JP2014218371A - Sheet feeder and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet feeder that can feed a sheet through electrostatic attraction with simple constitution and low noise, and an image formation apparatus.SOLUTION: An attraction member 400 is provided rotatably in synchronism with rotations of one driving roller (rotary member) 401, and after a stacked sheet is attracted by the attraction member 400 by increasing the quantity of downward slackening of the attraction member 400 during one rotation of the driving roller, the sheet attracted by the attraction member 400 is fed while the quantity of downward slackening of the attraction member 400 is decreased. Then the attraction member 400 returns to a standby position again after attracting and feeding the sheet from the standby position through one rotation of the driving roller 401.

Description

  The present invention relates to a sheet feeding apparatus and an image forming apparatus, and more particularly, to a sheet feeding apparatus using electrostatic attraction force.

  Conventional image forming apparatuses such as copiers and printers are provided with a sheet feeding device for feeding sheets. As such a sheet feeding device, the uppermost sheet is removed from a cassette on which a bundle of sheets is stacked with a rubber roller. There is a friction feeding type that separates and feeds using a frictional force. In the sheet feeding device of this friction feeding type, the uppermost sheet is fed out by rotating the rubber sheet while pressing the rubber roller against the sheet bundle. Here, when the sheets are sent out, a plurality of sheets are conveyed by friction between the sheets, so-called double feeding of the sheets may occur. In response to this, only the uppermost sheet is fed to the image forming unit by applying a conveyance resistance to the sheet other than the uppermost sheet by a separation pad or a retard roller.

  By the way, in such a sheet feeding device of the frictional separation system, since the sheet is fed while applying a large pressure to the sheet by the rubber roller, noise due to friction between the sheets and between the sheet and the rubber roller becomes a problem. Further, when the separation pad or the retard roller is used to prevent the sheets from being double-fed, a large rubbing noise is generated between the sheets. In addition, the separation pad and the retard roller provide resistance for transporting the uppermost sheet even when the sheet is not double-fed, so that a sound due to stick-slip between the separation pad or the retard roller and the sheet is generated. End up.

  Therefore, as a solution to this problem, there is a sheet feeding apparatus that uses an electrostatic attraction force, specifically, separates and feeds a sheet while adsorbing the sheet by an electric field formed on the belt surface (patent) Reference 1 and 2). In such an electrostatic adsorption separation type sheet feeding apparatus, the uppermost sheet can be conveyed so as to be peeled off from the sheet bundle, so that noise in the feeding portion can be greatly reduced. .

JP 2011-168396 A JP-A-5-139548

  However, in a sheet feeding apparatus that feeds a sheet using a conventional electrostatic attraction force, the configuration of Patent Document 1 can generate a sufficient electrostatic attraction force on the sheet. Occasionally, operating noise is generated because the frame carrying the suction belt is raised and lowered. Further, a collision sound with the seat is also generated. Furthermore, even when the sheet is curled, when the sheet is adsorbed, the sheet can be surely adsorbed, that is, the follow-up to the sheet curl when adsorbing the sheet of the adsorption belt can be secured. The belt distance is weakened by shortening the distance between the shafts. However, if the belt tension is weakened and the sheet is adsorbed, it is necessary to increase the tension during the separation operation. If the tension is increased in this way, string vibration occurs in the belt, and the vibration also causes sudden sound.

  In the configuration of Patent Document 2, the suction belt is used. However, the suction belt is not moved up and down with the frame, but the carrying roller is moved eccentrically, so that the sheet separation operation is performed. The sound is reduced. However, when the suction belt is surely brought into contact with the sheet bundle, a collision sound in which the roller collides with the sheet bundle via the suction belt is still generated. If an attempt is made to avoid the collision between the roller and the sheet bundle, the belt and the sheet bundle are separated from each other, and the suction of the sheet by the suction belt becomes unstable, resulting in poor feeding.

  Accordingly, the present invention has been made in view of such a current situation, and has a simple configuration, low noise, and a sheet feeding apparatus and an image that can stably perform sheet feeding by electrostatic attraction. An object of the present invention is to provide a forming apparatus.

  The present invention provides a stacking unit on which sheets are stacked, a rotating member disposed above the stacking unit, and a sheet that is provided so as to be movable in synchronization with the rotation of the rotating member. An adsorbing member that is electrically adsorbed; a driving unit that rotates the rotating member; and a control unit that controls the driving unit. The control unit increases the amount of slackening of the adsorbing member downward. In the sheet feeding device for feeding the sheet adsorbed by the adsorption member while reducing the amount of slack downward of the adsorption member after the sheet loaded on the stacking unit is adsorbed by the adsorption member The control means rotates the rotating member once to move the suction member from the standby position to suck and feed the sheet, and then moves the suction member to the standby position. You A sheet feeding apparatus.

  According to the present invention, by rotating the rotating member once, the suction member can be moved from the standby position to suck and feed the sheet, and then the suction member can be moved to the standby position. Therefore, it is possible to stably feed the sheet by electrostatic attraction with a simple configuration and low noise.

