TONER DENSITY CONTROLLING METHOD AND APPARATUS

A toner density controlling apparatus adapted to control toner density by sensing a T/D level in a developer vessel by using a toner sensor performs a toner density controlling operation on the basis of an output of the toner sensor while maintaining an input control voltage to be applied to the toner sensor at a predetermined level in a definite control range where the toner sensor output decreases proportionally to the T/D level in a linear relation. Conversely, in an indefinite control range where the relationship between the toner sensor output and the T/D level is nonlinear, the input control voltage to be applied to the toner sensor is variably controlled so that the toner sensor output can be adjusted to an upper or lower limit level of the definite control range, and the toner density controlling operation is performed on the basis of the input control voltage. With such an arrangement, even if the definite control range where the toner sensor output decreases proportionally to the T/D level in a linear relation is narrow, the toner density controlling operation can be performed on the basis of the input control voltage in the other control ranges. Therefore, even if an image forming apparatus provided with such a toner density controlling apparatus is used in an extensively varied environment, the toner density can properly be controlled by using a single toner sensor.