Patent Publication Number: US-11639065-B2

Title: Image formation apparatus and heating method for image formation apparatus

Description:
The entire disclosure of Japanese patent Application No. 2020-201126, filed on Dec. 3, 2020, is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technological Field 
     The present disclosure relates to an image formation apparatus and a heating method for the image formation apparatus. 
     Description of the Related art 
     Conventionally, there has been known an inkjet image formation apparatus (hereinafter, it is abbreviated as an “image formation apparatus”) that ejects ink from a plurality of nozzles provided in an inkjet head toward a paper conveyed by a conveyance device, to thereby form (record) an image on the paper (see, for example, WO 2013/165003). 
     In this type of image formation apparatus, after papers stacked on a sheet feed tray are separated one by one by a feeder board, the papers are transferred from the feeder board to a conveyance cylinder (for example, as illustrated in  FIG.  2    to be described later, a rotary conveyance body including a first conveyance cylinder and a second conveyance cylinder), and an image is formed on the papers by an inkjet head in the process of conveying the papers by the conveyance cylinder. 
     A paper is typically transferred from the feeder board to the conveyance cylinder in such a manner that the paper conveyed to a front end position of the feeder board is gripped by a claw part provided on the conveyance cylinder and the paper is drawn from the feeder board to the conveyance cylinder. 
       FIG.  1    is a view illustrating an example of the claw part provided on the conveyance cylinder. Note that the claw part illustrated in  FIG.  1    includes a plurality of grip claws provided at predetermined intervals along a paper width direction of the paper (that is, a direction orthogonal to a conveyance direction of the paper), and has a structure to grip the front end of the paper by the plurality of grip claws. 
     Incidentally, in this type of image formation apparatus, in order to enhance the wettability of ink on a paper when ink is discharged, a preheating mechanism is introduced in which the temperature of an outer peripheral surface of the conveyance cylinder is raised in advance to a predetermined temperature (for example, about 60° C.), and the temperature of the paper is raised to the predetermined temperature in the process of conveying the paper by the conveyance cylinder. 
     However, as a result of intensive studies by the inventors of the present application, it has become clear that due to this preheating mechanism, a large temperature difference occurs between the temperature of the paper being conveyed on the feeder board and the temperature of the outer peripheral surface of the conveyance cylinder, and due to this, when the paper P is transferred from a feeder board  12  to conveyance cylinders  21  and  22  (immediately after transfer and during conveyance thereafter), thermal expansion occurs in an area gripped by the claw part at the front end of the paper (typically, an area between respective grip claws of the claw part), and wrinkles occur. The wrinkles generated at the front end of the paper spread to a printing area of the paper, and induce landing deviation of the ink when the paper is conveyed to the position of the printing part (here, the position of the inkjet head). That is, such wrinkles cause deterioration in quality of an image formed on a paper. Further, when such wrinkles occur, a front end portion of the paper rises, and thus, due to this, the paper may collide with an ink head of the image formation apparatus, which may cause damage to the ink head. 
     Note that such wrinkles occur due to thermal expansion of the paper, and thus are likely to occur particularly in synthetic paper having a large thermal expansion coefficient in general. 
     SUMMARY 
     The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide an image formation apparatus and a heating method for the image formation apparatus capable of suppressing deterioration in image quality due to occurrence of wrinkles on paper during paper conveyance. 
     To achieve the abovementioned object, according to an aspect of the present invention, an image formation apparatus reflecting one aspect of the present invention comprises: a sheet feeder that conveys a paper fed from a sheet feed tray; a conveyance cylinder that includes a gripper that grips the paper, and receives the paper conveyed on the sheet feeder and conveys the paper to a position of a printing part in a state where the paper is gripped by the gripper; and a heater that is provided on an upstream side of the conveyance cylinder in a conveyance direction and heats the paper so as to satisfy a temperature condition of following Expression (1):
 
| T 1− T 2|/ T 1&lt;0.15   Expression (1)
 
where T1 is a temperature [° C.] of a paper end of the paper at the position of the printing part, and T2 is a temperature [° C.] of the paper end of the paper when the paper is transferred from the sheet feeder to the conveyance cylinder.
 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention: 
         FIG.  1    is a view illustrating an example of a claw part provided on a conveyance cylinder; 
         FIG.  2    is a diagram illustrating an overall configuration of an image formation apparatus according to an embodiment; 
         FIG.  3    is a schematic diagram illustrating a configuration of a head unit according to the embodiment; 
         FIG.  4    is a block diagram illustrating a configuration of a control system of the image formation apparatus according to the embodiment; 
         FIG.  5    is a plan view illustrating a configuration of a sheet feeder unit according to the embodiment; 
         FIG.  6    is a side view illustrating a configuration of a sheet feeder unit according to the embodiment; and 
         FIG.  7    is a flowchart illustrating an example of processing executed by a controller to control operation of a first heater in the image formation apparatus according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one or more preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, the scope of the invention is not limited to the disclosed embodiments. Note that in the present specification and the drawings, components having substantially the same function are denoted by the same reference numerals, and redundant description is omitted. 
