Abstract:
An image forming apparatus includes: an image forming unit that forms an image on a recording medium; a heating device that heats the image formed at the image forming unit, on the recording medium while recording medium is conveyed; a detecting device that is provided on a downstream side of the heating device in a recording medium conveying direction and detects image density and an image defect of the recording medium; and a stabilizing device that is provided between the detecting device and the heating device and stabilizes physical changes in the recording medium.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-013330 filed on Jan. 23, 2009. 
       BACKGROUND 
     Technical Field 
       [0002]    The present invention relates to an image forming apparatus. 
       SUMMARY 
       [0003]    One aspect of the invention is an image forming apparatus comprising: an image forming unit that forms an image on a recording medium; a heating device that heats the image formed at the image forming unit, on the recording medium while recording medium is conveyed; a detecting device that is provided on a downstream side of the heating device in a recording medium conveying direction and detects image density and an image defect of the recording medium; and a stabilizing device that is provided between the detecting device and the heating device and stabilizes physical changes in the recording medium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0005]      FIG. 1  is a schematic diagram illustrating an entire configuration of an image forming apparatus according to an exemplary embodiment of the present invention; 
           [0006]      FIG. 2  is a side view illustrating an image forming unit used in the image forming apparatus of the exemplary embodiment of the present invention; 
           [0007]      FIGS. 3A and 3B  indicate a vacuum conveying device used in the image forming apparatus of the exemplary embodiment of the present invention,  FIG. 3A  illustrates a perspective view of a vacuum conveying device and  FIG. 3B  illustrates a side view of the vacuum conveying device; 
           [0008]      FIG. 4  is a side view illustrating a fixing unit used in the image forming apparatus of the exemplary embodiment of the present invention; 
           [0009]      FIG. 5  is a perspective view illustrating a heat sink of a cooling unit used in the image forming apparatus of the exemplary embodiment of the present invention; 
           [0010]      FIG. 6  is a configuration diagram illustrating a decurl treatment unit used in the image forming apparatus of the exemplary embodiment of the present invention; 
           [0011]      FIGS. 7A and 7B  are side views illustrating a cam member of the decurl treatment unit used in the image forming apparatus of the exemplary embodiment of the present invention; 
           [0012]      FIG. 8  is a configuration diagram illustrating the decurl treatment unit used in the image forming apparatus of the exemplary embodiment of the present invention; 
           [0013]      FIGS. 9A and 9B  are side views illustrating the cam member and the like of the decurl treatment unit used in the image forming apparatus of the exemplary embodiment of the present invention; 
           [0014]      FIGS. 10A and 10B  are side views illustrating curl of a sheet member corrected by the decurl treatment unit used in the image forming apparatus of the exemplary embodiment of the present invention; 
           [0015]      FIG. 11  is a configuration diagram illustrating an in-line sensor unit used in the image forming apparatus of the exemplary embodiment of the present invention; and 
           [0016]      FIG. 12  is a configuration diagram illustrating a power unit used in the image forming apparatus of the exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    An image forming apparatus according to an exemplary embodiment of the present invention will be described below with reference to  FIGS. 1 to 12 . 
         [0018]    (Entire Configuration) 
         [0019]    As illustrated in  FIG. 1 , an image forming apparatus  10  is one that forms a full-color image or a monochrome image. The image forming apparatus  10  may be divided into a first chassis  10 A and a second chassis  10 B, the first chassis  10 A is disposed on one side (left of  FIG. 1 ) in a horizontal direction, and the second chassis  10 B is disposed on the other side (right of  FIG. 1 ) in the horizontal direction. 
         [0020]    An image signal processing section  13  is provided in an upper part of the second chassis  10 B, and the image signal processing section  13  performs image processing to image data transmitted from a personal computer and the like. 
         [0021]    (Toner Cartridge) 
         [0022]    On the other hand, in an upper part of the first chassis  10 A, toner cartridges  14 V,  14 W,  14 Y,  14 M,  14 C, and  14 K are horizontally arranged in a replaceable manner. First special color (V) toner, second special color (W) toner, yellow (Y) toner, magenta (M) toner, cyan (C) toner, and black (K) toner are respectively stored in the toner cartridges  14 V,  14 W,  14 Y,  14 M,  14 C, and  14 K. 
         [0023]    Special colors (including transparent color) except for the yellow, magenta, cyan, and black colors are appropriately selected as the first special color and the second special color. In the following description, members corresponding to the V, W, Y, M, C, and K colors are distinguished from one another by adding suffixes V, W, Y, M, C, and K, and the suffixes V, W, Y, M, C, and K are omitted when the members are not distinguished from one another. 
