JP2011051781A - Sheet conveying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent occurrence of shock jitter by preventing the transmission of vibration, which occurs when the rear end of a sheet is fallen from a nip of a pair of conveying rollers, to a writing means. <P>SOLUTION: In a sheet conveying device for conveying sheets by pinching the sheet between two conveying rollers forming a nip, the two conveying rollers are structured freely to be displaced, and include energizing force for energizing in directions opposite to each other, these energizing forces are set at a strength different from each other, and a positioning means is provided to the conveying roller having a larger energizing force. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet as an image recording medium, and an image forming apparatus such as a printer, a facsimile, and a copying machine including the sheet conveying apparatus.

  2. Description of the Related Art Conventionally, in an image forming apparatus, for example, a sheet is conveyed to an image forming unit in a timely manner in a mechanism having a registration roller pair, a drive source that supplies driving to the registration roller pair, and a drive connecting unit that transmits the driving. Since the drive coupling mechanism is rotating, if the frequency of the meshing vibration of the motor and gear is close to the resonance frequency of the registration roller, it will be amplified and leaked out of the image forming apparatus main body as noise. Has occurred.

  In order to solve such a problem, Patent Document 1 proposes to attach a flywheel to the registration roller shaft to solve the problem. However, there are a wide variety of problems caused by vibration.

  When the sheet that is nipped and conveyed by the nip of the registration roller pair passes through the nip, the registration driven roller moves by the thickness of the sheet. This is more conspicuous as the paper thickness is larger, and this vibration is transmitted to the housing, and the writing means supported by the housing is vibrated to cause horizontal lines in the image (hereinafter referred to as shock jitter). The trouble that appears becomes.

  Accordingly, a main object of the present invention is to prevent the vibration generated when the trailing edge of the sheet comes out from the nip of the conveying roller pair from being transmitted to the writing means. Then, while preventing the vibration generated when the trailing edge of the sheet comes out from the nip of the conveying roller pair from being transmitted to the writing means, the alignment of the conveying roller pair is maintained with high accuracy and the drive is transmitted to the conveying roller. Prevents vibration from occurring between gears. As a result, it is expected that no shock jitter will occur.

  The object is to provide a paper transporting device that sandwiches and transports paper by two transport rollers forming a nip, and the two transport rollers are configured to be displaceable, and each has a biasing force that biases them in opposite directions. This is achieved by setting the urging forces to different strengths and attaching positioning means to the conveying roller having the larger urging force.

  The two transport rollers are preferably supported by a single structure. Further, it is more effective if at least one of the two transport rollers is provided with a drive connecting means for transmitting driving from a drive source, and the driving connecting means is also provided with a biasing force.

  According to the present invention, the two conveying rollers are configured to be displaceable, and are provided with urging forces that urge in opposite directions, and the urging forces are set to different strengths. Since the positioning means is attached to the sheet, the vibration when the trailing edge of the sheet passes through the nip of the roller pair is absorbed by the two displaceable rollers having both urging forces and is not transmitted to the support body, thereby preventing shock jitter. .

  Since two rollers having urging force are supported by one structure, high-precision alignment can be ensured and stable paper conveyance can be realized. If the drive connecting means is attached to the conveying roller and the driving connecting means is given an urging force, it is possible to prevent the occurrence of vibration in the connecting means and to prevent shock jitter.

1 is a central sectional view showing an outline of a full-color printer according to the present invention. FIG. 2 is a central cross-sectional view illustrating an outline of a yellow image forming unit in the printer of FIG. 1. FIG. 2 is a partial cross-sectional view of the printer of FIG. 1 with a side frame opened. It is a fragmentary perspective view explaining attachment with the support plate of a registration roller pair. It is the schematic which looked at the registration roller pair from the main body front. It is the schematic sectional drawing which looked at the drive connection part of the registration roller pair from the main body rear surface. It is a schematic plan view which shows the pitch ring of the drive connection part of a registration roller pair.

