Abstract:
A fixing apparatus for fixing an image formed on the recording material, includes a fixing rotatable member for forming a fixing nip; a plurality of wrapping preventing members, each provided downstream of the fixing nip with respect to a feeding direction of the recording material, for preventing the recording material from wrapping around the fixing rotatable member, wherein when the recording material is jammed downstream of the fixing nip, the wrapping preventing members moves to narrow space from the fixing rotatable member by being pushed by the jammed recording material, wherein the wrapping preventing members are arranged in a direction substantially perpendicular to the recording material feeding direction; and a connecting portion for connecting adjacent ones of the wrapping preventing members to move, when one of the wrapping preventing members is pushed by the jammed recording material, also adjacent one of wrapping preventing members to narrow the space.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a fixing apparatus which is mountable in an image forming apparatus such as a copying machine and a printer. 
         [0002]    An image forming apparatus which uses such a recording technology as an electrophotographic process, an electrostatic process, and the like, transfers a toner image onto recording medium, and then, fixes the toner image (unfixed image) to the recording medium by applying heat and pressure to the recording medium and the toner image thereon. 
         [0003]    A fixing apparatus sometimes suffers from such a problem as a paper jam that causes the fixing apparatus to fail to properly convey recording medium through the fixing apparatus. If a paper jam occurs in a fixing apparatus, there is no place for recording medium to be conveyed. Consequently, recording medium is forced into the heating unit and/or pressing unit, being wrapped around the heat roller and/or pressure roller. In other words, a fixing apparatus sometimes needs to be restored. 
         [0004]    Thus, some fixing apparatuses are provided with a member for preventing recording medium from being wrapped around a heating unit. One of such fixing apparatuses is disclosed in Japanese Laid-open Patent Application 2002-99174. In the case of this fixing apparatus, the member for preventing recording medium from wrapping around the heating unit (heat roller) is on the downstream side of the heating nip in terms of the recording medium conveyance direction. Shown in  FIG. 8  is an example of a member  102  for preventing recording medium from being wrapped around a heating unit. The member  102  for preventing recording medium from being wrapped around the heating unit is on the downstream side of the nip between the heating unit  100  and pressing unit  101  of the fixing apparatus. The member  102  is rotationally movable about an axis, and is kept pressured by a spring  104  toward the recording medium conveyance passage of the fixing apparatus. 
         [0005]    More specifically, referring to  FIG. 9 , the fixing apparatus is structured so that when it is in the normal condition in the state of recording medium conveyance, the wrapping prevention member  102  is kept separated from the heating unit  100 , whereas when the amount of force applied to the wrapping prevention member  102  is greater than the normal amount, the wrapping prevention member  102  is placed in contact with, or moved into the adjacencies of, the heating unit  100  by the force applied to the wrapping prevention member  102  by the sheet P, whereby the recording medium is prevented by the wrapping prevention member  102  from entering the heating unit  100 . This fixing apparatus, however, suffered from the following problem. That is, if the wrapping prevention member  102  is inaccurate in dimension, the amount of pressure, which the wrapping prevention member  102  applies to the heating unit  100  as it is pressed by a jammed piece of paper or the like, is liable to become excessive enough to damage the heating unit  100 , or it fails to contact the heating unit  100 , allowing thereby the sheet P to slip by. 
         [0006]    In order to ensure that a jammed sheet of paper or the like is prevented from wrapping around the heating unit  100 , it is necessary to provide a fixing apparatus with a wrapping prevention member ( 102 ) which is as long as the heating unit  100  in terms of the widthwise direction of recording medium (direction perpendicular to recording medium conveyance direction). However, a wrapping prevention member ( 102 ) which is as long as the heating unit  100  is problematic in that it is liable to warp, and therefore, is difficult to be kept accurately positioned relative to the heating unit  100 . 
