Sheet feeding or delivering – Feeding – Separator and conveyor
Reexamination Certificate
1999-10-13
2001-07-17
Ellis, Christopher P. (Department: 3651)
Sheet feeding or delivering
Feeding
Separator and conveyor
C271S010010, C271S010090, C271S010110, C271S010130
Reexamination Certificate
active
06260840
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet feeding apparatus used in an image forming apparatus such as a copying machine, a printer and the like or in an image reading apparatus such as a facsimile, a scanner and the like.
2. Related Background Art
In the past, for example, in the sheet feeding portion of a copying machine or the like, sheet separation using a retard roller rotated in a direction opposite to a sheet feeding direction has mainly been used as sheet feeding means for preventing more than one sheets from being fed simultaneously (referred to as “double-feed” hereinafter).
Now, a conventional sheet feeding apparatus using a retard separation system will be briefly described.
FIG. 26
is a schematic side view of a sheet feeding apparatus of retard separation type comprising a sheet feeding roller (sheet pick-up roller) and a separating roller (refer to Japanese Patent Application Laid-open No. 3-18532, U.S. Pat. No. 5,016,866). This is referred to as a first earlier technology hereinafter.
As shown in
FIG. 26
, sheets S stacked on an intermediate plate
506
in a cassette
507
are lifted together with the intermediate plate
506
by a pressing arm
508
and a sheet pressing spring
505
to be always urged against a sheet feeding roller
501
, thereby providing sheet feeding pressure.
Further, the sheet feeding roller
501
receives retard pressure from a separating roller
502
. In this state, when the sheet feeding roller
501
is rotated in a sheet feeding direction, the sheet S urged against the sheet feeding roller
501
is picked up to reach a nip between the sheet feeding roller
501
and the separating roller
502
. At this time, if a single sheet is pinched by the nip, the separating roller
502
is rotatingly driven in the sheet feeding direction by rotation of the sheet feeding roller
501
due to the presence of a torque limiter
503
formed integrally with a shaft of the separating roller, thereby feeding the sheet S.
However, if a plurality of sheets are pinched by the nip, the separating roller
502
is rotated with predetermined torque in a direction along which the double-fed sheets are returned, with the aid of the torque limiter
503
, thereby preventing the sheet double-feed.
FIGS. 27 and 28
are schematic side views of a sheet feeding apparatus using a retard separation system constituted by a planetary gear mechanism (refer to Japanese Patent Publication No. 1-32134). This is referred to as a second earlier technology hereinafter.
As shown in
FIG. 27
, the sheet feeding apparatus utilizes a planetary gear mechanism comprising a sun gear
601
, an intermediate gear
602
, a planetary gear
603
and a connecting arm
604
, and a sheet feeding roller
607
is connected to the planetary gear
603
. Further, a separating roller
609
is connected to a drive shaft
606
through a torque limiter, and a pair of draw rollers
610
for feeding a sheet S at a speed higher than a speed at which the sheet feeding roller
607
feeds the sheets S are disposed at a downstream side of the sheet feeding roller
607
in a sheet feeding direction.
Now, an operation of the sheet feeding apparatus will be briefly described with reference to FIG.
28
.
First of all, by rotating the drive shaft
606
, the planetary gear
603
and the sheet feeding roller
607
are revolved in a direction indicated by the arrow A, with the result that the sheet feeding roller
607
abuts against an uppermost sheet S of a sheet stack contained within a sheet cassette. Further, in synchronous with such revolution, a lever
618
lifts an intermediate plate
623
on which the sheets are stacked toward the sheet feeding roller (in a direction indicated by the arrow G).
By this operation, the sheet S urged against the sheet feeding roller
607
is sent to a nip between the sheet feeding roller
607
and the separating roller
609
, thereby effecting separation and feed of the sheet. Further, the sheet S left the nip enters into the pair of draw rollers
610
, and the planetary gear mechanism and the sheet feeding roller
607
are returned to their original positions by transmitting a driving force of the pair of draw rollers
610
to the planetary gear mechanism through the sheet S. And, such operation is repeated.
Although two earlier technologies in the sheet feeding mechanism are shown, it is considered that such technologies can be improved in several points.
First, in the mechanism according to the first earlier technology, the sheets S stacked on the intermediate plate
506
within the cassette
507
are lifted together with the intermediate plate
506
by the sheet pressing spring
505
to be always urged against the sheet feeding roller
501
. Thus, a sheet feed/separation condition greatly depends upon the pressure of the intermediate plate, with the result that an optimum sheet feeding area is limited in consideration of the pressure of the intermediate plate as a function.
In particular, since the pressures of the intermediate plate generated by the sheet pressing spring
505
vary with the number of sheets stacked within the cassette
507
, the sheet feed/separation condition differs between a case where the cassette
507
is loaded up with the sheets and a case where a several number of sheets are stacked. Further, since the sheet S is always urged against the sheet feeding roller
501
, the pressure of the intermediate plate always acts on the stacked sheets S. Thus, while the uppermost sheet S is being fed, a next or succeeding sheet S′ is subjected to a feeding force due to friction between the sheets, with the result that the double-feed of sheet S′ will easily occur.
In addition, even if the double-fed sheets are separated and tried to be restored, the sheets are pinched between the sheet feeding roller
501
and the intermediate plate
506
so that the double-fed sheets may not be restored smoothly.
Further, an allowable range of the appropriate sheet feed area is further limited in dependence upon the kind of sheet (for example, sheet having great coefficient of friction) and reduction of coefficients of friction of the sheet feeding roller and the separating roller due to wears of the sheet feeding roller and the separating roller, thereby worsening the stability.
Therefore, it is hard to say that this mechanism is a sheet feeding mechanism having high stability and high reliability.
Incidentally, in this mechanism, in order to make it so the double-feed is hard to occur and the double-fed sheets can easily be restored, the restoring force provided by the torque limiter
503
must be set to a greater value or the retard force of the retard spring must be decreased considerably or the feeding pressure provided by the sheet pressing spring
505
must be decreased considerably.
However, in many cases, slip between the sheet feeding roller
501
and the sheet and/or between the separating roller
502
and the sheet may easily be generated, with the result that the wear of the sheet feeding roller
501
and the separating roller
502
is accelerated, thereby reducing the service life of the sheet feeding roller
501
and the separating roller
502
greatly. As a result, the number of periodical replacing operation for worn parts is increased to increase the maintenance cost of the apparatus. Further, torque of driving force applying means (motor) must be increased, thereby making the apparatus expensive and increasing power consumption.
Further, when the restoring force of the torque limiter
503
is set to a greater value, in a space Z formed between a nip X (between the sheet feeding roller
501
and the separating roller
502
) and an abutment area between the sheet feeding roller
501
and the intermediate plate
506
, it is considered that the double-fed sheet (particularly, thin sheet having poor rigidity) may be buckled, thereby causing sheet jam.
In addition, when a pair of feeding rollers are provided at a downstream side of the sheet feeding roller
501
and the separating roller
502
in the sheet
Suga Takeshi
Yano Takashi
Canon Kabushiki Kaisha
Ellis Christopher P.
Fitzpatrick ,Cella, Harper & Scinto
Shapiro Jeffrey A.
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