GB1001546A - Improvements in the production of electrostatic charge patterns - Google Patents

Abstract

1,001,546. Electric digital data stores; electrostatic recording. L. E. RAVICH. Nov. 24, 1961 [Nov. 25, 1960], No. 42065/61. Headings G4C and G5R. [Also in Divisions G2 and H1] A charge pattern is produced on a layer of photo-conductive insulating material by illuminating it with light to produce free charges and then separating the charges by an alternating electric field to provide a positive charge pattern on both faces. For instance the sheet may be illuminated in a pattern and the charges separated by a uniform or non-uniform field, or the sheet uniformly illuminated and the charges separated by a non-uniform field. Another possibility is to uniformly illuminate, apply a uniform field and then locally remove the charge on one or both faces by shining a pattern of light on it with the faces externally short-circuited to produce a negative image. If the light is heavily absorbed by the sheet the image appears only on the illuminated face, in which case a different image can be formed on the opposite face. Otherwise the same pattern appears at both faces. A negative image may alternatively be obtained by locally recombining the free charges produced in a first uniform illumination by illuminating again with a pattern of infra-red light before the alternating field is applied. The stored information may be read off by mechanically scanning a probe over one face of the sheet as illustrated in Figs. 4 and 5 (Fig. 4 not being shown). The probe connects the element in a series circuit including a resistor the voltage across which is amplified and then displayed on a cathode-ray tube. In the digital storage system shown in Fig. 8, the information is fed in in one of the above ways as a scanning light beam from cathode-ray tube 70 which is switched on or off in accordance with the information to be stored at a particular point. After separating the charges by an alternating field information can be read out by scanning with a uniform intensity light beam, the amplified information read out being displayed on cathoderay tubes 92, 86 synchronized with the scanning tube. Information may alternatively be fed in by a uniform intensity scanning beam projected through a patterned mask. In a modification of this system using an insulating sheet with sets of mutually perpendicular electrodes on opposite faces electronic switching is used to apply the separating field in accordance with signal information only to selected areas of the sheet. In this case charges are separated only at areas which are illuminated and subjected to the field. It is also possible to subsequently illuminate. with a further information containing pattern with the electrodes externally shorted to erase some of the information thus stored. Specification 672,767 is referred to.