Ricoh B889 Manual page 27

The second fold is made.
The process continues as described earlier.
Slide 27
The cycle repeats until all the folds are completed:
The fold plate motors alternate the raising and lowering of the fold plates to
push the paper into the front and back fan fold rollers that form the folds.
The fan fold motor switches the direction of rotation of the fan fold rollers, so
that the stack feeds forward and back after each section is folded.
The LED and sensor pairs detect the edges and start the pulse count that the
Fan Fold Unit uses to time the rotation of the fan folder motor. The time of
rotation determines how far the paper is fed in each direction.
Folding - 7/8
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B889 - Fan Fold Unit