| 摘要 |
PURPOSE:To eliminate the instability of image quality and to decrease the wasteful consumption of a carrier by providing a means for determining whether the simultaneous exchange of the developers in all developing tanks is necessary or not. CONSTITUTION:Means 11, 13 for detecting the number of image forming times which detect the number of the image forming times by using the same developer are provided to each of the developing tanks. The means 12 for determining whether the exchange of all the developers is necessary or not according to the number of the image forming times for each of the developing tanks and means 91a-91e for displaying whether the exchange of the developers is necessary or not are provided. The display to urge the exchange is, therefore, executable before the electrostatic chargeability of the developers is degraded at such a time when, for example, the number of use times of at least one developing tank attains the number of the limit use times slightly more than the number of the use times or when the average of the number of the use times of all the developing tanks attains 10,000 sheets or at the exact timing for the exchange by comparison with the developer which does not attain the number of the use times to the exchange. The fluctuation in the electrostatic chargeability, the wasteful consumption of the developers and the wasteful operation of maintenance, etc., are thereby eliminated. |
