Image forming apparatus

An image forming apparatus comprising:

• a conveyance part for conveying a sheet:
• an image forming part which on a basis of print data, forms an image on the sheet conveyed by the conveyance part;
• a sheet detection sensor which is placed on an upstream side of the image forming part in a sheet conveyance direction and which, on a basis of scanning image data formed by reading of the sheet, detects an edge position of the sheet in a sheet width direction perpendicular to the sheet conveyance direction;
• a sensor unit including the sheet detection sensor;
• and
• a controller which adjusts an image formation position on the sheet formed by the image forming part on a basis of a difference in the width direction between the edge position detected by the sheet detection sensor and a predetermined reference position, wherein
• the sheet detection sensor is configured that a plurality of sensor blocks each with a predetermined reading resolution and with a plurality of sensor elements mounted thereon at specified intervals are arrayed in the sheet width direction,
• the controller is enabled to execute a calibration which corrects an error in the sheet detection sensor caused by variations of intervals of the sensor elements at border portions between the plurality of the sensor blocks by inserting interpolation pixels into the scanning image data, and
• the controller forms, during execution of the calibration, the scanning image data by reading the sheet by means of the sheet detection sensor with a specified pixel count of the interpolation pixels inserted, and executes, repeatedly with the pixel count changed, image formation using second corrected image data obtained by cutting print image data of an image width A to make the print image data smaller than a width L of the sheet by a distance B, the print image data being obtained by deleting data overlapping with widthwise outer areas of the sheet from print image data formed of a solid image of an image width A′(A<A′) larger than the width L of the sheet by using the formed scanning image data, whereby the controller takes, as an optimum value, a pixel count of the interpolation pixels that causes a margin formed in the sheet with the second corrected image printed thereon to become B/2.