Abstract:
Disclosed is a fixing unit including a fixing member; a pressure member brought into press-contact with a front surface of the fixing member; a pressure mechanism that changes a position at which the pressure member is brought into press-contact with the fixing member, the pressure mechanism being capable of controlling a presence or absence and a width of the nip part; and a cleaning web unit having a contact roller brought into contact with at least the pressure member via a web, a supply roller that supplies a new web, and a winding roller that winds and collects the web having wiped off an attachment on the pressure roller. The contact roller is caused to move following a movement of the pressure mechanism to maintain a constant contact position, a constant contact direction, and a constant contact force thereof with respect to the pressure member.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a fixing unit and an electrophotographic image forming apparatus using the fixing unit, such as a copier, a printer, a facsimile machine, and a multi-task machine having plural such functions. 
         [0003]    2. Description of the Related Art 
         [0004]    As a mainstream technique for fixing toner onto a recording medium, a fixing unit using heat and pressure causes a pressure member to be brought into press-contact with a fixing member including a heat source and then causes a transfer sheet having an unfixed toner image thereon to pass through an area between the fixing member and the pressure member. 
         [0005]    The fixing member is subjected to treatment, such as fluorine coating, for preventing its front surface from having toner attached. However, a so-called offset phenomenon, in which toner on a recording medium is slightly attached to the fixing member, may occur depending on environment and conditions on the recording medium. It is known that the offset toner remains on the fixing member and the pressure member contacting the fixing member and is finally reversely transferred onto the recording medium to cause disturbances in an image. To prevent this problem, the fixing member is provided with a cleaning member such as a cleaning web and a cleaning roller. The cleaning member is brought into press-contact with the fixing member and the pressure member to collect the offset toner. 
         [0006]    Some of the fixing units like the one described above have the function of causing a pressure member to be moved relative to a fixing member to be brought into press-contact with the fixing member, reduce pressure between the pressure member and the fixing member, and separate the pressure member and the fixing member from each other. Further, it is known that this function is directed to prevent the degradation of the fixing member and the pressure member or used to separate, when the fixing unit is not used, the fixing member and the pressure member from each other so as not to put a load on the members and to cool only the pressure member. Further, other fixing units may have the function of establishing plural positional relationships between a pressure member and a fixing member such as a strong press-contact state and a weak press-contact state when the pressure member is brought into press-contact with the fixing member. It is known that this function is used to produce an optimum press-contact state between the pressure member and the fixing member depending on environment and conditions on a recording medium. 
         [0007]    To perform a constant cleaning function at any positional relationship between the pressure member and the fixing member when the cleaning member is brought into contact with the movable pressure member, it is preferable that the cleaning member be brought into contact with the pressure member at a prescribed contact position, at a prescribed contact angle, and with a prescribed contact force. If a distance between a contact roller and the pressure member becomes large and the contact force of a cleaning web becomes too weak, the cleaning function cannot be satisfactorily performed, which results in disturbances in an image. 
         [0008]    Further, if the distance between the contact roller and the pressure member becomes small and the contact force becomes too strong, there is a likelihood of a normal correction of toner with the cleaning web being hindered due to the degradation of the materials of the contact roller and the pressure member and an increase in a torque required for winding the cleaning web. 
         [0009]    Further, there is no problem with the cleaning member being completely fixed with respect to the fixing unit if the moving amount of the pressure member is substantially small at the contact position of the cleaning member. However, if the pressure member is separated from the fixing member, its moving amount becomes large, which may cause cleaned-up toner to be scattered and retransferred onto a recording medium. 
         [0010]    Further, if the cleaning member is a cleaning web, a positional relationship between the shafts of a cleaning web member that contacts the pressure member, a winding roller that collects a used cleaning web, and a supply roller that supplies a new cleaning web may be broken with the movement of the pressure member. This results in the cleaning web having slack, which may hinder a normal collection of a used cleaning web. To prevent this problem, it has been known to use a method for moving a cleaning web following the movement of a pressure member. 
         [0011]    The above method, however, requires a user to manually remove a recording medium if a jam occurs after the recording medium has passed through a nip. On this occasion, the pressure member may be driven in a direction opposite to its original driving direction (i.e., rotation a roller and reverse traveling of a belt) depending on how the recording medium is removed. Consequently, the cleaning web excessively wound off the supply roller has great slack at a cleaning nip formed when the cleaning member contacts the pressure member. If the cleaning web has great slack to the extent that a normal winding operation of the cleaning web cannot be performed, a cleaning failure occurs, with the result that an abnormal image may be formed on a recording medium due to black spots, escaping of toner, or the like, and the feeding of sheets may be disabled since the slack web reaches a fixing nip. 
         [0012]    As a countermeasure for this problem in terms of control, it has been known to use a method for feeding a next sheet after the cleaning web is wound by a certain amount following a jam. However, since this method causes a user to be on standby for a time required to wind the cleaning web by a certain amount and unnecessarily consumes the cleaning web, the service life of the cleaning web is reduced. 
