Browse Prior Art Database

Original Publication Date: 1988-Aug-31
Included in the Prior Art Database: 2004-Apr-04

Publishing Venue

Xerox Disclosure Journal


A device which measures the thickness of a developed liquid image by measuring the capacitance between developed regions on the photoconductive surface and precisely located facing electrodes. The device includes two, one square inch plates mounted in an insulated block. Each plate is positioned parallel to the photoconductive surface. These plates are mounted on a frame which is in rolling contact with the end regions of the photoconductive surface. Micrometers mounted on the frame ends enable the plates to be precisely adjusted to equalize the plate-to-photoconductor surface gap. The plates are electrically biased to function, in conjunction with the photoconductor ground plane, as capacitors. One plate measures the capacitance of the air gap and film thickness on the photoconductive surface while the other plate measures background areas of the photoconductor. The only difference in measurements is due to the developed image film thickness. The output signal corresponding to the amplified difference in these measurements can be calibrated for known film thickness and provides an indication of the variation of the thickness of particle pile height. The variations in thickness may be minimized by controlling charging of the photoconductive surface.