JP2015172718A - Sheet conveyance device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress flapping of sheets while minimizing the stress to the sheets.SOLUTION: A sheet conveyance device includes conveyance units each including: a first roller pair that holds and conveys a sheet at a first nip part; a second roller pair that holds and conveys the sheet conveyed by the first roller pair at a second nip part; and load means for applying load torque to the first roller pair after the leading end of the sheet conveyed by the first roller pair reaches the second nip part. At least two of the conveyance units are arranged in a direction of conveyance of the sheet.

Description

  The present invention relates to a sheet conveying apparatus used in an image forming apparatus such as a copying machine, a printer, and a facsimile using a method of fixing an unfixed toner image by heating and pressing, and a copying machine and a printer including the sheet conveying apparatus. The present invention relates to an image forming apparatus such as a facsimile.

  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, whereby an image is recorded and formed on the sheet.

  As a fixing device of such an image forming apparatus, a fixing nip portion is formed by pressing a resilient pressure roller against a fixing roller having a heat source such as a heater and maintained at a predetermined temperature. A heat roller fixing system is employed in which the toner image is fixed on the sheet at the part.

  In recent years, in an image forming apparatus (especially a full-color image forming apparatus) in which this type of fixing device is used, the heating time can be extended and the fixing can be performed from the viewpoint of improving the color developability and image quality of the toner image. A fixing device that can increase the speed is known. For example, as shown in Japanese Patent Laid-Open No. 5-150679, a so-called belt nip type fixing device is known in which an endless fixing belt stretched around a plurality of rolls is pressed against a heating roll.

  In recent years, it has become necessary to increase the process speed in order to increase the output speed of the image forming apparatus. For this reason, a wider nip width is required in the width direction perpendicular to the sheet conveyance direction, and a belt fixing system that secures a wide nip width by replacing the fixing roller and pressure roller or both with an endless belt. Has been proposed and commercialized.

Japanese Patent Laid-Open No. 5-150679

  However, in the heat fixing process of these fixing devices, heat and pressure are applied to the sheet on which the toner image has been transferred, so that moisture evaporates from the inside of the sheet after the pressure nip and the pressure nip. 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.

  The first cause of undulations at the end of the sheet is in the process of passing the sheet 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.

  The second cause of the occurrence of undulations 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. .

  In particular, in the belt fixing method in which the fixing roller and the pressure roller or both are replaced with an endless belt to ensure a wide nip width, the distance and time for the sheet to stay between the nips increase compared to the heat roller method. The problem of corrugation at the edge of the sheet tends to become prominent.

  Concerning the length of the sheet in the conveying direction, the tension in the conveying direction is applied to the central part of the sheet to the problem that the end in the width direction orthogonal to the conveying direction of the sheet extends to the vicinity of the central part. A countermeasure for correcting the length in the conveyance direction between the center and the edge of the sheet is conceivable. Although a tension (tension) in the conveyance direction is applied to the sheet, it is necessary to set the tension so as not to damage the sheet. In order to correct the length in the conveyance direction between the center and the edge of the sheet, it is necessary to pull the sheet a plurality of times with the set tension.

  However, when the sheet pulling and conveying apparatus passes a plurality of times, there is a problem that the length in the conveyance direction near the center of the sheet extends in the conveyance direction more than the vicinity of the end depending on the paper physical properties of the sheet.

  Accordingly, an object of the present invention is to improve sheet waviness while minimizing stress on the sheet.

  In order to achieve the above object, the present invention provides a first roller pair for nipping and conveying a sheet by a first nip portion, and a sheet nipped by the first roller pair for nipping by a second nip portion. And a load means for applying a load torque to the first roller pair after the leading edge of the sheet conveyed by the first roller pair reaches the second nip portion. , And at least two of the conveyance units are provided side by side in the sheet conveyance direction.

  According to the present invention, since tension is applied to the sheet in stages, the waviness of the sheet can be improved while minimizing the stress on the sheet.

1 is a cross-sectional view illustrating a tensile conveyance device of Example 1. FIG. 1 is a cross-sectional view illustrating an electrophotographic printer of Example 1. FIG. FIG. 3 is a block diagram showing a control relationship between the electrophotographic printer and the entire sheet wavy correction device. It is sectional drawing which shows the humidification apparatus of Example 1. It is a perspective view which shows the water storage tank periphery of the humidification apparatus of Example 1. FIG. It is a perspective view which shows the tension conveyance apparatus of Example 1. FIG. FIG. 3 is a top view illustrating the tensile conveyance device according to the first embodiment. It is a perspective view which shows the drive of the tension | pulling conveyance apparatus of Example 1. FIG. 3 is a flowchart illustrating control of the tensile conveyance device according to the first embodiment. It is sectional drawing which shows the control action of the tension | pulling conveyance apparatus of Example 1. FIG. It is sectional drawing which shows the control action of the tension | pulling conveyance apparatus of Example 1. FIG. It is sectional drawing which shows the control action of the tension | pulling conveyance apparatus of Example 1. FIG. It is sectional drawing which shows the control action of the tension | pulling conveyance apparatus of Example 1. FIG. It is explanatory drawing explaining the state of a sheet | seat state, and a measuring method. (A) (b) is a table | surface figure which shows the state of the sheet | seat by experiment. (A) (b) is a table | surface figure which shows the state of the sheet | seat by experiment. (A) (b) is a table | surface figure which shows the state of the sheet | seat by experiment. It is a perspective view which shows the tension conveyance apparatus of Example 2. FIG. 10 is an example of a problem of tension distribution on the sheet of Example 2. 10 is a result of countermeasures for tension distribution on the sheet of Example 2. 10 is a result of countermeasures for tension distribution on the sheet of Example 2. 6 is a cross-sectional view showing an electrophotographic printer of Example 3. FIG. 6 is a cross-sectional view illustrating a tensile conveyance device of Example 3. FIG. FIG. 10 is a perspective view showing a tensile conveyance device according to a modification of Example 3. FIG. 10 is a cross-sectional view illustrating a tensile conveyance device according to a modification of Example 3.

  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]
<Configuration of the entire device>
An image forming apparatus including the sheet conveying apparatus according to the first embodiment will be described with reference to FIGS. In the following description, the image forming apparatus will be described first, and then the sheet conveying apparatus will be described. In the present exemplary embodiment, an image forming system in which a sheet conveying apparatus is connected to the outside of the image forming apparatus will be described. However, even in a configuration of an image forming system in which the sheet conveying apparatus is integrated into the image forming apparatus. The present invention is effective.

  First, referring to FIG. 2, an image forming apparatus and a sheet conveying apparatus detachably connected to the image forming apparatus will be described as an example of an image forming system. FIG. 2 is a cross-sectional view schematically showing a color electrophotographic printer 500 that is an example of an image forming apparatus and a sheet wavy correction device 900 that includes a conveyance unit that is an example of a sheet conveying apparatus. FIG. In the following description, 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 500 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. An endless intermediate transfer belt 531 as an intermediate transfer member is disposed so as to face these image forming portions. In other words, the image forming apparatus adopts a tandem method in which processes up to visualization are processed in parallel for each color.

  Note that the arrangement order of the image forming units for each of the colors Y, M, C, and K is not limited to the arrangement order shown in FIG. In addition, the present invention is not limited to the full-color intermediate transfer type image forming apparatus shown in FIG.

  Each color image forming unit 510 includes the following process means. An electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 511 as an image bearing member that bears 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, A developing unit 514 is provided. 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 developed by the developing device 514 to be visualized as a toner image.

  Each toner image formed and carried on the surface of the photosensitive drum 511 is primarily 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. The

  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 P 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 531 is secondarily transferred collectively onto the sheet P by a secondary transfer roller 535 which is a transfer portion.

  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 a sheet waving correction device 900 as a sheet processing device that processes the sheet by the discharge roller pair 540, and after correcting the sheet waving by the sheet waving correction device 900, the discharge tray 565. To be discharged.

  Here, the fixing device will be described. 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 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 portion 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. As a result, the sheet P heated and pressed in the fixing nip portion is larger in the end side in the width direction perpendicular to the sheet conveyance direction than in the center side, and the fibers extend in the conveyance direction. (Hereinafter referred to as wavy) occurs.

  The sheet P on which the toner image is fixed by the fixing device 100 is sent to the sheet wavy correction device 900 by the discharge roller pair 540. The sheet P is transported along the transport guide 902 by the pair of entrance rollers 901 of the sheet wavy correction device 900. After the sheet P is turned vertically downward by the conveyance guide 902, the sheet P is sequentially sent to the humidifying device 400 as a humidifying unit and the sheet pulling and conveying devices 101, 201, and 301 as conveying units. The humidifying device 400 humidifies and conveys the sheet P in order to replenish moisture in the sheet P lost by the heat of the fixing device 100 and loosen the paper fibers of the sheet P. The sheet P that has passed through the humidifying device 400 sequentially passes through the sheet pulling and conveying devices 101, 201, and 301, and by pulling the central portion in the width direction perpendicular to the conveying direction of the sheet in the conveying direction, The difference in length in the conveyance direction of the central sheet is reduced.

