Image formation device and conveyance device

Abstract

To suppress buckling of a sheet.SOLUTION: A conveyance device for conveying a sheet has: (i) a first conveyance roller pair; (ii) a second conveyance roller pair for conveying a sheet so that the sheet arrivals at a position contacting the first conveyance roller pair; (iii) a moving member which is configured to be movable between a regulation position where the arrival of the sheet at the first conveyance roller pair is regulated, and a retreat position, to be moved to the retreat position from the regulation position by being pushed by the sheet; (iv) a first guide arranged between the moving member and the second conveyance roller pair; and (v) a first opposite guide which is opposite to the first guide, and is arranged between the moving member and the second conveyance roller pair. One of the first guide and the first opposite guide has a first curved part with which the sheet is brought into contact, and the other of the first guide and the first opposite guide has a second curved part with which the sheet is brought into contact.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a conveying device for conveying a sheet and an image forming apparatus using the same.

Background Art

[0002] Generally, image forming apparatuses such as copiers, printers, and facsimiles have a conveying means (conveying device) for conveying a sheet.

[0003] Patent Document 1 discloses an image forming apparatus having a duplex conveying path that guides the sheet back to the transfer unit after forming an image on the first side at the transfer unit so that image formation can be performed on both sides of the sheet.

[0004] In the image forming apparatus of Patent Document 1, when the sheet travels from the stacking means through the image forming means toward the discharge tray, it passes through a conveying path curved in an S shape. The duplex conveying path is disposed below the conveying path (single-sided conveying path) through which the sheet passes when single-sided printing is performed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] When the sheet is conveyed, a force (resistance force) may act on the sheet in a direction that hinders the conveyance of the sheet due to contact between the sheet and other components. For example, in an image forming apparatus having a conveying path curved in an S shape as in Patent Document 1, the curvature of the conveying path may increase and the resistance force may increase in front of the confluence of the single-sided conveying path and the duplex conveying path.

[0007] When a sheet is subjected to a large resistance force, it may buckle. The present invention aims to suppress sheet buckling in a sheet conveying device. [Means for solving the problem]

[0008] One of the inventions related to this application is as follows:

[0009] A conveying device for transporting sheets, A first conveying roller pair for conveying the sheet, comprising: a first roller; and a first conveying roller pair including a first opposing roller facing the first roller; A second conveyor roller pair for conveying the sheet toward the first conveyor roller pair, comprising a second roller and a second opposing roller facing the second roller, the second conveyor roller pair for conveying the sheet so that the sheet reaches a position where it contacts the first conveyor roller pair, A movable member that can move between a restricting position that restricts the sheet from reaching the first transport roller pair and a retracted position that is moved away from the restricting position, the movable member being configured to move from the restricting position to the retracted position when pushed by the sheet, A first guide for guiding the sheet being transported by the second pair of transport rollers, the first guide being positioned between the moving member and the second pair of transport rollers, A first opposing guide for guiding the sheet being transported by the second pair of transport rollers, the first opposing guide being opposed to the first guide and positioned between the moving member and the second pair of transport rollers, It has, One of the first guide and the first opposing guide has a first curved portion against which the sheet abuts, and the other of the first guide and the first opposing guide has a second curved portion against which the sheet abuts. The second pair of conveying rollers conveys the sheet such that the sheet contacts the first curved portion and then the second curved portion. A conveying device characterized by the following features. [Effects of the Invention]

[0010] As described above, according to the present invention, buckling of the sheet can be suppressed in a conveying device for conveying a sheet. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing the configuration of the printer according to this embodiment. [Figure 2] This is a cross-sectional view showing the double-sided transport section according to Example 1. [Figure 3] This is a cross-sectional view showing a double-sided transport section relating to a comparative example. [Figure 4] This is a cross-sectional view showing a modified double-sided transport section. [Modes for carrying out the invention]

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately modified depending on the configuration and various conditions of the apparatus to which the present invention is applied. Therefore, unless otherwise specifically stated, the scope of the present invention is not intended to be limited to those embodiments. [Examples]

[0013] First, the basic configuration and operation of the printer 100 as an image forming apparatus according to this embodiment will be explained using Figure 1. Figure 1 is a schematic cross-sectional view showing the configuration of the printer 100 according to this embodiment.

[0014] The printer 100 according to this embodiment is a laser beam printer that forms an image using an electrophotographic method and records that image onto a recording material (sheet) such as paper.

[0015] A printer 100 that forms an image on a sheet includes a device main body 100A, a paper feed cassette 20 as a loading unit on which the sheet S is loaded, a paper feed conveyance unit 30, an image forming unit 40, a fixing unit 50, a paper discharge reversing unit 60, and a duplex conveyance unit 70. The printer 100 has a control unit 100B for executing an image forming operation on the sheet S.

[0016] Among the printer 100, the part having the function of conveying the sheet S can also be called a conveyance device for the sheet S. In other words, it can also be said that the printer 100 has a conveyance device for the sheet S. For example, the paper feed cassette 20, the paper feed conveyance unit 30, the photosensitive drum 403, the transfer roller 404, the fixing unit 50, and the paper discharge reversing unit 60, and the duplex conveyance unit 70, and the paper discharge tray 604 to be described later are part of the conveyance device in this embodiment. Further, the conveyance device may include a conveyance path through which the sheet S passes and a guide member that forms the conveyance path and guides the sheet S.

[0017] The paper feed conveyance unit 30 includes a pick-up roller (paper feed roller, pick-up roller) 300, a conveyance roller 301, a separation roller 302 that abuts against the conveyance roller 301, an intermediate roller pair 303, a registration roller pair 304, and a registration shutter (shutter) 306. The registration roller pair 304 is a first conveyance roller pair that conveys the sheet S toward the image forming unit 40. The registration roller pair 304 includes a registration roller (first roller) 304b and a driving roller (first opposing roller) 304a. The registration roller 304b and the driving roller 304a face each other and abut. The registration roller 304b is rotated by the driving roller 304a.

[0018] The path through which the sheet S conveyed from the paper feed cassette 20 toward the image forming unit 40 passes is called a first conveyance path 307. The conveyance roller 301, the separation roller 302, the intermediate roller pair 303, the registration roller pair 304, and the registration shutter (shutter) 306 are arranged on the first conveyance path 307. The first conveyance path 307 may include a path from the image forming unit 40 to the paper discharge reversing unit 60.

