| 摘要 |
The invention concerns an illumination system for moving sheets which are scanned by an imaging device. Because the moving sheets can flutter as they are scanned, their distance from the imaging device can change, thereby changing the amount of light captured by the imaging device. The invention reduces this change, and provides a method for selecting a distance at which the changes are minimal. The invention also provides the following features: (1) An apparatus for illuminating the sheet uniformly, thus reducing the possibility that naturally dark regions of the sheet may be interpreted as data. (2) A method of selecting an optimal angle of incidence for incoming light, in order to maximize contrast between the sheet and data marks. (3) A procedure for collecting maximal light from a lamp, using a fiber optic bundle which is of a fixed diameter. (4) A procedure for improving light capture or image contrast, based on measured values of document specularity, mark specularity, fiber optic numerical aperture, reflectance of the sheet, and diffusion coefficient of the sheet. (5) Fiber optic light projectors whose projecting ends are bevelled in a single facet, thereby increasing the angle of incidence, without changing position of the fibers. (6) A procedure for accommodating the image shift caused by glass plates which guide the moving sheets, and through which the imaging device must look. (7) A procedure for reducing cross-talk between two illuminator-imaging device assemblies, which image opposite sides of the same sheet.
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