Lexmark X925 Service Manual page 177

7541-03x
The X925 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 X925 duplex ADF.
1. To transfer text or an image from physical media to another piece of physical media or a digital file, the
following steps occur. The first step of the process is the placement of the paper on the scanner. The paper is
placed on the flatbed or the ADF paper tray. Once the paper is placed in the device the scan or copy command
is initiated by the user. This command can be issued from a computer or on the scanner itself.
2. When the scan command is initiated, the ICC board on the scanner first polls the paper present sensor in the
ADF to see if there is paper in the ADF unit. If the paper present sensor indicates the presence of paper, the size
sensors are polled to determine the length and width of the paper. There are two paper length sensors. They are
found on the ADF input tray. These sensors detect A4 vs. folio for non-US users, and letter vs. legal for US
users. The ADF paper width sensor is composed of three photo interrupt sensors that are actuated by the paper
guides on the ADF tray. The position of the guides places the three actuators on the guides in position to leave
the sensor open or closed. The width sensors detect A4, B5, and A5 widths for non US users and statement,
executive, and letter widths for US users.
3. With the size of the paper determined by the width and length sensors, the cover open sensor is polled to
ensure the ADF top cover properly closed. If the cover is not properly closed and error is generated. If the cover
is closed, the pick up sensor is polled. The pickup sensor determines if the pick roll is in the proper position.
Before executing the pick, the pick roll is in the up position. If the sensor determines that the roll is in the up
position, the pick roll is moved to the down position to initiate the pick.
4. With the pick roll in the proper position, the signal to pick is generated from the ADF relay card. The top sheet
in the paper is pulled in to the ADF towards the feed roll. To prevent double feeds, a separator roll is present to
provide resistance, holding the other sheets in the paper input tray.
5. Once the top sheet passes the feed roll, it moves into the ADF paper path and triggers the gap sensor. When
the gap sensor is triggered by a physical actuator, it begins counting the time for the paper to pass over it. Based
on the paper length, the gap sensor can determine if a jam is encountered. Also, the paper length and position in
the paper path is determined by this sensor.
6. After passing over the gap sensor the paper reaches the paper in sensor. This is a reflective sensor that
determines paper position in the paper path and activates the actual scan image process.
7. 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
with the ADF scan sensor ensure that the media is travelling at the correct speed through the scan area. The
speed the document travels through the ADF scan area is dependent on the image DPI specified by the user.
8. After a predetermined number of counts, the media reaches the scan area and the image acquisition process
is initiated. While the image acquisition process is executing, the ADF scan sensor is being polled to determine
if the trailing edge of the media has reached the sensor.
9. Once the trailing edge of the scan media has reached the ADF scan sensor, that sensor goes to the off
position. After the ADF scan sensor is switched off, the image acquisition process continues for a predetermined
length of time.
10. When the image acquisition process is completed, the trailing edge of the media continues to the reverse
point. The duplex gate will be position by the gate solenoid to direct the paper to the pass through sensor.
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Diagnostic aids