GB1473215A - Electrostatic imaging system - Google Patents

Abstract

1473215 Copying by scanning J ST CLAIR KILBY 18 April 1974 [19 April 1973] 17030/74 Heading H4F [Also in Divisions B6 G4 and H1] A printing head includes a one- or twodimensional array of discrete electrode areas formed on a semi-conductor substrate, associated circuitry also being formed in the substrate so as to selectively charge the electrode areas to attract a toner including charged particles, for subsequent transfer to a sheet of paper. The electrode areas may be metallized areas or semi-conductor areas of one conductivity type (e.g. P-type) separated by semi-conductor regions of the other conductivity type. The charge on the electrode areas may be controlled in response to applied electric signals from a facsimile scanner or, for alphanumeric reproduction, a computer, the associated circuitry being in the form of shift registers controlled by first and second shift clock pulses and third transfer clock pulses for transferring the charges to the electrode areas. The printing head 10, Fig. 7, may be fixedly mounted on a shaft 152, a pair of cam plates 156 and three magnetic brushes 154 for stepwise, clockwise rotation. In the position 156a, shown in dotted lines, of the cam plates 156, head 10 is in contact with a sheet of paper carried by a platen 162, a transfer voltage applied to electrode 166 causing toner to be transferred from head 10 to the paper 158; cam plates 156 are then rotated, when the next line of signals has been read into the shift registers and paper 158 has been moved by one line-width, cam plates 156 rotating plates 162 about an axis 166 away from head 10 and passing one of the magnetic brushes 154, which has passed through a toner bath 157, near the face of head 10 to transfer toner thereto for the next line to be printed. The electrode areas may be in a one-dimensional array, each area being split into three or four sub-areas to provide for the reproduction of half-tone images (Fig. 14, not shown). In alternative embodiments either each electrode area has a phototransistor associated therewith, light of a desired pattern being shone on to the array, or an electrode of a desired pattern may be placed in close proximity to the electrode areas and resistively or capacitively coupled thereto. In either case the apparatus may include a drum 570, Fig. 28, carrying a font of characters, the drum being rotated to select a desired character, in the form of a transparency or an electrode, a light being shone through the desired transparency of a voltage being applied to the desired electrode to transfer a latent image to printing head 302a; drum 570 is then indexed to the next character position and the process repeated. When a whole line has been formed as a latent image on head 302a a toner is applied to the head, and from there to paper. A drum 570 may be provided for each character position in the line. Alternatively the font of characters may be formed on a non-conductive tape (602, Figs. 30, 31, not shown) carried by pulleys between the printing head and a plurality of light sources or electrodes, or it may be carried on a partcylindrical array (662, Fig. 32, not shown) having a font of characters for each character position in a line and partially surrounding a drum carrying the printing heads.