Patent ID: 7845633

Claim:
An abnormal sheet delivery detection device comprising: a convey device which includes sheet holding means for holding a sheet, and conveys the sheet held by said sheet holding means; a first pile device on which the sheet released from said sheet holding means at a predetermined sheet release position is piled; noncontact-type detection means arranged downstream of the sheet release position in a sheet convey direction for detecting one of a presence and an absence of the sheet; first releasing means for selectively switching between a first state in which the sheet held by said sheet holding means is released and piled on said first pile device, and a second state in which the sheet held by said sheet holding means is conveyed downstream in the sheet convey direction by said first convey device without releasing the sheet at the release position; and a control means for detecting abnormal sheet delivery based on an output from said detection means in a period elapsing from a time a trailing edge of a sheet held by said sheet holding means passes a detection position of said detection means until a next succeeding sheet holding means reaches the detection position of said detection means.