| 摘要 |
PURPOSE: To improve the latitude of exposure for operation in a 3-level xerography process by substituting a standard DC bias, which is given to one or both of developer housings for 3level image formation, with a chopper type DC developer bias. CONSTITUTION: In a development station C, a development system 30 supplies a developer so that it can be brought into contact with an electrostatic latent image. Colors in development of the electrostatic latent image are distinguished by circulating a photosensitive body once along two developer housings 32 and 34 where magnetic brush development rolls 35 to 38 are biased to a voltage offset from a background voltage VW. The chopper type DC bias is given to magnetic brush development rolls 35 to 38, that is, a first bias voltage is given for a prescribed time and a second voltage is next given for a second period different from the first period. Thus, the latitude of exposure for 3-level zerographic image formation is improved. |
