Patent GB-948138-A (GB)
Title: Electrostatographic apparatus
IPC: G03G15/08
Filed: 1960-02-05
Abstract: 948,138. Electrostatographic apparatus; document and microfilm copying. RANK-XEROX Ltd. Feb. 5, 1960 [Feb. 6, 1959], No. 4195/60. Headings G2A and G2H. Electrostatographic apparatus comprises means for defining a fixed path of a movable electrostatographic recording surface, a multiapertured development electrode in predetermined closely spaced relation to said path so as to define a small air gap with the surface when said surface is in position in the apparatus and is moving along said path, developing means for causing developer particles to flow through said air gap, and means permitting a suitable potential gradient to be established in the gap, the development electrode being so apertured that excess development is caused to overflow through the apertures away from the surface, whereby damage to the surface is prevented in the event of an excessive accumulation of developer in the gap. In an automatic xerographic printing machine as shown in Fig. 1, in which a photoconductive surface 28 on a rotatable drum 15 is charged at a station 16, exposed to either a microfilm or an opaque original at a slit aperture 43 and developed by a cascade developing apparatus 17, the development by an electroscopic toner powder and hard granular Bead carrier takes place under the influence of an electric field established between a development electrode 112 (Fig. 3) and the drum. The electrode plate 112 which has apertures 149 (Fig. 7) formed therein through which excess powder and beads may pass so as not to abrade the relatively soft photoconductive surface 28, is carried by means of shafts 134, 135, 136 slidable in a fixed T-plate 110 so that it may be moved to an ineffective position 112<SP>1</SP>, in which position a slidable catch 144 engages in a slot 125 in a shaft 126 connected to a manipulating knob 122. In a modification - Fig. 4, not shown - the spacing between the drum and the electrode plate is maintained under spring loading by wheel type followers carried by the plate supports, for example 114. In a further modification - Fig. 5, not shown - the plate at one end is supported by hinge means from the fixed housing 90 and at the other end has wheel type followers which are spring urged into engagement with the drum, the arrangement being such that the plate may be pivoted into an ineffective position. Specific examples of suitable drum to plate separations, aperture 149 dimensions, and drum to plate potentials are given in the Specification. The developer powder and carrier 81 in the developing apparatus 17 is conveyed by a bucket and chain feed means from the bottom of a housing 82 into a hopper 83, and is then cascaded under gravity over the rotating drum 15. A valve gate 84 is provided in the mouth of the hopper, with an overflow shoot 88 provided leading back to the bottom of housing 82, and the consumable toner powder is replenished from a dispenser 92 at a rate depending upon the speed of a motor 93. After development of the electrostatic image, it is transferred under the influence of an electrostatic charging unit 20 on to the surface of a moving web 19 and fixed thereon by a heat fuser 21. Brushes 23 remove excess powder from the surface of the drum. The projection apparatus 13 for opaque originals comprises endless belt feed means 26, driven by a motor 30 through a variable speed transmission 31, an illuminating lamp 39, glass plate 33, fixed mirror 40, lens 41 and a pivotable mirror 42. For varying the magnification, the speed of the belt feed, the position of lens 41 and the position of the lamp and feed belt unit are adjustable by means of knobs 48, 49 and 50 respectively. The projection apparatus 14 for microfilm 56 comprises a lamp 59, and a lens turret 63. For varying the magnification, the three lenses 60, 61, 62 are alternatively alignable with the optical path, the distance between the microfilm 56 and the surface 28 is adjustable by a knob 72, and the speed of the microfilm 56 can be correlated with the drum speed by means of motor speed and transmission speed selector knobs 70, 71.