JP2019018582A - Inkjet printer - Google Patents

Abstract

To prevent printing time from being elongated uselessly by performing control so that occurrence of streaky density unevenness is suppressed as necessary.SOLUTION: A recording sheet is conveyed while an inkjet head is passed twice precedently and subsequently so that scanned regions of respective nozzle rows 21 partly overlap with each other while the inkjet head is passed twice. Boundary positions 30 in use between used nozzles and unused nozzles are set within ranges at which scanned regions of each of the plurality of nozzle rows 21 overlap with each other between different passings of the head, with respect to respective passings of the inkjet head. Further, a control device sets a duty at the time of performing printing on the recording sheet, and the boundary positions 30 of the plurality of nozzle rows 21, of types of nozzle rows 21 to be used in performing printing on the recording sheet, according to at least one condition.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an ink jet printer that prints an image by ejecting ink onto a recording medium.

  As an ink jet printer, there is a type of printing an image by ejecting ink from a plurality of nozzles while moving an ink jet head having a plurality of nozzles in a predetermined scanning direction with respect to a recording medium. The printer alternately performs one movement (hereinafter also referred to as a pass) of the inkjet head in the scanning direction and a predetermined amount of conveyance of the recording medium in the conveyance direction, thereby performing an image on the recording medium. To print.

  By the way, the above-described inkjet printer has an image portion printed in the previous pass and an image portion printed in the subsequent pass shifted in the transport direction due to factors such as a shift in the transport amount. In some cases, shading unevenness (white stripes, black stripes) extending in the scanning direction in the form of stripes may occur. The occurrence of such shading unevenness greatly reduces the image quality of an image printed on a recording medium.

  In this regard, Patent Document 1 discloses a printer that can suppress the occurrence of the above-described stripe-like shading unevenness. In this printer, the scanning area of the previous pass and the scanning area of the subsequent pass are partially overlapped in the conveyance direction of the recording medium. Then, the boundary between the image portion printed in the previous pass and the image portion printed in the subsequent pass is changed in a zigzag manner. In addition, when printing in multiple colors, there is a description that the above-described boundary is not matched between nozzle rows of different colors. By adopting the printing method as described above, streaks between the image portion of the previous pass and the image portion of the subsequent pass are less noticeable. However, this Patent Document 1 does not describe under what conditions the above printing method is adopted.

JP-A-7-117241 (in particular, paragraphs 0019 and 0024)

  As described in Patent Document 1 above, the boundary between the image portion printed in the first pass and the image portion printed in the subsequent pass is made different between the nozzle rows of a plurality of colors. In addition, the generation of streaks between two image portions is suppressed. For example, when two image portions deviate in a direction away from each other, even when an ink of a certain color is not landed, the ink of another color is landed, thereby preventing the occurrence of white stripes.

  However, if the boundaries in the nozzle rows of multiple colors are made different for each ink color, it is necessary to generate as many boundaries as the number of colors in the overlapping range of the previous pass and the subsequent pass. It gets bigger. The larger the overlapping range, the smaller the number of nozzles used in each pass, and the smaller the width in the transport direction of the image portion that can be printed in one pass. In other words, by adopting the above printing method, the image quality may be improved, but the number of passes required to print one recording medium increases, and the printing time becomes longer. Therefore, there is a problem that the printing time is unnecessarily long even when the above-described printing method is not originally required, such as when the unevenness of density is hardly a problem such as when the duty is low.

  An object of the present invention is to waste printing time by performing control to suppress the occurrence of stripe-like shading unevenness only when necessary, such as when streaks are conspicuous between the image portions of the previous and subsequent passes. It is to prevent it from becoming long.

Means for Solving the Problems and Effects of the Invention

An ink jet printer according to a first aspect of the invention includes an ink jet head that ejects ink onto a recording medium while moving in a first direction, and the ink jet head in a second direction that intersects the first direction. A transport unit that transports the recording medium in a transport direction; a control unit that controls the inkjet head and the transport unit;
The inkjet head includes a plurality of nozzle groups each including a plurality of nozzles arranged along the second direction, and the first of the nozzles constituting the nozzle group among the plurality of nozzle groups. The positions in the two directions coincide with each other, and the controller scans each nozzle group on the recording medium between one pass and the next pass in the first direction of the inkjet head. In the overlapping range in which the recording medium is transported by the transport unit between the first and second passes so that the regions partially overlap, and the scanning regions of the two passes overlap, In the two directions, the inkjet head is printed separately in the first pass and the subsequent pass, and for each pass, the control unit is configured to use the nozzles within the overlapping range for each of the plurality of nozzle groups. A use boundary position of a use nozzle is set, and the control unit is a condition for at least one of a duty when printing on the recording medium and a kind of nozzle group used for printing on the recording medium. The use boundary positions of the plurality of nozzle groups are respectively set according to the above.

