U.S. patent application number 15/118179 was filed with the patent office on 2017-06-22 for sheet feeding apparatus and image forming apparatus.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Takaaki Aoyagi, Takeshi Aoyama, Isao Hayashi, Takashi Hiratsuka, Hisae Shimizu, Yasumi Yoshida.
Application Number | 20170174455 15/118179 |
Document ID | / |
Family ID | 55350413 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170174455 |
Kind Code |
A1 |
Aoyagi; Takaaki ; et
al. |
June 22, 2017 |
SHEET FEEDING APPARATUS AND IMAGE FORMING APPARATUS
Abstract
A sheet feeding apparatus includes a first and second electrode
elements arranged on an attracting member, including a plurality of
attracting force generation electrodes and power feeding electrodes
corresponding to the respective attracting force generation
electrodes. The attracting force generation electrodes of the first
and second electrode elements are alternately arranged. Further,
the sheet feeding apparatus includes a power feeding brush arranged
at a position different from an attracting position and capable of
supplying voltages to the electrode elements, respectively, and a
neutralization roller pair arranged at a position different from
the attracting position and the power feeding brush and configured
to be brought into contact with the electrode elements to remove a
residual charge on the attracting member. With this, decrease in
productivity is prevented by enabling both of the generation of the
electrostatic attracting force and the neutralization without
control of switching between power feeding and neutralization.
Inventors: |
Aoyagi; Takaaki;
(Kawasaki-shi, JP) ; Yoshida; Yasumi;
(Yokohama-shi, JP) ; Aoyama; Takeshi;
(Kawasaki-shi, JP) ; Hiratsuka; Takashi;
(Kashiwa-shi, JP) ; Hayashi; Isao; (Kawasaki-shi,
JP) ; Shimizu; Hisae; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
55350413 |
Appl. No.: |
15/118179 |
Filed: |
August 17, 2015 |
PCT Filed: |
August 17, 2015 |
PCT NO: |
PCT/JP2015/004074 |
371 Date: |
August 11, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B65H 2404/283 20130101;
B65H 1/04 20130101; B65H 2404/255 20130101; B65H 2404/251 20130101;
B65H 3/18 20130101 |
International
Class: |
B65H 3/18 20060101
B65H003/18; B65H 1/04 20060101 B65H001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2014 |
JP |
2014-169230 |
Claims
1. A sheet feeding apparatus, comprising: a stacking unit on which
a sheet is stacked; a first rotary member provided on an upside of
the stacking unit; a second rotary member provided on a downstream
in a sheet feeding direction with respect to the first rotary
member; an endless attracting member configured to rotate in a
peripheral direction of the endless attracting member whose inner
surface is supported by the first rotary member and the second
rotary member and to feed the sheet by attracting the sheet at an
attracting position opposed to the sheet stacked on the stacking
unit; a first electrode element and a second electrode element that
are provided on the endless attracting member, the first electrode
element and the second electrode element each including a plurality
of attracting force generation electrodes and a plurality of power
feeding electrodes, each of the attracting force generation
electrodes connected to each of attracting force generation
electrodes to correspond with each other, the plurality of
attracting force generation electrodes of the first electrode
element and the plurality of attracting force generation electrodes
of the second electrode element being alternately provided to be
spaced with each other in the peripheral direction of the endless
attracting member; a power feeding unit provided at a position
different from the attracting position and capable of supplying a
positive voltage and a negative voltage to the first electrode
element and the second electrode element, respectively; and a
neutralization unit provided at a position different from the
attracting position and the power feeding unit and configured to be
brought into contact with the first electrode element and the
second electrode element to remove a residual charge on the endless
attracting member, wherein the first electrode element and the
second electrode element each comprise connecting lines configured
to connect the plurality of attracting force generation electrodes
to the power feeding electrodes corresponding to the respective
plurality of attracting force generation electrodes so as to lie
next to each other in a width direction perpendicular to the
peripheral direction at positions different from each other in the
peripheral direction, and wherein the plurality of attracting force
generation electrodes of each of the first electrode element and
the second electrode element are configured to move to the
attracting position along with rotation of the endless attracting
member by feeding power from the power feeding unit through each of
the power feeding electrodes corresponding thereto, so that each of
the attracting force generation electrodes generates an
electrostatic attracting force.
2. A sheet feeding apparatus according to claim 1, wherein the
plurality of attracting force generation electrodes of the first
electrode element and the plurality of attracting force generation
electrodes of the second electrode element are configured to
alternately extend in a pectinate manner from the respective power
feeding electrodes in the width direction perpendicular to the
peripheral direction of the endless attracting member.
3. A sheet feeding apparatus according to claim 1, wherein the
power feeding unit comprises a power feeding brush configured to be
brought into contact with the power feeding electrodes to feed
power thereto.
4. A sheet feeding apparatus according to claim 3, further
comprising a tension providing unit configured to provide a tension
to the endless attracting member so as to be capable of maintaining
constant a contact pressure of the power feeding brush to the power
feeding electrodes provided to be opposed to the power feeding
brush in the endless attracting member.
5. A sheet feeding apparatus according to claim 4, wherein the
neutralization unit comprises a neutralization roller pair
configured to nip the endless attracting member in a form of being
extended in the width direction perpendicular to the peripheral
direction of the endless attracting member, and wherein the tension
providing unit is configured to apply a load to the neutralization
roller pair so as to apply, to the endless attracting member, a
load in a direction opposite to a rotating direction of the endless
attracting member, to thereby provide a tension to the power
feeding electrodes and the connecting lines.
6. A sheet feeding apparatus according to claim 4, wherein the
tension providing unit comprises a plate member provided on an
inner peripheral side of the endless attracting member and
configured to press the power feeding electrodes to the power
feeding brush.
7. A sheet feeding apparatus according to claim 1, wherein at least
the power feeding electrodes of each of the first electrode element
and the second electrode element are provided so as to be exposed
on an outer peripheral surface of the endless attracting
member.
8. A sheet feeding apparatus according to claim 1, wherein at least
the power feeding electrodes of each of the first electrode element
and the second electrode element are provided so as to be exposed
on an inner peripheral surface of the endless attracting member,
and wherein the power feeding unit comprises at least one of the
first rotary member or the second rotary member, and is configured
to be brought into contact with the power feeding electrodes
exposed on the inner peripheral surface to feed power thereto.
9. A sheet feeding apparatus according to claim 1, wherein, under a
state in which a plurality of the attracting force generation
electrodes of each of the first electrode element and the second
electrode element are electrically conducted with each other, the
plurality of the attracting force generation electrodes are
connected to corresponding one of the connecting lines.
10. A sheet feeding apparatus according to claim 1, further
comprising: a first nipping member configured to nip the endless
attracting member together with the first rotary member; a second
nipping member configured to nip the endless attracting member
together with the second rotary member; a first driving unit and a
second driving unit configured to drive the first rotary member and
the second rotary member, respectively; and a control unit
configured to control the first driving unit and the second driving
unit, wherein the control unit is configured to: control each of
the first driving unit and the second driving unit so as to provide
a difference in a rotational speed between the first rotary member
and the second rotary member, to thereby increase an amount that
the endless attracting member sags downward to attract the sheet on
the stacking unit to the endless attracting member; and then feed
the sheet attracted to the endless attracting member while
decreasing the amount that the endless attracting member sags
downward.
11. A sheet feeding apparatus according to claim 1, wherein the
connecting lines are respectively extended from the plurality of
attracting force generation electrodes to an upstream side in the
rotating direction of the endless attracting member, wherein the
power feeding unit is provided on the upstream side in the rotating
direction of the endless attracting member with respect to the
attracting position, and wherein the neutralization unit is
provided on a downstream side in the rotating direction of the
endless attracting member with respect to the attracting
position.
12. A sheet feeding apparatus according to claim 11, wherein the
connecting lines are each set to have such a length that the
plurality of attracting force generation electrodes moving from the
attracting position toward the neutralization unit are separated
from the power feeding unit before reaching the neutralization
unit.
13. A sheet feeding apparatus according to claim 1, wherein the
power feeding electrodes includes the connecting lines.
14. An image forming apparatus, comprising: an image forming unit
configured to form an image on a sheet; and a sheet feeding
apparatus of claim 1.
15. An image forming apparatus, comprising: an image forming unit
configured to form an image on a sheet; and a sheet feeding
apparatus of claim 2.
16. An image forming apparatus, comprising: an image forming unit
configured to form an image on a sheet; and a sheet feeding
apparatus of claim 3.
17. An image forming apparatus, comprising: an image forming unit
configured to form an image on a sheet; and a sheet feeding
apparatus of claim 4.
18. An image forming apparatus, comprising: an image forming unit
configured to form an image on a sheet; and a sheet feeding
apparatus of claim 5.
19. An image forming apparatus, comprising: an image forming unit
configured to form an image on a sheet; and a sheet feeding
apparatus of claim 6.
20. An image forming apparatus, comprising: an image forming unit
configured to form an image on a sheet; and a sheet feeding
apparatus of claim 7.
Description
TECHNICAL FIELD
[0001] The present invention relates to a sheet feeding apparatus
and an image forming apparatus, and more particularly, to a sheet
feeding apparatus and an image forming apparatus that are
configured to feed a sheet with use of an electrostatic attracting
force.
BACKGROUND ART
[0002] There have been proposed a large number of image forming
apparatus, such as a copying machine and a printer, employing a
friction separating system as a system for conveying sheets from a
cassette having the sheets stacked thereon. In the friction
separating system, a sheet feeding roller made of a rubber material
is rotated while being pressed against the sheets stacked on the
cassette, to thereby convey the uppermost sheet among the sheets
stacked on a middle plate. In this case, in order to prevent double
feeding in which a sheet arranged in contact under the uppermost
sheet is simultaneously conveyed, there is known a configuration of
conveying the sheet while pressing the sheet against a separation
pad, or a configuration of applying a force in a direction opposite
to the conveyance direction to the sheets other than the uppermost
sheet by a retard roller. In such a friction separating
configuration, the sheet is conveyed while being applied with a
large normal force, and hence noise due to the feeding operation
becomes a problem.
