Abstract: The apparatus includes an endless belt, an imaging station, a number of developing stations, and a number of transfer stations. A controllable belt drive drives the endless belt along a path through the imaging station, the developing stations and the transfer stations. A preformed timing mark is carried on the belt and a sensor is provided for sensing the passage of the timing mark past a sensing position. A control device controls the belt drive to run at a constant speed and controls the speed of the belt in response to the sensing of the timing mark. The maintenance of a constant belt speed can be more reliably assured.

Abstract: A plurality of electrostatic images are formed on a moving tensioned belt formed with an electrically conductive base having a non-conductive image-carrying surface layer. The images are developed by passing the belt through toner development stations, each of which includes a development unit including a magnetic roller and a backing member, in opposed position to the magnetic roller, over which the belt passes. Under non-ideal conditions, the image quality in terms of image density and uniformity of image density and rendition of sharp image transitions, is substantially improved by applying an alternating electrical field between the magnetic roller and the belt, with a peak-to-peak voltage greater than 800 volts.

Abstract: An image forming apparatus is used, in which an electrostatic image formed on a moving image forming belt is developed by AC development. Where the image forming belt moves at a speed of v.sub.p mm/s, the cleaning potential is V.sub.cl volts, and the AC bias frequency is f kHz, the function Z satisfies the following equation: ##EQU1## Images substantially free of background development are thereby obtained.