JP2015082064A - Sheet conveying device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet conveying device which is capable of suppressing the flapping of sheets.SOLUTION: There is provided a sheet conveying device that conveys sheets, and includes load application means for applying a tensile force in the conveyance direction to the sheets and load control means for variably controlling the load of the load application means, where the load control means controls the load applied to the sheets by the load application means according to information on the sheets input to the load control means.

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet and suppresses undulation or curling of the sheet, and an image forming apparatus including the sheet conveying apparatus.

  Conventionally, an image forming apparatus using an electrophotographic method develops a latent image formed on a photosensitive drum as an image carrier to form a visible image, and uses this visible image (toner image) on a sheet using electrostatic force. To transcribe. Next, the toner image on the sheet is fixed by heat and pressure, whereby an image is recorded and formed on the sheet.

  As a fixing device of such an image forming apparatus, an elastic pressure roller is pressed against a fixing roller having a heat source such as a heater and maintained at a predetermined temperature to form a nip portion. A heat roller fixing method for fixing a toner image on a sheet is employed.

  However, in the heat fixing process of these fixing devices, heat and pressure are applied to the sheet on which the toner image is transferred, so that the sheet passes through the nip portion of the fixing device or the sheet passes through the nip portion of the fixing device. After passing, moisture evaporates from the inside of the sheet. Due to the change in the amount of moisture due to the heat of the sheet and the stress caused by the pressure applied to the sheet, a phenomenon called a curl in which the sheet is curved and a phenomenon called a wave in which the sheet has a wavy shape occur.

  Here, a sheet-like paper that is most commonly used as a sheet is viewed at the fiber level. Paper is composed of short fibers entangled with each other, and moisture is contained inside or between the fibers. Furthermore, since the fiber and water are in an equilibrium state with hydrogen bonds formed, smoothness is maintained.

  However, when heat and pressure are applied to the paper in the fixing process, the fibers are displaced due to the pressure. When heat is applied and moisture evaporates in this state, further hydrogen bonds are formed between the fibers and deform. If this paper is left unattended, it absorbs moisture from the environment, and the hydrogen bonds between the fibers are cut off again to return to the original state. However, there is no moisture between some fibers of the paper, thereby maintaining the deformation of the paper. The deformation pattern includes the above-described curl and undulation, and the curl is generated due to a difference in expansion / contraction between the front and back of the paper, and the undulation is generated due to an expansion / contraction difference between the center and the edge of the paper.

  As described above, one of the causes of the undulation at the end of the sheet is the process in which the sheet passes through the nip portion of the fixing device. For example, in the case of a fixing device having a wide nip such as a belt fixing method, in order to prevent sheet wrinkling in the process of passing a sheet through the nip portion, an end portion from a central portion in the width direction perpendicular to the sheet conveyance direction in the nip Set the side transport speed higher. As a result, when the sheet has a squeezing action, the sheet end portion extends in the transport direction from the vicinity of the center after passing through the nip portion, and undulation is generated at the end portion of the sheet.

  Further, as described above, one of the causes of the undulation at the end of the sheet is after the sheet passes through the nip portion of the fixing device. In the state of being stacked as a sheet bundle, each sheet is in contact with the atmosphere at the end portion, so that moisture enters and exits rapidly. When heat is applied to the sheet during the fixing process and moisture inside the sheet evaporates, the sheet end also extends in the transport direction from the vicinity of the center, resulting in undulations at the end of the sheet. .

  Therefore, techniques for correcting the above-described deformation of the sheet have been proposed. Patent Document 1 discloses a sheet conveying apparatus in which two decurling means constituted by a plurality of roller groups for correcting sheet curling are arranged. Then, the curl of the sheet is corrected by sandwiching and conveying the sheet by a group of rollers constituting the decurling means.

JP 2008-94585 A

  However, in Patent Document 1, it is possible to correct the curl that the sheet is curved among the deformations of the sheet described above, but it is not possible to sufficiently correct the corrugation of the sheet due to the expansion and contraction difference between the center and the end of the sheet. Have difficulty.

  Further, the sheet has different deformation depending on the basis weight, type, image density, environmental humidity, and the like. For this reason, it is difficult to sufficiently improve the deformation of the sheet with different adjustments only by passing the decurling means as described above.

  Therefore, the present invention is a further development of the above-described conventional technique, and an object thereof is to provide a sheet conveying apparatus that can further improve the corrugation of the sheet.

  Another object of the present invention is to provide a sheet conveying apparatus that can further improve the waviness of the sheet even when the basis weight, type, image density, environmental humidity, etc. of the sheet are different. It is to be.

  In order to achieve the above object, according to the present invention, in a sheet conveying apparatus for conveying a sheet, load means for applying a tension in the conveying direction to the sheet, and load control means for variably controlling the load of the load means, And the load control means controls a load applied to the sheet by the load means in accordance with information on the sheet input to the load control means.

  According to the present invention, since tension in the conveyance direction is given to the sheet, even if there is a difference in expansion and contraction between the center and the end of the sheet, this difference can be reduced and the waviness of the sheet can be improved.

  Furthermore, even when the basis weight, type, image density, environmental humidity, and other conditions of the sheet are different, it is possible to apply tension to the sheet according to the conditions, and more effectively improve the corrugation of the sheet. be able to.

Sectional drawing which shows the sheet corrugation correction apparatus of Example 1. FIG. 1 is a cross-sectional view illustrating an electrophotographic printer of Example 1. FIG. Sectional drawing which shows the sheet | seat humidification apparatus of Example 1. FIG. 1 is an external view illustrating a sheet humidifying device according to Embodiment 1. FIG. FIG. 3 is a block diagram and a flowchart illustrating control of the electrophotographic printer, the sheet humidifier, and the sheet pulling and conveying apparatus according to the first exemplary embodiment. 6 is a flowchart illustrating control of the sheet pulling and conveying apparatus according to the first exemplary embodiment. (A) and (b) are sectional views showing a sheet pulling and conveying apparatus of Example 1. FIG. 3 is a perspective view illustrating a sheet pulling and conveying apparatus according to the first exemplary embodiment. FIG. 3 is a top view illustrating the sheet pulling and conveying apparatus according to the first exemplary embodiment. FIG. 3 is an external view showing the shape of a sheet P. The figure showing the relationship between the exciting current of the load means of Example 1, and brake torque. (A) (b) (c) is a table | surface figure which shows the state of the sheet | seat by experiment of Example 1. FIG. (A) (b) (c) is a table | surface figure which shows the state of the sheet | seat by experiment of Example 1. FIG. (A) and (b) are table | surface figures which show the state of the sheet | seat by experiment of Example 1. FIG. (A) and (b) are table | surface figures which show the state of the sheet | seat by experiment of Example 1. FIG. (A) and (b) are diagrams showing set values under various conditions of the sheet tension force of the first embodiment. FIG. 9 is a top view illustrating a sheet pulling and conveying apparatus according to a second embodiment. 10 is a flowchart illustrating control of the sheet pulling and conveying apparatus according to the second exemplary embodiment. Sectional drawing which shows the sheet corrugation correction apparatus of another Example.

  Hereinafter, exemplary 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 changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless specifically stated otherwise, the scope of the present invention is not intended to be limited thereto.

