Abstract:
A sheet conveyance device includes a support unit that supports a sheet; plural suction ports placed on the support unit; a suction unit that suctions the sheet toward the support unit, the suction unit being connected to the plural suction ports; plural valve systems, each valve system being placed between the corresponding suction port and the suction unit, each valve system being openable and closeable; plural valve interlocked suction ports that are to be covered by the sheet when the sheet is conveyed, the plural valve interlocked suction ports being arranged separately from the plural suction ports; and plural opening and closing units that open and close the plural valve systems, each opening and closing unit being placed between one of the valve interlocked suction ports and one of the valve systems.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments of the present invention relate to a recording device which forms an image on a sheet. Specifically, the embodiments of the present invention relate to a conveyance device having a suction conveyance unit that suctions and conveys various sizes of sheets of materials, which are recording media, using airflows. 
         [0003]    2. Description of the Related Art 
         [0004]    In a conveyance device used for an image forming device, such as a conventional inkjet printer, when an image is formed, it may be necessary to maintain a constant spacing between a recording unit and a recording medium. Thus, it is not possible to convey the recording medium while holding the recording medium. Therefore, when the recording medium is conveyed, it may be necessary that a deformation or a lifting of the recording medium is regulated. Further, during an image forming process, when a deformation of the recording medium itself occurs, for example, when stretching of the recording medium associated with adhesion of ink (hereinafter, referred to as stretching) or deformation of the recording medium associated with application of heat occurs, it may be necessary to provide a groove portion so that the deformation of the recording medium is released to the opposite side of the recording unit. As described above, the following conveyance device is known. Namely, as shown in  FIG. 8 , the conveyance device supports the reverse side of the recording medium on a conveyance surface in an image forming area. Further, the conveyance device includes plural suction ports for suctioning the recording medium from the reverse side, so as to prevent the recording medium from being lifted. The conveyance device conveys the recording medium while suctioning the recording medium in the image forming area. 
         [0005]    In the above described conveyance device, when the recording medium is conveyed to a position where the recording medium covers all the suction ports  22  of orifices  14 , which are arranged on the conveyance surface, since inside of each orifice  14  is sealed, a negative pressure increases and the suction force increases. In this manner, a deformation of the recording medium which exists prior to forming an image or a deformation of a recording medium caused by adhered ink when forming the image is suppressed, and the recording medium can be stably conveyed. Further, since the orifice  14  has a constant length, when a deformation, such as the stretching, occurs on the recording medium, an amount of the deformation can be released to the reverse side of the recording unit by the suction force. 
         [0006]    However, at a position shown in  FIG. 9 , where the recording medium only covers suction ports  22  placed at a front tip or a rear tip of the orifice  14 , the air is suctioned through suction ports  22  which are released. Thus, there is a problem that a lifting or a deformation of the recording medium is not sufficiently regulated, since the negative pressure inside the orifice  14  does not increase and the suction force does not increase. Therefore, techniques for controlling a suction force acting onto the recording medium or a suction timing to suction the recording medium in the above described conveyance device are disclosed, for example, in Patent Document 1 (Japanese Published Unexamined Publication No. S64-43430), Patent Document 2 (Japanese Published Unexamined Publication No. H09-058897), and Patent Document 3 (Japanese Registered Patent No. 3690182). 
         [0007]    Patent Document 1 discloses a technique such that, when a sheet covers suction ports, an output of a pump is reduced so as to prevent a suction force from becoming rapidly large. However, in this configuration, the air is always suctioned through suction ports other than the suction ports conveying the sheet. In such a case, it may be necessary to adjust the suction force of the pump, so that the sheet is surely conveyed, even if the sheet does not cover all the suction ports. Thus a large pump tends to be used. Therefore, the configuration disclosed in Patent Document 1 has problems that the device becomes large, and noise and cost increase. 
         [0008]    Patent Document 2 discloses a technique for avoiding unnecessary suctioning. In the technique, for the suction ports other than the suction ports conveying the sheet, a driving means for opening and closing a valve system and a sensor are used, so as to selectively avoid unnecessary suctioning. With this configuration, the size of the pump can be reduced. However, for example, when a surface for suctioning the sheet is large, in order to selectively avoid unnecessary suctioning at finer areas so as to prevent tips of the sheet from lifting, it may be necessary to place plural driving units for opening and closing the valve system. This leads to complication of the device and growth in size of the device. Further it can be a cause of a cost increase. 
