| 摘要 |
PURPOSE:To prevent a large error in measurement from occurring even if the kinds of sheets changes by measuring sheet length by utilizing plural optical detecting means which differ in spectral sensitivity characteristics. CONSTITUTION:A 1st optical detecting means PD1 which has a relatively large reflection factor and the peak of sensitivity at 580nm and 2nd optical detecting means PD2 and PD3 which the peak of sensitivity at 420nm wavelength different from the wavelength of light reflected by a pressure plate are used and then a relatively large signal level is obtained by either of the both for any sheet. Thus, the plural optical detecting means which differ in spectral sensitivity characteristics are utilized to reduce variance in detection level corresponding to the kind of a sheet and errors in measurement.
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