U.S. patent application number 13/431088 was filed with the patent office on 2012-10-04 for sheet conveying device that separates multi-fed sheets, and image reading apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Masahiro SERIZAWA.
Application Number | 20120248678 13/431088 |
Document ID | / |
Family ID | 46926141 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120248678 |
Kind Code |
A1 |
SERIZAWA; Masahiro |
October 4, 2012 |
SHEET CONVEYING DEVICE THAT SEPARATES MULTI-FED SHEETS, AND IMAGE
READING APPARATUS
Abstract
A sheet conveying device which makes it possible to facilitate
separation of multi-fed sheets. A separation pad and a separation
roller separate sheets from a sheet bundle placed on a sheet tray,
on a one-by-one basis. A pull-off roller section formed by a pair
of conveying rollers nips and conveys a fed sheet. The two
conveying rollers of the pull-off roller section have rotational
axes extending in respective different directions. A registration
roller further conveys the sheet conveyed by the pull-off roller
section. One roller of the pull-off roller section is disposed such
that the roller conveys a sheet in a direction in which the sheet
is to be conveyed by the registration roller, and the other roller
of the pull-off roller section is disposed such that the roller
conveys a sheet obliquely with respect to the sheet conveying
direction of the registration roller.
Inventors: |
SERIZAWA; Masahiro;
(Abiko-shi, JP) |
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
46926141 |
Appl. No.: |
13/431088 |
Filed: |
March 27, 2012 |
Current U.S.
Class: |
271/10.01 |
Current CPC
Class: |
B65H 2511/524 20130101;
B65H 2801/06 20130101; B65H 2511/12 20130101; B65H 7/125 20130101;
B65H 2701/1315 20130101; B65H 2511/514 20130101; B65H 2701/1315
20130101; B65H 2511/12 20130101; B65H 2553/416 20130101; B65H
3/5261 20130101; B65H 3/5223 20130101; B65H 2511/524 20130101; B65H
9/166 20130101; B65H 2220/03 20130101; B65H 2220/03 20130101; B65H
2220/01 20130101; B65H 9/006 20130101; B65H 2801/39 20130101 |
Class at
Publication: |
271/10.01 |
International
Class: |
B65H 7/12 20060101
B65H007/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2011 |
JP |
2011-069970 |
Mar 21, 2012 |
JP |
2012-064026 |
Claims
1. A sheet conveying device comprising: a sheet feed unit
configured to feed a sheet from a plurality of sheets placed on a
sheet tray, on a one-by-one basis, by separating the sheets; a
first conveying unit having a pair of conveying rollers configured
to convey the sheet fed from said sheet feed unit in a state nipped
therebetween, the conveying rollers having rotational axes
extending in respective different directions; and a second
conveying unit configured to further convey the sheet conveyed by
said first conveying unit, wherein one roller of the conveying
roller pair is disposed such that the roller conveys the fed sheet
in a direction in which the sheet is to be conveyed by said second
conveying unit, and the other roller of the conveying roller pair
is disposed such that the roller conveys the sheet obliquely with
respect to the sheet conveying direction of said second conveying
unit.
2. The sheet conveying device according to claim 1, further
comprising a multi-feed determination unit configured to determine
whether or not multi-feed has occurred in which the sheet conveyed
by said first conveying unit is in a state overlapping another
sheet, and a control unit configured to be operable when said
multi-feed determination unit determines that multi- feed has
occurred, to perform control such that rotation of one roller of
the conveying roller pair nipping the multi-fed sheets is stopped
or decelerated.
3. The sheet conveying device according to claim 2, further
comprising a sheet width detection unit disposed close to said
first conveying unit and configured to detect a sheet width in a
direction intersecting with a sheet conveying direction of said
first conveying unit, and wherein said multi-feed determination
unit determines whether or not multi-feed has occurred, based on a
change in the sheet width which is detected by said sheet width
detection unit during sheet conveyance by said first conveying
unit.
4. The sheet conveying device according to claim 3, wherein said
sheet width detection unit comprises a plurality of detectors
arranged in the direction intersecting with the sheet conveying
direction of said second conveying unit.
5. The sheet conveying device according to claim 1, further
comprising a switching unit configured to switch the conveying
roller pair between a contact state in which one roller and the
other roller of the conveying roller pair are brought into contact
with each other and a separation state in which the one roller and
the other roller of the conveying roller pair are spaced from each
other.
6. The sheet conveying device according to claim 5, wherein in
synchronism of the sheet reaching the conveying roller pair, said
switching unit switches the conveying roller pair held in the
separation state in advance to the contact state.
7. The sheet conveying device according to claim 1, wherein the one
roller of the conveying roller pair and the other of the conveying
roller pair are configured to have respective different conveying
forces.
8. The sheet conveying device according to claim 7, further
comprising a guide member for guiding the plurality of sheets which
are placed on the sheet tray, a portion of said guide member with
which a sheet bundle side is brought into contact being angled with
respect to the sheet conveying direction.
9. The sheet conveying device according to claim 8, wherein a
direction in which a sheet is conveyed by the one roller of the
conveying roller pair is the same as the sheet conveying direction
of said second conveying unit, and the conveying force of the one
roller of the conveying roller pair is larger than the conveying
force of the other roller of the conveying roller pair.