         [0009]    Patent Document 3 discloses a technique using a pressure adjustment valve. Namely, when a sheet covers a suction port, the pressure adjustment valve causes a suction force to be generated, and when the sheet does not cover the suction port, the pressure adjustment valve does not allow unnecessary suctioning to be performed. However, in this technique, a suction force is not obtained until the sheet completely covers an orifice (a suction port). Thus, the suction force at the tip of the sheet is always weaker than the suction force at the center of the sheet. Therefore, there is a problem that the technique does not handle the lifting of the tips of the sheet. Further, in this technique, the pressure adjustment valve is closed by fluid flow (wind). However, when the pressure adjustment valve is closed, the fluid does not flow, and the pressure adjustment valve is opened. Patent Document 3 does not disclose a technique to overcome this problem. However, as a technique to overcome this problem, a method in which the valve unit is not completely closed and the valve unit partially leaks the fluid, or a method of completely closing the pressure adjustment valve by a pressure difference between a suction side and an orifice side, the pressure adjustment valve being pinched between the suction side and the orifice side, can be considered. However, when the pressure adjustment valve is not completely closed, since not all the unnecessary suctioning is stopped, inefficiency of the suctioning remains. Further, in the method of completely closing the pressure adjustment valve by the pressure difference between the suction side and the orifice side, at an instant when the recording medium covers the orifice, the pressure difference for closing the pressure adjustment valve is not released, and the pressure adjustment valve is not opened. When the pressure inside the orifice is increased by leakage through a gap between the orifice and the recording medium, the pressure adjustment valve is opened. Therefore, the problem that the technique does not handle the lifting of the tips of the sheet remains. Further, in order to cause the pressure adjustment valve to be opened when a sheet covers a portion of an orifice, a valve may be opened and closed in response to a very small pressure difference or a very small flow difference of a fluid. Therefore, a highly precise valve system may be required, and a suction force from a suction mechanism may be very precise. Such a technique is not realistic, and it leads to problems, such as a cost increase, degradation of proccessability, and growth in size of the device. 
       SUMMARY OF THE INVENTION 
       [0010]    In one aspect, there is provided a sheet conveyance device including a support unit that supports a sheet; plural suction ports placed on the support unit; a suction unit that suctions the sheet toward the support unit, the suction unit being connected to the plural suction ports; plural valve systems, each valve system being placed between the corresponding suction port and the suction unit, each valve system being openable and closeable; plural valve interlocked suction ports that are to be covered by the sheet when the sheet is conveyed, the plural valve interlocked suction ports being arranged separately from the plural suction ports; and plural opening and closing units that open and close the plural valve systems, each opening and closing unit being placed between one of the valve interlocked suction ports and one of the valve systems. 
         [0011]    In another aspect, there is provided an image forming device including a sheet conveyance device. The sheet conveyance device includes a support unit that supports a sheet; plural suction ports placed on the support unit; a suction unit that suctions the sheet toward the support unit, the suction unit being connected to the plural suction ports; plural valve systems, each valve system being placed between the corresponding suction port and the suction unit, each valve system being openable and closeable; plural valve interlocked suction ports that are to be covered by the sheet when the sheet is conveyed, the plural valve interlocked suction ports being arranged separately from the plural suction ports; and plural opening and closing units that open and close the plural valve systems, each opening and closing unit being placed between one of the valve interlocked suction ports and one of the valve systems. 
