Patent Application
20160272442
The present invention relates to a sheet feeding device and an image forming apparatus, and more particularly, to a technique of feeding a sheet using electrostatic adsorption force.
An image forming apparatus such as a copying machine or a printer according to a related art includes a sheet feeding device that feeds a sheet, and as the sheet feeding device, there is a friction feed system in which a topmost sheet is separated and fed from a cassette on which a sheet bundle is loaded using frictional force of a rubber roller or the like. In the sheet feeding device of the friction feed system, the topmost sheet is fed by the rubber roller rotating while pressing the sheet bundle. Here, when a sheet is fed, multi-sheet feeding in which a plurality of sheets are conveyed by friction between sheets may occur. On the other hand, conveyance resistance works on the remaining sheets excluding the topmost sheet through a separating pad or a retard roller, and thus only the topmost sheet is fed to an image forming portion.
Meanwhile, in the sheet feeding device of the friction separation system, since the rubber roller feeds a sheet while applying great pressure to the sheet, noise generated by sliding friction between sheets or between the sheet and the rubber roller is problematic. In addition, when the multi-sheet feeding caused by the separating pad or the retard roller is prevented, sliding fricative between sheets is greatly generated. Further, since the separating pad or the retard roller serves as conveyance resistance of the topmost sheet even when the multi-sheet feeding does not occur, a sound is generated by stick slip between the separating pad or the retard roller and the sheet.
In this regard, as a technique of solving the problem, there is a sheet feeding device configured to separate and feed a sheet while adsorbing the sheet using electrostatic adsorption force, specifically, by an electric field formed on a belt surface (see Patent Literatures 1 and 2). In the sheet feeding device of the electrostatic adsorption separation system, since it is possible to convey the topmost sheet as if the topmost sheet is peeled off from the sheet bundle, it is possible to significantly reduce noise generated in a feeding portion.
However, in the sheet feeding device of the related art that feeds the sheet using electrostatic adsorption force, in a configuration of Patent Literature 1, it is possible to apply sufficient electrostatic adsorption force to the sheet, but when the sheet is separated, since lifting and lowering are performed for each frame on which the adsorbing belt is carried, an operation sound occurs. A collision sound with the sheet occurs as well. Further, when the sheet is adsorbed, belt tension is reduced by reducing an inter-axial distance so that a sheet can be adsorbed with certainty even when a sheet curls, that is, so that followability to the sheet curl can be secured when the adsorbing belt adsorbs the sheet. However, when the sheet is adsorbed in a state in which belt tension is reduced, it is necessary to increase tension at the time of the separation operation, and when the tension is increased as described above, string vibration occurs in the belt, and a sudden sound is caused by the vibration.
In a configuration of Patent Literature 2, the adsorbing belt is used, but since the sheet separation operation is performed by causing the carrying roller to perform an eccentric motion instead of lifting and lowering the adsorbing belt for each frame, a machinery operation sound is reduced. However, when the adsorbing belt comes into contact with the sheet bundle with certainty, the roller collides with the sheet bundle through the adsorbing belt, and thus a collision sound still occurs. Further, when an attempt to prevent a collision between the roller and the sheet bundle is made, the belt is separated from the sheet bundle, sheet adsorption by the adsorbing belt becomes unstable, leading to a feeding failure.
In this regard, in light of the foregoing, it is an object of the present invention to provide a sheet feeding device and an image forming apparatus, which are capable of stably performing sheet feeding by electrostatic adsorption at a low noise with a simple configuration.
The present invention provides a sheet feeding device, which includes a loading unit that loads a sheet, a rotary member arranged above the loading unit, an adsorbing member that is arranged to be movable in synchronization with rotation of the rotary member and electrically adsorbs the sheet loaded on the loading unit, a driving unit that rotates the rotary member, and a control unit that controls the driving unit, wherein the control unit causes the sheet loaded on the loading unit to be adsorbed on the adsorbing member by increasing a downward looseness amount of the adsorbing member, and then feeds the sheet adsorbed on the adsorbing member while reducing the downward looseness amount of the adsorbing member, and the control unit performs one rotation of the rotary member to move the adsorbing member from a standby position, causes the sheet to be adsorbed and fed, and then moves the adsorbing member to the standby position.
