| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical encoder which prevents an erroneous detection from occurring even when an encoder sheet is stained, and correctly detects a carriage position and a speed, and an image forming apparatus. SOLUTION: A margin portion having the same characteristics as a transmission portion is provided in an encoder sheet, and a reference voltage is generated by light transmissive into the margin portion. Thus the reference voltage is changed according to the stain of the transmission portion and the margin portion, and the transmission portion is detected by the comparison of the changed reference voltage with the voltage of the transmission portion, which enables the transmission portion to be surely detected. COPYRIGHT: (C)2010,JPO&INPIT
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