[0003] In order to solve this problem, there has been proposed an
apparatus having a configuration employing an electrostatic
attraction separating system (see PTL 1). In this apparatus, when
the sheet is to be attracted, an endless belt is caused to sag to
increase the attraction area for attraction and separation. After
the sheet is attracted and separated, a tension is provided to the
belt to obtain a flat-surface state, and the sheet is conveyed in
this state. Therefore, noise at a sheet feeding unit can be
significantly reduced.
[0004] Further, there has also been proposed an apparatus having a
configuration in which power is fed to an endless electrostatic
attraction belt including electrodes (see PTL 2 and PTL 3). In the
apparatus disclosed in PTL 2, positive power and negative power are
fed to integrated electrodes arranged on the endless electrostatic
attraction belt from two rollers configured to stretch the
electrostatic attraction belt. Further, the apparatus disclosed in
PTL 3 has a configuration in which power feeding brushes are
arranged, which are each brought into contact with only electrodes
in an attracting range among electrodes arranged on the endless
electrostatic attraction belt and divided in the peripheral
direction. Further, there has also been proposed an apparatus
having a configuration in which the position of the power feeding
unit and the position of the sheet attracting surface are offset in
the peripheral direction of the electrostatic attraction belt (see
PTL 4).
CITATION LIST
Patent Literature
[0005] PTL 1: Japanese Patent Application Laid-Open No.
2012-140224
[0006] PTL 2: Japanese Patent Application Laid-Open No.
H06-255823
[0007] PTL 3: Japanese Patent Application Laid-Open No.
2001-48370
[0008] PTL 4: Japanese Patent Application Laid-Open No.
2000-247474
SUMMARY OF INVENTION
Technical Problem
[0009] In the apparatus disclosed in PTL 2, each of the positive
power and the negative power is fed at one position, and hence
during power feeding, the voltage is applied to the entire region
of the electrostatic attraction belt. Therefore, the sheet is
separated from the electrostatic attraction belt under a state in
which the voltage is applied during sheet conveyance, and hence
charges remain on the electrostatic attraction belt due to
separating discharge. The residual charges deteriorate the
attracting force of the electrostatic attraction belt, and hence
the residual charges are required to be removed.
[0010] In the related art described above, the voltage is applied
to the entire region of the electrostatic attraction belt during
the operation of attracting the sheet, and hence even if a
neutralization unit is brought into contact with the electrostatic
attraction belt in this state, a sufficient neutralization effect
cannot be obtained. Therefore, after the conveyance of the
preceding sheet is completed, the endless electrostatic attraction
belt is rotated one lap under a state in which the power feeding is
stopped so that the entire region is brought into contact with the
neutralization unit for neutralization. Then, the power feeding is
restarted to carry out the operation of conveying the next sheet.
Therefore, the productivity may be remarkably reduced.
[0011] When the power feeding configuration disclosed in PTL 3 is
attempted to be applied to the apparatus disclosed in PTL 1, the
attracting range is vertically moved. Therefore, it is difficult to
feed power while reliably bringing the power feeding brushes into
contact with the electrodes arranged on the electrostatic
attraction belt.
[0012] Further, in PTL 4, there is disclosed an electrostatic
attraction conveyance belt configured to convey the sheet while
attracting the sheet by an electrostatic force, in which
opposite-polarity electrodes are sequentially arrayed on a flexible
base member. In this electrostatic attraction conveyance belt, the
electrodes are arranged on the inner peripheral side of the base
member and are arranged so as to be inclined by a predetermined
angle with respect to a belt rotating direction. A power feeder is
arranged on the inner peripheral side of the base member, and power
feeding terminals of the electrodes are made of a metal. Further,
the electrodes are not protected by a protective layer, and a
joining member of the endless belt is mounted on the outer
peripheral side of the base member. With this configuration, the
conveyance speed of the electrostatic attraction conveyance belt
can be set stable. However, even when the power feeding position
and the attracting position are offset on the same plane of the
electrostatic attraction belt as in PTL 4, it has been difficult to
solve the above-mentioned problems.
[0013] In view of this, the present invention has an object to
provide a sheet feeding apparatus and an image forming apparatus
that are capable of preventing decrease in productivity by enabling
both of generation of an electrostatic attracting force and
neutralization without control of switching between power feeding
and neutralization.
Solution to Problem
[0014] According to one embodiment of the present invention, there
is provided a sheet feeding apparatus, including a stacking unit on
which a sheet is stacked; a first rotary member arranged on an
upside of the stacking unit; a second rotary member arranged on a
downstream in a sheet feeding direction with respect to the first
rotary member; an endless attracting member configured to rotate in
a peripheral direction of the endless attracting member whose inner
surface is supported by the first rotary member and the second
rotary member and to feed the sheet by attracting the sheet at an
attracting position opposed to the sheet stacked on the stacking
unit; a first electrode element and a second electrode element that
are arranged on the endless attracting member, the first electrode
element and the second electrode element each including a plurality
of attracting force generation electrodes and a plurality of power
feeding electrodes, each of the attracting force generation
electrodes connected to each of attracting force generation
electrodes to correspond with each other, the plurality of
attracting force generation electrodes of the first electrode
element and the plurality of attracting force generation electrodes
of the second electrode element being alternately arranged to be
spaced with each other in the peripheral direction of the endless
attracting member; a power feeding unit arranged at a position
different from the attracting position and capable of supplying a
positive voltage and a negative voltage to the first electrode
element and the second electrode element, respectively; and a
neutralization unit arranged at a position different from the
attracting position and the power feeding unit and configured to be
brought into contact with the first electrode element and the
second electrode element to remove a residual charge on the endless
attracting member, wherein the first electrode element and the
second electrode element each comprise connecting lines configured
to connect the plurality of attracting force generation electrodes
to the power feeding electrodes corresponding to the respective
plurality of attracting force generation electrodes so as to lie
next to each other in a width direction perpendicular to the
peripheral direction at positions different from each other in the
peripheral direction, and wherein the plurality of attracting force
generation electrodes of each of the first electrode element and
the second electrode element are configured to move to the
attracting position along with rotation of the endless attracting
member by feeding power from the power feeding unit through each of
the power feeding electrodes corresponding thereto, so that each of
the attracting force generation electrodes generates an
electrostatic attracting force.
[0015] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
Advantageous Effects of Invention
[0016] According to the one embodiment of the present invention,
without the control of switching between the power feeding and the
neutralization, the attracting member can constantly maintain the
electrostatic attracting force at the attracting position
corresponding to the sheet, and the generation of the electrostatic
attracting force and the neutralization are both enabled to enable
sheet feeding without reducing the productivity.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is an illustration of a schematic configuration of an
image forming apparatus including a sheet feeding apparatus
according to a first embodiment of the present invention.
[0018] FIG. 2 is an illustration of the configuration of the
above-mentioned sheet feeding apparatus.
[0019] FIG. 3 is an illustration of a configuration of an
attracting member according to the first embodiment.
[0020] FIG. 4A is an illustration of a detailed configuration of
the above-mentioned attracting member and a principle of generating
an attracting force for attracting a sheet by the attracting
member.
[0021] FIG. 4B is an illustration of the detailed configuration of
the above-mentioned attracting member and the principle of
generating the attracting force for attracting the sheet by the
attracting member.
[0022] FIG. 4C is an illustration of the detailed configuration of
the above-mentioned attracting member and the principle of
generating the attracting force for attracting the sheet by the
attracting member.
[0023] FIG. 5 is an illustration of the above-mentioned sheet
feeding apparatus.
[0024] FIG. 6A is a sectional view for illustrating an operation of
the sheet feeding apparatus according to the first embodiment in
time series.
[0025] FIG. 6B is a sectional view for illustrating the operation
of the sheet feeding apparatus according to the first embodiment in
time series.
[0026] FIG. 6C is a sectional view for illustrating the operation
of the sheet feeding apparatus according to the first embodiment in
time series.
[0027] FIG. 7A is a sectional view for illustrating the operation
of the sheet feeding apparatus according to the first embodiment in
time series.
[0028] FIG. 7B is a sectional view for illustrating the operation
of the sheet feeding apparatus according to the first embodiment in
time series.
[0029] FIG. 7C is a sectional view for illustrating the operation
of the sheet feeding apparatus according to the first embodiment in
time series.
[0030] FIG. 8 is an illustration of a control block diagram of the
sheet feeding apparatus according to the first embodiment.
[0031] FIG. 9 is a sectional view for illustrating a sheet feeding
apparatus according to a second embodiment of the present
invention.
[0032] FIG. 10 is a perspective view for illustrating the sheet
feeding apparatus according to the second embodiment.
[0033] FIG. 11 is a plan view for illustrating a configuration of
an attracting member according to a third embodiment of the present
invention.
[0034] FIG. 12 is a perspective view for illustrating a
configuration for feeding power to the attracting member according
to the third embodiment.
[0035] FIG. 13 is a perspective view for illustrating a sheet
feeding apparatus according to the third embodiment.
[0036] FIG. 14 is a sectional view for illustrating a sheet feeding
apparatus according to the third embodiment.
[0037] FIG. 15 is a plan view for illustrating a configuration of
an attracting member according to a fourth embodiment of the
present invention.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0038] Now, an embodiment of the present invention is described in
detail with reference to the drawings. Note that, FIG. 1 is a view
for illustrating a schematic configuration of an image forming
apparatus including a sheet feeding apparatus according to this
embodiment.
[0039] In FIG. 1, an image forming apparatus 100 includes an image
reading unit 41 arranged in an upper part of an image forming
apparatus main body (hereinafter referred to as "apparatus main
body") 100A. The image reading unit 41 is configured to radiate
light to an original placed on a platen glass serving as an
original placing table, and includes an image sensor for converting
the reflected light into a digital signal. The apparatus main body
100A includes a control unit 70 including a CPU, a ROM, and a RAM
and being configured to control each unit of the apparatus.
[0040] Note that, the original from which an image is read is
conveyed onto the platen glass by an automatic original feeding
apparatus 41a. Further, the apparatus main body 100A includes an
image forming unit 55, sheet feeding apparatus 51 and 52 configured
to feed sheets S (hereinafter also referred to as "paper (S)") to
the image forming unit 55, and a sheet inverting unit 59 configured
to invert the sheet S and convey the inverted sheet S to the image
forming unit 55.