[Example 1]
The image forming apparatus according to this embodiment will be described with reference to FIGS.

<Image forming apparatus>
FIG. 2 is a cross-sectional view schematically showing a color electrophotographic printer 500 which is an example of an image forming apparatus, and is a cross-sectional view along the sheet conveyance direction. Here, the color electrophotographic printer is simply referred to as “printer”.

  The sheet is a sheet on which a toner image is formed. Specific examples of the sheet include plain paper, a resin sheet that is a substitute for plain paper, cardboard, and overhead projector.

  The printer shown in FIG. 2 includes an image forming unit 510 for each color of Y (yellow), M (magenta), C (cyan), and Bk (black). Each color image forming unit 510 forms a toner image of each color on a sheet. Each color image forming unit 510 includes the following process means. An electrophotographic photosensitive member (photosensitive drum) 511 as an image carrier that carries an electrostatic latent image on the surface corresponding to each of Y, M, C, and K colors, a charging roller 512, a laser scanner 513, and a developing device 514. The photosensitive drum 511 is charged in advance by the charging roller 512. Thereafter, the photosensitive drum 511 is exposed by a laser scanner 513 to form a latent image. The latent image is visualized as a toner image developed by the developing device 514.

  The toner images formed and carried on the surface of the photosensitive drum 511 are sequentially transferred onto the intermediate transfer belt 531 by the primary transfer roller 515 in a primary transfer portion between the photosensitive drum 511 and the primary transfer roller 515. Is done.

  On the other hand, the sheets P are fed one by one from the feeding cassette 520 and fed to the registration roller pair 523. The registration roller pair 523 temporarily receives the sheet P and corrects the skew when the sheet is skewed. The registration roller pair 523 sends the sheet to the secondary transfer portion between the intermediate transfer belt 531 and the secondary transfer roller 535 in synchronization with the toner image on the intermediate transfer belt 531. The color toner image on the intermediate transfer belt is secondarily transferred collectively onto the sheet P by a secondary transfer roller 535 which is a transfer body.

  Thereafter, the sheet on which the image (toner image) is formed by the image forming unit as described above is conveyed to the fixing device 100. The fixing device (fixing unit) 100 fixes the toner image on the sheet by sandwiching the sheet at the fixing nip and applying heat and pressure to the unfixed toner image. The sheet that has passed through the fixing device 100 is sent to the sheet corrugation straightening device 201 by the main body discharge roller 540, and after the corrugation correction by the sheet corrugation straightening device 201, the sheet is discharged onto the discharge tray 565.

<Fixing device>
Here, the fixing device will be described. As shown in FIG. 2, the fixing device 100 includes a fixing roller 110 that is a heating rotator and a pressure roller 111 that is a pressure rotator. The fixing roller 110 applies heat generated by an internal halogen heater (not shown) to the toner T on the sheet P and conveys the sheet P together with the pressure roller 111. The fixing roller 110 incorporates a halogen heater in a metallic core made of an aluminum cylindrical tube having an outer diameter of 56 mm and an inner diameter of 50 mm, for example. For example, an elastic layer made of silicon rubber having a thickness of 2 mm and a hardness (Asuka C) of 45 ° is coated on the surface of the metal core, and a PFA or PTFE heat release layer is coated on the surface of the elastic layer.

  The pressure roller 111 conveys the sheet P together with the fixing roller 110. The pressure roller 111 also has a metallic core made of an aluminum cylindrical tube having an outer diameter of 56 mm and an inner diameter of 50 mm, for example. For example, an elastic layer made of silicon rubber having a thickness of 2 mm and a hardness (Asuka C) of 45 ° is coated on the surface of the metal core, and a PFA or PTFE heat release layer is coated on the surface of the elastic layer.

  A fixing nip N shown in FIG. 2 is formed by the fixing roller 110 and the pressure roller 111. In the experiments of the present inventors, the sheet P is set under the conditions that the set temperature of the surface layer of the fixing roller 110 is 180 ° C., the set temperature of the surface layer of the pressure roller 111 is 100 ° C., the environmental temperature is 23 ° C., and the environmental humidity is 50%. Is conveyed at a conveyance speed of about 300 to 500 mm / sec. Then, the sheet P heated and pressed in the fixing nip N receives more heat from the fixing roller 110 having a higher temperature than the pressure roller 111, and the result is that the upper surface side of the sheet P is larger than the lower surface side and the fibers are extended. As a result, downward curling (hereinafter referred to as lower curling) occurs. In addition, the end of the sheet in the width direction perpendicular to the sheet conveyance direction is larger than the central portion, and the fiber is stretched in the conveyance direction. As a result, the length in the sheet conveyance direction differs between the edge and the center. Sheet edge undulation occurs.

<Control unit>
As the information regarding the sheet, the basis weight information of the sheet P in the feeding cassette 520 is input by the user using the operation panel 570, and is stored in the CPU and memory constituting the control unit 500C in the image forming apparatus shown in FIG. Information is sent.

  Here, the basis weight is exemplified in the present embodiment as information on the sheet that can be input from the operation panel, but the present invention is not limited to this. In addition to the basis weight, there are, for example, sheet type information (plain paper, coated paper, embossed paper, thin paper, recycled paper, etc.), size information, and the like. The information regarding the input sheet is sent to the control unit (load control means) 500C as described above.

  Further, the image density information of the toner image on the sheet P on which the image is formed by the image forming unit 510 is sent to the CPU and the memory constituting the control unit (load control means) 500C in the image forming apparatus shown in FIG. .

  A temperature and humidity in the image forming apparatus 500 are detected by an environmental sensor 500D installed on the upper side of the feeding cassette 520 in the image forming apparatus 500, and the temperature and humidity information is a CPU constituting the control unit 500C. Information is sent to memory. The environmental sensor 500D functions as a humidity detection unit that detects environmental humidity.

  Here, the control configuration of the entire apparatus will be described with reference to FIG. FIG. 5 is a block diagram showing a control relationship between the image forming apparatus 500 and the sheet corrugation straightening apparatus 201 as a whole. The control unit 500C of the image forming apparatus 500 and the control unit 201C of the sheet corrugation correction apparatus 201 have a CPU and a memory, and further have a calculation unit, an I / O port, a communication interface, a drive circuit, etc. (not shown). It is.

  Control by each control unit described above is performed by each CPU executing a predetermined program stored in a memory. Each control unit described above is connected via the communication unit COM and can exchange information. In the figure, the description of blocks not directly related to the description of the present invention is omitted.

<Sheet wavy straightening device>
Next, a sheet waviness correcting device 201 as a sheet conveying device that conveys a sheet that has passed through the fixing unit will be described with reference to FIG. FIG. 1 is a cross-sectional view showing the entire sheet corrugation straightening device 201. The sheet P on which the toner image is fixed by being heated and pressed by the fixing device 100 is sent to the inlet roller pair 207 (in the direction of arrow A in FIG. 1) of the sheet corrugation correction device 201 by the main body discharge roller 540. Further, the conveyance guide 208 turns the conveyance direction vertically downward (in the direction of arrow B in FIG. 1), and then the sheet is sent to a sheet humidifying device 202 as a moisture applying device. Here, the sheet P is humidified by the humidifying roller pairs 220 and 230 and the humidifying roller pairs 221 and 231.

