Xerox Phaser 6121MFP Service Manual page 78

Theory of Operation
2-36
To return the cleaning blade to the Transfer Belt:
1. The cleaning blade pressure/retraction solenoid (SD5) is energized rotating
the pressure cam a half turn. This pushes the lever backward.
2. When the lever is pushed backward, the cleaning blade is returned. Then, the
cleaning blade is pressed against the transfer belt.
Image development requires the creation of a composite image on the surface of
the Transfer Belt. The leading edge of each color component of the image must
register correctly on the Transfer Belt's surface. The position of the Transfer Belt is
monitored by the Transfer Belt Position Sensor. The optical sensor detects holes in
the Transfer Belt.
Two detection holes are punched in the Transfer Belt. The image write start
position varies according to the media size. For A4 or smaller media, the image
write start position, as determined by the sensor, is detection hole A. For a media
sizes larger than A4, detection hole B is the reference for the image write start
position.
Detection Hole B
Detection Hole A
Belt Positioning Sensor
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Phaser 6121MFP Service Manual