Patent Publication Number: US-2009220287-A1

Title: Image forming apparatus and recording media conveying method for image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior U.S.A. Patent Application No. 61/032,376, filed on 28th Feb., 2008, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to image forming apparatuses such as a copying machine and a printer, and, more particularly to an image forming apparatus in which occurrence of gloss unevenness in recording media is reduced and a recording media conveying method for the image forming apparatus. 
     BACKGROUND 
     An image forming apparatus such as a copying machine or a printer transfers a developer such as a toner onto a recording medium. The image forming apparatus includes a heating and fixing device that presses the recording medium, on which the developer is placed, while heating the recording medium. The image forming apparatus includes an inlet guide provided not to come into contact with a fixing roller and a pressing roller forming a nip of the heating and fixing device. The inlet guide guides the recording medium, on which the developer is placed, to the heating and fixing device. 
     An inlet guide in the past is formed by, for example, winding a PFA tape around the surface of a stainless steel plate (see, for example, JP-A-2008-241843). Therefore, in the inlet guide in the past, a surface that comes into contact with a recording medium is a plane. 
     However, a very small amount of a developer on a transfer belt may adhere to a transfer roller. The very small amount of the developer adheres to the inlet guide via a non-printing surface of the recording medium. Therefore, rear soiling may occur. 
     In order to solve this problem, JP-A-2004-157462 discloses a technique for providing ribs on a surface of an inlet guide that comes into contact with a recording medium. 
     However, when a large number of sheets are printed, the ribs are heated, some part of a developer tends to be melted by the heat, and gloss unevenness occurs. 
     SUMMARY 
     It is an object of the present invention to provide an image forming apparatus in which occurrence of gloss unevenness in recording media is reduced and a recording media conveying method for the image forming apparatus. 
     In an aspect of the present invention, an image forming apparatus includes: 
     an image forming unit that forms a developer image on an image bearing member; 
     a transfer unit that transfers the developer image onto a recording medium; 
     a heating and fixing device that fixes the developer image, which is transferred onto the recording medium by the transfer unit, on the recording medium; and 
     an inlet guide that is arranged upstream in a recording media conveying direction of a nip formed by a fixing roller and a pressing roller of the heating and fixing device and has, on a recording media contact surface thereof, plural ribs inclining to a further inner side farther toward a recording media conveying direction. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a configuration example of an image forming apparatus; 
         FIG. 2  is a diagram of a position of an inlet guide; 
         FIG. 3  is a top view of the inlet guide; 
         FIG. 4  is a sectional view of the inlet guide taken along an A-A line in  FIG. 3 ; 
         FIG. 5  is a sectional view of the inlet guide taken along a B-B line in  FIG. 3 ; and 
         FIG. 6  is a table of ranges of a tilt angle θ of ribs. 
     
    
    
     DETAILED DESCRIPTION 
     Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and methods of the present invention. 
     An image forming apparatus and a recording media conveying method for the image forming apparatus according to an embodiment of the present invention are explained in detail below with reference to the accompanying drawings. 
     Overview of the Image Forming Apparatus 
       FIG. 1  is a diagram of a configuration example of the image forming apparatus. As shown in  FIG. 1 , the image forming apparatus includes an original table  602  for original placement which is made of a transparent material such as a glass plate, in an upper part of an apparatus main body  601 . In the image forming apparatus, a cover  603  is openably and closably provided in the apparatus main body  601  to cover the original table  602 . 
     The image forming apparatus includes, on a lower surface side of the original table  602  in the apparatus main body  601 , a scan unit (not shown) that optically scans an image of an original placed on the original table  602 . For example, this scan unit includes a carriage  604 , reflection mirrors  606 ,  607 , and  608  that reflect light of an exposure lamp  605  reflected on the original, a magnification lens block  609  that magnifies the reflected light, and a CCD (Charge Coupled Device)  610 . The carriage  604  includes the exposure lamp  605  that irradiates light to the original table  602 . The image forming apparatus includes the carriage  604  such that the carriage  604  can reciprocatingly move along the lower surface of the original table  602 . 
     The carriage  604  moves forward while causing the exposure lamp  605  to light to expose the original placed on the original table  602 . The CCD  610  receives a reflected light image of the original on the original table  602  formed by the exposure via the reflection mirrors  606 ,  607 , and  608  and the magnification lens block  609 . The CCD  610  outputs image data corresponding to the received reflected light image of the original. 
     The image forming apparatus includes an image forming unit  220  below the scan unit in the apparatus main body  601 . The image forming unit  220  includes, for example, a print engine (not shown) and a process unit (not shown). 
     The print engine includes an exposing unit  611 . The process unit includes photoconductive drums  621 ,  622 ,  623 , and  624  serving as image bearing members located along the exposing unit  611 , an endless transfer belt  12  located in a position opposed to the exposing unit  611  across the photoconductive drums  621 ,  622 ,  623 , and  624 , a drive roller  626  that drives the transfer belt  12 , primary transfer rollers  641 ,  642 ,  643 , and  644  located in positions opposed to the photoconductive drums  621 ,  622 ,  623 , and  624  across the transfer belt  12 , and a transfer roller driving unit that drives the primary transfer rollers  641 ,  642 ,  643 , and  644 . 
     In the image forming apparatus, the transfer belt  12  is laid over the drive roller  626 , guide rollers  627 ,  628 , and  629 , and a driven roller  630 . The transfer belt  12  receives power from the drive roller  626  and rotationally travels in the counterclockwise direction. 
     In the image forming apparatus, the guide roller  627  is provided to freely move up and down. The guide roller  627  receives pivotal movement of a cam  631  and moves to the transfer belt  12  side. The guide roller  627  displaces the transfer belt  12  to the photoconductive drums  621 ,  622 ,  623 , and  624  side. 
     The image forming unit  220  executes an image forming process for forming an image based on image data (an image signal outputted from the CCD  610 ) and printing the image on a recording medium being conveyed. The image signal outputted by the CCD  610  is inputted to the exposing unit  611  after being appropriately processed. The exposing unit  611  emits a laser beam B 1  corresponding to a yellow image signal to the photoconductive drum  621  for yellow, emits a laser beam B 2  corresponding to a magenta image signal to the photoconductive drum  622  for magenta, emits a laser beam B 3  corresponding to a cyan image signal to the photoconductive drum  623  for cyan, and emits a laser beam B 4  corresponding to a black image signal to the photoconductive drum  624  for black. 
     The primary transfer rollers  641 ,  642 ,  643 , and  644  move (fall) to the transfer belt  12  side to thereby bring the transfer belt  12  into contact with the photoconductive drums  621 ,  622 ,  623 , and  624  and transfer visible images on the photoconductive drums  621 ,  622 ,  623 , and  624  onto the transfer belt  12 . 
     In the image forming apparatus, a drum cleaner, a charge removing lamp, and a charging unit, which are not shown in the figure, and a developing unit T 1  are provided in order around the photoconductive drum  621 . The drum cleaner has a drum cleaning blade that is set in contact with the surface of the photoconductive drum  621 . The drum cleaner scrapes off, with the drum cleaning blade, a developer remaining on the surface of the photoconductive drum  621 . 
     The charge removing lamp removes charges remaining on the surface of the photoconductive drum  621 . The charging unit applies high voltage to the photoconductive drum  621  to thereby charge the surface of the photoconductive drum  621  with electrostatic charges. The exposing unit  611  irradiates the laser beam B 1  on the charged surface of the photoconductive drum  621 . An electrostatic latent image is formed on the surface of the photoconductive drum  621  by the irradiation of the laser beam B 1 . The developing unit T 1  supplies a yellow developer (toner) to the surface of the photoconductive drum  621  to thereby visualize the electrostatic latent image on the surface of the photoconductive drum  621 . 
     In the same manner, electrostatic latent images on the surfaces of the other photoconductive drums  622 ,  623 , and  624  are respectively visualized by using developers of colors corresponding to the photoconductive drums  622 ,  623 , and  624 . 
     The image forming apparatus includes a cleaner  636  in a position opposed to the drive roller  626  of the image forming unit  220  across the transfer belt  12 . The cleaner  636  has a cleaning blade  673   a  that is set in contact with the transfer belt  12 . The cleaner  636  scrapes off, with the cleaning blade  673   a , a developer remaining on the transfer belt  12 . 
     Printing modes are changed as explained below. The image forming apparatus includes hooks  671 ,  672 ,  673 , and  674  near the primary transfer rollers  641 ,  642 ,  643 , and  644 . The hooks  671 ,  672 ,  673 , and  674  engage with shafts of the primary transfer rollers  641 ,  642 ,  643 , and  644  and lift the shafts while pivoting and move the primary transfer rollers  641 ,  642 ,  643 , and  644  in a direction away from the photoconductive drums  621 ,  622 ,  623 , and  624 . Printing modes such as a full-color mode, a total separation mode, and a monochrome mode are changed by not moving all of the primary transfer rollers  641 ,  642 ,  643 , and  644  or changing a combination of the primary transfer rollers to be moved. 
     A storing mechanism and a feeding mechanism for recording media are explained below. The image forming apparatus includes plural recording media cassettes  650 , which store recording media, below the exposing unit  611 . These recording media cassettes  650  store, in a stacked state, a large number of recording media P of types different from one another. The image forming apparatus includes, respectively in outlet sections (on the right side in the figure) of the recording media cassettes  650 , recording media feeding mechanisms  221  that feed the recording media in the recording media cassettes  650  one by one from the top. Each of the recording media feeding mechanisms  221  takes out the recording media P one by one from one of the recording media cassettes  650  corresponding thereto. The recording media feeding mechanism  221  for taking out the recording media P includes a pickup roller  651 , a recording media feeding roller  652   a , and a separation roller  652   b . The recording media feeding mechanism  221  separates the recording media P, which are taken out from the recording media cassette  650 , one by one and feeds the recording media P to a recording media conveying mechanism  653 . 
     A conveying path for the recording media is explained below. The recording media conveying mechanism  653  extends to a recording media discharge port  654  in an upper part through the driven roller  630  of the image forming unit  220 . The recording media discharge port  654  faces a recording media discharge section  655  that continues to an outer peripheral surface of the apparatus main body  601 . The image forming apparatus includes, on a start end side of the recording media conveying mechanism  653 , conveying rollers  656  near the recording media feeding mechanisms  221 , respectively. When any one of the recording media feeding mechanisms  221  feeds a recording medium, the recording media conveying mechanism  653  conveys the recording medium to the recording media discharge section  655 . 
     The image forming apparatus includes a secondary transfer roller  630   a  in a position along the recording media conveying mechanism  653  and opposed to the driven roller  630  across the transfer belt  12 . The image forming apparatus includes registration rollers  658  in a position before the driven roller  630  and the secondary transfer roller  630   a  in a conveying direction. 
     The registration rollers  658  deliver the recording medium P to between the transfer belt  12  and the secondary transfer roller  630   a  serving as transfer units at timing synchronizing with a transfer operation, which is an operation for transferring an image formed by a developer onto a recording medium, by the transfer belt  12  and the secondary transfer roller  630   a . The secondary transfer roller  630   a  transfers, while nipping the recording medium P delivered from the registration rollers  658  between the secondary transfer roller  630   a  and the transfer belt  12  on the driven roller  630 , a visible image formed by the developer, which is transferred onto the transfer belt  12 , onto the recording medium P and prints the visible image. In this way, the registration rollers  658  convey, in synchronization with the transfer operation of the image forming unit  220 , the recording medium P to the image forming unit  220  having the transfer belt  12  and the secondary transfer roller  630   a.    
     The image forming apparatus includes a heating and fixing device for heat fixing in a position further on a downstream side than the secondary transfer roller  630   a  of the recording media conveying mechanism  653 . The heating and fixing device includes a metal roller, a fixing roller  645 , a fixing belt laid over the metal roller and the fixing roller  645 , and a pressing roller  646  that is set in contact with the fixing roller  645  across the fixing belt. The pressing roller  646  includes a heating device such as a heater lamp in the inside thereof. 
     The heating and fixing device nips, with the fixing roller  645  and the pressing roller  646 , the recording medium P having the developer transferred thereon and heats and presses the recording medium P while conveying the same. When the recording medium P is heated and pressed, the developer is fixed on the recording medium P. The image forming apparatus includes a recording media discharge roller  661  at a terminal end of the recording media conveying mechanism  653 . 
     The image forming apparatus includes, upstream in the recording media conveying direction of the nip formed by the fixing roller  645  and the pressing roller  646  of the heating and fixing device, an inlet guide  10  that guides a sheet to the nip. 
     The image forming apparatus may include an automatic duplex unit (hereinafter referred to as ADU)  222  in the apparatus main body  601 . The ADU  222  is set to couple a sub-conveying path  662 , which is a path for conveying the recording medium P in the ADU  222 , to the terminal end of the recording media conveying mechanism  653  and an inlet to the registration rollers  658 . The sub-conveying path  662  branches from a downstream side of the recording media conveying mechanism  653  with respect to the image forming unit  220  (the terminal end of the recording media conveying mechanism  653 ) and merges into an upstream side of the recording media conveying mechanism  653  with respect to the image forming unit  220  (an upstream side position of the registration rollers  658 ). 
     The sub-conveying path  662  reverses the front and the back of the recording medium P for duplex printing. The image forming apparatus includes recording media feeding rollers  663 ,  664 , and  665  in the sub-conveying path  662 . The ADU  222  feeds backward the recording medium P conveyed to the recording media discharge section  655  by the image forming unit  220 , conveys the recording medium P through the sub-conveying path  662 , and merges the recording medium P into the recording media conveying mechanism  653  on the upstream side of the image forming unit  220 . When the recording medium P is conveyed in this way, the front and the back of the recording medium P are reversed. 
     After the recording medium P returned to the upstream side of the image forming unit  220  by the sub-conveying path  662  is merged into the recording media conveying mechanism  653 , the image forming apparatus delivers, while synchronizing with the transfer operation of the image forming unit  220  using the registration rollers  658 , the recording medium P into a transfer position where the transfer belt  12  and the secondary transfer roller  630   a  are in contact with each other. In this way, the image forming apparatus transfers a visible image on the transfer belt  12  onto the rear surface of the recording medium P as well to thereby print the visible image. 
     When the duplex printing is designated by, for example, an operation panel  724  provided in the apparatus main body  601  or a computer or the like connected to the apparatus main body  601  through a network, the sub-conveying path  662  of the ADU  222  changes to a state for performing an action for reversing the front and the back of the recording medium P. 
     Devices additionally provided in the image forming apparatus are explained below. The image forming apparatus includes a pair of the recording media cassettes  650  as feeding sources of recording media. The apparatus main body  601  may include a trio or more of recording media cassettes  650 . Besides, although not shown in the figure, a manual-feed recording media feeding mechanism (hereinafter referred to as SFB) and a large-capacity recording media feeder (hereinafter referred to as LCF), which is a recording media feeding mechanism that can store several thousands recording media in a stacked state, can also be provided. The image forming apparatus includes the SFB and the LCF in the apparatus main body  601  such that paths of the SFB and the LCF for feeing recording media merge into the recording media conveying mechanism  653 . 
     The image forming apparatus may include a recording media type sensor  223  in the apparatus main body  601 . The recording media type sensor  223  is provided in a position on the upstream side of the recording media conveying mechanism  653  with respect to the image forming unit  220  and further on the upstream side than the registration rollers  658 . The recording media type sensor  223  detects a recording media type of the recording medium P to be conveyed. As the recording media type sensor  223 , for example, a publicly-known sensor that determines a type of the recording medium P by detecting the thickness and the light transmittance of the recording medium P can be used. 
     When the SFB and the LCF are set, the recording media type sensor  223  is set further on the downstream side than a merging point of the recording media feeding paths from the SFB and the LCF and the recording media conveying mechanism  653 . By arranging the recording media type sensor  223  in this way, it is possible to detect, with a singularity of the recording media type sensor  223 , types of the recording media P conveyed on the recording media conveying mechanism  653  from all the feeding sources of recording media. 
     Inlet Guide 
       FIG. 2  is a diagram of a position of the inlet guide  10  according to this embodiment. The heating and fixing device includes the fixing roller  645  and the pressing roller  646  that is set in contact with the fixing roller  645  and has a heater lamp  646   a  in the inside thereof. 
     A fixing belt  645   a  is laid around the fixing roller  645  and a metal roller  645   b . The metal roller  645   b  has a heater lamp  645   c  in the inside thereof. 
     As indicated by an arrow X, the image forming apparatus conveys a recording medium to the heating and fixing device through between the driven roller  630  and the secondary transfer roller  630   a.    
     The image forming apparatus includes the inlet guide  10  upstream in the recording media conveying direction X of the nip formed by the fixing roller  645  and the pressing roller  646  not to come into contact with the fixing roller  645  and the pressing roller  646 . 
     In other words, the image forming apparatus includes the inlet guide  10  further downstream in the recording media conveying direction X than a nip formed by the driven roller  630  and the secondary transfer roller  630   a  and upstream in the recording media conveying direction X of the nip formed by the fixing roller  645  and the pressing roller  646 . 
     The recording medium comes into contact with the inlet guide  10  and changes a course thereof to a direction of the nip formed by the fixing roller  645  and the pressing roller  646 . Therefore, the image forming apparatus includes the inlet guide  10  on the opposite side of the direction to which the course is changed in the recording media conveying direction X. 
