Abstract: A photoconductive drum (32) is charged, radiated with a light image of an original document (34) and developed to produce a toner image. The density of the toner image is sensed and additional toner fed to a developing unit (37) if the sensed density is below a predetermined value. The sensed toner density is compensated for variations in charge potential, light image intensity, electrostatic image potential, developing bias voltage, power supply voltage and/or sensor output so as to be independent of these variables.

Abstract: In an electrophotographic copying machine, the copy image adjustment method for correcting copy image characteristics comprises the steps of measuring copying characteristics by use of a reference original and resetting development characteristics in accordance with the measurement results.

Abstract: An electrode (17) is provided adjacent to a photoconductive drum (12) to sense the background area potential at a leading edge of an electrostatic image on the drum (12). An electrically conductive shield (26) surrounds all surfaces of the electrode (17) except a surface which faces the drum (12). A voltage follower (18) has an input connected to the electrode (17) and an output connected to the shield (26). This makes the capacitance between the electrode (17) and the drum (12) much greater than the capacitance between the electrode (17) and ground. The surface of the electrode (17) facing the drum (12) is formed with a pattern of projections and depressions to increase the surface area thereof and thereby the capacitance between the electrode (17) and the drum (12).

Abstract: A photoconductive drum (12) is electrostatically charged and radiated with a light image of an original document (16) to form an electrostatic image. The average value of the electrostatic potential of the electrostatic image is sensed and a developing bias voltage controlled in accordance therewith. The bias voltage is progressively increased when the sensed electrostatic potential is below a predetermined value and is reduced to a lower value when the electrostatic potential exceeds the predetermined value. The electrostatic potential is below the predetermined value for original documents constituted by printed pages and above the predetermined value for original documents constituted by photographs and other continuous tone documents.

Abstract: Prior to optical scanning of an original document (14) for producing an electrostatic image thereof on a photoconductive drum (12), the optical density of the document (14) is sensed and a light image intensity and a developing bias voltage are set in accordance with a sensed minimum or background density of the document (14).

Abstract: A photosensitive material for use in electrophotography is disclosed which comprises a conductive support, a photoconductive layer superposed on said support and a protective layer superposed on said photoconductive layer, said surface protective layer containing an organic compound which has a structure according to the formula ##STR1## in a part of the molecule.