Curl straightening appliance and image forming apparatus

Abstract

Even when the cumulative number of sheets passing through the nip section increases, the goal is to provide the sheets with an appropriate amount of curl correction while suppressing deterioration in transportability and loading capacity. [Solution] The curl straightening device 90 changes the distance H1 between the rotating shaft portion 93a of the first hard roller 93 and the rotating shaft portion 94a of the first soft roller 94, and the distance H2 between the rotating shaft portion 95a of the second hard roller 95 and the rotating shaft portion 96a of the second soft roller 96, according to the cumulative number of sheets P passing through the nip portion N1 and the nip portion N2.

Description

Technical Field

[0001] The present invention relates to a curl correction device for correcting the curl of a sheet and an image forming apparatus including the curl correction device.

Background Art

[0002] In a conventional electrophotographic image forming apparatus such as a copier, a printer, or a facsimile, after transferring a toner image formed on a photosensitive drum (electrophotographic photoreceptor) provided in an image forming unit to a sheet, the sheet on which the toner image has been transferred is conveyed to a fixing device. The fixing device includes a heating roller for heating the toner image transferred to the sheet and a pressure roller that is pressed against the heating roller, and the toner image is fixed to the sheet by heating and pressing the sheet on which the toner image has been transferred with the heating roller and the pressure roller.

[0003] Then, the sheet on which the toner image has been fixed by the fixing device is sent to a sheet processing device that performs processes such as sorting, stapling, or punching. When forming an image on both sides of the sheet, the sheet having an image formed on one side is conveyed back to the image forming unit via a duplex path (re-conveying path) to form an image on the back side of the sheet.

[0004] In such an image forming apparatus, when generally fixing a sheet with a large amount of toner image, a curl may occur that is concave on the toner image side that is warped to the image forming surface side of the sheet on which the toner image is placed. Also, when fixing a thin sheet with little toner on it, a curl may occur that is convex on the toner image side that is warped to the non-image forming surface side of the sheet on which the toner image is not placed.

[0005] When a curled sheet is transported to a sheet processing device or a double-sided pass, it may cause problems such as transport failure (jamming) or loading failure. In addition, in the case of double-sided image forming, when the sheet is transported again to the image forming section, depending on the size or direction of the curl, the sheet may become entangled in the secondary transfer belt, resulting in poor separation of the sheet from the secondary transfer belt, or the sheet may get caught between the transport guides, causing transport failures. For this reason, conventional image forming apparatuses use a curl correction device to remove the curl from the sheet (for example, Patent Document 1), or to correct the curled sheet by curling it in the opposite direction.

[0006] Conventional curl straightening devices work by pressing a hard roller against a relatively soft roller, causing the hard roller to bite into the soft roller and form a nip. Then, as the sheet passes through the nip, the sheet is conveyed while being bent towards the hard roller, thereby straightening the curl. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2003-012215 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, in conventional curl straightening devices, as the cumulative number of sheets passing through the nip increases, the surface of the soft roller wears down, and the hard roller no longer penetrates the soft roller to the required extent in the nip. In this case, the straightening of the curl of the sheet becomes insufficient, leading to problems such as deterioration of transportability and loading performance in subsequent processes.

[0009] The object of the present invention is to provide a curl correction device and an image forming device that can provide an appropriate amount of curl correction to sheets even when the cumulative number of sheets passing through the nip section increases, and can suppress deterioration of transportability and stackability. [Means for solving the problem]

[0010] The curl correction device according to the present invention comprises a rotatable hard roller and a rotatable soft roller that is pressed against the hard roller to form a nip portion and has a lower hardness than the hard roller, and is a curl correction device for correcting the curl of a sheet in the nip portion, and is characterized by having an inter-axis distance changing means that changes the inter-axis distance between the rotating shaft portion of the hard roller and the rotating shaft portion of the soft roller according to the cumulative number of sheets passing through the nip portion. [Effects of the Invention]

[0011] According to the present invention, even when the cumulative number of sheets passing through the nip section increases, it is possible to provide an appropriate amount of curl correction to the sheets, while suppressing deterioration of transportability and loading performance. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. [Figure 2] This is a partially enlarged schematic diagram of a curl straightening device according to an embodiment of the present invention. [Figure 3] A schematic diagram of a curl straightening device according to an embodiment of the present invention. [Figure 4] This is a block diagram showing the configuration of an image reading device according to an embodiment of the present invention. [Figure 5] This is a flowchart of the image forming process with curl adjustment performed by an image reading device according to an embodiment of the present invention. [Figure 6] This figure shows the position where the first decurler cam of the curl straightening device according to an embodiment of the present invention contacts the first roller holding plate. [Modes for carrying out the invention]

[0013] The embodiments will be described in detail below with reference to the drawings.

[0014] <Configuration of an image forming apparatus> The configuration of the image forming apparatus 1 according to an embodiment of the present invention will be described in detail with reference to Figures 1 and 4.

[0015] Image forming apparatus 1, as exemplified here, is a color image forming apparatus using an electrophotographic method such as a printer. Image forming apparatus 1 includes an image forming unit 10, a secondary transfer unit 30, an intermediate transfer belt 31, a drive roller 33, a tension roller 34, primary transfer devices 35Y, 35M, 35C, 35K, and an air adsorption transport unit 42. Image forming apparatus 1 also includes a fixing unit 50, a sheet storage unit 61, a paper feeding unit 61a, a sheet storage unit 62, a paper feeding unit 62a, a sheet storage unit 63, a paper feeding unit 63a, a manual feed unit 64, a paper feeding unit 64a, and a paper discharge roller 77.

