Electrophotography – Document handling – Copy
Reexamination Certificate
2000-02-25
2001-06-12
Chen, Sophia S. (Department: 2852)
Electrophotography
Document handling
Copy
C271S188000, C399S045000, C399S389000, C493S459000
Reexamination Certificate
active
06246860
ABSTRACT:
RELATED APPLICATIONS
The present application claims priority to Japanese Patent Application No.
11-49571
filed Feb. 26, 1999, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a sheet decurling apparatus, and more particularly to a sheet decurling apparatus that removes the curling of sheets of paper caused by the thermal fixing of the toner image onto the sheet in image forming apparatuses such as copying machines, printers and facsimile machines.
2. Description of the Related Art
Conventionally, a sheet decurling apparatus of this kind has multiple conveyance paths and a fixed conveyance path alternating means that alternates the conveyance paths from one to the other depending on the degree of curling of the sheet, such that it automatically guides sheets that are curled to a prescribed degree or more at their top edges to a decurling conveyor path and sheets that are not curled to the prescribed degree to a non-decurling conveyance path, as disclosed in U.S. Pat. No. 5,300,012, for example. Technologies in which the degree and direction of the curling are detected by sensors and the appropriate conveyance path is selected accordingly, or in which the device is equipped with a decurling mechanism capable of varying the amount of decurling to ensure appropriate decurling have also been proposed.
Other technologies also exist in which the curling is removed by creating a loop in the sheet by stopping the rollers that convey the sheet for a prescribed period of time, as disclosed in Japanese Laid-Open Publication
1-167164,
or in which appropriate decurling is attempted by detecting the degree of curling by a sensor and varying the speeds of the rollers, as disclosed in Japanese Laid-Open Publication 4-173655.
However, in the method disclosed in U.S. Pat. No. 5,300,012, the selection of a conveyance path depends on the degree of curling at the top edge of the sheet, and therefore, even when a sheet that is not curled is flush with the upper guide plate, the decurling path is selected, resulting in a lack of accuracy. In addition, the direction of curling varies: some sheets curl along the direction of conveyance and some curl in the direction perpendicular to the direction of conveyance, depending on the direction of the grain of the paper. Consequently, using the method in which the degree and direction of curling are detected, it is difficult to accurately detect the degree of curling in both directions. Even if it could be done, this method would inevitably entail an increase in cost, and is therefore impractical.
Moreover, the sheet decurling device is set such that the curling of sheets of plain paper, which is used in most cases, may be appropriately removed, presenting the ancillary effect that when thick paper or transparencies pass through, the reverse effect occurs, resulting in large curling in the opposite direction.
In the technology disclosed in Japanese Laid-Open Publication 1-167164, while the amount of loop formed at the rear edge of the sheet is constant, the degree of curling that occurs through the thermal fixing process varies depending on the properties of the sheet. In addition, the degree of curling tends to increase as the number of sheets that pass through the apparatus increases in continuous printing mode, or under similar conditions. This results in the problem that the decurling effect is either insufficient if the degree of decurling is constant or excessive where the sheet curls in the opposite direction.
The technology disclosed in Japanese Laid-Open Publication 4-173655 detects the degree of curling at the top edge of the sheet by multiple transmission sensors, but the problem exists that the probability of erroneous detection can be high depending on the behavior of the sheet while it is passing through the apparatus.
SUMMARY OF THE INVENTION
The object of the present invention is to resolve the problems identified above.
Another object of the present invention is to provide a sheet decurling apparatus that does not decurl special types of paper such as thick paper and transparencies, and that decurls plain paper only without any increase in cost.
Yet another object of the present invention is to provide a sheet decurling apparatus capable of performing appropriate decurl using a simple construction by detecting the properties or parameters of the sheet and performing control so that an amount of loop specified in advance may be obtained, or by selecting a conveyance path based on the detection results.
These and other objects may be attained by a sheet decurling apparatus, comprising: a plurality of sheet supply units; a first conveyance path that has a decurling device within its length and that conveys the sheets supplied from a sheet supply unit; a second conveyance path that does not have a decurling device within its length and that conveys the sheets supplied from a sheet supply unit; and selecting means for selecting either the first or second conveyance path depending on the sheet supply unit used.
In the construction described above, prescribed types of sheet are placed in the sheet supply units, and selecting means operates a conveyance path alternating means to alternate the conveyance paths based on the setting of each sheet supply unit. Sheets supplied from a sheet supply unit that requires decurling are guided to the first conveyance path equipped with a decurling device, and sheets supplied from a sheet supply unit that does not require decurling are guided to the second conveyance path that is not equipped with a decurling device. Each sheet supply unit comprises a sheet cassette or manual sheet tray. A drive means such as a solenoid may be used for the conveyance alternating means. It is preferred that the decurling device comprises means for warping the sheet in the direction opposite the direction of the curling caused through the thermal fixing process.
The objects of the present invention are further attained by a sheet decurling apparatus, comprising: a plurality of sheet supply units; a conveyance path to convey the sheets supplied from the sheet supply units; a decurler that is located within the length of the conveyance path and that decurls the sheet; varying means for varies the degree of the curling effect exerted by the decurler; and controller that controls the varying means depending on the sheet supply unit used.
In this construction, the controller changes the degree of curling exerted by the decurler on the sheet based on the settings that are set in advance for each sheet supply unit. For vary means to vary the decurling effect, a mechanism that changes the amount of pressure exerted by the decurler using a drive means such as a cam or solenoid may be used. In addition, it is preferred that the degree of the effect by the decurler may be specified depending on the sheet supply unit used.
It is further preferred that it be specified in advance for each sheet supply unit whether or not decurling is to be performed, such that control may be performed based on that setting. For example, where sheets are supplied from a paper cassette, plain paper is used in most cases, and therefore it is more appropriate to select performance of decurling. In this case, setting should be made so that decurling will occur automatically. On the other hand, where sheets are supplied from a manual paper tray, it is highly likely that a special type of paper will be used, and it is thus safer not to perform decurling. Therefore, setting should be made so that automatic decurling will not be performed.
The objects are also attained by a sheet decurling apparatus comprising: first conveyance for conveying the sheets; second conveyance means that is located downstream from the first conveyance means; loop creating means that creates a loop in the sheet being conveyed by making the conveyance speed of the top edge of the sheet conveyed by the second conveyance means different from the speed by which it is conveyed by the first conveyan
Chen Sophia S.
McDermott & Will & Emery
Minolta Co. , Ltd.
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