Patent Publication Number: US-2023136810-A1

Title: Image heating apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an image heating apparatus for fixing a toner image transferred onto a recording material in an image forming apparatus that adopts an electrophotographic system or an electrostatic recording system, and the image forming apparatus. 
     Description of the Related Art 
     Hitherto, in an image forming apparatus adopting an electrophotographic system, an electrostatic latent image formed on a photosensitive drum serving as an image bearing member is developed using toner to form a toner image and the toner image is transferred to a recording material before the toner image is fixed to the recording material in a fixing unit, which is one example of an image heating apparatus. One example of a fixing unit used widely is a heat-pressure type unit that includes a heating rotary member and a pressing rotary member that applies pressure to the heating rotary member, wherein a fixing nip portion formed between the heating rotary member and the pressing rotary member nips and conveys the recording material, by which the toner borne on the recording material is fixed thereto by heat and pressure. 
     Processing speed of electrophotographic image forming apparatuses is increasing and in response thereto, the size of the heating rotary member in the fixing unit is increased. Therefore, a fixing unit has been developed in which the heating rotary member stretched across a fixing roller and a heating roller is formed of a thin belt member (refer to Japanese Patent Application Laid-Open Publication No. 2011-123181). According to the fixing unit disclosed in Japanese Patent Application Laid-Open Publication No. 2011-123181, for example, a heating unit including the heating rotary member can be replaced with respect to a frame member such as a casing of the fixing unit to facilitate maintenance and extend service life of the heating rotary member forming the fixing nip portion. 
     However, according to the fixing unit disclosed in the above-mentioned Japanese Patent Application Laid-Open Publication No. 2011-123181, a cover of the frame member provided in the fixing unit is designed to open to a direction toward which the heating unit is removed. Therefore, when removing the heating unit from the frame member for replacement, the opened cover may be in the way of with the heating unit and hinder the replacement operation of the heating unit. 
     The present invention provides an image heating apparatus and an image forming apparatus that enables to improve workability of attaching and detaching the heating unit to and from the frame member. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, an image heating apparatus includes a first rotary member configured to heat a toner image formed on a recording material, a second rotary member configured to contact the first rotary member and form a fixing nip portion with the first rotary member for conveying the recording material, a frame member configured to support the first rotary member and the second rotary member, a guide portion configured to guide the first rotary member to be moved upstream in a conveyance direction of the recording material when the first rotary member is being removed, and a cover attached to the frame member and configured to turn around a rotation shaft to open and close the guide portion. The cover is configured to turn in a direction toward the conveyance direction to open the guide portion. 
     According to a second aspect of the present invention, an image forming apparatus configured to form an image on a recording material includes the image heating apparatus, and a drawer portion configured to support the image heating apparatus and be drawn out from the image forming apparatus. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view illustrating a general configuration of an image forming apparatus according to an embodiment. 
         FIG.  2    is a control block diagram of the image forming apparatus according to the embodiment. 
         FIG.  3    is a cross-sectional view illustrating a state in which a heating unit is positioned at an attachment position and a cover is closed to form a fixing nip portion in a fixing unit according to the embodiment. 
         FIG.  4    is a cross-sectional view illustrating a state in which the heating unit is positioned at the attachment position with the cover opened in the fixing unit according to the embodiment. 
         FIG.  5    is a cross-sectional view illustrating a state in which the heating unit is positioned at an insertion start position with the cover opened in the fixing unit according to the embodiment. 
         FIG.  6    is a cross-sectional view illustrating a state in which the heating unit is positioned at an outer portion of the opening portion with the cover opened in the fixing unit according to the embodiment. 
         FIG.  7    is a cross-sectional view illustrating a state in which the heating unit is positioned at the attachment position with the cover not closed in the fixing unit according to the embodiment. 
         FIG.  8    is a cross-sectional view illustrating a state in which the heating unit is positioned at the attachment position with the cover closed and the fixing nip portion not formed in the fixing unit according to the embodiment. 
         FIG.  9    is a perspective view illustrating a state in which the fixing unit is drawn out of the image forming apparatus in the fixing unit according to the embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the present invention will be described in detail with reference to  FIGS.  1  to  9   . In the present embodiment, a tandem-type full color printer is illustrated as an example of an image forming apparatus  1 . However, the present technique is not limited to application to tandem-type image forming apparatuses  1 , and it can be applied to other types of image forming apparatuses. Further, the printer is not limited to full-color printers, and it can be monochrome or mono-color printers. 
