| 摘要 |
A flat bed scanner for accurate scanning of document information includes a means for moving an image-bearing member, such as a document, under a slot in a bottom of an enclosure. The enclosure has a diffusely-reflecting internal surface so as to define a light-integrating space within the enclosure. The slot and a window in the enclosure side provide access for light between the exterior and the interior of the enclosure. Means are provided for directing a scanning beam of light through the window and the slot to form a moving spot on a portion of the document. Detector means are provided for sensing the intensity of light diffusely reflected into the enclosed space from the spot. An electronic signal, related to the intensity of the reflected light, is produced to describe the scanned document information. To compensate for variation in the light path length due to an angular scanning motion, a beam path length compensation means is included. The compensation means includes a movable tapered-thickness optical plate which is positioned in the light path. As the plate is moved in a direction transverse to the light path direction, the beam encounters a varying plate cross-section such that the beam focal point changes proportionally. Movement of the plate is synchronized with the motion of the scanning beam.
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