GB1484762A - Multiple copy electrostatic hold-down apparatus - Google Patents

Abstract

1484762 Electrostatic sheet holding copyboard SIMCO CO Inc 25 Sept 1975 [11 Nov 1974] 39342/75 Heading G2A An electrostatic copyboard comprises an insulative plate, and an applicator forming the output of a uni-directional high voltage D.C. generator, which applicator can be traversed across a sheet lying on the plate, and having automatic switching means for cyclically altering the connection of the generator to the applicator so that the applicator and the other surface of the plate are coupled alternately to the same side or to opposite sides of the D.C. output. As shown, the insulative plate is a glass sheet A, and its lower surface is coated with a transparent conductive film 18. One or more negatives N are placed on the glass plate, and finally a photo-sensitive sheet P. The exposure is made by lamps 12 within a mounting cabinet 14. Alternatively the apparatus may be arranged for exposure from above. The high voltage generator B develops.a negative output with respect to ground across resistor 24, and is connected via resistor 22 and lead 21 to the electrode 18. The other side of the generator is connected by a lead 30 to the applicator C, which may be a roller or brush, and which can be traversed across a sheet lying on plate A. The power supply to'the generator has a switching device D comprising a pair of breaker points 32 opened and closed by a rotating cam 34. This is driven by a motor 36 so that the points 32 are closed, and then opened, at one second intervals. When the points are open, the copy board is connected to ground via resistors 22 and 24. When the points are closed a negative voltage is applied to electrode 18. When a negative sheet N is placed on plate A, and the applicator C drawn across it, the charges produced on sheet N will depend on the alternative negative and ground potentials produced on electrode 18, as seen in Fig. 2A (not shown). If a second negative N is laid over the first, the passage of the applicator will produce charges thereon as seen in Fig. 2B (not shown). If this is overlaid by a photo-sensitive sheet P, and the applicator passed once again, charges will be produced as in Fig. 2C (not shown). The varying distribution pattern of charges on the different sheets results in their being satisfactorily pinned together electrostatically, and any variation in the contact pressure between the applicator and the sheets, and also in the insulation characteristics of the sheets themselves, introduces random variation in the charge patterns which assist the pinning effect.