Patent Publication Number: US-6983122-B2

Title: Image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to image forming apparatus such as copiers, facsimile machines, and printers. 
   Some image forming apparatus such as printers, copiers, and facsimile machines have the function of printing both sides of a printing medium such as paper. 
     FIGS. 10 and 11  are illustrations showing a structure of the neighborhood of paper ejection rollers of an image forming apparatus according to the related art having the double side printing function. 
   In the image forming apparatus having the double side printing function, a first paper ejection roller  150 , a second paper ejection roller  160 , and a third paper ejection roller  170  are provided at a terminal end section of a paper transport path. The first paper ejection roller  150  located in the middle can be rotated in two directions, i.e., forward and reverse directions. Each of the second paper ejection roller  160  and the third paper ejection roller  170  provided in positions opposite to each other on both sides of the paper ejection roller  150  is urged into contact with the first paper ejection roller  150  and is rotated in the forward direction relative to the first paper ejection roller  150 . 
   In such a configuration, during double side printing, paper  90  which has been printed on one side thereof is switched back by the first and second paper ejection rollers  150  and  160  and is fed according to the next printing command to be subjected to the printing process again, whereby printing is performed on the other side. 
   Paper  90  on which printing has been completed on either single side printing basis or double side printing basis is sandwiched and transported by the first and third paper ejection rollers  150  and  170  to be ejected on to an ejected paper tray  130 . 
   Since the first, second, and third paper ejection rollers  150 ,  160 , and  170  rotate in two directions, i.e., forward and reverse directions, either of the pair of the first paper ejection roller  150  and the second paper ejection roller  160  and the pair of the first paper ejection roller  150  and the paper ejection roller  170  rotates in the direction opposite to the direction of ejecting the paper  90 , i.e., the direction of feeding the paper into the apparatus, depending on their rotating directions. 
   As thus described, in the image forming apparatus having the double side printing function, since either of the pairs of paper ejection rollers rotates in the direction of feeding the paper into the apparatus from the gap between them, when someone attempts to collect paper stored in the ejected paper tray after printing, the paper can be caught between such paper ejection rollers. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the invention to provide an image forming apparatus having the double side printing function in which there is no possibility that a recording medium on which printing has been completed is caught between paper ejection rollers. 
   In order to solve the problem, an image forming apparatus according to the invention has: a first paper ejection roller which is provided at a terminal end section of a recording media transport path and which can rotate in two directions, i.e., forward and reverse directions; a second paper ejection roller which is provided such that it is urged into contact with the first paper ejection roller and which rotates in the forward direction relative to the first paper ejection roller to switch back a recording medium which has been printed on one side thereof in a double side printing mode in cooperation with the first paper ejection roller; a third paper ejection roller which is provided in a position opposite to the second paper ejection roller, with the first paper ejection roller interposed between them, such that it is urged into contact with the first paper ejection roller and which rotates in the forward direction relative to the first paper ejection roller to eject a recording medium on which printing has been completed in the double side printing mode onto an ejected paper tray in cooperation with the first paper ejection roller; and a stopper for preventing a recording medium which has been ejected onto the ejected paper tray from being caught between the first paper ejection roller and the second paper ejection roller and between the first paper ejection roller and the third paper ejection roller. 