[0041] The image forming unit 55 includes an exposure unit 42, and
four process cartridges 43 (43y, 43m, 43c, and 43k) configured to
form toner images of four colors of yellow (Y), magenta (M), cyan
(C), and black (Bk). Further, the image forming unit 55 includes an
intermediate transfer unit 44, a secondary transfer unit 56, and a
fixing unit 57 provided on an upward side of the process cartridges
43.
[0042] In this case, the process cartridges 43 include
photosensitive drums 21 (21y, 21m, 21c, and 21k), charging rollers
22 (22y, 22m, 22c, and 22k), and developing rollers 23 (23y, 23m,
23c, and 23k). The process cartridges 43 also include drum cleaning
blades (24y, 24m, 24c, and 24k).
[0043] The intermediate transfer unit 44 includes an intermediate
transfer belt 25 stretched by a belt driving roller 26, a secondary
transfer inside roller 56a, and the like, and primary transfer
rollers 27 (27y, 27m, 27c, and 27k) brought into abutment against
the intermediate transfer belt 25 at positions opposed to the
photosensitive drums 21. Then, as described later, a positive
transfer bias is applied to the intermediate transfer belt 25 by
the primary transfer rollers 27 so that the negative-polarity toner
images on the photosensitive drums 21 are sequentially transferred
onto the intermediate transfer belt 25 in an overlapping manner.
With this, a full-color image is formed on the intermediate
transfer belt 25.
[0044] The secondary transfer unit 56 includes the secondary
transfer inside roller 56a and a secondary transfer outside roller
56b that is brought into contact with the secondary transfer inside
roller 56a across the intermediate transfer belt 25. Then, as
described later, a positive secondary transfer bias is applied to
the secondary transfer outside roller 56b, to thereby transfer the
full four-color image formed on the intermediate transfer belt 25
onto the sheet S.
[0045] The fixing unit 57 includes a fixing roller 57a and a fixing
backup roller 57b. Then, the sheet S is nipped and conveyed between
the fixing roller 57a and the fixing backup roller 57b, to thereby
pressurize and heat the toner image on the sheet S and fix the
toner image onto the sheet S. The sheet feeding apparatus 51 and 52
respectively include cassettes 51a and 52a configured to receive
the sheets S, and sheet attraction and separation feeding units 51b
and 52b having a function of feeding the sheets S received in the
cassettes 51a and 52a one by one while attracting the sheets S by
static electricity.
[0046] Note that, in FIG. 1, through a pre-secondary transfer
conveyance path 103, the sheets S fed from the cassettes 51a and
52a are conveyed to the secondary transfer unit 56. Through a
pre-fixing conveyance path 104, the sheets S conveyed to the
secondary transfer unit 56 are conveyed from the secondary transfer
unit to the fixing unit 57. Through a post-fixing conveyance path
105, the sheets S conveyed to the fixing unit 57 are conveyed from
the fixing unit 57 to a switching member 61. Through a discharge
path 106, the sheets S conveyed to the switching member 61 are
conveyed from the switching member 61 to a discharge unit 58.
Through a re-conveyance path 107, in order to form an image on the
back surface of the sheet S having an image formed on one surface
thereof by the image forming unit 55, the sheet S inverted by the
sheet inverting unit 59 is conveyed to the image forming unit 55
again.
[0047] Next, an image forming operation of the image forming
apparatus 100 having the above-mentioned configuration is
described. When the image forming operation is started, first, the
control unit 70 controls the exposure unit 42 to radiate laser
light on the surfaces of the photosensitive drums 21 based on image
information from a personal computer (not shown) or the like. At
this time, the surfaces of the photosensitive drums 21 are
uniformly charged to a predetermined polarity and potential by the
charging rollers 22. When the laser light is radiated, charges in a
region radiated by the laser light are decayed, to thereby form
electrostatic latent images on the surfaces of the photosensitive
drums.
[0048] After that, the control unit 70 develops the electrostatic
latent images by toner of yellow (Y), magenta (M), cyan (C), and
black (Bk) supplied respectively from the developing rollers 23, to
thereby visualize the electrostatic latent images as toner images.
Then, the toner images of the respective colors are sequentially
transferred onto the intermediate transfer belt 25 by a primary
transfer bias applied to each of the primary transfer rollers 27,
to thereby form a full-color toner image on the intermediate
transfer belt 25.
[0049] On the other hand, the control unit 70 actuates the sheet
feeding apparatus 51 and 52 in parallel with the above-mentioned
toner image forming operation, and controls the sheet attraction
and separation feeding units 51b and 52b to separate and feed only
one sheet S from each of the cassettes 51a and 52a. When the sheet
S is fed from the sheet feeding apparatus 51, the sheet S is
detected by a sheet leading edge detection sensor 51c and arrives
at a pull-out roller pair 71 including pull-out rollers 51d and
51e. Further, when the sheet S is fed from the sheet feeding
apparatus 52, the sheet S is detected by a sheet leading edge
detection sensor 52c and arrives at a pull-out roller pair 72
including pull-out rollers 52d and 52e. The sheet S nipped by the
pull-out roller pair 71 or 72 is fed through the conveyance path
103 to be brought into abutment against a nip portion of a stopped
registration roller pair 62 including registration rollers 62a and
62b, to thereby adjust the position of the leading edge (skew feed
correction).
[0050] Next, the control unit 70 drives the registration roller
pair 62 at a timing at which, in the secondary transfer unit 56,
the position of the full-color toner image on the intermediate
transfer belt matches with the position of the sheet S. With this,
the sheet S is conveyed to the secondary transfer unit 56, and in
the secondary transfer unit 56, the full-color toner image is
collectively transferred onto the sheet S by the secondary transfer
bias applied to the secondary transfer outside roller 56b.
[0051] The control unit 70 conveys the sheet S having the
full-color toner image transferred thereon to the fixing unit 57 to
heat and pressurize the sheet S by the fixing unit 57 and melt and
mix the toner of respective colors, to thereby fix the full-color
image onto the sheet S. After that, the control unit 70 discharges
the sheet S having the image fixed thereon through the discharge
unit 58 arranged on the downstream of the fixing unit 57. Note
that, when images are formed on both surfaces of the sheet S, the
conveyance direction of the sheet S is inverted by the sheet
inverting unit 59 to convey the sheet S to the image forming unit
55 again.
(Sheet Feeding Apparatus)
[0052] Now, the sheet attraction and separation feeding units 51b
and 52b in the sheet feeding apparatus 51 and 52 are described in
detail with reference to FIG. 1 and FIG. 2. Note that, in the
following description, the configuration of the sheet attraction
and separation feeding unit 51b in the sheet feeding apparatus 51
is mainly described. The sheet attraction and separation feeding
unit 52b in the sheet feeding apparatus 52 has a similar
configuration, and hence description thereof is omitted herein.
[0053] As described above, the sheet feeding apparatus 51 includes
the cassette 51a, and the sheet attraction and separation feeding
unit 51b configured to feed the sheets S received in the cassette
51a one by one while attracting the sheets S by static electricity.
The sheet feeding apparatus 51 further includes an elevating unit
301 capable of elevating a middle plate 301a serving as a stacking
unit on which the sheets are to be stacked and which is arranged to
be elevatable on the cassette 51a, and the sheet leading edge
detection sensor 51c configured to detect the passage of the sheet
fed by the sheet attraction and separation feeding unit 51b.
[0054] The elevating unit 301 (see FIG. 8) includes a lifter 301b
pivotably arranged below the middle plate 301a, and the positions
of the middle plate 301a and an uppermost sheet Sa stacked on the
middle plate 301a are changed depending on the pivoting angle of
the lifter 301b. The sheet leading edge detection sensor 51c (see
FIG. 8) is arranged in the sheet conveyance path between the sheet
attraction and separation feeding unit 51b and the pull-out roller
pair 71 (see FIG. 1). Then, depending on whether or not the sheet
leading edge detection sensor 51c detects the sheet S at a
predetermined timing, whether or not the sheet feeding has
succeeded is detected. In this embodiment, the sheet leading edge
detection sensor 51c is a non-contact reflective photosensor, which
is configured to radiate spot-light to a detection target and
measure the reflected light amount, to thereby detect
presence/absence of the detection target.
[0055] The sheet attraction and separation feeding unit 51b
includes a first nipping and conveying roller pair 202, a second
nipping and conveying roller pair 201, a neutralization roller pair
250, and a flexible and endless attracting member 200 to be nipped
and conveyed by those nipping and conveying roller pairs 201 and
202.
[0056] As illustrated in FIG. 2, on an upward side of the middle
plate 301a, a sheet surface height detection unit 302 (see FIG. 8)
is arranged, which is configured to detect the upper surface
position of the sheets S stacked on the middle plate 301a. The
sheet surface height detection unit 302 includes a sensor flag 302a
and a photosensor 302b. The sensor flag 302a is rotatably supported
by a support unit (not shown), and has one end at a position
capable of contacting with the upper surface of the uppermost sheet
Sa and the other end at a position capable of shielding the
photosensor 302b.
[0057] In this case, when the upper surface of the uppermost sheet
Sa is positioned at a predetermined height, in the sheet surface
height detection unit 302, the sensor flag 302a is pivoted to
change the shielding state of the photosensor 302b, to thereby
detect the upper surface position of the uppermost sheet Sa. The
control unit 70 controls the operation of the elevating unit 301 so
that the upper surface of the uppermost sheet Sa is always detected
by the sheet surface height detection unit 302, and the middle
plate 301a is maintained at a position at which the upper surface
height of the uppermost sheet Sa becomes substantially constant. As
a result, an air gap Lr between the first nipping and conveying
roller pair 202 and the upper surface of the uppermost sheet Sa is
maintained substantially constant.
[0058] The second nipping and conveying roller pair 201 is arranged
on the downstream in the sheet feeding direction with respect to
the first nipping and conveying roller pair 202, and includes a
second nipping and conveying inner roller 201a and a second nipping
and conveying outer roller 201b. The second nipping and conveying
inner roller 201a is arranged on the inner side of the attracting
member 200, and has a rotary shaft 201j rotatably supported by a
shaft support member (not shown) whose position is fixed. The drive
from a second driving unit 203 is transmitted to the second nipping
and conveying inner roller (second rotary member) 201a via a drive
transmitting unit (not shown).