10. An image reading apparatus comprising: a sheet tray on which a
plurality of sheets are placed; a sheet feed unit configured to
feed a sheet from the sheets placed on said sheet tray, on a
one-by-one basis, by separating the sheets; a first conveying unit
having a pair of conveying rollers configured to convey the sheet
fed from said sheet feed unit in a state nipped therebetween, the
conveying rollers having rotational axes extending in respective
different directions; a second conveying unit configured to further
convey the sheet conveyed by said first conveying unit; and a
reading unit configured to read an image from the sheet conveyed by
said second conveying unit, wherein one roller of the conveying
roller pair is disposed such that the roller conveys the fed sheet
in a direction in which the sheet is to be conveyed by said second
conveying unit, and the other roller of the conveying roller pair
is disposed such that the roller conveys the sheet obliquely with
respect to the sheet conveying direction of said second conveying
unit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a sheet conveying device
and an image reading apparatus, and more particularly to a
separating technique for separating multi-fed sheets when
multi-feed occurs in a conveying mechanism that conveys sheets
while separating the sheets one by one from a sheet bundle placed
on a sheet tray.
[0003] 2. Description of the Related Art
[0004] In an image reading apparatus provided with a conventional
sheet conveying device, when two or more sheets are conveyed in a
state overlapping each other, i.e. when multi-feed occurs, a sheet
jam or defective image reading can take place. In either case, a
user has to carry out work e.g. for removing sheets and setting
sheets again, and hence the apparatus is inevitably stopped during
execution of the work. To solve this problem, there has been
proposed a sheet conveying device configured to be operable when
multi-feed is detected, to convey multi-fed sheets in the reverse
direction, i.e. toward a sheet tray by a predetermined distance and
separate the sheets one from another using a separation mechanism
again (see e.g. U.S. Patent Publication No. 5,384,631).
[0005] In the above-described conventional sheet conveying device,
however, multi-feed occurs due to high adhesiveness between sheets,
so that re-use of the same separation mechanism cannot reliably
ensure separation of the sheets.
SUMMARY OF THE INVENTION
[0006] The present invention provides a sheet conveying device and
an image reading apparatus, which make it possible to facilitate
separation of multi-fed sheets to thereby improve sheet conveyance
efficiency.
[0007] In a first aspect of the present invention, there is
provided a sheet conveying device comprising a sheet feed unit
configured to feed a sheet from a plurality of sheets placed on a
sheet tray, on a one-by-one basis, by separating the sheets, a
first conveying unit having a pair of conveying rollers configured
to convey the sheet fed from the sheet feed unit in a state nipped
therebetween, the conveying rollers having rotational axes
extending in respective different directions, and a second
conveying unit configured to further convey the sheet conveyed by
the first conveying unit, wherein one roller of the conveying
roller pair is disposed such that the roller conveys the fed sheet
in a direction in which the sheet is to be conveyed by the second
conveying unit, and the other roller of the conveying roller pair
is disposed such that the roller conveys the sheet obliquely with
respect to the sheet conveying direction of the second conveying
unit.
[0008] In a second aspect of the present invention, there is
provided an image reading apparatus comprising a sheet tray on
which a plurality of sheets are placed, a sheet feed unit
configured to feed a sheet from the sheets placed on the sheet
tray, on a one-by-one basis, by separating the sheets, a first
conveying unit having a pair of conveying rollers configured to
convey the sheet fed from the sheet feed unit in a state nipped
therebetween, the conveying rollers having rotational axes
extending in respective different directions, a second conveying
unit configured to further convey the sheet conveyed by the first
conveying unit, and a reading unit configured to read an image from
the sheet conveyed by the second conveying unit, wherein one roller
of the conveying roller pair is disposed such that the roller
conveys the fed sheet in a direction in which the sheet is to be
conveyed by the second conveying unit, and the other roller of the
conveying roller pair is disposed such that the roller conveys the
sheet obliquely with respect to the sheet conveying direction of
the second conveying unit.
[0009] According to the present invention, one of the pair of
conveying rollers different in axial direction is disposed such
that the roller performs sheet conveyance in a sheet conveying
direction, and the other roller of the conveying roller pair is
disposed such that the roller performs sheet conveyance obliquely
with respect to the sheet conveying direction. This makes it easy
to separate the multi-fed sheets, and makes it possible to improve
sheet conveying efficiency.
[0010] 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
[0011] FIG. 1 is a schematic view of an image reading apparatus
provided with a sheet conveying device according to a first
embodiment of the present invention.
[0012] FIG. 2 is a schematic block diagram of the control systems
of an ADF and a reader section appearing in FIG. 1 and an image
controller.
[0013] FIGS. 3A and 3B are schematic views of a pull-off roller
section appearing in FIG. 1, in which FIG. 3A schematically shows
the pull-off roller section as viewed in a direction indicated by
an arrow A in FIG.
[0014] 1, and FIG. 3B schematically shows the pull-off roller
section as viewed in a direction indicated by an arrow B in FIG.
1.
