Medium conveyance device and image formation device

Abstract

To provide a medium conveyance device capable of suppressing the occurrence of wrinkles in a thin medium as compared with a case where a difference in conveyance speed is not set between an end portion and a central portion along the width direction of the medium, with respect to a plurality of conveyance roll pairs divided along the width direction crossing the conveyance direction of the medium.SOLUTION: Means for conveying a medium after the leading end position of the medium is aligned has a plurality of conveyance roll pairs which are divided into a plurality of sections along the width direction crossing the conveyance direction of the medium and convey the medium while nipping the medium. In the plurality of conveyance roll pairs, the conveyance speed of a central portion in the width direction of the medium is set to be higher than that of an end portion.SELECTED DRAWING: Figure 16

Description

[Technical Field]

[0001] The present invention relates to a medium transport device and an image forming apparatus. [Background technology]

[0002] Conventionally, techniques relating to medium transport devices have already been proposed, for example, as disclosed in Patent Documents 1 and 2.

[0003] In Patent Document 1, a pressing means for pressing either the drive roller or the driven roller toward the other is provided at a position other than both ends in the conveyance width direction.

[0004] Patent document 2 is configured to have a displacement guide means that is arranged on the outer side of the sheet conveying path between the moving guide means and the first conveying means, guides the sheet conveyed by the first conveying means to the moving guide means, and is displaceable in a direction away from the inner guide means. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-165648 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-120560 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of this invention is to prevent wrinkles from occurring in thin media, compared to when no difference in transport speed is set between the ends and center along the width direction of the media, for multiple pairs of transport rolls divided along the width direction intersecting the transport direction of the media. [Means for solving the problem]

[0007] The invention described in claim 1 is a means for conveying a medium after aligning the leading edge position of the medium, the means comprising a plurality of conveying roll pairs that are divided into a plurality of sections along a width direction that intersects with the conveying direction of the medium and that sandwich and convey the medium; The plurality of transport roll pairs are a medium transport device in which the transport speed is set to be faster in the center of the medium than at the edges along the width direction of the medium.

[0008] The invention described in claim 2 is a means for conveying a medium after aligning the leading edge position of the medium, the means comprising a plurality of conveying roll pairs that are divided into a plurality of sections along a width direction that intersects with the conveying direction of the medium and that sandwich and convey the medium; The plurality of transport roll pairs are a medium transport device that transports the medium while expanding the medium outward in the width direction of the medium.

[0009] A third aspect of the present invention is the medium transport device according to the first aspect, wherein the plurality of transport roll pairs are each composed of a drive roll and a driven roll that is in pressure contact with the drive roll.

[0010] The invention described in claim 4 is a medium conveying device described in claim 3, in which the pressure force with which the driven roll located in the center presses against the drive roll is set to be greater than the pressure force with which the driven roll located at the widthwise end of the medium presses against the drive roll.

[0011] The invention described in claim 5 is a media conveying device described in claim 1, in which the multiple pairs of conveying rolls, the pairs of conveying rolls located at the widthwise ends of the medium, are arranged at an incline toward the outside in the conveying direction of the medium.

[0012] The invention described in claim 6 is a media conveying device described in claim 5, in which the multiple transport roll pairs are arranged parallel to the width direction of the medium, with the transport roll pair located in the center of the width direction of the medium.

[0013] The invention described in claim 7 is a medium conveying device described in claim 6, in which, among the multiple conveying roll pairs, the conveying roll pair located at the widthwise end of the medium is positioned at the same clamping position as the conveying roll pair located at the widthwise center of the medium or downstream along the conveying direction of the medium.

[0014] The invention described in claim 8 is the medium transport device described in claim 1, wherein the outer diameter of the outer peripheral surface of the plurality of transport roll pairs is larger at the center than at the ends in the width direction of the medium.

[0015] The invention described in claim 9 is a medium conveying device described in claim 8, wherein the outer surfaces of the plurality of conveying roll pairs have inclined portions in which the outer diameter continuously increases from the widthwise end portion of the medium toward the center.

[0016] The invention described in claim 10 is a medium conveying device described in claim 3, wherein the outer diameter of the driven roll located in the center is set larger than that of the driven roll located at the widthwise end of the medium.

[0017] The invention described in claim 11 comprises a medium transport means for transporting a medium; an image forming means for forming an image on the medium transported by the medium transport means; Equipped with The image forming apparatus uses the medium transport device according to any one of claims 1 to 10 as the medium transport means. [Effects of the Invention]

[0018] According to the invention described in claim 1, it is possible to suppress the occurrence of wrinkles in thin media compared to when no difference in transport speed is set between the ends and center along the width direction of the media for multiple pairs of transport rolls divided along the width direction that intersects with the transport direction of the media.

[0019] According to the invention described in claim 2, the multiple pairs of transport rolls can prevent wrinkles from occurring in thin media compared to when the media is not transported while being expanded outward in the width direction of the media.

[0020] According to the invention described in claim 3, the configuration of the plurality of transport roll pairs can be simplified compared to when both of the transport rolls are driven.

[0021] According to the invention described in claim 4, the conveying speed of the conveying roll pairs can be easily set compared to when the pressure force with which the driven roll presses against the drive roll is not changed.

[0022] According to the invention described in claim 5, by simply tilting the transport roll pairs located at the widthwise ends of the medium, it is possible to transport the medium while expanding it, compared to when all transport roll pairs are arranged facing the transport direction of the medium.

[0023] According to the invention described in claim 6, the leading edge of the medium can be aligned more reliably than when multiple transport roll pairs are inclined, including the transport roll pair located in the center of the width of the medium.

[0024] According to the invention described in claim 7, a pair of transport rolls located at the widthwise end of the medium can align the leading edge of the medium with greater precision than when the clamping position of the medium is located upstream of a pair of transport rolls located in the center of the medium's width.

[0025] According to the invention described in claim 8, the multiple transport roll pairs can create differences in the transport speed of the medium simply by the configuration of the transport roll pairs, compared to when the outer peripheral surfaces of the transport roll pairs are uniform along the width direction of the medium.

[0026] According to the invention described in claim 9, the multiple transport roll pairs can accommodate media of different widths, compared to when the outer diameter of their outer surfaces discontinuously increases from the widthwise end portion of the medium toward the center.

[0027] According to the invention described in claim 10, multiple pairs of transport rolls can prevent wrinkles from occurring in thin media compared to when the outer diameters of the drive rolls located in the width direction of the media are all equal.

[0028] According to the invention described in claim 11, it is possible to prevent wrinkles from occurring in thin media compared to when a media conveying device described in any of claims 1 to 10 is not used. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is an overall configuration diagram showing an image forming apparatus to which a medium conveying device according to a first embodiment of the present invention is applied. [Figure 2] 1 is a configuration diagram showing an image forming device of an image forming apparatus according to a first embodiment of the present invention; [Figure 3] 1 is a configuration diagram showing a main part of an image forming apparatus according to a first embodiment of the present invention; [Figure 4] 1 is a configuration diagram showing a medium transport device according to a first embodiment of the present invention. [Figure 5] 1 is a plan view showing the configuration of a medium transport device according to a first embodiment of the present invention. [Figure 6] 1 is a perspective configuration diagram showing a medium transport device according to a first embodiment of the present invention. [Figure 7] 1 is a front configuration diagram showing a medium transport device according to a first embodiment of the present invention. [Figure 8] FIG. 10 is a schematic diagram illustrating the operation of a conventional medium transport device. [Figure 9] 1 is a configuration diagram showing a medium transport device according to a first embodiment of the present invention. [Figure 10] 1 is a side configuration diagram showing a medium transport device according to a first embodiment of the present invention. [Figure 11] 1 is a cross-sectional configuration diagram showing a main part of a medium conveying device according to a first embodiment of the present invention. [Figure 12] 3 is a configuration diagram showing a pressure setting unit of the medium conveying device according to the first embodiment of the present invention. FIG. [Figure 13] 3 is a configuration diagram showing a pressure setting unit of the medium conveying device according to the first embodiment of the present invention. FIG. [Figure 14] 3 is a configuration diagram showing a pressure setting unit of the medium conveying device according to the first embodiment of the present invention. FIG. [Figure 15] 10 is a graph showing the relationship between nip pressure and nip width of a medium transport device. [Figure 16] 3 is a configuration diagram illustrating the operation of the medium transport device according to the first embodiment of the present invention. FIG. [Figure 17] FIG. 10 is a configuration diagram showing a medium transport device according to a second embodiment of the present invention. [Figure 18] FIG. 10 is a configuration diagram showing a modified example of the medium transport device according to the second embodiment of the present invention. [Figure 19] FIG. 10 is a configuration diagram showing a medium transport device according to a third embodiment of the present invention. [Figure 20] FIG. 10 is a configuration diagram showing a medium transport device according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0031] [Embodiment 1] FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus to which a medium conveying device according to a first embodiment of the present invention is applied.

