JP2011073185A - Manufacturing method for printer, and printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a printer which can suppress degradation of an image quality. <P>SOLUTION: In the manufacturing method for the printer which prints an image while moving in a movement direction both a medium, and first and second nozzle arrays arranged forming an overlapping region, a pattern is printed in which small patterns of respective predetermined densities are formed on a plurality of different positions in the movement direction of the medium at every time of a plurality of the number of times when a relative position between the first nozzle array and the second nozzle array is changed, a density of an image part printed in the overlapping region of each small pattern is acquired, a difference of densities of the image parts of the small patterns formed respectively on the plurality of different positions in the movement direction is calculated for every relative position between the first nozzle array and the second nozzle array changed by the plurality of the number of times, a relative position between the first nozzle array and the second nozzle array is determined on the basis of the density difference, the relative position between the first nozzle array and the second nozzle array is adjusted to the determined relative position, a density correcting value to the image part printed in the overlapping region is calculated on the basis of the pattern printed by the first nozzle array and the second nozzle array on the determined relative position, and the density correcting value is stored in a memory. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a printing apparatus manufacturing method and a printing apparatus.

There is a printer that prints an image by relatively moving a short head having a nozzle row in which nozzles for ejecting ink are arranged in a predetermined direction and a medium in a moving direction that intersects the nozzle row direction. In such a printer, by arranging a plurality of short heads in the nozzle row direction, it is possible to shorten the printing time or print a wide image.
However, the nozzle interval in the nozzle row is very small. For this reason, if the arrangement of the heads arranged in the nozzle row direction is deviated, the density of the image portion formed at the joint of the heads becomes darker or lighter. In view of this, there has been proposed a printer in which a plurality of heads are arranged in the nozzle row direction by overlapping the end portions of each head (part of the nozzle row).

JP-A-6-255175

With the above-described printer, even if the positional relationship between adjacent heads arranged in the nozzle row direction is not in an ideal state, the density correction of an image formed at the joint of the heads can be performed according to the positional relationship between adjacent heads. .
However, if the plurality of heads and the medium move relative to each other while meandering in the moving direction, an image portion that cannot be corrected with the density unevenness correction value corresponding to the positional relationship between adjacent heads is generated. As a result, the image quality is deteriorated.
Therefore, an object of the present invention is to suppress image quality deterioration.

The main invention for solving the above problems is: (A) a first nozzle row in which first nozzles for ejecting ink are arranged in a predetermined direction, and a second nozzle in which second nozzles for ejecting ink are arranged in the predetermined direction. A second nozzle row that is arranged to form an overlapping region in which an end portion on one side in the predetermined direction overlaps an end portion on the other side in the predetermined direction of the first nozzle row, A method of manufacturing a printing apparatus that prints an image while moving the first nozzle row, the second nozzle row, and the medium in a moving direction that intersects the predetermined direction, and (B) the first nozzle row and the medium A plurality of relative positions of the second nozzle row are changed, and each time a change is made, printing a pattern in which small patterns having a predetermined density are formed at a plurality of different positions in the moving direction on the medium, respectively (C ) Each small pack Acquiring the density of the image portion printed in the overlapping area of the screen, and (D) for each of the relative positions of the first nozzle row and the second nozzle row changed a plurality of times. Calculating a difference in density of the image portion of each of the small patterns respectively formed at a plurality of different positions; and (E) based on the difference in density of the first nozzle row and the second nozzle row. Determining a relative position and adjusting the relative position of the first nozzle row and the second nozzle row to the determined relative position; and (F) the first nozzle row and the first nozzle at the determined relative position. Calculating a density correction value for an image portion printed in the overlapping area based on a pattern printed by a two-nozzle row; and (G) storing the density correction value in a storage unit of the printing apparatus. , (H) It is a manufacturing method for a printing apparatus, characterized by.
Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

FIG. 1A is a configuration block diagram of a printing system, and FIG. 1B is a schematic diagram of a printer. FIG. 2A is a diagram showing the arrangement of the heads, and FIG. 2B is a diagram showing the nozzle arrangement on the lower surface of the head. FIG. 3A is a diagram illustrating density unevenness of the printer of the comparative example, FIG. 3B is a diagram illustrating dot formation of the printer with overlapping end portions of adjacent heads, and FIG. 3C is a diagram when the paper is conveyed while meandering It is a figure which shows the dot formation of. FIG. 4A is a flow for calculating a density unevenness correction value, and FIG. 4B is a flow for determining an adjustment amount of the head position. FIG. 5A is a diagram showing a usage rate of each overlapping nozzle of an adjacent head, and FIG. 5B is a diagram showing a density variation influenced by an ink amount per unit area. 6A and 6B are diagrams showing density fluctuations affected by the coverage, and FIGS. 6C and 6D are combinations of density fluctuations influenced by the amount of ejected ink per unit area and density fluctuations affected by the coverage. It is a figure. 7A and 7B are diagrams showing density fluctuations affected by the coverage ratio, and FIGS. 7C and 7D are combinations of density fluctuations influenced by the amount of ejected ink per unit area and density fluctuations affected by the coverage ratio. It is a figure. FIG. 8A is a diagram showing a test pattern to be printed by changing a plurality of relative positions of adjacent heads, and FIG. 8B is a diagram for explaining a raster line constituting the test pattern. FIG. 9A is a diagram showing a test pattern formed by a printer meandering with a medium, and FIG. 9B is a diagram showing a reading result of overlapping images and non-overlapping images. It is a figure which shows the density fluctuation range as a result of changing the relative position of two heads adjacent in the paper width direction. It is a figure which shows the example which a certain raster line influences the density | concentration of an adjacent raster line. It is a figure which shows the test pattern for calculating an uneven density correction value. This is the result of reading a cyan test pattern with a scanner. 14A and 14B are diagrams showing a specific method for calculating the density unevenness correction value. It is a figure which shows the correction value table regarding each nozzle row. It is a figure which shows a mode that the correction value H corresponding to each gradation value is calculated. It is a figure which shows the mode of the weighted average at the time of calculating a density nonuniformity correction value.

=== Summary of disclosure ===
At least the following will become apparent from the description of the present specification and the accompanying drawings.

That is, (A) a first nozzle row in which first nozzles that eject ink are arranged in a predetermined direction, and a second nozzle row in which second nozzles that eject ink are arranged in the predetermined direction, And a second nozzle row arranged so as to overlap with an end portion on the other side in the predetermined direction of the first nozzle row, the first nozzle row and the first nozzle row A method of manufacturing a printing apparatus that prints an image while moving a two-nozzle row and a medium in a moving direction that intersects the predetermined direction, wherein (B) a relative position between the first nozzle row and the second nozzle row is determined. Printing a pattern in which a small pattern having a predetermined density is formed at a plurality of different positions in the moving direction on the medium each time the change is made, and (C) the pattern of the small patterns Mark with overlap area Acquiring the density of the image portion formed, and (D) for each of the relative positions of the first nozzle row and the second nozzle row that have been changed a plurality of times, each formed at a plurality of different positions in the moving direction. Calculating a density difference between the image portions of the small pattern; and (E) determining a relative position between the first nozzle array and the second nozzle array based on the density difference; and Adjusting the relative position of the row and the second nozzle row to the determined relative position, and (F) based on the pattern printed by the first nozzle row and the second nozzle row that are the determined relative positions. Calculating a density correction value for an image portion printed in the overlapping area, (G) storing the density correction value in a storage unit of the printing apparatus, and (H). Printing device It is a manufacturing method.
According to such a manufacturing method of a printing apparatus, it is possible to suppress density fluctuations that occur in an image formed in an overlapping region due to a medium conveyance error, and it is possible to suppress image quality deterioration.

In this printing apparatus manufacturing method, for each of the small patterns, the density of the image portion printed in the overlapping area of the small pattern and the density of the image portion printed by the nozzle that does not belong to the overlapping area. Each of the small patterns respectively formed at a plurality of different positions in the moving direction is obtained for each relative position of the first nozzle row and the second nozzle row obtained by obtaining a difference as a joint density difference. Calculating a difference in joint density difference as a fluctuation range, and determining a relative position between the first nozzle row and the second nozzle row based on the fluctuation range;
According to such a manufacturing method of a printing apparatus, it is possible to suppress density fluctuations that occur in an image formed in an overlapping region due to a medium conveyance error, and it is possible to suppress image quality deterioration.

In this method of manufacturing a printing apparatus, when the first nozzle row and the second nozzle row are at a certain relative position for each of the plurality of changed relative positions of the first nozzle row and the second nozzle row. The difference between the maximum value and the minimum value among the joint density differences of the plurality of formed small patterns is calculated as the variation range of the certain relative position, and the first nozzle row and the plurality of changed first nozzle rows and The minimum value in the fluctuation range corresponding to each relative position of the second nozzle row is determined, and the relative position corresponding to the fluctuation range of the minimum value is determined for the first nozzle row and the second nozzle row. Determine relative position.
According to such a printing apparatus, it is possible to suppress density fluctuations that occur in an image formed in an overlapping region due to a medium transport error, and it is possible to suppress image quality deterioration.

In this method of manufacturing a printing apparatus, when the first nozzle row and the second nozzle row are at a certain relative position for each of the plurality of changed relative positions of the first nozzle row and the second nozzle row. The joint density difference between the plurality of small patterns formed, and the plurality of small patterns formed when the first nozzle row and the second nozzle row are in relative positions in the vicinity of the certain relative position. The difference between the maximum value and the minimum value among the seam density differences is calculated as the fluctuation range of the certain relative position, and a plurality of changed relative positions of the first nozzle row and the second nozzle row are changed. Determining a minimum value in the fluctuation range corresponding to the position, and determining the relative position corresponding to the fluctuation range of the minimum value as a relative position of the first nozzle row and the second nozzle row;
According to such a manufacturing method of a printing apparatus, even if the relative positions of the first nozzle row and the second nozzle row are shifted due to secular change or the like, the density fluctuation generated in the image formed in the overlapping region due to the medium transport error. Can be suppressed.

In this method of manufacturing a printing apparatus, the pattern for calculating the density correction value is a pattern in which small patterns having a predetermined density are formed at a plurality of different positions in the moving direction on a medium. Calculating the density correction value based on a weighted average of the density of the image portion printed in the overlapping area of the small pattern.
According to such a method for manufacturing a printing apparatus, a density correction value having a correction effect can be calculated regardless of the position in the movement direction.

In this method of manufacturing a printing apparatus, the first nozzle row and the first nozzle row are arranged such that the first nozzle row and the second nozzle row determined based on the density difference are in the relative positions in the movement direction. Instead of adjusting the relative position of the two nozzle rows in the moving direction, the ink ejection interval between the first nozzle row and the second nozzle row is adjusted.
According to such a manufacturing method of a printing apparatus, it is possible to suppress density fluctuations that occur in an image formed in an overlapping region due to a medium conveyance error, and it is possible to suppress image quality deterioration.

(A) a first nozzle row in which first nozzles that eject ink are arranged in a predetermined direction, and a second nozzle row in which second nozzles that eject ink are arranged in the predetermined direction, And a second nozzle row arranged so as to overlap with an end portion on the other side in the predetermined direction of the first nozzle row, the first nozzle row and the first nozzle row A method of manufacturing a printing apparatus that prints an image while moving a two-nozzle array and a medium in a moving direction that intersects the predetermined direction,
(B) A plurality of ink ejection intervals of the first nozzle row and the second nozzle row are changed, and each time a change is made, a small pattern having a predetermined density is formed at a plurality of different positions in the moving direction on the medium. Printing a pattern; (C) obtaining a density of an image portion printed in the overlapping region of each of the small patterns; and (D) a plurality of the first nozzle row and the first Calculating a difference in density of the image portion of each of the small patterns formed at a plurality of different positions in the movement direction for each ink ejection interval of the two nozzle rows; and (E) based on the difference in density. Determining an ink ejection interval between the first nozzle row and the second nozzle row, and adjusting the ink ejection interval between the first nozzle row and the second nozzle row to the determined ink ejection interval. (F) calculating a density correction value for an image portion printed in the overlapping area based on the pattern printed by the first nozzle row and the second nozzle row which are the determined ink ejection intervals; , (G) storing the density correction value in a storage unit of the printing apparatus; and (H), a method for manufacturing a printing apparatus.
According to the manufacturing method of such a printing apparatus, it is possible to suppress density fluctuations that occur in an image formed in an overlapping region due to a medium conveyance error, and it is possible to suppress image quality deterioration.