[0015] FIGS. 4A to 4D are views useful in explaining the behavior
of a sheet in the pull-off roller section.
[0016] FIG. 5 is a flowchart of a sheet separation process executed
in the first embodiment by a CPU using the pull-off roller
section.
[0017] FIGS. 6A to 6C are views useful in explaining a multi-feed
determination method.
[0018] FIG. 7 is a diagram illustrating different degrees of change
in sheet width detected on sheets by a sheet width detection
section.
[0019] FIGS. 8A to 8D are views useful in explaining push-in
operation performed by the pull-off roller section to push a sheet
into a registration roller.
[0020] FIG. 9 is a partially see-through view of an ADF, as viewed
from above, of an image reading apparatus provided with a sheet
conveying device according to a second embodiment of the present
invention.
[0021] FIGS. 10A to 10C are views useful in explaining the behavior
of a sheet in the pull-off roller section.
DESCRIPTION OF THE EMBODIMENTS
[0022] The present invention will now be described in detail below
with reference to the accompanying drawings showing embodiments
thereof.
[0023] FIG. 1 is a schematic view of an image reading apparatus
provided with a sheet conveying device according to a first
embodiment of the present invention.
[0024] In FIG. 1, the image reading apparatus comprises an
automatic document feeder (hereinafter acronymized as "the ADF")
100 and an image reading section (hereinafter referred to as "the
reader section") 200. The ADF 100 has a sheet tray 30 on which a
sheet bundle S formed by one or more sheets is placed. Before the
start of a sheet feeding operation, the sheets of the sheet bundle
S are restricted by a separation pad 21 from entering the ADF 100.
When the sheet feeding operation is started, a sheet feed roller 1
urged on the sheet bundle S is driven to pull the sheets into the
ADF 100, and only an uppermost sheet of the sheet bundle S is fed
onto a conveying path by the separation pad 21 and a separation
roller 2.
[0025] In actuality, a case where the separation pad 21 and the
separation roller 2 fail to separate only an uppermost sheet can
occur depending on a sheet type or due to a difference in surface
frictional force between sheets. In the present embodiment, sheets
which are not separated one from another at the above-mentioned
time and are fed in a state overlapping each other will be referred
to as "multi-fed sheets".
[0026] A separation sensor 10 is disposed downstream of the
separation pad 21 and the separation roller 2 in the sheet
conveying direction. The separation sensor 10 is used for detection
of an interval between sheets after separation, which is performed
based on an output therefrom. Downstream of the separation sensor
10 is disposed a sheet width detection section 11 comprising a
plurality of sheet detectors arranged in a direction intersecting
with (e.g. orthogonal to) the sheet conveying direction
(hereinafter simply referred to as "the conveying direction"). The
sheet width detection section 11 detects the width of each fed
sheet based on whether or not the fed sheet has been detected by
the sheet detection sensors in predetermined timing before the
sheet is brought into abutment with a registration roller 4. Note
that the sheet width detection section 11 may be implemented by an
array sensor, such as a CCD or a CIS.
[0027] A sheet having passed the sheet width detection section 11
is conveyed by a pull-off roller section 3 and is brought into
abutment with the registration roller 4. At a time point when the
sheet reaches the registration roller 4, the registration roller 4
is in a state not being driven but at rest, so that the leading
edge of the sheet is prevented from being advanced. The sheet in
this state is pushed toward the registration roller 4 by pushing
operation of the pull-off roller section 3, whereby it is warped.
Even when the conveying process up to this time has brought the
sheet into a skewed state where the leading edge of the sheet is in
an oblique relation to the conveying direction, the skew of the
sheet is corrected by warping the sheet with its leading edge held
in abutment with the registration roller 4. Then, the registration
roller 4 is rotated to convey the sheet to a first conveying roller
5 and a roller 7, whereafter the sheet is conveyed by these rollers
onto a platen glass 201. The reader section 200 reads a
front-surface image from the sheet through the platen glass
201.
[0028] Then, the sheet is conveyed by a second conveying roller 6,
and is passed through between a roller 16 and a back
surface-reading glass 18. Then, the sheet is discharged onto a
discharge tray 31 via a discharge flapper 20 and a discharge roller
pair 8.
[0029] A back-surface image reading section 17 is a unit configured
to optically read image information from a sheet and output an
image signal subjected to photoelectric conversion to a subsequent
stage. The back-surface image reading section 17 is disposed on the
back side of the back surface-reading glass 18 opposed to the
roller 16. The back-surface image reading section 17 reads a
back-surface image on the sheet while the sheet is passing through
a clearance between the roller 16 and the back surface-reading
glass 18.
[0030] Each of sheet detection sensors 12, 13, and 14 detects
whether or not there is a sheet at an associated sensor position.
Further, conveyance guides, not shown, are disposed along the sheet
conveying path so as to restrict a sheet from deviating from a
predetermined range in a direction (hereinafter also referred to as
"the main scanning direction) orthogonal to the conveying
direction.
[0031] Similarly, the reader section 200 is a unit configured to
optically read image information from a sheet and output an image
signal subjected to photoelectric conversion to a subsequent stage.
