Image reading apparatus

An image reading apparatus, which is capable of conveying a sheet in a sheet-conveying path along an image reader unit in a predetermined sheet-conveying direction to scan a first side of the sheet passing by the image reader unit and returning the passed-by sheet to the image reader unit to scan a second side of the sheet after scanning the first side of the sheet, comprising:

• a sheet tray, in which the sheet to be scanned is stored;
• a separator, which is configured to frictionally pick up the sheet from the sheet tray and convey the picked-up sheet toward an entry side of the image reader unit, through which the sheet enters a position above the image reader unit, to have the first side of the sheet scanned by the image reader unit;
• a conveyer roller, which is arranged along the sheet-conveying path in the vicinity of the entry side of the image reader unit and is configured to rotate along with the sheet becoming in contact with the conveyer roller to convey the sheet in the sheet-conveying path to the image reader unit;
• a resisting force applier, which is configured to apply convey-resisting force to the sheet, of which first side has been scanned, being returned to the entry side of the image reader unit to have the second side of the sheet with the convey resistance scanned by the image reader unit;
• and
• a transmission,
• wherein the resisting force applier includes a returner roller, which is configured to rotate along with the sheet, of which first side has been scanned, becoming in contact with the returner roller and return the sheet to the conveyer roller;
• and
• wherein a peripheral velocity of the returner roller is smaller than a peripheral velocity of the conveyer roller;
• wherein the returner roller is a switchback roller, which is configured to switch rotating directions thereof from a normal rotating direction to a reverse rotating direction once a front end of the sheet being conveyed in the predetermined sheet-conveying direction reaches the returner roller to return the sheet to the conveyor roller;
• wherein the transmission includes a plurality of gears to transmit driving force from a drive source for rotating the returner roller and is configured to switch the rotating directions of the returner roller by switching transmission paths to transmit the driving force between a normal transmission path, in which the driving force for rotating the returner roller in the normal rotating direction is transmitted, and a reverse transmission path, in which the driving force for rotating the returner roller in the reverse rotating direction is transmitted;
• and
• wherein the peripheral velocity of the returner roller rotated in the reverse rotating direction to return the sheet to the conveyor roller is controlled to be smaller than the peripheral velocity of the returner roller rotated in the normal direction by setting a different transmission gear ratio in the reverse transmission path from a gear transmission ratio of the normal transmission path.