  The sheet P discharged from the sheet humidifying device 202 is continuously sent to the sheet pulling and conveying device (sheet conveying device) 101. After the sheet P is humidified by the sheet humidifying device 202 to a predetermined moisture amount or more, the sheet P passes through the sheet pulling / conveying device 101 and the central portion in the width direction orthogonal to the sheet conveying direction is larger in the conveying direction than the end. pull. Thereby, the difference in the length of the sheet in the conveyance direction of the sheet in the width direction of the sheet is reduced, and the waviness is improved. The sheet P that has passed through the sheet pulling and conveying device 101 is then turned in the conveying direction in the direction of arrow C in FIG. 1 by the conveying guide 209, and is then discharged out of the sheet wave correcting device 201 by the discharge roller pair 210. Loaded on top.

  In FIG. 1, the water storage tank 204 contains a humidifying liquid LQ1 for humidifying the sheet P. The humidifying liquid LQ1 accommodated in the water storage tank 204 is supplied by the pump 206 to the water tank 240 provided in the sheet humidifying device 202 through the water supply pipe 205 at any time in the direction of arrow D in FIG. The humidifying liquid supplied into the water tank 240 is LQ2. The humidifying liquids LQ1, LQ2 are mainly composed of water.

<Sheet humidifier>
Next, the sheet humidifying device 202 in the sheet corrugation correcting device will be described in detail with reference to FIGS. FIG. 3 is a cross-sectional view showing the entire sheet humidifying device 202, and FIG. 4 is an external view of the sheet humidifying device 202.

  The sheet P sent in the direction of the arrow B in FIG. 3 which is the same as the arrow B in FIG. It is humidified by being transferred to. The sheet P is further humidified by transferring the humidifying liquid LQ2 to the surface again in the process of passing through the nip portion of the second humidifying roller pair 221, 231.

  The sheet P that has passed through the nip portion of the second humidifying roller pair 221, 231 then passes through the conveying roller pair 222, 232 and is sent to the sheet pulling and conveying apparatus 101 through the humidifying portion discharge guide 251.

  Each of the humidifying rollers of the first humidifying roller pair 220, 230 and the second humidifying roller pair 221, 231 is a solid rubber mainly composed of NBR, silicon or the like on the shaft core surface made of a metal rigid body such as stainless steel. An elastic roller having a layer formed thereon.

  223, 224, 225, 233, 234, and 235 are used for sequentially supplying the humidifying liquid LQ2 in the water tank 240 to the humidifying rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231, respectively. It is a water supply roller. The water supply rollers 223, 224, 225, 233, 234, and 235 are mainly composed of a material having a hydrophilic surface capable of holding water on a shaft surface made of a metal rigid body such as stainless steel, such as NBR. An elastic roller having a solid rubber layer formed thereon. The solid rubber layer may be made of metal or a hydrophilic resin.

  The water supply roller 223 is in contact with both the humidifying roller 220 and the humidifying roller 221 among the humidifying rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231. Further, the water supply roller 224 is in contact with the water supply roller 223 and the water supply roller 225 is in contact with the water supply roller 224, thereby forming a water supply path from the water tank 240 toward the humidifying roller 220 and the humidifying roller 221.

  The water supply roller 233 is in contact with both the humidifying roller 230 and the humidifying roller 231 among the humidifying rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231. Further, the water supply roller 234 is in contact with the water supply roller 233 and the water supply roller 235 is in contact with the water supply roller 234, thereby forming a water supply path from the water supply tub 240 toward the humidification roller 230 and the humidification roller 231.

  226 and 236 are regulating rollers for regulating the amount of water supplied to the humidifying rollers of the first humidifying roller pair 220 and 230 and the second humidifying roller pair 221 and 231 respectively. The regulating rollers 226 and 236 are rollers in which nickel, chrome, or the like is plated on the shaft core surface made of a metal rigid body such as stainless steel.

  The regulating roller 226 is in contact with the water supply roller 224 and the regulating roller 236 is in contact with the water supply roller 234, respectively, and the amount of humidifying liquid held on the surface of each solid rubber layer is suppressed to an appropriate amount, and the amount of moisture supplied to the sheet P is reduced. regulate. That is, the regulation rollers 226 and 236 are pressed against the solid rubber layers of the water supply rollers 224 and 234, respectively, and deformed to squeeze the humidified liquid held on the surface. As a result, the sheet P is humidified to an optimal amount of water, and the tension effect is promoted by the sheet pulling and conveying apparatus 101 described above.

  The first humidifying roller pair 220, 230, the second humidifying roller pair 221, 231, the water supply rollers 223, 224, 225, 233, 234, 235, the regulating rollers 226, 236, and the conveying roller pairs 222, 232 are As shown in FIG. 3, the sheet P is disposed symmetrically with the sheet P interposed therebetween, and rotates in the direction of each arrow. As a result, moisture is evenly applied to both surfaces of the sheet P to perform humidification.

  Among the roller pairs described above, the humidifying rollers 230 and 231 and the conveying roller 232 disposed on the left side with respect to the sheet P have driving gears 260, 261, and 262 fixed to the ends as shown in FIG. Rotation drive is transmitted from a drive motor (not shown). The other rollers are driven to rotate by driving transmission from the respective surfaces of the humidifying rollers 230 and 231 and the conveying roller 232.

  By providing moisture to the sheet with the above-described humidifying roller pair that humidifies the sheet P, the moisture content is increased to a level necessary to promote expansion and contraction due to a tension load applied to the central portion in the width direction of the sheet P by the sheet pulling and conveying device 101. be able to.

<Sheet tension conveying device>
Next, the sheet pulling and conveying apparatus 101 in the sheet corrugation correcting apparatus will be described with reference to FIGS. 7 is a cross-sectional view illustrating the sheet pulling and conveying apparatus, FIG. 8 is a perspective view illustrating the sheet pulling and conveying apparatus, and FIG. 9 is a top view illustrating the sheet pulling and conveying apparatus.

  The sheet pulling and conveying apparatus 101 includes a first upper roller 104 and a first lower roller 105 that form the first roller pair shown in FIG. 7, and a second roller pair that is downstream in the conveying direction of the first roller pair. The sheet P is nipped and conveyed by the upper roller 106 and the second lower roller 107. The sheet pulling and conveying apparatus 101 applies tension to the sheet P for extending the sheet in the conveying direction while further holding and conveying the sheet. The sheet P is guided between the upper outlet guide 117 and the lower outlet guide 118 and is discharged out of the sheet pulling and conveying apparatus 101.

  As shown in FIG. 8, the first upper roller 104, the first lower roller 105, the second upper roller 106, and the second lower roller 107 have elastic rubbers 104b, 105b, 106b, and 107b such as silicon, NBR, and EPDM. doing. The elastic rubbers 104b, 105b, 106b, and 107b are formed on the surface layers of the roller shafts 104a, 105a, 106a, and 107a using high-rigidity materials such as stainless steel and steel, respectively. Here, the outer diameters φ of the elastic rubbers 104b, 105b, 106b, and 107b are all 20 mm. Further, as shown in FIG. 8, a region of the length L1 of the central portion in the width direction of the sheet so that the elastic rubbers 105b and 107b of the first lower roller 105 and the second lower roller 107 are equal to the sheet passing center Is formed. That is, the outer diameters of the first lower roller 105 and the second lower roller 107 are larger in the central region in the width direction orthogonal to the sheet conveying direction than in the end region. Here, the sheet passing center is a position in the center in the width direction which is a reference when the sheet is conveyed. The length L1 is shorter than the length in the width direction of the sheet P in which undulation shown in FIG. 10 is a problem. Here, L1 = 100 mm is set.

