Brother MFC620CN Service Manual page 95

(1) ADF scanning: Document moves across stationary CIS unit
(MFC620CN/425CN/420CN/DCP120C and FAX2440C only)
Placing a document face down in the document tray activates the document front sensor, switching
to ADF scanning.
The CIS drive mechanism (details below) operates for each scanning command executed. The CIS
unit first moves to the white-level reference film for white level compensation and then to the ADF
scanning position.
The ADF motor then rotates the document pull-in roller to pull the document into the ADF. This
new roller has become necessary because this machine has a horizontal document path. The
document separation roller feeds the pages one at a time, starting from the bottom, to the document
feed roller, which rotates to move the page in a curve left, up, and right. The page is scanned as it
passes over the CIS unit. It then leaves the machine face up onto the document eject support. The
machine inserts subsequent pages under this one to preserve the document page order.
(2) Flat-bed scanning: CIS unit moves under stationary document
The user lifts the document cover, places a page (or open book) face down on the glass plate, and
closes the document cover.
The CIS drive mechanism (details below) operates for each scanning command executed. The CIS
unit first moves to the white-level reference film for white level compensation. It then moves right,
scanning as it goes. It returns to its home position after the scan.
CIS drive mechanism
The contact image sensor (CIS) unit rides along the CIS rail driven by the CIS drive belt.
Clockwise motion of the CIS motor moves the unit to the left; counterclockwise motion, to the
right. This unit consists of the document illumination LED array, the lens array gathering the light
reflected from the scanned image, and the CIS PCB converting the light input to pixel data output .
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