Patent Publication Number: US-8995893-B2

Title: Fixing device and image forming apparatus

Description:
This application is based upon and claims the priority from Japanese Patent Application No. 2012-167977 filed in Japan Patent Office on Jul. 30, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present disclosure relates to a fixing device that fixes toner images on a sheet and an image forming apparatus applied with the fixing device. 
     The fixing device of the image forming apparatus includes a fixing nip portion formed by a fixing roller and a pressurizing roller being brought into press-contact with each other. When the sheet passes through the fixing nip portion, the sheet is pressurized and heated, whereby the toner images on the sheet are fixed on the sheet. Since the sheet is heated when passing through the fixing nip portion, the sheet sometimes adheres to the circumferential surface of the fixing roller. In this case, the sheet winds around the fixing roller after passing through the fixing nip portion. 
     In order to prevent such winding, a separating member for separating the sheet, which starts to wind around the fixing roller, from the fixing roller is arranged in a position close to the fixing roller on a rotating direction downstream side of the fixing roller. The separating member includes a tabular member extending in the axial direction of the fixing roller. When the distal end of the tabular member and the fixing roller circumferential surface are always in contact with each other, there is a concern that the fixing roller circumferential surface is damaged. When the toner on the sheet is fixed in a state in which the fixing roller circumferential surface is damaged, traces of damage sometimes remain on the toner images. Therefore, a gap having a predetermined distance is formed between the distal end of the tabular member and the fixing roller circumferential surface. The gap is formed by extending the distal end of the tabular member along the circumferential surface of the fixing roller to set the distal end of the tabular member and the axial direction of the fixing roller in parallel to each other. 
     If the distance of the gap is too small, paper powder sometimes accumulates in the gap portion. On the other hand, if the distance of the gap is too large, sheet separating performance is deteriorated. Therefore, the distance of the gap needs to be set to an appropriate distance that is neither too large nor too small. 
     However, depending on a twist of the tabular member or a result of alignment of a positional relation between the tabular member and the fixing roller, the distal end of the tabular member cannot be held in parallel to the axial direction of the fixing roller. In this case, the distance between the distal end of the tabular member and the fixing roller circumferential surface cannot be kept uniform. 
     SUMMARY 
     A fixing device according to an aspect of the present disclosure includes first and second rollers configured to form a fixing nip portion, a separating member for a sheet, a supporting mechanism, and contact members. The separating member is arranged further on a rotating direction downstream side of the first roller than the fixing nip portion and includes a tabular member extending in the axial direction of the first roller. The supporting mechanism pivotably supports the separating member to change a posture between a first posture in which the distal end of the tabular member comes close to the circumferential surface of the first roller and a second posture in which the distal end separates from the circumferential surface of the first roller. The contact members are attached to the separating member at both end positions of the tabular member respectively. In the first posture, the contact members come into contact with the circumferential surface near both ends of the first roller and form a gap having a predetermined distance between the distal end of the tabular member and the circumferential surface of the first roller. The supporting mechanism includes first and second fulcrum members respectively arranged to be opposed to the both end positions of the tabular member and functioning as a fulcrum for pivoting of the separating member and first and second holes provided in the separating member, the first fulcrum member being inserted into the first hole and the second fulcrum member being inserted into the second hole. The first hole is a hole that allows the separating member to substantially shift only in a predetermined direction. The second hole is a hole that does not substantially restrict displacement of the separating member. 
     An image forming apparatus according to another aspect of the present disclosure includes an image forming section configured to transfer a toner image onto a sheet and a fixing device configured to fix the toner image on the sheet. The fixing device includes the configuration explained above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view showing an overall configuration of an image forming apparatus according to an embodiment of the present disclosure; 
         FIG. 2  is a perspective view of a fixing unit incorporated in the image forming apparatus; 
         FIG. 3  is a perspective view of the fixing unit viewed from a different line of sight direction; 
         FIG. 4  is a main part perspective view of the fixing unit; 
         FIG. 5  is a schematic diagram showing a positional relation between contact members and a fixing roller; 
         FIG. 6A  is a perspective view showing the front surface side of a separating member; 
         FIG. 6B  is a perspective view showing the rear surface side of the separating member; 
         FIG. 7A  is a perspective view of the contact member on the side of an attachment surface to the separating member; 
         FIG. 7B  is a perspective view of the contact member on the side of a contact surface on a fixing belt; 
         FIG. 8A  is a perspective view of an end portion of the separating member on the side where a long hole is formed; 
         FIG. 8B  is a perspective view of an end portion of the separating member on the side where a large-diameter hole is formed; 
         FIG. 9  is a perspective view for explaining an attachment form (on the long hole side) of the separating member; 
         FIG. 10  is a perspective view for explaining an attachment form (on a large-diameter hole side) of the separating member; 
         FIG. 11  is a sectional view showing the separating member (on the long hole side) in a second posture; 
         FIG. 12  is an enlarged sectional view showing the separating member (on the long hole side) in a first posture; 
         FIG. 13  is an enlarged sectional view showing the separating member (on the large-diameter hole side) in the first posture; 
         FIG. 14  is a perspective view for explaining an urging state of the separating member; and 
         FIG. 15  is a sectional view showing another embodiment of an attachment form of the contact member to the separating member. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present disclosure is explained in detail below on the basis of the drawings.  FIG. 1  is a schematic sectional view showing an overall configuration of an image forming apparatus  1  according to the embodiment of the present disclosure. A color copying machine of a tandem type is illustrated as an example of the image forming apparatus. The image forming apparatus may be a monochrome copying machine, a printer, a facsimile apparatus, or a complex machine of these apparatuses. 
