| 摘要 |
PURPOSE:To form a satisfactory image by detecting the density of a conveyer belt by an AF sensor. CONSTITUTION:When the start of detecting the soil of the conveyer belt 8 is requested, the AF sensor 121 samples any density of the belt facing an original glass 101. Together with a mirror 105, the sensor 121 moves along the glass 101, samples densities at several locations, compares their average with a set reference value, decides whether the belt 8 is dirty or not, and displays the result on a message display 701. If the belt is decided as being dirty, a frame erasing mode is set, and a blank exposing unit 137 exposes a part corresponding to the frame of an image formed on a photosensitive drum 131 to erase the picture concerned. Thus, a picture of the conveyer belt, which has been formed around an original picture conventionally, disappears, and a satisfactory picture can be obtained. |
