U.S. patent application number 16/131565 was filed with the patent office on 2019-03-28 for sheet conveying apparatus and image forming apparatus.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Jiroh Itoh, Yoshiaki Kisara, Hideki Mori, Masanori Ozawa.
Application Number | 20190092594 16/131565 |
Document ID | / |
Family ID | 65808698 |
Filed Date | 2019-03-28 |
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United States Patent
Application |
20190092594 |
Kind Code |
A1 |
Mori; Hideki ; et
al. |
March 28, 2019 |
SHEET CONVEYING APPARATUS AND IMAGE FORMING APPARATUS
Abstract
Disclosed is a sheet conveying apparatus. The sheet conveying
apparatus includes a conveying roller pair (58) for conveying a
sheet, a registration roller pair (57) disposed downstream of the
conveying roller pair (58) and a guide portion for guiding the
sheet conveyed to the registration roller pair (57) by the
conveying roller pair (58) such that the sheet is deflected.
Further, the guide portion guides the sheet such that a number of
deflection nodes changes according to stiffness of the sheet.
Inventors: |
Mori; Hideki; (Toride-shi,
JP) ; Ozawa; Masanori; (Yokohama-shi, JP) ;
Itoh; Jiroh; (Yokohama-shi, JP) ; Kisara;
Yoshiaki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
65808698 |
Appl. No.: |
16/131565 |
Filed: |
September 14, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B65H 9/006 20130101;
B65H 2404/6111 20130101; B65H 9/18 20130101; B65H 5/36 20130101;
B65H 2515/81 20130101; B65H 9/002 20130101; B65H 5/062 20130101;
B65H 2801/06 20130101 |
International
Class: |
B65H 9/18 20060101
B65H009/18; B65H 5/36 20060101 B65H005/36; B65H 5/06 20060101
B65H005/06; B65H 9/00 20060101 B65H009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2017 |
JP |
2017-182156 |
Claims
1. A sheet conveying apparatus, comprising: a conveying roller pair
configured to convey a sheet; a registration roller pair disposed
downstream of the conveying roller pair, for correcting skew
feeding of the sheet with a leading end of the sheet conveyed by
the conveying roller pair abutting against the registration roller
pair; and a guide portion configured to guide the sheet conveyed to
the registration roller pair by the conveying roller pair such that
the sheet is deflected, wherein the guide portion includes a
movable guide that is movable from a first position where an
abutting portion of the guide portion for abutting the sheet that
is conveyed is located on one side of a nip line of the conveying
roller pair to a second position where the abutting portion is
located on the other side of the nip line.
2. The sheet conveying apparatus according to claim 1, wherein the
movable guide is displaced from the first position to the second
position when the movable guide is pressed by the sheet having a
predetermined or higher stiffness that is conveyed by the conveying
roller pair.
3. The sheet conveying apparatus according to claim 1, wherein the
guide portion includes: a first movable guide configured to
displace when the first movable guide is pressed by the sheet
having a predetermined or higher stiffness that is conveyed by the
conveying roller pair; and a second movable guide disposed
downstream of the first movable guide.
4. The sheet conveying apparatus according to claim 3, wherein the
first movable guide is movable from a first position where an
abutting portion of the first movable guide for abutting against
the sheet which is conveyed is located on one side of the nip line
of the conveying roller pair to a second position where the
abutting portion is located on the other side of the nip line when
the first movable guide is pressed by the sheet having a
predetermined or higher stiffness that is conveyed by the conveying
roller pair.
5. The sheet conveying apparatus according to claim 3, wherein the
first movable guide is movable from a first position where an
abutting portion of the first movable guide for abutting the sheet
which is conveyed is located on a side of the nip line of the
conveying roller pair with respect to an extended plane of a guide
surface of the second movable guide to a second position where the
abutting portion is away from the nip line when the first movable
guide is pressed by the sheet having a predetermined or higher
stiffness that is conveyed by the conveying roller pair.
6. The sheet conveying apparatus according to claim 5, wherein the
second movable guide is movable from a first position where an
abutting portion of the second movable guide for abutting the sheet
that is conveyed is located in a vicinity of a nip line of the
registration roller pair to a second position where the abutting
portion is away from the nip line when the second movable guide is
pressed by the sheet having a predetermined or higher stiffness
that is conveyed by the conveying roller pair.
7. The sheet conveying apparatus according to claim 3, wherein a
guide surface of the second movable guide intersects with the nip
line of the conveying roller pair.
8. The sheet conveying apparatus according to claim 3, wherein the
registration roller pair includes: a first roller disposed on one
side of a sheet conveying path; and a second roller disposed on the
other side of the sheet conveying path, stiffness of the second
roller being higher than that of the first roller, and wherein the
second movable guide is disposed on the other side of the sheet
conveying path and a fixed guide is disposed on the one side of the
sheet conveying path, the fixed guide being opposed to the second
movable guide.
