Duplex automatic document feeder

An automatic document feeder comprising:

• a feeding end;
• an outlet end:
• a scanning module adapted to scan a document;
• a first path adapted to guide movement of the document from said feeding end to said scanning module, said first path having an upstream end and a downstream end;
• a reversing mechanism disposed in proximity to said outlet end and including a pair of first and second roller units;
• a second path extending from said downstream end of said first path to said first roller unit and having a front section, and a rear section disposed behind said front section of said second path and in front of said first roller unit;
• a third path spaced apart from said second path and extending between said second roller unit and said first path, said third path having front and rear sections in spatial communication with an intermediate portion of said first path and said second roller unit, respectively;
• a fourth path having an upstream end in spatial communication with a junction between said front and rear sections of said second path, and a downstream end in spatial communication with a junction between said front and rear sections of said third path;
• a housing unit;
• and
• a guide unit including a switching gate disposed in said housing unit at a junction between said second and fourth paths and pivotable between a first position whereat movement of the document from said front section of said second path onto said rear section of said second path is prevented and whereat movement of the document from said front section of said second path onto said fourth path is allowed, and a second position whereat movement of the document from said front section of said second path onto said fourth path is prevented and whereat movement of the document from said front section of said second path onto said rear section of said second path is allowed;
• wherein said switching gate is configured as a curved rod, and has a middle portion disposed pivotally on said junction between said second and fourth paths, said switching gate being further pivotable to a third position whereat the document is limited to move between said second and fourth paths;
• wherein said guide unit further includes:
• a rotary disk disposed pivotally in said housing unit and having an outer periphery formed with first, second, and third positioning notches, said switching gate being connected fixedly to said rotary disk;
• a solenoid valve including an engaging member biased to move into said first positioning notch when said switching gate is disposed in said first position, into said second positioning notch when said switching gate is disposed in said second position, and into said third positioning notch when said switching gate is disposed in said third position, said solenoid valve being activated so as to remove said engaging member from said switching gate just before said switching gate is rotated in said housing unit.