1 is a diagram illustrating a schematic configuration of an image forming apparatus including a sheet feeding device according to a first embodiment of the present invention. The figure explaining the structure of the said sheet feeding apparatus. The figure explaining the detailed principle of the adsorption member of the sheet | seat adsorption | suction separation feeding part provided in the said sheet | seat feeding apparatus, and the generation | occurrence | production principle of the adsorption | suction force in which an adsorption member adsorb | sucks a sheet | seat. The figure explaining the voltage supply method to the adsorption | suction member of the sheet | seat adsorption | suction separation feeding part provided in the said sheet | seat feeding apparatus. The control block diagram of the said sheet feeding apparatus. The figure explaining the sheet | seat separation feeding operation | movement of the said sheet | seat adsorption | suction separation feeding part. 4 is a timing chart at the time of sheet separation and feeding by the sheet suction separation and feeding unit. The figure explaining the structure of the sheet feeding apparatus which concerns on the 2nd Embodiment of this invention. FIG. 6 is a diagram illustrating a configuration of a sheet feeding device according to a third embodiment of the present invention. The figure explaining the detailed generation structure of the suction member of the sheet | seat adsorption | suction separation feeding part provided in the said sheet | seat feeding apparatus, and the generation | occurrence | production principle of the adsorption | suction force in which an adsorption member adsorb | sucks a sheet | seat. The figure explaining the sheet | seat isolation | separation feeding operation | movement of the sheet | seat adsorption | suction separation feeding part provided in the said sheet feeding apparatus. 4 is a timing chart at the time of sheet separation and feeding by the sheet suction separation and feeding unit. The figure explaining the structure of the sheet feeding apparatus which concerns on the 4th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus including a sheet feeding device according to a first embodiment of the present invention.

  In FIG. 1, reference numeral 100 denotes an image forming apparatus, and 100A denotes an image forming apparatus main body (hereinafter referred to as an apparatus main body). An image reading unit 41 having an image sensor or the like that irradiates light on a document placed on a platen glass as a document placement table and converts reflected light into a digital signal is provided on the upper part of the apparatus main body 100A. A document for reading an image is conveyed onto the platen glass by the automatic document feeder 41a. Further, the apparatus main body 100A includes an image forming unit 55, sheet feeding devices 51 and 52 that feed the sheet S to the image forming unit 55, and a sheet reversing unit that reverses the sheet S and conveys it to the image forming unit 55. 59 is provided.

  The image forming unit 55 includes the exposure unit 42 and four process cartridges 43 (43y, 43m, 43) that form toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). 43c, 43k). The image forming unit 55 includes an intermediate transfer unit 44, a secondary transfer unit 56, and a fixing unit 57 disposed above the process cartridge 43.

  Here, the process cartridge 43 includes the photosensitive drum 21 (21y, 21m, 21c, 21k), the charging roller 22 (22y, 22m, 22c, 22k), and the developing roller 23 (23y, 23m, 23c, 23k). I have. The process cartridge 43 includes a drum cleaning blade 24 (24y, 24m, 24c, 24k).

  The intermediate transfer unit 44 includes a belt driving roller 26, an intermediate transfer belt 25 stretched around the secondary transfer inner roller 56a, and the like, and a primary transfer roller that contacts the intermediate transfer belt 25 at a position facing the photosensitive drum 21. 27 (27y, 27m, 27c, 27k). Then, as will be described later, a positive transfer bias is applied to the intermediate transfer belt 25 by the primary transfer roller 27 so that toner images having a negative polarity on the photosensitive drum 21 are sequentially transferred to the intermediate transfer belt 25 in a multiple transfer manner. Is done. As a result, a full color image is formed on the intermediate transfer belt 25.

  The secondary transfer unit 56 includes a secondary transfer inner roller 56 a and a secondary transfer outer roller 56 b that is in contact with the secondary transfer inner roller 56 a via the intermediate transfer belt 25. Then, as described later, a full-color image formed on the intermediate transfer belt 25 is transferred to the sheet S by applying a positive secondary transfer bias to the secondary transfer outer roller 56b.

  The fixing unit 57 includes a fixing roller 57a and a fixing backup roller 57b. Then, the sheet S is nipped and conveyed between the fixing roller 57a and the fixing backup roller 57b, whereby the toner image on the sheet S is pressurized and heated to be fixed to the sheet S. The sheet feeding devices 51 and 52 include cassettes 51a and 52a that are storage units (stacking units) for storing the sheets S, respectively. In addition, the sheet feeding devices 51 and 52 include sheet suction separation feeding units 51b and 52b having a function of feeding the sheets S stored in the cassettes 51a and 52a one by one while being attracted by static electricity. .

  In FIG. 1, reference numeral 103 denotes a pre-secondary transfer conveyance path for conveying the sheet S fed from the cassettes 51 a and 52 a to the secondary transfer unit 56, and reference numeral 104 denotes two sheets S conveyed to the secondary transfer unit 56. This is a pre-fixing transport path for transporting from the next transfer unit 56 to the fixing unit 57. Reference numeral 105 denotes a post-fixing conveyance path for conveying the sheet S conveyed to the fixing unit 57 from the fixing unit 57 to the switching member 61, and reference numeral 106 denotes a sheet S conveyed to the switching member 61 from the switching member 61 to the paper discharge unit 58. This is a paper discharge path. Reference numeral 107 denotes a re-conveying path for conveying the sheet S reversed by the sheet reversing unit 59 to the image forming unit 55 in order to form an image on the back surface of the sheet S on which an image is formed on one side by the image forming unit 55.

  Next, an image forming operation of the image forming apparatus 100 having such a configuration will be described. When the image forming operation is started, first, the exposure unit 42 irradiates the surface of the photosensitive drum 21 with laser light based on image information from a personal computer (not shown). At this time, the surface of the photosensitive drum 21 is uniformly charged to a predetermined polarity / potential by the charging roller 22, and when the laser beam is irradiated, the charge of the portion irradiated with the laser beam is attenuated, thereby exposing the photosensitive drum 21. An electrostatic latent image is formed on the surface of the body drum.

