Direct observation and numerical study on dynamics of toner particles in magnetic single-component development system of electrophotography

Dynamics of toner particles in the magnetic single-component development system of electrophotography have been investigated to utilize for the improvement of the system. Two approaches have been adopted for the investigation: One is the direct observation of the toner motion in a development area with a high-speed microscope camera and another is the numerical simulation with the distinct element method. We have manufactured the mock-up apparatus that consisted of a pseudo-photoconductor, development roller, stational magnetic roller inside it, and doctor blade to form thin toner layer on the development roller. The development roller, magnetic roller, and blade were diverted from a commercial printer. Thin line electrodes were embedded on the pseudophotoconductor drum to substitute for electrostatic latent images. The apparatus enabled high-speed (8,000 fps) observation of toner motion at the development gap with satisfactory image quality. Observed images showed that (1) toner particles formed chain-like clusters in the vicinity of the gap, (2) these chains vibrated at the development zone synchronized with an applied alternative electrostatic field, (3) at the latent image, chains crashed on the photoconductor and then fell apart from the photoconductor, and (4) at this moment, some of toner particles returned to the development roller but some adhered to the latent image to form a real image. Three-dimensional shapes of toner piles on the latent image were measured after the development by a scanned laser displacement meter. It has been clarified that both the width and height of the toner pile increased with an increase in the development voltage but these were saturated at the voltage higher than a threshold. Numerical simulation has been conducted to confirm the experimental results. The simulation method is based on a hard sphere model of the distinct element method with cyclic boundary condition. The method can be applied for the dynamics of small toner particles within reasonable calculation time.