(A) a first nozzle row in which first nozzles that eject ink are arranged in a predetermined direction, and a second nozzle row in which second nozzles that eject ink are arranged in the predetermined direction, And a second nozzle row arranged so as to overlap with an end portion on the other side in the predetermined direction of the first nozzle row, the first nozzle row and the first nozzle row A printing apparatus that prints an image while moving a two-nozzle row and a medium in a movement direction that intersects the predetermined direction, and (B) changes a plurality of relative positions of the first nozzle row and the second nozzle row. Printing a pattern in which a small pattern of a predetermined density is formed at a plurality of different positions in the moving direction on the medium each time it is changed, and (C) in the overlapping region of each of the small patterns Printed image Acquiring the density of the portion; and (D) each of the small patterns formed at a plurality of different positions in the moving direction for each of the relative positions of the first nozzle array and the second nozzle array that are changed a plurality of times. (E) determining a relative position between the first nozzle row and the second nozzle row based on the density difference, and determining the relative position between the first nozzle row and the second nozzle row. Adjusting the relative position of the second nozzle row to the determined relative position, and (F) based on the pattern printed by the first nozzle row and the second nozzle row being the determined relative position, A printing apparatus that calculates a density correction value for an image portion to be printed in an overlapping area and stores the density correction value acquired in (G) in a storage unit.
According to such a printing apparatus, it is possible to suppress density fluctuations that occur in an image formed in an overlapping region due to a medium transport error, and it is possible to suppress image quality deterioration.

=== About the printing system ===
The following embodiments will be described using a line head printer (hereinafter, printer 1) in an inkjet printer as a printing apparatus.

  FIG. 1A is a block diagram illustrating a configuration of a printing system in which the printer 1 and the computer 50 are connected. FIG. 1B is a schematic diagram of the printer 1 and illustrates how the printer 1 transports a sheet S (medium). is there. The printer 1 that has received print data from the computer 50, which is an external device, controls each unit (conveyance unit 20, head unit 30) by the controller 10 and prints an image on the paper S. Further, the detector group 40 monitors the situation in the printer 1, and the controller 10 controls each unit based on the detection result.

  The controller 10 is a control unit for controlling the printer 1. The interface unit 11 is for transmitting and receiving data between the computer 50 as an external device and the printer 1. The CPU 12 is an arithmetic processing unit for controlling the entire printer 1. The memory 13 is for securing an area for storing a program of the CPU 12, a work area, and the like. The CPU 12 controls each unit by a unit control circuit 14 according to a program stored in the memory 13.

  The transport unit 20 includes a transport belt 21 and transport rollers 22A and 22B, feeds the paper S to a printable position, and transports the paper S in the transport direction (movement direction) at a predetermined transport speed. The sheet S on the conveyor belt 21 may be electrostatically attracted or vacuum attracted from below.

  The head unit 30 is for ejecting ink droplets onto the paper S, and has a plurality of heads 31. A plurality of nozzles that are ink ejecting portions are provided on the lower surface of the head 31. Each nozzle is provided with a pressure chamber (not shown) containing ink and a drive element (piezo element) for changing the volume of the pressure chamber to eject ink.

  In such a printer 1, when the controller 10 receives print data from the computer 50, the controller 10 first sends the paper S onto the transport belt 21. Thereafter, the paper S is transported on the transport belt 21 without stopping at a constant speed, and faces the nozzle surface of the head 31. The controller 10 intermittently ejects ink droplets from each nozzle based on the image data while the paper S is conveyed under the head unit 30. As a result, a two-dimensional image in which dot rows (hereinafter also referred to as raster lines) along the transport direction are arranged in the paper width direction is printed on the paper S.

<About nozzle arrangement>
FIG. 2A is a diagram showing the arrangement of the heads 31 provided in the head unit 30, and FIG. 2B is a diagram showing the nozzle arrangement on the lower surface of the head 31. In the printer 1 of the present embodiment, as shown in FIG. 2A, a plurality of heads 31 are arranged side by side in the paper width direction (predetermined direction) intersecting the transport direction (in the figure, five heads 31 are arranged) The end portions of the head 31 are arranged so as to overlap each other. Further, the heads 31A and 31B adjacent in the paper width direction are arranged shifted in the transport direction (arranged in a staggered manner). Of the heads 31A and 31B adjacent in the paper width direction, the head 31A on the upstream side in the transport direction is referred to as “upstream head 31A”, and the head 31B on the downstream side in the transport direction is referred to as “downstream head 31B”. The heads 31A and 31B adjacent in the paper width direction are collectively referred to as “adjacent heads”.

  As shown in FIG. 2B, on the lower surface of each head 31, a black nozzle row K for ejecting black ink, a cyan nozzle row C for ejecting cyan ink, a magenta nozzle row M for ejecting magenta ink, and a yellow ink Is formed. Each nozzle row is composed of 180 nozzles (# 1 to # 180). The nozzles of each nozzle row are arranged at a constant interval (for example, 180 dpi) in the paper width direction. It should be noted that the nozzles belonging to each nozzle row are numbered sequentially from the left side in the paper width direction (# 1 to # 180).

  In the adjacent heads 31A and 31B arranged in the paper width direction, eight nozzles belonging to the end of the nozzle row of each head are arranged in an overlapping manner. Specifically, eight nozzles (# 173 to # 180) at the right end of the nozzle row of the upstream head 31A and eight nozzles (# 1 to ##) at the left end of the nozzle row of the downstream head 31B. 8) are overlapped, and the eight nozzles (# 1 to # 8) at the left end of the nozzle row of the upstream head 31A and the eight nozzles (# 173 to # 173 at the right end of the nozzle row of the downstream head 31B) # 180) is duplicated. In the adjacent heads 31A and 31B, a portion where the nozzles overlap is referred to as an “overlap region”. Further, the nozzles (# 1 to # 8, # 173 to # 180) belonging to the overlapping area are referred to as “overlapping nozzles”.

  Further, the positions of the overlapping nozzles at the end portions of the adjacent heads 31A and 31B coincide with each other in the paper width direction. That is, the position in the paper width direction of the end nozzle of the upstream head 31A is equal to the position in the paper width direction of the corresponding end nozzle of the downstream head 31B. For example, the position in the paper width direction of the rightmost nozzle # 180 of the upstream head 31A and the position of the eighth nozzle # 8 in the paper width direction from the left end of the downstream head 31B are equal, and the eighth position from the left end of the upstream head 31A. The position of the nozzle # 8 in the paper width direction is equal to the position of the rightmost nozzle # 180 of the downstream head 31B in the paper width direction.

  By arranging the plurality of heads 31 in this way, the nozzles can be arranged at equal intervals (180 dpi) over the entire region in the paper width direction. As a result, a dot row in which dots are arranged at equal intervals (180 dpi) can be formed over the paper width.

=== About density unevenness ===
<Overlapping head ends>
FIG. 3A is a diagram illustrating how uneven density occurs due to the head arrangement of the printer of the comparative example. Here, density unevenness that occurs when the ends of the adjacent heads 31 </ b> A and 31 </ b> B do not overlap will be described using a printer of a comparative example different from the present embodiment as an example. In the printer of the comparative example, by design, the interval between the rightmost nozzle (# 180) of the nozzle row of the upstream head 31A and the leftmost nozzle (# 1) of the nozzle row of the downstream head 31B is the nozzle pitch ( For example, it is set to 180 dpi.

  However, since the nozzle pitch is very small, the positional relationship between the adjacent heads 31A and 31B tends to shift. The left diagram in FIG. 3A shows a case where the downstream head 31B is shifted to the right in the paper width direction and the distance between the two heads 31A and 31B is wider than the designed distance (180 dpi). In this case, the interval between the raster line formed on the left end nozzle # 1 of the downstream head 31B and the raster line formed on the right end nozzle # 180 of the upstream head 31A is wider than the nozzle pitch 180 dpi. White streaks occur on the image.

  Conversely, the right diagram in FIG. 3A shows a case where the downstream head 31B is shifted to the left in the paper width direction and the distance between the two heads 31A and 31B is narrower than the designed distance. In this case, the raster line formed at the left end nozzle # 1 of the downstream head 31B and the raster line formed at the right end nozzle # 180 of the upstream head 31A overlap, resulting in black streaks on the image. End up.

  As described above, when the positional relationship between the adjacent heads 31A and 31B is deviated, density unevenness (white stripes or black stripes) occurs on the image, and the image quality deteriorates. Therefore, when density unevenness shown in FIG. 3A occurs, density unevenness correction is performed. If the raster lines formed on the end nozzles (# 1, # 180) overlap each other and appear dark as shown in the right diagram of FIG. 3A, the dot size formed by the end nozzles should be reduced. Thus, density correction can be performed.

  However, as shown in the left diagram of FIG. 3A, when the raster lines formed in the end nozzles (# 1, # 180) are spaced apart and are visually perceived as light, dots are formed in the spaced portions. Can not be formed. That is, since the dots cannot be filled in the white stripe region, the density unevenness cannot be corrected.

  FIG. 3B is a diagram illustrating dots formed by a printer in which the ends of adjacent heads 31A and 31B overlap. In FIG. 3B, the ends of the adjacent heads 31A and 31B are overlapped as in the printer 1 (FIG. 2) of the present embodiment, but the number of nozzles (the number of overlapping nozzles) is reduced to simplify the description. . Dots formed on the upstream head 31A are indicated by black circles, and dots formed on the downstream head 31B are indicated by white circles. In the drawing, dots are alternately formed by the overlapping nozzles of the upstream head 31A and the overlapping nozzles of the downstream head 31B.

  The left diagram in FIG. 3B shows dots formed when the positional relationship between the adjacent heads 31A and 31B is as designed. On the other hand, the right diagram in FIG. 3B shows dots formed when the downstream head 31B is displaced to the right in the paper width direction. In the right diagram of FIG. 3B, the downstream head 31B is displaced in a direction away from the upstream head 31A, as in the left diagram of FIG. 3A. However, since the ends of the adjacent heads 31A and 31B overlap in FIG. 3B, white streaks can be prevented from occurring as shown in the left diagram of FIG. 3A.

  However, if the downstream head 31B is displaced in a direction away from the upstream head 31A, the amount of ink ejected per unit area decreases, and the dots formed by the heads 31A and 31B overlap to fill the medium. Becomes worse. Therefore, in the right diagram of FIG. 3B, the density of the image portion formed at the joint (overlapping region) of the head is lighter than that in the left diagram of FIG. 3B. Therefore, in this case, the lightness of the image density can be corrected, for example, by performing density correction that increases the dot size formed by the overlapping nozzles.

<About transport error>
FIG. 3C is a diagram illustrating how dots are formed when the paper S is conveyed while meandering. Also in FIG. 3C, the number of nozzles (the number of overlapping nozzles) is reduced. FIG. 3C shows a state in which the paper S meanders to the left in the paper width direction after facing the upstream head 31A. The positional relationship between the adjacent heads 31A and 31B in FIG. 3C is as designed, and the position of the overlapping nozzle (eg, # 1) of the downstream head 31B in the paper width direction and the corresponding overlapping nozzle of the upstream head 31A (example) : # 5) The positions in the paper width direction are equal. In FIG. 3C, assuming that one dot row is formed along the paper width direction, ink droplets are ejected from nozzle # 6 # 8 among the overlapping nozzles (black circles) of the upstream head 31A, and the downstream head 31B overlaps. Ink droplets are ejected from nozzle # 1 # 3 of the nozzles (white circles).

  First, as shown in the left diagram of FIG. 3C, when a certain area on the paper S and the upstream head 31A face each other, ink droplets are ejected from the upstream head 31A. As a result, as shown in the central view of FIG. 3C, dots (black circles) formed by the upstream head 31A are formed in a certain area on the paper S side by side in the paper width direction. Thereafter, the sheet S is transported while shifting (meandering) to the left side in the sheet width direction after a certain area of the sheet S passes under the upstream head 31A and opposes the downstream head 31B. . Then, as shown in the right diagram of FIG. 3C, dots (white circles) formed by the downstream head 31B are formed at positions on the right side in the paper width direction from the positions (dotted line positions) that should be originally formed by the downstream head 31B. End up.

  In this way, even if the positional relationship between the adjacent heads 31A and 31B is as designed, when the paper S is conveyed while being shifted to the left in the conveyance direction as in the example shown in FIG. 3C, the dots ( Dots (white circles) formed by the downstream head 31B are formed to be shifted to the right in the paper width direction with respect to the black circles). That is, dots are formed in the same manner as when the downstream head 31B is displaced in the direction away from the upstream head 31A to the right in the paper width direction. Therefore, in FIG. 3C, as in the right diagram of FIG. 3B, the amount of ink ejected per unit area is reduced, the dots formed by the heads 31A and 31B overlap, and the medium is poorly filled. The image density formed in the region becomes light.

