US20170174455A1

US20170174455A1 - Sheet feeding apparatus and image forming apparatus

Info

Publication number: US20170174455A1
Application number: US15/118,179
Authority: US
Inventors: Takaaki Aoyagi; Yasumi Yoshida; Takeshi Aoyama; Takashi Hiratsuka; Isao Hayashi; Hisae Shimizu
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2014-08-22
Filing date: 2015-08-17
Publication date: 2017-06-22
Also published as: WO2016027449A1; JP2016044028A

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.

Description

TECHNICAL FIELD

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

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.
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.
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

PTL 1: Japanese Patent Application Laid-Open No. 2012-140224
PTL 2: Japanese Patent Application Laid-Open No. H06-255823
PTL 3: Japanese Patent Application Laid-Open No. 2001-48370
PTL 4: Japanese Patent Application Laid-Open No. 2000-247474

SUMMARY OF INVENTION

Technical Problem

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.
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.
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.
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.
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

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.
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

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

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.

FIG. 2 is an illustration of the configuration of the above-mentioned sheet feeding apparatus.

FIG. 3 is an illustration of a configuration of an attracting member according to the first embodiment.

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.

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.

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.

FIG. 5 is an illustration of the above-mentioned sheet feeding apparatus.

FIG. 6A is a sectional view for illustrating an operation of the sheet feeding apparatus according to the first embodiment in time series.

FIG. 6B is a sectional view for illustrating the operation of the sheet feeding apparatus according to the first embodiment in time series.

FIG. 6C is a sectional view for illustrating the operation of the sheet feeding apparatus according to the first embodiment in time series.

FIG. 7A is a sectional view for illustrating the operation of the sheet feeding apparatus according to the first embodiment in time series.

FIG. 7B is a sectional view for illustrating the operation of the sheet feeding apparatus according to the first embodiment in time series.

FIG. 7C is a sectional view for illustrating the operation of the sheet feeding apparatus according to the first embodiment in time series.

FIG. 8 is an illustration of a control block diagram of the sheet feeding apparatus according to the first embodiment.

FIG. 9 is a sectional view for illustrating a sheet feeding apparatus according to a second embodiment of the present invention.

FIG. 10 is a perspective view for illustrating the sheet feeding apparatus according to the second embodiment.

FIG. 11 is a plan view for illustrating a configuration of an attracting member according to a third embodiment of the present invention.

FIG. 12 is a perspective view for illustrating a configuration for feeding power to the attracting member according to the third embodiment.

FIG. 13 is a perspective view for illustrating a sheet feeding apparatus according to the third embodiment.

FIG. 14 is a sectional view for illustrating a sheet feeding apparatus according to the third embodiment.

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

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.
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.
Note that, the original from which an image is read is conveyed onto the platen glass by an automatic original feeding apparatus 41 a. 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.
The image forming unit 55 includes an exposure unit 42, and four process cartridges 43 (43 y, 43 m, 43 c, and 43 k) 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.
In this case, the process cartridges 43 include photosensitive drums 21 (21 y, 21 m, 21 c, and 21 k), charging rollers 22 (22 y, 22 m, 22 c, and 22 k), and developing rollers 23 (23 y, 23 m, 23 c, and 23 k). The process cartridges 43 also include drum cleaning blades (24 y, 24 m, 24 c, and 24 k).
The intermediate transfer unit 44 includes an intermediate transfer belt 25 stretched by a belt driving roller 26, a secondary transfer inside roller 56 a, and the like, and primary transfer rollers 27 (27 y, 27 m, 27 c, and 27 k) 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.
The secondary transfer unit 56 includes the secondary transfer inside roller 56 a and a secondary transfer outside roller 56 b that is brought into contact with the secondary transfer inside roller 56 a across the intermediate transfer belt 25. Then, as described later, a positive secondary transfer bias is applied to the secondary transfer outside roller 56 b, to thereby transfer the full four-color image formed on the intermediate transfer belt 25 onto the sheet S.
The fixing unit 57 includes a fixing roller 57 a and a fixing backup roller 57 b. Then, the sheet S is nipped and conveyed between the fixing roller 57 a and the fixing backup roller 57 b, 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 51 a and 52 a configured to receive the sheets S, and sheet attraction and separation feeding units 51 b and 52 b having a function of feeding the sheets S received in the cassettes 51 a and 52 a one by one while attracting the sheets S by static electricity.
Note that, in FIG. 1, through a pre-secondary transfer conveyance path 103, the sheets S fed from the cassettes 51 a and 52 a 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.
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.
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.
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 51 b and 52 b to separate and feed only one sheet S from each of the cassettes 51 a and 52 a. When the sheet S is fed from the sheet feeding apparatus 51, the sheet S is detected by a sheet leading edge detection sensor 51 c and arrives at a pull-out roller pair 71 including pull-out rollers 51 d and 51 e. 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 52 c and arrives at a pull-out roller pair 72 including pull-out rollers 52 d and 52 e. 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 62 a and 62 b, to thereby adjust the position of the leading edge (skew feed correction).
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 56 b.
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)

