| 摘要 |
An image reading apparatus optically reads a document, which is placed on a document platen facing upward, from above. The image reading apparatus has a ultrasonic sensor. A ultrasonic wave is emitted from the ultrasonic sensor toward the document placed on the document platen, and distance from the ultrasonic sensor to the document are detected based on the time differential of the reflected wave from the document. Furthermore, the position of the document can be detected based on the strength or weakness of the reflected wave from the document. In this way the shape of the document in the document height direction can be detected. Moreover, the shape of the document in the document height direction can be accurately detected regardless of the document color.
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