JP6148583B2 - Inkjet printing device - Google Patents

Description

  The present invention relates to an inkjet printing apparatus that performs printing by ejecting ink onto a printing medium.

  A line-type ink jet printing apparatus in which an ink jet head is constituted by a plurality of head units is known (for example, see Patent Document 1).

  As a head unit of such a line-type ink jet printing apparatus, a head unit in which two head modules each having a single nozzle row in which a plurality of nozzles are arranged along the main scanning direction may be used. . The two head modules are bonded so that the two nozzle rows are shifted from each other by a half pitch in the main scanning direction. Thereby, a head unit capable of printing with high resolution can be easily manufactured.

  Here, different colors of ink may be supplied to the two head modules of the head unit described above. Thereby, it is possible to eject two colors of ink from one head unit. As a result, in an inkjet printing apparatus capable of color printing, the number of inkjet heads can be reduced and the apparatus can be miniaturized.

JP 2011-143712 A

  In the ink jet printing apparatus capable of color printing using the head unit described above, there is a positional deviation between the nozzle rows in the main scanning direction. For this reason, the positional deviation of the dots of the ink of a plurality of colors corresponding to the same pixel occurs.

  If it is a portion other than the edge in the main scanning direction of the image, even if the dot is misaligned, it is difficult for the color to change due to the overlap with the adjacent dots, or the color is corrected with the image profile Is possible. However, at the edge of the image in the main scanning direction, the color of the ink ejected from the nozzles protruding in the main scanning direction has been enhanced. For this reason, the print image quality has deteriorated.

  The present invention has been made in view of the above, and an object of the present invention is to provide an ink jet printing apparatus that can reduce a decrease in print image quality.

  In order to achieve the above object, the first feature of the ink jet printing apparatus according to the present invention is that a plurality of nozzles arranged along the nozzle arrangement direction at predetermined intervals are ejected from the nozzles with different colors. A printing unit having a plurality of nozzle rows; and a control unit that controls the printing unit to print an image by discharging ink from the nozzles, and at least one nozzle row of the plurality of nozzle rows includes: With respect to at least one other nozzle row, the nozzle is arranged so that the position of the nozzle is shifted in the nozzle arrangement direction, and the control unit is configured to provide a boundary portion between the image and the outside in the nozzle arrangement direction. A reference color is selected from among the ink colors used for the pixels, and the front of the nozzles corresponding to the ink colors used for the pixels in the boundary portion. In the nozzle arrangement direction, the ejection amount of the ink of the color corresponding to the nozzle on the outer side of the image from the nozzle corresponding to the reference color is reduced with respect to the pixels at the boundary portion, and the image corresponding to the reference color is reduced from the nozzle. The ink ejection amount is corrected so as to increase the ejection amount of the ink of the color corresponding to the nozzle on the inner side of the boundary to the pixels at the boundary portion.

  A second feature of the ink jet printing apparatus according to the present invention is that the control unit corrects the ink discharge amount of each color for correcting the ink discharge amount according to the ink discharge amount before the correction of each color. It is in.

  A third feature of the ink jet printing apparatus according to the present invention is that the control unit responds to a deviation amount in the nozzle arrangement direction of each nozzle corresponding to each color for correcting the ink ejection amount with respect to the nozzle corresponding to the reference color. Thus, the ejection amount of each color ink is corrected.

  A fourth feature of the ink jet printing apparatus according to the present invention is that the control unit omits correction of the ink discharge amount for the pixel when the discharge amount of the reference color ink for the pixel in the boundary portion is equal to or greater than a threshold value. There is to do.

  A fifth feature of the ink jet printing apparatus according to the present invention is that the control unit selects, as a reference color, a color having the lowest lightness among the ink colors used for the pixels of the boundary portion.

  According to the first feature of the ink jet printing apparatus according to the present invention, the control unit includes the reference color in the nozzle arrangement direction among the nozzles corresponding to the ink colors used for the pixels at the boundary in the nozzle arrangement direction. The ejection amount for the pixels at the boundary portion of the color ink corresponding to the nozzles on the outer side of the image is reduced from the nozzles corresponding to. In addition, the control unit increases the ejection amount for the pixels at the boundary portion of the color ink corresponding to the nozzle on the inner side of the image from the nozzle corresponding to the reference color. Thereby, the color shift of the boundary part (contour) of the image resulting from the positional shift of the nozzles of the respective colors in the nozzle arrangement direction can be reduced. As a result, it is possible to reduce a decrease in print image quality.

  According to the second feature of the ink jet printing apparatus according to the present invention, the control unit corrects the ink discharge amount of each color for correcting the ink discharge amount according to the ink discharge amount before the correction of each color. . Thereby, it can suppress that an excessive change arises in printing image quality by setting it as the correction amount according to discharge amount.

  According to the third feature of the ink jet printing apparatus according to the present invention, the control unit responds to a deviation amount in the nozzle arrangement direction of each nozzle corresponding to each color for correcting the ink ejection amount with respect to the nozzle corresponding to the reference color. Thus, the ejection amount of each color ink is corrected. Accordingly, the correction amount can be appropriately adjusted according to the positional relationship between the nozzles corresponding to the respective colors for correcting the ink ejection amount.

  According to the fourth feature of the ink jet printing apparatus according to the present invention, when the discharge amount of the reference color ink for the pixel at the boundary portion in the nozzle arrangement direction is equal to or larger than the threshold, the control unit discharges the ink for the pixel. The correction of is omitted. As a result, it is possible to suppress the processing load on the control unit and suppress an unnecessary change in print image quality.

