Patent ID: 7907871

Claim:
An image forming apparatus, comprising: a latent image carrier; latent image forming means for forming a latent image on a uniformly charged surface; developing means for developing the latent image formed on the uniformly charged surface and for obtaining a toner image; transfer means for transferring the toner image formed on the uniformly charged surface to a transfer body; and charging means for uniformly charging a cylindrical rotating surface of the latent image carrier, the charging means includes: first charging means for charging the cylindrical rotating surface of the latent image carrier, the first charging means being supplied by a first power supply means, and the first charging means being in contact with a portion of the cylindrical rotating surface of the latent image carrier after the portion of the cylindrical rotating surface passes through the transfer means, and before the portion of the cylindrical rotating surface comes in contact with a second charging means; the second charging means for charging the cylindrical rotating surface of the latent image carrier, the second charging means being supplied by a second power supply means, and the second charging means being in contact with the portion of the cylindrical rotating surface after the portion of the cylindrical rotating surface passes through the first charging means, and before the portion of the cylindrical rotating surface comes in contact with a charging roller means, wherein during a first period, the first power supply means applies a first bias to the first charging means, when the first bias is applied, the first charging means charges a surface potential of the latent image carrier to a first value that has greater potential than a second bias applied by the second power supply means to the second charging means, the first value further having a same polarity as a charging polarity of a toner; and during a second period, the first power supply means applies a third bias to the first charging means, when the third bias is applied, the first charging means charges the surface potential of the latent image carrier to a second value that has a smaller potential than the second bias applied by the second power supply means to the second charging means, the second value also having the same polarity as the charging polarity of the toner.