Apparatus for forming multiple toner images in register with each other on a substrate

The apparatus comprises an endless belt (26), an imaging station (29), a plurality of developing stations (35, 36, 37, 38), and a plurality of transfer stations (40, 41, 42, 43). A controllable belt drive (56) drives the endless belt (26) along a belt path (58) through the imaging station (29), the developing stations (35, 36, 37, 38) and the transfer stations (40, 41, 42, 43). A controllable substrate drive (76) drives the substrate (78) in sheet form along a substrate path (17) into synchronous contact with the endless belt (26) at the transfer stations (40, 41, 42, 43). A preformed timing mark (44) is carried on the belt (26) and a sensor (49) is provided for sensing the passage of the timing mark (44) past a sensing position (48). A control device (50) is provided for controlling the belt drive (56) to run at a constant speed and to control the speed of the belt (26) in response to the sensing of the timing mark (44). The maintenance of a constant belt speed can be more reliably assured.