A biasing mechanism in an image forming apparatus exerts a variable force on a removable cartridge unit to generate a nip force between a roller in the cartridge unit and another roller. A pivot member is fixed to the apparatus housing. An arm is pivotally mounted in the housing about the pivot member, with the arm in contact with a protrusion on the cartridge unit. A force generating member is mounted in the housing and contacts the arm so as to urge the arm to pivot about the pivot member and press against the cartridge unit. The resulting force exerted on the cartridge unit by the arm varies according to the point of contact between the cartridge unit and the arm. In some embodiments, the arm and the cartridge unit protrusion are electrically conductive, and an electrical contact is established as the arm is pressed against the protrusion.