Patent Publication Number: US-9895880-B2

Title: Method for adjusting recording head, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2016-035841, filed on Feb. 26, 2016. The above application is hereby expressly incorporated by reference, in its entirety, into the present application. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a method for adjusting a recording head, and an image forming apparatus, and more particularly to a technique of adjusting discharge timing of an adjacent head module in a recording head formed by joining a plurality of head modules each of which is provided with a plurality of nozzles for discharging droplets. 
     Description of the Related Art 
     There is known a form using a line head formed by joining a plurality of head modules, as a recording head of an ink jet recorder as a form of an image forming apparatus. Japanese Patent Application Laid-Open No. 2014-136319 (Patent Literature 1) discloses a method of calculating a shift amount of an initial recording position in a Y-direction between a first head module and a second head module adjacent to each other. The Y-direction is a direction parallel to a paper sheet feeding direction. 
     In Patent Literature 1, a plurality of test patterns each with a different shift amount is recorded while a shift amount of a recording position in the Y-direction between the first head module and the second head module is changed, and concentration of a portion recorded by a recording element in a complementary region of the first head module and the second head module is acquired from readout data on the test patterns, and then a shift amount of an initial recording position in the Y-direction between the first head module and the second head module is calculated from a relationship between a shift amount and concentration. The “first head module” and the “second head module” in Patent Literature 1 are terms corresponding to a “first head module” and a “second head module” of the present specification, respectively. 
     Japanese Patent Application Laid-Open No. 2004-268452 (Patent Literature 2) describes a technique in which a shift amount of a printed letter between unit recording heads and that between recording heads in a paper sheet feeding direction is detected by reading an image for alignment adjustment to control ink injection timing so that a shift amount of a printed letter decreases. The “unit recording head” in Patent Literature 2 is a term corresponding to the “head module” of the present specification. The “shift amount of a printed letter” in Patent Literature 2 is a term corresponding to a “recording shift amount” in the present specification. The “ink injection timing” in Patent Literature 2 is a term corresponding to “discharge timing” of the present specification. 
     In addition, Japanese Patent Application Laid-Open No. 2011-168023 (Patent Literature 3) describes a technique in which drive timing is adjusted by outputting a predetermined test pattern to adjust a relative deposit position error being an amount of a level difference between sub heads by using an external reading device in a recording head formed by joining two or more sub heads. The “sub head” in Patent Literature 3 is a term corresponding to the “head module” of the present specification. The “relative deposit position error” in Patent Literature 3 is a term corresponding to the “recording shift amount” in the present specification. The “drive timing” in Patent Literature 3 is a term corresponding to the “discharge timing” of the present specification. 
     SUMMARY OF THE INVENTION 
     Conventional methods shown in Patent Literatures 1 to 3 are configured to adjust discharge timing of each of head modules so that a shift, in a Y-direction, of a deposition position of a droplet discharged from each of the head modules becomes minimum, in a complementary region that is a joined portion between the head modules adjacent to each other. A term complementary region may be understood by substituting an “overlapping region” for the term. An “overlapping portion between sub heads” in Patent Literature 2 is a term corresponding to the “complementary region”. 
     Unfortunately, any of the methods shown in Patent Literatures 1 to 3 is not in consideration of a shift of a deposition position in a non-complementary region, the shift occurring by influence of nozzle arrangement of a two-dimensional matrix in a head module. The non-complementary region is a region other than the complementary region in the nozzle array of the head module. The term “non-complementary region” can be understood by substituting “non-overlapping region” for the term. 
     In a case of a recording head including a plurality of nozzles arranged in a two-dimensional matrix shape, a difference in deposition timing in a paper sheet feeding direction may occur even in a non-complementary region in the same head module due to a difference between a paper sheet feeding speed and a discharge cycle, or a difference in a throw distance for each of nozzle arrays in a nozzle face, the nozzle arrays being different in a Y-direction position, because positions of respective nozzles are away from each other in a paper sheet feeding direction. The throw distance means a distance from a nozzle to a paper sheet. 
     Japanese Patent Application Laid-Open No. 2012-76301 (Patent Literature 4) shows a problem in which when a droplet is discharged on a recording medium that is fed while supported on a curved face such as a drum from a liquid discharge head including a nozzle array of a two-dimensional matrix, a shift of a deposition position occurs in a paper sheet feeding direction to deteriorate linearity of a linear image (refer to FIG. 10 of Patent Literature 4). 
     For this kind of problem, adjusting timing of discharge for each of nozzle arrays aligned at different positions in a paper sheet feeding direction enables a shift of a deposition position to be corrected. However, there is a problem in which a complex control system is required to control discharge timing for each of the nozzle arrays different in position in a paper sheet feeding direction, thereby increasing cost, or in which it takes long time to adjust discharge timing for each of the nozzle arrays. 
     As another method of adjusting discharge timing of nozzle arrays aligned at different positions in the paper sheet feeding direction, adjusting a discharge cycle of a recording head enables difference in deposition timing to be reduced to a minimum. In a case of an image forming apparatus with structure in which a plurality of line heads provided for respective ink colors is arranged in a row, such as a device form that forms a color image by combining inks of a plurality of colors such as cyan, magenta, yellow, and black, a discharge cycle needs to be identical in each line head because a discharge cycle different for each of the colors varies image length for each of the colors. 
     Under constraints where a discharge cycle of each of a plurality of line heads is to be identical, if deposition timing is different for each of the line heads due to an attachment error of the line heads, for example, deposition timing of all of the line heads cannot be optimized. Specifically, as an example of an attachment error of the line heads, it is conceived that an inclination of the line head with respect to a paper sheet feeding direction caused by turning in a θx-direction causes a throw distance on a near side in a paper sheet feeding direction and that on a far side therein to be different from each other, for example. The turning in the θx-direction indicates turning around a rotation shaft parallel to an X-direction. The X-direction indicates a paper sheet width direction orthogonal to the Y-direction. 
     In a state where difference in deposition timing occurs in a non-overlapping region of the line head as described above, if discharge timing between the head modules is adjusted to a state where a shift of a deposition position becomes a minimum in a complementary region between head modules adjacent to each other, as described in the methods disclosed in Patent Literatures 1 to 3, a recording shift amount is different between the complementary region where a recording shift amount is minimized due to effect of the adjustment and a non-complementary region where the effect of the adjustment is not reflected, whereby uneven concentration corresponding to the complementary region and the non-complementary region tends to easily occur. 
     In addition, if discharge timing is adjusted between head modules adjacent to each other so that a shift of a deposition position becomes a minimum in a complementary region while a shift of a deposition position in the Y-direction occurs at a paper feeding side nozzle and a paper ejection side nozzle in a non-complementary region in a nozzle array of the head modules, discharge timing in the non-complementary region other than the complementary region varies between the head modules adjacent to each other. 
     As a result, in a line head formed by arranging a plurality of head modules in a row, difference in discharge timing between each of the head modules is accumulated so that discharge timing at head modules at opposite ends becomes greatly different from each other, thereby causing a problem in which squareness of an image varies. 
     The squareness of an image is one of indexes indicating drawing performance when a straight line in a direction parallel to the X-direction is recorded. While it is desirable that ideally a straight line parallel to the X-direction orthogonal to the Y-direction can be recorded, a straight line recorded actually is not a straight line parallel to the X-direction, and thus squareness of the straight line with respect to the Y-direction may vary, or linearity may deteriorate. To achieve favorable recording, it is desirable to eliminate deviation of squareness of an image as far as possible. 
     The present invention is made in light of the above-mentioned circumstances, and an object thereof is to provide a method for adjusting a recording head, and an image forming apparatus, capable of solving at least one of the plurality of problems described above and achieving favorable recording by reducing at least one of occurrence of uneven concentration and deviation of image squareness. 
     A method for adjusting a recording head of a first aspect according to a viewpoint of the present disclosure is a method for adjusting discharge timing of a plurality of head modules in the recording head formed by joining the plurality of head modules each of which has a nozzle array in which a plurality of nozzles for discharging droplets are arranged at different positions in a first direction, wherein the plurality of head modules are joined in a second direction intersecting with the first direction, the recording head including a complementary region where a nozzle belonging to one of the head modules adjacent to each other in the second direction and a nozzle belonging to the other of the head modules complement each other to record a dot row aligned in the second direction. The method includes: a first measurement step of measuring a complementary region recording shift amount that is a recording shift amount in the first direction in the complementary region in a joined portion between a first head module and a second head module that are the head modules adjacent to each other, a second measurement step of measuring a first non-complementary region recording shift amount that is a recording shift amount in the first direction in a non-complementary region other than the complementary region in a nozzle array in the first head module, and a second non-complementary region recording shift amount that is a recording shift amount in the first direction in a non-complementary region other than the complementary region in a nozzle array in the second head module, and a timing adjustment step of adjusting discharge timing of at least one of the first head module and the second head module according to the complementary region recording shift amount measured in the first measurement step, and the first non-complementary region recording shift amount and the second non-complementary region recording shift amount, measured in the second measurement step, wherein adjustment is performed in the timing adjustment step so that the complementary region recording shift amount after being adjusted becomes a value between the first non-complementary region recording shift amount and the second non-complementary region recording shift amount. 
     The value between the first non-complementary region recording shift amount and the second non-complementary region recording shift amount is a value equal to the first non-complementary region recording shift amount and the second non-complementary region recording shift amount when the first non-complementary region recording shift amount and the second non-complementary region recording shift amount are the same value. In addition, when the first non-complementary region recording shift amount and the second non-complementary region recording shift amount are different values, the value between the first non-complementary region recording shift amount and the second non-complementary region recording shift amount is a value more than a value smaller of the first non-complementary region recording shift amount and the second non-complementary region recording shift amount, as well as less than a value larger of the first non-complementary region recording shift amount and the second non-complementary region recording shift amount. 
     According to the first aspect, discharge timing of adjacent head modules is adjusted so that a recording shift amount in a complementary region in a joined portion between the head modules adjacent to each other is within a range between recording shift amounts in non-complementary regions of the respective adjacent head modules. Accordingly, variation between the recording shift amount in the non-complementary region and the recording shift amount in the complementary region becomes moderate, and thus uneven concentration can be reduced. 
     In addition, the first aspect is less likely to cause a problem in that a difference in discharge timing between respective head modules is accumulated to reduce squareness of an image that is one of problems in a conventional method. 
     As a second aspect, in the method for adjusting a recording head of the first aspect, it can be configured that adjustment is performed in the timing adjustment step so that the complementary region recording shift amount after being adjusted becomes an average value of the first non-complementary region recording shift amount and the second non-complementary region recording shift amount. 
     Uneven concentration can be further reduced by adjusting the complementary region recording shift amount so that the amount becomes an average value of the first non-complementary region recording shift amount and the second non-complementary region recording shift amount. 
     As a third aspect, in the method for adjusting a recording head of the first aspect or the second aspect, it can be configured that the complementary region becomes an array form in which projection nozzles belonging to the first head module and projection nozzles belonging to the second head module are interleaved in a projected nozzle array in which the projection nozzles align along the second direction, the projection nozzles being acquired by projecting each of nozzles of the first head module and the second head module on a straight line along the second direction. 
     An “interleaved array form” is not limited to a form in which the projection nozzles belonging to the first head module and the projection nozzles belonging to the second head module alternately align one by one, and can be such as: a form in which two or more projection nozzles belonging to the second head module continuously align between each of the projection nozzles belonging to the first head module; a form in which two or more projection nozzles belonging to the first head module continuously align between each of the projection nozzles belonging to the second head module; and a form of an appropriate combination of the Mims described above. 
     As a fourth aspect, in the method for adjusting a recording head of any one of the first to third aspects, it can be configured that the first non-complementary region recording shift amount is measured at a position closer to the second head module than a center position of the first head module in the second direction in the non-complementary region of the first head module, and that the second non-complementary region recording shift amount is measured at a position closer to the first head module than a center position of the second head module in the second direction in the non-complementary region of the second head module. 
     It is preferable that measurement of a recording shift amount in the non-complementary region of each of the first head module and the second head module is performed at a position as close as possible to the complementary region in the joined portion between the first head module and the second head module. According to the fourth aspect, the first non-complementary region recording shift amount and the second non-complementary region recording shift amount each are measured at a position relatively close to the complementary region in the joined portion, in the non-complementary region of each of the first head module and the second head module. 
     As a fifth aspect, in the method for adjusting a recording head of any one of the first to fourth aspects, it can be configured to includes a first test pattern recording step of recording a first test pattern to be used to measure the complementary region recording shift amount on a recording medium with the first head module and the second head module, a second test pattern recording step of recording a second test pattern to be used to measure the first non-complementary region recording shift amount on a recording medium with the first head module and the second head module, and a third test pattern recording step of recording a third test pattern to be used to measure the second non-complementary region recording shift amount on a recording medium with the first head module and the second head module. 
     Each of test patterns of the first test pattern, the second test pattern, and the third test pattern, may be recorded in the same recording medium, or in a different recording medium. The complementary region recording shift amount can be measured on the basis of a recorded result of the first test pattern. The first non-complementary region recording shift amount can be measured on the basis of a recorded result of the second test pattern. The second non-complementary region recording shift amount can be measured on the basis of a recorded result of the third test pattern. 
