Elektrofotografische Bilderzeugungsvorrichtung

摘要

An image forming apparatus has a photoconductive element, a developing sleeve, a photosensor and a control device for controlling the dynamic range of an image. A background output VSG is produced from the photosensor when the photoconductive element is rotating and the developing sleeve is rotating and a background output VSG+ is produced from the photosensor when the photoconductive element is rotating and the developing sleeve is not rotating. The control device controls a developing bias, a charge potential, a quantity of exposing light or an amount of toner supply in response to the greater of the two values VSG or VSG+. Also, the gradient of the background output VSG is determined and is used to decide whether the image forming apparatus is in an unusual state or not.