9. An image forming apparatus, comprising: a sheet conveying
apparatus; and an image forming portion configured to form an image
on a sheet conveyed by the sheet conveying apparatus, wherein the
sheet conveying apparatus includes: a conveying roller pair
configured to convey the sheet; a registration roller pair disposed
downstream of the conveying roller pair, for correcting skew
feeding of the sheet with a leading end of the sheet conveyed by
the conveying roller pair abutting against the registration roller
pair; and a guide portion configured to guide the sheet conveyed to
the registration roller pair by the conveying roller pair such that
the sheet is deflected, wherein the guide portion includes a
movable guide that is movable from a first position where an
abutting portion of the guide portion for abutting the sheet that
is conveyed is located on one side of a nip line of the conveying
roller pair to a second position where the abutting portion is
located on the other side of the nip line.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a sheet conveying apparatus
capable of correcting skew, i.e. inclination of a conveyed sheet
relative to a conveyance direction and relates to an image forming
apparatus including such sheet conveying apparatus.
Description of the Related Art
[0002] A sheet fed from a cassette or the like in which sheets are
stacked may be skewed while being conveyed for various factors such
as a tapered shape of the conveying roller and misalignment of the
conveying roller with respect to the image forming portion or the
transfer portion.
[0003] In particular, when picking up a sheet from a cassette or
when separating a sheet from sheets so that a plurality of sheets
are not conveyed at the same time, skew feeding is likely to occur
for the sheet due to narrow width of the roller and insufficient
support of the sheet during turning.
[0004] Therefore, in order to obtain a good output image, it is
necessary to correct skew feeding of a sheet before the image is
transferred to the sheet at the image forming portion. Further, it
is more effective for the correction position to be closer to the
image forming portion.
[0005] As a means for correcting the skew feeding of the sheet, it
is common to correct the skew feeding by the sheet abutting against
the nip portion of the registration roller pair to make deflection
of the sheet. However, the abutting force against the roller nip
portion changes due to the deflection of the sheet because of the
difference in stiffness (rigidity) of the sheet. When the abutting
force of the sheet against the roller nip portion is weak, the
sheet does not abut against the registration roller pair.
Conversely, when the abutting force is strong, there is a problem
that the sheet penetrates the nip portion of the registration
roller pair.
[0006] In order to solve the above problem, Japanese Patent
Application Laid-Open No. H06-191686 proposes that the curvature of
the deflection is changed by pushing up a different guide according
to the level of the stiffness of the sheet, thereby appropriately
setting the abutting force against the nip portion of the
registration roller pair.
[0007] In addition, Japanese Patent Application Laid-Open No.
2003-72982 proposes that in order to make uniform contact with the
nip portion of the registration roller pair, it is preferable to
form an S-shaped deflection as seen in the cross section of the
sheet to be conveyed.
[0008] Recently, such an apparatus has been miniaturized and when
the S-shaped deflection is formed on the sheet in a narrow space,
the curvature of deflection becomes small. Then, if a sheet having
a high stiffness, for example, a thick sheet is conveyed so as to
form an S-shaped deflection having a small curvature, the sheet may
be deformed into a deflection shape, which is called "residual
curl". Due to this, problems (including sheet jam and a disturbance
of the printed image) may occur.
[0009] In addition, when the deflection amounts (feed amounts of
the conveying roller) are the same, the force with which the
deflection extends increases as the number of deflection nodes (the
number of curved portions) increases. For example, in the case of
the S-shaped deflection (number of nodes of 3), the conveying
roller needs higher torque for conveying the sheet for making
deflection than in the case of the C-shaped deflection (number of
nodes of 2). For this reason, there is a concern that the apparatus
becomes large, or the leading end of the sheet penetrates through
the nip portion of the registration roller pair and the skew
feeding remains.
SUMMARY OF THE INVENTION
[0010] A sheet conveying apparatus according to the present
invention, comprising: [0011] a conveying roller pair configured to
convey a sheet; [0012] a registration roller pair disposed
downstream of the conveying roller pair, for correcting skew
feeding of the sheet with a leading end of the sheet conveyed by
the conveying roller pair abutting against the registration roller
pair; and [0013] a guide portion configured to guide the sheet
conveyed to the registration roller pair by the conveying roller
pair such that the sheet is deflected, [0014] wherein the guide
portion includes a movable guide that is movable from a first
position where an abutting portion of the guide portion for
abutting the sheet that is conveyed is located on one side of a nip
line of the conveying roller pair to a second position where the
abutting portion is located on the other side of the nip line.
[0015] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a cross-sectional view showing a schematic
configuration of a printer which is an example of an image forming
apparatus according to embodiments of the present invention.
[0017] FIG. 2 is a perspective view for explaining a configuration
of a skew feeding correcting portion according to the first
embodiment.
[0018] FIG. 3 is a cross-sectional view for explaining a
configuration of a skew feeding correcting portion according to the
first embodiment of the present invention.
