| 摘要 |
PURPOSE:To detect defects accurately by making a linearly polarized light parallel with the incident plane while selecting the incident angle as specified to eliminate interference of a transmission light of a laser light. CONSTITUTION:A laser light 11 is polarized with a revolving polyhedral mirror 12 to scan a sheet-shaped product 13 width-wise B as being carried at a specified speed and then, it is detected with a photodetector 15 through a diffusion plate 14. When the polarization of the laser light 11 incident into the surface of the sheet-shaped product 13 is done parallel with the incident plane, refracted light and reflected light on the boundary are all within the incident plane. Then, if the incident angle of the laser light 11 is selected to be the Brewster's angle thetai with respect to the incident normal L2 drawn in the width-wise direction of the sheet-shaped product 13, there is no reflection because the reflected lights have no component parallel with the incident plane but that vertical thereto only. This prevents the generation of noise due to interference of the transmission light thereby enabling accurate detection of flaws, dirts and the like existing in the sheet-shaped product. |