  In the present invention, the ink jet head includes a plurality of nozzle groups in which the positions of the nozzles in the second direction coincide. Further, when printing an image on a recording medium by repeating a plurality of passes of the ink jet head, a part of the scanning region of each nozzle group is overlapped between the first and second passes, and this overlapping region In, the image is divided into two passes before printing. In addition, the use boundary positions of the used nozzles and the unused nozzles of the plurality of nozzle groups in each pass are individually set. Thereby, the use boundary position of the said nozzle can be varied between several nozzle groups about each pass. That is, in each pass, the positions of the end dots respectively formed by the plurality of nozzle groups can be intentionally dispersed in the second direction so that they are not aligned with each other. Accordingly, even when the image part formed in the previous pass and the image part formed in the subsequent pass are relatively shifted in the second direction, the shading is dispersed in the joint part of the two image parts. The shading unevenness is less likely to be a streak and less noticeable.

  However, by shifting the use boundary position among the plurality of nozzle groups, the overlapping range between the previous and subsequent two passes becomes larger. As a result, the width of the image portion that can be printed in each pass is reduced in the second direction, and as a result, the number of passes required to print an image on one recording medium increases. Therefore, in the present invention, the use boundary positions of a plurality of nozzle groups are respectively set according to the duty when printing an image on a recording medium or the type of nozzle group used for printing. When the duty is small, the shading is not noticeable even if the image portion of the two passes is shifted. Also, depending on the type of nozzle group (type of ink, etc.), there are some that do not easily affect density unevenness. According to the present invention, when it is not necessary to positively suppress uneven density, the use boundary position is not shifted between different nozzle groups, so that the number of passes is increased and the printing time is increased. It can prevent becoming long.

  The ink jet printer according to a second aspect is the ink jet printer according to the first aspect, wherein the control unit performs the plurality of nozzle groups according to the overall duty of the plurality of nozzle groups when printing on the recording medium. The use boundary positions are set respectively.

  The overall duty of the present invention is the maximum ink ejection amount when ink is ejected from all nozzles capable of ejecting ink to a predetermined area in all of a plurality of nozzle groups. The ratio of the amount of ink actually ejected. The higher the overall duty is, the more conspicuous the density unevenness occurs between the two image portions respectively formed in two passes. In other words, the lower the overall duty is, the less conspicuous even if shading unevenness occurs. Therefore, in the present invention, the use boundary positions of a plurality of nozzle groups are set in accordance with the overall duty, so that the use boundary positions are different between different nozzle groups only when it is necessary to suppress density unevenness. be able to.

  In the ink jet printer according to a third aspect of the present invention, in the second aspect of the invention, when the overall duty is greater than or equal to a predetermined first threshold value, the control unit includes the use boundary between all of the plurality of nozzle groups. When the positions are different from each other and the overall duty is less than the first threshold, the use boundary positions are made to coincide for at least two nozzle groups of the plurality of nozzle groups. is there.

  In the present invention, when the overall duty is higher than the first threshold value, the use boundary position is made different for all of the plurality of nozzle groups, thereby suppressing streak-like shading unevenness between the two previous passes. . On the contrary, when the overall duty is lower than the first threshold and is low, it is not necessary to positively suppress density unevenness, and the use boundary positions are made to coincide for at least two nozzle groups.

  An ink jet printer according to a fourth aspect of the present invention is the ink jet printer according to any one of the first to third aspects, wherein the control unit sets an individual duty for each of the plurality of nozzle groups when printing on the recording medium. Accordingly, the use boundary positions of the plurality of nozzle groups are respectively set.

