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Duplex automatic sheet feeder

1. Field of Invention

The invention relates to a duplex automatic sheet feeder, and more particularly to a duplex automatic sheet feeder capable of effectively preventing an ultra-thin sheet from buckling in a sheet passageway.

2. Related Art

In a conventional duplex scanner, an automatic sheet feeder usually has to turn a document thrice and transport the document through a scanning region thrice when the document is being scanned. When the document is transported across the scanning region at the first time, a front side of the document is scanned. When the document is transported across the scanning region at the second time, a backside of the document is scanned. When the document is transported across the scanning region at the third time, no scanning operation is carried out. The third document transporting operation is, carried out in order to keep the same order of the documents.

Thus, a next document cannot be fed until the current document is transported across the scanning region at the third time in each scan procedure. A lot of unessential waiting time is wasted so that the scanning operation cannot be carried rapidly in this conventional automatic sheet feeder.

In addition, many branch passageways are formed on the document transporting path for the purpose of turning over the sheet smoothly. In order to make the document travelling path become unidirectional, an elastic Mylar has to be disposed at the branching portion. The elastic Mylar may be pushed away by the sheet moving in a first direction, and guides the sheet, which is moving in a direction opposite to the first direction, to another branch passageway. In this case, when the sheet is too thin to have the sufficient rigidity, the sheet cannot push the elastic Mylar away and may buckle and be jammed in the passageway.

It is therefore an object of the invention to provide a duplex automatic sheet feeder capable of effectively preventing an ultra-thin sheet from buckling in a sheet passageway.

To achieve the above-identified object, the invention provides a duplex automatic sheet feeder including a sheet input tray, a first passageway, a sheet feeding mechanism, a second passageway, a third passageway, a fourth passageway, a fifth passageway, a sheet output tray, a guiding mechanism, a sheet detector and a transporting mechanism. The sheet input tray stores a plurality of sheets. The first passageway is connected to the sheet input tray. The sheet feeding mechanism feeds the sheets one by one to the first passageway. The second passageway is connected to the first passageway and has an image processing region. The third passageway is connected to the second passageway. The fourth passageway is connected to the third passageway and the second passageway. The fifth passageway is connected to the third passageway. The sheet output tray is connected to the fifth passageway. The guiding mechanism is located at a connection portion between the third passageway and the fifth passageway, and is for selectively guiding the sheet from the third passageway to the fifth passageway. The sheet detector is located at the third passageway and is for detecting the sheet moving through the third passageway. The transporting mechanism is for transporting the sheet from the first passageway to the sheet output tray sequentially through the second passageway, the third passageway, the fourth passageway, the second passageway, the third passageway and the fifth passageway.

Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a schematic illustration showing a duplex automatic sheet feeder according to a first embodiment of the invention;

FIG. 2 is a schematic illustration showing a duplex automatic sheet feeder according to a second embodiment of the invention;

FIG. 3 is a schematic illustration showing a duplex automatic sheet feeder according to a third embodiment of the invention;

FIG. 4 is a schematic illustration showing a duplex automatic sheet feeder according to a fourth embodiment of the invention.