[0032] <Overall configuration of image forming apparatus> An image forming apparatus 1 according to the first embodiment is configured as, for example, a color printer. As shown in FIG. 1, the image forming apparatus 1 is broadly divided into an image output device 2 and a large-capacity paper feeder 3. The image output device 2 forms (outputs) full-color images, such as yellow (Y), magenta (M), cyan (C), and black (K), on recording paper 5, which is an example of a medium. The large-capacity paper feeder 3 stores a large amount of recording paper 5 to be supplied to the image output device 2. Of course, the large-capacity paper feeder 3 is not necessarily provided. In this embodiment, a color image forming apparatus will be described, but the present invention is not limited to this, and the image forming apparatus may of course be a monochrome machine that forms monochrome images.

[0033] The image output device 2 includes multiple image forming devices 10, an intermediate transfer device 20, a paper feed device 50, a fixing device 40, and a paper transport device 60. Each of the multiple image forming devices 10 forms a toner image developed with toner constituting a developer. The intermediate transfer device 20 holds the toner image formed by each image forming device 10 and transports it to a secondary transfer position T where the toner image is finally transferred to a recording sheet 5 (an example of a medium). The paper feed device 50 stores and transports the required recording sheet 5 to be supplied to the secondary transfer position T of the intermediate transfer device 20. The fixing device 40 fixes the toner image on the recording sheet 5 that has been secondarily transferred by the intermediate transfer device 20. The paper transport device 60 transports the recording sheet 5 fed from the paper feed device 50 along a required transport path. The multiple image forming devices 10 and the intermediate transfer device 20 are examples of image forming means. Note that 2a in the figure indicates the main body of the image output device 2. The device main body 2a is composed of supporting structural members, an exterior cover, etc. The two-dot chain line in the figure indicates the main transport path along which the recording paper 5 is transported inside the device main body 2a, etc. In the figure, the symbol X indicates the horizontal direction of the image forming device 1, Y indicates the depth direction of the image forming device 1, and Z indicates the vertical direction of the image forming device 1.

[0034] The image forming device 10 is composed of four image forming devices 10Y, 10M, 10C, and 10K that are dedicated to forming toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K), respectively. These four image forming devices 10 (Y, M, C, K) are arranged in a line in the internal space of the device main body 2a along the horizontal direction X with required gaps between them.

[0035] As shown in FIG. 2 , each of the four image forming devices 10 includes, for example, a photosensitive drum 11 and an image forming member disposed around the photosensitive drum 11 to form a toner image of a desired color on the surface of the photosensitive drum 11. The photosensitive drum 11 is driven to rotate in the direction of arrow A. The image forming members included in each of the image forming devices 10 include a charging device 12, an exposure device 13, a developing device 14, a primary transfer device 15, and a drum cleaning device 16. Each of the image forming devices 10 forms an image of each color, yellow (Y), magenta (M), cyan (C), and black (K), on the circumferential surface of the corresponding photosensitive drum 11 using an electrophotographic method. However, the four image forming devices 10 are not limited to those that form images using an electrophotographic method. The four image forming devices 10 may also be those that form images of each color, such as yellow (Y), magenta (M), cyan (C), and black (K), using an inkjet recording method or an electrostatic recording method. If the imaging device 10 forms an image by inkjet recording, the intermediate transfer device 20 is not necessary, and an image can be formed directly from the imaging device 10 onto the recording paper 5. In this case, imaging devices that form images by inkjet recording for each color, such as yellow (Y), magenta (M), cyan (C), and black (K), are arranged along the transport direction of the recording paper 5. Here, the imaging devices that use inkjet recording for each color are examples of image forming means.

[0036] As shown in FIG. 1 , the intermediate transfer device 20 is positioned below the yellow (Y), magenta (M), cyan (C), and black (K) image forming devices 10 (Y, M, C, K) in the vertical direction Z. The intermediate transfer device 20 is mainly composed of an intermediate transfer belt 21, multiple belt support rolls 22-27, and a secondary transfer device 30. The intermediate transfer belt 21 rotates in the direction indicated by arrow B while passing through a primary transfer position between the photosensitive drum 11 and the primary transfer device 15 (primary transfer roll). The multiple belt support rolls 22-27 support the intermediate transfer belt 21 from its inner surface, maintaining it in a desired state and rotatably supporting it. The secondary transfer device 30 includes a secondary transfer roll 31 disposed on the outer peripheral surface (image bearing surface) of the intermediate transfer belt 21, which is supported by a belt support roll 26, and performs secondary transfer of the toner image on the intermediate transfer belt 21 to recording paper 5.

[0037] The fixing device 40 is configured by arranging a housing (not shown), a heating rotor 41, a pressure rotor 42, and the like. The housing is formed with an inlet and an outlet for the recording paper 5. The heating rotor 41 is a roll- or belt-shaped member that rotates in the direction indicated by the arrow and is heated by a heating means so that its surface temperature is maintained at a predetermined temperature. The pressure rotor 42 is a belt- or roll-shaped member that rotates in contact with the heating rotor 41 at a predetermined pressure and rotates substantially along the axial direction of the heating rotor 41. In this fixing device 40, the contact area between the heating rotor 41 and the pressure rotor 42 forms a fixing processing section where the required fixing process (heating and pressurizing) is performed.

[0038] As shown in FIG. 1, the paper feeder 50 is disposed below the intermediate transfer device 20 and the secondary transfer device 30. The paper feeder 50 is mainly composed of a plurality (or a single) of paper containers 51, 51... and feeders 52, 53. The paper containers 51, 51... contain stacks of recording paper 5 of desired sizes, types, etc. The feeders 52, 53 feed the recording paper 5 one sheet at a time from the paper container 51. The paper container 51 is attached so that it can be pulled out, for example, from the front side of the device main body 2a (the side that the user faces during operation).

[0039] Examples of the recording paper 5 include plain paper used in electrophotographic copiers and printers, thin paper such as tracing paper, and overhead projector sheets. To further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper 5 is as smooth as possible. Suitable examples of the recording paper 5 include coated paper in which the surface of plain paper is coated with a resin or the like, and so-called thick paper with a relatively high basis weight, such as art paper for printing.

[0040] The recording paper 5 is required to be compatible with a wide range of paper types, particularly in so-called production machines that produce printed materials for in-house use, commercial prints, etc. An example of the recording paper 5 is a particularly thin paper with a basis weight of about 40 gsm.

[0041] On the other hand, the large-capacity paper feed device 3 is equipped with multiple or a single paper storage body 31a having a larger capacity than the paper storage body 51 arranged inside the image output device 2 for storing recording paper 5 of the desired size, a manual feed storage section 32 for storing the desired recording paper 5 for manual feeding, and delivery devices 33, 34.

[0042] The paper transport device 60 is broadly divided into a paper feed path 61, an intermediate path 62, a discharge path 63, a reversing path 64, and a double-sided transport path 65. The paper feed path 61 transports the recording paper 5 sent out from the paper feed device 50 to the secondary transfer position T. The paper feed path 61 is composed of one or more pairs of paper transport rolls 66, 71, a transport guide, and the like. Here, the paper transport roll pair 71, which is disposed in the paper feed path 61 immediately before the secondary transfer position T, is configured as, for example, a roll (registration roll) that adjusts the transport timing of the recording paper 5. The intermediate path 62 transports the recording paper 5 onto which the toner image has been secondarily transferred at the secondary transfer position T to the fixing device 40. The intermediate path 62 is composed of one or more transport belts, not shown. The discharge path 63 transports the recording paper 5 onto which the toner image has been fixed by the fixing device 40 to a paper discharge section, a post-processing device, or the like, not shown. The discharge conveying path 63 is composed of one or more pairs of paper discharge rolls 67, a conveying guide, etc. The reversing conveying path 64 reverses the recording paper 5 on which the toner image has been fixed by the fixing device 40 without directly discharging it. The reversing conveying path 64 is composed of a pair of reversing conveying rolls 68, a conveying guide (not shown), etc. The double-sided conveying path 65 conveys the recording paper 5, which has been reversed by the reversing conveying path 64, back to the paper feed conveying path 61 to form images on both sides. The double-sided conveying path 65 is composed of multiple pairs of paper conveying rolls 69, a conveying guide, etc. Note that, of the paper conveying device 60, a pair of paper conveying rolls 71 arranged in a position immediately before the secondary transfer position T constitutes the medium conveying device 70 according to this first embodiment. Note that the medium conveying device 70 will be described in detail later.

