| 摘要 |
PROBLEM TO BE SOLVED: To avoid the collision between a sheet which is newly discharged to a discharge tray and a sheet which has already been stacked thereon, in an image forming device. SOLUTION: When a sheet discharged onto the discharge tray 91 is an A4 size, optical paths from a light emitting part 911 to a light receiving part 912 are indicated by an arrow R1 and an arrow R2. When the sheet is an A5 size, they are indicated by the arrow R1 and an arrow R3. When the sheet is an A3 size, they are indicated by the arrow R1 and an arrow R4. These optical paths cover the sheets on the discharge tray 91 from the rear end to the front end in the discharging direction R10 of the sheets into the discharge tray 91. When the optical paths are intercepted by the sheets placed on the discharge tray 91, the discharge tray 91 is determined to be full of sheets. COPYRIGHT: (C)2009,JPO&INPIT
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