| 摘要 |
PURPOSE:To immediately detect the abnormality of a toner concentration sensor by deciding the abnormality based on the variation of periodical sample value of toner concentration detected value for controlling the toner concentration. CONSTITUTION:When the toner concentration sensed by a toner concentration sensor 101 becomes lower than specified one, a toner replenishing roller 103 is started to be actuated through a comparison means 102 so as to replenish toner to a developing device from a hopper. Meanwhile, the toner concentration sensed by the sensor 101 is periodically sampled by a sampling means 104 so as to calculate the variation of the toner concentration in an operation means 105. When the calculated value which usually vibratingly changes becomes equal to or below the specified value, the abnormality can be decided through a comparison means 106 and decision means 107, etc., and the abnormality of the toner concentration sensor caused by the adhesion of the toner, etc., can be immediately detected. |
