| 摘要 |
A jam detecting device according to the present invention quickly outputs a jam detection signal when a part of a sheet is insufficiently conveyed during conveyance. A discharge detecting switch 55 is provided in the vicinity of discharge rollers 36. In addition, a plurality of (for example, three) pulse output units 230, 231 and 232 are provided in relation to the discharge detecting switch 55. Each of the pulse output units 230, 231 and 232 is so constructed as to output a pulse as the sheet is moved. In a jam judging circuit 235, when a signal of the discharge detecting switch 55 is on, a jam signal is outputted on the basis of the fact that no pulses are applied for not less than a predetermined time period from at least one of the pulse output units 230, 231 and 232. When a Jam occurs, therefore, the jam can be quickly detected. Consequently, the jam can be detected before a large sheet is crumpled or is tangled with a delivery roller in an image forming apparatus, whereby measures against the jam is easily taken.
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