Patent Publication Number: US-2011064501-A1

Title: Sheet-member transport device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-279640 filed Dec. 9, 2009. 
     BACKGROUND 
     The present invention relates to a sheet-member transport device and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a sheet-member transport device including an endless belt that is an endless band member formed by arranging fibers substantially in the form of a mesh, a surface at an outer periphery side of the endless belt being treated with surface processing so that the surface at the outer periphery side has a higher friction coefficient than a friction coefficient of a surface at an inner periphery side of the endless belt; and at least two rotary members, the endless belt being wound around the rotary members, the rotary members being rotated to move the endless belt around the two rotary members. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a perspective view showing a sheet-member transport device according to an exemplary embodiment of the invention; 
         FIG. 2  is a perspective view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 3  is a perspective view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 4  is a perspective view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 5  is a perspective view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 6  is a perspective view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIGS. 7A and 7B  are enlarged plan views each showing an endless belt used in the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 8  is a plan view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 9  is a perspective sectional view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 10  is a perspective sectional view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 11  is a perspective sectional view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 12  is a perspective sectional view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 13  is a perspective sectional view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 14  is a perspective view showing another sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 15  is a perspective view showing the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 16  is a table showing air volumes of a fan used in the sheet-member transport device according to the exemplary embodiment of the invention; 
         FIG. 17  is a side view showing the sheet-member transport devices according to the exemplary embodiment of the invention; 
         FIG. 18  is a schematic configuration diagram showing an image forming unit used in an image forming apparatus according to the exemplary embodiment of the invention; and 
         FIG. 19  is a schematic configuration diagram showing the image forming apparatus according to the exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Sheet-member transport devices and an image forming apparatus according to an exemplary embodiment of the present invention will be described below with reference to  FIGS. 1 to 19 . In the figures, arrow UP indicates upward in a vertical direction. 
     General Configuration 
     An image forming apparatus  10  according to the exemplary embodiment forms a full-color image or a monochrome image. Referring to  FIG. 19 , the image forming apparatus  10  includes a first housing  10 A and a second housing  10 B. The first housing  10 A houses a first processing unit that is a portion at one side in a horizontal direction (at a left side in  FIG. 19 ). The second housing  10 B is detachably connected with the first housing  10 A and houses a second processing unit that is a portion at the other side in the horizontal direction (at a right side in  FIG. 19 ). 
     An image signal processor  13  is provided in an upper portion of the second housing  10 B. The image signal processor  13  performs image processing on image data that is sent from an external device, such as a computer. 
     Toner cartridges  14 V,  14 W,  14 Y,  14 M,  14 C, and  14 K that respectively house toners of a first special color (V), a second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) are detachably provided in an upper portion of the first housing  10 A and arranged along the horizontal direction. 
     The first and second special colors may be selected from colors including a transparent color, except the yellow, magenta, cyan, and black. Also, in the following description, characters of V, W, Y, M, C, and K follow the reference numerals of components if the components for the first special color (V), second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) are distinguished. The characters V, W, Y, M, C, and K are omitted if the components for the first special color (V), second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) are not distinguished. 
     Six image forming units  16  are provided respectively below the toner cartridges  14  and arranged in the horizontal direction correspondingly to the toner cartridges  14 . 
     Optical scanning devices  40  are provided respectively for the image forming units  16 . The optical scanning devices  40  receive image data, on which the image processing has been performed by the image signal processor  13 , and irradiate image bearing members  18  (described later) with light beams L, which have been modulated in accordance with the image data (see  FIG. 18 ). 
     Referring to  FIG. 18 , each image forming unit  16  includes the image bearing member  18  that is rotationally driven in one direction (clockwise in  FIG. 18 ). When each optical scanning device  40  irradiates the corresponding image bearing member  18  with the light beam L, an electrostatic latent image is formed on the image bearing member  18 . 
     A scorotron charging device  20 , a developing device  22 , a blade  24 , and a discharging device  26  are provided around each image bearing member  18 . The scorotron charging device  20  is of corona discharge type (non-contact charging type). The scorotron charging device  20  is an example of a charging device that charges the image bearing member  18  with electricity. The developing device  22  develops the electrostatic latent image formed on the image bearing member  18  by the optical scanning device  40 , with a developer. The blade  24  serves as a removing member that removes the developer remaining on the image bearing member  18  after transferring. The discharging device  26  irradiates the image bearing member  18  with light after the transferring, to discharge the electricity from the image bearing member  18 . 
     The scorotron charging device  20 , the developing device  22 , the blade  24 , and the discharging device  26  face the surface of the image bearing member  18 , and are arranged in that order from an upstream side to a downstream side in a rotation direction of the image bearing member  18 . 
