Patent Publication Number: US-9904201-B2

Title: Image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. 119 from Japanese Patent Application No. 2016-009490 filed on Jan. 21, 2016. 
     TECHNICAL FIELD 
     The present invention relates to an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, an image forming apparatus is provided. The image forming apparatus includes a toner image carrier on which a toner image is formed to hold the toner image, a transfer unit that transfers, onto a continuous sheet of paper, the toner image on the toner image carrier, a fixing machine that fixes, on the continuous sheet of paper, the toner image transferred onto the continuous sheet of paper, a sheet transport unit that transports the continuous sheet of paper through a transport path passing through a transfer position at which the transfer unit transfers a toner image onto the continuous sheet of paper and a fixing position at which the fixing machine fixes, on the continuous sheet of paper, the toner image on the continuous sheet of paper, and an electric charge supply unit that is disposed upstream of the transfer position in a transport direction of the continuous sheet of paper by the sheet transport unit and at a position at which the continuous sheet of paper is placed between the toner image carrier and the electric charge supply unit, and that supplies electric charge having an orientation, in which transfer by the transfer unit is prevented, to a toner image present in a region on the toner image carrier, which is out of the continuous sheet of paper in a width direction intersecting with the transport direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic diagram illustrating a configuration of an image forming apparatus as an exemplary embodiment of the invention; 
         FIG. 2  is a schematic diagram illustrating a shape of a pin corotron and a positional relationship between an intermediate transfer belt and continuous sheet of paper; 
         FIG. 3  is a schematic diagram illustrating the shape of the pin corotron and another positional relationship between the intermediate transfer belt and the continuous sheet of paper; and 
         FIG. 4  is a graph illustrating a relationship between a current (horizontal axis) flowing in the pin corotron and a sheet smudge grade (vertical axis). 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an exemplary embodiment of the present invention will be described with reference to the drawings. 
       FIG. 1  is a schematic diagram illustrating a configuration of an image forming apparatus  1  according to an exemplary embodiment of the present invention. 
     The image forming apparatus  1  includes a sheet supply unit  10 , an image forming unit  20 , and a sheet winding unit  30 . 
     Continuous sheet of paper P wound into a roll shape is mounted on the sheet supply unit  10 , and the continuous sheet of paper P is unwound and is continuously supplied to the image forming unit  20 . An image is formed on the continuous sheet of paper P supplied to the image forming unit  20  through processes to be described below. The continuous sheet of paper P on which the image is formed by the image forming unit  20  is wound around the sheet winding unit  30  into a roll shape. 
     Six photoconductors  21  are arranged in an upper portion of the image forming unit  20 . A charging unit, an exposure device, a developing device, or the like (not illustrated) is disposed around each of the six photoconductors  21 . The photoconductors  21  have a drum shape and a different color toner image is formed on a circumferential surface of each photoconductor  21 , while the photoconductors  21  rotate in a direction of arrow A. 
     An endless intermediate transfer belt  23  is provided below the photoconductors  21  so as to be disposed along the photoconductors  21 . The intermediate transfer belt  23  is wound over a driving roll  24 , a tension roll  25 , and a backing roll  26 , is driven by the drive roll  24 , and circularly moves in a direction of arrow B. 
     The respective toner images formed on the respective photoconductors  21  are transferred onto the intermediate transfer belt  23  by operations of the respective primary transfer rolls  22 . 
     The photoconductors  21  and the intermediate transfer belt  23  are examples of a primary holding member and a secondary holding member, respectively. The photoconductors  21 , the intermediate transfer belt  23 , and a primary transfer roll  22  form an example of a toner image carrier. 
     A secondary transfer unit  27  is provided at a position at which the intermediate transfer belt  23  and the continuous sheet of paper P are interposed between the backing roll  26  and the secondary transfer unit  27 . The secondary transfer unit  27  is an example of a transfer unit. 
     The secondary transfer unit  27  has a structure in which an endless transfer belt  271  is wound over two rolls  272  and  273 , and circularly moves in a direction of arrow C. The toner image on the intermediate transfer belt  23  is transferred onto the continuous sheet of paper P at a transfer position at which the continuous sheet of paper P is in contact with the transfer belt  271  by an operation of the secondary transfer unit  27 . 
     Toner remaining on the intermediate transfer belt  23  after the transfer is removed from the intermediate transfer belt  23  by a cleaner  28 . 
     The toner image transferred onto the continuous sheet of paper P is further transferred in a direction of arrow X, and is fixed on the continuous sheet of paper P by being heated and pressurized while passing through a fixing position interposed between a heater  291  and a pressure device  292  that configure a fixing machine  29 . The continuous sheet of paper P, on which an image is formed by the fixing, is wound around the sheet winding unit  30  into a roll shape. 