     As a sixth aspect, in the method for adjusting a recording head of the fifth aspect, it can be configured that a pattern equivalent to the first test pattern is used for each of the second test pattern and the third test pattern, and that the first non-complementary region recording shift amount and the second non-complementary region recording shift amount are measured by a measurement method equivalent to a measurement method of the complementary region recording shift amount. 
     An “equivalent pattern” indicates that while a nozzle used for recording is different, a form of a pattern and output conditions of the pattern are similar. 
     As a seventh aspect, in the method for adjusting a recording head of the fifth aspect or the sixth aspect, it can be configured to include a reading step of creating readout data on each of the test patterns by reading out a recorded result of each of test patterns of the first test pattern, the second test pattern, and the third test pattern, and it can be configured that the complementary region recording shift amount, the first non-complementary region recording shift amount, and the second non-complementary region recording shift amount, are measured according to the readout data. 
     As an eighth aspect, in the method for adjusting a recording head of any one of the first to seventh aspects, it can be configured to include a calculation step of calculating an adjustment value of discharge timing according to the complementary region recording shift amount measured in the first measurement step, and the first non-complementary region recording shift amount and the second non-complementary region recording shift amount, measured in the second measurement step. 
     According to the eighth aspect, the adjustment value is calculated in the calculation step so that the complementary region recording shift amount becomes a value between the first non-complementary region recording shift amount and the second non-complementary region recording shift amount, and the discharge timing is adjusted on the basis of the calculated adjustment value. 
     As a ninth aspect, in the method for adjusting a recording head of any one of the first to eighth aspects, it can be configured that the first non-complementary region recording shift amount is acquired by measuring an amount of displacement of a recording position of each of nozzles as far as possible from each other in the first direction, in nozzles adjacent to each other in the second direction in a nozzle range in the second direction, with a width equivalent to a complementary region width that is a width of the complementary region in the second direction, in nozzles belonging to the non-complementary region of the first head module, and that the second non-complementary region recording shift amount is acquired by measuring an amount of displacement of a recording position of each of nozzles as far as possible from each other in the first direction, in nozzles adjacent to each other in the second direction in a nozzle range in the second direction, with a width equivalent to the complementary region width, in nozzles belonging to the non-complementary region of the second head module. 
     As a tenth aspect, in the method for adjusting a recording head of any one of the first to ninth aspects, it can be configured that the first direction is a feeding direction of a recording medium, and the recording head is a line head. 
     As a eleventh aspect, in the method for adjusting a recording head of any one of the first to tenth aspects, it can be configured that the head module includes a nozzle region where a plurality of nozzles are arranged to form a two-dimensional array, the nozzle region being in the shape of a parallelogram in plan view, and that the recording head is a line head formed by aligning the plurality of head modules each including the nozzle region in the shape of a parallelogram in plan view, in the second direction. 
     As a twelfth aspect, in the method for adjusting a recording head of any one of the first to eleventh aspects, it can be configured to include a feeding step of feeding a recording medium by bringing the recording medium into close contact with a curved face, and it can be configured that a droplet is discharged from the nozzle to the recording medium in close contact with the curved face. 
     An image forming apparatus of a thirteenth aspect according to another viewpoint of the present disclosure includes: a recording head formed by joining the plurality of head modules each of which has a nozzle array in which a plurality of nozzles for discharging droplets are arranged at different positions in a first direction, the head modules being joined in a second direction intersecting with the first direction, the recording head including a complementary region where a nozzle belonging to one of the head modules adjacent to each other in the second direction and a nozzle belonging to the other of the head modules complement each other to record a dot row aligned in the second direction; a first measurement unit that measures a complementary region recording shift amount that is a recording shift amount in the first direction in the complementary region in a joined portion between a first head module and a second head module that are the head modules adjacent to each other; a second measurement unit that measures a first non-complementary region recording shift amount that is a recording shift amount a recording shift amount in the first direction in a non-complementary region other than the complementary region in a nozzle array in the first head module, and a second non-complementary region recording shift amount that is a recording shift amount in the first direction in a non-complementary region other than the complementary region in a nozzle array in the second head module; and a timing adjustment unit that adjusts discharge timing of at least one of the first head module and the second head module according to the complementary region recording shift amount measured by the first measurement unit, and the first non-complementary region recording shift amount and the second non-complementary region recording shift amount, measured by the second measurement unit, wherein the timing adjustment unit performs adjustment so that the complementary region recording shift amount after being adjusted becomes a value between the first non-complementary region recording shift amount and the second non-complementary region recording shift amount. 
     As a fourteenth aspect, in the image forming apparatus of the thirteenth aspect, it can be configured that the image forming apparatus includes a plurality of recording heads. 
     In the image forming apparatus of the thirteenth aspect or the fourteenth aspect, a matter similar to the matters defined from the second aspect to the twelfth aspect can be appropriately combined. In that case, the steps defined in the method for adjusting a recording head can be grasped as means for performing a process or a function corresponding to the mater, a processing unit, or an element of an operation unit or the like. 
     According to the present invention, it is possible to achieve favorable recording by reducing at least one of occurrence of uneven concentration and deviation of squareness of an image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating an example of a recording head to be used for an ink jet recorder; 
         FIG. 2  is a plan view schematically illustrating a relationship between a recording head and a paper sheet; 
         FIG. 3  is a perspective view of a head module and includes a partly-sectioned view thereof; 
         FIG. 4  is a sectional view illustrating an internal structure of the head module; 
         FIG. 5  is a perspective plan view of a discharge face in the head module; 
         FIG. 6  illustrates an example of a nozzle array of the head module; 
         FIG. 7  illustrates images of a recording shift amount when a straight line parallel to the X-direction is recorded by a recording head with a nozzle array in which a paper feeding side nozzle and a paper ejection side nozzle are alternately aligned along an X-direction; 
         FIG. 8  schematically illustrates a method of adjusting recording shift of a comparative example; 
         FIG. 9  schematically illustrates a state where a difference in discharge timing between head modules is accumulated by aligning a plurality of head modules in which discharge timing is adjusted by the method illustrated in  FIG. 8 ; 
         FIG. 10  schematically illustrates a state where recording shifts at opposite ends of a line head are adjusted by turning the whole line head from the state illustrated in  FIG. 9 ; 
         FIG. 11  illustrates change in nozzle position when a head module is turned by an angle γ; 
         FIG. 12  illustrates a method for adjusting a recording head according to the present embodiment; 
         FIG. 13  is a schematic diagram illustrating an example of a pattern for measuring a recording shift amount using discharge control of one-on-one-off; 
         FIG. 14  is a block diagram illustrating an outline of a system configuration of an ink jet recorder according to the present embodiment; 
         FIG. 15  is a flow chart illustrating a procedure of a method for adjusting a recording head according to the present embodiment; 
         FIG. 16  is a schematic plane view of head modules adjacent to each other; 
         FIG. 17  is a general structural view of the ink jet recorder according to the present embodiment; and 
         FIG. 18  is a block diagram illustrating an outline structure of a control system of the ink jet recording device. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, preferable embodiments of the present invention will be described in detail with reference to accompanying drawings. 
     Configuration Example of Recording Head 
       FIG. 1  is a perspective view illustrating an example of a recording head to be used for an ink jet recorder.  FIG. 1  illustrates a state where a discharge face is viewed from an oblique downward direction of a recording head  10 . A recording head  10  is formed by joining a plurality of head modules  12  in a paper sheet width direction, as a line head of an elongated strip. 
     The plurality of head modules  12  is fixed to a base frame  14  to form one ink jet head bar. The base frame  14  is a frame body for coupling and fixing the plurality of head modules  12  in the shape of a bar. A flexible substrate  16  is connected to each of the head module  12 . The flexible substrate  16  is connected to a control device that is not illustrated in  FIG. 1 . While the recording head  10  illustrated in  FIG. 1  is formed by joining seventeen head modules  12  arranged in a row, structure of each of the head modules  12 , the number of the head modules  12 , and an array form thereof, are not limited to an example illustrated. In the present specification, a paper sheet feeding direction is indicated as a Y-direction, and a paper sheet width direction orthogonal to the Y-direction is indicated as an X-direction. In addition, a direction orthogonal to the X-direction as well as the Y-direction is indicated as a Z-direction. In the present example, a paper sheet that is not illustrated in  FIG. 1  is fed toward a positive direction of a Y-axis of an XYZ-orthogonal coordinates system. The recording head  10  is disposed at a position away from a recording face of the paper sheet in a positive direction of a Z-axis. 
       FIG. 2  is a plan view schematically illustrating a relationship between a recording head  10  and a paper sheet S.  FIG. 2  is illustrated as a perspective plan view in which the recording head  10  is viewed from above toward a negative direction of the Z-axis. The recording head  10  has structure in which a plurality of nozzle apertures is arranged in the X-direction orthogonal to the paper sheet feeding direction throughout a length exceeding the is full width L max  of a paper sheet S. In  FIG. 2 , an illustration of the nozzle apertures is omitted. 
     The same structure may be applied to each of the plurality of head modules  12 . In addition, the head module  12  may have structure that allows the head module  12  to serve alone as an ink jet head. 
     Configuration Example of Head Module 
       FIG. 3  is a perspective view of a head module  12  and includes a partly-sectioned view thereof. The head module  12  includes an ink supply chamber  22  and an ink circulate chamber  26 . The ink supply chamber  22  and the ink circulate chamber  26  are disposed on a side opposite to a discharge face  30  of a nozzle plate  28 . The ink supply chamber  22  is connected to an ink tank (not illustrated) through a supply line  32 . The ink circulate chamber  26  is connected to a recovery tank (not illustrated) through a circulation line  36 . 
       FIG. 4  is a sectional view illustrating an internal structure of the head module  12 . The head module  12  includes an ink supply channel  44 , an individual supply channel  46 , pressure chamber  48 , a nozzle communication passage  50 , an nozzle aperture  52 , a circulation individual flow channel  56 , a circulation common flow channel  58 , a piezoelectric element  60 , and a vibrating plate  62 . 
     The ink supply channel  44 , the individual supply channel  46 , the pressure chamber  48 , the nozzle communication passage  50 , the circulation individual flow channel  56 , and the circulation common flow channel  58 , are formed in a flow channel structure  68 . The nozzle aperture  52  is formed in the nozzle plate  28 . The nozzle section  54  may be formed by including the nozzle aperture  52  and the nozzle communication passage  50 . The nozzle aperture  52  serving as a discharge port of a droplet may sometimes called a “nozzle”. The nozzle aperture  52  corresponds to a form of the “nozzle”. 
     The individual supply channel  46  is a flow channel connecting the pressure chamber  48  and the ink supply channel  44  to each other. The nozzle communication passage  50  is a flow channel connecting the pressure chamber  48  and the nozzle aperture  52  to each other. The circulation individual flow channel  56  is a flow channel connecting the nozzle communication passage  50  and the circulation common flow channel  58  to each other. 
     The vibrating plate  62  is provided on the flow channel structure  68 . The piezoelectric element  60  is provided above the vibrating plate  62  through an adhesive layer  63 . The piezoelectric element  60  has a laminated structure composed of a bottom electrode  64 , a piezoelectric layer  65 , and an upper electrode  66 . The bottom electrode  64  may be sometimes called a common electrode, and the upper electrode  66  may be sometimes called an individual electrode. There is also available a form in which the bottom electrode  64  is directly deposited on the vibrating plate  62 , and in this case, the adhesive layer  63  is eliminated. 
     The upper electrode  66  is an individual electrode that is patterned in accordance with a plan-view shape of each of the pressure chambers  48 , and the piezoelectric element  60  is provided for each of the pressure chambers  48 . 
     The ink supply channel  44  is connected to the ink supply chamber  22  illustrated in  FIG. 3 . Ink is supplied to the pressure chamber  48  from the ink supply channel  44  through the individual supply channel  46 . When drive voltage is applied to the upper electrode  66  of the piezoelectric element  60  to be operated in accordance with image data, the piezoelectric element  60  and the vibrating plate  62  are deformed to change a volume of the pressure chamber  48 . 
     The head module  12  can discharge a droplet of the ink from the nozzle aperture  52  through the nozzle communication passage  50  by using pressure change with change in the volume of the pressure chamber  48 . In the head module  12 , drive of the piezoelectric element  60  corresponding to each of the nozzle apertures  52  is controlled in accordance with dot data created from the image data. 
     While the paper sheet S illustrated in  FIG. 2  is fed at a predetermined speed in the paper sheet feeding direction, a desired image is formed on the paper sheet S by controlling discharge timing of a droplet from each of the nozzle apertures  52  in accordance with a feeding speed of the paper sheet S. 
     The nozzle communication passage  50  communicates with the circulation individual flow channel  56 . It is desirable that a connecting portion between the nozzle communication passage  50  and the circulation individual flow channel  56  is close to the nozzle aperture  52  in the nozzle communication passage  50 . Ink that is not used for discharge in the ink supplied to the nozzle section  54  is recovered to the circulation common flow channel  58  through the circulation individual flow channel  56 . 
     The circulation common flow channel  58  is connected to the ink circulate chamber  26  illustrated in  FIG. 3 . Allowing ink to be always recovered to the circulation common flow channel  58  through the circulation individual flow channel  56  prevents viscosity of the ink in the nozzle section  54  from increasing during a non-discharge period. 