     The developing device  22  includes a developer container  22 A and a development roller  22 B. The developer container  22 A contains a developer G including a toner. The development roller  22 B supplies the image bearing member  18  with the developer G contained in the developer container  22 A. The developer container  22 A is connected with the toner cartridge  14  (see  FIG. 19 ) through a toner supply path (not shown), so that the toner is supplied to the developer container  22 A from the toner cartridge  14 . 
     Referring to  FIG. 19 , a transfer unit  32  is provided below the image forming units  16 . The transfer unit  32  includes a ring-like intermediate transfer belt  34  that is in contact with the image bearing members  18 , and first transfer rollers  36  as first transfer members that transfer toner images formed on the image bearing members  18  onto the intermediate transfer belt  34  in a superposed manner. 
     The intermediate transfer belt  34  is wound around a driving roller  38  that is driven by a motor (not shown), a tension roller  41  that applies a tension to the intermediate transfer belt  34 , an opposite roller  42  that faces a second transfer roller  62  (described later), and plural support rollers  44 , so that the intermediate transfer belt  34  is moved in one direction (counterclockwise in  FIG. 19 ) by the driving roller  38 . 
     Each first transfer roller  36  faces the image bearing member  18  of the corresponding image forming unit  16  with the intermediate transfer belt  34  interposed therebetween. A feed unit (not shown) applies a transfer bias voltage to the first transfer roller  36 . The transfer bias voltage has a polarity reverse to a toner polarity. With this configuration, the toner image formed on the image bearing member  18  is transferred on the intermediate transfer belt  34 . 
     A discharging device  46  faces the driving roller  38  with the intermediate transfer belt  34  interposed therebetween. The discharging device  46  has a blade, and brings the blade into contact with the intermediate transfer belt  34  to remove, for example, a remaining toner and paper dust on the intermediate transfer belt  34 . 
     Two recording medium containers  48  are provided below the transfer unit  32  and arranged in the horizontal direction. The recording medium containers  48  contain recording media P, such as sheets of paper, as an example of sheet members. 
     Each recording medium container  48  may be pulled out from the first housing  10 A. A feed roller  52  is provided above a portion at one end (at the right side in  FIG. 19 ) of each recording medium container  48 . The feed roller  52  feeds the recording media P from the recording medium container  48  to a transport path  60 . 
     Each recording medium container  48  has a bottom plate  50  therein, on which the recording media P are mounted. The bottom plate  50  is lowered upon an instruction from a controller (not shown) when the recording medium container  48  is pulled out from the first housing  10 A. Since the bottom plate  50  is lowered, the recording medium container  48  obtains a space for supplement of the recording media P by a user. 
     When the recording medium container  48  pulled out from the first housing  10 A is inserted into the first housing  10 A, the bottom plate  50  is lifted upon an instruction from the controller. Since the bottom plate  50  is lifted, the top one of the recording media P mounted on the bottom plate  50  contacts the feed roller  52 . 
     A separation roller  56  is provided at a downstream side in a transport direction of the recording medium P (hereinafter, also merely referred to as “downstream side”) with respect to the feed roller  52 . The separation roller  56  separates the recording media P one by one when the recording media P are double-fed from the recording medium container  48 . Plural transport rollers  54  are provided downstream the separation roller  56 . The transport rollers  54  transport the recording medium P to the downstream side in the transport direction. 
     The transport path  60  is provided between the recording medium container  48  and the transfer unit  32 . The transport path  60  extends to a transfer position T between the second transfer roller  62  and the opposite roller  42  such that the recording medium P, which has been fed from the recording medium container  48 , is returned at a first return portion  60 A to the left side in  FIG. 19  and then returned at a second return portion  60 B to the right side in  FIG. 19 . 
     A feed unit (not shown) applies a transfer bias voltage to the second transfer roller  62 . The transfer bias voltage has a polarity reverse to the toner polarity. With this configuration, the second transfer roller  62  secondarily transfers the toner images of the respective colors, which have been transferred on the intermediate transfer belt  34  in a superposed manner, on the recording medium P, which has been transported along the transport path  60 . 
     A spare path  66  extends from a side surface of the first housing  10 A to meet the transport path  60  at the second return portion  60 B. A recording medium P fed from another recording medium container (not shown) arranged adjacent to the first housing  10 A may be transported along the spare path  66  and enter the transport path  60 . 
     Plural transport belts  70  are provided downstream the transfer position T. The transport belts  70  transport the recording medium P with the toner images transferred thereon to the second housing  10 B. A sheet-member transport device  80  is provided in the second housing  10 B. The sheet-member transport device  80  transports the recording medium P transported by the transport belts  70  to the downstream side. 
     Each of the plural transport belts  70  has a ring-like shape, and is wound around a pair of support rollers  72 . One of the pair of support rollers  72  is arranged at an upstream side in the transport direction of the recording medium P (hereinafter, also merely referred to as “upstream side”) and the other is arranged at the downstream side. When either one of the pair of support rollers  72  is rotationally driven, the transport belt  70  is moved in one direction (clockwise in  FIG. 19 ). 