The reader section 200 comprises the platen glass 201, a platen
glass 202, a scanner unit 209, a second mirror 205, a third mirror
206, a lens 207, and a CCD (charge coupled device) 208. Note that
the scanner unit 209 comprises an illuminating lamp 203 and a first
mirror 204.
[0032] In reading a front-surface image from a sheet, the scanner
unit 209 is moved to a position below the platen glass 201 in
advance. Then, the illuminating lamp 203 is turned on in this
state, and reflected light from the front surface of the sheet
passing on the moving reading glass is guided to the lens 207 via
the first to third mirrors 204, 205, and 206, whereby it is caused
to form an image on the CCD 208. After this process, the
front-surface image from the sheet is photoelectrically converted
to a digital image signal by the CCD 208.
[0033] FIG. 2 is a schematic block diagram of the control systems
of the ADF 100 and the reader section 200 appearing in FIG. 1 and
an image controller 300.
[0034] In the reader section 200, a central processing unit
(hereinafter acronymized as "the CPU") 251 controls the ADF 100 and
the reader section 200. Connected to the reader section 200 are a
ROM 252 as a memory for storing programs and a RAM 253 as a memory
for providing work areas. The ROM 252 stores control programs for
the reader section 200 and the ADF 100, and the RAM 253 stores
input data for use in control and working data.
[0035] Connected to the CPU 251 are a motor driver section 256 as a
driver circuit for driving an optical motor that moves the scanner
unit 209 and a front-surface image reading section 260. The
front-surface image reading section 260 comprises the illuminating
lamp 203 and the CCD 208 mentioned above, and a signal controller
259 for converting an output from the CCD 208 to a digital image
signal. The CPU 251 controls the motor driver section 256 and the
front-surface image reading section 260 to read an image from the
front surface of an original.
[0036] A sheet interval correction section 254 corrects parameters
of the signal controller 259 according to a sheet interval (i.e. an
interval between the trailing edge of a preceding sheet and the
leading edge of the following sheet) between fed sheets. Although
in the present embodiment, the sheet interval is handled as a time
parameter, it may be handled as a distance parameter. An image
processing section 255 processes an image signal read by the
front-surface image reading section 260 or the back-surface image
reading section 17, generates a timing signal, and transmits the
signals to the image controller 300. An image buffer 261 is
controlled by the image processing section 255. The image buffer
261 is provided for temporarily storing the image signal read by
the front-surface image reading section 260 or the back-surface
image reading section 17.
[0037] The ADF 100 is connected to the input/output ports of the
CPU 251. Connected to the output port are a motor group 103 for
driving the conveying rollers, a solenoid group 101, and a clutch
group 102. On the other hand, connected to the input port are a
sensor group 104 for generating sheet conveying timing signals and
the sheet width detection section 11 for detecting the size of each
sheet during sheet conveyance.
[0038] The CPU 251 executes a control program stored in the ROM
252, to thereby control sheet conveying operation in the ADF 100.
The back-surface image reading section 17 comprises an illuminating
lamp 307 for back-surface image reading, a CIS (contact image
sensor) 308, and a signal controller 107. The back-surface image
reading section 17 is connected to the CPU 251. The back-surface
image reading section 17 reads a back-surface image from a sheet
according to a control signal from the CPU 251 and transfers the
read image to the image processing section 255.
[0039] Image signals stored in the image buffer 261 are read out
into the image processing section 255 in synchronism with a timing
signal, and is sequentially transferred to the image controller 300
via a controller interface section 350.
[0040] The image controller 300 has a CPU 301, a ROM 302, and a RAM
303 for image control, independently of the reader section 200. The
image signals delivered from the image processing section 255 to
the image controller 300 are subjected to input/output control by
an image input/output unit 304, and are sequentially stored and
accumulated as image data in an image memory 305.
[0041] An image processing section 310 performs various kinds of
image processing on image signals input from the image input/output
unit 304 or image data accumulated in the image memory 305. A
console section 309 is capable of notifying a user of the status of
the apparatus by screen display. Further, the console section 309
receives operation instructions given by the user to the apparatus.
In response to the instructions received via the console section
309, the CPU 301 reads out image data from the image memory 305 and
executes processing e.g. for transferring an image and information
to an external apparatus or a personal computer through a telephone
line or a network connected to an external interface 312.
[0042] Although in the present embodiment, the front-surface image
reading section of the reader section 200 is provided with the CCD
and the back-surface image reading section of the ADF 100 is
provided with the CIS, this is not limitative, but any other sensor
which is capable of image reading may be used in place of the CCD
or the CIS.
[0043] Next, the pull-off roller section 3 will be described in
detail.
[0044] FIGS. 3A and 3B are schematic views of the pull-off roller
section 3 appearing in FIG. 1. FIG. 3A schematically shows the
pull-off roller section 3 as viewed in a direction indicated by an
arrow A in FIG. 1, and FIG. 3B schematically shows the same as
viewed in a direction indicated by an arrow B in FIG. 1.
[0045] The pull-off roller section 3 comprises a conveying roller
pair formed by upper and lower rollers 3a and 3b. The upper roller
3a and the lower roller 3b rotate with a sheet P nipped
therebetween, to thereby convey the sheet P in the conveying
direction. The upper roller 3a and the lower roller 3b are driven
by respective different motors (included in the motor group 103 in
FIG. 2).