         [0024]    Six image forming units  16  corresponding to V, W, Y, M, C, and K colors are horizontally arranged bellow the toner cartridges  14  so as to face the toner cartridges  14 , and exposure units  40  are provided between each of the toner cartridges  14  and each of the image forming units  16 . 
         [0025]    (Exposure Unit) 
         [0026]    The exposure unit  40  provided every image forming unit  16  receives the image data to which the image signal processing section  13  performs the image processing, modulates a semiconductor laser (not illustrated) according to color gradation data, and the semiconductor laser emit exposure light L according to the color gradation data. 
         [0027]    More particularly, a surface of a photoreceptor  18  (see  FIG. 2 ) is irradiated with the exposure light L (LV, LW, LY, LM, LC, and LK) to form an electrostatic latent image on the photoreceptor  18 . 
         [0028]    As can be seen from  FIG. 1 , the exposure unit  40  is adjacent to the image signal processing section  13  provided in the second chassis  10 B such that wiring to connect the image signal processing section  13  with the exposure unit  40  is shortened. 
         [0029]    (Image Forming Unit) 
         [0030]    As illustrated in  FIG. 2 , the image forming unit  16  includes the photoreceptor  18  rotated in a direction (clockwise) of an arrow A. A corona discharge type (non-contact charging type) scorotron charger  20 , a developing device  22 , a cleaning blade  24 , and an erase lamp  26  are provided around the photoreceptor  18 . The scorotron charger  20  that is of an example of a charger evenly charges the photoreceptor  18 . The developing device  22  develops the electrostatic latent image formed on the photoreceptor  18  with the exposure light L emitted from the exposure unit  40  using each color developer (toner). The cleaning blade  24  cleans the surface of the photoreceptor  18  after transfer. The erase lamp  26  that is of an example of an electricity removing device irradiates the surface of the photoreceptor  18  with light to remove the electricity after transfer. 
         [0031]    The scorotron charger  20 , the developing device  22 , the cleaning blade  24 , and the erase lamp  26  are disposed in this order from the upstream side toward the downstream side in the rotating direction of the photoreceptor  18  while facing the surface of the photoreceptor  18 . 
         [0032]    The developing device  22  includes a developer storage member  22 A and a development roller  22 B. The developer storage member  22 A is disposed beside the photoreceptor  18  (right side in the exemplary embodiment), and filled with a developer G containing the toner. The development roller  22 B moves the toner stored in the developer storage member  22 A to the surface of the photoreceptor  18 . The developer storage member  22 A is communicated with the toner cartridge  14  (see  FIG. 1 ) through a toner supply passage (not illustrated), and the toner is supplied from the toner cartridge  14  to the developer storage member  22 A. 
         [0033]    (Transfer Section) 
         [0034]    As illustrated in  FIG. 1 , a transfer section  32  is provided below the image forming units  16 . The transfer section  32  includes an endless intermediate transfer belt  34  and six primary transfer rollers  36 . The intermediate transfer belt  34  is in contact with photosensitive bodies  18 . The primary transfer rollers  36  that are of primary transfer members are provided inside the intermediate transfer belt  34 , and the primary transfer rollers  36  multiply transfer the toner images formed on the photosensitive bodies  18  to the intermediate transfer belt  34 . 
         [0035]    The intermediate transfer belt  34  is entrained about a driving roller  38 , a tension imparting roller  41 , a backup roller  42 , and plural suspension rollers  44  with a constant tension, and the intermediate transfer belt  34  is circularly driven in a direction (counterclockwise) of an arrow B of  FIG. 1  by the driving roller  38 . The driving roller  38  is driven by a motor (not illustrated). The tension imparting roller  41  adjusts the tension of the intermediate transfer belt  34 . The backup roller  42  is disposed so as to face a secondary transfer roller  62  described later with the intermediate transfer belt  34  therebetween. 
         [0036]    More particularly, the primary transfer rollers  36  are disposed so as to respectively face the photosensitive bodies  18  of the image forming units  16 , with the intermediate transfer belt  34  therebetween. A power supply unit (not illustrated) applies a transfer bias voltage having a polarity opposite to a toner polarity to the primary transfer roller  36 . Therefore, the toner images formed on the photosensitive bodies  18  are transferred to the intermediate transfer belt  34 . 
         [0037]    On the other hand, a cleaning blade  46  is provided at the opposite side of the driving roller  38  with the intermediate transfer belt  34  therebetween and a tip end of the cleaning blade  46  is in contact with the intermediate transfer belt  34 . The cleaning blade  46  removes the residual toner or sheet dust on the circularly-moved intermediate transfer belt  34 . 