     Then, the sheet-member transport device  80  provided at the downstream side in the transport direction of the recording medium P with respect to the transport belt  70  transports recording medium P to a fixing unit  82 . The fixing unit  82  is an example of a fixer that fixes the toner images transferred on the surface of the recording medium P, to the recording medium P with heat and pressure. 
     The fixing unit  82  includes a fixing belt  84 , and a pressure roller  88 . The pressure roller  88  is arranged to contact the fixing belt  84  from below. A fixing portion N is defined between the fixing belt  84  and the pressure roller  88 . The toner images are fixed by applying the heat and pressure to the recording medium P at the fixing portion N. 
     The fixing belt  84  has a ring-like shape, and is wound around a driving roller  89  and a driven roller  90 . The driving roller  89  faces the pressure roller  88  from above. The driven roller  90  is arranged above the driving roller  89 . 
     The driving roller  89  and the driven roller  90  respectively include built-in heaters such as halogen heaters, and hence the fixing belt  84  is heated. 
     Referring to  FIG. 19 , a sheet-member transport device  108  is provided at the downstream side in the transport direction of the recording medium P with respect to the fixing unit  82 . The sheet-member transport device  108  transports the recording medium P output from the fixing unit  82 . 
     The sheet-member transport device  80  and the sheet-member transport device  108  will be described later in more detail. 
     A cooling unit  110  is provided downstream the sheet-member transport device  108 . The cooling unit  110  cools the recording medium P which has been heated by the fixing unit  82 . 
     The cooling unit  110  includes an absorption device  112  that absorbs the heat of the recording medium P, and a pressure device  114  that presses the recording medium P against the absorption device  112 . The absorption device  112  is provided at one side (an upper side in  FIG. 19 ) and the pressure device  114  is provided the other side (a lower side in  FIG. 19 ) with respect to the transport path  60 . 
     The absorption device  112  includes a ring-like absorption belt  116  that contacts the recording medium P and absorbs the heat of the recording medium P. The absorption belt  116  is wound around a driving roller  120  and plural support rollers  118 . The driving roller  120  transmits a driving force to the absorption belt  116 . 
     A heat sink  122  is provided at an inner periphery side of the absorption belt  116 . The heat sink  122  is formed of an aluminum material that contacts the absorption belt  116  by surface-to-surface contact and radiates the heat absorbed by the absorption belt  116 . 
     Also, fans  128  are arranged at a back side of the second housing  10 B (a far side in  FIG. 19 ). The fans  128  remove the heat from the heat sink  122  and exhaust the hot air to the outside. 
     The pressure device  114  that presses the recording medium P against the absorption device  112  includes a ring-like pressure belt  130  that transports the recording medium P while pressing the recording medium P against the absorption belt  116 . The pressure belt  130  is wound around plural support rollers  132 . 
     A straightening device  140  is provided downstream the cooling unit  110 . The straightening device  140  pinches and transports the recording medium P, and straightens curve (curl) of the recording medium P. 
     A sensor  180  is provided downstream the straightening device  140 . The sensor  180  detects, for example, a toner density defect, an image defect, and an image position defect in the toner image fixed to the recording medium P. 
     The sensor  180  includes a light source that emits light to the recording medium P, and a sensing element, such as a charge coupled device (CCD) image sensor, that detects the light emitted on the recording medium P and reflected from the recording medium P to the upper side. Thus, the sensor  180  detects, for example, a toner density defect, an image defect, and an image position defect. 
     An output roller  198  is provided downstream the sensor  180 . The output roller  198  outputs the recording medium P with an image formed on one side, to an output portion  196  that is attached to a side surface of the second housing  10 B. 
     If images are to be formed on both sides, the recording medium P from the sensor  180  is transported to a reverse path  202  provided downstream the sensor  180 . 
     The reverse path  202  includes a branch path  202 A that is branched from the transport path  60 ; a sheet transport path  202 B, along which the recording medium P transported along the branch path  202 A is transported to the first housing  10 A; and a reverse path  202 C that returns the recording medium P transported along the sheet transport path  202 B in the reverse direction, so that the recording medium P is switched back and the surfaces of the recording medium P are reversed. 
     With this configuration, the recording medium P, which has been switched back and transported along the reverse path  202 C, is transported to the first housing  10 A. The recording medium P enters the transport path  60  provided above the recording medium container  48 , and is transported to the transfer position T again. 
     Next, an image forming process of the image forming apparatus  10  will be described. 
     Image data, on which the image processing is performed by the image signal processor  13 , is sent to each optical scanning device  40 . The optical scanning device  40  emits the light beam L in accordance with the image data, and exposes the corresponding image bearing member  18 , which has been charged with electricity by the scorotron charging device  20 , with light. Thus, the electrostatic latent image is formed. 