[0019] FIG. 4 is a cross-sectional view for explaining a skew
feeding correcting operation for a sheet having a low stiffness in
a skew feeding correcting portion according to the first embodiment
of the present invention.
[0020] FIG. 5 is a cross-sectional view for explaining a skew
feeding correcting operation for a sheet having a high stiffness in
a skew feeding correcting portion according to the first embodiment
of the present invention.
[0021] FIG. 6 is a perspective view for explaining a configuration
of a skew feeding correcting portion according to the second
embodiment.
[0022] FIG. 7 is a cross-sectional view for explaining a
configuration of a skew feeding correcting portion according to the
second embodiment of the present invention.
[0023] FIG. 8 is a cross-sectional view for explaining a skew
feeding correcting operation for a sheet having a low stiffness in
a skew feeding correcting portion according to the second
embodiment of the present invention.
[0024] FIG. 9 is a cross-sectional view for explaining a skew
feeding correcting operation for a sheet having a high stiffness in
a skew feeding correcting portion according to the second
embodiment of the present invention.
[0025] FIG. 10 is a cross-sectional view for explaining a
configuration of a skew feeding correcting portion according to the
third embodiment of the present invention.
[0026] FIG. 11 is a cross-sectional view for explaining a skew
feeding correcting operation for a sheet having a low stiffness in
a skew feeding correcting portion according to the third embodiment
of the present invention.
[0027] FIG. 12 is a cross-sectional view for explaining a skew
feeding correcting operation for a sheet having a high stiffness in
a skew feeding correcting portion according to the third embodiment
of the present invention.
DESCRIPTION OF THE EMBODIMENTS
[0028] Next, a sheet conveying apparatus of the present invention
will be described in detail with an image forming apparatus having
this sheet conveying apparatus as an example.
[0029] {First Embodiment} <Overall Configuration of Image
Forming Apparatus> FIG. 1 is a cross-sectional explanatory view
of the image forming apparatus 100. As shown in this figure, at an
upper portion of the image forming apparatus body 101, an image
reading portion 130 for reading an original D placed on the platen
glass 120a as an original placing platen by the automatic document
feeding device 120. Under the image reading portion 130, there are
provided the image forming portion 102, the sheet conveying
apparatus 103 for conveying the sheet S to the image forming
portion 102, and the manual feeding portion 104.
[0030] The image forming portion 102 is provided with the laser
scanner unit 111, the photosensitive drum 112, the developing
device 113, and the like.
[0031] Further, the sheet conveying apparatus 103 includes sheet
storage cases 11 that accommodate the sheets S and are detachably
attached to the image forming apparatus main body 101, the pickup
rollers 21 that feed the sheets S stored in the sheet storage cases
11, and the like.
[0032] The manual feeding portion 104 includes the sheet tray 71 on
which the sheets S are stacked and which is provided on a side
surface of the image forming apparatus main body 101 which is a
main body of the apparatus so as to be freely opened and closed,
the feeding roller 51 for feeding the sheets S stacked on the sheet
tray 71, and the like. When using the manual feeding portion 104,
the sheet tray 71 is opened to protrude to a position where sheet
feeding is possible, the user sets desired sheets on the protruding
sheet tray 71, thereafter the sheets are fed. In FIG. 1, C denotes
a control portion.
[0033] Next, the image forming operation of the image forming
apparatus 100 having such a configuration will be described. When
an image reading signal is outputted from the control portion C
provided in the image forming apparatus main body 101 to the image
reading portion 130, the image is read by the image reading portion
130. Thereafter, the laser scanner unit 111 irradiates the
photosensitive drum 112 with laser light corresponding to this
electric signal.
[0034] At this time, the photosensitive drum 112 has been charged
in advance. An electrostatic latent image is formed by being
irradiated with light, and then the electrostatic latent image is
developed by the developing device 113, whereby a toner image is
formed on the photosensitive drum 112. The toner image thus formed
is primarily transferred to the outer periphery of the intermediate
transfer belt 110, whereby a toner image is formed on the
intermediate transfer belt 110.
[0035] When a feeding signal is outputted from the control portion
C to the sheet conveying apparatus 103, the sheet S is fed out from
the sheet storage case 11 as a sheet storing portion by the pickup
roller 21. When the feed signal is outputted from the control
portion C to the manual feeding portion 104, the sheet S is fed out
by the feeding roller 51 from the sheet tray 71 which is a sheet
storing portion. Thereafter, the skew feeding of the fed sheet S is
corrected by the skew feeding correcting portion including the
registration roller pair 57. Then, the sheet S is conveyed to the
transfer portion including the intermediate transfer belt 110 and
the secondary transfer roller 118 while being synchronized with the
toner image on the intermediate transfer belt 110.