  According to the fifth feature of the inkjet printing apparatus according to the present invention, the control unit selects, as a reference color, a color having the lowest lightness among the ink colors used for the pixels at the boundary in the nozzle arrangement direction. . Thereby, the color shift of a boundary part can be made inconspicuous by making a color with high visibility into a reference color.

It is a block diagram which shows the structure of the inkjet printing apparatus which concerns on embodiment. It is a schematic block diagram of a conveyance part and an inkjet head. It is a top view of a conveyance part and an inkjet head. It is a schematic block diagram of a head unit. It is a figure which shows the discharge amount corresponding | compatible correction coefficient table. It is a figure which shows the deviation amount corresponding | compatible correction coefficient table. It is a flowchart for demonstrating operation | movement of an inkjet printing apparatus. It is a figure which shows an example of the dot image of the image printed without performing discharge amount correction processing. It is a figure which shows an example of the dot image of the image printed by performing discharge amount correction processing. It is a figure which shows an example of the dot image of the pixel of the thin line of 1 pixel width along the subscanning direction printed without performing discharge amount correction | amendment processing. It is a figure which shows an example of the dot image of the pixel of the thin line of 1 pixel width along the subscanning direction printed by performing discharge amount correction processing. It is explanatory drawing of the head unit which has displaced. It is a figure which shows the other example of the dot image of the image printed without performing discharge amount correction processing. It is a figure which shows the other example of the dot image of the image printed by performing discharge amount correction processing. It is a figure which shows the other example of the dot image of the pixel of the thin line of 1 pixel width along the subscanning direction printed without performing discharge amount correction processing. It is a figure which shows the other example of the dot image of the pixel of the thin line of 1 pixel width along the subscanning direction printed by performing discharge amount correction processing.

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the embodiment described below exemplifies an apparatus or the like for embodying the technical idea of the present invention, and the technical idea of the present invention includes the material, shape, structure, The layout is not specified as follows. The technical idea of the present invention can be variously modified within the scope of the claims.

  FIG. 1 is a block diagram showing a configuration of an ink jet printing apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of the conveyance unit and the inkjet head of the inkjet printing apparatus shown in FIG. FIG. 3 is a plan view of the transport unit and the inkjet head. FIG. 4 is a schematic configuration diagram of the head unit.

  In the following description, the direction orthogonal to the paper surface of FIG. 2 is the front-rear direction, and the front surface direction is the front. Further, the top, bottom, left, and right of the paper surface in FIG. In FIG. 2, the direction from left to right is the conveyance direction of the paper PA. In the following description, upstream and downstream mean upstream and downstream in the transport direction.

  As shown in FIG. 1, the inkjet printing apparatus 1 according to the present embodiment includes a transport unit 2, a printing unit 3, and a control unit 4.

  The transport unit 2 transports the paper PA. As shown in FIG. 2, the transport unit 2 includes a transport belt 11, a driving roller 12, and driven rollers 13, 14, and 15.

  The transport belt 11 sucks and holds the paper PA and transports it. The conveyor belt 11 is an annular belt that is stretched around the driving roller 12 and the driven rollers 13 to 15. A number of belt holes for attracting and holding the paper PA are formed in the transport belt 11. The transport belt 11 sucks and holds the paper PA on the upper surface by the suction force generated in the belt hole by driving a fan (not shown). The conveyor belt 11 rotates in the clockwise direction in FIG. 2 to convey the suctioned and held paper PA in the right direction.

  The driving roller 12 rotates the conveyor belt 11. The drive roller 12 is driven by a motor (not shown).

  The driven rollers 13 to 15 are driven by the driving roller 12 via the conveyor belt 11. The driven roller 13 is disposed on the left side of the drive roller 12 at substantially the same height as the drive roller 12. The driven rollers 14 and 15 are spaced apart from each other in the left-right direction below the driving roller 12 and the driven roller 13 and are disposed at substantially the same height.

  The printing unit 3 prints an image on the paper PA conveyed by the conveyance unit 2. The printing unit 3 includes inkjet heads 21 </ b> A and 21 </ b> B and a head driving unit 22.

  The inkjet heads 21 </ b> A and 21 </ b> B are line-type inkjet heads, and eject ink onto the paper PA conveyed by the conveyance unit 2. The inkjet head 21A ejects cyan (C) and black (K) ink. The inkjet head 21B ejects magenta (M) and yellow (Y) ink. The inkjet heads 21A and 21B are arranged in this order from the upstream side along the conveyance direction (left-right direction) of the paper PA.

  Each of the inkjet heads 21A and 21B includes a plurality of head units 31A and a plurality of head units 31B. In the present embodiment, the inkjet heads 21A and 21B are each composed of six head units 31A and six head units 31B as shown in FIG.

  The six head units 31A are staggered along the front-rear direction (main scanning direction) orthogonal to the conveyance direction (sub-scanning direction) of the paper PA. That is, the six head units 31A are arranged along the front-rear direction, and every other head unit 31A is arranged with the positions in the left-right direction shifted. The six head units 31B are arranged in a staggered manner in the front-rear direction, similarly to the six head units 31A.

  As shown in FIG. 4, the head unit 31A is configured by bonding a head module 32C and a head module 32K. The head module 32C is disposed on the upstream side of the head module 32K. The head unit 31B is configured by bonding a head module 32M and a head module 32Y. The head module 32M is disposed on the upstream side of the head module 32Y. FIG. 4 is a view of the head units 31A and 31B as viewed from below.