  Thereafter, the electrostatic latent image is developed with yellow (Y), magenta (M), cyan (C), and black (Bk) toners respectively supplied from the developing roller 23, and the electrostatic latent image is developed as a toner image. Image. Each color toner image is sequentially transferred to the intermediate transfer belt 25 by the primary transfer bias applied to the primary transfer roller 27, whereby a full color toner image is formed on the intermediate transfer belt 25.

  On the other hand, in parallel with the toner image forming operation, the sheet feeding devices 51 and 52 separate and feed only one sheet S from the cassettes 51a and 52a by the sheet suction separation feeding units 51b and 52b. Thereafter, the sheet S is detected by the sheet leading edge detection sensors 51c and 52c, and reaches the drawing roller pair 51d and 51e. Further, the sheet S sandwiched between the drawing roller pairs 51d and 51e is sent to the pre-secondary transfer conveyance path 103, and the position of the leading edge is adjusted by contacting the stopped registration roller pair 62a and 62b.

  Next, in the secondary transfer unit 56, the registration roller pairs 62a and 62b are driven at a timing at which the full-color toner image on the intermediate transfer belt and the position of the sheet S coincide with each other. As a result, the sheet S is conveyed to the secondary transfer unit 56, and the full-color toner image is transferred onto the sheet S by the secondary transfer unit 56 by the secondary transfer bias applied to the secondary transfer outer roller 56b. Is done.

  The sheet S on which the full-color toner image has been transferred is conveyed to the fixing unit 57 where the toner of each color is melted and mixed by receiving heat and pressure, and is fixed on the sheet S as a full-color image. Thereafter, the sheet S on which the image is fixed is discharged by a paper discharge unit 58 provided downstream of the fixing unit 57. When forming images on both sides of the sheet, the conveyance direction of the sheet S is reversed by the sheet reversing unit 59 and the sheet S is conveyed to the image forming unit 55 again.

  Next, the configuration of the sheet feeding apparatus 51 according to the present embodiment will be described with reference to FIG. As described above, the sheet feeding device 51 includes the cassette 51a and the sheet suction separation feeding unit 51b that feeds the sheets S stored in the cassette 51a one by one while being electrically attracted by static electricity. ing. The sheet feeding device 51 is provided so as to be movable up and down in the cassette 51a. The sheet feeding device 51 lifts and lowers the middle plate 301a on which the sheet S is stacked, and the sheet S fed by the sheet suction separation feeding unit 51b. A sheet leading edge detection sensor 51c that detects passage is provided.

  The sheet adsorption / separation feeding unit 51b includes an adsorption member 400, a drive roller 401, a drive unit 203, and a power supply unit 205. The adsorbing member 400 is flexible and has an endless shape that is longer than the outer peripheral length of the drive roller 401, and the cross-sectional shape of the adsorbing member 400 is maintained in a substantially circular shape by its own elastic force. The drive roller 401 is rotatably supported by a shaft support member (not shown) whose arrangement position is fixed, and is arranged with a predetermined gap Lr from the upper surface of the uppermost sheet Sa stacked on the cassette 51a. Further, the driving force from the driving unit 203 is transmitted to the driving roller 401 via the driving transmission unit. Note that the sheet suction separation and feeding unit 52b provided in the sheet feeding device 52 has the same configuration as the sheet suction separation and feeding unit 51b of the sheet feeding device 51, and thus description thereof is omitted.

  Here, in the present embodiment, the adsorbing member 400 is provided with a gap G between the adsorbing member 400 and the driving roller 401, and a part thereof is fixed to the fixing portion 402 of the driving roller 401. In other words, the suction member 400 is supported by the drive roller 401 in a relaxed state. The suction member 400 may be fixed to the driving roller 401 with an adhesive or the like, or may be performed by sandwiching the suction member 400 between a fixing member (not shown) and the driving roller 401. When fixing the suction member 400 using the fixing member, the fixing member protrudes from the surface of the suction member 400. In this case, the suction member 400 is fixed by the fixing member at a portion that does not contact the sheet. By doing so, the sheet feeding operation is not adversely affected.

  The lifting / lowering means 301 includes a lifter 301b rotatably provided below the middle plate 301a, and the middle plate 301a and the uppermost sheet Sa stacked on the middle plate 301a according to the rotation angle of the lifter 301b. Change the position. The sheet leading edge detection sensor 51c is disposed in the sheet conveyance path between the sheet suction separation feeding unit 51b and the drawing roller pair 51d and 51e. The success or failure of sheet feeding is detected based on whether or not the sheet leading edge detection sensor 51c detects the sheet S at a predetermined timing. In the present embodiment, the sheet leading edge detection sensor 51c is a non-contact reflective photosensor, which irradiates a detection target with spot light and measures the amount of reflected light to detect the presence or absence of the detection target.

  In FIG. 2, reference numeral 302 denotes a paper surface height detecting means for detecting the upper surface position of the sheets S stacked on the intermediate plate 301a. The paper surface height detection means 302 is disposed above the intermediate plate 301a and is constituted by a sensor flag 302a and a photosensor 302b. The sensor flag 302a is rotatably supported by a support unit (not shown), and one end is disposed at a position where it can come into contact with the upper surface of the uppermost sheet Sa, and the other end is disposed at a position where the photosensor 302b can be shielded.