     The intermediate transfer belt  23  of the image forming unit  20  has a width wider than the continuous sheet of paper P, and a test pattern  532  (see  FIGS. 2 and 3 ) for adjusting image density or an image forming position is formed with toner in a non-image region  531  (see  FIGS. 2 and 3 ) of the intermediate transfer belt  23 , which is out of the continuous sheet of paper P in the width direction. Then, the test pattern  532  on the intermediate transfer belt  23  is read by a sensor  41  and adjustment of the image density or adjustment of the image forming position is performed according to the reading result. 
     Since the non-image region  531  is a region out of the continuous sheet of paper P, the test pattern formed in the non-image region  531  is aggressively transferred onto the transfer belt  271  by the operation of the secondary transfer unit  27  when there is no method of coping with the transfer. A cleaning brush  274  that removes toner or the like attached on the transfer belt  271  is provided in the secondary transfer unit  27 , and it is possible to remove a small amount of attached toner. However, the cleaning brush is not capable of rapidly removing a large amount of toner attached when the test pattern  532  is aggressively transferred. When the toner on the transfer belt  271  is not rapidly removed, there is a concern that the toner, which is not completely removed, will spread from the non-image region around an image region overlapping the continuous sheet of paper P, and a back surface of the continuous sheet of paper P will be smudged when the transfer belt  271  completes a 360-degree round. Thus, in the exemplary embodiment, the transfer of the test pattern formed in the non-image region to the transfer belt  271  is reduced by the following configuration and thereby smudge on the continuous sheet of paper P is prevented. 
     The image forming unit  20  includes a corotron  51  that eliminates charge from or charges the toner on the intermediate transfer member in a non-contacting manner. The pin corotron  51  is disposed upstream of the transfer position by the secondary transfer unit  27  in a transport direction X of the continuous sheet of paper P and at a position at which the continuous sheet of paper P is placed between the intermediate transfer belt  23  and the pin corotron. The pin corotron  51  has a shape in which plural pin-shaped electrodes  511  (see  FIGS. 2 and 3 ) are arranged in the width direction of the intermediate transfer belt  23 . The electrodes  511  may be arranged to a region overlapping the continuous sheet of paper P. The corotron  51  is an example of an electric charge supply unit. 
     A voltage from a power supply  52  is applied to the pin corotron  51 . A ground roll  53 , contacting an inner surface of the intermediate transfer belt  23 , is disposed such that the continuous sheet of paper P and the intermediate transfer belt  23  are interposed between the ground roll  53  and the pin corotron  51 . The ground roll  53  is electrically grounded. 
     The voltage from the power supply  52  is applied to the pin corotron  51  such that an electric charge having a polarity in an orientation, in which the secondary transfer unit  57  is prevented from performing the transfer to the transfer belt  571 , is supplied to the test pattern formed in the region of the intermediate transfer belt  23 , which is horizontally out of the continuous sheet of paper P, that is, the non-image region of the intermediate transfer belt, which is out of an image region on the continuous sheet of paper P, on which an image is formed. The continuous sheet of paper P plays a role of a shield from the supply of the electric charge in the image region overlapping the continuous sheet of paper P, and the toner image, which is formed in the image region, is not influenced by the electric charge. Hence, the toner image, which is formed in the image region and is scheduled to be transferred to the continuous sheet of paper P, is transferred onto the continuous sheet of paper P when the continuous sheet of paper P passes through a transfer region in which the intermediate transfer belt  23  and the transfer belt  271  are interposed therein. On the other hand, the test pattern formed in the non-image region on the intermediate transfer belt  23 , which is out of the continuous sheet of paper P, is not transferred, but passes through the transfer position. The test pattern, which is not transferred but remains on the intermediate transfer belt  23 , is removed from the intermediate transfer belt  23  by the cleaner  28  that removes the remaining toner on the intermediate transfer belt  23 . The intermediate transfer belt  23  is made of a hard resin, thus, a blade-shaped cleaner  28  is provided, and the toner on the intermediate transfer belt  23  is removed by a strong force. The transfer belt  271  is made of rubber so as not to excessively press the toner image interposed between the hard intermediate transfer belt  23  and the transfer belt. Therefore, it is not possible to use a cleaner, such as a blade, which is capable of performing strong removal and thus, in the exemplary embodiment, the cleaning brush  274  is used. 