  Incidentally, in the printer shown in FIG. 3C, the positional relationship between the adjacent heads 31A and 31B is as designed (ideal state). Therefore, for example, in the manufacturing process of the printer 1 and the like, even if the density unevenness correction value is calculated according to the positional relationship between the adjacent heads 31A and 31B, the printer shown in FIG. 3C does not need to perform density unevenness correction. Is done. Therefore, as shown in FIG. 3C, it is not possible to improve the lightness of density generated when the paper S meanders to the left.

  3C shows a case where the paper S meanders to the left side, but there is a case where the paper S meanders also to the right side during conveyance of the same paper S (not shown). In this case, dots are formed in the same manner as when the downstream head 31B is shifted to the left side with respect to the upstream head 31A, that is, when the downstream head 31B is shifted toward the upstream head 31A. It is formed. At this time, since the dots formed by the heads 31A and 31B overlap, the filling of the medium worsens, but the amount of ink per unit area increases. Therefore, compared to the case where the paper S meanders to the left side (FIG. 3C), when the paper S meanders to the right side, the image density formed in the overlapping region is lighter or the image density is darker. It becomes. Further, even when meandering in the same direction, if the amount of meandering is different, the amount of ink ejected per unit area and the degree of overlapping of dots (medium embedding degree) are different. The concentration is not constant.

  That is, in the printer 1 in which the heads 31A and 31B arranged in the paper width direction are shifted in the conveyance direction (the printer 1 in which the heads 31 are arranged in a staggered manner), the paper S is conveyed while meandering in the paper width direction. In accordance with the meandering direction and the meandering amount, the density of the image formed in the overlapping region of the adjacent heads 31A and 31B changes every moment. For this reason, even in a printer in which the positional relationship between the adjacent heads 31A and 31B is as designed, if the paper S is conveyed while meandering in the paper width direction, the density along the conveyance direction is formed on the image formed in the overlapping region. Unevenness occurs. Even in a printer in which correction values are set according to the positional relationship between the adjacent heads 31A and 31B, if the paper S is conveyed while meandering in the paper width direction, it is set according to the positional relationship between the adjacent heads. With one correction value, density unevenness cannot be corrected depending on the position in the transport direction.

  In particular, the direction of meandering during the conveyance of one medium is reversed, and the density of the image formed in the overlapping area becomes light at a certain position in the conveying direction, but it is formed in the overlapping area at another position in the conveying direction. Suppose that the density of the image becomes darker. Then, it is assumed that a correction value for increasing the density of the image formed in the overlapping area is calculated based on a test pattern formed at a certain position in the transport direction on the medium. As a result, the image density at a certain position in the transport direction is corrected, but the density unevenness of the image density at another position in the transport direction is deteriorated (printing is made darker).

  So far, the density unevenness caused by the meandering of the paper S in the paper width direction during conveyance, that is, the density unevenness caused by the deviation of the interval of the dots in the paper width direction has been described, but the present invention is not limited to this. In the printer 1 of the present embodiment, as shown in FIG. 2, the upstream head 31 </ b> A and the downstream head 31 </ b> B are arranged so as to be shifted in the transport direction. For this reason, the ejection timing of the ink droplets from the heads 31A and 31B is set in accordance with the distance (designed distance) in the transport direction between the upstream head 31A and the downstream head 31B. As a result, for example, as shown in the left diagram of FIG. 3B, dots (black circles) due to the overlapping nozzles of the upstream head 31A and dots (white circles) due to the overlapping nozzles of the downstream head 31B can be arranged at equal intervals in the transport direction. it can.

  However, if the positional relationship of the adjacent heads 31A and 31B in the transport direction is deviated, the dots formed by the heads 31A and 31B overlap each other, so that the medium is poorly filled and the image density formed in the overlapping region becomes light. End up. Therefore, by adjusting the ejection timing from each head 31A, 31B or adjusting the amount of ink ejected from each head 31A, 31B according to the positional relationship of the adjacent heads 31A, 31B in the transport direction, The lightness of the image density formed in the overlapping area can be prevented.

  However, even if the positional relationship of the adjacent heads 31A and 31B in the transport direction is an ideal state, or density unevenness correction (adjustment of ejection timing and ink discharge amount) is performed according to the positional relationship of the adjacent heads 31A and 31B in the transport direction. Even if the correction is performed, if the conveyance speed of the paper S varies, the positional relationship between the dots formed by the upstream head 31A and the dots formed by the downstream head 31B in the conveyance direction is shifted. As a result, the dots formed by the heads 31A and 31B overlap, so that the filling of the medium becomes worse, the overlapping degree of the dots formed by each head changes, and the filling condition of the medium also changes. That is, as in the case where the medium is conveyed while meandering in the paper width direction, if the speed of the medium conveyance varies, the density of the image formed in the overlapping region of the adjacent heads 31A and 31B changes every moment. , Density unevenness cannot be corrected.

  That is, even if the positional relationship (relative position) between the adjacent heads 31A and 31B in the paper width direction and the conveyance direction is an ideal state, or even if density unevenness correction is performed according to the positional relationship between the adjacent heads 31A and 31B. If the medium meanders in the paper width direction during the conveyance of the medium or if the conveyance speed is uneven, the paper width of the dots formed by the overlapping nozzles of the heads 31A and 31B during the printing of one medium. The positional relationship between the direction and the conveyance direction varies, and density unevenness (density variation) along the conveyance direction occurs in an image formed by overlapping nozzles. Therefore, with the correction value set according to the image density at a certain position in the transport direction, the image density at another position in the transport direction cannot be corrected. There is also a risk of deteriorating the image density. Further, if it is attempted to perform different density correction for each position in the transport direction with respect to density unevenness that occurs along the transport direction, the print control becomes complicated.

  Therefore, in the present embodiment, density unevenness along the transport direction that occurs in an image formed in the overlapping area of the adjacent heads 31A and 31B due to a medium transport error (meandering in the paper width direction and uneven speed) is suppressed as much as possible. The purpose is to make the density fluctuation as small as possible. As a result, image quality deterioration can be suppressed.

=== Regarding Head Position Adjustment and Correction Value Calculation ===
<Overview>
4A is a calculation flow of the density unevenness correction value H, and FIG. 4B is a flow for determining the adjustment amount of the head position. In order to minimize the density fluctuation along the conveyance direction that occurs in the image formed in the overlapping area of the adjacent head due to the medium conveyance error (meandering and uneven speed) during the manufacturing process and maintenance of the printer 1, Then, the head adjustment amount of the adjacent heads 31A and 31B is determined (S001 in FIG. 4A, details will be described later). That is, the optimum relative position of the adjacent head in which the density fluctuation of the image formed in the overlapping region is reduced is determined. Thereafter, the position of the head 31 is adjusted based on the determined head adjustment amount (S002). The position of the adjacent head in which the density fluctuation of the image formed in the overlapping area is small is not necessarily the position on the head design (FIG. 2B). Therefore, after the position of the head 31 is adjusted, a density unevenness correction value of an image formed in the overlapping region is calculated (S003).

<Differences in head position adjustment due to differences in printing methods>
Incidentally, in FIG. 3B described above, dots are alternately formed in the paper width direction and the transport direction by the overlapping nozzles of the upstream head 31A and the overlapping nozzles of the downstream head 31B. Not exclusively. In the following, two types of sorting methods are taken as examples, and the optimum relative positions where the density fluctuation is reduced by each method are shown. For the sake of simplicity, attention is paid to density fluctuations that occur when the medium meanders in the paper width direction, and the density fluctuations that occur due to speed irregularities are omitted. Further, here, a description will be given by replacing density fluctuations that occur when the medium meanders in the paper width direction with density fluctuations that occur when the relative positions of the adjacent heads 31A and 31B in the paper width direction shift.

  FIG. 5A is a diagram showing the usage rate of the overlapping nozzles of the adjacent heads 31A and 31B. FIG. 5B is a graph showing density fluctuations (ink amounts per unit area) with respect to a shift in the relative position of the adjacent heads 31A and 31B in the paper width direction. It is a figure which shows the density fluctuation | variation affected. In the drawing, the number of nozzles (the number of overlapping nozzles) is reduced, and the usage rate of the overlapping nozzles (# 11 to # 14) of the upstream head 31A is indicated by dotted lines, and the overlapping nozzles (# 1 to # 1) of the downstream head 31B are shown. The usage rate of # 4) is indicated by a one-dot chain line, and the total usage rate of the two heads 31A and 31B is indicated by a bold line. The usage rate in the upper diagram of FIG. 5A is the usage rate when the relative position of the adjacent heads 31A and 31B is an ideal position (designed position). Here, the usage rate of the overlapping nozzles is changed depending on the position in the paper width direction. For example, the overlapping nozzle of the upstream head 31A has a higher usage rate as the nozzle on the left side in the paper width direction (upstream head side), and the overlapping nozzle of the downstream head 31B has a higher usage rate as the nozzle on the right side in the paper width direction (downstream head side). high. The total usage rate (thick line) of each head 31A, 31B is set to 100%.

  In the drawing, the amount of deviation that the downstream head 31B shifts to the left in the paper width direction (Y direction) with respect to the upstream head 31A is shown as “−ΔY”, and the amount of deviation that shifts to the right in the paper width direction is “+ ΔY”. ". Further, the amount of deviation of the downstream head 31B with respect to the upstream head 31A in the transport direction (X direction) is indicated as “−ΔX”, and the amount of deviation in the downstream direction of the transport direction is indicated as “+ ΔX”. Show.

  The usage rate in the center diagram of FIG. 5A is the usage rate when the downstream head 31B is shifted to the left in the paper width direction with respect to the upstream head 31A, that is, the direction in which the widths of the adjacent heads 31A and 31B become narrower (−ΔY It is the usage rate when it deviates in the direction). In this case, the total usage rate (thick line) of the upstream head 31A and the downstream head 31B exceeds 100%, and the ink amount (number of dots) per unit area increases in the area on the medium to which the overlapping nozzles are assigned.

  On the other hand, the usage rate in the lower diagram of FIG. 5A is the usage rate when the downstream head 31B is shifted to the right side in the paper width direction with respect to the upstream head 31A, that is, the direction in which the widths of the adjacent heads 31A and 31B become wider (+ ΔY It is the usage rate when it deviates in the direction). In this case, the total usage rate (thick line) of the upstream head 31A and the downstream head 31B is lower than 100%, and the ink amount per unit area decreases in the area on the medium to which the overlapping nozzles are assigned.

  FIG. 5B shows the density change that occurs in the image formed in the overlapping region as a result of the downstream head 31B being displaced in the paper width direction relative to the upstream head 31A and the amount of ink ejected per unit area being changed. FIG. In the graph of FIG. 5B, the horizontal axis indicates the amount of deviation (ΔY) of the downstream head 31B, and the vertical axis indicates the density. Similarly to the usage rate shown in FIG. 5A, when the positional relationship between the adjacent heads is in an ideal state (ΔY = 0), the downstream head 31B is shifted in a narrowing direction (−ΔY direction, left side). The density increases as the density increases and the deviation amount (−ΔY) increases. Conversely, when the positional relationship between the adjacent heads is in an ideal state, the density decreases as the downstream head 31B shifts in the widening direction (+ ΔY direction, right side), and the density increases as the shift amount (+ ΔY) increases. Decrease.

  6A and 6B are diagrams showing density fluctuations affected by the coverage (medium filling condition) when dots are alternately formed by the overlapping nozzles of the adjacent heads 31A and 31B. FIG. 6 is a diagram in which density fluctuation (FIG. 5B) influenced by the amount of ejected ink per unit area and density fluctuation (FIG. 6B) influenced by the coverage ratio are combined in an image formed in the overlapping region. As shown in FIG. 6A, as one method of ink separation by overlapping nozzles, a dot (lower right oblique line) by the overlapping nozzle of the upstream head 31A and a dot (lower left oblique line) by the overlapping nozzle of the downstream head 31B overlap. In order to avoid this, there is a printing method in which printing is performed alternately in the paper width direction and the conveyance direction. In FIG. 5, it is assumed that the usage rate of the overlapping nozzles varies depending on the position in the paper width direction, but for simplicity of explanation, in FIG. 6A, the dots due to the overlapping nozzles of the upstream head 31A and the dots due to the overlapping nozzles of the downstream head 31B are used. Are formed alternately.

