Patent Publication Number: US-7583913-B2

Title: Recording medium conveying unit and image forming apparatus having recording medium reversing unit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present document incorporates by reference the entire contents of Japanese priority document, 2003-302983 filed in Japan on Aug. 27, 2003. 
   BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The present invention relates to a recording medium conveying unit and an image forming apparatus. 
   2) Description of the Related Art 
   In a conventional image forming apparatus, a transferring device transfers a toner image formed on an image bearing body to a recording medium delivered by a resist device. A fixing device fixes the toner image on the recording medium. A recording medium discharging device ejects to a discharge tray the recording medium bearing the fixed toner image. The image forming apparatus here refers to a multifunction product performing the functions of an electronic photocopying machine, a printer, and a facsimile or at least a combination of two of these. 
   The conventional image forming apparatuses have a structure that allow the recording medium to be easily released, should jamming occur, by providing a transferring device, fixing device, and recording medium discharging device, each of which can be independently drawn out of the main unit of the image forming apparatus. If jamming of the recording medium occurs when the recording medium is stretched across the transferring device and the fixing device, if only the transferring device is drawn out while the fixing device is still inside the main unit, there is a risk of the recording medium getting damaged due to the recording medium being still caught in the fixing device. Therefore, to correct this drawback, an image forming apparatus (see Japanese Patent Laid-Open Publication No. H2-149861 (Page 4, FIG. 1, and FIG. 3)) is provided in which the transferring device, the fixing device, and the recording medium discharging device form a single recording medium conveying unit that can be drawn out as a unit. This structure precludes the risk of releasing the recording medium from just one part, and leaving it caught in another part and thus damaging it. 
   However, some image forming apparatuses can form images on both sides of a recording medium. Once a toner image on a front surface is fixed, the recording medium is reversed and another toner image is formed on a back surface of the recording medium. These apparatuses are provided with a recording medium reversing device that delivers the recording medium once again to the resist device. If jamming of the recording medium occurs in such an image forming apparatus when the recording medium is stretched across the fixing device and the recording medium reversing device, there is a risk of the recording medium getting damaged because the recording medium reversing device remains inside the main unit of the image forming apparatus when the recording medium conveying unit is drawn out to release the jamming. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to solve at least the problems in the conventional technology. 
   A recording medium conveying unit according to an aspect of the present invention that can be drawn out of and pushed back into a main unit of an image forming apparatus and includes a resist unit that delivers a recording medium to an image bearing body at a predetermined time so that a toner image formed on the image bearing body is transferred to the recording medium; a fixing unit that fixes on the recording medium delivered by the resist unit the toner image formed on the image bearing body; a transferring unit that transfers the toner image formed on the image bearing body; a recording medium discharging unit that discharges to a recording medium discharge tray the recording medium bearing a fixed toner image; and a recording medium reversing unit that reverses the recording medium bearing the fixed toner image on a first surface so that a toner image may be formed on a second surface, and delivers the recording medium once again to the resist unit. 
   An image forming apparatus according to an aspect of the present invention includes the above recording medium conveying unit. 
   The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a vertical cross section of an image forming apparatus according to an embodiment of the present invention; 
       FIG. 2  is a perspective of the image forming apparatus; and 
       FIG. 3  is a perspective of a recording medium conveying unit drawn out of a main unit of the image forming apparatus. 
   

   DETAILED DESCRIPTION 
   Exemplary embodiments of a recording medium conveying unit and an image forming apparatus according to the present invention will be explained below while referring to the accompanying drawings. 
     FIG. 1  is a vertical cross section of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus includes a main unit  1  and an automatic document feeder  2  mounted on the main unit  1 . The main unit  1  houses a recording medium conveying unit, which is described later, and various other devices. The bold lines in  FIG. 1  represent cross-section. 
   The automatic document feeder  2  feeds documents (not shown) placed in a document feeding tray  3 , one document at a time, to a contact glass  4  disposed on upper side of the main unit  1  and discharges the document to a discharge tray  5  once an image is scanned on it. 
   When scanning images from both the surfaces of the document, the document delivered from the document feeding tray  3  moves over the contact glass and is re-fed to the contact glass  4  jointly by a roller  6  and a reversing nail  7 . An image is scanned on one surface of the document on the contact glass  4 . Once the scanning on the first surface is completed, the document is re-fed to the contact glass  4  jointly by the roller  6  and the transfer nail  7 . This time an image is scanned on the other surface of the document. Subsequently, the document is discharged to the discharge tray  5 . 