     The image forming apparatus  1  includes an apparatus main body  2  having a substantially rectangular parallelepiped housing structure and including an in-body space. The apparatus main body  2  applies image forming processing to a sheet. The apparatus main body  2  includes a substantially rectangular parallelepiped lower housing  21 , a substantially rectangular parallelepiped upper housing  22  disposed above the lower housing  21 , and a connecting housing  23  configured to connect the lower housing  21  and the upper housing  22 . Various devices for image formation are housed in the lower housing  21 . Various devices for optically reading a document image are housed in the upper housing  22 . An in-body space surrounded by the lower housing  21 , the upper housing  22 , and the connecting housing  23  is formed as an in-body paper discharge section  24  in which the sheet after the image formation can be stored. The connecting housing  23  is arranged on the side of a right side surface of the apparatus main body  2 . A discharge port  961  for discharging the sheet to the in-body paper discharge section  24  is provided in the connecting housing  23 . 
     The in-body space used as the in-body paper discharge section  24  is opened to the outside on a front surface and a left side surface of the apparatus main body  2 . A user can insert his or her hand from opening portions on the front surface and the left side surface and remove the sheet after the image formation from the in-body paper discharge section  24 . A bottom surface  241  of the in-body space is defined by an upper surface of the lower housing  21 . The sheet discharged from the discharge port  961  is stacked on the bottom surface  241 . 
     A paper feeding cassette  211  configured to store sheets to be subjected to the image forming processing is mounted in the lower housing  21 . The paper feeding cassette  211  can be drawn out in a near side direction from the front surface of the lower housing  21  (the apparatus main body  2 ). The paper feeding cassette  211  is a cassette provided for automatic paper feeding. 
     On the right side surface of the apparatus main body  2 , a multi-tray unit M for causing the user to perform manual paper feeding is mounted. The multi-tray unit M includes a paper feeding tray  30  on which a manually fed sheet is placed and a paper feeding unit  40  configured to transport the manually fed sheet into an image forming section in the lower housing  21 . The paper feeding tray  30  is openably/closably attached to the lower housing  21  at a lower end portion of the paper feeding tray  30  and is closed when not in use. When performing the manual paper feeding, the user opens the paper feeding tray  30  and places a sheet on the paper feeding tray  30 . 
     On the inside of the lower housing  21 , toner containers  99 Y,  99 M,  99 C, and  99 Bk, an intermediate transfer unit  92 , an image forming section  93 , an exposure unit  94 , and the paper feeding cassette  211  are housed in order from above. 
     In order to form a full-color toner image, the image forming section  93  includes four image forming units  10 Y,  10 M,  10 C, and  10 Bk configured to form toner images of yellow (Y), magenta (M), cyan (C), and black (Bk). Each of the image forming units  10 Y,  10 M,  10 C, and  10 Bk includes a photosensitive drum  11  and a charger  12 , a developing device  13 , a primary transfer roller  14 , and a cleaning device  15  arranged around the photosensitive drum  11 . 
     The photosensitive drum  11  rotates around the axis thereof. An electrostatic latent image and a toner image are formed on the circumferential surface of the photosensitive drum  11 . The charger  12  uniformly charges the circumferential surface of the photosensitive drum  11 . The circumferential surface of the photosensitive drum  11  after the charging is exposed to light by the exposure unit  94 . An electrostatic latent image is formed on the circumferential surface. 