         [0007]    As a means for preventing the wrapping prevention member ( 102 ) from warping, in order to keep the wrapping prevention member ( 102 ) precisely positioned relative to the heating unit  100 , it is possible to provide a fixing apparatus with multiple (two, for example) smaller wrapping prevention members  102   a  and  102   b  which are parallel to the heating unit  100 , as shown in  FIG. 10 , instead of providing the fixing apparatus with the single long wrapping prevention member ( 102 ). 
         [0008]    However, if a paper jam or the like occurs to a fixing apparatus having the two smaller wrapping prevention members  102   a  and  102   b , each of the two members  102   a  and  102   b  is moved into its position in which it remains in contact with, or its position in which it remains separated from, the heating unit  100 , independently from the other, as shown in  FIG. 11 . Thus, it is possible that the two wrapping prevention members  102   a  and  102   b  become different in position, creating thereby a gap between the two members  102   a  and  102   b . If a jammed paper or the like happens to enter this gap, the wrapping prevention member which is in its normal position, that is, the position in which it remains separated from the heating member  100  is prevented from returning to its position in which it remains in contact with the heating member  100 . If even one of the wrapping prevention members  102   a  and  102   b  fails to return to its normal position, it is liable for recording medium to enter the heating unit  100  through the gap. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention was made to solve the above-described problem. Thus, the primary object of the present invention is to provide a fixing apparatus which has multiple members for preventing recording medium from wrapping around the heating unit, and/or pressing unit, of the fixing apparatus, and yet, does not suffer from the problem that recording medium wraps around the heating and/or pressing unit. 
         [0010]    According to an aspect of the present invention, there is provided a fixing apparatus for fixing an image formed on the recording material, comprising a fixing rotatable member for forming a fixing nip a plurality of wrapping preventing members, each provided downstream of the fixing nip with respect to a feeding direction of the recording material, for preventing the recording material from wrapping around said fixing rotatable member, wherein when the recording material is jammed downstream of the fixing nip, said wrapping preventing members moves to narrow space from said fixing rotatable member by being pushed by the jammed recording material, wherein said wrapping preventing members are arranged in a direction substantially perpendicular to the recording material feeding direction; and a connecting portion for connecting adjacent ones of said wrapping preventing members to move, when one of said wrapping preventing members is pushed by the jammed recording material, also adjacent one of wrapping preventing members to narrow the space. 
         [0011]    These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic sectional view of a laser beam printer, which is an example of an image forming apparatus equipped with a fixing apparatus in accordance with the present invention, in the first embodiment of the present invention. It shows the general structure of the image forming apparatus. 
           [0013]      FIG. 2  is a schematic sectional view of the fixing apparatus in the first embodiment of the present invention when recording medium is being normally conveyed through the fixing apparatus 
           [0014]      FIG. 3  is a perspective view of the fixing apparatus in the first embodiment of the present invention when recording medium is being normally conveyed through the fixing apparatus. 
           [0015]      FIG. 4  is a schematic sectional view of the wrapping prevention member of the fixing apparatus in the first embodiment, and its adjacencies, of the fixing apparatus in the first embodiment, when the wrapping prevention member is in contact with the heating unit of the fixing apparatus because of the pressure from the jammed recording medium. 
           [0016]      FIG. 5  is a perspective view of the fixing apparatus in the second embodiment of the present invention. 
           [0017]      FIG. 6  is a schematic sectional view of the fixing apparatus in the third embodiment of the present invention. 
           [0018]      FIG. 7  is a perspective view of the fixing apparatus in the third embodiment of the present invention. 
           [0019]      FIG. 8  is a schematic sectional view of a fixing apparatus having a conventional member for preventing recording medium from wrapping around the heating unit of the fixing apparatus when the wrapping prevention member of the fixing apparatus is in its normal position. It shows the structure of the fixing apparatus. 
           [0020]      FIG. 9  is a schematic sectional view of the fixing apparatus having a conventional member for preventing recording medium from wrapping around the heating unit of the fixing apparatus when recording medium has become jammed in the fixing apparatus. It shows the state of the wrapping preventing member of the fixing apparatus. 