  The head modules 32C, 32K, 32M, and 32Y have nozzle rows 33C, 33K, 33M, and 33Y, respectively. The nozzle rows 33C, 33K, 33M, and 33Y include a plurality of nozzles 34C, a plurality of nozzles 34K, a plurality of nozzles 34M, and a plurality of nozzles 34Y, respectively. Note that alphabetic suffixes (C, K, M, Y) indicating colors in codes may be omitted when there is no need to distinguish colors.

  The nozzles 34C, 34K, 34M, and 34Y discharge cyan (C), black (K), magenta (M), and yellow (Y) inks, respectively. In the head module 32, the number of ink droplets (number of drops) ejected from one nozzle 34 to one pixel can be changed, and gradation printing that expresses the density by the number of drops is performed. . Specifically, the nozzle 34 can eject 1 to 7 drops per pixel. The nozzle 34 opens on the lower surface of the head module 32. In each nozzle row 33, the nozzles 34 are arranged at equal intervals at a predetermined pitch P along the main scanning direction (front-rear direction) which is the nozzle arrangement direction.

  In the head unit 31A, the nozzles 34C of the nozzle row 33C and the nozzles 34K of the nozzle row 33K are arranged so as to be shifted from each other by a half pitch (P / 2) in the main scanning direction. By bonding the head modules 32C and 32K so as to be shifted from each other in the main scanning direction, the nozzle rows 33C and 33K are shifted from each other by a half pitch as shown in FIG.

  Similarly, in the head unit 31B, the nozzles 34M of the nozzle row 33M and the nozzles 34Y of the nozzle row 33Y are arranged so as to be shifted from each other by a half pitch in the main scanning direction. The head modules 32M and 32Y are bonded so as to be shifted from each other in the main scanning direction, whereby the nozzle rows 33M and 33Y are shifted from each other by a half pitch.

  As shown in FIG. 4, the positions of the nozzles 34C of the nozzle row 33C of the head unit 31A and the nozzles 34M of the nozzle row 33M of the head unit 31B coincide with each other in the main scanning direction. Further, the nozzles 34K of the nozzle row 33K of the head unit 31A and the nozzles 34Y of the nozzle row 33Y of the head unit 31B coincide with each other in the main scanning direction. That is, the head unit 31A and the head unit 31B are arranged so that the positions of the nozzles 34 in the main scanning direction coincide with each other.

  Due to the arrangement of the nozzles 34 as shown in FIG. 4, in the inkjet printing apparatus 1, the nozzles 34 at positions separated from each other by a half pitch in the main scanning direction between adjacent nozzle rows are used for forming the same pixel. Accordingly, in the nozzles 34C, 34K, 34M, and 34Y corresponding to the same pixel, the positions in the main scanning direction are shifted by a half pitch between the nozzles 34C and 34M and the nozzles 34K and 34Y.

  The head drive unit 22 drives the inkjet heads 21A and 21B. Specifically, the head drive unit 22 drives the head module 32 to eject ink from the nozzles 34.

  The control unit 4 controls the operation of each unit of the inkjet printing apparatus 1. The control unit 4 includes a CPU, a RAM, a ROM, a hard disk, and the like.

  At the time of printing, the control unit 4 conveys the paper PA and, based on the drop data, discharges ink from the nozzles 34 of the inkjet heads 21A and 21B to the paper PA to print an image. To control. The drop data is image data in a format corresponding to ink ejection by the ink jet heads 21A and 21B, and is data indicating the number of ink drops of each color ejected to each pixel.

  The control unit 4 stores a discharge amount correspondence correction coefficient table 41 shown in FIG. As will be described later, the discharge amount corresponding correction coefficient table 41 is referred to in the discharge amount correction processing. The ejection amount correction processing is processing for correcting the number of ink drops (ejection amount) with respect to pixels at the boundary between the image and the outside in the main scanning direction. Outside the image is an area where the number of drops of all colors is zero in the drop data.

  The discharge amount correspondence correction coefficient table 41 holds values of a discharge amount correspondence reduction coefficient Kdc and a discharge amount correspondence increase coefficient Kdi corresponding to the number of drops before correction. The discharge amount corresponding reduction coefficient Kdc is used to determine the number of drops after reduction of the color ink whose number of drops is reduced in the discharge amount correction processing. The ejection amount corresponding increase coefficient Kdi is used to determine the number of drops after the increase in the color ink whose number of drops increases in the ejection amount correction process.

  Further, the control unit 4 stores a deviation amount corresponding correction coefficient table 42 shown in FIG. The deviation amount corresponding correction coefficient table 42 is referred to in the discharge amount correction processing, similarly to the above-described discharge amount corresponding correction coefficient table 41.

  The shift amount corresponding correction coefficient table 42 is a shift amount corresponding reduction coefficient Kgc corresponding to the shift amount in the main scanning direction with respect to the nozzle 34 corresponding to the reference color of the nozzle 34 corresponding to the color whose drop number is corrected in the discharge amount correction processing. Further, the value of the shift amount corresponding increase coefficient Kgi is held. The shift amount reduction coefficient Kgc is used to determine the number of drops after reduction of the color ink whose number of drops is reduced in the ejection amount correction process. The shift amount corresponding increase coefficient Kgi is used to determine the number of drops after the increase of the ink whose color increases in the discharge amount correction process.

  Next, the operation of the inkjet printing apparatus 1 will be described.

  FIG. 7 is a flowchart for explaining the operation of the inkjet printing apparatus 1. The process of the flowchart in FIG. 7 starts when image data to be printed is input to the inkjet printing apparatus 1.

  In step S1 in FIG. 7, the control unit 4 generates drop data from image data in RGB format.