  An embodiment of the present invention will be described with reference to the drawings. The image forming apparatus of this embodiment is a full-color printer that employs a so-called tandem method. First, the internal configuration of the full-color printer 100 will be described with reference to FIGS. The full color printer 100 includes four latent image carriers as image forming means for forming images of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). The drum-shaped photoconductors 2Y, 2C, 2M, and 2Bk are spaced apart at equal intervals in the left-right direction in the figure and arranged in parallel. During operation of the printer 100, the printer 100 is rotated in the direction of the arrow by a drive source (not shown). Around the photoconductor, members and devices necessary for electrophotographic image formation, such as a developing device, are provided and are configured as image forming units at four locations, corresponding to the toner color of the image to be formed For the sake of convenience, Y (yellow), C (cyan), M (magenta), and Bk (black) representing the color are appended as subscripts after the number indicating each image forming device for convenience. In particular, in the general description, these subscripts may be omitted. The four image forming units 1Y, 1C, 1M, and 1Bk all have the same configuration.

  Focusing on the image forming unit 1Y including the yellow image photoreceptor 2Y shown in FIG. 2, a charging device 4Y including a charging roller 4aY and a developing roller 5aY are arranged around the photoreceptor 2Y according to an electrophotographic process. An image forming member such as a developing device 5Y including a developing blade 5bY, a screw 5cY, and the like, a cleaning brush 3aY, a cleaning blade 3bY, a cleaning screw 3bY, and the like is sequentially disposed.

  The photoreceptor 2Y has a layer structure in which an organic semiconductor layer, which is a photoconductive substance, is disposed on an aluminum cylinder surface having a diameter of about 30 to 120 mm, for example. The other photosensitive members 2C, 2M, and 2Bk are the same in the members disposed around them. That is, only the color of the toner used for image formation is different. It is possible to use a belt-like photoconductor.

  Returning to FIG. 1, below the photoconductors 2Y, 2C, 2M, and 2Bk, a laser beam corresponding to image data for each color is scanned over the surface of each photoconductor 2 that has been uniformly charged by the charging means. An exposure device 8 for forming an electrostatic latent image is provided. An elongated space is secured between the charging device 4 and the developing device 5 in the direction of the rotation axis of the photoconductor 2 so that the laser light irradiated by the exposure device 8 enters the photoconductor.

  An exposure apparatus 8 in the illustrated example is a laser scanning type exposure apparatus using a laser light source, a polygon mirror, and the like. Beam light 8Y and 8C modulated from four semiconductor lasers (not shown) according to image data to be formed. , 8M, 8Bk. The exposure apparatus 8 accommodates optical parts and control parts by a metal or resin casing, and is provided with a light-transmitting dustproof member at the emission port on the upper surface. Although the embodiment is composed of a single housing, a plurality of exposure apparatuses can be individually provided in each image forming unit. In addition to an exposure apparatus that employs the above laser, an exposure apparatus that combines a known LED array and an imaging means can also be employed.

  When the yellow (Y), cyan (C), magenta (M), and black (Bk) toners are consumed by the developing devices 5Y, 5C, 5M, and 5Bk that handle the respective colors, they are detected by a toner detection unit (not shown). Then, the toner is supplied to each developing device 5 from a toner cartridge 40Y, 40C, 40M, 40Bk that is provided in the upper part of the printer 100 and stores toner of each color by a supply unit (not shown). Each toner cartridge is a container whose outer shell is made of resin or paper, has a discharge port, and can be easily attached to and detached from the mounting portion TS of the printer 100. When the toner cartridge is mounted, the discharge port is provided in the main body of the printer 100. And toner replenishing means. In order to prevent the toner cartridge 40 of each color from being erroneously mounted and supplying toner to a developing device that handles different colors, the mounting portion TS and the shape of the toner cartridge 40 are paired for each color, etc. Incorrect mounting prevention means are provided.

  As can be recognized in FIG. 2, the developing device 5 includes two screws 5 c for stirring and conveying the toner and the carrier. When the developing device 5 is attached to the printer 100, one end of the toner replenishing means is connected to the left screw 5c in FIG. The toner is supplied to the developing roller 5a rotating in the direction of the arrow by the screw 5c, but the toner layer on the surface of the developing roller 5a is regulated to have a predetermined thickness by the blade 5b. The developing roller 5a is made of a cylinder made of stainless steel or aluminum, and is supported by the frame of the developing device so as to be able to rotate and to ensure a regular distance from the photosensitive member 2, and has a predetermined line of magnetic force inside. A magnet is provided so as to be configured. The electrostatic latent image of each color formed on the surface of each photoreceptor 2 by the laser beam is developed by a developing device 5 that handles toner of a predetermined color, and becomes a visible image.