[0043] The large-capacity paper feed device 3 also includes a paper feed transport path 36 having a paper transport roll pair 35 that transports the recording paper 5 fed from the paper container 31a or the manual feed storage unit 32 to an external paper feed unit 37 of the image output device 2. The external paper feed unit 37 is made up of a paper feed transport roll pair 38 that transports the recording paper 5 to the paper feed transport path 61, a transport guide (not shown), and the like.

[0044] 1, reference numeral 100 denotes a control device that comprehensively controls the operation of the entire image forming apparatus 1, including the paper transport device 60. Reference numeral 101 denotes an operation panel that operates the image forming apparatus 1.

[0045] <Basic operations of image forming devices> The basic image forming operation of the image forming apparatus 1 will be described below.

[0046] Here, we will explain the image forming operation when forming a full-color image by combining toner images of four colors (Y, M, C, K) using the four image forming devices 10 (Y, M, C, K).

[0047] When the control device 100 of the image forming device 1 receives command information requesting an image formation operation (printing), the four image forming devices 10 (Y, M, C, K), the intermediate transfer device 20, the secondary transfer device 30, the fixing device 40, the paper feed device 50, and the paper transport device 60 start up.

[0048] In each of the image forming devices 10 (Y, M, C, K), an image of each color, such as yellow (Y), magenta (M), cyan (C), and black (K), is first formed on the photosensitive drum 11. When the toner image of each color formed on the photosensitive drum 11 of each of the image forming devices 10 (Y, M, C, K) is transported to the primary transfer position, the primary transfer device 15 performs primary transfer of the toner image of each color onto the intermediate transfer belt 21 of the intermediate transfer device 20, which rotates in the direction indicated by the arrow, in such a manner that the toner images are superimposed in order.

[0049] Next, the intermediate transfer device 20 holds the primarily transferred toner image by the rotation of the intermediate transfer belt 21 and transports it to the secondary transfer position T. Meanwhile, the paper feed device 50 sends out the required recording paper 5 to the paper feed conveyance path 61 in accordance with the image creation operation. The paper feed conveyance path 61 sends out and supplies the recording paper 5 to the secondary transfer position in accordance with the transfer timing.

[0050] At the secondary transfer position T of the intermediate transfer device 20, the secondary transfer device 30 performs secondary transfer of the toner images on the intermediate transfer belt 21 onto the recording paper 5 all at once. The recording paper 5 onto which the toner images have been secondarily transferred is separated from the intermediate transfer belt 21 and the secondary transfer device 30 and then transported to the fixing device 40. In the fixing device 40, the recording paper 5 after the secondary transfer is introduced into and passes through a fixing processing section between the rotating heating rotator 41 and the pressure applying rotator 42, whereby the necessary fixing processing (heating and pressurizing) is performed to fix the unfixed toner image onto the recording paper 5. After fixing is complete, the recording paper 5 is discharged via the discharge conveyance path 63 to, for example, a paper discharge section or post-processing device (not shown) located outside the image output device 2.

[0051] Furthermore, when forming images on both sides of the recording paper 5, the recording paper 5 with an image formed on one side is not directly discharged to a paper discharge section (not shown) via the discharge conveyance path 63, but is conveyed to the reversing conveyance path 64 by a switching means (not shown). Then, the recording paper 5 is reversed by the reversing conveyance path 64 and conveyed again to the paper feed conveyance path 61 via the double-sided conveyance path 65, where an image is formed on the back side of the recording paper 5.

[0052] On the other hand, when forming an image on one or both sides of recording paper 5 fed from an external paper feed device 3, the paper feed device 3 sends the recording paper 5 to the paper feed conveying path 36 in accordance with the image creation operation, and feeds the paper to the external paper feed section 37 of the image output device 2 by a paper conveying roll pair 35.

[0053] By the above operation, the recording paper 5 is outputted on which a full color image formed by combining four color toner images has been formed.

[0054] <Configuration of the medium transport device> FIG. 3 is a configuration diagram showing a main part of an image forming apparatus to which a medium conveying device according to the first embodiment of the present invention is applied.

[0055] 3, the medium transport device 70 according to the first embodiment includes a plurality of paper transport roll pairs 71 and transport guides 72-75. The plurality of paper transport roll pairs 71 are disposed in positions immediately prior to the secondary transfer position T in the paper feed transport path 61. The transport guides 72-75 are disposed in front of and behind the plurality of paper transport roll pairs 71 in the transport direction of the recording paper 5, and guide the recording paper 5. The plurality of paper transport roll pairs 71 align the leading edge position of the recording paper 5 and then transport the recording paper 5 to the secondary transfer position T of the intermediate transfer device 20. A paper sensor 76 that detects the leading edge of the recording paper 5 is disposed upstream of the plurality of paper transport roll pairs 71 in the transport direction of the recording paper 5.

[0056] The transport guide 73, located below and upstream of the plurality of paper transport roll pairs 71, is formed in a shape that curves downward along the vertical direction. The leading edge of the recording paper 5 transported by the paper transport roll pairs 66 acting as pre-registration rolls abuts against the nip portions of the plurality of stopped paper transport roll pairs 71, forming a loop along the transport guide 73. The recording paper 5 is transported using a so-called center registration method, in which the recording paper 5 is transported based on the center along the width direction, which intersects with the transport direction.

[0057] As shown in FIGS. 4 to 6, the plurality of paper transport roll pairs 71 constituting the medium transport device 70 according to the first embodiment are divided into a plurality of sections along the width direction W, which intersects with the transport direction D of the recording paper 5. In FIG. 6, reference numeral 102 denotes the frame of the paper transport device 60. The plurality of paper transport roll pairs 71 include a central paper transport roll pair 71a, 71b and edge paper transport roll pairs 71c, 71d and 71e, 71f. As shown in FIG. 4, the central paper transport roll pair 71a, 71b is disposed on each of the front and rear sides of the device body 2a of the image output device 2, with the center C along the width direction W of the recording paper 5 as a reference point. The edge paper transport roll pairs 71c, 71d and 71e, 71f are disposed on each of the front and rear sides of the central paper transport roll pair 71a, 71b along the width direction W (axial direction). The multiple paper transport roll pairs 71 consist of a total of six pairs of paper transport roll pairs 71a to 71f. However, the multiple paper transport roll pairs 71 are not limited to this, and may instead consist of two pairs of paper transport rolls 71c and 71d at the ends, one pair each axially outside the two central paper transport roll pairs 71a and 71b. In this case, the multiple paper transport roll pairs 71 consist of a total of four pairs of paper transport rolls 71a to 71d.

[0058] As shown in FIG. 7, each of the paper transport roll pairs 71a to 71f includes a drive roll 710 and a driven roll 711 that is in pressure contact with the drive roll 710. In the illustrated embodiment, the drive roll 710 is disposed vertically downward, and the driven roll 711 is disposed vertically upward. However, this is not a limitation, and the drive roll 710 may be disposed vertically upward, and the driven roll 711 may be disposed vertically downward. Furthermore, the driven roll 711 is not necessarily in pressure contact with the drive roll 710; it is of course also possible to configure the drive roll 710 to be in pressure contact with the driven roll 711. The drive roll 710 is driven to rotate at a required speed by a drive source, such as a drive motor or a drive force transmission gear (not shown).