         [0013]    Further, as a countermeasure for this problem in terms of a mechanical configuration, it has been known to use a technique disclosed in Patent Document 3 for preventing a cleaning web from having slack. This technique has a mechanism for controlling the intensity of the contact force of a contact roller or the contact/separation thereof and is aimed at realizing an optimum cleaning function according to use situations. In the case of applying this mechanism as a countermeasure for the above problem, the contact roller separating from a pressure member with which the contact roller is brought into contact at the time of processing the jam described above eliminates concern about an excessive winding of the cleaning web from a supply roller even if the pressure member is driven in any direction. However, this method not only increases a manufacturing cost by an amount corresponding to the mechanism allowing for controlling the intensity of the contact force of the contact roller and the contact/separation thereof but also results in complicated control. Further, there is a case in which toner on a recording medium may be unfixed when a jam is caused in a fixing unit. Therefore, it is necessary to assume a case in which the toner enters a cleaning nip. Moreover, there is a case in which the toner is solidified between the cleaning web and the pressure member if the entered toner is in a semi-molten state to bond the cleaning web and the pressure member together. Therefore, even if the contact roller is separated from the pressure member, the cleaning web is pulled by a bonding part between the contact roller and the pressure member, which results in the cleaning web being wound off the supply roller. 
         [0014]    Further, it has been known to use a mechanism for using a driving source for collecting a used cleaning web and supplying a new cleaning web. However, since a cleaning member is a consumable supply and required to be replaced, it is preferable that the number of replacement parts of the cleaning member be minimized in terms of manufacturing cost. 
         [0015]    Further, since the fixing unit is at high temperature immediately after its operation, it can be assumed that a cleaning web unit is also at high temperature when being replaced. Accordingly, it is desirable that an operator not replace the cleaning web unit immediately after its operation since the operator may have a risk of being injured such as burning his/her hands. However, the operator is notified of the risk only by an alert message, and thus reliability is lacking. Therefore, it is preferable that fixing unit itself have a safety system as a hardware device.
   Patent Document 1: JP-B2-4266027   Patent Document 2: JP-A-2009-037078   Patent Document 3: JP-A-2003-167465   Patent Document 4: JP-A-2000-321914   Patent Document 5: JP-A-2008-304714   
 
       SUMMARY OF THE INVENTION 
       [0021]    In view of the above problems, the present invention may have an object of providing a fixing unit capable of performing a prescribed cleaning function regardless of the position of a pressure member and having a cleaning web unit that does not cause unnecessary feeding of a web according to a change in the position of the pressure member, and providing an image forming apparatus using the fixing unit. 
         [0022]    According to an embodiment of the present invention, there is provided a fixing unit that causes a recording medium to pass through a nip part between a fixing member and a pressure member and applies heat and pressure to the recording medium to fix toner thereon, the fixing unit including the fixing member; the pressure member brought into press-contact with a front surface of the fixing member; a pressure mechanism that changes a position at which the pressure member is brought into press-contact with the fixing member, the pressure mechanism being capable of controlling a presence or absence and a width of the nip part; and a cleaning web unit having a contact roller brought into contact with at least the pressure member via a web, a supply roller that supplies a new web, and a winding roller that winds and collects the web having wiped off an attachment on the pressure roller. The contact roller of the cleaning web unit is caused to move following a movement of the pressure mechanism to maintain a constant contact position, a constant contact direction, and a constant contact force thereof with respect to the pressure member. 