     Image Forming Apparatus 
     As illustrated in  FIG.  1   , the image forming apparatus  1  is a full color printer that adopts an electrophotographic system in which four image forming units PY, PM, PC, and PK of yellow, magenta, cyan and black are provided in an apparatus body. The present embodiment adopts a tandem intermediate-transfer system in which the image forming units PY, PM, PC, and PK are arranged along a direction of rotation of an intermediate transfer belt  7  described later. The image forming apparatus  1  forms a toner image on a recording material S according to an image signal from a document reader not shown connected to the apparatus body or a host device such as a personal computer connected to and communicating with the apparatus body. Sheet materials such as paper, plastic film and cloth are examples of the recording material S. Further, the image forming apparatus  1  includes a control unit  20  for performing various controls such as an image forming process. 
     An image forming process will be described. At first, the image forming units PY, PM, PC, and PK will be described. In the present embodiment, the image forming units PY, PM, PC, and PK adopt approximately the same configuration except for the differences in toner colors, which are yellow, magenta, cyan, and black. The image forming unit PY of yellow toner will be described hereafter as an example, and descriptions of other image forming units PM, PC, and PK are omitted. 
     The image forming unit PY is mainly composed of a photosensitive drum  2 , a charging apparatus  3 , an exposing unit  4 , and a developing apparatus  5 . A surface of the photosensitive drum  2  serving as an example of an image bearing member being driven to rotate is uniformly charged in advance by the charging apparatus  3 , and thereafter, an electrostatic latent image is formed thereon by the exposing unit  4  driven based on an image information signal. That is, an electrostatic latent image is formed on the photosensitive drum  2 . The electrostatic latent image formed on the photosensitive drum  2  is developed by toner in the developing apparatus  5  and visualized as toner image. Toner in the developer consumed by image formation is replenished together with carrier from a toner cartridge not shown. 
     Thereafter, a predetermined pressurizing force and primary transfer bias are applied by a primary transfer roller  6  arranged opposed to the photosensitive drum  2  interposing the intermediate transfer belt  7 , and the toner image formed on the photosensitive drum  2  is primarily transferred to the intermediate transfer belt  7 . Transfer residual toner remaining slightly on the photosensitive drum  2  after primary transfer is removed by a cleaning device 8 to prepare the photosensitive drum  2  for a subsequent image forming process. 
     The intermediate transfer belt  7  is stretched across a tension roller  10 , a secondary transfer inner roller  11  and a drive roller  12 . The intermediate transfer belt  7  is driven to move in a direction of arrow R1 in the drawing by the drive roller  12 . Image forming processes of respective colors performed by the above-mentioned image forming units PY, PM, PC, and PK are carried out at timings set so that toner images are sequentially superposed to a toner image previously formed upstream in the direction of movement on the intermediate transfer belt  7  via primary transfer. As a result, a full-color toner image is finally formed on the intermediate transfer belt  7  and conveyed to a secondary transfer portion T 2 . The secondary transfer portion T 2  is a transfer nip portion formed between the intermediate transfer belt  7  stretched on the secondary transfer inner roller  11  and a secondary transfer outer roller  13 . Transfer residual toner that remains after passing through the secondary transfer portion T 2  is removed from the intermediate transfer belt  7  by a transfer cleaner device  14 . 
     A conveyance process of the recording material S to the secondary transfer portion T 2  is performed at a similar timing as a forming process of toner image that has been conveyed to the secondary transfer portion T 2 . In the conveyance process, the recording material S is fed from a sheet cassette and the like not shown and sent to the secondary transfer portion T 2  at a matched timing with the forming of image. At the secondary transfer portion T 2 , secondary transfer voltage is applied to the secondary transfer inner roller  11 . 
     As described, toner image is secondarily transferred from the intermediate transfer belt  7  to the recording material S at the secondary transfer portion T 2  by the image forming process and the conveyance process. Thereafter, the recording material S is conveyed to a fixing unit  30  and subjected to heat and pressure by the fixing unit  30 , according to which the toner image is melted and fixed to the recording material S. The fixing unit  30  is an example of the image heating apparatus for fixing an unfixed toner image formed by the image forming unit to the recording material S. The recording material S to which toner image has been fixed is discharged to a sheet discharge tray not shown by a sheet discharge roller. 
     Control Unit 
     The image forming apparatus  1  includes the control unit  20  for performing various controls such as the image forming operation described above. The operations of various units of the image forming apparatus  1  are controlled by the control unit  20  provided in the image forming apparatus  1 . The series of image forming operations are controlled by the control unit  20  based on various input signals entered through an operation portion provided on an upper side of the apparatus body or via a network. 