       FIG. 5  is a perspective plan view of the discharge face  30  in the head module  12 . The plurality of nozzle apertures  52  is arranged in a two-dimensional matrix shape in the nozzle plate  28  of one head module  12 .  FIG. 5  is a schematic diagram in which the number of the nozzle apertures  52  is reduced for convenience of illustration, and thus only a part of the nozzle apertures  52  constituting nozzle arrangement of a two-dimensional matrix is illustrated to partially eliminate illustration of the nozzle apertures  52  of nozzle arrays. 
     The nozzle plate  28  of the head module  12  is formed in a plane shape of a parallelogram with end faces each on a short side along a W-direction with an inclination of an angle α with respect to the Y-direction, and end faces each on a long side along a V-direction with an inclination of an angle β with respect to the X-direction. The angle α can be designed at an appropriate value more than 0°, and can be designed at a value satisfying the following: 0°&lt;α≦45°, for example. The angle β can be designed at an appropriate value equal to or more than 0°, and can be designed at a value satisfying the following: 0°≦β&lt;30°, for example. 
     In the discharge face  30  of the head module  12 , the plurality of nozzle aperture  52  is arranged in a two-dimensional matrix shape by aligning in a row direction along the V-direction and a column direction along the W-direction. An array form of the nozzle apertures  52  is not limited to the form illustrated in  FIG. 5 , and various array forms are available. 
     In a case of a liquid discharge head with a two-dimensional nozzle array, it can be conceived that a projected nozzle array in which each of nozzle apertures in the two-dimensional nozzle array is projected (orthogonal projection) so as to align along the X-direction is equivalent to a nozzle array of a line in which the nozzles align at approximately equal intervals at nozzle density for achieving a maximum recording resolution in the X-direction. The “approximately equal interval” means that a recordable depositing point in an ink jet recorder is set at a substantially equal interval. For example, a concept of the “equal interval” includes also a case where each of intervals is slightly varied in consideration of displacement of droplets on a paper sheet due to an error in manufacturing and interference of deposition. In consideration of the projected nozzle array (also referred to as a “substantial nozzle array”), a nozzle number indicating a nozzle position can be associated with the order of alignment of the projected nozzles aligning along the X-direction. 
     The recording head  10  shown in the present embodiment includes a joined portion between the head modules  12  adjacent to each other in the projected nozzle array in the X-direction, where the nozzle apertures  52  belonging to one of the head modules  12 , and the nozzle apertures  52  belonging to the other of the head modules  12 , are mixed to achieve a required recording resolution. 
     Specific Example of Nozzle Array 
       FIG. 6  illustrates an example of a nozzle array of the head module  12 .  FIG. 6  illustrates nozzle arrangement of the array of the nozzle apertures  52  formed in the nozzle plate  28 , illustrated in  FIGS. 4 and 5 , as viewed from a pressure chamber  48  side. In  FIG. 6 , a horizontal axis indicates a position in the X-direction, and a vertical axis indicates a position in the Y-direction. The paper sheet S that is not illustrated in  FIG. 6  is fed parallel to the vertical axis of  FIG. 6  and fed upward from a lower portion in  FIG. 6 . 
     In the nozzle arrangement of a two-dimensional matrix illustrated in  FIG. 6 , a nozzle array direction parallel to the V-direction is called a “row direction”, and a nozzle array direction parallel to the W-direction is called a “column direction”. A nozzle array in which the nozzle apertures  52  align in the row direction is called a “row direction nozzle array”, and a nozzle array in which the nozzle apertures  52  align in the column direction is called a “column direction nozzle array”. The number of the row direction nozzle arrays aligning in the Y-direction is called a “row number”, and the number of the column direction nozzle arrays aligning in the X-direction is called a “column number”. 
     A nozzle array  70  illustrated in  FIG. 6  includes a first nozzle group  71  composed of nozzle arrangement of a two-dimensional matrix of 16 rows by 64 columns, and a second nozzle group  72  composed of nozzle arrangement of a two-dimensional matrix of 16 rows by 64 columns, and the groups align away from each other in the Y-direction to form nozzle arrangement of a two-dimensional matrix of 32 rows by 64 columns as a whole. In the column direction nozzle array, a column number, such as the first column, the second column . . . the sixty fourth column, from a left end of  FIG. 6 , can be determined. In addition, in the row direction nozzle array, a row number, such as the first row, the second row . . . the thirty second row, from a lowermost row of  FIG. 6 , can be determined. 
     The first nozzle group  71  has matrix arrangement in which the nozzle apertures  52  align in the X-direction at a nozzle density of 600 npi. Likewise, the second nozzle group  72  has matrix arrangement in which the nozzle apertures  52  align in the X-direction at a nozzle density of 600 npi. The term “npi” means nozzles per inch, and is a unit representing the number of nozzles per inch. One inch is 25.4 millimeter (mm). Since one nozzle can record a dot of one pixel, the npi can be substituted with dpi to be understood. The term “dpi” means dots per inch, and is a unit representing the number of dots (points) per inch. Hereinafter, density of nozzle array is represented by “dpi”. 
     The first nozzle group  71  at 600 dpi and the second nozzle group  72  at 600 dpi are combined to enable recording at 1200 dpi in the X-direction to be performed in the entire head module. 
     That is, when a projected nozzle array acquired by projecting each of the nozzles in the nozzle arrangement illustrated in  FIG. 6  on an X-axis is viewed, nozzles belonging to the first nozzle group  71  on a paper feeding side and nozzles belonging to the second nozzle group  72  are adjacent to each other. The nozzles belonging to the first nozzle group  71  are called paper feeding side nozzles, and the nozzles belonging to the second nozzle group  72  are called paper ejection side nozzles. 
     Regarding Complementary Region and Non-complementary Region 
     As described above, the head module  12  includes a nozzle array in which a plurality of nozzles is arranged at different positions in the Y-direction. The recording head  10  formed by joining the plurality of head modules  12  in the X-direction has a complementary region in a joined portion between head modules adjacent to each other in the X-direction. The complementary region is a region where nozzles belonging to one of two head modules adjacent to each other in the X-direction and nozzles belonging to the other thereof complement each other to record a dot row aligning in the X-direction. 
     In the recording head  10 , one of two head modules adjacent to each other in the X-direction is called a first head module, and the other thereof is called a second head module. In the complementary region, a dot row in a recording line along the X-direction is formed of a mixed array of dots to be recorded by nozzles belonging to the first head module and dots to be recorded by nozzles belonging to the second head module. 
     When the complementary region is viewed from a viewpoint of a projected nozzle array, it also can be grasped as follows. That is, the complementary region becomes an array form in which projection nozzles belonging to the first head module and projection nozzles belonging to the second head module are interleaved in a projection nozzle array in which the projection nozzles acquired by projecting each of nozzles of the first head module and the second head module on a straight line along the X-direction align along the X-direction. An “interleaved array form” is not limited to regularly alternate array, and includes an array in which each of the nozzles aligns at an appropriate blend ratio. 
     In a case of the nozzle array illustrated in  FIG. 6 , nozzles corresponding to the complementary region are 64 nozzles in 4 columns at each of ends in the X-direction in the nozzle array. Specifically, in a joined portion in structure where two head modules each with the nozzle array illustrated in  FIG. 6  are joined side by side, nozzles corresponding to a complementary region of the head module on a left side are 64 nozzles of a total of nozzles from the twenty fifth row to the thirty second row in the sixty first column, from the seventeenth row to the thirty second row in the sixty second column, from the seventeenth row to the thirty second row in the sixty third column, and from the ninth row to the thirty second row in the sixty fourth column. 
     Meanwhile, in the joined portion in the structure where two head modules each with the nozzle array illustrated in  FIG. 6  are joined side by side, nozzles corresponding to a complementary region of the head module on a right side are 64 nozzles of a total of nozzles from the first row to the twenty fourth row in the first column, from the first row to the sixteenth row in the second column, from the first row to the sixteenth row in the third column, and from the first row to the eighth row in the fourth column. 
     In addition, a region in the nozzle array of the head module  12  other than the complementary region is a non-complementary region. In a case of the nozzle array illustrated in  FIG. 6 , a nozzle region except 64 nozzles in 4 columns at each of ends in the X-direction, described above, corresponds to the non-complementary region. The Y-direction corresponds to a form of the “first direction”, and the X-direction corresponds to a form of the “second direction”. 
     Description of Problem 
       FIG. 7  illustrates images of a recording shift amount when a straight line parallel to the X-direction is recorded by using a recording head in which a paper feeding side nozzle and a paper ejection side nozzle are alternately used to record pixels aligning in the X-direction. 
     For a plurality of head modules constituting a line head, a head module number can be determined according to an alignment order of the head modules from one end in the X-direction. For example, in the recording head  10  illustrated in  FIG. 2 , when a head module number is determined in order from a head module at a left end, such as the first, second, and third, a head module at the right-most end is the seventeenth head module. In a case where the number of head modules constituting a line head is indicated as Nm, and an integer representing a head module number is indicated as i, Nm is an integer of 2 or more, and i is an integer not less than 1 and not more than Nm. 
       FIG. 7  illustrates the n-th head module  12 - n  and the (n+1)th head module  12 -( n+ 1) that are head modules adjacent to each other in the X-direction, where n is an integer not less than 1 and less than Nm. 
     A pattern of a dot row designated by a reference numeral  80  in  FIG. 7  is an example of an X-direction recording line recorded by nozzles in a non-complementary region in a nozzle array of the n-th head module  12 - n . When the pattern  80  of a dot row aligned along the X-direction is recorded by using the nozzles in the non-complementary region in the n-th head module  12 - n , recording shift between a paper feeding side nozzle and a paper ejection side nozzle may occur due to a difference between paper sheet feeding speed and discharge timing, a difference in a throw distance, or the like, as described above. That is, a Y-direction position of a dot  81  recorded by a droplet discharged from the paper feeding side nozzle, and a Y-direction position of a dot  82  recorded by a droplet discharged from the paper ejection side nozzle, are displaced from each other in the Y-direction. 
     A pattern of a dot row designated by a reference numeral  84  in  FIG. 7  is an example of an X-direction recording line recorded by nozzles in a non-complementary region in a nozzle array of the (n+1)-th head module  12 -( n+ 1). As with the non-complementary region in the n-th head module  12 - n , recording shift between a paper feeding side nozzle and a paper ejection side nozzle occurs due to a difference between paper sheet feeding speed and discharge timing, a difference in a throw distance, or the like, also in a non-complementary region in the (n+1)-th head module  12 -( n+ 1). That is, a Y-direction position of a dot  85  recorded by a droplet discharged from the paper feeding side nozzle, and a Y-direction position of a dot  86  recorded by a droplet discharged from the paper ejection side nozzle, are displaced from each other. 
     A pattern of a dot row designated by a reference numeral  90  in  FIG. 7  is an example of an X-direction recording line recorded by using nozzles in a complementary region between the n-th head module  12 - n  and the (n+1)-th head module  12 -( n+ 1). 
     In the complementary region between the head modules adjacent to each other, each of the paper feeding side nozzle and the paper ejection side nozzle belongs to a different head module, and thus a dot  91  formed of a droplet discharged from the paper ejection side nozzle of the n-th head module  12 - n , and a dot  92  formed of a droplet discharged from the paper feeding side nozzle of the (n+1)-th head module  12 -( n+ 1), alternately align in the X-direction to form a recording line in the complementary region. 
     Adjusting discharge timing in units of a head module by using the conventional methods shown in Patent Literatures 1 to 3 enables a recording shift amount in a complementary region to be less than a recording shift amount in a non-complementary region.  FIG. 7  illustrates a state where an adjustment is performed so that a recording shift amount in a complementary region becomes substantially zero. 
     However, if discharge timing of a head module is adjusted by applying a conventional method so that a recording shift amount in a complementary region becomes a minimum, an arrangement state of dots is greatly different between a non-complementary region and the complementary region. As a result, uneven concentration or the like tends to easily occur. 
     In addition, if discharge timing is adjusted between head modules adjacent to each other so that a shift of a deposition position becomes a minimum in a complementary region while a shift of a deposition position in the Y-direction occurs at a paper feeding side nozzle and a paper ejection side nozzle in a non-complementary region of each of the head modules, discharge timing in a region other than the complementary region varies between the head modules adjacent to each other. 
       FIG. 8  schematically illustrates a method of adjusting recording shift of a comparative example. There is a recording shift in the Y-direction between a paper feeding side nozzle and a paper ejection side nozzle in a non-complementary region of the n-th head module, and an amount of the recording shift is indicated as d A (n). There is a recording shift in the Y-direction between the paper feeding side nozzle and the paper ejection side nozzle in a non-complementary region of the (n+1)-th head module, and an amount of the recording shift is indicated as d A (n+1). 
     In the comparative example of  FIG. 8 , discharge timing of the n-th head module and the (n+1)-th head module is relatively adjusted so that a recording shift between the paper feeding side nozzle and the paper ejection side nozzle is eliminated in the complementary region. In this case, as illustrated in  FIG. 8 , discharge timing between the head modules is adjusted so that a recording position of the paper ejection side nozzle of the n-th head module, and a recording position of the paper feeding side nozzle of the (n+1)-th head module, coincide with each other in the complementary region. 
     As a result, a recording line L(n)-A formed by supply side nozzles in a non-complementary region in the n-th head module, and a recording line L(n+1)-A formed by supply side nozzles in a non-complementary region in the (n+1)-th head module, are displaced from each other in the Y-direction. Likewise, a recording line L(n)-B formed by paper ejection side nozzles in the non-complementary region in the n-th head module, and a recording line L(n+1)-B formed by paper ejection side nozzles in the non-complementary region in the (n+1)-th head module, are displaced from each other in the Y-direction. 
