| 摘要 |
A photoconductive member (21) is provided with inner (21b) and outer (21c) photoconductive layers. An electrostatic charge is formed at the interface of the layers (21b), (21c), either by a combination of applied charge and semiconductive current flow through the inner layer (21b) or applied charge and radiation with light having a wavelength selected to render only one of the inner (21b) and outer (21c) layers conductive. Then, the member (21) is radiated with a light image of an original document (26) to form an electrostatic image at the interface. The electrostatic image is repeatedly developed and the resulting toner images transferred to copy sheets (34). Another charge may be applied to the member (21) after the first charge to form electrostatic dipoles across the layers (21b), (21c). The charge magnitudes as well as charge dissipation time constants across the layers (21b), (21c) are selected such that an increase in the surface potential on the member (21) due to charge dissipation across the layers (21b), (21c) is equal to a decrease in the surface potential due to charge leakage in the developing and transfer steps as functions of time, thereby providing constant copy density and contrast.
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