  Returning again to FIG. 1, an intermediate transfer unit 6 is disposed above the photoreceptors 2Y, 2C, 2M, and 2Bk. The roller 6b rotates so that the intermediate transfer belt 6a as an image carrier supported and stretched by a plurality of rollers 6b, 6c, 6d, and 6e travels in the direction of the arrow. The intermediate transfer belt 6a is endless, and is stretched so that a part of each photoconductor after the development process comes into contact. Primary transfer rollers 7 </ b> Y, 7 </ b> C, 7 </ b> M, and 7 </ b> BK are provided on the inner peripheral portion of the belt so as to face each photoconductor.

  A cleaning device 6h is provided on the outer peripheral portion of the intermediate transfer belt 6a at a position facing the left roller 6e in FIG. The cleaning device 6h wipes off unnecessary toner remaining on the surface of the intermediate transfer belt 6a and foreign matters such as paper dust. The roller 6e facing the cleaning device 6h includes a mechanism (not shown) that applies tension to the belt 6a. The roller 6e can move to always ensure an appropriate belt tension, but the opposing cleaning device 6h can also move in conjunction with it.

  The intermediate transfer belt 6a is a belt having, for example, a resin film or rubber having a base thickness of 50 to 600 μm as a base, and applies a toner image carried by each photoconductor 2 to the primary transfer roller 7. It has a resistance value that enables electrostatic transfer to the belt surface by a bias. The members related to the intermediate transfer belt 6 a described above are configured as the intermediate transfer unit 6 and can be attached to and detached from the printer 100.

As an embodiment of the intermediate transfer belt, the intermediate transfer belt 6a is obtained by dispersing carbon in polyamide and adjusting the volume resistance value thereof to about 10 ⁶ to 10 ¹² Ωcm.
Belt detent ribs for stabilizing the running of the belt are provided on one or both ends of the belt (not shown).

As one embodiment of the primary transfer roller, the primary transfer roller 8 is formed by coating the surface of a metal roller serving as a metal core with a conductive rubber material so that a bias is applied to the metal core part from a power source (not shown). It has become. In the conductive rubber material, carbon is dispersed in urethane rubber, and the volume resistance value is adjusted to about 10 ⁵ Ωcm. A metal roller that does not have a rubber layer can also be used.

A secondary transfer roller 14a is provided on the outer periphery of the intermediate transfer belt 6a and in the vicinity of the right support roller 6b in FIG. The secondary transfer roller 14a is made of a metal roller that is a core metal and is coated with a conductive rubber. A bias is applied to the core metal part from the power supply 14b. Carbon is dispersed in the rubber, and the volume resistance value is adjusted to about 10 ⁷ Ωcm. The toner image carried by the intermediate transfer belt 6a is electrostatically applied to the sheet S by applying a bias while passing a recording medium (hereinafter referred to as the sheet S) between the intermediate transfer belt 6a and the secondary transfer roller 14a. Is transcribed.

  Below the exposure device 8, a plurality of, for example, two-stage sheet feed trays 9 </ b> A and 9 </ b> B are arranged so that they can be pulled out. The paper S stored in these paper feed trays is selectively sent out by the rotation of the corresponding pickup roller (calling roller) 53, and sent out to the paper feed transport path P1 by the paper feed roller 51 and the transport roller pair 12. It is.

  A pair of registration rollers 13 is provided in the paper feed conveyance path P1 in order to take a feeding timing for feeding the paper S to the secondary transfer unit. The sheet S is conveyed from the registration roller pair 13 toward a secondary transfer portion configured by the intermediate transfer belt 6a and the secondary transfer roller 14a.

  The apparatus shown in FIG. 1 includes another sheet feeding device 50 below. In this example, the two paper feed cassettes 9C and 9D are provided. However, a type in which the number of paper feeding cassettes is further increased can be adopted, and a type having a built-in paper feeding tray having a larger number of paper storages may be used.

  The manual sheet feeding device 25 provided on the right side of FIG. 1 can be rotated around the rotation axis Fa and stored in the frame F of the printer 100 when not in use. When used, the uppermost sheet S stored in the manual sheet feeding device 25 is fed by the sheet feeding roller 26 and separated by the separating means 27 so that only one sheet is reliably conveyed, and the conveying path is conveyed by the conveying roller 22. It is sent to the registration roller 13 through P1.