  As shown in the upper diagram of FIG. 6A, when the relative position between the upstream head 31A and the downstream head 31B is an ideal position (ΔY = 0), the dots formed by the overlapping nozzles of the heads 31A and 31B have a predetermined interval. It is formed every other time, and the medium can be filled without a gap. However, as shown in the lower diagram of FIG. 6A, when the downstream head 31B is shifted to the left side in the paper width direction (−ΔY direction) with respect to the upstream head 31A, the dots by the overlapping nozzles of the heads 31A and 31B overlap. Will become worse (coverage will be reduced). Even when the downstream head 31B is shifted to the right side (not shown) with respect to the upstream head 31A (not shown), the dots due to the overlapping nozzles of the heads 31A and 31B overlap each other, and the filling of the medium becomes worse.

  FIG. 6B is a diagram showing density fluctuation (vertical axis) influenced by the coverage ratio with respect to the shift amount (ΔY: horizontal axis) of the downstream side head 31B in the paper width direction. As shown in FIG. 6A, when the positional relationship between the adjacent heads 31A and 31B is an ideal position (ΔY = 0), the medium is filled without a gap, so the density affected by the coverage is the highest, and the upstream head When the downstream head 31B is displaced in the paper width direction with respect to 31A, the dots formed by the heads 31A and 31B overlap each other and the filling of the medium becomes worse regardless of the deviation direction, so the density affected by the coverage is low. Become. Then, the density decreases as the deviation amount (ΔY) of the downstream head 31B increases, and when the downstream head 31B deviates the length of the nozzle pitch “180 dpi”, the dots due to the overlapping nozzles of each head completely overlap. Therefore, the medium filling becomes the worst, and the density affected by the coverage is the lowest.

  Then, based on the result of adding the density fluctuation influenced by the ink discharge amount per unit area in FIG. 5B and the density fluctuation influenced by the coverage in FIG. 6B (based on FIGS. 6C and 6D), FIG. When the printing method shown in FIG. 6A is performed, the relative positions of the adjacent heads 31A and 31B that can reduce the density fluctuation of the image formed in the overlapping region can be known. As shown in FIG. 6C, when the positional relationship between the adjacent heads is shifted from the ideal state (ΔY = 0) to the direction in which the width of the adjacent head becomes narrower (−ΔY), the ink amount per unit area is affected. The concentration (dotted line) increases and the concentration affected by the coverage (solid line) decreases. On the other hand, when the positional relationship between the adjacent heads is shifted from the ideal state (ΔY = 0) to the direction in which the width of the adjacent head becomes wider (+ ΔY), the density affected by the ink amount per unit area decreases, Concentrations affected by coverage are also reduced.

  For this reason, in the printing method shown in FIG. 6A, as shown in FIG. 6D, when the positional relationship between adjacent heads is shifted in a narrowing direction, the positional relationship between adjacent heads is shifted in a wider direction. Thus, the amount of density fluctuation with respect to the deviation amount of the head in the paper width direction (medium meandering amount / y1 in FIG. 6D) is small (d1 <d2). That is, in the printing method of FIG. 6A, by shifting the relative position of the adjacent head in the direction narrowing from the ideal position, the density generated in the image formed in the overlapping area even if the medium is meandered and conveyed in the paper width direction. Variation can be reduced.

  7A and 7B are diagrams showing density fluctuations affected by the coverage ratio in a printing method different from that in FIG. 6A. FIGS. 7C and 7D are density fluctuations influenced by the amount of ejected ink per unit area ( FIG. 5B is a combination of density fluctuations (FIG. 7B) influenced by the coverage. The printing method shown in FIG. 7A is a printing method in which dots by overlapping nozzles of the upstream head 31A and dots by overlapping nozzles of the downstream head 31B are printed in an overlapping manner. In this case, as shown in the upper diagram of FIG. 7A, even if the relative positions of the adjacent heads 31A and 31B are in an ideal state, the dots are formed so as to overlap each other. 7A, when the downstream head 31B is displaced in the paper width direction with respect to the upstream head 31A, dots formed in the ideal state are formed so as to be displaced, so that the medium is buried. Will be better. Therefore, in the printing method shown in FIG. 7A, as shown in FIG. 7B, when the positional relationship between adjacent heads is an ideal position (ΔY = 0), the density affected by the coverage is the lowest, and the upstream head 31A On the other hand, when the downstream head 31B is displaced in the paper width direction, the density affected by the coverage increases regardless of the direction of deviation.

  Then, based on the result (FIG. 7C, FIG. 7D) in which the density fluctuation influenced by the ink discharge amount per unit area in FIG. 5B and the density fluctuation influenced by the coverage shown in FIG. The optimum relative positions of the adjacent heads 31A and 31B when the printing method is performed can be known. As shown in FIG. 7C, when the positional relationship between the adjacent heads is shifted from the ideal state (ΔY = 0) to the direction in which the width of the adjacent head becomes narrower (−ΔY), the ink amount per unit area is affected. The concentration (dotted line) and the concentration affected by the coverage (solid line) also increase. On the other hand, when the positional relationship between the adjacent heads is shifted from the ideal state (ΔY = 0) to the direction in which the width of the adjacent head becomes wider (+ ΔY), the density affected by the ink amount per unit area decreases, The concentration affected by the coverage increases.

  For this reason, in the printing method shown in FIG. 7A, as shown in FIG. 7D, when the positional relationship between adjacent heads is shifted in a wider direction, the positional relationship between adjacent heads is shifted in a smaller direction. Thus, the amount of density variation with respect to the deviation amount of the head in the paper width direction (medium meandering amount; y2 in FIG. 7D) is small (d4 <d3). That is, in the printing method of FIG. 7A, the relative position of the adjacent heads is shifted in the direction of widening from the ideal position, thereby reducing the density fluctuation that occurs in the image formed in the overlapping area even if the medium meanders in the paper width direction. be able to.

  As described above, depending on how the inks are divided by the overlapping nozzles (FIGS. 6A and 7A), the density fluctuation generated in the image formed in the overlapping region due to the conveyance error (meandering of the medium and uneven speed) is reduced. The relative position is different. Therefore, in the present embodiment, the ink is formed in the overlapping region due to the transport error (meandering of the medium and uneven speed of the medium) in accordance with the ink dividing method (halftone process or the method of distributing the dots to the overlapping nozzle) by the overlapping nozzle. The relative position of the adjacent head is adjusted so that the density fluctuation generated in the image is reduced. Next, a method for determining the optimum relative position (head adjustment amount) of the adjacent head will be described.

=== About the method of determining the head adjustment amount ===
Since the method of ink placement by the overlapping nozzles is different for each model of the printer 1, the density of the image formed in the overlapping region (hereinafter, “duplicated image”) is reduced for each model of the printer 1 so that the density fluctuation of the head is reduced. It is necessary to determine the amount of adjustment. In addition, even if the method of ink placement by overlapping nozzles is the same, due to nozzle manufacturing errors, the dot landing position changes slightly for each printer, and the relative position of the head that reduces the density fluctuation of the overlapping image also changes. To do. Therefore, in the present embodiment, the head adjustment amount is determined for each printer 1 during the manufacturing process and maintenance of the printer 1. For example, in the manufacturing process of the printer 1, the printer 1 to be inspected for the head adjustment amount may be connected to a computer, and the head adjustment amount may be determined according to a head adjustment program installed in the computer. Hereinafter, a method of determining the head adjustment amount shown in the flow of FIG. 4B will be described.

<S101: Print Test Pattern>
FIG. 8A is a diagram showing a test pattern for printing by changing a plurality of relative positions of two heads 31 adjacent in the paper width direction, and FIG. 8B is a diagram for explaining raster lines constituting the test pattern. FIG. 9B is a diagram showing a test pattern formed by a printer in which the medium meanders during conveyance of the medium, and FIG. 9B shows an image part formed by an overlapping area (overlapping image) and an image part formed by a non-overlapping area ( FIG. 10 is a diagram showing a density fluctuation range as a result of changing the relative positions of two heads adjacent in the paper width direction.

  In order to determine the head adjustment amount, first, a plurality of relative positions of adjacent heads (adjacent heads) in the paper width direction are changed to print the test pattern shown in FIG. 8A (FIG. 4B, S101). Incidentally, as shown in FIG. 2A, in the printer 1 of the present embodiment, five heads 31 are provided in the head unit 30, and the head unit 30 has four overlapping regions. Then, in the four overlapping images formed in each overlapping region, it is necessary to determine the adjustment amount of the position of each head 31 so that the density fluctuation is reduced even if a transport error (meandering or uneven speed) occurs. However, it is difficult to determine the optimum positions of the five heads so that the test patterns are printed by changing the positions of the five heads and the density fluctuations of the four overlapping images are reduced. Therefore, in the present embodiment, as shown in FIG. 8A, a test pattern is printed by changing a plurality of relative positions for each of two heads adjacent in the paper width direction, and is formed by an overlapping region between the two heads. The optimum relative positions of the two heads are determined so that the density fluctuation of the image becomes small.

  For example, in the head unit 30 shown in FIG. 2A, the optimum relative position (head adjustment amount) of the heads 31 adjacent in the paper width direction is determined in order from the left head 31. In this case, the inspector changes a plurality of relative positions of the leftmost downstream head 31B (1) and the second upstream head 31A (2) from the left (or automatically changes the relative positions) to change the relative positions. The head adjustment program causes the printer 1 to print the test pattern shown in FIG. Based on the test pattern result, the head adjustment program determines the optimum relative position between the leftmost head 31B (1) and the adjacent head 31A (2). Thereafter, the test pattern is printed by changing a plurality of relative positions of the second upstream head 31A (2) from the left and the third downstream head 31B (3) from the left, and the optimum relative position is determined. Next, the optimum relative position of the two heads adjacent in the paper width direction is determined, such as determining the optimum relative position of the third head 31B (3) from the left and the adjacent head 31A (4). Determine the position.

  The “head adjustment amount” shown in the table of FIG. 10 is the adjustment amount with respect to the design position of the two heads 31 that print the test pattern. In the present embodiment, the position of one of the two heads 31 that print the test pattern is adjusted. For example, in the table of FIG. 10, the relative position of the first candidate of the two heads 31 for printing the test pattern is that one head 31 is shifted from the design position to the right side (+ ΔY side) in the paper width direction (Y direction). The relative position of the sixth candidate is a position shifted by “ΔY1” from the design position to the left side (−ΔY side) in the paper width direction. In addition to shifting the two heads 31 for printing the test pattern in the paper width direction, the test pattern is printed in the transport direction (X direction) as in the relative positions of the third and fourth candidates. Then, instead of shifting the head 31 in only one of the transport direction and the paper width direction, the test pattern is printed even if the head 31 is shifted in two directions at the same time, such as the relative position of the fifth candidate.

  In this way, a plurality of relative positions of the two heads 31 adjacent in the paper width direction are changed, and each time the change is made, the test pattern shown in FIG. 8A is printed. The head adjustment program prints five types of density test patterns for each relative position. In the printer 1 of the present embodiment, the density indicated by the print data is expressed by 256 gradations, and the higher the gradation value, the higher the density, and the lower the gradation value, the lower the density. The tone value for printing the test pattern is called a command tone value, the command tone value of the test pattern with a density of 30% is expressed as Sa (76), and the command tone value of the test pattern with a density of 40% is set as Sb (102 ), The command tone value of the test pattern with a density of 50% is represented as Sc (128), the command tone value of the test pattern with a density of 60% is represented as Sd (153), and the test pattern command with a density of 70% is designated. The gradation value is expressed as Se (178). In order to adjust the position in units of heads, even if a test pattern is printed with only one nozzle row (for example, a nozzle row that greatly affects density fluctuation) among the four nozzle rows (YMCK) of each head 31. A single test pattern may be printed by a plurality of nozzle rows, or a test pattern may be printed by a plurality of nozzle rows.

  Note that the printer 1 of the present embodiment prints A4 size paper, and the head adjustment amount so that the density fluctuation generated in the overlapped image is reduced by the transport error (meandering and uneven speed) when transporting the A4 size paper. (Optimum head position) is determined. Therefore, a test pattern is printed on A4 size paper.

  Each command tone value test pattern is composed of five small patterns. Five small patterns are respectively formed at a plurality of positions “position 1 to position 5” in the transport direction of A4 size paper, and the five small patterns extend in the transport direction over the entire area in the transport direction of A4 size paper. line up. The five small patterns printed on the same sheet are band-like images printed with the same command gradation value. One small pattern is formed by overlapping nozzles (# 1 to # 8, # 173 to # 180) of the two heads 31A and 31B and non-overlapping nozzles (# 9 to # 172) of the heads 31A and 31B. Is done. Therefore, as shown in FIG. 8B, one small pattern is formed by arranging raster lines (dot rows along the transport direction) formed by the nozzles in the paper width direction. Hereinafter, an area on the medium on which one raster line is formed is referred to as a “row area”.

