Patent Document

CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to Japanese Patent Application No. 2009-272531, filed Nov. 30, 2010, the entire subject matter and disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    1. Field of the Disclosure 
         [0003]    The features described herein relate generally to ink jet recording apparatuses that convey recording media by attracting them to a conveying device. 
         [0004]    2. Description of Related Art 
         [0005]    An ink jet recording apparatus which conveys recording media to a recording head by attracting them to a conveying belt is known. The ink jet recording apparatus attracts a recording medium to a conveying surface using electrodes disposed in the conveying belt. 
         [0006]    The above-described ink jet recording apparatus includes a member that comes into contact with a conveying belt, such as a sheet-pressing member. It may cause ink adhered to the conveying belt to spread in the moving direction of the conveying belt. Therefore, the spread ink may cause a short-circuit between the electrodes. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    According to one embodiment herein, an ink jet recording apparatus may include a conveying device configured to move a conveying belt to convey a recording medium, the conveying belt including a conveying surface on which the recording medium is placed. The ink jet recording apparatus may include a recording head configured to discharge ink onto the recording medium conveyed by the conveying device. The ink jet recording apparatus may include an attraction device including first and second electrodes facing a surface opposite the conveying surface and configured to apply a voltage between the first and second electrodes to attract the recording medium to the conveying surface. The ink jet recording apparatus may include a contact member which comes into contact with the conveying surface. The first and second electrodes may be disposed at a distance from each other in the width direction of the conveying belt perpendicular to the conveying direction of the recording medium. A contacting area of the conveying surface with which the contact member comes into contact may not extend over the first and second electrodes in the width direction. 
         [0008]    According to another embodiment herein, an ink jet recording apparatus may include a conveying device configured to move a conveying belt to convey a recording medium, the conveying belt including a conveying surface on which the recording medium is placed. The ink jet recording apparatus may include a recording head configured to discharge ink onto the recording medium conveyed by the conveying device. The ink jet recording apparatus may include an attraction device including first and second electrodes provided inside the conveying belt and configured to apply a voltage between the first and second electrodes to attract the recording medium to the conveying surface, the first and second electrodes sandwiching part of the conveying belt between the recording medium on the conveying surface and the first and second electrodes. The ink jet recording apparatus may include a contact member which comes into contact with the conveying surface. The first and second electrodes may be disposed at a distance from each other in the width direction of the conveying belt perpendicular to the conveying direction of the recording medium. A contacting area of the conveying surface with which the contact member comes into contact may not extend over the first and second electrodes in the width direction. 
         [0009]    Other objects, features and advantages will be apparent to persons of ordinary skill in the art from the following description with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic view schematically showing the internal configuration of an ink jet printer according to one embodiment. 
           [0011]      FIG. 2  is a plan view of a conveying mechanism and the vicinity thereof in  FIG. 1 , in which a part of the conveying belt is cut out to show an attraction platen therebeneath. 
           [0012]      FIG. 3  is an enlarged view of a charging roller and the vicinity thereof in  FIG. 1 . 
           [0013]      FIG. 4A  is a cross-sectional view taken along line IV-IV in  FIG. 2 , and  FIG. 4B  is a cross-sectional view showing another embodiment different from  FIG. 4A . 
           [0014]      FIG. 5A  shows an electric circuit formed between a recording medium, an attraction platen, and a conveying mechanism according to this embodiment, and  FIG. 5B  shows an electric circuit at the time when a partial short-circuit occurs in the electric circuit formed in this embodiment. 
           [0015]      FIG. 6A  is a plan view of a conveying belt according to another embodiment, and  FIG. 6B  is a cross-sectional view taken along line B-B in  FIG. 6A . 
           [0016]      FIG. 7  is a front view of a conveying mechanism according to another embodiment. 
           [0017]      FIG. 8  is a front view of a conveying mechanism according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Various embodiments, and their features and advantages, may be understood be referring to  FIGS. 1-8 , like numerals being used for corresponding parts in the various drawings. 