     The developing device  13  supplies a toner to the circumferential surface of the photosensitive drum  11  in order to develop the electrostatic latent image formed on the photosensitive drum  11 . The developing device  13  is a developing device for a two-component developer. The developing device  13  includes agitating rollers  16  and  17 , a magnetic roller  18 , and a developing roller  19 . The agitating rollers  16  and  17  circulate and carry the two-component developer while agitating the same to charge the toner. A two-component developer layer is born on the circumferential surface of the magnetic roller  18 . A toner layer formed by the toner being transferred by a potential difference between the magnetic roller  18  and the developing roller  19  is born on the circumferential surface of the developing roller  19 . The toner on the developing roller  19  is supplied to the circumferential surface of the photosensitive drum  11  to develop the electrostatic latent image. 
     The primary transfer roller  14  forms a nip portion together with the photosensitive drum  11  across an intermediate transfer belt  921  included in the intermediate transfer unit  92  and primarily transfers the toner image on the photosensitive drum  11  onto the intermediate transfer belt  921 . The cleaning device  15  cleans the circumferential surface of the photosensitive drum  11  after the toner image transfer. 
     The toner container for yellow  99 Y, the toner container for magenta  99 M, the toner container for cyan  99 C, and the toner container for black  99 Bk are respectively toner containers configured to store toners of the colors. The toner container for yellow  99 Y, the toner container for magenta  99 M, the toner container for cyan  99 C, and the toner container for black  99 Bk supply the toners of the colors to the developing devices  13  of the image forming units  10 Y,  10 M,  10 C, and  10 Bk respectively corresponding to the colors Y, M, C, and Bk through a not-shown supply route. 
     The exposure unit  94  configures a part of the image forming section  93 . The exposure unit  94  includes various optical devices such as a light source, a polygon mirror, a reflecting mirror, and a deflecting mirror. The exposure unit  94  irradiates light based on image data of a document image and forms an electrostatic latent image on the circumferential surface of the photosensitive drum  11  provided in each of the image forming units  10 Y,  10 M,  10 C, and  10 Bk. 
     The intermediate transfer unit  92  includes an intermediate transfer belt  921 , a driving roller  922 , and a driven roller  923 . Toner images are superimposed one on top of another on the intermediate transfer belt  921  from a plurality of the photosensitive drums  11  (primary transfer). The superimposed toner images are secondarily transferred onto a sheet supplied from the paper feeding cassette  211  or the paper feeding tray  30  in a secondary transfer section  98 . 
     The paper feeding cassette  211  stores a sheet bundle formed by a plurality of sheets being stacked. A pickup roller  212  is arranged in an upper part on the right end side of the paper feeding cassette  211 . Sheets in the top layer of the sheet bundle in the paper feeding cassette  211  are let out one by one and carried into a carrying and conveying path  26  by the driving of the pickup roller  212 . On the other hand, a sheet placed on the paper feeding tray  30  is carried into the carrying and conveying path  26  by the driving of the paper feeding roller  41  of the paper feeding unit  40 . 
     On the downstream side of the carrying and conveying path  26 , a sheet conveying path  28  extending to the discharge port  961  through the secondary transfer section  98 , a fixing unit (a fixing device)  97 , and a paper discharge unit  96  is provided. An upstream portion of the sheet conveying path  28  is formed between an inner wall formed in the lower housing  21  and an inner wall forming the inner side surface of a reverse conveying unit  29 . The outer side surface of the reverse conveying unit  29  forms one surface of a reverse conveying path  291  for reversing and conveying the sheet in duplex printing. A registration roller pair  27  is arranged further on the upstream side than the secondary transfer section  98  in the sheet conveying path  28 . The sheet is once stopped by the registration roller pair  27  and, after skew correction is performed, sent to the secondary transfer section  98  at predetermined timing for image transfer. 
     The fixing unit  97  and the paper discharge unit  96  are housed on the inside of the connecting housing  23 . The fixing unit  97  heats and pressurizes, in a fixing nip portion N, a sheet having the toner images secondarily transferred thereon in the secondary transfer section  98  to apply fixing to the sheet. The sheet with a color image subjected to the fixing is discharged from the discharge port  961  toward the in-body paper discharge section  24  by the paper discharge unit  96  arranged downstream of the fixing unit  97 . 
     A first contact glass  222  and a second contact glass  223  are fit in the upper surface of the upper housing  22 . The first contact glass  222  is provided for reading of a document sheet automatically fed from an auto document feeder (ADF; not shown in the figure) when ADF is arranged on the upper housing  22 . The second contact glass  223  is provided for reading of a document sheet manually placed thereon. 