         [0038]    (Sheet Feeding Cassette) 
         [0039]    Two large sheet feeding cassettes  48  are provided in parallel below the transfer section  32  in the first chassis  10 A. The sheet members P that are of recording mediums are stored in the sheet feeding cassettes  48 . That is, a large number of sheet members P may be stored in the sheet feeding cassettes  48 . Because the sheet feeding cassettes  48  have the same configuration, only one of the sheet feeding cassettes  48  will be described and the other will not be described. 
         [0040]    The sheet feeding cassette  48  is freely drawn from the first chassis  10 A. The bottom plate  50  is provided in the sheet feeding cassette  48 , and the sheet members P are stacked on the bottom plate  50 . When the sheet feeding cassette  48  is drawn from the first chassis  10 A, the bottom plate  50  is lowered by an instruction of a controller (not illustrated). When the bottom plate  50  is lowered, a user can supply the sheet members P to the sheet feeding cassette  48 . 
         [0041]    On the other hand, when the sheet feeding cassette  48  is attached to the first chassis  10 A, the bottom plate  50  is lifted by the instruction of the controller. A delivery roller  52  is provided on one end side of the sheet feeding cassette  48  in order to deliver the sheet member P from the sheet feeding cassette  48  to a conveying path  60 . The delivery roller  52  abuts on the uppermost sheet member P stacked on the lifted bottom plate  50 . 
         [0042]    (Conveying Path) 
         [0043]    A separation roller  56  is provided on the downstream side (hereinafter simply referred to as “downstream side”) of the delivery roller  52  in a sheet member conveying direction in order to prevent multi feeding of the sheet member P. Plural conveying rollers  54  are provided on the downstream side of the separation roller  56  in order to convey the sheet member P to the downstream side in the conveying direction. 
         [0044]    In the conveying path  60  provided between the sheet feeding cassette  48  and the transfer section  32 , the sheet member P delivered from the sheet feeding cassette  48  is turned back to the opposite side at a first fold-back part  60 A, and the sheet member P is turned back to the opposite side at a second fold-back part  60 B, whereby the sheet member P is advanced toward a transfer point T where the sheet member P is sandwiched between the secondary transfer roller  62  and the backup roller  42 . 
         [0045]    An aligner (not illustrated) is provided between the second fold-back part  60 B and the transfer point T in order to correct an inclination of the conveyed sheet member P, and an alignment roller  64  is provided between the aligner and the transfer point T in order to match the timing at which the toner image on the intermediate transfer belt  34  is moved with the timing at which the sheet member P is conveyed. 
         [0046]    A power supply unit (not illustrated) applies a transfer bias voltage having a polarity opposite to the toner polarity to the secondary transfer roller  62 . Therefore, the toner images multiply transferred on the intermediate transfer belt  34  are secondary-transferred to the sheet member P conveyed along the conveying path  60  by the secondary transfer roller  62 . 
         [0047]    An auxiliary path  66  extended from a side surface of the first chassis  10 A is provided so as to converge with the second fold-back part  60 A of the conveying path  60 . The sheet member P delivered from an external large-capacity tray disposed adjacent to the first chassis  10 A enters the conveying path  60  through the auxiliary path  66 . 
         [0048]    (Vacuum Conveying Device) 
         [0049]    On the downstream side of the transfer point T, plural vacuum conveying devices  70  are provided in order to convey the sheet member P onto which the toner image is transferred toward the second chassis  10 B. 
         [0050]    As illustrated in  FIGS. 3A and 3B , the vacuum conveying device  70  includes a driving roller  72  rotary driven, a driven roller  74  rotatably supported, and plural belt members  76  entrained about the driving roller  72  and driven roller  74 . 
         [0051]    Plural throughholes  76 A are formed over the entire surface of the belt member  76 . Sucking fans  78  are disposed on the backside of the first chassis  10 A (back side of  FIG. 1 ) so as to suck air from the throughhole  76 A into the inside of the belt member  76 . 
         [0052]    Therefore, in the sheet member P, a non-image surface in which the toner image is not formed is sucked to the belt member  76 , and the driving roller  72  is rotated so as to rotate the belt member  76 , thereby conveying the sheet member P toward the downstream side. 
         [0053]    The three vacuum conveying devices  70  are provided on the downstream side of the conveying path  60 , and downstream side of the conveying path  60  is extended from the first chassis  10 A to the second chassis  10 B. The sheet member P delivered by the vacuum conveying device  70  is received by a vacuum conveying device  80  provided in the second chassis  10 B, and the sheet member P is further conveyed to the downstream side. 