[0059] The second nipping and conveying outer roller 201b is
arranged at a position opposed to the second nipping and conveying
inner roller 201a under a state in which the endless belt-like
attracting member 200 is nipped between the second nipping and
conveying outer roller 201b and the second nipping and conveying
inner roller 201a. The shaft of the second nipping and conveying
outer roller 201b is supported rotatably by a shaft support member
(not shown). The second nipping and conveying outer roller 201b
rotate along with (following rotation) the attracting member 200
rotated in the arrow F direction by the second nipping and
conveying inner roller 201a rotating in the same direction. Note
that, a second pressure spring (not shown) is coupled to the shaft
support member (not shown), and the second nipping and conveying
outer roller 201b is biased in the axial center direction of the
second nipping and conveying inner roller 201a by the second
pressure spring to nip the attracting member 200 together with this
roller 201a.
[0060] The first nipping and conveying roller pair 202 includes a
first nipping and conveying inner roller 202a and a first nipping
and conveying outer roller 202b. The first nipping and conveying
inner roller 202a is arranged on the inner side of the attracting
member 200, and has a rotary shaft 202j rotatably supported by a
shaft support member (not shown) whose position is fixed. The drive
from a first driving unit 204 is transmitted to the first nipping
and conveying inner roller (first rotary member) 202a via a drive
transmitting unit (not shown).
[0061] Note that, the first nipping and conveying inner roller 202a
constructs the first rotary member arranged on the upward side of
the middle plate 301a serving as the stacking unit. Further, the
second nipping and conveying inner roller 201a constructs the
second rotary member arranged on the downstream in the feeding
direction of the sheet S (arrow J direction in FIG. 2) with respect
to the first nipping and conveying inner roller 202a. The
attracting member 200 has its inner surface supported by the first
nipping and conveying inner roller (first rotary member) 202a and
the second nipping and conveying inner roller (second rotary
member) 201a to be rotated in the peripheral direction (arrow H
direction in FIG. 3). Then, the attracting member 200 attracts the
sheet S at an attracting position (position represented by C in
FIG. 6C) opposed to the sheet S stacked on the middle plate 301a,
to thereby feed the sheet S.
[0062] The first nipping and conveying outer roller 202b is
arranged at a position opposed to the first nipping and conveying
inner roller 202a under a state in which the attracting member 200
is nipped between the first nipping and conveying outer roller 202b
and the first nipping and conveying inner roller 202a. The shaft of
the first nipping and conveying outer roller 202b is supported
rotatably by a shaft support member (not shown). The first nipping
and conveying outer roller 202b is rotated in association with the
attracting member 200 rotated in the arrow G direction by the first
nipping and conveying inner roller 202a rotating in the same
direction. Note that, a first pressure spring (not shown) is
coupled to the shaft support member (not shown), and the first
nipping and conveying outer roller 202b is biased in the axial
center direction of the first nipping and conveying inner roller
202a by the first pressure spring to nip the attracting member 200
together with this roller 202a.
[0063] In this embodiment, the endless attracting member 200 is
supported by the second nipping and conveying inner roller 201a,
the first nipping and conveying inner roller 202a, and a
neutralization inner roller 250a that are three rotary members
arranged along the sheet feeding direction. Then, the attracting
member 200 has a length larger than [sum D.sub.1+D.sub.2+D.sub.3 of
distances between rotation centers of the respective rollers 201a,
202a, and 250a]+[sum of wrapping lengths of the attracting member
200 on the respective rollers 201a, 202a, and 250a].
[0064] With such a length, the attracting member 200 can sag
downward while being rotated (moved) by the rotation of the second
nipping and conveying inner roller 201a and the first nipping and
conveying inner roller 202a. With this, although the air gap Lr
exists between the first nipping and conveying roller pair 202 and
the uppermost sheet Sa among the sheets S stacked on the middle
plate 301a, the attracting member 200 can be brought into contact
with the uppermost sheet Sa.
[0065] At positions along the outer peripheries of the attracting
member 200 different from the attracting position (position
represented by C in FIG. 6C), power feeding brushes 260a and 260b
serving as power feeding units are arranged. The power feeding
brushes 260a and 260b are respectively brought into contact with
power feeding electrodes 205a and 206a so that positive and
negative voltages from a positive voltage supply unit 265a and a
negative voltage supply unit 265b can be respectively supplied
(fed) to first and second electrode elements 205 and 206. At least
the power feeding electrodes 205a and 206a of the first and second
electrode elements 205 and 206 are arranged so as to be exposed on
the outer peripheral surface of the attracting member 200. Details
of the power feeding method are described later.
[0066] Further, as illustrated in FIG. 2, in the neutralization
roller pair 250, a neutralization outer roller 250b is connected to
an earth 255, and thus the residual charges on the surface of the
attracting member 200 can be removed. That is, the neutralization
roller pair 250 constructs a neutralization unit arranged at a
position different from the attracting position (position
represented by C in FIG. 6C) and the power feeding brushes (power
feeding units) 260a and 260b and configured to be brought into
contact with the first and second electrode elements 205 and 206 to
remove the residual charges on the attracting member 200.
[0067] Next, with reference to FIG. 3, the detailed configuration
of the attracting member 200 is described. Note that, FIG. 3 is a
plan view for illustrating the stretched attracting member 200 in a
state viewed from the outer peripheral side.
[0068] As illustrated in FIG. 3, the attracting member 200 includes
a base layer 200a, an attraction layer 200b, and the first and
second electrode elements 205 and 206. The first and second
electrode elements 205 and 206 respectively include a plurality of
attracting force generation electrodes 205c and 206c alternately
arranged so as to be spaced with each other in the peripheral
direction of the attracting member 200. Further, the first and
second electrode elements 205 and 206 respectively include the
plurality of power feeding electrodes 205a and 206a arranged so as
to extend in the width direction of the attracting member 200.
Further, the above-mentioned electrode elements 205 and 206
respectively include connecting lines 205b and 206b configured to
connect the attracting force generation electrodes 205c and 206c to
the power feeding electrodes 205a and 206a corresponding to the
respective electrodes 205c and 206c so as to lie next to each other
in a width direction perpendicular to the peripheral direction at
positions different from each other in the peripheral
direction.
[0069] That is, the above-mentioned electrode elements 205 and 206
on the base layer 200a respectively include the power feeding
electrodes 205a and 206a corresponding to power feeding sections
B.sub.1, the connecting lines 205b and 206b corresponding to offset
sections B.sub.2, and the attracting force generation electrodes
205c and 206c corresponding to an attraction section B.sub.3. The
attracting force generation electrodes 205c and 206c in the
attraction section B.sub.3 are arranged alternately into a
pectinate shape (alternately protrude in a pectinate manner).
[0070] The connecting lines 205b and 206b are each set to have such
a length that the attracting force generation electrodes 205c and
206c moving from the attracting position (C in FIG. 6C) toward the
neutralization roller pair 250 are separated from the power feeding
brushes 260a and 260b serving as the power feeding units before
reaching the neutralization roller pair 250. With this, the
attracting force generation electrodes 205c and 206c located at the
attracting position can be set into a floating state by reliably
stopping power feeding thereto before reaching the neutralization
roller pair 250, and the charges can be removed under this state.
Those configurations and effects are similarly applied also in
second to fourth embodiments to be described later.
[0071] The power feeding electrodes 205a and 206a corresponding to
the respective power feeding sections B.sub.1 at both end portions
in the width direction are respectively arranged in a collective
manner in the vicinity of both the end portions of the attracting
member 200 in the width direction. The connecting lines 205b and
206b corresponding to the offset sections B.sub.2 are wired to be
oblique to the width direction of the attracting member 200. The
respective surfaces of the power feeding electrodes 205a and 206a
are exposed on the surface in only parts corresponding to the power
feeding sections B.sub.1, and other parts are covered with the
attraction layer 200b.
[0072] As described above, the connecting lines 205b and 206b are
extended from the respective attracting force generation electrodes
205c and 206c toward the upstream side in the rotating direction of
the attracting member 200. Further, the power feeding brushes 260a
and 260b serving as the power feeding units are arranged on the
upstream side in the rotating direction of the attracting member
200 with respect to the attracting position (position represented
by C in FIG. 6C), and the neutralization roller pair 250 serving as
the neutralization unit is arranged on the downstream side in the
rotating direction of the attracting member 200 with respect to the
attracting position. This arrangement configuration is similarly
applied also in the second embodiment to be described later.
Further, the same is true also for power feeding rollers 202d and
202e serving as the power feeding units and the neutralization
roller pair 250 serving as the neutralization unit in the third
embodiment to be described later. Further, the same is true also
for the fourth embodiment to be described later.
[0073] With the configuration above, when the voltages are applied
to the respective power feeding electrodes 205a and 206a, the
attracting force generation electrodes 205c and 206c generate
electrostatic forces at positions shifted in the peripheral
direction of the attracting member 200 (rotating direction: arrow H
direction) with respect to the respective corresponding power
feeding electrodes 205a and 206a. That is, in the above-mentioned
electrode elements 205 and 206, the attracting force generation
electrodes 205c and 206c, which have moved to the attracting
position along with the rotation of the attracting member 200,
generate electrostatic attracting forces by being fed power from
the above-mentioned supply units 265a and 265b through the
corresponding power feeding electrodes 205a and 206a.
[0074] Note that, in this embodiment, the attraction layer 200b is
made of polyimide that is a dielectric having a volume resistivity
of 10.sup.8 .OMEGA.cm or more, and the layer thickness thereof is
set to about 100 .mu.m. Further, the first and second electrode
elements 205 and 206 are made of a conductor having a volume
resistivity of 10.sup.6 .OMEGA.cm or less, and copper having a
layer thickness of about 10 .mu.m is used as this conductor.
[0075] In this case, the connecting lines 205b and 206b
corresponding to the offset sections B.sub.2 of the respective
first and second electrode elements 205 and 206 are wired to be
inclined with respect to the width direction of the attracting
member 200, but the present invention is not limited thereto, and
may be wired in a stepped manner, for example. Note that,
considering the intervals between the adjacent connecting lines
205b and between the adjacent connecting lines 206b, it is most
efficient to wire the elements obliquely.
[0076] Further, in this embodiment, as described later, the
material and the thickness of the attracting member 200 are
adjusted so that the attracting member 200 is shaped to sag
downward when the attracting member 200 approaches the sheet S.
Thus, the attracting member 200 has an appropriate elasticity
(flexibility).