  Further, an upper conveyance guide 114 and a lower conveyance guide 115 which are guide members for guiding the sheet are provided between the nips of the first roller pair and the second roller pair, and the distance between the nips is set to 25 mm.

  In the first upper roller 104 and the second upper roller 106, both end portions of the roller shafts 104a and 106a are supported by the upper plate 119 via bearings (not shown).

  In the first lower roller 105, both end portions of the roller shaft 105a are supported by the first pressure plate 113 via bearings (not shown). The first pressure plate 113 is rotatably supported by the lower plate 120 via a first rotation shaft (not shown), and the bottom surface is urged by the first pressure spring 109. As a result, the first lower roller 105 is pressed against the first upper roller 104 to form a nip.

  In the second lower roller 107, both end portions of the roller shaft 107a are supported by the second pressure plate 112 via bearings (not shown). The second pressure plate 112 is rotatably supported by the lower plate 120 via the second rotation shaft 122, and the bottom surface is urged by the second pressure spring 108. As a result, the second lower roller 107 is pressed against the second upper roller 106 to form a nip.

  A reflected light type sheet sensor 103 that detects the arrival of the sheet P is disposed in the lower entrance guide 121.

  FIG. 9 is a top view illustrating driving of the first upper roller 104 and the second upper roller 106.

  In the figure, CPU is a control means for controlling the operation of an electromagnetic clutch CL as a clutch means (drive control means) and a drive motor M as a drive means.

  As shown in FIG. 9, a driving gear 104G1 is held and fixed to one end of the first upper roller 104. The first upper roller 104 is rotated by receiving a rotational drive through the drive transmission gears 123, 124, 125 and the clutch gear CLG by the motor gear MG of the drive motor M which is a drive source (drive means). The first lower roller 105 pressed by the first upper roller 104 rotates following the rotation of the first upper roller 104.

  A driving gear 106G is held and fixed at one end of the second upper roller 106. The second upper roller 106 is rotated by receiving a rotational drive via the drive transmission gears 126, 127, 128, and 129 by the motor gear MG of the drive motor M that is a drive source (drive means). The second lower roller 107 pressed by the second upper roller 106 rotates following the rotation of the second upper roller 106.

  The clutch gear CLG is fixed to the electromagnetic clutch CL. By energizing the electromagnetic clutch CL, the drive between the clutch gear CLG and the drive transmission gear 124 is transmitted through the clutch shaft 132, and the first upper roller 104 rotates. On the other hand, when the electromagnetic clutch CL is not energized, the drive between the clutch gear CLG and the drive transmission gear 124 is not transmitted, the drive of the drive motor M is not transmitted to the drive gear 104G, and the first upper roller 104 does not rotate.

  A driving gear 104G2 is fixed to the other end of the first upper roller 104. The drive gear 104G2 is connected to a load means 131 such as an electromagnetic powder brake or an electromagnetic hysteresis brake via a drive transmission gear 130.

  The load means 131 applies tension to the sheet in the conveying direction, and can change the brake torque according to the current value to be excited. In the following description, an electromagnetic hysteresis brake (electromagnetic brake) is illustrated as the load means. FIG. 11 shows the relationship between the excitation current and brake torque of the electromagnetic hysteresis brake used in this example. As shown in FIG. 11, the excitation current and the brake torque are in a proportional relationship, and the excitation current can be changed as necessary to change the electromagnetic hysteresis brake to a predetermined brake torque. In this embodiment, when the brake torque is 100%, the tension force applied to the seat is set to 8 kgf. In this embodiment, when the tension force is 8 kgf or more, the load becomes heavy, and the roller and the sheet slip at the nip portion of the second roller pair (106, 107).

  With the above configuration, the sheet P is conveyed while a tension force (tensile force in the sheet conveyance direction) is generated between the first roller pair and the second roller pair.

  FIG. 6 is a flowchart regarding the drive control of the present embodiment, and FIG. 5 is a block diagram regarding the drive control of the present embodiment. FIG. 7 is a front sectional view of the sheet pulling and conveying apparatus 101 for explaining the drive control of this embodiment. FIG. 7A is a front cross-sectional view at time 0 to Xmsec after the sheet sensor is turned on, and FIG. 7B is a front cross-sectional view at time Xmsec after the sheet sensor is turned on.

  When the paper passing job signal is input to the CPU (control means) (S6-1), the basis weight, type, image density, and humidity information as the information related to the sheet are confirmed (S6-2). Then, the exciting current is set so that the necessary brake torque of the electromagnetic hysteresis brake 131 as the load means becomes a brake torque corresponding to a predetermined seat tension force according to the information on the seat (S6-3). Details of the predetermined sheet tension according to the information about the sheet will be described later.

  Thereafter, energization of the drive motor M is turned on (S6-4), and the current of the electromagnetic hysteresis brake 131 is also turned on (S6-5). At the same time, the energization of the electromagnetic clutch CL is turned on to start the paper feeding (S6-6). As a result, the drive of the drive motor M is transmitted to the drive gears 104G1 and 106G via the drive transmission gear, whereby the first upper roller 104 and the second upper roller 106 rotate.

  Thereafter, when the sheet P is guided to the lower entrance guide 121 in the sheet pulling and conveying apparatus 101 and the ON signal of the sheet sensor 103 is confirmed (S6-7), the energization of the electromagnetic clutch CL is turned off after Xmsec (S6-). 8). When energization of the electromagnetic clutch CL is turned off, the drive to the first upper roller 104 is released. The value of the time X is the time from when the sheet sensor 103 is turned on to immediately after the leading edge of the sheet P is sandwiched between the nips of the second roller pair. It is determined by the distance to the nip of the roller pair. Here, since the conveyance speed of the sheet P is 300 mm / s and the distance from the sheet sensor 103 to the nip of the second roller pair is 45 mm, X = 160 msec is set.

  As shown in FIG. 7A, at 0 to Xmsec after the sheet sensor is turned on, the electromagnetic clutch CL is in the ON state, so that the drive is transmitted to the first upper roller 104 and the sheet P is fed to the first upper roller 104. It is conveyed by driving. On the other hand, as shown in FIG. 7B, at the point of X msec after the sheet sensor is turned on, the leading edge of the sheet P is immediately after reaching the nip of the second roller pair, and the sheet P is conveyed by driving the second upper roller 106. Is done. At the same time, the electromagnetic clutch CL is turned off and the drive is not transmitted to the first upper roller 104, so that the first roller pair is rotated by following the sheet conveyed by the second roller pair.

  During this driven rotation, the first upper roller 104 is connected to the load means 131 via the drive gear 104G2 and the drive transmission gear 130, so that the first upper roller 104 that has been released from driving is rotated. Generates a torque load. As a result, in FIG. 7B, the sheet P is conveyed while a tensile force (tension force) in the sheet conveying direction is generated between the first roller pair and the second roller pair in the sheet P. . In this embodiment, the load torque (brake torque) of the load means (electromagnetic hysteresis brake) 131 is set so that the tension force applied to the sheet P becomes a predetermined tension force based on the sheet-related information such as the paper type, image density, and humidity information. ) Is set.