[0059] As shown in FIGS. 5 and 6 , the drive rolls 710 constituting the multiple paper transport roll pairs 71 are formed in a cylindrical shape from an elastic material such as rubber or a non-elastic material such as synthetic resin. The drive rolls 710 are fixedly attached to a cylindrical metal drive shaft 712 at a required interval. The driven rolls 711 constituting the multiple paper transport roll pairs 71 are also formed in a cylindrical shape from an elastic material such as rubber, like the drive rolls 710. The driven rolls 711 are fixedly attached to a cylindrical metal rotation shaft 713 at a required interval. The drive shaft 712 and the rotation shaft 713 are rotatably supported by the frames 103 and 104, as shown in FIG. 4 . Note that one of the drive shaft 712 and the rotation shaft 713 may be supported movably along the vertical direction Z.

[0060] 7, when the recording paper 5 is fed from the paper feeder 50, the multiple paper transport roll pairs 71 are stopped with the drive roll 710 and the driven roll 711 in pressure contact. The recording paper 5 is transported by the paper transport roll pair 66 as a pre-registration roll located upstream in the transport direction of the recording paper 5, and is guided by transport guides 72, 73 (see FIG. 3) until its leading edge hits the nip portion where the drive roll 710 and the driven roll 711 are in pressure contact, forming a loop and stopping.

[0061] In this case, even if the recording paper 5 is transported at an angle relative to the transport direction D, i.e., so-called skew, the leading edge of the recording paper 5 comes into contact with the nip portion of multiple paper transport roll pairs 71 arranged along the width direction W that intersects with the transport direction D, forming a loop, thereby correcting the skew.

[0062] Then, in the media conveying device 70, multiple paper conveying roll pairs 71 are rotated and driven to convey the paper to the secondary transfer position T where the intermediate transfer belt 21 supported by the belt support roll 26 of the intermediate transfer device 20 abuts against the secondary transfer roll 31.

[0063] However, the media conveying device 70 configured as described above had a technical problem in that, as shown in Figure 8, when conveying extremely thin paper 5S, for example, with a basis weight of approximately 40 gsm and very low rigidity, paper wrinkles may occur in the thin paper 5S.

[0064] The multiple paper transport roll pairs 71 are divided into multiple parts along the axial direction, which is the width direction W that intersects with the transport direction of the recording paper 5. The drive rolls 710 and driven rolls 711 that make up the multiple paper transport roll pairs 71 have variations in outer diameter, width along the axial direction, or elastic modulus of the elastic material that makes up the rolls due to manufacturing tolerances, etc.

[0065] Therefore, as shown in FIG. 8 , when the multiple paper transport roll pairs 71 align and align the leading edge of the recording paper 5 and then transport the recording paper 5 to the secondary transfer position T of the intermediate transfer device 20, the transport speed of the recording paper 5 may vary along the width direction W. This causes variations in the transport distance of each of the paper transport roll pairs 71a-71f constituting the multiple paper transport roll pairs 71. In the case of thin paper 5S, which has a low basis weight of approximately 40 gsm and extremely low stiffness, if there is variation in the transport distance of each of the paper transport roll pairs 71a-71f, the thin paper 5S will be directly affected by the variation in the transport distance of each paper transport roll pair 71 and will not be transported uniformly downstream along the transport direction. As a result, the variation in the transport distance along the width direction W causes so-called "troughs" to be formed locally on the thin paper 5S transported by the multiple paper transport roll pairs 71, which have a difference in height compared to other areas.

[0066] This deformation, called a trough, is pressed against the intermediate transfer belt 21 and the secondary transfer roll 31 when the recording paper 5 passes through the secondary transfer position T of the intermediate transfer device 20, and the deformation is not resolved at the edge of the recording paper 5, causing paper wrinkles in the thin paper 5S.

[0067] In this way, paper wrinkles that occur, particularly in thin paper 5S, due to multiple paper transport roll pairs 71 can be eliminated, for example, by introducing a mechanism that varies the pressure contact force (pinch pressure) of the drive roll 710 and driven roll 711 that make up the multiple paper transport roll pairs 71.

[0068] However, the mechanism for varying the pinch pressure of the paper transport roll pairs 71 is configured by arranging a drive motor for displacing the driven rolls 711, 711, and a sensor for detecting the roll position on each of the driven rolls 711, 711, which make up the multiple paper transport roll pairs 71. As a result, the medium transport device 70 requires space to install the drive motor and sensor, which increases the size of the device and poses new technical challenges in that it leads to increased costs.

[0069] In addition, to eliminate paper wrinkles that occur in thin paper 5S, a service engineer or the like may adjust the pinch pressure of the drive roll 710 and driven roll 711 that make up the multiple paper transport roll pairs 71 to reduce it.

[0070] However, in this case, if the pinch pressure of the drive roll 710 and the driven roll 711 that make up the multiple paper transport roll pairs 71 is reduced, it becomes difficult to transport thick paper, causing the image forming device 1 to become a machine dedicated to thin paper, and sacrificing the transport performance for thick paper, which presents a new technical problem.

[0071] Furthermore, in order to eliminate paper wrinkles that occur in thin paper 5S, it is also possible to provide a nip release mechanism that can release the nip between the drive roll 710 and driven roll 711 that make up the multiple paper transport roll pairs 71, or the paper transport roll pair 66 located upstream of them.

[0072] However, even in this case, it is necessary to provide a nip release mechanism for each of the plurality of paper transport roll pairs 71 or paper transport roll pairs 66, which poses a technical problem of increasing the size and cost of the device.

[0073] Therefore, the medium transport device according to the first embodiment is configured such that the transport roll pairs are set to a transport speed that is faster in the center of the medium than at the edges along the width direction of the medium.

[0074] Furthermore, the medium transport device according to the first embodiment is configured so that the plurality of transport roll pairs transports the medium while expanding the medium outward in the width direction of the medium.

[0075] Furthermore, the media conveying device according to this embodiment 1 is configured such that the pressure applied by the driving roll located in the center to the driven roll is greater than that applied by the driving roll located at the end of the width direction of the media.

[0076] That is, as shown in FIG. 9, the multiple paper transport roll pairs 71 that make up the media transport device 70 of this embodiment 1 are equipped with a pressure contact force adjustment mechanism 80 that is set so that the pressure with which the drive rolls 710 of the paper transport roll pairs 71a and 71b located in the central portion press against the driven roll 711 is greater than the pressure with which the drive rolls 710 of the paper transport roll pairs 71c, 71d and 71e, 71f located at the ends of the width W of the recording paper 5 press against the driven roll 711.

[0077] The pressure contact force adjustment mechanism 80 has a plurality of pressure contact force application sections that are respectively arranged at the center along the axial direction of the rotating shaft 713 to which each of the driven rolls 711, 711... of the plurality of paper transport roll pairs 71 is attached and between the adjacent driven rolls 711, 711...

[0078] The multiple pressure contact force application sections include, for example, first to third pressure contact force application sections 81 to 83. The first pressure contact force application section 81 is located at the center C in the width direction W of the recording paper 5, which is a position between the two centrally located paper transport roll pairs 71a, 71b. The second pressure contact force application section 82 is located between the centrally located two paper transport roll pairs 71a, 71b and the two end paper transport roll pairs 71c, 71d located outside them in the axial direction. The third pressure contact force application section 83 is located between the end two paper transport roll pairs 71c, 71d and the two end paper transport roll pairs 71e, 71f located further outside them in the axial direction.

[0079] As shown in FIGS. 9 and 10 , the pressure contact force adjustment mechanism 80 is attached to a conveyance guide 74 disposed at a position corresponding to the plurality of paper transport roll pairs 71. The conveyance guide 74 is formed into a generally L-shaped side by bending a metal plate or the like. As shown in FIG. 10 , the conveyance guide 74 includes a horizontal plate portion 741 disposed in the horizontal direction X and a vertical plate portion 742 disposed at one end of the horizontal plate portion 741 along the conveyance direction of the recording paper 5, and bent upward along the vertical direction Z. As shown in FIG. 9( a), the horizontal plate portion 741 of the conveyance guide 74 is provided with planar rectangular openings 743, 743... at positions corresponding to each drive roll 710 of the plurality of paper transport roll pairs 71. A portion of each driven roll 711, 711... of the paper transport roll pair 71 protrudes downward along the vertical direction Z through the openings 743, 743... (see FIG. 10 ).