[0077] Now, with reference to FIG. 8, a control system common to
the sheet feeding apparatus 51 and 52 according to this embodiment
is described. That is, as illustrated in FIG. 8, the sheet surface
height detection unit 302, the sheet leading edge detection sensors
51c and 52c, and the like are connected to the input ports of the
control unit 70. The elevating unit 301, the first driving unit
204, the second driving unit 203, the positive voltage supply unit
(power supply) 265a, the negative voltage supply unit (power
supply) 265b, and the like are connected to the output ports of the
control unit 70.
[0078] As illustrated in FIG. 2, the first nipping and conveying
outer roller 202b constructs a first nipping member configured to
nip the attracting member 200 together with the first nipping and
conveying inner roller (first rotary member) 202a. The second
nipping and conveying outer roller 201b constructs a second nipping
member configured to nip the attracting member 200 together with
the second nipping and conveying inner roller (second rotary
member) 201a. The control unit 70 illustrated in FIG. 8 constructs
a control unit configured to control the first driving unit 204 and
the second driving unit 203. The control unit 70 controls each of
the driving units 203 and 204 so as to provide a difference in
rotational speed between the second nipping and conveying inner
roller 201a and the first nipping and conveying inner roller 202a.
With this, the amount that the attracting member 200 sags downward
is increased. Thus, the sheet on the middle plate 301a (on the
stacking unit) is attracted to the attracting member 200, and then
the sheet attracted to the attracting member 200 can be fed while
the amount that the attracting member 200 sags downward is
decreased.
[0079] The sheet surface height detection unit 302 illustrated in
FIG. 2 and FIG. 8 detects the upper surface position of the sheet S
stacked on the middle plate 301a arranged in each of the cassettes
51a and 52a. The middle plate 301a constructs the stacking unit on
which the sheets S are to be stacked.
[0080] The sheet leading edge detection sensors 51c and 52c
illustrated in FIG. 1 and FIG. 8 detect the passage of the sheets S
fed respectively by the sheet attraction and separation feeding
units 51b and 52b. The sheet leading edge detection sensor 51c is
arranged in the sheet conveyance path between the sheet attraction
and separation feeding unit 51b and the pull-out roller pair 71.
Further, the sheet leading edge detection sensor 52c is arranged in
the sheet conveyance path between the sheet attraction and
separation feeding unit 52b and the pull-out roller pair 72. Then,
depending on whether or not the sheet leading edge detection sensor
51c or 52c detects the sheet S at a predetermined timing, whether
or not the sheet feeding has succeeded is detected. In this
embodiment, the sheet leading edge detection sensors 51c and 52c
are each a non-contact reflective photosensor, which is configured
to radiate spot-light to a detection target and measure the
reflected light amount, to thereby detect presence/absence of the
detection target.
[0081] The elevating unit 301 is actuated through control of the
control unit 70 so as to elevate the middle plate 301a on which the
sheets S are to be stacked and which is arranged to be elevatable
on each of the cassettes 51a and 52a. The elevating unit 301
changes the positions of the middle plate 301a and the uppermost
sheet among the sheets S stacked on the middle plate depending on
the pivoting angle of the lifter 301b pivotably arranged below the
middle plate 301a.
[0082] The second driving unit 203 includes a pulse motor or the
like, and is controlled by the control unit 70 to rotationally
drive the second nipping and conveying inner roller 201a. Further,
the first driving unit 204 includes a pulse motor or the like, and
is controlled by the control unit 70 to rotationally drive the
first nipping and conveying inner roller 202a.
[0083] Next, with reference to FIG. 4A to FIG. 4C, the principle of
generating the attracting force for attracting the sheet S by the
attracting member 200, the influence on the attracting force by the
residual charge on the surface of the attracting member 200, and
neutralization conditions for the surface of the attracting member
200 are described.
[0084] As illustrated in FIG. 4A, when a positive voltage and a
negative voltage are applied to the first electrode element 205 and
the second electrode element 206, respectively, a non-uniform
electric field is formed in the vicinity of the surface of the
attraction layer 200b of the attracting member 200 by the first and
second electrode elements 205 and 206 to which the voltages are
applied. Then, when the attracting member 200 having such a
non-uniform electric field formed thereon is caused to approach the
sheet S, dielectric polarization is caused on the surface layer of
the sheet S being a dielectric, and an electrostatic attracting
force is generated between the attracting member 200 and the sheet
S due to the Maxwell stress.
[0085] When the sheet S is separated from the attracting member 200
from the state of FIG. 4A, because the first and second electrode
elements 205 and 206 to which the voltages are applied are in a
state of still attracting the charges, as illustrated in FIG. 4B,
the charges remain on the surface of the attracting member 200. The
charges remaining on the surface of the attracting member 200 have
polarities opposite to those of the voltages applied to the first
and second electrode elements 205 and 206.
[0086] Therefore, even when the sheet S is attempted to be
attracted to the attracting member 200 again as illustrated in FIG.
4C, the voltages applied to the first and second electrode elements
205 and 206 are canceled by the charges remaining on the surface of
the attracting member 200. With this, the force of the attracting
member 200 to attract the sheet S is reduced. Therefore, after the
sheet S is once conveyed, it is necessary to neutralize the surface
of the attracting member 200 to prepare for the conveyance of the
next sheet S.
[0087] However, even when the surface of the attracting member 200
is attempted to be neutralized under a state in which the voltages
are still applied to the first and second electrode elements 205
and 206, charges are attracted to the first and second electrode
elements 205 and 206, and hence the surface of the attracting
member 200 cannot be neutralized in this state. When the surface of
the attracting member 200 is neutralized, it is necessary to stop
the voltage application to the first and second electrode elements
205 and 206.
[0088] Next, with reference to FIG. 5, the configuration for
feeding voltages to the first and second electrode elements 205 and
206 on the attracting member 200, and the configuration for
neutralizing the surface of the attracting member 200 are
described. Note that, FIG. 5 is a perspective view for illustrating
the configuration of the sheet attraction and separation feeding
unit 51b including the power feeding unit and the neutralization
unit.
[0089] As illustrated in FIG. 5, the power feeding brushes 260a and
260b respectively including brush portions 261a and 261b are
arranged in the vicinity of both ends of the attracting member 200
in the width direction. The brush portions 261a and 261b are
respectively arranged in contact with the first and second
electrode elements 205 and 206 in the power feeding sections
B.sub.1 of FIG. 3. Therefore, the voltages applied from the
positive voltage supply unit (power supply) 265a and the negative
voltage supply unit (power supply) 265b are respectively supplied
to the first and second electrode elements 205 and 206 through the
brush portions 261a and 261b of the power feeding brushes 260a and
260b.
[0090] In this case, the first and second electrode elements 205
and 206 include the offset sections B.sub.2 as illustrated in FIG.
3, and hence the voltages are applied to the first and second
electrode elements 205 and 206 in the attraction section B.sub.3
arranged on the downstream side with respect to the power feeding
brushes 260a and 260b. Note that, in this embodiment, a positive
voltage of about +1 kV is supplied from the positive voltage supply
unit (power supply) 265a, and a negative voltage of about -1 kV is
supplied from the negative voltage supply unit (power supply)
265b.
[0091] On the downstream side of the second nipping and conveying
roller pair 201, the neutralization roller pair 250 is arranged so
as to nip the attracting member 200. The neutralization outer
roller 250b is connected to the earth 255. Therefore, the residual
charges on the surface of the attracting member 200, which may
decrease the electrostatic attracting force for the sheet S, can be
removed through the neutralization outer roller 250b.
[0092] Further, the neutralization inner roller 250a includes a
load torque applying unit 251, which serves as a conveyance
resistance against the direction of conveying the attracting member
200. The load torque applying unit 251 constructs a tension
providing unit configured to provide a tension to the attracting
member 200 so that the contact pressures of the power feeding
brushes 260a and 260b to the power feeding electrodes 205a and 206a
arranged to be opposed to the power feeding brushes 260a and 260b
in the attracting member 200 can be maintained constant.
[0093] The neutralization roller pair 250 is rotated in association
with the conveyance of the attracting member 200, and hence the
neutralization roller pair 250 that is rotated in association with
the first nipping and conveying roller pair 202 is continuously
pulled by the attracting member 200. Therefore, a tension
corresponding to the load torque of the load torque applying unit
251 serving as the tension providing unit is provided to the
attracting member 200 between the first nipping and conveying
roller pair 202 and the neutralization roller pair 250, and hence
the contact between the attracting member 200 and the power feeding
brushes 260a and 260b becomes reliable.
[0094] Note that, the neutralization roller pair 250 constructs the
neutralization unit configured to nip the attracting member 200 in
a form of being extended in the width direction (arrow I direction
in FIG. 3) perpendicular to the peripheral direction (arrow H
direction in FIG. 3) of the attracting member 200. The load torque
applying unit 251 applies a load to the neutralization roller pair
250 (neutralization inner roller 250a thereof) so as to apply, to
the attracting member 200, a load in a direction opposite to the
rotating direction of the attracting member 200, to thereby provide
a tension to the power feeding electrodes 205a and 206a and the
connecting lines 205b and 206b.
[0095] Next, with reference to FIG. 6A to FIG. 6C and FIG. 7A to
FIG. 7C, the sheet separation feeding operation of the sheet
attraction and separation feeding unit 51b according to this
embodiment is described. Note that, FIG. 6A to FIG. 6C and FIG. 7A
to FIG. 7C are schematic views for illustrating the operation of
feeding the sheet S by the sheet attraction and separation feeding
unit 51b in time series. The operation of feeding the sheet S
includes, in the order in time series, as illustrated in FIG. 6A to
FIG. 6C and FIG. 7A to FIG. 7C, six steps of an initial operation,
an approaching operation, a contact length increasing operation, an
attracting operation, a separating operation, and a conveying
operation.
[0096] Now, those steps are described in order. Note that, in this
embodiment, in each of the above-mentioned operation steps, as
described later, voltages are continuously applied from the
positive voltage supply unit 265a and the negative voltage supply
unit 265b to the power feeding brushes 260a and 260b, and the
attracting force is constantly generated on the attracting member
200. Further, the second driving unit 203 and the first driving
unit 204 illustrated in FIG. 2 may be each constructed by a stepper
motor. The driving unit can be rotated at a predetermined number of
steps, and then the process can transition to the next operation
step.
