Image reading apparatus including double feeding detecting unit

1. An image reading apparatus comprising:

a transport unit which can transport one of a carrier sheet in which two transparent sheets for interposing a document is bonded at a part of a peripheral edge portion, and in a state of interposing a document therebetween, and a document which is set along a transport path;

a reading unit which reads a document or a document interposed between the carrier sheet at a reading position in the middle of a path on which the document is transported by the transport unit;

at least one detecting unit which includes a double feeding detecting unit which detects double feeding of a document; and

a discrimination unit which discriminates double feeding of a document from a carrier sheet based on a first detection result which is obtained when the detecting unit detects a bonding portion of the carrier sheet, and a second detection result which is obtained when the double feeding detecting unit detects double feeding.

2. The image reading apparatus according to claim 1 ,

wherein the discrimination unit discriminates as a carrier sheet when obtaining the second detection result, after obtaining the first detection result which is obtained when the detecting unit detects the bonding portion of the carrier sheet, and discriminates as double feeding of a document, when obtaining the second detection result without obtaining the first detection result.

3. The image reading apparatus according to claim 2 ,

wherein the detecting unit is the double feeding detecting unit of an ultrasonic wave type,

wherein a first threshold value for detecting the bonding portion of the carrier sheet, and a second threshold value for detecting a doubly-fed portion of a document are set as threshold values which are used by the discrimination unit when performing a discrimination based on a detection value of the double feeding detecting unit, and

wherein the discrimination unit discriminates as a carrier sheet when obtaining the second detection result in which a detection value exceeds the second threshold value, after obtaining the first detection result in which the detection value is a value between the first threshold value and the second threshold value, and discriminates as double feeding of a document, when obtaining the second detection result without obtaining the first detection result.

4. The image reading apparatus according to claim 3 ,

wherein the discrimination unit assumes that the first detection result is obtained when a cumulative number of times in which a detection value of the double feeding detecting unit exceeds the first threshold value exceeds a first set number of times, and the second detection result is obtained when a cumulative number of times in which the detection value exceeds the second threshold value exceeds a second set number of times.

5. The image reading apparatus according to claim 1 ,

wherein a plurality of the detecting units which include the double feeding detecting unit, and a document presence detecting unit which detects a presence or absence of a document at a position on a downstream side of the double feeding detecting unit in a transport direction of a document, and

wherein the discrimination unit discriminates as a carrier sheet when the first detection result which is obtained when the document presence detecting unit detects a document is obtained, at a time of obtaining the second detection result which is obtained when the double feeding detecting unit detects the double feeding, and discriminate as double feeding when the first detection result is not obtained, at a time of obtaining the second detection result.

6. The image reading apparatus according to claim 5 ,

wherein the discrimination unit obtains a distance from a tip end of a carrier sheet to a double feeding detecting start position at which double feeding starts to be detected, by the double feeding detecting unit, and discriminates as the carrier sheet when the distance is in an allowable range corresponding to a width of the bonding portion of the carrier sheet in the transport direction.

7. The image reading apparatus according to claim 1 ,

wherein the discrimination unit continues an image reading operation using the transport unit and the reading unit when discriminating as a carrier sheet, and stops the image reading operation using the transport unit and the reading unit when discriminating as double feeding of a document.

8. The image reading apparatus according to claim 7 ,

wherein the discrimination unit sets the double feeding detecting unit to an OFF state in which detecting is not possible, when discriminating as a carrier sheet.