Now, the sheet attraction and separation feeding units 51 b and 52 b 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 51 b in the sheet feeding apparatus 51 is mainly described. The sheet attraction and separation feeding unit 52 b in the sheet feeding apparatus 52 has a similar configuration, and hence description thereof is omitted herein.
As described above, the sheet feeding apparatus 51 includes the cassette 51 a, and the sheet attraction and separation feeding unit 51 b configured to feed the sheets S received in the cassette 51 a 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 301 a serving as a stacking unit on which the sheets are to be stacked and which is arranged to be elevatable on the cassette 51 a, and the sheet leading edge detection sensor 51 c configured to detect the passage of the sheet fed by the sheet attraction and separation feeding unit 51 b.
The elevating unit 301 (see FIG. 8) includes a lifter 301 b pivotably arranged below the middle plate 301 a, and the positions of the middle plate 301 a and an uppermost sheet Sa stacked on the middle plate 301 a are changed depending on the pivoting angle of the lifter 301 b. The sheet leading edge detection sensor 51 c (see FIG. 8) is arranged in the sheet conveyance path between the sheet attraction and separation feeding unit 51 b and the pull-out roller pair 71 (see FIG. 1). Then, depending on whether or not the sheet leading edge detection sensor 51 c 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 51 c 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.
The sheet attraction and separation feeding unit 51 b 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.
As illustrated in FIG. 2, on an upward side of the middle plate 301 a, 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 301 a. The sheet surface height detection unit 302 includes a sensor flag 302 a and a photosensor 302 b. The sensor flag 302 a 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 302 b.
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 302 a is pivoted to change the shielding state of the photosensor 302 b, 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 301 a 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.
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 201 a and a second nipping and conveying outer roller 201 b. The second nipping and conveying inner roller 201 a is arranged on the inner side of the attracting member 200, and has a rotary shaft 201 j 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) 201 a via a drive transmitting unit (not shown).
The second nipping and conveying outer roller 201 b is arranged at a position opposed to the second nipping and conveying inner roller 201 a under a state in which the endless belt-like attracting member 200 is nipped between the second nipping and conveying outer roller 201 b and the second nipping and conveying inner roller 201 a. The shaft of the second nipping and conveying outer roller 201 b is supported rotatably by a shaft support member (not shown). The second nipping and conveying outer roller 201 b rotate along with (following rotation) the attracting member 200 rotated in the arrow F direction by the second nipping and conveying inner roller 201 a 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 201 b is biased in the axial center direction of the second nipping and conveying inner roller 201 a by the second pressure spring to nip the attracting member 200 together with this roller 201 a.
The first nipping and conveying roller pair 202 includes a first nipping and conveying inner roller 202 a and a first nipping and conveying outer roller 202 b. The first nipping and conveying inner roller 202 a is arranged on the inner side of the attracting member 200, and has a rotary shaft 202 j 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) 202 a via a drive transmitting unit (not shown).
Note that, the first nipping and conveying inner roller 202 a constructs the first rotary member arranged on the upward side of the middle plate 301 a serving as the stacking unit. Further, the second nipping and conveying inner roller 201 a 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 202 a. The attracting member 200 has its inner surface supported by the first nipping and conveying inner roller (first rotary member) 202 a and the second nipping and conveying inner roller (second rotary member) 201 a 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 301 a, to thereby feed the sheet S.
The first nipping and conveying outer roller 202 b is arranged at a position opposed to the first nipping and conveying inner roller 202 a under a state in which the attracting member 200 is nipped between the first nipping and conveying outer roller 202 b and the first nipping and conveying inner roller 202 a. The shaft of the first nipping and conveying outer roller 202 b is supported rotatably by a shaft support member (not shown). The first nipping and conveying outer roller 202 b is rotated in association with the attracting member 200 rotated in the arrow G direction by the first nipping and conveying inner roller 202 a 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 202 b is biased in the axial center direction of the first nipping and conveying inner roller 202 a by the first pressure spring to nip the attracting member 200 together with this roller 202 a.
In this embodiment, the endless attracting member 200 is supported by the second nipping and conveying inner roller 201 a, the first nipping and conveying inner roller 202 a, and a neutralization inner roller 250 a that are three rotary members arranged along the sheet feeding direction. Then, the attracting member 200 has a length larger than [sum D₁+D₂+D₃of distances between rotation centers of the respective rollers 201 a, 202 a, and 250 a]+[sum of wrapping lengths of the attracting member 200 on the respective rollers 201 a, 202 a, and 250 a].
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 201 a and the first nipping and conveying inner roller 202 a. 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 301 a, the attracting member 200 can be brought into contact with the uppermost sheet Sa.
