U.S. patent application number 12/461185 was filed with the patent office on 2010-02-11 for sheet feeding device and image forming apparatus.
This patent application is currently assigned to RICOH COMPANY, LTD.. Invention is credited to Hideto Higaki, Toshifumi Togashi.
Application Number | 20100032891 12/461185 |
Document ID | / |
Family ID | 41652175 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100032891 |
Kind Code |
A1 |
Togashi; Toshifumi ; et
al. |
February 11, 2010 |
Sheet feeding device and image forming apparatus
Abstract
A sheet feeding device including a belt including a dielectric
material seamlessly wound about rollers and disposed opposite a top
surface of a stack of multiple sheets placed on a sheet storage
stand to attract a sheet from the stack of multiple sheets and
convey the sheet, and a charger to form a predetermined charge
pattern on a surface of the belt. A shaft of one of the rollers
provided downstream from the other roller in a direction of sheet
feed serves as a pivot of the belt about which the belt swings, and
the belt swings around the pivot such that the surface of the belt
facing the top surface of the stack of multiple sheets and a
surface of the sheet storage stand facing the surface of the belt
are substantially parallel to each other.
Inventors: |
Togashi; Toshifumi;
(Zama-shi, JP) ; Higaki; Hideto; (Yokohama-shi,
JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Assignee: |
RICOH COMPANY, LTD.
|
Family ID: |
41652175 |
Appl. No.: |
12/461185 |
Filed: |
August 4, 2009 |
Current U.S.
Class: |
271/18.1 ;
271/34 |
Current CPC
Class: |
B65H 2515/716 20130101;
B65H 3/18 20130101; B65H 2515/716 20130101; B65H 3/047 20130101;
B65H 2220/02 20130101; B65H 2801/06 20130101 |
Class at
Publication: |
271/18.1 ;
271/34 |
International
Class: |
B65H 3/18 20060101
B65H003/18; B65H 3/04 20060101 B65H003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 5, 2008 |
JP |
2008-201628 |
Claims
1. A sheet feeding device, comprising: a belt comprising a
dielectric material seamlessly wound about rollers and disposed
opposite a top surface of a stack of multiple sheets placed on a
sheet storage stand to attract a sheet from the stack of multiple
sheets and convey the sheet; and a charger to form a predetermined
charge pattern on a surface of the belt, wherein: a shaft of one of
the rollers provided downstream from the other roller in a
direction of sheet feed serves as a pivot of the belt about which
the belt swings; and the belt swings around the pivot such that the
surface of the belt facing the top surface of the stack of multiple
sheets and a surface of the sheet storage stand facing the surface
of the belt are substantially parallel to each other.
2. The sheet feeding device according to claim 1, wherein a leading
edge of the stack of multiple sheets is positioned opposite a
bottom part of a curved portion of the belt on a downstream side
relative to the direction of sheet feed.
3. The sheet feeding device according to claim 1, wherein the
charger is provided adjacent to the pivot of the belt.
4. The sheet feeding device according to claim 1, wherein a
pivot-side roller around which the belt is wound is rotatably
driven.
5. The sheet feeding device according to claim 1, further
comprising an upper guide plate provided downstream from a leading
edge side of the stack of multiple sheets placed on a sheet storage
stand in the direction of sheet feed, wherein a surface of a curved
portion of the belt provided downstream in the direction of sheet
feed intersects with the upper guide plate.
6. The sheet feeding device according to claim 1, further
comprising a biasing member to lift a free edge of the belt
opposite an end of the belt at the pivot.
7. The sheet feeding device according to claim 1, further
comprising a unit to keep the belt horizontal at an uppermost
position at a top of an arc through which the belt swings.
8. The sheet feeding device according to claim 1, further
comprising an insulating sheet disposed on a bottom plate portion
of the sheet feeding device, wherein at least a portion of the
insulating sheet disposed near the surface of the sheet storage
stand contacting the belt comprises an insulating material.
9. The sheet feeding device according to claim 1, further
comprising a unit to feed each sheet from the stack of multiple
sheets using frictional force between the unit and sheets at a
position where the sheets are separated from the belt.
10. The sheet feeding device according to claim 1, further
comprising a separation unit contacting the belt, wherein the
separation unit swings together with the belt.
11. The sheet feeding device according to claim 10, wherein the
separation unit comprises a separation pick.
12. The sheet feeding device according to claim 10, wherein the
separation unit comprises a friction pad.
13. The sheet feeding device according to claim 10, wherein the
separation unit comprises a separation roller.
14. The sheet feeding device according to claim 13, wherein the
separation roller is reversely rotatable.