[0016] Furthermore, the image forming apparatus 1 includes a reversing roller 79, a paper discharge unit 80, a switching unit 81, a straight transport unit 82, a reversing double-sided transport unit 83, a double-sided reversing roller 86, a double-sided transport unit 87, a curl correction device 90, and a pair of registration rollers 110. In addition, the image forming apparatus 1 includes a pair of pre-registration rollers 120, a transport roller 130, a control unit 500, a user interface unit 510, an ambient temperature sensor 550, and an ambient humidity sensor 551.

[0017] The image forming unit 10 forms toner images of each color of yellow (Y), magenta (M), cyan (C), and black (Bk) by performing parallel processing of the image forming processes of each color of yellow (Y), magenta (M), cyan (C), and black (Bk). The image forming unit 10 includes photoreceptors 11Y, 11M, 11C, 11K, charging devices 12Y, 12M, 12C, 12K, exposure devices 13Y, 13M, 13C, 13K, and developing devices 14Y, 14M, 14C, 14K.

[0018] The photoreceptors 11Y, 11M, 11C, 11K rotate in the counterclockwise direction in FIG. 1. The photoreceptors 11Y, 11M, 11C, 11K are uniformly charged by the charging devices 12Y, 12M, 12C, 12K. An electrostatic latent image is formed on the photoreceptors 11Y, 11M, 11C, 11K by the exposure devices 13Y, 13M, 13C, 13K, and a toner image is formed on the photoreceptors 11Y, 11M, 11C, 11K by the developing devices 14Y, 14M, 14C, 14K.

[0019] The charging devices 12Y, 12M, 12C, 12K uniformly charge the surfaces of the photoreceptors 11Y, 11M, 11C, 11K.

[0020] The exposure devices 13Y, 13M, 13C, 13K expose the photoreceptors 11Y, 11M, 11C, 11K charged by the charging devices 12Y, 12M, 12C, 12K based on image information input from an image reading device (not shown) or the like. The exposure devices 13Y, 13M, 13C, 13K form an electrostatic latent image on the photoreceptors 11Y, 11M, 11C, 11K by exposure.

[0021] The developing devices 14Y, 14M, 14C, 14K form a toner image on the photoreceptors 11Y, 11M, 11C, 11K by toner-developing the electrostatic latent image formed on the photoreceptors 11Y, 11M, 11C, 11K by the exposure devices 13Y, 13M, 13C, 13K.

[0022] The secondary transfer unit 30, as a transfer means, includes a secondary transfer inner roller 32 and a secondary transfer outer roller 41 that face each other via an intermediate transfer belt 31, and the secondary transfer inner roller 32 and the secondary transfer outer roller 41 form a toner image transfer nip. The secondary transfer unit 30 transfers the toner image that was primarily transferred to the intermediate transfer belt 31 to the sheet P, which is being transported by the registration roller pair 110, by applying a predetermined pressure and electrostatic bias at the toner image transfer nip. The secondary transfer unit 30 then transports the sheet P with the transferred toner image to the air adsorption transport unit 42.

[0023] The intermediate transfer belt 31 is stretched by the secondary transfer rollers 32, drive rollers 33, and tension rollers 34, etc., and is driven to transport in the direction of arrow B in Figure 1. A full-color toner image is formed on the intermediate transfer belt 31 by primary transfer devices 35Y, 35M, 35C, and 35K, which sequentially transfer toner images from the upstream color at the appropriate timing. The intermediate transfer belt 31 then transports the formed full-color toner image to the secondary transfer section 30.

[0024] The drive roller 33, along with the secondary transfer roller 32 and tension roller 34, stretches the intermediate transfer belt 31.

[0025] The tension roller 34, along with the secondary transfer roller 32 and the drive roller 33, stretches the intermediate transfer belt 31.

[0026] The primary transfer devices 35Y, 35M, 35C, and 35K, by applying a predetermined pressure and electrostatic bias, transfer the toner image formed on the photoreceptor 11Y, 11M, 11C, and 11K by the developing devices 14Y, 14M, 14C, and 14K onto the intermediate transfer belt 31.

[0027] The air adsorption transport unit 42 transports the sheet P, which is transported by the secondary transfer unit 30, to the fixing unit 50.

[0028] The fixing unit 50, acting as a fixing means, applies pressure to the sheet P being transported by the air adsorption transport unit 42 and heats it, thereby melting and fixing the toner image to the sheet P. The fixing unit 50 then transports the sheet P, on which the toner image has been melted and fixed, to the straight transport unit 82 or the inverted double-sided transport unit 83.

[0029] Seats P are stored in seat storage compartment 61. Seats P of a different size from those stored in seat storage compartments 62 and 63 are stored in seat storage compartment 61, for example.

[0030] The paper feeding unit 61a feeds the sheets P stored in the sheet storage compartment 61 to the transport rollers 130.

[0031] The seat storage compartment 62 stores seats P. For example, the seat storage compartment 62 stores seats P of a different size than those stored in the seat storage compartments 61 and 63.

[0032] The paper feeding unit 62a feeds the sheets P stored in the sheet storage compartment 62 to the transport rollers 130.

[0033] The seat storage compartment 63 stores seats P. For example, the seat storage compartment 63 stores seats P of a different size than those stored in the seat storage compartments 61 and 62.

