| 摘要 |
In an image forming apparatus of the type forming a multicolor toner image on an image carrier and then transferring it to a transfer medium at a time, a first developing unit develops a latent image with a developer of first color while a second developing unit develops a latent image with a developer of second color. The second developing unit has a developer carrier for depositing the developer of second color thereon, and a bias power source for applying to the developer carrier a bias voltage for development which changes periodically and has one period made up of a first and a second period of time. During the first period of time, the bias power source applies to the developer carrier a first voltage generating an electric field which causes the developer to fly toward the image area and non-image area of the image carrier in a gap between the image carrier and the developer carrier. During the second period of time, the power source applies a second voltage generating, in the gap, an electric field returning the developer having flied toward the non-image area during the first period of time to the developer carrier while preventing the developer of first color existing on the image carrier from leaving the image carrier. The first period of time is selected such that the developer of second color does not reach the non-image area and the developer of first color existing on the image carrier does not fly to the developer carrier.
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