[0097] The initial operation illustrated in FIG. 6A is an operation
of arranging the attracting member 200 to a feeding operation
initial position. In this embodiment, the sag of the attracting
member 200 is collected between the second nipping and conveying
roller pair 201 and the neutralization roller pair 250. For setting
of the initial state, the second nipping and conveying roller pair
201 is rotated at a speed faster than that of the first nipping and
conveying roller pair 202 in the arrow R direction, and the sag of
the attracting member 200 is fed to the downstream side with
respect to the second nipping and conveying roller pair 201.
[0098] As described above, the neutralization inner roller 250a
includes the load torque applying unit 251 as illustrated in FIG.
5, which serves as the conveyance resistance against the direction
of conveying the attracting member 200. The sag of the attracting
member 200 is not fed to the downstream side by the neutralization
roller pair 250, and hence can be collected between the second
nipping and conveying roller pair 201 and the neutralization roller
pair 250.
[0099] In this case, the first nipping and conveying roller pair
202 may be rotated or stopped. When the initial operation is
completed, the distance between the uppermost sheet Sa and the
attracting member 200 is in a state of being separated by the air
gap Lr between the uppermost sheet Sa and the first nipping and
conveying inner roller 202a. The second nipping and conveying
roller pair 201 and the first nipping and conveying roller pair 202
may transition to the next operation under a state of being
continuously rotated from the initial operation, or may transition
to the next operation after stopping the rotation once.
[0100] The approaching operation illustrated in FIG. 6B is an
operation of deforming the attracting member 200 so as to sag
downward so that the attracting surface side of the attracting
member 200 approaches the uppermost sheet Sa. The second nipping
and conveying roller pair 201 and the first nipping and conveying
roller pair 202 are rotated in the arrow R direction to convey the
attracting member 200. In this case, the first nipping and
conveying roller pair 202 is rotated faster than the second nipping
and conveying roller pair 201 to deform the attracting member 200
so that the lower side thereof sags. In this case, the second
nipping and conveying roller pair 201 may be rotated or stopped.
The attracting member 200 is deformed as described above so that
the surface of the attracting member 200 is brought into contact
with the uppermost sheet Sa.
[0101] The contact length increasing operation illustrated in FIG.
6C is an operation of continuing the above-mentioned approaching
operation to bring the surface of the attracting member 200 into
contact with the uppermost sheet Sa, and further increasing a
contact length Mc. In this embodiment, similarly to the approaching
operation, the first nipping and conveying roller pair 202 is
rotated faster than the second nipping and conveying roller pair
201 in the arrow R direction, to thereby increase the contact
length Mc. Voltages are constantly applied from the positive
voltage supply unit 265a and the negative voltage supply unit 265b
to the attracting member 200, and as illustrated in FIG. 6C, the
contact length Mc is included in the attracting position (position
represented by C). Therefore, the electrostatic attracting force
acts between the attracting member 200 and the uppermost sheet
Sa.
[0102] However, when the contact length Mc is smaller than a
predetermined length, the force of the attracting member 200 to
attract the uppermost sheet Sa is also small, and hence the force
cannot overcome the conveyance resistance acting on the uppermost
sheet Sa. Therefore, the contact length increasing operation is
continued while keeping the uppermost sheet Sa received in the
cassette 51a.
[0103] The attracting operation illustrated in FIG. 7A is an
operation of, after the upper surface of the uppermost sheet Sa and
the surface of the attracting member 200 are brought into surface
contact with each other with a predetermined contact length Mn,
starting conveyance of the uppermost sheet Sa by the attracting
member 200. When the contact length becomes Mn and the conveyance
force for the uppermost sheet Sa is increased after the
above-mentioned contact length increasing operation is continued,
the conveyance force overcomes the conveyance resistance to start
the conveyance of the uppermost sheet Sa. In this case, the
attracting position (position represented by C in FIG. 6C) formed
in the attracting member 200 by the voltages applied from the
positive voltage supply unit 265a and the negative voltage supply
unit 265b is set to a length that includes the entire contact
length Mn.
[0104] The separating operation illustrated in FIG. 7B is an
operation of raising the uppermost sheet Sa attracted to the
attracting member 200 to separate the uppermost sheet Sa from a
sheet Sb positioned thereunder. In the separating operation, the
second nipping and conveying roller pair 201 is rotated at a speed
faster than that of the first nipping and conveying roller pair 202
in the arrow R direction. With this, the sag of the surface of the
attracting member 200 opposed to the uppermost sheet Sa is fed to
the downstream side with respect to the second nipping and
conveying roller pair 201.
[0105] Further, the load torque applying unit 251 on the shaft of
the neutralization inner roller 250a serves as a resistance against
the direction of conveying the attracting member 200, and hence the
neutralization roller pair 250 rotated in association with the
first nipping and conveying roller pair 202 is continuously pulled
by the attracting member 200. In other words, a tension is
constantly provided to the attracting member 200 between the first
nipping and conveying roller pair 202 and the neutralization roller
pair 250, and the sag of the attracting member 200 is collected
between the second nipping and conveying roller pair 201 and the
neutralization roller pair 250.
[0106] As a result, the sag of the surface of the attracting member
200 opposed to the uppermost sheet Sa is eliminated and the
attracting member 200 is elastically deformed into a substantially
linear shape. Thus, the uppermost sheet Sa attracted to the
attracting member 200 is raised to be separated from the sheet Sb
positioned thereunder. In this case, when the speed difference
between the second nipping and conveying roller pair 201 and the
first nipping and conveying roller pair 202 is small, the leading
edge of the uppermost sheet Sa reaches the downstream side with
respect to the attracting position (position of reference symbol
C), which causes peeling of the leading edge of the uppermost sheet
Sa from the attracting member 200.
[0107] For example, when there is no speed difference between the
second nipping and conveying roller pair 201 and the first nipping
and conveying roller pair 202, the sheet Sa is conveyed while the
attracting member 200 is still in a sagging state as illustrated in
FIG. 7A. Then, the leading edge of the uppermost sheet Sa departs
from the attracting position (position of reference symbol C)
before reaching the position of the second nipping and conveying
roller pair 201, and hence the leading edge of the uppermost sheet
Sa is peeled from the attracting member 200. Therefore, it is
necessary to set the speed difference so that, before the leading
edge of the uppermost sheet Sa reaches the second nipping and
conveying roller pair 201, the sag of the surface of the attracting
member 200 opposed to the uppermost sheet Sa is eliminated to
obtain a substantially linear shape. In this manner, the attracting
position (position of reference symbol C) can surely include a
length Ms in which the attracting member 200 and the uppermost
sheet Sa are brought into contact with each other.
[0108] The conveying operation illustrated in FIG. 7C is an
operation of conveying the attracting member 200 whose attracting
surface for the uppermost sheet Sa has deformed into a
substantially linear shape, to thereby attract the uppermost sheet
Sa and feed the attracted uppermost sheet Sa to the pull-out roller
pair 71 on the sheet feeding downstream. In this operation, the
rotational speeds of the second nipping and conveying roller pair
201 and the first nipping and conveying roller pair 202 are set to
substantially match with each other, to thereby convey the
attracting member 200 having the uppermost sheet Sa attracted
thereto while maintaining the substantially linear shape of the
attracting surface side.
[0109] In this case, the attracting position (position of reference
symbol C) formed in the attracting member 200 by the voltages
applied from the positive voltage supply unit 265a and the negative
voltage supply unit 265b surely includes a region between the
second nipping and conveying roller pair 201 and the first nipping
and conveying roller pair 202. With this, the elimination of the
attracting force at the leading edge of the uppermost sheet Sa is
prevented, to thereby prevent the peeling of the leading edge of
the uppermost sheet Sa from the attracting member 200.
[0110] With this, the uppermost sheet Sa is conveyed while being
attracted to the attracting member 200 and maintaining a state in
which at least the leading edge portion is separated from the sheet
Sb positioned thereunder. After that, when the leading edge of the
uppermost sheet Sa arrives at the vicinity of the curved portion of
the attracting member 200 formed by the second nipping and
conveying inner roller 201a, the leading edge of the uppermost
sheet Sa is peeled off from the attracting member 200.
[0111] This peel-off occurs because the bending reactive force of
the sheet Sa becomes larger than the electrostatic attracting force
generated in the attracting member 200. In other words, in this
embodiment, the magnitude of the electrostatic attracting force
generated in the attracting member 200 is set so as to attract the
sheet with a force smaller than the bending reactive force of the
sheet Sa. That is, with this conveying operation, the attracting
member 200 moves to a position at which the uppermost sheet Sa is
separated (separating position).
[0112] Note that, after the leading edge is peeled off from the
attracting member 200 as described above, the uppermost sheet Sa is
increasingly peeled off from the leading edge, but the trailing
edge region of the sheet Sa is attracted by the attracting member
200. With this, the sheet Sa is continuously conveyed by the
attracting member 200, and through the leading edge detection at
the sheet leading edge detection sensor 51c, the sheet Sa is passed
to the pull-out roller pair 71. In a part of the attracting member
200 from which the sheet Sa is peeled off, a residual charge region
E is generated.
[0113] The residual charge region E reaches the neutralization
roller pair 250 through continuous conveyance of the attracting
member 200. Even under a state in which voltages for attracting the
sheet Sa to the attracting member 200 are applied, at the position
of the neutralization roller pair 250 arranged outside of the
attracting position (position of reference symbol C), no electric
field is generated to inhibit the neutralization. Therefore, even
under a state in which the sheet S is fed, the neutralization of
the residual charge region E on the surface of the attracting
member 200 can be executed by the neutralization outer roller
250b.
[0114] In this case, when the sheet Sa is not detected within a
predetermined time period by the sheet leading edge detection
sensor 51c, the control unit 70 (FIG. 1 and FIG. 8) determines that
an error is caused in the feeding operation of the sheet Sa, and
the feeding operation is started over again from the approaching
operation (FIG. 6B).
[0115] With the above-mentioned six steps, only the one uppermost
sheet Sa among the plurality of sheets S stacked on the cassette
51a is fed. Then, the six steps are repeated to enable continuous
feeding of the sheets S one by one.
[0116] In this case, the voltages are continuously applied to the
first and second electrode elements 205 and 206, but the present
invention is not limited to this state. In the initial operation,
the voltage supply may be stopped, and the voltages may be applied
after the attracting member 200 and the uppermost sheet Sa are
brought into contact with each other. The operation steps are
managed with the number of rotation steps of the driving units 203
and 204, but the present invention is not limited to this method.