[0034] The paper feeding unit 63a feeds the sheets P stored in the sheet storage compartment 63 to the transport rollers 130.

[0035] Sheet P is loaded onto the manual feed unit 64.

[0036] The paper feeding unit 64a feeds the sheets P loaded in the manual feed unit 64 to the registration roller pair 110.

[0037] The paper discharge roller 77 transports the sheet P, which is conveyed by the straight transport unit 82, to the curl correction device 90.

[0038] In the case of face-down feeding, the reversing roller 79 temporarily stops transporting the sheet P when the rear end of the sheet P being transported from the fixing unit 50 to the reversing double-sided transport unit 83 remains upstream of the transport direction of the sheet P (hereinafter simply referred to as "transport direction") by a predetermined distance. After temporarily stopping transport, the reversing roller 79 rotates in the reverse direction to transport the sheet P to the paper discharge roller 77.

[0039] The paper discharge unit 80 discharges the sheets P, which are transported by the curl correction device 90, to the outside of the image forming apparatus 1. If an optional unit (not shown) is connected to the downstream side of the paper discharge unit 80 in the transport direction, the paper discharge unit 80 transports the sheets P, which are transported by the curl correction device 90, to the connected optional unit. Here, the optional unit is a unit that is detachable from the image forming apparatus 1 and is a unit that performs processing on the sheets P, such as stacking, stapling, or binding.

[0040] The switching unit 81 switches the sheet P being transported by the fixing unit 50 to the inverted double-sided transport unit 83 when the paper is fed face down or when an image is formed on only one side in double-sided paper feeding. The switching unit 81 switches the sheet P being transported by the fixing unit 50 to the straight transport unit 82 when the paper is fed face up or when an image is formed on both sides in double-sided paper feeding.

[0041] The straight transport unit 82 transports the sheet P, which is transported by the fixing unit 50, to the paper discharge roller 77.

[0042] The reversing double-sided transport unit 83 transports the sheet P, which is being transported by the fixing unit 50, to the reversing roller 79.

[0043] The double-sided reversing roller 86 temporarily stops conveying the sheet P, which is being conveyed by the reversing double-sided conveying unit 83, when the rear end in the conveying direction remains a predetermined distance upstream of the double-sided reversing roller 86. After temporarily stopping conveying, the double-sided reversing roller 86 reverses direction to convey the sheet P to the double-sided conveying unit 87.

[0044] The double-sided conveying unit 87 conveys the sheet P, which is being conveyed by the double-sided reversing roller 86, to the conveying roller 130.

[0045] The curl correction device 90 corrects the curl (bending) of the sheet P being transported by the paper discharge roller 77. The curl correction device 90 then transports the straightened sheet P to the paper discharge section 80. Details of the configuration of the curl correction device 90 will be described later.

[0046] The registration roller pair 110 transports the sheet P, either carried by the pre-registration roller pair 120 or fed by the paper feed unit 64a, to the secondary transfer unit 30 in accordance with the timing at which the toner image on the intermediate transfer belt 31 is transferred to the sheet P.

[0047] The pre-registration roller pair 120 corrects the skewness of the sheet P by causing it to loop, by abutting the leading edge of the sheet P being conveyed by the transport roller 130 against the nip portion of the registration roller pair 110 that is holding the sheet P in place.

[0048] The transport roller 130 transports the sheet P, which is fed or transported by the paper feeding section 61a, paper feeding section 62a, paper feeding section 63a or the double-sided transport section 87, to the pre-registration roller pair 120.

[0049] The control unit 500 controls the overall operation of the image forming apparatus 1 based on electrical signals input from the user interface unit 510. The control unit 500 includes a CPU 501, a ROM 502, a RAM 503, and a storage unit 506.

[0050] The CPU 501 controls the operation of each component of the image forming apparatus 1 using the RAM 503, based on the data and information stored in the ROM 502, by executing a program stored in the memory unit 506. The CPU 501 controls the operation of the image forming unit 10 to perform image forming processing and also controls the operation of the curl correction device 90 by executing the curl adjustment image forming process described later based on electrical signals input from the user interface unit 510. The CPU 501 includes an interface control unit 511, a decurler control unit 512, and a table calculation unit 513.

[0051] The interface control unit 511 controls the operation of the user interface unit 510 by executing a program stored in the storage unit 506. The interface control unit 511 obtains information about the type of sheet P from the electrical signals input from the user interface unit 510. The interface control unit 511 sets a job based on the electrical signals input from the user interface unit 510. The interface control unit 511 obtains the additional adjustment value A, described later, from the electrical signals input from the user interface unit 510, and stores the obtained additional adjustment value A in the user adjustment value storage unit 507 of the storage unit 506.

[0052] The decurler control unit 512 controls the operation of the curl straightening device 90 by executing a program stored in the memory unit 506.

[0053] The table calculation unit 513 executes a program stored in the storage unit 506, thereby performing predetermined processing based on various tables stored in the table storage unit 508 of the storage unit 506.

[0054] ROM502 has predetermined data and information stored in it beforehand.

[0055] The RAM 503 stores predetermined data and information by the CPU 501.

[0056] The storage unit 506 is a non-volatile memory such as a hard disk or EEPROM. The storage unit 506 stores programs for controlling the operation of the image forming unit 10, the curl correction device 90, and the user interface unit 510. The storage unit 506 includes a user adjustment value storage unit 507, a table storage unit 508, and a counting unit 509.

