Belt driving device and transfer device

A belt driving device comprising:

• an annular belt member comprising a first edge and a second edge;
• a plurality of rotary members that extend in parallel and rotate, the belt member being wound around the rotary members, the belt member circulating;
• a protrusion that protrudes from an inner peripheral surface of the belt member, the protrusion extending along the second edge of the belt member, the protrusion being arranged in a direction parallel to an extending direction of the rotary member, the protrusion being provided at the second edge;
• and
• a contact member that is closer to the first edge than the second edge, the contact member and the belt member being arranged side by side, wherein
• when the belt member deviates in the extending direction, the contact member comes into contact with the belt member to limit the deviating of the belt member, and
• the belt member has a size such that prevention of the deviating of the belt member by the protrusion being in contact with an end surface of one of the rotary members and the prevention of the deviating of the belt member by the belt member being in contact with the contact member occur simultaneously.

A transfer device comprising:

• an annular belt member comprising an outer peripheral surface, a first edge, and a second edge, the annular belt member being configured to transfer an image onto a recording material by (i) the outer peripheral surface coming into contact with the recording material and (ii) receiving a voltage;
• a plurality of rotary members that extend in parallel and rotate, the belt member being wound around the rotary members, the belt member circulating;
• a protrusion that protrudes from an inner peripheral surface of the belt member, the protrusion extending along the second edge of the belt member, the protrusion being arranged in a direction parallel to an extending direction of the rotary members, the protrusion being provided at the second edge;
• and
• a contact member that is closer to the first edge than the second edge, the contact member and the belt member being arranged side by side, wherein
• when the belt member deviates in the extending direction, the contact member comes into contact with the belt member to limit the deviating of the belt member, and
• a difference between a position of the belt member when the protrusion comes into contact with an end surface of one of the rotary members and a position of the belt member when the belt member comes into contact with the contact member is equal to or less than a width of the protrusion in the extending direction.