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 260 a and 260 b serving as power feeding units are arranged. The power feeding brushes 260 a and 260 b are respectively brought into contact with power feeding electrodes 205 a and 206 a so that positive and negative voltages from a positive voltage supply unit 265 a and a negative voltage supply unit 265 b can be respectively supplied (fed) to first and second electrode elements 205 and 206. At least the power feeding electrodes 205 a and 206 a 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.
Further, as illustrated in FIG. 2, in the neutralization roller pair 250, a neutralization outer roller 250 b 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) 260 a and 260 b 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.
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.
As illustrated in FIG. 3, the attracting member 200 includes a base layer 200 a, an attraction layer 200 b, 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 205 c and 206 c 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 205 a and 206 a 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 205 b and 206 b configured to connect the attracting force generation electrodes 205 c and 206 c to the power feeding electrodes 205 a and 206 a corresponding to the respective electrodes 205 c and 206 c 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.
That is, the above-mentioned electrode elements 205 and 206 on the base layer 200 a respectively include the power feeding electrodes 205 a and 206 a corresponding to power feeding sections B₁, the connecting lines 205 b and 206 b corresponding to offset sections B₂, and the attracting force generation electrodes 205 c and 206 c corresponding to an attraction section B₃. The attracting force generation electrodes 205 c and 206 c in the attraction section B₃are arranged alternately into a pectinate shape (alternately protrude in a pectinate manner).
The connecting lines 205 b and 206 b are each set to have such a length that the attracting force generation electrodes 205 c and 206 c moving from the attracting position (C in FIG. 6C) toward the neutralization roller pair 250 are separated from the power feeding brushes 260 a and 260 b serving as the power feeding units before reaching the neutralization roller pair 250. With this, the attracting force generation electrodes 205 c and 206 c 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.
The power feeding electrodes 205 a and 206 a corresponding to the respective power feeding sections B₁at 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 205 b and 206 b corresponding to the offset sections B₂are wired to be oblique to the width direction of the attracting member 200. The respective surfaces of the power feeding electrodes 205 a and 206 a are exposed on the surface in only parts corresponding to the power feeding sections B₁, and other parts are covered with the attraction layer 200 b.
As described above, the connecting lines 205 b and 206 b are extended from the respective attracting force generation electrodes 205 c and 206 c toward the upstream side in the rotating direction of the attracting member 200. Further, the power feeding brushes 260 a and 260 b 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 202 d and 202 e 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.
With the configuration above, when the voltages are applied to the respective power feeding electrodes 205 a and 206 a, the attracting force generation electrodes 205 c and 206 c 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 205 a and 206 a. That is, in the above-mentioned electrode elements 205 and 206, the attracting force generation electrodes 205 c and 206 c, 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 265 a and 265 b through the corresponding power feeding electrodes 205 a and 206 a.
Note that, in this embodiment, the attraction layer 200 b is made of polyimide that is a dielectric having a volume resistivity of 10⁸Ωcm or more, and the layer thickness thereof is set to about 100 μm. Further, the first and second electrode elements 205 and 206 are made of a conductor having a volume resistivity of 10⁶Ωcm or less, and copper having a layer thickness of about 10 μm is used as this conductor.
In this case, the connecting lines 205 b and 206 b corresponding to the offset sections B₂of 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 205 b and between the adjacent connecting lines 206 b, it is most efficient to wire the elements obliquely.
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).
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 51 c and 52 c, 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) 265 a, the negative voltage supply unit (power supply) 265 b, and the like are connected to the output ports of the control unit 70.
As illustrated in FIG. 2, the first nipping and conveying outer roller 202 b constructs a first nipping member configured to nip the attracting member 200 together with the first nipping and conveying inner roller (first rotary member) 202 a. The second nipping and conveying outer roller 201 b constructs a second nipping member configured to nip the attracting member 200 together with the second nipping and conveying inner roller (second rotary member) 201 a. 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 201 a and the first nipping and conveying inner roller 202 a. With this, the amount that the attracting member 200 sags downward is increased. Thus, the sheet on the middle plate 301 a (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.
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 301 a arranged in each of the cassettes 51 a and 52 a. The middle plate 301 a constructs the stacking unit on which the sheets S are to be stacked.
The sheet leading edge detection sensors 51 c and 52 c illustrated in FIG. 1 and FIG. 8 detect the passage of the sheets S fed respectively by the sheet attraction and separation feeding units 51 b and 52 b. The sheet leading edge detection sensor 51 c is arranged in the sheet conveyance path between the sheet attraction and separation feeding unit 51 b and the pull-out roller pair 71. Further, the sheet leading edge detection sensor 52 c is arranged in the sheet conveyance path between the sheet attraction and separation feeding unit 52 b and the pull-out roller pair 72. Then, depending on whether or not the sheet leading edge detection sensor 51 c or 52 c 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 51 c and 52 c 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.