     As illustrated in  FIG.  2   , the control unit  20  includes a CPU (Central Processing Unit)  21  serving as an arithmetic control unit, a ROM (Read Only Memory)  22 , a RAM (Random Access Memory)  23  and so on. The CPU  21  reads programs corresponding to control procedures stored in the ROM  22  to carry out control of various units of the image forming apparatus  1 . The RAM  23  stores working data and input data, and the CPU  21  refers to the data stored in the RAM  23  based, for example, on the program mentioned earlier to perform control. A drive motor M 1  for driving a fixing belt  41  and a pressure roller  32  of the fixing unit  30  described later, a heater  48  and a thermistor  49  described later are connected to the control unit  20 . 
     Fixing Unit 
     Next, the fixing unit  30  will be described in detail with reference to  FIG.  3   . As illustrated in  FIG.  3   , the fixing unit  30  is a belt heating-type heating apparatus that is in the form of a cartridge being detachably attached to the apparatus body of the image forming apparatus  1  (refer to  FIG.  1   ). The fixing unit  30  includes a casing  31 , which is an example of a frame member, a heating unit  40 , a pressure roller  32  serving as a second rotary member, a separation unit  50  and a cover  60 . The casing  31  according to the present embodiment is formed by welding together a plurality of metal plates. However, the metal plates can be fixed by methods other than welding, such as by screw engagement. 
     Meanwhile, according to the present embodiment, the fixing unit  30  is supported by a drawer portion  100  that can be drawn out of the image forming apparatus  1 , as illustrated in  FIG.  9   . In a state where a cover  101  of the image forming apparatus  1  is opened and the drawer portion  100  is drawn out to a drawing direction Y, the fixing unit  30  can be accessed. In the present embodiment, the drawing direction Y is a horizontal direction that is orthogonal to a conveyance direction X, i.e., sheet conveyance direction, of the recording material. 
     The heating unit  40  includes the fixing belt  41  serving as a first rotary member that is a rotatable endless belt, a pressure pad  42  serving as a fixing member, a heating roller  43 , a steering roller  44 , a stay  45 , and unit side plates  46  that integrate these members as a cartridge. The heating unit  40  is attached in a detachable manner to the casing  31 . 
     The fixing belt  41  is a thin, cylindrical belt member having thermal conductivity and heat resisting property, and can abut against and heat the recording material S. In the present embodiment, the fixing belt  41  adopts a three-layer structure including a base layer, an elastic layer formed on a circumference of the base layer, and a releasing layer formed on a circumference of the elastic layer. The base layer is formed of polyimide resin (PI) and has a thickness of 30 µm, and the elastic layer is formed of silicone rubber and has a thickness of 300 µm. The releasing layer is formed of PFA (tetrafluoro-ethylene-perfluoro alkoxy ethylene copolymer resin) as fluororesin and has a thickness of 30 µm. The fixing belt  41  is stretched across the pressure pad  42 , the heating roller  43  and the steering roller  44 . An outer diameter of the fixing belt  41  is, for example, 120 mm. 
     The pressure pad  42  is supported by the stay  45  and pressed by the pressure roller  32  interposing the fixing belt  41 . The stay  45  is formed of stainless steel, and both ends in the rotational axis direction of the stay  45  are supported by fixing frames  33  of the casing  31  of the fixing unit  30 . The stay  45  includes a separation plate positioning portion  45   a . A fixing nip portion N is formed by a contact portion of the fixing belt  41  and the pressure roller  32 . The rotational axis direction refers to a direction orthogonal to a sheet conveyance direction X of the recording material S that had passed through the fixing nip portion N. 
     The pressure pad  42  is formed, for example, of LCP (liquid crystal polymer) resin. A lubricating sheet  47  is interposed between the pressure pad  42  and the fixing belt  41 . API (polyimide) sheet being coated with PTFE (polytetrafluoroethylene) with a thickness of 100 µm is used as the lubricating sheet  47 . The PI sheet has 100-µm projections formed at 1-mm intervals to reduce a contact area with the fixing belt  41 , to thereby reduce sliding resistance. A lubricant is applied to an inner side of the fixing belt  41  so that the fixing belt  41  slides smoothly on the pressure pad  42 . The lubricant can be, for example, a silicone oil. 
     The heating roller  43  is a stainless-steel pipe with a thickness of 1 mm and having the heater  48  (refer to  FIG.  2   ) formed of a halogen heater arranged in the interior of the heating roller  43  to heat the roller to a predetermined temperature. The fixing belt  41  is heated by the heating roller  43  and controlled to a predetermined target temperature set according to sheet types based on temperature detected by the thermistor  49  (refer to  FIG.  2   ). Further, the heating roller  43  has a gear not shown fixed to a first end thereof in the rotational axis direction, and the heating roller  43  is connected via the gear to the drive motor M 1  (refer to  FIG.  2   ) that drives the heating roller  43  to rotate. The fixing belt  41  is driven to rotate following the rotation of the heating roller  43 . 