         [0023]    Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1A  is a conceptual view showing a basic configuration example of a fixing unit according to embodiments of the present invention; 
           [0025]      FIG. 1B  is a conceptual view showing a modification of the configuration example shown in  FIG. 1A ; 
           [0026]      FIG. 1C  is a conceptual view showing another modification of the configuration example shown in  FIG. 1A ; 
           [0027]      FIG. 1D  is a conceptual view showing still another modification of the configuration example shown in  FIG. 1A ; 
           [0028]      FIG. 1E  is a conceptual view showing where the configuration example shown in  FIG. 1A  reproduces its pressure-reducing state and pressure-increasing state; 
           [0029]      FIG. 1F  is a conceptual view showing an example in which a cleaning web unit is applied to the configuration example shown in  FIG. 1A ; 
           [0030]      FIG. 2A  is a view showing the pressure-increasing state according to a first embodiment of the present invention; 
           [0031]      FIG. 2B  is a view showing the pressure-increasing state according to the first embodiment of the present invention; 
           [0032]      FIG. 3  is a view showing a pressure-reducing state according to the first embodiment of the present invention; 
           [0033]      FIG. 4  is a view showing a winding roller and a supply roller in the pressure increasing state according to a second embodiment of the present invention; 
           [0034]      FIG. 5  is a view showing the winding roller and the supply roller in the pressure reducing state according to the second embodiment of the present invention; 
           [0035]      FIG. 6  is a conceptual view showing an example of the fixed cleaning web unit according to the second embodiment of the present invention; 
           [0036]      FIG. 7  is a conceptual view showing where the cleaning web unit is attached according to a third embodiment of the present invention; 
           [0037]      FIG. 8  is a conceptual view showing where the cleaning web unit is being detached according to the third embodiment of the present invention; 
           [0038]      FIG. 9  is a conceptual view showing where the detachment of the cleaning web unit is completed according to the third embodiment of the present invention; 
           [0039]      FIG. 10  is a conceptual view showing where the driving source unit for winding a cleaning web is positioned (at the pressure increasing state) according to a fourth embodiment of the present invention; 
           [0040]      FIG. 11  is a conceptual view showing where the driving source unit for winding the cleaning web is not positioned (at the pressure reducing state) according to the fourth embodiment of the present invention; 
           [0041]      FIG. 12A  is a conceptual view showing where the driving source unit for winding the cleaning web is positioned (at the pressure increasing state) according to a fifth embodiment of the present invention; 
           [0042]      FIG. 12B  is a conceptual view showing where the driving source unit for winding the cleaning web is not positioned (at the pressure reducing state) according to the fifth embodiment of the present invention; 
           [0043]      FIG. 13A  is a conceptual view showing where the driving source unit for winding the cleaning web is positioned (at the pressure increasing state) according to a sixth embodiment of the present invention; 
           [0044]      FIG. 13B  is a conceptual view showing where the driving source unit for winding the cleaning web is not positioned (at the pressure reducing state) according to the sixth embodiment of the present invention; and 
           [0045]      FIG. 14  is a vertical cross-sectional front view schematically showing the entire configuration of a full-color image forming apparatus as an object in which the embodiments of the present invention are carried out. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0046]    Hereinafter, embodiments of the present invention are described with reference to the accompanying drawings. 
       EMBODIMENTS 
       [0047]      FIG. 14  is a vertical cross-sectional front view schematically showing the entire configuration of a full-color image forming apparatus as an object in which the embodiments of the present invention are carried out. An image forming apparatus  100  of the embodiments is a tandem-type (parallel-arrangement-type) full-color image forming apparatus using an electrophotographic system. The image forming apparatus  100  has an image forming section (printer engine)  300  acting as an image forming unit at the central part of an apparatus main body and has a sheet feeding section  200  acting as a sheet feeding unit right below the image forming section  300 . The sheet feeding section  200  has, for example, four-column sheet feeding cassettes  21   a  through  21   d  each acting as a sheet storage section. These sheet feeding cassettes  21   a  through  21   d  are provided in a manner capable of being freely extracted and inserted in a back-and-forth direction (in the front/rear direction of the space of  FIG. 14 ) with respect to the apparatus main body of the image forming apparatus  100 . Further, a scanning section (scanner)  400  that scans a document image is provided above the printer engine  300 . Further, a sheet catching tray  8  to which a printed sheet is ejected is provided on the downstream side (at the upper left part of the space of  FIG. 14 ) of the sheet conveyance direction of the printer engine  300 . Note that a manual sheet feeding tray  6  acting as a sheet storage section through which a sheet is manually fed is provided on the upstream side (at the upper right part of the space of  FIG. 14 ) of the sheet conveyance direction of the printer engine  300 . 
         [0048]    In the printer engine  300 , four image forming units for the colors of yellow (Y), cyan (C), magenta (M), and black (K) are arranged in parallel above an intermediate transfer belt  30  formed of an endless belt constituting a sheet transfer unit  5 . In each of the four image forming units, electrophotographic processing members or units such as a charging unit, an optical writing unit, a development unit, and a cleaning unit are arranged along the periphery of corresponding one of drum-like photosensitive bodies  1 Y,  1 M,  1 C, and  1 K provided for the respective colors. 
