Patent Publication Number: US-9884494-B2

Title: Inkjet printing machine

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to an inkjet printing machine configured to discharge ink from inkjet heads to perform printing. 
     2. Related Art 
     There is known a line-type inkjet printing machine configured to perform printing by discharging ink from fixed inkjet heads onto a sheet, while transferring the sheet. A so-called air suction transfer mechanism to transfer sheets is widely used in the line-type inkjet printing machine (see, for example, Japanese Patent Application Laid-Open Publication No. 2007-31007). 
     The air suction transfer mechanism sucks air with a fan through a large number of suction holes provided on a conveyer belt, and sucks and holds a sheet on the conveyer belt by suction force caused by negative pressure generated at the suction holes. The conveyer belt moves while thus sucking and holding a sheet to transfer the sheet. 
     SUMMARY 
     Problems to be Solved by the Invention 
     In an inkjet printing machine using an air suction transfer mechanism, a portion of ink mist generated by discharging of ink is carried on an airflow caused by air suction toward the suction holes. Therefore, adhering of the carried ink mist to a sheet on the conveyer belt may stain the sheet. 
     The present invention has been made in view of the above problem. An object of the present invention is to provide an inkjet printing machine which can reduce the staining of sheets. 
     Means to Solve the Problem 
     In order to achieve the aforementioned object, a first feature of the inkjet printing machine according to the present invention includes: a paper feeder configured to feed a sheet; a transfer unit having a conveyer belt with a plurality of suction holes formed thereon and configured to transfer a sheet fed by the paper feeder while sucking and holding the sheet on the conveyer belt by suction force which is generated at the suction holes; inkjet heads configured to discharge ink on a sheet being transferred by the transfer unit; and a controller configured to perform printing by controlling the paper feeder to feed a sheet, controlling the transfer unit to transfer the fed sheet, and controlling the inkjet heads to discharge ink on the sheet, wherein the plurality of suction holes of the conveyer belt is arranged, when the leading edge of the sheet in the transfer direction does not overlap with the suction holes, the trailing edge of the sheet also does not overlap with the suction holes, and the controller controls the paper feeder to feed at a timing when the leading edge and the trailing edge of the sheet in the transfer direction do not overlap with the suction holes. 
     A second feature of the inkjet printing machine according to the present invention lies in that the plurality of suction holes of the conveyer belt is arranged so that an edge of the sheet in a sheet-width direction perpendicular to the transfer direction does not overlap with the suction holes. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will now be described with reference to the accompanying drawings wherein: 
         FIG. 1  is a block diagram illustrating a configuration of an inkjet printing machine according to an embodiment; 
         FIG. 2  is an outline configuration diagram of a paper feeder and a printer of the inkjet printing machine illustrated in  FIG. 1 ; 
         FIG. 3  is a partial enlarged plan view of a conveyer belt and a platen plate of the printer illustrated in  FIG. 2 ; 
         FIG. 4  is a flowchart for explaining an operation of the inkjet printing machine illustrated in  FIG. 1 ; 
         FIG. 5  is an explanatory diagram of a positional relation between a sheet and suction holes of the conveyer belt at the front end portion of the sheet; 
         FIG. 6  is an explanatory diagram of a positional relation between a sheet and suction holes of the conveyer belt at the rear end portion of the sheet; 
         FIG. 7  illustrates a positional relation between the flow of ink mist caused by air suction and the sheet according to the embodiment; and 
         FIG. 8  illustrates a positional relation between the flow of an ink mist caused by air suction and the sheet when the leading edge of the sheet overlaps with the suction holes. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments of the present invention will be described with reference to the drawings. Throughout the drawings, identical or equivalent parts or components are provided with identical or equivalent symbols. 
     The embodiment described below exemplifies devices or the like for realizing the technical idea of the invention, the technical idea of the invention not being intended to limit the material, shape, structure, arrangement, or the like, of each component to those described in the following. The technical idea of the invention may be modified in various ways within the scope of claims. 
       FIG. 1  is a block diagram illustrating a configuration of an inkjet printing machine according to an embodiment of the present invention.  FIG. 2  is an outline configuration diagram of a paper feeder and a printer of the inkjet printing machine illustrated in  FIG. 1 .  FIG. 3  is a partial enlarged plan view of a conveyer belt and a platen plate of the printer illustrated in  FIG. 2 . 
     In the following description, a direction perpendicular to the plane of  FIG. 2  is assumed to be a forward-backward direction with a front side of the plane indicating a forward direction, unless otherwise stated. In addition, an up-down and a right-left directions in the plane of  FIG. 2  are assumed to be a vertical and a horizontal directions respectively. In  FIG. 2 , the direction from the left to the right is the transfer direction of sheets P which are the print media. The upstream and the downstream which appear in the following description indicate the upstream and the downstream in the transfer direction. 
