Patent ID: 7639957

Claim:
An image forming apparatus, comprising: an image carrier configured to form a latent image thereon with a light beam; a developing unit configured to develop the latent image formed on the image carrier with a two-component image developer including toner particles and carrier particles; a concentration sensor configured to detect a toner ratio in the developing unit; a toner supplying unit configured to supply fresh toner particles to the developing unit; a developer supplying unit configured to supply fresh image developer to the developing unit; an ejector configured to eject the image developer to an outside of the developing unit; a condition detector configures to detect a condition of the image developer being used for an image forming operation, and to determine a supply amount of the image developer to supply to the developing unit, the condition including a degradation level of the image developer in the developing unit; and a controller configured to compute a historically-averaged amount of toner particles consumed and supplied in the developing unit, based on a detection result of the condition detector, and to adjust an amount of any one of the image developer and the toner particles to be supplied to the developing unit based on an operated time of the developing unit obtained from a timer and a current condition of the image developer, determined based on the computed historically-averaged amount of toner particles.