[0080] 12, the first pressure contact force application portion 81 includes a holding member 84, a movable member 85, and a tension coil spring 86 as an example of a biasing means. The holding member 84 is fixedly attached to the horizontal plate portion 741 of the conveying guide 74. The movable member 85 is disposed so as to be movable along the axial direction of the rotation shaft 713 relative to the holding member 84. Both ends of the tension coil spring 86 are respectively engaged with the holding member 84.

[0081] The holding member 84 is formed into a planar rectangular frame shape by bending a metal plate or the like. The holding member 84 includes a planar rectangular bottom plate portion 840, first and second upright plate portions 841, 842, and left and right side wall portions 843, 844. As shown in FIG. 10, the first and second upright plate portions 841, 842 are arranged at both longitudinal ends of the bottom plate portion 840 in a state of standing upward along the vertical direction Z with the rotation shaft 713 sandwiched therebetween. As shown in FIG. 12, the left and right side wall portions 843, 844 are formed by bending both widthwise ends of the holding member 84 upward along the vertical direction Z so as to be parallel to the rotation shaft 713. The left and right side wall portions 843, 844 are arranged slightly closer to one end (the right side in the figure) than the center along the longitudinal direction of the holding member 84. Furthermore, upper half portions 843a, 844a of the longitudinally centered ends of the left and right side wall portions 843, 844 are bent in a generally L-shape in plan view toward the rotation shaft 713. Furthermore, upper end portions 843b, 844b of the longitudinally centered ends of the lower half portions of the left and right side wall portions 843, 844 are provided so as to protrude in a hook-like shape along the axial direction of the rotation shaft 713. Circular ends 86a, 86b of a tension coil spring 86, which serves as an example of a biasing means, are engaged with the hook-shaped upper end portions 843b, 844b, respectively.

[0082] 11 and 12(c), a bearing member 87 made of a ball bearing or the like is attached to the rotating shaft 713 at a position corresponding to the approximate center along the axial direction of the holding member 84. The bearing member 87 is attached so as to be movable along the axial direction of the rotating shaft 713 while rotatably supporting the rotating shaft 713.

[0083] A coil spring 86, which is a tension spring whose ends are respectively engaged with the hook-shaped upper ends 843b, 844b of the holding member 84, is wound around the outer periphery of the bearing member 87. Therefore, a downward pressing force acts on the bearing member 87 due to the elastic restoring force of the coil spring 86. Therefore, at the support position where the rotating shaft 713 is rotatably supported by the bearing member 87, a pressing force acts on the rotating shaft 713 due to the elastic restoring force of the coil spring 86, pressing the driven roll 711 of the central paper transport roll pair 71a, 71b against the driving roll 710. The pressing force with which the driven roll 711 presses against the driving roll 710 is determined by the elastic restoring force of the coil spring 86 and the outer diameter of the bearing member 87, which determine the deformation amount of the coil spring 86. Of the first to third pressure contact force acting portions 81 to 83, the first pressure contact force acting portion 81 equipped with a bearing member 87 is set to have the largest pressure contact force for pressing the driven roll 711 against the drive roll 710 compared to the second and third pressure contact force acting portions 82, 83. The biasing means is not limited to the tension coil spring 86, and a compression coil spring, a leaf spring, or the like may also be used.

[0084] As shown in Figures 11 and 12, the movable member 85 is integrally formed from synthetic resin or the like. The movable member 85 includes a tapered portion 851, a cylindrical portion 852, and a connecting portion 854. The tapered portion 851 is disposed at one end (the left end in the figure) along the axial direction of the rotating shaft 713, with the bearing member 87 sandwiched therebetween. The cylindrical portion 852 is disposed at the other end (the right end in the figure) along the axial direction of the rotating shaft 713, with the bearing member 87 sandwiched therebetween. The connecting portion 854 integrally connects the tapered portion 851 and the cylindrical portion 852 on the bottom plate portion 840 of the holding member 84.

[0085] The tapered portion 851 of the movable member 85 is tapered so that the outer diameter of its upper end gradually increases toward one end along the axial direction of the rotary shaft 713. The end of the tapered portion 851 on the bearing member 87 side has an outer diameter slightly larger than that of the bearing member 87. One end of the tapered portion 851 is provided with an operation portion 853 having a generally U-shaped side surface for manually operating the movable member 85. When the movable member 85 is pushed rightward in FIG. 11 , the coil spring 86 wound around the outer periphery of the bearing member 87 moves toward the tapered portion 851, and as shown in FIG. 13 , the elastic restoring force of the coil spring 86 no longer acts on the rotary shaft 713. In other words, the first pressure force application portion 81 can adjust the elastic restoring force of the coil spring 86 acting on the rotary shaft 713 in two stages by manually moving the movable member 85.

[0086] Furthermore, the connecting portion 854 of the movable member 85 is provided with a fitting groove (or fitting hole) 854a into which the lower end of the bearing member 87 is fitted while allowing the bearing member 87 to move up and down.

[0087] The cylindrical portion 852 of the movable member 85 is provided at its lower end with a sliding portion 855 that slides on the bottom plate portion 840 of the holding member 84 along the axial direction of the rotation shaft 713 .

[0088] The operation of moving the movable member 85 can of course be performed by a service engineer, but it can also be performed by the user, who is the operator, by pulling out part of the paper transport device 60 toward the front side of the device main body 2a.

[0089] The second and third pressure contact force acting portions 82, 83 are configured in the same manner except for the elastic modulus of the coil spring 90. Here, only the second pressure contact force acting portion 82 will be described, and the third pressure contact force acting portion 83 will be designated by the corresponding reference numeral and its description will be omitted.

[0090] 14, the second pressure contact force application portion 82 includes a holding member 88, a movable member 89, and a tension coil spring 90 as an example of a biasing means. The holding member 88 is fixedly attached to the horizontal plate portion 741 of the conveying guide 74. The movable member 89 is disposed so as to be movable in the vertical direction Z relative to the holding member 88. Both ends of the coil spring 90 are respectively engaged with the holding member 88.

[0091] The holding member 88 is formed into a planar rectangular frame shape by bending a metal plate or the like. The holding member 88 includes a planar rectangular bottom plate portion 880, an upright plate portion 881, and left and right side wall portions 882, 883. As shown in FIG. 14 , the upright plate portion 881 is disposed at one end (the left end in the drawing) along the longitudinal direction of the bottom plate portion 880, and is disposed in an upright state facing upward along the vertical direction Z, with the rotation shaft 713 sandwiched between them. The left and right side wall portions 882, 883 are formed by bending both ends along the width direction of the holding member 88 upward along the vertical direction Z so as to be parallel to the rotation shaft 713. The left and right side wall portions 882, 883 are disposed slightly toward one end (the right side in the drawing) of the holding member 88 from the center along the longitudinal direction. Furthermore, the left and right side wall portions 882, 883 are provided with upper half portions 882a, 883a of their longitudinally centered ends that protrude in a hook shape along the axial direction of the rotation shaft 713. Circular ends 90a, 90b of a coil spring 90, which serves as an example of a biasing means, are respectively engaged with the hook-shaped upper ends 882a, 883a.

[0092] As shown in FIG. 14 , the movable member 89 is integrally formed from a synthetic resin or the like. The movable member 89 includes a cylindrical portion 891 formed in a substantially U-shaped side surface. The inner diameter of the cylindrical portion 891 is set slightly larger than the outer diameter of the rotation shaft 713, and the movable member 89 is disposed so as to contact the upper portion of the rotation shaft 713. Upright walls 892, 893 are provided at both axial ends of the cylindrical portion 891. The cylindrical portion 891, including the upright wall 892, is sandwiched between two upright plate portions 881 of the holding member 88, and is movable along the vertical direction Z. Furthermore, a flange portion 894 is provided at one axial end of the cylindrical portion 891, outside the upright wall 892, along the upright plate portions 881 of the holding member 88.