     If a plurality of head modules in which discharge timing is adjusted between adjacent head modules as described above is aligned in the X-direction, a difference in discharge timing between each of the head modules is accumulated to cause a problem in that discharge timing is greatly displaced from each other between a head module at one end of a line head in the X-direction and a head module at the other end thereof to vary squareness or the like. 
       FIG. 9  schematically illustrates a state where a difference in discharge timing between head modules is accumulated by aligning a plurality of head modules in which discharge timing is adjusted by the method illustrated in  FIG. 8 .  FIG. 9  illustrates displacement of a recording position in alignment of five head modules of the (n−2)-th to the (n+2)-th head modules by centering the n-th head module, the displacement being caused by influence of a difference in discharge timing of only paper feeding side nozzles in a non-complementary region in each of the head modules or a difference in discharge timing of only paper ejection side nozzles therein. 
     As illustrated in  FIG. 9 , a difference in discharge timing is accumulated according to the order of alignment of the head modules, squareness of an X-direction recording line varies. 
     As one of correction methods of correcting this kind of variation of squareness, the squareness can be corrected by adjusting an angle of a line head itself in a θz-direction. The θz-direction is a rotation direction with respect to a rotation shaft parallel to the Z-direction. Rotation in the θz-direction is rotation in a plane parallel to a discharge face of the line head. 
       FIG. 10  schematically illustrates a state where recording shifts at opposite ends of a line head are adjusted by turning the entire line head in the θz-direction by an angle γ from the state illustrated in  FIG. 9 . As illustrated in  FIG. 10 , the squareness illustrated in  FIG. 9  can be improved by adjusting an angle of the entire line head in the θz-direction. 
     However, if angle adjustment in the θz-direction, such as illustrated in  FIG. 10 , is performed, there is a problem in that unevenness and streaks tend to easily occur. Hereinafter, a phenomenon of the problem will be described. 
       FIG. 11  illustrates a state of one of head modules when recording shift in the Y-direction between each of the head modules at opposite ends of a line head is corrected by performing angle adjustment of an angle γ in the θz-direction from a state of  FIG. 10 .  FIG. 11  is a schematic diagram illustrating a state where the head module is turned in the θz-direction by an angle γ. In  FIG. 11 , a bottom left corner of the head module is set as a reference position, for convenience of illustration, and the reference position serves as an original point of nozzle coordinates. In addition, rotation adjustment of an angle γ will be described so as to be performed by setting the reference position as the center of rotation in the θz-direction. 
     As illustrated in  FIG. 6 , in a case of nozzle arrangement of a two-dimensional matrix, nozzle positions of two nozzles for recording pixels adjacent to each other in the X-direction are away from each other in the Y-direction. The focused two nozzles each are indicated as either a nozzle a or a nozzle b. A nozzle coordinate of the nozzle a is indicated as (Xa, Ya), and a nozzle coordinate of the nozzle b is indicated as (Xb, Yb). Since the angle γ is a minute amount, approximation of cos γ≈1 and sin γ≈γ holds, where γ is in units of radian unit. 
     When a head module is turned by an angle γ, a displacement distance ΔYa of the nozzle a in the Y-direction and a displacement distance ΔYb of the nozzle b in the Y-direction can be respectively expressed as follows.
 
Δ Ya=Xa ×sin γ
 
Δ Yb=Xb ×sin γ
 
     Thus, a variation (ΔYa−ΔYb) of a distance in the Y-direction of the nozzle a and the nozzle b caused by rotation of an angle γ is as follows.
 
Δ Ya−ΔYb =( Xa−Xb )×γ
 
     However, a value of Xa−Xb is small, and the variation is so small to be negligible. 
     Meanwhile, when a head module is turned by an angle γ, a displacement distance ΔXa of the nozzle a in the X-direction and a displacement distance ΔXb of the nozzle b in the X-direction can be respectively expressed as follows.
 
Δ Xa=Ya×γ 
 
Δ Xb=Yb×γ 
 
     Thus, a variation (ΔXa−ΔXb) of a distance in the X-direction of the nozzle a and the nozzle b caused by rotation of an angle γ is as follows.
 
Δ Xa−ΔXb =( Ya−Yb )×γ
 
     That is, a relative distance in the X-direction of nozzles away from each other in the Y-direction by an amount of (Ya−Yb) varies by an amount of (Ya−Yb)×γ by rotation of an angle γ in the θz-direction. For example, when a value of (Ya−Yb) is 10 millimeter and γ is 0.5 milli-radian, a relative distance in the X-direction varies by about 5 micrometer, and thus may cause a problem at the time of dense recording at a level of 1200 dpi. 
     Means for Solve Problem According to the Present Embodiment 
     In the present embodiment, a recording shift amount in each of non-complementary regions of respective adjacent head modules, and a recording shift amount in a complementary region that is a joined portion between both the head modules, are measured, and relative discharge timing of the adjacent head modules is adjusted on the basis of the measured recording shift amounts so that the recording shift amount in the complementary region becomes an intermediate value between the recording shift amount in each of the non-complementary region in the respective adjacent head modules. 
     The “adjacent head modules” is synonymous with the “head modules adjacent to each other”. The sentence of “relative discharge timing is adjusted” indicates that a relative time difference in discharge timing is adjusted in head modules adjacent to each other. Discharge timing of one of adjacent head modules may be adjusted with reference to discharge timing of the other of the adjacent head modules, or discharge timing of each of the adjacent head modules may be adjusted. 
     The “intermediate value” is not limited to an average value to be the exactly middle value, and indicates a value between two values. In the “intermediate value”, a preferable example in which effect of reducing uneven concentration is a maximum is the “average value”, and thus, a specific example described below shows an example in which relative discharge timing of adjacent head modules is adjusted so that a recording shift amount in a complementary region becomes an average value of a recording shift amount in a non-complementary region in each of adjacent head modules. 
       FIG. 12  illustrates a method for adjusting a recording head according to the present embodiment. In  FIG. 12 , an element identical or similar to that illustrated in  FIG. 7  is designated by the same reference numeral. When a recording shift amount in a non-complementary region in the n-th head module is indicated as d A (n) and a recording shift amount in a non-complementary region in the (n+1)-th head module is indicated as d A (n+1), relative discharge timing of the n-th and the (n+1)-th head modules is adjusted so that a recording shift amount d B (n, n+1) in a complementary region after adjustment becomes [d A (n)+d A (n+1)]/2. 
     For example, when a recording shift amount in a complementary region before adjustment is indicated as d B   _   be (n, n+1), a recording shift amount in the complementary region after the adjustment is indicated as d B   _   af (n, n+1), and feeding speed of a paper sheet S being a recording medium is indicated as V Y , a time difference t d  in discharge timing between adjacent head modules causing the recording shift amount d B   _   af (n, n+1) in the complementary region to be [d A (n)+d A (n+1)]/2 can be expressed by the following expression.
 
 t   d   =[d   B   _   be ( n,n+ 1)−( d   A ( n )+ d   A ( n+ 1))/2]/ V   Y  
 
     Adjustment performed as described above relatively reduces a difference between a recording shift amount in a non-complementary region in adjacent head modules and a recording shift amount in a complementary region therein, and thus a variation between a recording shift amount in the non-complementary region and a recording shift amount in the complementary region becomes moderate (smooth), whereby uneven concentration is less likely to occur. 
     The method of the present embodiment achieves considerable improvement effect particularly in an angle shift in the θx-direction of the entire line head, or in a case where a recording shift amount in the Y-direction uniformly occurs in the entire line head, such as a case where a curved face like a paper sheet held by a drum is recorded. 
     In a case of a recording head using a head module with nozzle arrangement illustrated in  FIG. 6 , a complementary region in adjacent head modules has 128 pixels, and in 64 pixels in a central portion of the 128 pixels, nozzles of each of adjacent head modules are to be alternately used in the X-direction. In this embodiment, since there is a relationship in which one nozzle is assigned to recording of one pixel position, the 128 pixels in the complementary region are synonymous with 128 nozzles corresponding to the respective pixels. 
     In the present embodiment, a recording shift amount of each of adjacent head modules is measured by using a region of 64 pixels corresponding to a central portion of a complementary region. For example, an X-direction line is recorded by using nozzles of only one of adjacent head modules according to discharge control of one-on-one-off, and a position in the Y-direction of each of a line recorded by using nozzles of only the n-th head module and a line recorded by using nozzles of only the (n+1)-th head module is measured to enable a recording shift amount in a complementary region to be measured. 
     The discharge control of one-on-one-off performs recording in which dot-on and dot-off are alternately repeated for a row of pixels along the X-direction. In a case where a recording resolution in the X-direction is 1200 dpi like the present example, a line of a dot row in which dots align can be recorded at 600 dpi by the discharge control of one-on-one-off. Changing a combination of a pixel of dot-on and a pixel of dot-off enables a line to be recorded at 600 dpi by changing nozzles to be used. 
     Applying discharge control of one-on-one-off to 64 pixels in a central portion of 128 pixels in a complementary region can form a line pattern in which a line of a dot row recorded by using only paper ejection side nozzles of the n-th head module, and a line of a dot row recorded by using only paper feeding side nozzles of the (n+1)-th head module, align in the Y-direction away from each other on a paper sheet. 
     In a case where two head modules each with the nozzle array illustrated in  FIG. 6  are joined side by side, a region of 64 pixels corresponding to a central portion in a complementary region is a range of a total of 64 nozzles where nozzles from the seventeenth row to the thirty second row of each of the sixty second column and the sixty third column of the head module on a left side, and nozzles from the first row to the sixteenth row of each of the second column and the third column of the head module on a right side, overlap with each other so as to alternately align in the X-direction. 
     In addition, a recording shift amount is measured for not only the complementary region, but also a non-complementary region in each of the adjacent head modules. As with the complementary region, a position in the Y-direction of each of a line recorded by using only paper feeding side nozzles, and a line recorded by using only paper ejection side nozzles, according to one-on-one-off, is measured to enable a recording shift amount to be measured. 
     Example of Method of Measuring Recording Shift Amount 
       FIG. 13  is a schematic diagram illustrating an example of a pattern for measuring a recording shift amount using discharge control of one-on-one-off. Hereinafter, a case of measuring a recording shift amount in a non-complementary region in the n-th head module  12 - n  will be described. 
     A paper sheet S being a recording medium is fed in the Y-direction at a predetermined feeding speed. Nozzles of a recording head  10  discharge droplets to the paper sheet S. In an example of  FIG. 13 , discharge control of one-on-one-off is applied to a non-complementary region in the n-th head module  12 - n  to record a plurality of X-direction recording lines on the paper sheet S by alternately changing a nozzle group to be used for discharge at predetermined time intervals. 
     In the nozzle array illustrated in  FIG. 6 , when a nozzle number of paper feeding side nozzles is an odd number and a nozzle number of paper ejection side nozzles is an even number, an X-direction recording line recorded by a nozzle with an odd number, and an X-direction recording line recorded by a nozzle with an even number, are to be alternately aligned and recorded in the Y-direction on the paper sheet S according to the discharge control of one-on-one-off. 
     An X-direction recording line L A [ 1 ] drawn in the uppermost row in  FIG. 13  represents a dot row recorded by paper feeding side nozzles in a non-complementary region. An X-direction recording line L B [ 1 ] in the second row from the top in  FIG. 13  represents a dot row recorded by the paper feeding side nozzles in the non-complementary region. 
     An X-direction recording line L A [ 2 ] in the third row from the top in  FIG. 13  represents a dot row recorded by the paper feeding side nozzles in the non-complementary region. An X-direction recording line L B [ 2 ] in the fourth row from the top in  FIG. 13  represents a dot row recorded by the paper feeding side nozzles in the non-complementary region. 
     A pattern for measurement including X-direction recording lines, recorded by alternately changing nozzles to be used as described above, is recorded to measure a distance in the Y-direction between each of the X-direction recording lines. 
     If a recording shift amount in the non-complementary region is zero, a distance in the Y-direction between each line is equal. Meanwhile, if there is a recording shift amount in the non-complementary region, a distance in the Y-direction between each line is a different value reflecting the shift amount. 
     A distance A[ 1 ] in the Y-direction between the X-direction recording line L A [ 1 ] of the first row and the X-direction recording line L B [ 1 ] of the second row, as well as, a distance B[ 1 ] in the Y-direction between the X-direction recording line L B [ 1 ] of the second row and the X-direction recording line L A [ 2 ] of the third row is measured, and a difference between the A[ 1 ] and the B[ 1 ] is acquired to enable a recording shift amount to be measured. Similar measurement may be performed multiple times to increase accuracy of measurement by using statistical processing such as adopting an average value of measurement results. 
     A recording shift amount in a complementary region also can be measured by using a method similar to the method illustrated in  FIG. 13 . 
     A measurement pattern to be used for measurement of a recording shift amount, as well as a method for the measurement is not limited to the example described above. For example, a method of measuring a recording shift amount by using a scanner, an external measurement device, or the like, may be used, or a method of measuring concentration when lines are recorded by varying recording timing to measure a recording shift amount from a relationship between a shift amount and concentration, such as described in Japanese Patent Application Laid-Open No. 2014-136319, may be used. 
