Sheet transport device and automatic document feeder

A sheet transport device comprising:

• a sheet setting portion for accepting a sheet at a set position at an feed-in port;
• a main transport route for transporting the sheet in a sheet transport direction from the sheet setting portion via said feed-in port to one of an image reading position and an image forming position, said main transport route including a main transport route transport mechanism for transporting the sheet along the main transport route;
• sheet guides disposed on the sheet setting portion positioned to contact lateral opposing edges of the sheet to align the sheet at said set position on the sheet setting portion to prevent the sheet having a skewed orientation relative to said sheet transport direction;
• a switchback route, extending from an intersection with a junction portion along the main transport route, for receiving the sheet from the main transport route and guiding a lead end of the sheet into the pair of sheet guides and guiding the sheet back to the main transport route;
• a switchback mechanism for transporting the sheet from the main transport route into and along the switchback route with the lead end preceding a tail end and for returning the sheet into the main transport route with the tail end preceding the lead end thereby reversing a direction of travel of the sheet;
• said main transport route having first and second transport plates opposing each other defining a guide path therebetween through which the sheet is guided, said first and second transport plates respectively defining first and second roller apertures;
• and
• said main transport route transport mechanism including:
• a drive roller accessing said guide path via said first aperture;
• a driven roller accessing said drive path via said second aperture;
• and
• the drive roller and driven roller being disposed to nip the sheet at a nip position substantially aligned with a surface of said second transport plate at said second roller aperture.

A sheet transport device comprising:

• a sheet setting portion for accepting a sheet at a set position at an feed-in port;
• a main transport route for transporting the sheet in a sheet transport direction from the sheet setting portion via said feed-in port to one of an image reading position and an image forming position, said main transport route including a main transport route transport mechanism for transporting the sheet along the main transport route;
• sheet guides disposed on the sheet setting portion positioned to contact lateral opposing edges of the sheet to align the sheet at said set position on the sheet setting portion to prevent the sheet having a skewed orientation relative to said sheet transport direction;
• a switchback route, extending from an intersection with a junction portion along the main transport route, for receiving the sheet from the main transport route and guiding a lead end of the sheet into the pair of sheet guides and guiding the sheet back to the main transport route;
• a switchback mechanism for transporting the sheet from the main transport route into and along the switchback route with the lead end preceding a tail end and for returning the sheet into the main transport route with the tail end preceding the lead end thereby reversing a direction of travel of the sheet;
• said main transport route having first and second transport plates opposing each other defining a guide path therebetween through which the sheet is guided, said first and second transport plates respectively defining first and second roller apertures;
• and
• said main transport route transport mechanism including:
• a drive roller accessing said guide path via said first aperture;
• a driven roller accessing said drive path via said second aperture;
• and
• the drive roller and driven roller being disposed to nip the sheet at a nip position substantially aligned with a surface of one of said first and second transport plates at a respective one of said first and second roller apertures.

A sheet transport device comprising:

• a sheet setting portion for accepting a sheet at a set position at an feed-in port;
• a main transport route for transporting the sheet in a sheet transport direction from the sheet setting portion via said feed-in port to one of an image reading position and an image forming position, said main transport route including a main transport route transport mechanism for transporting the sheet along the main transport route;
• sheet guides disposed on the sheet setting portion positioned to contact lateral opposing edges of the sheet to align the sheet at said set position on the sheet setting portion to prevent the sheet having a skewed orientation relative to said sheet transport direction;
• a switchback route, extending from an intersection with a junction portion along the main transport route, for receiving the sheet from the main transport route and guiding a lead end of the sheet into the pair of sheet guides and guiding the sheet back to the main transport route;
• a switchback mechanism for transporting the sheet from the main transport route into and along the switchback route with the lead end preceding a tail end to a position whereat the lead end is between the sheet guides while the tail end is within the switchback mechanism and for returning the sheet into the main transport route with the tail end preceding the lead end thereby reversing a direction of travel of the sheet;
• said switchback mechanism including:
• an inverting roller provided along the switchback route and rotatable in a forward direction and a backward direction;
• an inverting driven roller opposing said inverting roller;
• and
• a pressing actuator for engaging and disengaging said inverting roller and said inverting driven roller with one another to place said inverting roller and said inverting driven roller in a nipping state and a non-nipping state to effect selective nipping of the sheet;
• and
• a controller for controlling the pressing actuator to disengage the inverting driven roller from the inverting roller for a predetermined time period to un-nip the sheet when the lead end of the sheet is between the sheet guides to free the sheet and effect skew correction of the sheet by the sheet guides during said predetermined time period and for controlling the pressing actuator to re-nip the sheet at a termination of said predetermined time period.