         [0019]    Referring to  FIG. 1 , an ink jet printer  1  according to an embodiment may include a rectangular-parallelepiped-shaped housing  1   a  having a sheet-output portion  15  on top thereof. The inside of the housing  1   a  may be divided into two, namely, from the top, a space S 1  and a space S 2 . The space S 1  may accommodate, from the top, a plurality of, e.g., four, ink jet heads  2  that discharge magenta ink, cyan ink, yellow ink, and black ink, and a conveying mechanism  50  that conveys a sheet P in a conveying direction A. The space S 2  may accommodate a sheet-feed unit  10 . Furthermore, the ink jet printer  1  may include a control unit  100  that controls the operations of these components. In this embodiment, the direction parallel to the conveying direction A, in which the sheet P is conveyed by the conveying mechanism  50 , is defined as the sub-scanning direction, and the direction perpendicular to the sub-scanning direction and along the horizontal surface is defined as the main scanning direction. 
         [0020]    A sheet conveying path may be formed in the ink jet printer  1 , along which the sheet P is conveyed from the sheet-feed unit  10  to the sheet-output portion  15 , as indicated by thick arrows in  FIG. 1 . The sheet-feed unit  10  may include a sheet-feed cassette  11  that can accommodate a stack of sheets P, a sheet-feed roller  12  that feeds the sheets P from the sheet-feed cassette  11 , and a sheet-feed motor (not shown) that rotates the sheet-feed roller  12  under the control of the control unit  100 . 
         [0021]    The sheet-feed roller  12  may feed the sheet P on the top of the stack of sheets P stored in the sheet-feed cassette  11 . A conveyance guide  17  that extends upward in a curved manner from the sheet-feed cassette  11  may be provided on the left side of the conveying mechanism  50  in  FIG. 1 . 
         [0022]    In this configuration, by rotating the sheet-feed roller  12  clockwise in  FIG. 1  under the control of the control unit  100 , the sheet P in contact with the sheet-feed roller  12  may be fed to the conveying mechanism  50  through the conveyance guide  17 . 
         [0023]    Referring to  FIGS. 1 and 2 , the conveying mechanism  50  may be disposed at a position facing the plurality of, e.g., four, ink jet heads  2 . The conveying mechanism  50  may include a plurality of, e.g., two, belt rollers  51  and  52 , an endless conveying belt  53  stretched between and wound around the rollers  51  and  52 , a conveying motor (not shown) that rotates the belt roller  52  under the control of the control unit  100 , and an attraction platen  60  facing the plurality of, e.g., four, ink jet heads  2 . The plurality of, e.g., two, belt rollers  51  and  52  may be disposed in the conveying direction A and may be supported by the housing  1   a  so as to be rotatable. The upper surface of the attraction platen  60  may be disposed at substantially the same height as the upper ends of the belt rollers  51  and  52 , and the conveying belt  53  may be stretched between the belt rollers  51  and  52  horizontally. 
         [0024]    The conveying belt  53  may be flexible. The conveying belt  53  may include, for example, polyimide or fluoroplastic, and may have a volume resistivity of about 108 to 1014 Ωcm (for example, about 1012 Ωcm). The conveying belt  53  may be made of any material as long as it provides the above-described volume resistivity and flexibility. 
         [0025]    Referring to  FIGS. 2 and 4 , the attraction platen  60  may include a plate-like base member  61  composed of an insulating material, and electrodes  62  and  63  attached to an upper surface  61   a  thereof. The electrodes  62  and  63  may include a plurality of interdigital portions  62   a  and  63   a  extending in the conveying direction A. The interdigital portions  62   a  and  63   a  may be arranged alternately in the main scanning direction in an interdigital shape. The area provided with the electrodes  62  and  63  may have substantially the same width as the sheet P in the main scanning direction and may be larger than the area provided with the ink jet heads  2  in the sub-scanning direction. The upper surfaces of the electrodes  62  and  63  may be formed horizontally and may be disposed at the same height. The electrode  62  may be connected to a power source  69  provided in the housing  1   a , and the electrode  63  may be connected to the ground. The power source  69  may be controlled by the control unit  100 . The electrodes  62  and  63  may include a material having high electrical conductivity, such as metal. A protection layer including a resin material or the like may be formed on the upper surfaces of the electrodes  62  and  63 . 
