Traction-drive type driving-force transmission mechanism and image forming apparatus equipped therewith

An image forming apparatus comprising:

• an image forming section including at least a photosensitive drum, or a photosensitive drum and an intermediate transfer belt;
• a driving source operable to generate a driving force for driving said photosensitive drum, or at least one of said photosensitive drum and said intermediate transfer belt;
• and
• a traction-drive type driving-force transmission mechanism operable to transmit the driving force of said driving source to a rotary shaft of said photosensitive drum, or a driving member of said intermediate transfer belt, said traction-drive type driving-force transmission mechanism including:
• a sun roller having a first central axis, said sun roller being rotatable about said first central axis;
• a plurality of shaft members each having a second central axis, each of said shaft members being disposed such that said second central axis is aligned with a respective one of a plurality of adjacent axes parallel to said first central axis;
• a plurality of planetary rollers rotatably arranged along an outer peripheral surface of said sun roller while being supported by respective ones of said shaft members;
• a guide member adapted to guide each of said shaft members displaceably in a radial direction of said sun roller while maintaining the parallel relationship between said first central axes and said second central axes;
• and
• a pressing member adapted to press an outer peripheral surface of each of said planetary rollers against said outer peripheral surface of said sun roller so as to allow said driving force to be transmitted through means of a traction force between said sun roller and each of said planetary rollers, wherein
• said pressing member includes two outer rings provided respectively with pressing surfaces, said pair of outer rings being disposed to sandwich said planetary rollers therebetween, and
• each of said planetary rollers has pressure-receiving surfaces disposed and configured to be pressed by said pressing surfaces to displace said planetary rollers in a direction toward said sun roller.