[0019] The image forming unit 40 forms an image on the sheet S conveyed from the paper feed cassette 20. The image forming unit 40 includes a photosensitive drum (image carrier) 403 that carries an electrostatic latent image, a developing roller (developer carrier) 402 that carries toner as a developer, and develops the electrostatic latent image formed on the photosensitive drum 403 with the toner. Further, the image forming unit 40 includes a laser scanner 401 as an exposure device that exposes the photosensitive drum 403 to form an electrostatic latent image corresponding to the image information on the photosensitive drum 403, and a transfer roller (transfer member) 404 disposed opposite to the photosensitive drum 403.

[0020] In the present embodiment, a cartridge P having the photosensitive drum 403, toner, and the developing roller 402 is detachably attached to the apparatus main body 100A of the printer 100.

[0021] When image information and an image forming command are output from an external device such as a computer connected to the printer 100 to the printer 100, an image forming process (image forming operation) on the sheet S by the image forming unit 40 is started based on the image information.

[0022] The photosensitive drum 403 is charged by a charging device (not shown). The laser scanner 401 irradiates laser light toward the photosensitive drum 403 based on the input image information. By irradiating the laser light, an electrostatic latent image corresponding to the image information is formed on the photosensitive drum 403. Toner is supplied from the developing roller 402 to the photosensitive drum 403 according to the electrostatic latent image formed on the photosensitive drum 403, and a toner image is formed on the photosensitive drum 403.

[0023] On the other hand, in parallel with the above-described image forming operation, the sheet S stacked in the paper feed cassette 20 is conveyed by the pick-up roller 300. When a plurality of sheets S are conveyed, one sheet S is separated from the plurality of sheets S and conveyed at a separation nip formed between the conveying roller 301 and the separation roller 302. The conveyed sheet S is conveyed to the registration roller pair 304 via the intermediate roller pair 303.

[0024] Meanwhile, a shutter 306 is positioned near the registration roller 304b. The shutter 306 is configured to rotate coaxially with the registration roller 304b. In other words, the shutter 306 and the registration roller 304b are configured to rotate around a common axis of rotation, which is a first axis.

[0025] The shutter 306 is a movable member that can move between a restricting position that restricts the sheet S from reaching the registration roller pair 304 and a retracted position that is moved away from the restricting position. When the shutter 306 is moved to the retracted position, the sheet S can come into contact with the registration roller pair 304. The shutter 306 is moved from the restricting position to the retracted position by being pushed by the sheet S.

[0026] More specifically, the shutter 306 is positioned in a restricted position when it is not in contact with the sheet S. When the leading edge of the sheet S comes into contact with the shutter 306 in the restricted position, the sheet S flexes and a loop is formed. As a result, the skew of the sheet S is corrected. Subsequently, the shutter 306 is pushed up by the force it receives from the conveyed sheet S, and the shutter 306 moves to a retracted position. When the shutter 306 is pushed up, the sheet S reaches the nip portion of the registration roller pair 304, which is formed by the registration roller 304b and the drive roller 304a, and is conveyed by the registration roller pair 304.

[0027] The sheet S is transported by the registration roller pair 304 toward the transfer nip (transfer area) formed by the photosensitive drum 403 and the transfer roller 404. A transfer bias is applied to the transfer roller 404 from a power supply (not shown), and the toner image formed on the photosensitive drum 403 is transferred to the sheet S at the transfer nip.

[0028] The fixing unit 50 includes a fixing roller 501 and a pressure roller 502. The sheet S that has passed through the transfer nip is heated and pressurized by the fixing roller 501 and the pressure roller 502, thereby fixing the toner image onto the sheet S.

[0029] The paper output reversal unit 60 includes an output roller 601, a first driven roller 602, and a second driven roller 603. A paper output tray 604 is provided on the upper part of the main body 100A of the device.

[0030] When single-sided printing is performed, in which an image is formed on one side of the sheet S, the sheet S with the fixed toner image is transported by the discharge roller 601 and the first driven roller 602 and discharged into the output tray 604. When double-sided printing is performed, in which an image is formed on both sides of the sheet S, the sheet S with the fixed toner image is not discharged into the output tray 604, but is transported toward the double-sided transport unit 70.

[0031] Specifically, a movable reversal guide 605 is positioned downstream of the fixing unit 50. The sheet S, on which the toner image has been fixed to the first surface, is guided by the reversal guide 605 to the reversal transport path 606 and transported to a predetermined position by the discharge roller 601 and the second driven roller 603. Subsequently, the drive of the discharge roller 601 is reversed, reversing the transport direction of the sheet S, and the sheet S is transported to the double-sided transport path 701.

[0032] The double-sided transport path 701 is a second transport path through which the sheet S, after an image has been formed by the image forming unit 40, is transported back towards the image forming unit 40. The double-sided transport path 701 is connected to the first transport path 307 at the merging section 701a. After passing through the image forming unit 40 (more specifically the transfer unit), the sheet S passes through the double-sided transport path 701, enters the first transport path 307 from the merging section 701a, and is transported again towards the image forming unit 40 and the transfer unit. The registration roller pair 304 and the shutter 306 are located between the merging section 701a and the image forming unit 40.

[0033] The double-sided transport path 701 is equipped with a pair of double-sided transport rollers 702 that transport the sheet S toward the pair of registration rollers 304. The sheet S transported to the double-sided transport path 701 passes through the intermediate transport path 704, which is part of the double-sided transport path 701, via the pair of double-sided transport rollers 702, is bent by the first outer turn guide 707, and is then transported again toward the pair of registration rollers 304.

[0034] Subsequently, the image forming unit 40 forms an image on the second surface (back side) of the sheet S. In other words, toner is transferred to the second surface at the transfer nip. The sheet S, with toner transferred to the second surface, is discharged to the output tray 604 via the fuser unit 50, just as when single-sided printing is performed.

[0035] As described above, in the printer 100 according to this embodiment, the sheet S is transported from the paper feed cassette 20 to the paper output reversal unit 60 in an S-shaped trajectory. The sheet S is bent in the opposite direction to the direction in which it is fed out from the paper feed cassette 20, and then transported so as to come into contact with the lower part of the photosensitive drum 403.