         [0054]    The downstream side of the vacuum conveying device  80  is disposed in the second chassis  10 B, and a fixing unit  82  is provided on the downstream side of the vacuum conveying device  80  in order to fix the toner image, which is transferred on the surface of the sheet member P, onto the sheet member P by heat and pressure. 
         [0055]    (Fixing Unit) 
         [0056]    As illustrated in  FIG. 4 , the fixing unit  82  includes a fixing belt module  86  and a pressure roller  88 . The fixing belt module  86  includes a fixing belt  84 , and the pressure roller  88  is disposed in the fixing belt module  86  while being in press contact with the fixing belt module  86 . A nip part N is formed between the fixing belt module  86  and the pressure roller  88 . In the nip part N, the sheet member P is pressurized and heated to fix the toner image onto the sheet member P. 
         [0057]    The fixing belt module  86  includes a fixing belt  84 , a heating roller  89 , and a stretching roller  90 . The heating roller  89  is rotary driven by a torque of a motor (not illustrated) while stretching the fixing belt  84 . The stretching roller  90  stretches the fixing belt  84  from the inside. The fixing belt module  86  also includes a stretching roller  92  and a posture correcting roller  94 . The stretching roller  92  is disposed outside the fixing belt  84  to define a circulating path of the fixing belt  84 . The posture correcting roller  94  located between the heating roller  89  and the stretching roller  90  to correct a posture of the fixing belt  84 . 
         [0058]    The fixing belt module  86  also includes a peeling pad  96  and a stretching roller  98 . The peeling pad  96  is disposed in a downstream-side region in the nip part N, in which the fixing belt module  86  and the pressure roller  88  are in press contact with each other, and near the heating roller  89 . The stretching roller  98  stretches the fixing belt  84  on the downstream side of the nip part N. 
         [0059]    The heating roller  89  is a hard roller in which a fluororesin coating having a thickness of 200 μm is formed on a cylindrical core roller made of aluminum in order to prevent metallic abrasion of the surface of the core roller. A halogen heater  102  is provided as a heating device in the heating roller  89 . 
         [0060]    The stretching roller  90  is a cylindrical roller made of aluminum. A halogen heater  104  is provided as a heating source inside the stretching roller  90 , and the halogen heater  104  heats the fixing belt  84  from the inner surface side. A spring member (not illustrated) is provided in both end parts of the stretching roller  90  in order to outwardly press the fixing belt  84 , and a tension of the fixing belt  84  is set to 15 kgf. 
         [0061]    The stretching roller  92  is a cylindrical roller made of aluminum. A separation layer made of fluororesin is formed on the surface of the stretching roller  92 , and the separation layer has the thickness of 20 μm. The separation layer prevents a tiny amount of toner or sheet dust from depositing on the stretching roller  92 , which invades from an outer circumferential surface of the fixing belt  84 . 
         [0062]    A halogen heater  106  is provided as a heating source inside the stretching roller  92 , and the halogen heater  106  heats the fixing belt  84  from the outer circumferential surface side. That is, in the exemplary embodiment, the fixing belt  84  is heated by the heating roller  89 , the stretching roller  90 , and the stretching roller  92 . 
         [0063]    The posture correcting roller  94  is a cylindrical roller made of aluminum. A belt edge position sensing mechanism (not illustrated) is disposed near the posture correcting roller  94  in order to detect an edge position of the fixing belt  84 . An axis displacement mechanism is provided in the posture correcting roller  94  so as to control meandering of the fixing belt  84  (belt walk). The axis displacement mechanism displaces a contact position in the axial direction of the fixing belt  84  according to the detection result of the belt edge position sensing mechanism. 
         [0064]    The peeling pad  96  is a block-like member made of a rigid material such as stainless steel (SUS) and resin, and has a length corresponding to the heating roller  89 . A sectional shape of the peeling pad  96  is formed into a substantial arc shape. The peeling pad  96  includes an inner surface  96 A, a pressing surface  96 B, and an outer surface  96 C. The inner surface  96 A faces the heating roller  89 . The pressing surface  96 B presses the fixing belt  84  against the pressure roller  88 . The outer surface  96 C has a predetermined angle with respect to the pressing surface  96 B to bend the fixing belt  84 . 
         [0065]    Particularly a corner portion G formed by the pressing surface  96 B and the outer surface  96 C bends the fixing belt  84  that is pressed against the corner portion G by the pressure roller  88 , and the corner portion G peels the leading edge of the sheet member P from the fixing belt  84  when the leading edge of the sheet member P passes by the corner portion G. 
