William Y. Fowlkes

The nondestructive measurement of the charge-to-mass ratio of an insulating tone layer present on a photoconductor

Nondestructively measuring the charge present in a toner layer based upon a noncontacting measurement of the potential across the layer and the solution of Poissons equation for the toner layer is addressed. The former is easily accomplished using commercially available electrostatic voltmeters. The latter requires detailed knowledge of the toner layer morphology. Solid-area continuous-tone images of various densities have been studied microscopically to determine toner stack height and volume-mass density. From these data, the toner charge-to-mass ratio is determined. An adjustment of the data for stack height to account for the surface-layer topology (roughness) yields a final accuracy of about 6%. >

An off-the-shelf high-performance primary corona charger for use in an electrophotographic engine

An off-the-shelf high-performance charger has been designed, implemented, and shown to deliver a high degree of uniformity. The design is based on the Ektaprint 100/150 and 250 primary chargers used in a booster-trimmer mode of operation. The performance characteristics of the chargers are measured. The DC Ektaprint 100/150 charger operates efficiently at a low impedance but with low uniformity; it is used as the booster in the final design. The AC Ektaprint 250 charger operates with a slightly higher impedance but has a very stable cutoff potential and good uniformity; it is used as the trimmer. The AC charger cutoff potential is kept stable by the application of the forced balance technique. The system uniformity requirements are defined in terms of a design parameter known as the charger sensitivity. The sensitivity requirement is used with a suitable analytical theory to design the charger. The design is implemented on an electrophotographic breadboard. The grid bias is controlled by dynamic impedance adjustment. The charger sensitivity is measured and is found to exceed the specified design criteria. The ability of the charger to surpass its predicted performance is attributed to the overshoot-trim mode of operation. >