  In this way, the sheet P with improved waviness at the end in the width direction of the sheet is then conveyed by the conveyance roller pair 904 while turning the conveyance direction vertically upward by the conveyance guides 903 and 905. Thereafter, the sheet P is conveyed by the conveyance roller pair 906 and 908 while being guided by the conveyance guides 907 and 909, discharged by the discharge roller pair 910 to the outside of the sheet waviness correction device 900, and stacked on the discharge tray 565.

  Here, the control relationship of the entire image forming system will be described with reference to FIG. FIG. 3 is a block diagram showing a control relationship between the printer 500 and the sheet wavy correction device 900 constituting the image forming system. The control unit 500C of the printer 500 and the control unit 901C of the sheet wavy correction device 900 are computer systems having a CPU, a memory, an arithmetic unit, an I / O port, a communication interface, a drive circuit, and the like.

  The control by each of the control units 500C and 901C described above is performed by each CPU executing a predetermined program stored in the memory. The control unit 901C of the sheet wavy correction device 900 controls operations of the humidifying device 400 and the sheet pulling and conveying devices 101, 201, and 301 constituting the device. In addition, the above-described control units 500C and 901C are connected via the communication unit COM and can exchange information.

  Here, a configuration in which the control unit (control unit) 901C included in the sheet wavy correction device 900 is controlled by the control unit (control unit) 500C included in the printer 500 to control the operation of the sheet wavy correction device 900 is illustrated. However, the present invention is not limited to this. For example, the sheet waviness correction apparatus may have no control means, and the control means of the printer may control the operation of the sheet waviness correction apparatus.

<Description of humidifier>
Hereinafter, the humidifier 400 will be described with reference to FIGS. 2, 4, and 5. FIG. 4 is a cross-sectional view of the humidifying device 400.

  The sheet P sent in the direction of the arrow B in FIG. 4 as with the arrow B in FIG. 2 is guided by the inlet guide 414 and enters the nip portion of the humidifying roller pair 401, 402. Then, the humidifying liquid L is transferred onto the surface (both sides) of the sheet P by the humidifying roller pair 401, 402, whereby the sheet P is humidified.

  The humidifying roller pair 401, 402 is an elastic roller in which a solid rubber layer mainly composed of NBR, silicon or the like is formed on the surface of a shaft core made of a metal rigid body such as stainless steel.

  The water supply rollers 407 and 408 are water supply members for sequentially supplying the humidifying liquid L to the humidifying rollers 401 and 402. The water supply rollers 407 and 408 are formed with a solid rubber layer mainly composed of a material having a hydrophilic surface capable of holding the humidifying liquid L on the shaft core surface made of a metal rigid body such as stainless steel, such as NBR. Elastic roller. The solid rubber layer may be made of metal or a hydrophilic resin.

  The supply / drainage of the humidifying liquid L to the water storage tank and the humidifying device will be described with reference to FIGS. FIG. 5 is an explanatory view showing the vicinity of the water storage tank.

  400A shown in FIG. 2 is a water storage tank in which a humidifying liquid L for humidifying the sheet P is accommodated. The humidifying liquid L stored in the water storage tank 400A is supplied to the water tank (water storage unit) 412 of the humidifying device 400 as needed by the water supply pump 400B. In the present embodiment, the humidifying liquid L is mainly composed of water, and a liquid in which a surfactant is blended in consideration of humidification efficiency and permeability to the sheet P is used.

  The water storage tank 400A is connected to water tanks 411 and 412 provided in the humidifier 400 via a water supply pump 400B. FIG. 4 shows the connection.

  The humidifying liquid L accommodated in the water supply pipe 400C is directed toward the water supply basins 411 and 412 by the water supply pump 400B, through the branch part 400C1 provided in the water supply pipe 400C, and arrows F1 and F2 shown in FIGS. Branch water is supplied as needed in each direction. Each branched pipe of the water supply pipe 400C is connected to water supply holes 411a and 412b provided at the bottoms of the water supply tanks 411 and 412 (substantially directly below the water supply rollers 407 and 408), respectively.

  The lower portions of the water supply rollers 407 and 408 are immersed in the humidified liquid L supplied by the water supply pump 400B and accumulated at the bottom of the water supply tanks 411 and 412 through the water supply holes 411a and 412b. The water supply rollers 407 and 408 supply the humidifying liquid L to the humidifying rollers 401 and 402 by rotating in the arrow direction shown in FIG. The humidifying liquid L is pumped up by its own viscosity, surface tension, wettability of the rubber surface layers of the water supply rollers 407 and 408, and the like.

  The humidifying liquid held on the surface layer of the water supply rollers 407 and 408 is further transferred to the surface layer of the humidifying rollers 401 and 402 and simultaneously squeezed from the scraping rollers 403 and 404. Therefore, the humidifying liquid L is transferred to the surface layer of each of the humidifying rollers 401 and 402 while maintaining uniformity. The scraper rollers 403 and 404 are made of, for example, a material obtained by performing hard chrome plating on the surface of stainless steel or steel.

  The humidification roller 401, the water supply roller 408, and the scraping roller 404 are pressed (biased) against the humidification roller 402 by a not-shown pressure spring. Further, the water supply roller 407 and the scraping roller 403 are pressed (biased) against the humidifying roller 401 by a pressure spring (not shown).

  As shown in FIG. 1, the sheet P that has passed through the humidifying device 400 is guided between the guides 501 and 502, conveyed to the inlet roller pairs 503 and 504, and the inlet guides 102 and 121 in the sheet pulling and conveying device 101. Be guided during.

<Description of tensile conveying device>
Next, the configuration of each sheet pulling and conveying apparatus (101, 201, 301) as a conveying unit will be described with reference to FIGS. In this embodiment, the configurations of the first sheet pulling and conveying apparatus 101, the second sheet pulling and conveying apparatus 201, and the third sheet pulling and conveying apparatus 301 are the same. The first sheet pulling / conveying device 101, the second sheet pulling / conveying device 201, and the third sheet pulling / conveying device 301 are a plurality of roller pairs that apply tension to the sheet to extend the central portion in the width direction of the sheet P in the conveying direction. It has. For this reason, component parts (symbols) are used in combination for the description of the configuration of the sheet pulling and conveying apparatus described later.

  The sheet conveyance speed by the roller pair (or roller) described below means the rotation speed (linear speed) of the roller pair (or roller).

  FIG. 1 is a front cross-sectional view illustrating sheet pulling and conveying apparatuses 101, 201, and 301 according to the present embodiment. 6 is a perspective view illustrating the sheet pulling and conveying apparatuses 101, 201, and 301 according to the present embodiment, and FIG. 7 is a left side view illustrating the sheet pulling and conveying apparatuses 101, 201, and 301 according to the present embodiment.

  Each sheet pulling and conveying device includes a first roller pair described below and a second roller pair provided on the downstream side in the conveying direction from the first roller pair as a plurality of roller pairs.

  The first roller pair is a first upper roller that is a rotatable first roller, and a first pressure roller that is pressed against the first upper roller to form a nip portion and sandwich and convey the sheet. It consists of a certain first lower roller.

  The second roller pair is provided on the downstream side in the transport direction from the first roller pair. The second roller pair is a second upper roller, which is a rotatable second roller, and a second pressure roller that is pressed against the second upper roller to form a nip portion to sandwich and convey the sheet. It consists of a second lower roller.

  The first sheet pulling and conveying apparatus 101 includes a first upper roller 104 and a first lower roller 105 that constitute a first roller pair, and a second upper roller 106 and a second lower roller 107 that constitute a second roller pair. The sheet P is nipped and conveyed. The second sheet pulling and conveying apparatus 201 includes a first upper roller 204 and a first lower roller 205 that constitute a first roller pair, and a second upper roller 206 and a second lower roller 207 that constitute a second roller pair. The sheet P is nipped and conveyed. The third sheet pulling / conveying device 301 includes a first upper roller 304 and a first lower roller 305 that constitute a first roller pair, and a second upper roller 306 and a second lower roller 307 that constitute a second roller pair. The sheet P is nipped and conveyed. Each of the sheet pulling and conveying apparatuses 101, 201, and 301 applies a tension to the sheet P in order to extend the central portion in the width direction of the sheet P in the conveying direction while sequentially conveying the sheet P.

  The first upper rollers 104, 204, 304, the first lower rollers 105, 205, 305, the second upper rollers 106, 206, 306, and the second lower rollers 107, 207, 307 are high rigidity such as stainless steel and steel, respectively. Roller shafts 104a, 105a, 106a, 107a, 204a, 205a, 206a, 207a, 304a, 305a, 306a, 307a using materials are formed on the elastic rubber 104b, 105b, 106b, 107b, silicon, NBR, EPDM, etc. 204b, 205b, 206b, 207b, 304b, 305b, 306b, 307b are formed.

  Further, as shown in FIG. 6, the elastic rubbers 105b, 107b, 205b, 207b, 305b, and 307b of the first lower rollers 105, 205, and 305 and the second lower rollers 107, 207, and 307 are arranged at the center in the sheet width direction. It is formed in a region of length L1. The elastic rubbers 105b, 107b, 205b, 207b, 305b, and 307b of each lower roller are formed so as to be even with respect to the sheet passing center (width direction center). 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 sheet width (length in the width direction of a sheet of a predetermined size) of the sheet P in which undulation shown in FIG. 8 is a problem. In this embodiment, L1 = 100 mm. The sheet of a predetermined size is a sheet of a size that is frequently used by the apparatus. For example, an A3 size sheet (297 mm) corresponds to this.