[0046] The upper roller 3a and the lower roller 3b have respective
rotational axes extending in different directions, respectively.
Specifically, the lower roller 3b is a conveying roller having a
rotational axis extending in the same direction as the rotational
axes of the sheet feed roller 1 and the separation roller 2 and
that of the registration roller (i.e. in the direction orthogonal
to the sheet conveying direction) and configured to convey a sheet
P straight in the downstream direction. On the other hand, the
upper roller 3a is an obliquely conveying roller having a
rotational axis horizontally inclined with respect to the direction
orthogonal to the sheet conveying direction. In the present
embodiment, the inclination angle of the upper roller 3a with
respect to the lower roller 3b is set to 20 degrees. Note that the
inclination angle can be changed according e.g. to the material,
size, or frictional force of a roller, and therefore it is not
limited to 20 degrees. Further, the directional relationship
between the rotational axis of the upper roller 3a and that of the
lower roller 3b may be reversed.
[0047] The upper roller 3a and the lower roller 3b are configured
to apply respective different conveying forces to a sheet. The
reason for this will be described hereinafter.
[0048] Further, the upper roller 3a and the lower roller 3b are
constructed such that switching can be performed between contact
and separation states. This is because if the two rollers different
in axial direction are rotated in direct contact with each other in
a state where no sheet exists therebetween, abrasion or deformation
can occur to cause damage to the rollers. Switching between contact
and separation between the upper roller 3a and the lower roller 3b
is performed by driving a specific solenoid of the solenoid group
101 according to a control signal from the CPU 251. In short, the
specific solenoid functions as a switching unit for switching
between contact and separation between the upper roller 3a and the
lower roller 3b. Note that any other construction and method may be
employed for switching between contact and separation between the
upper roller 3a and the lower roller 3b.
[0049] Next, a description will be given, with reference to FIGS.
4A to 4D, of the behavior of a sheet P in the pull-off roller
section 3. Although in FIGS. 4A to 4D, only the obliquely conveying
roller (upper roller 3a) is shown as the pull-off roller section 3,
it is assumed that the conveying roller (lower roller 3b), not
shown, is disposed at a location opposed to the obliquely conveying
roller. Further, in the vicinity of the pull-off roller section 3
is disposed the sheet width detection section 11 for detecting
sheet width in the direction intersecting with the sheet conveying
direction of the registration roller 4 (or the lower roller
3b).
[0050] FIG. 4A shows a state before the sheet P reaches the
pull-off roller section 3. In the state shown in FIG. 4A, it is not
apparent whether the sheet P has been conveyed in a state normally
separated as a single sheet or in a multi-fed state in which the
sheet P overlaps another sheet. When the sheet P reaches the
pull-off roller section 3, control is performed to switch the upper
roller 3a and the lower roller 3b from the separation state to the
contact state.
[0051] Now, a description will be given of conveying forces of the
respective upper and lower rollers 3a and 3b for conveying a sheet.
It is assumed that the conveying forces are determined using, as
parameters, driving forces of the motors for driving the respective
upper and lower motors 3a and 3b, the frictional forces of the
respective two rollers, angle difference between the rotational
axes of the respective rollers, and so forth.
[0052] First, a case where the sheet P has been conveyed as a
single sheet will be described.
[0053] FIG. 4B shows an example of a state where the conveying
forces have been set in advance such that the conveying force of
the upper roller 3a is larger than that of the lower roller 3b. In
this case, since the conveying force of the upper roller 3a is
larger, the sheet P is skewed and conveyed obliquely. On the other
hand, FIG. 4C shows a state where the conveying forces have been
set in advance such that the conveying force of the upper roller 3a
is smaller than that of the lower roller 3b. In this case, since
the conveying force of the lower roller 3b is larger, the sheet P
is conveyed straight forward.
[0054] Next, a description will be given of a case where the sheet
P has been conveyed in a state overlapping another sheet.
[0055] When the upper roller 3a and the lower roller 3b are
switched to the contact state, the upper sheet P of the multi-fed
sheets receives a force acting in an oblique direction from the
upper roller 3a. On the other hand, a lower sheet Pa receives a
force acting straight in the conveying direction from the lower
roller 3b. As a consequence, a twist occurs between the upper sheet
and the lower sheet of the multi-fed sheets, which causes
separation between the sheet P and the sheet Pa fed together with
the sheet P, as shown in FIG. 4D. In this case, whichever of the
upper roller 3a and the lower roller 3b applies a larger force, it
is known that the behavior for separation is substantially the
same. Note that a skew of a sheet caused by the conveying force of
the upper roller 3a is corrected by the registration roller 4. A
sheet having its skew corrected and conveyed by the registration
roller 4 may have its position in a transverse direction orthogonal
to the conveying direction adjusted by shifting of the registration
roller 4 in its axial direction.
[0056] FIG. 5 is a flowchart of a sheet separation process executed
in the present embodiment by the CPU 251 using the pull-off roller
section 3.