         [0026]    A charging roller  70  may be disposed at the upstream end of the attraction platen  60 , at a position facing the belt roller  51 . The charging roller  70  may be urged downward and may be pressed against an outer circumferential surface  54  of the conveying belt  53 . The charging roller  70  may generally have a cylindrical shape whose axial direction is aligned with the main scanning direction. The charging roller  70  may extend substantially from one end to the other end of the conveying belt  53  in the main scanning direction. Referring to  FIGS. 4A and 4B , the charging roller  70  may include a rotation shaft  71  and a roller body  72  fixed to the outer circumference thereof. The rotation shaft  71  and the roller body  72  may include metal having high electrical conductivity or a semiconductive material having a certain electrical conductivity. The rotation shaft  71  may be connected to a power source  79 , and the power source  79  may be controlled by the control unit  100 . On the other hand, a rotation shaft  51   a  of the belt roller  51  may be connected to the ground. Both the belt roller  51  and the rotation shaft  51   a  may include a material having high electrical conductivity, and, the belt roller  51  may have a ground potential by connecting the rotation shaft  51   a  to the ground. 
         [0027]    In this configuration, the conveying belt  53  may be rotated by rotating the belt roller  52  clockwise in  FIG. 1  under the control of the control unit  100 . On the other hand, the sheet P fed from the sheet-feed unit  10  may be attracted to the outer circumferential surface  54  of the conveying belt  53  by the charging roller  70 , the belt roller  51 , and the attraction platen  60 , as follows. First, the sheet P may be nipped between the outer circumferential surface  54  of the conveying belt  53  and the charging roller  70 . Because the charging roller  70  is urged downward, the sheet P may be pressed against the outer circumferential surface  54 . At this time, if a predetermined level of voltage is supplied to the rotation shaft  71  of the charging roller  70 , electric discharge from the charging roller  70  to the sheet P may occur, causing the sheet P to be positively charged. On the other hand, negative charges may be supplied to the conveying belt  53  through the belt roller  51  connected to the ground, negatively charging the conveying belt  53 . Thus, the positively charged sheet P may be electrostatically attracted to the negatively charged outer circumferential surface  54  of the conveying belt  53 . 
         [0028]    The sheet P attracted to the outer circumferential surface  54  by the electric discharge from the charging roller  70  may be conveyed above the attraction platen  60  along with the movement of the conveying belt  53 . At the attraction platen  60 , a positive potential may be applied to the electrode  62  and a ground potential may be applied to the electrode  63  under the control of the control unit  100 . Any configuration may be employed as long as it generates any potential difference between the electrodes  62  and  63 . For example, a negative potential may be applied to the electrode  62 , or, a ground potential may be applied to the electrode  62  while applying another potential to the electrode  63 . 
         [0029]    When a voltage is applied between the electrodes  62  and  63 , a current may flow between the electrodes  62  and  63  through the conveying belt  53  and the sheet P.  FIG. 5A  shows an electric circuit at the time when a voltage V is applied between the electrodes  62  and  63 . The electric circuit shown in  FIG. 5A  is one example that can be considered when this embodiment is idealized as an electrical configuration. 
         [0030]    This electric circuit may include a main path from the electrode  62 , to the conveying belt  53 , to the sheet P, to the conveying belt  53 , to the electrode  63 . In  FIG. 5A , reference signs Rk, Rgb, Rb, Rgp, and Rp represent the electric resistances of respective parts in the main path. More specifically, Rk corresponds to the electric resistance of the protection layer formed on the upper surfaces of the electrodes  62  and  63 . Rgb corresponds to the electric resistance of the gap between the protection layer and the conveying belt  53 . Rb corresponds to the electric resistance of the conveying belt  53 . Rgp corresponds to the electric resistance of the gap between the conveying belt  53  and the sheet P. Rp corresponds to the electric resistance of the sheet P. 
