| 摘要 |
PURPOSE:To prevent trouble due to the use of a developing device after running- out of toner by providing a magnet coaxially arranged in a developing roll and a fixing and releasing means which fixes this magnet in a developable position and releases the fixing state by a toner end signal to disable development. CONSTITUTION:A rotatable developing roll 3, a magnet 3a rotatably and coaxially arranged in this roll 3, and fixing and releasing means 9 to 11 which fix the magnet 3a in the developable position and receive the toner end signal to release the fixing stage of the magnet 3a to a undevelopable position are provided. That is, the magnet 3a is rotated to the position where developer is attracted to the surface of the developing roll 3, and the position where developer is not attracted there, and fixing and releasing means 9 to 11 normally fix the magnet 3a in the developable position and release it to the undevelopable position at the time of running-out of toner. Thus, the replacement time of the developing device is clearly reported to a user to prevent trouble due to a lack of toner. |
