Automatic document feeder having document size detecting device

Abstract

The present invention relates to an automatic document feeder having a document size detecting device. The document size detecting device includes a first paper guide plate, a second paper guide plate, a first elongated perforation, a second elongated perforation, a rack movement mechanism and a plurality of sensing members. The first paper guide plate includes a first paper stopping slice, a first rack and a rib, wherein the rib is disposed on the bottom of the paper input tray. The second paper guide plate includes a second paper stopping slice and a second rack. By moving the first paper guide plate to have the rib located between an optical emitter and an optical receiver of a specified sensing member, the size of the document placed on the paper input tray is realized.

1 . An automatic document feeder having a document size detecting device, said automatic document feeder including a paper input tray for placing a document thereon, and said document size detecting device comprising:
 a first paper guide plate including a first paper stopping slice for positioning said document on a surface of said paper input tray, a first rack on a bottom of said paper input tray, and a rib on said bottom of said paper input tray;   a second paper guide plate including a second paper stopping slice for positioning said document on said surface of said paper input tray and a second rack on said bottom of said paper input tray;   a first elongated perforation formed in said paper input tray, wherein said first paper guide plate is partially penetrated through said first elongated perforation such that said first paper stopping slice is disposed on said surface of said paper input tray and said first rack and said rib are disposed on said bottom of said paper input tray;   a second elongated perforation formed in said paper input tray, wherein said second paper guide plate is partially penetrated through said second elongated perforation such that said second paper stopping slice is disposed on said surface of said paper input tray and said second rack is disposed on said bottom of said paper input tray;   a rack movement mechanism engaged with said first rack and said second rack such that said first paper guide plate and said second paper guide plate are movable along said first elongated perforation and said second elongated perforation, respectively; and   a plurality of sensing members disposed under said bottom of said paper input tray and having respective optical emitters and respective optical receivers, wherein said rib is moved with movement of said first paper guide plate to a selected location between said optical emitter and said optical receiver of a specified sensing member, thereby realizing the size of said document.   
     
     
         2 . The automatic document feeder having a document size detecting device according to  claim 1  wherein said first paper stopping slice, said first rack and said rib of said first paper guide plate are integrally formed into one-piece. 
     
     
         3 . The automatic document feeder having a document size detecting device according to  claim 1  wherein said second paper stopping slice and said second rack of said second paper guide plate are integrally formed into one-piece. 
     
     
         4 . The automatic document feeder having a document size detecting device according to  claim 1  wherein said rack movement mechanism includes a gear, a rotating disc and a rotating shaft.