Sheet feeding or delivering – Feeding – Separators
Reexamination Certificate
2001-12-14
2002-10-22
Bollinger, David H. (Department: 3651)
Sheet feeding or delivering
Feeding
Separators
C271S125000
Reexamination Certificate
active
06467767
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet feeding apparatus capable of feeding various sheets and an image forming apparatus equipped with the sheet feeding apparatus.
2. Description of the Related Art
As for a related art sheet feeding apparatus, a sheet feeding apparatus without any pickup roller in a retard separation system is described as an example by the use of FIG.
9
. When a not shown solenoid is turned on to start the feeding operation of sheets S stacked and stored on a sheet stacking tray
74
, the sheets S are pressed to a sheet feeding roller
51
by an intermediate plate
70
. When the pressing has been completed, rotation driving in the clockwise direction in the figure is transmitted to the sheet feeding roller
51
through a sheet feeding roller shaft
52
to pick up a sheet.
Because a separation roller
53
is connected directly with the sheet feeding roller
51
in driving, rotation driving in the direction for pressing back a sheet to the sheet stacking tray
74
(in the clockwise direction in the figure) is transmitted to the separation roller
53
at the same timing as the driving of the sheet feeding roller
51
. Because the separation roller
53
is fitted to a separation roller shaft
54
through a torque limiter
61
for generating predetermined torque, the separation roller
53
is constantly giving a fixed separation force (a force operating to press a sheet back to the sheet stacking tray
74
) to the sheet during the conveyance operation of the sheet feeding roller
51
.
Moreover, the abutting pressure of the separation roller
53
and the value of the torque limiter
61
are set such that the separation roller
53
is dragged by the sheet feeding roller
51
when only one sheet is nipped at a nipping portion between the sheet feeding roller
51
and the separation roller
53
, and that the separation roller
53
rotates in the direction of pressing back a sheet piled on and sent with another sheet when two sheets or more are nipped at the nipping portion. When the leading end of the sheet has passed the nipping portion between the sheet feeding roller
51
and the separation roller
53
, the pressuring of the sheet by the intermediate plate
70
is released. After that, when the leading end of the sheet reaches evulsion rollers
55
a
and
55
b,
the drive of the sheet driving roller
51
is cut off, and the sheet is pulled out by the evulsion rollers
55
a
and
55
b
to be conveyed.
Because, in such a sheet feeding apparatus, one sheet feeding roller
51
performs both the operation of the picking up of a sheet and the operation of the separation and the conveyance of the sheet, the sheet feeding apparatus has many merits such as the structure thereof is simple and the costs thereof is low and further the apparatus has a high separation performance. On the contrary, because it is difficult to enter a sheet horizontally to a nip tangent of the sheet feeding roller
51
and the separation roller
53
owing to the structure thereof, the sheet feeding apparatus has a weakness such that the apparatus is not suitable for the feeding of special sheets such as a thick sheet, a thin sheet and an envelope.
The reason is described by the use of concrete numerical values in the following. When the outer diameters of the sheet feeding roller
51
and the separation roller
53
are respectively assumed to be 36 mm and 24 mm, a realistic incident angle of a sheet is about 25 degrees at the lowest (the angle changes according to the number of stacked sheets within a range of about 25 to 40 degrees). When the picking up of a sheet is performed at that incident angle, the leading end of the sheet is contacted with the outer peripheral surface of the separation roller
53
at an angle of 40 degrees (when the incident angle is 40 degrees, the contact angle is 65.5 degrees).
The contact pressure of the separation roller
53
to the sheet feeding roller
51
and the returning torque of the torque limiter
61
are designed in a delicate balance for the compatibility of the durability and the document stopping performance of the rollers
51
and
53
. Consequently, when a sheet hard to fold such as a thick sheet abuts against the separation roller
53
at such a steep angle, the abutting breaks the dragged movement of the separation roller
53
by the sheet feeding roller
51
, and then the separation roller
53
stops rotating before the sheet reaches the nipping portion. Because the conveyance force of the sheet feeding roller
51
is not so strong as to be able to rotate the separation roller
53
compulsorily to push the sheet into the nip, the sheet cannot advance beyond the position. As a result, feed trouble occurs and a jam (sheet clogging) is generated.
Moreover, because the separation roller
53
follows the sheet feeding roller
51
with the lord of the torque limiter
61
, the separation roller rotates at a speed slower than the conveyance speed of sheet feeding roller
51
by about 20%. In addition to that, there is a relative speed difference in the sheet conveying direction between the speed of the movement of the leading end of the sheet along the outer periphery of the separation roller
53
and the conveyance speed of the sheet by the sheet feeding roller
51
, and the latter tends to send the sheet faster than the former. If the sheet is an ordinal one, the sheet absorbs the speed difference by bending instantaneously, and the sheet can be fed without any problem. However, if the sheet is easy to fold like a thin sheet or a sheet is weak at end portions like an envelope, the leading end of the sheet is downward bent or crashed.
For resolving these problems, two methods have conventionally been used. (1) One of them is to make it hard that the leading end of a sheet hits the outer periphery of the separation roller
53
by adjusting the space gap between a feed guide in the vicinity of the separation roller
53
and the sheet feeding roller
51
to be smaller for correcting the turning direction of the leading end of the sheet by the feed guide to be as near as possible to the nip tangent. (2) The other of them is to prevent the aforesaid problems previously by providing a lever for switching the largeness of the applying pressure of the separation roller
53
to the sheet feeding roller
51
, and by a user's selection of a condition according to a sheet to make it easy to feed the sheet.
However, the former method has the problems such that the construction cost thereof becomes high because the method requires the special adjustment, and that a sheet curled downward becomes apt to be caught by the entrance of the feed guide because the feed guide is disposed fairy near to a sheet conveying surface in design. Moreover, the latter method has problems such that, although the method can deal with sheets to a certain extent, the tolerance range of the method is narrow from a point of view of coping with sheet in a wide range, and that the conveyance with a piled sheet and a feed trouble are generated if a user mistook the selection of a feed condition, above all.
SUMMARY OF THE INVENTION
The present invention resolves the aforesaid conventional problems, and aims to provide a sheet feeding apparatus and an image forming apparatus that respectively have a simple structure and can perform stable feeding of various sheets.
According to the present invention, the foregoing and other objects and advantages are attained by a sheet feeding apparatus comprising:
sheet supporting means for supporting sheets;
sheet feeding means for feeding the sheets supported by the sheet supporting means;
separating means for separating the sheets between the sheet feeding means;
separation force giving means for supplying a separation force to the separating means in a direction reverse to a sheet feeding direction; and
separation force switching means for being switched between a connection state for supplying the separation force to the separating means by the separation force giving means and a cut-off state in wh
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