Sheet feeding or delivering – Delivering – With transfer means between conveyor and receiver
Reexamination Certificate
2001-01-18
2004-05-18
Ellis, Christopher P. (Department: 3651)
Sheet feeding or delivering
Delivering
With transfer means between conveyor and receiver
C399S364000
Reexamination Certificate
active
06736390
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus for recording images on both sides of a sheet by reversing and re-feeding the sheet, and more particularly, to an image forming apparatus for improving throughput of a sheet re-feed device.
2. Description of the Related Art
Hitherto, many image forming apparatuses having an image forming unit for recording an image on one side of a sheet have been proposed. These image forming apparatuses are arranged so as to record images on both sides of the sheet by re-feeding it to the image forming unit after the front and back sides thereof are reversed.
A sheet re-feed device for reversing and re-feeding sheets is typically arranged such that (1) sheets are placed on an intermediate tray while being bent and reversed in a sheet feed direction and then fed again or (2) the leading end and the trailing end of the sheets are changed by being switched back by a reverse unit and then sequentially fed again from a re-feed unit.
In the latter system, the maximum number of sheets exiting on a transportation path (a reverse unit and the re-feed unit) of the sheet re-feed device is set in accordance with a sheet having a maximum length capable of being handled by the sheet re-feed device. When, for example, the maximum number of sheets is two sheets, an image forming apparatus feeds a first sheet to the re-feed unit of the sheet re-feed device and places it in a standby state there and then feeds a second sheet with an interval between it and the first preceding sheet to prevent the first sheet from colliding against the second sheet and places the second sheet in a standby state on the reverse unit of the sheet re-feed device. Subsequently, the first sheet, which was placed in the standby state on the sheet re-feed device, is fed again to an image forming unit where an image is recorded on the back side of the first sheet, and then the first sheet is discharged to an outside of the image forming apparatus. Then, the second sheet, which was placed in the standby state on the reverse unit, is fed to the re-feed unit while a third sheet is transported to and placed in a standby state on the reverse unit. Repetition of the above operations permits images to be continuously recorded on both sides of the first, second, and third sheets.
Recently, when an image is recorded on sheets having a short length by an image forming apparatus, those sheets are fed at short intervals so as to increase the number of sheets processed in a unit time (hereinafter, referred to as “throughput”). However, the number of sheets that can be placed in a standby state on the re-feed unit is set in accordance with a sheet having a maximum length as described above. As such, a problem arises in that the throughput cannot be increased.
To solve this problem, it has been contemplated to make a sheet transportation speed higher in the sheet re-feed device than in the main body of the image forming apparatus. However, the sheet transportation speed in the main body of the image forming apparatus is sufficiently increased by an increase in the throughput of the main body. Thus, it is necessary to increase the size of a transportation motor to transport sheets at a higher speed in the sheet re-feed device, which thereby increases the manufacturing cost of the image forming apparatus.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a sheet re-feed device capable of increasing the throughput of sheets having a short length without increasing a transportation speed in the sheet re-feed device, and to provide an image forming apparatus on which the sheet re-feed device is mounted.
Further, to solve the above problem, a sheet re-feed device and an image forming apparatus according to the present invention are typically arranged such that the sheet re-feed device, which includes a sheet reverse unit, a re-feed path for guiding sheets, and a re-feed unit disposed downstream of the re-feed path, comprises a plurality of sheet sensing devices and a sheet transportation stop unit for transporting and stopping the sheets, which are disposed in the re-feed path, so that more sheets are placed in a standby state when they are short than when they are long.
As described above, in the sheet re-feed device and the image forming apparatus according to the present invention, more sheets can be placed in the standby state on the transportation path of the sheet re-feed device, which can increase the throughput of short sheets when images are recorded on both the sides thereof.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.
REFERENCES:
patent: 5703693 (1997-12-01), Morikawa
patent: 5893020 (1999-04-01), Atsumi
patent: 6226069 (2001-05-01), Tabuchi et al.
patent: 6320674 (2001-11-01), Soma et al.
Canon Kabushiki Kaisha
Deuble Mark A.
Ellis Christopher P.
Fitzpatrick ,Cella, Harper & Scinto
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