  If the two heads 31 for printing the test pattern are at ideal positions, and if there is no conveyance error (meandering / velocity unevenness) when printing the test pattern, as shown in FIG. The small patterns formed at the positions (1 to 5) are printed with a uniform density. Further, if the two heads 31 for printing the test pattern are deviated from the ideal position, a difference in density occurs between the overlapping image and the non-overlapping image in the small pattern, but if no transport error occurs when the test pattern is printed. The overlapping images of small patterns formed at different positions in the transport direction are printed at a uniform density.

  However, even if the two heads for printing the test pattern are at the ideal position or shifted from the ideal position, if a transport error (meandering / velocity unevenness) occurs when printing the test pattern, as shown in FIG. 9A. Moreover, the density of overlapping images of small patterns formed at different positions in the transport direction is different. For example, when the test pattern of FIG. 9A is printed, the medium is meandered and conveyed to the left side in the paper width direction at position 1, and the medium is meandered and conveyed to the right side in the paper width direction at position 5. Then, at position 1, the dots formed by the overlapping nozzles of the upstream head 31A and the dots formed by the overlapping nozzles of the downstream head 31B are shifted in the direction away from each other, so that the overlapping image is printed relatively lightly. Since the dots formed by the 31B overlapping nozzles are shifted in the approaching direction, the overlapping images are printed relatively darkly.

  In the present embodiment, the optimum head adjustment amount (in the following processing) is performed so that the density difference between overlapping images of small patterns formed at different positions (1 to 5) in the transport direction is as small as possible. The optimum relative position of the two heads on which the test pattern is printed is determined.

<S102: Reading by scanner>
For each of the two heads 31 aligned in the paper width direction, after changing the relative positions of the two heads 31 and printing a test pattern, the inspector sets the test pattern result on the scanner, and the test pattern is placed on the scanner. To read. Therefore, a scanner is also connected to the computer connected to the printer 1 to be inspected for the head adjustment amount. The head adjustment program acquires a result (read gradation value) obtained by reading the test pattern by the scanner (S102 in FIG. 4B). In the scanner, the original is irradiated with light, and the reflected light from the original is detected by a line sensor (CCD sensor) to read an image. The result sensed by the line sensor in the scanner is referred to as “read gradation value”, and is referred to as “density” representing the density of the image. When a color image is read, the reflected light from the document is separated into three RGB data by color separation, and represents the density of the color component. Here, it is assumed that the higher the reading gradation value by the scanner, the higher the density, and the lower the reading gradation value, the lighter the density. Further, the density unevenness occurring in the overlapping image is not limited to “density”, but may be expressed by, for example, lightness (L) indicating the brightness of the image.

  For example, FIG. 9B shows the reading result of the small pattern at position 5 of the test pattern (FIG. 9A) printed with the command gradation value Sc by a certain two heads 31 arranged in the paper width direction. In FIG. 9B, the read gradation value (density / vertical axis) with respect to the position in the paper width direction (row region / horizontal axis) is shown. In the small pattern at position 5 of the test pattern in FIG. 9A, the overlapping image is printed darker than the non-overlapping image. Therefore, in the reading result of FIG. 9B, the reading result of the overlapping image has a higher reading gradation value (darker density) than the reading result of each non-overlapping image of the two heads 31A and 31B on which the test pattern is printed. Show.

<S103: Calculation of Seam Density Difference Δd>
The head adjustment program obtains the reading result of the scanner, and thereafter, for each relative position of each adjacent head candidate (for each head adjustment amount), each command gradation value (Sc to Se), and each position in the transport direction (1 to 5) Then, a “joint density difference Δd” is calculated. The joint density difference Δd is a difference between the density (dc) of the overlapping images and the density (du · dl) of the non-overlapping images of each small pattern. In other words, the head adjustment program calculates the joint density difference Δd for each small pattern, and calculates the density difference between the overlapping image and the non-overlapping image that occur at different positions (1 to 5) in the transport direction.

  In order to calculate the joint density difference Δd, the head adjustment program first calculates the non-overlapping image density du of the upstream head 31A, the overlapping image density dc, and the non-overlapping of the downstream head 31B for each small pattern. The image density dl is calculated. Although the small pattern is printed with a constant command gradation value, since there is a characteristic difference for each nozzle, even in the same overlapping image or in the same non-overlapping image, as shown in FIG. There is a slight difference in density every time. Therefore, the head adjustment program sets the average value of the read gradation values of the row area corresponding to the non-overlapping image of the upstream head 31A as “density du”, and sets the read gradation value of the row area corresponding to the overlap image. The average value is “density dc”, and the average value of the read gradation values in the row region corresponding to the non-overlapping image of the downstream head 31B is “density dl”.

In addition, even if the non-overlapping images are printed with the same command gradation value, there is a difference in the characteristics of the head 31, so the density du of the non-overlapping image of the upstream head 31A and the density dl of the non-overlapping image of the downstream head 31B. There is a slight density difference. Therefore, the head adjustment program calculates the difference between the density dc of the overlapping image and the average value (= (du + dl) / 2) of the non-overlapping images of the upstream head 31A and the downstream head 31B as a joint density difference. Calculated as Δd. For example, as shown in FIG. 9B, the joint density difference Δd5 (c) in the small pattern at the position 5 of the test pattern of the command gradation value Sc is calculated by the following equation.
Δd5 (c) = dc5 (c) − (du5 (c) + dl5 (c)) / 2
In this way, the head adjustment program also calculates the joint density differences Δd1 to Δd4 of the small patterns formed at the other positions 1 to 4, and the test patterns formed at other command gradation values. The joint density difference Δd (a) to Δd (e) is also calculated.

  In this embodiment, the average value of the read gradation values of the row region corresponding to each image is calculated as the density of each image. However, the present invention is not limited to this. For example, the read gradation value at a certain point in the image is used. May be calculated as the density of the image. The difference between the density dc of the overlapping image and the average value of the densities (du, dl) of the non-overlapping images of the adjacent heads 31A and 31B is calculated as the joint density difference Δd. The difference between the density dc and the density of the non-overlapping image of any one of the heads 31 may be calculated as the joint density difference Δd.

  In this embodiment, a large number of test patterns shown in FIG. 8A are printed, and the test patterns are read by the scanner. If the scanner scans the same image at different timings, a slight error may occur in the read tone value. In the present embodiment, since a number of test patterns are read by the scanner at different timings, there may be a case where the reading error of the scanner is included in the test pattern reading result. Therefore, it is preferable to print an image (test patch) having the same density on all test patterns. In addition, in the test pattern printed by the same head 31, the test patch may be printed by the same nozzle. By doing so, the reading error of the scanner can be eliminated based on the difference between the reading results of the test patches printed on each test pattern, and the adjustment amount of the head can be calculated with higher accuracy.

<S104 / S105: Calculation of Fluctuation Range C>
In this way, the head adjustment program prints test patterns of five types of densities Sa to Se for each relative position of the candidates for the adjacent heads 31A and 31B, and “joins” for each of the five small patterns constituting each test pattern. Density differences Δd1 to Δd5 (density unevenness between overlapping images and non-overlapping images) ”are calculated. Next, the head adjustment program sets, for each relative position of the candidates for the adjacent heads 31A and 31B, the density variation range of the overlapping image of the test pattern printed at the relative position, that is, each position 1 to 5 in the transport direction. The density fluctuation range of the overlapping image of the small pattern printed in this way is calculated.

  For this purpose, the head adjustment program first calculates an average joint density ΔD (S105 in FIG. 4B). The average joint density difference ΔD is an average value of joint density differences Δd (a) to Δd (e) of five types of density. That is, the head adjustment program is formed at the same position (1 to 5) in the transport direction in the test patterns of five types of densities (Sa to Se) when the adjacent heads 31A and 31B are printed at a certain relative position. The average value of the joint density differences (Δd (a) to Δd (e)) of the small patterns thus obtained is calculated.

For example, the average joint density difference ΔD1-7 circled in the table of FIG. 10 is formed at position 1 in the test pattern formed when the relative position of the adjacent head is the seventh candidate position. It is an average value of each joint density difference (Δd1 (a) to Δd1 (e)) of the five kinds of small patterns of density. Therefore, the average joint density difference ΔD1 at position 1 is calculated by the following equation.
ΔD1 = (Δd1 (a) + Δd1 (b) + Δd1 (c) + Δd1 (d) + Δd1 (e)) / 5
As a result, as shown in the table of FIG. 10, the average joint density difference (ΔD1 to ΔD5) of each position 1 to 5 in the transport direction is calculated for each relative position of the adjacent head candidate.

  Thereafter, the head adjustment program calculates a variation range C of the average joint density difference (ΔD1 to ΔD5) at each position (1 to 5) for each relative position of the candidate for the adjacent head. That is, the head adjustment program uses the average joint density difference (ΔD1 to ΔD5) at each position (1 to 5) in different transport directions in the test pattern formed when the adjacent head is at a relative position of a candidate. Are determined, and the difference (maxΔD−minΔD) between the maximum value and the minimum value of the average seam density difference is calculated as the fluctuation range C.

  For example, in the test pattern shown in FIG. 9A, the density dc1 of the overlapping image of the small pattern formed at position 1 is the lightest, and the difference from the density of the non-overlapping image (joint density difference Δd1) is a negative value. The density dc5 of the overlapping image of the small pattern formed at position 5 is the highest, and the difference from the density of the non-overlapping image (joint density difference Δd5) is a positive value. If similar density unevenness occurs in other small patterns of command gradation values, the average joint density difference ΔD1 at position 1 becomes the minimum value, and the average joint density difference ΔD5 at position 5 becomes the maximum value. Therefore, the head adjustment program calculates the difference between the average joint density differences (ΔD1 · ΔD5) between the position 1 and the position 5 as the fluctuation range C.

  The smaller the fluctuation range C, the smaller the density unevenness (density fluctuation) along the transport direction that occurs in the overlapped image due to transport errors (meandering and speed unevenness) during transport of one medium. Therefore, the head adjustment program determines the minimum value of the variation range (C1...) Calculated for each relative position of the adjacent head candidate. Then, the head adjustment program determines the relative position (head adjustment amount) where the density fluctuation range C of the overlapping image is the minimum value as the optimum relative position (optimum head adjustment amount) (S106 in FIG. 4B). In the present embodiment, since the fluctuation range of the average value ΔD of the joint density differences Δd (a) to Δd (e) of the five command gradation values Sc to Se is compared, it is not dependent on the image density. Thus, it is possible to reduce the fluctuation range of the density generated in the overlapping image.

  Here, since the head unit 30 has five heads 31 as shown in FIG. 2A, the optimum positions of the leftmost downstream head 31B (1) and the second upstream head 31A (2). And the optimum positions of the second upstream head 31A (2) and the third downstream head 31B (3), the third downstream head 31B (3) and the fourth upstream head 31A (4). The optimum positions and the optimum positions of the fourth upstream head 31A (4) and the fifth downstream head 31B (5) are determined.

  In summary, in this embodiment, in order to calculate the head adjustment amount for each of the two heads 31A and 31B arranged in the paper width direction, the relative positions of the adjacent heads 31A and 31B are changed in plural in the paper width direction and the transport direction. Print a test pattern. Then, the relative position where the variation range C of the density of the overlapping images formed at different positions in the transport direction in the test pattern (the joint density difference Δd with the non-overlapping images) is minimized is determined. By adjusting the positions of the adjacent heads 31A and 31B to the determined relative positions, for example, even if a transport error (meandering or uneven speed) occurs when printing an image having a predetermined gradation value, the adjacent heads 31A and 31A An image formed in the overlap region of 31B is formed with a density as uniform as possible. That is, even if a conveyance error (meandering / velocity unevenness) occurs in an image formed in the overlapping region, a density difference due to a difference in position in the conveyance direction can be reduced, and deterioration in image quality can be suppressed.

  In this embodiment, in each small pattern, the density difference (joint density Δd) between the overlapping image and the non-overlapping image is calculated, and based on the density fluctuation range of the joint density difference Δd (average joint density difference ΔD). The optimum head adjustment amount (relative position) is determined, but the present invention is not limited to this. The problem is that density differences occur in overlapping images formed at different positions 1 to 5 in the transport direction. Therefore, the relative position of the adjacent head when the test pattern in which the variation range of the density (dc1 to dc5) of the overlapping images formed at the respective positions 1 to 5 is small may be determined as the optimum relative position. . Further, as shown in FIG. 8A, five types of density test patterns are printed for each relative position, but this is not limiting, and only one type of density test pattern may be printed. However, by forming test patterns having a plurality of densities (command gradation values), it is possible to reduce the density fluctuation range of overlapping images regardless of the image density.