     Referring to  FIG. 18 , the electrostatic latent image formed on the image bearing member  18  is developed by the developing device  22 . The toner images of the respective colors including the first special color (V), second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) are formed. 
     Referring to  FIG. 19 , the toner images of the respective colors formed on the image bearing members  18  of the image forming units  16 V,  16 W,  16 Y,  16 M,  16 C, and  16 K are successively transferred on the intermediate transfer belt  34  in a superposed manner by the six first transfer rollers  36 V,  36 W,  36 Y,  36 M,  36 C, and  36 K. 
     The second transfer roller  62  secondarily transfers the toner images of the respective colors, which have been transferred on the intermediate transfer belt  34  in a superposed manner, on the recording medium P, which has been transported from the recording medium container  48 . The recording medium P with the toner images transferred thereon is transported by the transport belt  70  to the fixing unit  82  provided in the second housing  10 B. 
     The fixing unit  82  fixes the toner images of the respective colors on the recording medium P to the recording medium P by applying the heat and pressure to the toner images. The recording medium P with the toner images fixed thereto passes through the cooling unit  110 . The cooling unit  110  cools the recording medium P. Then, the recording medium P is transported to the straightening device  140 . The straightening device  140  straightens the curve generated at the recording medium P. 
     The sensor  180  detects an image defect or the like of the recording medium P with the curve thereof straightened. Then, the output roller  198  outputs the recording medium P to the output portion  196 . 
     Meanwhile, when an image is to be formed on a surface on which no image is formed (in a case of duplex printing), the recording medium P is reversed at the reverse path  202  after the recording medium P has passed through the sensor  180 . The recording medium P is transported to the transport path  60  provided above the recording medium container  48 , and toner images are formed on the back surface of the recording medium P by the above-described process. 
     In the image forming apparatus  10  according to the exemplary embodiment, parts for forming images of the first and second special colors (image forming units  16 V and  16 W, optical scanning devices  40 V and  40 W, toner cartridges  14 V and  14 W, and first transfer rollers  36 V and  36 W) are detachably attached to the first housing  10 A as optional parts depending on the user&#39;s choice. Hence, the image forming apparatus  10  may have a configuration without the parts for forming the images of the first and second special colors, or a configuration with the parts for forming the image of one of the first and second special colors. 
     Configuration of Major Portion 
     Next, the sheet-member transport device  80  arranged upstream the fixing unit  82  will be described. 
     Referring to  FIGS. 14 and 17 , the sheet-member transport device  80  includes a driving roller  302  as an example of a driving member that is rotationally driven, a driven roller  304  as an example of a driven member that is provided downstream the driving roller  302  and rotatably supported, four endless belts  306  wound around the driving roller  302  and the driven roller  304 , and a hollow air duct  308  arranged at an inner periphery side of the endless belts  306  and supporting the driven roller  304  at the upstream side. That is, rotary members that cause the endless belts  306  to move include the driving roller  302  and the driven roller  304 . When the driving roller  302  is rotationally driven, the endless belts  306  are moved. Since the driven roller  304  contacts the moving endless belts  306 , the driven roller  304  is rotated. 
     More specifically, the driven roller  304  that supports inner peripheral surfaces of the endless belts  306  is molded with a resin material. An outer peripheral portion of the driving roller  302  that supports the inner peripheral surfaces of the endless belts  306  is formed of a rubber material. 
     A motor  310  and a gear train  312  are provided below the endless belts  306 . The motor  310  is an example of a drive source supported by a bracket  311  fixed to the air duct  308 . The gear train  312  is supported by a bracket  313  fixed to the air duct  308  and by an output shaft  310 A of the motor  310 . A gear  314  is provided at one end portion of the driving roller  302 . A driving force is transmitted to the gear  314  from the output shaft  310 A of the motor  310  through the gear train  312 . 
     Referring to  FIG. 17 , a controller  316  is provided as an example of a first controller that controls driving of the motor  310 . The controller  316  drives the motor  310  during image formation in which an image is formed on a recording medium P (a sheet member), and drives the motor  310  also during image non-formation (a standby state) in which no image is formed on a recording medium P (a sheet member), to move the endless belts  306 . 
     Also, referring to  FIG. 14 , a substantially circular opening portion  308 A is provided at one end of the hollow air duct  308 . The opening portion  308 A is attached to an air inlet (not shown) of a fan  326  as an example of a suction member that is provided in the apparatus body and sucks the air. 
     Plural openings (not shown) are made in an upper surface of the air duct  308  facing the transported recording medium P with the endless belts  306  interposed therebetween. When the fan  326  in the apparatus body is operated, the air is sucked into the air duct  308  through the openings in the upper surface of the air duct  308 . 
