Patent Publication Number: US-9885981-B2

Title: Image forming device

Description:
RELATED APPLICATIONS 
     The present application is a national stage entry according to 35 U.S.C. § 371 of PCT application No.: PCT/JP2015/062556 filed on Apr. 24, 2015, which claims priority from Japanese application No.: 2014-110842 filed on May 29, 2014 and is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to an image forming device such as a copier, a printer, a facsimile, and a multifunction peripheral having a combination of such functions. 
     BACKGROUND 
     Conventional image forming devices such as copiers or printers are generally provided with a paper path extending in a vertical direction at the vicinity of the side face of the main body of the device for downsizing the overall system. The paper path extending in a vertical direction is provided with a pair of conveying rollers for conveying a sheet of paper. It is common to install a conveying unit having one roller of the pair of conveying rollers, a transfer roller which is pressed by an image carrier to be brought into contact with the image carrier to form a transfer nip part, and the like, and to design a structure capable of opening and closing the conveying unit in relation to the main body of the device for easy clearance of paper jams and maintenance of the device in a condition where a wide range of the paper path is exposed. 
     For example, the patent document 1 discloses a paper conveying device having at least two parallel paper paths where a paper jam occurred therein can be cleared from only one direction. This paper conveying device includes at least two swing guide plates for opening the at least two paper paths, an opening/closing mechanism for opening or closing the swing guide plates, and an exterior cover for opening and closing the main body of the device. The swing guide plates are configured to be opened or closed with the movement of an opening or closing action of the exterior cover. 
     The patent document 2 discloses a constitution, in which a transfer roller is provided with a bearing member that rotatably supports a rotation axis, a spring member that presses the bearing member to the side of a photoreceptor drum, and a bearing holder that houses the bearing member and supports the bearing member so that the bearing member is movable in the housing. In this constitution, when a cover member, which is provided with the transfer roller, is closed in relation to the main body of the device, a bearing member freely moves in the housing of the bearing holder on the side of the main body of the device, and the rotation axis of the transfer roller is fitted into a guiding groove of the bearing guide of the main body of the device so that the rotation axis is opposed to the guiding groove. Thus, the transfer roller is pressed against the photoreceptor drum so that the transfer roller is brought into contact with the photoreceptor, and thereby a nip part that enables nipped transfer of a recording medium is formed. 
     REFERENCES 
     Patent Documents 
     [Patent document 1] JP 10-147451 A 
     [Patent document 2] JP 2007-240834 A 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     In a conveying unit provided with a conveying roller and a transfer roller, which enables clearance of a paper jam and maintenance of the device under a condition where the conveying unit is opened or closed in relation to the main body of the device, a conveying roller or a transfer roller is pressed against the opposing transfer roller or image carrier with a relatively great pressing force so that a sufficient nip width (that is, paper conveying ability) should be maintained. When an angle between the direction of this pressing force and the direction of the orbital of opening/closing a conveying unit is large, force required to release pressing force imposes a load on opening or closing the conveying unit, and thus operability upon opening/closing the conveying unit is lowered. 
     In view of the state of the art, the present invention has an object to provide an image forming device which enables an easy release of pressing force between a roller installed in the convey unit and a rotor on the side of the main body of the device upon opening/closing operation of the conveying unit. 
