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SCANNER
30 November, 1999
4. Image Scanning
[A]
[B]
[C]
H545D503.WMF
The image sensor [B] consists of a row of photosensitive elements (B4 width x 8
dots/mm). The document reflects light from the LED array and the rod lens array
focuses it onto the image sensor. Because of the short optical path inside the CIS,
the focal depth is much shorter than for a CCD type scanner. Consequently, the
spring plates [C] push the white roller [A] so that the document surface always
touches the exposure glass at the scan line.
The image sensor assembly is factory adjusted, so it does not require adjustment
or replacement in the field.
The image sensor scans the original one line at a time, and outputs an analog
signal for each line. The voltage from each element depends on the intensity of the
light reflected from the original onto the element; the light intensity depends on the
darkness of the document area it was reflected from.
The white roller [A] must be kept clean, because the machine scans it every page
to calibrate the white level (auto shading).
2-2
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