Document conveyance device, image reading device and image forming apparatus

1. A document conveyance device comprising:

a supply tray on which a document is placed;

a discharge tray disposed below the supply tray;

a conveyance part which feeds the document on the supply tray to a document conveyance path one by one and conveys the document along the document conveyance path;

a discharge part which discharges the document conveyed by the conveyance part to the discharge tray; and

a lifting and lowering part which lifts and lowers the supply tray and the discharge part, wherein

the lifting and lowering part lifts the supply tray and the discharge part according to a feeding of the document,

when the feeding of the document to the document conveyance path is completed and then the supply tray is lifted, in a large number of documents discharge state where a height of the documents stacked on the discharge tray is more than a specified value, the lifting and lowering part positions the supply tray at a taking out position depart upward from an uppermost document of the documents stacked on the discharge tray by a predetermined space,

when the feeding of the document to the document conveyance path is completed and then the supply tray is lifted, in a small number of documents discharge state where the height of the documents stacked on the discharge tray is less than the specified value, the lifting and lowering part positions the supply tray at a taking out position depart upward from the specified value by the predetermined space.

2. The document conveyance device according to claim 1 , wherein

the lifting and lowering part includes:

a first detection part which is provided in the supply tray and detects a distance between the uppermost document on the discharge tray and the supply tray;

a second detection part which is provided in the discharge part and detects a number of sheets of the documents discharged on the discharge tray; and

a third detection part which is provided in the conveyance part and detects the supply tray disposed at the taking out position, wherein

the lifting and lowering part determines whether it is in the large number of document discharge state or the small number of documents discharge state, based on a detection result of the second detection part,

in the large number of documents discharge state, the lifting and lowering part controls a height of the supply tray based on a detection result of the first detection part, and

in the small number of documents discharge state, the lifting and lowering part controls the height of the supply tray based on a detection result of the third detection part.

3. The document conveyance device according to claim 1 , further comprising a discharged document detection part which detects the documents stacked on the discharge tray, wherein

while the discharged document detection part detects the document, the lifting and lowering part positions the supply tray at a position higher than the taking out position, and

when the discharged document detection part that has detected the document no longer detects the document, the lifting and lowering part lowers the supply tray to a lowermost position and lowers the discharge part to a lowermost position.

4. The document conveyance device according to claim 1 , wherein

the predetermined space is a space in which a user can enter his hand.

5. An image reading device comprising:

the document conveyance device according to claim 1 ; and

a reading part which reads an image of the document conveyed along the document conveyance path by the conveyance part.

6. An image forming apparatus comprising the image reading device according to claim 5 .