   Since a recording medium which has been ejected is thus prevented by the stopper from coming near the gaps between the paper ejection rollers, there is no possibility that the recording medium on which printing has been completed will be caught between the paper ejection rollers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustration showing a configuration of an image forming apparatus that is an embodiment of the invention; 
       FIG. 2  is an illustration showing a paper transport system for double side printing in the image forming apparatus in  FIG. 1 ; 
       FIG. 3  is an illustration showing an operation of the apparatus and a paper transport path in the paper transport system shown in  FIG. 2  associated with printing of a top side of paper in a double side printing mode; 
       FIG. 4  is an illustration showing an operation of the apparatus and a paper transport path in the paper transport system in  FIG. 2  associated with switching back of the paper after the top side printing in the double side printing mode; 
       FIG. 5  is an illustration showing an operation of the apparatus an a paper transport path in the paper transport system in  FIG. 2  associated with printing of the opposite side (bottom side) of the paper in the double side printing mode; 
       FIG. 6  is an illustration showing rotations of the first to third paper ejection rollers and an operation of the stopper in  FIG. 3 ; 
       FIG. 7  is an illustration showing rotations of the first to third paper ejection rollers and an operation of the stopper in  FIGS. 4 and 5 ; 
       FIG. 8  is a perspective view of a stopper in a second embodiment of the invention; 
       FIG. 9  is a partial perspective showing a mounted state of stoppers in the second embodiment of the invention; 
       FIG. 10  is an illustration showing a structure of the neighborhood of paper ejection rollers in an image forming apparatus having a double side printing function according to the related art; and 
       FIG. 11  is an illustration of the structure of the neighborhood of the paper ejection rollers in the image forming apparatus having a double side printing function according to the related art, in which the paper ejection rollers are shown in states of rotation different from those in FIG.  10 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In an aspect of the invention, there is provided an image forming apparatus having: a first paper ejection roller which is provided at a terminal end section of a recording media transport path and which can rotate in two directions, i.e., forward and reverse directions; a second paper ejection roller which is provided such that it is urged in contact with the first paper ejection roller and which rotates in the forward direction relative to the first paper ejection roller to switch back a recording medium which has been printed on one side thereof in a double side printing mode in cooperation with the first paper ejection roller; a third paper ejection roller which is provided in a position opposite to the second paper ejection roller, with the first paper ejection roller interposed between them, such that it is urged into contact with the first paper ejection roller and which rotates in the forward direction relative to the first paper ejection roller to eject a recording medium on which printing has been completed in the double side printing mode onto an ejected paper tray in cooperation with the first paper ejection roller; and a stopper for preventing a recording medium which has been ejected onto the ejected paper tray from being caught between the first paper ejection roller and the second paper ejection roller and between the first paper ejection roller and the third paper ejection roller. Since a recording medium which has been ejected is thus prevented by the stopper from coming near the gaps between the paper ejection rollers, there is no possibility that the recording medium on which printing has been completed will be caught between the paper ejection rollers. 
   In another aspect of the invention, there is provided an image forming apparatus as described above, wherein the stopper is mounted on a shaft of the first paper ejection roller and wherein a section of the stopper in a direction orthogonal to the axial direction of the shaft has a V-like shape that diverges in the direction in which a recording medium is ejected. Since a recording medium which has been ejected is thus prevented by the stopper from coming near the gaps between the paper ejection rollers, there is no possibility that the recording medium on which printing has been completed will be caught between the paper ejection rollers. 
   Preferred embodiments of the invention will now be described with reference to  FIGS. 1  to  9 . Like members are indicated like reference numerals in those figures and will not be described repeatedly. 
   (First Embodiment) 
   First, an image forming apparatus according to a first embodiment of the invention will be schematically described. The image forming apparatus described in the present embodiment is an apparatus employing electrophotography and, in particular, it is a tandem type apparatus which has a developer for each of toners in four basic colors that contribute to color development of a color image and in which images in the four colors are overlapped with each other on a transfer body and are transferred to a sheet material at a time. However, the invention is not limited tandem type image forming apparatus and may obviously applied to any type of image forming apparatus regardless of the number of developers and the presence of an intermediate transfer body. 
   Referring to  FIG. 1 , provided around photosensitive drums  10   a ,  10   b ,  10   c , and  10   d  are: charging units  20   a ,  20   b ,  20   c , and  20   d  for uniformly charging surfaces of the photosensitive drums  10   a ,  10   b ,  10   c , and  10   d , respectively, at a predetermined potential; an exposure unit  30  for irradiating the charged photosensitive drums  10   a ,  10   b ,  10   c , and  10   d  with scan lines  30 K,  30 C,  30 C, and  30 Y that are laser beams associated with image data in certain colors to form electrostatic latent images on them; developing units  40   a ,  40   b ,  40   c , and  40   d  for developing the electrostatic latent images formed on the photosensitive drums  10   a ,  10   b ,  10   c , and  10   d ; transfer units  50   a ,  50   b ,  50   c , and  50   d  for transferring toner images developed on the photosensitive drums  10   a ,  10   b ,  10   c , and  10   d  onto an endless intermediate transfer belt (intermediate transfer body)  70 ; and cleaning units  60   a ,  60   b ,  60   c , and  60   d  for removing any residual toner present on the photosensitive drums  10   a ,  10   b ,  10   c , and  10   d  after the toner images are transferred from the photosensitive drums  10   a ,  10   b ,  10   c , and  10   b  to the intermediate transfer belt  70 . 