         [0049]    Although not specifically shown in  FIG. 14 , the charging units perform charging processing on the front surfaces of the photosensitive bodies  1 Y,  1 M,  1 C, and  1 K, and the optical writing units irradiate the front surfaces of photosensitive bodies  1 Y,  1 M,  1 C, and  1 K with laser beams as image information. The development units visualize electrostatic latent images exposed and formed on the front surfaces of the photosensitive bodies  1 Y,  1 M,  1 C, and  1 K into images, and then the cleaning units eliminate and collect toner or the like remaining on the front surfaces of the photosensitive bodies  1 Y,  1 M,  1 C, and  1 K after the transfer of the images. After that, the images of the respective colors are successively formed on the intermediate transfer belt  30  and then overlapped one on another to form a single color image. At this time, Y (yellow) toner is first developed by the Y (yellow) image forming unit and transferred onto the intermediate transfer belt  30 . Next, C (cyan) toner is developed by the C (cyan) image forming unit and transferred onto the intermediate transfer belt  30 . Then, M (magenta) toner is developed by the M (magenta) image forming unit and transferred onto the intermediate transfer belt  30 . Finally, K (black) toner is developed by the K (black) image forming unit and transferred onto the intermediate transfer belt  30 . In the manner described above, the four colors of the toner particles are overlapped one on another to form a full-color toner image. The full-color toner image formed on the intermediate transfer belt  30  is transferred onto a transfer sheet, which is fed from the sheet feeding section  200 , by the sheet transfer unit  5 , and then fixed onto the transfer sheet by a fixing unit  7 . Finally, the transfer sheet is ejected to the sheet catching tray  8  by a sheet ejecting roller. Meanwhile, after the full-color toner image is transferred onto the transfer sheet, toner or the like remaining on the front surface of the intermediate transfer belt  30  is eliminated and collected by a belt cleaning unit. 
         [0050]    The sheet feeding section  200  is composed of the four-column sheet feeding cassettes  221   a  through  221   d  in which transfer sheets installed by a user are stuck and held. The user may set the sizes and types of the sheets installed in the sheet feeding cassettes  221   a  through  221   d  by himself or herself. Further, the sheet feeding section  200  may have a unit that automatically sets conditions for installing the sheets in the sheet feeding cassettes  221   a  through  221   d  by automatically determining the types and thicknesses of the sheets according to the positions of side fences that align the transfer sheets with each other inside the sheet feeding cassettes  221   a  through  221   d  and measurement devices that measure the resistance of the stuck sheets. The sheet feeding cassettes  221   a  through  221   d , the manual sheet feeding tray  6 , and a pair of resist rollers  11  are connected to each other by a conveyance path  12 . The transfer sheet fed from any sheet feeding place is conveyed to the pair of resist rollers  11  via the conveyance path  12 . The pair of resist rollers  11  temporarily stops the conveyance of the transfer sheet and then feeds the same to a sheet transfer section at a timing at which a given positional relationship can be established between a toner image on the intermediate transfer belt  30  and the tip end of the transfer sheet. The pair of resist rollers also performs the same function as the above on the transfer sheet fed from the manual sheet feeding tray  6 . 
         [0051]    Although not specifically shown in  FIG. 14 , plural scanning bodies on which are mounted a document illuminating light source and a mirror reciprocate to scan a document placed on a contact glass  401  in the scanner  400 . Image information scanned by the scanning bodies is condensed onto the image forming surface of a CCD by a lens provided on a rear side, and then read as an image signal by the CCD. The read image signal is digitized and subjected to image processing. Based on the image signal subjected to the image processing, optical writing is applied to the front surfaces of the photosensitive bodies by the illumination of laser diodes LD of the optical writing unit to form electrostatic latent images. Optical signals from the laser diodes LD reach the photosensitive bodies via a polygon mirror and lenses. Further, an automatic document feeder  500  that automatically feeds a document onto the contact glass is mounted above the scanner  400 . 
         [0052]      FIG. 1A  is a conceptual view showing a basic configuration example of a fixing unit according to the embodiments of the present invention. The fixing unit shown in  FIG. 1A  has a fixing belt  23  as an example of an endless fixing member, and the fixing belt  23  is laid and wound on a fixing roller  21  and a heating roller  24 . The endless belt may be laid and wound on three or more rollers or silding members. A pressure roller  22  as an example of a pressure member is brought into press-contact with the front surface of the fixing belt  23 . In an example shown in  FIG. 1A , the pressure roller  22  is brought into press-contact with a part of the fixing belt  23  wound on the fixing roller  21 . 
         [0053]    The pressure roller  22  is driven to rotate by a motor (not shown) in a direction as indicated by arrow A in  FIG. 1A . The rotation of the pressure roller  22  is transmitted to the fixing roller  21  via a gear (not shown), and the fixing roller  21  is driven to rotate in a direction as indicated by arrow B in  FIG. 1A . Further, the fixing belt  23  is driven to run in a direction as indicated by arrow C in  FIG. 1A  with the rotation of the fixing roller  21 . Furthermore, the heating roller  24  is driven to rotate in a direction as indicated by arrow D in  FIG. 1A  with the driving of the fixing belt  23 . 
