Brother MFC-9420CN Service Manual page 81

(1) ADF scanning: Document moves across stationary CIS unit
Placing a document face up in the document support 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.
The document separation roller feeds the pages one at a time, starting from the top, to the
document feed roller, which rotates to move the page in a curve left, down, and right.
The page is scanned as it passes over the CIS unit. It then leaves the machine face down onto
the document cover. 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 self-focus lens array
gathering the light reflected from the scanned image, the CIS PCB converting the light input to
pixel data output, and a glass cover.
The CIS unit can scan the color document. When scanning the color document, the unit turns on
the three-color LED lines of red, green and blue (R, G, B) alternately and illuminates the document.
When scanning the black/white document, it turns on the green LED line only to scan.
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