     A controller  328  is provided as an example of a second controller that controls the operation of the fan  326 . The controller  328  operates the fan  326  during the image formation in which an image is formed on a recording medium P (a sheet member), and operates the fan  326  also during the image non-formation (the standby state) in which no image is formed on a recording medium P, so that the air is sucked into the air duct  308  through the openings in the upper surface of the air duct  308 . 
     Referring to  FIG. 7A , each endless belt  306  is a ring-like band member formed by weaving fibers  306 A substantially in the form of a mesh (in the exemplary embodiment, 60 meshes/2.54 cm with a thickness of 280 μm and an opening area of 42%). The fibers  306 A are molded with a resin material (in the exemplary embodiment, polyester resin with a line diameter of 150 μm). A weaving direction of the fibers  306 A is oblique to the transport direction of the recording medium P (a direction indicated by arrow A in  FIGS. 7A and 7B ). 
     Since the weaving direction of the fibers  306 A is oblique to the transport direction of the recording medium P, referring to  FIG. 7B , the endless belt  306  is capable of stretching in the transport direction of the recording medium P. Also, since the endless belt  306  is substantially the mesh, a sucking force for sucking the air at an outer periphery side of the endless belt  306  into the air duct  308  through mesh holes  306 B (openings) is substantially uniform over the outer peripheral surface of the endless belt  306 . Unevenness in temperature of the recording medium P (the sheet member) due to the air sucked into the air duct  308  hardly occurs. 
     Joint portions generated when each endless belt  306  is formed into the ring-like shape are made by heat sealing to be oblique to the transport direction of the recording medium P. 
     Further, the outer peripheral surface of each endless belt  306  is treated with surface processing (in the exemplary embodiment, a material for the surface processing is urethane resin), so that the outer peripheral surface of the endless belt  306  has a higher friction coefficient with respect to the transported recording medium P than a friction coefficient of the inner peripheral surface of the endless belt  306 . It is to be noted that only the outer peripheral surface is treated with the surface processing to prevent an increase in rotation load due to friction between the inner peripheral surface of the endless belt  306  and the air duct and the like arranged in the endless belt  306  because the surface processing is applied to the inner peripheral surface. The color of the surface processing is black. Thus, contamination resulted from the developer or the like is not noticeable, and since the color of the fibers  306 A is white, the front and back surfaces of the endless belt  306  may be easily distinguished by the color difference. 
     Referring to  FIGS. 14 and 17 , a plate-like guide member  318  is provided downstream the endless belt  306 . The guide member  318  guides the recording medium P transported by the endless belts  306  to the fixing unit  82 . Also, a discharging brush  320  is provided at a distal end portion (a downstream end portion) of the guide member  318 . The discharging brush  320  discharges electricity from the transported recording medium P. 
     Referring to  FIG. 15 , a cleaning roller  322  is provided below the endless belts  306 . The cleaning roller  322  is in contact with the outer peripheral surfaces of the endless belts  306  and is rotated thereby. The cleaning roller  322  cleans up the outer peripheral surfaces of the endless belts  306 . 
     Further, limit members  324  protrude from a lower surface (a surface on which the recording medium P is not transported) of the air duct  308 . The limit members  324  contact end portions of the endless belts  306  and limit movement of the endless belts  306  in a direction orthogonal to the transport direction of the recording medium P (a thrust direction). 
     Next, the sheet-member transport device  108  arranged downstream the fixing unit  82  will be described. 
     Referring to  FIGS. 1 and 4 , the sheet-member transport device  108  includes a driving roller  330  as an example of a driving member that is rotationally driven, a driven roller  332  as an example of a driven member that is provided upstream the driving roller  330  and rotatably supported, and two endless belts  334  wound around the driving roller  330  and the driven roller  332 . 
     In addition, a driven roller  336  is provided between the driving roller  330  and the driven roller  332 . The driven roller  336  contacts inner peripheral surfaces of the moving endless belts  334  and is rotationally driven by the endless belts  334 . The driven roller  336  lifts upper surfaces (surfaces for transporting the recording medium P) of the endless belts  334  upward to incline entrance regions  334 C for the recording medium P. 
     In other words, since the entrance regions  334 C are provided, the upper surfaces of the endless belts  334  are inclined to the transport direction of the recording medium P sent from the fixing unit  82  such that a surface to be transported of the recording medium P gradually approaches the upper surfaces of the endless belts  334  toward the downstream side. 
     Further, an endless belt  338  is provided between the two endless belts  334 . The endless belt  338  is wound around the driving roller  330  and the driven roller  336 . A length of a transport surface for transporting the recording medium P of the endless belt  338  is smaller than a length of a transport surface for transporting the recording medium P of each endless belt  334 . Rotary members that cause the endless belts  334  and  338  to move include the driving roller  330  and the driven rollers  332  and  336 . The endless belt  338  has a smaller dimension in a width direction (a direction orthogonal to the transport direction of the recording medium P) than a dimension in the width direction of each endless belt  334 . 