     [Schematic Configuration of Inkjet Image Formation Apparatus] 
     Hereinafter, a schematic configuration of an image formation apparatus according to an embodiment of the present invention will be described with reference to  FIGS.  2  to  4   . 
       FIG.  2    is a diagram schematically illustrating an overall configuration of an image formation apparatus  1  according to the present embodiment. 
     The image formation apparatus  1  includes a sheet feeder unit  10 , an image former  20 , a sheet ejection unit  30 , and a controller  40  (see  FIG.  4   ). 
     Under the control of the controller  40 , the image formation apparatus  1  conveys a paper P stored in the sheet feeder unit  10  to the image former  20 , forms an image on the paper P in the image former  20 , and conveys the paper P on which the image is formed to the sheet ejection unit  30 . As the paper P on which an image is to be formed by the image formation apparatus  1 , any type of paper such as plain paper (paper produced using wood pulp as a main raw material) and synthetic paper (paper produced using synthetic resin as a main raw material) can be used. 
     The sheet feeder unit  10  includes a sheet feed tray  11  that stores the paper P, a feeder board  12  that conveys the paper P from the sheet feed tray  11  to the image former  20  (second conveyance cylinder  22 ), and a first heater  13  that heats a front end of the paper P before the paper P is transferred from the feeder board  12  to the second conveyance cylinder  22  of the image former  20 . Note that a detailed configuration of the sheet feeder unit  10  will be described later with reference to  FIGS.  5  and  6   . 
     The image former  20  includes a first conveyance cylinder  21 , a second conveyance cylinder  22 , a second heater  23   a,  a third heater  23   b,  a fourth heater  23   c,  a head unit  24 , a fixing unit  25 , a first temperature sensor  26   a,  a second temperature sensor  26   b,  and a delivery unit  28 . 
     The first conveyance cylinder  21  has a cylindrical shape, holds the paper P on its own outer peripheral surface (that is, a conveyance surface), and conveys the paper P (also referred to as a printing cylinder) to a position where an image is formed by the head unit  24  (corresponding to a “printing part” of the present invention). The first conveyance cylinder  21  includes a claw part  21   a  and a suction part (not illustrated) for holding the paper P on an outer peripheral surface thereof. The end of the paper P is pressed by the claw part  21   a,  and the paper P is sucked to the outer peripheral surface by the suction part to be held on the outer peripheral surface. The first conveyance cylinder  21  is connected to a motor (not illustrated) and rotates by an angle proportional to a rotation amount of the motor. Then, the first conveyance cylinder  21  rotates about a rotation shaft (cylindrical shaft) extending in an X direction (a direction perpendicular to the paper surface of  FIG.  2   ) to circulate, to thereby convey the paper P along a rotation direction of the first conveyance cylinder  21 . 
     The second conveyance cylinder  22  has a cylindrical shape, holds the paper P on its own outer peripheral surface (that is, the conveyance surface), and conveys the paper P (also referred to as a preheat cylinder). The second conveyance cylinder  22  is interposed between the feeder board  12  and the first conveyance cylinder  21 , receives the paper P from the feeder board  12  at a position where the second conveyance cylinder  22  faces the feeder board  12 , conveys the paper P to a position where the second conveyance cylinder  22  faces the first conveyance cylinder  21 , and then passes the paper P to the first conveyance cylinder  21 . The second conveyance cylinder  22  is configured such that, for example, when the first conveyance cylinder  21  rotates by one holding area (for example, 120°) of the paper P in conjunction with the rotation operation of the first conveyance cylinder  21  by a gear mechanism (not illustrated), the second conveyance cylinder  22  makes one rotation in an opposite direction. 
     Similarly to the first conveyance cylinder  21 , for example, the second conveyance cylinder  22  includes a claw part  22   a  and a suction part (not illustrated) for holding the paper P on the outer peripheral surface thereof. The claw part  22   a  (corresponding to a “gripper” of the present invention) is disposed on the outer peripheral surface (that is, the conveyance surface) of the second conveyance cylinder  22 , and grips the end (here, the front end) of the paper P conveyed to the front end position of the feeder board  12  to draw the paper P from the feeder board  12  onto the outer peripheral surface of the second conveyance cylinder  22 . Then, the end of the paper P is pressed by the claw part  22   a,  and the paper P is sucked to the outer peripheral surface by the suction part to be held on the outer peripheral surface. Note that, for example, as illustrated in  FIG.  1   , the claw part  22   a  includes a plurality of grip claws provided at predetermined intervals along the paper width direction of the paper P. 