[0036] The toner image is transferred onto the sheet conveyed to
the transfer portion, thereafter the sheet is conveyed to the
fixing portion 114. The unfixed transferred image is permanently
fixed on the sheet S by being heated and pressed by the fixing
portion 114. The sheet on which the image has been fixed is
discharged from the image forming apparatus main body 101 to the
discharge tray 117 by the discharge roller 116.
[0037] <Sheet Conveying Apparatus> Next, the configuration of
the sheet conveying apparatus that conveys the sheet to the image
forming unit 102 will be described. Especially, the configuration
of the skew feeding correcting portion for correcting the skew
feeding of the conveyed sheet will be mainly described.
[0038] FIG. 2 is a perspective view of the skew feeding correcting
portion, and FIG. 3 is a cross-sectional view of the skew feeding
correcting portion. The conveying roller pair 58 including the
driving roller 58a and the driven roller 58b is disposed on the
sheet conveying path. The conveying roller pair 57 including the
driving roller 57a and the driven roller 57b is disposed downstream
in the sheet conveying direction (hereinafter referred to as
"downstream") of the conveying roller pair 58. The fed sheet is
conveyed to the registration roller pair 57, which is a second
roller pair by the conveying roller pair 58, which is a first
conveying roller pair. The leading end of the sheet is brought into
contact with the nip portion of the registration roller pair 57 in
the halt state with a predetermined pressing force thereby
correcting the skew feeding of the sheet.
[0039] The first fixed guide 63 is provided on one side of the
sheet conveying path between the conveying roller pair 58 and the
registration roller pair 57. The first fixed guide 63 has a portion
that curves so as to be separated from the nip line Nh of the
conveying roller pair 58 downstream of the conveying roller pair 58
and that thereafter guides the sheet toward the nip portion of the
registration roller pair 57.
[0040] The second fixed guide 64 is disposed on the side of the
driving roller 57a and upstream in the sheet conveying direction
(hereinafter referred to as "upstream") of the registration roller
pair 57. The third fixed guide 65 is disposed on the side of the
driven roller 58b of the conveying roller pair 58.
[0041] The movable guide 62 for guiding the sheet fed by the
conveying roller pair 58 is attached to the first fixed guide 63 so
as to be rotatable in the direction of the arrow A in FIG. 3. The
movable guide 62 is disposed in the vicinity of the downstream side
of the conveying roller pair 58. The movable guide 62 is usually
urged by an urging member such as a spring (not shown) so as to be
in a state indicated by a solid line in FIG. 3, and when pressed by
the conveyed sheet, the movable guide 62 can be displaced to the
state shown by the broken line in FIG. 3 resisting the urging force
of the urging member.
[0042] When the movable guide 62 is in the first position shown by
the solid line in FIG. 3, the guide portion 62b (abutting portion)
which abuts against the sheet to be conveyed and guides the sheet
is placed on the side of the third fixed guide 65 with respect to
the nip line Nh. When the movable guide 62 is in the second
position shown by the broken line in FIG. 3, the guide portion 62b
is placed on the side of the first fixed guide 63 with respect to
the nip line Nh. Namely, the movable guide 62 can be displaced from
the first position where the guide portion 62b to abut against the
conveyed sheet is positioned on one side of the nip line Nh to the
second position where the guide portion 62b is positioned on the
other side of the nip line Nh when the movable guide 62 is pressed
with a pressing force which is equal to or stronger than a
predetermined value by the sheet conveyed by the conveying roller
pair 58.
[0043] Further, the movable guide 62 is so configured that when the
movable guide 62 is in the first position, the angle 0 formed
between the guide surface of the movable guide 62 and the nip line
Nh of the conveying roller pair 58 is 45.degree. or less. As a
result, the sheet that is conveyed by the conveyance roller pair 58
and that abuts against the movable guide 62 is smoothly conveyed
along the guide surface.
[0044] <Sheet Conveyance States> Next, the conveyance states
of the sheet conveyed by the conveying roller pair 58, guided by
the movable guide 62, and to abut against the registration roller
pair 57 will be explained in two cases including the case where the
stiffness (strength of rigidity) of the sheet is low and the case
where the stiffness (strength of the stiffness) of the sheet is
high.
[0045] (Case Where A Sheet Whose Stiffness Is Lower Than A
Predetermined Value) The skew feeding correcting operation in the
case where the stiffness of the sheet S is lower than a
predetermined value (for example, in the case of a thin paper
having basis weight of 64 g/m.sup.2) will be described with
reference to FIG. 4.
[0046] Since the stiffness of the sheet S fed by the conveying
roller pair 58 is low, even if the sheet S abuts against the
movable guide 62, the sheet S does not overcome the urging force of
the urging member of the movable guide 62. Therefore, the movable
guide 62 is maintained in the first position and the sheet is
guided along the movable guide 62 to the second fixed guide 64.
Further, as is clear from FIG. 3, the extended line of the guide
surface of the second fixed guide 64 intersects with the guide
surface of the first fixed guide 63 along the nip line Nr of the
registration roller pair 57. Therefore, after the sheet is guided
to the first fixed guide 63 along the second fixed guide 64, the
sheet is conveyed to the registration roller pair 57 in the halt
state along the first fixed guide 63.
