Fujitsu ScanSnap iX1500 Consumable Replacement And Cleaning Instructions page 11

(2) Fit the left end of the BR-Shaft-ASSY in the slot (①), then install the rest of the shaft in place (②).
ATTENTION
Confirm that the brake roller is installed properly. Otherwise, paper jams or other feeding errors may occur.
(3) Guide-R-ASSY.
(4) Close the ADF top section.
Be careful not to get your fingers caught when closing the ADF.