Medium transport device and image reading device

A medium transport device comprising:

• a transport roller unit including a plurality of transport rollers configured to transport a medium;
• a drive unit configured to drive the plurality of transport rollers, wherein
• the drive unit includes
• a power transmitting portion,
• a toothed belt, and
• a pulley around which the toothed belt is wound to rotate,
• the transport roller unit further includes a power transmitted portion,
• the power transmitting portion and the power transmitted portion are brought into a coupled state by the transport roller unit moving in a direction approaching the drive unit, and
• the power transmitting portion and the power transmitted portion are brought into an uncoupled state by the transport roller unit moving in a direction away from the drive unit;
• a first frame;
• and
• a second frame facing the first frame, wherein
• the transport roller unit further includes a first shaft configured to support a transport roller of the plurality of transport rollers,
• the first frame is located on a first end side of the first shaft,
• the second frame is located on a second end side of the first shaft,
• the drive unit is held by the first frame,
• the transport roller unit is brought into the coupled state or the uncoupled state by moving in a direction along the first shaft through an insertion portion of the second frame,
• the power transmitted portion located at one end of the first shaft is a first gear,
• the power transmitting portion is a second gear that meshes with the first gear, and
• the second gear is attached to a second shaft serving as a rotation center of the pulley, and rotates integrally with the pulley.

A medium transport device comprising:

• a transport roller unit including a plurality of transport rollers configured to transport a medium;
• a drive unit configured to drive the plurality of transport rollers, wherein
• the drive unit includes a power transmitting portion,
• the transport roller unit further includes a power transmitted portion,
• the power transmitting portion and the power transmitted portion are brought into a coupled state by the transport roller unit moving in a direction approaching the drive unit, and
• the power transmitting portion and the power transmitted portion are brought into an uncoupled state by the transport roller unit moving in a direction away from the drive unit;
• a first frame;
• and
• a second frame facing the first frame, wherein
• the transport roller unit further includes
• a first shaft configured to support a transport roller of the plurality of transport rollers,
• a support portion configured to rotatably support the first shaft, and
• a guide portion configured to guide the support portion at a time of movement is included between the first frame and the second frame, the first frame is located on a first end side of the first shaft,
• the second frame is located on a second end side of the first shaft,
• the support portion is electrically conductive, and includes
• a first support portion located on the first end side of the first shaft and supporting the first shaft via a first bearing;
• a second support portion located on the second end side of the first shaft and supporting the first shaft via a second bearing;
• and
• a base support portion configured to couple the first support portion to the second support portion,
• the first shaft and the support portion are coupled by a conductive member,
• the drive unit is held by the first frame, and
• the transport roller unit is brought into the coupled state or the uncoupled state by moving in a direction along the first shaft through an insertion portion of the second frame.