Image forming apparatus using measurement images to control speed of photoreceptors and intermediate transfer member

An image forming apparatus comprising:

• a first image forming unit having a first photoreceptor and configured to form a first image on the first photoreceptor by using a first color toner;
• a second image forming unit having a second photoreceptor and configured to form a second image on the second photoreceptor by using a second color toner which is different from the first color toner;
• an intermediate transfer member configured to rotate in a predetermined direction and to which the first image and the second image are transferred;
• a transfer unit configured to transfer the first image and the second image from the intermediate transfer member to a sheet;
• a first sensor configured to measure measurement images on the first photoreceptor;
• a second sensor configured to measure measurement images on the intermediate transfer member;
• and
• a controller configured to:
• control the first image forming unit to form first measurement images, wherein the first measurement images are formed along a rotation direction of the first photoreceptor;
• control the first sensor to measure the first measurement images on the first photoreceptor;
• control the first image forming unit and the second image forming unit to form a plurality of measurement images while a rotation speed of the first photoreceptor is being controlled based on measurement results of the first measurement images by the first sensor, wherein the plurality of measurement images are formed along the predetermined direction of the intermediate transfer member, wherein the plurality of measurement images include reference measurement images formed by using the first color toner and second measurement images formed by using the second color toner, wherein positions at which the second measurement images are transferred on the intermediate transfer member are different from positions at which the reference measurement images are transferred on the intermediate transfer member in a direction orthogonal to the predetermined direction;
• control the second sensor to measure the plurality of measurement images;
• control a rotation speed of the second photoreceptor based on measurement results of the plurality of measurement images by the second sensors;
• control the first image forming unit to form third measurement images while the rotation speed of the first photoreceptor is being controlled based on the measurement results of the first measurement images by the first sensor, wherein the third measurement images are formed along the predetermined direction of the intermediate transfer member;
• control the second sensor to measure the third measurement images;
• and
• control a rotation speed of the intermediate transfer member based on measurement results of the third measurement images by the second sensor.