Abstract: An electrode (12) for sensing a surface potential is connected to a non-inverting input of an operational amplifier (14). The output of the operational amplifier (14) is connected to the inverting input thereof in a voltage follower configuration. The output of the operational amplifier (14) is also connected to one or more shield electrodes (19) which are operatively disposed adjacent to the sensing electrode (12). An offset bias voltage of the operational amplifier (14) is adjusted to cancel an input bias current thereof. An operational amplifier (33) may be mounted on a flat substrate (112), with sensing and shield electrodes (113), (114), (116) formed on the substrate (112) by printing. The shield electrodes (114), (116) surround the sensing electrode (113) and also the operational amplifier (33).

Abstract: A detecting electrode (22) is formed on a substrate (28), an amount of potential from a charged surface (23) induced in the detecting electrode (22) corresponding to a potential on the surface (23). A guard electrode (26) formed on the same surface of the substrate (28) as the detecting electrode (22) surrounds the detecting electrode (22). Part of the guard electrode (26b) is formed on the back surface of the substrate (28). The detecting electrode (22) is connected to a non-inverting input of an operational amplifier (24). The output of the operational amplifier (24) is connected to the inverting input thereof and also to the guard electrode (26) to produce unity gain and place the guard electrode (26) at the same potential as the detecting electrode (22). The substrate (28) is formed of a material such that the electrical resistance between the detecting electrode (22) and the guard electrode (26) is at least 10.sup.9 ohms to reduce zero drift to a negligible value.

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: A photoconductive drum or sheet is movable relative to a developing electrode which is biased to a voltage which prevents smearing of the background areas of the copy. A sensing electrode is disposed upstream of the developing electrode in the direction of movement of the drum or sheet which senses the voltage on the drum or sheet. The sensing electrode is provided in a plurality of independent segments, and a computing circuit selects the voltage on the segment which is lowest in magnitude and which corresponds to a background area of the copy and applies the biasing voltage to the developing electrode in dependence on the sensed voltage. An auxiliary electrode is provided so that the combination of the sensing electrode and the auxiliary electrode is coextensive with the drum or sheet in a direction perpendicular to the movement thereof to prevent streaking of the copy.

Abstract: A photoconductive member utilized in a wet-type electrophotographic device is charged and radiated with a light image to produce an electrostatic image. Sensing electrode automatically sense through the developing solution the remaining potential in a portion of the electrostatic image corresponding to a background area of the original document scanned to produce the light image. In one embodiment the area is a white reference document disposed adjacent to the original document. In another embodiment a reference document is not provided and a plurality of portions of the electrostatic image are sensed. The lowest value of the sensed potential is utilized. Computing circuits compute and apply the biasing voltage to the developing electrode as a predetermined function of the sensed potential.

Abstract: A photoconductive member is charged and radiated with a light image to produce an electrostatic image. Sensing electrodes automatically sense the remaining potential in a portion of the electrostatic image corresponding to a background area of the original document scanned to produce the light image. In one embodiment the area is a white reference document disposed adjacent to the original document. In another embodiment a reference document is not provided and a plurality of portions of the electrostatic image are sensed. The lowest value of the sensed potential is utilized. Computing means compute and apply the biasing voltage to the developing electrode as a predetermined function of the sensed potential.

Abstract: A photoconductive member is charged and radiated with a light image to produce an electrostatic image. Sensing electrodes automatically sense the remaining potential in a portion of the electrostatic image corresponding to a background area of the original document scanned to produce the light image. In one embodiment the area is a white reference document disposed adjacent to the original document. In another embodiment a reference document is not provided and a plurality of portions of the electrostatic image are sensed. The lowest value of the sensed potential is utilized. Computing means compute and apply the biasing voltage to the developing electrode as a predetermined function of the sensed potential.