[0057] The user adjustment value storage unit 507 stores the additional adjustment value A.

[0058] The table storage unit 508 stores various tables, which will be described later.

[0059] The counting unit 509 counts the total number of sheets that pass through the curling device 90, and updates and stores the count value of the counted total number of sheets.

[0060] The user interface unit 510 is a touch panel or the like that operates under the control of the interface control unit 511. The user interface unit 510 receives operations from the user and outputs an electrical signal corresponding to the received operation to the control unit 500.

[0061] The ambient temperature sensor 550 detects the ambient temperature inside the image forming apparatus 1 and outputs an electrical signal corresponding to the detected ambient temperature to the control unit 500.

[0062] The environmental humidity sensor 551 detects the environmental humidity inside the image forming apparatus 1 and outputs an electrical signal corresponding to the detected environmental humidity to the control unit 500.

[0063] In this embodiment, the curl correction device 90 is provided on the downstream side of the paper discharge roller 77 in the transport direction. However, the curl correction device 90 may be provided at a location other than the downstream side of the paper discharge roller 77 in the transport direction. For example, the curl correction device 90 may be provided in the double-sided transport unit 87, in the optional unit, or in the paper feeding unit.

[0064] <Structure of a curling orthodontic appliance> The configuration of the curl straightening device 90 according to an embodiment of the present invention will be described in detail with reference to Figures 2 and 3.

[0065] The curl straightening device 90 has a first curl straightening section 91 and a second curl straightening section 92.

[0066] The first curl straightening unit 91 straightens the sheet P, which is curled upward in a convex shape as shown in Figure 2 and transported by the paper discharge roller 77, so that it becomes flat, and then transports the flattened sheet P to the second curl straightening unit 92.

[0067] The first curl straightening unit 91 comprises a first hard roller 93, a first soft roller 94, a first backup roller 901, and a first roller holding plate 903. The first curl straightening unit 91 also comprises a first decal cam 905, a first decal cam eccentric shaft 907, a first decal cam HP sensor 909, and a first decal cam adjustment motor M1. The first roller holding plate 903 and the first decal cam 905 constitute a means for changing the distance between axes.

[0068] The first hard roller 93 is a metal roller, and it rotates when rotational driving force from a motor (not shown) is transmitted via a gear train. The first hard roller 93 is rotatably supported at both ends of its rotating shaft portion 93a in the axial direction (the direction perpendicular to the plane of the paper in Figure 2) by bearings provided on a frame (not shown) of the image forming apparatus 1. The first hard roller 93 forms a nip portion N1 by pressing against the first soft roller 94.

[0069] The first soft roller 94 is made of a material that is easily elastically deformable, such as a sponge, and has a lower hardness than the first hard roller 93. The first soft roller 94 is rotatably supported at both ends of its rotating shaft portion 94a in the axial direction (the direction perpendicular to the plane of the paper in Figure 2) by bearings provided on a frame (not shown) of the image forming apparatus 1. The first soft roller 94 rotates driven by the frictional force with the circumferential surface of the first hard roller 93. The first soft roller 94 forms a nip portion N1 by pressing against the first hard roller 93.

[0070] The first backup roller 901 is cylindrical in shape and is positioned in the axial center of the first hard roller 93, opposite the nip portion N1 of the first hard roller 93. The first backup roller 901 contacts the axial center of the first hard roller 93 and rotates integrally with the first hard roller 93, while also preventing the first hard roller 93 from bending and deforming due to the pressing force from the first soft roller 94.

[0071] The first roller retaining plate 903 is pivotably mounted on a frame (not shown) of the curl straightening device 90. The first soft roller 94 is rotatably mounted on one end of the first roller retaining plate 903 in the longitudinal direction intersecting the direction of oscillation. The first roller retaining plate 903 is biased by a biasing member (not shown) in the direction of contact with the first de-curling cam 905. The first roller retaining plate 903 pivots about its pivot center 903a when its other longitudinal end is pressed by the first de-curling cam 905. By pivoting, the first roller retaining plate 903 moves the first soft roller 94 such that the distance H1 between the rotational shaft portion 93a of the first hard roller 93 and the rotational shaft portion 94a of the first soft roller 94 changes.

[0072] The first decal cam 905 is in contact with the first roller holding plate 903. The first decal cam 905 rotates around the first decal cam eccentric shaft 907 when driven by the first decal cam adjustment motor M1. The first decal cam 905 is provided with a flag (not shown) that indicates the home position (HP). The flag returns to its original position when the first decal cam 905 completes one rotation.

[0073] The first dekarra cam eccentric axis 907 is the rotation center of the first dekarra cam 905.

[0074] The first decal cam HP sensor 909 is located near the first decal cam 905 and detects the home position of the first decal cam 905 in the rotational direction by detecting a flag provided on the first decal cam 905. The first decal cam HP sensor 909 outputs an electrical signal to the control unit 500 according to the home position detection result.

[0075] The first decal cam adjustment motor M1 is driven by power supplied from a power source (not shown) and rotates the first decal cam 905 under the control of the decal control unit 512 of the CPU 501.

[0076] The second curl straightening unit 92 has a configuration that is the inverse of the first curl straightening unit 91, and straightens the curl of the sheet P in the opposite direction to the direction in which the first curl straightening unit 91 straightens the curl of the sheet P. The second curl straightening unit 92 straightens the sheet P, which is curled downward in a convex shape as shown in Figure 2 and transported by the first curl straightening unit 91, so that it becomes flat, and transports the straightened sheet P to the paper discharge unit 80.