The elevating unit 301 is actuated through control of the control unit 70 so as to elevate the middle plate 301 a on which the sheets S are to be stacked and which is arranged to be elevatable on each of the cassettes 51 a and 52 a. The elevating unit 301 changes the positions of the middle plate 301 a and the uppermost sheet among the sheets S stacked on the middle plate depending on the pivoting angle of the lifter 301 b pivotably arranged below the middle plate 301 a.
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 201 a. 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 202 a.
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.
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 200 b 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.
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.
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.
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.
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 51 b including the power feeding unit and the neutralization unit.
As illustrated in FIG. 5, the power feeding brushes 260 a and 260 b respectively including brush portions 261 a and 261 b are arranged in the vicinity of both ends of the attracting member 200 in the width direction. The brush portions 261 a and 261 b are respectively arranged in contact with the first and second electrode elements 205 and 206 in the power feeding sections B₁of FIG. 3. Therefore, the voltages applied from the positive voltage supply unit (power supply) 265 a and the negative voltage supply unit (power supply) 265 b are respectively supplied to the first and second electrode elements 205 and 206 through the brush portions 261 a and 261 b of the power feeding brushes 260 a and 260 b.
In this case, the first and second electrode elements 205 and 206 include the offset sections B₂as illustrated in FIG. 3, and hence the voltages are applied to the first and second electrode elements 205 and 206 in the attraction section B₃arranged on the downstream side with respect to the power feeding brushes 260 a and 260 b. Note that, in this embodiment, a positive voltage of about +1 kV is supplied from the positive voltage supply unit (power supply) 265 a, and a negative voltage of about −1 kV is supplied from the negative voltage supply unit (power supply) 265 b.
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 250 b 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 250 b.
Further, the neutralization inner roller 250 a 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 260 a and 260 b to the power feeding electrodes 205 a and 206 a arranged to be opposed to the power feeding brushes 260 a and 260 b in the attracting member 200 can be maintained constant.
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 260 a and 260 b becomes reliable.
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 250 a 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 205 a and 206 a and the connecting lines 205 b and 206 b.
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 51 b 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 51 b 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.
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 265 a and the negative voltage supply unit 265 b to the power feeding brushes 260 a and 260 b, 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.
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.
As described above, the neutralization inner roller 250 a 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.
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 202 a. 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.
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.
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 265 a and the negative voltage supply unit 265 b 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.
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 51 a.
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 265 a and the negative voltage supply unit 265 b is set to a length that includes the entire contact length Mn.
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.
Further, the load torque applying unit 251 on the shaft of the neutralization inner roller 250 a 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.
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.
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.
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.
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 265 a and the negative voltage supply unit 265 b 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.
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 201 a, the leading edge of the uppermost sheet Sa is peeled off from the attracting member 200.
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).
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 51 c, 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.
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 250 b.
In this case, when the sheet Sa is not detected within a predetermined time period by the sheet leading edge detection sensor 51 c, 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).
With the above-mentioned six steps, only the one uppermost sheet Sa among the plurality of sheets S stacked on the cassette 51 a is fed. Then, the six steps are repeated to enable continuous feeding of the sheets S one by one.
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.
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.
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 201 a and the first nipping and conveying inner roller 202 a (D₁in FIG. 2). Then, the length of the attracting position (position of reference symbol C) and an offset amount L₁of the first electrode element 205 in the offset section B₂of 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 260 a and 260 b 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.
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.
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.
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.
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