         [0031]    This electric circuit may include bypass paths connected in parallel to the main path, and reference signs Rkm and Rbm indicate the electric resistances of these bypass paths. More specifically, Rkm indicates the electric resistance of the bypass path connecting the electrodes  62  and  63  via the protection layer. Rbm indicates the electric resistance of the bypass path connecting the electrodes  62  and  63  via the conveying belt  53  but not via the sheet P. 
         [0032]    Referring to  FIG. 5A , capacitors connected in parallel to the electric resistances may be formed in the electric circuit. When a voltage is applied between the electrodes  62  and  63 , a minute current may flow through the gap between the sheet P and the conveying belt  53 , generating a potential difference in this gap. As a result, an attraction force due to Johnsen-Rahbeck force may be generated between the sheet P and the conveying belt  53 . By this attraction force, the sheet P on the conveying belt  53  may be electrostatically attracted to the outer circumferential surface  54 . 
         [0033]    The reason why the conveying belt  53  includes a material having certain high volume resistivity, as described above, is as follows. If the electric resistance of the conveying belt  53  is small, the electric resistance Rbm of the bypass path connecting the electrodes  62  and  63  via the conveying belt  53  is small, making it easy for the current to flow through the bypass path but difficult to flow through the sheet P. On the other hand, if the electric resistance of the conveying belt  53  is too large, it is difficult for the current to flow from the conveying belt  53  to the sheet P. Accordingly, the attraction force due to Johnsen-Rahbeck force is small if the electric resistance of the conveying belt  53  is too small or too large. 
         [0034]    The sheet P fed from the sheet-feed unit  10  may be conveyed in the conveying direction A while being attracted to the outer circumferential surface  54  by the attraction force of the charging roller  70  and attraction platen  60 . Furthermore, at this time, when the sheet P conveyed while being attracted to the outer circumferential surface  54  of the conveying belt  53  passes immediately below the plurality of, e.g., four, ink jet heads  2  (i.e., an area facing a discharge surface  2   a ), the ink jet heads  2  may discharge ink of different colors onto the sheet P, under the control of the control unit  100 . Thus, a desired color image may be formed on the sheet P. 
         [0035]    When a printing sheet having a size different from the specified size is used, or when a paper jam occurs, ink discharged from the ink jet heads  2  may be adhered to the outer circumferential surface  54  of the conveying belt  53 . If the portion of the outer circumferential surface  54  of the conveying belt  53  where the ink is adhered is conveyed to a position facing the attraction platen  60 , and, if that portion extends over the interdigital portions  62   a  and  63   a , as an area X in the  FIG. 2 , the electrodes  62  and  63  may be short-circuited. That is, if the ink adhered to the conveying belt  53  spreads over the interdigital portions  62   a  and  63   a , a bypass path indicated by the resistance Ri, which short-circuits the main path, may be formed because of a current passing through the adhered ink, not the sheet P (resistance Rp), as indicated by a resistance Ri in  FIG. 5B . If such a bypass path is formed, the current may mainly flow through the resistance Rp and may be less likely to flow through the resistance Ri because the resistance Ri of the ink is smaller than the resistance Rp of the sheet P. Thus, the attraction force for attracting the sheet P to the conveying belt  53  may decrease. 
         [0036]    Referring to  FIGS. 2 and 4A , the roller body  72  of the charging roller  70  may be divided into several segments in the main scanning direction. That is, the roller body  72  may include a plurality of roller segments  72   a  arranged at intervals. Each roller segment  72   a  may have a cylindrical shape whose axial direction is aligned with the main scanning direction, and the rotation shaft  71  may be fixed to the center of the cylinder. The roller segments  72   a  may be disposed such that the areas of the outer circumferential surface  54  of the conveying belt  53  with which the roller segments  72   a  can be brought into contact do not extend over the interdigital portions  62   a  and  63   a  in the main scanning direction. The areas of the outer circumferential surface  54  of the conveying belt  53  with which the roller segments  72   a  can be brought into contact may be the entire areas defined by an area Y in  FIG. 2 , corresponding to the width of the roller segment  72   a  in the main scanning direction, extended along the conveying belt  53 . That is, the roller body  72  may be disposed such that the above-described areas do not extend over the interdigital portions  62   a  and  63   a.    
