Patent ID: 7904010

Claim:
A belt unit comprising: a belt; a contact member that is configured to come into contact with the belt; a movable member; an eccentric cam mounted on a housing; a contact-separation mechanism that allows the movable member to move based on rotation of the eccentric cam to control contact and separation between the contact member and the belt; a braking unit, mounted on the housing, that controls the rotation of the eccentric cam by a predetermined angle, and a transfer member connected to the movable member and located to face the image carrier via the belt, wherein a braking force applied by the braking unit satisfies a relation A≧B+C where A is a maximum value of a driving torque of the eccentric cam without the braking unit when the transfer member separates from the belt, B is a maximum value of the driving torque at a fulcrum in an equilibrium area of the eccentric cam without the braking unit when the transfer member separates from the belt, and C is a torque acting about a center of the eccentric cam due to a braking force of the braking unit.