  Further, conveyance guides 114, 115, 214, 215, 314, and 315, which are guide members for guiding sheets, are provided between the nip portions of the first roller pair and the second roller pair, and the distance between the nip portions is as follows. It is 25 mm.

  The first upper rollers 104, 204, 304 and the second upper rollers 106, 206, 306 have bearings (not fixed) on both ends of the roller shafts 104 a, 106 a, 204 a, 206 a, 304 a, 306 a on the upper plates 119, 219, 319. (Shown).

  The first lower rollers 105, 205, and 305 are supported at both ends of the roller shafts 105a, 205a, and 305a on the pressure plate 112 via bearings (not shown). The first lower rollers 105, 205, and 305 are urged by first pressure springs 109, 209, and 309 between the pressure plate 112 and a bearing (not shown). Thus, the first lower rollers 105, 205, and 305 are pressed against the first upper rollers 104, 204, and 304 to form first nip portions N11, N12, and N13 that are first nip portions. Yes. In the present embodiment, the urging forces of the first pressure springs 109, 209, and 309 are set so that the applied pressure is about 39 N (4 kgf).

  The second lower rollers 107, 207, and 307 are supported at both ends of the roller shafts 107a, 207a, and 307a by the pressure plate 112 via bearings (not shown). The second lower rollers 107, 207, and 307 are urged by the second pressure springs 108, 208, and 308 between the pressure plate 112 and a bearing (not shown). Thus, the second lower rollers 107, 207, and 307 are pressed against the second upper rollers 106, 206, and 306, thereby forming second nip portions N21, N22, and N23 that are second nip portions. Yes. In this embodiment, the urging forces of the second pressure springs 108, 208, and 308 are set so that the applied pressure is about 39 N (4 kgf).

<Description of drive>
Here, the driving of the first upper rollers 104, 204, 304 and the second upper rollers 106, 206, 306 will be described with reference to FIGS. 6 and 7 are a perspective view and a side view for explaining the driving of the first upper rollers 104, 204, 304 and the second upper rollers 106, 206, 306, respectively.

  The driving of the sheet pulling and conveying apparatus 101 alone will be described with reference to FIG. FIG. 8 is a perspective view illustrating driving of the first upper roller 104 and the second upper roller 106 included in the sheet pulling and conveying apparatus 101. The sheet pulling and conveying apparatuses 201 and 301 have the same configuration as that of the sheet pulling and conveying apparatus 101, and the description of the drive configuration for both is omitted.

<Regarding driving of a plurality of tensile conveyance devices>
The first upper rollers 104, 204, 304 and the second upper rollers 106, 206, 306 are rotated by receiving a rotational driving force from the motor gears MG1, MG2, MG3 of the driving motors M1, M2, M3 which are driving sources. . The first upper rollers 104, 204, 304 are a drive transmission gear 123, a clutch gear CLG1, a drive transmission gear 124, 125, 104G1, a drive transmission gear 223, a clutch gear CLG2, a drive transmission gear 224, 225, 204G1, a drive transmission gear. 323 is rotated by receiving a rotational driving force through the clutch gear CLG3, the drive transmission gears 324, 325, and 304G1. The second upper rollers 106, 206, and 306 are rotated by receiving a rotational driving force via the drive transmission gears 123, 127, 128, 129, 223, 227, 228, 229, 323, 327, 328, and 329. .

  The first lower rollers 105, 205, 305 and the second lower rollers 107, 207, 307 are pressed against the first upper rollers 104, 204, 304 and the second upper rollers 106, 206, 306, respectively. The first lower rollers 105, 205, 305 and the second lower rollers 107, 207, 307 rotate in accordance with the rotation of the first upper rollers 104, 204, 304 and the second upper rollers 106, 206, 306, respectively.

  Further, as shown in FIG. 7, the drive gears 104G2, 204G2, and 304G2 are fixed to the other ends of the first upper rollers 104, 204, and 304, and the drive transmission gears 130, 230, and 330 are connected to each other. The torque limiters 131, 231 and 331 are connected. Here, the torque limiters 131, 231 and 331 are only required to apply a driving load to the first upper rollers 104, 204 and 304, and may be load means such as an electromagnetic brake and a brake pad. In the present embodiment, when the same sheet P exists in both the first nip portions N11, N12, and N13 and the second nip portions N21, N22, and N23, the tension applied to the sheet P is about 68 N (7 kgf). The set value of the torque limiter is set as follows. The set values of the torque limiters 131, 231 and 331 are set in a range in which a sufficient tension is applied to the sheet P and no damage is given to the sheet P itself.

<Clutch mechanism>
FIG. 8 is a perspective view illustrating driving of the first upper roller 104 and the second upper roller 106. Note that the CPU (see FIG. 3) as the control means is driven by the electromagnetic clutch CL1 (CL2, CL3) as the clutch means (drive control means) and the drive as the drive means according to the signal of the sheet sensor 103 (203, 203). The operation of the motor M1 (M2, M3) is controlled.

  As shown in FIG. 8, the driving gear 104G1 and the driving gear 106G are held and fixed at one end of the first upper roller 104 and the second upper roller 106. The first upper roller 104 is rotated by the motor gear MG1 of the drive motor M1, which is a drive source, by receiving rotational driving via the drive transmission gear 123, the clutch gear CLG1, the drive transmission gear 125, and the drive gear 104G1. . The second upper roller 106 is rotated by receiving rotational driving via the drive transmission gears 127, 128, and 106G by the motor gear MG1 of the driving motor M1 that is a driving source. The first lower roller 105 and the second lower roller 107 pressed by the first upper roller 104 and the second upper roller 106 are rotated by the rotation of the first upper roller 104 and the second upper roller 106.

  The clutch gear CLG1 is fixed to the electromagnetic clutch CL1. By energizing the electromagnetic clutch CL1, the driving force between the clutch gear CLG1 and the drive transmission gear 123 is transmitted through the clutch shaft 132, and the first upper roller 104 rotates. On the other hand, if the electromagnetic clutch CL1 is not energized, the driving force between the clutch gear CLG1 and the drive transmission gear 123 is not transmitted, the driving force of the driving motor M1 is not transmitted to the driving 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. A drive transmission gear (drive transmission member) 130 is connected to load means 131 such as a torque limiter and an electromagnetic brake.

<Multiple arrangement of tension conveying device>
Hereinafter, the relationship between at least two sheet pulling and conveying apparatuses (101, 201, 301) will be described. In this embodiment, as at least two sheet pulling and conveying apparatuses, as shown in FIG. 1, three sheet pulling and conveying apparatuses 101, 201, and 301 are provided in the sheet conveying direction in the vertical direction (gravity direction, vertical direction). Is illustrated.

  The reason why at least two sheet pulling and conveying devices are provided is to sufficiently obtain the tensile effect in the conveying direction of the sheet P. The tensile effect of the sheet P increases the tension between the first nip portion N11 and the second nip portion N21, between the first nip portion N12 and the second nip portion N22, and between the first nip portion N13 and the second nip portion N23. It can also be increased by making it. However, if this tension (tensile force in the sheet conveyance direction) is excessively increased and a stress is applied to the sheet P suddenly, damage to the sheet P may increase and the quality of the product may deteriorate. This is because, as the speed of the apparatus increases in recent years, the time for the sheet to pass through the sheet pulling and conveying apparatus is shortened. Therefore, if the tensile force is increased and a sudden tensile force is applied to the sheet, a large stress is applied to the sheet. This is because there is a possibility of damaging it.

  Further, since the load for the second upper roller 206 to be pulled out from the first nip portion N11 becomes large, slip occurs in the second nip portion N21, resulting in variations in the tensile effect of the sheet P and variations in the conveyance speed. There is a possibility that. Therefore, by providing at least two sheet pulling and conveying devices and pulling the sheet P stepwise, a tensile effect can be imparted to the sheet P without these problems. In the present embodiment, for example, if a tension of 98 N (10 kgf) or more is applied, the damage to the sheet P is increased, and the quality of the product is deteriorated. Therefore, the tension setting values of the torque limiters 131, 231 and 331 are set to about 68 N (7 kgf), and a plurality of sheet pulling and conveying apparatuses 101, 201 and 301 are provided.