     Further, a hollow air duct  340  is provided at inner periphery sides of the endless belts  334  and  338 . 
     Referring to  FIGS. 1 and 4 , the driven rollers  332  and  336  that support the inner peripheral surfaces of the endless belts  334  and  338  are molded with a resin material. An outer peripheral portion of the driving roller  330  that supports the inner peripheral surfaces of the endless belts  334  and  338  are formed of a rubber material. Also, a driving-force limit member  342  (for example, a torque limiter) is provided at one end portion of the driving roller  330 . The driving-force limit member  342  is an example of a driving-force limit unit that limits transmission of a driving force of a motor  344 . The motor  344  is an example of a drive source. Thus, a transport velocity at which the recording medium P is transported by the sheet-member transport device  108  follows a transport velocity at which the recording medium P is transported by the fixing unit  82  (see  FIG. 17 ). Further, a pulley  350  is attached to the driving-force limit member  342 . A driving force is transmitted from an output shaft  344 A of the motor  344  provided below the air duct  340  to the pulley  350  through a gear train  346  and a driving-force transmitting belt  348 . 
     A tension roller  352  is also provided. The tension roller  352  presses an outer peripheral surface of the driving-force transmitting belt  348  and applies a tension to the driving-force transmitting belt  348 . The motor  344  is a stepping motor that is operated in synchronization with a pulse voltage. In this exemplary embodiment, the driving-force limit member  342  has a set value of 150 (mN·m) by taking into consideration a motor load torque and waving of the recording medium P. 
     A controller  378  is provided as an example of a controller that controls driving of the motor  344 . The controller  378  controls driving of the motor  344  such that a set velocity of the sheet-member transport device  108  (a peripheral velocity of a belt), at which the recording medium P is transported, is higher by 0.5% than a set velocity of the fixing unit  82  (a peripheral velocity of a roller), at which the recording medium P is transported. 
     The air duct  340  arranged at the inner periphery side of the endless belts  334  and  338  includes an upstream air duct  354  arranged upstream the driven roller  336 , and a downstream air duct  356  arranged downstream the driven roller  336 . 
       FIG. 2  illustrates the sheet-member transport device  108  when one of the endless belts  334  is removed. Referring to  FIG. 2 , the upstream air duct  354  that faces the transported recording medium P with the endless belt  334  interposed therebetween has plural openings  358  in an upper surface of the upstream air duct  354 . Similarly, the downstream air duct  356  has plural openings  360  in an upper surface thereof. 
     Referring to  FIG. 8 , the positions of the openings  358  and  360  are determined so that the recording medium P is capable of being sucked to the upper surfaces of the endless belts  334  and  338  without being loosened regardless of the size of the recording medium P. 
     Referring to  FIG. 2 , a recess  362  that supports the driven roller  332  is provided at an upstream end portion of the upstream air duct  354 , and a recess  364  that supports the driven roller  336  is provided at an upstream end portion of the downstream air duct  356 . 
     Referring to  FIGS. 11 and 12 , a rectifying plate  366  is provided in the downstream air duct  356 . The rectifying plate  366  divides the inside space of the downstream air duct  356  into an upper space  368  and a lower space  370 . The rectifying plate  366  has a slit  372  that extends in the direction orthogonal to the transport direction of the recording medium P and that allows the upper space  368  to communicate with the lower space  370 . Referring to  FIGS. 9 and 10 , the upper space  368  is divided into plural space sections by plural partitions  381 . 
     Referring to  FIGS. 9 ,  10 ,  11 , and  12 , a hollow support member  380  is provided below the air duct  340  with lower surfaces of the endless belts  334  interposed therebetween. More specifically, the support member  380  is hollow, and has two spaces  382  arranged in the direction orthogonal to the transport direction of the recording medium P. A recess  384  whose top is open is provided between the two spaces  382  of the support member  380 . 
     Openings  386  are provided at outer sides (at axial ends, see  FIG. 6 ) of the upper surface of the support member  380 . The spaces  382  are open through the openings  386 . The downstream air duct  356  facing the openings  386  in the vertical direction has openings  388 . The lower space  370  is open through the openings  388 . Thus, the spaces  382  communicate with the lower space  370  through the openings  386  and  388 . 
     Fans  390  (see  FIG. 5 ) are provided on a lower surface of the support member  380 . The fans  390  each are an example of a suction member that sucks the air in the spaces  382 . 
     Referring to  FIGS. 9 ,  10 ,  11 ,  12 , and  13 , when the fans  390  are operated, the air around an upper surface of the upstream air duct  354  enters an upstream space  374  through the openings  358  (see  FIG. 2 ), enters the lower space  370  through an opening  376 , enters the spaces  382  through the openings  386  and  388 , is sucked by the fans  390 , and is exhausted to the outside. 