     A scanning mechanism  224  and an image pickup element  225  for optically reading document information are housed on the inside of the upper housing  22 . The scanning mechanism  224  includes a light source, a moving carriage, and a reflecting mirror and guides reflected light from a document to the image pickup element  225 . The image pickup element  225  photoelectrically converts the reflected light into an analog electric signal to thereby acquire image data of the document. 
     A detailed configuration of the fixing unit  97  is explained below.  FIG. 2  is a perspective view of the fixing unit  97 .  FIG. 3  is a perspective view of the fixing unit  97  viewed from a line of sight direction different from that in  FIG. 2 .  FIG. 4  is a main part perspective view of the fixing unit  97 . The fixing unit  97  includes a fixing housing H and a fixing roller  100  (a first roller), a pressurizing roller  101  (a second roller), a separating member  102 , supporting members  103 , contact members  104 , and conveying rollers  105  housed in the fixing housing H. 
     The fixing housing H is a hosing having a substantially square pole shape long in the front back direction (a direction orthogonal to the paper surface of  FIG. 1 ). Near the top surface of the fixing housing H, the conveying rollers  105  applied with a rotation driving force for conveying a sheet and a cover member  108  configured to cover the top surface are arranged. The cover member  108  pivots around a pivoting fulcrum  106 , thereby being capable of opening and closing with respect to the fixing housing H. In  FIGS. 2 and 3 , the cover member  108  is opened with respect to the fixing housing H. A guide surface for a sheet is formed on the inner wall surface of the cover member  108 . A plurality of conveying rollers  107  are arranged on the guide surface. The conveying rollers  107  come into contact with the conveying rollers  105  and form a conveying nip portion when the cover member  108  is closed with respect to the fixing housing H. 
     The fixing roller  100  and the pressurizing roller  101  are rotatably held in the fixing housing H. The rollers are brought into press-contact with each other, whereby the fixing nip portion N is formed. The fixing roller  100  includes, as shown in  FIG. 11 , a shaft (not shown in the figure) functioning as a rotating shaft, a cylindrical elastic base material  100 E provided around the shaft, and a fixing belt  100 S overlaid in the outer circumference of the elastic base material  100 E. The elastic base material  100 E is formed by elastic rubber such as silicon rubber, urethane foam, or the like. The fixing belt  100 S is a metal belt such as a stainless steel belt. The pressurizing roller  101  is a roller having rigidity. The pressurizing roller  101  includes a cylindrical metal roller main body and a shaft member extended from both ends of the roller main body. 
     A sheet having toner images transferred thereon is conveyed in the direction of a thick solid line arrow C in  FIG. 4  in the fixing unit  97 . In  FIG. 4 , the cover member  108  is not shown. When passing through the fixing nip portion N, the sheet is heated by the fixing roller  100  and pressurized by the pressurizing roller  101 . The toner images are fixed on the sheet by the heating and pressurizing actions. 
     In the fixing unit  97  configured as explained above, in this embodiment, the separating member  102  is arranged further on a conveying direction downstream side than the fixing nip portion N. The separating member  102  is a member for preventing the sheet passed through the fixing nip portion N from sticking and winding around the circumferential surface of the fixing roller  100 . That is, since the sheet is heated when passing through the fixing nip portion N, in some case, the toner images on the sheet melt and stick to the circumferential surface of the fixing roller  100  and the sheet winds around the fixing roller  100 . In order to prevent the sheet from winding around the fixing roller  100 , the separating member  102  is arranged further on the rotating direction downstream side of the fixing roller  100  than the fixing nip portion N to separate the sheet from the circumferential surface of the fixing roller  100 . 
     The separating member  102  is a substantially rectangular thin tabular member extending in the axial direction of the fixing roller  100 . The separating member  102  is supported on the side of the proximal end portion thereof by a pair of supporting members  103  arranged in the vicinities of both ends of the fixing roller  100 . The supporting members  103  are fixedly held by the fixing housing H. A gap G having a predetermined distance is secured between a distal end portion  102 A of the separating member  102  opposed to the circumferential surface of the fixing roller  100  and the circumferential surface of the fixing roller  100 . 
     When the sheet passed through the fixing nip portion N reaches the gap G while winding around the fixing roller  100 , the leading end of the sheet comes into contact with the distal end portion  102 A of the separating member  102 . Consequently, the sheet is separated from the fixing roller  100 . In general, a margin region to which the toner images are not transferred is present at a conveying direction leading end of the sheet. The leading end does not adhere to the fixing roller  100 . Therefore, even if the sheet winds around the fixing roller  100 , the conveying direction leading end rises from the circumferential surface of the fixing roller  100 . Therefore, the separation explained above can be performed even if the distal end portion  102 A is not in contact with the circumferential surface of the fixing roller  100 . 
