Image forming apparatus to perform phase matching control to match phases of image-density cycle fluctuations

An image forming apparatus, comprising:

• a plurality of image formers each including:
• Y, M, C, and B (Yellow, Magenta, Cyan and Black) image bearers;
• a plurality of chargers to uniformly charge each of the image bearers;
• and
• a plurality of developer bearers corresponding to the image bearers to attach developer to an electrostatic latent image on each of the image bearers to form a visible image;
• an irradiator to illuminate each of the image bearers charged by the chargers to form the electrostatic latent image on each of the image bearers;
• and
• circuitry configured to:
• acquire an image-density cycle fluctuation in the visible image for each of the plurality of image formers;
• and
• perform image-density fluctuation-reduction control to cyclically change image forming conditions to reduce the image-density cycle fluctuation for each of the plurality of image formers on basis of the image-density cycle fluctuation of each of the plurality of image formers acquired by the circuitry,
• the circuitry being further configured to perform:
• first fluctuation-reduction control to correct a developing bias applied to the developer bearers, which is one of the image forming conditions, to cancel an image-density cycle fluctuation of a high-density image pattern acquired by the circuitry;
• second fluctuation-reduction control to, after the first fluctuation-reduction control, correct a charging bias applied to the chargers, which is one of the image forming conditions, to cancel an image-density cycle fluctuation of a first low-density image pattern acquired by the circuitry;
• and
• third fluctuation-reduction control to, after the first fluctuation-reduction control and the second fluctuation-reduction control, correct an exposure light amount of the irradiator, which is one of the image forming conditions, to cancel an image-density cycle fluctuation of a second low-density image pattern acquired by the circuitry, the high-density image pattern being higher in image density than each of the first low-density image pattern and the second low-density image pattern,
• wherein:
• the circuitry is configured to perform phase matching control which matches phases of image-density cycle fluctuations of the plurality of image formers on a recording medium, based on the image-density cycle fluctuations of the plurality of image formers acquired by the circuitry,
• the circuitry rotates the Y, M, and C image bearers to match the phases of the Y, M, and C image-density cycle fluctuations, and
• colors subjected to the phase matching control include the Y, M, and C colors.