         [0054]    As described above, the fixing unit of the embodiments has the endless belt laid and wound on the plural rollers and driven to run. In the example shown in  FIG. 1A , the endless belt acts as the fixing belt  23  laid and wound on at least the two rollers of the fixing roller  21  and the heating roller  24 , and the pressure member acting as the pressure roller  22  is brought into press-contact with the front surface of the fixing belt  23 . As the pressure member, a pressure belt or the like may be used. The heating roller  24  is formed to be hollow, and heaters  25  are arranged in the inner parts of the heating roller  24 . The heating roller  24  and the fixing belt  23  are heated by the heaters  25 . Alternatively, the pressure roller  22  and the fixing roller  21  may have a hollow shaft and a heater arranged therein so as to be heated. Further, temperature sensors (not shown) are oppositely arranged at a part of the fixing belt  23  in contact with the heating roller  24 , a part of the fixing belt  23  in contact with the fixing roller  21 , and the pressure roller  22 , respectively. Based on temperature detection results by the respective sensors, application of a current to the respective heaters is controlled such that the fixing belt  23  and the pressure roller  22  are set at temperatures suitable for fixing a toner layer. The fixing belt  23  is composed of, for example, a base material made of polyimide, silicon rubber formed on the base material, and a front layer made of a fluorine resin laminated on the front surface of the silicon rubber. 
         [0055]    The fixing unit shown in  FIG. 1B  shows the configuration of a modification composed of a separation roller  41 , a tension roller  42 , a fixing roller  21   a , the heating roller  24 , and a fixing belt  23   a  as an example of an endless belt laid and wound on these rollers. 
         [0056]    Further, like one shown in  FIG. 1C , the fixing unit may be configured to have the pressure member composed of two pressure rollers  22   a  and  22   b  and an endless fixing belt  23   b  laid and wound on the two pressure rollers. 
         [0057]    Furthermore, like one shown in  FIG. 1D , the fixing unit may be configured to have the pressure member shown in  FIG. 1C  in addition to the fixing member composed of the fixing belt  23  and a fixing roller  21   a  and the heating roller  24  on which the fixing belt  23  is laid and wound. 
         [0058]    According to the configuration of the fixing unit shown in  FIG. 1A , the pressure roller  22  can rotate and move about a rotation center shaft  26  as shown in  FIG. 1E  and arbitrarily reproduce its pressure-reducing state  22 - 1  and pressure-increasing state  22 - 2  with a driving unit (not shown). According to the configuration examples of the fixing units shown in  FIGS. 1B ,  1 C, and  1 D, the respective pressure members can rotate and move about rotation center shafts (not shown) and arbitrarily reproduce their pressure-increasing states and pressure-reducing states with driving units (not shown). 
         [0059]    Furthermore, like one shown in  FIG. 1F , the fixing unit may be configured to have a cleaning web unit composed of at least a cleaning web contact roller  51 , a cleaning web winding roller  52 , a cleaning web supply roller  53 , a cleaning web  54 , and a driving unit (not shown in  FIG. 1F ) that drives the cleaning web winding roller  52 . The cleaning web unit is arranged with respect to the pressure roller  22  serving as the pressure member. Thus, the fixing unit may be configured to wipe off toner remaining on the pressure roller  22  when the cleaning web  54  is brought into contact with the pressure roller  22  by the cleaning web contact roller  51 . 
         [0060]    In this example, the used cleaning web  54  having wiped off the toner is wound and collected in a direction as indicated by arrow G when the cleaning web winding roller  52  is driven to rotate in a direction as indicated by arrow E by a driving unit (not shown), while a new cleaning web  54  is wound off in a direction as indicated by arrow H and supplied to a contact part between the contact roller  51  and the pressure roller  22  when the cleaning web supply roller  53  is driven to rotate in a direction as indicated by arrow F. Note that the configuration of the fixing unit shown in  FIG. 1F  may be those composed of the fixing member and the pressure member as shown in  FIGS. 1A ,  1 C, and  1 D. 
       First Embodiment 
       [0061]    A first embodiment of the present invention is shown in  FIGS. 2A ,  2 B, and  3 . In the fixing unit composed of the fixing roller  21 , the pressure roller  22 , the heating roller  24 , the fixing belt  23 , and the heaters  25  as described above, the cleaning web unit has a member  81  shown in  FIG. 2A  and the member  81  has positioning pins  82  and  83  and a square-hole-shaped part  56 . 
         [0062]    In this fixing unit, a member  91  shown in  FIG. 2A  is freely rotatable about a rotation shaft  26  fixed inside the fixing unit, has a hole shape for holding the journal part of the pressure roller  22 , and is shaped in a manner capable of fixing a distance between the shafts of the pressure roller  22  and the rotation shaft  26 . Moreover, the member  91  has a hole-shaped part capable of completely fixing the member  81  in an XY plane when the positioning pins  82  and  83  are inserted. 
         [0063]    Moreover, in  FIG. 2B  showing a modification in which the member  91  shown in  FIG. 2A  is omitted, the member  81  can hold a slide bearing  57  allowed to move only in a direction parallel to a vector as indicated by arrow I inside the square-hole-shaped part  56 . The slide bearing  57  is pressed to the pressure roller  22  by a compression spring  55 . On this occasion, the square-hole-shaped part  56  is provided to be parallel to the vector. Therefore, the slide bearing  57  is also pressed only in the direction of the vector. 