  In this embodiment, as shown in FIG. 8, the length L1 of the central portion in the sheet width direction is set so that the nip portion between the first roller pair and the second roller pair is uniform with respect to the sheet passing center. It is formed in a region (here, 100 mm). Accordingly, the sheet P between the first roller pair and the second roller pair is configured to apply a predetermined tension force only from the front end to the rear end only in the center portion in the width direction. Here, the tension in the conveyance direction applied to the sheet is only the central portion in the width direction, but is not limited thereto. The conveyance direction tension applied to the sheet may be larger in the width direction center region than in the end region so that the expansion / contraction difference between the width direction center portion and the end portion is reduced.

  Thereafter, it is confirmed whether or not the job is finished (S6-9). If the job is not finished, the flow from S6-2 is repeated based on the basis weight, type, image, and humidity information of the next input again. If the job is finished, the drive motor M and the electromagnetic hysteresis brake 131 are turned off to finish the paper feeding (S6-10), and the job is finished (S6-11).

  FIG. 10 illustrates the curl generated in the sheet P, the features of the edge wavy shape, and the measurement method. The undulation is measured with the sheet P placed on the measurement surface plate 700. Here, the length of the end portion of the sheet P in the sheet conveyance direction is L edge [mm], and the center length is L center [mm].

  Further, the curved shape Pwave generated at the upper or lower side of the sheet P shown in FIG. 10, that is, the end in the width direction orthogonal to the conveying direction is referred to as end undulation, and among these, the gap between the measurement platen 700 and the gap is measured. The maximum value Xmax was used as the object of evaluation as the amount of undulations.

  FIG. 12 to FIG. 15 show examples of the results of an experiment for confirming the effect of the tensile conveyance device 101 in the present example conducted by the present inventors. Specifically, the end length L edge [mm], the central length L center [mm], and the maximum waving amount X max [mm] of each sheet P under various conditions were measured.

  As basic experimental conditions of this experiment, the toner image density fixed on the sheet in a normal environment (temperature 23 ° C., humidity 50%) is set to be less than 50%. Further, when the sheet humidifying apparatus 202 of the present embodiment is passed under the above basic experimental conditions, the sheet moisture content immediately after the passage is 7% or more.

  The amount of water contained in the sheet in this example was measured by the present inventors using the sheet P immediately after the sheet P passed through the sheet corrugation correction device 201 and was discharged onto the discharge tray 565. Here, a microwave paper moisture meter was used.

  Here, the maximum waviness of the sheet is set to 1.0 mm or less as a condition for achieving waviness correction.

  In FIGS. 12A to 12C, plain paper having a basis weight of 81 gsm is passed as information regarding sheets other than the basic experimental conditions. FIG. 12A shows the case where the image forming apparatus alone (the sheet wavy correction device does not pass paper), and FIGS. 12B and 12C show the case where the sheet wavy correction device 201 passes. The sheet tension force in FIG. 12B was 1 kgf, and the sheet tension force in FIG. 12C was 3 kgf.

  In the case of FIG. 12A (no tension force), the extension amount of the end length of the sheet is 0.6 mm, the extension amount of the central length of the sheet is 0.0 mm, and the maximum undulation amount is 3.3 mm. It was.

  Compared with the case without the tension force, the case with the tension force was as follows.

  In the case of FIG. 12B (tension force 1 kgf), the extension amount of the end length of the sheet is 0.6 mm, the extension amount of the center length of the sheet is 0.3 mm, and the maximum corrugation amount is 1.7 mm. It was. On the other hand, in the case of FIG. 12C (sheet tension force 3 kgf), both the end length and the center length of the sheet were 0.6 mm, and the maximum waviness was 1.0 mm.

  Thus, in the basic experimental conditions, it was confirmed that there was a difference in the amount of elongation of the center length of the sheet when the sheet tension force was 1 kgf and 3 kgf in the case of plain paper with a basis weight of 81 gsm. If the sheet tension force is 3 kgf or more, the difference between the length of the end portion and the center can be set to 0 mm, and the maximum sheet corrugation amount is changed from 3.3 mm in FIG. 12A to 1 in FIG. It was possible to improve to 0 mm. In addition, in the said FIG.12 (b) and FIG.12 (c), the moisture content of the sheet | seat was 8.0%.

  In FIG. 13A to FIG. 13C, thick paper having a basis weight of 157 gsm is passed as information regarding sheets other than the basic experimental conditions. FIG. 13A shows the case where the image forming apparatus alone (the sheet wavy correction device does not pass paper), and FIGS. 13B and 13C show the case where the sheet wavy correction device 201 passes. The sheet tension force in FIG. 13B was 3 kgf, and the sheet tension force in FIG. 13C was 4 kgf.

  In the case of FIG. 13A (no tension force), the extension of the end length of the sheet is 0.5 mm, the extension of the center length of the sheet is 0.0 mm, and the maximum waviness is 2.5 mm. It was.

  Compared with the case without the tension force, the case with the tension force was as follows.

  In the case of FIG. 13B (tension force 3 kgf), the elongation of the end length of the sheet is 0.5 mm, the elongation of the central length of the sheet is 0.3 mm, and the maximum waviness is 1.7 mm. It was. On the other hand, in the case of FIG. 13C (sheet tension force 4 kgf), both the end length and the center length of the sheet were 0.5 mm, and the maximum waviness was 1.0 mm.

  Thus, in the basic experiment conditions, in the case of thick paper with a basis weight of 157 gsm, if the sheet tension force was 4 kgf or more, the difference between the lengths of the end and the center could be 0 mm. Further, the maximum sheet corrugation amount could be improved from 2.5 mm in FIG. 13A to 1.0 mm in FIG. As in the case of the thick paper shown in FIG. 13, when the sheet basis weight is higher than that of the plain paper shown in FIG. In FIGS. 13B and 13C, the moisture content of the sheet was 7.7%.

  14 (a) and 14 (b) show the information regarding the sheet as a high image density (toner density of 50% or more) by fixing a toner density of less than 50% under the basic experimental conditions to 50% or more. The cardboard having a basis weight of 157 gsm is passed through.

  FIGS. 14A and 14B show a case where the sheet corrugated straightening device 201 is passed. The sheet tension force in FIG. 14A was 4 kgf, and the sheet tension force in FIG. 14B was 5 kgf.

  In the case of FIG. 14A (tension force 4 kgf), the extension amount of the end length of the sheet is 0.5 mm, the extension amount of the center length of the sheet is 0.3 mm, and the maximum corrugation amount is 1.7 mm. It was. On the other hand, in the case of FIG. 14B (sheet tension force 5 kgf), both the end length and the central length of the sheet were 0.5 mm, and the maximum waviness was 1.0 mm.

  As described above, at a high image density (toner density of 50% or more), in the case of thick paper having a basis weight of 157 gsm, if the sheet tension force is 5 kgf or more, the difference between the edge length and the center length of the sheet is set to 0 mm. The maximum sheet corrugation was improved to 1.0 mm.