[0036] Here, the rotation axes of the double-sided conveying roller 702a, the driven roller 702b, the driving roller 304a, the driving roller 304a, the registration roller 304b, the pick roller 300, and the photosensitive drum 403 are parallel to each other.

[0037] When viewed in the direction of the rotation axis of the registration roller 304b, the distance between the pick roller 300 and one end (first end) of the device body 100A is shorter in the horizontal direction than the distance between the pick roller 300 and the other end (second end, opposite to the first end) of the device body 100A. In other words, the pick roller 300 is closer to one end of the device body 100A than to the other end. On the other hand, the distance between the paper discharge reversal unit 60 and the other end of the device body 100A is shorter than the distance between the paper discharge reversal unit 60 and one end of the device body 100A. In other words, the paper discharge reversal unit 60 is closer to the other end of the device body 100A than to one end.

[0038] Furthermore, the double-sided transport path 701 passes below the photosensitive drum 403 and above the paper feed cassette 20. In the horizontal direction, the double-sided transport path 701 extends from one side of the photosensitive drum 403 to the other side.

[0039] <Double-sided transport unit> The double-sided transport unit 70 will be described in detail using Figures 1 and 2. Figure 2 (Figures 2(a), (b), (c), (d)) is a cross-sectional view showing the double-sided transport unit 70 according to this embodiment.

[0040] The double-sided conveying section 70 includes a pair of double-sided conveying rollers (a second pair of conveying rollers) 702, an outer turn guide 707 (described later), an inner turn guide 708, an upper conveying guide 705, and a lower conveying guide 706.

[0041] In the transport path from the double-sided transport roller pair 702 to the registration roller pair 304, the double-sided transport roller pair 702 is positioned next to the registration roller pair 304 and hands over the leading edge of the sheet S to the registration roller pair 304. In other words, the double-sided transport roller pair 702 transports the sheet S just before the registration roller pair 304 and transports the sheet S so that it reaches a position where it contacts the registration roller pair 304. To put it another way, the double-sided transport roller pair 702 transports the sheet S until the leading edge of the sheet S exceeds the nip portion of the registration roller pair 304 formed by the registration roller 304b and the drive roller 304a. The double-sided transport roller pair 702 includes a double-sided transport roller (second roller) 702a and a driven roller (second opposing roller) 702b. The double-sided transport roller 702a and the driven roller 702b are in contact with each other and face each other.

[0042] Here, according to the specifications of the printer 100, the smallest size sheet that the printer 100 can handle is referred to as the minimum sheet. The minimum sheet is the smallest size sheet among the sheets S that the printer 100 can transport and perform image forming operations on. In this embodiment, the minimum sheet refers to a sheet of a size that allows for double-sided printing, and specifically, it is the smallest size sheet among the sheets S that can be transported by the registration roller pair 304 and the double-sided transport roller pair 702.

[0043] Furthermore, the length of sheet S along the conveying direction of sheet S is called the sheet length, and the sheet length of the smallest sheet is specifically called the minimum length.

[0044] The position of the double-sided conveyor roller pair 702 relative to the registration roller pair 304 is set based on the distance at which the minimum sheet can be nipped by both the double-sided conveyor roller pair 702 and the registration roller pair 304. This allows the minimum sheet to be transferred from the conveyor roller pair 702 to the registration roller pair 304.

[0045] Specifically, the position of the double-sided conveyor roller pair 702 relative to the registration roller pair 304 is set based on the following formula. (Nip position N1 of registration roller pair 304) - (Nip position N2 of double-sided conveyor roller pair 702) = (shortest length) - (maximum deflection) - (minimum sheet tolerance) - (leading edge overhang) - (rear edge overhang) ... (Equation 1) Here, nip position N1 is the position where the registration roller pair 304 nips the sheet S, and is the position of the contact area (first nip area, first contact area) where the registration roller 304b and the drive roller 304a come into contact. Nip position N2 is the position where the double-sided conveyor roller pair 702 nips the sheet S, and is the position of the contact area (second nip area, second contact area) where the double-sided conveyor roller 702a and the driven roller 702b come into contact. The maximum deflection amount is a value used to account for the effect when the minimum sheet deflects the most within the conveyor path between the registration roller pair 304 and the double-sided conveyor roller pair 702.

[0046] Furthermore, in order to reliably transport the sheet S by the double-sided transport roller pair 702 and the registration roller pair 304, it is preferable that the double-sided transport roller pair 702 transport the sheet S until the leading edge of the sheet S protrudes a predetermined amount from the first nip portion. Also, when the leading edge of the sheet S protrudes a predetermined amount from the first nip portion, it is preferable that the rear end of the sheet S protrudes a predetermined amount from the second nip portion. The amount of sheet S protruding from the first nip portion on the leading edge side of the sheet S is called the leading edge protrusion amount, and the amount of sheet S protruding from the second nip portion on the rear end side of the sheet S is called the rear end protrusion amount.

[0047] Furthermore, due to design constraints of the printer 100 and in order to reduce the size of the printer 100, the double-sided transport roller pair 702 may be positioned away from the registration roller pair 304 and the outer turn guide 707. If the double-sided transport roller pair 702 can be positioned away from the registration roller pair 304 and the outer turn guide 707, the design flexibility of the printer 100 will also be improved. In addition, by increasing the distance between one roller pair and the adjacent roller pair (the roller pair that transports the sheet S immediately before it), the total number of roller pairs arranged along the transport path of the sheet S can be reduced.

[0048] The distance between the double-sided transport roller pair 702 and the registration roller pair 304 along the transport path of the sheet S can be 45% or more of the shortest length. In other words, when the smallest sheet is held between the registration roller pair 304 and the double-sided transport roller pair 702, 45% or more of the shortest length is located between the registration roller pair 304 and the double-sided transport roller pair 702. In this embodiment, the smallest sheet in the printer 100 is an A5 size sheet, and its shortest length is 210 mm. Therefore, when the sheet S is held between the registration roller pair 304 and the double-sided transport roller pair 702, the sheet S is located between the registration roller pair 304 and the double-sided transport roller pair 702 for a length of 100 mm or more.