     The air around an upper surface of the downstream air duct  356  enters the upper space  368  through the openings  360  (see  FIG. 2 ), enters the lower space  370  through the slit  372  provided in the rectifying plate  366 , enters the spaces  382  through the openings  386  and  388 , is sucked by the fans  390 , and is exhausted to the outside. Accordingly, the recording medium P is attracted to the outer peripheral surfaces of the endless belts  334  and  338 . 
     The shape of the slit  372  provided in the rectifying plate  366  is adjusted such that an attracting force generated at the upper surface of the upstream air duct  354  is greater than an attracting force generated at the upper surface of the downstream air duct  356 . 
     A controller  392  is provided as an example of a controller that controls the air volume of the fans  390 . Referring to  FIG. 16 , when the recording medium P is a sheet of paper, the controller  392  controls the sucking force of the fans  390  to be constant regardless of the basis weight of the sheet, or the controller  392  controls the sucking force (the air volume) of the fans  390  to be greater if the basis weight of the sheet is small as compared with a case in which the basis weight of the sheet is large. The sucking force (the air volume) is increased as the numerical value indicative of the air volume in  FIG. 16  is increased. 
     The controller  392  controls the sucking force of the fans  390  to be constant regardless of whether the recording medium P is normal paper or coated paper, or the controller  392  controls the sucking force of the fans  390  to be greater if the recording medium P is normal paper as compared with a case in which the recording medium P is coated paper. 
     Referring to  FIG. 7A , the endless belts  334  and  338  are ring-like band members formed by weaving fibers  334 A and  338 A substantially in the forms of meshes (in the exemplary embodiment, 60 meshes/2.54 cm with a thickness of 280 μm and an opening area of 42%). The fibers  334 A and  338 A are molded with a resin material (in the exemplary embodiment, polyester resin with a line diameter of 150 μm). A weaving direction of the fibers  334 A and  338 A is oblique to the transport direction of the recording medium P (a direction indicated by arrow A in  FIGS. 7A and 7B ). 
     Since the weaving direction of the fibers  334 A and  338 A is oblique to the transport direction of the recording medium P, referring to  FIG. 7B , the endless belts  334  and  338  are capable of stretching in the transport direction of the recording medium P. Also, since the endless belts  334  and  338  are substantially the meshes, sucking forces for sucking the air at an outer periphery side of the endless belts  334  and  338  into the air duct  340  through mesh holes  334 B and  338 B (openings) are substantially uniform over the outer peripheral surfaces of the endless belts  334  and  338 . Unevenness in temperature of the recording medium P (the sheet member) due to the air sucked into the air duct  340  hardly occurs. 
     Joint portions generated when the endless belts  334  and  338  are formed into the ring-like shapes are made by heat sealing to be oblique to the transport direction of the recording medium P. 
     Further, the outer peripheral surfaces of the endless belts  334  and  338  are treated with surface processing (in the exemplary embodiment, a material for the surface processing is urethane resin), so that the outer peripheral surfaces of the endless belts  334  and  338  have a higher friction coefficient with respect to the transported recording medium P than a friction coefficient of the inner peripheral surfaces of the endless belts  334  and  338 . It is to be noted that only the outer peripheral surfaces are treated with the surface processing to prevent an increase in rotation load due to friction between the inner peripheral surfaces of the endless belts  334  and  338  and the air duct and the like arranged in the endless belts  334  and  338  because the surface processing is applied to the inner peripheral surfaces. The color of the surface processing is black. Thus, contamination resulted from the developer or the like is not noticeable, and since the color of the fibers  334 A and  338 A is white, the front and back surfaces of the endless belts  334  and  338  may be easily distinguished by the color difference. 
       FIG. 6  illustrates the sheet-member transport device  108  when the air duct  340  is rotated around the driving roller  330 . Referring to  FIG. 6 , limit members  394  protrude from a lower surface (a surface on which the recording medium P is not transported) of the upstream air duct  354 . The limit members  394  contact end portions of the endless belts  334  and limit movement of the endless belts  334  in a direction orthogonal to the transport direction of the recording medium P (a thrust direction). 
     A tension roller  396  is provided so as to protrude from a lower surface of the downstream air duct  356 . The tension roller  396  applies a tension to the endless belt  338 . The tension roller  396  is accommodated in the recess  384  provided at the support member  380 . 
     Referring to  FIGS. 1 and 3 , a sensor  398  is provided between the two endless belts  334 . The sensor  398  is located upstream the endless belt  338  (at a position upstream the region between the driven roller  336  and the driving roller  330 ), in the upper surface of the upstream air duct  354 . The sensor  398  detects the transported recording medium P. 