     A pair of contact members  104  is respectively attached to both ends of the separating member  102  (both end positions of the main body section  102 C explained below) to secure the gap G between the distal end portion  102 A and the circumferential surface of the fixing roller  100 .  FIG. 5  is a diagram showing a positional relation between the contact members  104  and the fixing roller  100 . The contact members  104  are members arranged to project further forward than the distal end portion  102 A of the separating member  102 . The contact members  104  come into contact with the circumferential surface of the fixing roller  100  to form the gap G. 
     A passing region  100 A where the sheet passes is set on the circumferential surface of the fixing roller  100 . Non-passing regions  100 B where the sheet does not pass are set at both ends of the passing region  100 A. The contact members  104  come into contact with the non-passing regions  100 B, with which the sheet passing through the fixing nip portion N does not come into contact, to thereby form the gap G between the distal end portion  102 A and the circumferential surface of the fixing roller  100 . 
       FIG. 6A  is a perspective view showing the front surface side of the separating member  102 .  FIG. 6B  is a perspective view showing the rear surface side (a side facing the fixing roller  100 ) of the separating member  102 .  FIG. 7A  is a perspective view of the contact member  104  on the side of an attachment surface to the separating member  102 .  FIG. 7B  is a perspective view of the contact member  104  on the side of a contact surface on the fixing roller  100 . 
     The separating member  102  includes a thin flat main body section  102 C (a tabular member) extending toward the axial direction of the fixing roller  100  and a holding sheet metal  102 S (a holding plate) configured to hold the main body section  102 C. The lower end edge of the main body section  102 C is the distal end portion  102 A. The holding sheet metal  102 S has a holding flat surface extending toward the axial direction of the fixing roller  100 . The main body section  102 C is held in close contact with the holding flat surface. The distal end portion  102 A projects from the lower end of the holding sheet metal  102 S (see  FIGS. 11 and 12 ). 
     Screw holes  102 E and through-holes  102 F for attaching the holding sheet metal  102 S to the main body section  102 C are provided at both ends of the holding sheet metal  102 S in order to attach the contact members  104  to the separating member  102  (see  FIG. 6B ). Screw holes  102 EA drilled in positions overlapping the screw holes  102 E are provided at both ends of the main body section  102 C. On the other hand, holes corresponding to the through-holes  102 F are not drilled in the main body section  102 C. 
     As shown in  FIGS. 7A and 7B , the contact member  104  includes an attaching section  104 A attached to both ends of the holding sheet metal  102 S of the separating member  102 . In the attaching section  104 A, a screw hole  104 E for attaching the contact member  104  to the holding sheet metal  102 S of the separating member  102  is provided. On a side edge of the attaching section  104 A, a pair of positioning pins  104 D for positioning and attaching the contact member  104  to the holding sheet metal  102 S of the separating member  102  is protrudingly provided across the screw hole  104 E. 
     A main body section  104 B having a bent shape is provided continuously to the attaching section  104 A. A contact section  104 C that comes into contact with the circumferential surface of the fixing roller  100  is protrudingly provided at the distal end of the main body section  104 B. 
     When the contact member  104  is attached to the separating member  102 , first, the front side (a side exposed in  FIG. 7A ) of the attaching section  104 A of the contact member  104  is brought into contact with both ends of the rear side (a side exposed in  FIG. 6B ) of the holding sheet metal  102 S of the separating member  102 . The positioning pins  104 D of the contact member  104  are inserted into the through-holes  102 F of the holding sheet metal  102 S. The screw hole  104 E of the contact member  104  and the screw hole  102 E of the holding sheet metal  102 S are aligned by the insertion. Thereafter, an attachment screw  109  (see  FIGS. 11 and 12 ) is screwed into the screw hole  104 E of the contact member  104  and the screw hole  102 E of the separating member  102  from the rear side of the separating member  102 . Consequently, the contact member  104  is attached to the separating member  102 . 
     A first end plate  102 B 1  and a second end plate  102 B 2  supported by the supporting member  103  are respectively provided at both ends of the holding sheet metal  102 S. The end plates  102 B 1  and  102 B 2  are portions bent perpendicularly to the holding flat surface of the holding sheet metal  102 S. A long hole  102 G (a first hole) is provided in the first end plate  102 B 1 . A large-diameter hole  102 H (a second hole) is provided in the second end plate  102 B 2 . The long hole  102 G and the large-diameter hole  102 H are arranged on the proximal end side of the separating member  102  and are drilled in order to axially support the separating member  102  pivotably around an axis parallel to the axial direction of the fixing roller  100 . 