     As illustrated in  FIG. 1 , an inkjet printing machine  1  according to the embodiment includes a paper feeder  2 , a printer  3 , and a controller  4 . 
     The paper feeder  2  feeds the sheets P to the printer  3 . As illustrated in  FIG. 2 , the paper feeder  2  includes a paper feed tray  11 , a paper feed roller  12 , a paper feed motor  13 , a resist roller  14 , and a resist motor  15 . 
     The paper feed tray  11  is loaded with the sheets P to be used for printing. 
     The paper feed roller  12  performs primary paper feeding. The primary paper feeding feeds sheets from the paper feed tray  11  to the resist roller  14 . Specifically, the paper feed roller  12  picks up the sheet P one by one from the paper feed tray  11  and transfers it, then the paper feed roller  12  makes the sheet P butt against the sheet P against the resist roller  14  and stops the sheet P. 
     The paper feed motor  13  rotationally activates the paper feed roller  12 . 
     The resist roller  14  performs secondary paper feeding. The secondary paper feeding feeds sheets from the resist roller  14  to the printer  3 . Specifically, the resist roller  14  temporarily stops the sheet P which has been transferred by the paper feed roller  12  and subsequently transfers the sheet P toward the printer  3 . The resist roller  14  is provided on the downstream side of the paper feed roller  12 . 
     The resist motor  15  rotationally activates the resist roller  14 . 
     The printer  3  performs printing while transferring the sheet P. The printer  3  is provided on the downstream side of the paper feeder  2 . The printer  3  includes a transfer unit  21  and four inkjet heads  22 . 
     The transfer unit  21  transfers the sheet P fed by the paper feeder  2 . The transfer unit  21  includes a conveyer belt  31 , a drive roller  32 , driven rollers  33 ,  34  and  35 , a belt motor  36 , an encoder  37 , a platen plate  38 , a fan  39 , and a belt position sensor  40 . 
     The conveyer belt  31  transfers the sheet P while sucking and holding it. The conveyer belt  31  is a looped belt stretched across the drive roller  32  and the driven rollers  33  to  35 . The conveyer belt  31 , having plasticity, is made of a material such as rubber, resin, or the like which generates a suitable frictional force against the sheet P. 
     As illustrated in  FIG. 3 , the conveyer belt  31  is formed with a plurality of suction holes  41 . The conveyer belt  31  sucks and holds on its top surface the sheet P by suction force which is generated at the suction holes  41  by driving of the fan  39 . The conveyer belt  31  rotates in the clockwise direction to transfer the sucked and held sheet P rightward, as illustrated in  FIG. 2 . 
     The suction holes  41  are arranged in the transfer direction (right-left direction) with a predetermined pitch. In addition, the suction holes  41  of the next stage adjacent in the sheet-width direction (forward-backward direction) perpendicular to the transfer direction are arranged in a manner displaced relative to the suction holes  41  of the preceding stage by as much as a half pitch in the transfer direction. In other words, the suction holes  41  are arranged in a staggered manner. 
     The suction holes  41  are arranged so that, when the leading edge of the sheet P in the transfer direction does not overlap with the suction holes  41 , the trailing edge of the sheet P also does not overlap with the suction holes  41 , the sheet P of various standard sizes which are used in the inkjet printing machine  1 . 
     In addition, the suction holes  41  are arranged so that the edge of the sheet P in the sheet-width direction does not overlap with the suction holes  41 , the sheet P of various standard sizes used in the inkjet printing machine  1 . Here, the position in the sheet-width direction of the sheet P on the conveyer belt  31  corresponds to the position in the sheet-width direction of the sheet P on the paper feed tray  11 . On the paper feed tray  11 , the sheet P is loaded in a manner positioned in the sheet-width direction. 
     In addition, among the suction holes  41  of the conveyer belt  31 , those located in a region adjacent to the edge in the sheet-width direction of the sheet P are formed to be smaller than the other suction holes  41 . Specifically, the suction holes  41  which are adjacent to the outside of the sheet P with respect to one or the other edge in the sheet-width direction of the sheet P of various standard sizes which are used in the inkjet printing machine  1  are formed to be smaller than the other suction holes  41 . 
