Image forming apparatus for detecting speed fluctuation

An image forming apparatus comprising:

• an image carrier that has a visible image carried on a rotating peripheral surface thereof;
• a driving source that generates a driving force for rotating and driving the image carrier;
• a rotation detection unit that detects a rotational angle speed or a rotational angle displacement of the image carrier;
• and
• a control unit that performs
• fluctuation pattern recognition processing for detecting a speed fluctuation of the image carrier based on an output from the rotation detection unit while driving the driving source in a state in which a print job in accordance with a user's instruction is not performed, thereby recognizing a speed fluctuation pattern per integer rotation of the image carrier,
• control pattern construction processing for constructing a speed control pattern of the driving source that reduces a cyclic speed fluctuation of the image carrier based on the speed fluctuation pattern,
• speed fine-adjustment processing for finely adjusting a driving speed of the driving source in accordance with the speed control pattern during a transfer process including at least a process for transferring the visible image on the peripheral surface of the image carrier to a transfer body or a process for transferring a visible image on another image carrier to the peripheral surface of the image carrier, and
• remaining pattern recognition processing for detecting a remaining speed fluctuation remaining in the image carrier even after the speed fine-adjustment processing is performed, thereby recognizing a remaining speed fluctuation pattern per integer rotation of the image carrier;
• wherein
• the control unit is configured to perform control pattern correction processing for setting a frequency band of the remaining speed fluctuation to be detected by the remaining pattern recognition processing narrower than a frequency band of the speed fluctuation to be detected by the fluctuation pattern recognition processing and correcting the speed control pattern so as to be a pattern capable of reducing even the remaining speed fluctuation based on the remaining speed fluctuation pattern recognized by the remaining pattern recognition processing.