     The second conveyance cylinder  22  is provided with, for example, a cam mechanism (not illustrated) that opens and closes the claw part  22   a  and controls the receiving operation and transfer operation of the paper P at the second conveyance cylinder  22 . When the claw part  22   a  reaches a position close to and facing the feeder board  12 , the cam mechanism changes the claw part  22   a  from an open state to a closed state, and causes the claw part  22   a  to perform an operation of receiving the paper P. Further, when the claw part  22   a  reaches a position close to and facing the claw part  21   a  of the first conveyance cylinder  21 , the cam mechanism changes the claw part  22   a  from the closed state to the open state, and causes the claw part  22   a  to perform an operation of transferring the paper P from the claw part  22   a  to the claw part  21   a  of the first conveyance cylinder  21 . 
     Note that a passing claw that supports transfer of the paper P from the feeder board  12  to the second conveyance cylinder  22  may be provided adjacent to a position where the second conveyance cylinder  22  and the feeder board  12  face each other. 
     Note that in the present embodiment, as an example of a conveyance cylinder that receives the paper P conveyed on the feeder board  12  and conveys the paper P to the print execution position, an aspect including the first conveyance cylinder  21  and the second conveyance cylinder  22  is illustrated. However, in the present invention, the configuration of the conveyance cylinder may be any configuration, and the conveyance cylinder may include only the first conveyance cylinder  21 . Hereinafter, when the first conveyance cylinder  21  and the second conveyance cylinder  22  are not distinguished from each other, they are also simply referred to as a “conveyance cylinder  21 ,  22 ”. 
     The second heater  23   a  is a heater that heats the paper P conveyed by the first conveyance cylinder  21  so that the paper P has a temperature within a predetermined temperature range. The second heater  23   a  is constituted by, for example, an infrared heater, and heats the paper P conveyed while being held on the outer peripheral surface of the first conveyance cylinder  21  from a front surface side thereof The second heater  23   a  is provided to face the outer peripheral surface of the first conveyance cylinder  21  at a position on a downstream side in the conveyance direction of a position facing the second conveyance cylinder  22  and on an upstream side in the conveyance direction of a position facing the head unit  24  in the outer peripheral surface of the first conveyance cylinder  21 . 
     The third heater  23   b  is a heater that heats the outer peripheral surface (that is, the conveyance surface) of the first conveyance cylinder  21 . Similarly to the second heater  23   a,  for example, the third heater  23   b  is constituted by an infrared heater, and irradiates the outer peripheral surface of the first conveyance cylinder  21  with infrared rays to heat the outer peripheral surface of the first conveyance cylinder  21 . The third heater  23   b  is provided to face the outer peripheral surface of the first conveyance cylinder  21  at a position on a downstream side in the conveyance direction of the position facing the delivery unit  28  and on an upstream side in the conveyance direction of the position facing the second conveyance cylinder  22  in the outer peripheral surface of the first conveyance cylinder  21 . 
     In the image formation apparatus  1  according to the present embodiment, the second heater  23   a  directly heats the paper P before the ink discharged from the head unit  24  lands, and the third heater  23   b  raises the temperature of a paper conveyance area (that is, an area of conveyance from paper receiving position to a print execution position) of the outer peripheral surface of the first conveyance cylinder  21  to a predetermined temperature, to thereby maintain the paper P before and after the ink lands at an appropriate temperature. 
     Note that the operations of the second heater  23   a  and the third heater  23   b  are controlled by the controller  40  (see  FIG.  4   ). The second heater  23   a  is controlled, for example, so that the temperature of the paper P is within a predetermined temperature range (for example, 45° C. to 60° C.) at the time of ink landing, and the third heater  23   b  is controlled, for example, so that the temperature of the outer peripheral surface of the first conveyance cylinder  21  is within a predetermined temperature range (for example, 50° C. to 65° C.). For example, the controller  40  controls the second heater  23   a  and the third heater  23   b  based on temperature information indicated by the first temperature sensor  26   a  and the second temperature sensor  26   b.    
     The fourth heater  23   c  is a heater that heats the outer peripheral surface (that is, the conveyance surface) of the second conveyance cylinder  22 . The fourth heater  23   c  is constituted by, for example, an infrared heater, and irradiates the outer peripheral surface of the second conveyance cylinder  22  with infrared rays to heat the outer peripheral surface of the second conveyance cylinder  22 . The second conveyance cylinder  22  preliminarily heats the paper P in the process of conveying the paper P while holding the paper P on its own outer peripheral surface. 
     The operation of the fourth heater  23   c  is controlled by the controller  40  (see  FIG.  4   ), and the fourth heater  23   c  is controlled so that the temperature of the outer peripheral surface of the second conveyance cylinder  22  falls within a predetermined temperature range (for example, 50° C. to 65° C.). 