  Here, when the upper surface of the uppermost sheet Sa is positioned at a predetermined height, the sensor flag 302a rotates and the photosensor 302b is shielded from light. Note that the control unit 70 shown in FIG. 5 described later detects the upper surface position of the uppermost sheet Sa by detecting the light shielding state of the photosensor 302b. Then, 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 paper surface height detecting unit 302, and the position of the middle plate 301a is set to the upper surface height of the uppermost sheet Sa. Is kept at a substantially constant position. As a result, the gap Lr between the driving roller 401 and the upper surface of the uppermost sheet Sa is also kept substantially constant.

  Here, in the present embodiment, when adsorbing and conveying the sheet to the adsorbing member 400, the adsorbing member 400 is elastically deformed after adsorbing the sheet to the adsorbing member 400 by static electricity so that the sheets do not rub against each other. It is trying to pull it upwards. And the sheet | seat is isolate | separated from another sheet | seat by pulling up upwards, making the adsorption member 400 elastically deform in this way.

  Therefore, in the present embodiment, the length of the adsorbing member 400 is determined so as to secure a sheet contact area Mn shown in FIG. 6D (described later) from which the sheet adsorbing force necessary for the adsorbing separation can be obtained. ing.

  The power supply unit 205 includes a positive voltage supply unit 205a that is a first power supply, a negative voltage supply unit 205b that is a second power supply, and switches 205c and 205d that control the respective voltage supplies. The voltage generated by the power supply unit 205 is supplied to the suction member 400 via the drive roller 401, and an electrostatic suction force that attracts the sheet S to the suction member 400 is generated by these applied voltages.

  Next, the detailed configuration of the suction member 400 provided in the sheet suction separation conveyance unit 51b and the generation principle of the suction force by which the suction member 400 sucks the sheet S will be described with reference to FIG. FIG. 3 is a schematic diagram showing the configuration of the adsorption member 400. 3A shows the surface of the adsorbing member 400, FIG. 3B shows the cross section of the feeding portion of the adsorbing member 400, and FIG. 3C shows the concept of the electrostatic adsorbing force acting on the adsorbing member 400 and the sheet S. Each of the cross-sectional views is shown.

The adsorbing member 400 includes a base layer 400c, a positive electrode 400a, and a negative electrode 400b. In the base layer 400c, comb-shaped positive electrodes 400a and similarly comb-shaped negative electrodes 400b are alternately arranged. ing. In the present embodiment, the base layer 400c is a polyimide which is a dielectric having a volume resistance of 10 ⁸ Ωcm or more, and the layer thickness is about 100 μm. The positive electrode 400a and the negative electrode 400b are conductors having a volume resistance of 10 ⁶ Ωcm or less, and copper having a layer thickness of about 10 μm is used.

  On the back surface of the adsorption member 400, exposed regions 400d and 400e where the positive electrode 400a and the negative electrode 400b as the other electrode are exposed are provided. A voltage from the positive voltage supply unit 205a is supplied to the exposed region 400d of the positive electrode 400a, and a voltage from the negative voltage supply unit 205b is supplied to the exposed region 400e of the negative electrode 400b through the driving roller 401, respectively. ing. Thus, in this embodiment, the positive electrode 400a and the negative electrode 400b each have a positive / negative voltage of about 1 kV.

  An unequal electric field is formed near the surface of the adsorption member 400 by the positive electrode 400a and the negative electrode 400b to which a voltage is applied. When the attracting member 400 is brought close to the sheet S, dielectric polarization occurs in the surface layer of the sheet S, which is a dielectric, and an electrostatic attracting force is generated between the attracting member 400 and the sheet S due to Maxwell stress.

  Further, as shown in FIG. 4, the drive roller 401 includes an insulating shaft 401c and conductive portions 401a and 401b attached to both ends of the insulating shaft 401c. The insulating shaft 401c may be formed of an insulating resin or the like, or may be formed by applying an insulating coating on the surface of a metal shaft. The conductive portions 401a and 401b may be formed by fixing a metallic cylindrical cover to the insulating shaft 401c, or may be formed by patterning a conductive material around the insulating shaft 401c. The plate springs 406a and 406b are in contact with the conductive portions 401a and 401b, respectively, and positive and negative voltages are supplied to the plate springs 406a and 406b from the positive voltage supply means 205a and the negative voltage supply means 205b, respectively. The

  In FIG. 4, 400a is a positive electrode of the adsorption member 400, 400b is a negative electrode of the adsorption member 400, 400d is an exposed region where the positive electrode 400a is exposed, and 400e is an exposed region where the negative electrode 400b is exposed. The adsorption member 400 is fixed to the drive roller 401 so that the exposed regions 400d and 400e are in contact with the conductive portions 401a and 401b. With this configuration, the positive voltage generated by the positive voltage supply means 205a passes through the leaf spring 406a and the conductive portion 401a to the positive electrode 400a, and the negative voltage generated by the negative voltage supply means 205b passes through the leaf spring 406b and the conductive portion 401b. To the negative electrode 400b.

  FIG. 5 is a control block diagram of the sheet feeding apparatus 51 according to the present embodiment. In FIG. 5, reference numeral 70 denotes a control unit. The control unit 70 is connected to the driving unit 203, the positive voltage supply unit 205a, the negative voltage supply unit 205b and the like in addition to the sheet leading edge detection sensor 51c and the paper surface height detection unit 302 described above.

