Sheet feeding or delivering – Feeding – Separator and conveyor
Reexamination Certificate
2001-04-06
2002-11-12
Skaggs, H. Grant (Department: 3651)
Sheet feeding or delivering
Feeding
Separator and conveyor
C271S121000, C271S123000, C271S127000
Reexamination Certificate
active
06478294
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to and claims priority, under 35 U.S.C. § 119, from Japanese Patent Application No. 2000-104492, filed on Apr. 6, 2000, and Japanese Patent Application No. 2001-056186 filed on Mar. 1, 2001, and the entire contents of both Japanese patent applications are hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet feeding device having a base plate which is configured to be rotatable so that sheets, which are stacked on the base plate, are pressed against a feeding roller in order to be fed, and an image forming apparatus using the sheet feeding device.
2. Discussion of Background
Japanese Patent Laid-Open Publication No. 5-170347 discloses a sheet feeding device which feeds sheets stacked on a rotatable base plate with a feeding roller. Beginning with the uppermost sheet of the stacked sheets, the sheets are fed one by one by pressing the base plate toward the feeding roller so that the stack of sheets stacked on the base plate are pressed against and into contact with the feeding roller. As the number of sheets stacked on the base plate decreases, the base plate rotates toward the feeding roller such that an uppermost sheet, of the stack of sheets stacked on the base plate, is pressed against and into contact with the feeding roller.
It is known to provide a friction member on an upper surface of the base plate in the vicinity of a part of the base plate opposed to the feeding roller, i.e., at a part of a free end side of the base plate. This gives a frictional resistance to a bottom sheet of the stack of sheets stacked on the base plate. Thus, the bottom sheet, of the stack of sheets stacked on the base plate, is prevented from being pulled out from its position against the base plate when the uppermost sheet is fed.
The above-described sheet feeding device must be configured so that only the uppermost sheet is reliably pulled out from the stack of sheets stacked on the base plate. In other words, the uppermost sheet of the stack of sheets stacked on the base plate must slip relative to adjacent and subsequent sheets stacked on the base plate. Further, even when the number of sheets in the stack of sheets stacked on the base plate has been decreased such that the bottom sheet of the stack of sheets receives a gripping force from the feeding roller, the bottom sheet must be prevented from being pulled out from its position against the base plate via the frictional resistance of the friction member against the bottom sheet. Furthermore, the sheet feeding device must be configured such that when only one sheet, i.e., the last sheet of the stack of sheets, remains on the base plate, the feeding roller pulls out the last sheet using a pulling force which is larger than the frictional resistance which the friction member provides with respect to the last sheet of the stack of sheets stacked on the base plate.
The sheet feeding device includes a feeding roller which feeds out the uppermost sheet of the stack of sheets stacked on the base plate via a pulling force Fa of the feeding roller acting on the uppermost sheet. A frictional resistance Fb acts between each sheet of the stack of sheets stacked on the base plate. A friction member is located at a free end side of the base plate and provides a frictional resistance Fc to a bottom sheet of the stack of sheets stacked on the base plate. The sheet feeding device is configured so that the relationship Fa>Fc>Fb is satisfied.
However, even when a sheet feeding device is designed so as to satisfy the relationship Fa>Fc>Fb, sheets may still be double-fed (i.e., a plurality of sheets are pulled out at the same time from the stack of sheets stacked on the base plate). Of course, the occurrence of the double-feeding phenomenon in part depends upon the quality of the sheets, the environmental conditions (e.g., temperature and humidity), the state of static electricity, and the resilience of the sheets, etc. Therefore, for preventing such a double feeding of sheets, a separation device is generally arranged in the vicinity of an end of the base plate at the downstream side of the sheet feeding device in the sheet feeding direction so as to oppose the feeding roller. The relationship Fa>Fc>Fb is further desired to be satisfied such that the burden on the separation device is decreased and thereby the sheet separation performance is enhanced and each sheet of the stack of sheets stacked on the base plate are reliably fed from first sheet to last sheet.
Changes in the quality of the sheets, the environmental conditions, such as temperature and humidity, the state of the static electricity, and the resilience of the sheets affect the pulling force Fa, and the frictional resistances Fb and Fc.
Moreover, as the number of sheets of the stack of sheets stacked on the base plate increases, the base plate is positioned lower relative to the feeding roller so as to contract a base plate pressing member which upwardly biases the base plate. Thereby, the pulling force Fa, acting on the uppermost sheet of the stack of sheets stacked on the base plate, increases, but only slightly.
The frictional resistance Fc of the friction member provided with respect to the bottom sheet of the stack of sheets stacked on the base plate changes according to the variation in the friction coefficient of the friction member. Moreover, because a reaction force, corresponding to the pulling force Fa from the feeding roller, acts on the friction member via the stack of sheets stacked on the base plate, the frictional resistance Fc further changes. Thus, the frictional resistance Fc changes goes through a larger magnitude of change than does either the pulling force Fa or the frictional resistance Fb.
When the sheet feeding device is configured such that the base plate is moved toward the feeding roller for sheet feeding and is moved away from the feeding roller during the intervals of sheet feeding, as disclosed in Japanese Patent Laid-Open Publication No. 9-202475, the position of the base plate, when moved toward the feeding roller, changes according to the amount of play of a rotation support part of the base plate. This further increases the variation in the frictional resistance Fc.
Further, when the sheet feeding device is configured such that the base plate is inclined downwardly (i.e., from the side of the rotation center of the base plate toward the side on which the feeding roller is located), in order to reduce the installation space for the sheet feeding device in the horizontal direction, the inclination of the base plate relative to the vertical direction increases as the number of sheets of the stack of sheets stacked on the base plate increases. Thus, the stack of sheets stacked on the base plate tends to plunge between the feeding roller and the friction member under the weight of the stack of sheets. Such a plunging of the stack of sheets is more remarkable as the size of the sheets increases and thus, the phenomenon of double feeding of the sheets tends to occur more easily. Therefore, to avoid double feeding of sheets, the value of the frictional resistance Fc needs to be set relatively high. It is difficult to properly set the frictional resistance Fc since it should correspond to the inclining angle of the base plate.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-discussed and other problems of the prior art.
Preferred embodiments of the present invention provide a sheet feeding device that can reliably separate and feed a stack of sheets stacked on a base plate from a first sheet to a last sheet of the stack of sheets.
According to a preferred embodiment of the present invention, a sheet feeding device includes a feeding roller, which is driven to rotate, and a base plate on which to stack sheets to form a stack of sheets. The sheet feeding device is preferably configured to rotate around a supporting axis thereof in directions to contact and separate from the
Ricoh & Company, Ltd.
Skaggs H. Grant
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