  Further, the sheet P discharged from the fixing device 100 or the sheet pulling and conveying devices 101 and 201 upstream in the conveying direction has different directions and amounts of curl depending on the basis weight, stiffness, moisture amount, image pattern, environmental state, etc. of the sheet P. Arise. In particular, curl is likely to occur in the weak sheet P. On the other hand, the first sheet pulling / conveying device 101, the second sheet pulling / conveying device 201, and the third sheet pulling / conveying device 301 are respectively the first sheet pulling / conveying device 101, the second sheet pulling / conveying device 201, The third sheet pulling and conveying device 301 is arranged in this order. The sheet P is conveyed in the order of the first sheet pulling and conveying apparatus 101, the second sheet pulling and conveying apparatus 201, and the third sheet pulling and conveying apparatus 301. Further, a straight line connecting the first nip portion N11 and the second nip portion N21 of the first sheet pulling and conveying device 101, and a straight line connecting the first nip portion N12 and the second nip portion N22 of the second sheet pulling and conveying device 201. The sheet pulling and conveying devices are arranged so that the straight line connecting the first nip portion N13 and the second nip portion N23 of the third sheet pulling and conveying device 301 is substantially on the same straight line. Thereby, since the sheet P is conveyed in the direction of gravity, even when a plurality of sheet pulling and conveying apparatuses are provided, the sheet pulling and conveying apparatuses 101, 201, and 301 are not affected by curl. Stable delivery is possible.

  In addition, with the above arrangement, the sheet is bent by a guide or the like between the plurality of sheet pulling and conveying apparatuses 101, 201, and 301, the sheet receives stress from the guide, and the curling of the sheet increases. It can prevent damage on the image.

<Problems to switch by basis weight>
As described above, the plurality of sheet pulling and conveying apparatuses are provided in order to sufficiently obtain the tensile effect of the sheet P. The tension applied to the sheet P by each sheet pulling and conveying device is set to a tension setting value of the torque limiters 131, 231 and 331 of about 68 N (7 kgf) so that the sheet P is not damaged. 201 and 301 are provided.

  However, when the sheet pulling / conveying device is passed through a plurality of times, depending on the paper physical properties of the sheet P, there arises a problem that the sheet length in the vicinity of the center portion of the sheet P extends in the transport direction more than the vicinity of the end portion. . An example is shown below.

<Measurement method of undulation>
FIG. 14 illustrates the curl generated in the sheet P, the features of the edge corrugation shape, and the measurement method. The sheet P that has passed through only the nip portion N of the fixing device 100 is placed on a measurement surface plate 650 shown in FIG. Alternatively, after passing through the nip portion N of the fixing device 100, the sheet that has passed through the first sheet pulling and conveying device 101, the second sheet pulling and conveying device 201, and the third sheet pulling and conveying device 301 as shown in FIG. P is placed on a measuring platen 650 shown in FIG. Here, the edge length 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. 14, that is, the end in the width direction orthogonal to the conveying direction is referred to as end undulation, and among them, the gap between the measurement platen 650 and the gap is measured. The maximum value Xmax was used as the object of evaluation as the amount of undulations. Further, the maximum Y max among the distances from the measuring platen 650 at the four corner ends of the sheet P was set as the object of evaluation as the maximum curl amount.

<Relationship between number of pulls and elongation at center>
FIG. 15 shows the results of basic experiments in which the first sheet pulling and conveying apparatus 101 in the present example performed by the present inventors was used to measure the number of pulls and the change in sheet length at the center and end of the sheet P. Show.

  FIG. 15A and FIG. 15B show experimental results for plain paper having a basis weight of 81 gsm and 157 gsm of plain paper, respectively. The tension applied to the sheet P by the first sheet pulling and conveying apparatus 101 was 68 N (7 kgf).

  Regarding the measurement of the sheet length of the sheet P, specifically, the left and right end lengths L edge [mm] of the sheet P shown in FIG. 14 at both ends: L edge (R), L edge (L), and the center length This is a result of measuring L center [mm].

  In addition, when the sheet humidifying apparatus 400 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 sheet moisture content in this example was measured by the present inventors using the sheet P immediately after the sheet P passed through the sheet wavy correction device 900 and was discharged onto the discharge tray 565. In this example, a microwave paper moisture meter was used.

  Each measurement data will be described. The length immediately after passing the fixing device 100 is indicated by “before countermeasure” of a two-dot chain line. Further, the result when only the first sheet pulling / conveying apparatus 101 is passed is indicated by “one time” indicated by an alternate long and short dash line, and the result when the first sheet pulling / conveying apparatus 101 is passed twice is indicated by “2 times” indicated by a solid line. ”, The result when the first sheet pulling and conveying apparatus 101 is passed three times is indicated by the dotted line“ 3 times ”.

  As shown in FIGS. 15 (a) and 15 (b), for the plain paper having a basis weight of 81 gsm and 157 gsm of plain paper, fixing as shown by the two-dot chain line (before countermeasures) graphs, respectively. In the paper immediately after passing through the apparatus 100, the end portion of the sheet P is longer than the central portion. In the drawing, L edge (R) and L edge (L) are end portions of the sheet P, and L center is a central portion of the sheet P. With respect to plain paper having a basis weight of 81 gsm and plain paper having 157 gsm, the end portions of the sheet P are longer by 0.6 mm and 0.5 mm than the center portion. This is because, in the case of the fixing device having the wide nip as described above, the end portion in the sheet width direction extends in the transport direction from the vicinity of the center after the nip is discharged. In a fixing device having a wide nip, in order to prevent sheet wrinkling as the sheet passes through the nip, the conveying speed on the edge side from the center in the sheet width direction is set higher in the nip to give the sheet a squeezing action. Yes. For this reason, in the case of a fixing device having a wide nip, the end in the sheet width direction extends in the transport direction from the vicinity of the center after the nip is discharged.

  First, the result of 157 gsm plain paper will be described with reference to FIG. According to the number of times of passing the sheet pulling and conveying apparatus 101 shown in the present embodiment, the central portion is 0.2 mm in the order of “one time” of the alternate long and short dash line, “two times” of the solid line, “three times” of the dotted line, It extends by 0.2mm and 0.1mm. From this result, it is understood that it is necessary to pull the sheet P three times in order to apply the above-described tensile force (tension) to the sheet P and correct the difference in sheet length between the central portion and the end portion of the sheet.

  Next, the result of 81 gsm plain paper will be described with reference to FIG. According to the number of times of passing the sheet pulling and conveying apparatus 101 shown in the present embodiment, the central portion is 0.3 mm in order of “one time” indicated by a one-dot chain line, “two times” indicated by a solid line, and “three times” indicated by a dotted line. It is growing. From this result, it is possible to extend the center portion of the sheet and correct the difference between the end portion and the center portion of the sheet P. As indicated by the solid line “twice” result, when the tension force is applied to the sheet P twice by the sheet pulling and conveying apparatus (101, 201, 301), the lengths of the end portion and the central portion of the sheet P are shown. Can be corrected to 0 mm.

  However, the length of the vicinity of the central portion of the sheet P exceeds the length of the end portion from the result of “three times” when the sheet pulling and conveying apparatus 101, 201, 301 is passed. From this result, when the above-described tensile force (tension) is applied to 81 gsm plain paper and pulled three times in the same manner as 157 gsm plain paper, the problem arises that the correction amount near the center of the sheet P is exceeded. .

  As described above, when a plurality of sheets are arranged on the sheet P as in the sheet pulling and conveying apparatuses 101, 201, and 301, if the number of pulls is not controlled according to the paper type, the correction amount near the center of the sheet P is exceeded. The problem of end up occurs.

  As a countermeasure against this, the application of tension to the sheet P by the sheet pulling and conveying apparatuses 101, 201, 301 is switched according to the information on the sheet P.

  In the present embodiment, the basis weight of the sheet P is used as information related to the sheet P (tension application switching information). Specifically, for a paper type in which the basis weight of the sheet P is greater than 90 gsm, the sheet pulling and conveying apparatuses 101, 201, and 301 apply tension to the sheet P three times to correct waviness. On the other hand, for a paper type of 90 gsm or less, the tension is applied twice only by the sheet pulling and conveying apparatuses 101 and 201, and the sheet pulling and conveying apparatus 301 is not applied with the tension, and the wavy is corrected. The drive control operation will be described below.

  Here, the paper type information of the sheet P in the feeding cassette 520 is input by the user using the operation panel 570 (see FIG. 2), and the control unit having the CPU and memory in the printer 500 shown in FIG. Sent to 500C. Alternatively, information relating to the sheet P may be detected by the detection sensor 500D installed on the upper side of the feeding cassette 520 in the printer 500, and the detection information may be sent to the control unit 500C having the CPU and memory. Alternatively, the sheet information may be input from an external computer connected to the printer 500. The operation panel, the detection sensor, and the external computer are an example of an acquisition unit that acquires information about the sheet.

<Flowchart>
Hereinafter, the drive control sequence of this embodiment will be described with reference to FIGS. 3, 9, and 10 to 13.

  In the following description, the basis weight of the sheet is exemplified as information regarding the sheet. Moreover, 90 gsm is illustrated as a basic weight of the sheet | seat P, 90 gsm or less is made into the 1st basic weight, and the basic weight larger than 90 gsm is made into the 2nd basic weight.

  FIG. 3 is a block diagram relating to drive control of the present embodiment. FIG. 9 shows a flowchart regarding drive control of this embodiment. 10 to 13 are front sectional views of the sheet pulling and conveying apparatuses 101 and 201 for explaining the drive control of this embodiment. Here, the sheet pulling / conveying device 301 operates in the same manner as the sheet pulling / conveying device 201, and thus the description thereof is omitted.