   The main unit  1  includes an optical scanning system  8  provided beneath the contact glass  4 . The optical scanning system  8  includes an exposure lamp  9 , a first mirror  10 , a second mirror  11 , a third mirror  12 , a lens  13 , and a photoelectric converter made of a charge-coupled device (CCD)  14 . When scanning an image on the document, a not shown stepping motor moves the exposure lamp  9  and the first mirror  10  at a constant speed in a sub-scanning direction, that is, towards the right in  FIG. 1 , and light from the exposure lamp  9  exposes the image on the document set on the contact glass  4 . The stepping motor also moves the second mirror  11  and the third mirror  12 , but at half the speed of the exposure lamp  9  and the first mirror  10 . The first mirror  10 , the second mirror  11 , and the third mirror  12  reflect the light on the document and the reflected light passes through the lens  13 . The image on the document is formed on an acceptance surface of the CCD  14  and a photoelectric conversion takes place. 
   The main unit  1  also includes an image bearing body  15  in the form of a photosensitive drum, and an optical writing unit  16 . During image formation, the image bearing body  15  is driven to turn in a clockwise direction in  FIG. 1 . A charging device  17  charges the entire surface of the image bearing body  15  to a uniform polarity. A black laser light L 1 , which is optically modulated according to the image information scanned by the optical scanning system  8 , emitted by the optical writing unit  16  exposes the surface of the charged image bearing body  15 , forming a latent image on the image bearing body  15 . A black developing device  18  develops the latent image into a visible black toner image. Next, a red laser light L 2 , emitted by the optical writing unit  16 , exposes the surface of the image bearing body  15  and forms a latent image. A red developing device  19  develops this latent image into a visible red toner image. 
   Sheet feeders  20 A through  20 E are provided below the main unit  1 . Each of the sheet feeders  20 A through  20 E includes a feeding tray  21  and a feed roller  22 . The feeding tray  21  houses recording medium P, which may be transfer sheets or a resin films. One of the feeding devices  20 A through  20 E is selected and the feed roller  22  rotates and delivers the topmost sheet of the recording medium P from the feeding tray  21 . 
   The recording medium delivered by the feed roller  22  is conveyed to the conveying rollers  50  and  51 . The conveying rollers  50  and  51  transfer the recording medium to a pair of resist rollers  23 , which is an example of a resist device. Upon coming in contact with the resist rollers  23 , the recording medium halts briefly. Once the resist rollers  23  start rotating at a predetermined time, the recording medium is conveyed towards the image bearing body  15 . A transferring device  24  transfers the toner image on the image bearing body  15  to the recording medium. In this way, the resist device rotates at a predetermined time and delivers the recording medium to the image bearing body so that the toner image formed on the image bearing body is transferred to the recording medium. 
   The transferring device transfers the toner image formed on the image bearing body to the recording medium delivered by the resist device. The transferring device may be of any form. However, the transferring device shown in  FIG. 1  includes a plurality of support rollers  25  and  26 , a transfer belt  27  that is stretched across and is supported by the support rollers  25  and  26  and is driven in the direction indicated by the arrow A, and a bias member  28  disposed on the inner surface of the transfer belt  27  substantially facing the image bearing body  15 . When the transfer belt  27  carries the recording medium to the image bearing body  15 , a transfer voltage is applied on the bias member  28  by which the toner image on the image bearing body  15  is transferred to the recording medium. 
   A cleaning device  29  removes the toner left over on the image bearing body  15  after the transfer of the toner image and a not shown neutralizing device resets the voltage on the surface of the image bearing body  15 . 
   The recording medium leaves the transfer belt  27  and passes through a fixing device  30 . The fixing device  30  shown in  FIG. 1  is only an example and includes a fixing roller  31  and a pressure roller  32 , which rotate against one another, a not shown heater provided inside the fixing roller  31 , and a casing  34  that houses and rotatably supports the fixing roller  31  and the pressure roller  32 . When the recording medium passes between the fixing roller  31  heated by the heater and the pressure roller  32 , the toner image on the recording medium is fixed to the recording medium by application of heat and pressure. 
   After passing through the fixing device  30 , the recording medium is discharged by a recording medium discharging device  35  in the direction indicated by the arrow B and is stacked on a recording medium discharge tray  36 . The recording medium discharging device  35  shown in  FIG. 1  includes a set of conveying rollers  37 ,  38 , and  39 , and guide plates  40 . Thus, the recording medium bearing a fixed toner image is discharged by the recording medium discharging device  35  on a recording medium discharging tray  36 , and can be removed via the front opening  36 A ( FIG. 2 ). 