[0093] A coil spring 90 is wound around the outer periphery of the cylindrical portion 891 of the movable member 89. Therefore, a downward pressing force is applied to the cylindrical portion 891 of the movable member 89 by the elastic restoring force of the coil spring 90. Therefore, at the contact position where the movable member 89 contacts the rotating shaft 713, a pressing force is applied by the elastic restoring force of the coil spring 90 to press the driven rolls 711 of the end paper transport roll pairs 71c, 71d and 71e, 71f against the driving roll 710. The pressing force with which the driven roll 711 presses against the driving roll 710 is determined by the elastic restoring force of the coil spring 90 and the outer diameter of the cylindrical portion 891 of the movable member 89, which determines the deformation amount of the coil spring 90. Of the first to third pressure contact force acting portions 81 to 83, the second pressure contact force acting portion 82 having a movable member 89 is set to apply a pressure force that presses the driven roll 711 against the drive roll 710 smaller than that of the first pressure contact force acting portion 81 and larger than that of the third pressure contact force acting portion 83, compared to the first and third pressure contact force acting portions 81, 83. Therefore, the first to third pressure contact force acting portions 81 to 83 are set so that the pressure forces that press the driven roll 711 against the drive roll 710 increase in the order of the first pressure contact force acting portion 81 > the second pressure contact force acting portion 82 > the third pressure contact force acting portion 83.

[0094] Changing the pressure contact force (nip pressure) that presses the driven roll 711 against the drive roll 710 changes the width of the pressure contact area where the driven roll 711 and the drive roll 710 are in pressure contact, i.e., the nip width. When the nip width where the driven roll 711 and the drive roll 710 are in pressure contact changes, the larger the nip width, the faster the conveying speed of the recording paper 5 becomes, assuming that the rotation speed (angular velocity) of the drive shaft 712 is constant.

[0095] The inventors conducted an experiment to determine the relationship between the nip pressure at which the driven roll 711 is pressed against the drive roll 710 and the nip width. The experiment to determine the relationship between the nip pressure and the nip width was carried out by applying a marking to the drive roll 710 while the drive roll 710 was separated from the driven roll 711, nipping the drive roll 710 with the driven roll 711 with the recording paper 5 interposed therebetween, and measuring the trace of the drive roll 710 on the recording paper 5 as the nip width while varying the nip pressure. Note that the recording paper 5 used was an ultra-thin paper with a basis weight of 42 gsm, A4L (T-grain) Oak MC.

[0096] FIG. 15 is a graph showing the results of the above experiment.

[0097] 15, the relationship between nip pressure and nip width shows a linear correlation, although there is some variation. Therefore, by employing the first to third pressure contact force application units 81 to 83, it is possible to change the nip width by changing the nip pressure between the drive roll 710 and the driven roll 711 that make up the multiple paper transport roll pairs 71, and to appropriately set the transport speed of the recording paper 5 at each drive roll 710 of the multiple paper transport roll pairs 71.

[0098] <Action of the medium transport device> In the media conveying device of embodiment 1 of the present invention, it is possible to prevent wrinkles from occurring in thin media compared to when no difference in conveying speed is set between the ends and center along the width direction of the media for multiple pairs of conveying rolls divided along the width direction intersecting the conveying direction of the media, as follows.

[0099] That is, in the image forming apparatus 1 to which the medium conveying device 70 according to the first embodiment of the present invention is applied, as shown in FIG. 1, during image formation, the desired recording paper 5 stored in the paper container 51 is fed from the paper feed device 50 and transported to the secondary transfer position T of the intermediate transfer device 20 via the paper feed transport path 61.

[0100] At this time, as shown in Figure 7, the leading edge of the recording paper 5 is aligned by multiple paper transport roll pairs 71 arranged just before the secondary transfer position of the intermediate transfer device, and then the recording paper 5 is transported to the secondary transfer position T by the multiple paper transport roll pairs 71 in synchronization with the image on the intermediate transfer belt 21 of the intermediate transfer device 20.

[0101] Incidentally, various types of recording paper 5 are used for forming images, and some users use thin paper 5S, which has a basis weight of about 40 gsm and low rigidity.

[0102] Thin paper 5S as recording paper 5 is transported by a plurality of paper transport roll pairs 71 that are divided into a plurality of sections along the width direction of the recording paper 5.

[0103] At this time, the multiple paper transport roll pairs 71 are set by the first to third pressure contact force application sections 81 to 83 so that the pressure contact force of the paper transport roll pair 71a, 71b in the center along the width direction W of the recording paper 5 is the greatest, and the pressure contact force of the paper transport roll pairs 71c, 71d at both ends, and further the pressure contact force of the paper transport roll pairs 71e, 71f at both ends, gradually becomes smaller.

[0104] Therefore, as shown in Figure 16, when transporting thin paper 5S as recording paper 5, the multiple paper transport roll pairs 71 are transported so that the pressure force at the center along the width direction of the recording paper 5 is the greatest, resulting in the fastest transport speed of the recording paper 5, and the pressure force at the ends is small, resulting in the slowest transport speed of the recording paper 5.

[0105] As a result, the thin paper 5S as the recording paper 5 is transported so that the transport speed at the center along its width direction is the fastest and the transport speed at the edges along its width direction is slower than that at the center.

[0106] Therefore, thin paper 5S as recording paper 5 is transported in an expanded state toward the outside of the width direction of thin paper 5S according to the speed difference between the multiple paper transport roll pairs 71a-71f. When ultra-thin paper 5S as recording paper 5 reaches the multiple paper transport roll pairs 71a-71f, its leading edge along the transport direction abuts on the nip portions of the multiple paper transport roll pairs 71a-71f, eliminating skew and aligning it.

[0107] Therefore, the thin paper 5S as the recording paper 5 is conveyed to the secondary transfer position T of the intermediate transfer device 20 with its leading edge aligned and the thin paper 5S expanded outward in the width direction.

[0108] Thereafter, the thin paper 5S is conveyed at the secondary transfer position T of the intermediate transfer device 20 while being sandwiched between the intermediate transfer belt 21 and the secondary transfer roll 31 and subjected to a uniform conveying force, thereby reliably preventing or suppressing the occurrence of wrinkles.

[0109] In this way, according to the media conveying device 70 of this embodiment 1, it is possible to prevent or suppress the occurrence of paper wrinkles in thin paper 5S and the like, compared to when no difference in conveying speed is set between the ends and center along the width direction W of the recording paper 5 for multiple paper conveying roll pairs 71a to 71f divided along the width direction W that intersects with the conveying direction D of the recording paper 5.

[0110] [Embodiment 2] 17 is a structural diagram showing a medium transport device according to embodiment 2 of the present invention. The medium transport device according to embodiment 2 is configured such that the transport roll pairs located at the width direction ends of the medium are arranged at an incline outward in the transport direction of the medium.

[0111] In addition, the medium conveying device of embodiment 2 is configured such that the multiple conveying roll pairs located in the center of the width direction of the medium are arranged parallel to the width direction of the medium.

[0112] Furthermore, the media conveying device of this embodiment 2 is configured so that, among the multiple conveying roll pairs, the conveying roll pair located at the widthwise end of the media is positioned so that the clamping position of the media is the same as that of the conveying roll pair located at the center of the media's widthwise direction or is positioned downstream along the media conveying direction.

[0113] That is, as shown in Figure 17, the media conveying device 70 of embodiment 2 has multiple paper conveying roll pairs, including a paper conveying roll pair 71a arranged in the center along the width direction of the recording paper, and paper conveying roll pairs 71b and 71c arranged at both ends along the axial direction of the paper conveying roll pair 71a.

[0114] The paper transport roll pair 71a located in the center and the paper transport roll pairs 71b and 71c located at both ends are configured separately. The paper transport roll pair 71a located in the center has a drive roll 710 and a driven roll 711 arranged parallel to the width direction of the recording paper 5. In contrast, the paper transport roll pairs 71b and 71c located at both ends are arranged symmetrically and inclined at a required angle outward in the transport direction D of the recording paper 5. The transport speed of each paper transport roll pair 71a to 71c relative to the recording paper 5 is set to the same value.

[0115] 17 shows the driven rolls 711 of each of the paper transport roll pairs 71a to 71c, and the rotation shafts 713a of the driven rolls 711 are also arranged at an incline, similar to the rotation shafts 713c of the driven rolls 711. Furthermore, unlike the driven rolls 711, the drive rolls 710 may be arranged parallel to the width direction of the recording paper 5 at a position corresponding to the driven rolls 711.

