Patent GB-1391019-A (GB)
Title: Scanning apparauts
IPC: H04N1/06
Filed: 1973-10-12
Abstract: 1391019 Facsimile scanners PERKINELMER CORP 12 Oct 1973 [13 Oct 1972] 47694/73 Heading H4F [Also in Division G1] A scanner employed in a facsimile transmission system includes a drum for supporting the material to be scanned together with a hollow tubular member, coaxial with the drum, and through which scanning radiation is directed such that surface of the drum is scanned when either the drum or the tubular member is rotated about and translated along the common axis, the surface of the tubular member, or of the drum, having a region of reflectivity differing from the remainder of the surface and the region being shaped such that, when relative movement between the drum and the tubular member occurs, signals are produced, via an optical pick-up device, which signals indicate, by their spacing and duration, the relative rotational and translational position of the member (drum or tubular member), which moves. Fig. 1 shows one embodiment in which the drum 14 is stationary and the tubular member 24, supported by air bearings 20, is rotatable about and translatable along the common axis by means of, respectively, a winding 26 which forms an eddy current motor and a winding'28 which forms a linear induction motor so that the radiation beam, derived from a laser 38 and directed via mirror 34 produces a spiral scan of the material D which is placed inside the drum via a door 16. When the arrangement is operated as a "reader" (i.e. to produce video signals by scanning, e.g. a document), a (e.g. acoustic), modulator 40 through which the laser radiation passes is inactivated, and the radiation beam is expanded by means 50 and reflected by a small mirror 48 carried by a window 46 after which the beam is collimated by lens 52 and then focused on the document by lens 32 via mirror 34. To prevent damage (e.g. scorching), to the document the laser power is reduced by reducing the power to the pump lamps or by introducing a neutral density filter in the path of the beam and to prevent specular reflection back to the laser (which would shut it off), the angle of mirror 34 is other than 45 degrees and in practice is made 52À5 degrees. The diffuse reflection from the document is then redirected by the mirror 34 through the lens 32 which collimates it and via lens 52 which focuses it via window 16 on an optical pick-up device 54 by which the video signals are generated. In this embodiment the region of different reflectivity is provided on the tubular member 24 and comprises a shaded triangular area 62 (Fig. 3), which in co-operation with an optical pick-up device 30 produces on each rotation of member 24, a pulse (see Fig. 4), the leading edges of which (caused by the "leading-edge" 62a of the shaded area), occur at equal time intervals for a constant rotational speed whilst the trailing edges (caused by the "trailing-edge" 62b of the shaded area), occur at intervals which are a measure of the linear position of the member 24. Thus the repetition frequency of (the leading edges of), the pulses is a measure of the rotational speed and the lengths of the pulses a measure of the linear position. The pulses so generated and the video signals together with a "start" signal are encoded and transmitted to a remote "writer" scanner by which the document is reproduced (Fig. 5, not shown). The basic scanner may be operated as a "writer" by replacing the window 46 and small mirror 48 by a large mirror, producing a beam of sufficient width to "fill" such mirror by means of the expander means 50, positioning a photographic film inside the drum and supplying the decoded video signals to the modulator 40 and employing the decoded position control (synchronizing), signals to control the rotation and translation of the tubular member 24 (also Fig. 2, not shown). In a second embodiment, particularly useful for scanning transparencies, the drum 70 (Fig. 6), has a transparent surface 72 and is mounted on tubular members 74, 76 for rotation and translation in air bearings 78, 80 laser light being directed via a hollow stationary tube 8 and focused on the transparency which is mounted on the surface 72 the light passing through the transparency being detected by stationary pickup device 88. By inverting the polarity of the video signals a negative may be transmitted as a positive or vice versa and if the reader and the writer rotate in opposite directions a mirror image is produced.