     Means to Solve the Problem 
     To accomplish the above object, a first constitution of the present invention relates to an image forming device including a cover member, a conveying unit, a first rotor, a second rotor, a bearing unit, a biasing member, and a link member. The cover member includes a hook that is openably or closably supported in relation to the main body of the image forming device and is configured to engage with the main body of the image forming device, and an opening/closing lever that moves the hook to a position where the engagement between the hook and the main body of the image forming device is released. The conveying unit is disposed on the inner side of the cover member, and is rotatably supported between an opened position and a closed position in relation to the main body of the image forming device. The first rotor is rotatably supported on the inner side of the conveying unit. The second rotor is rotatably supported on the side of the main body of the image forming device. The bearing unit is supported movably to the conveying unit, and rotatably supports the rotation axis of the first rotor. The biasing member biases the bearing unit so as to press the first rotor towards the axial core of the second rotor. The link member is swingably supported on the conveying unit, and is configured to engage with the bearing unit. When the conveying unit is in a closed position, the first rotor is pressed by the second rotor to form a nip part for conveying a recording medium. In the image forming device, by operating the opening/closing lever in a state where the conveying unit is in a closed position, the link member is pressed by the hook to swing so that the first rotor of the bearing unit should move away from the second rotor against biasing force from the biasing member. 
     Effect of the Invention 
     According to the first constitution of the present invention, the pressure contact state between a first rotor and a second rotor can be released by operating the opening/closing lever in a state where the conveying unit is in a closed position. Thus, the conveying unit can be released by relatively smaller force than the conventional devices since the force of the first rotor to press the second rotor does not impose a load upon operation of opening/closing operation. As a result, operability of the conveying unit is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of the entire constitution of the image forming device  100  according to one embodiment of the present invention. 
         FIG. 2  is a sectional view around the paper path  14  and the inversion paper path  21  in the image forming device  100  of this embodiment. 
         FIG. 3  is a partial enlarged view around the secondary transfer roller  9  in  FIG. 2 . 
         FIG. 4  is a perspective view of the side cover  33  and the conveying unit  35  seen from the front side of the image forming device  100 . 
         FIG. 5  is a partial enlarged view around the bearing guide member  41  from which the link member  43  is removed. 
         FIG. 6  is a perspective view of the link member  43  seen from the back side (the side of the bearing guide member  41 ). 
         FIG. 7  is a perspective view of the link member  43  seen from the front side (the side of the hook  37 ). 
         FIG. 8  is a perspective view illustrating a condition where the hook  37  pushes down the arm  43   c  of the link member  43 . 
         FIG. 9  is a view illustrating the relation between the distance L 1  from the bearing hole  43   a  of link member  43  to the engagement part  43   b  and the distance L 2  from the bearing hole  43   a  to the arm  43   c.    
         FIG. 10  is an enlarged view of the part overlapping the conveying unit  35  in the back side frame  101   b  of the main body of the image forming device  100 . 
         FIG. 11  is a partial enlarged view illustrating a condition where the conveying unit  35  is rotated by a predetermined amount in the closing direction from an opening state, whereby the arm  43   c  of the link member  43  is brought into contact with a first guide face  51   a  of the guide element  51 . 
         FIG. 12  is a partial enlarged view illustrating a condition where the conveying unit  35  is further rotated from the condition illustrated in  FIG. 11 , whereby the arm  43   c  is brought into contact with a second guide face  51   b.    
         FIG. 13  is a partial enlarged view illustrating a condition where the conveying unit  35  is further rotated from the condition illustrated in  FIG. 12 , whereby the arm  43   c  moves along a third guide face  51   c.    
         FIG. 14  is a partial perspective view of the conveying unit  35  which is rotated until the conveying unit  35  completely becomes a closed state in relation to the main body of the image forming device  100 . 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention is now described with reference to drawings.  FIG. 1  is a sectional view of the schematic constitution of the image forming device  100  according to one embodiment of the present invention. In this embodiment, the image forming device  100  is a four tandem-type color copier that forms an image using four photoreceptor drums  1   a ,  1   b ,  1   c  and  1   d , corresponding to four different colors (namely, magenta, cyan, yellow and black), which are parallely arranged in the color copier. 
     In a case illustrated in  FIG. 1 , four image forming parts Pa, Pb, Pc and Pd are disposed sequentially in this order from the left side of  FIG. 1  in the main body of the image forming device  100 . These image forming parts Pa, Pb, Pc and Pd are disposed so as to form images of four different colors (namely, magenta, cyan, yellow, and black), and respectively form magenta, cyan, yellow, and black images in a sequence each through the steps of electrification, exposure to light, development, and transfer. 