     Depending on a kind of measurement pattern to be used, or a method for measurement, a measurement value of a recording shift amount may vary, and thus it is desirable that a combination of a measurement pattern to be used for measurement of a recording shift amount in a complementary region and a method for the measurement is identical to a combination of a measurement pattern to be used for measurement of a recording shift amount in a non-complementary region and a method for the measurement. 
     In addition, since nozzles belonging to each of adjacent head modules complement each other to record an X-direction recording line in a complementary region, discharge timing of each of the adjacent head modules needs to appropriately coincide with each other. Accordingly, it is necessary to grasp an amount of shift of a recording position caused by dots of droplets discharged from each of the head modules for the complementary region. Thus, it is desirable that a recording shift amount in the non-complementary region is measured by using a method equivalent to the method of measurement used for measurement of the complementary region. 
     Example of System Configuration of Ink Jet Recorder 
       FIG. 14  a block diagram illustrating an outline of a system configuration of an ink jet recorder according to the present embodiment. An ink jet recorder  100  includes a recording head  10 , a feeding unit  112 , and a scanner  114 . In addition, the ink jet recorder  100  includes an image input interface  120 , an image processing unit  122 , a test pattern creation unit  124 , a control unit  126 , an image analysis unit  128 , a reference signal generation unit  130 , and a timing adjustment unit  132 . Each unit illustrated in  FIG. 14  can be configured by appropriately combining hardware and software. 
     The recording head  10  is a line head formed by joining a plurality of head modules  12 - i  in the X-direction. In the reference numeral “ 12 - i ”, “i” represents a head module number, and is an integer from 1 to Nm. 
     The feeding unit  112  includes a mechanism of feeding a paper sheet as a recording medium in the Y-direction, and a power source for feed drive. 
     The image input interface  120  acquires image data through a wired or wireless communication interface. The image processing unit  122  applies a required image processing to the received image data. The image processing unit  122  performs image processing such as color conversion processing, gradation conversion processing, and halftone processing. 
     The test pattern creation unit  124  creates data on various test patterns. The test pattern creation unit  124  can create data on various test patterns such as a pattern for measurement to be used for measuring a recording shift amount in a non-complementary region in each of adjacent head modules in the recording head  10 , a pattern for measurement to be used for measuring a recording shift amount in a complementary region therein, and a pattern for inspection to be used for inspecting a discharge state of each nozzle in the recording head. 
     The control unit  126  performs integrated control for each unit in the ink jet recorder  100 . The control unit  126  can control the recording head  10 , the reference signal generation unit  130 , the timing adjustment unit  132 , the feeding unit  112 , the scanner  114 , and the image analysis unit  128 , on the basis of at least one of image data processed by the image processing unit  122  and data on test patterns to be acquired from the test pattern creation unit  124 . The control unit  126  serves as an arithmetic processing unit that performs various calculations. 
     The reference signal generation unit  130  includes an oscillation circuit, a divider circuit, and a waveform shaping circuit, which are not illustrated, and generates a reference signal of a drive waveform signal to be supplied to a discharge energy generation element corresponding to one of nozzles provided in the corresponding head module  12 - i.    
     The timing adjustment unit  132  includes timing correction units  134 - i  (i=1, 2, . . . Nm) for the corresponding head modules  12 - i  to correct discharge timing. The timing adjustment unit  132  corrects timing for each head module  12 - i  with respect to the reference signal received from the reference signal generation unit  130 , and supplies a corrected timing signal to each head module  12 - i.    
     The timing correction unit  134 - i  includes a delay circuit, which can set a delay amount, to delay a received reference signal by a set delay amount, and supplies the reference signal to each head module  12 - i . Accordingly, discharge timing of a nozzle can be set to appropriate timing for each head module  12 - i , and thus discharge timing can be relatively varied between head modules. 
     In addition, the control unit  126  supplies a nozzle selection signal to each head module  12 - i  to select a nozzle for discharging a droplet. Accordingly, a droplet can be discharged from a desired nozzle of each head module  12 - i  at desired timing to record a dot on a recording face of a paper sheet S. 
     The control unit  126  can cause the recording head  10  to record an image on the recording face of the paper sheet S by controlling the recording head  10  and the feeding unit  112 . 
     The scanner  114  is disposed downstream of the recording head  10  in a paper sheet feeding direction in a paper sheet feeding path to read out an image recorded on the paper sheet S by the recording head  10 . In the present embodiment, a resolution less than a recording resolution of the recording head  10  is used as a reading resolution of the scanner  114 . For example, a reading resolution of the scanner  114  in the X-direction is 480 dpi, and a reading resolution thereof in the Y-direction is 100 dpi. 
     Readout data read out by the scanner  114  is inputted into the image analysis unit  128 . The image analysis unit  128  measures a recording shift amount from the received readout data. The image analysis unit  128  includes a first measurement unit  141  and a second measurement unit  142 . The first measurement unit  141  measures a complementary region recording shift amount, which is a recording shift amount in the Y-direction in a complementary region in a joined portion between the n-th head module and the (n+1)-th head module that are head modules adjacent to each other, on the basis of the readout data. 
     The second measurement unit  142  measures a first non-complementary region recording shift amount, which is a recording shift amount in the Y-direction in a non-complementary region in a nozzle array of the n-th head module, and a second non-complementary region recording shift amount, which is a recording shift amount in the Y-direction in a non-complementary region in a nozzle array of the (n+1)-th head module, on the basis of the readout data. 
     Information on the complementary region recording shift amount, the first non-complementary region shift amount, and the second non-complementary region shift amount, acquired by the image analysis unit  128 , is transmitted to the control unit  126 . The control unit  126  calculates a timing adjustment value to adjust discharge timing of adjacent head modules on the basis of the first non-complementary region shift amount and the second non-complementary region shift amount, acquired from the image analysis unit  128 . The control unit  126  includes a calculation unit (not illustrated) that performs calculation to calculate a timing adjustment value. The calculation unit for calculating a timing adjustment value may be included in the image analysis unit  128 . The control unit  126  sets a delay amount of the corresponding timing correction unit  134 - i  in the timing adjustment unit  132  in accordance with the calculated timing adjustment value. 
     Method of Adjusting Discharge Timing of Recording Head 
       FIG. 15  is a flow chart illustrating a procedure of a method for adjusting a recording head according to the present embodiment. Each step of the flow chart illustrated in  FIG. 15  is performed by a processing function of the control unit  126  in the ink jet recorder  100 , or operation of the ink jet recorder  100  according to control of the control unit  126 , for example. The flow chart illustrated in  FIG. 15  is performed as a method of adjustment when some of the head modules  12  in the recording head  10  being a line head is exchanged, for example. 
     In step S 11 , the control unit  126  first designates a head module to be adjusted. Here, the n-th head module and the (n+1)-th head module adjacent to each other are designated as head modules to be adjusted. For example, when a head module in a recording head is exchanged, an operator performs input operation to identify a head module to be adjusted, through an appropriate user interface. According to the input operation, the head module to be adjusted is determined. Alternatively, a head module to be adjusted may be automatically designated by configuring the control unit  126  to automatically recognize an exchanged head module. Here, the n-th head module and the (n+1)-th head module adjacent to each other are designated as head modules to be adjusted. Hereinafter, the n-th head module is referred to as a “first head module”, and the (n+1)-th head module is referred to as a “second head module”. 
     Next, in step S 12 , the ink jet recorder  100  records a pattern for measurement to be used for measuring a recording shift amount in a complementary region on a paper sheet S by using the first head module and the second head module to be adjusted, according to control of the control unit  126 . The pattern for measurement recorded in step S 12  corresponds to a form of the “first test pattern”. Step S 12  corresponds to a form of a “step of recording the first test pattern”. In addition, in step S 13 , the ink jet recorder  100  records a pattern for measurement to be used for measuring a recording shift amount in a non-complementary region in the first head module on a paper sheet S, according to control of the control unit  126 . The pattern for measurement recorded in step S 13  corresponds to a form of the “second test pattern”. Step S 13  corresponds to a form of a “step of recording the second test pattern”. 
     Further, in step S 14 , the ink jet recorder  100  records a pattern for measurement to be used for measuring a recording shift amount in a non-complementary region in the second head module on a paper sheet S, according to control of the control unit  126 . The pattern for measurement recorded in step S 14  corresponds to a form of the “third test pattern”. Step S 14  corresponds to a form of a “step of recording the third test pattern”. 
     Each of the first test pattern that is a pattern for measurement to be used for measuring a recording shift amount in a complementary region, the second test pattern that is a pattern for measurement to be used for measuring a recording shift amount in a non-complementary region in the first head module, and the third test pattern that is a pattern for measurement to be used for measuring a recording shift amount in a non-complementary region in the second head module, may be recorded on the same paper sheet S, or may be separately recorded in different paper sheets S. Implement order of the step of recording the first test pattern of step S 12 , the step of recording the second test pattern of step S 13 , and the step of recording the third test pattern of step S 14 , is not limited, and a plurality of steps of recording a test pattern may be simultaneously implemented. 
     In each of the step of recording the first test pattern of step S 12 , the step of recording the second test pattern of step S 13 , and the step of recording the third test pattern of step S 14 , a step of feeding a recording medium corresponds to a form of the “feeding step”. 
     In step S 15 , a recorded result of each of patterns for measurement of the first test pattern, the second test pattern, and the third test pattern, is read out by using the scanner  114 . The scanner  114  reads out the recorded result of each of the patterns for measurement to create readout data. 
     The recorded result of each of patterns for measurement of the first test pattern, the second test pattern, and the third test pattern, may be separately read out, or the patterns for measurement may be collectively read out at a time. In step S 15 , readout data on the recorded result of each of the first test pattern, the second test pattern, and the third test pattern, is acquired. Step S 15  corresponds to a form of the “reading step”. 
     In step S 16 , the first measurement unit  141  of the image analysis unit  128  measures a recording shift amount in a complementary region on the basis of readout data on the first test pattern. The recording shift amount in the complementary region measured in step S 16  corresponds to a form of the “complementary region recording shift amount”. Step S 16  corresponds to a form of the “first measurement step”. 
     In step S 17 , the second measurement unit  142  of the image analysis unit  128  measures a recording shift amount in a non-complementary region in each of the first head module and the second head module on the basis of readout data on the second test pattern and the third test pattern. The recording shift amount in the non-complementary region in the first head module is measured from readout data on the second test pattern. The recording shift amount in the non-complementary region in the second head module is measured from readout data on the third test pattern. 
     The recording shift amount in the non-complementary region in the first head module measured in step S 17  corresponds to a form of the “first non-complementary region recording shift amount”. The recording shift amount in the non-complementary region in the second head module measured in step S 17  corresponds to a form of the “second non-complementary region recording shift amount”. Step S 17  corresponds to a form of the “second measurement step”. 
     In step S 18 , the control unit  126  calculates a timing adjustment value so that a recording shift amount in a complementary region to be adjusted becomes an average value of a recording shift amount in the non-complementary region in the first head module and a recording shift amount in the non-complementary region in the second head module. The timing adjustment value calculated in step S 18  corresponds to a form of the “adjustment value of discharge timing”. Step S 18  corresponds to a form of the “calculation step”. The timing adjustment value may indicate an adjustment amount of discharge timing of each of the first head module and the second head module, or may indicate an adjustment amount of discharge timing of any one of the first head module and the second head module. 
     In step S 19 , the control unit  126  adjusts relative discharge timing of the first head module and the second head module in accordance with the timing adjustment value calculated in step S 18 . The control unit  126  sets a delay amount of each of the corresponding timing correction units  134 - n  and  134 -( n+ 1) in the timing adjustment unit  132  in accordance with the timing adjustment value. A combination of step S 18  and step S 19  corresponds to a form of the “timing adjustment step”. 
     Preferable Conditions for Measuring Recording Shift Amount 
     Preferable conditions for measuring a recording shift amount in a non-complementary region in each of head modules adjacent to each other will be described. 
     Preferable Condition 1 
     It is preferable that a recording shift amount in a non-complementary region in each of head modules adjacent to each other is measured at a position close to a complementary region. This enables uneven concentration caused by a difference in recording shift amount between the non-complementary region and the complementary region to be further reduced. 
     A guideline of the “position close to the complementary region” will be described with reference to  FIG. 16 .  FIG. 16  is a schematic plane view of the n-th head module  12 - n  and the (n+1)-th head module  12 -( n+ 1). In  FIG. 16 , illustration of nozzles is eliminated. 
     There is a complementary region  150  in a joined portion between the n-th head module  12 - n  as the first head module, and the (n+1)-th head module  12 -( n+ 1) as the second head module. When the first non-complementary region recording shift amount that is a recording shift amount in the non-complementary region in the first head module is measured, it is preferable to measure it by using a region  152  closer to the (n+1)-th head module  12 -( n+ 1) than a center position C 1  of the head module  12 - n  in the X-direction in a non-complementary region  151  in the n-th head module  12 - n . It is further preferable to measure the first non-complementary region recording shift amount at a position in proximity to the complementary region  150 , as designated by a reference numeral  153 . 
     Likewise, when the second non-complementary region recording shift amount that is a recording shift amount in the non-complementary region in the second head module is measured, it is preferable to measure it by using a region  157  closer to the n-th head module  12 - n  than a center position C 2  of the head module  12 -( n+ 1) in the X-direction in a non-complementary region  156  in the (n+1)-th head module  12 -( n+ 1). It is further preferable to measure the second non-complementary region recording shift amount at a position in proximity to the complementary region  150 , as designated by a reference numeral  158 . 
