Image forming system and method of detecting color misregistration

An image forming system, comprising:

• multiple image carriers;
• an optical writing unit configured to optically write images on respective surfaces of the multiple image carriers;
• a transfer member in a form of a closed loop extended by a drive roller and at least one driven roller and configured to receive the images formed on the multiple image carriers on one of a surface thereof and a recording medium carried thereby;
• a rotation detector configured to detect a rotation condition of the at least one driven roller;
• a roller driving unit configured to drive the drive roller;
• a belt controller configured to transmit detection results obtained by the rotation detector to the roller driving unit;
• an image detector configured to detect the images formed on the surface of the transfer member at given intervals along a travel direction of the transfer member and obtain detection data;
• and
• a controller configured to calculate an amount of misregistration with respect to a reference interval of the images based on the detection data obtained by the image detector and correct relative misregistration of a scanning line between adjacent image carriers,
• a distance from a first transfer position of each of the multiple image carriers to a detection position of the image detector being an integer multiple of a travel distance of the transfer member during one revolution of the at least one driven roller, the at least one driven roller being a different size than the drive roller and including the rotation detector, the rotation detector detecting the rotation condition.