REVERSE SIDE SCANNING
22 December 1998
2-22
2.5.2 CIS (CONTACT IMAGE SENSOR) UNIT
The CIS unit consists of the LED array (68 chips/line x 2 lines) [A], rod lens array
[B], five CCDs [C], and the CIS drive board [D] (this contains the CCD drive circuit,
analog processing circuit, A/D converter, shading correction IC, and LED drive
circuit). The CIS unit scans 4800 pixels in the main scan direction at a resolution of
400 dpi (15.7 lines/mm).
There is a row of LEDs on each side of the CCD so that the light is of almost equal
intensity in all directions. This reduces shadows at the edges of documents.
The five CCDs are arranged as shown above (viewed from directly above the
original feed path). The CCDs have dummy pixels at the ends, so to get a
continuous scan across the page, the CCDs have to overlap. However, as a result,
a continuous line cannot be scanned across the page at the same time. Data is
held in memory and combined later.
In book mode when scanning the front side, the scanner may stop if the buffer fills
up. This may happen if the data is complex. Scanning may not start again in
exactly the same place, due to mechanical inaccuracies. This is not a big problem
when scanning the front side. However, for the reverse side, because a complete
scan line is not scanned at the same time, it could mean loss of data.
Because of this, reverse side scanning is only enabled at 6 reproduction ratios
(expressed in the driver as dpi: 100, 200, 300, 400, 500, and 600 dpi). This is
because there is not enough memory to buffer the data and calculate the pixels for
the resulting image at other resolutions without stopping the scanner.
G411D513.WMF
G411D528.WMF
[A]
[C]
[D]
[B]
[C]