     Preferable Condition 2 
     In addition, it is preferable that measurement of a recording shift amount is performed to measure an amount of displacement of a recording position of each of nozzles away from each other in the Y-direction to the maximum in nozzles in proximity to each other in the X-direction. A guideline of proximity in “nozzles in proximity to each other in the X-direction” can be represented as nozzles in proximity to each other in the X-direction within a nozzle range in the X-direction with a width equivalent to a width of a complementary region that is a width of the complementary region  150  in the X-direction, for example. In a case of the nozzle array illustrated in  FIG. 6 , a range of nozzles in the X-direction to be used for measurement of a recording shift amount in a complementary region is 64 pixels, and thus when a recording shift amount in a non-complementary region is measured, it is preferable to measure an amount of displacement of a recording position of each of nozzles away from each other in the Y-direction to the maximum within a range of nozzles in the X-direction equivalent to 64 pixels in the non-complementary region. 
     That is, when the first non-complementary region recording shift amount is measured, it is preferable to measure an amount of displacement of a recording position of each of nozzles away from each other in the Y-direction to the maximum, in nozzles in proximity to each other in the X-direction within a range of nozzles in the X-direction with a width equivalent to a width of a complementary region that is a width of the complementary region  150  in the X-direction, in nozzles belonging to a non-complementary region  151  in the first head module. In addition, when the second non-complementary region recording shift amount is measured, it is preferable to measure an amount of displacement of a recording position of each of nozzles away from each other in the Y-direction to the maximum, in nozzles in proximity to each other in the X-direction within a range of nozzles in the X-direction with a width equivalent to a width of a complementary region, in nozzles belonging to a non-complementary region  156  in the second head module. 
     In a case of the nozzle array illustrated in  FIG. 6 , nozzles belonging to a nozzle array in a row direction in the first row on the most paper feeding side, and nozzles belonging to a nozzle array in a row direction in the thirty second row on the most paper ejection side, correspond to the “nozzles away from each other to the maximum”. 
     It is further preferable to satisfy the conditions of both of the “preferable condition 1” and the “preferable condition 2” described above. 
     Configuration Example of Ink Jet Recorder 
       FIG. 17  is a general structural view of the ink jet recorder according to the present embodiment. The ink jet recorder  100  is an image forming apparatus of a single pass method, provided with a line head, and draws an image on a cut-sheet paper S by using ink. The paper sheet S is a form of a “recording medium” to be used for image formation. 
     The ink jet recorder  100  includes a paper feeding unit  212 , a treatment liquid applying unit  214 , a treatment liquid drying processing unit  216 , a drawing unit  218 , an ink drying processing unit  220 , and a paper ejection unit  224 . 
     The paper feeding unit  212  includes a paper feeding base  230 , a paper feeding device  232 , a pair of paper feeding rollers  234 , a feeder board  236 , a front stopper  238 , and a paper feeding barrel  240 . The paper sheets S loaded on the paper feeding base  230  is pulled up one by one from top to bottom by suction fitting of the paper feeding device  232  to be fed to the pair of paper feeding rollers  234 . In the present example, while cut-sheet paper is used as the paper sheet S, there is available a configuration of feeding a paper sheet by cutting a continuous paper sheet into a sheet of a required size. 
     The paper sheet S fed to the pair of paper feeding rollers  234  is fed forward in a paper sheet feeding direction by the pair of paper feeding rollers  234  to be loaded on the feeder board  36 . The paper sheet S loaded on the feeder board  236  is pressed on a feeding face of the feeder board  236  by a retainer  236 A and a guide roller  236 B during a feeding process by using the feeder board  236 , and thus its unevenness is corrected. 
     A leading end of the paper sheet S fed by the feeder board  236  is brought into contact with the front stopper  238 , and then an inclination of the paper sheet S is corrected. After that, the paper sheet S is delivered to the paper feeding barrel  240 . 
     The paper feeding barrel  240  includes a gripper  240 A. The gripper  240 A is holding means for holing a leading end of the paper sheet S. The gripper  240 A includes a plurality of claws, a claw base, and a gripper shaft, which are not illustrated. The plurality of claws of the gripper  240 A is arranged along a direction parallel to a rotation shaft  240 B of the paper feeding barrel  240 . Base ends of the plurality of claws are supported by a gripper shaft in a swingable manner. Arrangement intervals of the plurality of claws, and a length of a region where the plurality of claws is arranged, are determined in accordance with a size of the paper sheet S. The claw base is a member whose longitudinal direction is parallel to the rotation shaft  240 B of the paper feeding barrel  240 . A length of the claw base is equal to or more than the length of the region where the plurality of claws is arranged in a longitudinal direction of the paper feeding barrel  240 . The claw base is arranged at a position facing leading ends of the plurality of claws. 
     The paper sheet S delivered from the feeder board  236  to the paper feeding barrel  240  is fed to the treatment liquid applying unit  214  while its leading end is held by the gripper  240 A of the paper feeding barrel  240 . 
     The treatment liquid applying unit  214  is means for applying a treatment liquid on a recording face of the paper sheet S. The treatment liquid applying unit  214  includes a treatment liquid barrel  242 , and a treatment liquid applying device  244 . The treatment liquid contains a component that agglomerates color material in ink, or increases viscosity of the color material. A specific method of agglomerating color material, or increasing viscosity of the color material, includes a method of using treatment liquid that reacts with ink to precipitate or insolubilize color material in the ink, and a method of using treatment liquid that creates gel being a semi-solid substance containing color material in ink. Means for causing reaction between ink and treatment liquid includes a method of causing anionic color material in ink and a cationic compound in treatment liquid to react with each other, a method of mixing ink and treatment liquid, having potential of hydrogen (pH) different from each other, to change the pH of the ink to cause distribution rupture of a pigment in ink, thereby agglomerating the pigment, and a method of causing distribution rupture of a pigment in ink by using reaction to multivalent metal salt in treatment liquid to agglomerate the pigment, for example. 
     The treatment liquid barrel  242  has a diameter double that of the paper feeding barrel  240 . The treatment liquid barrel  242  is provided with grippers  242 A at two respective places in the circumferential direction. Placement positions of the two respective grippers  242 A are 180° apart on an outer peripheral surface  242 C of the treatment liquid barrel  242 . The gripper  242 A may have structure similar to that of the gripper  240 A of the paper feeding barrel  240 . 
     The treatment liquid barrel  242  has structure in which a paper sheet S is fixed to the outer peripheral surface  242 C on which the paper sheet S is supported. An example of the structure in which a paper sheet S is fixed to the outer peripheral surface  242 C of the treatment liquid barrel  242  includes structure in which the outer peripheral surface  242 C of the treatment liquid barrel  242  is provided with a plurality of absorption holes so that negative pressure is applied to the plurality of absorption holes. As structure of the treatment liquid barrel  242  other than that described above, structure similar to that of the paper feeding barrel  240  can be used. Reference numeral  242 B designates a rotation shaft of the treatment liquid barrel  242 . 
     The treatment liquid applying device  244  may use a roller coating method. The treatment liquid applying device  244  of the roller coating method may use structure in which a treatment liquid reservoir, a metering roller, and a coating roller are provided. An illustration of each of the treatment liquid reservoir, the metering roller, and the coating roller is eliminated. 
     The treatment liquid reservoir stores treatment liquid that is supplied from a treatment liquid tank through a treatment liquid supply system. An illustration of each of the treatment liquid supply system and the treatment liquid tank is eliminated. The metering roller measures the treatment liquid stored in the treatment liquid reservoir. The metering roller transfers the measured treatment liquid to the coating roller. The coating roller applies the treatment liquid to a paper sheet S. 
     The structure of the treatment liquid applying device  244  described above is only an example, and the treatment liquid applying device  244  may use another method. In addition, the treatment liquid applying device  244  may have another structure. An example of another method of the treatment liquid applying device  244  includes coating using a blade, discharge by an ink-jet method, and spray by a spray method. 
     Turning the treatment liquid barrel  242  while a leading end of a paper sheet S is held by the gripper  242 A allows the paper sheet S to be fed along an outer peripheral surface of the treatment liquid barrel  242 . The treatment liquid applying device  244  applies treatment liquid to the paper sheet S fed along the outer peripheral surface of the treatment liquid barrel  242 . The paper sheet S to which the treatment liquid is applied is fed to the treatment liquid drying processing unit  216 . 
     The treatment liquid drying processing unit  216  includes a treatment liquid drying processing barrel  246 , a paper sheet feeding guide  248 , and a treatment liquid drying processing unit  250 . The treatment liquid drying processing unit  216  applies drying processing to the paper sheet S to which the treatment liquid is applied. The treatment liquid drying processing barrel  246  has a diameter equivalent to that of the treatment liquid barrel  242 , and is provided with grippers  246 A at two respective places in a circumferential direction, as with the treatment liquid barrel  242 . The gripper  246 A may have structure similar to that of the gripper  240 A of the paper feeding barrel  240 . Reference numeral  246 B designates a rotation shaft of the treatment liquid drying processing barrel  246 . 
     The paper sheet feeding guide  248  is disposed at a position facing the outer peripheral surface  246 C of the treatment liquid drying processing barrel  246 . The paper sheet feeding guide  248  is disposed on a lower side of the treatment liquid drying processing barrel  246 . In the present specification, the “lower side” is a side of a direction of gravitational force, and an “upper side” is a side opposite to the direction of gravitational force. 
     The treatment liquid drying processing unit  250  is disposed inside the treatment liquid drying processing barrel  246 . The treatment liquid drying processing unit  250  includes a blower that blows toward the outside of the treatment liquid drying processing barrel  246 , and a heater that heats air. For convenience of illustration, a reference numeral of each of the blower and the heater is eliminated. 
     A leading end of the paper sheet S delivered from the treatment liquid applying unit  214  to the treatment liquid drying processing unit  216  is held by the gripper  246 A of the treatment liquid drying processing barrel  246 . 
     The paper sheet S is held by the gripper  246 A while its face coated with the treatment liquid faces the inside of the treatment liquid drying processing barrel  246 , and its face opposite to the face coated with the treatment liquid is supported by the paper sheet feeding guide  248 . Turning the treatment liquid drying processing barrel  246  allows the paper sheet S to be fed along the outer peripheral surface  246 C of the treatment liquid drying processing barrel  246 . 
     The treatment liquid drying processing unit  250  blows heated air to the paper sheet S fed by the treatment liquid drying processing barrel  246  to perform drying processing. 
     When the drying processing is applied to the paper sheet S, a solvent component in the treatment liquid applied to the paper sheet S is removed to form a treatment liquid layer in the face coated with the treatment liquid of the paper sheet S. The paper sheet S to which the drying processing is applied by the treatment liquid drying processing unit  216  is delivered to the drawing unit  218 . 
     The drawing unit  218  includes a drawing barrel  252 , a paper sheet pressing roller  254 , recording heads  256 C,  256 M,  256 Y, and  256 K, and an in-line sensor  258 . A gripper  252 A of the drawing barrel  252  is disposed in a recessed portion provided in the outer peripheral surface  252 C of the drawing barrel  252 . Structure similar to that of the gripper  240 A of the paper feeding barrel  240  may be used for structure of the gripper  252 A other than placement thereof. 
     The grippers  252 A are disposed at two respective places in the drawing barrel  252 , as with the treatment liquid barrel  242 . In addition, absorption holes for absorbing a paper sheet S are arranged in a medium support region, where the paper sheet S is to be supported, in the outer peripheral surface  252 C of the drawing barrel  252 . An illustration of each of the absorption hole, and the medium support region is eliminated. As structure of the drawing barrel  252  other than that described above, structure similar to that of the treatment liquid barrel  242  can be used. Reference numeral  252 B designates a rotation shaft of the drawing barrel  252 . 
     The paper sheet pressing roller  254  presses a paper sheet S toward the drawing barrel  252  to bring the paper sheet S into close contact with an outer peripheral surface of the drawing barrel  252 . The paper sheet pressing roller  254  is disposed downstream of a delivery position of a paper sheet S, as well as upstream of the recording head  256 C, in a feeding direction of a paper sheet S in the drawing barrel  252 . In the following description, the feeding direction of a paper sheet S may be sometimes referred to as a paper sheet feeding direction. The outer peripheral surface of the drawing barrel  252  corresponds to a form of the “curved face”. A step of feeding a paper sheet S by using the drawing barrel  252  corresponds to a form of the “feeding step”. 
     Each of the recording heads  256 C,  256 M,  256 Y, and  256 K is an ink jet head in which liquid is discharged by an ink-jet method. The letter added to a reference numeral of each of the recording heads represents color of ink. The letter C represents cyan. The letter M represents magenta. The letter Y represents yellow. The letter K represents black. 
     Each of the recording heads  256 C,  256 M,  256 Y, and  256 K is equivalent to the recording head  10  illustrated in  FIG. 1 . To each of the recording heads  256 C,  256 M,  256 Y, and  256 K, ink is supplied from an ink tank (not illustrated) that is an ink supply source of the corresponding color through a piping path (not illustrated). 
