Contactless system for detecting subtle surface potential charge patterns

A contactless process for detecting surface potential charge patterns in an electrostatographic imaging member comprising

• providing a cylindrical electrostatographic imaging member having an outer imaging surface and an imaginary axis,
• providing an electrostatic voltmeter probe having a charge measuring end spaced from the outer imaging surface,
• maintaining the distance between the charge measuring end of the probe and the imaging surface substantially constant, the distance between the charge measuring end and the imaging member being slightly greater than the minimum distance at which Paschen breakdown will occur to form a parallel plate capacitor with a gas between the probe and the imaging surface,
• establishing relative movement between the probe and the imaging surface,
• depositing a charge on the imaging surface along a narrow predetermined path immediately prior to relative movement of the probe over the charge on the imaging surface, the deposited charge having a surface potential pattern containing low resolution variations having of a width of between about 0.1 millimeter and about 5 millimeters,
• repetitively measuring the deposited charge on the imaging surface with the electrostatic voltmeter probe, the frequency of repetition being selected to cause all time dependent signals to fall out of phase by a predetermined amount after each revolution, and
• averaging the out of phase time dependent signals over a sufficient number of measuring repetitions to eliminate the time dependent signals to detect the low resolution variations in the surface potential charge pattern.

A contactless process for detecting thickness profiles in an electrostatographic imaging member comprising

• providing a cylindrical electrostatographic imaging member having an imaging layer having an outer imaging surface and an imaginary axis,
• providing an electrostatic voltmeter probe having a charge measuring end spaced from the outer imaging surface,
• maintaining the distance between the charge measuring end of the probe and the imaging surface substantially constant, the distance between the charge measuring end and the imaging member being slightly greater than the minimum distance at which Paschen breakdown will occur to form a parallel plate capacitor with a gas between the probe and the imaging surface,
• establishing relative movement between the probe and the imaging surface,
• depositing a charge on the imaging surface along a narrow predetermined path by a corotron in which the current through the imaging layer is held fixed by a feedback control system immediately prior to relative movement of the probe over the charge on the imaging surface, the deposited charge having a surface potential pattern replicating the thickness profile of imaging layer containing low resolution variations having of a width of between about 0.1 millimeter and about 5 millimeters,
• repetitively measuring the deposited charge on the imaging surface by the electrostatic voltmeter probe, the frequency of repetition being selected to cause all time dependent signals to fall out of phase by a predetermined amount after each revolution, and averaging the out of phase time dependent signals over a sufficient number of measuring repetitions to eliminate the time dependent signals to detect the low resolution variations in the surface potential thickness profiles in the electrostatographic imaging member charge pattern.