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Scanner theory
Duplex ADF
The following illustration shows the paperpath, rollers and sensors used in the MF923 duplex ADF.
The MF923 duplex ADF enables the user to create duplex scans automatically, eliminating the need to
stop the scanning process to flip the media being duplicated over. The ADF uses a step motor, and a series of
sensors to determine the media's position in the paper path during the scan process.
The following steps are performed in creating a duplex scan on the MF923 duplex ADF.
1. The scanner control unit, on the controller board receives a command to create a scan, fax, or copy.
2. A signal is sent to the ADF to poll the paper present sensor to check if the media to be scanned is in the
correct position. The media must be placed in the ADF input tray so it actuates the paper present sensor. If the
ADF paper present sensor isn't actuated, a flatbed scan is run by default.
3. If the media has actuated the paper present sensor, an ADF scan is executed. At this point the roller on the
pick arm assembly drops and advances the paper into the ADF, actuating the document sensor. Actuating this
sensor determines that this will be the first side of the document to be scanned.
4. When the document sensor is actuated, a signal is sent to flatbed to move the CCD imaging unit to the ADF
scan area. When the CCD reaches the ADF scan area, a calibration is performed on the CCD.
5. The media is advanced to ADF scan sensor which is located by the takeaway roll. If the paper does not reach
the ADF scan sensor in a predetermined length of time a jam error will be generated.
6. When the ADF scan sensor is actuated the paper advances to the scan area. While the paper is advancing to
the scan area, the ADF motor generates pulses which are stored in an on-board counter. These counts along
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Diagnostic aids
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