       FIG. 8A  is a perspective view of an end portion of the first end plate  102 B 1  on a side where the long hole  102 G is formed and  FIG. 8B  is a perspective view of an end portion of second end plate  102 B 2  on a side where the large-diameter hole  102 H is formed.  FIGS. 9 and 10  are perspective views for explaining an attachment form of the separating member  102 .  FIG. 9  shows the long hole  102 G side and  FIG. 10  shows the large-diameter hole  102 H side. 
     As shown in  FIG. 9 , in the supporting member  103 , a first fulcrum member  103 A 1  is vertically provided in the axial direction of the fixing roller  100  to correspond to the first end plate  102 B 1 . The first fulcrum member  103 A 1  is a columnar member and is inserted into the long hole  102 G provided in the first end plate  102 B 1 . As shown in  FIG. 10 , in the supporting member  103 , similarly, a second fulcrum member  103 A 2  is vertically provided to correspond to the second end plate  102 B 2 . The second fulcrum member  103 A 2  is also a columnar member and is inserted into the large-diameter hole  102 H provided in the second end plate  102 B 2 . 
     In this way, the first and second fulcrum members  103 A 1  and  103 A 2  are respectively arranged to be opposed to both end positions of the main body section  102 C and are respectively inserted into the long hole  102 G and the large-diameter hole  102 H to function as a fulcrum for pivotably supporting the separating member  102 . That is, the separating member  102  can pivot around the axis of the first and second fulcrum members  103 A 1  and  103 A 2 . As a result, the separating member  102  can change a posture between a first posture in which the distal end portion  102 A of the separating member  102  comes close to the circumferential surface of the fixing roller  100  and a second posture in which the distal end portion  102 A separates from the circumferential surface of the fixing roller  100 . In this embodiment, a supporting mechanism for pivotably supporting the separating member  102  is configured by the first and second end plates  102 B 1  and  102 B 2  and the first and second fulcrum members  103 A 1  and  103 A 2 . 
     Referring to  FIG. 8A , the long hole  102 G drilled in the first end plate  102 B 1  is a long hole including a short-diameter portion SD substantially equal to the diameter of the first fulcrum member  103 A 1  formed by a columnar body and a long-diameter portion LD longer (about 1.5 to 2 times longer) than the diameter of the first fulcrum member  103 A 1 . The long-diameter portion LD extends in a predetermined direction in which the separating member  102  should be shifted (moved). In this relation between the long hole  102 G and the first fulcrum member  103 A 1 , the separating member  102  cannot move in the direction of the short-diameter portion SD and is allowed to substantially shift only in a predetermined direction in which the long-diameter portion LD extends. 
     Referring to  FIG. 8B , a large-diameter hole  102 H drilled in the second end plate  102 B 2  is a circular hole having an inner diameter larger (1.3 to 2 times larger) than the diameter of the second fulcrum member  103 A 2  formed by a columnar body. Therefore, in a state in which the second fulcrum member  103 A 2  is inserted into the large-diameter hole  102 H, play based on the diameter difference is present. In this relation between the large diameter hole  102 H and the second fulcrum member  103 A 2 , the displacement of the separating member  102  is not substantially restricted. The separating member  102  can be displaced in all directions within the range of the play. 
     With the fixing unit  97  according to this embodiment, the contact members  104  attached at both ends of the separating member  102  come into contact with the circumferential surface of the fixing roller  100 , whereby the gap G having the predetermined distance is formed between the distal end portion  102 A of the main body section  102 C and the circumferential surface of the fixing roller  100 . The long hole  102 G allows the separating member  102  to substantially shift only in the predetermined direction in which the long-diameter portion LD extends. The large-diameter hole  102 H does not substantially restrict the displacement of the separating member  102 . Therefore, the fulcrum of the separating member  102  is not fixed. The separating member  102  can shift within the shift allowing range of the long hole  102 G. Therefore, even if deviation occurs in parallelism between the distal end portion  102 A of the separating member  102  and the axis of the fixing roller  100 , since the contact section  104 C and the circumferential surface of the fixing roller  100  come into contact with each other, a fulcrum position of the separating member  102  shifts on the insides of the long hole  102 G and the large-diameter hole  102 H to correct the deviation. Therefore, it is possible to maintain the parallelism between the distal end portion  102 A and the circumferential surface of the fixing roller  100  and appropriately secure the gap G. 