     Note that from the viewpoint of suppressing occurrence of wrinkles in the paper P due to thermal expansion of the paper P when the paper P is transferred from the second conveyance cylinder  22  to the first conveyance cylinder  21 , the temperature difference between the temperature of the outer peripheral surface of the second conveyance cylinder  22  and the temperature of the outer peripheral surface of the first conveyance cylinder  21  is preferably small, and is typically set to substantially the same temperature. However, from the viewpoint of gradually increasing the temperature of the paper P, the temperature of the outer peripheral surface of the first conveyance cylinder  21  may be set to be higher than the temperature of the outer peripheral surface of the second conveyance cylinder  22 . Conversely, from the viewpoint of increasing the temperature of the paper P from an early stage, the temperature of the outer peripheral surface of the second conveyance cylinder  22  may be set to be higher than the temperature of the outer peripheral surface of the first conveyance cylinder  21 . 
     The head unit  24  (hereinafter, it is also referred to as a printing part  24 ) is disposed facing a predetermined position of the outer peripheral surface of the first conveyance cylinder  21  in a state where its own ink ejection surface and the outer peripheral surface of the first conveyance cylinder  21  are separated by a predetermined distance. Then, the head unit  24  ejects ink onto the paper P held on the outer peripheral surface of the first conveyance cylinder  21  to form an image at an appropriate timing according to the rotation of the first conveyance cylinder  21  holding the paper P. 
     In the image formation apparatus  1  according to the present embodiment, four head units  24  respectively corresponding to inks of four colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged at predetermined intervals in the order of Y, M, C, and K colors from the upstream side in the conveyance direction of the paper P. 
       FIG.  3    is a schematic diagram illustrating a configuration of the head unit  24  according to the present embodiment. Here, a surface of the head unit  24  facing the outer peripheral surface of the first conveyance cylinder  21  is illustrated. 
     The head unit  24  includes four inkjet heads  242  attached to an attachment member  244 . Each of the inkjet heads  242  is provided with a plurality of image formation elements (recording elements) each including a pressure chamber that stores ink, a piezoelectric element provided on a wall surface of the pressure chamber, and a nozzle  243 . In this image formation element, when a drive signal for operating the piezoelectric element to deform is input, the pressure chamber is deformed by the deformation of the piezoelectric element, the pressure in the pressure chamber changes, and ink is discharged from a nozzle communicating with the pressure chamber. 
     The four inkjet heads  242  are arranged in a staggered pattern such that arrangement ranges of nozzle rows in the X direction are connected without any discontinuity. The arrangement ranges of the nozzles  243  included in the head unit  24  in the X direction cover the width in the X direction of an area where an image is formed in the paper P conveyed by the first conveyance cylinder  21 , and the position of the head unit  24  is fixed with respect to the rotation shaft of the first conveyance cylinder  21  when the image is formed. That is, the head unit  24  includes a line head capable of ejecting ink over an image formable width in the X direction with respect to the paper P. 
     The inkjet head  242  includes an ink heating unit (not illustrated) that heats the ink stored in the inkjet head  242 , and ejects the heated ink in a sol state. When this sol-state ink is discharged onto the paper P, ink droplets land on the paper P and then are naturally cooled, so that the ink quickly turns into a gel state and solidifies on the paper P. 
     The fixing unit  25  has a light emitting unit disposed over the width of the first conveyance cylinder  21  in the X direction, and irradiates the paper P placed on the first conveyance cylinder  21  with energy rays such as ultraviolet rays from the light emitting unit to cure and fix the ink (gel ink) discharged on the paper P. The light emitting unit of the fixing unit  25  is arranged to face the outer peripheral surface of the first conveyance cylinder  21  between the arrangement position of the head unit  24  and the arrangement position of a transfer cylinder  281  of the delivery unit  28  in the conveyance direction. 
     The first temperature sensor  26   a  detects the temperature of the paper conveyance area of the outer peripheral surface of the first conveyance cylinder  21 . The first temperature sensor  26   a  is disposed to face the outer peripheral surface of the first conveyance cylinder  21  at a position on a downstream side in the conveyance direction of the second heater  23   a  and on an upstream side in the conveyance direction of the head unit  24 . As the first temperature sensor  26   a,  for example, a non-contact type temperature sensor such as a thermopile is used. 
     The second temperature sensor  26   b  detects the temperature of the paper P after the ink is applied by the head unit  24 . The second temperature sensor  26   b  is disposed to face the outer peripheral surface of the first conveyance cylinder  21  at a position on a downstream side in the conveyance direction of the head unit  24  and on an upstream side in the conveyance direction of the fixing unit  25 . As the second temperature sensor  26   b,  for example, a non-contact type temperature sensor such as a thermopile is used. 