           [0021]      FIG. 10  is a schematic sectional view of the fixing apparatus having multiple (two, for example) wrapping prevention members, when recording medium has become jammed in the fixing apparatus. It shows the state of the wrapping preventing member of the fixing apparatus. 
           [0022]      FIG. 11  is a perspective view of the fixing apparatus having multiple (two, for example) wrapping prevention members, when recording medium has become jammed in the fixing apparatus. It shows the state of the wrapping preventing member of the fixing apparatus. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       [0023]    Hereinafter, the fixing apparatuses and image forming apparatuses in the preferred embodiments of the present invention are described with reference to the appended drawings. 
       &lt;General Structure of Image Forming Apparatus&gt; 
       [0024]      FIG. 1  is a schematic sectional view of a laser beam printer, which is an example of an image forming apparatus equipped with a fixing apparatus in accordance with the present invention. It shows the general structure of the image forming apparatus. 
         [0025]    The image forming apparatus A in this embodiment is a laser beam printer which forms images with the use of an electrophotographic method. To describe the general structure of the image forming apparatus along with the image forming operation of the apparatus, there are four process cartridges  1 Y,  1 M,  1 C, and  1 K in the image forming portion of the apparatus. Each process cartridge  1  contains a photosensitive drum, a developing device, etc., and is removably mountable in the image forming portion. To describe the image forming operation of the apparatus, first, yellow, magenta, cyan, and black toner images are formed on the four photosensitive drums in the four process cartridges  1 , one for one. Then, a full-color toner image is formed on the intermediary transfer belt  3  of the apparatus by the sequential transfer of the four toner images, different in color, from the photosensitive drums onto the intermediary transfer belt  3 . Then, the full-color toner image is transferred onto recording medium (sheet of paper, which is going to be referred to simply as sheet). More specifically, while the full-color image is being formed, one of the sheets P in a sheet cassette  4  which is in the bottom portion of the main assembly of the image forming apparatus is conveyed to the second transfer portion of the apparatus by a sheet feeder roller  5  and a pair of recording medium conveyance rollers  6  with such a timing that the sheet P arrives at the second transfer portion at the same time as the full-color toner image arrives at the second transfer portion. Then, while the sheet P is conveyed through the second transfer portion, the full-color toner image on the intermediary transfer belt  3  is transferred onto the sheet P by applying bias to a second transfer roller  7 . 
         [0026]    After the transfer of the full-color toner image onto the sheet P, the sheet P is conveyed to the fixing apparatus B which is above the second transfer portion. Then, while the sheet P is conveyed through the fixing apparatus B, the sheet P and the full-color toner image thereon are subjected to heat and pressure, whereby the full-color toner image is fixed to the sheet P. Then, the sheet P is discharged into a delivery tray  9  by a pair of discharge rollers  8  while being guided by sheet guiding members  32  and  38 . 
       &lt;Fixing Apparatus&gt; 
       [0027]    Next, the fixing apparatus B in this embodiment is described. The fixing apparatus B in this embodiment has: a heating means for heating the sheet P and the full-color toner image thereon after the transfer of the full-color toner image onto the sheet P; and a pressure unit  31  which is pressed upon the heating means to form a heating nip (fixation nip). The fixing apparatus B fixes the full-color toner image to the sheet P by heating the sheet P and the full-color toner image thereon while conveying the sheet P through the nip. 
         [0028]    Referring to  FIG. 2 , the heating unit  30 , which is a sheet heating means, is made up of a cylindrical fixation film  33  (circularly movable member), a heater  34 , and a stay  35 . The fixation film  33 , which is thin and cylindrical, is formed of highly heat-resistant and thermally conductive plastic or the like. The heater  34  is in contact with the inward surface of the fixation film  33  and heats the fixation film  33 . The stay  35  is rigid and heat resistant. It also is in contact with the inward surface of the fixation film  33 . 
         [0029]    The heater  34  is a ceramic heater, or a carbon heater, for example. It is a heat generating member which is in connection with an unshown electric power source, and generates heat as electric current is flowed through it. It is solidly supported by the stay  35  by being fitted in a groove of the stay  35 . The fixation film  33  is fitted around the heater  34  and stay  35 , and is circularly movable. 