[0057] First, in response to a reading operation start instruction
from the image controller 300, the CPU 251 performs control such
that a sheet pickup operation for picking up a sheet on the ADF is
started (step S800). Specifically, the sheet feed roller 1 is
turned on whereby it is driven and lowered into contact with the
upper surface of a sheet bundle S to convey sheets P to the
separation roller 2. The separation roller 2 attempts to separate
an uppermost sheet P and then conveys the separated sheet P into
the apparatus.
[0058] Then, when a predetermined time period elapses after the
start of the pickup operation, the CPU 251 causes the sheet width
detection section 11 to start sheet width detection (step
S801).
[0059] Thereafter, the CPU 251 waits until the sheet P reaches the
pull-off roller section 3 (step S802). Immediately before the sheet
P reaches the pull-off roller section 3, the CPU 251 switches the
pull-off roller section 3 held in the separation state in advance
to the contact state, and causes rotation of the upper roller 3a
and the lower roller 3b (step S803). Then, the CPU 251 drivingly
controls the upper roller 3a and the lower roller 3b to pull off
(separate) the sheet P as shown in FIG. 4D (step S803).
[0060] Next, the CPU 251 terminates the pickup operation in timing
substantially synchronous with execution of the step S803 to
thereby facilitate the sheet pull-off operation by the pull-off
roller section 3 (step S804). Specifically, the CPU 251 stops
driving of the sheet feed roller 1 to allow the same to move upward
away from the sheet bundle S, and stops driving of the separation
roller 2 at the same time to thereby facilitate the sheet pull-off
operation by the pull-off roller section 3.
[0061] Then, the CPU 251 determines, based on a change in sheet
width detected by the sheet width detection section 11, whether or
not the sheet P currently conveyed is in a state overlapping
another sheet (step S805).
[0062] Now, a description will be given of determination of
multi-feed of sheets with reference to FIGS. 6A to 6C.
[0063] In the present embodiment, multi-feed determination is
performed based on a sheet width detected by the sheet width
detection section 11.
[0064] FIG. 6A shows an example of a state before a sheet P reaches
the pull-off roller section 3.
[0065] In the illustrated example, a detected sheet width L0 of the
sheet P detected by the sheet width detection section 11 is the
same as the actual sheet width of the sheet P.
[0066] FIG. 6B shows a case where under a condition that the
conveying force of the upper roller 3a is larger than that of the
lower roller 3b, a single sheet P reaches the pull-off roller
section 3, and since the conveying force of the upper roller 3a is
larger than that of the lower roller 3b, the single sheet P is
brought into a skewed state.
[0067] Now, a detected sheet width of the sheet P detected by the
sheet width detection section 11 in the FIG. 6B example is
represented by L1. In this example, since the sheet P is caused to
be skewed, L1 is larger than L0 (L1>L0). Note that under a
condition that the conveying force of the upper roller 3a is
smaller than that of the lower roller 3b, if a single sheet P
reaches the pull-off roller section 3, the sheet P advances
straight forward. Therefore, in this case, a detected sheet width
of the sheet P detected by the sheet width detection section 11 is
equal to L0 similarly to FIG. 6A.
[0068] FIG. 6C shows a state where multi-fed sheets reach the
pull-off roller section 3 and the sheets start to be separated.
[0069] Now, a detected sheet width of the sheet P detected by the
sheet width detection section 11 in the FIG. 6C example is
represented by L2. The apparent sheet width L1 or L2 detected by
the sheet width detection section 11 changes in the sheet
conveyance and separation process. FIG. 7 is a graph showing the
different degrees of change in each sheet width detected by the
sheet width detection section 11 after each sheet reaches the
pull-off roller section 3. In the FIG. 7 graph, the vertical axis
represents detected sheet width, and the horizontal axis represents
elapsed time t. A time point t0 indicates a timing in which the
sheet width detection section 11 detects the sheet width at a
leading end of the sheet, and a time point t1 indicates a timing in
which the sheet reached the pull-off roller section 3.
[0070] Referring to FIG. 7, when the sheet is single, the detected
sheet width L1 is constant after the leading end of the sheet has
started to be detected by the sheet width detection section 11
until the sheet reaches the pull-off roller section 3. After the
sheet reaches the pull-off roller section 3, the detected sheet
width L1 of the single sheet, under the condition that the
conveying force of the upper roller 3a is set to be larger than
that of the lower roller 3b, progressively increases as the sheet
is further skewed. Note that the increase in the detected sheet
width L1 stops when the skew of the sheet P becomes equal in value
to the inclination of the upper roller 3a. On the other hand, when
sheets are multi-fed, an upper sheet P is conveyed while being
skewed, whereas a lower sheet Pa is conveyed straight. For this
reason, the amount of change in the detected sheet width L2, i.e.
the inclination of the graph associated with the detected sheet
width L2 is larger than that of the detected sheet width L1. Note
that the value of the detected sheet width L2 is maximized when the
skew of the sheet P becomes equal in value to the inclination of
the upper roller 3a.
[0071] Therefore, when it is determined, by referring to
time-varying change in the sheet width detected after a sheet P
reaches the pull-off roller section 3, that the degree of the
change has exceeded e.g. a predetermined threshold value T, it is
possible to judge that the conveyed sheet P is in a state
overlapping another sheet.
