| 摘要 |
PURPOSE:To reduce the influence of the irregular reflection of projection light due to a flaw of the substrate of a roller, etc., and to prevent measurement accuracy from decreasing by measuring the thickness of an ink film by a detector without setting the detector in focus on the roller surface. CONSTITUTION:The detector is so constituted that a measurement is taken without setting its focal length to the roller surface. Consequently, when laser light 3 is projected on the substrate 8 of a roller 1 which has the flaw 12, light reflected there is converged 4, but the screen 7 of the detector 5 is positioned in front of the focus of a lens and the spread of an image increases, so that a brightness distribution 10 becomes hard to have an error. Therefore, the influence of the irregular reflection of the projection light due to the flaw of the substrate of the roller, etc., is reducible.
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