Drive transmission mechanism and image forming apparatus with the same

A drive transmission mechanism comprising:

• a drive unit including a drive section and a drive-side coupling part to which a rotary driving force of the drive section is to be transmitted;
• and
• a removable unit attachable to and removable from the drive unit, wherein the removable unit includes a cover part having a circular opening formed in a portion of an outside surface thereof, a driven-side coupling part provided within the opening and mating with the drive-side coupling part in an attached state where the removable unit is attached to the drive unit, and a driven section capable of being driven by the rotary driving force transmitted from the drive-side coupling part to the driven-side coupling part,
• wherein the drive-side coupling part comprises:
• a first base including a first opposed surface facing the driven-side coupling part in the attached state;
• a semispherical projection raised from the first opposed surface at a rotational center of the drive-side coupling part;
• and a cylindrical projection being integrally formed with a first projection of an arcuate pillar shape centered on the rotational center of the drive-side coupling part, a second projection of an arcuate pillar shape having a shorter inside diameter than an inside diameter of the first projection, and a stepped portion extending in a radial direction and connecting the first projection and the second projection,
• the driven-side coupling part comprises:
• a second base including a second opposed surface facing the drive-side coupling part in the attached state;
• a columnar projection raised from the second opposed surface at a rotational center of the driven-side coupling part;
• a peripheral projection raised radially from an outer periphery of the columnar projection;
• and a recess depressed from a top surface of the columnar projection at the rotational center of the driven-side coupling part, and wherein
• when in the attached state the semispherical projection fits in the recess, the opening surrounds the cylindrical projection, and the cylindrical projection surrounds the columnar projection and the peripheral projection, the rotational center of the drive-side coupling part coincides with the rotational center of the driven-side coupling part and the stepped portion engages against the peripheral projection in a direction of rotation of the drive-side coupling part and the driven-side coupling part, resulting in a state where a rotary driving force is transmittable from the drive-side coupling part to the driven-side coupling part.