  Next, in step S2, the control unit 4 analyzes the drop data and detects a pixel at the boundary in the main scanning direction as a pixel to be corrected. The pixel at the boundary in the main scanning direction is a pixel at the boundary between the image and the outside in the main scanning direction.

  As the pixels at the boundary in the main scanning direction, there are a pixel at the front end and a pixel at the rear end in the main scanning direction (front-rear direction) of the image to be printed. In addition, a pixel with a thin line having a width of one pixel printed along the sub-scanning direction (left-right direction) is also included in the pixels at the boundary in the main scanning direction.

  Next, in step S3, the control unit 4 performs a discharge amount correction process on the correction target pixel detected in step S2.

  Specifically, first, the control unit 4 selects a reference color in the correction target pixel. Here, the control unit 4 selects a color having the lowest brightness among the ink colors used for the correction target pixel as a reference color for the pixel. For example, when four colors of cyan, black, magenta, and yellow are used for a pixel to be corrected, the control unit 4 uses black, which is the color with the lowest brightness among them, as a reference color for the pixel. select.

  Then, when the number of drops of the reference color is less than a threshold value (for example, 5 drops), the number of ink drops of colors other than the reference color for the correction target pixel is corrected. When the number of drops of the reference color is equal to or greater than the threshold, the control unit 4 omits correction of the number of ink drops for the pixel.

  When the number of drops of the reference color is less than the threshold, the control unit 4 reduces the number of drops of the ink of the color to be reduced in the correction target pixel from the number of drops before correction in the drop data. The color to be reduced corresponds to the nozzle 34 on the outer side of the image with respect to the nozzle 34 corresponding to the reference color in the main scanning direction among the nozzles 34 corresponding to the ink colors used for the pixel to be corrected. Color.

  In addition, the control unit 4 increases the number of drops of the color ink to be increased in the correction target pixel from the number of drops before correction in the drop data. The increase target color corresponds to the nozzle 34 located on the inner side of the image with respect to the nozzle 34 corresponding to the reference color in the main scanning direction among the nozzles 34 corresponding to the ink colors used for the correction target pixel. Color.

  Here, a specific example of a method for determining the above-described reduction target color and increase target color will be described. As will be described later, the mounting positions of the head units 31A and 31B may be misaligned. Here, there is no misalignment, and the nozzles 34C, 34K, 34M, and 34Y of the head units 31A and 31B are shown in FIG. It is assumed that the positional relationship is as follows.

  For example, assume that four colors of cyan, black, magenta, and yellow are used for pixels to be corrected at the front end of the image in the front-rear direction (main scanning direction). In this case, the reference color is black. Further, at the front end of the image, the front side is the outer side of the image, and the rear side is the inner side of the image.

  From the arrangement of the nozzles 34 as shown in FIG. 4, among the nozzles 34 corresponding to the respective colors used for the correction target pixel, the nozzle 34K corresponding to the reference color black is located on the outer side (front side) of the image. There are nozzles 34C and 34M corresponding to cyan, magenta, respectively. On the other hand, there is no nozzle on the inner side (rear side) of the image than the nozzle 34K. Therefore, in the pixels to be corrected at the front end of the image as in this example, the colors to be reduced are cyan and magenta, and there are no colors to be increased.

  Further, for example, it is assumed that four colors of cyan, black, magenta, and yellow are used for pixels to be corrected at the rear end of the image in the front-rear direction. At the rear end of the image, the rear side is the outer side of the image, and the front side is the inner side of the image.

  In this case, among the nozzles 34 corresponding to the respective colors used for the correction target pixel, the nozzle 34C corresponding to cyan and magenta on the inner side (front side) of the image from the nozzle 34K corresponding to the reference color black. , 34M. On the other hand, there is no nozzle on the outside (rear side) of the image from the nozzle 34K. Therefore, in the pixel to be corrected at the rear end of the image as in this example, there is no color to be reduced, and the colors to be increased are cyan and magenta.

  Further, for example, it is assumed that four colors of cyan, black, magenta, and yellow are used for pixels of a thin line with a width of one pixel printed in the sub-scanning direction (left-right direction). Here, as described above, a pixel with a thin line with a width of one pixel printed along the sub-scanning direction is also included in the boundary pixel in the main scanning direction and becomes a pixel to be corrected.

  In a thin line having a width of one pixel along the sub-scanning direction, the thin line as an image has a width of only one pixel in the main scanning direction, so that both the front side and the rear side of the thin line can be regarded as the outside of the image. Therefore, in this case, among the nozzles 34 corresponding to the respective colors used for the pixel to be corrected, the nozzles 34C and 34M respectively corresponding to cyan and magenta are located outside the image from the nozzle 34K corresponding to black. On the other hand, there is no nozzle inside the image from the nozzle 34K. Therefore, in the pixels to be corrected which are thin line pixels as in this example, the colors to be reduced are cyan and magenta, and there are no colors to be increased.

  As described above, the color to be reduced and the color to be increased in the ejection amount correction process are determined.

  When reducing or increasing the number of drops in the reduction target color or the increase target color, the control unit 4 refers to the ejection amount correspondence correction coefficient table 41 in FIG. 5 and the deviation amount correspondence correction coefficient table 42 in FIG. Then, for the ink of the color to be reduced in the pixel to be corrected, a value obtained by rounding down the decimal point of the Dcc value calculated by Expression (1) is determined as the number of drops after reduction (after correction). Here, Dc in equation (1) is the number of drops of ink to be reduced in the correction target pixel before correction in the drop data.