         [0012]    Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic diagram of a major portion of an inkjet recording device, to which an embodiment of the present invention can be applied; 
           [0014]      FIG. 2  is a schematic diagram of a conveyance device used in a first embodiment of the present invention; 
           [0015]      FIG. 3  is a schematic diagram illustrating an opening and closing unit used in the first embodiment of the present invention; 
           [0016]      FIG. 4  is a schematic diagram illustrating the opening and closing unit used in the first embodiment of the present invention; 
           [0017]      FIG. 5  is a schematic diagram of a conveyance device used in a second embodiment of the present invention; 
           [0018]      FIG. 6  is a schematic diagram of a conveyance device used in a third embodiment of the present invention; 
           [0019]      FIG. 7  is a schematic diagram of a conveyance device used in a fourth embodiment of the present invention; 
           [0020]      FIG. 8  is a schematic diagram illustrating a problem; 
           [0021]      FIG. 9  is a schematic diagram illustrating the problem. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    It is an objective of embodiments of the present invention to solve the above described problems. Further, it is an objective of the embodiments of the present invention to provide a conveyance device that can suction a sheet immediately before the sheet covers a suction port, that can keep suctioning the sheet until the sheet is completely separated from the suction port, that can surely prevent the sheet from lifting, and that can perform efficient and stable sheet conveyance, without additionally arranging a sensor or an actuator. 
         [0023]      FIG. 1  is a schematic diagram of an inkjet recording device  10 , which is an image forming device to which an embodiment of the present invention can be applied. The inkjet recording device  10  includes a carriage  21  which can reciprocate in a main scanning direction. Here, the main scanning direction is a width direction of a recording paper, and the main scanning direction is perpendicular to a conveyance direction of the recording paper. The carriage  21  includes a recording head (not shown in the figure) which discharges black ink, magenta ink, cyan ink, and yellow ink. A guide plate  23  is placed at upstream side of the carriage  21  in the conveyance direction of the recording paper. The guide plate  23  serves as a supporting unit. On an upper surface of the guide plate  23 , a recording paper is conveyed. As shown in  FIG. 2 , plural orifices  24  are formed on the guide plate  23 . The plural orifices  24  are formed in a conveyance direction of a sheet  1  and in a width direction of the sheet  1 . Here, the sheet  1  is conveyed on the guide plate  23 . A suction port  25  is formed inside each orifice  24 . The suction port  25  is connected to a suction unit  20  which incorporates a pump. Further, an openable and closeable valve system  26  is placed between the suction port  25  and the suction unit  20 . 
         [0024]    A valve interlocked suction port  27  is placed at upstream side of the corresponding suction port  25  on the guide plate  23  in the conveyance direction of the sheet  1 . The valve interlocked suction port  27  is connected to the suction unit  20 . In the channel connecting the valve interlocked suction port  27  and the suction unit  20 , an opening and closing unit  28  for opening and closing the valve system  26  is placed. As shown in  FIG. 3 , the opening and closing unit  28  includes a flexible member  30  which is arranged in an air chamber  29 . The flexible member  30  is placed at one side of the air chamber  29 . The flexible member  30  is connected to one end of an on-off valve  31 , which is included in the valve system  26 . The valve system  26  includes the L shaped on-off valve  31 . A bent portion of the on-off valve  31  is rotatably attached to a wall portion of a flow channel connected to the suction unit  20 . Further, a pair of conveyance rollers  32  for conveying the sheet  1  is placed at upstream side of the valve interlocked suction port  27  in the conveyance direction of the sheet  1 . Additionally, a pair of conveyance rollers  33  for conveying the sheet  1  is placed at downstream side of the orifice  24  in the conveyance direction of the sheet  1 . 
         [0025]    With the above described configuration, in a state shown in  FIG. 3  in which the sheet  1  has not reached the valve interlocked suction port  27 , since the on-off valve  31  blocks the flow channel, a suction force does not act at the suction port  25 , even if the suction unit  20  is working. In this case, the suction force only acts at the valve interlocked suction port  27 . When the valve interlocked suction port  27  is blocked by the conveyed sheet  1  as shown in  FIG. 4 , the pressure inside the air chamber  29  becomes a negative pressure by the operation of the suction unit  20 . Thus the flexible member  30  is deformed. With the deformation of the flexible member  30 , the on-off valve  31  connected to the flexible member  30  rotates and the flow channel is released. Then the suction force from the suction unit  20  also acts at the suction port  25 . 