15. An image forming apparatus comprising a sheet feeding device,
the sheet feeding device comprising: a belt comprising a dielectric
material seamlessly wound about rollers and disposed opposite a top
surface of a stack of multiple sheets placed on a sheet storage
stand to attract a sheet from the stack of multiple sheets and
convey the sheet; and a charger to form a predetermined-charge
pattern on a surface of the belt, wherein: a shaft of one of the
rollers provided downstream from the other roller in a direction of
sheet feed serves as a pivot of the belt about which the belt
swings; and the belt swings around the pivot such that the surface
of the belt facing the top surface of the stack of multiple sheets
and a surface of the sheet storage stand facing the surface of the
belt are substantially parallel to each other.
Description
PRIORITY STATEMENT
[0001] The present patent application claims priority from Japanese
Patent Application No. 2008-201628, filed on Aug. 5, 2008 in the
Japan Patent Office, which is hereby incorporated herein by
reference in its entirety.
BACKGROUND
[0002] 1. Technical Field
[0003] Illustrative embodiments described in this patent
specification generally relate to a sheet feeding device to
separate a stack of sheets and feed the sheets one by one, and an
image forming apparatus including the sheet feeding device.
[0004] 2. Description of the Related Art
[0005] Related-art image forming apparatuses, such as copiers,
facsimile machines, printers, or multifunction devices having two
or more of copying, printing, scanning, and facsimile functions,
typically form a toner image on a recording medium (e.g., a sheet)
according to image data using an electrophotographic method. In
such a method, for example, a charger charges a surface of a latent
image bearing member (e.g., a photoconductor); an irradiating
device emits a light beam onto the charged surface of the
photoconductor to form an electrostatic latent image on the
photoconductor according to the image data; a developing device
develops the electrostatic latent image with a developer (e.g.,
toner) to form a toner image on the photoconductor; a transfer
device transfers the toner image formed on the photoconductor onto
a sheet; and a fixing device applies heat and pressure to the sheet
bearing the toner image to fix the toner image onto the sheet. The
sheet bearing the fixed toner image is then discharged from the
image forming apparatus.
[0006] The image forming apparatuses further include a sheet
feeding device to feed recording media such as a sheet. A friction
paper feed method using a pickup member is widely employed in the
sheet feeding device. Examples of the pickup member include a
roller and a belt each including a material having a larger
coefficient of friction such as rubber. However, although a
configuration of the sheet feeding device can be simplified by
employing the friction paper feed method, the pickup member needs
to be pressed against the sheet using a spring or the like to
obtain a larger fictional force. Because the coefficient of
friction at the surface of the material having a larger coefficient
of friction such as rubber is changed over time and by
environmental factors, the friction paper feed method cannot stably
provide a higher ability to reliably feed the sheet.
[0007] In recent years, a wider variety of recording media
including special paper such as coated paper and label paper have
been used as well as plain paper in the image forming apparatuses
by diverse users, and it is expected that the number of different
types of recording media demanded by users will further increase in
the future. However, because the coefficient of friction at the
surface of some types of special paper is extremely small, it is
often difficult to separate the sheets of special paper from one
another using friction alone. Further, peeling may occur at a
release part of release paper when the sheets of release paper are
frictionally separated from one another using a roller and a
pressing member.
[0008] One possible solution to the above-described problems is to
employ an air suction method in which negative pressure is
generated by air suction to suction and convey the recording media.
However, although providing a more reliable ability to feed the
recording media compared to the friction paper feed method, the air
suction method is noisy and causes an increase in size and costs of
the sheet feeding device. Consequently, the air suction method is
not practical for image forming apparatuses installed in an office
or the like.
[0009] As another approach, a sheet feeding device including a
seamless dielectric belt rotated in a direction of sheet feed has
been proposed. The seamless dielectric belt contacts a top surface
of a stack of sheets, and alternating charges (that is, electrical
charges of alternating polarity) are applied to a surface of the
seamless dielectric belt by a member. The member includes a
charging unit to form an alternating charge pattern on the surface
of the seamless dielectric belt and a neutralizing unit to
de-charge, or neutralize, the surface of the seamless dielectric
belt. The charges thus applied to the surface of the seamless
dielectric belt generate an electric field that in turn generates
an attractive electrostatic force that attracts the sheet to the
surface of the seamless dielectric belt. Accordingly, a sheet
placed at the top of the stack of sheets (hereinafter referred to
as a top sheet) is separated from the rest of the stack of sheets
and is conveyed in the direction of sheet feed.
[0010] However, for a certain period of time after the seamless
dielectric belt contacts the top sheet the attractive force thus
generated by the electric field tends also to act on multiple other
sheets in the stack of sheets as well as the top sheet.
Consequently, these multiple other sheets are also attracted to the
seamless dielectric belt together with the top sheet, and all
sheets are conveyed in the direction of sheet feed without being
separated from one another, causing multiple sheet feeding.
