Detection of toner depletion in an electrophotographic printing system

Abstract

A toner depletion detection system in an electrophotographic printer uses an optical density sensor to detect the depletion of toner. The optical density sensor is used by the electrophotographic printer to maintain the developed optical density at an optimum value by adjusting a DC offset voltage supplied to a developer to compensate for changes in the developed optical density. Additionally, the optical density sensor is used in a calibration which linearizes the relationship between the optical density of a developed halftone pattern and increments of the laser pulse width. In a first embodiment of the toner depletion detection system, the magnitude of the DC offset voltage supplied to the developer to compensate for changes in the developed optical density is monitored. When the magnitude of this DC offset voltage exceeds an empirically determined threshold value, the toner depletion condition is indicated. In a second embodiment of the toner depletion detection system, the relationship between the optical density of a developed halftone pattern and increments of the laser pulse width is periodically determined by the electrophotographic printer. When this relationship has shifted sufficiently, relative to a empirically determined threshold relationship, the toner depletion condition is indicated.