         [0066]    On the other hand, the pressure roller  88  is a soft roller in which an elastic layer  88 B and a peeling layer are laminated in the order on a base that is of a cylindrical roller  88 A made of aluminum. The elastic layer  88 B having the thickness of  10  mm is made of silicone rubber with rubber hardness 30° (JIS-A). The peeling layer is made of a PFA tube having a thickness of 100 μm. The pressure roller  88  is rotatably supported, and a biasing member such as a spring or the like (not illustrated) presses the pressure roller  88  against the fixing belt  84  at a region where the fixing belt  84  is entrained about the heating roller  89 . Therefore, as the heating roller  89  of the fixing belt module  86  is rotary driven in a direction of an arrow C, the pressure roller  88  is driven by the heating roller  89  and rotated in a direction of an arrow E. 
         [0067]    (Sheet Cooling Unit) 
         [0068]    As illustrated in  FIG. 1 , a vacuum conveying device  108  is provided on the downstream side of the fixing unit  82  in order to convey the sheet member P delivered from the fixing unit  82  to the downstream side. A cooling unit  110  is provided on the downstream side of the vacuum conveying device  108  in order to cool the sheet member P heated by the fixing unit  82 . 
         [0069]    In the cooling unit  110 , an absorbing device  112  that absorbs heat of the sheet member P is provided on one side (upper side in the exemplary embodiment) of the conveying path  60 , and a press-down device  114  that presses down the conveyed sheet member P on the absorbing device  112  is provided on the other side (lower side in the exemplary embodiment). 
         [0070]    An endless absorbing belt  116  is provided in the absorbing device  112 . The absorbing belt  116  comes into contact with the sheet member P to absorb the heat of the sheet member P. Plural stretching rollers  118  that support the absorbing belt  116  and a driving roller  120  that transmits a driving force to the absorbing belt  116  are provided inside the absorbing belt  116 . 
         [0071]    A heat sink  122  is also provided inside the absorbing belt  116 . The heat sink  122  is in surface contact with the absorbing belt  116  to radiate the heat absorbed by the absorbing belt  116 . 
         [0072]    As illustrated in  FIG. 5 , the heat sink  122  includes a substantial U-shape abutment member  124  and plural radiator plates  126 . An upper side of a region where the absorbing belt  116  abuts on the sheet member P is opened in the abutment member  124 . The plural radiator plates  126  are mounted on the abutment member  124 , and the heat is transmitted from the abutment member  124  to the plural radiator plates  126 . 
         [0073]    Sucking fans  128  are disposed on the back side of the second chassis  10 B (back side of  FIG. 1 ) such that the heat is drawn from the radiator plate  126  and hot air is exhausted to the outside. 
         [0074]    On the other hand, as illustrated in  FIG. 1 , the press-down device  114  that presses down the conveyed sheet member P onto the absorbing device  112  includes an endless press-down belt  130  and plural stretching rollers  132 . The press-down belt  130  comes into contact with the sheet member P to press down the sheet member P onto the absorbing device  112 . The press-down belt  130  is entrained about, and rotatably supported by, the plural stretching rollers  132 . 
         [0075]    Therefore, the heat is drawn from the sheet member P to cool the sheet member P. 
         [0076]    (Decurl Treatment Unit) 
         [0077]    A decurl treatment unit  140  is provided on the downstream side of the cooling unit  110  in order to correct curl of the sheet member P. 
         [0078]    As illustrated in  FIG. 6 , a guide member  152  that guides the sheet member P is provided on an upstream side of the decurl treatment unit  140  in the sheet member conveying direction upstream side (hereinafter simply referred to as “upstream side”). A recess  152 A opened upward is formed in the guide member  152 . 
         [0079]    A conveying roller  150  that is rotatably axially supported at the apparatus main body is formed in the recess  152 A. An elastic roller  142  is provided so as to face the conveying roller  150  with the conveying path  60  therebetween, and the elastic roller  142  is driven by the conveying roller  150 . In the elastic roller  142 , the surface thereof is made of an elastic material to enlarge a diameter of the elastic roller  142 . 
         [0080]    A rotating shaft  142 A of the elastic roller  142  is rotatably supported by a central side of a plate-like bracket  144  whose central side is bent. One end side of the bracket  144  is rotatably supported by a shaft  146  of a frame member (not illustrated), and the other end abuts on a cam surface  148 A of a cam member  148 , thereby positioning the bracket  144 . 
         [0081]    That is, the elastic roller  142  abuts on the conveying roller  150  to deform the surface of the elastic roller  142 , thereby generating a restoring force of the elastic roller  142 . The other end of the bracket  144  is biased toward the cam surface  148 A by the restoring force of the elastic roller  142  to determine the position of the bracket  144 . 