According to the present invention, it is possible to cause the rotary member to perform one rotation to move the adsorbing member from the standby position, cause the adsorbing member to adsorb and feed the sheet, and then cause the adsorbing member to move the standby position. Thus, it is possible to stably perform sheet feeding by electrostatic adsorption at a low noise with a simple configuration.
Hereinafter, embodiments of the present invention will be described in detail with reference to the appended drawings.
In
The image forming portion 55 includes an exposure unit 42 and four process cartridges 43 (43y, 43m, 43c, and 43k) for forming toner images of four colors, that is, yellow (Y), magenta (M), cyan (C), and black (Bk). The image forming portion 55 further includes an intermediate transfer unit 44, a secondary transfer portion 56, and a fixing portion 57 arranged above the process cartridge 43.
Here, the process cartridge 43 includes a photosensitive drum 21 (21y, 21m, 21c, and 21k), a charging roller 22 (22y, 22m, 22c, and 22k), and a developing roller 23 (23y, 23m, 23c, and 23k). The process cartridge 43 further includes a drum cleaning blade 24 (24y, 24m, 24c, and 24k).
The intermediate transfer unit 44 includes a belt driving roller 26, an intermediate transfer belt 25 stretching to an inner secondary transfer roller 56a or the like, and primary transfer roller 27 (27y, 27m, 27c, and 27k) that abuts the intermediate transfer belt 25 at a position opposite to the photosensitive drum 21. As will be described later, as transfer bias of a positive polarity is applied to the intermediate transfer belt 25 through the primary transfer roller 27, toner images having a negative polarity on the photosensitive drum 21 are sequentially multi-transferred onto the intermediate transfer belt 25. As a result, a full color image is formed on the intermediate transfer belt 25.
The secondary transfer portion 56 is configured with the inner secondary transfer roller 56a and an outer secondary transfer roller 56b that comes into contact with the inner secondary transfer roller 56a with the intermediate transfer belt 25 interposed therebetween. Further, as will be described later, as secondary transfer bias of a positive polarity is applied to the outer secondary transfer roller 56b, the full color image formed on the intermediate transfer belt 25 is transferred onto the sheet S.
The fixing portion 57 includes a fixing roller 57a and a fixing backup roller 57b. The sheet S is nipped and conveyed between the fixing roller 57a and the fixing backup roller 57b, and thus the toner image on the sheet S is pressed and heated, and then fixed onto the sheet S. The sheet feeding devices 51 and 52 include cassettes 51a and 52a, respectively, serving as a storage unit (loading unit) that stores the sheet S and sheet adsorption separation feeding portions 51b and 52b, respectively, having a function of feeding the sheets S one by one while adsorbing the sheet S stored in the cassettes 51a and 52a by static electricity.
In
Next, an image forming operation of the image forming apparatus 100 having the above configuration will be described. When the image forming operation starts, the exposure unit 42 first irradiates the surface of the photosensitive drum 21 with laser beams based on image information provided from a personal computer (not illustrated) or the like. At this time, the surface of the photosensitive drum 21 is uniformly charged to a predetermined polarity and potential by the charging roller 22, and when the laser beams are irradiated, charges of a portion irradiated with the laser beams are attenuated, and thus an electrostatic latent image is formed on the surface of the photosensitive drum.
