Image forming apparatus with a two component developer, toner density detection and toner density correction

Abstract

An image forming apparatus in which a predetermined image density can be obtained by correcting a toner density control target value without consuming toner. The output value Vt of the magnetic permeability sensor and the target output value Vtare compared, and the toner density is controlled by controlling a powder pump on the basis of the comparative result thereof so that the output value Vt approximates the target output value Vt. In addition, the target output value Vtis corrected on the basis of the detected result of the image coverage ratio so as to maintain a predetermined development potential of the development apparatus. By virtue of this, even when image forming that involves a significant change in the toner replacement amount in the development apparatus is performed, for example, even when an image of high image coverage ratio is output, the toner density is adjusted to maintain the development capability at a constant, and a predetermined image density is ensured. Moreover, because the image coverage ratio can be detected without consuming toner, toner does not need to be consumed when the target output value Vtis corrected.