=== Regarding Head Position Adjustment and Density Unevenness Correction Value Calculation ===
<Head position adjustment>
After the optimum relative position (head adjustment amount) is determined for each of the two heads 31 arranged in the paper width direction in this way, the position of the head 31 is adjusted so as to be the relative position determined by the inspector (FIG. 4A). S002). A structure in which the position of the head 31 is automatically adjusted may be used. In this embodiment, since the head adjustment amount (optimal relative position) is determined for each of the two heads 31 arranged in the paper width direction, for example, the two heads 31B (1) and 31A (2) at the left end in the paper width direction are used. In the case of adjusting the position in order, the adjustment amount of the already adjusted head 31 is accumulated and adjusted when the right head 31 is adjusted. Therefore, the head (head 31B (3) in FIG. 2A) located in the center in the paper width direction is used as a reference head, and the position of the reference head 31 is set as a design position without adjustment. Then, the head position may be adjusted in order from the heads 31 on both sides of the reference head (31B (3)) in the paper width direction. By doing so, the cumulative value of the head adjustment amount can be reduced. After adjusting the head position in this way, the density unevenness correction value H is calculated (S003 in FIG. 4A).

<Calculation of density unevenness correction value>
In the present embodiment, adjacent heads 31A and 31B are used in order to minimize density fluctuations caused by transport errors (meandering and uneven speed) in overlapping images formed by overlapping nozzles of two heads 31 aligned in the paper width direction. Perform position adjustment. Therefore, the relative position of the adjacent heads 31A and 31B is not always the ideal position. For example, in the printing method shown in FIG. 6A, as shown in FIG. 6D, by adjusting the position of the adjacent head so that the width of the adjacent head becomes narrower, the density fluctuation with respect to the deviation in the paper width direction (meandering during medium conveyance). Can be reduced. However, if the position of the adjacent head is adjusted so that the width of the adjacent head becomes narrower, the density of the overlapping image is slightly higher than that of the non-overlapping image even when there is no conveyance error (meandering or uneven speed). It will be printed. Therefore, the density unevenness correction value H is calculated for the head whose position is adjusted so that the density fluctuation of the overlapping image is reduced.

  FIG. 11 is a diagram illustrating an example in which a certain raster line affects the density of an adjacent raster line. Not only the density unevenness generated in the overlapped image and the non-overlapping image due to the head position adjustment, but also the density unevenness occurs due to a problem of nozzle processing accuracy. Therefore, in this embodiment, not only the density unevenness correction value for the overlapping image but also the density unevenness correction value for the nozzle processing accuracy is calculated. That is, the density unevenness correction value H generated in the overlapping image and the non-overlapping image is calculated.

  Further, as shown in FIG. 11, the raster line formed in the second row region is formed near the third row region due to the flight curve of the ink droplets ejected from the nozzles. As a result, the second row region is visually recognized as light, and the third row region is visually recognized as dark. On the other hand, the amount of ink droplets ejected to the fifth row region is smaller than the prescribed amount, and the dots formed in the fifth row region are small. As a result, the fifth row region becomes light. This appears as uneven density on the image. Therefore, correction is made so that the lightly printed row region is printed dark, and the darkly printed row region is corrected so as to be printed lightly. The reason why the third row region becomes dark is not due to the influence of the nozzle assigned to the third row region, but to the influence of the nozzle assigned to the adjacent second row region.

  Therefore, in the present embodiment, the correction value H for each row region is calculated in consideration of the influence of adjacent nozzles as well as the nozzles assigned to the row region. The correction value calculation target printer 1 is connected to a computer, and a correction value acquisition program is installed in the computer. Also assume that a scanner is connected to the computer. Hereinafter, a method for calculating the density unevenness correction value H for each row region will be described. Note that a column region in which a raster line along the transport direction is formed corresponds to a plurality of pixel columns (pixel columns) arranged in the x direction corresponding to the transport direction on the data.

  FIG. 12 is a diagram showing a test pattern for calculating a density unevenness correction value. First, the correction value acquisition program causes the printer 1 in which the position of the head 31 is adjusted to print a test pattern as shown in FIG. When calculating the head adjustment amount, in order to calculate the adjustment amount for each of the two heads 31, a test pattern is printed for each of the two heads 31 as shown in FIG. 8A. When calculating, the test pattern is printed by all the heads 31 (five heads 31 in the figure). Further, in order to calculate the correction value H for each nozzle row (for each ink), a test pattern is printed for each nozzle row. The test pattern shown in FIG. 12 is a cyan test pattern, and although not shown, other yellow, magenta, and black test patterns are also printed.

  The test pattern is composed of a belt-like pattern having five types of density. Similar to the test pattern of FIG. 8A, a belt-like pattern with a command gradation value Sa (= 76 · density 30%), a belt-like pattern with a command gradation value Sb (= 102 · density 40%), and a command gradation value The band pattern of Sc (= 128 · density 50%), the band pattern of command tone value Sd (= 153 · density 60%), and the command tone value from the band pattern of Se (= 178 · density 70%). Composed. The test pattern in FIG. 12 is also configured with raster lines arranged in the paper width direction, similar to the test pattern in FIG. 8B. Here, the left nozzles in the paper width direction (nozzles # 1 of the head 31B (1)) are numbered sequentially from the corresponding row region. In this embodiment, a correction value is set for the row region corresponding to the total number of nozzles of the non-overlapping nozzles of each head 31 and the number of overlapping nozzles of adjacent heads.

  Since the head adjustment amount is determined before the density unevenness correction value H is calculated, even if a transport error (meandering or speed unevenness) occurs, the density variation of overlapping images formed at different positions in the transport direction can be performed. As small as possible. Therefore, even if the correction value is calculated based on the belt-like pattern formed at a certain position in the transport direction as in the test pattern shown in FIG. 12, the overlapping image formed at another position in the transport direction by the correction value. Can be corrected.

  However, the test pattern is not limited to the test pattern illustrated in FIG. 12, and may be a test pattern in which small patterns are formed at a plurality of different positions in the transport direction, such as the test pattern illustrated in FIG. 8A. In such a test pattern, the density unevenness correction value may be calculated based on the average value of the read gradation values of the small patterns formed from position 1 to position 5. By doing so, it is possible to correct the density unevenness of the overlapped image on the average regardless of the position in the transport direction.

  Further, when the relative position of the adjacent head when the test pattern is actually printed is determined as an appropriate relative position, the test pattern shown in FIG. 8A has already been printed. Therefore, the density unevenness correction value may be calculated based on the test pattern printed to determine the head adjustment amount. However, there is a case where the density unevenness correction value cannot be calculated by using the printed test pattern as it is to determine the head adjustment amount. For example, in the present embodiment, the positions of all the heads 31 included in the head unit 30 are adjusted by accumulating the head adjustment amounts calculated for every two adjacent heads. For this reason, in consideration of the adjustment by accumulating the head adjustment amount, the calculation calculation of the uneven density correction value may be complicated.

  Further, the command gradation values Sa to Se (density) for forming the five strip patterns constituting the test pattern shown in FIG. 12, and the command gradation values Sa to Se for forming the test pattern shown in FIG. 8A. (Concentration) is made equal, but may be different. By doing so, each test pattern can be printed with a command gradation value suitable for calculating the head adjustment amount and a command gradation value suitable for calculating the density unevenness correction value, An accurate head adjustment amount and density unevenness correction value can be calculated.

  FIG. 13 shows the result of reading a cyan test pattern with a scanner. Hereinafter, explanation will be given by taking cyan read data as an example. The inspector sets the test pattern on the scanner, and the correction value acquisition program acquires the result of reading the test pattern by the scanner. In the graph of FIG. 13, the horizontal axis is the row area number, and the vertical axis is the read gradation value of each row area. After acquiring the reading result of the scanner, the correction value acquisition program associates the pixel columns in the read data with the column regions constituting the test pattern on a one-to-one basis, and then for each strip pattern, the density ( Reading gradation value) is calculated. Specifically, the average value of the read gradation values of each pixel belonging to the pixel column corresponding to a certain row region is set as the read gradation value of that row region.

  Although each belt-like pattern is uniformly formed with each command gradation value, as shown in FIG. 13, the reading gradation value varies for each row region. For example, in the graph of FIG. 13, the read gradation value Cbi of the i column region is relatively lower than the read gradation value of the other column region, and the read gradation value Cbj of the j column region is read of the other column region. It is relatively higher than the gradation value. That is, the i-th row region is visually recognized as light, and the j-th row region is viewed as dark. Such variation in the read gradation value of each row region is uneven density occurring in the print image. In the present embodiment, the relative positions of the adjacent heads are adjusted so that density fluctuations that occur in overlapping images due to transport errors (meandering and uneven speed) are suppressed. That is, the position of the adjacent head may be adjusted so as to deviate from the ideal state (designed position). For this reason, the reading gradation value of the row region to which the overlapping nozzle is assigned may have a large difference from the reading gradation value of the row region to which the non-overlapping nozzle is assigned. In the test pattern reading result shown in FIG. 13, the row area formed by the overlapping nozzles has a lower reading gradation value (becomes lighter) than the row region formed by other non-overlapping nozzles.

  By bringing the read gradation value of each row region close to a constant value, it is possible to improve the density difference (joint density difference Δd) between the overlapping image and the non-overlapping image and the density unevenness due to the processing accuracy of the nozzles. Therefore, the average value Cbt of the read gradation values of all the row regions is set as the “target value Cbt” at the same command gradation value (for example, Sb / density 40%). Then, the pixel column data (gradation value) corresponding to each column region is corrected so that the read gradation value of each column region at the command gradation value Sb approaches the target value Cbt.

  Specifically, the gradation value indicated by the pixel column corresponding to the column region i having a reading gradation value lower than the target value Cbt is corrected to a gradation value darker than the command gradation value Sb. On the other hand, the gradation value indicated by the pixel column corresponding to the column region j having a reading gradation value higher than the target value Cbt is corrected to a gradation value lighter than the command gradation value Sb. In other words, the correction value acquisition program corrects the pixel column data (gradation value) corresponding to each column region so that the density of all the column regions approaches a certain value for the same gradation value. The value H is calculated.

14A and 14B are diagrams illustrating a specific method for calculating the density unevenness correction value H. FIG. First, FIG. 14A shows a state in which the target command tone value (Sbt) for the command tone value (Sb) is calculated in the i-th row region where the read tone value is lower than the target value Cbt. The horizontal axis indicates the gradation value, and the vertical axis indicates the read gradation value in the test pattern result. On the graph, the read gradation values (Cai, Cbi, Cci) are plotted against the command gradation values (Sa, Sb, Sc). The target command tone value Sbt for representing the i-th row region with the target value Cbt with respect to the command tone value Sb is calculated by the following equation (linear interpolation based on the straight line BC).
Sbt = Sb + {(Sc−Sb) × (Cbt−Cbi) / (Cci−Cbi)}

Similarly, as shown in FIG. 14B, in the j-th row area having a reading gradation value higher than the target value Cbt, the target command for representing the j-th row area with the target value Cbt with respect to the command tone value Sb. The gradation value Sbt is calculated by the following equation (linear interpolation based on the straight line AB).
Sbt = Sa + {(Sb−Sa) × (Cbt−Caj) / (Cbj−Caj)}

Thus, the target command tone value Sbt of each row region with respect to the command tone value Sb is calculated. Then, the correction value acquisition program calculates a cyan correction value Hb for the command gradation value Sb of each row region by the following equation. Similarly, the correction value acquisition program calculates correction values for other command gradation values (Sa, Sc, Sd, Se) and correction values for other colors (yellow, magenta, black) (FIG. 4A). S003).
Hb = (Sbt−Sb) / Sb

  FIG. 15 is a diagram illustrating a correction value table for each nozzle row (CMYK). The correction values H calculated as described above are collected in the correction value table shown in the figure. In the correction value table, correction values (Ha, Hb, Hc, Hd, He) respectively corresponding to five command gradation values (Sa, Sb, Sc, Sd, Se) are set for each row region. Such a correction value table is stored in the memory 13 (storage unit) of the printer 1 on which the test pattern is printed in order to calculate the correction value H. Thereafter, the printer 1 is shipped to the user.

