Sheet conveyor and image forming apparatus

A sheet conveyer, comprising:

• a 1st conveying roller configured to rotate about a 1st rotation axis by a driving force from a driving source;
• a 1st support part configured to support the 1st conveying roller;
• a 1st helical gear configured to rotate about the 1st rotation axis together with the 1st conveying roller and to generate thrust, on the 1st support part, in a particular direction along the 1st rotation axis;
• a 2nd conveying roller disposed at a position where a conveying surface of the 2nd conveying roller faces a conveying surface of the 1st conveying roller, the 2nd conveying roller being configured to be rotatable about a 2nd rotation axis parallel with the 1st rotation axis;
• a 2nd support part configured to support the 2nd conveying roller;
• a 2nd helical gear configured to generate thrust, on the 2nd support part, in the particular direction;
• a 3rd helical gear configured to engage with the 1st helical gear;
• a 4th helical gear configured to engage with the 2nd helical gear;
• and
• a clutch configured to connect or disconnect transmission of a driving force between the 3rd helical gear and the 4th helical gear,
• wherein:
• when the clutch disconnects transmission of the driving force between the 3rd helical gear and the 4th helical gear, the 1st conveying roller and the 2nd conveying roller are disposed at an initial position,
• when the clutch connects transmission of the driving force between the 3rd helical gear and the 4th helical gear, the 1st conveying roller and the 2nd conveying roller move from the initial position in the particular direction.