     These image forming parts Pa, Pb, Pc and Pd are respectively provided with the photoreceptor drums  1   a ,  1   b ,  1   c , and  1   d  that each carry a visible image (a toner image) of a predetermined color. Further, an intermediate transfer belt  8  that rotates counterclockwise in  FIG. 1  is provided adjacently to the image forming parts Pa, Pb, Pc, and Pd. Toner images formed on these photoconductor drum  1   a ,  1   b ,  1   c , and  1   d  are sequentially transferred on the intermediate transfer belt  8 , which is moving while contacting with the photoconductor drum  1   a ,  1   b ,  1   c , and  1   d . The toner images are then transferred to a paper sheet P at a time on a secondary transfer roller  9 , and then fixed on the paper sheet P in a fixing unit  15 . Then, the paper sheet P is discharged from the image forming device  100 . The image formation process on the photoreceptor drums  1   a ,  1   b ,  1   c , and  1   d  is performed during clockwise rotation the photoreceptor drums  1   a ,  1   b ,  1   c , and  1   d  are in  FIG. 1 . 
     The paper sheet P to which toner images are transferred is stored in a paper cassette  16  disposed at a lower part of the main body of the image forming device  100 , and is conveyed to the secondary transfer roller  9  through a paper feed roller  12 , a pair of resist rollers  13 , and a paper path  14 . A sheet made of a dielectric resin is used as the intermediate transfer belt  8 , and a belt which does not have any joints (namely, a seamless belt) is mainly used. The intermediate transfer belt  8  and the secondary transfer roller  9  are rotationally driven at the same line speed as the photoconductor drums  1   a ,  1   b ,  1   c , and  1   d  by a belt driving motor (not illustrated). In the downstream of the secondary transfer roller  9 , a blade-like belt cleaner  19  to remove toners remained on the surface of the intermediate transfer belt  8  is disposed. 
     Next, the image forming parts Pa, Pb, Pc, and Pd are described. Around and below the rotatably disposed photoreceptor drums  1   a ,  1   b ,  1   c , and  1   d , electrification devices  2   a ,  2   b ,  2   c , and  2   d  to electrify the photoreceptor drums  1   a ,  1   b ,  1   c , and  1   d , an exposure unit  5  to expose the photoreceptor drums  1   a ,  1   b ,  1   c , and  1   d  to light on the basis of the image data, developing devices  3   a ,  3   b ,  3   c , and  3   d  to develop electrostatic latent images formed on the photoreceptor drums  1   a ,  1   b ,  1   c , and  1   d  by a toner, and cleaning devices  7   a ,  7   b ,  7   c  and  7   d  to recover or remove developers (toners) remained after the transfer of toner images on the photoreceptor drums  1   a ,  1   b ,  1   c , and  1   d  are disposed. 
     The image reader  23  is composed of a scanning optical arrangement that loads a scanner lamp to light up a manuscript at the time of copying and a mirror to change an optical path of reflected light from the manuscript, a condensing lens that condenses reflected light that is reflected on a manuscript, and forms an image, and a CCD sensor that converts the condensed light of the formed image into electrical signals, and the like (all of them are not illustrated). The image reading part  23  reads an image of a manuscript and converts into image data. 
     When copying operation is performed, the image data of the manuscript is converted into a read image signal in the image reader  23 . Meanwhile, the surfaces of photoconductor drums  1   a ,  1   b ,  1   c , and  1   d  are evenly electrified by electrification devices  2   a ,  2   b ,  2   c , and  2   d , and then the photoconductor drums  1   a ,  1   b ,  1   c , and  1   d  are irradiated with light on the basis of image data by the exposure unit  5 , and electrostatic latent images corresponding to the image data are formed on the photoconductor drums  1   a ,  1   b ,  1   c , and  1   d . The developing devices  3   a ,  3   b ,  3   c , and  3   d  include developing rollers (developer carriers) disposed at opposed positions to the photoconductor drums  1   a ,  1   b ,  1   c , and  1   d , and are each filled with a predetermined quantity of a two-component developer that includes one toner of magenta, cyan, yellow and black. 
