Patent ID: 8562096

Claim:
An image forming apparatus comprising: a first carriage comprising a print head independently movable in a main scanning direction; a second carriage comprising a print head integrally movable in the main scanning direction together with the first carriage; an encoder sheet useable in detecting positions of the first carriage and the second carriage in the main scanning direction; a first home position reference unit associated with the first carriage; a second home position reference unit associated with the second carriage; a home position detector configured to detect the first home position reference unit and the second home position reference unit; a first position detector associated with the first carriage, and configured to detect a position of the first carriage by reading the encoder sheet; a second position detector associated with the second carriage, and configured to detect a position of the second carriage by reading the encoder sheet; and a control unit comprising a central processing unit, configured to control ejection of ink from the print head of the first carriage based on an output from the first position detector when the home position detector detects the first home position reference unit, and to control ejection of ink from the print head of the second carriage based on an output from the second position detector when the home position detector detects the second home position reference unit, wherein one of the first carriage and the second carriage further comprises a relative position encoder sheet, useable in detecting a position in the main scanning direction, and the other of the first carriage and the second carriage further comprises a third position detector configured to detect relative positions of the first carriage and the second carriage by reading the relative position encoder sheet, and wherein a relative tilt between the first carriage and the second carriage is detected based on outputs of the first position detector, the second position detector, and the third position detector.