     In addition, the position of the separating member  102  with respect to the fixing roller  100  is determined by three points, i.e., contact positions of the two contact members  104  (the contact sections  104 C), which are arranged at both ends of the separating member  102 , with the fixing roller  100  and a receiving position of the first fulcrum member  103 A 1  by the long hole  102 G. That is, the large-diameter hole  102 H is a circular hole having a diameter larger than the second fulcrum member  103 A 2  and substantially does not restrict the displacement of the separating member  102 . Therefore, the large-diameter hole  102 H does not contribute to the positioning of the separating member  102 . 
     If the large-diameter hole  102 H is a circular hole having an inner diameter substantially the same as the outer diameter of the second fulcrum member  103 A 2  or if the large-diameter hole  102 H is a long hole same as the long hole  102 G, the position of the separating member  102  with respect to the fixing roller  100  is determined by three points, i.e., receiving positions at two points of the first and second fulcrum members  103 A 1  and  103 A 2  and a contact position of one contact member  104  out of the two contact members  104  with the fixing roller  100 . In this case, a linear pressure in a portion where the one contact member  104  comes into contact with the fixing roller  100  increases and could damage the fixing roller  100 . Further, since it could occur that the other contact member  104  of the two contact members  104  does not come into contact with the fixing roller  100 , appropriate securing of the gap G could be hindered. On the other hand, in this embodiment, both two contact members  104  contribute to the positioning of the separating member  102 . Therefore, it is possible to reduce linear pressure in portions where the contact members  104  are in contact with the fixing roller  100  and stably maintain the gap G. 
       FIG. 11  is a main part sectional view (on the long hole  102 G side) of the fixing unit  97  showing a state in which the distal end (the contact section  104 C) of the contact member  104  is separated from the circumferential surface of the fixing roller  100  (a state in which the separating member  102  is in the second posture).  FIG. 12  is an enlarged sectional view of  FIG. 11  showing a state in which the contact section  104 C is in contact with the circumferential surface of the fixing roller  100  (the first posture).  FIG. 13  is a main part sectional view (the large-diameter hole  102 H side) of the fixing unit  97  showing a state in which the separating member  102  is in the first posture. 
     In  FIG. 11 , the fixing roller  100  rotates in the counterclockwise direction and the pressurizing roller  101  rotates in the clockwise direction. Whereas most of the fixing roller  100  is a roller configured by the elastic base material  100 E, the pressurizing roller  101  is a roller having rigidity. Therefore, in the fixing nip portion N, the circumferential surface of the pressurizing roller  101  pushes in the circumferential surface of the fixing roller  100 . The separating member  102  is arranged further on the rotating direction downstream side of the fixing roller  100  than the fixing nip portion N. 
     In the second posture shown in  FIG. 11 , the contact section  104 C of the contact member  104  is not in contact with the circumferential surface of the fixing roller  100 . However, in the first posture shown in  FIGS. 12 and 13 , the contact section  104 C is in contact with the circumferential surface of the fixing roller  100 . In a state in which the contact member  104  is in contact with the circumferential surface of the fixing roller  100 , the gap G having a distance d is formed between the distal end portion  102 A of the separating member  102  and the circumferential surface of the fixing roller  100 . 
     In  FIG. 12 , the first fulcrum member  103 A 1  is in contact with an end edge  102 GE of the long hole  102 G on a side separating from the fixing roller  100 . In  FIG. 13 , the second fulcrum member  103 A 2  is in contact with a circumferential edge  102 HE of the large-diameter hole  102 H. Such contacts are realized by an urging spring  110  (an urging member) configured to urge the contact member  104 , which is attached to the separating member  102 , toward the circumferential surface of the fixing roller  100 . 
       FIG. 14  is a perspective view for explaining an attachment form of the urging spring  110 . Referring to  FIGS. 13 and 14 , the urging spring  110  is a helical torsion coil spring including a cylindrical coil section  110 C, a bar-like first locking section  110 E 1  extended from one end side of the coil section  110 C, and a bar-like second locking section  110 E 2  extended from the other end side. 
     The coil section  110 C of the urging spring  110  is inserted through the second fulcrum member  103 A 2 . The inner diameter of the coil section  110 C is substantially the same as the inner diameter of the large-diameter hole  102 H. The first locking section  110 E 1  is locked to a receiving section (not shown in the figure) provided in the holding sheet metal  102 S of the separating member  102 . The second locking section  110 E 2  is extended to the outside from the separating member  102  and locked to a locking hole  111  provided in the supporting member  103 . The second locking section  110 E 2  is in contact with the locking hole  111  with an urging force. Consequently, an urging force is applied to the separating member  102  such that the distal end portion  102 A of the main body section  102 C thereof pivots around the axis of the first and second fulcrum members  103 A 1  and  103 A 2  in a direction toward the circumferential surface of the fixing roller  100 . 