         [0064]    The slide bearing  57  is configured to support the journal part of the cleaning web contact roller  51  and press the cleaning web contact roller  51  in the direction of the vector, i.e., in the direction of the pressure roller  22 . 
         [0065]    In such a fixing unit, when the pressure roller  22  performs a pressure-reducing operation and a pressure-increasing operation, e.g., when the pressure roller  22  moves from the pressure-increasing state shown in  FIGS. 2A and 2B  to the pressure-reducing state shown in  FIG. 3 , the cleaning web contact roller  51  and the pressure roller  22  move to positions as shown in  FIG. 3 . In this case, however, the member  91  is only rotated and moved about the rotation shaft  26 . Therefore, a positional relationship between the cleaning web contact roller  51  and the pressure roller  22  with respect to the member  91  and the vector of the pressing force of the cleaning web contact roller  51  as viewed from the pressure roller  21  remain the same. 
         [0066]    Note that this fixing unit may be replaced by any of the fixing units shown in  FIGS. 1B ,  1 C, and  1 D. 
       Second Embodiment 
       [0067]    A second embodiment of the present invention is shown in  FIGS. 4 ,  5 , and  6 . This embodiment is directed to the fixing unit composed of the fixing roller  21 , the pressure roller  22 , the heating roller  24 , the fixing belt  23 , the heaters  25 , the cleaning web contact roller  51 , the cleaning web  54 , and the compressing spring  55  acting as a pressure mechanism. As shown in  FIGS. 4 and 5 , in this fixing unit, a cleaning web winding roller  52 - 2  and a cleaning web supply roller  53 - 2  in the pressure-increasing state shown in  FIG. 4  and a cleaning web winding roller  52 - 1  and a cleaning web supply roller  53 - 1  in the pressure reducing state shown in  FIG. 5  are fixed in their positions with respect to the pressure roller  22  regardless of how the pressure roller  22  is arranged. The fixing unit of this embodiment has a mechanism, for example, shown in  FIG. 6  such that these rollers move following the pressure roller  22  to maintain a positional relationship between these rollers and the pressure roller  22 . 
         [0068]    The member  91  shown in  FIG. 6  has its shaft fixed in a manner capable of being freely rotated about the rotation shaft  26 , and a journal part  22   x  of the pressure roller  22  has its shaft fixed in a manner capable of being rotated. Moreover, the member  81  inside the cleaning web unit has its shaft fixed in a manner capable of being freely rotated with respect to the cleaning web winding roller  52  and the cleaning web supply roller  53 , and has the positioning pins  82  and  83  (hereinafter referred to as a main reference pin  82  and a sub-reference pin  83 , respectively). When the main reference pin  82  and the sub-reference pin  83  are inserted in the member  81  as shown in  FIG. 6 , a positional relationship between the member  81  and the member  91  is completely maintained in the XY plane. Accordingly, in the fixing unit, the positional relationship in the XY plane between the pressure roller  22 , the cleaning web winding roller  52 , and the cleaning web supply roller  53  can be completely maintained. 
         [0069]    Note that the fixing unit may be replaced by any of the fixing units shown in  FIGS. 1B ,  1 C, and  1 C. 
       Third Embodiment 
       [0070]    A third embodiment of the present invention is shown in  FIG. 7 . This embodiment is directed to the fixing unit composed of the fixing roller  21 , the pressure roller  22 , the heating roller  24 , the fixing belt  23 , the heaters  25 , the cleaning web contact roller  51 , the cleaning web  54 , the compression spring  55 , the cleaning web winding roller  52 , and the cleaning web supply roller  53 . In this fixing unit, the cleaning web unit includes a freely-rotatable rotation shaft  63  in which a pin  64  is press-fit, in addition to the cleaning web contact roller  51 , the cleaning web  54 , the compression spring  55 , the cleaning web winding roller  52 , and the cleaning web supply roller  53 . Further, the rotation shaft  63  has a worm gear  62  inserted and fixed therein. Moreover, a spur gear  61  is inserted and fixed in the cleaning web winding roller  52  to be meshed with the worm gear  62 . Thus, the driving of the worm gear  62  can be transmitted to the cleaning web winding roller  52 . 
         [0071]    Outside the fixing unit, a driving source unit composed of a driving source  71 , a driving shaft  72 , and a driving transmission part  73  shown in  FIG. 7  is arranged. The driving shaft  72  is arranged coaxially with the rotation shaft  63 . The driving transmission part  73  has a convex part  73   a . When the convex part  73   a  is caught in the pin  64 , the driving torque of the driving source is transmitted to the rotation shaft  63  in a direction as indicated by arrow K, so that the rotation shaft  63  is driven to rotate in a direction as indicated by arrow J. Then, the driving torque is transmitted to the cleaning web winding roller  52  via the spur gear  61 , and the used cleaning web  54  is collected. 