     When the proportion of the toner in a two-component developer filled in each of the developing devices  3   a ,  3   b ,  3   c , and  3   d  falls below the specified value by the formation of toner images which will be described below, developers are supplied in the developing devices  3   a ,  3   b ,  3   c , and  3   d  from containers  4   a ,  4   b ,  4   c , and  4   d . The toners in these developers are supplied on the photoconductor drums  1   a ,  1   b ,  1   c , and  1   d  by the developing devices  3   a ,  3   b ,  3   c , and  3   d  and electrostatically attach to corresponding photoconductor drums  1   a ,  1   b ,  1   c , and  1   d . Thus, toner images which correspond to electrostatic latent images formed by exposure to light in the exposure unit  5  are formed. 
     Then, a predetermined transfer voltage is applied between primary transfer rollers  6   a ,  6   b ,  6   c , and  6   d  and corresponding photoconductor drums  1   a ,  1   b ,  1   c , and  1   d  by the primary transfer rollers  6   a ,  6   b ,  6   c , and  6   d . Thus, toner images of magenta, cyan, yellow, or black on the photoconductor drums  1   a ,  1   b ,  1   c , and  1   d  are primarily transferred on the intermediate transfer belt  8 . These four-colored images are formed with a predetermined positional relationship for predetermined full color image formation. The primary transfer rollers  6   a ,  6   b ,  6   c , and  6   d  are rotationally driven at the same line speed as the photoconductor drums  1   a ,  1   b ,  1   c , and  1   d  and the intermediate transfer belt  8  by a primary transfer driving motor (not illustrated). Then, for formation of a new electrostatic latent image which will be sequentially performed, the toner remained on the surface of the photoconductor drums  1   a ,  1   b ,  1   c , and  1   d  are removed by corresponding cleaning units  7   a ,  7   b ,  7   c , and  7   d.    
     The intermediate transfer belt  8  is bridged over the driven roller  10  and the driving roller  11 . When the intermediate transfer belt  8  starts counterclockwise rotation with a rotation of the driving roller  11  driven by the belt driving motor, a paper sheet P is conveyed from the pair of resist rollers  13  to the nip part (secondary transfer nip part) formed between the secondary transfer roller  9 , which is disposed adjacently to the intermediate transfer belt  8 , and the intermediate transfer belt  8  at a predetermined timing. A full color image is secondarily transferred on a paper sheet P in the nip part. The paper sheet P on which toner images are transferred is conveyed to the fixing unit  15  through the paper path  14 . 
     The paper sheet P conveyed to the fixing unit  15  is heated and pressurized when passing through the nip part of a pair of fixing rollers  15   a  (fixing nip part). At the time, toner images are fixed on the surface of the paper sheet P, whereby a predetermined full color image on the paper sheet is formed. The conveying direction of the paper sheet P on which a full color image is formed is sorted by a branching part  17  that diverges in plural directions. When an image is formed only on one side of the paper sheet P, the paper sheet P is directly discharged on the discharge tray  20  by a pair of discharging rollers  18 . 
     Meanwhile, when images are formed on both sides of the paper sheet P, part of the paper sheet P which passed through the fixing unit  15  are once made to project from the pair of discharging rollers  18  to the exterior of the device. Then, the paper sheet P is sorted at the branching part  17  to the inversion paper path  21  by inversely rotating the pair of discharging rollers  18  and is conveyed again to the secondary transfer roller  9  in a state where the surface on which the image has been formed is inversed. Then, the next image formed on the intermediate transfer belt  8  is transferred to the surface, on which no image is formed, of the paper sheet P by the secondary transfer roller  9 . The paper sheet P is conveyed to the fixing unit  15 , and a toner image is fixed. After then, the paper sheet P is discharged on the discharge tray  20  by the pair of discharging rollers  18 . 