     The contact member  104  attached to the separating member  102  is brought into press-contact with the circumferential surface of the fixing roller  100  by the urging force. The contact member  104  is surely set in contact with the circumferential surface of the fixing roller  100 . In addition, at least the first fulcrum member  103 A 1  is in contact the circumferential edge of the long hole  102 G with the urging force. Therefore, the separating member  102  is positioned by locking at three points of the two contact member  104  and the first fulcrum member  103 A 1 . In this way, the contact member  104  can be surely brought into contact with the circumferential surface of the fixing roller  100  by the urging spring  110 . Therefore, the gap G having a predetermined distance is surely and stably formed between the separating member  102  and the fixing roller  100 . The contact member  104  comes into contact with the non-passing regions  100 B where a sheet does not pass on the circumferential surface of the fixing roller  100 . Therefore, traces of damage are not left on toner images on the sheet. 
     Subsequently, a more preferable attachment form of the contact member  104  to the separating member  102  is illustrated. In the example explained in the embodiment, the contact member  104  is fixedly attached to the holding sheet metal  102 S of the separating member  102  by the attachment screw  109 . Instead, the contact member  104  can be attached to the separating member  102  in a state that the contact member  104  can be shifted in the radial direction of the fixing roller  100 . 
       FIG. 15  is a sectional view showing a modified embodiment of an attachment form of the contact member  104  to the separating member  102 . An end portion on the first end plate  102 B 1  where the long hole  102 G is drilled is shown. In this modified embodiment, a SEMS screw  112  (an attachment member) is used instead of the attachment screw  109 . The SEMS screw  112  includes a screw head  112 A, a cylindrical section  112 B provided continuously to the screw head  112 A, and a tap section  112 C provided continuously to the distal end side of the cylindrical section  112 B. The cylindrical section  112 B is a flat cylindrical portion without thread ridges. The tap section  112 C is a portion with thread ridges. 
     The SEMS screw  112  is screwed in the screw hole  102 E of the holding sheet metal  102 S through the screw hole  104 E provided in the attaching section  104 A of the contact member  104 . More specifically, while the tap section  112 C is screwed in the screw hole  102 E, the circumferential wall of the screw hole  104 E and the circumferential surface of the cylindrical section  112 B are not restricted. The length of the cylindrical section  112 B is sufficiently larger than the thickness of the attaching section  104 A. Therefore, the contact member  104  can shift between the rear surface of the screw head  112 A and the starting end of the tap section  112 C along the circumferential surface of the cylindrical section  112 B. Consequently, the contact member  104  can shift in the radial direction of the fixing roller  100 . Therefore, even if outer diameter fluctuation occurs in the fixing roller  100  or unevenness occurs on the circumferential surface of the fixing roller  100 , it is possible to displace the contact member  104  following the outer diameter fluctuation or the unevenness and stably bring the contact section  104 C into contact with the circumferential surface of the fixing roller  100 . Therefore, it is possible to stably maintain the gap G. 
     This modified embodiment is particularly useful when the fixing unit includes the configuration shown in  FIG. 11 . As explained above, the fixing roller  100  includes the elastic base material  100 E (a roller member) having elasticity and the fixing belt  100 S fit on the elastic base material  100 E. The contact section  104 C of the contact member  104  is in contact with the circumferential surface of the fixing belt  100 S. When the fixing roller  100  has the structure in which the fixing belt  100 S is overlaid in the circumference of one roller member in this way, arbitrary tension cannot be applied to the fixing belt  100 S. Therefore, the roller outer diameter of the fixing roller  100  tends to fluctuate because of thermal expansion or the like of the elastic base material  100 E. Further, flapping of the fixing belt  100 S sometimes occurs. Therefore, in the fixing roller  100 , an advantage of using the attachment structure for the contact member  104  by the SEMS screw  112  is large. 
     As explained above, with the fixing unit  97  according to this embodiment, it is possible to appropriately secure, with the contact member  104 , the gap G between the distal end portion  102 A of the separating member  102  and the circumferential surface of the fixing roller  100 . Further, it is possible to suppress a pressure applied to the circumferential surface of the fixing roller  100  by the contact member  104  and stably maintain the gap G. Therefore, it is possible to surely prevent winding of a sheet around the fixing roller  100 . 
     Although the present disclosure has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present disclosure hereinafter defined, they should be construed as being included therein.