Image forming apparatus that forms color image by superimposing plurality of images in different colors

An image forming apparatus that is capable of forming an image at a plurality of image forming speeds, the image forming apparatus comprising:

• an image forming unit that has a first image forming part configured to form a first image of a first color and a second image forming part configured to form a second image of a second color different from the first color, the image forming unit configured to form the image using the first image forming part and the second image forming part;
• a sheet container configured to contain a sheet;
• an image bearing member configured to bear the first image and the second image, and to convey the first image and the second image;
• a transfer unit configured to transfer the first and second images borne by the image bearing member to the sheet;
• a controller configured to control the image forming unit to form a measurement pattern including a first measurement image formed by the first image forming part and a second measurement image formed by the second image forming part;
• a measurement unit configured to measure the measurement pattern formed on the image bearing member;
• a determination unit configured to determine first information related to a relative position of the first measurement image and the second measurement image in a conveyance direction of the image bearing member based on a first measurement result of a first measurement pattern, by the measurement unit, formed by the image forming unit at a first image forming speed, and to determine second information related to a relative position of the first measurement image and the second measurement image in the conveyance direction of the image bearing member based on a second measurement result of a second measurement pattern, by the measurement unit, formed by the image forming unit at a second image forming speed different from the first image forming speed;
• a generating unit configured to generate correlation data based on the first information and the second information determined by the determination unit;
• and
• a correction unit configured to, in a case where the image forming unit forms the image at the first image forming speed, correct a relative position of the first image and the second image in the conveyance direction based on the first information determined by the determination unit, and to, in a case where the image forming unit forms the image at the second image forming speed, correct a relative position of the first image and the second image in the conveyance direction based on the first information determined by the determination unit and correlation data generated by the generating unit,
• wherein the controller is further configured to execute a first image forming process when the image forming unit forms the measurement pattern at the first image forming speed in a case where a first condition is satisfied, and to execute a second image forming process when the image forming unit forms the measurement pattern at both the first image forming speed and the second image forming speed in a case where a second condition is satisfied while the sheet container contains a sheet corresponding to the second image forming speed, and
• wherein the second image forming process is not executed if the second condition is satisfied while the sheet container does not contain a sheet corresponding to the second image forming speed.