End portion member, photosensitive drum unit and process cartridge

An end portion member which is disposed at an end portion of a photosensitive drum unit that is detachably mounted to an image forming apparatus body which includes a driving shaft having a recessed portion which is a twisted hole with a substantially triangular cross-sectional shape, comprising:

• a cylindrical or columnar bearing member which is able to be engaged with and be separated from the recessed portion,
• wherein the bearing member has no undercut portion on an outer peripheral surface in a direction along an axis, and while the bearing member is in an attitude of being engaged into the recessed portion, at any part where the bearing member comes into contact with the recessed portion, a cross-sectional area occupancy ratio which is a degree of area occupied by a cross-section of the bearing member with respect to a cross-section of the recessed portion in a cross-section orthogonal to a direction in which the axis extends is 15% or higher and 75% or less, and
• an outer peripheral shape of the bearing member in a cross-section orthogonal to the direction in which the axis extends is a hexagon, and assuming that a radius of a circumscribed circle of the hexagon of the bearing member is r1g, and when a hexagon is formed by sides enclosed by a triangle formed at an opening of the recessed portion when the recessed portion is viewed from a front in the axial direction and a triangle formed at a bottom of the recessed portion, a radius of an inscribed circle of the hexagon of the recessed portion is r2h,
• r1g−r2h>0.

An end portion member which is disposed at an end portion of a photosensitive drum unit that is detachably mounted to an image forming apparatus body which includes a driving shaft having a recessed portion which is a twisted hole with a substantially triangular cross-sectional shape, comprising:

• a cylindrical or columnar bearing member which is able to be engaged with and be separated from the recessed portion,
• wherein the bearing member has no undercut portion in an axial direction of an outer peripheral surface thereof, and while the bearing member is in an attitude of being engaged into the recessed portion, a volume occupancy ratio which is a degree of volume occupied by the bearing member with respect to a capacity of the recessed portion is 20% or higher and 70% or less, and
• an outer peripheral shape of the bearing member in a cross-section orthogonal to the axial direction is a hexagon, and assuming that a radius of a circumscribed circle of the hexagon of the bearing member is r1g, and when a hexagon is formed by sides enclosed by a triangle formed at an opening of the recessed portion when the recessed portion is viewed from a front in the axial direction and a triangle formed at a bottom of the recessed portion, a radius of an inscribed circle of the hexagon of the recessed portion is r2h,
• r1g−r2h>0.