[0049] In this embodiment, the distance between the double-sided conveying roller pair 702 and the registration roller pair 304 along the conveying path of the sheet S is 85% to 95% (specifically 90%) of the shortest length. In other words, when the smallest sheet is held between the registration roller pair 304 and the double-sided conveying roller pair 702, 85% to 95% (specifically 90%) of the shortest length is located between the registration roller pair 304 and the double-sided conveying roller pair 702. Therefore, when the sheet S is held between the registration roller pair 304 and the double-sided conveying roller pair 702, the sheet S is located between the registration roller pair 304 and the double-sided conveying roller pair 702 for a length of 180 mm or more.

[0050] The printer 100 may have a detection unit 305 that detects the sheet length of the sheet S being transported. The control unit 100B may restrict the image forming operation on the sheet S or the operation of transporting the sheet S if the sheet length is outside a predetermined range as detected by the detection unit 305. For example, if the sheet length of the sheet S being transported is shorter than the minimum length, the control unit 100B may restrict the image forming operation on the sheet S or the operation of transporting the sheet S.

[0051] Next, we will describe the guide members that are placed in the double-sided transport path 701.

[0052] Regarding the conveying direction of the sheet S from the double-sided conveying roller pair 702 toward the registration roller pair 304, an outer turn guide 707 and an inner turn guide 708 are positioned upstream of the registration roller pair 304, the shutter 306, and the confluence section 701a. The outer turn guide (U-turn guide, bending guide, return guide, second guide, second curving guide) 707 and the inner turn guide 708 are positioned in the double-sided conveying path 701, specifically between the relay conveying path 704 and the confluence section 701a.

[0053] The outer turn guide 707 guides the sheet S, which has been transported by the double-sided conveyor roller pair 702, toward the registration roller pair 304. The sheet S is bent by contact with the outer turn guide 707, and the direction of movement of the leading edge of the sheet S changes from away from the registration roller pair 304 and shutter 306 to toward the registration roller pair 304 and shutter 306. In other words, the outer turn guide 707 causes the sheet S to make a U-turn and guides it toward the registration roller pair 304 and shutter 306.

[0054] Between the outer turn guide 707 and the inner turn guide 708, a return path (U-turn path) 703 is formed through which the sheet S, which is bent and makes a U-turn as described above, passes. The outer turn guide 707 is positioned on the outside (outside in the radial direction of the curve) of the curved return path 703, and the inner turn guide 708 is positioned on the inside (inside in the radial direction of the curve) of the curved return path 703.

[0055] The double-sided transport path 701 is equipped with an upper transport guide (first guide, first curved guide) 705 and a lower transport guide (first opposing guide, first opposing curved guide) 706 that is opposite to the side transport guide 705. The upper transport guide 705 and the lower transport guide 706 are configured to guide the sheet S being transported by the double-sided transport roller pair 702.

[0056] The upper transport guide 705 and the lower transport guide 706 are located between the shutter 306 and the double-sided transport roller pair 702. Alternatively, the upper transport guide 705 and the lower transport guide 706 may be located between the registration roller pair 304 and the double-sided transport roller pair 702, or between the outer turn guide 707 and the double-sided transport roller pair 702.

[0057] The intermediate transport path 704 of the double-sided transport path 701 is formed between the upper transport guide 705 and the lower transport guide 706. In the vertical direction, the upper transport guide 705 is positioned above the lower transport guide 706.

[0058] The sheet S is subjected to frictional resistance from the outer turn guide 707. In addition, the sheet S is subjected to a reaction force from the shutter 306. The frictional resistance that the sheet S receives from the outer turn guide 707 and the reaction force that the sheet S receives from the shutter 306 can be called forces (resistance forces, transport resistance forces) that act in a direction that hinders the transport of the sheet S.

[0059] In a transport path like that of the printer 100 according to this embodiment, it is preferable to reduce the radius and increase the curvature of the outer turn guide 707 in order to miniaturize the printer 100, but in that case the frictional resistance that the sheet S receives from the outer turn guide 707 will also increase. Also, since the double-sided transport roller pair 702 is positioned far from the registration roller pair 304, the distance between the registration roller pair 304, the shutter 306, the outer turn guide 707 and the double-sided transport roller pair 702 will also increase.

[0060] If the resistance force on sheet S is too great, sheet S may buckle, causing multiple small bends, which may make it difficult to properly push up the shutter 306, for example.

[0061] This phenomenon tends to occur more frequently when using thin sheets S. Furthermore, it is more likely to occur the longer the distance from the upstream conveyor roller pair (double-sided conveyor roller pair 702) to the downstream conveyor roller pair (registration roller pair 304).

[0062] According to the inventors' research, when a sheet S is held between a pair of registration rollers 304 and a pair of double-sided transport rollers 702, buckling of the sheet S is more likely to occur if the sheet S is positioned between the pair of registration rollers 304 and the pair of double-sided transport rollers 702 for a distance of 100 mm or more. It is even more likely to occur if the sheet S is positioned between the pair of registration rollers 304 and the pair of double-sided transport rollers 702 for a distance of 180 mm or more. In other words, increasing the distance between the pair of registration rollers 304 and the pair of double-sided transport rollers 702 has advantages such as improving the design flexibility of the printer 100, but it makes the sheet S more prone to buckling.

[0063] In this embodiment, the printer 100 is provided with curved sections in the upper transport guide 705 and the lower transport guide 706, thereby significantly bending the sheet S and suppressing buckling of the sheet S.

[0064] The shapes of the upper transport guide 705 and the lower transport guide 706 in this embodiment will be explained in detail using Figures 2(a) to 2(d). Figures 2(a) to 2(d) are views of the double-sided transport roller 702a along the direction of its rotation axis.

[0065] Here, the direction perpendicular to the conveying direction and thickness direction of the sheet S is called the width direction of the sheet S. The width direction is parallel to the direction of the rotation axis of each of the double-sided conveying rollers 702a, driven rollers 702b, drive rollers 304a, and registration rollers 304b.

[0066] The upper transport guide 705 has a first upper curved section (first curved section) 705a, a second upper curved section 705b, and a third upper curved section (third curved section) 705c, each having a predetermined curvature. The second upper curved section 705b is positioned between the first upper curved section 705a and the third upper curved section 705c. The first upper curved section 705a and the third upper curved section 705c are positioned at a distance from each other.

