Sheet feeding or delivering – Feeding – Separator and conveyor
Reexamination Certificate
2000-05-12
2002-04-30
Bollinger, David H. (Department: 3651)
Sheet feeding or delivering
Feeding
Separator and conveyor
C271S117000, C271S121000, C271S124000
Reexamination Certificate
active
06378858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet feeding apparatus for separating and feeding a sheet sheet by sheet and to an image forming apparatus such as a copying machine, a printer or the like or an image reading apparatus having the apparatus.
2. Related Background Art
Conventionally, for example, in a sheet feeding section of a copying machine or the like, a sheet separation using a retard roller rotating in a direction opposite to a sheet feeding direction has mainly used as a sheet feeding means for preventing a plurality of sheets from being fed (referred to as “double-feed” hereinafter).
A summary of a conventional sheet feeding apparatus utilizing a retard separation system will be described hereinafter.
FIG. 25
is a schematic side view of a sheet feeding apparatus utilizing a retard separation method constituted of a sheet feeding roller and a separation roller (see, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 3-18532, U.S. Pat. No. 5,016,866). This is referred to as a first prior art hereinafter.
First, as shown in
FIG. 25
, sheets S stacked on a intermediate plate
206
in a cassette
207
are lifted together with the intermediate plate
206
by a pressing arm
208
and a sheet pressing spring
205
to be always pressingly contacted with the sheet feeding roller
201
, thereby gaining sheet feeding pressure.
Also, the sheet feeding roller
201
receives retard pressure (separation roller pressure) from a separation roller
202
. In this state, when the sheet feeding roller
201
rotates in a sheet feeding direction, the sheets S pressingly contacted with the sheet feeding roller
201
are fed out to reach a nip formed by the sheet feeding roller
201
and the separation roller
202
. At this time, when a single sheet S is pinched by the nip, the separation roller
202
is also rotationally driven in the sheet feeding direction together with the sheet feeding roller
201
due to a torque limiter
203
formed integrally with a separation roller shaft, thereby feeding the sheet S.
When a plurality of the sheets are pinched in the nip, however, the separation roller
202
is rotated with predetermined torque in a direction to which the double-fed sheets are restored, with the operation of the torque limiter
203
, thereby preventing the sheet double-feed.
In addition, FIG.
26
and
FIG. 27
are schematic side views of a sheet feeding apparatus utilizing a retard separation system with a planetary gear mechanism (see, Japanese Patent Publication (KOKOKU) Heisei No. 1-32134). This is referred to as a second prior art hereinafter.
As shown in
FIG. 26
, this sheet feeding mechanism utilizes a planetary gear mechanism constituted of a sun gear
301
, an intermediate gear
302
, a planetary gear
303
and a connecting arm
304
, and a sheet feeding roller
307
is connected to the planetary gear
303
. Furthermore, a separation roller
309
is connected to a driving shaft
306
through a torque limiter, and a pair of draw rollers
310
for conveying a sheet S at a speed higher than a speed at which the sheet feeding roller
307
feeds the sheet S is disposed on a downstream of the sheet feeding roller
307
in a sheet feeding direction.
An operation of the sheet feeding mechanism will be briefly described hereinafter with reference to FIG.
27
.
First, by rotation of the driving shaft
306
, the planetary gear
303
and the sheet feeding roller
307
revolve in a direction indicated by an arrow A in
FIG. 27
, with the result that the sheet feeding roller
307
pressingly contacts with an uppermost sheet S of the sheets stacked within a sheet cassette. Also, in synchronous with the rotation, a lever
318
lifts an intermediate plate
323
stacking the sheets toward a direction of the sheet feeding roller (a direction indicated by an arrow G in FIG.
27
).
By this operation, the sheet S pressingly contacted with the sheet feeding roller
307
is sent into a nip formed by the sheet feeding roller
307
and the separation roller
309
, thereby feeding and separating the sheet S. Furthermore, the sheet S after passing through the nip enters into the pair of draw rollers
310
, and the planetary gear mechanism and the sheet feeding roller
307
are returned to the initial positions by transmitting the driving force of the pair of draw rollers
310
through the sheet S to the planetary gear mechanism, and this operation is repeated.
Although the two prior arts in the sheet feeding mechanism are shown, it is considered that the respective prior arts can be improved in several points.
First, in the mechanism of the first prior art, the sheets S stacked on the intermediate plate
206
in the cassette
207
are lifted together with the intermediate plate
206
to be always pressed by the sheet pressing spring
205
. Consequently, a sheet feed and separation condition greatly depends on the pressure of the intermediate plate, resulting in that an appropriate sheet feed area is limited in consideration of the pressure of the intermediate plate as a function.
In particular, because the pressures of the intermediate plate generated by the sheet pressing spring
205
vary with the number of sheets stacked in the cassette
207
, the sheet feed and separation condition differs between a case where the sheets are fully loaded and a case where a several number of the sheets are loaded. Also, the pressure of the intermediate plate is always generated on the stacked sheets S since the sheets S are always pressingly contacted with the sheet feeding roller
201
. Therefore, while the sheet S as the uppermost sheet is being fed, the sheet S′ to be succeedingly fed is subjected to a conveying force by friction between the sheets, with the result that the double-feed of the sheet S′ tends to easily occur.
In addition, even if the double-fed sheets are separated and tried to be returned to the former position, the sheet S is pinched by the sheet feeding roller
201
and the intermediate plate
206
, and therefore the double-fed sheet may not be returned smoothly.
Furthermore, an allowable range of the appropriate sheet feed area is limited in dependence upon the kind of sheet (for example, sheet having great coefficient of the friction) or the reduction of frictional coefficients of the sheet feeding roller and the separation roller caused by wears, and as a result, the stability might be worsened. Therefore, it is hard to say that this mechanism is a sheet feeding mechanism having high stability and high reliability.
Incidentally, in this mechanism, when it is tried that the double-feed is hard to occur and the double-fed sheets can easily restored, the restoring force provided by the torque limiter
203
must be set to a greater value; the retard pressure of the retard spring must be considerably decreased; or the pressure of the intermediate plate provided by the sheet pressing spring
205
must be considerably decreased.
In any cases, however, slip between the sheet feeding roller
201
and the separation roller may be generated, with the result that the wear of the sheet feeding roller
201
and the separation roller
202
is accelerated, thereby considerably reducing enduring lifetime of the sheet feeding roller
201
and the separation roller
202
. As a result, the number of periodical replacing operation for worn parts is increased to increase the maintenance cost of the sheet feeding apparatus. Furthermore, torque of the driving force applying means (motor) is required to increase, resulting that not only the cost of the apparatus but also power consumption must be increased.
In addition, when the restoring force of the torque limiter
203
is set to be a greater value, in a space Z formed between a nip portion X constituted of the sheet feeding roller
201
and the separation roller
202
, and a pressingly contacting part Y between the sheet feeding roller
201
and the sheets on the intermediate plate
206
, it is considered that the double-fed sheet (especially, thin sheet having poor elasticity) may be buck
Bollinger David H.
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
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