| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a paper feeder capable of detecting skewing and double feeding of sheets and existence of the sheet inexpensively without requiring a large space, and an image forming apparatus including the same. <P>SOLUTION: A document feeder 27 includes an optical sensor 81 outputting a first signal, and an ultrasonic sensor 82 outputting a second signal, and a controller 91. The controller 91 drives a paper feeding part 71 to rotate so as to feed a document by a prescribed amount M on the basis of a signal showing passage of the sheet being either the first or the second signal so that the document may butt against a nip part of a resist roller pair 36, while the controller 91 determines the passage of the document according to an effect that an output level of the second signal gets lower than when the document does not pass through, and determines a double feeding state of the document according to an effect that the output level of the second signal gets lower than a prescribed threshold, and further determines a skew feeding state of the document from a lag between passing timing of the document based on the first signal and passing timing of the document based on the second signal. <P>COPYRIGHT: (C)2012,JPO&INPIT |
