Image formation system including an intermediate transfer belt and method for sensing and correcting speed and position variations of the belt

摘要

A registration pattern is formed on an intermediate transfer belt by using one photosensitive body. Pattern parts transferred onto the intermediate transfer belt vary in spacing due to speed variation occurring at the transfer time. The passing timing of the registration pattern is read through a read section placed downstream from the photosensitive body and speed (position) variation is sensed. The sense data is gotten over several cycles of the intermediate transfer belt and a low-frequency component caused by thickness unevenness of the intermediate transfer belt is extracted. The extracted data is subjected to the effects of variations at both the formation time and read time of the registration pattern and thus is corrected of calculating true speed (position) variation data. For example, a drive roll is controlled based on the data and an image is formed.