       FIG. 2  is a sectional view around the paper path  14  and the inversion paper path  21  in the image forming device  100  of this embodiment.  FIG. 3  is a partial enlarged view around the secondary transfer roller  9  in  FIG. 2 .  FIG. 4  is a perspective view of the side cover  33  and the conveying unit  35  seen from the front side of image forming device  100 .  FIG. 4  illustrates a constitution of the side cover  33  and the conveying unit  35  at one end (the front side) in the axial direction of the conveying unit  35 . The constitution and the operation of the side cover  33  and the conveying unit  35  at the other end (the back side) are the same as the constitution and the operation at the front side. 
     The side cover  33  constitutes the side face  102  of the image forming device  100 , and is rotatably supported at the fulcrum  33   a  that is provided in a lower part of the main body of the image forming device  100  body. The inner surface of the side cover  33  constitutes one conveying face of the inversion paper path  21 . A wide range of the inversion paper path  21  is exposed by rotating only the side cover  33  in the opening direction in relation to the image forming device  100 . By rotating the side cover  33  together with the conveying unit  35  in an opening direction, the conveying unit  35  moves away from the main body of the image forming device  100 , and thereby a wide range of the paper path  14  is exposed. Meanwhile, by rotating the side cover  33  together with the conveying unit  35  in a closing direction, the conveying unit  35  is brought into contact with the side of the main body of the image forming device  100 , and the secondary transfer roller  9  is pressed to push the driving roller  11 . 
     The inside of the side cover  33  is provided with the conveying unit  35 . The conveying unit  35  is rotatably supported around a spindle  35   a  by the main body of the image forming device  100 , and constitutes part of the conveying surfaces of the paper path  14  and the inversion paper path  21 . The inversion paper path  21  extends vertically along the side face  102  of the image forming device  100  between the side cover  33  and the conveying unit  35 , and has a structure of substantially C-shaped, curved shape which finally joins the paper path  14 . On the inner surface of the conveying unit  35 , one roller  13   b  constituting the pair of the resist roller  13  and the secondary transfer roller  9  which is a first roller are arranged sequentially in this order from the upstream side (bottom of  FIG. 2 ) of the conveying direction of a paper sheet. The secondary transfer roller  9  pushes the driving roller  11 , which is a second roller, with sandwiching the intermediate transfer belt  8 . 
     As illustrated in  FIG. 3 , the secondary transfer roller  9  is rotatably supported by the bearing unit  40 . The bearing unit  40  is swingably supported to the conveying unit  35  around a swing axis  45  (see  FIG. 5 ) as the fulcrum, and is biased in the direction (arrow A direction) towards the axial core of the driving roller  11  by a compression spring  38  and a pressing member  39 . In the state of  FIG. 2 , the secondary transfer roller  9  is placed at the position where the secondary transfer roller  9  is brought into contact with the driving roller  11  at a predetermined pressure by biasing force from the compression spring  38 , to form a secondary transfer nip part with the intermediate transfer belt  8 . 
     As illustrated in  FIG. 4 , a hook  37  is disposed at a side edge of the side cover  33 . The hook  37  holds the side cover  33  in a closed state by engaging with the engagement pins  47  (see  FIG. 10 ) which are disposed on each of the front side frame  101   a  and the back side frame  101   b  of the main body of the image forming device  100 . The hook  37  is biased in the direction to engage with the engagement pins  47  (the upper direction in  FIG. 4 ) by a spring (not illustrated). The hook  37  is disposed to move with the opening/closing lever  34  of the side cover  33 , which is connected to the rotating axis of the hook  37 . By holding and drawing up the bottom end of the opening/closing lever  34 , the rotating axis rotates to swing the hook  37 , to release the engagement between the hook  37  and the engagement pins. Thus, the side cover  33  can be opened. 