  14A and 14B, in the case of a high density image (toner density of 50% or more), the amount of water penetrating the sheet is reduced by the influence of the toner image, so the sheet tension force is reduced to a low density image. (Compared) need to be high. In addition, in the said FIG.14 (b) and FIG.14 (c), the moisture content of the sheet | seat was 7.3%.

  FIGS. 15 (a) and 15 (b) show a paper with a basis weight of 157 gsm fixed at a high image density (toner density of 50% or more) in a low humidity environment of less than 20%. ing. In this embodiment, an environment with a humidity of less than 20% is a low humidity environment, and an environment with a humidity of 20% or more is a normal environment.

  FIGS. 15A and 15B show a case where the sheet corrugated straightening device 201 is passed through. The sheet tension force in FIG. 15A was 5 kgf, and the sheet tension force in FIG. 15B was 6 kgf.

  In the case of FIG. 15A (tension force 5 kgf), the extension amount of the end length of the sheet is 0.5 mm, the extension amount of the center length of the sheet is 0.3 mm, and the maximum corrugation amount is 1.7 mm. It was. On the other hand, in the case of FIG. 15B (sheet tension force 6 kgf), both the end length and the center length of the sheet were 0.5 mm, and the maximum waviness was 1.0 mm.

  Thus, in a low humidity environment (humidity of less than 20%) and high image density (toner concentration of 50% or more), for thick paper with a basis weight of 157 gsm, if the sheet tension force is 6 kgf or more, the edge and center of the sheet The difference in length between the two was able to be 0 mm. Moreover, the maximum sheet corrugation amount could be improved to 1.0 mm.

  15A and 15B, in a low humidity environment (humidity less than 20%) and a high density image (toner density of 50% or more), the amount of water penetrating the sheet is less than the normal humidity environment. It is necessary to increase the sheet tension force. In FIGS. 15A and 15B, the moisture content of the sheet was 7.0%.

  FIG. 16 shows a set value of the sheet tension force in this embodiment, which was obtained from the experimental results under various conditions including the experimental results. As a result of performing the confirmation experiment again under various conditions with the set values shown in FIG. 16, it was confirmed that the waviness amount was 1.0 mm or less under all conditions.

  That is, FIG. 16A shows a case where the basis weight is less than 90 gsm, a case where the basis weight is 90 gsm or more, and a case where the image density is less than 50% and 50% or more in a normal environment (humidity of 20% or more). In a low humidity environment (humidity less than 20%), the basis weight is less than 90 gsm, 90 gsm or more, and the image density is less than 50% and 50% or more, as shown in FIG. .

  For example, in a normal environment (humidity of 20% or more) and the image density is less than 50%, when the basis weight is different, the control unit 500C serving as a load control unit performs control as shown in FIG. That is, the controller 500C applies a tension (first tension) of 3 kgf to the sheet having a basis weight of less than 90 gsm (first basis weight) using the load unit 131 as a first load. On the other hand, for a sheet having a basis weight of 90 gsm or more (second basis weight) greater than the first basis weight, the load means 131 is set to a second load greater than the first load. A tension of 4 kgf (second tension) greater than the tension of 2 is applied. Thereby, the corrugation amount of the sheet can be improved to 1.0 mm or less. In addition, if the load by the load unit 131 on the sheet having a low basis weight is excessively increased, the sheet may be damaged, which is not preferable.

  Further, for example, when the basis weight of the sheet is less than 90 gsm in a normal environment (humidity of 20% or more) and the image density is different, the control unit 500C serving as a load control unit performs control as illustrated in FIG. . That is, the controller 500C applies a tension of 3 kgf (first tension) to the sheet having an image density of less than 50% (first density) by using the load unit 131 as a first load. On the other hand, for a sheet having an image density of 50% or more (second density) greater than the first density, the load means 131 is set to a second load greater than the first load. A tension (second tension) of 4 kgf greater than the tension is applied. Thereby, the corrugation amount of the sheet can be improved to 1.0 mm or less.

  Further, for example, in the case of a sheet having an image density of less than 50% and a basis weight of less than 90 gsm, when the environmental humidity is different, the control unit 500C as load control means is shown in FIGS. 16 (a) and 16 (b). To control. That is, when the humidity is 20% or more (first humidity), the controller 500C applies the tension of 3 kgf (first tension) to the sheet with the load means 131 as the first load. On the other hand, when the humidity is lower than the first humidity and less than 20% (second humidity), the load means 131 is set to a second load larger than the first load, and the sheet is subjected to the first tension. A large tension of 4 kgf (second tension) is applied. Thereby, the corrugation amount of the sheet can be improved to 1.0 mm or less.

  In this embodiment, when the sheet tension force is high, the load torque applied to the motor and gear increases, and the temperature rise and noise increase. Therefore, the optimum sheet tension force is set according to various conditions. This makes it possible to significantly improve the waving amount while setting the brake torque low for plain paper (basis weight less than 90 gsm) with a low density image (less than 50% toner image) at normal environmental humidity where the frequency of passing paper is the highest. It was.

  As described above, moisture is applied to the sheet, humidified to a predetermined moisture amount or more, and then passed through a tension conveyance device to pull the sheet in the width direction in the conveyance direction. It is possible to reduce the difference in length in the sheet conveyance direction with respect to the portion and improve the waviness.

  In addition, by selecting (variing) the sheet tension force when pulling according to information (basis weight, paper type, density, environmental humidity) regarding the sheet, it is possible to more effectively improve the corrugation of the sheet.

[Example 2]
The configuration of the sheet pulling and conveying apparatus of the present embodiment will be described with reference to FIGS. FIG. 17 is a top view of the sheet pulling and conveying apparatus 101 used in this embodiment. Since the present embodiment is different from the first embodiment only in the sheet pulling and conveying apparatus 101, the description of the same configuration as that in the first embodiment is omitted.

  In the above-described embodiment, the electromagnetic hysteresis brake (electromagnetic brake) that can change the brake torque by changing the exciting current is exemplified as the load means. On the other hand, in the present embodiment, a configuration in which a plurality of torque limiters TL1 to TL3 are connected to the drive gear 104G2 of the first upper roller 104 via the clutches CL2 to CL4 is exemplified as the load means. Then, the load control means selectively connects or disconnects the clutches CL2 to CL4 to control the load torque by the torque limiters TL1 to TL3 to be variable (in the following description, every 1 kgf between 3 kgf to 6 kgf). . This will be described in detail below.

  As shown in FIG. 17, the first torque limiter TL1 is connected to the drive gear 104G2 of the first upper roller 104 via the electromagnetic clutch CL2, the clutch gear CLG2, and the torque limiter gear TLG1. The third torque limiter TL3 is connected to the drive gear 104G2 of the first upper roller 104 via the electromagnetic clutch CL4, the clutch gear CLG4, and the torque limiter gear TLG3.

  Further, the second torque limiter TL2 is connected in series to the clutch gear CLG2 connected to the drive gear 104G2 of the first upper roller 104 via the electromagnetic clutch CL3, the clutch gear CLG3, and the torque limiter gear TLG2.

  In this embodiment, the torque setting value of the first torque limiter TL1 is set so that the sheet tension force is 3 kgf. The torque set value of the second torque limiter TL2 is set so that the sheet tension force is 2 kgf. The torque set value of the third torque limiter TL3 is set so that the sheet tension force is 1 kgf.