Thereafter, the electrostatic latent image is developed by yellow (Y), magenta (M), cyan (C), and black (Bk) toners supplied from the developing roller 23, and thus the electrostatic latent image is visualized as toner images. Then, the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 25 by primary transfer bias applied to the primary transfer roller 27, and thus 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, in the sheet feeding devices 51 and 52, only one piece of sheet S is separated and fed from the cassettes 51a and 52a through the sheet adsorption separation feeding portions 51b and 52b. Thereafter, the sheet S is detected by sheet leading end detecting sensors 51c and 52c and reaches a pair of drawing rollers 51d and 51e. Further, the sheet S nipped between the pair of drawing rollers 51d and 51e is fed to the conveyance path 103 and abuts a pair of registration rollers 62a and 62b that is stopped, so that a position of the leading end thereof is adjusted.
Then, in the secondary transfer portion 56, the pair of registration rollers 62a and 62b are driven at a timing at which the full color toner image on the intermediate transfer belt matches the position of the sheet S. As a result, the sheet S is conveyed to the secondary transfer portion 56, and in the secondary transfer portion 56, the full color toner image is collectively transferred onto the sheet S through secondary transfer bias applied to the outer secondary transfer roller 56b.
The sheet S onto which the full color toner image has been transferred is conveyed to the fixing portion 57 and receives heat and pressure in the fixing portion 57, and the toners of the respective colors undergo melting and color mixture and are fixed as a full color image to the sheet S. Thereafter, the sheet S to which the image has been fixed is discharged through the discharge portion 58 installed in the downstream of the fixing portion 57. Further, when an image is formed on both sides of the sheet, the conveyance direction of the sheet S is reversed by the sheet reversing portion 59, so that the sheet S is conveyed to the image forming portion 55 again.
Next, a configuration of the sheet feeding device 51 according to the present embodiment will be described with reference to
The sheet adsorption separation feeding portion 51b includes an adsorbing member 400, a driving roller 401, a driving unit 203, and a power source unit 205. The adsorbing member 400 has flexibility and has an endless shape larger than an outer circumference length of the driving roller 401, and the adsorbing member 400 has a cross sectional shape in which substantially a circular shape is maintained by its own elastic force. The driving roller 401 is rotatably shaft-supported by a shaft support member (not illustrated) whose arrangement position is fixed, and arranged with a predetermined gap Lr from the top surface of the topmost sheet Sa loaded on the cassette 51a. Further, driving force from the driving unit 203 is transmitted to the driving roller 401 through the driving transmission unit. The sheet adsorption separation feeding portion 52b arranged in the sheet feeding device 52 has the same configuration as the sheet adsorption separation feeding portion 51b of the sheet feeding device 51, and thus a description thereof is omitted.
Here, in the present embodiment, a gap G is formed between the adsorbing member 400 and the driving roller 401, and a part of the adsorbing member 400 is fixed to a fixing portion 402 of the driving roller 401. In other words, the adsorbing member 400 is supported by the driving roller 401 in a loose state. The fixing of the adsorbing member 400 to the driving roller 401 may be performed using an adhesive or the like or may be performed by holding the adsorbing member 400 by a fixing member (not illustrated) and the driving roller 401. Further, when the adsorbing member 400 is fixed using the fixing member, the fixing member protrudes from the surface of the adsorbing member 400, but in this case, by fixing the adsorbing member 400 in a portion that does not come into contact with the sheet by the fixing member, the negative effects of the sheet feeding operation are prevented.
The lifting and lowering unit 301 includes a lifter 301b that is installed to be rotatable down the sheet supporting plate 301a, and changes the position of the sheet supporting plate 301a and the position of a topmost sheet Sa loaded on the sheet supporting plate 301a according to a rotation angle of the lifter 301b. The sheet leading end detecting sensor 51c is arranged in the sheet conveyance path between the sheet adsorption separation feeding portion 51b and the pair of drawing rollers 51d and 51e. Success or failure of sheet feeding is detected by detecting whether or not the sheet leading end detecting sensor 51c detects the sheet S at a predetermined timing. In the present embodiment, the sheet leading end detecting sensor 51c is a non-contact reflective photo sensor, and detects the presence or absence of a detection target by irradiating the detection target with spotlight and measuring reflected light quantity thereof.