         [0026]    In the above described embodiment  1 , the air is suctioned prior to the front tip of the sheet  1  reaching the orifice  24 . When the front tip of the sheet  1  reaches the orifice  24 , a sufficient suction force from the suction unit  20  is acting. Therefore, by using a lower cost configuration in which sensors or electrical driving mechanisms are not used, the sheet  1  can be stably conveyed while the lifting of the front tip of the sheet  1  is prevented. Further, plural of the suction ports  25  and plural of the valve interlocked suction ports  27  are arranged in the width direction of the sheet  1 . Therefore, when a sheet having a different width is conveyed, an unnecessary suction is not performed, and the sheet can be stably conveyed while the lifting of the sheet is prevented. Further, since the valve interlocked suction port  27  is placed at upstream side of the suction port  25  in the sheet conveyance direction, it is ensured that the front tip of the sheet  1  is suctioned first. Therefore, the sheet  1  can be stably conveyed while the lifting of the tip of the sheet  1  is surely prevented. Further, since the plural suction ports  25  are also arranged in the sheet conveyance direction, an unnecessary suction is not performed when an image is formed over a long distance in the sheet conveyance direction. Therefore, the sheet  1  can be stably conveyed while the lifting of the tip of the sheet  1  is prevented. Further, when a pressure difference between the atmospheric pressure and the pressure inside the valve interlocked suction port  27  is greater than a predetermined value, the opening and closing unit  28  opens the on-off valve  31 . Therefore, the valve system  26  can be opened and closed more reliably. 
         [0027]    In the embodiment, the valve interlocked suction port  27  is arranged at downstream side of the pair of conveyance rollers  32  in the sheet conveyance direction. However, the position of the valve interlocked suction port  27  is not limited to this. It is preferable that the valve interlocked suction port  27  be arranged at a suitable position depending on a conveyance speed of the sheet  1 , or a layout of the inkjet recording device  10 . Further, in the configuration of the embodiment, the flexible member  30  is used in the opening and closing unit  28 . However, a piston mechanism can be used instead of the flexible member  30 . 
         [0028]      FIG. 5  shows a second embodiment of the present invention. Compared to the first embodiment, the second embodiment is different from the first embodiment in the following points. A valve interlocked suction port  34  is arranged at downstream side of the orifice  24  in the sheet conveyance direction. At the same time, in a flow channel connecting the valve interlocked suction port  34  and the suction unit  20 , an opening and closing unit  35  similar to the opening and closing unit  28  is arranged. The flow channel connecting the suction port  25  and the suction unit  20  is divided into two flow channels. The valve system  26  is arranged in the first flow channel, and the valve system  36  similar to the valve system  26  is arranged in the second flow channel. The valve system  26  is opened and closed by the opening and closing unit  28 , and the valve system  36  is opened and closed by the opening and closing unit  35 . 
         [0029]    With the above described configuration, in addition to the effect of the first embodiment, the following effects can be obtained. Namely, in the state shown in  FIG. 5  in which the end tip of the sheet  1  is not completely covering the orifice  24 , since the sheet  1  is covering the valve interlocked suction port  34 , the suction force from the suction unit is acting at the suction port  25 . Therefore, the air is suctioned from the suction port  25  after the end tip of the sheet  1  has passed through the upstream end portion of the orifice  24 . Therefore, by using a low cost configuration in which sensors or electrical driving mechanisms are not used, the sheet  1  can be stably conveyed while the lifting of the end tip of the sheet  1  is prevented. Further, with such a configuration, an unnecessary suction that might be performed after the end tip of the sheet  1  is completely separated from the orifice  24  can be avoided. 
