDARD TELEPHONES & CABLES Ltd. March 10, 1961 [March 14, 1960], No. 8857/61. Heading H4F. A large area display system for image information in two colours comprises a relatively thin sheet of transparent dielectric material 70 which is traversed over rollers 24, 26 by drive motor 32, and first and second transverse rows of electrodes 40 for forming charge patterns on the material in accordance with the information to be displayed, a device 66 for applying charged toner material in a first colour, e.g. black, being provided adjacent the outer surface of the material following the first row, and a device 68 for applying charged toner material in a second colour, e.g. red, being provided adjacent the inner surface of the material following the second row. After forming the image, the material may be stopped to permit viewing when the image is positioned adjacent an opaque backing shield 72 and an aperture in a front shield 94. Alternatively the material motion may be continuous. Erase heads 92 are provided so that a recorded image may be removed and the material used for a further recording. The information to be displayed is made available in the form of conventional television-type signals the vertical sweep generator 76 which controls the production of the signals being synchronized with the drive motor 32, and the horizontal sweep generator 74 being synchronized with the operation of switching devices 44 and 46 by which the electrodes in the rows are brought successively into operation. Signals representative of the colours for a particular position in the image field are available simultaneously, but since the second colour is recorded at a position spaced from the first, the second colour signal is delayed appropriately in a device 64 and the control signal to switching device 46 is delayed correspondingly in a device 62. The invention, which is stated to be used for the display of words, numbers, maps and graphs, is described as applied to a system, Fig. 3 (not shown), for displaying a page of characters in response to a digital pulse-code signal. The characters are selected from and generated one at a time by a monoscope tube which is scanned over the selected characters in a conventional television raster and are first read into a cathode-ray storage tube where they are positioned on the target in a desired order and also recorded at one of two possible signal levels to indicate in which of the two colours they are each to be produced. When a complete page of characters has been recorded, the whole page is read out as one image by a raster which scans over the whole target and the resulting signals are applied to the large area display system. Limiter circuits responsive to the two possible signal levels determine to which of the rows of electrodes the signals are applied. The switching arrangement for a row of electrodes is shown in Fig. 4 where there are 1024 electrodes in the row formed into 32 groups 40-1, 40-2, . . . 40-32, each of 32 electrodes. Each group of electrodes is associated with a single backing electrode 42-1, 42-2 . . . 42-32. The switching is controlled by a 256 kc. pulse generator which triggers first and second 32-step counters 168, 212. The first counter 168, via a diode matrix 180, controls the electrode groups 40-1, 40-2 . . . 40-32 which have corresponding electrodes in each group connected in parallel, whilst the second counter 212, which steps once for each complete cycle of counter 168, controls the backing electrodes via diode matrix 214 and modulator stages 52-1, 52-2, &c. The video signal is applied in common to the cathodes of the modulator stages. Specification 936,967 is referred to.