     The bearing guide member  41  are disposed at the both ends of the bearing unit  40 . The bearing guide member  41  has a positioning boss  41   a  that projects coaxially on the axis of rotation of secondary transfer roller  9 . The secondary transfer roller  9  is pressed by the driving roller  11  in a condition where the positioning boss  41  is fitted into the second guide groove  53  (see  FIG. 10 ) which is formed on the side frame  101  of the main body of the image forming device  100 . 
     To clear a paper jam occurred in the inversion paper path  21 , the inversion paper path  21  is opened by rotating only the side cover  33  clockwise from the position illustrated in  FIG. 2 . Meanwhile, to clear a paper jam occurred in the paper path  14 , the paper path  14  is opened by rotating the conveying unit  35  and the side cover  33  clockwise. At this time, the secondary transfer roller  9  moves away from the driving roller  11 , and one roller  13   b , which constitutes the pair of the resist rollers  13 , moves away from the other roller  13   a . After a paper sheet is removed, the conveying unit  35  and the side cover  33  are rotated counterclockwise in  FIG. 2  to return to the original state illustrated in  FIG. 2 . Thus, the conveying unit  35  is placed at the position where the secondary transfer roller  9  is pressed by the driving roller  11  so as to be brought into contact with the driving roller  11 , and the roller  13   b  is pressed by the roller  13   a  so as to be brought into contact with the roller  13   a.    
     When the conveying unit  35  is rotated in the opening direction from the state illustrated in  FIG. 2 , the secondary transfer roller  9  also moves over an arc around the spindle  35   a  in the direction represented by the arrow B. At this time, the secondary transfer roller  9  is pressed by the compression spring  38  and the pressing member  39  in the direction represented by the arrow A. As illustrated in  FIG. 3 , the angle between the pressing direction (direction represented by the arrow A) of secondary transfer roller  9  and the moving direction (direction represented by the arrow B) of the secondary transfer roller  9  becomes relatively great as an angle of near 90°. Therefore, the pressing force imposed on the driving roller  11  from the secondary transfer roller  9  imposes a load upon rotation of the conveying unit  35 , and operability of the conveying unit  35  is lowered. 
     Thus, the image forming device  100  of the present embodiment is provided with a roller retraction mechanism that moves the secondary transfer roller  9  in a direction away from the driving roller  11  at the time of operation of the conveying unit  35 . The roller retraction mechanism consists of a hook  37 , a bearing guide member  41 , and a link member  43  placed between the hook  37  and the bearing guide member  41 . 
       FIG. 5  is a partial enlarged view around the bearing guide member  41  from which the link member  43  is removed.  FIGS. 6 and 7  are perspective views of the link member  43  seen from the back side (the side of the bearing guide member  41 ) or from the front side (the side of the hook  37 ). 
     The link member  43  is a resin-made member having a bearing hole  43   a , an engagement part  43   b , and an arm  43   c . The bearing hole  43   a  is swingably fitted to the swing axis  45  provided on the bearing unit  40 . The engagement part  43   b  is formed on the back side of the link member  43  so as to engage with the engaged part  41   b  which is formed on the bearing guide member  41 . The arm  43   c  projects into the front surface of the link member  43  to be brought into contact with the lower end of the hook  37 . 
     Then, operations on opening the paper path  14  by rotating the conveying unit  35  are described. First of all, by pulling up the bottom end of the opening/closing lever  34  (see  FIG. 2 ) with a finger, the hook  37 , which is provided on both edges of the side cover  33 , rotates to release engagement with the engagement pins  47  on the side of the main body of the image forming device  100 . 
