Image forming apparatus and image forming method that perform inspection using line sensors

An image forming method comprising:

• forming an image on at least one of front and back surfaces of a sheet being transported in a transportation path along a transportation direction;
• forming marks for position detection on the front and back surfaces;
• reading the front surface using a first line sensor disposed on a front surface side and
• reading the back surface using a second line sensor disposed on a back surface side, wherein when viewed in a width direction of the sheet perpendicular to the transportation direction, the first and second line sensors are disposed such that:
• a first detection range of the first line sensor on the front surface partially overlaps a second detection range of the second line sensor on the back surface;
• and
• a part of the first detection range and a part of the second detection range that do not overlap each other extend in one direction and another direction along the sheet width direction, and
• the marks are formed in four corners of the first detection range and in four corners of the second detection range;
• storing, in a storage, relative positional information between a position detected by the first line sensor and a position detected by the second line sensor, wherein
• the relative positional information is measured based on images that are formed on the sheet with a width smaller than a region in which the first and second detection ranges overlap each other and that are read by the first and second line sensors;
• calculating:
• a positional deviation between the images formed on the front and back surfaces based on positions of the marks on the front surface read by the first line sensor and positions of the marks on the back surface read by the second line sensor;
• a size of the sheet read by the second line sensor from a sheet edge position detected by the first line sensor and the relative positional information;
• and
• a size of the sheet read by the first line sensor from a sheet edge position detected by the second line sensor and the relative positional information;
• and
• adjusting positions of the images formed on the front and back surfaces.

A non-transitory computer-readable recording medium storing a program causing a computer to execute:

• controlling an image forming apparatus that comprises a first line sensor that is disposed on a front surface side and reads a front surface of a sheet being transported in a transportation path along a transportation direction, and a second line sensor that is disposed on a back surface side and reads a back surface of the sheet, wherein
• when viewed in a width direction of the sheet perpendicular to the transportation direction, a first detection range of the first line sensor on the front surface partially overlaps a second detection range of the second line sensor on the back surface, and
• a part of the first detection range and a part of the second detection range that do not overlap each other extend in one direction and another direction along the sheet width direction,
• wherein the program causes a computer to execute:
• forming an image on at least one of the front and second surfaces;
• forming marks for position detection on the front and second surfaces, wherein the marks are formed in four corners of the first detection range and in four corners of the second detection range;
• reading the front surface using the first line sensor and reading the back surface using the second line sensor;
• storing, in a storage, relative positional information between a position detected by the first line sensor and a position detected by the second line sensor, wherein
• the relative positional information is measured based on images that are formed on the sheet with a width smaller than a region in which the first and second detection ranges overlap each other and that are read by the first and second line sensors;
• calculating:
• a positional deviation between the images formed on the front and back surfaces based on positions of the marks on the front surface read by the first line sensor and positions of the marks on the back surface read by the second line sensor;
• a size of the sheet read by the second line sensor from a sheet edge position detected by the first line sensor and the relative positional information;
• and
• a size of the sheet read by the first line sensor from a sheet edge position detected by the second line sensor and the relative positional information;
• and
• adjusting positions of the images formed on the front and back surfaces.