   The exposure unit  30  is provided with a predetermined inclination relative to the photosensitive drums  10   a ,  10   b ,  10   c , and  10   d . The intermediate transfer belt  70  rotates in the direction of the arrow A in the illustrated case. A black image, a cyan image, a magenta image, and a yellow image are formed at image forming stations Pa, Pb, Pc, and Pd, respectively. Single color images in respective colors formed on the photosensitive drums  10   a ,  10   b ,  10   c , and  10   d  are sequentially transferred onto the intermediate transfer body in an overlapping relationship to form a full color image on the same. 
   A paper supply cassette  100  containing sheets of paper (recording media)  90  is detachably provided in a lower part of the apparatus. The sheets of paper  90  are fed by a paper feed roller  80  one by one from the paper supply cassette  100  into a paper transport path (recording media transport path). 
   On the paper transport path, there is provided a paper transfer roller  110  which is put in contact with an outer circumferential surface of the intermediate transfer belt  70  over a predetermined distance to transfer a color image formed on the intermediate transfer belt  70  onto a sheet of paper  90  and an IH (induction heating) fixing device  120  for fixing the color image transferred to the sheet of paper  90  on the sheet of paper  90  using a pressure resulting from the sandwiching with and the rotation of the roller and using heat. 
   In the image forming apparatus having such a configuration, a latent image of image information in black component color is formed on the photosensitive drum  10   a  by the charging unit  20   a  of the image forming station Pa and the exposure unit  30 . The latent image is visualized by the developing unit  40   a  having black toner into a black toner image which is then transferred by the transfer unit  50   a  onto the intermediate transfer belt  70 . 
   A latent image in cyan component color is formed at the image forming station Pb while the back toner image is transferred onto the intermediate transfer belt  70 , and a cyan toner image is then developed by the developing unit  40   b . The cyan toner image is then transferred by the transfer unit  50   b  of the image forming station Pb onto the intermediate transfer belt  70  on which the transfer of the black toner image at the preceding image forming station Pa has been completed, the cyan toner image being then overlapped with the black toner image. 
   Thereafter, a magenta toner image and a yellow toner image are formed according to the same method. When the toner images in four colors are overlapped with each other on the intermediate transfer belt to, the toner images in four colors are transferred by the paper transfer roller  110  at a time onto a sheet of paper  90  fed by the paper feed roller  80  from the paper supply cassette  100 . The transferred toner images are heated and fixed on the paper  90  by the IH fixing device  120  to form a full color image on the paper  90 . 
   A paper transport system in such an image forming apparatus will now be described. 
   As shown in  FIG. 2 , in a paper transport path from the paper supply cassette  100  to the ejected paper tray  130 , there is provided a registration roller for timing a transfer onto a sheet of paper  90  under transportation, the paper transfer roller  110  for transferring toner images on the intermediate transfer belt  70  onto a sheet of paper  90 , and the fixing device  120  for fixing the toner images on the paper  90 . In the case of an image forming apparatus having the double side printing function, a first paper ejection roller  130 , a second paper ejection roller  150 , and a third paper ejection roller  170  are provided at a terminal section of the paper transport path. 
   The first paper ejection roller  150  located in the middle can be rotated in two directions, i.e., forward and reverse directions. Each of the second paper ejection roller  150  and the third paper ejection roller  170  provided on both sides of the first paper ejection roller  150  in positions opposite to each other is urged into contact with the first paper ejection roller  150  and is rotated in the forward direction relative to the first paper ejection roller  170 . 
