Photocopying – Projection printing and copying cameras – Combined with or convertible to a contact printer
Patent
1975-10-20
1978-05-02
Shoop, William M.
Photocopying
Projection printing and copying cameras
Combined with or convertible to a contact printer
355 10, G03G 1500
Patent
active
040871711
ABSTRACT:
Imaging means are provided to radiate a light image of an original document onto a photoconductive drum to produce an electrostatic image. A developing electrode is disposed adjacent to the drum and voltage source means apply a biasing voltage to the developing electrode. Sensing means sense the electrostatic potential of a background area of the electrostatic image and control the voltage source means in accordance therewith. Limiting means limit the biasing voltage to one of a first upper limit or a higher second upper limit. In order to improve the reproduction of low contrast documents, the exposure intensity is reduced to a value at which the difference in brightness of the light and dark areas of the document will produce a maximum difference in electrostatic potential on the drum. For normal documents, the biasing voltage is limited to the first upper limit. For low contrast, low density documents, the biasing voltage is limited to the second upper limit to prevent darkening of the light areas of the copy. For documents having low contrast and large dark areas, the biasing voltage is limited to the first upper limit so that the dark areas will be reproduced with high density.
REFERENCES:
patent: 2956487 (1960-10-01), Giaimo
patent: 3732003 (1973-05-01), Altmann
patent: 3892481 (1975-07-01), Schaefer et al.
Jordan Frank J.
Ricoh Co. Ltd.
Shoop William M.
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