     The delivery unit  28  includes a cylindrical transfer cylinder  281  that transfers the paper P from the first conveyance cylinder  21  to the belt loop  282 , and a belt loop  282  having a ring-shaped belt whose inside is supported by two rollers, and the paper P transferred from the first conveyance cylinder  21  onto the belt loop  282  by the transfer cylinder  281  is conveyed and sent to the sheet ejection unit  30  by the belt loop  282 . 
     The sheet ejection unit  30  includes a plate-like sheet ejection tray  31  on which the paper P fed from the image former  20  by the delivery unit  28  is placed. 
       FIG.  4    is a block diagram illustrating a configuration of a control system of the image formation apparatus  1  according to the present embodiment. 
     The control system of the image formation apparatus  1  includes the controller  40 , a head drive unit  241 , the fixing unit  25 , a conveyance drive unit  51 , an operation display unit  52 , an input-output interface  53 , a heater drive unit  54 , and the like. 
     The controller  40  is, for example, a microcomputer including a central processing unit (CPU)  41 , a random access memory (RAM)  42 , a read only memory (ROM)  43 , and a storage unit  44 . 
     The CPU  41  reads various control programs and setting data stored in the ROM  43 , stores the programs in the RAM  42 , and executes the programs to perform various arithmetic processing. Further, the CPU  41  integrally controls the entire operation of the image formation apparatus  1 . The RAM  42  provides the CPU  41  with a working memory space and stores temporary data. The RAM  42  may include a nonvolatile memory. The ROM  43  stores various control programs executed by the CPU  41 , setting data, and the like. Note that instead of the ROM  43 , a rewritable nonvolatile memory such as an electrically erasable programmable read-only memory (EEPROM) or a flash memory may be used. 
     The storage unit  44  stores a print job (image forming command) input from an external device  2  via the input-output interface  53 , image data related to the print job, and the like. Among these, the print job includes information (for example, the size and thickness of the paper P) related to the type of paper P on which an image is formed, in addition to information specifying image data related to an image to be formed. As the storage unit  44 , for example, a hard disk drive (HDD) is used, and a dynamic random access memory (DRAM) or the like may be used in combination. 
     The conveyance drive unit  51  supplies a drive signal to the motor of the first conveyance cylinder  21  based on a control signal supplied from the controller  40  to rotate the first conveyance cylinder  21  at a predetermined speed and timing In addition, the conveyance drive unit  51  supplies a drive signal to motors for operating the feeder board  12 , the second conveyance cylinder  22 , and the delivery unit  28  based on a control signal supplied from the controller  40  to supply the paper P to the first conveyance cylinder  21  and discharge the paper P from the first conveyance cylinder  21 . 
     The operation display unit  52  includes a display device such as a liquid crystal display or an organic EL display, and an input device such as an operation key or a touch panel disposed to overlap a screen of the display device. The operation display unit  52  displays various types of information on the display device, converts a user&#39;s input operation on the input device into an operation signal, and outputs the operation signal to the controller  40 . 
     The input-output interface  53  mediates transmission and reception of data between the external device  2  and the controller  40 . The input-output interface  53  includes, for example, any one of or a combination of various serial interfaces and various parallel interfaces. Note that the external device  2  is, for example, a personal computer, and supplies a print job, image data, and the like to the controller  40  via the input-output interface  53 . 
     The heater drive unit  54  is a drive circuit that drives the first heater  13 , second heater  23   a,  third heater  23   b,  and fourth heater  23   c.  The heater drive unit  54  is capable of independently controlling operation of each of the first heater  13 , the second heater  23   a,  the third heater  23   b,  and the fourth heater  23   c  based on a control signal supplied from the controller  40 . 
     The head drive unit  241  supplies a drive signal for operating the piezoelectric element to deform according to the image data to the image formation element of the inkjet head  242  at an appropriate timing to cause the nozzles  243  of the inkjet head  242  to eject ink of an amount corresponding to the pixel value of the image data. 
     [Detailed Configuration of Sheet Feeder Unit  10 ] 
       FIG.  5    is a plan view illustrating a configuration of the sheet feeder unit  10  according to the present embodiment, and  FIG.  6    is a side view illustrating a configuration of the sheet feeder unit  10  according to the present embodiment. 
     The feeder board  12  (corresponding to a “sheet feeder” of the present invention) is continuously installed on the sheet feed tray  11 , and the paper P stacked on the sheet feed tray  11  is separated into one or a plurality of papers by a sheet feed mechanism (for example, a mechanism that attracts and conveys the paper P on an uppermost stage of the bunch of papers stacked on the sheet feed tray  11 ) (not illustrated) and fed to the feeder board  12 . 
