| 摘要 |
A light beam 2 from a laser light source 30 is split by a beam splitting arrangement 21, 22 into two slightly convergent light beams which are deflected by a deflecting mirror 31 onto the surface of a mirror wheel 23. The mirror wheel 23 that deflects these light beams via deflecting mirrors 24', 25' onto two strip-like concave mirrors 24, 25 which produce respective parallel scanning light beams which are continuously displaced parallel to themselves in the image spaces of the strip-like concave mirrors. These scanning light beams fall on respective rows of inclined dividing mirrors 9 and 10 which are arranged one behind the other in an alternating sequence. The inclined mirrors deflect the incident light beams through substantially 90 DEG to form a continuous light curtain which can be used to scan web material. Light reflected from the surface of the web or transmitted through holes in the web falls on light gathering devices in the form of either two rows of strip-like Fresnel lenses 5, 6 or two rows of light conducting rods 5', 6'. One light gathering device is associated with each of the inclined mirrors 9, 10. Light gathered by each of the light gathering devices is directed to an associated photoelectric detector 7 which is connected to an electronic processing circuit 8 for evaluating the signals from all the photoelectric detectors.
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