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.
This embodiment differs from the first embodiment in that, in order to reliably bring the attracting member 200 and the power feeding brushes 260 a and 260 b 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.
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 260 a and 260 b 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 205 a and 206 a to the power feeding brushes 260 a and 260 b.
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 261 a and 261 b of the power feeding brushes 260 a and 260 b. 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.
In this embodiment having the above-mentioned configuration, it is possible to reliably bring the power feeding brushes 260 a and 260 b into contact with the power feeding electrodes 205 a and 206 a 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 260 a and 260 b 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

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.
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 200 a, a back surface layer 200 c, and the first and second electrode elements 205 and 206. The first and second electrode elements 205 and 206 arranged on the base layer 200 a each have parts corresponding to the power feeding section B₁and the attraction section B₃. The parts of the first and second electrode elements 205 and 206 corresponding to the attraction section B₃are arranged alternately into a pectinate shape, similarly to the first embodiment.
The power feeding electrodes 205 a and 206 a are each set to have such a length that the attracting force generation electrodes 205 c and 206 c moving from the attracting position (C of FIG. 6C) toward the neutralization roller pair 250 are separated from the power feeding rollers 202 d and 202 e serving as the power feeding units before reaching the neutralization roller pair 250. With this, the attracting force generation electrodes 205 c and 206 c 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 205 a and 206 a corresponding to the respective power feeding sections B₁at 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 205 a and 206 a are wired to be oblique to the width direction of the attracting member 200.
As described above, the power feeding electrodes 205 a and 206 a of this embodiment are configured to have also the role of the connecting lines 205 b and 206 b in the first embodiment and the second embodiment.
In this embodiment described above, in the first and second electrode elements 205 and 206, at least the power feeding electrodes 205 a and 206 a are exposed on the inner peripheral surface of the attracting member 200. Then, the power feeding rollers 202 d and 202 e serving as the power feeding units also serve as the first nipping and conveying inner roller (first rotary member) 202 a, and are brought into contact with the power feeding electrodes 205 a and 206 a exposed on the inner peripheral surface to feed power. Note that, in this embodiment, the power feeding rollers 202 d and 202 e also serve as the first nipping and conveying inner roller 202 a, but the present invention is not limited thereto, and the power feeding rollers 202 d and 202 e may be configured to also serve as the second nipping and conveying inner roller (second rotary member) 201 a.
