Controlling timing for starting image formation

An image forming apparatus for forming a full color image by superimposing a plurality of color images including a first color image, a second color image, a third color image, and a fourth color image, the apparatus comprising:

• an image carrier configured to rotate in a first direction;
• an intermediate transfer body including a mark thereon, configured to rotate in a direction opposite to the first direction;
• a mark detector provided in a vicinity of the intermediate transfer body and configured to output an image forming start signal when the mark rotates one revolution together with the intermediate transfer body;
• a light detector provided in a vicinity of the image carrier and configured to output a synchronization signal at a timing determined by a periodic cycle value T;
• a timing controller configured to determine:
• a first time value based on an initial value of the first time value;
• a second time value based on a first difference value, wherein the first difference value corresponds to a difference between the first time value and an initial value of the second time value;
• a third time value based on a fourth difference value, wherein the fourth difference value corresponds to a difference between an initial value of the third time value and the second time value;
• and
• a fourth time value based on a fifth difference value, wherein the fifth difference value corresponds to a difference between an initial value of the fourth time value and a third average value being obtained by averaging the second time value and the third time value,
• wherein the initial value of each one of the first time value, the second time value, the third time value, and the fourth time value is determined based on a time period between a timing when the image forming start signal is output and the timing when the synchronization signal is output;
• and
• an optical writing device configured to scan an n number of light beams in a direction perpendicular to the first direction to form, on a surface of the image carrier, the first color image at a timing indicated by the first time value, the second color image at a timing indicated by the second time value, the third color image at a timing indicated by the third time value, and the fourth color image at a timing indicated by the fourth time value.

A method for controlling a timing for staring formation of a plurality of images formed by irradiating a plurality of light beams, the method comprising:

• obtaining a timing when a first synchronization signal for a preceding image is firstly detected after a timing when an image forming start signal for the preceding image is detected;
• determining whether the first synchronization signal can be used as a first reference synchronization signal for the preceding image by comparing the timing when the first synchronization signal is detected with a first reference value to generate a first comparison result;
• starting formation of the preceding image at a first timing determined based on the first comparison result;
• obtaining a timing when a second synchronization signal for a following image is firstly detected after a timing when an image forming start signal for the following image is detected;
• determining whether the second synchronization signal can be used as a second reference synchronization signal for the following image by comparing the timing when the second synchronization signal is detected with the first timing to generate a second comparison result;
• determining whether a preceding one of the plurality of light beams, which is output at the timing when the second synchronization signal is detected, can be used as a reference beam for the following image by comparing the timing when the second synchronization signal is detected with the first timing to generate a third comparison result;
• and
• starting formation of the following image at a second timing determined based on the second comparison result and the third comparison result.