Sheet feeding apparatus with rotary power transmission mechanism

A sheet feeding device, comprising:

• a rotary shaft rotatable in a sheet feeding direction;
• a separation roller mounted on the rotary shaft;
• a retardation roller in contact with the separation roller with a certain pressure;
• an arm adapted to move vertically relative to the rotary shaft;
• a pick up roller mounted on an end of the arm;
• a rotary power transmission mechanism connected with the arm for transmitting rotary power from the rotary shaft to the pick up roller and moving the arm downward,
• a rotatable member for transmission of the rotary power to the rotary power transmission mechanism, the rotatable member and the separation roller being rotatable relative to the rotary shaft;
• and
• a coil spring fixed to the rotary shaft at one end thereof and to the separation roller at the other end, the coil spring being in spaced relationship with the rotatable member, having a diameter that is modifiable by rotation of the rotary shaft and being loosely fitted over the rotary shaft to form a spring clutch,
• wherein as the diameter of the coil spring becomes smaller upon rotation of the rotary shaft, the coil spring tightly engages the rotatable member to transmit the rotary power of the rotary shaft to the rotatable member, whereas as the separation roller performs an idle rotation relative to the rotary shaft, the diameter of the coil spring is enlarged and the engagement between the coil spring and the rotatable member is released, whereby the rotary power of the rotary shaft is not transmitted to the rotatable member.