  Next, a sheet feeding operation by the sheet suction separation feeding unit 51b according to the present embodiment will be described with reference to FIG. FIG. 6A shows an initial operation of disposing the suction member 400 at the initial position of the feeding operation. At the time of this operation, for example, the control unit 70 shown in FIG. 5 described above stops the driving roller 401 so that the suction member 400 is separated from the sheet S by a predetermined gap Lr. In this embodiment, the driving means 203 is a stepping motor provided with an encoder, and the position where a sensor (not shown) detects the home position of the encoder is the initial position of the feeding operation of the suction member 400.

  FIG. 6B shows an approaching operation. In this operation, the control unit 70 rotates the driving roller 401 in the direction of arrow F. Here, in the present embodiment, the center Cb of the attracting member 400 is eccentric from the rotation center Cr of the drive roller 401. For this reason, when the drive roller 401 is rotated in the direction of arrow F, the suction member 400 approaches the upper surface of the uppermost sheet Sa.

  FIG. 6C shows an operation for increasing the contact area. In this operation, the control unit 70 rotates the drive roller 401 in the direction of the arrow F in the same way as the approaching operation, so The contact area Mc with the upper sheet Sa is increased. In the present embodiment, since the driving unit 203 is a stepping motor, the position that becomes the sheet contact area Mn can be determined by managing the rotation angle from the initial operation by the number of steps of the stepping motor. FIG. 6D shows an adsorption operation. In this operation, the control unit 70 increases the sheet contact area to Mn by the contact area increasing operation, and then starts to apply a voltage to the suction member 400 from the positive voltage supply unit 205a and the negative voltage supply unit 205b. An electrostatic attraction force is applied between 400 and the sheet S.

  FIG. 6E shows a conveying operation. At this time, the control unit 70 continues to rotate the driving roller 401 in the direction of arrow F after the above-described suction operation. As a result, the leading end of the uppermost sheet Sa adsorbed to the adsorbing member 400 is lifted in the direction of arrow D and separated from the lower sheet Sb. In this embodiment, a conveyance guide 303 is installed downstream of the driving roller 401 in the sheet feeding direction. The transport guide 303 guides the leading end of the uppermost sheet Sa adsorbed to the adsorbing member 400 away from the adsorbing member 400 due to the rigidity of the sheet Sa, and conveys the uppermost sheet Sa to the drawing roller pairs 51d and 51e. To do.

  FIG. 6F shows the separation operation. In this operation, the control unit 70 moves the uppermost sheet Sa being conveyed between the drawing roller pairs 51d and 51e to the suction member 400. Stop the voltage supply. Thus, the sheet Sa sucked and conveyed by the suction member 400 is conveyed by the pair of drawing rollers 51d and 51e that are sandwiched. Thereafter, when the driving roller 401 further rotates, the suction member 400 is separated from the sheet Sa being conveyed, and enters an initial state shown in FIG. If no sheet Sa is detected by the sheet leading edge detection sensor 51c, it is determined that an error has occurred in the sheet S feeding operation, and the feeding operation is restarted from the approaching operation. Through the above six processes, only one sheet is fed from the plurality of sheets S stacked on the cassette 51a. If these six steps are repeated, the sheets S can be continuously fed one by one.

  FIG. 7 is a timing chart of the initial operation, the approach operation, the contact area increasing operation, the suction operation, the transport operation, and the separation operation shown in FIG. Here, the conveyance speed u of the driving roller 401, the supply voltage vp from the positive voltage supply unit 205a, the supply voltage vn from the negative voltage supply unit 205b, and the detection pulse ps of the sheet leading edge detection sensor 51c are shown. In FIG. 7, a section from time T0 to T1 indicated by P1 is an initial operation section, and the transport speed u is set to 0, the supply voltage vp, and the supply voltage vn are set to 0, respectively. A section from time T1 to T2 indicated by P2 is an approaching operation section, and the conveyance speed u is set to U.

  A section from time T2 to T3 indicated by P3 is a contact area increasing operation section, and the speed U is set as the transport speed u continuously from time T1. Time T3 is a time point at which the adsorption operation is performed. At this time, + V is set for the supply voltage vp and -V is set for the supply voltage vn. A section from time T3 to T5 indicated by P4 is a transport operation section, and U is continuously set for the transport speed u, + V is set for the supply voltage vp, and -V is set for the supply voltage vn. The detection pulse ps is output at time T4 immediately after time T3. Then, the control unit 70 determines the feeding retry depending on whether or not the time T4 is within a predetermined value range.

  A section from time T5 to T6 indicated by P5 is a separation operation section. Although U is set for the transport speed u, the supply voltage vp and the supply voltage vn are set to 0 again at time T5, and 0 is set to the transport speed u at time T6. A section from time T6 to time T8 indicated by P6 is an initial operation section, and is prepared for feeding the next sheet S. Even in the initial operation section P6, the sheet Sa that has been sucked and transported to the suction member 400 so far is transported by the drawing roller pairs 51d and 51e disposed downstream. Therefore, the feeding of the next sheet can be started after time T7 when the detection pulse ps is not output. Thereafter, if the above is repeated, continuous sheet feeding is performed.

  As described above, in the present embodiment, the suction member 400 is provided to be rotatable in synchronization with the rotation of one drive roller (rotating member) 401. Then, by increasing the downward slack amount of the adsorption member 400, the stacked sheets are adsorbed by the adsorption member 400 and then adsorbed by the adsorption member 400 while reducing the downward slack amount of the adsorption member 400. Feed the sheet. At this time, while the drive roller 401 makes one rotation, the suction member 400 sucks and feeds the sheet from the standby position, and then the suction member 400 returns to the standby position again.