         [0030]    Next, referring to  FIG. 2 , the pressing unit  31 , which is a pressure applying means, is made up of a pressure roller  36  and a compression spring  37 , etc. The compression spring  37  is for keeping the pressure roller  36  pressed upon the heating unit  30 . The pressure roller  36  is made up of a metallic core  36   a  and an elastic layer  36   b . The elastic layer  36   b  is cylindrical and heat resistant. It is molded so that it covers the entirety of the peripheral surface of the metallic core  36   a . In other words, the surface layer of the pressure roller  36  is elastic. Therefore, as the pressure roller  36  is pressed upon the heating unit  30 , a nip N is formed between the pressure roller  36  and heating unit  30 . The nip N is preset in width in terms of the recording medium conveyance direction, and also, is preset in internal pressure. The pressure roller  36  is rotated by an unshown power source at a preset peripheral velocity. As the pressure roller  36  is rotated, friction is generated between the fixation film  33  and pressure roller  36 , whereby the fixation film  33  is rotated by the friction in a manner to follow the rotation of the pressure roller  36 . 
         [0031]    As the fixing apparatus B becomes ready for fixation, that is, when the pressure roller  36  is being rotated; the fixation film  33  is rotated by the rotation of the pressure roller  36 ; and the temperature of the heater  34  is being kept at a preset level by the electric current flowed through the heater  34 , the sheet P, on which the unfixed full-color toner image is borne, is conveyed through the nip N between the fixation film  33  and pressure roller  36 , remaining pinched between the fixation film and pressure roller, while the nip N is kept at a preset level in temperature. Thus, while the sheet P is conveyed through the nip N, the heat from the heater  34  is given to the sheet P through the fixation film  33 . Consequently, the unfixed full-color tone image is melted and fixed to the sheet P by the heat and pressure applied to the sheet P in the nip N. 
         [0000]    (Wrapping Prevention Member: Member for Preventing Recording Medium from Wrapping around Heating Unit) 
         [0032]    After the sheet P is conveyed out of the heating nip N, it is separated from the pressure roller  36  by the curvature of the peripheral surface of the pressure roller  36 . The fixing apparatus B is provided with a guiding means for guiding the sheet P after the sheet P is convey through the heating nip N. The guiding means is on the downstream side of the nip N in terms of the sheet conveyance direction. Referring to  FIG. 3 , the guiding means is made up of multiple (two in this embodiment) guiding members  32  ( 32   a  and  32   b ), which are in alignment with each other in the widthwise direction of the sheet P, that is, the direction perpendicular to the sheet conveyance direction. 
         [0033]    In this embodiment, it is each of the guiding members  32  that plays the role of a member (wrapping prevention member) for preventing the sheet P from wrapping around the fixation film  33 . However, the wrapping prevention member does not need to have a function of guiding recording medium (sheet P). This is also true with the second and third embodiments of the present invention which will be described later. 
         [0034]    The wrapping prevention member is a member for preventing recording medium from wrapping around the rotational fixing member of the fixing apparatus B, and is on the downstream side of the fixation nip N in terms of the recording medium conveyance direction, as described above. 
         [0035]    After the sheet P is conveyed through the heating nip N, it is discharged into the delivery tray  9  by the pair of discharge rollers  8  while remaining pinched between the two discharge rollers  8  and being guided by the aforementioned guiding members  32   a  and  32   b.    
         [0036]    The guiding members  32   a  and  32   b  are attached to the main assembly of the fixing apparatus B in such a manner that they are rotationally movable about the axis  40 . They are kept pressured by springs  39  toward the sheet conveyance passage. When the sheet P is being normally conveyed through the fixing apparatus B, stoppers  41  are kept anchored to the stopper seat portions of the main assembly of the fixing apparatus B, by the springs  36 . While the stoppers  41  remain anchored to the stopper seat portions  42 , the edge of each of the guiding members  32   a  and  32   b  is not in contact with the heating unit  30  (there is a gap between edge of guiding member and fixation film), and therefore, the guiding members  32   a  and  32   b  function as a member for guiding the sheet P after the sheet P is conveyed through the heating nip N. 
