Photocopying – Projection printing and copying cameras – Combined with or convertible to a contact printer
Patent
1983-02-18
1985-07-16
Braun, Fred L.
Photocopying
Projection printing and copying cameras
Combined with or convertible to a contact printer
355 14E, 430120, G03G 1508
Patent
active
045292930
ABSTRACT:
Electrophotographic copying by use of a machine in which a charge image is developed by the application of electrically conductive marking (toner) particles can be carried out so as to produce well imaged copies of low-contrast originals that contain weak image information by effecting the copying under conditions which cause the charge image to be developed with a grayish background of sparsely attracted particles and, during the developement, applying between an electrode of the developing device and the photoconductive element an a.c. voltage having a frequency of between 1 and 7 kHz and an amplitude of at least 50 volts, thereby rendering the background homogeneous in tone. In positive working processes, illumination that underexposes the element is used and only the a.c. voltage need be applied in development. In negative working processes, illumination that over-exposes the element is used and in development the a.c. voltage is superimposed onto a d.c. voltage applied between the developing electrode and the element. Copying machines of the invention are provided with control systems which in one setting thereof will establish conditions of exposure and development suited for normal copying of well imaged originals, to produce images with background substantially free of marking particles, and in another setting will establish the conditions suited for producing images of low-contrast originals with homogeneous grayish backgrounds.
REFERENCES:
patent: 2956487 (1960-10-01), Giaimo
patent: 3346475 (1967-10-01), Matkan et al.
patent: 3805739 (1974-04-01), Feldeisen et al.
patent: 4102305 (1978-07-01), Scharz
patent: 4256401 (1981-03-01), Fujimura et al.
patent: 4265197 (1981-05-01), Toyono et al.
Patent Abstracts of Japan, vol. 6, No. 13, (Jan. 26, 1982), p-99, [891]; No. 8, (Jan. 19, 1982), p-98, [886].
Braun Fred L.
Johnston Albert C.
Oce'-Nederland, B.V.
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