   The image forming apparatus has a two-surface mode in which it allows image formation on both the surfaces of the recording medium. In the two-surface mode, by the switching of a switching nail  41  provided between the fixing device  30  and the recording medium discharging device  35 , the recording medium emerging out of the fixing device  30  is guided by a guide plate  42  in the direction indicated by the arrow C into a recording medium reversing device  43 . 
   The recording medium reversing device  43  shown in  FIG. 1  is only an example and includes a pair of inlet rollers  44 , a plurality of pairs of conveying rollers  45  through  47  arranged substantially horizontally, a reversing roller  48 , and a casing  49  that houses and rotatably supports the inlet rollers  44 , the conveying rollers  45  through  47 , and the reversing roller  48 . The recording medium is conveyed through the inlet rollers  44  over the top rollers of the conveying rollers  45  through  47  in the direction indicated by the arrow D. The top rollers of the conveying rollers  45  through  47  rotate clockwise. 
   The top rollers of the conveying rollers  45  through  47  and the inlet rollers  44  now turn counter-clockwise, causing the recording medium to be conveyed in the direction opposite to the direction indicated by the arrow D. The reversing roller  48  conveys the recording medium in the direction indicated by the arrow E. The conveying rollers  45  through  47  then convey the recording medium in the direction indicated by the arrow F. Thus, the recording medium is flipped to the reverse side. The conveying rollers  50 ,  52 , and  51  convey the recording medium that emerges from the recording medium reversing device  43  once again to the resist rollers  23 , where the recording medium halts briefly. The subsequent steps are identical to the steps of toner image formation on the first surface. That is, the transferring device  24  transfers the toner image from the image bearing body  15  to the second surface of the recording medium following which the recording medium passes through the fixing device  30  and is discharged to the recording medium discharge tray  36  by the recording medium discharging device  35 . 
   Thus, the recording medium reversing device reverses the recording medium that emerges from the fixing device so that a toner image may be formed on the second surface and delivers the recording medium once again to the resist device. 
   The resist rollers  23  that form the resist device, the transferring device  24 , the fixing device  30 , the recording medium discharging device  35 , and the recording medium reversing device  43  are fitted as a single recording medium conveying unit  53  that can be drawn out of or pushed back into the main unit  1 . In  FIG. 1 , the recording medium conveying unit  53  is supported against the main unit  1  in such a way that it can be drawn out in a substantially orthogonal direction with respect to the conveying direction of the recording medium, that is, substantially orthogonal to the surface of the sheet on which  FIG. 1  appears on the near side, and pushed back in the opposite direction. 
   To be more specific, the resist rollers  23  that form the resist device, the transferring device  24 , the fixing device  30 , the recording medium discharging device  35 , and the recording medium reversing device  43  are fitted as a unit in a unit frame  54 , forming a recording medium conveying unit  53 . In  FIG. 1 , the guide plates  40 ,  42 , and other guide plates are integral with the unit frame  54 . Two movable guide rails  55  are secured, one on each side of the unit frame  54 . Each movable rail  55  is swingably secured to a fixed guide rail  56  secured to the main unit  1 . 
     FIG. 2  is an oblique view of the image forming apparatus. A front door  57  on the near side of the main unit  1  is supported to swivel open and close. Let us suppose that jamming of the recording medium has occurred while on the recording-medium conveying unit  53 , causing the image formation process of the image forming apparatus to halt. To release the jammed recording medium, the front door shown in  FIG. 3  is first opened to draw out the recording medium conveying unit  53 . The drawing causes the movable guide rails  55  secured to the unit frame  54  of the recording medium conveying unit  53  to slide against the fixed guide rails  56  secured to the main unit  1 , making it possible to draw the entire recording medium conveying unit  53  out of and in front of the main unit  1 . In this way, the resist device, the transferring device  24 , the fixing device  30 , the recording medium discharging device  35 , and the recording medium reversing device  43  that form the recording medium conveying unit  53  are all exposed, making it easy to release the jammed recording medium. Further, even if jamming of the recording medium has occurred between any two of these devices, the recording medium can be released without any damage since these devices, namely, the resist device, the transferring device  24 , the fixing device  30 , the recording medium discharging device  35 , and the recording medium reversing device  43 , are fitted as a unit and can be drawn out of the main unit  1  as a unit. Thus, this structure allows the jamming of the recording medium to be released even more effectively. 