  A fixing device 15 having a heating unit is provided above the secondary transfer unit. In this example, it is composed of rollers 15a and 15b with built-in heaters, but a type employing a belt and a heating method employing IH can be appropriately employed.

  The switching guide G1 disposed downstream of the fixing device 15 in the paper conveyance direction is rotatable. In the state shown in the drawing, the fixing-finished paper S is guided to the paper discharge path P3, and the pair of paper discharge rollers 16 causes the printer to operate. The paper is discharged and stacked on the paper discharge stack T on the top surface of 100.

  The printer 100 can also automatically form images on both sides of the paper. For this purpose, the printer 100 includes a conveyance path and a roller for reversing and refeeding the paper. Specifically, a switchback path P5 and a refeed path P6 are provided inside the frame F, and the switching guides G1, G2 and the like can be reversed so as to transport the sheet S on which single-sided image formation has been completed to the feed path P1. A roller 18a, a reversible transport roller 22 and the like are provided.

  Rollers 23 and 24 are in contact with the reversible drive conveyance roller 22 with the conveyance roller 22 interposed therebetween. When the drive conveyance roller 22 rotates in the clockwise direction, the manual sheet feeding device cooperates with the roller 24. When the paper is conveyed from 25 and rotated counterclockwise, the one-sided image-formed paper can be fed again in the direction of the registration roller 13 in cooperation with the roller 23.

  When the switching guide G1 is rotated in the clockwise direction from the state shown in the figure, the fixed sheet S is guided to the conveyance path P4 by the roller pair 17 and conveyed to the rollers 18a and 18b via the switching guide G2. And once sent to the switchback path P5. As the roller 18a rotates counterclockwise and the switching guide G2 rotates counterclockwise, the sheet is fed to the refeed path P6. The sheet conveyed by the roller pair 20 and 21 further passes through the rollers 22 and 23 and reaches the registration roller pair 13.

  The printer 100 further guides the sheet S after fixing by rotating a third switching guide G3 located above the fixing device 15 and downstream of the roller pair 17 in the sheet conveyance direction from the state of FIG. Then, it can be conveyed to the paper discharge path P8 and discharged to another paper discharge device (not shown). As another discharge device, for example, a bin tray having several discharge trays is used.

  An operation during single-sided printing in which an image is formed on one side of the paper S in the above configuration will be described. First, laser light 8Y corresponding to image data for yellow emitted from a semiconductor laser by the operation of the exposure device 8 is irradiated onto the surface of the photoreceptor 2Y uniformly charged by the charging roller 4aY, thereby causing electrostatic latent An image is formed. This electrostatic latent image is subjected to development processing by the developing roller 5aY and is developed with yellow toner, becomes a visible image, and receives a transfer action by the primary transfer roller 7Y on the surface of the intermediate transfer belt 6a that moves in synchronization with the photoreceptor 2Y. The primary transfer. Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the photoconductors 2C, 2M, and 2Bk. As a result, yellow Y, cyan C, magenta M, and black Bk toner images are carried on the surface of the intermediate transfer belt 6a as four-color toner images that overlap one another in the direction of the arrow (with the intermediate transfer belt 6a). Move counterclockwise. On the other hand, the remaining toner and foreign matter are cleaned on the surface of the photoreceptor 2 by the cleaning device 3.

  The four-color toner image formed on the intermediate transfer belt 6a is transferred onto the sheet S conveyed in synchronization with the intermediate transfer belt 6a by receiving a transfer action by the secondary transfer roller 14a. The surface of the intermediate transfer belt 6a is cleaned by a belt cleaning device 6h to prepare for the next image formation / transfer process.

The sheet S on which the image has been transferred is subjected to a fixing action by the fixing device 15 and is discharged by the sheet discharge roller 16 onto the sheet discharge stack T with the image surface facing downward (face down).
An operation during double-sided recording in which images are formed on both sides of the paper S will be described. By the above operation, first, the sheet S with the image fixed on one side is guided to the roller pair 17 by switching the first switching guide G1 instead of the sheet discharge conveyance path P3. The sheet that passes through the third switching guide G3 and the conveyance path P4 provided on the downstream side of the sheet conveyance of the roller pair 17 and moves above the second switching guide G2 at the rotation position in FIG. 1 is transferred to the switchback conveyance path P5. Although it is conveyed by 18a and 18b, the driving roller 18a reverses in the counterclockwise direction at a predetermined timing, and reversely feeds the paper together with the roller pair 19 that also rotates in the reverse direction. At that time, the second switching guide G2 rotates counterclockwise from the posture shown in the drawing, and the sheet is conveyed on the conveyance path P6 by the roller pair 20 and 21 with the former end as the leading edge. It reaches the registration roller pair 13. The toner image on the intermediate transfer belt 6a is conveyed by transporting the sheet S having an image on one side again toward the secondary transfer portion having the secondary transfer roller 14a at the timing of the registration roller pair 13. Is transferred to the other side of the sheet S.