Dcc = Kdc × Kgc × Dc (1)
In addition, for the ink of the color to be increased in the pixel to be corrected, a value obtained by rounding up the decimal point of the value of Dac calculated by Expression (2) is determined as the number of drops after the increase (after correction). Here, Da in Expression (2) is the number of drops before correction in the drop data of the ink of the increase target color in the correction target pixel.

Dac = Kdi × Kgi × Da (2)
As shown in FIG. 5, the discharge amount correspondence reduction coefficient Kdc is a coefficient that increases the drop number reduction rate as the number of drops before correction increases. Further, the ejection amount corresponding increase coefficient Kdi is a coefficient that increases the increase rate of the drop number as the drop number before correction is small. This suppresses an excessive change in the print image quality. Also, as shown in FIG. 6, the shift amount reduction coefficient Kgc increases the drop number reduction rate as the shift amount increases. The coefficient. Further, the shift amount corresponding increase coefficient Kgi is a coefficient that increases the drop rate increase rate as the shift amount increases. Thus, the correction amount is appropriately adjusted according to the positional relationship between the nozzles 34 corresponding to the same pixel.

  Here, in the inkjet printing apparatus 1, as shown in FIG. 4, the head unit 31A and the head unit 31B are arranged so that the positions of the nozzles 34 in the main scanning direction coincide with each other. Therefore, if the mounting positions of the head units 31A and 31B are accurate, the deviation amount in the main scanning direction of the nozzle 34 corresponding to the reference color of the nozzle 34 corresponding to the color whose number of drops is corrected is 0 or P / 2

  However, as described above, there is a possibility that a displacement occurs in the mounting positions of the head units 31A and 31B. That is, the positions of the nozzle 34C and the nozzle 34M in the main scanning direction may be shifted, and similarly, the positions of the nozzle 34K and the nozzle 34Y in the main scanning direction may be shifted.

  When there is such a positional deviation, the correspondence relationship between the nozzles 34C, 34K, 34M, and 34Y is determined so that the positional deviation in the main scanning direction at the nozzles 34C, 34K, 34M, and 34Y corresponding to the same pixel is minimized. The Here, due to the positional relationship between the head units 31A and 31B, a positional shift of 3P / 4 at the maximum occurs in the main scanning direction among the nozzles 34C, 34K, 34M, and 34Y corresponding to the same pixel. Therefore, in consideration of the displacement of the mounting positions of the head units 31A and 31B, the displacement amount in the main scanning direction of the nozzle 34 corresponding to the reference color of the nozzle 34 corresponding to the color whose number of drops is corrected is 3P / 4 at the maximum. It becomes. For this reason, the value of the shift amount in FIG. 6 is not limited to 0 and P / 2, and the maximum value is 3P / 4.

  Here, the positional deviation of the head units 31A and 31B occurs for each set of the head units 31A and 31B arranged in parallel along the sub-scanning direction. Whether the head units 31A and 31B are misaligned is detected in advance by printing a test pattern or the like. Further, for each set of head units 31A and 31B, the front-rear positional relationship and the distance between them in the main scanning direction of the nozzles 34C, 34K, 34M, and 34Y corresponding to the same pixel are also detected in advance, and nozzle position information including them is obtained. It is stored in the control unit 4.

  In the discharge amount correction processing, the control unit 4 determines the front-rear positional relationship between the nozzle 34 corresponding to the reference color and the nozzle 34 corresponding to another color in the correction target pixel based on the nozzle position information described above, and the reduction is performed. Determine the target color and the color to be increased.

  Further, when reducing or increasing the number of drops, the control unit 4 calculates a deviation amount in the main scanning direction of the nozzle 34 corresponding to another color with respect to the nozzle 34 corresponding to the reference color based on the nozzle position information. To do. Then, the control unit 4 selects values of the shift amount corresponding reduction coefficient Kgc and the shift amount corresponding increase coefficient Kgi according to the calculated shift amount.

  As described above, when the number of drops after correction of the ink of the correction target color in the correction target pixel is determined using the equations (1) and (2), in step S4 in FIG. Execute printing.

  Specifically, the control unit 4 rotationally drives the drive roller 12 of the transport unit 2. Thereby, the conveyance belt 11 rotates. When paper PA is fed from a paper feed unit (not shown), the paper PA is transported by the transport unit 2. The controller 4 drives the ink jet heads 21 </ b> A and 21 </ b> B to eject ink droplets on the paper PA transported by the transport unit 2 based on the drop data after the ejection amount correction processing. Thereby, an image is printed on the paper PA.

  Here, FIG. 8 shows an example of a dot image of an image printed without performing the ejection amount correction processing of the present embodiment. FIG. 8 is printed using four colors of cyan, black, magenta, and yellow by the head units 31A and 31B having no positional deviation as shown in FIG. In FIG. 8, the dots 51C, 51K, 51M, and 51Y of the respective colors are drawn while being shifted up and down on the paper surface for the sake of easy viewing, but they are actually hit on the same line along the main scanning direction. is there.

  With the arrangement of the nozzles 34 as shown in FIG. 4, cyan dots 51C and magenta dots 51M are formed so as to protrude to the front, which is the outside of the image, at the front end portion of the image surrounded by broken lines in FIG. ing. Further, at the rear end portion of the image surrounded by the alternate long and short dash line, the black dot 51K and the yellow dot 51Y are formed so as to protrude to the rear side which is the outer side of the image.

  For this reason, in the image of FIG. 8, the hue by cyan and magenta is emphasized at the front end. On the other hand, at the rear end, the hues of black and yellow are emphasized.