     The steering roller  44  has a pivot axis that is arranged approximately in a vertical direction at a first end or near a center portion in the rotational axis direction, and pivots with respect to the fixing belt  41  to create a tension difference in the main scanning direction and adjust the position of the fixing belt  41  in the main scanning direction. Further, the steering roller  44  is urged by a spring not shown supported by a frame of the heating unit  40  and serves as a tension roller for applying predetermined tension to the fixing belt  41 . 
     The pressure roller  32  is opposed to and abuts against the fixing belt  41 , forming the fixing nip portion N where pressure is applied between the pressure roller  32  and the fixing belt  41 . The pressure roller  32  is a roller in which an elastic layer is formed on a circumference of a shaft and a releasing layer is formed on a circumference of the elastic layer. In the pressure roller  32 , the shaft is formed of stainless steel, and the elastic layer is formed of conductive silicon rubber having a thickness of 3 mm. The releasing layer is formed of PFA (tetrafluoro-ethylene-perfluoro alkoxy ethylene copolymer resin) as fluororesin having a thickness of 30 µm. The pressure roller  32  is axially supported by the fixing frames  33  on the casing  31  of the fixing unit  30 , and a gear is fixed to a first end of the pressure roller  32  in the rotational axis direction, wherein the pressure roller is connected through the gear to the drive motor M 1  (refer to  FIG.  2   ) and rotated. 
     The recording material S (refer to  FIG.  1   ) bearing a toner image is nipped by the fixing nip portion N formed between the fixing belt  41  and the pressure roller  32 , and the toner image is heated while the recording material is being conveyed. As described, the fixing unit  30  nips and conveys the recording material S while fixing the toner image to the recording material S. Therefore, the fixing unit  30  must realize both a function to apply heat and pressure and a function to convey the recording material S. 
     The separation unit  50  is provided on the fixing frames  33  and includes a separation plate  51 , and a guide shaft  52  and a rotation shaft  53  which are protruded toward either side in the rotational axis direction. The separation unit  50  is axially supported in a swingable manner by the rotation shaft  53  on the fixing frames  33 . The separation plate  51  is provided to separate the recording material S having passed through the fixing nip portion N from the fixing belt  41 , and it is formed by adhering a fluorine-based tape on a metal plate to prevent adhesion of toner and damaging of image on the recording material S by slide movement. The guide shaft  52  is arranged upstream in the sheet conveyance direction (direction D1 in the drawing) X of the rotation shaft  53 . 
     The fixing frames  33  are arranged in a fixed manner on both side portions of the casing  31  with respect to the rotational axis direction, and each fixing frame  33  is provided with a guide portion  34 , a pressing frame  35  and a pressurizing spring  36 . The stay  45  of the heating unit  40  is inserted to the guide portion  34 , pressed against and fixed to the guide portion  34  by a pressing portion  80  described later. After fixing the stay  45  to the guide portion  34 , the pressing frame  35  is moved toward the heating unit  40  by a drive source and a cam not shown, by which the pressure roller  32  is pressed against the pressure pad  42  via the fixing belt  41 . The pressurizing force of the pressure roller  32  to the pressure pad  42  during image forming operation is set to 1000 N, for example. 
     The guide portion  34  includes a support surface  34   a , a positioning surface  34   b  serving as an example of a positioning portion, a sliding surface  34   c  and an opening portion  34   d . The support surface  34   a  is formed on an opposing side of the pressure roller  32  along an attachment direction D1 for inserting the heating unit  40 , and in a state where the heating unit  40  is positioned at the attachment position illustrated in  FIG.  3   , the fixing belt  41  supports a reaction force received from the pressure roller  32  at an inner circumference side of the fixing belt  41 . The positioning surface  34   b  is formed approximately perpendicularly at a deepest portion in the attachment direction D1 of the guide portion  34 , and in the state where the heating unit  40  is positioned at the attachment position, the heating unit  40  is positioned by abutting against the positioning surface  34   b  in the attachment direction D1. The sliding surface  34   c  is opposed to the support surface  34   a  and formed along the attachment direction D1 to guide the stay  45  by sliding movement when inserting or removing the heating unit  40 . The opening portion  34   d  is an opening that communicates the inner and outer sides of the guide portion  34 . By inserting the stay  45  through the opening portion  34   d  to the guide portion  34 , the heating unit  40  can be moved to the attachment position, and by removing the stay  45  through the opening portion  34   d  to the outer side of the guide portion  34 , the heating unit  40  can be removed from the casing  31 . The guide portion  34  has a first guide portion  34   e  extended in the horizontal direction and a second guide portion  34   f  connected to the first guide portion  34   e  and extended diagonally upward in a direction opposite to the sheet conveyance direction X. 
