| 摘要 |
PURPOSE: To correctly decide the deteriorated state of the developer and to prevent the deterioration of image quality and economical loss caused by the erroneous exchanging time of the developer by deciding the deteriorated state of the developer based on the density of one toner image for controlling density out of plural toner images for controlling density. CONSTITUTION: The density of the 1st toner image for controlling density is measured by a photosensor 10 so as to decide whether the measured density of the toner image is within the control limit of 1st reference density previously set. In the case it is within the control limit, the density of the 2nd toner image for controlling density is measured after forming the 2nd toner image for controlling density having a different dot area rate from the 1st toner image for controlling density on an image carrier 110. Whether the density of the 2nd toner image for controlling density is within the control limit of 2nd reference density previously set, that is, whether or not the developer is required to be exchanged is decided. In the case of deciding that the exchange is required, a signal showing that the developer is required to be exchanged is outputted. |
