Numerical Simulation of the Lateral Conductivity of a Photoconductor Surface

Abstract

Lateral motion of charge carriers at the photoconductor surface is numerically calculated and analyzed. Surface conduction is assumed to take place in a very thin surface charge layer. Our findings, based on the assumption that surface conduction is the predominant factor for image blurring, lead us to believe that the carrier mobility at the surface is field dependent, and consequently surface conduction is not Ohmic, although it has the appearance of being so after a sufficient amount of time has elapsed. Using a field enhanced surface mobility, time-dependent dynamics of photogenerated charge carriers as they arrive at the surface and begin to spread out in the surface charge layer are accounted for by empirically approximating vertical charge motion with an exponential rise expression that closely mimics the behavior of the carriers as they reach the surface. We found that vertical charge motion has a negligibly small effect on surface conduction over a period of time relatively long compared to the vertical transit time of the carriers, and surface conduction can remove jaggedness inherent in certain features. A developed toner mass (DMA) estimation procedure is presented using electric fields and potential in the developer gap. Quantitative comparisons between measurements printed from a test print engine and calculated toner mass arising from surface conduction are made using different input bitmaps, which are in good agreement. Our DMA calculation procedure can account for variation in surface conduction rate and it is validated using two toner cartridges of significantly different surface conduction rates.