On the degradation process in electrophotographic cadmium sulphide binder layers

The two stages of degradation in electrophotographic cadmium sulphide binder layers-fatigue and ageing are investigated. The dependences of the photoinduced decay of the potential and the contrast potential vs the exposure time during the first cycle and in fatigue show that this process probably occurs in the bulk of the semiconductor particles. The changes of the photoinduced decay of the potential during the second stage of degradation, ageing, may be associated with changes in the barrier structure.     

Synthesis of new hole-transporting molecular glass with pendant carbazolyl moieties

The synthesis and properties of amorphous hole-transporting 4,4′-bis[11-carbazol-9-yl)-6,8,10-tri(carbazol-9-methyl)-3-hydroxy-5,7,9-trioxa-1-thia]thiobisbenzene with two end and six pendant carbazolyl moieties, separated from the main chain by CH₂ spacers, is reported. It was prepared by a multistep synthesis route from 1,6-di(carbazol-9-yl)-5-(carbazol-9-methyl)-4-oxa-2-hexanol glycidyl ether. Glass transition temperatures of intermediate and final products established by differential scanning calorimetry are reported. The hole drift mobility, measured by the time of flight technique, in this well defined molecular glass depends little on the strength of the electric field and exceeds 10⁻⁵ cm² V⁻¹ s⁻¹. The ionization potentials measured by electron photoemission method, light absorption and fluorescence spectra are closed to those reported for the other organic photoconductors containing electronically isolated carbazole moieties.     

Halftone banding reduction for a class of electrophotographic systems – Part I: Characterization and modeling

This paper proposes new insights and methodologies that complement existing techniques for characterizing and modeling halftone banding, an artifact of periodic light and dark bands across a printed image perpendicular to the print direction, for a class of electrophotographic (EP) systems, which is commercially known as laser printers. For characterizing banding based on transmission error measurement, specific frequency-domain signal processing, i.e., order analysis, was applied to help identify possible disturbance sources with certain gear components. For characterizing banding based on absorptance measurement on printed images, it was pointed out that a good metric should incorporate appropriate nonlinear operator that characterizes the human visual system. This proposition was supported by simulation results obtained from a three-stage visual model. For modeling banding, a more comprehensive EP model was developed to include transmission parameters such as laser scanning frequency, gear dimension, and angular velocity. Simulation study was performed on the simplified version of the derived model, which demonstrated close correlation between halftone banding and transmission quality. This motivates control of the motor/gear transmission system for reducing banding artifact in EP processes.     

Electrophotographic characteristics of CdS binder layers after heat and light treatment effects

The effect of heat and simultaneous heat-light treatment on aged in darkness CdS binder layers is investigated. The CdS powder is doped with copper and iron in various concentrations. The heat treatment in the temperature range from 80 to 150°C with or without illumination in the spectral interval from 500 nm to 750 nm is studied. The dependence of the contrast potential vs the exposure time as well as the residual potential after various sample treatments are given. It is suggested that the applied treatments on the aged in darkness samples may be associated with the reversible changes in shape and structure of the intercrystalline or interface barriers and with photochemical reactions in the bulk of the CdS particles.     

A fuzzy neural approach to design of a Wiener printer model incorporated into model-based digital halftoning

This paper presents the design of a Wiener model for a class of laser electrophotographic printers utilizing a fuzzy neural approach. The feasibility and effectiveness of incorporating the proposed spatial-based Wiener printer model into the framework of model-based digital halftoning is also investigated. The Wiener model comprises a two-dimensional FIR filter followed by a nonlinear static mapping. The nonlinear static mapping is synthesized based on a fuzzy neural network to account for the tone distortion commonly observed in a printing system. A set of systematic steps for parametric identification/optimization and evaluation of the Wiener printer model is proposed. Experimental results as well as a comparative study show that the Wiener model-based halftoning approach is superior (in terms of image quality) to conventional ones and comparable to the one utilizing a comprehensive printer model. Another comparative study reveals that the Wiener printer model, though computationally less efficient than the conventional dot-overlap model, consumes significantly less time to process an image than the comprehensive printer model does.     

Halftone banding reduction for a class of electrophotographic systems – Part II: Closed-loop control

A new control configuration for laser printing process was proposed, which constructs a feedback controller for regulation of the motor/gear transmission subsystem using direct velocity measurement from the imaging component. Causal connection between banding artifact and transmission errors has been demonstrated previously. Two controller design approaches were suggested for reducing banding artifact. The proposed designs were based on the internal model principle and H_∞ robust control theories, both have two degree of freedom control structure. The controllers were implemented on a monochrome laser printer, for which latent images are formed on a cylindrical photoconductor drum. Experimental results showed significant reduction in the measured velocity error for the photoconductor drum as well as noticeable banding reduction on the printed images.     

激光打即技术用有机光导鼓的试验研究

通过对系列酞菁类光导材料和各种迁移材料的合成、处理、性能表征以及光导器件的工艺制作及其光电特征的测定等一系列试验研究，制成了具有良好性能的有机光导器件，经测定在780nm曝光．其灵敏度为1Lxs，分辨力达400点／英寸，耐印力达15000次。用这种材料制成的OPC鼓，经激光打印机打印试验，其打印效果与国外Canon和HP原装鼓相当。