[0077] The second curl straightening section 92 includes a second hard roller 95, a second soft roller 96, a second backup roller 902, and a second roller holding plate 904. The second curl straightening section 92 also includes a second decal cam 906, a second decal cam eccentric shaft 908, a second decal cam HP sensor 910, and a second decal cam adjustment motor M2. The second roller holding plate 904 and the second decal cam 906 constitute a means for changing the distance between axes.

[0078] The second hard roller 95 is a metal roller, and both are rotated by rotational driving force transmitted from a motor (not shown) via a gear train. The second hard roller 95 is rotatably supported at both ends of the axial direction of the rotating shaft portion 95a (the direction perpendicular to the plane of the paper in Figure 2) by bearings provided on a frame (not shown) of the image forming apparatus 1. The second hard roller 95 forms a nip portion N2 by pressing against the second soft roller 96.

[0079] The second soft roller 96 is made of a material that is easily elastically deformable, such as a sponge, and has a lower hardness than the second hard roller 95. The second soft roller 96 rotates in a driven manner relative to the second hard roller 95 due to the frictional force on the circumferential surface of the second hard roller 95. The second soft roller 96 forms a nip portion N2 by pressing against the second hard roller 95.

[0080] The second backup roller 902 is cylindrical in shape and is positioned in the axial center of the second hard roller 95 on the opposite side of the nip portion N2 formed between the second hard roller 95 and the second soft roller 96. The second backup roller 902 contacts the axial center of the second hard roller 95 and rotates integrally with the second hard roller 95, while also preventing the second hard roller 95 from bending and deforming due to the pressing force from the second soft roller 96.

[0081] The second roller retaining plate 904 is pivotably mounted on a frame (not shown) of the curl straightening device 90. The second soft roller 96 is rotatably mounted on one end of the second roller retaining plate 904 in the longitudinal direction intersecting the direction of oscillation. The second roller retaining plate 904 is biased by a biasing member (not shown) in a direction toward contact with the second de-curling cam 906. The second roller retaining plate 904 pivots about its pivot center 904a when its other longitudinal end is pressed by the second de-curling cam 906. By pivoting, the second roller retaining plate 904 moves the second soft roller 96 such that the distance H2 between the rotational shaft portion 95a of the second hard roller 95 and the rotational shaft portion 96a of the second soft roller 96 changes.

[0082] The second decal cam 906 is in contact with the second roller holding plate 904. The second decal cam 906 rotates around the second decal cam eccentric shaft 908 when driven by the second decal cam adjustment motor M2. The second decal cam 906 is provided with a flag (not shown) that indicates the home position (HP). The flag returns to its original position when the second decal cam 906 completes one rotation.

[0083] The second dekarra cam eccentric axis 908 is the rotation center of the second dekarra cam 906.

[0084] The second decal cam HP sensor 910 is located near the second decal cam 906 and detects the home position of the second decal cam 906 in the rotational direction by detecting a flag provided on the second decal cam 906. The second decal cam HP sensor 910 outputs an electrical signal to the control unit 500 according to the home position detection result.

[0085] The second decal cam adjustment motor M2 is driven by power supplied from a power source (not shown) and rotates the second decal cam 906 under the control of the decal control unit 512 of the CPU 501.

[0086] In this embodiment, a first curl-correcting section 91 and a second curl-correcting section 92 are provided, but the invention is not limited to this, and either the first curl-correcting section 91 or the second curl-correcting section 92 may be provided alone.

[0087] <Operation of the curling brace> The operation of the curl straightening device 90 according to an embodiment of the present invention will be described in detail with reference to Figures 2 and 3.

[0088] The first curl straightening unit 91 straightens the curl of the sheet P while conveying it by clamping it between the first hard roller 93 and the first soft roller 94 at the nip section N1. Specifically, the first curl straightening unit 91 conveys the sheet P at the nip section N1 formed by making the first hard roller 93 bite into the first soft roller 94 and allowing it to penetrate by a certain amount. At this time, the first curl straightening unit 91 straightens the curl of the sheet P by applying a force to the sheet P that stretches the surface toward the first soft roller 94, causing the sheet P to bend toward the first hard roller 93 while being conveyed.

[0089] Similarly, the second curl correction section 92 also corrects the curl of the sheet P while conveying it by clamping it between the second hard roller 95 and the second soft roller 96 in the nip section N2. Specifically, the second curl correction section 92 conveys the sheet P in the nip section N2 formed by embedding the second hard roller 95 into the second soft roller 96 by a certain amount. At this time, the second curl correction section 92 corrects the curl of the sheet P by applying a force to the sheet P that stretches the surface toward the second soft roller 96, causing the sheet P to bend toward the second hard roller 95 while being conveyed.

[0090] The first roller retaining plate 903 swings around the pivot center 903a as the first decara cam 905 rotates. The first soft roller 94 moves together with the first roller retaining plate 903 as the first roller retaining plate 903 swings, moving in the thickness direction of the sheet P. This allows the distance H1 between the rotating shaft portion 93a of the first hard roller 93 and the rotating shaft portion 94a of the first soft roller 94, i.e., the amount of roller penetration r1 of the first hard roller 93 relative to the first soft roller 94, to be changed and adjusted.