     When attaching the heating unit  40  to the casing  31 , the guide portion  34  guides and causes the heating unit  40  to be attached from an insertion start position (refer to  FIG.  5   ) to an attachment position (refer to  FIG.  3   ) so that the fixing belt  41  is positioned at the fixing nip portion N. The attachment position is a position where the stay  45  is abutted against the positioning surface  34   b  and the fixing belt  41  is positioned at the fixing nip portion N. In the present embodiment, the insertion start position is a position where an end portion in the attachment direction D1 of the stay  45  is inserted between the support surface  34   a  and the sliding surface  34   c , where guiding by the guide portion  34  is started during insertion and guiding by the guide portion  34  is ended during removal, as illustrated in  FIG.  5   . Further, an area in which the heating unit  40  is movable between the insertion start position and the attachment position (illustrated by the imaginary line in  FIG.  5   ) is referred to as a movable area A r   1  . 
     In the present embodiment, the attachment direction D1 for inserting the heating unit  40  is a direction along the sheet conveyance direction of the recording material S nipped by the fixing nip portion N, which is set parallel in the illustrated example. However, the attachment direction D1 is not limited to being completely parallel with the sheet conveyance direction X at the fixing nip portion N, and it can be approximately parallel, or the attachment direction D1 and the sheet conveyance direction X can be set to opposite directions. 
     Further, in a state where the heating unit  40  is positioned at the attachment position as illustrated in  FIG.  3   , the position of the separation unit  50  with respect to the fixing belt  41  is determined by the guide shaft  52  of the separation unit  50  engaging with the separation plate positioning portion  45   a  of the stay  45 . That is, the separation unit  50  retained in a swingable manner around the rotation shaft  53  is engaged by the guide shaft  52  being pressed against the engagement portion of the separation plate positioning portion  45   a , by which the position of the separation unit  50  in a swinging direction is determined, and the positioning of the separation unit  50  and the fixing nip portion N is enabled. 
     The unit side plates  46  are provided on both sides in the rotational axis direction. Each unit side plate  46  includes a first abutment surface  46   a  and a second abutment surface  46   b . The second abutment surface  46   b  is arranged along the attachment direction D1 and disposed continuously with the first abutment surface  46   a  but with a different angle value. The details of the first abutment surface  46   a  and the second abutment surface  46   b  will be described later. 
     Cover 
     Next, the cover  60  will be described in detail. The cover  60  is provided to cover the opening portion of the casing  31  and the heating unit  40  attached to the casing  31  to thereby protect and shield heat from the heating unit  40 . The cover  60  includes a cover body  61 , a cleaning unit  70  and the pressing portion  80 . 
     The cover body  61  can cover the upper portion of the casing  31 , both end portions in the rotational axis direction thereof, and both upstream and downstream side portions in the attachment direction D1 thereof. Both end portions in the rotational axis direction of the cover body  61  are axially supported pivotably on the fixing frame  33  through a swing shaft  62 , which is an example of a rotation shaft. In the present embodiment, the swing shaft  62  is arranged downstream in the attachment direction D1 of the heating unit  40  positioned at the attachment position. That is, the cover body  61  is provided in a swingable manner with a swinging center regarding the casing  31  arranged downstream in the attachment direction D1 of the heating unit  40  positioned at the attachment position or the fixing nip portion N. The swing shaft  62  is not limited to being arranged downstream in the attachment direction D1 of the heating unit  40  positioned at the attachment position, and for example, even if the swing shaft  62  is not arranged downstream in the attachment direction D1 of the heating unit  40 , the cover  60  should merely be openable in the attachment direction D1. 
     The cover body  61  includes an opening/closing engagement shaft  63  provided on both sides in the rotational axis direction on an outer diameter side of the swing shaft  62 . The opening/closing engagement shaft  63  engages with the fixing frame  33  when the cover  60  is closed, by which the position of the cover  60  in the swinging direction with respect to the fixing frame  33  is determined. 
     The cover body  61  is movable by swinging motion between a first position and a second position. The first position is a position where the cover  60  covers the heating unit  40  positioned at the attachment position, as illustrated in  FIG.  3   . That is, the state in which the cover body  61  is positioned at the first position is a closed state where the guide portion  34  is closed. The second position is a position where the cover  60  has been retracted from the movable area A r   1  (refer to  FIG.  5   ) of the heating unit  40  and the heating unit  40  is attachable to or removable from the casing  31 , as illustrated in  FIG.  4   . In other words, the state in which the cover body  61  is positioned at the second position is an opened state where the guide portion  34  is opened. 