  FIG. 10 is a front cross-sectional view at time 0 to Xmsec after the sheet sensor 103 is turned on, and FIG. 11 is a front cross-sectional view at time Xmsec after the sheet sensor 103 is turned on. FIG. 12 is a front sectional view at time 0 to Ymsec after the sheet sensor 203 is turned on, and FIG. 13 is a front sectional view at time Ymsec after the sheet sensor 203 is turned on.

  After the paper passing job signal 51 is input to the CPU (control means) (S7-1), the paper type information (basis weight) of the sheet P is input to the CPU (control means) (S7-2), and the drive motor M1. , M2 and M3 are turned on (S7-3). The drive motors M1, M2, and M3 are V1> when the conveying speeds of the sheet pulling and conveying apparatuses 101, 102, and 103 are V1 [mm / s], V2 [mm / s], and V3 [mm / s], respectively. V2> V3 is set. A conveyance speed V1 [mm / s] of the first sheet pulling and conveying apparatus 101 is a rotation speed of the first upper roller 104 and the second upper roller 106. The conveyance speed V2 [mm / s] of the second sheet pulling and conveying apparatus 201 is the rotation speed of the first upper roller 204 and the second upper roller 206. The conveyance speed V3 [mm / s] of the third sheet pulling and conveying apparatus 301 is the rotation speed of the first upper roller 304 and the second upper roller 306. In this embodiment, the speed V2 is set 0.5% slower than the speed V1, and the speed V3 is set 0.5% slower than the speed V2, V1 = 300 mm / s, V2 = 298.5 mm / s, V3 = 297 mm. / S (S7-4). In the present embodiment, the conveying speeds V1, V2, and V3 are achieved by changing the rotational speeds of the drive motors M1 and M2 based on the reduction ratio of the drive gear.

  Immediately after the drive motors M1, M2, and M3 are turned on, the energization of the electromagnetic clutches CL1, CL2, and CL3 is also turned on, and paper feeding is started (S7-5). As a result, as described above, the driving force of the driving motors M1 and M2 is transmitted to the driving gears 104G1, 204G1, 304G1, 106G, 206G, and 306G via the driving transmission gear, so that the first upper roller 104 , 204, 304 and the second upper rollers 106, 206, 306 rotate.

  The control of the sheet pulling / conveying devices 101, 201, 301 is switched according to the paper type information of the sheet P input to the CPU (control means) (S7-6). Hereinafter, switching of control according to the basis weight of the sheet as the paper type information of the sheet P will be described.

  First, a case where the basis weight of the sheet P is a paper type greater than 90 gsm will be described.

  When the sheet P is guided to the inlet guides 102 and 121 in the first sheet pulling and conveying apparatus 101 and the ON signal of the sheet sensor 103 is confirmed (S7-7), the energization of the electromagnetic clutch CL1 is turned off after Xmsec (S7). -8). The value of X is the time from when the sheet sensor 103 is turned on until immediately after the leading edge of the sheet P is caught in the nip portion of the second roller pair of the first sheet pulling and conveying apparatus 101. The value of X is determined by the conveyance speed V1 of the sheet P of the first sheet pulling and conveying apparatus 101 and the distance from the sheet sensor 103 to the nip portion of the second roller pair. In the present embodiment, the conveyance speed V1 of the sheet P of the first sheet pulling and conveying apparatus 101 is 300 mm / s, and the distance from the sheet sensor 103 to the nip portion of the second roller pair is 45 mm. Therefore, X is set to 160 msec. doing.

  When the energization of the electromagnetic clutch CL1 is turned off Xmsec after the sheet sensor 103 is turned on, the driving of the first upper roller 104 is released. That is, as shown in FIG. 10, the electromagnetic clutch CL1 is in the ON state at 0 to Xmsec after the sheet sensor 103 is turned on, so that the first upper roller 104 is transported to convey the sheet P. . Thereafter, as shown in FIG. 11, at the Xmsec time point after the sheet sensor 103 is turned ON, the leading edge of the sheet P is immediately after reaching the nip portion of the second roller pair of the first sheet pulling and conveying apparatus 101, The sheet P is conveyed by driving the second upper roller 106. At the same time, the electromagnetic clutch CL1 is turned off and no driving force is transmitted to the first upper roller 104, so the first roller pair of the first sheet pulling and conveying apparatus 101 is driven to rotate. Since the first upper roller 104 is connected to the load means 131 via the drive gear 104G2 and the drive transmission gear 130, a torque load is generated to rotate the first upper roller 104. As a result, in FIG. 11, the sheet P is conveyed while a tension force (tension) is generated between the first roller pair and the second roller pair in the sheet P. In this embodiment, the load torque of the load means 131 is set so that the tension force applied to the sheet P is about 59 N (about 6 kgf).

  In this embodiment, as shown in FIG. 6, the nip portion between the first roller pair and the second roller pair of the first sheet pulling and conveying apparatus 101 is the central portion in the width direction orthogonal to the sheet conveying direction. The width (length L1) is 100 mm. Accordingly, the sheet P is configured to apply a tension force (tension) of about 59 N (about 6 kgf) from the front end to the rear end only at the center in the width direction.

  Thereafter, when the sheet P is guided to the inlet guides 202 and 221 in the second sheet pulling and conveying apparatus 201 and the ON signal of the sheet sensor 203 is confirmed (S7-9), the energization of the electromagnetic clutch CL2 is turned off after Ymsec. (S7-10). The value of Y is the time from when the sheet sensor 203 is turned on until immediately after the leading edge of the sheet P is caught in the nip portion of the second roller pair of the second sheet pulling and conveying apparatus 201. The value of Y is determined by the conveyance speed V2 of the sheet P of the second sheet pulling and conveying apparatus 201 and the distance from the sheet sensor 203 to the nip portion of the second roller pair. In this embodiment, since the conveyance speed V2 of the sheet P of the second sheet pulling and conveying apparatus 201 is 298.5 mm / s and the distance from the sheet sensor 203 to the nip portion of the second roller pair is 45 mm, Y = 161 msec. Is set.

  When the energization of the electromagnetic clutch CL2 is turned off Ymsec after the sheet sensor 203 is turned on, the driving of the first upper roller 204 is released. That is, as shown in FIG. 12, the electromagnetic clutch CL2 is in the ON state at 0 to Ymsec after the sheet sensor 203 is turned on, so that the first upper roller 204 is conveyed to convey the sheet P. . Thereafter, as shown in FIG. 13, at the time of Ymsec after the sheet sensor 203 is turned on, the leading edge of the sheet P is immediately after reaching the nip portion of the second roller pair of the second sheet pulling and conveying device 201, The sheet P is conveyed by driving the second upper roller 206. At the same time, the electromagnetic clutch CL2 is turned off, and the drive is not transmitted to the first upper roller 204, so that the first roller pair of the second sheet pulling and conveying apparatus 201 is driven to rotate. Since the first upper roller 204 is connected to the load means 231 via the drive gear 204G2 and the drive transmission gear 230, a torque load is generated to rotate the first upper roller 204. As a result, in FIG. 13, the sheet P is conveyed while a tension force (tension) is generated between the first roller pair and the second roller pair in the sheet P. In this embodiment, the load torque of the load means 231 is set so that the tension force applied to the sheet P of the second sheet pulling and conveying apparatus 201 is about 59 N (about 6 kgf).

  Further, in this embodiment, as shown in FIG. 6, the nip portion between the first roller pair and the second roller pair of the second sheet pulling and conveying apparatus 201 is the central portion in the width direction orthogonal to the sheet conveying direction. The width (length L1) is 100 mm. Accordingly, the sheet P is configured to apply a tension force (tension) of about 59 N (about 6 kgf) from the front end to the rear end only at the center in the width direction.

  Thereafter, the sheet P is guided to the inlet guides 302 and 321 in the third sheet pulling and conveying apparatus 301, and the third sheet pulling and conveying apparatus 301 is operated in the same manner as the second sheet pulling and conveying apparatus 201 described above (S7- 11, S7-12). In the present embodiment, the value of Z for turning off the energization of the electromagnetic clutch CL3 is a value corresponding to the conveyance speed V3 of the sheet P of the third sheet pulling and conveying apparatus 301 = 297 mm / s.

  Thereafter, when the sheet passing is finished, the drive motors M1, M2, and M3 are turned off (S7-13), and the process is finished (S7-14).

  On the other hand, the case where the basis weight of the sheet P is a paper type of 90 gsm or less will be described (S7-6).

  When a tension force (tension) is applied to the sheet P having a basis weight of 90 gsm or less by the sheet pulling / conveying apparatus 201 or 301 in addition to the sheet pulling / conveying apparatus 101, the correction amount near the center of the sheet P is exceeded. End up. As a countermeasure, tension is applied to the sheet P only by the sheet pulling / conveying device 101, and the sheet pulling / conveying devices 201 and 301 convey the sheet without applying tension.

  When the sheet P is guided to the entrance lower guide 121 in the first sheet pulling and conveying apparatus 101 and the ON signal of the sheet sensor 103 is confirmed (S7-15), the energization of the electromagnetic clutch CL1 is turned off after Xmsec (S7-). 16).