[0091] Thus, the first hard roller 93 can change the roller penetration amount r1 by the oscillation of the first soft roller 94 together with the first roller holding plate 903. Therefore, the first curl straightening section 91 can change its curl straightening ability for the sheet P, and can straighten any shape of curled sheet P into a flat shape.

[0092] Furthermore, the second roller holding plate 904 swings around the pivot center 904a as the second decara cam 906 rotates. The second soft roller 96 moves together with the second roller holding plate 904 as the second roller holding plate 904 swings, moving in the thickness direction of the sheet P. This allows the distance H2 between the rotating shaft portion 95a of the second hard roller 95 and the rotating shaft portion 96a of the second soft roller 96, i.e., the amount of roller penetration r2 of the second hard roller 95 relative to the second soft roller 96, to be changed and adjusted.

[0093] Thus, the second hard roller 95 can change the roller penetration amount r2 independently of the first hard roller 93 by the oscillation of the second soft roller 96 together with the second roller holding plate 904. Therefore, the second curl straightening section 92 can change its curl straightening ability for the sheet P, and can straighten any shape of curled sheet P into a flat shape.

[0094] <Image formation processing with curl adjustment> The image forming process with curl adjustment performed by the image forming apparatus 1 according to an embodiment of the present invention will be described in detail with reference to Figures 1 to 6.

[0095] In Figure 6, Figure 6(a) shows the position where the first decara cam 905 contacts the first roller retaining plate 903. Figure 6(b) shows the position where the first decara cam 905 contacts the first roller retaining plate 903 when the first decara cam 905 is rotated a predetermined amount counterclockwise from the state shown in Figure 6(a). The dashed line in Figure 6(b) indicates the position where the first decara cam 905 contacts the first roller retaining plate 903 in Figure 6(a).

[0096] Here, the table storage unit 508 stores various tables used in the image forming process with curl adjustment. Specifically, the table storage unit 508 stores a decurler table for each type of sheet P, which associates the density of the image formed on the sheet P with information on whether the sheet P is fed on one side or both sides, the ambient temperature, the ambient humidity, the roller penetration amount r1, and the roller penetration amount r2.

[0097] Furthermore, the table storage unit 508 stores a first rotation amount calculation table that associates the roller penetration amount r1 with the rotation amount of the first decalar cam 905. In addition, the table storage unit 508 stores a second rotation amount calculation table that associates the roller penetration amount r2 with the rotation amount of the second decalar cam 906.

[0098] Roller penetration amount r1 is the amount of penetration of the first hard roller 93 into the first soft roller 94. Roller penetration amount r2 is the amount of penetration of the second hard roller 95 into the second soft roller 96. Thus, the distance H1 between the rotating shaft portion 93a of the first hard roller 93 and the rotating shaft portion 94a of the first soft roller 94 changes in millimeters according to the change in roller penetration amount r1. Also, the distance H2 between the rotating shaft portion 95a of the second hard roller 95 and the rotating shaft portion 96a of the second soft roller 96 changes in millimeters according to the change in roller penetration amount r2.

[0099] The image forming process with curl adjustment shown in Figure 5 is initiated when the user starts operating the user interface unit 510.

[0100] First, the interface control unit 511 of the CPU 501 acquires information about the type of sheet P to be printed, as set by the user, from the electrical signals input from the user interface unit 510 (S10). For example, the interface control unit 511 acquires information about the type of sheet P in broad categories such as plain paper, cardboard, or glossy paper, or it acquires information about the type of sheet P for each brand of sheet P.

[0101] In this case, if an additional adjustment value A is set by the user in the electrical signal input from the user interface unit 510, the interface control unit 511 stores the set additional adjustment value A in the user adjustment value storage unit 507 of the storage unit 506. Here, the additional adjustment value A is a value used by the user to adjust the roller penetration amount r1 and the roller penetration amount r2, respectively.

[0102] Next, the interface control unit 511 sets up a job based on the electrical signals input from the user interface unit 510 (S11). Setting up a job means saving the settings for the data to be printed, whether to print on one side or two sides, whether to staple or not, whether to perform binding or not, or the format of the output as a job in RAM 503.

[0103] Next, the CPU 501 acquires a detected value of the ambient temperature inside the image forming apparatus 1 based on the electrical signal input from the ambient temperature sensor 550. The CPU 501 also acquires a detected value of the ambient humidity inside the image forming apparatus 1 based on the electrical signal input from the ambient humidity sensor 551 (S12).

[0104] Next, the table calculation unit 513 of the CPU 501 determines the roller penetration amounts r1 and r2 based on the sheet type information, the decara table stored in the table storage unit 508, the image density, and the detected values ​​of ambient temperature and ambient humidity (S13). At this time, the sheet type information obtained in step S10 is used. The image density is the density of the image formed on the sheet S, and is calculated from the print data set by the job in step S11. The detected values ​​of ambient temperature and ambient humidity obtained in step S12 are used.

[0105] Specifically, the table calculation unit 513 retrieves a decara table from the decara tables stored in the table storage unit 508 that corresponds to the type of sheet P that has been acquired. Then, the table calculation unit 513 determines the roller penetration amounts r1 and r2, which are associated with the image density calculated from the data to be printed and the detected values ​​of the acquired ambient temperature and ambient humidity, using the acquired decara table.

