Power transmission apparatus and image forming apparatus having the same

A power transmission apparatus for transmitting driving power from a driving power source to at least first and second movable members of an image forming apparatus, the driving power being a bi-directional rotational power in first and second directions of rotation, the power transmission apparatus comprising:

• a driving unit configured to receive the driving power transmitted from the driving power source and to convey the driving power to the first movable member so as to cause the first movable member to rotate in the first and second directions;
• a driven unit coupled to the second movable member;
• an elastic clutch including a coil spring which is wound in a direction of driving the second movable member in the first direction and provided between the driving unit and the driven unit;
• a driven gear coupled to a third movable member;
• and
• a swing gear unit having a gear train supported on a swing gear unit frame, the gear train including a center gear configured to receive the driving power from the driving power source, a first number of first side gears on a first side of the center gear and a second number of second side gears on a second side opposite to the first side, the first number being different from the second number, the frame being configured rotate about an axis such that when the driving power is in the first direction the frame rotates to allow one of the first side gears to engage the driven gear to cause the third movable member to rotate in the first direction, the frame being further configured rotate about the axis such that when the driving power is in the second direction the frame rotates to allow one of the second side gears to engage the driven gear to cause the third movable member to rotate in the first direction.

An image forming apparatus comprising:

• a developing unit which forms an image on a print medium;
• a duplex carrying unit which returns the print medium, one side of which has a formed image, to the developing unit;
• a driving power source configured to produce a driving power, the driving power being a bi-directional rotational power in first and second directions of rotation;
• an ejection roller configured to rotate in the first direction to eject the printing medium, which has been processed, out of the image forming apparatus, the ejection roller being configured to rotate in the second direction to direct the printing medium towards the duplex carrying unit;
• a bi-directional power conveyance mechanism disposed between the driving power source and the ejection roller, the bi-directional power conveyance mechanism being configured to convey the driving power from the driving power source to the ejection roller so as to cause the ejection roller to rotate in the first direction and in the second direction;
• a driving unit configured to receive the driving power from the driving power source;
• a driven unit coupled to a movable member of the developing unit;
• and
• an elastic clutch including a coil spring which is wound in a direction of driving the movable member of the developing unit in the first direction and provided between the driving unit and the driven unit.

A power transmission apparatus to transmit a driving power to at least first and second movable members of an image forming apparatus, the power transmission apparatus comprising:

• a driving unit which receives the driving power from a driving power source and rotates in forward and backward directions;
• a driven unit which transmits the driving power from the driving unit to the first movable member;
• and
• an elastic clutch including a coil spring which is wound in a direction of driving the first movable member in the forward direction and provided between the driving unit and the driven unit to transmit the driving power from the driving unit to rotate the first movable member in a first direction and to control the driving power not to rotate the first movable member in a second direction while the driving power from the driving unit rotates the second movable member in both the first and second directions,
• wherein the first movable member comprises a developing unit.

An image forming apparatus comprising:

• a developing unit which forms an image on a print medium;
• a duplex carrying unit which returns the print medium, one side of which has a formed image, to the developing unit;
• and
• a power transmission apparatus which transmits driving power from a driving power source to rotate the developing unit in a forward direction and to rotate the duplex carrying unit in forward and backward directions,
• wherein the power transmission apparatus comprising
• a driving gear which rotates in the forward and backward directions by receiving the driving power from the driving power source and transmits the driving power to the duplex carrying unit;
• a driven gear which transmits the driving power from the driving gear to the developing unit;
• and
• an elastic clutch including a coil spring which is wound in a direction of driving the developing unit in the forward direction and which is provided between the driving gear and the driven gear, transmits the driving power to rotate the driven gear in a forward direction and prevents the driven gear from rotating in a backward direction while the driving gear rotates in the backward direction.