Abstract: An apparatus for controlling toner concentration includes a toner concentration detector, a toner supplier, a wave-former that periodically scrapes off toner from a detecting face of the toner concentration detector and thereby forms a wave of decreasing output of the toner concentration detector, and an about-minimum value detector that detects a minimum of the decreasing output. A toner concentration detection retarder is actuated from the time the minimum is detected. The toner supplier is actuated based on the detected toner concentration after the toner concentration detection retarder is released of action.

Abstract: The present invention provides a toner concentration control device which can measure the concentration of toner stably in an extended period of time without influenced by the shape of a developer stirring mixer rib and mounting position of a toner concentration detecting censer, with a result the stagnation or adhesion of toner in the proximity of the toner concentration detecting censer is eliminated, by so composing a toner concentration control device having a toner concentration censer for detecting magnetically the concentration of toner mounted facing a developer stirring mixer in a developing vessel, so that a waveform detection means which detects the output of the toner concentration censer for at least over one cycle before a toner supply means is activated, and an about-minimum value judging means which judges the minimum value or its vicinity detected by the waveform detection means are provided, and an about-minimum detection means is activated on the basis of the value judged as minimum or its

Abstract: An apparatus for controlling the density of a developer is described. The apparatus includes a developer container 51 in which a developer is enclosed; a detector 58 for magnetically detecting information about the density of the toner; toner supply for supplying toner in accordance with an output value from the detecting means; waveform forming for reducing an output value from the detecting means by operating mechanical means 56a for periodically raking out the developer existing on a detecting surface of the detecting means 58; and delaying means for inhibiting detection of the density of toner from a predetermined time at which the output value has been reduced to a time at which the output value is restored to a stable output value. The toner supply means can be operated in accordance with a value detected after the delay means has been suspended.