Patent ID: 8342628

Claim:
An image forming apparatus, comprising: a carriage comprising image forming units, the carriage driven reciprocally back and forth in a main scanning direction; a conveyance unit to convey a sheet of recording media to a position where the image forming units perform image formation; a first detector provided to the carriage, the first detector comprising a light emitting part and a light receiving part to periodically detect a pattern from a surface of the sheet, and the detected pattern including light and dark portions on the surface of the sheet; a calculation unit to calculate a relative amount of movement between the sheet and the image forming units by comparing patterns periodically detected by the first detector; and a control unit to control a timing to perform image formation by the image forming units and an amount of conveyance of the sheet conveyed by the conveyance unit based on a result calculated by the calculation unit, wherein the calculation unit calculates the relative amount of movement between the sheet and the image forming units by comparing a first pattern detected by the first detector including a particular arrangement of light and dark portions on the surface of the sheet and a second pattern detected by the first detector including the particular arrangement of light and dark portions on the surface of the sheet, the first pattern and the second pattern having been detected by the first detector at different points in time during movement of the carriage.