Patent GB-1057006-A (GB)
Title: A facsimile printer
IPC: H04N1/29
Filed: 1964-08-04
Abstract: 1,057,006. Copying by scanning. RANK XEROX Ltd. Aug. 4, 1964 [Sept. 9, 1963; Sept. 16, 1963], No. 31337/64. Heading H4F. In a facsimile printer comprising a rotating conductive drum cylinder 10a coated with a photoconductive layer 10b e.g. amorphous selenium, and a stationary length of transparent insulating material 11a mounted so as to touch the photoconductive layer and having coated on, or embedded in, its surface parallel to the axis of rotation of the cylinder 10a a strip 11c of transparent conductive material between which and cylinder 10a a variable voltage corresponding to a video signal is applied, the arrangement is such that when a linearly scanning light spot of constant intensity is projected through transparent strip 11c and transparent insulating layer 11a on to the photoconductive layer, the photoconductive layer becomes conductive and electric charge is deposited on its surface, the magnitude of the charge varying as the applied voltage corresponding to the video signal. The electrostatic image thus formed on the insulating photoconductive layer is then developed by allowing it to collect finely divided powder particles which are later transferred to a permanent support e.g. a sheet of paper. The photoconductive layer is then cleaned by revolving fur brushes and any residual charge is removed by a discharge lamp before it is reused. The light spot is arranged to linearly scan the selenium-coated cylinder causing it to become conductive so that positive charges corresponding to the applied video voltage will flow from the drum to the surface of the selenium layer and become trapped thereon upon separation of the insulating and selenium layers (explained with reference to Fig. 3, not shown) by means of a flying spot scanner, Fig. 1 (not shown), or a rotating reflecting polygon. The length of strip 11c is at least equal to the line scan length of the light spot and its width is slightly greater than the spot size. To help hold the insulating material 11a in contact with the selenium surface a conductive strip 11d having a negative bias is coated on, or embedded in, the insulator surface parallel to and upstream from transparent conductor 11c. To prevent attenuation of the electrostatic image i.e. prevent positive charge being transferred from the selenium surface 10b to the insulator surface 1 la during their separation, a polarity-reversing positive potential element 11e is coated on, or embedded in, the surface of insulator 11a downstream from transparent conductor 11c (explained with reference to Fig. 4, not shown). Alternately the electrostatic image may be formed by a charge induction deposition method depending on positive charge moving toward the conducting drum cylinder, the selenium surface being charged by a positive ion source 15 before the process begins (the basic principles of this method are explained with reference to Fig. 4, not shown). In further embodiments, Figs. 6 and 7 (not shown), the induction apparatus (11a, 11c, lie) is mounted on a transparent inductor body and a gas film is produced between the seleniumcoated cylinder and the inductor body either by coupling a gas source to a passageway in the inductor body or by hydrodynamic gas-bearing principles. In a further embodiment, Figs. 8 and 9 (not shown), the length of transparent insulating material 11a is replaced by an endless and transparent flexible belt (111) that is maintained in firm contact with a small part of the surface of the selenium-coated cylinder by a pair of pressure rollers and comprises a transparent conductive coating (111a) sandwiched between a transparent dielectric material (111b) and a transparent backing layer (111c) that provides strength and protection. Conductive contact strips (111d) and (111e) are located along the edges of the belt flush with the backing layer (111c) and in contact with the conductive coating (111a) so that the video voltage which is applied between the drum cylinder and pressure rollers is actually applied between the drum cylinder and the transparent conductive layer (111a). The electrostatic image is then formed as before. In a further embodiment, Figs. 11 and 12 (not shown), a segmented belt (111) is used comprising a transparent dielectric layer (124) over which is mounted a second layer made up of transparent conductive segments (125) narrowly separated from each other by similar segments (126) of a transparent and highly-resistive material, these layers being backed by a transparent layer (127) having a plurality of conductive contact elements (128) embedded in it along its edges superimposed upon transparent conductive segments (125). The video voltage signal is applied between the drum cylinder and the conductive segments (125) by applying it between plurality of metal wheels (130) which make contact with elements (128) and the drum cylinder, at least one of the contact wheels (130) being in contact with a conductive element (128) at all times, said conductive element (128) being coincident with the plane of the scanning light spot. A positive potential is applied to the pressure roller downstream from the metal wheels (130) to prevent the image charges from leaving the drum cylinder surface during the separation.