  The individual duty of the present invention is the actual ink discharge amount when the ink is discharged from all the nozzles that can discharge ink to a predetermined area in one nozzle group. This is the ratio of the amount of ink ejected to the ink. When the individual duty for a certain nozzle group is high, shading unevenness between two image portions respectively formed in two passes by the nozzle group tends to be noticeable. Therefore, in the present invention, the use boundary position of each of the plurality of nozzle groups is set according to the individual duty for each of the plurality of nozzle groups. Make them different.

  An ink jet printer according to a fifth aspect of the present invention is the ink jet printer according to the fourth aspect, wherein when the individual duty of a certain nozzle group is equal to or greater than a predetermined second threshold value, the control unit determines the use boundary position of the nozzle group. , And different from the use boundary position of the other nozzle groups.

  In the present invention, when the individual duty of a certain nozzle group is higher than the second threshold value, the use boundary position of the nozzle group is made different from that of the other nozzle groups to suppress streaky density unevenness.

  An ink jet printer according to a sixth aspect of the present invention includes the image data acquisition unit for acquiring image data to be printed in any one of the first to fifth aspects of the invention, and the control unit is acquired from the image data acquisition unit. The duty condition is determined from the image data thus obtained.

  In the present invention, the duty condition is determined from the image data acquired from the image data acquisition unit, and the use boundary position of each nozzle group is set based on the condition.

  An ink jet printer according to a seventh aspect is the ink jet printer according to any one of the first to sixth aspects, wherein the control unit changes the use boundary position of each nozzle group between different passes. is there.

  When the use boundary position of each nozzle group is the same in every pass, there is a nozzle that is not used in any pass in each nozzle group. In such a nozzle, ink is not ejected at all during printing on the recording medium, so that the ink in the nozzle is easily dried and thickened. Therefore, the control unit varies the use boundary position of each nozzle group between different passes.

  The ink jet printer according to an eighth aspect of the present invention is the ink jet printer according to any one of the first to seventh aspects, wherein the control unit changes the use boundary position of each nozzle group during one pass. The use boundary position is set.

  In this way, by changing the use boundary position of each nozzle group during one pass, the light and shade produced between the two image portions respectively formed in the two passes is further dispersed and conspicuous. It becomes difficult.

An ink jet printer according to a ninth aspect of the invention includes an ink jet head that ejects ink to a recording medium while moving in a first direction, and the ink jet head in a second direction that intersects the first direction. When printing on the recording medium using the transport unit that transports the recording medium in the transport direction, the control unit that controls the inkjet head and the transport unit, and the inkjet head and the transport unit, A print setting acquisition unit that acquires print setting information including a condition related to at least one of a print speed and a print resolution;
The inkjet head includes a plurality of nozzle groups each including a plurality of nozzles arranged along the second direction, and the first of the nozzles constituting the nozzle group among the plurality of nozzle groups. The positions in the two directions coincide with each other, and the controller scans each nozzle group on the recording medium between one pass and the next pass in the first direction of the inkjet head. In the overlapping range in which the recording medium is transported by the transport unit between the first and second passes so that the regions partially overlap, and the scanning regions of the two passes overlap, In the two directions, the inkjet head is printed separately in the first pass and the subsequent pass, and for each pass, the control unit is configured to use the nozzles within the overlapping range for each of the plurality of nozzle groups. The use boundary positions of the use nozzles are set, and the control unit sets the use boundary positions of the plurality of nozzle groups according to the print setting information acquired by the print setting acquisition unit. Is.

  In the present invention, the use boundary positions of the plurality of nozzle groups are respectively set according to the print setting information acquired by the print setting acquisition unit and including conditions relating to at least one of the print speed and the print resolution. Thereby, for example, in the case of a print setting that places importance on the printing speed, printing is performed with few passes without changing the use boundary position among the plurality of nozzle groups. On the other hand, in the case of a print setting that places importance on the print resolution, the use boundary position is made different among a plurality of nozzle groups so that the shading unevenness between the two passes is not noticeable.

1 is a schematic plan view of a printer according to an embodiment. FIG. 2 is a block diagram illustrating an electrical configuration of a printer. It is a figure which shows the nozzle arrangement | sequence of an inkjet head. It is a figure which shows the image printing which does not overlap the scanning area | region of a nozzle row between passes. It is a figure which shows the image printing which overlaps the scanning area | region of a nozzle row between passes. It is a figure which shows the use boundary position of each nozzle row in the overlapping range of the scanning area | region between two passes, and the arrangement | positioning map of the dot each formed by two passes. It is a figure which shows the example in case the image part formed in two passes | deviates, (a) is a direction where two image parts leave | separate, (b) is a direction in which two image parts approach Each case is shown. It is a flowchart of a shading unevenness suppression process. It is a figure which shows the setting of the use boundary position in Example 1. FIG. It is a figure which shows the setting of the use boundary position in Example 2. FIG. It is a figure which shows the nozzle arrangement | sequence of the inkjet head of a change form.