         [0037]    It is also possible that, as shown in a charging roller  170  in  FIG. 4B , a roller body  172  is composed of a plurality of thin disc-like rollers such that they do not extend over the interdigital portions  62   a  and  63   a  in the main scanning direction. 
         [0038]    The charging roller  70  is urged against the outer circumferential surface  54  of the conveying belt  53 . Therefore, if ink is adhered to the outer circumferential surface  54 , the ink adhered to the outer circumferential surface  54  may be spread by the charging roller  70  when the conveying belt  53  is conveyed. To counter this, the embodiment described above is configured such that the areas with which the roller segments  72   a  can be brought into contact do not extend over the interdigital portions  62   a  and  63   a  in the main scanning direction. Thus, even if the charging roller  70  spreads ink on the outer circumferential surface  54 , the spread ink may tend to stay within the area corresponding to the width of each roller segment  72   a  (i.e., the area Y in  FIG. 2 ). Referring to  FIG. 4A , these areas may extend over one of the interdigital portions  62   a  and  63   a , but may not over the other of them. Accordingly, the spread ink may be less likely to cause a short-circuit between the electrodes  62  and  63 , whereby a problem of a decrease in the attraction force for attracting the sheet P to the conveying belt  53  may be less likely to occur. The same holds in the case where the charging roller  170  in  FIG. 4B  may be employed. 
         [0039]    Referring to  FIG. 6 , another embodiment will be described. Although the attraction platen  60  may be provided as an attraction mechanism in the embodiment described above, the attraction mechanism is provided on the conveying belt side in this embodiment. More specifically, although a conveying belt  253  according to this embodiment may be an endless belt stretched between and wound around the rollers  51  and  52 , similarly to the conveying belt  53  according to the embodiment described above, the electrodes  62  and  63  may be provided inside the conveying belt  253 . Referring to  FIG. 6B , the electrodes  62  and  63  may be disposed such that a portion of the conveying belt  253  (i.e., a portion denoted by Z in  FIG. 6B ) is sandwiched between the electrodes  62  and  63  and the sheet P disposed on an outer circumferential surface  254  of the conveying belt  253 . 
         [0040]    The outer circumferential surface  254  of the conveying belt  253  may have a plurality of recesses  253   a  and  253   b . The recesses  253   a  may be arranged along the interdigital portion  63   a  disposed on the extreme left side in  FIG. 6A . The recesses  253   b  may be arranged along the interdigital portion  62   a  disposed on the extreme right side in  FIG. 6A . The interdigital portion  63   a  may be exposed from the recesses  253   a . The interdigital portion  62   a  may be exposed from the recesses  253   b . This configuration may enable a voltage to be applied between the electrodes  62  and  63  by providing brush electrodes that come into contact with the interdigital portions  62   a  and  63   a  through the recesses  253   a  and  253   b  from above the conveying belt  253 . 
         [0041]    In this embodiment too, the roller body  72  of the charging roller  70  may be disposed such that it does not extend over the interdigital portions  62   a  and  63   a  in the main scanning direction. Therefore, even if the charging roller  70  spreads ink on the outer circumferential surface  254 , the spread ink may be less likely to be spread over the interdigital portions  62   a  and  63   a . Accordingly, ink on the outer circumferential surface  254  may be less likely to cause a short-circuit between the electrodes  62  and  63 , making a problem of a decrease in the attraction force for attracting the sheet P to the conveying belt  253  less likely to occur. 