Such a method that the speeds of the nipping and conveying roller
pairs 201 and 202 are controlled while detecting the shape of the
attracting member 200 or the timing of attraction of the uppermost
sheet Sa may be employed.
[0117] Further, in FIG. 3 and FIG. 5, the first and second
electrode elements 205 and 206 are illustrated in sizes that assist
the description, but the actual dimensions are set as follows.
First, the length necessary for the attracting position (position
of reference symbol C) in FIG. 6A to FIG. 6C and FIG. 7A to FIG. 7C
is determined.
[0118] In this case, the attracting position is set to have a
length that substantially matches with the distance between the
second nipping and conveying inner roller 201a and the first
nipping and conveying inner roller 202a (D.sub.1 in FIG. 2). Then,
the length of the attracting position (position of reference symbol
C) and an offset amount L.sub.1 of the first electrode element 205
in the offset section B.sub.2 of FIG. 3 are set to substantially
match with each other. Further, the length of the attracting
position (position of reference symbol C) and the length of the
power feeding brushes 260a and 260b along the attracting member 200
are also set to substantially match with each other. With this,
during the conveying operation illustrated in FIG. 7C, the
electrostatic attracting force can be generated from the vicinity
of the region directly below the first nipping and conveying roller
pair 202 to the vicinity of the second nipping and conveying roller
pair 201.
[0119] Further, the voltages are not supplied to the first and
second electrode elements 205 and 206 located at the position of
the neutralization roller pair 250, and hence the residual charges
on the surface of the attracting member 200, which may decrease the
sheet attracting force, can be reliably removed by the
neutralization roller pair 250.
[0120] With the above-mentioned configuration, it is possible to
provide the sheet feeding apparatus 51 and capable of reliably and
smoothly executing the operation steps illustrated in FIG. 6A to
FIG. 6C and FIG. 7A to FIG. 7C.
[0121] In the above-mentioned embodiment, even under a state in
which the voltages for attracting the sheet S to the attracting
member 200 are continuously applied, the residual charges on the
attracting member 200 can be reliably removed, and hence the
neutralization can be executed in parallel while feeding the sheet
without reducing the throughput.
[0122] In this embodiment, with the electrode configuration capable
of feeding power to the attracting member 200 regardless of the
shape of the sheet attracting surface and capable of partially
generating the electrostatic attracting force, the feeding of the
sheet and the neutralization can be executed in parallel. Further,
sheet feeding with reduced noise is possible without reducing the
throughput of printing. As described above, without control of
switching between power feeding and neutralization, the attracting
member 200 can constantly maintain the electrostatic attracting
force at the attracting position corresponding to the sheet S, and
the generation of the electrostatic attracting force and the
neutralization are both enabled to enable sheet feeding without
reducing the productivity.
Second Embodiment
[0123] Next, a second embodiment of the present invention is
described with reference to FIG. 9 and FIG. 10. FIG. 9 is a
sectional view for illustrating a sheet feeding apparatus according
to this embodiment, and FIG. 10 is a perspective view for
illustrating the sheet feeding apparatus. Note that, in this
embodiment, the same members as the first embodiment are denoted by
the same reference symbols, and description of members having the
same configuration and function is omitted herein.
[0124] This embodiment differs from the first embodiment in that,
in order to reliably bring the attracting member 200 and the power
feeding brushes 260a and 260b into contact with each other, a plate
member 252 is arranged instead of the load torque applying unit 251
(see FIG. 5) in the first embodiment. Note that, the principle of
generating the electrostatic attracting force for attracting the
sheet S to the attracting member 200, and the conditions for
removing the residual charges on the surface of the attracting
member 200 are the same as those described in the first embodiment.
Further, the sheet separation feeding operation by the sheet
feeding apparatus 51 can be executed in a sequence similar to that
in the first embodiment.
[0125] As illustrated in FIG. 9 and FIG. 10, the configuration for
reliably feeding power to the attracting member 200 includes the
plate member 252 on the opposite side to the power feeding brushes
260a and 260b across the attracting member 200. The plate member
252 constructs the tension providing unit arranged on the inner
peripheral side of the attracting member 200 and configured to
press the power feeding electrodes 205a and 206a to the power
feeding brushes 260a and 260b.
[0126] The attracting member 200 in this embodiment is brought into
pressure-contact with the plate member 252 through the spring
performance of the brush portions 261a and 261b of the power
feeding brushes 260a and 260b. The surface of the plate member 252
is subjected to low frictional processing, and the plate member 252
is configured so as not to be a large conveyance resistance when
the attracting member 200 is conveyed by the second nipping and
conveying roller pair 201 and the first nipping and conveying
roller pair 202.
[0127] In this embodiment having the above-mentioned configuration,
it is possible to reliably bring the power feeding brushes 260a and
260b into contact with the power feeding electrodes 205a and 206a
of the first and second electrode elements 205 and 206 on the
attracting member 200. As described above, with a simpler
configuration, the attracting member 200 and the power feeding
brushes 260a and 260b can be reliably brought into contact with
each other, and the attraction of the sheet S to the attracting
member 200 and the neutralization of the surface of the attracting
member 200 can be executed in parallel.
Third Embodiment
[0128] Next, a third embodiment of the present invention is
described with reference to FIG. 11 to FIG. 14. FIG. 11 is a plan
view for illustrating a configuration of an attracting member
according to this embodiment, and FIG. 12 is a perspective view for
illustrating a configuration for feeding power to the attracting
member. FIG. 13 is a perspective view for illustrating a sheet
feeding apparatus according to this embodiment, and FIG. 14 is a
sectional view for illustrating the sheet feeding apparatus. Note
that, in this embodiment, the same members as the first embodiment
are denoted by the same reference symbols, and description of
members having the same configuration and function is omitted
herein.
[0129] This embodiment differs from the first embodiment mainly in
the configuration of the attracting member 200 and the
configuration of the power feeding unit. That is, the attracting
member 200 in this embodiment includes, as in FIG. 11 for
illustrating the stretched attracting member 200 viewed from the
inner peripheral side, the base layer 200a, a back surface layer
200c, and the first and second electrode elements 205 and 206. The
first and second electrode elements 205 and 206 arranged on the
base layer 200a each have parts corresponding to the power feeding
section B.sub.1 and the attraction section B.sub.3. The parts of
the first and second electrode elements 205 and 206 corresponding
to the attraction section B.sub.3 are arranged alternately into a
pectinate shape, similarly to the first embodiment.
[0130] The power feeding electrodes 205a and 206a are each set to
have such a length that the attracting force generation electrodes
205c and 206c moving from the attracting position (C of FIG. 6C)
toward the neutralization roller pair 250 are separated from the
power feeding rollers 202d and 202e serving as the power feeding
units before reaching the neutralization roller pair 250. With
this, the attracting force generation electrodes 205c and 206c
located at the attracting position can be set into a floating state
by reliably stopping power feeding thereto before reaching the
neutralization roller pair 250, and the charges can be removed
under this state.
[0131] The power feeding electrodes 205a and 206a corresponding to
the respective power feeding sections B.sub.1 at both end portions
in the width direction are respectively arranged in a collective
manner in the vicinity of both the end portions of the attracting
member 200 in the width direction. Further, the power feeding
electrodes 205a and 206a are wired to be oblique to the width
direction of the attracting member 200.
[0132] As described above, the power feeding electrodes 205a and
206a of this embodiment are configured to have also the role of the
connecting lines 205b and 206b in the first embodiment and the
second embodiment.
[0133] In this embodiment described above, in the first and second
electrode elements 205 and 206, at least the power feeding
electrodes 205a and 206a are exposed on the inner peripheral
surface of the attracting member 200. Then, the power feeding
rollers 202d and 202e serving as the power feeding units also serve
as the first nipping and conveying inner roller (first rotary
member) 202a, and are brought into contact with the power feeding
electrodes 205a and 206a exposed on the inner peripheral surface to
feed power. Note that, in this embodiment, the power feeding
rollers 202d and 202e also serve as the first nipping and conveying
inner roller 202a, but the present invention is not limited
thereto, and the power feeding rollers 202d and 202e may be
configured to also serve as the second nipping and conveying inner
roller (second rotary member) 201a.
[0134] With such a configuration, in the power feeding sections
B.sub.1, different voltages are respectively applied to the first
and second electrode elements 205 and 206 from the power feeding
rollers 202d and 202e arranged on the back surface. In the
attraction section B.sub.3, the electrostatic force can be
generated at a position shifted in the peripheral direction (arrow
H direction in FIG. 11) of the attracting member 200 with respect
to the power feeding position. Note that, in this embodiment, the
base layer 200a is made of polyimide that is a dielectric having a
volume resistivity of 10.sup.8 0 cm or more, and the layer
thickness thereof is set to about 100 .mu.m. Further, the first and
second electrode elements 205 and 206 are each made of a conductor
having a volume resistivity of 10.sup.6 .OMEGA.cm or less, and
copper having a layer thickness of about 10 .mu.m is used as this
conductor.
[0135] As described also in the first embodiment, in this
embodiment as well, the material and the thickness of the
attracting member 200 are adjusted so that the attracting member
200 is shaped to sag downward when the attracting member 200
approaches the sheet S. Thus, the attracting member 200 has an
appropriate elasticity. Further, the principle of generating the
electrostatic attracting force for attracting the sheet S to the
attracting member 200, and the conditions for removing the residual
charges on the surface of the attracting member 200 are the same as
those described in the first embodiment.
[0136] Next, with reference to FIG. 12 and FIG. 13, the
configuration of feeding voltages to the first and second electrode
elements 205 and 206 on the attracting member 200 is described in
detail. FIG. 12 is a perspective view for illustrating the power
feeding units from the inner peripheral side of the attracting
member 200, and FIG. 13 is a perspective view for illustrating the
configuration of the sheet attraction and separation feeding unit
51b.