  Images to be formed on the second surface of the paper are sequentially formed by an image forming process started when the paper S is conveyed to a predetermined position. The image forming process in this case is also the same as the above-described full-color toner image formation during single-sided printing, and this full-color toner image is carried on the intermediate transfer belt 6a. However, since the front and rear of the paper are reversed in the transport path, the image data emitted from the exposure apparatus is created so that the image is formed in the reverse direction in the paper transport direction compared to when the image is formed on the first surface. Is controlled and executed.

  The sheet S on which the full-color toner images are transferred on both sides in this way is again discharged onto the discharge stack portion T by the discharge roller 16 after the fixing process by the fixing device 15. In order to increase the efficiency of double-sided image formation, several sheets of paper can be transported simultaneously on the transport path. The formation timing of the images to be formed on the first and second surfaces of the paper is executed by a control means (not shown).

  Incidentally, in this embodiment, the polarity of the toner image formed on the photosensitive member 2 is negative, and the toner image on the photosensitive member 2 is transferred to the surface of the intermediate transfer belt 6a by applying a positive charge to the primary transfer roller 7. Is transcribed. Further, the toner image on the surface of the intermediate transfer belt 6a is transferred onto the sheet S by applying a positive charge to the secondary transfer roller 14a.

  The single-sided printing and double-sided printing operations have been described with reference to an example in which full-color printing is performed. However, there are photosensitive members that are not used during black-and-white printing. Therefore, not only the unused photoreceptors 2Y, 2C, 2M or the developing devices 5Y, 5C, 5M are operated, but also a mechanism for keeping these unused photoreceptors and the intermediate transfer belt 6a in a non-contact state is provided. Yes. In the present embodiment, the inner frame 6f that supports the roller 6d and the primary transfer rollers 7Y, 7C, and 7M is supported so as to be rotatable about the right shaft 6g in FIG. 1 and away from the photosensitive member (in FIG. 1). By rotating in the clockwise direction, only the photoreceptor 2Bk is brought into contact with the intermediate transfer belt 6a, and an image forming process is executed to create a monochrome image using black toner. Such a configuration is advantageous in terms of improving the life.

  When the necessity for maintenance or parts replacement occurs, the exterior cover (not shown) is opened and maintenance is performed, but the members constituting the image forming unit 1 shown in FIG. It is convenient to exchange. When the image forming unit 1 shown in FIG. 2 is configured as a process cartridge, a guide unit and a handle for mounting to the printer 100 are provided in the apparatus main body to facilitate attachment and detachment. Such a configuration is known and will not be described in detail here. In addition, it is convenient to provide a storage device (for example, an IC tag) or the like for storing the characteristics of the process cartridge and the operation status, as a guideline for maintenance.

  Further, when maintenance or replacement is performed on the intermediate transfer belt unit 6, the belt and the photosensitive member can be separated and the intermediate transfer belt unit can be pulled out. FIG. 3 is a partial view showing a state in which the frame F is opened from the state shown in FIG. This shows that the upper part is openable with the lower pivot axis Fa as the pivot center. Prior to opening, most of the transport path can be opened by opening a lock lever (not shown), so that jammed paper can be easily treated.

  The secondary transfer unit 14 in which the transport paths P2 and P5 are formed on both sides has the center of the lower roller 23 as the center of rotation, and when the frame F is opened as shown in FIG. The secondary transfer unit 14 is given a turning habit so as to be away from the belt 6a and so that one of the roller pair 21 of the refeed path P6 is separated from the other. The secondary transfer unit 14 includes a power source 14b inside, and a unit having a paper transport function outside the case.