         [0037]    The amount of the resiliency of the guide spring  39  is set to such a value that the amount of the force generated by the guide springs  39  allows the guiding members  32   a  and  32   b  to move to the heating unit  30  if the sheet P fails to be properly conveyed through the fixing apparatus B (for example, if the sheet P is jammed) after it is conveyed through the heating nip N, Thus, as recording medium is jammed in the downstream portion (space) of the recording medium passage in the fixing apparatus B in terms of the recording medium conveyance direction, each of the wrapping prevention members moves by being pressed by the jammed recording medium, in the direction to narrow the gap (G in  FIG. 2 ) between itself and the rotational fixing member. 
         [0038]    Next, referring to  FIG. 3 , the guiding member  32   a  is provided with a pair of tabs  32   a   1  and  32   a   2 , and the guiding member  32   b  is provided with a pair of tabs  32   b   1  and  23   b   2 . More specifically, the pair of tabs  32   a   1  and  32   a   2  of the first guiding member  32   a , and the pair of tabs  32   b   1  and  32   b   2  of the second guiding member  32   b , are shaped and position so that as one of the guiding members  32   a  and  32   b  is rotationally moved by the jammed recording medium, the two pairs of tabs interlock with each other. 
         [0039]    That is, the tab  32   a   1  of the first guiding member  32   a  is positioned closer to the sheet passage than the tab  32   b   1  of the second guiding member  32   b . Further, the tab  32   b   2  of the second guiding member  32   b  is positioned closer to the sheet passage than the tab  32   a   2  of the first guiding member  32   a . Therefore, as the guiding member  32   a  ( 32   b ) moves, the guiding member  32   b  ( 32   a ) is moved by the movement of the guiding member  32   a  ( 32   a ). 
         [0040]    Since the fixing apparatus B is structure as described above, if the sheet P fails to be properly conveyed, for example, the sheet P becomes jammed between the nip N and pair of discharge rollers  8 , after it is conveyed through the nip N, the sheet P presses on one or both of the guiding members  32   a  and  32   b  because the sheet P has no place to go. 
         [0041]      FIG. 4  is a schematic sectional view of the guiding members  32   a  and  32   b  and their adjacencies, when they are kept in contact with the heating unit  30  by the jammed sheet P. For example, if the amount of the force which the first guiding member  32   a  receives from the jammed sheet P is greater than the amount of the pressure which the first guiding member  32   a  receives from the springs  39 , the guiding member  32   a  moves toward the heating unit  30 . As the guiding member  32   a  moves toward the heating unit  30 , the tabs  32   a   1  and  32   a   2  press on the tabs  32   b   1  and  32   b   2 , respectively, and therefore, the second guiding member  32   b  is moved by the movement of the guiding member  32   a , being thereby moved toward the heating unit  30  with the first guiding member  31   a . That is, each wrapping prevention member has a pair of tabs, which interlock with the tabs of the adjacent wrapping prevention member so that as one of the guiding members  32   a  and  32   b  is pressed by the jammed recording medium (sheet P), the adjacent guiding member also is moved in the direction to reduce the gap between the guiding member and the rotational fixing member. 
         [0042]    That is, the fixing apparatus B is structured so that as a sheet of recording medium becomes jammed on the downstream side of the fixation nip N in terms of the recording medium conveyance direction, the guiding members  32   a  and  32   b  are placed in contact with the heating unit  30  to block the sheet passage (gap between guiding members  32  and heating unit  30 ) which allows the jammed sheet to wrap around the heating unit  30 . 
         [0043]    To summarize, the guiding means  32  of the fixing apparatus B in this embodiment is made up of two guiding members  32   a  and  32   b , which are virtually half in size compared to a conventional guiding member  32 , being therefore unlikely to warp. In other words, the guiding means  32  in this embodiment, which is a combination of the guiding members  32   a  and  32   b , is likely to remain more accurate in shape and dimension than a conventional guiding member ( 32 ), and therefore, contacts, and remains in contact with the heating unit  30  more precisely than a conventional one, when the sheet P happens to become jammed. 