   A sheet of paper  90  which has been printed on one side thereof in the double side printing mode is switched back by the first and second paper ejection rollers  150  and  160 , and a sheet of paper  90  on which printing (double side printing or single side printing) has been completed is ejected by the first paper ejection roller  150  and the third paper ejection roller  170  onto the ejected paper tray  130 . 
   A stopper  220  is attached to a shaft of the first paper ejection roller  150 , a section of the stopper in a direction orthogonal to the axial direction of the shaft of the first paper ejection roller  150  having a V-like shape that diverges in the direction in which a sheet of paper  90  is ejected. 
   The stopper  220  having such a shape prevents a sheet of paper  90  which has been ejected onto the ejected paper tray  130  from being caught between the first paper ejection roller  150  and the second paper ejection roller  160  or between the first paper ejection roller  150  and the third paper ejection roller  170 . Any shape other than the shape in the present embodiment may be employed for the stopper as long as it prevents a sheet of paper  90  ejected on the ejected paper tray  130  from being caught between the paper ejection rollers  150 ,  160 , and  170 . 
   A paper-inverting transport path  180  is formed to extend from the neighborhood of the terminal section of the paper transport path to a position before the transfer section, the transport path  180  inverting printed surfaces of a sheet of paper  90  which has been switched back. A guide member  190  is provided at a branch point between the paper transport path and the paper-inverting transport path  180  in the vicinity of the paper ejection rollers  150 ,  160 , and  170 . The guide member  190  switches the traveling path of sheets of paper  90  between first and second positions. In the first position, a sheet of paper  90  which has been printed and transported through the paper transport path to be subjected to double side printing is guided to the gap between the first paper ejection roller  150  and the second paper ejection roller  160 . In the second position, a sheet of paper  90  which has been switched back by the first paper ejection roller  150  and the second paper ejection roller  160  is guided to the paper-inverting transport path  180 . Also in the second position, a sheet of paper  90  which has been transported through the paper transport path after being printed (the paper having been printed on both sides in the double printing mode or printed on one side in the single side printing mode) is guided to the gap between the first paper ejection roller  150  and the third paper ejection roller  170 . 
   A registration roller  200  is provided on the paper-inverting path  180  to time a transfer onto a sheet of paper  90  that is transported after being inverted, and appropriate sensors  210  are provided on the paper transport path and the paper-inverting transport path  180 . 
   In such a configuration, when one side of a sheet of paper  90  is printed in the double side printing mode, the guide member  190  assumes the first position as shown in  FIG. 3  in which the first paper ejection roller  150  and the second paper ejection roller  160  rotate in the direction of sending the paper toward the ejected paper tray  130 . 
   When printing is completed on one side of the paper  90 , almost the entire area of the paper  90  is exposed toward the ejected paper tray  130 , the paper  90  still sandwiched between the first paper ejection roller  150  and the second paper ejection roller  160 . 
   Thereafter, as the guide member  190  is switched to the second position as shown in  FIG. 4 , the first paper ejection roller  150  and the second paper ejection roller  160  start rotating in the reverse direction. As a result, the paper  90  is switched back by the first paper ejection roller  150  and the second paper ejection roller  160  and is guided by the guide member  190  to the paper-inverting transport path  180 . 
   Then, the paper  90  passes through the paper-inverting transport. path  180  and is guided to the paper transport path again as shown in  FIG. 5  to be printed on the opposite side. The paper is then sandwiched and transported by the first and third paper ejection rollers  150  and  170  to be ejected on to the ejected paper tray  130 . In the single side printing mode, the guide member  190  assumes the second position in which the paper  90  is sandwiched and transported by the first and third paper ejection rollers  150  and  170  to be ejected onto the ejected paper tray  130 . 