  As described above, since the energization of the electromagnetic clutch CL1 is turned off and the drive is not transmitted to the first upper roller 104, the first roller pair of the first sheet pulling and conveying apparatus 101 is driven to rotate. Since the first upper roller 104 is connected to the load means 131 via the drive gear 104G2 and the drive transmission gear 130, a torque load is generated to rotate the first upper roller 104. As a result, as shown in FIG. 11, the sheet P is conveyed while a tension force (tension) is generated between the first roller pair and the second roller pair on the sheet P.

  After that, when the sheet P is guided to the lower entrance guide 221 in the second sheet pulling and conveying apparatus 201 and the ON signal of the sheet sensor 203 is confirmed (S7-17), the energization of the electromagnetic clutch CL2 is turned OFF after Ymsec ( S7-18).

  As described above, since the energization of the electromagnetic clutch CL2 is turned off and the drive is not transmitted to the first upper roller 204, the first roller pair of the second sheet pulling and conveying apparatus 201 is driven to rotate. Since the first upper roller 204 is connected to the load means 231 via the drive gear 204G2 and the drive transmission gear 230, a torque load is generated to rotate the first upper roller 204. As a result, as shown in FIG. 13, the sheet P is conveyed while a tension force (tension) is generated between the first roller pair and the second roller pair on the sheet P.

  Thereafter, the sheet P discharged from the second sheet pulling and conveying apparatus 201 is conveyed to the third sheet pulling and conveying apparatus 301. In the third sheet pulling and conveying apparatus 301, the electromagnetic clutch CL3 remains in the ON state, and the driving force is transmitted to the first roller pair so that no load torque is applied to the first roller pair. For this reason, no tension force (tension) is applied to the sheet P, and the sheet P is conveyed and discharged from the third sheet pulling and conveying apparatus 301.

  Thereafter, when the sheet passing is finished, the drive motors M1, M2, and M3 are turned off (S7-13), and the process is finished (S7-14).

  Note that the above flow is repeated for the second and subsequent sheets.

<Results of study of this example>
FIGS. 16 and 17 show the results of the experiment for confirming the effect of the sheet pulling and conveying apparatuses 101, 201, and 301 on the sheet P having a basis weight of 81 gsm and 157 gsm, respectively.

  In FIG. 16A, the length L edge [mm] of the end portion of the sheet P in the state immediately after passing through the fixing device 100 and not passing through the first sheet pulling and conveying device 101 of this embodiment, and the center length L center [ mm]. Further, the maximum corrugation amount X max [mm] of the sheet P was measured. In FIG. 16B, the length L edge [edge] of the end of the sheet P in a state where the sheet P is tensioned and passed only by the sheet pulling and conveying apparatuses 101 and 201 of this embodiment after passing through the fixing device 100. mm] and the central length L center [mm]. Further, the maximum corrugation amount X max [mm] of the sheet P was measured.

  First, FIG. 16 is used to show the results of an effect confirmation experiment of the sheet pulling and conveying apparatuses 101, 201, and 301 for plain paper having a basis weight of the sheet P of 81 gsm.

  As shown in FIG. 16A, the elongation amount of the center length L center of the sheet P is 0 mm immediately after passing through the fixing device, whereas the elongation amount of the end length L edge is 0.6 mm. The end is longer than the center by 0.6 mm. This is because, in the case of the fixing device having the wide nip as described above, the end portion in the sheet width direction extends in the transport direction from the vicinity of the center after the nip is discharged. In the case of a fixing device equipped with a wide nip, in order to prevent sheet wrinkling as the sheet passes through the nip, the feeding speed on the edge side is set higher than the central portion in the sheet width direction in the nip to act on the sheet. Is given. For this reason, in the case of a fixing device having a wide nip, the end in the sheet width direction extends in the transport direction from the vicinity of the center after the nip is discharged.

  On the other hand, as shown in FIG. 16B, after passing through the fixing device (passing paper at 300 mm / s), the first sheet pulling and conveying device 101 (passing paper at 300 mm / s) and the second sheet pulling and conveying device 201 of this embodiment. Pass the paper in the order of (passing paper at 298.5 mm / s). In this case, the extension amount of the center length L center immediately after passing through the third sheet pulling and conveying apparatus 301 is 0.6 mm. On the other hand, the extension amount of the end portion length L edge is 0.6 mm, and the difference between the end portion and the center length is 0 mm. That is, the first sheet pulling / conveying apparatus 101 and the second sheet pulling / conveying apparatus 201 pass the paper in the conveying direction, and as a result, the difference between the end and the center is reduced. As a result, the difference in sheet length between the end and the center is reduced, so that the maximum undulation amount is from 3.3 mm as shown in FIG. 16 (a), and 1. as shown in FIG. 16 (b). Improved to 0 mm.

  Next, using FIG. 17, results of an effect confirmation experiment of the sheet pulling and conveying apparatuses 101, 201, and 301 for plain paper having a basis weight of the sheet P of 157 gsm are shown.

  As shown in FIG. 17A, immediately after passing through the fixing device, the elongation amount of the center length L center of the sheet P is 0 mm, whereas the elongation amount of the end length L edge is 0.5 mm. The end is longer than the center by 0.5 mm.

  On the other hand, as shown in FIG. 17B, after passing through the fixing device, the first sheet pulling / conveying device 101, the second sheet pulling / conveying device 201, and the third sheet pulling / conveying device 301 are passed in this order. Here, the fixing device passes the paper at 300 mm / s. In the first sheet pulling and conveying apparatus 101 of this embodiment, the sheet is passed at 300 mm / s, in the second sheet pulling and conveying apparatus 201, the sheet is passed at 298.5 mm / s, and in the third sheet pulling and conveying apparatus 301, 297.0 mm / s. Pass through s. In this case, the elongation amount of the center length L center immediately after passing through the third sheet pulling and conveying apparatus 301 is 0.5 mm. On the other hand, the extension amount of the end portion length L edge is 0.5 mm, and the difference between the end portion and the center length is 0 mm. That is, the first sheet pulling / conveying device 101, the second sheet pulling / conveying device 201, and the third sheet pulling / conveying device 301 pass the paper in the conveying direction, and as a result, the difference between the end portion and the center became small. As a result, the difference in the sheet length between the end and the center is reduced, so that the maximum undulation amount is improved from 5 mm as shown in FIG. 17 (a) to 1mm as shown in FIG. 17 (b). .

  As described above, the sheet P is conveyed to a plurality of sheet tension conveyance devices of the first sheet tension conveyance device 101, the second sheet tension conveyance device 201, and the third sheet tension conveyance device 301, whereby the tensile effect of the sheet P is increased. Give enough. As a result, the difference in sheet length between the end and the center was reduced, and the waviness could be improved.

<Effect of this embodiment>
As described above, according to this embodiment, by providing a plurality of sheet pulling and conveying devices, it is possible to control the number of tensions at a time without adding a sudden tension to the sheet at once, and to apply tension in stages. Can be added. In addition, the operations of the plurality of sheet pulling apparatuses can be switched according to the paper type of the sheet P.

  As a result, damage to the sheet P due to sudden tension application can be suppressed. In addition, the number of pulls in the vicinity of the center of the sheet P can be controlled according to the paper type information relating to the sheet, and the amount for correcting the difference in length from the vicinity of the end can be controlled. As a result, the waviness of the sheet P can be improved according to the paper type while minimizing the stress on the sheet P.

[Example 2]
<Description of a configuration in which the conveyance roller width in each tensile conveyance device is different>
Next, an image forming apparatus including the sheet conveying apparatus according to the second embodiment will be described. The second embodiment differs from the plurality of sheet pulling and conveying apparatuses of the first embodiment in the following points.

  In the first embodiment described above, as shown in FIG. 6, the elastic rubbers 105 b and 107 b of the first lower rollers 105, 205 and 305 and the second lower rollers 107, 207 and 307 in the sheet pulling and conveying apparatuses 101, 201 and 301 are used. , 205b, 207b, 305b, and 307b are uniformly formed in the region of the length L1 of the central portion in the width direction of the sheet so as to be uniform with respect to the sheet passing center (width direction center).

  On the other hand, in the present embodiment, as shown in FIG. 18, the elastic rubbers 105b, 107b, 205b, 207b, 305b, 307b of the first lower rollers 105, 205, 305 and the second lower rollers 107, 207, 307 are passed through. The lengths of the central portions in the width direction of the sheet are formed in different regions L1, L2, and L3 so as to be even with respect to the paper center (width direction center). Here, the case where the relationship between the lengths L1, L2, and L3 of the central portion in the sheet width direction is L1 <L2 <L3 is illustrated. That is, the length in the width direction of the first nip portion and the second nip portion of the downstream sheet pulling and conveying device in the sheet conveying direction is the same as that of the first nip portion and the first nip portion of the upstream sheet pulling and conveying device. The relationship is longer than the length of the nip portion 2 in the width direction. For example, when the upstream side is the sheet pulling and conveying apparatus 101, the downstream side is the sheet pulling and conveying apparatus 201, and when the upstream side is the sheet pulling and conveying apparatus 201, the downstream side is the sheet pulling and conveying apparatus 301, and each nip portion Is the above relationship.

  In this embodiment, the first lower rollers 105, 205, 305 and the second lower rollers 107, 207, 307 incorporated in the sheet pulling and conveying apparatuses 101, 201, 301 will be described. The driving configuration of the sheet pulling and conveying apparatuses 101, 201, and 301 and the configuration with the image forming apparatus main body are the same as those in the first embodiment, and thus the description regarding the configuration and operation is omitted.