[0011] To prevent multiple sheet feeding, a technique in which the
sheets are separated from one another and conveyed one by one a
predetermined period of time after the seamless dielectric belt
contacts the top sheet has been proposed.
[0012] For example, a separation/conveyance device is used that
includes an attraction/separation unit to alternately attract and
support a top sheet placed at the top of the stack of sheets using
an attractive force generated by a non-uniform electric field and
separate the top sheet from the stack of sheets. The
separation/conveyance device further includes a drive control unit
to move the attraction/separation unit, a sheet conveyance unit to
convey the top sheet thus separated, and an auxiliary separation
unit to assist the attraction/separation unit to separate the top
sheet from the stack of sheets. The drive control unit moves the
attraction/separation unit from a leading edge side of the top
sheet to a predetermined position to contact the top sheet, and
stops the attraction/separation unit at that position. After a
predetermined period of time elapses, the drive control unit moves
the attraction/separation unit again. The auxiliary separation unit
applies a predetermined force between the top sheet attracted to
the attraction/separation unit and a second sheet, that is, a next
sheet placed immediately beneath the top sheet, to separate the top
sheet from the second sheet.
[0013] However, although it can prevent multiple sheet feeding,
higher-speed sheet feeding cannot be achieved by the
above-described separation/conveyance device due to the stop time
involved.
[0014] Yet another approach is to measure a property (property
value) of a target sheet to be separated from the stack of sheets
to adjust the charge on the belt accordingly, that is, to control
the amount of charges applied to the surface of the seamless
dielectric belt, distance between each charge, and period of time
to attract the target sheet to the surface of the seamless
dielectric belt based on the property value thus measured.
[0015] However, because the target sheet first needs to be
separated from the stack of sheets in order to measure the property
value thereof, the above-described control cannot be performed on
the target sheet itself separated from the stack of sheets.
Further, the above-described control cannot be performed when
sheets each having a different property value are included in the
same stack of sheets.
[0016] Still yet another approach is to provide a prevention member
to the seamless dielectric belt. The prevention member is either
fixed on or provided movably to the seamless dielectric belt in a
direction opposite the direction of sheet feed, with a sheet feed
path therebetween.
[0017] For example, a sheet feeding device may include a pickup
member contacting a top surface of the stack of sheets to convey
the sheets in the direction of sheet feed. The pickup member
includes a unit to apply alternating charges to the seamless
dielectric belt. The unit has a charger to form a charge pattern on
the surface of the seamless dielectric belt and a neutralizer to
remove that charge. The pickup member further includes a prevention
member to assist to separate the sheets from one another.
[0018] For another example, a sheet feeding separation device
includes a sheet feeding member and a separation member provided
opposite the sheet feeding member. Alternating charges are applied
to both the sheet feeding member and the separation member to form
an alternating charge pattern on a surface of each of the sheet
feeding member and the separation member. Accordingly, the sheet is
alternately attracted to and separated from the sheet feeding
member and the separation member by an attractive force generated
as Maxwell stress. The sheet feeding separation device further
includes a seamless dielectric belt and a seamless belt serving as
a prevention member provided opposite the seamless dielectric belt.
Alternatively, a rubber friction pad may be provided as the
prevention member.
[0019] However, because the attractive force is also applied to
multiple other sheets placed beneath the top sheet as well as the
top sheet, it is difficult to reliably separate the sheets from one
another using the prevention member.
[0020] Published unexamined Japanese Patent Application No.
(hereinafter referred to as JP-A-) 2002-211777 discloses an image
forming apparatus including a sheet conveyance device including
sheet supply means that attracts the sheets using electrostatic
attraction to supply the sheets stored in a sheet storage to a
conveyance path. The sheet conveyance device further includes
separation means that uses electrostatic attraction to separate a
target sheet to be conveyed from multiple other sheets supplied by
the sheet supply means.
[0021] In order to reliably attract the sheet to the seamless
dielectric belt, it is important to provide a wide contact area
between the seamless dielectric belt and the sheet. At the same
time, however, although reliable attraction of the sheet to the
seamless dielectric belt is required to separate the sheets from
one another, a leading edge of the sheet needs to be securely
removed from the seamless dielectric belt once the sheets are
separated from one another. Further, multiple sheets attracted to
the seamless dielectric belt must be reliably separated from one
another in order to achieve high-speed sheet feeding without
causing multiple sheet feeding.
SUMMARY
[0022] In view of the foregoing, illustrative embodiments described
herein provide a sheet feeding device to reliably separate a sheet
from a stack of multiple sheets and feed the sheets one by one over
time even when a wider variety of sheets is used, and an image
forming apparatus including the sheet feeding device.