[0067] The lower transport guide 706 has a first lower curved section 706a, a second lower curved section (second curved section) 706b, and a third lower curved section 706c, each having a predetermined curvature. The second lower curved section 706b is positioned between the first lower curved section 706a and the third lower curved section 706c. The first lower curved section 706a and the third lower curved section 706c are positioned at a distance from each other.

[0068] The first upper curved portion 705a and the third upper curved portion 705c are curved portions (curved surfaces) that are curved such that the surface facing the sheet S and the relay transport path 704 is concave. The first upper curved portion 705a and the third upper curved portion 705c can be described as curved surfaces that are curved away from the sheet S and the relay transport path 704 in the thickness direction of the sheet S (the direction perpendicular to the transport direction and width direction of the sheet S). The second upper curved portion 705b is a curved portion (curved surface) that is curved such that the surface facing the sheet S and the relay transport path 704 is convex. The second upper curved portion 705b can be described as a curved surface that is curved towards the sheet S and the relay transport path 704 in the thickness direction of the sheet S. In this embodiment, the first upper curved portion 705a, the second upper curved portion 705b, and the third upper curved portion 705c are arc-shaped.

[0069] The first lower curved portion 706a and the third lower curved portion 706c are curved portions (curved surfaces) that are curved such that the surface facing the sheet S and the relay transport path 704 is convex. The first lower curved portion 706a and the third lower curved portion 706c can be described as curved surfaces that are curved in the direction approaching the sheet S and the relay transport path 704 with respect to the thickness direction of the sheet S (the direction perpendicular to the transport direction and width direction of the sheet S). The second lower curved portion 706b is a curved portion (curved surface) that is curved such that the surface facing the sheet S and the relay transport path 704 is concave. The second lower curved portion 706b can be described as a curved surface that is curved in the direction away from the sheet S and the relay transport path 704 with respect to the thickness direction of the sheet S. In this embodiment, the first lower curved portion 706a, the second lower curved portion 706b, and the third lower curved portion 706c are arc-shaped.

[0070] The first upper curved section 705a and the first lower curved section 706a, the second upper curved section 705b and the second lower curved section 706b, and the third upper curved section 705c and the third lower curved section 706c face each other and form a curved transport path through which the sheet S passes.

[0071] The double-sided conveying roller pair 702 conveys the sheet S such that the sheet S contacts the first upper curved portion 705a, then the second lower curved portion 706b, and then the third upper curved portion 705c.

[0072] Here, looking in the direction of the rotation axis of the double-sided conveying roller 702a, the line connecting the rotation center of the double-sided conveying roller 702a and the rotation center of the driven roller 702b is defined as the first line L1. Furthermore, the line perpendicular to the first line L1 and passing through the position where the double-sided conveying roller 702a and the driven roller 702b come into contact (second nip portion N2) is defined as the second line L2. In this embodiment, the second line L2 is the tangent (common tangent) between the double-sided conveying roller 702a and the driven roller 702b.

[0073] The double-sided conveying roller pair 702 pushes the sheet S along the second straight line L2. The direction in which the double-sided conveying roller pair 702 pushes and conveys the sheet S is called the push direction Nf2. The push direction Nf2 is the direction of movement of the sheet S in the portion between the double-sided conveying roller 702a and the driven roller 702b.

[0074] The first upper curved section 705a is positioned downstream of the double-sided conveyor roller pair 702 and intersects the second straight line L2 in the conveying direction of the sheet S by the double-sided conveyor roller pair 702. The upper guide entrance section (parallel section) 705d is positioned between the double-sided conveyor roller pair 702 and the first upper curved section 705a and is formed parallel to the second straight line L2.

[0075] As shown in Figure 2(a), the sheet S passing through the double-sided transport path 701 is nipped by the double-sided transport roller pair 702 and moves in the extrusion direction N2f, then moves along the upper guide entrance portion 705d, and then comes into contact with the first upper curved portion 705a.

[0076] The sheet S, which is in contact with the first upper curved portion 705a, is guided by the first upper curved portion 705a from the upper transport guide 705 toward the lower transport guide 706 in the shape of an arc S1a, and comes into contact with the second lower curved portion 706b.

[0077] The sheet S, which is in contact with the second lower curved portion 706b, is guided by the second lower curved portion 706b from the lower transport guide 706 toward the upper transport guide 705 in a circular arc S1b, and comes into contact with the third upper curved portion 705c.

[0078] The sheet S, which is in contact with the third upper curved portion 705c, is guided by the third upper curved portion 705c from the upper transport guide 705 toward the lower transport guide 706 in a circular arc S1c, and comes into contact with the outer turn guide 707.

[0079] Next, as shown in Figure 2(b), the sheet S is transported along the outer turn guide 707. At this time, the sheet S is prone to buckling due to the frictional resistance it receives from the outer turn guide 707. However, because arcs S1a, S1b, and S1c are formed in the sheet S along the first upper curved portion 705a, the second lower curved portion 706b, and the third upper curved portion 705c, the sheet S is kept bent at the desired curvature, and buckling is avoided.

[0080] As the sheet S moves further, as shown in Figure 2(c), the tip of the sheet S reaches the shutter 306. The tip of the sheet S is restricted by the shutter 306, a loop is formed in the sheet S, and the oblique angle of the sheet S is corrected. At this time, the sheet S is in a state where it is prone to buckling due to the reaction force received from the shutter 306. However, because arcs S1a, S1b, and S1c are formed in the sheet S along the first upper curved portion 705a, the second lower curved portion 706b, and the third upper curved portion 705c, the sheet S is maintained in a state where it is bent with the desired curvature, and the occurrence of buckling is avoided.

[0081] When the skew of the sheet S is corrected, the entire sheet S presses against the shutter 306 in the width direction. In this state, when the conveying force (pressing force) of the sheet S overcomes the force that holds the shutter 306 in the restricted position, the sheet S pushes up the shutter 306 and moves forward, as shown in Figure 2(d). The sheet S, having pushed the shutter 306 to the retracted position, reaches the first nip portion of the registration roller pair 304 and is conveyed by the registration roller pair 304. The shutter 306 may be positioned in the restricted position by its own weight, or by a biasing member such as a spring.

[0082] As described above, with the printer 100 according to this embodiment, when the sheet S receives frictional resistance from the outer turn guide 707, buckling of the sheet S is suppressed. Furthermore, when the sheet S receives a reaction force from the shutter 306, buckling of the sheet S is suppressed.