<Problem with constant transport roller width in each tension transport device>
FIG. 19 is a result showing the amount of tension applied to the sheet P when the sheet P is nipped and conveyed by the first roller pair and the second roller pair in the sheet pulling and conveying apparatus 101. In the sheet pulling and conveying apparatus 101, the first upper roller 104 and the first lower roller 105 constitute a first roller pair, and the second upper roller 106 and the second lower roller 107 constitute a second roller pair.

  As shown in FIG. 6, the elastic rubber 105b, 107b, 205b, 207b, 305b, 307b of the first lower rollers 105, 205, 305 and the second lower rollers 107, 207, 307 in the sheet pulling and conveying apparatuses 101, 201, 301 are provided. The lengths of the central part in the sheet width direction are configured with the same length L1. In this case, there is a possibility that the tension is always applied to the vicinity of the end of the length P1 in the sheet width direction in the sheet P by the sheet pulling and conveying apparatuses 101, 201, and 301, and the sheet P may be damaged.

  Accordingly, in this embodiment, in order to solve the above problem, as shown in FIG. 18, the first lower rollers 105, 205, 305, the second lower rollers 107, 207, The elastic rubbers 105b, 107b, 205b, 207b, 305b, 307b of 307 have different lengths at the center in the width direction of the sheet so as to be even with respect to the sheet passing center (width direction center), L1, It forms in the area | region of L2 and L3.

  The length L1 is shorter than the sheet width of the sheet P in which undulation shown in FIG. In this embodiment, L1 = 100 mm, L2 = 110 mm, and L3 = 120 mm are set (L1 <L2 <L3). The lengths L1, L2, and L3 are shorter than the length in the width direction (sheet width) of the sheet P having a predetermined size, and are not limited to the above. Here, the length in the width direction of the sheet P compared with the lengths L1, L2, and L3 is the length in the width direction of the sheet of a predetermined size. Here, the sheet of the predetermined size is shown in FIG. The sheet P in which the wavy shown in FIG. The sheet of a predetermined size is a sheet of a size that is frequently used by the apparatus. For example, an A3 size sheet (297 mm) corresponds to this.

<Effects of configurations with different conveying roller widths in each tensile conveying device>
FIG. 20 shows a tension distribution applied to the sheet P when the sheet P is pulled and conveyed by a roller having elastic rubber having different lengths at the center in the width direction of the sheet shown in FIG. In the present embodiment, as described above, the first lower rollers 105, 205, and 305 and the second lower rollers 107, 207, and 307 included in the tensile conveyance devices 101, 102, and 103 have a long central portion in the sheet width direction. Elastic rubbers 105b, 107b, 205b, 207b, 305b, and 307b of L1, L2, and L3 having different lengths are formed.

  The tension distribution by the first lower roller 105 and the second lower roller 107 having a roller width of length L1 in the sheet pulling and conveying apparatus 101 is indicated by a solid line. A tension distribution by the first lower roller 205 and the second lower roller 207 having a roller width of L2 in the sheet pulling and conveying apparatus 201 is indicated by a one-dot chain line. A tension distribution by the first lower roller 305 and the second lower roller 307 having the L3 roller width in the sheet pulling and conveying apparatus 301 is indicated by a two-dot chain line.

  As shown in FIG. 20, the peak of tension applied to the sheet P by the sheet pulling and conveying apparatuses 101, 201, and 301 can be dispersed in the vicinity of each end of the L1, L2, and L3 regions having different lengths. Accordingly, the tension is always applied to the sheet P in the vicinity of the roller width L1 in the sheet pulling and conveying apparatuses 101, 201, and 301 shown in FIGS. 6 and 18, and damage to the sheet P can be suppressed.

<Effect of this embodiment>
The effect of the present embodiment will be described with reference to FIG.

  21A shows elastic rubbers 105b, 107b, 205b of the first lower rollers 105, 205, 305 and second lower rollers 107, 207, 307 in the sheet pulling and conveying apparatuses 101, 201, 301 shown in FIG. FIG. 6 is a diagram schematically showing a relationship between a change in shape of a sheet P and a tension distribution with respect to the sheet P when the lengths of the central portions in the sheet width direction of 207b, 305b, and 307b are both L1. Regarding the sheet P, a shape indicated by a dotted line is a target shape obtained by correcting the length of the sheet at the center and the end in the width direction.

  On the other hand, FIG. 21B shows the elasticity of the first lower rollers 105, 205, 305 and the second lower rollers 107, 207, 307 in the sheet pulling and conveying apparatuses 101, 201, 301 according to the present embodiment shown in FIG. The relationship between the shape change of the sheet P and the tension distribution with respect to the sheet P when the lengths of the central portions of the rubbers 105b, 107b, 205b, 207b, 305b, and 307b are L1, L2, and L3, respectively. It is the figure shown typically.

  As shown in the tension distribution for the sheet P in FIG. 21A, the sheet P that has a peak near the end of the roller width L1 and is tension-conveyed by the tension has a remarkable elongation near the end of the L1, and the target There is a deviation from the dotted line shape.

  On the other hand, as shown by the tension distribution on the sheet P in FIG. 21B, the tension peaks applied to the sheet P by the sheet pulling and conveying apparatuses 101, 201, and 301 in FIG. 20 are L1, L2, and L3 having different lengths. It can be dispersed near each end of the region. The sheet P pulled and conveyed by the tension can be corrected to a dotted line shape which is a target shape.

  With the above configuration, the results regarding the length of the sheet when the central portion of the sheet P is pulled and conveyed are the same as those in the first embodiment, and are omitted.

  As described above, also in this embodiment, it is possible to improve the undulation of the sheet P according to the paper type while minimizing the stress on the sheet P.

Example 3
<Tension conveyance device is built in the main body of the image forming apparatus and has a horizontal path>
Next, an image forming apparatus including the sheet conveying apparatus according to the third embodiment will be described. In the third embodiment, the plurality of sheet pulling and conveying apparatuses are arranged in the vertical direction (gravity direction, vertical direction) in the above-described first embodiment, whereas the plurality of sheet pulling and conveying apparatuses are arranged in the lateral direction (direction intersecting the vertical direction). ) Is different. In this embodiment, an image forming system in which the sheet conveying apparatus is integrated into the image forming apparatus will be described. However, as in the above-described embodiment, the sheet conveying apparatus is connected to the outside of the image forming apparatus. The present invention is effective even with an image forming system configuration. In the description of the third embodiment below, the description of the configuration and operation common to the first embodiment will be omitted as appropriate.

  FIG. 22 is a schematic sectional view of an image forming apparatus in which the sheet conveying apparatus according to the third embodiment is integrated. The configuration of the image forming apparatus according to the present embodiment is substantially the same as the configuration described with reference to FIG. 2 in the above-described first embodiment, and therefore, members having the same functions are denoted by the same reference numerals and detailed here. Description is omitted.

  Hereinafter, the sheet conveying apparatus integrally incorporated in the image forming apparatus shown in FIG. 22 will be described with reference to FIG. In this embodiment, the sheet conveying apparatus has two sheet pulling and conveying apparatuses as a plurality of tension applying apparatuses, and two sheet pulling and conveying apparatuses are arranged in the lateral direction downstream of the fixing apparatus 100 in the conveying direction. Yes. Regarding the sheet pulling and conveying apparatuses 101 and 201, the configuration in which tension is applied to the sheet P by the two pairs of rollers is the same as that in the first embodiment, and thus the description thereof is omitted.

  Also in this embodiment, as in the above-described embodiments, by providing a plurality of sheet pulling and conveying devices, it is possible to control the number of pulling steps step by step without adding a sudden tension to the sheet at once. Tension can be added. In addition, the operations of the plurality of sheet pulling apparatuses can be switched according to the paper type of the sheet P.

  As a result, damage to the sheet P due to sudden tension application can be suppressed. In addition, the number of pulls in the vicinity of the center of the sheet P can be controlled according to the paper type information relating to the sheet, and the amount for correcting the difference in length from the vicinity of the end can be controlled. As a result, the waviness of the sheet P can be improved according to the paper type while minimizing the stress on the sheet P.

<Other Example 1>
<Tension roller crown>
In the above-described embodiment, the widths of the elastic rubbers 105b and 107b of the first lower roller 105 and the second lower roller 107 of the first sheet pulling and conveying apparatus 101 are set to 100 mm. However, the present invention is not limited to this. The outer diameter of at least one of the first roller pair and the second roller pair constituting the sheet pulling and conveying device may be configured so that the central portion in the rotation axis direction is larger than the end portion in the rotation axis direction. .

  Specifically, for example, as shown in FIG. 24, the length in the width direction of the elastic rubber 1105b, 1107b of the first lower roller 1105 and the second lower roller 1107 is longer than the length in the width direction of the maximum sheet. Also good. Alternatively, the outer diameters of the elastic rubbers 1105b and 1107b of the first lower roller 1105 and the second lower roller 1107 may be D2, and the outer diameters of both ends may be D1 and D3 smaller than D2 (D2> D1, D3). In FIG. 24, D2 = 25 mm, D1, and D3 = 24.7 mm. The width of D2 has a straight shape only at the central portion of 100 mm, and the outer diameter decreases from the tapered shape toward the end portion.