[0047] Even after the leading end of the sheet reaches the
registration roller pair 57, the sheet S is fed by a predetermined
length by the conveying roller pair 58. As a result, as shown in
FIG. 4, the sheet S is bent from the nip portion of the conveying
roller pair 58 toward the side of the third fixed guide 65 between
the registration roller pair 57 and the conveying roller pair 58.
Thereafter, the sheet S is further bent toward the side of the
fixed guide 63. Then, the sheet S is further bent toward the nip
portion of the registration roller pair 57. That is, the deflection
of S-shape having three deflection nodes occurs.
[0048] As described above, when the number of deflection nodes
increases, the force with which the deflection expands under the
same deflection amounts (feed amounts of the conveying roller)
becomes greater than when the number of nodes is smaller. Due to
the deflection, the leading end of the sheet S is uniformly brought
into contact with the registration roller pair 57 so that the
correction of the skew feeding is surely performed.
[0049] (Case Where A Sheet Whose Stiffness Is Higher Than A
Predetermined Value) Next, the skew feeding correcting operation in
the case where the stiffness of the sheet S is higher than a
predetermined value (for example, in the case of thick paper having
a basis weight of 256 g/m.sup.2) will be described with reference
to FIG. 5.
[0050] Since the sheet S fed from the conveying roller pair 58 has
high stiffness, when the sheet S abuts against the movable guide 62
and presses down the movable guide 62, the sheet S overcomes the
urging force of the urging member of the movable guide 62 to move
the movable guide 62 toward the side of the second position. As a
result, the sheet S is guided to the guide surface of the first
fixed guide 63 along the nip line Nr of the registration roller
pair 57, which intersects with the nip line Nh of the conveying
roller pair 58. Thereafter, the sheet S is positioned along the
guide surface of the first fixed guide 63 and reaches the
registration roller pair 57 in the halt state.
[0051] Even after the leading end of the sheet reaches the
registration roller pair 57, the sheet S is fed by the
predetermined length by the conveying roller pair 58. At this time,
the sheet S is bent so as to press down the movable guide 62
between the registration roller pair 57 and the conveying roller
pair 58. Further, and as shown in FIG. 5, the sheet S is bent from
the nip portion of the conveying roller pair 58 toward the side of
the first fixed guide 63. Then, the sheet S is further bent along
the curvature of the pressed down movable guide 62 and the first
fixed guide 63 and is conveyed toward the nip portion of the
registration roller pair 57. Namely, the deflection of C-shape
having two deflection nodes occurs. Due to the deflection, the
leading end of the sheet S is uniformly brought into contact with
the registration roller pair 57 so that the skew feeding is
corrected.
[0052] In the case of a sheet with high stiffness, the curvature
radius of deflection of the sheet S increases from Rs (FIG. 4) to
Rc (FIG. 5). As a result, even a sheet having a high stiffness does
not undergo residual curl. In addition, when the deflection amounts
(feed amounts of the conveying roller) are the same, the force with
which the deflection extends becomes smaller as the number of
deflection nodes decreases. Therefore, as compared with the
S-shaped deflection (number of nodes 3), the torque of the
conveying rollers for conveying the sheet for making deflection can
be smaller in the C-shaped deflection(number of nodes 2).
Therefore, it is possible to reduce the size of the driving device.
Further, it is possible to prevent skew feeding caused by the
leading end of the sheet passing through the nip portion of the
registration roller pair 57.
[0053] As described above, by making the movable guide 62 move in
accordance with the stiffness of the sheet and by guiding and
conveying the sheet so as to generate a number of deflection nodes
on the sheet, corresponding to the stiffness, skew feeding
correcting can be properly performed irrespective of the stiffness
of the sheet.
[0054] {Second Embodiment} Next, the second embodiment of the
present invention will be described. In the first embodiment
described above, only one movable guide is used, but in the present
embodiment two movable guides are used. Since the basic
configuration of the apparatus of the present embodiment is the
same as that of the above-described embodiment, duplicate
explanation will be omitted, and the configuration that is the
characterizing feature of this embodiment will be described here.
In addition, members having the same functions as those in the
above-described embodiment are denoted by the same reference
numerals.
[0055] (First Movable Guide) FIG. 6 is a perspective view of the
skew feeding correcting portion and FIG. 7 is a cross-sectional
view of the skew feeding correcting portion. The first fixed guide
63 is provided with the first movable guide 62 which is rotatable
in the direction of the arrow A in FIG. 7 around a rotational shaft
62a positioned in the vicinity of the conveying roller pair 58.
