A mathematical analysis has been performed on rotor dynamics of a high-speed polygonal mirror scanner motor in digital electrophotography. The rotor is assumed rigid and vertically supported by air bearings with an effective length that is not negligible compared to the rotor length. The model is a four-degree-of-freedom system that includes the gyroscopic effect and nonorthogonal force of the air bearing. The model also includes the effects of longitudinal bearing length and radially unstable magnetic stiffness of a driving motor and/or a magnetic bearing. A simulation program was coded to calculate complex eigenvalues, static and dynamic stability, critical speeds, unbalance responses, and external excitation responses. The results indicated that although the effects of bearing length and magnetic unstable stiffness were ignored in the past, these simplifications result in substantial error for the evaluation of rotor dynamics. The model is utilized to realize high-performance scanner motors.

This study reports the results of work carried out to investigate the high-frequency periodical break-up process of a liquid jet using an electrohydrodynamic (EHD) multimode jet stimulation device. The aims of this study were to optimize the different parameters and to generate droplets of conducting fluid in a controlled fashion. In particular, the experiments were performed for wavenumbers k ≤ 0.5 with the second harmonic purposely introduced in the excitation signals. A dimensional analysis applied to the problem provided the main dimensionless parameters whose influence on jet break-up mechanisms were examined. We found different regimes of break-up depending on both the electrostatic pressure ratio and the phase shift between the fundamental and the second harmonic. In addition, various patterns of drop production and boundaries between regions of parameter space with different drop break-up behaviors were clearly identified using image processing techniques. Other features of jet break-up such as satellite droplet diameters and lifetimes were also considered in detail. Finally, our focus was to find the most suitable conditions for jet printer operation.

Reduction sensitization with various sensitizers, silver digestion, and hydrogen hypersensitization were applied to octahedral and cubic silver bromide emulsion grains to form P centers, identified by the observation of sensitivity increase and photoconductivity decrease caused by the centers, and absorption band characteristic of the centers. It was found that P centers decreased the ionic conductivity of the grains, which was proportional to the concentration of interstitial silver ions. By taking into account the fact that silver ions at kink sites are in equilibrium with interstitial silver ions, we propose that a P center was formed adjacent to a silver ion at a kink site and prevented it from going into an interstitial position in an emulsion grain. It is further proposed that a P center of a silver dimer is not merely Ag₂ in adjacent to Ag⁺ at a kink site, but a center as expressed by Ag₃⁺. The new model for an R center and a P center was successfully applied to the explanation of the formation, property, and behavior of silver clusters of photographic interest.

A new method is described for measuring the exposure threshold of laser thermal imaging materials exposed by pulses from a laser with a Gaussian radial spatial profile. This method, termed the maximum spot method, involves placing the material in the focused beam of a repetitively pulsed laser and exposing a series of spots of different sizes by moving the material through and beyond the beam focus. The exposure threshold can be deduced by knowing the radius of the largest exposed spot and the pulse energy. The method is demonstrated on a laser ablation transfer film (Lasermask™) and a direct imaging film developed by Presstek, Inc., for computer-to-plate imaging applications. It is shown that the new method, which is convenient and quick, gives the same results with fewer sources of experimental errors as conventional threshold measurement methods. The convenience of the new method permits systematic studies of the dependence of exposure properties on material properties or laser imaging conditions. As an example, the imaging threshold of Lasermask is measured as a function of laser pulse duration from 10⁻¹² to 10⁻⁴ s.

In the Belousov-Zhabotinsky reaction system bromide ions are generated periodically. When AgNO₃ solution was added to this system, AgBr grains were prepared and the periodical pBr oscillation was sustained during addition of the solution. In previous research we added drops of AgNO₃ solution synchronously to the pBr oscillation. This time we added AgNO₃ solution by continuous flow and observed the pAg (pBr) oscillation and grain shapes. The periodical pAg oscillation was also sustained. At some addition rates, dendrite grains with four, five, six, or eight long branches were formed. In some grains, secondary nucleation took place on the surface of branches and many warts aligned. We believe that the grain corners grew preferentially.

White spots observed in electrophotography were investigated. Magnetic toners were prepared by the conventional toner preparation method and applied to a laser printer and copiers produced by Canon Co., Japan. White spots were found to be generated during the development step. Toner particles constituting the white spots were analyzed by scanning electron microscopy and energy dispersive x-ray spectroscopy. It was concluded that white spots were caused by either silica-induced toner agglomerates, or the agglomerates fused together by frictional heating during charging of toner particles on the magnetic roller.

A new electrophotographic developing system was created to simplify the developing unit. The new developing unit is simple and features a hot spatial ??? frequency magnet roller without a sleeve. The sleeveless magnet roller was made of a sintered ferrite magnet 20 mm in diameter and magnetized with 32 poles. This developing system can be applied to both mono-component magnetic toners and conventional dual-component developers. Factors and developing conditions that influence image quality were examined using a variety of developers where both the toner and carriers were magnet. Images printed with the new developing unit were not influenced by either toner concentration or electric resistivity of the carrier, but were affected by the size of the carrier. The best image quality was obtained by using a carrier 35 μm in diameter. The new system demonstrated print image quality that was nearly as high as that produced by conventional developing units with a sleeve.

The layer model of single-component development is applied to investigate toner charging and deposition, in particular, the electrical interaction of the toner mass with the solid layers it comes into contact during these two processes. By considering the time dependence of charging and deposition, it is shown that the dielectric relaxation times of the metering blade and the donor-roll coating play important roles in maintaining ghost-free image quality. A possible mechanism of ghost image formation is suggested. The optimum values of the dielectric relaxation times are specified in relation to the development time and charging time, and, hence, also in relation to the process speed and development housing geometry.