  Thereby, the position of the adsorption member 400 can be controlled simply and accurately. Further, the suction member 400 can be moved to a suction position where the suction member 400 is brought into surface contact with the sheet, a separation position where the suctioned sheet is separated from the lower sheet while eliminating the bending, and a separation position where the sucked sheet is separated. . Further, the suction member 400 is rotated to suck the sheet, and after the sucked sheet is delivered to the pair of drawing rollers 51d and 51e, the suction member 400 is stopped at a position away from the sheet (standby position). . As a result, the sheets can be separated and fed without moving the frame carrying the adsorbing member 400, the driving means, the rollers, and the like. As a result, the sheet can be stably fed by electrostatic attraction with a simple configuration and low noise.

  In the present embodiment, the sheet S is separated and fed by the operation process described above, but the present invention is not limited to this. For example, in the initial operation of the present embodiment, the drive roller 401 is stopped, but the drive roller may continue to rotate at a constant speed from the separation operation so as to match the timing of the approaching operation. Further, in the separation operation of the present embodiment, the voltage supply to the suction member 400 is stopped and the suction member 400 and the sheet S are separated from each other. However, the voltage supply is continued and the sheet S is conveyed by the suction member 400. May be.

  Furthermore, in the present embodiment, an electrostatic attracting force is generated between the attracting member 400 and the sheet S in the configuration as described above, but the present embodiment is not limited to this. For example, the positive electrode 400a and the negative electrode 400b do not need to have a comb-teeth shape, and may have a shape like a uniform electrode in which an electric field is formed between the sheet S and the sheet S can be dielectrically polarized.

  Next, a second embodiment of the present invention will be described. FIG. 8 is a diagram illustrating the configuration of the sheet feeding apparatus according to the present embodiment. In FIG. 8, the same reference numerals as those in FIG. 2 described above indicate the same or corresponding parts.

  In FIG. 8, reference numeral 407 denotes a cylindrical sponge member that is an elastic member provided between the drive roller 401 and the suction member 400, and the sponge member 407 is eccentrically fixed to the outer periphery of the drive roller 401. An endless suction member 400 is fixed to the outer periphery of the sponge member 407.

  Then, by fixing the suction member 400 to the outer periphery of the sponge member 407 as in the present embodiment, the suction member 400 can be fixed more reliably and easily, and the cost can be reduced. . In addition, the suction member 400 can be prevented from being deformed to the drive roller side (rotating member side). In the present embodiment, the endless suction member 400 is fixed to the outer periphery of the sponge member 407. However, the present invention is not limited to this. For example, the end-shaped adsorption member may be fixed to a part of the sponge member, or an electrode having the same function as the adsorption member may be disposed on the surface of the sponge member.

  Next, a third embodiment of the present invention will be described. FIG. 9 is a diagram illustrating the configuration of the sheet feeding apparatus according to the present embodiment. In FIG. 9, the same reference numerals as those in FIG. 2 described above indicate the same or corresponding parts.

  In FIG. 9, 450 is a resin adsorbing member having no electrode inside. Reference numeral 251c denotes a charging roller that is provided above the suction member 450 and is a voltage application member that press-contacts the suction member 450 from above. The charging roller 251c is rotatably supported by a shaft support member (not shown) whose arrangement position is fixed, and is driven to rotate as the suction member 450 moves. An AC power source 252 is connected to the charging roller 251c, and the surface of the attracting member 450 is charged by contact charging by the charging roller 251c, and an electrostatic attracting force that attracts the sheet S by the applied charge. Occurs.

  Next, the detailed configuration of the suction member 450 and the principle of generation of the suction force by which the suction member 450 sucks the sheet S will be described with reference to FIG. FIG. 10A is a perspective view of the suction member 450, and FIG. 10B shows a cross section of the suction member 450.

The adsorption member 450 is a resin-made member having a single-layer structure, and is a dielectric having a volume resistance of 10 ⁸ Ωcm or more. Then, an alternating voltage is applied from the charging roller 251c pressed against the surface of the adsorption member 450. As a result, as shown in FIG. 10A, the surface of the adsorption member 450 has a positively charged region at intervals according to the frequency of the AC power supply 252 and the surface movement speed of the adsorption member 450. A negatively charged region is formed in a striped pattern. An unequal electric field is formed in the vicinity of the surface of the adsorbing member 450 by the positive and negative charging regions formed alternately in stripes. Then, when the suction member 450 having the unequal electric field formed in this manner is brought close to the sheet S, dielectric polarization occurs in the surface layer of the dielectric, and the Maxwell stress causes the suction member 450 between the suction member 450 and the sheet S. Electrostatic adsorption force is generated.

  Next, the sheet separating and feeding operation of the sheet suction separating and feeding unit 51b according to the present embodiment will be described. FIG. 11 is a schematic diagram expressing the operation of feeding the sheet S by the sheet suction separation feeding unit 51b in time series.

  FIG. 11A shows an initial operation of arranging the suction member 450 at the initial position of the feeding operation. At the time of this operation, the control unit 70 shown in FIG. 5 described above separates the suction member 450 from the charging roller 251c with a predetermined gap Lc, and moves the suction member 450 from the sheet S to the predetermined gap Lb. Thus, the driving roller 401 is stopped so as to be in the initial position of being separated.