With such a configuration, in the power feeding sections B₁, different voltages are respectively applied to the first and second electrode elements 205 and 206 from the power feeding rollers 202 d and 202 e arranged on the back surface. In the attraction section B₃, 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 200 a is made of polyimide that is a dielectric having a volume resistivity of 10⁸0 cm or more, and the layer thickness thereof is set to about 100 μm. Further, the first and second electrode elements 205 and 206 are each made of a conductor having a volume resistivity of 10⁶Ωcm or less, and copper having a layer thickness of about 10 μm is used as this conductor.
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.
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 51 b.
As illustrated in FIG. 12, the power feeding rollers 202 d and 202 e are arranged coaxially with the first nipping and conveying inner roller 202 a, and leaf-spring power feeding members 270 a and 270 b are brought into pressure-contact with the power feeding rollers 202 d and 202 e, respectively. The leaf-spring power feeding members 270 a and 270 b are respectively connected to the positive voltage supply unit (power supply) 265 a and the negative voltage supply unit (power supply) 265 b. Therefore, the voltages from the positive voltage supply unit 265 a and the negative voltage supply unit 265 b are supplied to the power feeding rollers 202 d and 202 e through the leaf-spring power feeding members 270 a and 270 b, respectively.
The power feeding rollers 202 d and 202 e are arranged so as to be respectively brought into contact with at least the power feeding electrodes 205 a and 206 a of the first and second electrode elements 205 and 206 in the power feeding sections B₁illustrated in FIG. 11. Therefore, the voltages from the positive voltage supply unit 265 a and the negative voltage supply unit 265 b are reliably supplied to the first and second electrode elements 205 and 206 through the power feeding rollers 202 d and 202 e.
In this case, in the first and second electrode elements 205 and 206, as illustrated in FIG. 11, the power feeding electrodes 205 a and 206 a in the power feeding sections B₁are 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 205 c and 206 c in the attraction section B₃arranged on the downstream side with respect to the power feeding rollers 202 d and 202 e. Note that, in this embodiment, a positive voltage of about +1 kV is supplied from the positive voltage supply unit 265 a, and a negative voltage of about −1 kV is supplied from the negative voltage supply unit 265 b.
In this embodiment described above, the attracting member 200 is nipped between the first nipping and conveying outer roller 202 b and the first nipping and conveying inner roller 202 a ( power feeding rollers 202 d and 202 e). 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 265 a and the negative voltage supply unit 265 b can be reliably supplied to the first and second electrode elements 205 and 206.
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 250 a and the neutralization outer roller 250 b 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 250 b is connected to the earth 255.
In this case, FIG. 11 to FIG. 13 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. 14 is determined. In this case, the attracting position is set to have a length that substantially matches with the distance (D₁in FIG. 14) between the second nipping and conveying inner roller 201 a and the first nipping and conveying inner roller 202 a. Then, the length of the attracting position (position of reference symbol C) and an offset amount L₂of the first and second electrode elements 205 and 206 in the power feeding sections B₁of FIG. 11 are set to substantially match with each other.
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.
As described above, even when the power feeding rollers 202 d and 202 e 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