[0083] Arcs S1a, S1b, and S1c are formed in the sheet S along the first upper curved section 705a, the second lower curved section 706b, and the third upper curved section 705c, thereby applying the necessary conveying force to the sheet S and transporting it to the registration roller pair 304. In other words, the sheet S is bent by the first upper curved section 705a, the second lower curved section 706b, and the third upper curved section 705c, and the double-sided conveying roller pair 702 transports the sheet S in this bent state, handing it over to the registration roller pair 304. As a result, buckling of the sheet S between the double-sided conveying roller pair 702 and the registration roller pair 304, and between the double-sided conveying roller pair 702 and the shutter 306 is suppressed.

[0084] The radii 705Ra of the first upper curved section 705a, the radii 706Rb of the second lower curved section 706b, and the radii 705Rc of the third upper curved section 705c are all larger than the radius 707R of the outer turn guide 707. Therefore, the frictional resistance received from the first upper curved section 705a, the second lower curved section 706b, and the third upper curved section 705c is smaller than the frictional resistance received from the outer turn guide 707. As a result, buckling of the sheet S is suppressed by the first upper curved section 705a, the second lower curved section 706b, and the third upper curved section 705c.

[0085] According to the inventors' studies, the gap between the first lower curved portion 706a and the first upper curved portion 705a is preferably 10 mm or less, and more preferably 5 mm or less. The same applies to the gap between the second upper curved portion 705b and the second lower curved portion 706b, and the gap between the third lower curved portion 706c and the third upper curved portion 705c. Furthermore, the first lower curved portion 706a is concentrically arranged with the first upper curved portion 705a, the second upper curved portion 705b with the second lower curved portion 706b, and the third lower curved portion 706c with the third upper curved portion 705c.

[0086] The configurations of the first lower curved section 706a, the second upper curved section 705b, and the third lower curved section 706c are not limited to those described above. The center of the radius of the first lower curved section 706a and the center of the radius 705Ra of the first upper curved section 705a may be different. The radius of the first lower curved section 706a may be the same as or different from the radius 705Ra of the first upper curved section 705a. The same applies to the relationship between the second upper curved section 705b and the second lower curved section 706b, and the relationship between the third upper curved section 705c and the third lower curved section 706c. Furthermore, at least a portion of the first lower curved section 706a, the second upper curved section 705b, and the third lower curved section 706c may be formed in a straight line.

[0087] Furthermore, according to the inventors' studies, in order to suppress buckling of the sheet S, it is preferable that the radius 705Ra of the first upper curved portion 705a, the radius 706Rb of the second lower curved portion 706b, and the radius 705Rc of the third upper curved portion 705c be between 90 mm and 160 mm. This corresponds to a length of approximately 40% to 80% of the shortest length (210 mm).

[0088] Furthermore, the radius 705Ra of the first upper curved portion 705a can be made larger than the radius 706Rb of the second lower curved portion 706b. The radius 705Rc of the third upper curved portion 705c can be made larger than the radius 705Ra of the first upper curved portion 705a.

[0089] Furthermore, the radius 705Ra of the first upper curved section 705a can be 125 mm or more and 145 mm or less. The radius 706Rb of the second lower curved section 706b can be 90 mm or more and 110 mm or less. The radius 705Rc of the third upper curved section 705c can be 140 mm or more and 160 mm or less.

[0090] <Structure of the comparative example> The configuration of the comparative example will be explained using Figure 3. Figure 3 (Figures 3(a), (b), (c), and (d)) are cross-sectional views showing the double-sided transport section 170 of the comparative example. The double-sided transport section 170 of the comparative example has an upper transport guide 1705 and a lower transport guide 1706 that have different shapes from the upper transport guide 705 and lower transport guide 706. Otherwise, the configuration of the double-sided transport section 170 and the double-sided transport section 70 are the same. The upper transport guide 1705 and the lower transport guide 1706 do not have curved sections and are formed in a straight line. A relay transport path 1704 is formed between the upper transport guide 1705 and the lower transport guide 1706.

[0091] In Figure 3(a), the sheet S being transported along the double-sided transport path 1701 is transported to the intermediate transport path 1704 by the double-sided transport roller pair 1702. The sheet S moves in a nearly straight line along the lower transport guide 1706 and reaches the outer turn guide 707.

[0092] Next, as shown in Figure 3(b), the sheet S is transported along the outer turn guide 707. At this time, the sheet S is subjected to frictional resistance from the outer turn guide 707. If the transport force of the sheet S is overcome by the frictional resistance, small buckling begins to occur near the center of the sheet S within the relay transport path 1704.

[0093] As the sheet S is further transported, the leading edge of the sheet S reaches the shutter 306, as shown in Figure 3(c). The leading edge of the sheet S contacts the shutter 306, forming a loop and correcting the skew of the sheet S. However, the sheet S receives a reaction force from the shutter 306, causing further buckling to occur from near the center to the rear end of the sheet S within the relay transport path 1704.

[0094] As a result, as shown in Figure 3(d), the sheet S is unable to push up the shutter 306 and cannot reach the first nip portion of the registration roller pair 304. In this state, if the sheet S is further conveyed by the double-sided convey roller pair 702, further buckling of the sheet S occurs within the conveying path 1704. As a result, the normal conveyance of the sheet S is hindered.

[0095] Buckling of the sheet S due to frictional resistance from the outer turn guide 707 and reaction force from the shutter 306 is more likely to occur when the sheet S is thin.

[0096] <Variation> The configuration of the modified example will be explained using Figure 4. Figure 4 is a diagram illustrating the double-sided transport unit 270 according to the modified example. The double-sided transport unit 270 according to the modified example has an upper transport guide 2705 and a lower transport guide 2706 that have different shapes from the upper transport guide 705 and lower transport guide 706. Otherwise, the configuration of the double-sided transport unit 270 and the double-sided transport unit 70 are the same.