         [0072]    The driving transmission part  73  and the pin  64  are dedicated to transmitting the torque in the direction as indicated by arrow K with the catching of the convex part  73   a . The fixing unit is capable of being separated from the driving source unit at a driving connection part in a direction as indicated by arrow L in  FIG. 8 . 
         [0073]    Moreover, the cleaning web unit composed of the cleaning web contact roller  51 , the cleaning web  54 , the compression spring  55 , the cleaning web winding roller  52 , and the cleaning web supply roller  53  is singly detachable from the fixing unit by a holding unit (not shown) as shown in dotted lines and solid lines in  FIG. 9 . 
       Fourth Embodiment 
       [0074]    A fourth embodiment of the present invention is shown in  FIGS. 10 and 11 . This embodiment is directed to the fixing unit composed of the fixing roller  21 , the pressure roller  22 , the heating roller  24 , the fixing belt  23 , the heaters  25 , the cleaning web contact roller  51 , the cleaning web  54 , the compression spring  55 , the cleaning web winding roller  52 , and the cleaning web supply roller  53 , and directed to the driving source unit provided outside the fixing unit and composed of the driving source  71 , the driving shaft  72 , and the driving transmission part  73 . The driving source unit has a positioning pin  74  as shown in  FIGS. 10 and 11 , and the cleaning web unit provided in the fixing unit has the member  81 . The member  81  is fixed with respect to the shaft positions of the cleaning web winding roller  52  and the cleaning web supply roller  53  in the XY plane of a coordinate system XYZ fixed to the member  81 . 
         [0075]    Moreover, the member  81  has a cross-sectional shape part  81   a  having a circular hole. When the positioning pin  74  is inserted in the circular hole of the cross-sectional shape part  81   a , the cleaning web unit and the driving source unit are fixed in their positions about the X-axis direction and the Z-axis direction in the coordinate system XYZ. Further, when the driving source unit is connected to the fixing unit by a detachment and attachment unit (not shown), the driving source unit is coaxially fixed to the rotation center shaft  26  on the fixing unit shown in  FIG. 10  and freely rotatable about the rotation center shaft  26 . That is,  FIG. 10  shows where the driving source unit for winding the cleaning web is positioned (at the pressure increasing state) according to the fourth embodiment, and  FIG. 11  shows where the driving source unit for winding the cleaning web is not positioned (at the pressure reducing state). 
       Fifth Embodiment 
       [0076]    A fifth embodiment of the present invention is shown in  FIGS. 12A and 12B . This embodiment is directed to the fixing unit composed of the fixing roller  21 , the pressure roller  22 , the fixing belt  23 , the heaters  25 , the cleaning web contact roller  51 , and the pressure mechanism  55 . As shown in  FIGS. 7  and  8 , in this fixing unit, the cleaning web winding roller  52  and the cleaning web supply roller  53  at the pressure increasing state and the cleaning web winding roller  52  and the cleaning web supply roller  53  at the pressure reducing state shown are fixed in their positions with respect to the pressure roller  22  regardless of how the pressure roller  22  is arranged. This fixing unit has a mechanism similar to those, for example, shown in  FIG. 6  such that the rollers move following the pressure roller  22  to maintain a constant positional relationship between the rollers and the pressure roller  22 . 
         [0077]    Further, a support member  32  that supports a friction sliding part  33  is arranged as shown in  FIGS. 12A and 12B  such that the friction sliding member  33  is pressed to the rotation shaft of the cleaning web contact roller  51  in a direction perpendicular to the vector as indicated by arrow I. Thus, the support member  32  is completely fixed to the fixing unit at a fixing surface  31 . The friction sliding member  33  may be a plate spring formed of stainless steel or a sliding member formed of silicon rubber. Thus, when the friction sliding member  33  friction-slides with the rotation of the rotation shaft of the cleaning web contact roller  51 , the perpendicular reaction force of the friction sliding member  33  acts in a direction perpendicular to the vector as indicated by arrow I exerted by the pressure mechanism  55  of the cleaning web contact roller  51 . Note that when the fixing unit forms a fixing nip to fix unfixed toner on a recording medium, i.e., at the pressure increasing state, the friction sliding member  33  and the support member  32  are arranged such that the friction sliding member  33  is separated from the rotation shaft of the cleaning web contact roller  51  as shown in  FIG. 12A  and a friction sliding load is not applied even if the cleaning web contact roller  51  rotates. 
