Roller supporting structure using a dynamic pressure

A roller and roller support structure for rotatably supporting said roller, comprising:

• a hollow roller;
• a shaft rotatably supporting said roller and allowing axial movement of said roller therealong;
• a plurality of first grooves in at least one of an inner peripheral surface of said hollow roller and an outer peripheral surface of said shaft for generating a dynamic pressure between said shaft and said roller when said roller is rotated on said shaft;
• first and second retaining plates fixed to said shaft at axially opposite ends of said hollow roller and having roller-facing faces confronting respective end faces of said hollow roller;
• a plurality of second grooves in at least one of one end face of said hollow roller and the roller-facing face confronting said one end face of said hollow roller, and in at least one of the other end face of said hollow roller and the roller-facing face confronting said other end face, said roller and said retaining plates having a size and said second grooves having a shape for, when said end faces of said hollow roller and the roller-facing faces confronting the respective end faces are spaced less than a predetermined distance, generating a gradually increasing dynamic pressure between said roller and the respective end plates the closer said end faces and roller facing faces come when said roller and said shaft are relatively rotated under predetermined conditions of speed and viscosity of medium between said end faces and said retaining plates;
• said roller-facing faces being spaced from each other a distance greater than the axial length of said hollow roller plus twice said predetermined distance;
• said predetermined distance being a distance which, when said hollow roller has said end faces spaced from said roller facing faces at least said predetermined distance, said second grooves at most generate substantially no dynamic pressure when said roller and said shaft are relatively rotated at said predetermined conditions of speed and viscosity of medium, and when said hollow roller moves axially along said shaft to bring one or the other end faces closer to a respective roller-facing face than said predetermined distance while said roller and said shaft are relatively rotating at said predetermined conditions of speed and viscosity of medium, a gradually increasing dynamic pressure greater than said substantially no dynamic pressure is generated between said roller and the respective roller facing end face.