[0106] Next, the table calculation unit 513 calculates the count value stored in the count unit 509 of the storage unit 506 as the additional adjustment value B (S14). The additional adjustment value B is a value that indicates the amount of roller wear due to the durability of the first soft roller 94 and the second soft roller 96.

[0107] Next, the interface control unit 511 determines whether or not an additional adjustment value A has been set by the user in the electrical signal input from the user interface unit 510 (S15).

[0108] If additional adjustment value A is set (step S15: Yes), the table calculation unit 513 calculates the roller penetration amount r1 based on the calculated roller penetration amount r1, the additional adjustment value A stored in the user adjustment value storage unit 507, and the calculated additional adjustment value B. The table calculation unit 513 also calculates the roller penetration amount r2 based on the calculated roller penetration amount r2, the additional adjustment value A stored in the user adjustment value storage unit 507, and the calculated additional adjustment value B (S16).

[0109] Specifically, the table calculation unit 513 calculates a new roller penetration amount r1 by adding the roller penetration amount r1 calculated in step S13, the set additional adjustment value A, and the calculated additional adjustment value B. The table calculation unit 513 also calculates a new roller penetration amount r2 by adding the roller penetration amount r2 calculated in step S13, the set additional adjustment value A, and the calculated additional adjustment value B. In this way, the roller penetration amounts r1 and r2 can be adjusted by the additional adjustment value A input by the user through the user interface unit 510.

[0110] The table calculation unit 513 added the roller penetration amount r1, additional adjustment value A, and additional adjustment value B, but it is not limited to this method. It may also obtain a new roller penetration amount r1 by multiplying the roller penetration amount r1 by additional adjustment value A and additional adjustment value B, for example. Similarly, the table calculation unit 513 added the roller penetration amount r2, additional adjustment value A, and additional adjustment value B, but it is not limited to this method. It may also obtain a new roller penetration amount r2 by multiplying the roller penetration amount r2 by additional adjustment value A and additional adjustment value B, for example.

[0111] On the other hand, if no additional adjustment value A is set (step S15: No), the table calculation unit 513 calculates the roller penetration amount r1 based on the calculated roller penetration amount r1 and the calculated additional adjustment value B. The table calculation unit 513 also calculates the roller penetration amount r2 based on the calculated roller penetration amount r2 and the calculated additional adjustment value B (S17).

[0112] Specifically, the table calculation unit 513 calculates a new roller penetration amount r1 by adding the roller penetration amount r1 calculated in step S13 and the calculated additional adjustment value B. Furthermore, the table calculation unit 513 calculates a new roller penetration amount r2 by adding the roller penetration amount r2 calculated in step S13 and the calculated additional adjustment value B.

[0113] The table calculation unit 513 added the roller penetration amount r1 and the additional adjustment value B, but it is not limited to this; it may also obtain a new roller penetration amount r1 by multiplying the roller penetration amount r1 by the additional adjustment value B, etc. Similarly, the table calculation unit 513 added the roller penetration amount r2 and the additional adjustment value B, but it is not limited to this; it may also obtain a new roller penetration amount r2 by multiplying the roller penetration amount r2 by the additional adjustment value B, etc.

[0114] Furthermore, the table calculation unit 513 converts the roller penetration amount r1 obtained in the processing of step S16 or step S17 into the rotation amount of the first decara cam 905. Also, the table calculation unit 513 converts the roller penetration amount r2 obtained in the processing of step S16 or step S17 into the rotation amount of the second decara cam 906.

[0115] Specifically, the table calculation unit 513 determines the amount of rotation corresponding to the roller penetration amount r1 in the first rotation amount calculation table stored in the table storage unit 508. The table calculation unit 513 also determines the amount of rotation corresponding to the roller penetration amount r2 in the second rotation amount calculation table stored in the table storage unit 508.

[0116] Then, the decal control unit 512 of the CPU 501 drives the first decal cam adjustment motor M1. As a result, the decal control unit 512 rotates the first decal cam 905 by an amount of rotation determined by the table calculation unit 513 from the home position detected based on the electrical signal input from the first decal cam HP sensor 909. The decal control unit 512 also drives the second decal cam adjustment motor M2. As a result, the decal control unit 512 rotates the second decal cam 906 by an amount of rotation determined by the table calculation unit 513 from the home position detected based on the electrical signal input from the second decal cam HP sensor 910.

[0117] Next, the CPU 501 performs printing according to the job set in step S11 (S18). At this time, the CPU 501 causes the counting unit 509 to count the number of sheets P that have been fed through, and also causes the counting value to be accumulated.

[0118] Next, the curl correction device 90 corrects the curl of the sheet P (S19).

[0119] Next, the CPU 501 discharges the sheet P, whose curl has been corrected, from the image forming apparatus 1 and completes the job (S20).

[0120] Next, the CPU 501 updates and stores the count value accumulated in the counting unit 509 as the total number of papers passed (S21), and then terminates the image forming process with curl adjustment.

[0121] In this way, by controlling the roller penetration amounts r1 and r2 using the additional adjustment value B, the necessary curl correction force can be maintained even if the surface of the first soft roller 94 or the second soft roller 96 is worn down due to durability. Furthermore, even if the cumulative number of sheets P passing through the first soft roller 94 and the second soft roller 96 increases, an appropriate amount of curl correction can be applied to the sheets P.