     The feeder board  12  includes a sheet feed belt  12   a  that conveys the paper P fed from the sheet feed tray  11  to the feeder board  12  in the paper conveyance direction, a sheet pressing roller  12   b  that presses the paper P conveyed on the sheet feed belt  12   a  from above, a positioner  12   c  as a register that positions the paper P conveyed on the feeder board  12  at a position (that is, the front end position of the feeder board  12 ) where the paper P is transferred from the feeder board  12  to the second conveyance cylinder  22 , and the like. 
     For example, the feeder board  12  is configured to convey the paper P fed from the sheet feed tray  11  by a stream feeder method. In the stream feeder method, the papers P are fed from the sheet feed tray  11  to the feeder board  12  in a state where a plurality of papers P is stacked while every one of the papers P is shifted by about 20 cm. 
     Here, the positioner  12   c  is, for example, a front stopper provided at the front end position of the feeder board  12 . That is, the paper P fed from the sheet feed tray  11  to the feeder board  12  is conveyed by the sheet feed belt  12   a  and collides with the positioner  12   c,  so that the paper P is stopped and positioned at the front end position of the feeder board  12 . Note that the surface of the positioner  12   c  on the side colliding with the paper P is an abutting surface extending in a direction orthogonal to the paper conveyance direction, and the paper P colliding with the positioner  12   c  is positioned such that the front end of the paper P is parallel to the direction orthogonal to the paper conveyance direction. 
     The paper P positioned by colliding with the positioner  12   c  is then gripped by the claw part  22   a  of the second conveyance cylinder  22  and transferred from the feeder board  12  to the second conveyance cylinder  22 . 
     For example, the positioner  12   c  is configured to change between a tilted state and an upright state with respect to the conveying surface of the feeder board  12  as indicated by an arrow in  FIG.  6    according to a rotational position of the second conveyance cylinder  22 . More specifically, the positioner  12   c  is in the upright state when the claw part  22   a  of the second conveyance cylinder  22  has not reached the front end position of the feeder board  12 , and is changed to the tilted state when the claw part  22   a  of the second conveyance cylinder  22  has reached the front end position of the feeder board  12 . At this time, the front end of the paper P positioned at the front end position of the feeder board  12  is held by the claw part  22   a,  and the paper P is drawn from the feeder board  12  onto the outer peripheral surface of the second conveyance cylinder  22  and held on the outer peripheral surface of the second conveyance cylinder  22  as the second conveyance cylinder  22  rotates. Then, the paper P is conveyed along the rotation direction of the second conveyance cylinder  22  in a state of being held on the outer peripheral surface of the second conveyance cylinder  22 . 
     Note that the state of the positioner  12   c  is changed by, for example, a cam mechanism (not illustrated) that operates in conjunction with the rotational operation of the second conveyance cylinder  22 , or a drive motor (not illustrated) that operates the positioner  12   c  in accordance with the rotational position of the second conveyance cylinder  22 . 
     The first heater  13  heats the paper P such that the temperature of the front end of the paper P falls within a predetermined temperature range before the paper P is transferred from the feeder board  12  to the conveyance cylinders  21  and  22 . That is, the first heater  13  preheats the front end of the paper P before the front end of the paper P comes into contact with the outer peripheral surfaces of the conveyance cylinders  21  and  22  (here, the second conveyance cylinder  22 ), and suppresses occurrence of wrinkles at the front end of the paper P when the paper P is transferred from the feeder board  12  to the conveyance cylinders  21  and  22  (that is, immediately after transfer and during conveyance thereafter). 
     Typically, the wrinkles generated at the front end of the paper P rely on a phenomenon in which the temperature of the front end of the paper P rises to near the temperature of the outer peripheral surfaces of the conveyance cylinders  21  and  22  in a state where the front end of the paper P is pressed by the grip claw of the claw part  22   a,  and thereby the area between respective grip claws of the claw part  22   a  at the front end of the paper P is thermally expanded to be wrinkled. That is, the wrinkles at the front end of the paper P occur due to a rapid rise in temperature of the front end of the paper P when the paper P is transferred from the feeder board  12  to the conveyance cylinder  21  or  22 , and the wrinkles further grows and spreads until the paper P is conveyed to the position of the printing part  24  by the conveyance cylinder  21  or  22 . 
     Therefore, in the image formation apparatus  1  according to the present embodiment, by preheating the front end of the paper P using the first heater  13 , when the paper P is transferred from the feeder board  12  to the conveyance cylinders  21  and  22  (that is, immediately after transfer and during conveyance thereafter), excessive thermal expansion of the area between the respective grip claws of the claw part  22   a  at the front end of the paper P is suppressed. 
     From such a viewpoint, for example, the first heater  13  heats the paper P so as to satisfy the temperature condition of the following Expression (1).
