Patent ID: 7384117

Claim:
An ink jet printer comprising: an ink tank for storing ink therein and a recording head for ejecting the ink stored in the ink tank as ink drops and forming an image on a recording paper sheet; a carriage on which the ink tank is attached; a driving mechanism for driving the carriage so as to move reciprocally in a direction substantially perpendicular to a direction for conveying the recording paper sheet; a displacement detection sensor for reading a predetermined displacement detection pattern formed on the recording paper sheet by the recording head; and a displacement correction control means for correcting a displacement of printing position by controlling ejection timing of the ink drops from the recording head based on a result of reading the displacement detection pattern by the displacement detection sensor; wherein the displacement detection sensor has: a light emitting device for emitting diffused light; a light receiving device for receiving the light emitted from the light emitting device and reflected by the recording paper sheet, converting the received light into an electric signal and outputting the electric signal to the displacement correction control means; a first lens for focusing the diffused light emitted from the light emitting device on the recording paper sheet; and a second lens for focusing the light reflected by the recording paper sheet on the light receiving device; and in the displacement detection sensor, the diffused light emitted from the light emitting device is focused by the first lens and reflected by the recording paper sheet, and then the diffused light is focused on the light receiving device by the second lens, wherein resin molded lenses according to a same standard are used for the first lens and the second lens, the first lens is disposed closer to the recording paper sheet than the second lens, and an optical axis of the first lens and an optical axis of the second lens are symmetrical with respect to a normal that is perpendicular to the recording paper sheet.