         [0030]      FIG. 6  shows a third embodiment of the present invention. In the third embodiment, plural orifices  24  are arranged in the sheet conveyance direction. The valve interlocked suction port  27  is arranged at upstream side of an orifice  24 - 1  in the sheet conveyance direction. Here, the orifice  24 - 1  is arranged at the upstream most position among the plural orifices. A valve mechanism  26 - 1  arranged in a first flow channel of first divided flow channels is opened and closed by an opening and closing unit  28 - 1  which is arranged between the valve interlocked suction port  27  and the suction unit  20 . The valve interlocked suction port  34  is arranged at downstream side of an orifice  24 - 2  in the sheet conveyance direction. Here, the orifice  24 - 2  is arranged at the downstream most position among the plural orifices. A valve mechanism  36 - 2  arranged in a second flow channel of second divided flow channels is opened and closed by an opening and closing unit  35 - 2  which is arranged between the valve interlocked suction port  34  and the suction unit  20 . At a position where the orifices  24 - 1  and  24 - 2  are neighboring each other, an opening and closing unit  35 - 1  arranged in the second flow channel of the first divided flow channels of the upstream side orifice  24 - 1  opens and closes a valve mechanism  26 - 2  arranged in the first flow channel of the second divided flow channels of the downstream side orifice  24 - 2 . Further, an opening and closing unit  28 - 2  arranged in the first flow channel of the second divided flow channels of the downstream side orifice  24 - 2  opens and closes a valve mechanism  36 - 1  arranged in the second flow channel of the first divided flow channels of the upstream side orifice  24 - 1 . Further, check valves  37  are arranged at a downstream position of the opening and closing unit  28 - 1 , a downstream position of a position at which the first divided flow channels of the upstream side orifice  24 - 1  meet, a downstream position of a position at which the second divided flow channels of the downstream side orifice  24 - 2  meet, and a downstream position of the opening and closing unit  35 - 2 , respectively. 
         [0031]    With the above described configuration, when plural orifices are densely arranged, a valve system arranged in a first orifice can be opened and closed by a pressure difference between the atmospheric pressure and the pressure in a second orifice, which is neighboring to the first orifice, without introducing a new valve interlocked suction port. Therefore, a stable conveyance can be realized without cost increase. Further, since check valves are provided, even if the suction ports  25  neighboring to each other are opened, the valve mechanisms  26 ,  35  can be surely operated. 
         [0032]      FIG. 7  shows a fourth embodiment of the present invention. In this embodiment, one valve interlocked suction port  27  is placed for plural suction ports  25 . Specifically, for the plural suction ports  25  included in an area A of central six rows, a valve interlocked suction port  27 - 1  is arranged. For the plural suction ports  25  included in an area B of upper two rows, a valve interlocked suction port  27 - 2  is arranged. Further, for the plural suction ports  25  included in an area C of lower two rows, a valve interlocked suction port  27  is arranged. When the valve interlocked suction port  27 - 1  is covered with the sheet  1 , the suction ports  25  included in the area A start suctioning. When the valve interlocked suction port  27 - 2  is covered with the sheet  1 , the suction ports  25  included in the area B start suctioning. Further, when the valve interlocked suction port  27  is covered with the sheet  1 , the suction ports  25  included in the area C start suctioning. 
         [0033]    In the above configuration, when types of the sheet  1  are limited to several types, and, for example, when the sheet  1  is conveyed while the sheet  1  is aligned to the central portion, the width of the area A may be adjusted to be a width of the smallest type of the sheet  1  to be conveyed. Further, it is not necessary that a valve interlocked suction port  27  be placed for each suction port  25 . With the above configuration, cost reduction may be achieved. Additionally, the above configuration is advantageous as a layout of the inkjet recording device  10 . 
         [0034]    With the configurations shown in the embodiments, when plural sheets  1  are conveyed while the sheets  1  are evenly spaced apart in the conveyance direction or in the width direction, it is possible to cause the suction ports  25 , above which the sheets  1  do not exist, not to suction, and cause the only suction ports  25 , to which the sheets  1  are to be conveyed immediately after, to suction. Therefore, recording papers are efficiently suctioned, and the recording papers can be stably conveyed. Further, when an image is formed by a single scanning across the spacing of the sheets (for example, when the sheets are conveyed while the sheets are evenly spaced apart in the conveyance direction, a case in which an image is formed by a single scanning of a rear end portion of the front sheet and a front end portion of the successive sheet), an occurrence of an air current caused by the suction can be minimized by eliminating redundant suction operations, which are the suction operations between the sheets. In this case, adverse effects on ink discharge caused by the occurrence of the air current can be reduced. 
         [0035]    The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
         [0036]    The present application is based on Japanese Priority Application No. 2011-011092, filed on Jan. 21, 2011, the entire contents of which are hereby incorporated herein by reference.