| 摘要 |
PURPOSE:To discriminate a defect of sheet due to a bug easily and accurately, by computing an electrical signal level value due to changes in the quantity of light in terms of reflection and that due to the changes in the quantity of light of transmission type for the same defect. CONSTITUTION:An electrical signal is outputted to a circuit section 11 according to the quantity of light of light receiving units 4, 7 and 10 and the level thereof is adjusted to be constant by gain adjustment of an amplifier 12. Then, the difference in the phase due to the difference of measuring positions is adjusted with a shift circuit 13 to make the phase the same. With any defect on a sheet, the reflectance and transmissivity and the like changes and signals corresponding to the defect are inputted into the amplifier 12 from light receivers 4, 7 and 10, the output of which is a mixed signal wave of a defect signal and a noise. The defect signal alone is pick up with the subsequent discriminator and inputted into a control section 15 to compare the level values of defect electrical signals from upper/lower surface reflection type defect detectors 2 and 5 and the level value thereof from a transmission type detect detector 8. When the level values of the units 2 and 5 are equal to or larger than the level value of the unit 8, the defect due to a bug is discriminated. |