  FIG. 11B shows a charging operation in which the suction member 450 is brought into contact with the charging roller 251c and the surface of the suction member 450 is charged by an alternating voltage from the AC power supply 252. In this operation, the control unit 70 is charged. Rotates the drive roller 401 in the direction of arrow F. Here, since the center Cb of the adsorption member 450 is eccentric from the rotation center Cr of the drive roller 401, when the drive roller 401 is rotated from the initial state, the adsorption member 450 starts to contact the charging roller 251c. Then, by applying an alternating voltage while rotating the driving roller 401, a charging region Ch in which positive polarity and negative polarity are alternately charged is formed on the adsorption member 450.

  FIG. 11C shows an approaching operation in which the charging region Ch formed on the surface of the adsorption member 450 approaches the upper surface of the uppermost sheet Sa. At this time, the control unit 70 continues to operate. The drive roller 401 is rotated in the direction of arrow F. When the drive roller 401 is rotated in this way, the center Cb of the suction member 450 is decentered from the rotation center Cr of the drive roller 401, so that the surface of the suction member 450 approaches the upper surface of the uppermost sheet Sa.

  FIG. 11D shows a contact area increasing operation in which the approaching operation is continued to bring the surface of the adsorption member 450 into contact with the uppermost sheet Sa and the contact area Mc is increased. During this operation, the control unit 70 rotates the drive roller 401 in the direction of arrow F as in the approach operation. As a result, the charging region Ch of the suction member 450 comes into contact with the uppermost sheet Sa, and the uppermost sheet Sa is sucked by the suction member 450. When the driving roller 401 further rotates, the contact area Mc between the charging region Ch of the adsorption member 450 and the uppermost sheet Sa increases.

  FIG. 11E shows that the sheet Sa adsorbed on the charging area Ch of the adsorbing member 450 is separated from the stacked next sheet Sb when the sheet contact area Mn is obtained by the operation for increasing the contact area described above. The operation of conveying to the drawing roller pair 51d, 51e is shown. The sheet contact area Mn is a conveyance force that overcomes the conveyance resistance acting on the uppermost sheet Sa when the uppermost sheet Sa adsorbed on the adsorption member 450 is conveyed by the adsorption member 450. It is the area when. When the sheet contact area reaches Mn as described above, the uppermost sheet Sa starts to be conveyed toward the drawing roller pairs 51d and 51e.

  FIG. 11F shows a separating operation for separating the conveyed uppermost sheet Sa from the adsorbing member 450 after the uppermost sheet Sa is sandwiched between the drawing roller pairs 51d and 51e. When the sheet Sa is sandwiched between the pair of drawing rollers 51d and 51e, the charging region Ch of the suction member 450 does not come into contact with the uppermost sheet Sa, so that the suction force of the suction member 450 does not work. When the suction force of the suction member 450 stops working, the transported uppermost sheet Sa is transported by the pair of drawing rollers 51d and 51e that are sandwiched.

  Thereafter, when the driving roller 401 continues to rotate in the direction of the arrow F, the suction member 450 is positioned away from the conveyed sheet Sa as shown in FIG. Return to the initial state of waiting for the transport of Sb. If no sheet Sa is detected by the sheet leading edge detection sensor 51c, it is determined that an error has occurred in the sheet S feeding operation, and the feeding operation is restarted from the approaching operation. Through the above six processes, only one sheet is fed from the plurality of sheets S stacked on the cassette 51a. If these six steps are repeated, the sheets S can be continuously fed one by one.

  FIG. 12 is a timing chart of the initial operation, the charging operation, the approaching operation, the contact area increasing operation, the conveying operation, and the separating operation shown in FIG. Here, the conveyance speed u of the driving roller 401, the supply voltage v from the AC power supply 252, and the detection pulse ps of the sheet leading edge detection sensor 51c are shown in time series. In FIG. 12, a section from time T0 to T1 indicated by P1 is an initial operation section. At this time, 0 is set for the conveyance speed u and 0 is set for the supply voltage v. A section from time T1 to T2 indicated by P2 is a charging operation section, and U is set as the conveyance speed u and an alternating voltage of ± V is set as the supply voltage.

  A section from time T2 to T3 indicated by P3 is an approaching operation section. The speed U is set as the transport speed u continuously from time T1, and the supply voltage v is set to 0 again at time T2. A section from time T3 to T4 indicated by P4 is a contact area increasing operation section, and the speed U is continuously set as the transport speed u. A section from time T4 to T6 indicated by P5 is a transport operation section, and the speed U is continuously set as the transport speed u. The detection pulse ps is output at time T5 immediately after time T4. Further, the control unit 70 determines the feeding retry depending on whether or not the time T5 is within a predetermined value range.

  A section from time T6 to T7 indicated by P6 is a separation operation section. Although U is set for the transport speed u, 0 is set for the transport speed u at time T7. A section from time T7 to T9 indicated by P7 is an initial operation section, and is prepared for feeding the next sheet S. Even in this initial operation section P7, the sheet Sa is conveyed by the pair of drawing rollers 51d and 51e. Therefore, the feeding of the next sheet can be started after time T8 when the detection pulse ps is not output. Thereafter, if the above is repeated, continuous sheet feeding is performed.

  As described above, in the present embodiment, the sheet adsorbing force can be obtained by charging the surface of the adsorbing member from the outside by the charging roller 251c. As a result, the adsorption member 450 can be charged without disposing an electrode inside the adsorption member, so that the configuration of the adsorption member 450 can be simplified and the cost can be reduced.

  In the present embodiment, the sheet S is separated and fed by performing the feeding operation including the above six steps, but the present invention is not limited to this. Alternatively, a direct current may be connected to the charging roller 251c so that a charging region having the same polarity on the entire surface may be formed without forming the positive and negative alternating charging regions on the adsorption member 450. In that case, although the electrostatic attraction force per unit area becomes small, the electrostatic attraction force can be more easily generated.

  Next, a fourth embodiment of the present invention will be described. FIG. 13 is a diagram illustrating the configuration of the sheet feeding apparatus according to the present embodiment. In FIG. 13, the same reference numerals as those in FIG. 2 described above indicate the same or corresponding parts.

  In FIG. 13, reference numeral 270 denotes a suction member, and 271 denotes a drive roller. The drive roller 271 is rotatably supported by a shaft support member (not shown) whose arrangement position is fixed, and is arranged with a predetermined gap Lr from the upper surface of the uppermost sheet Sa stacked on the cassette 51a. In addition, the driving force from the driving unit 203 is transmitted to the driving roller 271 via the driving transmission unit.

  Further, a fixing member 272 for fixing the suction member 270 is fixed to the driving roller 271. In the present embodiment, the suction member 270 is a flexible member having an end shape that is longer than the length of the peripheral surface of the drive roller 271, and both ends of the suction member 270 are half of their own elastic force. It is fixed to the fixing member 272 so as to draw a substantially arc shape longer than the arc.

  And by making the adsorption member 270 into the end shape as in this embodiment, the same effect as the first embodiment described above can be obtained and the length of the adsorption member 270 can be shortened. Thus, cost reduction can be achieved.

  In the embodiment described so far, the sheet S is attracted to the attracting member by the electrostatic attracting force, but the present invention is not limited to this. For example, a fine fiber structure of submicron order may be formed on the adsorbing member and adsorbed by an intermolecular attractive force acting between the sheet S.

51, 52 ... Sheet feeding device, 51a, 52a ... Cassette, 51b, 52b ... Sheet adsorption separation feeding unit, 51c ... Sheet tip detection sensor, 51d, 51e ... Pulling roller pair, 55 ... Image forming unit, 70 ... Control , 100 ... Image forming apparatus, 100A ... Image forming apparatus main body, 203 ... Driving means, 205 ... Power supply unit, 205a ... Positive voltage supply means, 205b ... Negative voltage supply means, 251c ... Charging roller, 252 ... AC power supply, 270 ... Adsorption member, 271 ... Drive roller, 272 ... Fixing member, 400 ... Adsorption member, 400a ... Positive electrode, 400b ... Negative electrode, 401 ... Driving roller, 401a, 401b ... Conducting part, 402 ... Fixing part, 407 ... Sponge member , 450 ... Adsorption member, G ... Gap, Mn ... Sheet contact area, S ... Sheet, Sa ... Top sheet

Claims (12)

A stacking means on which sheets are stacked;
A rotating member disposed above the stacking means;
An adsorbing member provided so as to be movable in synchronization with the rotation of the rotating member, and electrically adsorbing the sheets stacked on the stacking means;
Driving means for rotating the rotating member;
Control means for controlling the driving means,
The control means increases the amount of slackness of the suction member downward, causes the sheets stacked on the stacking means to be attracted to the suction member, and then reduces the amount of slackness of the suction member downward. In the sheet feeding device for feeding the sheet adsorbed by the adsorption member,
The controller is configured to move the suction member to the standby position after the suction member is moved from the standby position to suck and feed the sheet by rotating the rotating member once. Sheet feeding device.   The sheet feeding apparatus according to claim 1, wherein the suction member is supported by the rotating member in a slack state.   The sheet feeding apparatus according to claim 1, wherein the suction member is an endless member, and a part of the suction member is fixed to the rotating member.   The sheet feeding apparatus according to claim 1, wherein the suction member is supported by the rotating member via an elastic member attached to a peripheral surface of the rotating member.   3. The suction member is an end-shaped member, and both ends thereof are fixed to a fixing member attached to the rotating member and are supported by the rotating member while forming an arc shape. The sheet feeding apparatus described in 1.   6. The sheet feeding apparatus according to claim 1, further comprising a power source for applying a voltage to the attraction member and applying an attraction force for attracting the sheet by static electricity. The adsorption member is provided with two electrodes,
The power supply includes a first power supply that applies a positive voltage to one of the two electrodes, and a second power supply that applies a negative voltage to the other of the two electrodes. 6. The sheet feeding device according to 6.   A voltage application member is provided between the suction member and the power source, and contacts the suction member before the suction member contacts the sheet to apply a voltage from the power source to the suction member. The sheet feeding apparatus according to claim 6.   9. The sheet feeding apparatus according to claim 8, wherein the power source is an AC power source.   The magnitude of the adsorption force due to static electricity when the adsorption member eliminates the slack is set such that the sheet is separated from the adsorption member due to the rigidity of the sheet. The sheet feeding apparatus according to any one of 1 to 9.   The suction member has flexibility, a standby position away from the sheets stacked on the stacking means, a suction position for sucking the sheets stacked on the stacking means, and a lower position by moving the sucked sheets upward 11. The sheet feeding apparatus according to claim 1, wherein the sheet feeding device is provided so as to be moved to a separation position for separating from the sheet and a separated position where the adsorbed sheet is separated from the adsorption member. An image forming unit for forming an image on a sheet;
An image forming apparatus comprising: the sheet feeding device according to claim 1, wherein the sheet feeding device feeds a sheet to the image forming unit.

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