     The cover body  61  includes a shielding portion  64  positioned upstream in the attachment direction D1 of the heating unit  40  in the first position, as illustrated in  FIG.  3   . In the present embodiment, in a state where the cover body  61  is positioned at the first position, the shielding portion  64  extends in an up-down direction at an upstream in the attachment direction D 1  of the heating unit  40  and positioned to overlap with the movable area A r   1  (refer to  FIG.  5   ) of the heating unit  40 . Therefore, the heating unit  40  positioned at the attachment position cannot be removed, or the heating unit  40  cannot be attached from the outer side. Further, the shielding portion  64  is moved to swing along with the swinging movement of the cover body  61  when the cover body  61  is positioned at the second position, as illustrated in  FIG.  4   , the position of the shielding portion  64  being downstream in the attachment direction D 1  than its position in a state where the cover body  61  is positioned at the first position. Therefore, the heating unit  40  positioned at the attachment position can be removed easily or the heating unit  40  can be attached easily from the outer side without the interference of the cover  60 . When the cover body  61  is positioned at the second position, the cover body  61  will be in contact with a stopper not shown provided on the casing  31  and cannot be opened further. 
     The cleaning unit  70  is an example of a contact portion, and it is provided to clean the surface of the fixing belt  41 . The cleaning unit  70  is arranged to abut against the fixing belt  41  of the heating unit  40  positioned at the attachment position when positioned at the first position as illustrated in  FIG.  3   , and to be separated therefrom when positioned at the second position as illustrated in  FIG.  4   . The cleaning unit  70  includes an arm  71 , a swing shaft  72 , and a cleaning roller  73 . The arm  71  is supported in a swingable manner by the swing shaft  72  with respect to the cover  60 . The cleaning roller  73  is provided to remove foreign substances attached to a surface of the fixing belt  41 . In the present embodiment, the cleaning roller  73  is, for example, a brush roller having an outer diameter of approximately 10 mm formed by winding a pile brush having fiber bundles embedded therein around a surface of a core metal formed of metal such as stainless steel or plated iron and having a diameter of 6 mm. A pressing unit not shown moves the cleaning roller axially supported on the arm  71  between the contact position and the separated position, and in the contact position, the cleaning roller  73  is caused to contact the fixing belt  41  by a power of approximately 20 N. In the present embodiment, the cleaning roller  73  abuts against the fixing belt  41  during image forming operation and is separated therefrom during non-image forming operation including maintenance operation. 
     The pressing portion  80  is provided to press the stay  45  of the heating unit  40  attached to the casing  31  against the positioning surface  34   b  and position the heating unit  40  at the attachment position. The pressing portion  80  is a lock mechanism that stabilizes the position of the heating unit  40  with respect to the fixing unit  30  by pressing the heating unit  40  against the fixing frame  33  in a state where the cover  60  is closed and positioned at the first position. The pressing portion  80  includes a pressing arm  81 , a swing shaft  82 , a pressing roller  83 , a pressing spring  84 , and a stopper  85 . 
     The pressing arm  81  is axially supported in a swingable manner by the swing shaft  82  on both side portions in the rotational axis direction of the cover body  61 . The pressing roller  83  is axially supported in a rotatable manner by the pressing arm  81 . The pressing spring  84  is formed of a tension coil spring, for example, and the pressing roller  83  urges the pressing arm  81  toward the direction to press the heating unit  40 . Further, as illustrated in  FIG.  4   , in a state where the pressing roller  83  is not in contact with the heating unit  40 , the pressing arm  81  contacts the stopper  85  and regulates rotation of the pressing arm  81 . 
     Removal Operation of Heating Unit 
     Next, an operation for removing the heating unit  40  from the fixing unit  30  according to the present embodiment will be described with reference to  FIGS.  4  to  6   . Normally, maintenance operation is carried out when the image forming process is not performed. Therefore, removal of the heating unit  40  is carried out in a state where the pressure roller  32  and the cleaning roller  73  are separated from the fixing belt  41  from the state illustrated in  FIG.  3   . As illustrated in  FIG.  4   , in a state where regulation by the opening/closing engagement shaft  63  is cancelled and the cover  60  is swung to a swinging direction R2 around the swing shaft  62 , the cover  60  is moved to the second position. Thereby, the pressing portion  80  that had been pressing the heating unit  40  moves upward to the attachment direction D1, and the pressure applied to the heating unit  40  is cancelled. Thereby, the heating unit  40  can be removed toward a removal direction D2 that is opposite from the attachment direction D1. 