  In contrast, FIG. 9 shows a dot image of an image obtained by printing the same image as that shown in FIG. 8 by performing the ejection amount correction processing according to the present embodiment. In the image of FIG. 9, black having the lowest brightness among cyan, black, magenta, and yellow is the reference color.

  From the arrangement of the nozzles 34 as shown in FIG. 4, at the front end of the image in FIG. 9, nozzles corresponding to cyan and magenta on the outer side (front side) of the image from the nozzle 34K corresponding to the reference color black. There are 34C and 34M. On the other hand, there is no nozzle on the inner side (rear side) of the image than the nozzle 34K. Accordingly, in the pixels at the front end, cyan and magenta are the colors to be reduced, and there are no colors to be increased.

  For this reason, in FIG. 9, cyan dots 61 </ b> C and magenta dots 61 </ b> M are formed of ink with the number of drops reduced from the number of drops in the original drop data in the pixels at the front end. Accordingly, the dots 61C and 61M in FIG. 9 are smaller than the dots 51C and 51M in FIG. 8, respectively. As a result, in the image of FIG. 9, the amount of projection of cyan dots and magenta dots at the front end to the outside (front side) is reduced compared to the image of FIG.

  On the other hand, at the rear end of the image in FIG. 9, there are nozzles 34C and 34M respectively corresponding to cyan and magenta on the inner side (front side) of the image from the nozzle 34K corresponding to the reference color black. On the other hand, there is no nozzle on the outside (rear side) of the image from the nozzle 34K. Therefore, in the pixels at the rear end, there is no reduction target color, and cyan and magenta are the increase target colors.

  For this reason, in FIG. 9, cyan dots 62C and magenta dots 62M are formed of ink having the number of drops increased from the number of drops in the original drop data in the pixels at the rear end. Accordingly, the dots 62C and 62M in FIG. 9 are larger than the dots 51C and 51M in FIG. 8, respectively. Thereby, in the image of FIG. 9, the protrusion amount of the black dots and the yellow dots at the rear end to the outside (rear side) is reduced as compared with the image of FIG.

  As described above, in the image of FIG. 9, the protrusion amount of cyan dots and magenta dots at the front end is reduced compared to the image of FIG. 8, and black dots and yellow dots at the rear end are reduced. The amount of protrusion has decreased. As a result, in the image of FIG. 9, color misregistration at the front end and the rear end is reduced compared to the image of FIG.

  Next, FIG. 10 shows an example of a dot image of a pixel of a thin line having a width of one pixel along the sub-scanning direction printed without performing the ejection amount correction process of the present embodiment. FIG. 10 is printed using four colors of cyan, black, magenta, and yellow by the head units 31A and 31B having no positional deviation as shown in FIG.

  With the arrangement of the nozzles 34 as shown in FIG. 4, the cyan and magenta dots 51 </ b> C and 51 </ b> M and the black and yellow dots 51 </ b> K and 51 </ b> Y are formed so as to be shifted in the front-rear direction. For this reason, the color of cyan and magenta is emphasized on the front side of the thin line. On the other hand, on the back side of the thin line, the color tone of black and yellow is emphasized.

  On the other hand, FIG. 11 shows a dot image of fine line pixels printed by performing the discharge amount correction processing of the present embodiment on the fine line pixels similar to FIG.

  As described above, in a thin line image having a width of one pixel along the sub-scanning direction, both the front side and the rear side of the thin line can be regarded as the external side of the image. Therefore, from the arrangement of the nozzles 34 as shown in FIG. 4, in the thin line image of FIG. 10, the nozzles 34C and 34M respectively corresponding to cyan and magenta are located on the outer side of the image from the nozzle 34K corresponding to the reference color black. is there. On the other hand, there is no nozzle inside the image from the nozzle 34K. Therefore, the colors to be reduced are cyan and magenta, and there are no colors to be increased.

  For this reason, in FIG. 11, cyan dots 71 </ b> C and magenta dots 71 </ b> M are formed of ink with the number of drops reduced from the number of drops in the original drop data. Accordingly, the dots 71C and 71M in FIG. 11 are smaller than the dots 51C and 51M in FIG. 10, respectively. Accordingly, in the thin line by the pixel of FIG. 11, the forward protrusion amount of the cyan dot and the magenta dot with respect to the black dot 51K and the yellow dot 51Y is reduced as compared with the thin line by the pixel of FIG. . As a result, the color shift between the front side and the rear side of the thin line is reduced.

  Next, a case where the head units 31A and 31B are attached to the mounting positions will be described.

  Here, as shown in FIG. 12, it is assumed that the positions of the nozzles 34C and 34M in the main scanning direction are shifted from each other by P / 4 due to the positional shift between the head units 31A and 31B. The positions of the nozzle 34K and the nozzle 34Y in the main scanning direction are also shifted from each other by P / 4. One of the combinations of nozzles 34 corresponding to the same pixel in the head units 31A and 31B in FIG. 12 is surrounded by a one-dot chain line.

  FIG. 13 shows an example of a dot image of an image printed by the head units 31A and 31B arranged as shown in FIG. 12 without performing the ejection amount correction processing of the present embodiment. FIG. 13 is printed using four colors of cyan, black, magenta, and yellow.

  With the arrangement of the nozzles 34 as shown in FIG. 12, the cyan dot 51C protrudes the most on the front side, which is the outer side of the image, and the magenta dot 51M is the next at the front end portion of the image surrounded by the broken line in FIG. Is formed to protrude. Further, at the rear end portion of the image surrounded by the alternate long and short dash line, the yellow dot 51Y protrudes most to the rear side, which is the outer side of the image, and the black dot 51K protrudes next.

