Abstract: The object of this invention is to provide an image forming apparatus capable of preventing decrease in image density at a rear end part of an image. A change in waveform in sensor outputs which is produced when a toner patch image is read by an optical sensor used for the process control is detected. The difference (Vg−Vd) between grid voltage Vg and development bias voltage Vd is changed only between a target value of 300 V corresponding to low-output side threshold value Va and a target value of 100 V corresponding to high-output side threshold value Vb according to the sensor output deflection &Dgr;V so that the difference (Vg−Vd) decreases as the image loss level increases. The difference between the grid voltage Vg and the development bias voltage Vd is set so as to prevent the image loss in the rear end part of an image.

Abstract: An image forming apparatus including a developing unit for stocking a developing agent containing toner and forming a toner image on a photosensitive medium with the developing agent, a toner supply unit for supplying the toner to the developing unit, a toner specific concentration detecting unit for detecting the toner specific concentration of the developing agent stocked in the developing unit, a humidity detecting unit for detecting humidity in the neighborhood of the developing unit, a storage unit for storing the humidity information detected by the humidity detecting unit, and a toner specific concentration correcting unit for controlling the toner supply amount of the toner supply unit on the basis of the humidity information stored to correct the toner specific concentration, wherein the toner specific concentration correcting unit compares newly-detected humidity with reference humidity corresponding to the humidity which is detected at the time when the developing agent is stocked into the developi

Abstract: The object of this invention is to provide an image forming apparatus capable of preventing decrease in image density at a rear end part of an image. A change in waveform in sensor outputs which is produced when a toner patch image is read by an optical sensor used for the process control is detected. The difference (Vg-Vd) between grid voltage Vg and development bias voltage Vd is changed only between a target value of 300 V corresponding to low-output side threshold value Va and a target value of 100 V corresponding to high-output side threshold value Vb according to the sensor output deflection &Dgr;V so that the difference (Vg-Vd) decreases as the image loss level increases. The difference between the grid voltage Vg and the development bias voltage Vd is set so as to prevent the image loss in the rear end part of an image.