  When the user starts using the printer 1, the user installs a printer driver in the computer 50 connected to the printer 1. Then, the printer driver requests the printer 1 to transmit the correction value H stored in the memory 13 to the computer 50. The printer driver stores the correction value H transmitted from the printer 1 in a memory in the computer 50.

  When the printer driver receives a print command and image data from various application programs, the printer driver creates print data for the printer 1 to perform printing. First, the printer driver converts the resolution of the image data from the application program to the print resolution by resolution conversion processing. Next, the printer driver converts the image data, which is RGB data, into YMCK data corresponding to the color of the ink used for printing by color conversion processing. Thereafter, the printer driver corrects the gradation value (for example, 256 gradation values) indicated by each pixel with the correction value H for each row area, each color, and each instruction gradation value.

If the gradation value S_in before correction is the same as one of the command gradation values Sa, Sb, Sc, Sd, Se, the correction value H corresponding to each command gradation value is stored in the memory of the computer 50. The corrected correction values Ha, Hb, Hc, Hd, and He can be used as they are. For example, if the gradation value S_in before correction is S_in = Sc, the gradation value S_out after correction is obtained by the following equation.
S_out = Sc × (1 + Hc)

  FIG. 16 is a diagram illustrating how the correction value H corresponding to each gradation value is calculated for the nth row region of cyan. The horizontal axis is the gradation value S_in before correction, and the vertical axis is the correction value H_out corresponding to the gradation value S_in before correction. When the gradation value S_in before correction is different from the command gradation value, the correction value H_out corresponding to the gradation value S_in before correction is calculated.

For example, as shown in FIG. 16, when the gradation value S_in before correction is between the command gradation values Sa and Sb, the linearity of the correction value Ha of the command gradation value Sa and the correction value Hb of the command gradation value Sb. A correction value H_out is calculated by the following equation by interpolation, and a corrected gradation value S_out is calculated.
H_out = Ha + {(Hb−Ha) × (S_in−Sa) / (Sb−Sa)}
S_out = S_in × (1 + H_out)

  When the gradation value S_in before correction is smaller than the command gradation value Sa, the correction value H_out is calculated by linear interpolation between the minimum gradation value 0 and the command gradation value Sa, and the gradation value before correction is calculated. When S_in is larger than the command gradation value Se, the correction value H_out is calculated by linear interpolation between the maximum gradation value 255 and the command gradation value Se.

  In this way, the printer driver corrects the gradation value S_in (256 gradation data) indicated by the pixel in the density correction process using the correction value H set for each color, each column region to which the pixel data belongs, and each gradation value. To do. By doing so, the gradation value S_in of the pixel corresponding to the row region where the density is visually recognized is corrected to the dark gradation value S_out, and the gradation value S_in indicated by the pixel corresponding to the row region where the density is visually recognized is dark. Is corrected to a light gradation value S_out. As a result, density unevenness caused by the processing accuracy of the nozzle can be suppressed. Even if the relative position of the adjacent head is adjusted so as to deviate from the designed position in order to suppress the density fluctuation that occurs in the overlapping image due to the conveyance error (meandering and uneven speed), the non-overlapping image and the overlapping image Uneven density can be suppressed.

  After the density correction processing, the printer driver performs high tone number (256 tone) data by halftone processing, and low tone number data that can be formed by the printer 1 (indicating dot ON / OFF). Data). Finally, the printer driver rearranges the matrix-like image data for each data in the order to be transferred to the printer 1 by rasterization processing, and transmits the data to the printer 1 together with the command data. The printer 1 executes printing based on the received print data.

  In the present embodiment, the density unevenness correction value H is calculated for each row region, but the present invention is not limited to this. In order to suppress density fluctuations that occur in overlapping images due to transport errors (meandering and uneven speed), if the relative position of adjacent heads is shifted from the design position, density differences (joints) between overlapping images and non-overlapping images A density difference Δd) occurs. Therefore, for example, in order to make the density of the overlapping image and the non-overlapping image uniform, only one correction value for the overlapping image may be calculated, or the correction value for the non-overlapping image may be calculated.

=== Second Embodiment ===
FIG. 17 is a diagram illustrating a weighted average when calculating the uneven density correction value H. In FIG. In the above-described embodiment, when the density unevenness correction value H is calculated, a test pattern in which a belt-like pattern is located at a certain position in the transport direction is printed as shown in FIG. Absent. In order to calculate the density unevenness correction value H, a test pattern in which small patterns are formed at a plurality of positions in different transport directions may be printed, such as the test pattern shown in FIG. 8A. By calculating the density unevenness correction value based on the average value of the read gradation values of the small patterns formed from the position 1 to the position 5, the density unevenness of the overlapped image can be averaged regardless of the position in the transport direction. It can be corrected.

  In the second embodiment, the reading gradation values of the small patterns formed at the respective positions 1 to 5 are weighted and averaged, and the density unevenness correction value H is calculated based on the weighted average result. Again, the density unevenness correction value H is calculated for each row region. For example, in a test pattern (FIG. 8A) printed with a specified gradation value S, the reading gradation value at position 1 in a certain row area i is “DSi1”, and the reading gradation value at position 2 is “DSi2”. The read tone value at position 3 is “DSi3”, the read tone value at position 4 is “DSi4”, and the read tone value at position 5 is “DSi5”. Rather than simply averaging the read gradation values of the respective positions 1 to 5 in the row region i, the average values are multiplied by the weighting coefficient W.

The weighting coefficient W is used in combination when calculating a density unevenness correction value H corresponding to not only a certain command gradation value S but also other command gradation values. Therefore, the average value of joint density differences Δd (a) to Δd (e) (density differences between overlapping images and non-overlapping images of each small pattern) of all the command gradation values Sa to Se for each position 1 to 5, that is, The weighting coefficient W is calculated based on the average joint density difference ΔD. It is assumed that the weighting coefficient at position 1 is W1, the weighting coefficient at position 2 is W2, the weighting coefficient at position 3 is W3, the weighting coefficient at position 4 is W4, and the weighting coefficient at position 5 is W5. The read gradation value DSi of the row region i for calculating the density unevenness correction value H is calculated by the following equation.
DSi = W1 × DSi1 + W2 × DSi2 + W3 × DSi3 + W4 × DSi4 + W5 × DSi5
FIG. 17 shows average seam density differences ΔD1 to ΔD5 at the respective positions 1 to 5. In the case of this figure, the relationship of the average joint density difference ΔD at each position 1 to 5 is “ΔD1 <ΔD2 <(ΔD1 + ΔD5) / 2 <ΔD3 <ΔD4 <ΔD5”. According to this relationship, it is preferable that the density difference between the overlapping image and the non-overlapping image is large at positions 3 to 5 and the density unevenness correction value H is set to a large value. At positions 1 and 2, the density difference between the overlapping image and the non-overlapping image is preferred. The density unevenness correction value H is preferably set to a small value. That is, there are three positions where the density unevenness correction value H should be increased, and there are 2 positions where the density unevenness correction value H should be decreased. For this reason, if the read tone values at the positions 1 to 5 are simply averaged, the density unevenness correction value H becomes relatively large, and the positions 1 and 2 may be overcorrected.

Therefore, based on the read gradation value of “position 2 and position 3” that is the boundary between the average value ((ΔD1 + ΔD5) / 2) of the maximum average joint density difference ΔD5 and the minimum average joint density difference ΔD1. The unevenness correction value is calculated. Therefore, the weighting coefficients at position 1 and positions 4 and 5 are zero (W1 = W4 = W5 = 0). The weighting coefficient W2 at position 2 and the weighting coefficient W3 at position 3 are calculated by the following equations.
W2 = {ΔD3- (ΔD1 + ΔD5) / 2} / (ΔD3-ΔD2)
W3 = {(ΔD1 + ΔD5) / 2−ΔD2} / (ΔD3−ΔD2)
For example, ΔD1 = 4, ΔD2 = 5, ΔD3 = 8, ΔD4 = 9, and ΔD5 = 10. Then, the weighting coefficient W2 at the position 2 is “1/3”, and the weighting coefficient W3 at the position 3 is “2/3”.

  In this way, the weighting coefficients W1 to W5 of the respective positions 1 to 5 are calculated, and the reading gradation values of the small patterns formed at the respective positions 1 to 5 are weighted and averaged, so that regardless of the position in the transport direction. , Uneven density of overlapping images can be suppressed.

=== Third Embodiment ===
In the above-described embodiment, the relative positions of the heads 31A and 31B aligned in the paper width direction are set to the transport direction and the paper width direction so that density fluctuations along the transport direction that occur in overlapping images due to transport errors (meandering and speed unevenness) are reduced. However, the adjustment is not limited to this. As a result of printing the test pattern, when the relative positions of the upstream head 31A and the downstream head 31B adjacent in the paper width direction are shifted in the transport direction (for example, when it is the third candidate position in FIG. 10), the duplicate image It is assumed that the density fluctuation range C of the image becomes the smallest. In this case, in the above-described embodiment, the relative positions in the transport direction of the upstream head 31A and the downstream head 31B are actually shifted. As a result, the positional relationship in the conveyance direction between the dot landing position by the overlapping nozzle of the upstream head 31A and the dot landing position by the overlapping nozzle of the downstream head 31B is shifted, and the density fluctuation range C of the overlapping image becomes small.

  On the other hand, in the third embodiment, as a result of the test pattern, when it is found that the density fluctuation range C of the overlapping image can be reduced by shifting the relative positions of the adjacent heads 31A and 31B in the transport direction, The ink ejection timing (ink ejection interval) from each overlapping nozzle of the adjacent heads 31A and 31B is adjusted. Adjusting the relative position of the adjacent heads in the transport direction means that the positional relationship in the transport direction of dots formed by the overlapping nozzles of the adjacent heads 31A and 31B changes. Similarly, by adjusting the ink ejection timing from the overlapping nozzles, the positional relationship in the transport direction of dots formed by the overlapping nozzles of the adjacent heads 31A and 31B can be changed. As a result, the density fluctuation range C of the overlapping image can be reduced.

  That is, when it is necessary to adjust the relative positions of the adjacent heads 31A and 31B in the transport direction in order to reduce the density fluctuation along the transport direction that occurs in the overlapped image due to the transport error (meandering and uneven speed). Instead of shifting the position of the head 31, the ink ejection timing from the overlapping nozzles of the adjacent heads 31A and 31B may be adjusted.

  In the above-described embodiment, the test patterns are printed by actually changing the relative positions of the adjacent heads 31A and 31B in the transport direction (example: candidate positions 3 to 5 in FIG. 10), but the present invention is not limited to this. . Instead of changing a plurality of relative positions in the transport direction of the adjacent heads 31A and 31B, a test pattern is printed by changing a plurality of ink ejection timings (ink ejection intervals) from the overlapping nozzles of the adjacent heads 31A and 31B. Also good. In the test pattern thus printed, the ejection timing at which the density fluctuation range of the overlapping images (the fluctuation range of the average joint density difference ΔD) becomes small is determined. Then, for example, a control method (such as a drive waveform for ejecting ink from the nozzles) of the controller 10 of the printer 1 may be adjusted so that ink droplets are ejected from the overlapping nozzles at the ejection timing.

=== Fourth Embodiment ===
In the above-described embodiment, the relative positions of the adjacent heads actually changed based on the result of printing the test pattern by changing the relative positions of the adjacent heads 31A and 31B (density variation range C of the overlapping image) are changed. Although the optimum relative position of the adjacent head is determined from the inside, it is not limited to this. A result (density fluctuation range C) corresponding to the relative position between the actually changed relative positions by interpolating the result (density fluctuation range C of the overlapping image) calculated by actually changing the relative position of the adjacent head. May be calculated. By doing so, the optimum relative position can be determined from among the relative position candidates of more adjacent heads without increasing the trouble of printing a test pattern, etc., and the density fluctuation of the overlapping image can be reduced. can do.

  For example, in the result shown in FIG. 10, the density fluctuation range C1 (first candidate position) when one head of the adjacent head is shifted by “ΔY1” in the paper width direction (Y direction), and one head of the adjacent head. Is obtained as a density fluctuation range C2 (second candidate position) in the case where is shifted by “ΔY2” in the paper width direction. Therefore, the density fluctuation range C1.5 when one head of the adjacent head is shifted by the adjustment amount “ΔY1.5” between the adjustment amounts ΔY1 and ΔY2 in the paper width direction is adjusted without printing the test pattern. It may be calculated by linear interpolation or the like based on the result C1 corresponding to the amount ΔY1 and the result C2 corresponding to the adjustment amount ΔY2.