  Next, an embodiment of the present invention will be described. FIG. 1 is a schematic plan view of a printer according to the present embodiment. FIG. 2 is a block diagram showing the electrical configuration of the printer. 1 are defined as “front”, “rear”, “left”, and “right” of the printer. Also, the front side of the page is defined as “up”, and the other side of the page is defined as “down”. Below, it demonstrates using each direction word of front, back, left, right, up and down suitably.

(Printer configuration)
As shown in FIG. 1, the inkjet printer 1 includes a platen 2, a carriage 3, an inkjet head 4, a transport mechanism 5, a control device 6, and the like.

  On the upper surface of the platen 2, a recording sheet 100 as a recording medium is placed. The carriage 3 is configured to be capable of reciprocating in the left-right direction (hereinafter also referred to as the scanning direction) along the two guide rails 10 and 11 in a region facing the platen 2. An endless belt 14 is connected to the carriage 3, and the endless belt 14 is driven by a carriage drive motor 15, whereby the carriage 3 moves in the scanning direction.

  The inkjet head 4 is attached to the carriage 3 and moves in the scanning direction together with the carriage 3. The inkjet head 4 is connected to a cartridge holder 7 to which ink cartridges 17 of four colors (black, yellow, cyan, and magenta) are mounted and tubes 16 respectively. The ink jet head 4 has a plurality of nozzles 20 formed on the lower surface (the surface on the other side of the paper in FIG. 1).

  FIG. 3 is a diagram showing the nozzle arrangement of the inkjet head 4. As shown in FIG. 3, the plurality of nozzles 20 are arranged along a transport direction (front-rear direction) that intersects the scanning direction, and constitutes four nozzle rows 21 arranged in the scanning direction. The four nozzle rows 21k, 21y, 21c, and 21m are nozzle rows 21 that eject ink of four colors (black, yellow, cyan, and magenta), respectively. In the following invention, “k”, “y”, “c”, and “m” added after the reference numerals of the constituent elements respectively correspond to black, yellow, cyan, and magenta inks. It shows that there is. For example, the nozzle row 21k is a nozzle row composed of nozzles 20k that discharge black ink. Between the four nozzle rows 21k, 21y, 21c, and 21m, the positions of the nozzles 20k, 20y, 20c, and 20m constituting each nozzle row 21 are the same in the transport direction.

  As shown in FIG. 1, the transport mechanism 5 includes two transport rollers 18 and 19 arranged so as to sandwich the platen 2 in the front-rear direction. The two transport rollers 18 and 19 are driven synchronously by a transport motor 22 (see FIG. 2). This transport mechanism 5 transports the recording paper 100 placed on the platen 2 in the transport direction by driving the two transport rollers 18 and 19 by the transport motor 22.

As shown in FIG. 2, the control device 6 includes a CPU (Central Processing Unit) 24, a ROM
(Read Only Memory) 25, RAM (Random Access Memory) 26, and ASIC (Application Specific Integrated Circuit) 27 including various control circuits. The control device 6 is connected to the inkjet head 4, various motors such as a carriage drive motor 15 and a conveyance motor 22, an operation panel 23, and the like. In addition, the control device 6 is connected to an external device 29 such as a PC via the communication unit 28, and image data to be printed is input from the external device 29. The external device 29 includes various devices that can output image data to the printer 1, such as a digital camera and a storage device, in addition to a PC. The control device 6 causes the ASIC 27 to execute various processes such as printing on the recording paper 100 by executing the program stored in the ROM 25 by the CPU 24.