   Further, a structure may be provided wherein, when no image formation is taking place, the fixing roller  31  and the pressure roller  32  of the fixing device  30  are separated by a not shown driving device, and the transfer belt  27  of the transferring device  24  is not in contact with the image bearing body  15 . In such a structure, jamming of the recording medium leads to the separation of the fixing roller  31  and the pressure roller  32  as well as separation of the transfer belt  27  and the image bearing body  15 . This facilitates easy release of the jammed recording medium once the recording medium conveying unit  53  is drawn out of the main unit  1 . 
   After releasing the jammed recording medium, the recording medium conveying unit  53  is pushed back into the main unit  1 . As shown in  FIG. 1 , positioning slots  58  and  59  provided on the unit frame  54  engage into positioning pins  60  and  61  protruding from the side walls at the far end of the main unit  1 . Once the recording medium conveying unit  53  is engaged into the main unit  1 , image formation process can be restarted after closing the front door  57  as shown in  FIG. 2 . 
   The unit frame  54  of the recording medium conveying unit  53  and the guide plates  40  and  42  may be formed from resin. As compared to a metal structure, this helps reduce the overall weight of the recording medium conveying unit  53 , making it easier to draw it out and push it in. 
   It is preferable to use a transparent material, such as a transparent resin, for at least a part of, and preferably, the entire unit frame  54 . This enables the user to visually ascertain if jamming has indeed taken place when the recording medium conveying unit  53  is drawn out of the main unit  1 . The guide plates  40  and  41  should also be preferably made of a transparent material. 
   Further, as shown in  FIG. 1 , the fixing device  30  may be detachably fitted into the unit frame  54 . This structure enables easy replacement of the fixing device  30 . To be specific, a pocket  62  may be provided in the unit frame  54  into which the fixing device  30  can be detachably engaged. When the recording medium conveying unit  53  is pushed back into the main unit  1 , positioning pins  63  located at the far end of the casing  34  of the fixing device  30  engage into the positioning slots provided on the side walls at the far end of the main unit  1 , securing the fixing device  30  in the main unit  1 . 
   Similarly, the transferring device  24  may also be detachably fitted into the unit frame  54  to make it easier to replace. 
   A structure may be provided wherein the recording medium reversing device  43  is supported such that it can be shifted downward with respect to the unit frame  54  once the recording medium conveying unit  53  is drawn out of the main unit  1 . This facilitates the release of the jammed recording medium. For instance, the recording medium  43  and the unit frame  54  may be connected with the aid of not shown pivot pins provided at the far end of each side of the casing  49  of the recording medium reversing device  43 . When the recording medium conveying unit  53  is drawn out of the main unit  1 , the recording medium reversing device  43  can be pivoted around the pivot pins, and the parts of the recording medium reversing device  43  at the near end can be shifted downward. 
   Apart from the recording medium conveying unit  53 , the image forming apparatus according to the present example includes a plurality of sheet feeders  20 A through  20 E, each of which feed a recording medium P of a different size to the resist device formed by the resist rollers  23 . The size of the recording medium in the conveyance direction represents the length of the recording medium. The length of the longest recording medium from among the recording mediums being used is set as the length L of the recording medium reversing device  43 . 
   If the length L of the recording medium reversing device  43  is set greater than the length of the longest recording medium, the recording medium reversing device  43  can reverse even the longest recording medium, enabling toner image formation on the reverse surface of the recording medium. However, there are other elements, such as the conveying roller  50 , etc., next to the recording medium reversing device  43 . Therefore, if the length L of the recording medium reversing device  43  is set greater than the length of the longest recording medium being used, the width of the main unit  1  in the horizontal direction in  FIG. 1  will become very large. 
   Therefore, the length L of the recording medium reversing device  43  is kept less than the length of the longest recording medium being used. In this structure, the recording medium reversing device  43  cannot reverse the longest recording medium, and hence no toner image can be formed on the reverse surface of the longest recording medium. This is a trade-off for achieving compactness of the model. 
   In the example described so far the image forming apparatus has an image bearing body which itself is a light-sensitive body. However, the present invention can also be adapted to an image forming apparatus in which the image bearing body is an intermediate transfer body to which the toner image is transferred from a light-sensitive body. Apart from photocopying machines, the present invention can also be applied to other image forming apparatuses such as printers, facsimiles, or multifunction products that include these devices. 
   According to the present invention, it is possible to prevent damage to a recording medium in the event of jamming of the recording medium in either a recording medium reversing device or other devices next to the recording medium reversing device. 
   Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.