  For this reason, in the image of FIG. 13, the color tone due to cyan and magenta, particularly cyan, is emphasized at the front end. On the other hand, at the rear end, yellow and black, particularly yellow, are emphasized.

  On the other hand, FIG. 14 shows a dot image of an image printed by performing the ejection amount correction processing of the present embodiment on the same image as in FIG. 13 by the head units 31A and 31B arranged as shown in FIG.

  From the arrangement of the nozzles 34 as shown in FIG. 12, at the front end portion of the image in FIG. 14, nozzles corresponding to cyan and magenta on the outer side (front side) of the image from the nozzle 34K corresponding to the reference color black. There are 34C and 34M. Further, there is a nozzle 34Y corresponding to yellow on the inner side (rear side) of the image than the nozzle 34K. Accordingly, in the pixels at the front end, cyan and magenta are the colors to be reduced, and yellow is the color to be increased.

  For this reason, in FIG. 14, cyan dots 81 </ b> C and magenta dots 81 </ b> M are formed of ink with the number of drops reduced from the number of drops in the original drop data in the pixels at the front end. Accordingly, the dots 81C and 81M in FIG. 14 are smaller than the dots 51C and 51M in FIG. In FIG. 14, in the pixels at the front end, yellow dots 81Y are formed of ink with the number of drops increased from the number of drops in the original drop data. Accordingly, the dot 81Y in FIG. 14 is larger than the dot 51Y in FIG. Accordingly, in the image of FIG. 14, the positional deviation between the front ends of the dots of the respective colors in the pixels at the front end is smaller than in the image of FIG. 13.

  On the other hand, at the rear end of the image in FIG. 14, there are nozzles 34C and 34M corresponding to cyan and magenta on the inner side (front side) of the image from the nozzle 34K corresponding to the reference color black. On the other hand, there is a nozzle 34Y corresponding to yellow on the outside (rear side) of the image from the nozzle 34K. Therefore, in the pixels at the rear end, cyan and magenta are the colors to be increased, and yellow is the color to be reduced.

  For this reason, in FIG. 14, cyan dots 82 </ b> C and magenta dots 82 </ b> M are formed of ink with the number of drops increased from the number of drops in the original drop data in the pixels at the rear end. Accordingly, the dots 82C and 82M in FIG. 14 are larger than the dots 51C and 51M in FIG. 13, respectively. In FIG. 14, in the pixels at the rear end, yellow dots 82Y are formed of ink with the number of drops reduced from the number of drops in the original drop data. Accordingly, the dots 82Y in FIG. 14 are smaller than the dots 51Y in FIG.

  Accordingly, in the image of FIG. 14, the mutual positional deviation of the position of the rear end of each color dot in the pixel at the rear end is smaller than that of the image of FIG. 13.

  As described above, in the image of FIG. 14, the positional deviation between the front end of each color dot in the pixels at the front end is smaller than in the image of FIG. 13. Further, in the image of FIG. 14, the positional deviation between the positions of the rear end of each color dot in the pixels at the rear end is smaller than that of the image of FIG. 13. As a result, in the image of FIG. 14, color misregistration at the front end and the rear end is reduced compared to the image of FIG. 13.

  Next, an example of a dot image of a thin line pixel having a width of 1 pixel along the sub-scanning direction printed without performing the discharge amount correction processing of the present embodiment by the head units 31A and 31B arranged as shown in FIG. As shown in FIG. FIG. 15 is printed using four colors of cyan, black, magenta, and yellow.

  12, the cyan dots 51C, magenta dots 51M, black dots 51K, and yellow dots 51Y are shifted from each other in this order from the front side in the thin line pixels shown in FIG. Has been. For this reason, the color of cyan and magenta is emphasized on the front side of the thin line. On the other hand, on the back side of the thin line, the color tone of black and yellow is emphasized.

  On the other hand, the dot units of the fine line pixels printed by performing the ejection amount correction processing of the present embodiment on the fine line pixels similar to those in FIG. 15 by the head units 31A and 31B arranged as shown in FIG. Shown in

  As described above, in a thin line image having a width of one pixel along the sub-scanning direction, both the front side and the rear side of the thin line can be regarded as the external side of the image. Accordingly, from the arrangement of the nozzles 34 as shown in FIG. 12, in the thin line image of FIG. 15, the nozzles 34C, C, C, C, C, C, C, There are 34M and 34Y. On the other hand, there is no nozzle inside the image from the nozzle 34K. Therefore, the reduction target colors are cyan, magenta, and yellow, and there is no increase target color.

  For this reason, in FIG. 16, cyan dots 91C, magenta dots 91M, and yellow and dots 91Y are formed of ink with the number of drops reduced from the number of drops in the original drop data. Accordingly, the dots 91C, 91M, and 91M in FIG. 16 are smaller than the dots 51C, 51M, and 51Y in FIG. Thereby, in the fine line by the pixel of FIG. 16, compared with the fine line by the pixel of FIG. 15, the cyan dot, the magenta dot, and the yellow dot to the external side (front side and rear side) with respect to the black dot 51K. The amount of protrusion has decreased. As a result, the color shift between the front side and the rear side of the thin line is reduced.