     A plate-like guide member  400  is provided downstream the endless belts  334  and  338 . The guide member  400  guides the recording medium P transported by the endless belts  334  and  338 , to the cooling unit (see  FIG. 19 ). 
     Operation 
     Referring to  FIGS. 17 and 19 , the toner images of the respective colors transferred on the intermediate transfer belt  34  in a superposed manner are secondarily transferred on the recording medium P transported by the second transfer roller  62 . The recording medium P with the toner images transferred thereon is transported by the transport belts  70  to the sheet-member transport device  80  arranged upstream the fixing unit  82 . 
     Referring to  FIGS. 14 and 17 , when the controller  316  of the sheet-member transport device  80  drives the motor  310 , the driving roller  302  is rotationally driven. When the driving roller  302  is rotationally driven, the endless belts  306  are moved. The driven roller  304  is in contact with the moving endless belts  306 , and rotated by the endless belts  306 . 
     The controller  328  operates the fan  326 . The fan  326  sucks the air in the air duct  308  and exhausts the air to the outside. The air is sucked into the air duct  308  through the plural openings provided in the upper surface of the air duct  308 . When the air is sucked into the air duct  308  through the plural openings, the air at the outer periphery side of the endless belts  306  is sucked into the air duct  308  through the mesh holes  306 B of the endless belts  306 . Thus, the recording medium P from the transport belt  70  is transported while being attracted to the moving endless belts  306 . 
     The recording medium P transported by the moving endless belts  306  while being attracted to the endless belts  306  contacts the discharging brush  320 , and the recording medium P is guided to the fixing unit  82  by the plate-like guide member  318 . 
     The fixing unit  82  fixes the toner images transferred on the surface of the recording medium P to the recording medium P by applying the heat and pressure to the toner images. Then, the fixing unit  82  transports the recording medium P to the sheet-member transport device  108 . 
     Referring to  FIGS. 4 and 17 , when the controller  378  of the sheet-member transport device  108  drives the motor  344 , the driving roller  330  is rotationally driven. When the driving roller  330  is rotationally driven, the endless belts  334  and  338  are moved. The driven rollers  332  and  336  contact the moving endless belts  334  and  338 , and are rotated by the driven rollers  332  and  336 . 
     Referring to  FIG. 9 , the controller  392  operates the fans  390 . The fans  390  suck the air in the air duct  340  and exhaust the air to the outside. Accordingly, the air is sucked into the air duct  340  through the openings  358  and  360  (see  FIG. 2 ) provided in the upper surface of the air duct  340 . 
     More specifically, referring to  FIGS. 9 ,  10 ,  11 ,  12 , and  13 , by operating the fans  390 , the air around the upper surface of the upstream air duct  354  enters the upstream space  374  through the openings  358  (see  FIG. 2 ), enters the lower space  370  through the opening  376 , enters the spaces  382  through the openings  386  and  388 , is sucked by the fans  390 , and is exhausted to the outside. 
     The air around the upper surface of the downstream air duct  356  enters the upper space  368  through the openings  360  (see  FIG. 2 ), enters the lower space  370  through the slit  372  provided in the rectifying plate  366 , enters the spaces  382  through the openings  386  and  388 , is sucked by the fans  390 , and is exhausted to the outside. 
     When the air is sucked into the air duct  340  through the openings  358  and  360  (see  FIG. 2 ), the air at the outer periphery side of the endless belts  334  and  338  is sucked into the air duct  308  through the mesh holes  334 B and  338 B of the endless belts  334  and  338 . Accordingly, the transported recording medium P is attracted to the outer peripheral surfaces of the endless belts  334  and  338 . 
     As a surface to be transported of the recording medium P sent from the fixing unit  82  is moved to the downstream side, the recording medium P gradually approaches the upper surfaces of the endless belts  334 . The recording medium P is attracted to the moving endless belts  334  by the attracting force generated at the upper surface of the upstream air duct  354 . The sensor  398  detects the transported recording medium P. The recording medium P is transported while being attracted to the mesh-like endless belts  334  and  338 . 
     As described above, the outer peripheral surfaces of the endless belts  306 ,  334 , and  338  are treated with the surface processing, and hence have the high friction coefficients with respect to the transported recording medium P. 
     In the above-described exemplary embodiment, the endless belts  306 ,  334 , and  338  of the sheet-member transport devices  80  and  108  provided upstream and downstream the fixing unit  82  in the transport direction of the recording medium P are substantially the meshes. However, the meshes do not have to be applied to only the sheet-member transport devices at these positions. The meshes may be applied to another endless belt in a sheet-member transport device at another position (for example, the transport belt  70 ). 
     In the above-described exemplary embodiment, the controllers  316 ,  328 ,  378 , and  392  are individually provided. However, a single controller may provide the respective controls. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.