[0116] 17, in the medium transport device 70 according to the second embodiment, the paper transport roll pairs 71b, 71c arranged at both ends in the width direction W of the recording paper 5 are arranged at an incline outward in the transport direction D of the recording paper 5. Therefore, the transport speed of the recording paper 5 is slower at the paper transport roll pairs 71b, 71c at both ends compared to the paper transport roll pair 71a in the center by the amount of the inclination.

[0117] Moreover, the paper transport roll pairs 71b, 71c at both ends are arranged at an angle relative to the paper transport roll pair 71a at the center, making it possible to transport the recording paper while expanding it outward in the width direction W of the recording paper 5.

[0118] Therefore, according to the medium conveying device 70 of the second embodiment, even when the recording paper is thin paper 5S or the like, it is possible to reliably prevent or suppress the occurrence of paper wrinkles.

[0119] FIG. 18 is a configuration diagram showing a modified example of the medium transport device 70 according to the second embodiment.

[0120] In a modified example of the medium conveying device 70 according to this embodiment 2, as shown in FIG. 18, among the multiple paper conveying roll pairs, the paper conveying roll pair 71b, 71c located at the end of the width direction W of the recording paper 5 is configured so that the clamping position of the recording paper 5 is the same as that of the paper conveying roll pair 71a located in the center along the width direction W of the recording paper 5, or is positioned downstream along the conveying direction D of the recording paper 5.

[0121] That is, in the case of the media conveying device 70 shown in Figure 18, the driven rolls 711 of the paper conveying roll pairs 71b, 71c at both ends are arranged inclined toward the upstream outward side along the conveying direction D of the recording paper 5, together with the rotating shafts 713b, 713c, relative to the paper conveying roll pair 71a at the center along the width direction of the recording paper 5.

[0122] Therefore, in the medium transport device 70 having such a configuration, when the leading edge of the recording paper 5 is abutted against and aligned, the leading edge of the recording paper 5 first abuts against the paper transport roll pairs 71b, 71c at both ends. At this time, because the paper transport roll pairs 71b, 71c at both ends are positioned at an angle, there is a risk that the skewed leading edge of the recording paper 5 will not necessarily be aligned when the leading edge of the recording paper 5 is abutted against and aligned.

[0123] Therefore, in a modified example of the media conveying device 70 according to this embodiment 2, as shown in FIG. 18, among the multiple paper conveying roll pairs 71, the paper conveying roll pair 71b, 71c located at the end of the width direction W of the recording paper 5 are arranged so that the clamping position of the recording paper 5 is the same as that of the paper conveying roll pair 71a located at the center of the width direction W of the recording paper 5.

[0124] As a result, in the medium transport device 70 according to this modified example, when the leading edge of the recording paper 5 is abutted against and aligned, the leading edge of the recording paper 5 can be brought into contact with the paper transport roll pair 71a in the center and the paper transport roll pairs 71b, 71c at both ends at the same time. Therefore, with this medium transport device 70, good alignment is possible even when the recording paper 5 is skewed.

[0125] The other configurations and operations are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0126] [Embodiment 3] 19 is a structural diagram showing a medium transport device according to embodiment 3 of the present invention. In the medium transport device according to embodiment 3, the outer diameter of each of the plurality of transport roll pairs is larger at the center of the outer peripheral surface than at the ends in the width direction of the medium.

[0127] In addition, in the media conveying device of this embodiment 3, the multiple conveying roll pairs are configured so that their outer surfaces have inclined portions in which the outer diameter continuously increases from the widthwise end portion of the media toward the center.

[0128] That is, as shown in Figure 19, the media conveying device of embodiment 3 has multiple paper conveying roll pairs 71, namely, first and second paper conveying roll pairs 71a, 71b, which are respectively arranged at symmetrical positions on the front and rear sides with respect to the center along the width direction of the recording paper 5.

[0129] The driven rolls 711 of the first and second paper transport roll pairs 71a, 71b are configured so that the outer diameter of their outer peripheral surfaces is larger at the center than at the ends in the width direction of the recording paper 5. More specifically, the driven rolls 711 of the first and second paper transport roll pairs 71a, 71b are configured so that the outer diameter of their outer peripheral surfaces has tapered inclined portions 711a, 711b in which the outer diameter increases continuously (linearly) from the ends in the width direction of the recording paper 5 toward the center.

[0130] When the drive roll 710 is driven to rotate, the driven rolls 711 of the first and second paper transport roll pairs 71a, 71b rotate at a rotational speed corresponding to their outer diameters, with the inclined portions 711a, 711b including the central portion and the ends along the width direction of the recording paper 5.

[0131] The driven rolls 711 of the first and second paper transport roll pairs 71a, 71b have a larger outer diameter at the center along the width direction of the recording paper 5 than at the ends, and the outer diameter changes continuously. Therefore, the driven rolls 711 are rotated so that the rotation speed at the center along the width direction of the recording paper 5 is faster and the rotation speed at the ends is slower.

[0132] Therefore, the recording paper 5 transported by the paper transport roll pair 71a, 71b can be transported while expanding the recording paper 5 outward in the width direction of the recording paper 5 in accordance with the outer diameter of the driven roll 711.

[0133] Therefore, according to the medium conveying device 70 of the third embodiment, even when the recording paper is thin paper 5S or the like, it is possible to reliably prevent or suppress the occurrence of paper wrinkles.

[0134] In addition, in the media transport device 70 of this embodiment 3, the paper transport roll pairs 71a, 71b are not limited to two pairs of paper transport roll pairs arranged on the front and rear sides, but may also be configured with a total of four pairs of paper transport roll pairs 71a to 71d, with two pairs of paper transport roll pairs 71a, 71b arranged on the front and rear sides, as shown in Figure 19(b).

[0135] The other configurations and operations are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0136] [Embodiment 4] Figure 20 is a structural diagram showing a medium transport device according to embodiment 4 of the present invention. The medium transport device according to embodiment 4 is configured such that the outer diameter of the driven roll located in the center of the transport roll pairs is set larger than the outer diameter of the driven rolls located at the ends in the width direction of the medium. Note that, for convenience, in Figure 20, the drive roll 710 and driven rolls 711a to 711f are illustrated above the recording paper 5, but the drive roll 710 is disposed on the back side of the recording paper 5.

[0137] That is, unlike in embodiment 3, the medium transport device 70 according to embodiment 4 does not use a plurality of transport roll pairs whose outer diameter is larger at the center of the outer peripheral surface than at the ends in the width direction of the medium. The medium transport device 70 according to embodiment 4 is configured such that the outer diameters of driven rolls 711a-711f of a plurality of paper transport roll pairs 71, which are divided into a plurality of parts along the width direction W that intersects with the transport direction D of the recording paper 5, are made different between the center and the ends, and the outer diameter of the driven rolls 711a, 711b in the center is larger than the outer diameters of the driven rolls 711c, 711d and 711e, 711f at the ends.

[0138] In Figure 20, for convenience, in order to show the characteristics of the medium conveying device 70 according to this fourth embodiment, the drive roll 710 and the driven roll 711 located on the outside along the width direction are shown separated from each other, but in reality, the drive roll and the driven roll are pressed against each other.

[0139] 20, in the medium transport device 70 according to the fourth embodiment, the outer diameter of the driven rolls 711a, 711b of the paper transport roll pair 71a, 71b located in the center is set to be the largest. Also, in this medium transport device 70, the outer diameter of the driven rolls 711c, 711d located on the outer side in the axial direction of the paper transport roll pair 71a, 71b located in the center is set to be the next largest, and the outer diameter of the driven rolls 711e, 711f of the paper transport roll pair 71e, 71f located on the outermost side in the axial direction of the rotation shaft 713 is set to be the smallest.

[0140] Therefore, when the drive roll 710 of each of the paper transport roll pairs 71a to 71f is rotationally driven by the drive shaft 712, the driven roll 711 of each of the paper transport roll pairs 71a to 71f is rotated at a rotation speed according to its outer diameter.

[0141] Therefore, the driven rolls 711a to 711f of each paper transport roll pair 71a to 71f are set so that the outer diameter of the central portion along the width direction of the recording paper 5 is larger than that of the ends. Therefore, the driven roll 711 is rotated so that the rotation speed of the driven rolls 711a and 711b located in the central portion along the width direction of the recording paper 5 is high, and the rotation speed of the driven rolls 711c to 711f located at the ends is low.