     Here, a “region adjacent to the edge” refers to a region located within a predetermined distance in the sheet-width direction from the edge in the sheet-width direction of the sheet P. The predetermined distance is approximately equal to the interval of the arrangement of the sheet-width direction of the suction holes  41  which are arranged in a staggered manner. In other words, when the suction holes  41  are adjacent to the outside of the sheet P, the distance from the suction holes  41  to the edge in the sheet-width direction of the sheet P becomes shorter than the interval of the arrangement of the suction holes  41  in the sheet-width direction. 
     Giving a full detail of the suction holes  41 , a small-diameter suction holes column  42  is formed on the conveyer belt  31 , as illustrated in  FIG. 3 . The small-diameter suction holes column  42  is configured to arrange the suction holes  41  having a smaller diameter than the suction holes  41  at other positions in the transfer direction. The four columns of small-diameter suction holes  42  in  FIG. 3  are each adjacent to one of the edges in the sheet-width direction of the sheet P of four types of standard sizes. A plurality of columns of small-diameter suction holes  42  may be provided to each edge in the sheet-width direction of the sheet P of each size. 
     The drive roller  32  rotates the conveyer belt  31  in the clockwise direction in  FIG. 2 . In other words, operation of the drive roller  32  causes the conveyer belt  31  to proceed over the upper side of the platen plate  38  in the transfer direction. 
     The driven rollers  33  to  35  support the conveyer belt  31  together with the drive roller  32 . The driven rollers  33  to  35  follow the movement of the drive roller  32  via the conveyer belt  31 . The driven roller  33  is provided on the left side of the drive roller  32  at the same height as the drive roller  32 . The driven rollers  34  and  35  are provided at the same height under the drive roller  32  and the driven roller  33  in a manner separated rightward and leftward from each other. 
     The belt motor  36  rotationally activates the drive roller  32 . 
     The encoder  37  outputs a pulse signal at each predetermined rotation angle of the driven roller  33 . 
     The platen plate  38 , which is arranged under the conveyer belt  31  and between the drive roller  32  and driven roller  33 , supports the back side of the conveyer belt  31  in a slidable manner. The platen plate  38  is made of metal, resin, or the like. The platen plate  38  has a plurality of concave portions  46  which is dented from the upper surface to the lower surface at a position where the suction holes  41  pass, and a plurality of through-holes  47  which penetrates from a part of the bottom surface of the concave portion  46  to the lower surface of the platen plate  38 . 
     The fan  39  generates a downward airflow. Accordingly, the fan  39  sucks air via the through-hole  47  of the platen plate  38 , the concave portion  46 , and the suction holes  41  of the conveyer belt  31  to generate negative pressure in the suction holes  41 , and sucks the sheet P on the conveyer belt  31 . The fan  39  is provided under the platen plate  38 . 
     The belt position sensor  40  detects a reference hole  61  formed on the conveyor belt  31 . 
     The inkjet heads  22  discharge ink onto the sheet P which is transferred by the transfer unit  21  to print an image thereon. The four inkjet heads  22  discharge four colors of ink: black, cyan, magenta and yellow, respectively. The inkjet heads  22  are arranged above the transfer unit  21 . 
     The controller  4  controls operation of each part of the inkjet printing machine  1 . The controller  4  is configured to include a CPU, a RAM, a ROM, a hard disk, or the like. 
     Specifically, the controller  4  performs control so that the paper feeder  2  feeds the sheet P and, while the transfer unit  21  transfers the sheet P, the inkjet heads  22  discharge the ink to perform printing on the sheet P. Here, the controller  4  controls the paper feeder  2  to feed a sheet at a timing when the leading edge and the trailing edge of the sheet P in the transfer direction do not overlap with the suction holes  41 . 
     Next, an operation of the inkjet printing machine  1  will be described. 
       FIG. 4  is a flowchart which explains an operation of the inkjet printing machine  1 . Processing of the flowchart of  FIG. 4  starts by inputting a print job to the inkjet printing machine  1 . 
     At step S 1  of  FIG. 4 , the controller  4  activates the transfer unit  21 . Specifically, the controller  4  activates the drive roller  32  using the belt motor  36 . Accordingly, circulation of the conveyer belt  31  is started. The controller  4  drives the drive roller  32  so that the transfer speed of the sheet P by the conveyer belt  31  is adjusted to a predetermined print transfer speed. In addition, the controller  4  activates the fan  39 . 
     Subsequently, the controller  4  determines, at step S 2 , whether or not the reference hole of the conveyer belt  31  has been detected by the belt position sensor  40 . When it is determined that the reference hole has not been detected (NO at step S 2 ), the controller  4  repeats step S 2 . 
     When the controller  4  determines that the reference hole has been detected (YES at step S 2 ), the controller  4  starts, at step S 3 , counting the number of pulses output by the encoder  37 . 