[0023] At least one embodiment provides a sheet feeding device
including a belt including a dielectric material seamlessly wound
about rollers and disposed opposite a top surface of a stack of
multiple sheets placed on a sheet storage stand to attract a sheet
from the stack of multiple sheets and convey the sheet, and a
charger to form a predetermined charge pattern on a surface of the
belt. A shaft of one of the rollers provided downstream from the
other roller in a direction of sheet feed serves as a pivot of the
belt about which the belt swings, and the belt swings around the
pivot such that the surface of the belt facing the top surface of
the stack of multiple sheets and a surface of the sheet storage
stand facing the surface of the belt are substantially parallel to
each other.
[0024] At least one embodiment provides an image forming apparatus
including the sheet feeding device described above.
[0025] Additional features and advantages of the illustrative
embodiments will be more fully apparent from the following detailed
description, the accompanying drawings, and the associated
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] A more complete appreciation of the illustrative embodiments
described herein and the many attendant advantages thereof will be
readily obtained as the same becomes better understood by reference
to the following detailed description when considered in connection
with the accompanying drawings, wherein:
[0027] FIG. 1 is a schematic view illustrating an example of a
configuration of an image forming apparatus according to
illustrative embodiments;
[0028] FIG. 2 is a perspective view illustrating an example of a
sheet attraction/separation unit included in a sheet feeding device
according to a first illustrative embodiment;
[0029] FIG. 3 is a schematic cross-sectional view illustrating the
sheet attraction/separation unit illustrated in FIG. 2;
[0030] FIGS. 4A and 4B are schematic cross-sectional views
illustrating operation of the sheet attraction/separation unit
illustrated in FIGS. 2 and 3;
[0031] FIG. 5 is a schematic cross-sectional view illustrating a
variation of the sheet attraction/separation unit included in the
sheet feeding device according to the first illustrative
embodiment;
[0032] FIGS. 6A to 6D are timing charts each illustrating a control
sequence of an applied voltage and a frequency in the sheet feeding
device;
[0033] FIG. 7 is a schematic cross-sectional view illustrating a
sheet attraction/separation unit included in a sheet feeding device
according to a second illustrative embodiment;
[0034] FIG. 8 is a schematic cross-sectional view illustrating a
sheet attraction/separation unit included in a sheet feeding device
according to a third illustrative embodiment;
[0035] FIG. 9 is a schematic cross-sectional view illustrating a
sheet attraction/separation unit included in a sheet feeding device
according to a fourth illustrative embodiment;
[0036] FIG. 10 is a schematic cross-sectional view illustrating a
sheet attraction/separation unit included in a sheet feeding device
according to a fifth illustrative embodiment;
[0037] FIG. 11 is a schematic cross-sectional view illustrating a
sheet attraction/separation unit included in a sheet feeding device
according to a sixth illustrative embodiment;
[0038] FIG. 12 is a perspective view illustrating a separation unit
included in the sheet feeding device according to the sixth
illustrative embodiment; and
[0039] FIG. 13 is a schematic cross-sectional view illustrating a
sheet attraction/separation unit included in a sheet feeding device
according to a seventh illustrative embodiment.
[0040] The accompanying drawings are intended to depict
illustrative embodiments and should not be interpreted to limit the
scope thereof. The accompanying drawings are not to be considered
as drawn to scale unless explicitly noted.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0041] In describing illustrative embodiments illustrated in the
drawings, specific terminology is employed for the sake of clarity.
However, the disclosure of this specification is not intended to be
limited to the specific terminology so selected, and it is to be
understood that each specific element includes all technical
equivalents that operate in a similar manner and achieve a similar
result.
[0042] Reference is now made to the drawings, wherein like
reference numerals designate identical or corresponding parts
throughout the several views.
[0043] FIG. 1 is a schematic view illustrating an example of a
configuration of a copier serving as an image forming apparatus 1
according to illustrative embodiments. The image forming apparatus
1 includes a document reading unit 2, an image forming unit 3, and
a sheet feeder 4. In the image forming apparatus 1, the image
forming unit 3 and the sheet feeder 4 are separately formed, and
are detachably attachable to each other.
[0044] The sheet feeder 4 includes a sheet feeding device 5. The
sheet feeding device 5 includes a sheet attraction/separation unit
7, a charging roller 8, and a friction pad 9. The sheet
attraction/separation unit 7 contacts a top surface of a stack of
sheets 6 stored in a sheet feed cassette, not shown, to attract a
top sheet 6a placed at the top of the stack of sheets 6, and
separates the top sheet 6a from the stack of sheets 6. According to
illustrative embodiments, the sheet attraction/separation unit 7 is
detachably attachable to the sheet feeder 4.