     Each of the recording heads  256 C,  256 M,  256 Y, and  256 K is an ink jet head of a full line type with a width in which drawing is allowed, the width corresponding to a maximum width of an image formation region in a paper sheet S. Each of the recording heads  256 C,  256 M,  256 Y, and  256 K has structure equivalent to that of the recording head  10  illustrated in  FIG. 1 . In a discharge face of each of the recording heads  256 C,  256 M,  256 Y, and  256 K, nozzle arrays in each of which a plurality of nozzle apertures being liquid discharge ports is arranged are formed throughout the width in which drawing is allowed. In the present disclosure, a recording head may be sometimes referred to as simply a “head”. 
     Each of the recording heads  256 C,  256 M,  256 Y, an  256 K is disposed above the drawing barrel  252  in a posture in which a nozzle face of each of the heads is inclined with respect to a horizontal surface so that a nozzle face of each of the heads has a substantially constant interval with respect to a peripheral surface of the drawing barrel  252 . That is, the recording heads  256 C,  256 M,  256 Y, and  256 K are radially disposed on a concentric circle centering the rotation shaft  252 B of the drawing barrel  252  at predetermined intervals in a circumferential direction. In the present example, the four heads are symmetrically disposed across a vertical line (center line) passing through the rotation center of the drawing barrel  252 . 
     As described above, the nozzle face of each of the recording heads  256 C,  256 M,  256 Y, and  256 K is disposed to face the outer peripheral surface of the drawing barrel  252 , as well as is disposed at a position at a predetermined height from the outer peripheral surface of the drawing barrel  252  in a radial direction (direction perpendicular to the outer peripheral surface). That is, the same amount of gap is formed between the outer peripheral surface of the drawing barrel  252  and the nozzle face of each of the heads. 
     The recording heads  256 C,  256 M,  256 Y, and  256 K are disposed along a circumferential direction of the drawing barrel  252  in the order of the recording head  256 C, the recording head  256 M, the recording head  256 Y, and the recording head  256 K from an upstream side in the paper sheet feeding direction. 
     While the present example shows a configuration in which four color inks of standard colors of CMYK are used, a combination of ink color and the number of colors is not limited to that of the present embodiment. Any one of a light color ink, a dark color ink, a specific color ink, and the like may be added to a configuration in which four color inks of CMYK are used, as needed. For example, there are also available a configuration in which a recording head for discharging a light color ink such as light cyan and light magenta is added, and a configuration in which a recording head for discharging a specific color ink such as green and orange is added. In addition, the order of placement of a recording head of each color is not particularly limited. 
     While there is no illustration, the four recording heads  256 C,  256 M,  256 Y, and  256 K are supported by a common head support frame. The entire head unit composed of the four recording head  256 C,  256 M,  256 Y, and  256 K, attached to the head support frame, can be moved together with the head support frame in a radial direction of the drawing barrel  252 . In addition, the entire head unit of the four recording heads  256 C,  256 M,  256 Y, and  256 K can be moved together with the head support frame in an axial direction of the drawing barrel  252 . 
     Further, while there is no illustration, each of the recording heads  256 C,  256 M,  256 Y, and  256 K is supported by a movable support mechanism that is movable in a normal direction of the nozzle face. The movable support mechanism is able to adjust a distance (gap) between the nozzle face of each of the heads and the outer peripheral surface of the drawing barrel  252 , as well as change height of the head at a maintenance position for each of the heads. 
     During a process in which a paper sheet S is fed by the drawing barrel  252 , ink is deposited on the paper sheet S from the recording heads  256 C,  256 M,  256 Y, and  256 K to record an image on the paper sheet S. Feeding a paper sheet S at a predetermined speed by using rotation of the drawing barrel  252  and performing relative movement between the paper sheet S and each of the recording heads  256 C,  256 M,  256 Y, and  256 K in the paper sheet feeding direction only once enable an image to be recorded in an image formation region in the paper sheet S. A recording method of completing an image by one scan as described above is called a single pass method. 
     The in-line sensor  258  is disposed downstream of the recording head  256 K in the paper sheet feeding direction. The in-line sensor  258  includes an imaging element, a periphery circuit of the imaging element, and a light source. Illustration of each of the imaging element, the periphery circuit of the imaging element, and the light source, is eliminated. As the imaging element, a solid imaging element, such as a CCD image sensor and a CMOS image sensor, is available. The CCD is an abbreviation of charge coupled device. The CMOS is an abbreviation of complementary metal-oxide semiconductor. 
     The periphery circuit of the imaging element includes a processing circuit of an output signal of the imaging element. The processing circuit includes a filter circuit of removing a noise component from an output signal of the imaging element, an amplifier circuit, and a waveform shaping circuit, for example. Illustration of each of the filter circuit, the amplifier circuit, and the waveform shaping circuit, is eliminated. 
     The light source is disposed at a position from which a reading object of the in-line sensor  258  can be irradiated with illumination light. An LED, a lamp, and the like are available for the light source. The LED is an abbreviation of light emitting diode. The in-line sensor  258  corresponds to an element illustrated in  FIG. 14  as the scanner  114 . 
     A leading end of a paper sheet S delivered from the treatment liquid drying processing unit  216  to the drawing unit  218  is held by the gripper  252 A of the drawing barrel  252 . The paper sheet S whose leading end is held by the gripper  252 A of the drawing barrel  252  is fed along the outer peripheral surface  252 C of the drawing barrel  252  by rotation of the drawing barrel  252 . 
     The paper sheet S is pressed on the outer peripheral surface  252 C of the drawing barrel  252  when passing through below the paper sheet pressing roller  254 . The paper sheet S passing through below the paper sheet pressing roller  254  reaches a position immediately below the recording heads  256 C,  256 M,  256 Y, and  256 K, and then an image is formed on the paper sheet S by ink discharged from each of the recording heads  256 C,  256 M,  256 Y, and  256 K. 
     The image formed on the paper sheet S by the recording heads  256 C,  256 M,  256 Y, and  256 K is read out by the in-line sensor  258  in a reading region of the in-line sensor  258 . 
     The paper sheet S from which the image is read out by the in-line sensor  258  is delivered from the drawing unit  218  to the ink drying processing unit  220 . It may be determined whether there is abnormal discharge from a result of image reading performed by the in-line sensor  258 . 
     The ink drying processing unit  220  includes a chain gripper  264 , an ink drying processing unit  268 , and a guide plate  272 . The chain gripper  264  includes a first sprocket  264 A, a second sprocket  264 B, a chain  264 C, and a plurality of grippers  264 D. 
     The chain gripper  264  has a structure in which a pair of endless chains  264 C is stretched between a pair of the first sprockets  264 A and a pair of the second sprockets  264 B.  FIG. 17  illustrates only one of the pair of first sprockets  264 A, one of the pair of second sprockets  264 B, and one of the pair of chains  264 C. 
     The chain gripper  264  also has a structure in which the plurality of grippers  264 D is disposed between the pair of chains  264 C. In addition, the chain gripper  264  has a structure in which the plurality of grippers  264 D is disposed at respective positions in the paper sheet feeding direction.  FIG. 17  illustrates only one of the plurality of grippers  264 D disposed between the pair of chains  264 C. 
     A feeding path of a paper sheet S by using the chain gripper  264  includes a horizontal feeding region where a paper sheet S is fed along a horizontal direction, and an inclined feeding region where a paper sheet S is fed in an oblique upward direction. 
     The ink drying processing unit  268  is disposed above a feeding path of a paper sheet S in the chain gripper  264 . A structural example of the ink drying processing unit  268  includes a structure provided with a heat source, such as a halogen heater and an infrared ray heater. Another structural example of the ink drying processing unit  268  includes a structure provided with a fan that blows air heated by the heat source to a paper sheet S. The ink drying processing unit  268  may include not only the heat source but also the fan. 
     While detailed illustration of the guide plate  272  is eliminated, a plate-shaped member may be used for the guide plate  272 . The guide plate  272  has a length in a direction orthogonal to the paper sheet feeding direction, the length exceeding an overall length of a paper sheet S. 
     The guide plate  272  is disposed along a feeding path of a paper sheet S by using the chain gripper  264  in the horizontal feeding region. The guide plate  272  is disposed below the feeding path of a paper sheet S by using the chain gripper  264 . The guide plate  272  has a length in the paper sheet feeding direction, the length corresponding to a length of a processing region of the ink drying processing unit  268 . 
     The length corresponding to the length of the processing region of the ink drying processing unit  268  is a length of the guide plate  272 , allowing a paper sheet S to be supported by the guide plate  272 , during processing of the ink drying processing unit  268 . For example, there is provided an aspect in which a length of the processing region of the ink drying processing unit  268  is equal to a length of the guide plate  272 , in the paper sheet feeding direction. The guide plate  272  may include a function of absorbing and supporting a paper sheet S. 
     A leading end of the paper sheet S delivered from the drawing unit  218  to the ink drying processing unit  220  is held by a gripper  264 D. When at least one of the first sprocket  264 A and the second sprocket  264 B is turned clockwise in  FIG. 17  to run the chain  264 C, the paper sheet S is fed along a running path of the chain  264 C. 
     When a paper sheet S passes through the processing region of the ink drying processing unit  268 , the ink drying processing unit  268  applies ink drying processing to the paper sheet S. 
     The paper sheet S to which the ink drying processing unit  268  applies the ink drying processing is fed to the paper ejection unit  224  by the chain gripper  264 . 
     The chain gripper  264  feeds the paper sheet S in an oblique upper left direction in  FIG. 17  on a downstream side of the ink drying processing unit  268  in the paper sheet feeding direction. In a feeding path in an inclined feeding region where the paper sheet S is fed in the oblique upper left direction in  FIG. 17 , a guide plate  273  is disposed. For the guide plate  273 , a member similar to the guide plate  272  is available. Descriptions of a structure and a function of the guide plate  273  are eliminated. 
     The paper ejection unit  224  includes a paper ejection base  276 . The chain gripper  264  is used for feeding of a paper sheet S in the paper ejection unit  224 . The paper ejection base  276  is disposed below the feeding path of a paper sheet S by using the chain gripper  264 . The paper ejection base  276  may include a lifting mechanism (not illustrated). The paper ejection base  276  can be moved up and down in accordance with increase and decrease in the number of loaded paper sheets S to maintain a paper sheet S placed at an uppermost position at a predetermined height. 
     The paper ejection unit  224  recovers a paper sheet S to which a series of processing of image formation is applied. When a paper sheet S reaches a position of the paper ejection base  276 , the gripper  264 D releases holding of the paper sheet S. The paper sheet S is then loaded on the paper ejection base  276 . 
     While  FIG. 17  illustrates the ink jet recorder  100  including the treatment liquid applying unit  214  and the treatment liquid drying processing unit  216 , a form without the treatment liquid applying unit  214  and the treatment liquid drying processing unit  216  is also available. 
     In addition, while  FIG. 17  illustrates the chain gripper  264  as a structure for feeding a paper sheet S after being drawn, another structure, such as belt-feeding and drum-feeding, may be available for feeding a paper sheet S after being drawn. 
     While illustration is eliminated in  FIG. 17 , the ink jet recorder  100  includes a maintenance unit. The maintenance unit is juxtaposed with the drawing barrel  252  in an axial direction of the rotation shaft  252 B of the drawing barrel  252 . 
     Description of Control System of Ink Jet Recorder  100   
       FIG. 18  is a block diagram illustrating an outline structure of a control system of the ink jet recording device  100 . The ink jet recorder  100  includes a system controller  300 . The system controller  300  includes a CPU  300 A, a ROM  300 B, and a RAM  300 C. The CPU is an abbreviation of central processing unit. The ROM is an abbreviation of read only memory. The RAM is an abbreviation of random access memory. Memory such as the ROM  300 B and the RAM  300 C may be provided outside the system controller  300 . 
     The system controller  300  serves as a general control unit for integrally controlling each unit of the ink jet recorder  100 . In addition, the system controller  300  serves as a calculation unit for performing various kinds of calculation processing. Further, the system controller  300  serves as a memory controller for controlling reading of data and writing of data in memory such as the ROM  300 B and the RAM  300 C. 
     The ink jet recorder  100  includes a communication unit  302 , an image memory  304 , a feeding control unit  310 , a paper feeding control unit  312 , a treatment liquid applying control unit  314 , a treatment liquid drying control unit  316 , a drawing control unit  318 , an ink drying control unit  320 , and a paper ejection control unit  324 . 
     The communication unit  302  includes a communication interface (not illustrated), and is capable of performing transmission and reception of data with a host computer  400  connected to the communication interface. 
     The image memory  304  serves as a temporarily storage unit for various kinds of data including image data. Image data taken from the host computer  400  through the communication unit  302  is temporarily stored in the image memory  304 . 
     The feeding control unit  310  controls operation of a feeding system  211  of a paper sheet S in the ink jet recorder  100 . The feeding system  211  includes the treatment liquid barrel  242 , the treatment liquid drying processing barrel  246 , the drawing barrel  252 , and the chain gripper  264 , illustrated in  FIG. 17 . 
     The paper feeding control unit  312  illustrated in  FIG. 18  operates the paper feeding unit  212  in response to a command from the system controller  300 . The paper feeding control unit  312  controls a supply start operation of a paper sheet S and a supply stop operation of a paper sheet S, for example. 
     The treatment liquid applying control unit  314  operates the treatment liquid applying unit  214  in response to a command from the system controller  300 . The treatment liquid applying control unit  314  controls a quantity of application of treatment liquid and timing of the application, for example. 
