Patent ID: 8712266

Claim:
An image forming apparatus, comprising: a first image bearing member configured to bear a toner image: a first developing device capable of coming into contact with and separating from the first image bearing member and configured to form a toner image on the first image bearing member; a second image bearing member configured to bear a toner image; a second developing device capable of coming into contact with and separating from the second image bearing member and configured to form a toner image on the second image bearing member; a rotary member onto which the toner images are transferred from the first and second image bearing members or configured to convey a recording medium onto which the toner images are transferred, the rotary member coming into contact with the first and second image bearing members so that the rotary member forms transfer sections with the first and second image bearing members, respectively; a patch detector configured to detect a toner patch transferred onto the transfer member from the first and second image bearing members; and a control device configured to control a relative velocity between the rotary member and the first and second image bearing members, wherein the image forming apparatus is capable of forming first and second toner patch patterns on the rotary member, the first toner patch pattern including a first toner patch to be transferred from the first image bearing member to the rotary member and a second toner patch to be transferred from the second image bearing member to the rotary member while the first and second developing devices are in contact with the first and second image bearing members, respectively, and the second toner patch pattern including a third toner patch to be transferred from the first image bearing member to the rotary member while the first and second developing devices are in contact with the first and second image bearing members, respectively, and a fourth toner patch to be transferred from the second image bearing member to the rotary member while the first developing device is separated from the first image bearing member and the second developing device is in contact with the second image bearing member, and wherein the control device controls the relative velocity between the rotary member and the first and second image bearing members based on detection results of detecting the first and second toner patch patterns by the patch detector.