         [0042]    Referring to  FIG. 7 , another embodiment will be described. A conveying mechanism  350  according to this embodiment may include the belt rollers  51  and  52 , an endless conveying belt  353  stretched between the belt rollers  51  and  52 , and the attraction platen  60 . The upper surface of the attraction platen  60  may be disposed above the upper ends of the belt rollers  51  and  52 , whereby the conveying belt  353  runs along a path projecting upward from the belt roller  51  and  52 . The conveying belt  353  may be subjected to a greater tension by the attraction platen  60  compared with the case of the embodiment described above. This tension may be particularly great at the corners of the attraction platen  60  in the main scanning direction. Accordingly, charging due to friction may occur at the corners, causing the conveying belt  353  to be attracted to the attraction platen  60  and increasing the running load of the conveying belt  353  to an excessive level. 
         [0043]    In this embodiment, charging prevention members  364  and  365  may be provided at the corners of the attraction platen  60  in the main scanning direction. The charging prevention members  364  and  365  may be provided so as not to overlap the electrode  62  or the electrode  63 , or so as to overlap the electrode  62  or the electrode  63 . The charging prevention members  364  and  365  may include a material having the same polarity as the material of the top surface of the conveying belt  353 . More specifically, if the material of the top surface of the conveying belt  353  has a polarity that tends to be charged with positive charge, a material that tends to be charged with positive charge may be used in the charging prevention members  364  and  365 . On the other hand, if the material of the top surface of the conveying belt  353  has a polarity that tends to be charged with negative charge, a material that tends to be charged with negative charge may be used in the charging prevention members  364  and  365 . The charging prevention members  364  and  365  may include a material having minimum electric resistance. 
         [0044]    By forming the charging prevention members  364  and  365  from a material having the same polarity as the top surface of the conveying belt  353  and having minimum electric resistance, the charging prevention members  364  and  365  may be less likely to be charged by the friction between the conveying belt  353  and the charging prevention members  364  and  365 . Accordingly, the running load of the conveying belt  353  may be prevented from reaching an excessive level. 
         [0045]    Referring to  FIG. 8 , another embodiment will be described. In this embodiment, a tension roller  470  that functions as a conveying roller to convey the conveying belt  53  and comes into contact with the outer circumferential surface  54  may be provided in addition to the belt rollers  51  and  52 . In the embodiment described above, the charging roller  70  may be in contact with the outer circumferential surface  54  of the conveying belt  53 . However, in the case where a roller other than the charging roller  70  comes into contact with the outer circumferential surface  54 , ink spread by such a roller may cause a short-circuit between the electrodes  62  and  63 . In this embodiment, similarly to the charging roller  70 , the tension roller  470  may be disposed such that the area of the outer circumferential surface  54  with which the tension roller  470  comes into contact does not extend over the electrodes  62  and  63 . Thus, the ink on the outer circumferential surface  54  may be less likely to cause a short-circuit between the electrodes  62  and  63 . 
         [0046]    Furthermore, in the embodiment described above, the charging roller  70  that performs electric discharge on the sheet P may be used as the roller that presses the sheet P against the outer circumferential surface  54  of the conveying belt  53 . However, a roller that does not perform electric discharge on the sheet P but simply performs pressing may be used. 
         [0047]    Furthermore, in the embodiment described above, rotary bodies such as the charging roller  70  and the conveying roller may be assumed as the contact members that come into contact with the sheet P and the outer circumferential surface  54  of the conveying belt  53 . However, a rotary body, such as a rotary brush, which cleans the sheet P or the outer circumferential surface  54  may be provided. Furthermore, not a rotary body, but a fixed contact member, such as a wiper blade that wipes ink adhered to the outer circumferential surface  54 , may be provided. 
         [0048]    While the invention has been described in connection with various exemplary structures and illustrative embodiments, it will be understood by those skilled in the art that other variations and modifications of the structures and embodiments described above may be made without departing from the scope of the invention. Other structures and embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples are illustrative with the true scope of the invention being defined by the following claims.

Technology Category: 7