Namely, the first movable guide 62 can be displaced from the first
position (indicated by the solid line in FIG. 7) where the guide
portion 62b (abutting portion) to abut against the sheet conveyed
by the conveying roller pair 58 is positioned on one side (namely,
the driven roller 58b side) of the nip line Nh of conveying roller
pair 58 the to the second position (indicated by the broken line in
FIG. 7) where the guide portion 62b is positioned on the other side
(namely, the driving roller 58a side) of the nip line Nh.
[0056] The first movable guide 62 is urged by an urging member such
as a spring (not shown) and is normally at the first position. When
the first movable guide 62 is pressed by the conveyed sheet, the
first movable guide 62 can be displaced to the second position,
resisting the urging force of the urging member.
[0057] (Second Movable Guide) The fourth fixed guide 60 is provided
downstream of the first fixed guide 63, and in the vicinity of the
upstream side of the registration roller pair 57. The fourth fixed
guide 60 is provided with the second movable guide 61 that is
rotatable in the direction of the arrow B in FIG. 7 about the
rotational shaft 61a. The second movable guide 61 is movable from
the first position (indicated by a solid line in FIG. 7) where the
guide surface 61b (abutting portion) for abutting against the
conveyed sheet is positioned in the vicinity of the nip line Nr of
the registration roller pair 57 to the second position (indicated
by a broken line in FIG. 7) where the guide surface 61b is away
from the nip line when the second movable guide 61 is pressed by
the sheet which is conveyed by the first conveying roller pair and
which has a predetermined or higher stiffness. The second movable
guide 61 is urged by an urging member such as a spring (not shown)
and is normally at the first position. When the second movable
guide 61 is pressed by the conveyed sheet, the second movable guide
61 can be displaced to the second position, resisting the urging
force of the urging member.
[0058] Also, the third fixed guide 65 is disposed on the opposite
side of the first movable guide 62, and the second fixed guide 64
is disposed on the opposite side of the second movable guide
61.
[0059] (Case Where A Sheet Whose Stiffness Is Lower Than A
Predetermined Value) The skew feeding correcting operation of the
sheet conveying apparatus with the above-described configuration in
the case where the stiffness of the sheet S is lower than a
predetermined value (for example, in the case of a thin paper
having basis weight of 64 g/m.sup.2) will be described with
reference to FIG. 8.
[0060] Since the stiffness of the sheet S conveyed by the conveying
roller pair 58 is low, even if the sheet S abuts against the first
movable guide 62, the sheet S does not overcome the urging force of
the urging member of the first movable guide 62. Therefore, the
first movable guide 62 is maintained in the first position and the
sheet is guided along the first movable guide 62 to the second
fixed guide 64. Further, the sheet is guided along the second fixed
guide 64 to the second movable guide 61. Even if the sheet abuts
against the second movable guide 61, the sheet does not overcome
the urging force of the urging member of the second movable guide
61 since the stiffness is low. As a result, the second movable
guide 61 is maintained at the first position. After being guided by
this second movable guide 61, the sheet is conveyed to the
registration roller pair 57 in the halt state along the fourth
fixed guide 60.
[0061] Even after the leading end of the sheet reaches the
registration roller pair 57, the sheet S is fed by a predetermined
length by the conveying roller pair 58. As a result, the S-shaped
deflection occurs on the sheet S between the registration roller
pair 57 and the conveying roller pair 58 as in the first embodiment
described above. Namely, as shown in FIG. 8, the sheet S is bent
from the nip portion of the conveying roller pair 58 toward the
side of the third fixed guide 65. Thereafter, the sheet S is bent
toward the side of the second movable guide 61. Then, the sheet S
is bent toward the nip portion of the registration roller pair
57.
[0062] Due to the S-shaped deflection having three deflection
nodes, the leading end of the sheet S is uniformly brought into
contact with the registration roller pair 57 so that the correction
of the skew feeding is surely performed.
[0063] (Case Where A Sheet Whose Stiffness Is Higher Than A
Predetermined Value) Next, the skew feeding correcting operation in
the case where the stiffness of the sheet S is higher than a
predetermined value (for example, in the case of thick paper having
a basis weight of 256 g/m.sup.2) will be described with reference
to FIG. 9.
[0064] The sheet S fed from the conveying roller pair 58 is
conveyed while pressing the first movable guide 62. At this time,
since the stiffness of the sheet is high, the sheet overcomes the
urging force of the urging member of the first movable guide 62 and
is guided to the second movable guide 61 while pressing down the
movable guide 62 to the side of the second position. Since the
sheet S has high stiffness, as in the case of the first movable
guide 62, the sheet S overcomes the urging force of the urging
member of the second movable guide 61 so that the sheet S is
conveyed to the registration roller pair 57 in the halt state along
the second movable guide 61 while pressing down the second movable
guide 61 to the side of the second position.