  Hereinafter, in particular, the image printing process for the recording paper 100 will be described in detail. First, a print command is input from the external device 29 such as a PC or the operation panel 23 to the control device 6 of the printer 1. At this time, print setting information including conditions related to the print resolution or the print speed is also input from the external device 29 or the operation panel 23. At the same time, image data to be printed is input from the external device 29 via the communication unit 28. When the print command is input, the control device 6 controls the inkjet head 4, the carriage drive motor 15, and the like to print the image acquired from the external device 29 on the recording paper 100. Specifically, the ASIC 27 of the control device 6 causes the recording paper 100 to be ejected by the ink ejecting operation of ejecting ink from the plurality of nozzles 20 while moving the inkjet head 4 together with the carriage 3 in the scanning direction, and the transport rollers 18 and 19. The carrying operation of carrying a predetermined amount in the carrying direction is alternately performed.

  Furthermore, in this embodiment, when printing an image by a plurality of scans (hereinafter referred to as “pass”) of the inkjet head 4, the control device 6 prints the image portion printed in the previous pass and the subsequent pass. Control is performed to suppress streak-like shading unevenness between the image portions. This density unevenness suppression printing will be described in detail below.

(Details of density unevenness suppression printing)
First, FIG. 4 is a diagram illustrating image printing in which the scanning regions of the nozzle row 21 are not overlapped between passes. In FIG. 4, an image is printed on the recording paper 100 by three passes of the inkjet head 4. That is, an image is printed by an operation of ink ejection in the first pass → conveying the recording paper 100 by a predetermined amount → ink ejection in the second pass → conveying the recording paper 100 by a predetermined amount → ink ejection in the third pass. In FIG. 4, the scanning regions 41 a, 41 b, 41 c of the nozzle row 21 on the recording paper 100 do not overlap each other between three passes.

  Here, between the two passes, the recording mechanism 100 is formed in two passes due to factors such as a slight shift in the transport amount of the recording paper 100 by the transport mechanism 5 or expansion and contraction of the recording paper 100 due to ink landing. The two image portions may be displaced in the transport direction. When the two image portions are displaced in the direction away from each other, a gap is generated between the two image portions, and white stripes appear. Further, when the two image portions are shifted in the approaching direction, the dots of the two image portions partially overlap to darken the portion, and black stripes appear. The white stripes and black stripes are particularly noticeable when the printing duty, that is, the amount of ink ejected onto the recording paper 100 is large.

  FIG. 5 is a diagram illustrating image printing in which the scanning region of the nozzle array 21 is partially overlapped between passes. In order to make the white stripes and black stripes inconspicuous, in the shading unevenness suppression printing of the present embodiment, the scanning area 51 of the nozzle row 21 in the previous pass, and the scanning area 51 of the nozzle row 21 in the subsequent pass However, the conveyance amount of the recording paper 100 between the first and second passes is set so as to partially overlap. In addition, although the scanning area 51 (area in which the nozzle array 21 moves) of the nozzle array 21 is overlapped between the passes, the two image portions respectively formed in the two passes are partially overlapped. Do not mean. That is, in the overlapping range 50 where the scanning areas 51 of the two passes overlap, the image is printed in two passes with a certain boundary in the transport direction interposed therebetween. That is, in this overlapping range 50, there is a boundary between two image portions formed in two passes. This will be explained in more detail below.

  FIG. 6 shows an arrangement diagram of the use boundary position 30 of each nozzle row 21 and the dot D formed by each of the two passes in the overlapping range 50 between the two passes. In FIG. 6, the arrangement of the dots D includes a black dot Dk, a yellow dot Dy, a cyan dot Dc, a magenta dot Dm, and four color dots Dk, Dy, Dc, The figure of the state which accumulated Dm on each other is shown.

  In FIG. 6, the range 50 where the scanning region 51 of the nozzle row 21 overlaps between two passes is a range for eight nozzles (a range of 8 dots). When an image is printed in this range 50, eight nozzles (1) to (8) located at the rear end of the nozzle row 21 are used in the previous pass. In the subsequent pass, eight nozzles (a) to (h) located at the front end of the nozzle row 21 are used. In addition, for each pass, for each of the four-color nozzle rows 21, which of the eight nozzles 20 is to be used, that is, the use boundary position 30 of the nozzle to be used and the unused nozzle is set. The In other words, the “use boundary position 30” is the number of used nozzles in each pass when an image of the overlapping range 50 where two passes overlap is formed separately in the previous pass and the subsequent pass. It can be said that it is a boundary position.

