Adf Scanning; Flat-Bed Scanning; Cis Drive Mechanism - Brother DCP6690CW Service Manual

The scanner mechanism offers two types of scanning: ADF scanning and flat-bed scanning. It
automatically switches to the former at the start of a scan operation if the document front sensor
inside the ADF detects a document.
(1) ADF scanning: Document moves across stationary CIS unit
Placing a document face up in the ADF activates the document front sensor, switching to ADF
scanning. At the same time, the document width sensor signals whether the document size is B4
or greater in width.
The CIS drive mechanism (details below) operates for each scanning command executed. First,
the CIS motor moves the CIS unit to the white reference film for white level compensation.
Secondly, the ADF motor rotates the document pull-in roller to pull the document into the ADF.
Thirdly, the CIS motor again moves the CIS unit to the ADF scanning position.
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 ejects subsequent pages above 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 with the left and top
edges fitting on the left and top guidelines 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 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, the CIS PCB converting the light input to pixel data output,
and the CIS glass.
The CIS unit used in the machine supports color scanning. In scanning color documents, the
CIS unit illuminates them by turning on the red (R), green (G), and blue (B) LEDs alternately.
In scanning monochrome documents, it turns on the green LEDs only.
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