  As a result, the conveyance speed of the sheet P (rotational speed of the roller) is faster in the central portion in the width direction than in the end portion, and the nip pressure in the central portion is increased, so that a tension force is applied to the central portion of the sheet. Thus, as in the above-described embodiment, by pulling the sheet central portion in the conveying direction, the difference in sheet length between the end portion and the center can be reduced and undulation can be improved. In FIG. 24, the outer diameter shape of the roller is tapered, but the outer diameter shape may be a crown shape having a parabolic shape. 25 may be used in the second sheet pulling and conveying apparatus 201.

<Other Example 2>
In the above-described embodiment, a configuration in which two sheet pulling and conveying apparatuses (101, 201) are connected and passed as a plurality of conveying units of the sheet conveying apparatus is illustrated, but the present invention is not limited thereto. It is not a thing. In order to lengthen the sheet center pulling time, three or more sheet pulling / conveying apparatuses may be connected to pass the sheet.

<Other Example 3>
In the first embodiment described above, a configuration in which three sheet pulling and conveying apparatuses (101, 201, and 301) are connected and passed as a plurality of conveying units included in the sheet conveying apparatus is illustrated. It is not limited.

  As shown in FIG. 24, a configuration may be adopted in which two are arranged by combining the tension conditions of a plurality of sheet tension conveying devices.

  Further, as tension conditions for the sheet P, the tension setting values of the torque limiters 131, 231 and 331 of each sheet pulling and conveying apparatus are made uniform, but may be set individually by each sheet pulling and conveying apparatus.

  In addition, the basis weight of the sheet P is used as the sheet type information of the sheet P as the switching condition of the plurality of sheet pulling and conveying apparatuses, but the sheet type of the sheet P (plain paper, presence or absence of a coating layer) Image information and the moisture content of the sheet may be used.

<Other Example 4>
In the above-described embodiment, the configuration in which a plurality of sheet pulling and conveying apparatuses are connected in the lateral direction is exemplified in the sheet conveying apparatus integrally included in the image forming apparatus, but the present invention is not limited to this. In the sheet conveying apparatus integrally included in the image forming apparatus, a plurality of sheet pulling and conveying apparatuses may be connected in the vertical direction (gravity direction, vertical direction). Further, in the sheet conveying apparatus that is detachable as an optional external apparatus with respect to the image forming apparatus, the configuration in which a plurality of sheet pulling and conveying apparatuses are coupled in the vertical direction (gravity direction, vertical direction) is exemplified, but the present invention is not limited thereto. It is not a thing. In a sheet conveying apparatus that is detachable as an optional external apparatus with respect to the image forming apparatus, a plurality of sheet pulling and conveying apparatuses may be coupled in the lateral direction. Further, it is sufficient that at least two sheet pulling / conveying apparatuses as a plurality of conveying units are arranged side by side, or two sheet pulling / conveying apparatuses are arranged in the sheet conveying direction, or three or more sheet pulling / conveying apparatuses are arranged in a sheet. The arrangement may be arranged in the transport direction. Any configuration may be used as long as the load torque by the load means of at least one of the transport units is switched. By applying the present invention to such a sheet conveying apparatus, the same effect can be obtained as the entire image forming system.

<Other Example 5>
Further, although the configuration in which the operation of the sheet pulling and conveying apparatus is controlled by the control unit included in the image forming apparatus is exemplified, the sheet pulling and conveying apparatus may include the control unit and the operation may be controlled by the control unit. Alternatively, the control unit included in the sheet pulling and conveying apparatus may be controlled by the control unit included in the image forming apparatus to control the operation of the sheet pulling and conveying apparatus. Even if comprised in this way, the same effect can be acquired.

<Other Example 6>
In the above-described embodiments, the 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. The image forming apparatus may be an image forming apparatus that uses a sheet carrier and sequentially transfers the toner images of the respective colors onto the sheet carried on the sheet carrier. The image forming apparatus or the sheet pulling and conveying apparatus included in the image forming apparatus The same effect can be obtained by applying the present invention.

CL1, CL2 ... Electromagnetic clutches CLG1, CLG2 ... Clutch gears M1, M2, M3 ... Drive motors MG1, MG2, MG3 ... Motor gears N11, N12, N13 ... First nip part N21, N22, N23 ... Second nip part P ... Sheet DESCRIPTION OF SYMBOLS 100 ... Fixing device 101,201,301 ... sheet tension conveyance apparatus 102,121,202,221,302,321 ... entrance guide 103,203 ... sheet sensor 104,204,304 ... first upper roller 104G1,204G1,104G2, 204G2, 304G2, 106G, 206G ... Drive gears 104a, 105a, 106a, 107a, 204a, 205a, 206a, 207a, 304a, 305a, 306a, 307a ... Roller shafts 104b, 105b, 106b, 107b, 204b, 205 , 206b, 207b, 304b, 305b, 306b, 307b ... elastic rubber 105, 205, 305 ... first lower rollers 106, 206, 306 ... second upper rollers 107, 207, 307 ... second lower rollers 108, 208, 308 ... second pressure springs 109, 209, 309 ... first pressure spring 110 ... fixing roller 111 ... pressure rollers 112,212,113,213 ... pressure plates 114,115,214,215,314,315 ... conveying guide 123,124,125,126,127,128,129,223,224,225,226,227,228,229,323,324,325,326,327,328,329,130,230,330 ... drive transmission Gears 131, 231 and 331 ... Torque limiter 400 ... Humidifier 400A ... Water storage unit 400B ... Water supply pump 400C ... Water supply pipe 400C1 ... Branching part 401, 402 ... Humidification roller pair 403,404 ... Scraping roller 407,408 ... Water supply roller 411,412 ... Water supply 414 ... Inlet guide 500 ... Printer 500C, 901C ... Control 501, 502, guides 503, 504, inlet roller pair 510, image forming unit 511, photosensitive drum 512, charging roller 513, laser scanner 514, developing device 515, primary transfer roller 520, feeding cassette 523, registration roller pair 531 ... Intermediate transfer belt 535 ... Secondary transfer roller 540 ... Discharge roller pair 565 ... Discharge tray 650 ... Surface plate for measurement 900 ... Sheet wavy correction device

Claims (13)

A first pair of rollers for nipping and conveying the sheet by the first nip portion;
A second roller pair that conveys the sheet conveyed by the first roller pair while being nipped by a second nip portion;
A conveying unit having a load unit that applies a load torque to the first roller pair after the leading edge of the sheet conveyed by the first roller pair reaches the second nip portion;
A sheet conveying apparatus, wherein at least two of the conveying units are arranged side by side in the sheet conveying direction.   Of the first nip portion or the second nip portion, the length of the narrower nip portion in the width direction perpendicular to the sheet conveyance direction is the first nip portion or the second nip portion of another conveyance unit. The sheet conveying apparatus according to claim 1, wherein a width of the narrower nip portion of the nip portions is different from a length in the width direction.   2. The width direction perpendicular to the sheet conveyance direction, wherein at least one of the first nip portion or the second nip portion is shorter than a length of a sheet having a predetermined size. The sheet conveying apparatus according to 2.   4. The sheet conveying apparatus according to claim 2, wherein the first nip portion and the second nip portion of each of the conveying units have the same length in the width direction. 5.   In the sheet conveying direction, the length in the width direction perpendicular to the sheet conveying direction of the first nip portion and the second nip portion of the conveying unit provided on the downstream side is a conveying unit provided on the upstream side. 5. The sheet conveying apparatus according to claim 1, wherein a length of the first nip portion and the second nip portion is longer than a length in the width direction.   The first nip portion and the second nip portion are provided in a region of a central portion of a sheet to be conveyed in a width direction orthogonal to the sheet conveying direction. The sheet conveying apparatus according to any one of 5.   The sheet conveying apparatus according to claim 1, wherein the load unit includes a torque limiter.   8. The sheet conveyance according to claim 1, wherein at least two of the conveyance units are provided side by side in the vertical direction, and convey the sheet from the upper side to the lower side in the vertical direction. apparatus.   8. The sheet conveying apparatus according to claim 1, wherein at least two of the conveying units are arranged side by side in a direction intersecting the vertical direction. 9.   10. The sheet conveying apparatus according to claim 1, wherein the conveying unit applies a tension in a conveying direction to a central region in a width direction perpendicular to the conveying direction of the sheet.   11. The outer diameter of at least one roller of the first roller pair and the second roller pair is larger in the central portion in the rotation axis direction than in the end portion in the rotation axis direction. Sheet transport device.   The humidifying means for imparting moisture to the sheet is provided, and the humidifying means is disposed upstream of the conveying unit in the sheet conveying direction. Sheet conveying device. An image forming unit for forming a toner image on a sheet;
A fixing unit that heats and fixes the toner image on the sheet formed by the image forming unit to the sheet;
The sheet conveying apparatus according to any one of claims 1 to 12, which conveys a sheet that has passed through the fixing unit.
An image forming apparatus comprising:

Images