     Subsequently, the controller  4 , at step S 4 , drives the paper feed roller  12  using the paper feed motor  13  to perform a primary paper feeding. Specifically, the controller  4  controls so that, after the paper feed roller  12  has picked up the sheet P from the paper feed tray  11  and the sheet P is butted against the resist roller  14  and the sheet P is stopped by slackening. Accordingly, skew of the sheet P is corrected. 
     Subsequently, the controller  4  determines, at step S 5 , whether or not the pulse count value is within a range of values allowing a secondary paper feeding to be started. The start-of-secondary-paper-feeding allowable range is a range of pulse count values corresponding to the start timing of the resist roller  14  at which the leading edge of the sheet P in the transfer direction being transferred to the transfer unit  21  by the resist roller  14  does not overlap with the suction holes  41 . The start-of-secondary-paper-feeding allowable range is preliminarily set in accordance with the arrangement of the suction holes  41 . When the controller  4  determines that the pulse count value is outside the start-of-secondary-paper-feeding allowable range (NO at step S 5 ), the controller  4  repeats step S 5 . 
     When the controller  4  determines that the pulse count value is within the start-of-secondary-paper-feeding allowable range (YES at step S 5 ), the controller  4  activates the resist roller  14  using the resist motor  15  at step S 6 . Accordingly, the sheet P starts transferring toward the transfer unit  21  using the resist roller  14 . The controller  4  controls the resist roller  14  so that the sheet P reaches the conveyer belt  31  at the print transfer speed. 
     When the leading edge of the sheet P reaches the conveyer belt  31 , the sheet P is transferred by the conveyer belt  31  and the resist roller  14  while gradually being sucked to the conveyer belt  31  from the front end side of the sheet P. 
     Here, the controller  4  activates the resist roller  14  when the pulse count value is within the start-of-secondary-paper-feeding allowable range and therefore the leading edge Ef of the sheet P in the transfer direction does not overlap with the suction holes  41 , as illustrated in  FIG. 5 . In other words, the leading edge Ef of the sheet P is located within a range A in which the suction holes  41  do not exist in the transfer direction of the conveyer belt  31 . 
     In addition, an edge Ew in the sheet-width direction of the sheet P is located within a range B in which the suction holes  41  do not exist in the sheet-width direction of the conveyer belt  31 . In addition, the suction holes  41  which are adjacent to the outside of the sheet P with respect to the edge Ew in the sheet-width direction are set to be the suction holes  41  in the small-diameter suction holes column  42 . Although the edge Ew of one side of the sheet-width direction is illustrated in  FIG. 5 , the edge Ew of the other side is arranged in a similar manner. 
     Referencing again to  FIG. 4 , the controller  4  starts, at step S 7  subsequent to step S 6 , printing by the inkjet heads  22  after the sheet P has reached a predetermined position under the inkjet heads  22 . 
     Subsequently, the controller  4  determines, at step S 8 , whether or not a resist roller stop timing has arrived. The resist roller stop timing is a timing at which the trailing edge of the sheet P in the transfer direction leaves the resist roller  14 . The resist roller stop timing is set in accordance with the length of the sheet P in the transfer direction. When the controller  4  determines that the resist roller stop timing has not arrived (NO at step S 8 ), the controller  4  repeats step S 8 . 
     When the controller  4  determines that the resist roller stop timing has arrived (YES at step S 8 ), the controller  4  stops the resist roller  14  at step S 9 . 
     After the trailing edge of the sheet P has left the resist roller  14 , the sheet P is subjected to printing while being transferred by the conveyer belt  31  in the printer  3 . 
     Here, the leading edge Ef of the sheet P in the transfer direction does not overlap with the suction holes  41  and therefore the trailing edge Er also does not overlap with the suction holes  41 , as illustrated in  FIG. 6 . In other words, the trailing edge Er of the sheet P is located within the range A in which the suction holes  41  do not exist in the transfer direction of the conveyer belt  31 , as with the leading edge Ef. 
     Referring again to  FIG. 4 , the controller  4  determines, at step S 10  subsequent to step S 9 , whether or not printing and transfer of the sheet P in the printer  3  have finished. When the controller  4  determines that printing and transfer have not finished (NO at step S 10 ), the controller  4  repeats step S 10 . 
     When the controller  4  determines that printing and transfer have finished (YES at step S 10 ), the controller  4  stops the transfer unit  21  at step S 11 . Specifically, the controller  4  activates the drive roller  32 , as well as stopping the fan  39 . Accordingly, the series of operation comes to an end. 