[0122] The position at which the first decarra cam 905 contacts the first roller holding plate 903 to achieve the roller penetration amount r1 determined by the process in step S13 is, for example, a position in one of the phases from Q0 to Q7, as shown in Figure 6(a). Similarly, the position at which the second decarra cam 906 contacts the second roller holding plate 904 to achieve the determined roller penetration amount r2 is, although not shown in the figure, a position in one of the phases similar to that of the first decarra cam 905.

[0123] Furthermore, when the first decara cam 905 rotates after the processing in step S16 or step S17, the position where the first decara cam 905 contacts the first roller holding plate 903 will be, for example, one of the phases Q10 to Q17 in Figure 6(b). The phases Q10 to Q17 are the result of the rotation of the first decara cam 905 causing a shift in the phases Q1 to Q7 shown in Figure 6(a). Also, when the second decara cam 906 rotates after the processing in step S16 or step S17, the position where the second decara cam 906 contacts the second roller holding plate 904 will be one of the phases similar to that of the first decara cam 905, although this is not shown in the figure.

[0124] Furthermore, when curl correction is not performed in either the first curl correction unit 91 or the second curl correction unit 92, the CPU 501 minimizes the roller penetration amount r1 or r2 on the side where curl correction is not performed. This prevents curl correction from being performed when it is not necessary, thus preventing deterioration of transportability or loading performance, and transport defects such as corner bending or jamming of paper in subsequent processes.

[0125] Incidentally, conventionally, regardless of whether curl correction was performed or not, the roller penetration depth was uniformly set to a predetermined value. As a result, the surface of the soft rollers wore down, and the roller penetration depth became "0". In this case, the corners of the sheet P would be bent or jams would form, resulting in conveying problems.

[0126] In this embodiment, the inter-axis distances H1 and H2 are changed according to the cumulative number of sheets P passing through the nip sections N1 and N2. This makes it possible to apply an appropriate amount of curl correction to the sheets P even when the cumulative number of sheets P passing through the nip sections N1 and N2 increases, while suppressing deterioration of transportability and loading performance.

[0127] The present invention is not limited to the embodiments described above, and it goes without saying that various modifications are possible without departing from the spirit of the invention.

[0128] Specifically, in the above embodiment, the roller penetration amounts r1 and r2 were changed based on the cumulative number of sheets P passing through nip sections N1 and N2, as well as the type of sheet, the density of the image formed on the sheet, the ambient temperature, and the ambient humidity. However, the invention is not limited to this, and the roller penetration amounts r1 and r2 may also be changed based on at least one of the following: the type of sheet, the density of the image formed on the sheet, the ambient temperature, and the ambient humidity, in addition to the cumulative number of sheets P passing through nip sections N1 and N2.

[0129] Furthermore, in the above embodiment, the roller penetration amounts r1 and r2 were changed based on the type of sheet, the density of the image formed on the sheet, the ambient temperature, and the ambient humidity, in addition to the cumulative number of sheets P passing through the nip sections N1 and N2. However, the invention is not limited to this, and the roller penetration amounts r1 and r2 may be changed based solely on the cumulative number of sheets P passing through the nip sections N1 and N2. [Explanation of Symbols]

[0130] 1. Image forming apparatus 10 Image forming unit 30 Secondary transfer section 35Y Primary Transfer Apparatus 35M Primary Transfer Device 35C Primary Transfer Apparatus 35K Primary Transfer Apparatus 90 Curl Orthodontic Appliance 91 First Curl Orthodontic Department 92 Second Curl Orthodontic Unit 93 First Hard Roller 93a Rotating shaft 94 First Soft Roller 94a Rotating shaft 95 Second hard roller 95a Rotating shaft 96 Second soft roller 96a Rotating shaft section 500 Control Unit 501 CPU 507 User adjustment value storage unit 508 Table Storage Unit 510 User Interface Section 511 Interface Control Unit 512 Decal Control Unit 513 Table Calculation Unit 550 Ambient Temperature Sensor 551 Environmental Humidity Sensor

Claims

1. A curl correction device comprising a rotatable hard roller and a rotatable soft roller that presses against the hard roller to form a nip portion and has a lower hardness than the hard roller, for correcting the curl of a sheet at the nip portion, The system has an axis distance changing means that changes the axis distance between the rotating shaft of the hard roller and the rotating shaft of the soft roller according to the cumulative number of sheets passing through the nip section. A curl correction device characterized by the following features.

2. The aforementioned hard roller is It consists of a first hard roller and a second hard roller provided downstream of the first hard roller in the sheet conveying direction, The aforementioned soft roller is It consists of a first soft roller that presses against the first hard roller to form the nip portion, and a second soft roller that presses against the second hard roller to form the nip portion, The first hard roller and the first soft roller are, The curl of the sheet is corrected in the opposite direction to the direction in which the curl of the sheet is corrected by the second hard roller and the second soft roller. The curl correction device according to feature 1.

3. The means for changing the distance between axes is, In addition to the aforementioned number of cumulative sheets, the inter-axis distance is changed according to at least one of the following: the type of sheet, the density of the image formed on the sheet, the ambient temperature, and the ambient humidity. A curl straightening device according to claim 1 or 2.

4. A curl straightening device according to claim 1 or claim 2, Image forming means for forming a toner image, A transfer means for transferring a toner image formed by the image forming means onto a sheet, A fixing means for fixing the toner image transferred to the sheet by the transfer means to the sheet by applying pressure and heating, It has, The curl straightening device described above is The curl of the sheet on which the toner image has been fixed by the fixing means is corrected. An image forming apparatus characterized by the following:

Images