  With the above configuration, when the electromagnetic clutches CL2, CL3, and CL4 are OFF, the connection of the torque limiters TL1, TL2, and TL3 to the drive gear 104G2 of the first upper roller 104 is released, so that no tension force is applied to the sheet.

  On the other hand, when the electromagnetic clutch CL2 is ON, the electromagnetic clutch CL3 is OFF, and the electromagnetic clutch CL4 is OFF, the first torque limiter TL1 is connected to the drive gear 104G2 of the first upper roller 104 by the electromagnetic clutch CL2. As a result, the load torque (3 kgf) of the first torque limiter TL1 is applied to the first upper roller 104, and the sheet tension force becomes 3 kgf.

  Further, when the electromagnetic clutch CL2 is ON, the electromagnetic clutch CL3 is OFF, and the electromagnetic clutch CL4 is ON, the drive torque 104G2 of the first upper roller 104 is moved to the first torque limiter TL1, third torque by the electromagnetic clutch CL2, CL4. A limiter TL3 is connected. As a result, the load torque (3 kgf) of the first torque limiter TL1 and the load torque (1 kgf) of the third torque limiter TL3 are applied to the first upper roller 104, and the sheet tension force becomes 4 kgf.

  Similarly, when the electromagnetic clutch CL2 is ON, the electromagnetic clutch CL3 is ON, and the electromagnetic clutch CL4 is OFF, the first torque limiter TL1 and the second torque are applied to the drive gear 104G2 of the first upper roller 104 by the electromagnetic clutch CL2 and CL3. A limiter TL2 is connected. As a result, the load torque (3 kgf) of the first torque limiter TL1 and the load torque (2 kgf) of the second torque limiter TL2 are applied to the first upper roller 104, and the sheet tension force becomes 5 kgf.

  Similarly, when the electromagnetic clutch CL2 is ON, the electromagnetic clutch CL3 is ON, and the electromagnetic clutch CL4 is ON, the drive gear 104G2 of the first upper roller 104 is connected to all the torque limiters TL1, by all the electromagnetic clutches CL2, CL3, and CL4. TL2 and TL3 are connected. Thereby, the load torque (3 kgf) of the first torque limiter TL1, the load torque (2 kgf) of the second torque limiter TL2, and the load torque (1 kgf) of the third torque limiter TL3 are applied to the first upper roller 104. The sheet tension force is 6 kgf.

  With the above configuration and control, the sheet tension force can be changed between 3 to 6 kgf for each 1 kgf. The predetermined sheet tension force of the present embodiment is the same as the setting of FIG.

  FIG. 18 is a flowchart showing the control of this embodiment. Description of the same control as that of the first embodiment shown in FIG. 6 is omitted.

  When the paper passing job signal is input to the CPU (control means) (S18-1), the basis weight, type, image density, and humidity information as the information about the sheet are confirmed (S18-2). Then, the electromagnetic clutches CL2, CL3, and CL4 are turned on so that the required brake torque of the torque limiters TL1, TL2, and TL3 as the load means becomes a brake torque corresponding to a predetermined seat tension force according to the information on the seat. / OFF is set (S18-3). Note that the predetermined sheet tension force corresponding to the information related to the sheet is the same as in the first embodiment, and based on this, the energization ON and OFF of the electromagnetic clutches CL2, CL3, and CL4 is controlled as described above.

  Thereafter, energization of the drive motor M is turned on (S18-4), and energization of the electromagnetic clutches CL2, CL3, and CL4 is turned on or off (S18-5). At the same time, the energization of the electromagnetic clutch CL is turned on and the paper feeding is started (S18-6). As a result, the drive of the drive motor M is transmitted to the drive gears 104G1 and 106G via the drive transmission gear, whereby the first upper roller 104 and the second upper roller 106 rotate.

  Thereafter, when the sheet P is guided to the lower entrance guide 121 in the sheet pulling and conveying apparatus 101 and the ON signal of the sheet sensor 103 is confirmed (S18-7), the energization of the electromagnetic clutch CL is turned off after Xmsec (S18-). 8). When the energization of the electromagnetic clutch CL is turned off, the tension force set on the sheet is applied and the sheet is pulled as in the first embodiment.

  Also in this embodiment, as in the first embodiment, as shown in FIG. 8, the sheet width is set so that the nip portions of the first roller pair and the second roller pair are even with respect to the sheet passing center. It is formed in a region having a length L1 (here, a width of 100 mm) at the center in the direction. Accordingly, the sheet P between the first roller pair and the second roller pair is configured to apply a predetermined tension force in the transport direction from the front end to the rear end only at the center in the width direction.

  Thereafter, it is confirmed whether or not the job is finished (S18-9). If the job is not finished, the flow from S17-2 is repeated based on the basis weight, type, image, and humidity information of the next input again. If the job is finished, the drive motor M and the electromagnetic clutches CL2, CL3, and CL4 are turned off, the paper passing is finished (S18-10), and the job is finished (S18-11).

  The set value of the sheet tension force in this embodiment is the same as that in Embodiment 1, and is shown in FIG. As a result of performing the confirmation experiment again under various conditions with the set values shown in FIG. 16, it was confirmed that the waviness amount was 1.0 mm or less as in Example 1 under all conditions.

  As described above, moisture is applied to the sheet, humidified to a predetermined moisture amount or more, and then passed through a tension conveyance device to pull the sheet in the width direction in the conveyance direction. It is possible to reduce the difference in length in the sheet conveyance direction with respect to the portion and improve the waviness.

  In addition, by selecting (variing) the sheet tension force when pulling according to information (basis weight, type, concentration, environmental humidity) regarding the sheet, it is possible to more effectively improve the corrugation of the sheet.

[Other Examples]
In addition, since various conditions such as basis weight, type, image density, and environmental humidity as information regarding the sheets in Example 1 and Example 2 are examples, the method for setting conditions is changed to other condition setting values. It doesn't matter. For example, as shown in FIG. 19, in the configurations of the first and second embodiments, the amount of moisture that is detected downstream of the humidifying device 202 and upstream of the tensile conveyance device 101 is detected. A detection means 601 (eg, an infrared moisture meter) is provided. The sheet tension force applied to the sheet may be changed according to the moisture content of the sheet detected by the moisture content detection means. In this case, when the amount of moisture contained in the sheet is large, the tension force on the sheet is made smaller than when the amount of water is small.

  Specifically, the control unit 500C causes the load unit 131, TL1 to TL3 to be the first load when the moisture amount of the sheet detected by the moisture amount detection unit 601 is the second moisture amount greater than the first moisture amount. A smaller second load is applied to the sheet to provide a second tension less than the first tension.

  Also, the tension force setting value may be changed depending on the sheet type (coated paper, embossed paper, thin paper, recycled paper, etc.) under various conditions.

  The present invention also provides information on the sheet based on information on at least one of sheet basis weight, sheet type, environmental humidity, moisture content contained in the sheet, and image density on the sheet. It only needs to be changed.

