Developing unit for an image forming apparatus

Abstract

A developing unit incorporated in an image forming apparatus and capable of transporting a developer or a toner deposited on a developing roller in a predetermined direction without rotating the developing roller, or developer carrier. The developing roller has an unrotatable base roller, a stationary body provided on the base roller and made of an insulating material, and a plurality of drive electrodes buried in the stationary body. The drive electrodes are divided into three electrode groups. Voltages whose polarities change at predetermined intervals are applied to the three electrode groups, causing the toner to be transported by the coaction of the charge of the toner and the charges of the drive electrodes. The drive electrodes are arranged at a pitch which is substantially one-third of the particle size of the toner, so that the toner may be deposited on the developing roller substantially without any clearance. To enhance repulsion acting on the toner and, therefore, efficient development, higher voltages are applied to part of the drive electrodes located in a developing region than part of the drive electrodes located in a transporting region. Such voltages may be replaced with voltages on which alternating voltages are superposed.