[0045] Specifically, the sheet attraction/separation unit 7
attracts the stack of sheets 6 including the top sheet 6a placed at
the top thereof, and the friction pad 9 separates the top sheet 6a
from the stack of sheets 6. Accordingly, the sheets included in the
stack of sheets 6 are fed to a pair of registration rollers 11 one
by one. Each sheet is then conveyed to a transfer device 12 from
the pair of registration rollers 11, and a toner image formed by
the image forming unit 3 is transferred onto the sheet in the
transfer device 12. Thereafter, the sheet having the toner image
thereon is conveyed to a fixing device 13, and heat and pressure
are applied to the sheet to fix the toner image to the sheet. The
sheet having the fixed toner image thereon is discharged by a
discharge roller 14 to a discharge tray 15.
[0046] It is to be noted that the sheet feeding device 5 according
to illustrative embodiments is also applicable to image forming
apparatuses other than the image forming apparatus 1 employing
electrophotography, such as inkjet type image forming apparatuses.
Further, the sheet feeding device 5 according to illustrative
embodiments is applicable to facsimile machines, printers,
multifunction devices having two or more of copying, printing,
scanning and facsimile functions, and so forth, as well as copiers
as described above. It is also to be noted that the sheet feeding
device 5 is also known as a sheet feeding/separation device.
[0047] A description is now given of the sheet
attraction/separation unit 7 included in the sheet feeding device 5
according to a first illustrative embodiment with reference to FIG.
2.
[0048] The sheet attraction/separation unit 7 includes a drive
roller 22, a driven roller 23, and a seamless belt 19 including a
dielectric material stretched between the drive roller 22 and the
driven roller 23. Specifically, the belt 19 includes a dielectric
material having a resistivity of 10.sup.8 .OMEGA.cm or greater. An
example of the dielectric material includes a polyethylene
terephthalate film, having a thickness of about 100 .mu.m. The
sheet attraction/separation unit 7 further includes a bottom plate
28 and an insulating sheet 29 provided on the bottom plate 28. The
insulating sheet 29 enables the bottom plate 28 to be formed of a
metal material, providing higher rigidity to the bottom plate 28.
As a result, even a last sheet placed at the bottom of the stack of
sheets 6 can be reliably fed to the image forming unit 3.
[0049] FIG. 3 is a schematic cross-sectional view illustrating the
sheet attraction/separation unit 7 illustrated in FIG. 2. As
illustrated in FIG. 3, the belt 19 is double-layered, including a
top layer 19a and a bottom layer 19b. The top layer 19a includes a
dielectric material having a resistivity of 10.sup.8 .OMEGA.cm or
greater, and the bottom layer 19b includes a conductive material
having a resistivity of 10.sup.6 .OMEGA.cm or less. Because a
charging electrode 21 can be used as a counter electrode grounded
to the bottom layer 19b, the charging electrode 21 may be provided
at any position contacting the surface of the belt 19, that is, the
top layer 19a. According to the first illustrative embodiment, the
charging electrode 21, including a roller connected to an AC power
supply 24, is provided such that the charging electrode 21 contacts
the belt 19 at a position where the belt 19 is wound around the
drive roller 22. The stack of sheets 6 is positioned so as to
obtain an area of the sheet attracted to the belt 19 sufficient for
reliable removal. The drive roller 22 includes a conductive rubber
layer having a resistivity of about 10.sup.6 .OMEGA.cm on a surface
thereof. The driven roller 23 is a metal roller. Both the drive
roller 22 and the driven roller 23 are grounded. An upper guide
plate 26 and a lower guide plate 27 each restricting conveyance of
the sheets are provided on a downstream side from the belt 19
relative to a direction of sheet feed. Specifically, the surface of
the belt 19 facing the stack of sheets 6 is provided in parallel to
a surface of the bottom plate 28 on which the stack of sheets 6 is
placed. Further, the sheet attraction/separation unit 7 is provided
on a downstream side from a leading edge of the top sheet 6a to be
separated from the stack of sheets 6 relative to the direction of
sheet feed, such that the leading edge of the top sheet 6a never
contacts the belt 19 including a dielectric material. As a result,
the top sheet 6a can be effectively removed from the belt 19 using
a curvature of the belt 19.
[0050] The belt 19 swings around a shaft 22a of the drive roller 22
as a pivot as illustrated in FIG. 4A, and is positioned at a front
part of an upper surface of the top sheet 6A of the stack of sheets
6 to contact the top sheet 6A. The pivot is positioned such that
the top surface of the stack of sheets 6 on the bottom plate 28
pushed upward by a spring 37 is on a tangential line to the
curvature of the belt 19 on the drive roller 22 side.
[0051] In addition, one side of the belt 19, that is, the driven
roller 23 side in the case of FIGS. 4A and 4B because the shaft 22a
of the drive roller 22 serves as the pivot as described above,
swings to maximize an area of contact between the stack of sheets 6
and the belt 19. Because the sheet attraction/separation unit 7 is
designed to have an attractive force sufficient to remove the top
sheet 6A, the spring 37 only pushes the stack of sheets 6 upward
via the bottom plate 28 such that the stack of sheets 6 touches the
sheet attraction/separation unit 7. Further, a force that attracts
a next sheet to be fed can be increased, and a space is formed so
that the sheets are reliably separated from one another.
