Apparatus for controlling toner concentration in an electrophotographic device

A toner concentration control device comprising:

• a toner concentration detection means for detecting magnetically a toner concentration information of a toner in a developer vessel, the developer vessel storing a developer composed of a carrier and the toner;
• a toner supply means for supplying the developer based on the output of the toner concentration information;
• a wave-forming means for forming a wave of decreasing output of the toner concentration detection means reduced through periodically scraping off the toner on a detecting face of the toner concentration detection means;
• an about-minimum value detection means for detecting the minimum or its vicinity of the descending output reduced by the wave-forming means;
• wherein a toner concentration detection retarding means is actuated from the time the minimum value or its vicinity is detected,
• wherein the toner supply means is actuated based on the detected toner concentration information after the toner concentration detection retarding means is released of action;
• and
• wherein the toner concentration detection means includes a waveform measuring means which measures the output of the toner concentration detection means over a predetermined period longer than the period of one cycle of a scraping cycle, and an about-minimum value judging means which determines the minimum or its vicinity of the output value measured by the waveform measuring means;
• and the toner concentration determining means is actuated based on the value judged as the minimum or its vicinity the about-minimum judging means before the toner supply means is actuated.