  In some cases, the test pattern for determining the head adjustment amount (FIG. 8A) and the test pattern for calculating the density unevenness correction value are shared. In this case, when the relative position (for example, ΔY1.5) corresponding to the density fluctuation range (for example, C1.5) calculated by interpolation is determined to be the optimum relative position, the adjacent head has a relative position in the vicinity of the relative position. It is necessary to calculate a density unevenness correction value by interpolating a test pattern result (for example, a test pattern of ΔY1 or ΔY2) printed at the position.

=== Fifth Embodiment ===
In the above-described embodiment, the optimum relative position is determined only from the result of the test pattern printed at the relative position of a certain candidate of the adjacent head. For example, the test pattern “ΔD1-1, ΔD2-1, ΔD3-1, ΔD4-1, ΔD5-1” formed when the relative position of the adjacent head is the relative position of the first candidate in the table of FIG. The difference between the maximum average seam density and the minimum average seam density (maxΔD and minΔD) is calculated as the density fluctuation range C. However, the present invention is not limited to this.

  The positional relationship between adjacent heads adjacent in the paper width direction may deviate from the positional relationship between adjacent heads at the time of determining the head adjustment amount (for example, during manufacturing) depending on the aging of the printer 1 and the usage environment. Therefore, when calculating the density fluctuation range C of the relative position of a certain candidate of the adjacent head, not only the test pattern result printed when the relative position of the adjacent head is the relative position of the candidate, The test pattern result printed when the position is a relative position in the vicinity of the candidate relative position may also be considered.

  For example, when calculating the density fluctuation range C of the overlapping image when one head of the adjacent head is shifted 100 μm to the right in the paper width direction (Y direction), the test pattern result when one head is shifted 100 μm to the right In addition, the test pattern result when one head is shifted 90 μm to the right side and the test pattern result when one head is shifted 110 μm to the right side are considered (considering the test pattern results before and after). That is, the difference between the maximum average seam density and the minimum average seam density (maxΔD and minΔD) is calculated as the density fluctuation range C from the test pattern results at the relative positions of the three patterns of adjacent heads.

  As described above, in the fifth embodiment, for each relative position candidate of the adjacent head, the density fluctuation range C of the overlapping image when the adjacent head is the relative position of the candidate, and the adjacent head of the relative position of the candidate. The overlapping image density fluctuation range C at the relative position in the vicinity is considered. In other words, the density fluctuation that occurs in the overlapping image at the current relative position of the adjacent head is reduced, and when the relative position of the adjacent head is shifted due to secular change (and the ejection timing is shifted), the overlapping image is displayed. The relative position of the adjacent head is determined so that the generated density fluctuation is also reduced. Therefore, image quality deterioration can be suppressed over a long period of time. Further, not only when the head adjustment amount is calculated, but in addition to the test pattern (FIG. 12 and FIG. 8A) formed at the relative position (current relative position) of the adjusted adjacent head, the adjacent head indicates the current relative position. The density unevenness correction value may be calculated in consideration of a test pattern formed when the position is a relative position in the vicinity (position that may be shifted in the future). At this time, the adjusted test pattern result of the relative position (current relative position) of the adjacent head is reflected in the density unevenness correction value H more than the test pattern result of the relative position near the current relative position. A weighted average may be performed.

=== Other Embodiments ===
Each of the above embodiments has been described mainly for a printing system having an ink jet printer, but includes disclosure of a density unevenness correction method and the like. The above-described embodiments are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof. In particular, the embodiments described below are also included in the present invention.

<About print mode>
Relative positions of adjacent heads 31A and 31B (see FIG. 6A and FIG. 7A) such that the density fluctuation range generated in the overlapping image becomes small due to transport error (meandering / velocity unevenness) according to the ink placement method of the overlapping area (FIGS. 6A and 7A). 6D and FIG. 7D) are different. There is a case where the method of ink placement in the overlapping area is different depending on the print mode in one printer. In this case, if the position of the head 31 is a printer that can be automatically adjusted, depending on the print mode (according to the ink placement method of the overlapping area), the density fluctuation range that occurs in the overlapping image is reduced. Position adjustment may be performed at the relative position. If only the positional relationship in the transport direction of the adjacent heads needs to be adjusted according to the ink placement method for the overlapping area, the printer can be used according to the print mode even if the head 31 is not automatically adjusted. It is preferable to adjust the ejection timing of the ink from each overlapping nozzle of the adjacent head (according to the ink placement method of the overlapping area). The ink ejection timing described in the embodiments means adjusting the ink ejection interval, and other methods for adjusting the ink ejection interval are not intended to limit the present invention. Absent.

<About the printer>
In the above-described embodiment, a printer (so-called line head printer) that forms an image by arranging a plurality of heads over the width of the paper and conveying the paper under the fixed head is taken as an example. Not limited to this. For example, the plurality of heads are arranged in the nozzle row direction so that the end portions of the nozzle rows of the plurality of heads overlap. The operation of forming an image while moving the plurality of heads in the direction intersecting the nozzle row direction with respect to the paper and the operation of conveying the paper in the nozzle row direction with respect to the plurality of heads are alternately repeated. A printer (a so-called serial printer) may be used. In the serial printer, an image is printed while the head moves in a moving direction intersecting the nozzle row direction by a carriage. For this reason, density unevenness (density fluctuation) along the moving direction is generated in the overlapped image due to uneven carriage speed or meandering of the carriage (guide rail), and this case is effective.

<About printing devices>
The ink ejection method may be a piezo method in which a fluid is ejected by applying a voltage to a drive element (piezo element) to expand and contract an ink chamber, or by generating bubbles in a nozzle using a heating element, A thermal method in which liquid is ejected by the bubbles may be used.

1 Printer, 10 Controller, 11 Interface section,
12 CPU, 13 memory, 14 unit control circuit,
20 transport unit, 21 transport belt, 22A, 22B transport roller,
30 head units, 31 heads,
40 detector groups, 50 computers

Claims (8)

(A) a first nozzle row in which first nozzles that eject ink are arranged in a predetermined direction, and a second nozzle row in which second nozzles that eject ink are arranged in the predetermined direction, and one side in the predetermined direction And a second nozzle row arranged to form an overlapping region that overlaps with the other end portion in the predetermined direction of the first nozzle row, and the first nozzle row and the second nozzle A method of manufacturing a printing apparatus that prints an image while moving a row and a medium in a moving direction that intersects the predetermined direction,
(B) A pattern in which a plurality of relative positions of the first nozzle row and the second nozzle row are changed, and each time a change is made, a small pattern having a predetermined density is formed at a plurality of different positions in the moving direction on the medium. Printing,
(C) obtaining a density of an image portion printed in the overlap area of each of the small patterns;
(D) For each of the relative positions of the first nozzle row and the second nozzle row that are changed a plurality of times, a difference in density of the image portion of each of the small patterns formed at a plurality of different positions in the movement direction is calculated. To calculate,
(E) Based on the density difference, the relative position between the first nozzle row and the second nozzle row is determined, and the relative position between the first nozzle row and the second nozzle row is determined as the relative position. Adjusting,
(F) calculating a density correction value for an image portion printed in the overlapping region based on a pattern printed by the first nozzle row and the second nozzle row which are the determined relative positions;
(G) storing the density correction value in a storage unit of the printing apparatus;
A method of manufacturing a printing apparatus comprising (H). A method of manufacturing a printing apparatus according to claim 1,
For each of the small patterns, a density difference between an image portion printed in the overlapping area of the small pattern and a density of an image portion printed by a nozzle not belonging to the overlapping area is acquired as a joint density difference,
For each relative position of the first nozzle row and the second nozzle row that have been changed a plurality, the difference in the joint density differences of the small patterns respectively formed at a plurality of different positions in the movement direction is set as a variation range. Calculate
Determining relative positions of the first nozzle row and the second nozzle row based on the variation range;
A method for manufacturing a printing apparatus. A method for manufacturing a printing apparatus according to claim 2,
Each of the plurality of small patterns formed when the first nozzle row and the second nozzle row are in a certain relative position for each of the relative positions of the first nozzle row and the second nozzle row that have been changed a plurality of times. The difference between the maximum value and the minimum value in the joint density difference is calculated as the fluctuation range of the certain relative position,
Determining a minimum value in the fluctuation range corresponding to each relative position of the first nozzle row and the second nozzle row changed in plural,
The relative position corresponding to the fluctuation range of the minimum value is determined as a relative position of the first nozzle row and the second nozzle row.
A method for manufacturing a printing apparatus. A method for manufacturing a printing apparatus according to claim 2,
Each of the plurality of small patterns formed when the first nozzle row and the second nozzle row are in a certain relative position for each of the relative positions of the first nozzle row and the second nozzle row that have been changed a plurality of times. Among the joint density differences and the joint density differences of the plurality of small patterns formed when the first nozzle row and the second nozzle row are in relative positions in the vicinity of the certain relative position. The difference between the maximum value and the minimum value is calculated as the fluctuation range of the certain relative position,
Determining a minimum value in the fluctuation range corresponding to each relative position of the first nozzle row and the second nozzle row changed in plural,
The relative position corresponding to the fluctuation range of the minimum value is determined as a relative position of the first nozzle row and the second nozzle row.
A method for manufacturing a printing apparatus. A method for manufacturing a printing apparatus according to any one of claims 1 to 4,
The pattern for calculating the density correction value is a pattern in which small patterns having a predetermined density are formed at a plurality of different positions in the moving direction on the medium,
Calculating the density correction value based on the result of weighted average of the density of the image portion printed in the overlapping area of each of the small patterns;
A method for manufacturing a printing apparatus. A method for manufacturing a printing apparatus according to any one of claims 1 to 5,
The relative positions of the first nozzle row and the second nozzle row in the movement direction so as to be the relative positions of the first nozzle row and the second nozzle row determined based on the density difference. Instead of adjusting
Adjusting an ink ejection interval between the first nozzle row and the second nozzle row;
A method for manufacturing a printing apparatus. (A) a first nozzle row in which first nozzles that eject ink are arranged in a predetermined direction, and a second nozzle row in which second nozzles that eject ink are arranged in the predetermined direction, and one side in the predetermined direction And a second nozzle row arranged to form an overlapping region that overlaps with the other end portion in the predetermined direction of the first nozzle row, and the first nozzle row and the second nozzle A method of manufacturing a printing apparatus that prints an image while moving a row and a medium in a moving direction that intersects the predetermined direction,
(B) A plurality of ink ejection intervals of the first nozzle row and the second nozzle row are changed, and each time a change is made, a small pattern having a predetermined density is formed at a plurality of different positions in the moving direction on the medium. Printing patterns,
(C) obtaining a density of an image portion printed in the overlap area of each of the small patterns;
(D) A difference in density of the image portions of the small patterns respectively formed at a plurality of different positions in the movement direction for each of the ink ejection intervals of the first nozzle row and the second nozzle row that are changed a plurality of times. Calculating
(E) Based on the density difference, the ink ejection interval between the first nozzle row and the second nozzle row is determined, and the ink ejection interval between the first nozzle row and the second nozzle row is determined. Adjusting the injection interval,
(F) calculating a density correction value for an image portion printed in the overlapping region based on a pattern printed by the first nozzle row and the second nozzle row which are the determined ink ejection intervals;
(G) storing the density correction value in a storage unit of the printing apparatus;
A method of manufacturing a printing apparatus comprising (H). (A) a first nozzle row in which first nozzles that eject ink are arranged in a predetermined direction, and a second nozzle row in which second nozzles that eject ink are arranged in the predetermined direction, and one side in the predetermined direction And a second nozzle row arranged to form an overlapping region that overlaps with the other end portion in the predetermined direction of the first nozzle row, and the first nozzle row and the second nozzle A printing apparatus that prints an image while moving a row and a medium in a moving direction that intersects the predetermined direction,
(B) A pattern in which a plurality of relative positions of the first nozzle row and the second nozzle row are changed, and each time a change is made, a small pattern having a predetermined density is formed at a plurality of different positions in the moving direction on the medium. Printing,
(C) obtaining a density of an image portion printed in the overlap area of each of the small patterns;
(D) For each of the relative positions of the first nozzle row and the second nozzle row that are changed a plurality of times, a difference in density of the image portion of each of the small patterns formed at a plurality of different positions in the movement direction is calculated. To calculate,
(E) Based on the density difference, the relative position between the first nozzle row and the second nozzle row is determined, and the relative position between the first nozzle row and the second nozzle row is determined as the relative position. Adjusting,
(F) calculating a density correction value for an image portion printed in the overlapping region based on a pattern printed by the first nozzle row and the second nozzle row which are the determined relative positions;
The printing apparatus which memorize | stored the said density | concentration correction value acquired by (G) in the memory | storage part.