         [0044]    Further, even though the guiding means  32  is made up of multiple (two) guiding members ( 32   a  and  32   b ), the multiple guiding members are structured so that as one of the multiple guiding members is moved by the jammed paper or the like, the other guiding member is moved by the first guiding member. Therefore, the guiding members are positioned and kept positioned with higher level of accuracy, being therefore capable of ensuring that the sheet P is prevented from entering the heating unit. 
         [0045]    Incidentally, in this embodiment, the fixing apparatus B is structured so that the guiding members  32   a  and  23   b  come into contact with the heating unit  30  to prevent the jammed sheet from entering the heating unit  30 . However, it is possible to structure the fixing apparatus B so that the guiding members  32   a  and  32   b  come into contact with the pressing unit  31  to prevent the jammed sheet from entering the pressing unit  31 . 
       Embodiment 2 
       [0046]    Next, referring to  FIG. 5 , the fixing apparatus in the second preferred embodiment of the present invention is described. The basic structure of the fixing apparatus in this embodiment is the same as that of the fixing apparatus in the first embodiment, and therefore, is not going to be described here, in order not to repeat the same description. Here, therefore, only the structural features of the fixing apparatus in this embodiment, which characterizes this embodiment, are described. Further, the structural components of the fixing apparatus in this embodiment, which are the same in function as the counterparts in the first embodiment, are given the same referential codes as those given to the counterparts, one for one. 
         [0047]    In the first embodiment, the fixing apparatus B had two guiding members  32   a  and  32   b . In this embodiment, the fixing apparatus B is provided with three guiding members. That is, it has one more guiding member than the fixing apparatus B in the first embodiment. More specifically, the guiding means in this embodiment is made up of three guiding members, that is, first, second, and third guiding members  32   a ,  32   b , and  32   c , respectively, which are in alignment in the lengthwise direction of the heating nip N. Further, the three guiding members  32   a ,  32   b , and  32   c  are parallel to each other. The fixing apparatus is structured so that the three guiding members  32   a ,  32   b , and  32   c  are rotationally movable amount the axis  40 , and also, so that when the fixing apparatus is normal in the state of sheet conveyance, the stopper of each of the three guiding members  32   a ,  32   b , and  33   c  is kept in contact with the corresponding stopper seat of the main frame of the fixing apparatus, by the corresponding spring  39 . 
         [0048]    Further, the first guiding member  32   a  is provided with a pair of tabs  32   a   1  and  32   a   2 , and the second guiding member  32   b  is provided with a pair of tabs  32   b   1  and  32   b   2  and a pair of tabs  32   b   3  and  32   b   4 . The third guiding member  32   c  is provided with a pair of tabs  32   c   1  and  32   c   2 . The pair of tabs  32   a   1  and  32   a   2 , pair of tabs  32   b   1  and  32   b   2 , pair of tabs  32   b   3  and  32   b   4 , and pair of tabs  32   c   1  and  32   c   2  are shaped and positioned so that as one of the guiding members  32   a ,  32   b , and  32   c  is moved by the jammed recording medium (paper), the pair of tabs  32   a   1  and  32   a   2  interlock with the pair of tabs  32   b   1  and  32   b   2 , and the pair of tabs  32   b   3  and  32   b   4  interlock with the pair of tabs  32   c   1  and  32   c   2 . 
         [0049]    Thus, if one of the three guiding members  32   a ,  32   b , and  32   c  is moved by the sheet P, the other guides also move with the guiding member moved by the sheet P, as in the case of the first embodiment. 