     A sheet regulating roll  61  is disposed upstream of the pin corotron  51  in the transport direction X described above, and a sheet regulating roll  62  is disposed on the downstream side of the transfer position. The position of the continuous sheet of paper P is regulated by the sheet regulating rolls  61  and  62  during the transport. In addition, an approach angle of the continuous sheet of paper P to the transfer position is stabilized particularly by the sheet regulating roll  61  on the upstream side. Thus, an effect of the continuous sheet of paper P as the shield from the electric charge that is supplied from the pin corotron  51  is stabilized. The sheet regulating roll  61  on the upstream side is an example of a position regulating member. 
       FIG. 2  is a schematic diagram illustrating a shape of the pin corotron and a positional relationship between the intermediate transfer belt and the continuous sheet of paper. 
     The intermediate transfer belt  23  approaches in the direction of arrow B, and the continuous sheet of paper P approaches, in the direction of arrow X as the same direction of the arrow B at the transfer position, the central region of the intermediate transfer belt  23  in the width direction. In  FIG. 2 , continuous sheet of paper P 1  having the minimum width of the continuous sheet of paper P, which can be used in the image forming apparatus  1 , is illustrated. Various test patterns  532  are formed in the right and left non-image regions  531  on the intermediate transfer belt  23 , which do not overlap the continuous sheet of paper P 1 . 
     A plurality of pin-shaped electrodes  511  are arranged in the pin corotron  51  in the width direction in the entire region in the width direction of the intermediate transfer belt  23  except for the region overlapping the continuous sheet of paper P 1  having the minimum width. The electric charge from the pin corotron  51  is supplied to the test pattern  532  formed in the non-image region  531  of the intermediate transfer belt  23 , which is out of the continuous sheet of paper P, and thus, the test pattern  532  is prevented from being transferred to the transfer belt  271  (see  FIG. 1 ). 
       FIG. 3  is a schematic diagram illustrating the shape of the pin corotron and another positional relationship between the intermediate transfer belt and the continuous sheet of paper, similar to  FIG. 2 . 
     In  FIG. 3 , continuous sheet of paper P 2  having the maximum width of the continuous sheet of paper P, which can be used in the image forming apparatus  1 , is illustrated. Meanwhile, a pin corotron  51  is the same pin corotron as the pin corotron  51  illustrated in  FIG. 2 . 
     Also in  FIG. 3 , similar to  FIG. 2 , various test patterns  532  are formed in the right and left non-image regions  531  on the intermediate transfer belt  23 , which do not overlap the continuous sheet of paper P 2 . The electric charge is applied to the test pattern  532  by the pin corotron  51 . The pin-shaped electrodes  511  are arranged on the pin corotron  51  to a region overlapping the continuous sheet of paper P 2 ; however, the continuous sheet of paper P 2  plays the role of the shield from the electric charge, and the electric charge is not supplied to the toner image that is formed in the image region on the intermediate transfer belt  23 , which is overlapping the continuous sheet of paper P 2 . Hence, the toner image, which is formed in the image region, is normally transferred onto the continuous sheet of paper P 2 . 
       FIG. 4  is a graph illustrating a relationship between a current (horizontal axis) flowing in the pin corotron and a sheet smudge grade (vertical axis). In the sheet smudge grade on the vertical axis, as a position is higher, a level of smudge is increased. In addition, a threshold value is set at a boundary of whether or not it is possible to visually recognize the smudge. 
     A hole is punched on an end portion of the continuous sheet of paper P in the with direction, a toner image having 50% of an area ratio is formed in a region on the intermediate transfer belt  23 , which corresponds to the hole, a voltage, which is applied to the pin corotron  51 , is changed such that a current flowing to the pin corotron  51  is measured, and toner smudge on a back surface of the continuous sheet of paper P at a position after a 360-degree round of the transfer belt  271  from the hole is checked. The operations described above are repeated. 
     In  FIG. 4 , when the current value is 0.4 (μA/cm) or higher, it is found that this is a level at which it is not possible to visually recognize the smudge on the back surface of the continuous sheet of paper P. In other words, the pin corotron  51  used in the exemplary embodiment is used, and thereby it is found that it is possible to effectively prevent the smudge on the back surface of the continuous sheet of paper P. 
     While the pin corotron  51 , in which the electrodes  511  are arranged in the region except for the region which is overlapping the continuous sheet of paper P 1  (see  FIG. 2 ) having the minimum width, is used in the exemplary embodiment described above, since the continuous sheet of paper P plays the role of the shield from the electric charge, the electrodes  511  may be arranged, for example, over the entire width of the intermediate transfer belt  23 , regardless of the width of the continuous sheet of paper P. 
     In addition, although a so-called pin corotron is used in the exemplary embodiment described above, an electric charge supply unit other than the pin corotron may be used, and the continuous sheet of paper P may play a role of a shield from the electric charge. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.