 
| T 1− T 2|/ T 1&lt;0.15   Expression (1)
 
where T1 is a temperature [° C.] of the front end of the paper P at the position of the printing part 24, and T2 is a temperature [° C.] of the front end of the paper P when the paper P is transferred from the feeder board  12  to the conveyance cylinder  21  or  22 . Thus, it is possible to suppress thermal expansion of the paper P that occurs when the paper P is transferred from the feeder board  12  to the conveyance cylinders  21  and  22  (that is, immediately after transfer and during conveyance thereafter), so that it is possible to suppress wrinkles that occur at the front end of the paper P. Note that the temperature of the front end of the paper P at the position of the printing part  24  may be defined by, for example, the sensor value of the first temperature sensor  26   a  (and/or the sensor value of the second temperature sensor  26   b ), or may be defined on the basis of the temperature of the outer peripheral surfaces of the conveyance cylinders  21  and  22 .
 
     At this time, more preferably, for example, the first heater  13  heats the paper P so as to satisfy the temperature condition of the following Expression (2).
 
( T 1− T 2)/ T 1&lt;0   Expression (2)
 
where T1 is a temperature [° C.] of the front end of the paper P at the position of the printing part 24, and T2 is a temperature [° C.] of the front end of the paper P when the paper P is transferred from the feeder board  12  to the conveyance cylinder  21  or  22 .
 
     Further, more preferably, when the paper P is transferred from the feeder board  12  to the conveyance cylinder  21  or  22 , the first heater  13  heats the front end of the paper P in advance so that the temperature of the front end of the paper P becomes equal to or higher than the temperature of the paper conveyance area of the outer peripheral surface of the conveyance cylinder  21  or  22 . 
     Note that, here, it has been assumed that the temperature of the paper conveyance area of the outer peripheral surface of the first conveyance cylinder  21  and the temperature of the paper conveyance area of the outer peripheral surface of the second conveyance cylinder  22  are the same. However, in a case where the temperature of the paper conveyance area of the outer peripheral surface of the first conveyance cylinder  21  and the temperature of the paper conveyance area of the outer peripheral surface of the second conveyance cylinder  22  are different, the above-described temperature condition is typically set on the basis of the temperature of the paper conveyance area of the outer peripheral surface of the second conveyance cylinder  22 . 
     For example, as illustrated in  FIGS.  5  and  6   , the first heater  13  is disposed at a position adjacent to the feeder board  12  and facing the positioner  12   c,  and is configured to heat the front end of the paper P when the paper P is positioned at the front end position of the feeder board  12 . That is, the paper P is heated by the first heater  13  at the timing when positioned by the positioner  12   c,  and during the waiting time until the paper P is transferred from the feeder board  12  to the conveyance cylinder  21  or  22 , the front end of the paper P is heated at least until the temperature difference between the temperature of the front end of the paper P and the temperature of the paper conveyance area of the outer peripheral surface of the conveyance cylinder  21  or  22  becomes substantially 7.5° C. or less. Note that, with such a configuration, the front end of the paper P can be efficiently heated in a short time, and a decrease in the temperature of the front end of the paper P from when the first heater  13  is subjected to the heat treatment to when the paper P is transferred to the conveyance cylinders  21  and  22  is also suppressed. 
     Note that in the stream feeder method, the feeder board  12  conveys a plurality of papers P in an overlapping state on the sheet feed tray  11  side, and separates the papers P one by one at the front end position (that is, the position where the paper P is transferred to the conveyance cylinders  21  and  22 ) side. Therefore, by disposing the first heater  13  at a position facing the positioner  12   c,  the first heater  13  is capable of separately heating the front end of each paper P. 
     As the first heater  13 , for example, an air heating type heater that heats the paper P by blowing heated air is preferably used. The air heating type heater is useful in that local heating is possible and a high heating rate can be secured. Furthermore, since the temperature of the entire paper P is not unnecessarily raised, the occurrence of wrinkles can be suppressed with the minimum amount of heat. However, as the first heater  13 , an infrared heater that heats the paper P by lamp irradiation, an electric resistance heater provided on the feeder board  12 , or the like may be used. 
     Further, the first heater  13  preferably selectively heats the non-printing area adjacent to the front end of the paper P. This makes it possible to suppress the occurrence of temperature unevenness in the printing area of the paper P. 
     The operation of the first heater  13  is controlled by the controller  40 , and is controlled to execute the heating operation, for example, at the timing when the paper P is conveyed on the feeder board  12 . 
     However, the operation of the first heater  13  is preferably controlled to be in an operating state in a case where the type of the paper P is synthetic paper, and to be in a non-operating state in a case where the type of the paper P is non-synthetic paper (for example, plain paper). This is because the thermal expansion coefficient is small depending on the type of the paper P, and the wrinkle of the paper P does not cause a problem even when the paper P is transferred from the feeder board  12  to the conveyance cylinders  21  and  22  (that is, immediately after transfer and during conveyance thereafter). Specifically, since the wrinkle of the paper P is likely to occur to such an extent as to cause ink landing deviation particularly only when the type of the paper P is the synthetic paper, the first heater  13  may be set to the operating state only when the paper P as a print target is the synthetic paper from the viewpoint of suppressing energy consumption. 