         [0050]    Incidentally, the sheet guiding means of the fixing apparatus may be made up of four or more guiding members, as long as the multiple guiding members interlock with each other as one of the guiding members is moved by the jammed recording medium. The greater the number of the sheet guiding members of the sheet guiding means of the fixing apparatus, the smaller in size each of the sheet guiding members, and therefore, the fixing apparatus is less likely to suffer from the effects of the warping of the sheet guiding members, that is, the problem that recording medium is wrapped around the heating unit because of the warping of the sheet guiding means. 
       Embodiment 3 
       [0051]    Next, referring to  FIGS. 6 and 7 , the fixing apparatus in the third of the preferred embodiments of the present invention is described. The fixing apparatus in this embodiment is the same as that in the first embodiment except for the structure of the guiding member  32 . Therefore, the portions of the fixing apparatus in this embodiment other than the guiding member  32  are not going to be described. 
         [0052]    Referring to  FIGS. 6 and 7 , the guiding means  32  in this embodiment is made up of a pair of guiding members  32   a  and  32   b , which are referred to as the first and second guiding members, respectively. The first and second guiding members  32   a  and  32   b  are in alignment in the direction parallel to the lengthwise direction of the heating nip N, and are parallel to each other. 
         [0053]    Each of the guiding members  32   a  and  32   b  are attached to a guiding member supporting portion which has projections  50 , whereas the main frame of the fixing apparatus is provided with a pair of guiding member guiding portions  51  which have elongated holes one for one. Each projection  50  is fitted in the hole of the corresponding guiding member guiding portion  51  so that it is vertically slidable in the hole. Therefore, the guiding members  32   a  and  32   b  are vertically movable within a range which corresponds in size to the vertical dimension of the elongated hole of the guiding member guiding portion  51 . Further, the guiding members  32   a  and  32   b  are kept pressured upward by a pair of springs  39 . That is, the fixing apparatus is structured so that when it is normal in the state of recording medium conveyance, each projection  50  is in contact with the seat portion β of the guiding member guiding portion  51 . 
         [0054]    The resiliency of the spring  39  is set to such a value that after the fixation of the full-color toner image to the sheet P, if the fixing apparatus suffers from a recording medium conveyance error, such as a paper jam, and the guiding members  32   a  and  32   b  are pressed by the jammed sheet P, the guiding members  32   a  and  32   b  are downwardly moved by the jammed paper to be placed in contact with the heating unit  30 . 
         [0055]    Further, the first guiding member  32   a  is provided with a pair of tabs  32   a   1  and  32   a   2 , and the second guiding member  32   b  is provided with a pair of tabs  32   b   1  and  32   b   2 , as in the first embodiment. The pair of tabs  32   a   1  and  32   a   2  and pair of tabs  32   b   1  and  32   b   2  are shaped and positioned so that if the guiding member  32   a  ( 32   b ) vertically moves, the tabs  32   a   1  and  32   a   2  ( 32   b   1  and  32   b   2 ) interlock with the tabs  32   b   1  and  32   b   2  ( 32   a   1  and  32   a   2 ), respectively, and causes the guiding member  32   b  ( 32   a ) to move with the guiding member  32   a  ( 32   b ). 
         [0056]    Thus, if the fixing apparatus suffers from the problem that after the sheet P is conveyed through the heating nip N, it becomes stuck between the heating nip N and pair of discharge rollers  8  because of sheet conveyance error, the sheet P pushes one or both of the guiding members  32   a  and  32   b  downward since the sheet P has no place to go. If the amount of force applied to one of the guiding members is greater than the amount of force applied to the guiding member by the springs  39 , the other guiding member is slid downward by the guiding member which is under the pressure from the jammed paper. Consequently, the guiding members  32   a  and  32   b  come into contact with the heating unit  30 , blocking thereby the passage (gap between guiding members and heating unit) which allows the sheet P to wrap around the heating unit  30 . 
         [0057]    According to the present invention, even if the fixing apparatus is provided with multiple (two, for example) sheet guiding members and is structured so that the guiding members vertically slide, the multiple guiding members can be moved together. 
         [0058]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
         [0059]    This application claims priority from Japanese Patent Application No. 038897/2010 filed Feb. 24, 2010 which is hereby incorporated by reference.