[0052] The charging electrode 21 is provided on the drive roller 22
side so that a load applied to the stack of sheet 6 from the sheet
attraction/separation unit 7 swung around the shaft 22a of the
drive roller 22 by its own weight is reduced, causing a decrease in
a frictional force between the top sheet 6a and a second sheet 6b,
that is, the second sheet from the top of the stack of sheets
6.
[0053] Further, returning to FIG. 3, the friction pad 9 in the
first illustrative embodiment engages the sheet
attraction/separation unit 7, so that the friction pad 9 swings
together with the sheet attraction/separation unit 7. As a result,
an angle of approach of the sheet to the friction pad 9 can be kept
constant. In place of the friction pad 9, for example, a retard
roller may be used. As illustrated in FIG. 3, the friction pad 9
and the lower guide member 27 are pushed upward by a spring 38.
[0054] When driving of the drive roller 22 is stopped, a free edge
side of the bottom plate 28 is pushed upward by the spring 37 as
illustrated in FIG. 4B, and one edge side of the sheet
attraction/separation unit 7 is moved upward due to swinging
movement. It is to be noted that a stopper, not shown, that keeps
the sheet attraction/separation unit 7 swingingly moved upward
horizontal may be preferably provided. Specifically, when a free
edge of the bottom plate 28 pushed upward contacts the pivot of the
belt 19, only the weight of the belt 19 keeps the belt 19 in
contact with the stack of sheets 6. Accordingly, a pressure applied
to the stack of sheets 6 can be kept constant regardless of the
number of sheets in the stack of sheets 6, and a frictional force
between each sheet in the stack of sheets 6 can be reduced.
Further, the area of contact between the belt 19 and the stack of
sheets 6 can be effectively used, providing the ability to
consistently separate the stack of sheets 6 from one another
without causing multiple sheet feeding and moreover without
wrinkling the next sheet.
[0055] FIG. 5 is a schematic cross-sectional view illustrating a
variation of the sheet attraction/separation unit 7. As illustrated
in FIG. 5, the stack of sheets 6 on the bottom plate 28 can be
moved upward or downward by a pushing device 40, and a sensor 30 is
provided to detect the upper surface of the top sheet 6a at the top
of the stack of sheets 6. Accordingly, a distance and a pressure
between the belt 19 and the top sheet 6a can be appropriately
controlled.
[0056] It is to be noted that the AC power supply 24 may supply a
direct current varied between alternating high and low electric
potentials as well as an alternating current. In the first
illustrative embodiment, an alternating current having an amplitude
of 4 KV is applied to the surface of the belt 19. FIGS. 6A to 6D
are timing charts each showing a control sequence of an applied
voltage and a frequency in the sheet feeding device 5.
[0057] The belt 19 having a charge pattern thereon contacts the
front part on the upper surface of the top sheet 6a at a position
where the belt 19 is wound around the driven roller 23.
Accordingly, the Maxwell stress acts on the top sheet 6a due to a
non-uniform electric field formed by the charge pattern on the
surface of the belt 19. As a result, only the top sheet 6a is
attracted to the belt 19 and is conveyed in the direction of sheet
feed to the pair of registration rollers 11 through the upper guide
member 26 and the lower guide member 27. Thereafter, the top sheet
6a is further conveyed to the image forming unit 3 by the pair of
registration rollers 11. The force that attracts the top sheet 6a
generated by the charge pattern as described above also acts on the
second sheet 6b and some other sheets beneath the second sheet 6b
for a certain period of time from when the top sheet 6a is
attracted to the belt 19. However, after the certain period of time
has elapsed, the force acts only on the top sheet 6a so that the
second sheet 6b and the other sheets beneath the second sheet 6b
are no longer attracted to the belt 19. Accordingly, the top sheet
6a can be separated from the stack of sheets 6 without using a
prevention member with enough time.
[0058] As illustrated in FIG. 2, the insulating sheet 29 is
provided on the contact surface between the bottom plate 28 and the
belt 19 to generate a force that attracts the last sheet, that is,
the sheet at the bottom of the stack of sheets 6. Further, as
illustrated in FIG. 3, a neutralizing electrode 25 connected to a
neutralizing power supply 16 serving as an alternate power supply
is provided on an upstream side from the charging electrode 21
relative to the direction of sheet feed and a downstream side from
a position where the sheet is separated from the belt 19 relative
to the direction of sheet feed. The neutralizing electrode 25
contacts the belt 19 or is provided near the belt 19. In the sheet
attraction/separation unit 7 according to the first illustrative
embodiment, the AC power supply 24 and the neutralizing power
supply 16 are controlled such that the force on the belt 19 that
attracts the sheet is eliminated at a position where the leading
edge of the, sheet contacts the pair of registration rollers 11.
