| 摘要 |
PURPOSE:To shorten a magnetic brush to keep it out of contact with a photosensitive body by stopping a sleeve and moving a magnet roll when a developing device is operated and printing is not operated. CONSTITUTION:A doctor gap M and the length N of the magnetic brush of a developer are as shown in the figure. When the magnetic force of a magnet roll 3 is 400-1,400G, always N is longer than M. When the sleeve 2 is stopped and only the magnet roll is rotated, the brush of the developer is in the region of (b) and N becomes shorter than M. It is due to the fact that friction resistance occurs for conveyance of the developer and the developer is accumulated with the blade 5. Therefore, the gap between a photosensitive body 1 and the sleeve 2 is longer than the doctor gap M, and the body 1 is kept out of contact with the magnetic brush on the sleeve 2 by stopping the sleeve 2 and rotating only the magnet roll 3. |