   While the first paper ejection roller  150  and the second paper ejection roller  160  are rotating in the direction of ejecting a sheet of paper  90 , the first paper ejection roller  150  and the third paper ejection roller  170  rotate in the direction of feeding the paper  90  into the apparatus through the gap between them. Even if someone attempts to collect sheets of papers  90  accumulated in the ejected paper tray  130  at this time, no sheet of paper  90  will be caught between the first paper ejection roller  150  and the third paper ejection roller  170  because any sheet of paper  90  coming near the gap between the first paper ejection roller  90  and the third paper ejection roller  170  will be blocked by the stopper  220 , as shown in FIG.  6 . 
   While the first paper ejection roller  150  and the second paper ejection roller  160  are rotating in the direction of switching back a sheet of paper  90  or while the first paper ejection roller  150  and the third paper ejection roller  170  are rotating in the direction of ejecting the sheet of paper  90 , the first paper ejection roller  150  and the second paper ejection roller  160  rotate in the direction of feeding the sheet of paper  90  into the apparatus through the gap between them. Even if someone attempts to collect sheets of papers  90  accumulated in the ejected paper tray  130  at this time, no sheet of paper  90  will be caught between the first paper ejection roller  150  and the second paper ejection roller  160  because any sheet of paper  90  coming near the gap between the first paper ejection roller  90  and the second paper ejection roller  160  will be blocked by the stopper  220  again, as shown in FIG.  7 . 
   As thus described, in the image forming apparatus of the present embodiment, since a sheet of paper  90  which has been ejected is prevented by the stopper  220  from coming near the gap between the paper ejection rollers, there is no possibility that a sheet of paper  90  on which printing has been completed will be caught between the paper ejection rollers  150 ,  160 , and  170 . 
   (Second Embodiment) 
   A second embodiment of the invention will now be described with reference to  FIGS. 8 and 9 . The second embodiment is different from the first embodiment in the shape of a stopper  320  and, since the configurations of the embodiments are otherwise substantially identical, the description will omit elements other than the stopper. 
   A stopper  320  corresponding to the stopper  220  of the first embodiment has a catch preventing portion  301  and a rotation preventing portion  303 , and it is integrally molded from a resin. A ring portion  305  has a cutout in a part thereof. The ring portion  305  is slidably fitted to the shaft of the first paper ejection roller  150  with a small gap left therebetween. Therefore, the stopper  320  is kept in the position shown in  FIG. 9  by the weight of the stopper  320  itself when the first paper ejection roller  150  rotates in the forward or reverse direction. When a sheet of paper  90  which has been printed on both sides thereof is ejected from the gap between the paper ejection roller  150  and the paper ejection roller  170 , the paper  90  is ejected onto the ejected paper tray  130  while pushing the stopper  320 . At this time, the stopper  320  is rotated in the forward rotating direction of the paper ejection roller  150  as shown in  FIG. 5  relative to the paper ejection roller  150 . 
   Even when the stopper  320  is greatly rotated in the forward rotating direction of the paper ejection roller  150 , since the rotation preventing portion  33  abuts on a part  310  of the housing of the image forming apparatus, the stopper  320  is unable to rotate any more and is returned to the position shown in  FIG. 9  by the weight of the stepper  320  itself. 
   Further, two such stoppers  320  made of resin are provided on the shaft of the paper ejection roller  150  as shown in  FIG. 9  to accommodate various sizes of paper. 
   In the second embodiment, even when a sheet of paper  90  which has been ejected onto the ejected paper tray  130  comes near the gap between the paper ejection rollers  150  and  160  or the gap between the paper ejection rollers  150  and  170  because of wind, since the paper  90  is blocked by the stoppers  320 , it is possible to prevent the paper  90  from being caught between the paper ejection rollers  150  and  160  or between the paper ejection rollers  150  and  170 . 
   Further, since the stoppers  320  have the rotation preventing portions  303 , the rotation of the stoppers  320  is limited to always keep the stoppers  320  in the position shown in FIG.  9 . 
   According to the present invention, the rollers  150  and  160  form a paper reversible mechanism, while the rollers  150  and  170  form a paper ejection mechanism. The paper ejection roller  150  is commonly used. Alternatively, two pairs of the paper ejection rollers may be used separately as a paper reversible mechanism and a paper ejection mechanism.