         [0082]    A controller  156  is provided to control a rotation angle of the cam member  148 . The controller  156  rotates the cam member  148  to move the elastic roller  142  between a retracted position where the elastic roller  142  is lightly pressed against the conveying roller  150  (see  FIGS. 6 and 7A ) and a pressing position where the surface of the elastic roller  142  is elastically deformed to project the conveying path  60  by strongly pressing the elastic roller  142  against the conveying roller  150  (see  FIGS. 8 and 9A ). 
         [0083]    Stretching rollers  160  and  162  are provided on the downstream side of the conveying roller  150  while horizontally separated from each other. Plural elastic belt members  164  whose upper surfaces constitute the conveying path  60  of the sheet member P are entrained about the stretching rollers  160  and  162 . 
         [0084]    A pressing roller  166  is rotatably provided at the opposite side of the conveying path  60  of the elastic belt members  164  with the conveying path  60  therebetween so as to press the elastic belt member  164 . On a side of the pressing roller  166  opposite to the elastic belt members  164 , there is provided a support roller  168 , which is supported at both end parts thereof by the bracket  158  (see  FIG. 7B ) that is the same as that for the pressing roller  166 . The bracket  158  that supports the pressing roller  166  and support roller  168  at both the end parts is supported by the apparatus main body while being movable in a direction in which the bracket  158  is brought close to or separated from the elastic belt member  164 . 
         [0085]    A circular pressing member  170  whose diameter is larger than that of the support roller  168  is provided in the rotatably-supported support roller  168 , and an end face of the pressing member  170  abuts on a cam surface  172 A of a cam member  172  provided above the support roller  168 , thereby determining the position of the pressing member  170 . 
         [0086]    That is, the pressing roller  166  abuts on the elastic belt member  164  to deform the elastic belt member  164 , thereby generating a restoring force of the elastic belt member  164 . The pressing member  170  is biased toward the cam surface  172 A by the restoring force of the elastic belt member  164  to determine the position of the pressing member  170 . 
         [0087]    The controller  156  controls the rotation angle of the cam member  172  and rotates the cam member  172  to move the pressing roller  166  between the retracted position where the pressing roller  166  is lightly pressed against the elastic belt member  164  (see  FIGS. 8 and 9B ) and the pressing position where the surface of the elastic belt member  164  is elastically deformed to indent the conveying path  60  by strongly pressing the pressing roller  166  against the elastic belt member  164  (see  FIGS. 6 and 7B ). 
         [0088]    Therefore, as illustrated in  FIG. 10A , in cases where the end part of the conveyed sheet member P is curled downward, the controller  156  rotates the cam member  148  to move the elastic roller  142  to the retracted position (see  FIGS. 6 and 7A ), and rotates the cam member  172  to move the pressing roller  166  to the pressing position (see  FIGS. 6 and 7B ), thereby concavely deforming the conveying path  60 . Therefore, downwardly-curled sheet member P is flatly corrected. 
         [0089]    On the other hand, as illustrated in  FIG. 10B , in cases where the end part of the conveyed sheet member P is curled upward, the controller  156  rotates the cam member  172  to move the pressing roller  166  to the retracted position (see  FIGS. 8 and 9B ), and rotates the cam member  148  to move the elastic roller  142  to the pressing position (see  FIGS. 6 and 7B ), thereby convexly deforming the conveying path  60 . Therefore, upwardly-curled sheet member P is flatly corrected. 
         [0090]    A curl direction and a degree of curl of the sheet member P depend on a type (plain paper or coated paper) of the sheet member P, a basic weight (grammage) of the sheet member P, a size, a delivery direction, image density (that may be predicted by image data information transmitted to the exposure unit), shape of the sheet running path dedicated to the machine, and characteristics of units disposed on the path. The controller  156  predicts the curl direction or the degree of curl from the pieces of information forementioned and may change the rotation angles of the cam members  148  and  172  to adjust the degree of concavity or convexity of the conveying path  60 . 
         [0091]    (In-line Sensor Unit) 
         [0092]    As illustrated in  FIG. 1 , an in-line sensor unit  180  is provided on the downstream side of the decurl treatment unit  140  in order to detect a toner density defect, an image defect, and an image position defect of the toner image fixed to the sheet member P. 