       FIG.  7    is a flowchart illustrating an example of processing executed by the controller  40  to control the operation of the first heater  13  in the image formation apparatus  1  according to the present embodiment. The flowchart illustrated in  FIG.  7    is, for example, processing repeatedly executed by the controller  40  at predetermined intervals (for example, every 100 msec) according to a computer program. 
     In step S 1 , the controller  40  determines whether or not there is a print execution command Then, in a case where there is a print execution command (S 1 : YES), the controller  40  advances the processing to step S 2 , and in a case where there is no print execution command (S 1 : NO), the controller ends the processing of the flowchart of  FIG.  7    without particularly performing the processing. 
     In step S 2 , the controller  40  determines whether or not the paper P as a print target is synthetic paper. Then, in a case where the paper P as a print target includes the synthetic paper (S 2 : YES), the controller  40  advances the processing to step S 3 , and in a case where the paper P as a print target is not the synthetic paper (S 2 : NO), the controller  40  ends the processing of the flowchart of  FIG.  7    without performing any particular processing. 
     In step S 3 , the controller  40  turns on the operation of the first heater  13 . Thus, the first heater  13  enters the operating state, and operates to perform a heat treatment on the front end of the paper P conveyed from the feeder board  12  and positioned by the positioner  12   c.    
     By repeatedly executing such a series of processes, the controller  40  switches on and off of the operation of the first heater  13  according to the type of the paper P. 
     [Effects] 
     As described above, the image formation apparatus  1  according to the present embodiment includes: 
     a sheet feeder (for example, the feeder board  12 ) that conveys a paper fed from a sheet feed tray (for example, the sheet feed tray  11 ); 
     a conveyance cylinder (for example, the conveyance cylinders  21  and  22 ) that includes a gripper (for example, the claw part  22   a ) that grips the paper, and receives the paper conveyed by the sheet feeder and conveys the paper to a position of a printing part in a state where the paper is gripped by the gripper; and 
     a heater (for example, first heater  13 ) that is provided on an upstream side of the conveyance cylinder in a conveyance direction and heats the paper so as to satisfy a temperature condition of the following Expression (3) before the paper is transferred from the sheet feeder to the conveyance cylinder.
 
 |T 1− T 2|/ T 1&lt;0.15   Expression (3)
 
where T1 is a temperature [° C.] of a paper end of the paper at the position of the printing part, and T2 is a temperature [° C.] of the paper end of the paper when the paper is transferred from the sheet feeder to the conveyance cylinder.
 
     Therefore, with the image formation apparatus  1  according to the present embodiment, it is possible to suppress deterioration in image quality due to occurrence of wrinkles on a paper during paper conveyance. 
     Other Embodiments 
     The present invention is not limited to the above embodiment, and various modifications are conceivable. 
     For example, in the embodiment described above, as an example of the conveyance cylinder that receives the paper P conveyed on the feeder board  12  and conveys the paper P to the print execution position, an aspect including the first conveyance cylinder  21  and the second conveyance cylinder  22  has been described. However, in the present invention, the configuration of the conveyance cylinder may be any configuration, and the conveyance cylinder may include only the first conveyance cylinder  21 . Note that in this case, the first heater  13  is configured to heat the paper P so as to satisfy a temperature condition similar to the above Expressions (1) and (2) on the basis of the temperature of the front end of the paper P when the paper P is transferred from the feeder board  12  to the first conveyance cylinder  21  and the temperature in the paper conveyance area of the outer peripheral surface of the first conveyance cylinder  21 . 
     Further, in the above embodiment, as an example of the claw part  22   a,  an aspect in which the claw part includes a plurality of grip claws provided side by side along the paper width direction of the paper P has been described. However, in the present invention, the configuration of the claw part  22   a  may be any configuration, and for example, the claw part  22   a  may include a plurality of grip claws provided side by side along the conveyance direction of the paper P. Note that in a case where the claw part  22   a  includes a plurality of grip claws provided side by side along the conveyance direction of the paper P, the above-described wrinkle caused by thermal expansion mainly occurs at a lateral end of the paper P gripped by the plurality of grip claws. Therefore, in such a case, the first heater  13  is preferably configured to heat the lateral end of the paper P. 
     Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims The technology described in the claims includes various modifications and changes of the specific examples exemplified above. 
     INDUSTRIAL APPLICABILITY 
     With the image formation apparatus of the present invention, it is possible to suppress deterioration in image quality due to occurrence of a wrinkle on a paper during paper conveyance. 
     Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims.