Patent Publication Number: US-8109511-B2

Title: Paper discharger and image forming apparatus

Description:
CROSS REFERENCE 
     This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2009-153815 filed in Japan on Jun. 29, 2009, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a paper discharger and an image forming apparatus that are configured so as to perform paper conveying process to a first stacking tray and paper conveying process to a second stacking tray by a driving force from a single motor capable of reversible rotation in both directions. 
     In an image forming apparatus, paper is conveyed to a stacking tray by a plurality of conveyor rollers. To the plurality of conveyor rollers, driving force is supplied ordinarily by a motor as driving source via a gear train as power transmission mechanism. 
     Here, among conventional gear trains are those configured so as to be divisible in the middle. For example, for a gear train supplying driving force to the conveyor rollers that are included in a movable unit capable of attachment and detachment, it is necessary to be configured so as to be divisible with the movement of the movable unit. 
     Then, among the apparatus employing such a gear train that is divisible as stated above, as shown in Japanese Patent Unexamined Publication No. 2007-055706 bulletin, there have been those employing a structure to absorb positional deviation that is attributed to the division, by supporting a gear disposed at the division point with a swingable arm. 
     In the case where a swingable arm according to the above-mentioned Patent literature is employed, it has been often that direction of the rotation is designed in order that, when the gear supported by the swingable arm rotates together with the other gear engaged therewith, the swingable arm hardly comes apart from the gear. 
     However, in circumstances where it is required to rotate a gear supported by the swingable arm in both directions, it is unavoidable to rotate the gear supported by the swingable arm in the direction whereby the swingable arm is apt to come apart from the gear engaged therewith. Therefore, the swingable arm has occasionally been likely to shake with the rotation of the supported gear, causing malfunction such as tooth jump of the gear and emission of abnormal sound. Namely, it may be said that in a configuration, for example, so as to convey paper to a plurality of stacking trays by driving force from a single driving source, because it is necessary to change the direction of rotation of a gear train appropriately, the aforementioned malfunction is prone to occur. 
     In order to get rid of such a deficiency, it is possible to have a configuration in which separate driving forces are provided from separate driving sources for respective sides of a division point of a gear train; however, employing such a configuration would require an additional driving source, thereby resulting in a complicated configuration, and hence an increased cost. 
     The present invention is directed to providing, with a simple configuration, a paper discharger that is capable of effectively suppressing occurrence of tooth jump at a division point in a gear train, even when the gear train that is divisible is rotated reversibly in both directions, and an image forming apparatus. 
     SUMMARY OF THE INVENTION 
     A paper discharger according to the present invention is configured so as to perform paper conveying process to a first stacking tray and paper conveying process to a second stacking tray by a driving force from a single motor that is capable of reversible rotation in both directions. The paper discharger comprises, at least, a door that is supplied to a housing so as to support the second stacking tray, and a gear train. 
     The gear train is configured so as to drive a paper discharge roller that discharges paper to the second stacking tray by a driving force from a motor, and so as to be divisible on opening of the door. Further, the gear train comprises a swingable arm to support a gear that is disposed at a division point and moves together with the door. Moreover, between the gear train and the discharge roller, a one way clutch is installed that is configured so as to transmit the driving force to the discharge roller only in the direction of discharging paper to the second stacking tray. 
     In this configuration, the gear train is divided when the door is opened and closed, and in the driving configuration in which the direction of rotation via the drive transmission is reversible, the one way clutch configuration is employed in between the gear train and the discharge roller that gives rise to a rotational load at the time of reversion. As a result, when the direction of rotation via the drive transmission is reversed, the driving load attributed to the discharge roller becomes almost zero, and thus tooth jump of the gear that would have been caused by shaking of the swingable arm at the division point of the gear train is prevented from occurring. 
     By the present invention, it is enabled, with a simple configuration, to effectively suppress the occurrence of tooth jump at the division point of the gear train, even when the divisible gear train is reversibly rotated in both directions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing showing an outline configuration of an image forming apparatus according to an embodiment of the present invention. 
         FIG. 2  is a drawing showing an outline configuration of a second stacking tray. 
         FIG. 3  is a drawing showing one side of the housing of the image forming apparatus in a state when the door is opened. 
         FIG. 4  is a drawing showing a configuration of a driving system that conveys paper to a first stacking tray and the second stacking tray. 
         FIGS. 5A and 5B  are drawings showing outline configurations of a second gear train. 
         FIGS. 6A through 6D  are drawings explaining operations of the second gear train. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a drawing showing an outline of an image forming apparatus  50  according to an embodiment of the present invention. The image forming apparatus  50 , which forms a multicolor and/or monochromatic image onto a predetermined sheet of paper (recording paper) depending on the image data that have been transmitted from outside, comprises an image forming section  82  and a document reading section  58 . 
     The image forming section  82  comprises four image forming stations that form black (K), cyan (C), magenta (M), and yellow (Y) color images, respectively. Each image forming station comprises a developing device  91 , a photoreceptor drum  90 , a cleaner unit  93  and an electrifier  92 . 
     The image forming section  82  further comprises an optical scanner  88 , an intermediate transfer belt unit  95 , a fuser unit  74 , a paper cassette  71 , a first stacking tray  80 , a second stacking tray  100 , a plurality of flappers (illustration omitted) to switch direction of conveying paper, etc. 
     Above the image forming section  82  is installed a document table  54  made of a transparent glass on which a document is placed, and to the upper side of the document table  54  is attached an automated document processing unit  56 . The automated document processing unit  56  conveys a document onto the document table  54  automatically. Additionally, the automated document processing unit  56  is configured so as to swing freely, and thus allows for manual placement of a document when the upper part of the document table  54  is opened. 
     The electrifier  92  is a charging means in order to charge the surface of the photoreceptor drum  90  uniformly at a predetermined electrostatic potential, and other than a non-contact type electrifier as shown in  FIG. 1 , a contact type electrifier of such as roller, brush or otherwise may be used occasionally. 
     The optical scanner  88  is configured so as to form an electrostatic latent image on the surface of each photoreceptor drum  90  based on the inputted image data. 
     Each developing device  91  makes the electrostatic latent image formed on corresponding photoreceptor drum  90  a developed image with a four-colored toner. Additionally, the cleaner unit  93  removes and collects the toner remaining on the surface of the photoreceptor drum  90  after a transfer process. 
     The intermediate transfer belt unit  95  disposed above the photoreceptor drum  90  comprises an intermediate transfer belt  94 , an intermediate transfer belt drive roller  85 , an intermediate transfer belt compliance roller  84 , four intermediate transfer rollers  96 , and an intermediate transfer belt cleaning unit  86 . 
     The intermediate transfer belt drive roller  85 , intermediate transfer belt compliance roller  84 , and intermediate transfer roller  96  are configured so as to suspend the intermediate transfer belt  94  in a tensioned condition. In addition, each intermediate transfer roller  96  is configured so as to transcribe a toner image of the corresponding photoreceptor drum  90  onto the intermediate transfer belt  94 . 
     The intermediate transfer belt  94  is installed so as to come into contact with each photoreceptor drum  90 , and performs a function to form onto the intermediate transfer belt  94  color toner images (multicolor toner images) by transcribing the toner images of each color formed on the photoreceptor drums  90  onto the intermediate transfer belt  94  through a sequential superimposition. The intermediate transfer belt  94  is made up in an endless shape using a film, for example, of around 100 μm-150 μm in thickness. 
     When transfer of the toner image from the photoreceptor drum  90  onto the intermediate transfer belt  94  is performed, a high voltage transfer bias (a high voltage of reverse polarity (+) with respect to the electrostatic charge polarity (−) of the toner) is applied to the intermediate transfer roller  96  in order to transcribe the toner image. The intermediate transfer roller  96  is a roller based on a metal (e.g. stainless steel) shaft with a diameter of 8-10 mm and of which surface is covered by an electrically conductive elastomer (e.g. EPDM, urethane foam, etc.). With the electrically conductive elastomer, a high voltage can be applied uniformly to the intermediate transfer belt  94 . Although roller geometry is used as a transfer electrode in this embodiment, other transfer electrodes of such as brush geometry or otherwise may be used. 
     The electrostatic images that have been developed on each photoconductor drum  90  in response to each hue as aforementioned are superimposed by the intermediate transfer belt  94 . In this manner, with the rotation of the intermediate transfer belt  94 , the superimposed image information is transcribed onto paper by an undermentioned secondary transfer roller  87  disposed at the position where the paper comes into contact with the intermediate transfer belt  94 . 
     At this time, the intermediate transfer belt  94  and the secondary transfer roller  87  are pressure contacted with a predetermined nip, and a voltage for transcribing the toner onto paper is applied to the secondary transfer roller  87  (a high voltage of reverse polarity (+) with respect to the electrostatic charge polarity (−) of the toner). Further, so as to constantly obtain the above-mentioned nip, either of the secondary transfer roller  87  or the intermediate transfer belt drive roller  85  is made of a rigid material (a metal, etc.), and an elastic roller made of such as a flexible material (an elastic rubber roller or foam resin roller, etc.) is employed to the other. 
     Also, because the toner, which adhered to the intermediate transfer belt  94  when the intermediate transfer belt  94  came into contact with the photoreceptor drum  90  as mentioned above, or which remained on the intermediate transfer belt  94  when transfer therefrom had not been made onto paper by the secondary transfer roller  87 , causes color mixture of the toner in the next step, an intermediate transfer belt cleaning unit  86  is set up so as to remove and collect the toner. To the intermediate transfer belt cleaning unit  86 , a cleaning blade, for example, is mounted as a cleaning member that comes into contact with the intermediate transfer belt  94 , and the intermediate transfer belt  94  which the cleaning blade comes into contact with is supported by the intermediate transfer belt compliance roller  84  from backside. 
     A paper cassette  71  is a tray to store paper (recording sheets) to be used for image formation, and is installed in the lower side of the optical scanner  88  of the image forming section  82 . Besides, paper to be used for image formation can be placed onto a hand-fed paper cassette  78 . 
     Further, the first stacking tray  80  is installed in the upper side of the image forming section  82 , and it is configured such that sheets of paper that are finished with printing accumulate with their printed face facing downwards. On the other hand, the second stacking tray  100  is disposed outside the housing of the image forming device  50 , and it is configured such that sheets of paper that are finished with printing accumulate with their printed face facing upwards. 
     Also, in the image forming section  82 , a paper conveying path  77  of generally vertical shape is provided so as to transmit paper of the paper cassette  71  and the hand-fed paper cassette  78 , by way of the secondary transfer roller  87  and the fuser unit  74 , to the first stacking tray  80  or the second stacking tray  100 . In the vicinity of the paper conveying path  77 , which extends from the paper cassette  71  or the hand-fed paper cassette  78  to the first stacking tray  80  and the second stacking tray  100 , are disposed pickup rollers  73 ,  75 , a plurality of conveyor rollers  62 ,  64 ,  66 ,  68 , a registration roller  79 , a secondary transfer roller  87 , a fuser unit  74 , and so on. 
     The conveyor rollers  62 ,  64 ,  66 ,  68  are small rollers to facilitate and aid conveyance of paper, and a plurality of them are installed along the paper conveying path  77 . Additionally, the pickup roller  73 , which is installed in the vicinity of an edge of the paper cassette  71 , supplies paper by picking it up piece by piece from the paper cassette  71  to the paper conveying path  77 . Similarly, the pick-up roller  73 , which is installed in the vicinity of an edge of the hand-fed paper cassette  78 , also supplies paper by picking it up piece by piece from the hand-fed paper cassette  78  to the paper conveying path  77 . 
     Then, the registration roller  79 , which holds the paper temporarily while it is conveyed through the paper conveying path  77 , performs a function to convey paper to the secondary transfer roller  87  with a timing that adjusts the leading edge of toner image on the photoreceptor drum  90  to the leading edge of the paper. 
