Patent ID: 7343122

Claim:
An image forming apparatus, comprising: a latent image bearing member; a developer bearing member disposed opposite said latent image bearing member; a magnetic field generating device to generate a magnetic field to be applied onto a surface of said developer bearing member; and a bias voltage power source to generate a developing bias voltage to be applied to a gap between said latent image bearing member and said developer bearing member, in which a DC current component and an AC current component are overlapped with each other; wherein a contact developing employing a two components developer including toner and carrier is conducted in such a manner that said latent image bearing member and said developer bearing member move in directions being opposite relative to each other at a developing region where said latent image bearing member and said developer bearing member are opposed to each other; and wherein a frequency of said AC current component and a line velocity of said latent image bearing member fulfill a first condition indicated as follow: vp/f≦ 70 condition 1 where vp (mm/see): line velocity of said latent image bearing member, f (kHz): frequency of said AC current component; and wherein a peak value of said AC current component effective for a developing operation, a developing gap, being a shortest distance between said latent image bearing member and said developer bearing member, and a fog margin fulfill a second condition indicated as follow: ( Vh+Vdc )/ Ds≦ 3.8 condition 2 where Vh (kV): peak value of said AC current component (Vh=Vac/2, Vac: peak-to-peak voltage) AVdc: fog margin Ds (mm): developing gap.