Patent ID: 8279491

Claim:
An image formation apparatus comprising: a plurality of image carriers; a transfer belt on which toner images formed on the image carriers are sequentially transferred; a pattern formation unit configured to prepare a reference pattern with a plurality of lines formed by a black color as a reference color, the reference pattern having a predetermined pitch between the lines, to prepare a color pattern to be corrected with a plurality of lines formed by a color toner, the color pattern having an equal pitch to the pitch in the reference pattern, to form a patch by superposing the reference pattern as a last color to be superposed on the color pattern, to prepare a plurality of patches each in which a position of the lines in the color pattern with respect to the lines in the reference pattern is shifted by a shift quantity in a pitch direction of the lines, to arrange the plurality of patches on the transfer belt along a movement direction thereof, to select, as a reference patch, either one of a patch in which the color pattern to be corrected is completely superposed by the reference pattern and a patch in which the color pattern to be corrected is completely displaced from the reference pattern, and to form a continuously formed patch group including the reference patch and the patches as a correction pattern; a detection sensor configured to detect diffused light output components of the continuously formed patch group; and a misalignment quantity correction unit configured to identify the reference patch and other patches based on an output signal from the detection sensor, to determine a misalignment quantity based on a position of the reference patch with respect to a span of the plurality of patches, and to correct the misalignment quantity.