| 摘要 |
PURPOSE:To prevent developers of different color from being mixed together owing to the approximation of different polarities and to improve the color quality of an image by equalizing the polarities of both magnetic poles of magnetic rolls of the 2st and the 2nd adjacent developing devices which approach to each other opposite. CONSTITUTION:When the 1st developing device 321 is selected, the sleeve 441 of the 1st developing roller 311 rotates clockwise to develop a latent image on a photosensitive drum 7. When this development is completed, a magnetic roll 431 is switched to a nonoperation position shown by a broken line and the sleeve 441 further rotates for a specific time after the formation of a magnetic brush is stopped, carrying on developer removal. The magnetic roll 432 of the 2nd developing device 322 is rotated temporarily to a development operation position shown by a broken line during the developer removal of the sleeve 441. Consequently, the N pole of the main magnetic pole part 472 of a lower magnetic roll 432 leaves the S pole of an upper magnetic pole part 461 and the S pole of a magnetic pole part 482 becomes an opposite pole to prevent an intense magnetic field from being established between different poles. A developer is therefore prevented from falling from the 1st developing device 321 on the 2nd developing device 322. |