         [0093]    As illustrated in  FIG. 11 , two light-emitting members  184  are provided in a chassis  182  of the in-line sensor unit  180  in order to irradiate the sheet member P conveyed by the conveying roller  178  with light. A mirror  186  and a mirror  188  are also provided in the chassis  182 . The mirror  186  reflects the light which is emitted from the light-emitting member  184  and upwardly reflected by the sheet member P toward the horizontal direction. The mirror  188  reflects upwardly the light horizontally reflected by the mirror  186 . A mirror  192  is also provided in the chassis  182 , and the mirror  192  folds the light upwardly reflected by the mirror  188  toward a CCD type optical sensor  190 . A collective lens  194  is provided between the mirror  192  and an optical sensor  190 , and the collective lens  194  collects the reflected light onto the optical sensor  190 . 
         [0094]    Therefore, the optical sensor  190  may detect the toner density defect, the image defect, and the image position defect and the like. 
         [0095]    (Inverting Unit) 
         [0096]    As illustrated in  FIG. 1 , a discharge roller  198  is provided on the downstream side of the in-line sensor unit  180 . The discharge roller  198  discharges the sheet member P of which the image is formed in one side to a discharge tray  196  attached to a side surface of the second chassis  10 B. 
         [0097]    In cases where the images are formed in both the side of the sheet member P, the sheet member P delivered from (passing by) the in-line sensor unit  180  is conveyed to an inverting unit  200  provided on the downstream side of the in-line sensor unit  180 . 
         [0098]    Particularly, a switching member (not illustrated) guides the sheet member P to an inverting path  202  provided in the inverting unit  200 . 
         [0099]    A branch passage  202 A, a sheet conveying passage  202 B, and an inverting passage  202 C are provided in the inverting path  202 . The branch passage  202 A is branched from the conveying path  60 . The sheet conveying passage  202 B conveys the sheet member P conveyed along the branch passage  202 A toward the side of the first chassis  10 A. The inverting passage  202 C turns back the sheet member P conveyed along the sheet conveying passage  202 B toward the opposite direction to turn the sheet member P over, that is, performs switchback conveyance to turn the sheet member P over. 
         [0100]    By this configuration, the sheet member P switchback-conveyed by the inverting passage  202 C is conveyed toward the first chassis  10 A, the sheet member P enters the conveying path  60  provided above the sheet feeding cassette  48 , and the sheet member P is delivered to the transfer point T again. 
         [0101]    (Power Unit) 
         [0102]    A power unit  210  that takes in an alternating current from the outside will be described below. 
         [0103]    As illustrated in  FIG. 12 , the power unit  210  is provided in the back surface (back side) of the second chassis  10 B. An input power cord  212  is provided in the power unit  210  in order to take in the alternating current from the outside. One end of a distributor  214  that distributes the alternating current is connected to the input power cord  212 , and the other end of the distributor  214  is connected through a wiring cord  217  to one end of the circuit breaker  216  that shuts off overcurrent. 
         [0104]    The other end of the circuit breaker  216  is connected through a wiring cord  219  to one end of each of noise filters  218 A,  218 B, and  218 C that cut a noise of the alternating current. The other end of each of the noise filters  218 A and  218 B is connected to one end of a control board  222  for the fixing unit  82 (see  FIG. 1 ) through a transformer  220  that boosts or lowers the voltage. 
         [0105]    The other end of the noise filter  218 C is connected through a wiring cord  225  to one end of a control board  224  for a constant-voltage power supply. The other end of the control board  224  is connected to the control board  222  for the fixing unit  82  (see  FIG. 1 ) and through a wiring cord  226  to a power supply unit  230  (see  FIG. 1 ) that converts the alternating current into a direct current. 
         [0106]    The other end of the control board  222  is connected to the fixing unit  82  (see  FIG. 1 ) through a wiring cord  223  such that the alternating current is supplied through the control board  222  to the fixing unit  82  in which a large output is required. 
         [0107]    On the other hand, as illustrated in  FIG. 1 , a power supply unit  230  connected to a control board  224  through a wiring cord  226  is disposed between the fixing unit  82  and the image signal processing section  13  in the second chassis  10 B. The direct current converted by the power supply unit  230  is supplied to other units (such as the image forming unit  16 ) except for the fixing unit  82 . 
         [0108]    (Operation) 
         [0109]    An image forming process of the image forming apparatus  10  will be described below. 
         [0110]    As illustrated in  FIG. 12 , the alternating current is supplied from the outside through the input power cord  212  to the power unit  210  provided in the back surface of the second chassis  10 B, supplied through the control board  222  to the fixing unit  82  provided in the second chassis  10 B, and supplied through the control board  224  to the power supply unit  23  provided in the second chassis  10 B. 
         [0111]    As illustrated in  FIG. 1 , the alternating current supplied to the power supply unit  23  is converted into the direct current, and the direct current is supplied to each unit, thereby activating each unit. 
