Patent GB-845762-A (GB)
Title: Method and apparatus for image reproduction
IPC: G03G15/34
Filed: 1957-04-01
Abstract: 845,762. Copying by scanning. ADDRESSOGRAPH-MULTIGRAPH CORPORATION. April 1, 1957 [Sept. 21, 1956 (2)], No. 10599/57. Class 40(3). In an arrangement for reproducing an image by scanning a sheet of dielectric material with a suitable electrode carrying modulating signals representative of the image so as to form an electrostatic charge pattern corresponding to the image which pattern is rendered visible by "dusting" the dielectric material with a suitable medium which adheres thereto by electrostatic attraction, the "dusting" medium is supplied simultaneously with the scanning action in the region immediately adjacent the scanning electrode. Fig. 1, shows the basic arrangement in which the dielectric material, comprising a paper web 18, is scanned, transversely of its length, by means of a scanning head 30 carrying a plurality of stylii rotated by a motor 42 synchronously with the scanning action at a facsimile transmitter 41, 42 the image signals generated by which are supplied, with positive polarity, to the scanning head 30. The web 18 is moved past the region of the head by the motion of a conducting drum 10 maintained at earth potential by a brush contact 13 and the curved surface of which is covered by an insulating coating 15. In operation, the coating 15 is brought to earth potential (to remove any charge thereon) by means of a blade 22 (which also serves to separate the web 18 from the drum) and may in addition be given a negative charge by means of a contact member 17 (or by means of a discharge grid electrode 39) so that, as the drum rotates in the direction of arrow 12, a uniformly charged portion of the coating 15 comes under the web in the region scanned by the head 30. The charge pattern formed by the scanning action is then simultaneously developed into a visible image by flooding the region immediately adjacent the path of the stylii with suitable developer material 36 (e.g. electroscopic powder) from a hopper 33 (maintained at earth potential) any excess powder falling into a receiving hopper 35 from which it may be transferred to the discharge hopper 33 by known means. As the drum continues rotating the web 18 carrying the now visible image is separated therefrom by the blade 22 and, when the developer 36 comprises heatsensitive materials, passed through a "fixing" zone established by heater elements 25, 26 which render the image permanent. Other known development and "fixing" techniques may be employed if desired. Fig. 2 shows the construction of the scanning head 30 which comprises a plurality of stylii 45 spring urged outwardly from a central hub 50 so as to remain in contact with the paper web 18 during scanning. To prevent the stylii from tearing the web at the commencement of each traverse the dielectric coating 15 is provided with a raised edge portion 56. In an alternative construction (Fig. 3 not shown) the stylii may project from the periphery of the hub parallel to the axis of rotation thereof, the scanning trace in this case comprising arcuate lines instead of linear ones as produced by the head shown in Fig. 2. Instead of being resiliently mounted the stylii may be L shaped and extend radially from the hub. Fig. 4 shows a second embodiment in which the paper web 68 is in direct contact with the earthed drum 60 (the insulating coating 15 of Fig. 1 being omitted) and scanning to form the charge pattern effected by means of a rotating head 80 provided with a helical electrode (Fig. 5 not shown) forming a "lawn-mower" type of scan. Development of the charge pattern, in this case, is effected by driving developer material (contained in a receptacle 91) towards the region over which the scan is effected by means of an impeller 92, the surplus material returning to the bottom of the receptacle for recirculation and "fixing" of the image is subsequently effected by means of pressure rollers 74, 75. In a further embodiment Fig. 6, (which is generally similar to the embodiment of Fig. 1) the stylii carried by the rotating scanning head 230 are of hollow construction and by means of an impeller 239 and feed conduit 238 are continuously fed with developer material 236 which is thus applied to the web 18 simultaneously with the formation of the charge pattern. The image is then "fixed" as described in connection with Fig. 1. The construction of the head 230 is shown in Fig. 7 each stylus 264 being in communication with the feed conduit 239 so as to be continuously supplied with developer material. To prevent the stylus bore outlet from being closed by contact with the web 18 the opening 279 is formed as shown in Fig. 8, Instead of employing hollow stylii the latter may be of solid construction, as shown at 284 (Fig. 9), formed integrally with a hollow tubular member 285 through an opening 286 in which developer material fed from the feed conduit 238 is ejected adjacent the tip of the stylus. Instead of projecting radially from the scanning head the stylii may be peripherally mounted parallel to the axis of rotation (Fig. 10, not shown). Specification 690,162 is referred to.