     As described above, the suction holes  41  of the conveyer belt  31  in the inkjet printing machine  1  are arranged so that, when the leading edge of the sheet P in the transfer direction does not overlap with the suction holes  41 , the trailing edge of the sheet P also does not overlap with the suction holes  41 . The controller  4  thus controls the paper feeder  2  to feed a sheet at a timing when the leading edge Ef and the trailing edge Er of the sheet P in the transfer direction do not overlap with the suction holes  41 . 
     Accordingly, in the printer  3 , the sheet P is subjected to printing with ink discharged from the inkjet heads  22 , while being transferred in a state that the leading edge Ef and the trailing edge Er in the transfer direction do not overlap with the suction holes  41 . 
     When the ink is discharged from the inkjet head  22 , as illustrated in  FIG. 7 , a main droplet  51  of the ink flies and a fine ink mist  52  is generated. A part of the ink mist  52  is carried away by an airflow W which is caused by air suction toward the suction holes  41 . 
     Unlike the present embodiment, if the leading edge Ef of the sheet P overlaps with the suction holes  41 , as illustrated in  FIG. 8 , the ink mist  52  which is carried away by the airflow W tends to adhere to the front end portion of the sheet P. In addition, when the trailing edge Er of the sheet P overlaps with the suction holes  41 , the ink mist  52  which is carried away by the airflow W tends to adhere to the rear end portion of the sheet P. 
     In the inkjet printing machine  1  of the present embodiment, in contrast, the leading edge Ef of the sheet P does not overlap with the suction holes  41 , as shown in  FIG. 7 , and therefore the ink mist  52  is unlikely to adhere to the sheet P even when the ink mist  52  is carried away by the airflow W toward the suction holes  41 . Similarly, at the rear end side of the sheet P, the trailing edge Er of the sheet P does not overlap with the suction holes  41  and therefore the ink mist  52  is unlikely to adhere to the sheet P even when the ink mist  52  is carried away toward the suction holes  41  by the airflow W caused by air suction. Accordingly, the amount of the ink mist  52  which may adhere to the front end portion and the rear end portion of the sheet P can be reduced. As a result, the stain on the sheet P can be reduced. 
     In addition, in the inkjet printing machine  1 , the suction holes  41  of the conveyer belt  31  are arranged so that both edges in the sheet-width direction of the sheet P do not overlap with the suction holes  41 . Accordingly, it is possible to reduce the amount of the ink mist  52  which may adhere to the edge portion of the sheet P in the sheet-width direction, as with the front end portion and the rear end portion of the sheet P in the transfer direction. As a result, the stain on the sheet P can be further reduced. 
     In addition, in the inkjet printing machine  1 , the suction holes  41  in a region adjacent to an edge of the sheet P in the sheet-width direction are formed to be smaller than the other suction holes  41 . Accordingly, the amount of the ink mist  52  which may flow into the suction holes  41  in the region adjacent to the edge of the sheet P in the sheet-width direction can be reduced. It is therefore possible to reduce the amount of the ink mist  52  which may adhere to the edge of the sheet P in the sheet-width direction. As a result, the stain on the sheet P can be further reduced. 
     The present invention is not limited to the aforementioned embodiment as it is, and may be implemented by modifying the components thereof within a range that does not deviate from its scope. In addition, a variety of inventions can be made by combining as appropriate a plurality of components disclosed in the aforementioned embodiment. For example, some of the components may be deleted from the entirety of components described in the embodiment. 
     In addition, for example, each of the functions of the described embodiments may be implemented by one or more processing circuits. A processing circuit includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC) and conventional circuit components arranged to perform the recited functions. 
     The present application claims priority based on Japanese Patent Application No. 2014-241105 filed on Nov. 28, 2014, entire content of which is incorporated herein by reference. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, a plurality of suction holes of a conveyer belt is arranged so that, when the leading edge of sheet in the transfer direction does not overlap with the suction holes, the trailing edge of the sheet also does not overlap with the suction holes. A controller controls a paper feeder to feed the sheet at a timing when the leading edge and the trailing edge of the sheet in the transfer direction do not overlap with the suction holes. Accordingly, it is possible to reduce the amount of ink mist which may adhere to the front end portion and the rear end portion of the sheet in the transfer direction. As a result, stain on the sheet can be reduced. 
     In addition, the plurality of suction holes of the conveyer belt is arranged so that the edge of the sheet in a sheet-width direction perpendicular to the transfer direction does not overlap with the suction holes. Accordingly, it is possible to reduce the amount of ink mist which may adhere to the edge of the sheet in the sheet-width direction. As a result, stain on the sheet can be further reduced.