[0097] In the double-sided conveying section 70 shown in Figures 2(a) to (d), the sheet S conveyed by the double-sided conveying roller pair 702 contacted the first upper curved section 705a, the second lower curved section 706b, and the third upper curved section 705c in that order. However, the present invention is not limited to this form. The curved sections corresponding to the first upper curved section 705a and the third upper curved section 705c can be provided on one of the upper conveying guide 705 and the lower conveying guide 706, and the curved section corresponding to the second lower curved section 706b can be provided on the other of the upper conveying guide 705 and the lower conveying guide 706. Furthermore, the curved section corresponding to the third upper curved section 705c can be omitted.

[0098] Specifically, as shown in Figure 4, the lower transport guide 2706 has a first lower curved section (first curved section) 2706a and a second lower curved section 2706b having a predetermined curvature. The upper transport guide 2705 has a first upper curved section 2705a and a second upper curved section (second curved section) 2705b having a predetermined curvature.

[0099] In the vertical direction, the upper transport guide 2705 is positioned above the lower transport guide 2706. A relay transport path 2704 is formed between the upper transport guide 2705 and the lower transport guide 2706.

[0100] The first lower curved portion 2706a is a curved portion (curved surface) that is curved such that the surface facing the sheet S and the relay transport path 2704 is concave. The first lower curved portion 2706a can be described as a curved surface that is curved away from the sheet S and the relay transport path 2704 in the thickness direction of the sheet S. The second lower curved portion 2706b is a curved portion (curved surface) that is curved such that the surface facing the sheet S and the relay transport path 2704 is convex. The second lower curved portion 2706b can be described as a curved surface that is curved towards the sheet S and the relay transport path 2704 in the thickness direction of the sheet S. In this embodiment, the first lower curved portion 2706a and the second lower curved portion 2706b are arc-shaped.

[0101] The first upper curved portion 2705a is a curved portion (curved surface) that is curved such that the surface facing the sheet S and the relay transport path 2704 is convex. The first upper curved portion 2705a can be described as a curved surface that is curved in the direction approaching the sheet S and the relay transport path 2704 with respect to the thickness direction of the sheet S (the direction perpendicular to the transport direction and width direction of the sheet S). The second upper curved portion 2705b is a curved portion (curved surface) that is curved such that the surface facing the sheet S and the relay transport path 2704 is concave. The second upper curved portion 2705b can be described as a curved surface that is curved in the direction away from the sheet S and the relay transport path 2704 with respect to the thickness direction of the sheet S. In this embodiment, the first upper curved portion 2705a and the second upper curved portion 2705b are arc-shaped.

[0102] The first lower curved section 2706a and the first upper curved section 2705a, and the second lower curved section 2706b and the second upper curved section 2705b face each other and form a curved transport path through which the sheet S passes.

[0103] The double-sided conveying roller pair 702 conveys the sheet S such that the sheet S contacts the first lower curved portion 2706a and then the second upper curved portion 2705b.

[0104] Similar to the configuration shown in Figures 2(a) to (d), buckling of the sheet S is suppressed by bending along the first lower curved section (first curved section) 2706a and the second upper curved section 2 (second curved section) 705b.

[0105] The first lower curved section 2706a is positioned downstream of the double-sided conveyor roller pair 702 and intersects with the second straight line L2 in the conveying direction of the sheet S by the double-sided conveyor roller pair 702. The lower guide entrance section (parallel section) 2706d is positioned between the double-sided conveyor roller pair 702 and the first lower curved section 2706a and is formed parallel to the second straight line L2.

[0106] The radius 2706Ra of the first lower curved section 2706a is the same as the radius 705Ra mentioned above. The radius 2705Rb of the second upper curved section 2705b is the same as the radius 706Rb mentioned above.

[0107] The gap between the first lower curved portion 2706a and the first upper curved portion 2705a is the same as the gap between the first upper curved portion 705a and the first lower curved portion 706a described above. The gap between the second upper curved portion 2705b and the second lower curved portion 2706b is the same as the gap between the second lower curved portion 706b and the second upper curved portion 705b described above. The first lower curved portion 2706a is concentric with the first upper curved portion 2705a, and the second upper curved portion 2705b is concentric with the second lower curved portion 2706b.

[0108] Furthermore, the configuration of the first upper curved portion 2705a and the second lower curved portion 2706b is not limited to those described above. The center of the radius of the first upper curved portion 2705a and the center of the radius of the first lower curved portion 2706a may be different. The radius of the first upper curved portion 2705a may be the same as or different from the radius of the first lower curved portion 2706a. The same applies to the relationship between the second lower curved portion 2706b and the second upper curved portion 2705b. In addition, at least a portion of the first upper curved portion 2705a and the second lower curved portion 2706b may be formed in a straight line.

[0109] As explained above, by arranging a first curved section on one of the upper transport guide 705 (2705) and the lower transport guide 706 (2706), and providing a second curved section on the other, buckling of the sheet S is suppressed, and the sheet S is transported stably.

[0110] Furthermore, according to the present invention, the distance from the registration roller pair 304 to the double-sided conveying roller pair 702 that conveys the sheet S directly in front of the registration roller pair 304 can be increased. As described above, when the minimum sheet is held between the registration roller pair 304 and the double-sided conveying roller pair 702, the registration roller pair 304 is positioned near the downstream end of the minimum sheet, and the double-sided conveying roller pair 702 is positioned near the upstream end of the minimum sheet.

[0111] By increasing the distance between pairs of rollers that transport the sheet, the number of roller pairs arranged in the printer 100 can be reduced. As a result, the space required for arranging the roller pairs can be reduced, and the drive train for driving the roller pairs can be omitted. In addition, the load on the drive source for driving the roller pairs can be reduced. As a result, it becomes possible to miniaturize the printer 100 and reduce the cost of the printer 100.

[0112] Furthermore, the present invention is not limited to laser printers, but can also be applied to photocopiers, so-called LED printers using light-emitting diodes, inkjet printers, and the like.