     When removing the heating unit  40  from the guide portion  34 , the removal direction D2 is regulated by the sliding surface  34   c , as illustrated in  FIG.  5   . In a state where the heating unit  40  is moved to the removal direction D2, the engagement between the separation plate positioning portion  45   a  and the guide shaft  52  is released. The heating unit  40  is moved to the removal direction D2 until the stay  45  exits through the opening portion  34   d  of the guide portion  34  formed on the fixing frame  33 . 
     When the stay  45  exits through the opening portion  34   d  to the exterior, the heating unit  40  can be removed from the fixing unit  30 , as illustrated in  FIG.  6   . In a state where the heating unit  40  is removed from the fixing unit  30 , the separation plate  51  and the pressure roller  32  remain in the fixing unit  30 . The cover  60  is positioned at the second position where the cover is retracted to an opposite direction as the removal direction D2 in which the heating unit  40  is removed, and the entire body of the cover  60  is retracted from a work area A r   2  (area shown between long and short dashed lines) for attaching and detaching the heating unit  40 . Therefore, during the removal operation and the attaching operation of the heating unit  40 , the cover  60  will not interfere with the line of movement of the heating unit  40  and will not hinder the operation. 
     Therefore, the operator will not have to take an unreasonable posture of working with the cover  60  placed therebetween and can work in a natural posture, so that deterioration of workability due to the presence of the cover  60  or occurrence of excessive operation of removing the cover  60  can be prevented. In a state where the cover  60  is positioned at the second position, the cleaning roller  73  is separated from the fixing belt  41  and moved to a retracted position in the removal direction D2 of the heating unit  40 . Thereby, during the removal operation and the attaching operation of the heating unit  40 , the risk of the cleaning roller  73  being in contact with the fixing belt  41  and damaging the fixing belt  41  can be suppressed. 
     Attaching Operation of Heating Unit 
     Next, the operation for attaching the heating unit  40  to the fixing unit  30  according to the present embodiment will be described with reference to  FIGS.  6 ,  5 ,  4 ,  7 , and  8    in the named order. As illustrated in  FIG.  6   , when attaching the heating unit  40 , the stay  45  is inserted to the opening portion  34   d  of the guide portion  34  and the stay  45  is placed on the sliding surface  34   c , as illustrated in  FIG.  5   . Then, the heating unit  40  swings to the attachment direction D1, and the stay  45  is abutted against the positioning surface  34   b , as illustrated in  FIG.  4   . In this state, the guide shaft  52  of the separation unit  50  is engaged with the separation plate positioning portion  45   a , and the relative positions of the heating unit  40  and the separation plate  51  are determined. 
     As illustrated in  FIG.  7   , in a state where the cover  60  is swung to a swinging direction R3, the pressing arm  81  is moved in a state abutted against the stopper  85 , and the pressing roller  83  abuts against the second abutment surface  46   b  formed on the heating unit  40 . In a state where the cover  60  swings further to the swinging direction R3 with the pressing roller  83  abutted against the second abutment surface  46   b , the pressing arm  81  swings in the swinging direction R2 around the swing shaft  82  via the pressing roller  83  and separates from the stopper  85  against the pressing spring  84 . Thereby, the pressing force by the pressing spring  84  is caused to act on the heating unit  40 . That is, in a state where the heating unit  40  is positioned at the attachment position and the cover  60  is moved from the second position to the first position, the pressing roller  83  abuts against the second abutment surface  46   b  before abutting against the first abutment surface  46   a . 
     As illustrated in  FIG.  8   , in a state where the cover  60  is closed and positioned at the first position, the pressing roller  83  presses the first abutment surface  46   a  of the heating unit  40  by the pressing spring  84 . That is, in a state where the heating unit  40  is positioned at the attachment position and the cover  60  is positioned at the first position, the pressing roller  83  abuts against the first abutment surface  46   a . In this state, pressing force is divided according to an angle formed by the inclination angle of the first abutment surface  46   a  and the pressing direction of the pressing roller  83 , and a pressing force is applied in the attachment direction D1 pressing the heating unit  40  against the fixing frame  33 . Thereby, the pressing portion  80  abuts against the heating unit  40  positioned at the attachment position when the cover  60  is positioned at the first position to press the heating unit  40  downstream in the attachment direction D1 and position the heating unit  40  against the positioning surface  34   b . 
     The angle formed by the first abutment surface  46   a  with the attachment direction D 1  should be close to 90 degrees to press the heating unit  40  effectively against the fixing frame  33 . Therefore, the first abutment surface  46   a  preferably forms an angle of 45 degrees or greater and 90 degrees or smaller with the attachment direction D1. 
