Importance

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Abstract

A surface capable of holding electrical charge wherein at least one sensing electrode having an edge is located in close physical proximity to the surface and is disposed so that upon relative movement between the surface and sensing electrode, charge on the surface crosses the edge of the electrode. The sensing electrode has a surface area facing the surface which is sufficiently small so as to minimize electrical noise when the electrode is in close proximity to the surface. Electrical charge is applied to the surface and relative movement is provided between the surface and sensing electrode while maintaining a constant distance therebetween. A current signal is induced in the sensing electrode in response to a variation in the surface charge crossing the edge of the electrode, and the signal is detected and electrical parameters thereof are measured to provide information on the charge density of the surface to determine the physical uniformity of the surface. Preferably a plurality of sensing electrodes are provided in a path extending along the surface in a direction generally cross-wise of the direction of relative movement between the surface and the sensing electrodes, and the detected current signals from the electrodes are scanned and then measured to obtain the aforesaid information. As a result, the size, number, and location of surface defects are readily determined.

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First Claim