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.
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 200 a, the back surface layer 200 c, and the first and second electrode elements 205 and 206. The first and second electrode elements 205 and 206 arranged on the base layer 200 a each have parts corresponding to the power feeding section B₁and the attraction section B₃. The parts of the first and second electrode elements 205 and 206 corresponding to the attraction section B₃are arranged alternately into a pectinate shape, similarly to the third embodiment.
The length of each of the power feeding electrodes 205 a and 206 a is set as follows. That is, the power feeding electrodes 205 a and 206 a are each set to have such a length that the attracting force generation electrodes 205 c and 206 c moving from the attracting position (C of FIG. 6C) toward the neutralization roller pair 250 are separated from the power feeding rollers 202 d and 202 e (see FIG. 12) before reaching the neutralization roller pair 250 (see FIG. 14). With this, the attracting force generation electrodes 205 c and 206 c 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 205 a and 206 a corresponding to the respective power feeding sections B₁at 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 205 a and 206 a are wired to be oblique to the width direction of the attracting member 200.
Note that, in the third embodiment, the attracting force generation electrodes 205 c and 206 c in the attraction section B₃are all independent of each other. However, in this embodiment, under a state in which each four of the attracting force generation electrodes 205 c are electrically conducted with each other and each four of the attracting force generation electrodes 206 c are electrically conducted with each other, the four attracting force generation electrodes 205 c are connected to one power feeding electrode 205 a in the power feeding section B₁and the four attracting force generation electrodes 206 c are connected to one power feeding electrode 206 a in the power feeding section B₁. That is, under a state in which each plurality of the attracting force generation electrodes 205 c in this embodiment are electrically conducted with each other and each plurality of the attracting force generation electrodes 206 c in this embodiment are electrically conducted with each other, the plurality of the attracting force generation electrodes 205 c are connected to corresponding one of the power feeding electrodes 205 a and the plurality of the attracting force generation electrodes 206 c are connected to corresponding one of the power feeding electrodes 206 a. Note that, this configuration can be similarly implemented in the above-mentioned first to third embodiments.
In the respective power feeding sections B₁of the first and second electrode elements 205 and 206, the power feeding electrodes 205 a and 206 a 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 205 a and 206 a 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 200 c, and only a part of the power feeding section B₁is exposed on the back surface.
In this embodiment described above, it is not necessary to wire the power feeding electrodes 205 a and 206 a in a collective manner at narrow intervals in the power feeding sections B₁, and the wiring of the power feeding electrodes 205 a and 206 a 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.
Also in this embodiment, similarly to the third embodiment, the power feeding electrodes 205 a and 206 a are configured to have also the role of the connecting lines 205 b and 206 b in the first and second embodiments.
Note that, in this embodiment, each four of the attracting force generation electrodes 205 c are conducted to corresponding one of the power feeding electrodes 205 a and each four of the attracting force generation electrodes 206 c are conducted to corresponding one of the power feeding electrodes 206 a, but the present invention is not limited thereto. That is, it is sufficient that at least two of the attracting force generation electrodes 205 c be conducted to corresponding one of the power feeding electrodes 205 a and at least two of the attracting force generation electrodes 206 c be conducted to corresponding one of the power feeding electrodes 206 a. In this case, effects similar to the above can be obtained.
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.
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

51, 52 sheet feeding apparatus
55 image forming unit
70 control unit
100 image forming apparatus
200 attracting member
201 a second nipping and conveying inner roller (second rotary member)
201 b second nipping and conveying outer roller (second nipping member)
202 a first nipping and conveying inner roller (first rotary member)
202 b first nipping and conveying outer roller (first nipping member)
202 d, 202 e power feeding roller (power feeding unit)
203, 204 second driving unit, first driving unit
205, 206 first electrode element, second electrode element
205 a, 206 a power feeding electrode
205 b, 206 b connecting line
205 c, 206 c attracting force generation electrode
250 neutralization roller pair (neutralization unit)
251 load torque applying unit (tension providing unit)
252 plate member (tension providing unit)
260 a, 260 b power feeding brush (power feeding unit)
301 a middle plate (stacking unit)
C attracting position
S sheet

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.
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.

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.