     The second abutment surface  46   b  and the first abutment surface  46   a  have different inclination angles but are arranged continuously. Thus, the pressing roller  83  can contact the second abutment surface  46   b  and apply rotational force by the pressing spring  84  while moving to the first abutment surface  46   a , so that the pressing portion  80  can press the heating unit  40  after coming into contact therewith. If the heating unit  40  is merely attached to place by the user, there may be a gap between the stay  45  of the heating unit  40  and the positioning surface  34   b  of the guide portion  34 . In contrast, by having the pressing roller  83  contact the first abutment surface  46   a , a force pressing the stay  45  against the positioning surface  34   b  can be generated, and the position and posture of the heating unit  40  can be set preferably. 
     As described, according to the fixing unit  30  of the present embodiment, in a state where the cover  60  is opened and positioned at the second position, the cover  60  is positioned downstream in the attachment direction D1 than when the cover  60  is closed and positioned at the first position. Therefore, by positioning the cover  60  at the second position that is retracted to the opposite direction as the removal direction D 2  for removing the heating unit  40 , the entire body of the cover  60  can be retracted from the work area A r   2  (refer to  FIG.  6   ) for attaching and detaching the heating unit  40 . Thereby, during the attaching and detaching operation of the heating unit  40 , the cover  60  will not be overlapped with the line of movement of the heating unit  40 , so that the hinderance of operation can be suppressed and the workability can be improved. According to the present embodiment, a pivoting angle from the first position where the cover body  61  is closed to a position where the cover body  61  is abutted against a stopper not shown provided on the fixing unit  30  and opened should preferably be 90 degrees or greater and 135 degrees or smaller. 
     According to the fixing unit  30  of the present embodiment, the cover  60  includes the pressing portion  80 . Therefore, when attaching the heating unit  40 , the heating unit  40  can be pressed toward the attachment direction D1 by simply closing the cover  60 , and the heating unit  40  can be accurately positioned and attached to the fixing unit  30 . 
     Further according to the fixing unit  30  of the present embodiment, the cover  60  includes the cleaning unit  70 . Therefore, when attaching and detaching the heating unit  40 , members and mechanisms that contact the surface of the fixing belt  41  can be retracted, and the attaching and detaching of the heating unit  40  can be facilitated. 
     According further to the fixing unit  30  of the present embodiment, the second abutment surface  46   b  and the first abutment surface  46   a  are arranged continuously with different inclination angles. Therefore, the contact and pressing operations of the pressing roller  83  to the heating unit  40  can be performed continuously, and the heating unit  40  can be positioned smoothly to the attachment position. 
     The fixing unit  30  of the present embodiment described above has been illustrated of a case where both the heating roller  43  and the pressure roller  32  are driven by driving the drive motor M 1 , but the present technique is not limited thereto. For example, it is possible to have the pressure roller  32  driven by the drive motor M 1  and the fixing belt  41  rotated following the rotation of the pressure roller  32 . In that case, the heating unit  40  is pressed toward the sheet conveyance direction X, so that it is advantageous from the point of view of force to attach the heating unit  40  in the sheet conveyance direction X. According to the fixing unit  30  of the present embodiment, the attachment direction D 1  of the heating unit  40  is set to a direction parallel to the sheet conveyance direction X of the recording material S nipped by the fixing nip portion N, so that it is also preferable in the case mentioned above. 
     Further, the fixing unit  30  of the present embodiment described above has been illustrated of a case where the cleaning unit  70  and the pressing portion  80  are provided to the cover  60 , but the present technique is not limited thereto, and these members can be omitted. According further to the fixing unit  30  of the present embodiment described above, the cover  60  has been opened and closed by swinging motion, but the present technique is not limited thereto. For example, the cover  60  can be opened and closed by sliding motion. 
     Even further, the fixing unit  30  of the present embodiment described above has been illustrated using a belt as the first rotary member, but the present technique is not limited thereto, and for example, the first rotary member can be a roller. Moreover, the heating roller  43  can be omitted, and the heating source for heating the heating unit  40  can adopt a configuration of heating the first rotary member from an outer side of the heating unit  40 . 
     Furthermore, the fixing unit  30  of the present embodiment described above has adopted a configuration where the heating unit  40  is attached to and detached from the fixing unit  30  independently from the pressing roller  32 , but the present technique is not limited thereto, and a configuration can be adopted where the heating unit  40  and the pressure roller  32  are integrally attached to and detached from the fixing unit  30 . 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2020-083700, filed May 12, 2020 which is hereby incorporated by reference herein in its entirety.