         [0112]    The image signal processing section  13  in the activated state performs the image processing to the image data, and the image data is converted into color gradation data and supplied to each exposure unit  40 . Each exposure unit  40  emits the exposure light L according to color gradation data to perform scanning exposure to the photoreceptor  18  charged by the scorotron charger  20 , thereby forming the latent image (the electrostatic latent image). 
         [0113]    As illustrated in  FIG. 2 , the developing devices  22  develop the electrostatic latent images formed on the photosensitive bodies  18 , and the electrostatic latent images are visualized as the first special color (V), second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) toner images (developer images). 
         [0114]    As illustrated in  FIG. 1 , the first special color (V), second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photosensitive bodies  18  of the image forming units  16 V,  16 W,  16 Y,  16 M,  16 C, and  16 K are multiply transferred onto the intermediate transfer belt  34  by the six primary transfer rollers  36 V,  36 W,  36 Y,  36 M,  36 C, and  36 K. 
         [0115]    The first special color (V), second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) toner images multiply transferred onto the intermediate transfer belt  34  are secondary-transferred onto the sheet member P conveyed from the sheet feeding cassette  48  by the secondary transfer roller  62 . The vacuum conveying device  70  conveys the sheet member P to which the toner images are transferred toward the fixing unit  82  provided in the second chassis  10 B. 
         [0116]    The fixing unit  82  heats and pressurizes the sheet member P to fix the first special color (V), second special color (W), yellow (Y), magenta (M), cyan (C), and black (K) toner images onto the sheet member P. The sheet member P to which the toner images are fixed is cooled by passing by the cooling unit  110 . Then the sheet member P is delivered to the decurl treatment unit  140  to correct the curl generated in the sheet member P. 
         [0117]    The in-line sensor unit  180  detects the image defect of the sheet member P in which the curl is corrected, and the discharge roller  198  discharges the sheet member P to the discharge tray  196 . 
         [0118]    On the other hand, in cases where the image is formed in the non-image surface in which the image is not formed (in the case of the duplex printing), after the sheet member P passes by the in-line sensor unit  180 , the switching member (not illustrated) delivers the sheet member P to the inverting unit  200 . The sheet member P delivered to the inverting unit  200  is inverted by passing through the inverting path  202 , the sheet member P is delivered to the conveying path  60  provided above the sheet feeding cassette  48 , and the toner images are formed in the back surface by the above-described procedure. 
         [0119]    As described above, the cooling unit  110  is provided between the fixing unit  82  and the in-line sensor unit  180  in order to cool the sheet member P. That is, because the heat is drawn from the sheet member P delivered to the in-line sensor unit  180 , a change in optical path length between the optical sensor  190  and a reflection region of the sheet member P where the light emitted from the light-emitting member  184  is reflected, which is caused by increase of a temperature at the in-line sensor unit  180 , is suppressed. 
         [0120]    The decurl treatment unit  140  is provided between the fixing unit  82  and the in-line sensor unit  180  in order to correct the curl of the sheet member P. That is, the flat sheet member P is delivered to the in-line sensor unit  180 , a change in position of the reflection region of the sheet member P where the light emitted from the light-emitting member  184  is reflected is prevented and the change in optical path length between the reflection region and the optical sensor  190  is suppressed. 
         [0121]    The suppression of the change in optical path length between the reflection region and the optical sensor  190  improves the detection accuracy when the in-line sensor unit  180  detects the toner density defect, image defect, and image position defect of the image formed in the sheet member P. 
         [0122]    The decurl treatment unit  140  is provided on the downstream side of the cooling unit  110 . For example, when the decurl treatment unit is provided on the upstream side of the cooling unit, the roller provided in the decurl treatment unit abuts partially on the sheet member P that is delivered from and heated by the fixing unit  82 , and the roller draws the heat from the region where the roller abuts on the sheet member P, which may cause a problem in that the region differs from other regions in surface quality (such as glossiness). However, as described above, the decurl treatment unit  140  is provided on the downstream side of the cooling unit  110 , thereby suppressing such the problem that the region where the roller abuts on the sheet member P differs from other regions in surface quality. 
         [0123]    Although the specific exemplary embodiment is described in detail, the invention is not limited to the exemplary embodiment. It is understood for those skilled in the art that various modifications can be made without departing from the scope of the invention. For example, in the exemplary embodiment, the xerographic image forming apparatus is described only by way of example. In an inkjet image forming apparatus, the above-described layout of the exemplary embodiment may be provided on the downstream side of the heating device that dries ink ejected to the sheet member P using hot air. 
         [0124]    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 exemplary 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.