  As described above, in the inkjet printing apparatus 1, the control unit 4 corrects the ink ejection amount (drop number) for the pixels at the boundary in the main scanning direction. Specifically, the control unit 4 is a nozzle located on the outer side of the image from the nozzles 34 corresponding to the reference color in the main scanning direction among the nozzles 34 corresponding to the ink colors used for the pixels at the boundary portion. 34, the ejection amount for the pixels at the boundary portion of the color ink corresponding to 34 is reduced. Further, the control unit 4 increases the ejection amount for the pixels at the boundary portion of the color ink corresponding to the nozzle 34 on the inner side of the image from the nozzle 34 corresponding to the reference color. Thereby, it is possible to reduce the color shift at the boundary portion (outline) of the image due to the position shift of the nozzles 34 of the respective colors in the main scanning direction. As a result, it is possible to reduce a decrease in print image quality.

  Further, the control unit 4 corrects the ink discharge amount of each color for correcting the ink discharge amount according to the ink discharge amount before correction of each color. Specifically, the control unit 4 uses a discharge amount correspondence reduction coefficient Kdc and a discharge amount correspondence increase coefficient Kdi corresponding to the number of drops (discharge amount) before correction in order to determine the discharge amount after correction. Thereby, it can suppress that an excessive change arises in printing image quality by setting it as the correction amount according to discharge amount.

  Further, the control unit 4 corrects the ink discharge amount of each color according to the shift amount in the main scanning direction of the nozzle 34 corresponding to each color for correcting the ink discharge amount with respect to the nozzle 34 corresponding to the reference color. To do. Specifically, in order to determine the corrected ejection amount, the control unit 4 responds to a deviation amount corresponding to the deviation amount in the main scanning direction with respect to the nozzle 34 corresponding to the reference color of the nozzle 34 corresponding to the color to be corrected. The reduction coefficient Kgc and the shift amount corresponding increase coefficient Kgi are used. Thus, the correction amount can be appropriately adjusted according to the positional relationship of the nozzles 34 corresponding to the colors for correcting the ink discharge amount.

  Further, when the discharge amount (drop number) of the reference color for the pixel at the boundary portion in the main scanning direction is equal to or greater than the threshold, the control unit 4 omits correction of the ink discharge amount for the pixel. If the discharge amount of the reference color is large and the dot is large, the reference color dot overlaps with the other color dot in a wide range, and the protrusion amount of the other color dot from the reference color dot to the outside is small. Become. For this reason, the color shift at the boundary is not noticeable. Therefore, when the discharge amount of the reference color is equal to or greater than the threshold value, the correction of the ink discharge amount for the pixel is omitted, thereby reducing the processing load on the control unit 4 and suppressing an unnecessary change in print image quality.

  Further, the control unit 4 selects, as a reference color, a color having the lowest brightness among the ink colors used for the pixels at the boundary in the main scanning direction. Thereby, the color shift of a boundary part can be made inconspicuous by making a color with high visibility into a reference color.

  In the above embodiment, two nozzle rows 33 are arranged in each of the two inkjet heads 21A and 21B. However, the configuration of the nozzle rows is not limited to this. At least one nozzle row among a plurality of nozzle rows corresponding to different color inks is arranged so that the position of the nozzle is shifted in the main scanning direction with respect to at least one other nozzle row. If so, the present invention is applicable.

  In the above-described embodiment, the line-type inkjet printing apparatus that performs printing with the fixed inkjet head while moving the paper has been described. However, the present invention also applies to a serial-type inkjet printing apparatus that performs printing while moving the inkjet head. Applicable.

  The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment.

DESCRIPTION OF SYMBOLS 1 Inkjet printing apparatus 2 Conveyance part 3 Printing part 4 Control part 21A, 21B Inkjet head 31A, 31B Head unit 32C, 32K, 32M, 32Y Head module 33C, 33K, 33M, 33Y Nozzle row 34C, 34K, 34M, 34Y Nozzle 41 Discharge amount corresponding correction coefficient table 42 Deviation amount corresponding correction coefficient table

Claims (5)

A printing unit comprising a plurality of nozzles each of which is composed of a plurality of nozzles arranged along the nozzle arrangement direction at predetermined intervals and ejects different color inks from the nozzles;
A control unit for controlling the printing unit to print an image by discharging ink from the nozzle,
At least one nozzle row of the plurality of nozzle rows is arranged so that the position of the nozzle is shifted in the nozzle arrangement direction with respect to at least one other nozzle row,
The control unit selects a reference color from among the ink colors used for pixels at the boundary between the image and the outside in the nozzle arrangement direction, and is used for the pixels at the boundary. Among the nozzles corresponding to each ink color, the ejection amount of the ink of the color corresponding to the nozzle on the outer side of the image with respect to the nozzle corresponding to the reference color in the nozzle arrangement direction is reduced with respect to the pixels at the boundary portion. The ink ejection amount is corrected so as to increase the ejection amount of the color ink corresponding to the nozzle located on the inner side of the image from the nozzle corresponding to the reference color to the pixel at the boundary portion. Inkjet printing device.   The ink jet printing apparatus according to claim 1, wherein the control unit corrects the ink discharge amount of each color for correcting the ink discharge amount according to the ink discharge amount before correction of each color.   The control unit corrects the ink discharge amount of each color according to the shift amount in the nozzle arrangement direction of each nozzle corresponding to each color for correcting the ink discharge amount with respect to the nozzle corresponding to the reference color. The ink jet printing apparatus according to claim 1 or 2, characterized in that   4. The control unit according to claim 1, wherein the control unit omits correction of the ink ejection amount for the pixel when the ejection amount of the reference color ink for the pixel at the boundary is equal to or greater than a threshold value. 5. 2. An ink jet printing apparatus according to item 1.   5. The control unit according to claim 1, wherein the control unit selects, as a reference color, a color having the lowest lightness among the ink colors used for the pixels in the boundary portion. 6. Inkjet printing device.