  The fixing device 15 also has one roller of the roller pair 20 of the refeed path P6 and a guide surface for conveyance. The fixing device 15 is supported in the state shown in FIG. 3 so that it can be pulled out to the right in the drawing. Therefore, it is possible to easily handle a paper jam that has occurred inside the fixing device.

  As shown in FIGS. 4 and 5, the registration roller pair 13 is composed of a resist driving roller 13a made of a metal shaft and rubber and a resist driven roller 13b which is a metal shaft. The resist driven roller 13 b is rotatably supported by a driven bearing 31, and the driven bearing 31 is rotatably supported with respect to the support plate 30. The registration drive roller 13a is rotatably supported by a drive bearing 32, and the drive bearing 32 is supported to be slidable in a direction connecting the centers of the registration roller pair 13. The slidable drive bearing 32 is pressurized toward the resist driven roller 13b by the urging means 34 and abuts against a positioning portion 30a provided on the support plate 30 at a design target position. A biasing means 33 is attached to one end of the driven bearing 31, and the driven bearing 31 is pressurized toward the registration driving roller 13 a by the biasing means 33. Here, by setting the urging force of the urging means 34 to be larger than the urging force of the urging means 33, the registration driving roller 13a hits the positioning portion 30a provided on the support plate 30, and the registration driven roller 13b is registered with the registration driving roller. The state where the nip is formed in contact with 13a is maintained.

  In this embodiment, when the trailing edge of the conveyed paper passes through the nip of the registration roller pair 13, the registration driven roller 13b separated by the thickness of the paper contacts the registration driving roller 13a. When the drive bearing 32 is directly supported by the support plate 30, vibration generated upon contact is transmitted. In the present invention, the biasing means 34 plays a role of a damper and transmits the vibration to the support plate 30. Can be prevented.

  Each of the bearings 31 and 32 of the registration roller pair 13 is held by a single support plate 30 and is not divided, so that highly accurate alignment can be ensured and stable conveyance can be performed without skew of the paper.

  As can be recognized in FIGS. 6 and 7, a registration gear 35 is fixed to an end of the registration driving roller 13 a that does not overlap the driving bearing. The swing gear 36 that meshes with the resist gear 35 is rotatably supported by a bracket 37 that is swingably supported. An idler gear 38 is rotatably held on the swing fulcrum shaft of the bracket 37. Drive is transmitted from an unillustrated motor in the order of idler gear 38 → swing gear 37 → registration gear 38. Further, the end of the bracket 37 opposite to the swing fulcrum is urged toward the registration gear 35 by the urging means 39, and the pitch ring of the registration gear 35 and the oscillating gear 36 comes into contact with each other. The pitch is secured.

  When the trailing edge of the sheet passes through the registration roller pair and the registration driven roller 13b contacts the registration driving roller 13a, the center position of the registration driving roller 13a fluctuates momentarily, but not only the urging means 34 but also the urging force. Since the fluctuation is also absorbed by the means 39, it is possible to prevent generation of vibration due to collision between gears and transmission of vibration due to collision between registration rollers.

1 Image forming unit (process cartridge)
DESCRIPTION OF SYMBOLS 2 Photoconductor 3 Cleaning device 4 Charging device 5 Developing device 6 Intermediate transfer unit 6a Intermediate transfer belt 7 Primary transfer roller 8 Exposure device 13 Registration roller pair 14 Secondary transfer unit 15 Fixing device 25 Manual feed device 30 Support plate 31 Driven bearing 32 Drive bearing 33, 34 Energizing means 35 Registration gear 36 Oscillating gear 37 Bracket 38 Idler gear 39 Energizing means

JP 2003-146487 A

Claims (4)

  In a paper transport apparatus that sandwiches and transports a sheet by two transport rollers forming a nip, the two transport rollers are configured to be displaceable, and each has a biasing force that biases in opposite directions, and the biasing forces are different from each other. A sheet conveying apparatus characterized in that a positioning means is attached to a conveying roller set to a strength and having a larger urging force.   2. The paper transport apparatus according to claim 1, wherein the two transport rollers are supported by one structure.   3. The sheet conveying apparatus according to claim 1, wherein at least one of the two conveying rollers is provided with drive coupling means for transmitting driving from a driving source, and the driving coupling means is provided with a biasing force. A sheet conveying device characterized by that.   An image forming apparatus comprising the sheet conveying device according to claim 1.

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