Jeffrey J. Folkins

Intermediate conductivities-the crossover function for insulative and conductive two-component magnetic brush development in electrophotography

A derivation is presented using a macroscopic three-slab charge flow model of xerographic magnetic brush development which results in an analytic exponential crossover function connecting the expressions for the solid-area developed mass/area between the insulative and conductive material regimes. The crossover function is dependent on a lumped parameter called the charge flow, which is the sum of the developer conductivity, connectivity, etc. All of the model parameters can be explicitly measured. Charge flow, developability, and line/solid ratio measurements made with several materials are found to agree very well with the model. Charge-flow measurements of some supposedly insulative materials show currents which, together with the model, appear to account for their higher than expected developabilities. >

Electrophotographic process control systems utilizing development bias currents

Both electrostatic and toner concentration (TC) electrophotographic process control systems can be constructed with the proper use of bias current measurements of the development subsystem. A TC I developability controller can be made by measuring the development bias current for each print or copy, summing the measurements, subtracting offset currents and dispensing toner proportionally to this developed charge measurement. If certain constraints are fulfilled, the system will operate at a constant developed toner mass. Similarly, a photoconductor electrostatic measurement I control system can be made by utilizing bias currents. This is accomplished by choosing a stable portion on the developed charge vs development voltage relationship of the development subsystem. This setpoint is then used to measure photoconductor test patch voltages by monitoring the bias current. In some cases this provides the same function as an electrostatic voltmeter. These low cost techniques enable the practical process control implementations in low and medium speed electrophotographic machines.