     The inlet guide  10  is formed of a plate of metal such as stainless steel and coated with fluorine resin. Specifically, the inlet guide  10  has, on the surface thereof, a plated layer of nickel (Ni) containing 15 volume % or more of PTFE (polytetrafluoro-ethylene). If the content of PTFE is smaller than 15 volume %, the developer adheres to the inlet guide  10  and sets because of the heat of the heating and fixing device, and it becomes difficult to clean the inlet guide  10 . 
     The thickness of the nickel plated layer is usually equal to or larger than 5 μm and equal to or smaller than 6 μm. The inlet guide  10  may be coated with PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) instead of the nickel plated layer. 
       FIG. 3  is a top view of the inlet guide  10  according to this embodiment. As shown in  FIG. 3 , the inlet guide  10  has plural ribs  11  on a surface that comes into contact with a recording medium. The inlet guide  10  has the plural ribs  11  line symmetrical to each other with respect to a center line O of the inlet guide  10 . The center line O is located in the center in the width direction of a recording medium conveyed by the image forming apparatus. Therefore, the ribs  11  prevent the recording medium from shifting in a direction perpendicular to a recording media conveying direction Y indicated by an arrow. 
     The ribs  11  are arranged such that the width between a pair of the ribs  11  in positions line symmetrical to each other with respect to the center line O is reduced toward the recording media conveying direction Y. In other words, the ribs  11  incline to an inner side in the recording media conveying direction Y toward the center line O. 
     The ribs  11  are arranged, concerning a size of each of recording medium treated by the image forming apparatus, in positions that come into contact with sides P 0  and P 1  of the recording medium in the recording media conveying direction Y. Therefore, the recording-medium does not bend to an outer side when the recording medium comes into contact with the inlet guide  10 . 
     The inlet guide  10  further has a plurality of the ribs  11  on an inner side of the ribs  11  that come into contact with the sides P 0  and P 1  in the recording media conveying direction Y. Therefore, the recording medium does not bend to an inner side when the recording medium comes into contact with the inlet guide  10 . 
     Width w 1  between each of the ribs  11  and the rib  11  closest thereto is desirably equal to or smaller than 40 mm. If the width w 1  is larger than 40 mm, the recording medium may bend. When the recording medium comes into contact with a plane portion of the inlet guide  10  because of the bend, soiling may occur on the rear surface of the recording medium. 
     A tilt angle θ of each of the ribs  11 , i.e., an acute angle formed by a center line Z in a longitudinal direction of the ribs  11  and a straight line Y 1  parallel to the recording media conveying direction Y is equal in the ribs  11  located in positions line symmetrical to each other with respect to the center line O. It is desirable that the tilt angle θ is equal in all the ribs  11 . 
       FIG. 4  is a sectional view of the inlet guide  10  along an A-A line in  FIG. 3 . As shown in  FIG. 4 , the rib  11  is formed in a streamline shape long in the recording media conveying direction Y. The rib  11  has inclined portions L 2  and L 3  at both ends in the longitudinal direction. 
     It is desirable that total length L 1  in the longitudinal direction of the rib  11  is equal to or larger than 25 mm and equal to or smaller than 35 mm, lengths L 2  and L 3  of the inclined portions are equal to or larger than 2 mm and equal to or smaller than 6 mm, and height H of the rib  11  is equal to or larger than 0.3 mm and equal to or smaller than 1.0 mm. 
       FIG. 5  is a sectional view of the inlet guide  10  along a B-B line in  FIG. 3 . As shown in  FIG. 5 , the rib  11  is formed in a semicircular shape in section. It is most desirable that sectional width D of the rib is 1 mm and a radius R of the section is 0.5 mm. 
       FIG. 6  is a table of ranges of the tilt angle θ of the ribs  11 . As shown in  FIG. 6 , gloss unevenness occurs if the tilt angle θ of the ribs  11  is smaller than 5°. If the tilt angle θ of the ribs  11  exceeds 20°, a developer adheres to the ribs  11  and sets and lib soiling occurs. Therefore, the tilt angle θ is desirably equal to or larger than 5° and equal to or smaller than 20°. 
     As explained above, the image forming apparatus according to this embodiment includes the inlet guide  10  having the ribs  11  inclining to the inner side in the recording media conveying direction. Therefore, there is an effect that gloss unevenness does not occur and rib soiling does not occur either. 
     Although exemplary embodiments of the present invention have been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications, or alterations to the invention as described herein may be made, none of which depart from the spirit of the present invention. All such changes, modifications, and alterations should therefore be seen as within the scope of the present invention.