Therefore, the sheet sandwiched by the pair of registration rollers
11 is conveyed only by the pair of the registration rollers 11
without being affected by the belt 19.
[0059] A description is now given of operations of the sheet
feeding device 5. When an electromagnetic clutch is turned on in
response to a sheet feed signal, the drive roller 22 is driven to
rotate the belt 19. Alternating charges are applied to the belt 19
from the AC power supply 24 through the charging electrode 21 so
that a charge pattern alternating with a pitch corresponding to an
AC power frequency and a rotation speed of the belt 19 is formed on
the surface of the belt 19. It is to be noted that the pitch is
preferably set in a range from 5 mm to 15 mm.
[0060] A linear velocity of the pair of registration rollers 11 is
the same as that of the belt 19. When the pair of registration
rollers 11 is driven intermittently with intervals, the belt 19 is
driven intermittently. The belt 19 is separated from the stack of
sheets 6 before a rear edge of the top sheet 6a reaches a position
facing the driven roller 23 so that the second sheet 6b is not
attracted to the belt 19. The sheet is separated from the belt 19
at the drive roller 22 by the curvature of the belt 19 against the
drive roller 22 thereat, and further separated from the belt 19
using the upper guide plate 26 and the lower guide plate 27
illustrated in FIG. 3.
[0061] According to the first illustrative embodiment, the top
sheet 6a is attracted to the belt 19 having the alternating charge
pattern thereon and is separated from the stack of sheets 6.
Thereafter, the top sheet 6a passes through the friction pad 9
using friction. Accordingly, even when multiple sheets are
attracted to the belt 19 at the same time, those sheets are
separated one by one by the friction pad 9. As a result, the sheets
are reliably separated from one another and fed one by one,
preventing multiple sheet feeding.
[0062] It is preferable to provide a cleaning mechanism for the
belt 19 in order to prevent paper dust and other foreign substances
attached to the belt 19 from disturbing attraction of the sheets to
the belt 19.
[0063] The sheet feeding device 5 according to the first
illustrative embodiment can handle a wider variety of sheets
regardless of a coefficient of friction thereof, and provide an
image forming apparatus including a sheet feeding device having an
ability to reliably separate the sheets one by one.
[0064] A description is now given of the sheet feeding device 5
according to a second illustrative embodiment. FIG. 7 is a
schematic cross-sectional view illustrating the sheet
attraction/separation unit 7 included in the sheet feeding device 5
according to the second illustrative embodiment. As illustrated in
FIG. 7, a separation pick 33 is provided so that the sheet is
further reliably separated from the belt 19 using the separation
pick 33 as well as the curvature of the belt 19 at the drive roller
22. The rest of the configuration and operations of the sheet
feeding device 5 according to the second illustrative embodiment
are same as those of the sheet feeding device 5 according to the
first illustrative embodiment, and a description thereof is
omitted.
[0065] FIG. 8 is a schematic cross-sectional view illustrating the
sheet attraction/separation unit 7 included in the sheet feeding
device 5 according to a third illustrative embodiment. In the
foregoing illustrative embodiments, the sheet attraction/separation
unit 7 is provided on a downstream side from the leading edge of
the top sheet 6a to be separated from the stack of sheets 6
relative to the direction of sheet feed. By contrast, according to
the third illustrative embodiment, the sheet attraction/separation
unit 7 is provided on an upstream side from the leading edge of the
top sheet 6a relative to the direction of sheet feed. As a result,
a number of drive transmission parts can be reduced compared to the
case in which the drive roller 22 is provided on the free edge side
of the bottom plate 28, and the weight of the belt 19 can be
reduced.
[0066] FIG. 9 is a schematic cross-sectional view illustrating the
sheet attraction/separation unit 7 included in the sheet feeding
device 5 according to a fourth illustrative embodiment. As
illustrated in FIG. 9, in the sheet feeding device 5 according to
the fourth illustrative embodiment, a separation unit 31 is
provided on a downstream side from the sheet attraction/separation
unit 7 relative to the direction of sheet feed. The separation unit
31 includes a paper feed roller 18 and a roller member 34 serving
as a prevention member provided facing the paper feed roller 18. A
one-way clutch, not shown, is provided to the roller member 34 to
prevent the roller member 34 from rotating together with conveyance
of the sheets. The roller member 34 is pressed against the paper
feed roller 18 by a spring 34a. Specifically, the roller member 34
is pressed against the paper feed roller 18 at a very small
pressure of, for example, 500 gf or less. When multiple sheets
including the top sheet 6a and the second sheet 6b are attracted
and conveyed by the belt 19, the second sheet 6b is separated from
the top sheet 6a by friction between the second sheet 6b and the
roller member 34, and conveyance of the second sheet 6b is stopped
at the roller member 34. Because the pressure applied to the paper
feed roller 18 from the roller member 34 is very small, conveyance
of the top sheet 6a frictionally supported by the paper feed roller
18 is not prevented. More specifically, a coefficient of friction
between the roller member 34 and the top sheet 6a is greater than a
coefficient of friction between the top sheet 6a and the second
sheet 6b. Accordingly, only the top sheet 6a is supported by the
paper feed roller 18, and is conveyed to a pair of conveyance
rollers 17 provided on a downstream side from the paper feed roller
18 relative to the direction of sheet feed.