     The treatment liquid drying control unit  316  operates the treatment liquid drying processing unit  216  in response to a command from the system controller  300 . The treatment liquid drying control unit  316  controls a drying temperature, a flow rate of drying gas, and injection timing of the drying gas, for example. 
     The drawing control unit  318  controls operation of the drawing unit  218  in response to a command from the system controller  300 . 
     The drawing control unit  318  includes an image processing section, a waveform creation section, a waveform storage section, and a driving circuit. Illustration of the image processing section, the waveform creation section, the waveform storage section, and the driving circuit, is eliminated. The image processing section forms dot data from input image data. The waveform creation section creates a waveform of driving voltage. The waveform storage section stores the waveform of driving voltage. The driving circuit creates driving voltage with a driving waveform corresponding to dot data. The driving circuit supplies driving voltage to a liquid discharge head. 
     The image processing section applies the following to input image data: color separation processing of separating input image data into each color of RGB; color conversion processing of converting RGB into CMYK; correction processing, such as gamma correction and unevenness correction; and halftone processing of converting a gradation value for each color pixel into a gradation value less than an original gradation value. 
     The input image data includes raster data indicated by digital values from 0 to 255, for example. The dot data acquired as a result of the halftone processing may be a binary image, or a multiple value image of not less than a ternary value and less than a gradation value before the halftone processing. 
     Discharge timing and an amount of discharge of ink, at each pixel position, are determined on the basis of the dot data created through processing by the image processing section. Then, driving voltage in accordance with the discharge timing and the amount of discharge of ink, at each pixel position, and a control signal of determining discharge timing of the each pixel, are created. The driving voltage is supplied to the liquid discharge head, and dots are recorded with ink discharged from the liquid discharge head. 
     The drawing control unit  318  may include a correction processing section (not illustrated). The correction processing section performs correction processing for an abnormal nozzle. When the correction processing is performed, deterioration in image quality caused by occurrence of an abnormal nozzle is reduced. 
     The ink drying control unit  320  operates the ink drying processing unit  220  in response to a command from the system controller  300 . The ink drying control unit  320  controls a temperature of drying gas, a flow rate of the drying gas, or injection timing of the drying gas, for example. 
     The paper ejection control unit  324  operates the paper ejection unit  224  in response to a command from the system controller  300 . In a case where the paper ejection base  276  illustrated in  FIG. 17  includes a lifting mechanism, the paper ejection control unit  324  controls operation of the lifting mechanism in accordance with increase and decrease in the number of paper sheets S. 
     In addition, the ink jet recorder  100  includes an operation unit  330 , a display  332 , a parameter storage unit  334 , and a program storage unit  336 . 
     The operation unit  330  includes an operation member such as an operation button, a keyboard, and a touch panel. The operation unit  330  may include a plurality of kinds of operation member. Illustration of the operation member is eliminated. 
     Information inputted through the operation unit  330  is transmitted to the system controller  300 . The system controller  300  causes various kinds of processing to be performed in accordance with the information transmitted from the operation unit  330 . 
     The display  332  includes a display device such as a liquid crystal panel, and a display driver. Illustration of the display device and the display driver is eliminated. The display  332  causes a display device to display various kinds of information, such as various kinds of setting information on devices, and abnormality information, in response to a command from the system controller  300 . The operation unit  330  and the display  332  constitute a user interface. 
     The parameter storage unit  334  stores various parameters to be used in the ink jet recorder  100 . The various parameters stored in the parameter storage unit  334  are read out through the system controller  300  to be set in each unit of the recorder. 
     The program storage unit  336  stores programs to be used in respective units in the ink jet recorder  100 . The various programs stored in the program storage unit  336  are read out through the system controller  300  to be executed in the respective units of the recorder. 
     The ink jet recorder  100  includes a maintenance control unit  338 . The maintenance control unit  338  controls operation of the maintenance unit  280  in response to a command from the system controller  300 . 
       FIG. 18  illustrates respective units for each function in the ink jet recorder  100 . Each of the units illustrated in  FIG. 18  can be appropriately integrated, separated, shared, or eliminated. Each of the units illustrated in  FIG. 18  can be configured by appropriately combining hardware and software. 
     The system controller  300  is able to serve as the image processing unit  122 , the test pattern creation unit  124 , the control unit  126 , and the image analysis unit  128 , illustrated in  FIG. 14 . In addition, the drawing control unit  318  or the system controller  300 , or a combination thereof, is able to serve as the reference signal generation unit  130  and the timing adjustment unit  132 , illustrated in  FIG. 14 . The feeding system  211  illustrated in  FIG. 18  includes the feeding unit  112  illustrated in  FIG. 14 . The communication unit  302  illustrated in  FIG. 18  is able to serve as the image input interface illustrated in  FIG. 14 . 
     Discharge timing is adjusted by using a method for adjusting a recording head, illustrated in  FIGS. 12 to 16 , for each of the recording heads  256 C,  256 M,  256 Y, and  256 K in the ink jet recorder  100  illustrated in  FIGS. 17 and 18 . 
     Advantages of Embodiment 
     The present embodiment described above has advantages as follow. 
     (1) According to the present embodiment, uneven concentration in a joined portion between head modules constituting a recording head can be prevented from occurring. 
     (2) According to the present embodiment, a recording shift of a recording head can be adjusted without adjusting an angle in a θz-direction, being an attachment angle of the recording head, and thus deviation of squareness of an image, which is a problem caused by a conventional method, is less likely to occur. 
     (3) The method for adjusting a recording head described in the present embodiment particularly has an effect in a case where an image is recorded on a paper sheet S in close contact with a curved face, such as a drum-feeding structure illustrated in  FIG. 17 . 
     (4) Since the present embodiment does not need to provide a structure for adjusting discharge timing for each of nozzle arrays different in position in the Y-direction, uneven concentration of a recording head can be prevented by a structure for relatively adjusting discharge timing in units of head module. Thus, reduction in uneven concentration can be achieved with a simple structure as compared with a system configuration in which discharge timing is adjusted for each nozzle array. 
     Variation 1 
     While  FIG. 6  illustrates a nozzle array in which a paper feeding side nozzle group at 600 dpi and a paper ejection side nozzle group at 600 dpi are disposed away from each other in the Y-direction, a placement of the nozzle groups is not limited to that in which the paper feeding side nozzle group and the paper ejection side nozzle group are away from each other in the Y-direction, when the invention is practiced. Even in a nozzle array of a single nozzle group, it can be relatively divided into a paper feeding side nozzle and a paper ejection side nozzle. For example, in a nozzle array of a two dimensional matrix, a nozzle disposed in a region on a paper feeding side, being a proximal side in the paper sheet feeding direction, can serve as a paper feeding side nozzle, and a nozzle disposed in a region on a paper ejection side, being a back side in the paper sheet feeding direction, can serve as a paper ejection side nozzle. 
     Variation 2 
     While an example in which discharge timing is adjusted so that a recording shift amount in a complementary region in adjacent head modules becomes an average value of a first non-complementary region recording shift amount and a second non-complementary region recording shift amount in the embodiment described above, a form of adjusting discharge timing is not limited to that in which discharge timing is adjusted so that a recording shift amount in the complementary region becomes an average value of the first non-complementary region recording shift amount and the second non-complementary region recording shift amount, when the invention is practiced. There is also available a form in which discharge timing is adjusted so that a recording shift amount in a complementary region in adjacent head modules becomes an appropriate value between the first non-complementary region recording shift amount and the second non-complementary region recording shift amount. 
     In addition, in a case where the first non-complementary region recording shift amount and the second non-complementary region recording shift amount in adjacent head modules are equal to each other, or where a difference between the recording shift amounts is very small, discharge timing may be adjusted so that a recording shift amount in a complementary region in a joined portion becomes equal to either the first non-complementary region recording shift amount or the second non-complementary region recording shift amount. 
     Variation 3 
     The performing order of the first measurement step at step S 16  and the second measurement step at step S 17  illustrated in  FIG. 15  is not limited to an example illustrated in  FIG. 15 , and the order can be changed. The first measurement step at step S 16  and the second measurement step at step S 17  may be processed in parallel. 
     In addition, in the second measurement step at step S 17 , a step of measuring the first non-complementary region recording shift amount of the first head module and a step of measuring the second non-complementary region recording shift amount of the second head module may be performed at different timing. 
     Each of a step of measuring the complementary region recording shift amount, a step of measuring the first non-complementary region recording shift amount, and a step of measuring the second non-complementary region recording shift amount of the second head module, can be performed at appropriate timing within a range where advantageous effects of the invention can be acquired. 
     Variation 4 
     While, in the embodiment described above, there is illustrated a recording head in which a head module having a nozzle region where a plurality of nozzles are arranged to form a two-dimensional array, the nozzle region being in the shape of a parallelogram in plan view, is arranged in a row in the X-direction, an array form of head modules in the recording head is not limited to the form in which a plurality of head modules is aligned along the X-direction, and there is available a form in which a plurality of head modules are arranged along the X-direction in a zigzag manner. In addition, there is also available a head module with a nozzle region in the shape of a trapezoid or a rectangle in plan view. 
     Regarding Discharge System 
     A device for generating discharge energy for a discharge system of the head module  12  is not limited to a piezoelectric element, and various discharge energy generation elements, such as a heat generation element and an electrostatic actuator, are available. For example, there is available a system in which a droplet is discharged by using pressure caused by film boiling of liquid heated by a heat generation element. Depending on a discharge system of a liquid discharge head, a corresponding discharge energy generation element is provided in a flow channel structure. 
     Regarding Device for Feeding Paper Sheet 
     A device for feeding a paper sheet S is not limited to the drum-feeding mechanism illustrated in  FIG. 17 , and there are available various forms, such as a belt feeding mechanism, a nip feeding mechanism, a chain feeding mechanism, and a pallet feeding mechanism, and also these mechanisms can be appropriately combined. 
     Regarding Device for Reading Image 
     As a device for reading out recorded results of a first test chart, a second test chart, and a third test chart, each of which is a chart for measurement to be used for measuring a recording shift amount, a scanner separated from the ink jet recorder  100  is available instead of the in-line sensor  258 . As the separated scanner, for example, there is available a scanner of a flat bed type so-called an off-line scanner that is available off-line. 
     Regarding Combination of Examples of Control or the Like 
     The structure described in the embodiment above and the matters described in the variations can be appropriately combined to be used, and some of the matters also can be substituted. 
     Regarding Terms 
     The term “orthogonal” or “vertical” in the present specification includes an aspect having an operation effect similar to that in a case of an intersection at an angle of a substantially 90°, in an aspect of an intersection at an angle less than 90°, or an angle exceeding 90°. 
     The term “parallel” in the present specification includes a substantially parallel state where even if two directions intersect with each other, an operation effect equivalent to that in a parallel state is achieved. That is, the term “parallel” includes an allowable range in which even a strictly non-parallel state can be deemed substantially parallel. 
     The term “barrel” in the present specification is synonymous with a “drum”. The drum is a feeding member with a cylindrical shape, and holds at least a part of a medium. The feeding member is turned around a center axis of the cylindrical shape to feed the medium along an outer peripheral surface of the cylindrical shape. 
     The term “paper sheet” used in the present specification is synonymous with a “medium” to which liquid discharged from a recording head is to be attached. The “paper sheet” is synonymous with terms, such as a recording medium, a print sheet, a recording paper sheet, a printing medium, a medium to be printed, a medium to be recorded, an image formation medium, an image formed medium, a medium receiving an image, and a medium to be discharged. The medium is not particularly limited in material, shape, and the like, and a resin sheet, a film, a cloth, a nonwoven cloth, and another material, are available other than paper material, and also various forms, such as a continuous paper sheet, a cut paper sheet (cut-sheet paper), and a seal paper sheet, are available. 
     The term “image” is broadly interpreted, and includes a color image, a black-and-white image, a single color image, a gradation image, a uniform concentration (solid) image, and the like. The “image” is not limited to a photographic image, and is used as a comprehensive term including a pattern, a character, a mark, a line drawing, a mosaic pattern, a pattern formed with different colors, a line pattern, and other various patterns, or an appropriate combination thereof. The term “recording” includes concepts of terms, such as printing, a printed letter, formation of an image, drawing, and a print. 
     The term “recorder” is synonymous with terms such as a printing device, a printing machine, a printer, an image recorder, and a drawing device. The recorder is included in a concept of an “image forming apparatus”. 
     The term “recording head” can be understood by being substituted with the term “liquid discharge head” or “ink jet head”. 
     Example of Application to Another Apparatus 
     While an example of application to an ink jet recorder for graphic printing has been described in the embodiment described above, the scope of application of the present invention is not limited to the example. For example, the present invention can be widely used for an image forming apparatus that can form various shapes and patterns by using functional liquid material, such as a wiring drawing apparatus for drawing a wiring pattern of an electronic circuit, a manufacturing apparatus for various devices, a resist printer that uses resin liquid as a functional liquid for discharge, a color filter manufacturing apparatus, and a fine structure forming apparatus that forms a fine structure by using a material for material deposition. 
     In the embodiment of the present invention described above, constituent features can be appropriately modified, added, and eliminated within a range without departing from the spirit of the present invention. The present invention is not limited to the embodiments described above, and a person with ordinary skill in the field can make many modifications within a technical idea of the present invention.