In
Here, when the top surface of the topmost sheet Sa is positioned at a predetermined height, the sensor flag 302a rotates, and the photo sensor 302b is light-shielded. A controller 70 of
Here, in the present embodiment, when the adsorbing member 400 adsorbs and conveys the sheet, the adsorbing member 400 adsorbs the sheet by static electricity so that the sheets do not undergo sliding friction, and then the adsorbing member 400 is pulled upward while elastically deforming the adsorbing member 400. As the adsorbing member 400 is pulled upward while elastically deforming the adsorbing member 400 as described above, the sheet is separated from another sheet.
In this regard, in the present embodiment, the length of the adsorbing member 400 is decided so that a sheet contact area Mn illustrated in (a) of
Further, the power source unit 205 includes a positive voltage supply unit 205a serving as a first power source, a negative voltage supply unit 205b serving as a second power source, and switches 205c and 205d that control voltage supply. The voltages generated by the power source unit 205 are supplied to the adsorbing member 400 through the driving roller 401, and the applied voltages generate the electrostatic adsorption force of attracting the sheet S in the adsorbing member 400.
Next, a detailed configuration of the adsorbing member 400 of the sheet adsorption separation conveying portion 51b and a generation principle of the adsorption force by which the adsorbing member 400 adsorbs the sheet S will be described with reference to
The adsorbing member 400 includes a base layer 400c, a positive electrode 400a, and a negative electrode 400b, and the positive electrode 400a of the comb teeth shape and the negative electrode 400b of the comb teeth shape are alternately arranged inside the base layer 400c. In the present embodiment, the base layer 400c is of polyimide serving as a dielectric having volume resistance of 108 Ωcm or more and has a thickness of about 100 μl. The positive electrode 400a and the negative electrode 400b are conductors having volume resistance of 106 Ωcm or less and made of copper having a thickness of about 10 μm.
Exposure regions 400d and 400e in which the positive electrode 400a and the negative electrode 400b serving as the other electrode are exposed are form on the back surface of the adsorbing member 400. A voltage from the positive voltage supply unit 205a and a voltage from the negative voltage supply unit 205b are supplied to the exposure region 400d of the positive electrode 400a and the exposure region 400e of the negative electrode 400b through the driving roller 201, respectively. As a result, in the present embodiment, the positive electrode 400a and the negative electrode 400b become the positive and negative voltages of about 1 kV, respectively.
An unequal electric field is formed near the surface of the adsorbing member 400 by the positive electrode 400a and the negative electrode 400b to which the voltage is applied. When the adsorbing member 400 approaches the sheet S, dielectric polarization occurs on the surface layer of the sheet S serving as a dielectric, and the electrostatic adsorption force is generated between the adsorbing member 400 and the sheet S due to Maxwell's stress.
The driving roller 401 includes an insulating shaft 401c and conducting portions 401a and 401b attached to both end portions of the insulating shaft 401c as illustrated in
In
Next, the sheet feeding operation performed by the sheet adsorption separation feeding portion 51b according to the present embodiment will be described with reference to
(b) of
(c) of
(e) of
(f) of
A zone from the time T2 to a time T3 indicated by P3 is a contact area increase operation zone, and subsequently from the time T1, the conveyance velocity u is set to a velocity U. The time T3 is a point in time at which the adsorption operation is performed, and at this time, the supply voltage vp is set to +V, and the supply voltage vn is set to −V. A zone from the time T3 to a time T5 indicated by P4 is a conveyance operation zone, and continuously, the conveyance velocity u is set to U, the supply voltage vp is set to +V, and the supply voltage vn is set to −V. At a time T4 directly after the time T3, the detection pulse ps is output. Further, the controller 70 determines whether or not the feeding is retried according to whether or not the time T4 falls within a predetermined value range.
A zone from the time T5 to a time T6 indicated by P5 is a separation operation zone. The conveyance velocity u is set to U, but at the time T5, the supply voltage vp and the supply voltage vn are set to 0 again, and at the time T6, the conveyance velocity u is set to 0. A zone from the time T6 to a time T8 indicated by P6 is the initial operation zone, and preparation for feeding of the next sheet S is performed. In the initial operation zone P6, the sheet Sa adsorbed and conveyed on the adsorbing member 400 until now is conveyed by the pair of drawing rollers 51d and 51e arranged in the downstream. For this reason, the feeding of the next sheet can start after the time T7 at which the output of the detection pulse ps is stopped. Thereafter, the above operation is repeated, and thus continuous sheet feeding is performed.
As described above, in the present embodiment, the adsorbing member 400 is arranged to be rotatable in synchronization with the rotation of one driving roller (rotary member) 401. Further, the loaded sheet is adsorbed on the adsorbing member 400 by increasing the downward looseness amount of the adsorbing member 400, and then the sheet adsorbed on the adsorbing member 400 is fed while reducing the downward looseness amount of the adsorbing member 400. At this time, while the driving roller 401 perform one rotation, after the adsorbing member 400 adsorbs and feeds the sheet from the standby position, the adsorbing member 400 returns to the standby position again. As a result, it is possible to control the position of the adsorbing member 400 easily and accurately. Further, the adsorbing member 400 is movable to the adsorption position at which the adsorbing member 400 comes into surface contact with the sheet and adsorbs the sheet, the separation position at which the adsorbed sheet is separated from the lower sheet while eliminating the bending, and the separation position at which the adsorbed sheet is separated. In addition, the adsorbing member 400 rotates to adsorb the sheet and hands the adsorbed sheet over to the pair of drawing rollers 51d and 51e, and thereafter, the adsorbing member 400 is stopped at a position (a standby position) away from the sheet. Thus, it is possible to separate and feed the sheet without moving the frame carrying the adsorbing member 400, the driving unit, the roller, and the like. As a result, it is possible to stably performing sheet feeding by the electrostatic adsorption at a low noise with a simple configuration.
Further, in the present embodiment, the sheet S is separated and fed through the above operation processes, but the present invention is not limited to this example. For example, in the initial operation of the present embodiment, the driving roller 401 is stopped, but the driving roller may continuously rotate at a constant velocity from the separation operation according to a timing of the approach operation. Further, in the separation operation of the present embodiment, the voltage supply to the adsorbing member 400 is stopped, and the adsorbing member 400 is separated from the sheet S, but the voltage may be continuously supplied, and the sheet S may be conveyed by the adsorbing member 400.
In addition, in the present embodiment, the electrostatic adsorption force is generated between the adsorbing member 400 and the sheet S through the above-described configuration, but the present embodiment is not limited to this example. For example, the positive electrode 400a and the negative electrode 400b may not have the comb teeth shape and may have a shape of a uniform electrode in which the electric field can be formed between the electrodes 400a and 400b and the sheet S to dielectric-polarize the sheet S.
Next, a second embodiment of the present invention will be described.
In
As the adsorbing member 400 is fixed to the outer circumference of the sponge member 407 as in the present embodiment, it is possible to fix the adsorbing member 400 easily with certainty and reduce the cost. Further, it is possible to prevent the adsorbing member 400 from being deformed to the driving roller side (the rotary member side). In the present embodiment, the endless adsorbing member 400 is fixed to the outer circumference of the sponge member 407, but the present embodiment is not limited to this example. For example, an open-ended adsorbing member may be fixed to a part of the sponge member, or an electrode having the same function as the adsorbing member may be arranged on the surface of the sponge member.
Next, a third embodiment of the present invention will be described.
In
Next, a detailed configuration of the adsorbing member 450 and a generation principle of the adsorption force by which the adsorbing member 450 adsorbs the sheet S will be described with reference to
The adsorbing member 450 is a member having a single layer structure made of resin and serves as a dielectric having volume resistance of 108 Ωcm or more. Further, an alternating voltage is applied from the charging roller 251c pressed on the surface of the adsorbing member 450. As a result, a region charged to a positive polarity and a region charged to a negative polarity are formed on the surface of the adsorbing member 450 in a stripe form at intervals corresponding to the frequency of the AC power source 252 and the surface moving velocity of the adsorbing member 450 as illustrated in (a) of
Next, a sheet separation feeding operation of the sheet adsorption separation feeding portion 51b according to the present embodiment will be described.
(a) of
(b) of
(c) of
(d) of
(e) of
(f) of
Thereafter, when the driving roller 401 further rotates in the arrow F direction continuously, the adsorbing member 450 moves to the position at which the adsorbing member 450 is separated from the sheet Sa being conveyed and returns to the initial state in which it is on standby for conveyance of the next sheet Sb as illustrated in (a) of
A zone from the time T2 to a time T3 indicated by P3 is the approach operation zone, and subsequently from the time T1, the conveyance velocity u is set to the velocity U, and at the time T2, the supply voltage v is set to 0 again. A zone from the time T3 to a time T4 indicated by P4 is the contact area increase operation zone, and the conveyance velocity u is continuously set to the velocity U. A zone from the time T4 to a time T6 indicated by P5 is the conveyance operation zone, and the conveyance velocity u is continuously set to the velocity U. The detection pulse ps is output at the time T5 directly after the time T4. The controller 70 determines whether or not the feeding is retried according to whether or not the time T5 falls within a predetermined value range.
A zone from the time T6 to a time T7 indicated by P6 is the separation operation zone. The conveyance velocity u is set to U, but at the time T7, the conveyance velocity u is set to 0. A zone from the time T7 to a time T9 indicated by P7 is the initial operation zone, and preparation for feeding of the next sheet S is performed. In the initial operation zone P7, the sheet Sa is conveyed by the pair of drawing rollers 51d and 51e. For this reason, the feeding of the next sheet can start after the time T8 at which the output of the detection pulse ps is stopped. Thereafter, the above operation is repeated, and thus continuous sheet feeding is performed.
As described above, in the present embodiment, it is possible to obtain the sheet adsorption force by charging the surface layer of the adsorbing member from the outside through the charging roller 251c. As a result, since it is possible to charge the adsorbing member 450 without arranging the electrode inside the adsorbing member, it is possible to simplify the configuration of the adsorbing member 450 and reduce the cost.
Further, in the present embodiment, the sheet S is separated and fed by performing the feeding operation including the six processes, but the present invention is not limited to this example. A DC current may be connected to the charging roller 251c to form a charged region in which an entire surface has a homopolarity without forming the positive and negative charged regions alternately on the adsorbing member 450. In this case, the electrostatic adsorption force per unit area is reduced, but the electrostatic adsorption force can be generated more conveniently.
Next, a fourth embodiment of the present invention will be described.
In
Further, a fixing member 272 for fixing the adsorbing member 270 is fixed to the driving roller 271. In the present embodiment, the adsorbing member 270 is an open-ended member having flexibility larger than the length of the circumferential surface of the driving roller 271, and both ends of the adsorbing member 270 are fixed to the fixing member 272 so that a substantially circular arc shape larger than a semicircular arc is drawn by its own elastic force.
As the adsorbing member 270 has an open-ended shape as in the present embodiment, it is possible to obtain the same effects as in the first embodiment, and it is possible to reduce the cost by reducing the length of the adsorbing member 270.
In the embodiment described so far, the sheet S is adsorbed on the adsorbing member by the electrostatic adsorption force, but the present invention is not limited to this example. For example, a fine fiber structure of a submicron order may be formed on the adsorbing member, and the sheet S may adsorbed by intermolecular attractive force working between the sheet S and the fine fiber structure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-083584 | Apr 2013 | JP | national |
| 2014-056024 | Mar 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/060410 | 4/10/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2014/060410 | Apr 2014 | US |
| Child | 14777622 | US |