         [0078]    In this embodiment, the friction sliding member  33  can apply a friction sliding load to the cleaning web contact roller  51  only when the fixing unit is in the pressure reducing state. Therefore, when a normal cleaning web winding operation is performed during the fixing of unfixed toner on a recording medium, i.e., at the pressure increasing state, the friction sliding load is not applied. As a result, it is possible to reduce a torque required for winding a cleaning web and realize the power saving of a motor as the driving source and the downsizing of the unit. Further, the cleaning web winding roller  52  and the cleaning web supply roller  53  are fixed in their positions with respect to the pressure mechanism  55  that presses the pressure roller  22  acting as the pressure member and the cleaning web contact roller  51 , and move following the pressure mechanism  55 . Therefore, it is possible to maintain a positional relationship between the contact part of the cleaning web, the cleaning web winding roller  52 , and the cleaning web supply roller  53  and reliably collect and supply the cleaning web regardless of the position where the pressure roller  22  acting as the pressure member is arranged. 
         [0079]    In this embodiment, even if the pressure roller  22  is driven in a direction opposite to that when a recording medium passes through, the friction sliding member  33  is brought into contact with the rotation shaft of the cleaning web contact roller  51  to apply the friction sliding load thereto. Thus, the rotation of the cleaning web contact roller  51  is stopped to prevent the cleaning web from being excessively wound from the cleaning web supply roller  53 . Further, the friction sliding member  33  is brought into contact with the rotation shaft of the cleaning web contact roller  51  at an angle perpendicular to the vector of the contact force applied from the cleaning web contact roller  51  to the pressure roller  22 . Therefore, it is possible to form an ensured cleaning nip without having an impact on the direction and size of the vector of the contact force and realize a constant cleaning function. 
       Sixth Embodiment 
       [0080]    A sixth embodiment of the present invention is shown in  FIGS. 13A and 13B . This embodiment is directed to the fixing unit composed of the fixing roller  21 , the pressure roller  22 , the fixing belt  23 , the heating roller  24 , the heaters  25 , the cleaning web contact roller  51 , a cleaning web  54 - 1 , and the pressure mechanism  55  as in the fifth embodiment. As shown in  FIGS. 13A and 13B , in this fixing unit, a cleaning web winding roller  52 - 2  and a cleaning web supply roller  53 - 2  at the pressure increasing state shown in  FIG. 13A  and a cleaning web winding roller  52 - 1  and a cleaning web supply roller  53 - 1  at the pressure reducing state shown in  FIG. 13B  are fixed in their positions with respect to the pressure roller  22  regardless of how the pressure roller  22  is arranged. This fixing unit has a mechanism similar to that, for example, shown in  FIG. 6  such that the rollers move following the pressure roller  22  to maintain a constant positional relationship between the rollers and the pressure roller  22 . 
         [0081]    Further, as in the fifth embodiment, the friction sliding member  33  and the support member  32  that supports the friction sliding member  33  are arranged as shown in  FIGS. 13A and 13B . The support member  32  is completely fixed to the fixing unit at the fixing surface  31 . Since the material or the like of the friction sliding member  33  is similar to that of the fifth embodiment and the cleaning web winding roller  52  and the cleaning web supply roller  53  other than the friction sliding member  33  and the support member  32  are similar to those shown in  FIG. 6 , their duplicated descriptions are omitted here. In the fixing unit of this embodiment, when the fixing unit forms a fixing nip to fix unfixed toner on a recording medium, i.e., at the pressure increasing state, the friction sliding member  33  and the support member  32  are arranged such that the friction sliding member  33  is separated from the rotation shaft of the cleaning web supply roller  53  as shown in  FIG. 13A  and a friction sliding load is not applied even if the cleaning web supply roller  53  rotates. Further, at the pressure increasing state, the friction sliding member  33  and the support member  32  are arranged such that the friction sliding member  33  is brought into contact with the rotation shaft of the cleaning web supply roller  53  to apply a friction sliding load as shown in  FIG. 13B . 
         [0082]    That is, in this embodiment, even if the pressure member is driven in a direction opposite to that when a recording medium passes through, the friction sliding member  33  is brought into contact with the rotation shaft of the cleaning web supply roller  53 - 1  to apply the friction sliding load. Thus, the rotation of the cleaning web supply roller  53 - 1  is stopped to prevent the cleaning web from being excessively wound from the cleaning web supply roller  53 - 1 . As a result, it is possible to form an ensured cleaning nip and realize a constant cleaning function. 
         [0083]    In any of the above embodiments, although not shown in the figures, it is preferable to cover, among those whose temperature becomes high at the operation of the unit, parts that an operator possibly touches or is highly likely to touch at replacement with a resin material or the like having high heat insulation. If some of the parts are not covered due to their structures, the parts that possibly become in high temperature may be directly subjected to hair implantation or the like to increase their heat insulation. Moreover, in the conveyance direction of a transfer sheet or the like acting as a recording medium, parts on the downstream side of the fixing units in the above embodiments are omitted in the figures, but a gloss application unit, e.g., a second fixing unit may be provided. 
         [0084]    The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
         [0085]    The present application is based on Japanese Priority Application Nos. 2010-062534 filed on Mar. 18, 2010 and 2010-267561 filed on Nov. 30, 2010, the entire contents of which are hereby incorporated herein by reference.