     At this time, as illustrated in  FIG. 8 , the bottom end of the hook  37  pushes down the arm  43   c  of the link member  43 , whereby the link member  43  rotates in the lower direction (the clockwise direction in  FIG. 8 ) around the swing axis  45  as the fulcrum. Then, the bearing guide member  41  is also pulled down in the lower direction by the rotation of the link member  43  because the engagement part  43   b  of the link member  43  engages with the engaged part  41   b  (see  FIG. 5 ) of bearing guide member  41 . As a result, the bearing unit  40  moves in the lower direction against biasing force from the compression spring  38 , and the secondary transfer roller  9  moves away from the driving roller  11 . 
     Because the pressing force of the secondary transfer roller  9  to the driving roller  11  does not impose a load upon opening operation of the conveying unit  35 , the conveying unit  35  can be released by a smaller force compared with conventional devices. Thus, operability of the conveying unit  35  is improved. In this embodiment, the swing fulcrum of the link member  43  and the swing axis  45  of the bearing unit  40  are common. However, the swing fulcrum of the link member  43  may be disposed on the conveying unit  35  separately from the swing axis  45 . 
     As illustrated in  FIG. 9 , assuming that the distance from the swing fulcrum (the bearing hole  43   a ) of the link member  43  to the point of action (the engagement part  43   b ) into which the link member  43  draws the bearing guide member  41  (the bearing unit  40 ) is set as L 1 , and the distance from the swing fulcrum to the point of action (the arm  43   c ) to rotate the link member  43  with the hook  37  is set as L 2 , the L 1  becomes a half or less of the L 2 . This enables to reduce required force to operate the opening/closing lever using the principle of leverage. 
       FIG. 10  is an enlarged view of the part overlapping the conveying unit  35  in the back side frame  101   b  of the main body of the image forming device  100 . On the back side frame  101   b , the engagement pins  47  with which the hook  37  of the side face cover  33  is to be engaged, a first guide groove  50  that guides the link member  43 , and a second guiding groove  53  that guides the positioning boss  41   a  of the bearing guide member  41  are formed. On the top surface of the first guiding groove  50 , a guide element  51  that is brought into contact with the arm  43  and makes the link member  43  to swing is formed. Explanation of the front side frame  101   a  of image forming device  100  is omitted because it has similar constitution to the back side frame  101   b  except that it is a mirror image of the back side frame  101   b.    
     Then, operations on closing the paper path  14  by rotating the conveying unit  35  are described. When the side cover  33  and the conveying unit  35  which are in an opened position are rotated counterclockwise, the arm  43   c  of the link member  43  is guided into the first guiding groove  50 . 
       FIG. 11  is a partial enlarged view illustrating a condition where the conveying unit  35  is rotated by a predetermined amount in the closing direction from an opened state, whereby the arm  43   c  of the link member  43  is brought into contact with the guide element  51 . As illustrated in  FIG. 11 , the guide element  51  has a first guide surface  51   a , a second guide surface  51   b , and a third guide surface  51   c  arranged in this order from the upstream (the right direction in  FIG. 11 ) of the arm  43   c.    
     Then, the conveying unit  35  is rotated in the closing direction (the counterclockwise direction in  FIG. 2 ) by a predetermined amount, the link member  43  further moves to the closing direction together with the conveying unit  35 . The link member  43  is biased in the upper direction (the counterclockwise direction in  FIG. 11 ) by biasing force from the compression spring  38  that biases the bearing unit  40 . At this time, the arm  43   c  of the link member  43  moves in the lower direction along the first guide surfaces  51   a . Thus, the link member rotates in a lower direction (the clockwise direction in  FIG. 11 ) against the biasing force from the compression spring  38 . 
     As illustrated in  FIG. 12 , when the conveying unit  35  rotates to the position where the arm  43   c  is brought into contact with the second guide surface  51   b , the link member  43  rotates to the lowest point, and the bearing guide member  41  that engages with the link member  43  is also drawn down in the lower direction. As a result, the bearing unit  40  also moves to the lower direction against the biasing force from the compression spring  38 , and the secondary transfer roller  9  retracts in the lower direction together with the bearing unit  40 . 