[0065] Even after the leading end of the sheet reaches the
registration roller pair 57, the sheet S is fed by a predetermined
length by the conveying roller pair 58. As a result, the sheet S
presses down the first movable guide 62 and the second movable
guide 61 between the registration roller pair 57 and the conveying
roller pair 58 so that the C-shaped deflection with two deflection
nodes occurs on the sheet S. Due to this deflection, the leading
end of the sheet S is uniformly brought into contact with the
registration roller pair 57 so that the skew feeding is
corrected.
[0066] As a result, the curvature radius Rc of deflection of the
sheet S is larger than the curvature radius Rs (see FIG. 8) of the
S-shaped deflection shown in FIG. 8. Consequently, even a sheet
having high stiffness, which is easy to be deformed into a
deflected shape and to undergo so-called residual curl is used,
residual curl does not remain. In the first embodiment, only one
movable guides is used, but in the present embodiment, the second
movable guide 61 is additionally provided downstream of the first
movable guide 62 such that both movable guides are displaced to the
second position when the sheet having high stiffness is used so
that the sheet can be deflected with a larger curvature radius than
in the case of the first embodiment.
[0067] Also, as in the case of the first embodiment, the number of
C-shaped deflection nodes is smaller than the number of S-shaped
deflection nodes if both deflection amounts (feed amounts of the
conveying roller) are the same. Therefore, even if a sheet having
high stiffness is used, it is possible to prevent skew feeding
caused by the leading end of the sheet passing through the nip
portion of the registration roller pair 57 without increasing the
sheet conveying torque of the conveying roller pair 58.
[0068] (Stiffness Of Registration Roller Pair) In this embodiment,
the registration roller pair 57 has the driving roller 57a and the
driven roller 57b, each of which is formed of an elastic body such
as rubber. Further, the driving roller 57a and the driven roller
57b have different stiffness. More specifically, the driven roller
(first roller) 57b disposed on one side of the sheet conveying path
has larger stiffness than the driving roller (second roller) 57a
disposed on the other side of the sheet conveying path. The second
movable guide 61 is disposed on the one side, that is, on the side
on which the driven roller 57b is disposed with respect to the
sheet conveying path. The second fixed guide 64 opposed to the
second movable guide 61 is disposed on the other side, that is, on
the side where the driving roller 57a is disposed.
[0069] With the configuration described above, it is possible to
configure the guide surface of the second fixed guide such that the
leading end of the sheet does not directly touch the driving roller
57a. As a result, by the second fixed guide 64, it is possible to
prevent the sheet from directly abutting against the driving roller
58a which has low stiffness. Thus, regardless of how the second
movable guide 61 is displaced, the leading end of the sheet to be
conveyed is first brought into contact with the driven roller 57b
having high stiffness and is guided to the roller nip portion so
that the driving roller 57a whose stiffness is made low in order to
increase sheet conveyance property is protected.
[0070] {Third Embodiment} Next, the third embodiment of the present
invention will be described. Since the basic configuration of the
present embodiment is the same as that of the above-described
embodiments, duplicate explanation will be omitted, and the
configuration that is the characterizing feature of this embodiment
will be described here. In addition, members having the same
functions as those in the above-described embodiments are denoted
by the same reference numerals.
[0071] FIG. 10 is a cross-sectional view of the skew feeding
correcting portion. The configuration of the skew feeding
correcting portion of the present embodiment will be described with
reference to FIG. 10.
[0072] The present embodiment also has two movable guides between
the conveying roller pair 58 and the registration roller pair 57.
The first movable guide 62 that is rotatable in the direction of
the arrow A is provided downstream of the conveying roller pair 58.
The second movable guide 61 that is rotatable in the direction of
the arrow B is provided downstream thereof.
[0073] The first movable guide 62 can be displaced from the first
position indicated by the solid line in FIG. 10 to the second
position indicated by the broken line in FIG. 10. The first
position is a position where the leading end (abutting portion) of
the guide portion 62 to abut against the conveyed sheet is located
on the side of the nip line Nh of the conveying roller pair 58 with
respect to the extended plane of the guide surface 61b of the
second movable guide 61. The second position is a position where
the first movable guide 61 is away from the nip line Nh when the
first movable guide 61 is pressed by the sheet having a
predetermined stiffness or higher, conveyed by the conveying roller
pair 58.
[0074] The second movable guide 61 can be disposed from the first
position (indicated by a solid line in FIG. 10) where the guide
surface 61b (abutting portion) for abutting against the conveyed
sheet is positioned in the vicinity of the nip line Nr of the
registration roller pair 57 to the second position (indicated by a
broken line in FIG. 10) where the guide surface 61b is away from
the nip line Nr when the second movable guide 61 is pressed by the
sheet which is conveyed by the conveying roller pair 58 and which
has a predetermined or higher stiffness. Each of the movable guides
is urged by an urging member (not shown), and is normally held at
the first position. Further, in the present embodiment, as shown in
FIG. 10, the flexible guide 66 is provided at a position opposed to
the guide portion of the first movable guide 62 with the sheet
conveying path interposed between the guide portion of the first
movable guide 62 and the flexible guide 66 when the first movable
guide 62 is in the first position. The flexible guide 66 is
composed of a flexible sheet. When the flexible guide 66 is pressed
by the sheet on which a loop formed by deflection grows, the
flexible guide 66 guides the sheet while pushing the sheet back
with elasticity.
