Reel shaft device of a magnetic recording tape running apparatus

A reel shaft device of a magnetic recording tape running apparatus comprising:

• a rotatable reel hub engaging member to be engaged with a reel hub to rotate therewith;
• a rotating member capable of rotating with respect to said reel hub engaging member, said rotating member having a circumferential surface;
• a rotatable driving member having a circumferential surface facing said circumferential surface of said rotating member and being capable of rotating concentrically with said reel hub engaging member, said driving member being adapted to be selectively rotated in either of two directions by a rotary power supply means;
• a plurality of rolling members having axes about which they are rotatable, said rolling member being disposed between said circumferential surface of said rotating member and said facing circumferential surface of said driving member so as to be rotatable about their own axes;
• a cam member disposed on one of the respective circumferential surfaces of said rotating member and said driving member, said cam member holding said plurality of rolling members in cooperation with the other of the respective circumferential surfaces of said rotating member and said driving member to rotate said rotating member together with said driving member in one direction when said driving member rotates in said one direction, and releasing said hold on said plurality of rolling members to allow said rotating member to rotate independently of said driving member when said driving member rotates in the other direction;
• and
• a variable rotation transmitting means for transmitting rotation between said reel hub engaging member and said rotating member such that the rotation transmissibility between said reel hub engaging member and said rotating member increases substantially in inverse proportion to a decrease of the magnitude of a torque applied to said reel hub engaging member;
• said rotating member having a sliding surface touching and in sliding contact with said reel hub engaging member along the rotating axis of said reel hub engaging member and along the circumferential direction, respectively;
• and
• said plurality of rolling members being held within the same plane with said sliding surface by the other of said circumferential surface of said rotating member and said circumferential surface of said driving member and said cam member when said driving member rotates in said one direction.