[0142] Therefore, the recording paper 5 transported by the paper transport roll pairs 71a to 71f can be transported while expanding outward in the width direction of the recording paper 5 in accordance with the outer diameters of the driven rolls 711a to 711f.

[0143] Therefore, according to the medium conveying device 70 of the fourth embodiment, even when the recording paper is thin paper 5S or the like, it is possible to reliably prevent or suppress the occurrence of paper wrinkles.

[0144] In the medium conveying device 70 according to the fourth embodiment, there is a difference in the outer diameter of the driven roll along the width direction of the recording paper 5, which may cause deformation such as waving of the recording paper 5. However, to deal with deformation such as waving of the recording paper 5, it is possible to prevent the deformed recording paper 5 from coming into contact with the conveying guides 72 to 75 by setting the gaps between the conveying guides 72 to 75 and the like wider than usual.

[0145] The other configurations and operations are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0146] (Addendum) (((1))) a means for conveying the medium after aligning the leading edge position of the medium, the means including a plurality of conveying roll pairs that are divided into a plurality of sections along a width direction intersecting with the conveying direction of the medium and that sandwich and convey the medium; The plurality of transport roll pairs are configured so that the transport speed is faster in the center of the medium than at the ends along the width direction of the medium. (((2))) a means for conveying the medium after aligning the leading edge position of the medium, the means including a plurality of conveying roll pairs that are divided into a plurality of sections along a width direction intersecting with the conveying direction of the medium and that sandwich and convey the medium; The plurality of transport roll pairs transport the medium while expanding the medium outward in the width direction of the medium. (((3))) The medium transport device according to (((1))), wherein the plurality of transport roll pairs are each composed of a drive roll and a driven roll that is in pressure contact with the drive roll. (((4))) The media transport device described in (((3))) is configured such that the pressure force with which the driven roll located in the center presses against the drive roll is greater than the pressure force with which the driven roll located at the widthwise end of the media presses against the drive roll. (((5))) The media transport device described in (((1))) is such that the transport roll pairs located at the widthwise ends of the media are arranged inclined outward in the transport direction of the media. (((6))) The medium transport device according to (((5))), wherein the plurality of transport roll pairs are arranged in parallel along the width direction of the medium, with the transport roll pair located at the center of the width direction of the medium. (((7))) A medium conveying device as described in (((6))) in which, among the plurality of conveying roll pairs, the conveying roll pair located at the widthwise end of the medium is positioned at the same clamping position as the conveying roll pair located at the widthwise center of the medium or downstream along the conveying direction of the medium. (((8))) The medium transport device according to (((1))), wherein the outer diameter of the outer peripheral surface of each of the plurality of transport roll pairs is larger at the center than at the ends in the width direction of the medium. (((9))) The media transport device according to (((8))), wherein the outer peripheral surfaces of the plurality of transport roll pairs have inclined portions whose outer diameters increase continuously from the widthwise ends of the media toward the center. (((10))) The media transport device described in (((3))) above, wherein the outer diameter of the driven roll located in the center of the plurality of transport roll pairs is set to be larger than that of the driven roll located at the end of the width direction of the media. (((11))) a medium transport means for transporting a medium; an image forming means for forming an image on the medium transported by the medium transport means; Equipped with An image forming apparatus using the medium transport device according to any one of (((1))) to (((10))) as the medium transport means.

[0147] According to the media conveying device of (((1))), it is possible to suppress the occurrence of wrinkles in thin media, compared to a case where no difference in conveying speed is set between the ends and the center along the width direction of the media, for multiple pairs of conveying rolls divided along the width direction that intersects with the conveying direction of the media. According to the media conveying device of (((2))), the multiple pairs of conveying rolls can prevent wrinkles from occurring in thin media compared to when the media is not conveyed while expanding outward in the width direction of the media. According to the medium transport device of (((3))), the configuration of the plurality of transport roll pairs can be simplified compared to when both transport rolls are driven. According to the medium conveying device of (((4))), the conveying speed of the conveying roll pairs can be easily set compared to when the pressure force with which the driven roll presses against the drive roll is not changed. According to the medium conveying device of (((5))), it is possible to convey the medium while expanding it by simply tilting the conveying roll pairs located at the widthwise ends of the medium, compared to when all of the conveying roll pairs are arranged facing the conveying direction of the medium. According to the medium conveying device of (((6))), the leading edge of the medium can be reliably aligned compared to when the plurality of conveying roll pairs are inclined, including the conveying roll pair located in the center of the width of the medium. According to the medium conveying device of (((7))), the pair of conveying rolls located at the widthwise end of the medium can align the leading edge of the medium with higher precision than when the clamping position of the medium is located upstream of the pair of conveying rolls located at the center of the width of the medium. According to the medium conveying device of (((8))), the multiple pairs of conveying rolls can set different medium conveying speeds simply by the configuration of the pairs of conveying rolls, compared to when the outer peripheral surfaces of the pairs of conveying rolls are uniform along the width direction of the medium. According to the medium conveying device of (((9))), the pairs of conveying rolls can accommodate media of different widths, compared to when the outer diameter of the outer peripheral surface of the medium increases discontinuously from the widthwise end toward the center. According to the medium conveying device of (((10))), the plurality of pairs of conveying rolls can suppress the occurrence of wrinkles in thin media compared to when the outer diameters of the drive rolls positioned in the width direction of the media are all equal. According to the image forming apparatus of (((11))), it is possible to prevent wrinkles from occurring in thin media compared to when a media conveying device described in any of (((1))) to (((10))) is not used. [Explanation of symbols]

[0148] 1...Image forming device 60...Paper transport device 70...medium transport device 71a to 71f... Plural paper transport roll pairs 710...Drive roll 711...Driven roll 712...Drive shaft 713...Rotation axis 80...Pressure contact force adjustment mechanism 81 to 83: First to third pressure contact force acting portions

Claims

1. a means for conveying the medium after aligning the leading edge position of the medium, the means including a plurality of conveying roll pairs that are divided into a plurality of sections along a width direction intersecting with the conveying direction of the medium and that sandwich and convey the medium; The plurality of transport roll pairs are configured so that the transport speed is faster in the center of the medium than at the ends along the width direction of the medium.

2. a means for conveying the medium after aligning the leading edge position of the medium, the means including a plurality of conveying roll pairs that are divided into a plurality of sections along a width direction intersecting with the conveying direction of the medium and that sandwich and convey the medium; The plurality of transport roll pairs transport the medium while expanding the medium outward in the width direction of the medium.

3. The medium transport device according to claim 1 , wherein the plurality of transport roll pairs each include a drive roll and a driven roll that is in pressure contact with the drive roll.

4. The medium transport device according to claim 3 , wherein the plurality of transport roll pairs are set so that the pressure force with which the driven roll located in the center presses against the drive roll is greater than that of the driven roll located at the end of the width direction of the medium.

5. The medium transport device according to claim 1 , wherein the transport roll pairs located at the ends in the width direction of the medium are arranged so as to be inclined outward in the transport direction of the medium.

6. The medium transport device according to claim 5 , wherein the plurality of transport roll pairs are arranged such that the transport roll pair located at the center in the width direction of the medium is parallel to the width direction of the medium.

7. A medium conveying device as described in claim 6, wherein among the multiple pairs of conveying rolls, the pair of conveying rolls located at the widthwise end of the medium are positioned at the same clamping position as the pair of conveying rolls located at the center of the widthwise portion of the medium or downstream along the conveying direction of the medium.

8. The medium transport device according to claim 1 , wherein the outer diameter of the outer peripheral surface of each of the plurality of transport roll pairs is larger at a center portion than at an end portion in the width direction of the medium.

9. The medium transport device according to claim 8 , wherein the outer peripheral surfaces of the plurality of transport roll pairs have inclined portions whose outer diameters increase continuously from the ends of the medium in the width direction toward the center.

10. The medium transport device according to claim 3 , wherein the outer diameter of the driven rolls located in the center of the plurality of transport roll pairs is set to be larger than that of the driven rolls located at the ends in the width direction of the medium.

11. a medium transport means for transporting a medium; an image forming means for forming an image on the medium transported by the medium transport means; Equipped with 11. An image forming apparatus using the medium transport device according to claim 1 as the medium transport means.

Images