[0113] Furthermore, although the side transport guide 705 (2705) and the lower transport guide 706 (2706) were arranged on the double-sided transport path 701, they may also be arranged on transport paths other than the double-sided transport path 701. However, as the sheet S passes through the fixing section 50, curling may occur in the sheet S, making it more susceptible to buckling. In this case as well, as in the printer 100 according to this embodiment, buckling of the sheet S can be suppressed by arranging the side transport guide 705 (2705) and the lower transport guide 706 (2706) on the double-sided transport path 701 downstream of the fixing section 50. [Explanation of Symbols]

[0114] 100 printers S Seat 304 Registration Roller 306 Shutter 40 Image forming unit 70, 170, 270 Double-sided transport section 701 Double-sided transport route 702 Double-sided conveyor roller pair 705, 1705, 2705 Upper transport guide 706, 1706, 2706 Lower transport guide 707 Outer Turn Guide

Claims

1. A conveying device that conveys a sheet, a first conveying roller pair for conveying the sheet, the first conveying roller pair including a first roller and a first opposing roller opposed to the first roller; a second conveying roller pair that conveys the sheet toward the first conveying roller pair, the second conveying roller pair including a second roller and a second opposing roller that faces the second roller, and that conveys the sheet so that the sheet reaches a position where the sheet contacts the first conveying roller pair; a movable member movable between a restricting position where the sheet is restricted from reaching the first conveying roller pair and a retracted position retracted from the restricting position; a first guide configured to guide the sheet conveyed by the second conveying roller pair, the first guide being disposed between the moving member and the second conveying roller pair; a first opposing guide that guides the sheet conveyed by the second conveying roller pair, the first opposing guide being opposed to the first guide and disposed between the moving member and the second conveying roller pair; having the second conveying roller pair is configured to convey the sheet such that, after the sheet abuts against the moving member and the skew of the sheet is corrected, the sheet moves the moving member from a regulating position to a retracted position, and the sheet reaches a position where the sheet contacts the first conveying roller pair, One of the first guide and the first opposing guide has a first curved portion against which the sheet comes into contact, and the other of the first guide and the first opposing guide has a second curved portion against which the sheet comes into contact, the second conveying roller pair conveys the sheet such that the sheet abuts on the first curved portion, and then abuts on the second curved portion, and then reaches the moving member, and the sheet is conveyed to the first conveying roller pair in a curved state by the first curved portion and the second curved portion; A conveying device characterized by the above.

2. The sheet conveyed by the second conveying roller pair is further provided with a second guide that guides the sheet conveyed by the second conveying roller pair toward the first conveying roller pair, and the second guide makes a U-turn of the sheet conveyed by the second conveying roller pair.

2. The conveying device according to claim 1.

3. The sheet conveyed by the second conveying roller pair further includes a second guide that guides the sheet conveyed by the second conveying roller pair toward the first conveying roller pair, and the second guide bends the sheet such that a moving direction of a leading end of the sheet is changed from a direction away from the first conveying roller pair to a direction approaching the first conveying roller pair.

2. The conveying device according to claim 1.

4. 4. The conveying device according to claim 2, wherein the first guide and the first opposing guide are disposed between the second guide and the second pair of conveying rollers.

5. A conveying device as described in any one of claims 1 to 4, characterized in that the radius of the first curved portion is larger than the radius of the second curved portion.

6. A conveying device as described in any one of claims 1 to 5, characterized in that each of the first curved portion and the second curved portion is concave.

7. the one of the first guide and the first opposing guide has a third curved portion with which the sheet comes into contact, the second conveying roller pair conveys the sheet such that the sheet abuts on the second curved portion and then abuts on the third curved portion; 7. The conveying device according to claim 1, wherein the conveying device is a conveying device.

8. The conveying device according to claim 7 , wherein the first guide is disposed above the first opposing guide in the vertical direction.

9. The conveying device according to claim 8 , wherein the first curved portion and the third curved portion are provided on the first guide.

10. A conveying device described in any one of claims 7 to 9, characterized in that the radius of the third curved portion is larger than the radius of the first curved portion.

11. A conveying device described in any one of claims 7 to 10, characterized in that the third curved portion is concave.

12. A conveying device described in any one of claims 1 to 11, characterized in that when viewed in the direction of the rotation axis of the second roller, a line connecting the center of the second roller and the center of the second opposing roller is defined as a first line, and a line that is perpendicular to the first line and passes through a position where the second roller and the second opposing roller abut is defined as a second line, the first curved portion is positioned at a position intersecting the second line.

13. The conveying device according to claim 12 , further comprising a parallel portion that is parallel to the second straight line and is provided between the first conveying roller pair and the first curved portion.

14. 14. The conveying device according to claim 1, wherein the first roller and the moving member are rotatable about a first axis.

15. When the smallest sheet that can be transported by the first transport roller pair and the second transport roller pair is defined as a minimum sheet, the first transport roller pair and the second transport roller pair are arranged such that when the minimum sheet is sandwiched between the first transport roller pair and the second transport roller pair, a portion of 45% or more of the length of the minimum sheet in the transport direction of the minimum sheet by the first transport roller pair and the second transport roller pair is located between the first transport roller pair and the second transport roller pair.

15. A conveying device according to any one of claims 1 to 14.

16. 16. The transport device according to claim 1, wherein the radius of the first curved portion is not less than 90 mm and not more than 160 mm.

17. 17. The transport device according to claim 16, wherein the radius of the second curved portion is not less than 90 mm and not more than 160 mm.

18. the first conveying roller pair and the second conveying roller pair are disposed so that, when the sheet is sandwiched between the first conveying roller pair and the second conveying roller pair, the sheet is positioned between the first conveying roller pair and the second conveying roller pair over a range of 100 mm or more; 18. A conveying device according to any one of claims 1 to 17.

19. the first conveying roller pair and the second conveying roller pair are disposed so that, when the sheet is sandwiched between the first conveying roller pair and the second conveying roller pair, the sheet is positioned between the first conveying roller pair and the second conveying roller pair over a range of 180 mm or more; 19. A conveying device according to any one of claims 1 to 18.

20. An image forming apparatus for forming an image on a sheet, A conveying device according to any one of claims 1 to 19, a stacking section on which the sheets are stacked; an image forming section that forms an image on the sheet conveyed from the stacking section; 1. An image forming apparatus comprising:

21. a first transport path through which the sheet passes when the sheet is transported from the stacking unit toward the image forming unit; a second transport path through which the sheet passes and is transported again toward the image forming unit after an image is formed by the image forming unit, the second transport path being connected to the first transport path at a junction; the first conveying roller pair is disposed between the junction and the image forming unit and configured to convey the sheet toward the image forming unit; the second conveying roller pair, the first guide, and the first opposing guide are disposed on the second conveying path; 21. The image forming apparatus according to claim 20.

Images