| 摘要 |
<p>PURPOSE:To detect whether there is a sheet or not surely, so as to prevent any false detection due to a color of the sheet, by photoelectrically converting reflected or transmitted light from a light source through a receiving element, and judging the existence of the sheet when a potential in the absence of the sheet differs from that in the existence thereof to an extent exceeding a predetermined value. CONSTITUTION:Optical sensors 22, 23 are provided for detecting whether there is a document 3 or not when the document 3 is fed in the direction of an arrow 21 along a guide 20. A first sensor 22 for detecting the document 3 is located near by the guide 20, and a second sensor 23 is provided on the outside area of the guide 20, where there is not any possible passing of the document 3. Photoelectrically converted outputs 22a, 23a of receiving elements of both sensors 22, 23 are inputted to a comparing amplifier 28 through level regulating amplifiers 26, 27 in a processor 30. If the amplifiers 26, 27 are previously adjusted to equalize the levels of both outputs 22a, 23a in the absent state of the document 3, the converted output 22a is increased by the existence of the document 3, and it is judged that there is a document 3 when a potential difference exceeds a predetermined value. Thereby, it is possible to surely detect whether there is the document 3 or not without the occurrence of any false detection due to a color.</p> |