[0067] FIG. 10 is a schematic cross-sectional view illustrating the
sheet attraction/separation unit 7 included in the sheet feeding
device 5 according to a fifth illustrative embodiment. As
illustrated in FIG. 10, a roller member 35 including a torque
limiter is provided facing the paper feed roller 18 in the
separation unit 31. The torque limiter causes the roller member 35
to rotate in a direction indicated by an arrow a in FIG. 10 when
multiple sheets including the top sheet 6a and the second sheet 6b
are conveyed between the paper feed roller 18 and the roller member
35 to stop the conveyance of the second sheet 6b at the roller
member 35 and separate the second sheet 6b from the top sheet 6a.
By contrast, the roller member 35 is rotated in a direction
indicated by an arrow b in FIG. 10 along with rotation of the paper
feed-roller 18 by a friction when only the top sheet 6a is conveyed
between the paper feed roller 18 and the roller member 35. The
roller member 35 is pressed against the paper feed roller 18 by a
spring 35a. The rest of the configuration and operations of the
sheet feeding device 5 according to the fifth illustrative
embodiment are same as those of the sheet feeding device 5
according to the fourth illustrative embodiment, and a description
thereof is omitted.
[0068] In the sheet feeding device 5 according to the fifth
illustrative embodiment, the sheet attracted to the belt 19 is
reliably separated from the belt 19 by the roller member 35 at a
predetermined position so that the leading edge of the sheet is
reliably guided to the separation unit 31. Because the leading edge
of the top sheet 6a at the top of the stack of sheets 6 does not
contact the belt 19 as described in the first illustrative
embodiment, the leading edge of the top sheet 6a is reliably guided
to the separation unit 31 without using secondary means such as a
separation pick.
[0069] FIG. 11 is a schematic cross-sectional view illustrating the
sheet attraction/separation unit 7 included in the sheet feeding
device 5 according to a sixth illustrative embodiment. FIG. 12 is
an enlarged perspective view illustrating the separation unit 31
included in the sheet feeding device 5 according to the sixth
illustrative embodiment. As illustrated in FIGS. 11 and 12, the
separation unit 31 includes the friction pad 9 including a friction
member 36 and a bracket 44. The friction member 36 attached to the
bracket 44 is provided facing the paper feed roller 18, and is
pressed against the paper feed roller 18 at a very small pressure
by a spring 38. The rest of the configuration and operations of the
sheet feeding device 5 according to the sixth illustrative
embodiment are same as those of the sheet feeding device 5
according to the fifth illustrative embodiment, and a description
thereof is omitted. According to the sixth illustrative embodiment,
an angle of approach of the sheet to the friction pad 9 from the
belt 19 can be kept constant, reliably providing the ability to
separate the sheets from one another.
[0070] FIG. 13 is a schematic cross-sectional view illustrating the
sheet attraction/separation unit 7 included in the sheet feeding
device 5 according to a seventh illustrative embodiment. As
described above, in the foregoing illustrative embodiments, the
sheet is separated from the belt 19 by the curvature of the belt 19
at the drive roller 22. By contrast, in the seventh illustrative
embodiment, the sheet is separated from the belt 19 using only the
upper guide plate 26. Because the sheet is separated from the
surface of the belt 19 without using a separation pick, the number
of components can be reduced.
[0071] Further, in the seventh illustrative embodiment, a friction
pad system is employed in the separation unit 31. Accordingly, a
configuration of the separation unit 31 can be simplified, reducing
costs and a number of components.
[0072] An image forming apparatus including the sheet feeding
device 5 according to the foregoing illustrative embodiments can
handle a wider variety of sheets regardless of a coefficient of
friction thereof, and reliably separate the sheets from one
another.
[0073] It is to be noted that illustrative embodiments of the
present invention are not limited to those described above, and
various modifications and improvements are possible without
departing from the scope of the present invention. It is therefore
to be understood that, within the scope of the associated claims,
illustrative embodiments may be practiced otherwise than as
specifically described herein. For example, elements and/or
features of different illustrative embodiments may be combined with
each other and/or substituted for each other within the scope of
the illustrative embodiments.
* * * * *