Image forming apparatus with intermediate belt mark detection for image registration

Abstract

Depending on an arbitrarily set magnification of an image forming apparatus, either pulses of a line synchronization signal or pulses of a motor driving signal are selected. Each of the pulses of the line synchronization signal being generated when the laser beam scans the photosensitive drum in a main scan direction and the pulses of the motor driving signal are used for driving a scanner motor provided in an original reading unit at different speeds so as to enable the original to be read at different speeds so as to enable the magnification to be set to different values. The pulses of the signal thus selected are counted and a thus-obtained count value is output. Based on the count value, a time period between a time a reference mark provided on an intermediate transfer belt is detected and a time an electrostatic latent image is written on a photosensitive drum, when the electrostatic latent image is formed using image data output by the original reading unit directly and the electrostatic latent image is formed using image data stored and read out from a memory.