Patent ID: 8577278

Claim:
An image forming apparatus that forms an image on a sheet, the image forming apparatus comprising: an image forming portion that forms an image on a sheet, having an intermediate transfer belt onto which a toner image formed on a photosensitive drum is primary-transferred and a secondary transfer device which transfers the toner images formed on the intermediate transfer belt onto the sheet; a sheet feeding portion that feeds a sheet from a sheet storing portion that stores sheets, to the image forming portion through a feeding path; a registration roller pair that conveys the sheet fed by the sheet feeding portion to the image forming portion; a sheet re-conveying portion that conveys a sheet on a first side of which an image has been formed in the image forming portion, to the image forming portion to form an image on a second side of the sheet through a re-conveying path; an edge position detecting sensor, disposed upstream of the registration roller pair and downstream of a confluence of the feeding path and the re-conveying path, configured to detect a first side edge position along a sheet feeding direction of a sheet fed to the image forming portion by the sheet feeding portion and to detect a second side edge position along a sheet conveying direction of a sheet conveyed to the image forming portion by the sheet re-conveying portion; and a control portion configured to adjust, after images are formed on a first side and a second side of a first sheet and based on a detected first side edge position of the first sheet fed by the sheet feeding portion, a detected second side edge position of the first sheet conveyed by the sheet re-conveying portion detected by the edge position detecting sensor, and a detected first side edge position of a second sheet fed by the sheet feeding portion, an image position of an image of the image forming portion to be formed on a second side of the second sheet, wherein, for each set of a first and second consecutive sheet in a job, the control portion: computes, as a computed difference, a difference between a detected first side edge position of the first sheet fed by the sheet feeding portion and a detected second side edge position of the first sheet conveyed by the sheet re-conveying portion detected by the edge position detecting sensor, computes, by adding the computed difference to a detected first side edge position of the second sheet fed by the sheet feeding portion, a computed second side edge position in the image forming portion of the second sheet conveyed by the sheet re-conveying portion, and adjusts the image position of the image to be formed on the second side of the second sheet based on the computed second side edge position in the image forming portion of the second sheet.