[0075] (Case Where A Sheet Whose Stiffness Is Lower Than A
Predetermined Value) The skew feeding correcting operation of the
sheet conveying apparatus with the above-described configuration in
the case where the stiffness of the sheet S is lower than a
predetermined value (for example, in the case of a thin paper
having basis weight of 64 g/m.sup.2) will be described with
reference to FIG. 11.
[0076] The rotational tip (guide portion) of the first movable
guide 62 is positioned between the nip line Nh of the conveying
roller pair 58 and the nip line Nr of the registration roller pair
57. Thus, the leading end of the sheet S fed from the conveying
roller pair 58 reaches the second movable guide 61 without
contacting the first movable guide 62. The sheet S is conveyed
while being guided by the second movable guide 61. Because of the
low stiffness, the sheet S does not overcome the urging force of
the urging member of the second movable guide 61. Therefore, the
sheet S is guided to the registration roller pair 57 in the halt
state along the guide surface of the second movable guide 61 that
is maintained in the first position.
[0077] In the present embodiment, the guide surface 61b of the
second movable guide is disposed so as to have such positional
relationship that the guide surface 61b intersects with the nip
line Nh of the conveying roller pair 58. As a result, when the
leading end of the sheet is conveyed by the conveying roller pair
58 without being guided by the first movable guide, the leading end
of the sheet reaches the guide surface 61b of the second movable
guide.
[0078] Even after the leading end of the sheet reaches the
registration roller pair 57, the sheet S is fed by a predetermined
length by the conveying roller pair 58 so that the deflection grows
until it comes into contact with the first movable guide 62. When
the deflection further grows, the sheet S cannot overcome the
urging force of the urging member of the first movable guide 62
because the stiffness of the sheet S is low so that the first
movable guide 62 is kept to be maintained at the first position.
Then, the sheet S is pushed back by the first movable guide 62, and
the deflection on the upstream side grows toward the side opposite
to the first movable guide 62.
[0079] The deflection of the sheet S which has grown toward the
side opposite to the first movable guide 62 becomes in contact with
the flexible guide 66 and further grows while elastically deforming
the flexible guide 66. Finally, an S-shaped deflection occurs
between the registration roller pair 57 and the conveying roller
pair 58 as shown in FIG. 11.
[0080] Due to the S-shaped deflection having three deflection nodes
of the sheet S, the leading end of the sheet S is uniformly brought
into contact with the registration roller pair 57 so that the skew
feeding is corrected.
[0081] (Case Where A Sheet Whose Stiffness Is Higher Than A
Predetermined Value) Next, the skew feeding correcting operation in
the case where the stiffness of the sheet S is higher than a
predetermined value (for example, in the case of thick paper having
a basis weight of 256 g/m.sup.2) will be described with reference
to FIG. 12.
[0082] The leading end of the sheet S fed from the conveying
rollers pair 58 reaches the second movable guide 61. Since the
stiffness of the sheet S is high, the sheet S overcomes the urging
force of the urging member of the second movable guide 61 and is
guided to the registration roller pair 57 in the halt state along
the second movable guide 61 while pressing down the second movable
guide 61 to the side of the retracted position. Even after the
leading end of the sheet reaches the registration roller pair 57,
the sheet S is fed by a predetermined length by the conveying
roller pair 58. Since the stiffness of the sheet S is high, the
sheet S overcomes the urging force of the urging members of the
first movable guide 62 and the second movable guide 61. As a
result, the sheet S presses down the first movable guide 62 and the
second movable guide 61 between the registration roller pair 57 and
the conveying roller pair 58 so that C-shaped deflection occurs on
the sheet S. Due to this C-shaped deflection, the leading end of
the sheet S is uniformly brought into contact with the registration
roller pair 57 so that the skew feeding is corrected.
[0083] Due to this, the curvature radius of deflection of the sheet
S increases from Rs (FIG. 11) to Rc (FIG. 12). As a result, even a
sheet having a high stiffness, which is easy to undergo residual
curl does not undergo residual curl.
[0084] Also, as in the case of the above-described embodiments, the
number of C-shaped deflection nodes is smaller than the number of
S-shaped deflection nodes if both deflection amounts (feed amounts
of the conveying roller) are the same. Therefore, even if a sheet
having high stiffness is used, it is possible to prevent skew
feeding caused by the leading end of the sheet passing through the
nip portion of the registration roller pair 57 without increasing
the sheet conveying torque of the conveying roller pair 58.
[0085] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0086] This application claims the benefit of Japanese Patent
Application No. 2017-182156, filed Sep. 22, 2017, which is hereby
incorporated by reference herein in its entirety.
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