Driving force transmission device, medium transport device, image reading apparatus and image forming apparatus

1. A medium transport device comprising:

a feeding unit that feeds a medium from a medium storage portion;

a transport unit that transports the medium fed by the feeding unit;

a driving source;

a transport driving unit for driving the transport unit, the transport driving unit being driven by the driving source;

a feeding driving unit for driving the feeding unit; and

a driving force transmission unit that transmits the driving force from the transport driving unit to the feeding driving unit;

wherein the driving force transmission unit comprises:

a connection-and-disconnection unit that connects and disconnects a transmission of the driving force from the transport driving unit to the feeding driving unit; and

a driving force transmission device transmitting the driving force from the transport driving unit to the connection-and-disconnection unit,

wherein the driving force transmission device comprises:

a first rotating portion having a first facing portion;

a second rotating portion having a second facing portion, the second rotating portion having an operation range partially overlapping with that of the first rotating portion; and

a cushioning member provided between the first facing portion and the second facing portion, the cushioning member being deformed by being applied with a pressure;

wherein the first rotating portion and the second rotating portion transmit a driving force in a state where the cushioning member is deformed by application of the pressure; and

wherein the driving force transmission device absorbs a change in load caused when the connection-and-disconnection unit connects or disconnects the transmission of the driving force.

2. The medium transport device according to claim 1 , wherein the first rotating portion includes an inner ring fixed to a rotation shaft;

wherein the second rotating portion includes an outer ring provided outside the inner ring;

wherein the inner ring has a first engaging portion extending outwardly in a radial direction, the first engaging portion having a first end surface in a circumferential direction;

wherein the outer ring has a second engaging portion extending inwardly in the radial direction, the second engaging portion having a second end surface in the circumferential direction;

wherein the cushioning member is fixed to one of the first end surface and the second end surface, and contacts the other of the first end surface and the second end surface to transmit the driving force.

3. The medium transport device according to claim 2 , wherein an inner circumferential surface of the second engaging portion is slidable on an outer circumferential surface of the inner ring at a portion where the first engaging portion is not disposed.

4. An image reading apparatus comprising:

the medium transport device according to claim 1 ; and

a reading unit that reads an image on the medium transported by the medium transport device.

5. An image forming apparatus comprising:

the medium transport device according to claim 4 ; and

an image forming unit that forms an image on the medium transported by the medium transport device.