摘要 |
PURPOSE:To perform developer change, machine stop, etc., at proper timing by detecting a corrected reference value as reaching a prescribed value in a detection part, counting the number of cycles continuing the prescribed value and discriminating the service life of developer concentration. CONSTITUTION:An electrostatic latent image on a photosensitive body 1 is developed by a developing means 4, which is provided with an F sensor 30 for detecting the developer concentration. Toner is supplied to the developing means 4 from a supplying means 10 when the developer concentration detected by the F sensor 30 drops to the reference value or below. The developer concentration of a picture developed on the photosensitive body 1 is detected by a P sensor 25 facing with the photosensitive body 1 and the reference value of the developer concentration is corrected according to the outputs of the P sensor 25. When the corrected reference value is detected as reaching the prescribed value in the detection part, the number of cycles continuing the prescribed value is counted and the developer service life is thus judged. Thereby, the developer change, the machine stop, etc., can be performed at proper timing. |