[0072] Although in the present embodiment, multi-feed determination
is performed based on a change in sheet width detected by a sheet
width detection sensor, this is not limitative, but a dedicated
sensor for detecting multi-feed may be additionally provided.
[0073] Referring again to FIG. 5, if it is determined in a step
S806 that multi-feed has occurred, the CPU 251 stops driving of the
lower roller 3b of the pull-off roller section 3 and performs sheet
conveyance by driving the upper roller 3a alone (step S807). As a
consequence, only the upper one of the sheets to be separated is
conveyed first. Then, the CPU 251 waits until the upper sheet
reaches the registration roller 4 (step S808). When the upper sheet
reaches the registration roller 4 and is pushed against the
registration roller 4 to have the skew of the upper sheet
corrected, the CPU 251 causes the upper roller 3a to be spaced from
the lower roller 3b and stops the driving of the upper roller 3a
(step S809).
[0074] Now, a description will be given, with reference to FIGS. 8A
to 8D, of the push-in operation performed by the pull-off roller
section 3 for pushing a sheet into the registration roller 4.
[0075] FIG. 8A shows a skewed state of the sheet P before reaching
the registration roller 4. Note that the upper portion of each of
FIGS. 8A to 8D shows the registration roller 4, the pull-off roller
section 3, and the sheet P, as viewed from above, and the lower
portion shows these as viewed just from a side.
[0076] Note that in FIGS. 8A to 8D hatching provided on a roller
indicates that the roller is in a driven state.
[0077] In a state shown in FIG. 8B, the leading edge of the sheet P
has reached the registration roller 4, but since the registration
roller 4 is at rest, the sheet P cannot advance. On the other hand,
the sheet P is pushed from behind by the pull-off roller section 3,
so that the sheet P starts to be warped.
[0078] FIG. 8C shows a state where the push-in operation by the
pull-off roller section 3 has been completed and the sheet P has
been warped. In this stage, the leading edge of the sheet has been
brought into abutment with the registration roller 4 by sheet
stress and restriction of conveying guides (not shown), whereby the
skew of the sheet has been eliminated. The registration roller 4 is
driven for rotation in predetermined timing to convey the sheet
having its skew eliminated downstream toward an image reading
position, as shown in FIG. 8D.
[0079] Referring again to FIG. 5, in a step S810, the CPU 251 waits
until the sheet P is conveyed downstream by the registration roller
4 and the separation is completed. The completion of the separation
is judged from time elapsed after the start of driving of the
registration roller 4 until passing of the trailing end of the
upper sheet through the registration roller 4. After confirming
completion of the sheet separation, the CPU 251 stops driving of
the registration roller 4, terminates the spacing of the upper
roller 3a from the lower roller 3b, and restarts driving of both
the upper and lower rollers 3a and 3b of the pull-off roller
section 3 (step S811) to cause the lower one of the multi-fed
sheets to be conveyed toward the registration roller 4, and then
proceeds to a step S812. Processing in the step S812 et seq. is the
same as in a case where it is determined in the step S806 that
multi-feed has not occurred.
[0080] If it is determined in the step S806 that multi-feed has not
occurred, the CPU 251 continues sheet conveyance to cause the sheet
to reach the registration roller 4. Then, after confirming arrival
of the sheet at the registration roller 4 (step S812), the CPU 251
stops driving of the pull-off roller section 3 in a predetermined
timing to thereby return the upper roller 3a and the lower roller
3b to the separation state (step S813). Finally, the CPU 251 stops
operation of the sheet width detection section 11 (step S814) to
thereby terminate sheet width detection and multi-feed detection
based on time-varying change of a width detection signal. This
completes a sequence of sheet-pulling off operations.
[0081] Although in the sheet conveying device of the present
embodiment, the conveying force of the lower roller 3b configured
to convey a sheet in the same conveying direction as the
registration roller 4 does is set to be smaller than that of the
upper roller 3a, the upper roller 3a may have a smaller conveying
force than the lower roller 3b.
[0082] As described above, according to the above-described
embodiment, one roller of the pair of conveying rollers different
in axial direction is disposed such that it conveys a sheet in the
conveying direction, and the other roller is disposed such that it
conveys a sheet obliquely with respect to the conveying direction
so as to separate multi-fed sheets. This makes it possible to
facilitate separation of multi-fed sheets to thereby improve sheet
conveyance efficiency. Further, it is not required to stop the
apparatus, and hence it is possible to further improve sheet
conveyance efficiency.
[0083] In the above-described embodiment, since the registration
roller 4 is disposed downstream of the pull-off roller section 3 in
the conveying direction, it is determined in the steps S808 and
S812 whether or not a sheet has reached the registration roller 4.
However, a roller that can be disposed downstream of the pull-off
roller section is not limited to the registration roller, but
another kind of roller may be disposed downstream of the pull-off
roller section.
[0084] Next, a second embodiment of the present invention will be
described with reference to drawings.
[0085] FIG. 9 is a partially see-through view of an ADF 1100, as
viewed from above, of an image reading apparatus provided with a
sheet conveying device according to the second embodiment of the
present invention.