     The fuser unit  74  comprises a heating roller  72  and a pressure roller  76 , and the heating roller  72  and pressure roller  76  are configured so as to rotate holding the paper between them. Then the heating roller  72  is set by the control section to a predetermined fusing temperature, based on the signal from a temperature sensor which is not illustrated. The heating roller  72 , together with the pressure roller  76 , performs function of heat fusing on paper by means of the thermo-compression bonding of toner onto the paper, and hence through fusing, mixing and pressure-contacting transcribed multicolor toner images to the paper. Also provided is an external heating belt  70  for heating the heating roller  72  from outside. 
     Subsequently, a detailed description of the paper conveying path follows. As described above, the image forming apparatus comprises a paper cassette  71  for receiving paper in advance, and a hand-fed paper cassette  78 . To perform feed of paper from these paper cassettes  71 ,  78 , the pick-up rollers  73 ,  75  are disposed respectively so as to lead the paper piece by piece to the conveying path  77 . 
     The paper conveyed from each of paper cassettes  71 ,  78  is conveyed to the registration roller  79  by the conveyor roller  62  of the paper conveying path  77 . Then the paper is conveyed to the secondary transfer roller  87  with a timing that adjusts the front edge of the paper to the front edge of image information on the intermediate transfer belt  94 , whereby the image information is written on the paper. Subsequently, the paper, after passing through the fuser unit  74 , thereby pre-fused toner on the paper thermally fused and fixed, and then traveling via the conveyor roller  68  that is disposed downstream, is discharged to the first stacking tray  80  or the second stacking tray  100 . 
     The aforementioned conveying path is one which is provided for single sided printing on paper. In contrast, in the case of duplex printing, the paper that has been finished with a single sided printing and has passed the fuser unit  74  as described above is held at the rear edge thereof by the final conveyor roller  68 . After that, the rotation of the conveyor roller  68  is reversed and the position of the flapper (illustration omitted) is switched, whereby the paper is led to the return conveying path in which the conveyor rollers  66  and  64  are disposed. The paper, from the return conveying path via the registration roller  79 , reaches the contact position with the intermediate transfer belt  94 , where a printing is performed on its rear face. Then the paper is discharged to the first stacking tray  80 . 
       FIG. 2  shows an outline configuration of the second stacking tray  100 . As shown in the figure above, the second stacking tray  100  is installed outside a door  104  configuring part of the housing of the image forming apparatus  50 , and is disposed below a discharge port  107  formed on the door  104 . Above the second stacking tray  100  is mounted a paper sensor  102  to detect the state at which the second stacking tray  100  is loaded with full sheets of paper. A handle  106  is attached to the door  104 , and a user, by opening the door with the handle  106 , can expose outwards part of the interior of the image forming apparatus  50 . 
       FIG. 3  shows a state of one side of the housing of the image forming apparatus  50  when the door  104  is opened. The door  104  is configured so as to rotate around a shaft that is extending in vertical direction and installed at the backside of the image forming apparatus  50 . For example, when a jam occurred with the paper that had passed the fuser unit  74 , a user can remove the paper involved in the jam by opening the door  104 . In this embodiment, although a configuration is employed such that the door  104  is opened by pulling the door  104  backwards to the right, and that the door  104  is closed by returning the door  104  forward to the left, embodiment of opening and closing of the door  104  is not limited as such. 
       FIG. 4  shows a configuration of the driving system to convey paper to the first stacking tray  80  and the second stacking tray  100 . Here, in order to simplify configuration of the driving system, a configuration is employed in which conveyance of the paper which has passed the fuser unit  74  is performed solely by the driving force from a single motor  110 . 
     The motor  110  is configured so as to reversibly rotate in both directions. The motor  110 , as shown in  FIG. 4 , is connected to a first gear train  120  configured so as to drive a group of rollers which convey paper to the first stacking tray  80 . The first gear train  120  is connected to a second gear train  130  via a gear  122 . The second gear train  130  is configured so as to drive a group of rollers which convey paper to the second stacking tray  100 , and comprises five gears  132 ,  134 ,  135 ,  136  and  138 . The second gear train  130  is also configured so as to be divisible with the opening of the door  104 . Here, the second gear train  130  is configured so as to be divided between a gear  136  and gear  135  when the door  104  is opened. 
