Patent ID: 8179569

Claim:
An image forming apparatus comprising: a plurality of image forming sections that forms images of different colors, respectively; a correction image formation controlling section that forms correction images, for density correction and color deviation correction, of the respective colors, by causing the image forming sections to draw the correction images and transferring the correction images onto an image carrying body; a density sensor that detects a density of each of the correction images in synchronization with passage of each of the correction images on the image carrying body; a detecting section that detects a position and the density of each of the correction images, based on a binary signal of a density detection output of each of the correction images; a density correction controlling section that corrects and controls a density of an image of a color whose density is abnormal, based on the detected density of each of the correction images; and a color deviation correction controlling section that corrects and controls a color deviation of an image of a color in which color deviation occurs, based on the detected position of each of the correction images, wherein the detecting section compares the density detection output of the density sensor with a first threshold value and a second threshold value, the first threshold value being larger than the second threshold value, the density detection output has characteristics of falling at the time of passage of a leading edge part of the correction images and rising at the time of passage of a rear edge part of the correction images, the detecting section detects the density of each of the correction images, based on (i) a width of time during which the density detection output varies from the first threshold value to the second threshold value at the time of falling or (ii) a width of time during which the density detection output varies from the second threshold value to the first threshold value at the time of rising, and the detecting section detects the position of each of the correction images, based on a width of time when the density detection output is at or exceeds the first threshold value from the time of falling to the time of rising.