US 3,944,354 AGranted

Voltage measurement apparatus

AssigneeEastman Kodak Company

InventorsBruce R. Benwood, Howard D. Siebenrock

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Abstract

Apparatus for measuring the surface potential of moving electrostatically charged elements uses at least one electrically conducting detector mounted on the outer periphery of a grounded roller. An insulated ring secured around each end of the roller in an edge contacting relationship with the charged element under measurement provides a friction drive for the roller and maintains the detector in a spaced and non-contacting position from the charged element. As the roller is rotated, the detector is alternately exposed to the charged element and to a grounded shell arranged in a spaced and non-contacting manner from both the charged element and the roller and builds an A.C. voltage on a sampling capacitor. The output of the sampling capacitor is connected to a circuit which determines the envelope of the A.C. voltage and provides a differential D.C. voltage representative of the surface potential of the charged element. This D.C. voltage can be used as a control signal in an electrophotographic copying machine to control the charging, exposing, developing and/or cleaning operations of the machine.

Claims6

Dependent claims

An electrometer adapted for in situ operation in a copying machine of the type including a recording element which is driven along a predetermined path past a plurality of processing stations including stations which (1) form a latent electrostatic image on the recording element and (2) apply developer particles to the latent image to form a visible image, said electrometer comprising:

a. probe means having at least one electrically conducting detector arranged in a spaced and noncontacting manner from the recording element;
b. a capacitor coupled to said detector;
c. a grounded shell surrounding said probe means, said shell having an aperture therein to expose said detector to the image bearing surface of the recording element;
d. means positioned in frictional contact with the recording element for rotating one of said grounded shell and said probe member in response to movement of the recording element whereby said detector charges said capacitor upon exposure to the recording element to a voltage level which is a function of the surface voltage of the recording element and discharges said capacitor upon exposure to said grounded shell to produce an a.c. voltage on said capacitor;
e. circuit means coupled to said capacitor for determining the envelope of said a.c. voltage and for producing a differential d.c. control voltage signal representative of the surface voltage on the recording element;
and
f. means for applying said control signal to at least one processing station of the copying machine.

4 more elements

Apparatus for determining the amplitude of the voltage of a moving, electrostatically charged surface, comprising:

a. a grounded roller;
b. a plurality of probe pairs positioned at equally spaced intervals around the outer periphery of said roller, each of said probe pairs comprising two opposed electrically conducting detecting members extending in a direction parallel to the longitudinal axis of said roller from the opposite ends of said roller to the approximate center of said roller;
c. means operatively associated with said roller for maintaining said probe pairs at a fixed distance from the charged surface and for rotating said roller in response to movement of the charged surface;
d. a grounded shell surrounding said roller, said shell having a slit along its length dimensioned so as to expose only one probe pair at a time to the moving charged surface;
and
e. first and second circuit means, said first circuit means being connected to one member of each probe pair and said second circuit means being connected to the opposed member of each probe pair, each of said circuit means comprising a sampling capacitor and a peak-to-peak detector, said detecting members alternately charging said capacitor upon exposure to the charged surface to a voltage level which is a function of the voltage on the charged surface and discharging said capacitor upon exposure to the grounded shell to build an a.c. voltage on said capacitor, said peak-to-peak detector being responsive to the a.c. signal on said capacitor for producing a differential d.c. voltage representative of the voltage on the charged surface.

3 more elements

Dependencies are inferred from the claim text.