     When the conveying unit  35  is further rotated in the closing direction by a predetermined amount, the link member  43  further moves to the closing direction with the conveying unit  35 . As a result, as illustrated in  FIG. 13 , the biasing force from the compression spring  38  to rotate the link member  43  in the upper direction (the counterclockwise direction in  FIG. 13 ) is imposed on the link member  43 , and thus, the arm  43   c  moves in the upper direction along the third guide surface  51   c.    
       FIG. 14  is a partial perspective view of the conveying unit  35  which is rotated until the conveying unit  35  completely becomes a closed state in relation to the main body of the image forming device  100 . As illustrated in  FIG. 14 , when the side cover  33  and the conveying unit  35  are rotated to a completely closed state, the arm  43   c  of the link member  43 , which is disposed at the side edge of the conveying unit  35 , fits into the deepest part of the first guide groove  50  that is formed on each of the front side frame  101   a  and the back side frame  101   b . The positioning boss  41   a  of the bearing guide member  41  is fitted into the second guiding groove  53  (see  FIG. 10 ) that is formed on each of the front side frame  101   a  and the back side frame  101   b . Thus, the secondary transfer roller  9  is pressed by the driving roller  11 , and a transfer nip part is formed between the secondary transfer roller  9  and the intermediate transfer belt  8 . The hook  37  of the side cover  33  engages with the engagement pins  47 , whereby the conveying unit  35  and the side cover  33  are held in a closed state. 
     As described above, the secondary transfer roller  9  once retracts in the lower direction (the direction away from the driving roller  11 ) in the course of closing the conveying unit  35 , and then moves in the upper direction (the direction to be brought into contact with the driving roller  11  by pressure). Thus, interference between the secondary transfer roller  9  and the driving roller  11  can be prevented at the time of the closing operation of the conveying unit  35 , and the conveying unit  35  can be closed smoothly. 
     As illustrated in  FIG. 12 , when the conveying unit  35  is closed, a load to compress the compression spring  38  causes until the arm  43   c  travels over the second guide surfaces  51   b . As illustrated in  FIG. 13 , after the arm  43   c  has traveled over the second guide surface  51   b , the arm  43   c  moves to the inside (the left direction in  FIG. 13 ) of the image forming device  100  along the third guide surfaces  51   c  by restoring force of the compressed compression spring  38 . That is, the biasing force of the compression spring  38  acts as force to draw the conveying unit  35 , and thus an assistant force on closing the conveying unit  35  can be imparted. Also, the operator can feel a snapping operation feeling, and thereby recognizes the completion of rotation of the conveying unit  35  to a predetermined position. 
     The present invention is not limited to the embodiment mentioned above, and various modifications are possible without departing from the purpose of the invention. For example, in the embodiment mentioned above, the bearing guide member  41  is disposed on both ends of the bearing unit  40 , and the bearing unit  40  engages with the link member  43  via the bearing guide member  41 . However, the bearing unit  40  may engage directly with the link member  43  without intervention of the bearing guide member  41 . 
     In the embodiment mentioned above, the roller retraction mechanism in the combination of the secondary transfer roller  9  with the driving roller  11  are described as an example. However, the present invention is not limited to this embodiment. Alternatively, the present invention may be applied to pressure contacting or separation of other pairs of rollers disposed in the conveying unit  35 , such as the pair of resist rollers  13 . Alternatively, the present invention may be applied to pressure contacting or separation of a transfer roller and a photoconductor drum in an image forming apparatus of the direct-transfer system. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to image forming devices such as a copier, a printer, a facsimile, and a multifunction peripheral having a combination of such functions. The present invention can provide an image forming device which can easily release the pressing force between a roller disposed on a conveying unit and a rotor of the main body of a device at the time of the opening and closing operation of the conveying unit.