[0086] As shown in FIG. 9, the ADF 1100 has a sheet tray 1030 on
which a sheet bundle S formed by one or more sheets can be placed.
The sheet tray 1030 is disposed such that a front side (lower side
as viewed in FIG. 9) thereof obliquely extends in an expanding
manner, i.e. along with a sheet guide member 1040 provided in a
manner angled with respect to a conveying direction (left-right
direction as viewed in FIG. 9). This configuration of the sheet
tray 1030 enables a user standing in front of the apparatus (at the
lower side as viewed in FIG. 9) to place the sheet bundle S on the
sheet tray 1030 without stretching out his/her arms. In short, the
user can place a sheet bundle on the sheet tray 1030 in an
ergonomically comfortable fashion.
[0087] At the rear (upper side as viewed in FIG. 9) of the sheet
tray 1030, there is a space formed in a manner extending along the
conveying direction. The space is thus formed so as to enable the
trailing end of a sheet, which was pulled in obliquely with respect
to the conveying direction from the sheet bundle S placed along the
front side of the sheet tray 1030, to freely move when the sheet
turns its direction to the conveying direction.
[0088] Each of separation rollers 1002 has its pull-in angle set
such that the axis of the separation roller 1002 is directed in a
direction orthogonal to the gradient of a portion of the sheet
guide member 1040 with which a sheet bundle side is brought into
contact. The cross-sectional view of the ADF 1100 is substantially
the same as FIG. 1 as described in the first embodiment, and
therefore it is omitted. Note that in addition to the sheet tray 30
appearing in FIG. 1, the sheet feed roller 1, the separation pad
21, the separation roller 2, and the separation sensor 10 are
arranged obliquely according to the angle of the sheet tray 1030
with respect to the conveying direction.
[0089] A conveying roller pair of a pull-in roller section 1003 is
disposed such that an upper roller as one of the rollers conveys a
sheet in the sheet conveying direction and a lower roller as the
other of the rollers conveys a sheet in the same direction as a
direction in which a sheet bundle S on the sheet tray is pulled in.
In short, the lower roller is disposed so as to convey a sheet
obliquely with respect to the sheet conveying direction.
[0090] The conveying forces of the two conveying rollers of the
pull-in roller section 1003 are set such that the conveying force
of the upper roller for conveying a sheet in the conveying
direction is larger than that of the lower roller.
[0091] Note that the image reading apparatus of the present
embodiment is identical in configuration to that of the first
embodiment, and therefore a control block diagram thereof and
description thereof are omitted.
[0092] Next, the behavior of a sheet P in the pull-in roller
section 1003 will be described with reference to FIGS. 10A to 10C.
Although not shown, the lower roller is disposed such that the
roller conveys a sheet in the direction in which the sheet is
pulled in from the sheet tray 1030. A sheet width detecting section
1011 is disposed in a manner orthogonal to the sheet guide 1040,
and has the same construction as that of the sheet width detection
section 11 in the first embodiment.
[0093] FIG. 10A shows a state before the sheep P reaches the
pull-in roller section 1003. Similarly to the first embodiment, in
this state, it is not apparent whether or not the sheet P has been
conveyed as a single sheet or in a state overlapping another sheet.
At this time point, the pull-in roller section 1003 is held in the
separation state as in the first embodiment.
[0094] FIG. 10B shows a case where the sheet P has been conveyed as
a single sheet. In this case, the pull-in roller section 1003 is
switched to the contact state, but since the conveying force of the
upper roller is larger, the sheet P has its direction turned in the
sheet conveying direction.
[0095] FIG. 10C shows a case where the sheet P is in a state
overlapping another sheet. In this case as well, the pull-in roller
section 1003 is switched to the contact state in timing synchronous
with arrival of the sheet P. In the present case, the upper one of
the multi-fed sheets receives a force from the upper roller whereby
it is directed in the conveying direction. On the other hand, the
lower sheet receives a force from the lower roller so that it
remains directed in the sheet feed direction. As a consequence, a
twist occurs between the upper and lower ones of the multi-fed
sheets, whereby separation of the multi-fed sheets is achieved.
[0096] Control of the pull-in roller section 1003 in the present
embodiment is performed following the same control procedure as in
the first embodiment, and therefore description thereof is
omitted.
[0097] As described above, also in the sheet conveying device
having the sheet tray extending in a manner expanding toward the
front side so as to facilitate user operation for placing sheets on
the sheet tray, the pull-in roller section 1003 is formed by the
pair of rollers different in conveying direction. This makes it
possible to switch the sheet conveying direction to the direction
of conveyance by a downstream conveying roller (e.g. the
registration roller 4) and positively perform separation of
multi-fed sheets.
[0098] Although in the above-described first and second
embodiments, the image reading apparatus provided with the sheet
conveying device is described, this is not limitative, but the
present invention is also applicable to an image forming apparatus
including an image forming section (printer section) in addition to
an image reading section having the above-described
construction.
[0099] 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.
[0100] This application claims priority from Japanese Patent
Application No. 2011-069970 filed Mar. 28, 2011, and Japanese
Patent Application No. 2012-064026 filed Mar. 21, 2012, which are
hereby incorporated by reference herein in their entirety.
* * * * *