Image forming device having transfer registration control

An image forming apparatus which repeats image create/transfer processing, which is serial processing of forming a toner image on a photosensitive member while rotating said photosensitive member and a transfer medium in a sub scanning direction and thereafter transferring said toner image onto said transfer medium, for a plurality of toner colors, to thereby lay toner images in said respective toner colors over each other on said transfer medium and accordingly form a color image,

• said apparatus comprising:
• abutting means which temporarily contacts said transfer medium, in one sequence which corresponds to an operation state of said apparatus, while said image create/transfer processing is repeated;
• memory means which stores a plurality of registration control amounts which are necessary to correct relative registration deviations among toner images on said transfer medium which are created because of contact and separation from said transfer medium;
• control means which reads one of said plurality of registration control amounts which corresponds to said one sequence from said memory means and corrects transfer start positions for toner images in said respective toner colors based on a read registration control amount;
• said control means executes a registration control amount establish processing before the color image is formed, to thereby identify one of said plurality of registration control amounts;
• said registration control amount establish processing used to identify one of said plurality of registration control amounts while allowing said abutting means to contact and move away from said transfer medium which is in rotation in a dedicated sequence which is different from a printing sequence which is for forming a color image;
• a drive source which generates rotational drive force;
• power transmission means which comprises a plurality of power transmission members which transmit the rotational drive force from said drive source to said photosensitive member and said transfer medium, wherein said transfer medium is a transfer belt;
• at least one of said plurality of power transmission members or said transfer medium is elastically deformed in accordance with a load change which is generated as said abutting means contacts and moves away from said transfer medium, to thereby create said registration deviations;
• and
• reference signal detecting means which outputs a reference signal in relation to rotation of said transfer medium,
• wherein said registration control amount establish processing is used,
• to measure based on said reference signal,
• (a) a period during which said abutting means which used to be away from said transfer medium contacts said transfer medium,
• (b) a period during which said abutting means remains contacting said transfer medium,
• (c) a period during which said abutting means which used to remain contacting said transfer medium moves away from said transfer medium, and
• (d) a period during which said abutting means remains separated away from said transfer medium, and
• to identify one of said plurality of registration control amounts based on an amount of a difference between these periods.