     The gear  135  is supported by a rocker arm  140 . The rocker arm  140  is configured, even when division of the second gear train  130  is caused to occur, so as to absorb misalignment of the gears  136  and  135  between which the division point occurs. 
     Subsequently, using  FIG. 5A  and  FIG. 5B , configuration of the second gear train  130  is explained further. As shown in the figures above, the conveyor roller  69  to convey paper to the first stacking tray  100  is connected to the gear  132  that is disposed most downstream in the second gear train  130 . In this embodiment, because the gear  132  is connected to the upper side conveyor roller  69 , when the gear  132  rotates counterclockwise in the figures, the conveyor roller  69  rotates in the direction of discharging paper onto the second stacking tray  100 . 
     Subsequently, movement of the second gear train  130  is explained, using  FIG. 6A  through  FIG. 6D . 
     As shown in  FIG. 6A , the opening movement of the door  104  causes the rocker arm  140  to be lifted, and engagement state with one another of the gear  135  and gear  136  to be released. Also, closing the door  104  causes the gear  135  and gear  136  again to come to the engagement state with each other, and causes the driving force from the motor  110  to be transmitted to the gear  132 . 
     Here, in this embodiment, a one way clutch  150  for transmitting a rotatory force only counterclockwise (in the direction of discharging paper onto the second stacking tray  100 ) to the conveyor roller  69  is provided between the gear  132  and the conveyor roller  69 . The reason for providing the one way clutches  150 , as will be described below, is to prevent tooth jump from occurring (see  FIG. 6D ) at the division point between the gears  135  and  136  of the second gear train  130  when paper is discharged to the first stacking tray  80 . 
       FIG. 6B  shows movement of the second gear train  130  when paper is discharged to the second stacking tray  100 . Here, because the gear  136  rotates in the direction of attracting the rocker arm  140  to the gear  136 , the rocker arm  140  will not rise with the rotation of the gear  136 , so that tooth jump will not occur between the gear  135  and gear  136 . 
       FIG. 6C  shows movement of the second gear train  130  when paper is discharged to the first stacking tray  80 . Here, the gear  136  rotates in the direction in which the rocker arm  140  is apt to come apart from the gear  136 . However, because the one way clutch  150  for transmitting the drive to only one direction (direction to discharge paper to the second stacking tray  100 ) is employed in between the gear  132  and conveyor roller  69  as a load section, driving load at the time of reversion is almost free of load. Therefore, the gear  135 , gear  134  and gear  132  rotate, accompanying the rotation of the gear  136 , in a state of nearly free of load, so that the rocker arm  140  is hardly caused to rise by the rotation of the gear  136 . As a result, tooth jump between the gear  135  and gear  136  is suppressed, and emission of abnormal sound resultant therefrom is also prevented. For instance, shown in  FIG. 6D  is an illustration in which a one way clutch  150  is not employed; in this case, the rocker arm  140  rises with the rotation of the gear  136 , thereby tooth jump occurs between the gear  135  and gear  136 , and abnormal sound occurs due to clash of these gears. 
     By employing a configuration according to an embodiment of the present invention, such a malfunction as shown in  FIG. 6D  is prevented from occurring when paper is discharged to the first stacking tray  80 . Thereby it is also capable of preventing, at the same time, occurrence of such a malfunction that causes the paper on the second stacking tray  100  being caught by the conveyor roller  69  rotating in reverse direction when the paper is discharged to the first stacking tray  80 . 
     By the foregoing configuration, while cost reduction is attempted by implementing a gear layout with a small number of motors, tooth jump at the division point of the second gear train  130  that is reversibly rotated in both directions can effectively be prevented from occurring. 
     The above explanation of the embodiment is nothing more than illustrative in any respect, nor should be thought of as restrictive. Scope of the present invention is indicated by claims rather than the above embodiments. Further, it is intended that all changes that are equivalent to a claim in the sense and realm of the doctrine of equivalence be included within the scope of the present invention.