  In the above-described embodiment, a printer is exemplified as the image forming apparatus, but the present invention is not limited to this. For example, the image forming apparatus may be another image forming apparatus such as a copying machine or a facsimile machine, or another image forming apparatus such as a multi-function machine combining these functions. Further, the image forming apparatus is exemplified in which an intermediate transfer member is used, toner images of respective colors are sequentially transferred onto the intermediate transfer member, and the toner images carried on the intermediate transfer member are collectively transferred to a sheet. However, the present invention is not limited to this. For example, an image forming apparatus that uses a sheet carrier and sequentially superimposes and transfers the toner images of the respective colors on the sheet carried on the sheet carrier. The same effect can be obtained by applying the present invention to a sheet corrugation correcting device used in these image forming apparatuses.

  Further, in the above-described embodiments, the sheet corrugation correction apparatus that is detachable from the image forming apparatus is exemplified, but the present invention is not limited to this. For example, it may be a sheet waviness correcting device that the image forming apparatus has integrally, and the same effect can be obtained by applying the present invention to the sheet waviness correcting device.

  In the above-described embodiments, the sheet corrugation correction apparatus (sheet processing apparatus) that is detachable as an optional external apparatus with respect to the image forming apparatus is illustrated, but the present invention is not limited to this. For example, it may be a sheet waviness correction device that is integrally provided with the image forming apparatus. By applying the present invention to the sheet waviness correction device, the same effect can be obtained as the entire image forming system. Moreover, although the control part which a sheet corrugation correction apparatus has is controlled by the control part which an image forming apparatus has, the structure which controls operation | movement of a sheet corrugation correction apparatus was illustrated, However, It is not limited to this. For example, only the image forming apparatus may have a control unit, and the control unit of the image forming apparatus may control the operation of the sheet wave straightening device. Even if comprised in this way, the same effect can be acquired.

  In the embodiment described above, the outer diameters of the first lower roller 105 and the second lower roller 107 are set so that the central region in the width direction orthogonal to the sheet conveying direction is larger than the end region. Although the configuration is exemplified, the configuration is not limited to this. Other configurations may be used as long as tension in the conveyance direction is applied to the central region in the width direction of the sheet. Specifically, the outer diameter of at least one of the rollers constituting the first roller pair and the second roller pair is set so that the central region in the width direction perpendicular to the sheet conveying direction is larger than the end region. Any configuration may be used.

CL, CL2, CL3, CL4 ... Electromagnetic clutch CLG, CLG2, CLG3, CLG4 ... Clutch gear M ... Drive motor MG ... Motor gear P ... Seat TL1, TL2, TL3 ... Torque limiter TLG1, TLG2, TLG3 ... Torque limiter gear 100 ... Fixing Device 101 ... Sheet tension conveying device 103 ... Sheet sensor 104 ... First upper roller 104G2 ... Drive gears 104a, 105a, 106a, 107a ... Roller shafts 104b, 105b, 106b, 107b ... Elastic rubber 105 ... First lower roller 106 ... First Two upper rollers 107 ... second lower roller 108 ... second pressure spring 109 ... first pressure spring 112 ... second pressure plate 113 ... first pressure plate 114 ... transport upper guide 115 ... transport lower guide 117 ... outlet upper guide 118 ... Exit lower guide 119 ... Upper plate 1 0 ... lower plate 121 ... inlet lower guide 122 ... second rotary shaft 131 ... load means (electromagnetic hysteresis brake)
DESCRIPTION OF SYMBOLS 201 ... Sheet corrugation correction apparatus 202 ... Sheet humidification apparatus 500C ... Control part 500D ... Environmental sensor 510 ... Image formation part 570 ... Operation panel 601 ... Water content detection means

Claims (11)

In a sheet conveying apparatus that conveys a sheet,
Load means for applying tension in the conveying direction to the sheet;
Load control means for variably controlling the load of the load means,
The load control unit controls a load applied to the sheet by the load unit in accordance with information on the sheet input to the load control unit. In a sheet conveying apparatus that conveys a sheet,
Load means for applying tension in the conveying direction to the sheet;
Load control means for variably controlling the load of the load means,
For the first basis weight sheet, the load control means sets the load by the load means as the first load, and for the second basis weight sheet having a basis weight larger than the first basis weight. In this case, the load by the load means is a second load that is larger than the first load. A first roller pair consisting of a first upper roller and a first lower roller that is pressed against the first upper roller to form a nip and sandwich and convey the sheet;
A second upper roller, and a second lower roller that is pressed against the second upper roller to form a nip and sandwich and convey the sheet, and a second roller pair downstream in the conveying direction of the first roller pair;
Have
The outer diameter of at least one of the first upper roller, the first lower roller, the second upper roller, and the second lower roller is larger in the central region in the width direction perpendicular to the sheet conveying direction. Larger than the division area,
The load means applies a load to the first roller pair, and sandwiches the first roller pair and the second roller pair to convey the sheet in the conveyance direction in a central region in a width direction orthogonal to the conveyance direction of the sheet. The sheet conveying apparatus according to claim 1 or 2, wherein tension is applied.   The load unit includes an electromagnetic brake that changes a brake torque by changing an excitation current, and the load control unit variably controls a load by changing a current value excited in the load unit. The sheet conveying apparatus according to any one of claims 1 to 3.   The load means has a plurality of torque limiters and a plurality of clutches that connect or disconnect the torque limiters, and the load control means selectively connects or disconnects the clutches to vary the load by the torque limiters. The sheet conveying apparatus according to any one of claims 1 to 3, wherein the sheet conveying device is controlled as follows.   6. The information on the sheet is information on at least one of sheet basis weight, sheet type, environmental humidity, moisture content contained in the sheet, and image density on the sheet. The sheet conveying apparatus according to any one of the above.   When the basis weight of the sheet is the first basis weight, the load control means applies the first tension to the sheet by setting the load means as the first load, and the basis weight of the sheet is greater than the first basis weight. 2. The second load larger than the first tension is applied to the sheet by setting the load means to a second load larger than the first load when the second basis weight is large. The sheet conveying apparatus according to any one of claims 3 to 6.   When the image density on the sheet is the first density, the load control means applies the first tension to the sheet by setting the load means as the first load, and the image density on the sheet is higher than the first density. The second load larger than the first tension is applied to the sheet by setting the load means as a second load larger than the first load when the second concentration is large. Item 8. The sheet conveying apparatus according to any one of Items 7 above. Has humidity detection means to detect environmental humidity,
When the environmental humidity detected by the humidity detection means is the first humidity, the load control means applies the first tension to the sheet by setting the load means as the first load, and detects the environment detected by the humidity detection means. When the humidity is a second humidity lower than the first humidity, the load means is set to a second load larger than the first load, and a second tension larger than the first tension is applied to the sheet. The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus. A moisture applying device for applying moisture to the sheet;
The sheet conveying apparatus according to any one of claims 1 to 9, provided downstream of the moisture applying apparatus in a sheet conveying direction,
The load control means sets a load by the load means as a first load for a sheet having a first moisture content, and a second moisture content sheet having a moisture content greater than the first moisture content. 10. The sheet conveying apparatus according to claim 1, wherein the load unit is a second load smaller than the first load. 11. An image forming unit for forming a toner image;
A fixing unit that heats and fixes the toner image on the sheet formed by the image forming unit to the sheet;
An image forming apparatus comprising: the sheet conveying apparatus according to claim 1, which conveys a sheet that has passed through the fixing unit.

Images