[0137] As illustrated in FIG. 12, the power feeding rollers 202d
and 202e are arranged coaxially with the first nipping and
conveying inner roller 202a, and leaf-spring power feeding members
270a and 270b are brought into pressure-contact with the power
feeding rollers 202d and 202e, respectively. The leaf-spring power
feeding members 270a and 270b are respectively connected to the
positive voltage supply unit (power supply) 265a and the negative
voltage supply unit (power supply) 265b. Therefore, the voltages
from the positive voltage supply unit 265a and the negative voltage
supply unit 265b are supplied to the power feeding rollers 202d and
202e through the leaf-spring power feeding members 270a and 270b,
respectively.
[0138] The power feeding rollers 202d and 202e are arranged so as
to be respectively brought into contact with at least the power
feeding electrodes 205a and 206a of the first and second electrode
elements 205 and 206 in the power feeding sections B.sub.1
illustrated in FIG. 11. Therefore, the voltages from the positive
voltage supply unit 265a and the negative voltage supply unit 265b
are reliably supplied to the first and second electrode elements
205 and 206 through the power feeding rollers 202d and 202e.
[0139] In this case, in the first and second electrode elements 205
and 206, as illustrated in FIG. 11, the power feeding electrodes
205a and 206a in the power feeding sections B.sub.1 are wired to be
oblique to the width direction (arrow I direction of FIG. 11).
Therefore, voltages are reliably applied to the attracting force
generation electrodes 205c and 206c in the attraction section
B.sub.3 arranged on the downstream side with respect to the power
feeding rollers 202d and 202e. Note that, in this embodiment, a
positive voltage of about +1 kV is supplied from the positive
voltage supply unit 265a, and a negative voltage of about -1 kV is
supplied from the negative voltage supply unit 265b.
[0140] In this embodiment described above, the attracting member
200 is nipped between the first nipping and conveying outer roller
202b and the first nipping and conveying inner roller 202a (power
feeding rollers 202d and 202e). With this configuration, even
without the load torque applying unit 251 or the like described in
the first embodiment, the voltages from the positive voltage supply
unit 265a and the negative voltage supply unit 265b can be reliably
supplied to the first and second electrode elements 205 and
206.
[0141] As illustrated in FIG. 13, on the downstream side of the
second nipping and conveying roller pair 201, the neutralization
roller pair 250 is arranged so as to nip the attracting member 200
by the neutralization inner roller 250a and the neutralization
outer roller 250b of the neutralization roller pair 250. The
neutralization roller pair 250 is rotated in association with the
conveyed and moved attracting member 200. The neutralization outer
roller 250b is connected to the earth 255.
[0142] In this case, FIG. 11 to FIG. 13 are illustrated in sizes
that assist the description, but the actual dimensions are set as
follows.
[0143] First, the length necessary for the attracting position
(position of reference symbol C) in FIG. 14 is determined. In this
case, the attracting position is set to have a length that
substantially matches with the distance (D.sub.1 in FIG. 14)
between the second nipping and conveying inner roller 201a and the
first nipping and conveying inner roller 202a. Then, the length of
the attracting position (position of reference symbol C) and an
offset amount L.sub.2 of the first and second electrode elements
205 and 206 in the power feeding sections B.sub.1 of FIG. 11 are
set to substantially match with each other.
[0144] In this manner, the voltages are not supplied to the first
and second electrode elements 205 and 206 located at the position
of the neutralization roller pair 250, and hence the residual
charges on the surface of the attracting member 200, which may
decrease the sheet attracting force, can be reliably removed by the
neutralization roller pair 250. With the above-mentioned
configuration, in a sequence similar to the operation steps
illustrated in FIG. 6A to FIG. 6C and FIG. 7A to FIG. 7C of the
first embodiment, the sheet separation feeding operation by the
sheet feeding apparatus 51 is enabled.
[0145] As described above, even when the power feeding rollers 202d
and 202e are used to configure simpler power feeding units, the
generation of the electrostatic force for attracting the sheet S to
the attracting member 200 and the neutralization of the surface of
the attracting member 200 can be executed in parallel. With this,
the sheet can be fed without reducing the throughput.
Fourth Embodiment
[0146] Subsequently, a fourth embodiment of the present invention
is described. Note that, the same configurations as the third
embodiment are denoted by the same reference symbols, and detailed
description thereof is omitted herein. This embodiment differs from
the third embodiment in the electrode shape of the attracting
member 200.
[0147] With reference to FIG. 15, the configuration of the
attracting member 200 is described. FIG. 15 is a view for
illustrating the stretched attracting member 200 viewed from the
inner peripheral side, and the attracting member 200 includes the
base layer 200a, the back surface layer 200c, and the first and
second electrode elements 205 and 206. The first and second
electrode elements 205 and 206 arranged on the base layer 200a each
have parts corresponding to the power feeding section B.sub.1 and
the attraction section B.sub.3. The parts of the first and second
electrode elements 205 and 206 corresponding to the attraction
section B.sub.3 are arranged alternately into a pectinate shape,
similarly to the third embodiment.
[0148] The length of each of the power feeding electrodes 205a and
206a is set as follows. That is, the power feeding electrodes 205a
and 206a are each set to have such a length that the attracting
force generation electrodes 205c and 206c moving from the
attracting position (C of FIG. 6C) toward the neutralization roller
pair 250 are separated from the power feeding rollers 202d and 202e
(see FIG. 12) before reaching the neutralization roller pair 250
(see FIG. 14). With this, the attracting force generation
electrodes 205c and 206c located at the attracting position can be
set into a floating state by reliably stopping power feeding
thereto before reaching the neutralization roller pair 250, and the
charges can be removed under this state. The power feeding
electrodes 205a and 206a corresponding to the respective power
feeding sections B.sub.1 at both the end portions in the width
direction are respectively arranged in a collective manner in the
vicinity of both the end portions of the attracting member 200 in
the width direction. Further, the power feeding electrodes 205a and
206a are wired to be oblique to the width direction of the
attracting member 200.
[0149] Note that, in the third embodiment, the attracting force
generation electrodes 205c and 206c in the attraction section
B.sub.3 are all independent of each other. However, in this
embodiment, under a state in which each four of the attracting
force generation electrodes 205c are electrically conducted with
each other and each four of the attracting force generation
electrodes 206c are electrically conducted with each other, the
four attracting force generation electrodes 205c are connected to
one power feeding electrode 205a in the power feeding section
B.sub.1 and the four attracting force generation electrodes 206c
are connected to one power feeding electrode 206a in the power
feeding section B.sub.1. That is, under a state in which each
plurality of the attracting force generation electrodes 205c in
this embodiment are electrically conducted with each other and each
plurality of the attracting force generation electrodes 206c in
this embodiment are electrically conducted with each other, the
plurality of the attracting force generation electrodes 205c are
connected to corresponding one of the power feeding electrodes 205a
and the plurality of the attracting force generation electrodes
206c are connected to corresponding one of the power feeding
electrodes 206a. Note that, this configuration can be similarly
implemented in the above-mentioned first to third embodiments.
[0150] In the respective power feeding sections B.sub.1 of the
first and second electrode elements 205 and 206, the power feeding
electrodes 205a and 206a are respectively wired in a collective
manner in the vicinity of both the end portions of the attracting
member 200. Then, the power feeding electrodes 205a and 206a are
wired to be oblique to the width direction of the attracting member
200. Further, the back surface of the attracting member 200 is
covered with the back surface layer 200c, and only a part of the
power feeding section B.sub.1 is exposed on the back surface.
[0151] In this embodiment described above, it is not necessary to
wire the power feeding electrodes 205a and 206a in a collective
manner at narrow intervals in the power feeding sections B.sub.1,
and the wiring of the power feeding electrodes 205a and 206a is
extremely facilitated. Even with this configuration, the
electrostatic force can be generated at a position shifted in the
peripheral direction (arrow H direction) of the attracting member
200 with respect to the power feeding position.
[0152] Also in this embodiment, similarly to the third embodiment,
the power feeding electrodes 205a and 206a are configured to have
also the role of the connecting lines 205b and 206b in the first
and second embodiments.
[0153] Note that, in this embodiment, each four of the attracting
force generation electrodes 205c are conducted to corresponding one
of the power feeding electrodes 205a and each four of the
attracting force generation electrodes 206c are conducted to
corresponding one of the power feeding electrodes 206a, but the
present invention is not limited thereto. That is, it is sufficient
that at least two of the attracting force generation electrodes
205c be conducted to corresponding one of the power feeding
electrodes 205a and at least two of the attracting force generation
electrodes 206c be conducted to corresponding one of the power
feeding electrodes 206a. In this case, effects similar to the above
can be obtained.
[0154] Also in this embodiment, the principle of generating the
electrostatic attracting force for attracting the sheet S to the
attracting member 200, and the conditions for removing the residual
charges on the surface of the attracting member 200 are the same as
those described in the third embodiment. Further, the sheet
separation feeding operation by the sheet feeding apparatus 51 and
52 can be executed in a sequence similar to that in the first
embodiment.
[0155] As described above, even with the configuration of this
embodiment in which the electrode configuration of the attracting
member 200 is simpler, the generation of the electrostatic force
for attracting the sheet S to the attracting member 200 and the
neutralization of the surface of the attracting member 200 can be
executed in parallel. With this, the sheet can be fed without
reducing the throughput.
REFERENCE SIGNS LIST
[0156] 51, 52 sheet feeding apparatus [0157] 55 image forming unit
[0158] 70 control unit [0159] 100 image forming apparatus [0160]
200 attracting member [0161] 201a second nipping and conveying
inner roller (second rotary member) [0162] 201b second nipping and
conveying outer roller (second nipping member) [0163] 202a first
nipping and conveying inner roller (first rotary member) [0164]
202b first nipping and conveying outer roller (first nipping
member) [0165] 202d, 202e power feeding roller (power feeding unit)
[0166] 203, 204 second driving unit, first driving unit [0167] 205,
206 first electrode element, second electrode element [0168] 205a,
206a power feeding electrode [0169] 205b, 206b connecting line
[0170] 205c, 206c attracting force generation electrode [0171] 250
neutralization roller pair (neutralization unit) [0172] 251 load
torque applying unit (tension providing unit) [0173] 252 plate
member (tension providing unit) [0174] 260a, 260b power feeding
brush (power feeding unit) [0175] 301a middle plate (stacking unit)
[0176] C attracting position [0177] S sheet
[0178] 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.
[0179] This application claims the benefit of Japanese Patent
Application No. 2014-169230, filed Aug. 22, 2014, which is hereby
incorporated by reference herein in its entirety.
* * * * *