  For example, taking the black nozzle row 21 as an example, the use boundary position 30k in the overlapping range 50 is between the nozzle (4) and the nozzle (5) in the previous pass, and the nozzle (d) and the nozzle ( set during e). That is, in the previous pass, the nozzles (5) to (8) are used, and the nozzles (1) to (4) on the rear end side are not used. In the subsequent pass, the nozzles (e) to (h) are used, and the nozzles (a) to (d) on the front end side are not used.

  Here, if the use boundary positions 30y, 30c and 30m of the nozzle row 21 of the other three colors coincide with the black use boundary position 30k, the image portions 52a and 52b printed between the two passes are displayed. When a deviation in the conveying direction occurs between the lines, stripe-like shading unevenness (white stripes, black stripes) occurs as in FIG. Therefore, the use boundary position 30 in the overlapping range 50 is made different among the nozzle rows 21 of the four colors. In FIG. 6, the use boundary position 30y of the yellow nozzle row 21y is set between the nozzle (3) and the nozzle (4) in the previous pass and between the nozzle (e) and the nozzle (f) in the subsequent pass. ing. The use boundary position 30c of the cyan nozzle row 21c is set between the nozzle (5) and the nozzle (6) in the previous pass and between the nozzle (c) and the nozzle (d) in the subsequent pass. The use boundary position 30m of the magenta nozzle row 21m is set between the nozzle (6) and the nozzle (7) in the previous pass and between the nozzle (b) and the nozzle (c) in the subsequent pass. Thus, in each pass, the positions of the end dots D formed by the four nozzle rows 21 are not intentionally aligned within the overlapping range 50.

  FIG. 7 is a diagram illustrating an example of a case where an image portion formed by two passes is shifted. FIG. 7A shows a case where the two image portions 52a and 52b are displaced in the direction of leaving. In this case, for the ink of a certain color, even if the dot D formed in the previous pass and the dot D formed in the subsequent pass are separated, the other color dot D is arranged so as to fill the space between them. White stripes do not occur between the two image portions 52a and 52b respectively formed in two passes. On the other hand, FIG. 7B shows a case where the two image portions 52a and 52b are shifted in the approaching direction. In this case, since the positions where the dots D formed in two passes partially overlap are different in the transport direction among the four color inks, the overlapping positions are dispersed in the transport direction and black lines are formed. Less noticeable.

  By the way, when the above-described uneven density suppression printing is performed, in order to make the use boundary positions 30 different among the nozzle rows 21 of the four colors, the overlapping range 50 needs to have a certain width or more. That is, since it is necessary to overlap the scanning regions 51 of the nozzle rows 21 with a certain width between the previous pass and the subsequent pass, the image portion 52 printed on the recording paper 100 in one pass is small. Accordingly, the number of passes required to print an image on one recording sheet 100 increases accordingly. This can be easily understood by comparing FIG. 4 in which density unevenness suppression printing is not performed with FIG. 5 in which density unevenness suppression printing is performed. Since the printing time becomes longer as the number of passes increases, it is preferable not to perform the density unevenness suppression printing when unnecessary, such as when the density unevenness is not so noticeable. In addition, when performing density unevenness suppression printing, the effect of suppressing streaky density unevenness is greater as the use boundary position of the four-color nozzle row 21 is set farther apart. The possible range is even smaller and the number of passes increases.

  Therefore, in the present embodiment, the use boundary positions of the four-color nozzle rows 21 are set according to the duty when printing an image on the recording paper 100. The “duty” in the present embodiment includes the overall duty Da for all four color nozzle rows 21 and the individual duty Dk, Dy, Dc, for each of the four color nozzle rows 21k, 21y, 21c, and 21m. Dm.

  The total duty Da is the ink actually ejected with respect to the total ink amount Vmax when ink is ejected from all the nozzles 20 that can eject to a predetermined area in the four nozzle arrays 21. The ratio of the amount V (V / Vmax). When the size of the ink droplets ejected from one nozzle 20 can be changed, the above Vmax is the total ink amount when the maximum volume of ink droplets is ejected from each nozzle 20.

  On the other hand, the individual duty is a duty for one color ink. The black individual duty Dk will be described as an example. Black that is actually ejected with respect to the total ink amount Vkmax when ejected from all the nozzles 20k that can be ejected to a predetermined area in the black nozzle row 21k. The ink amount Vk is a ratio (Vk / Vkmax).

  As the overall duty is higher, the shading unevenness between the two image portions 52a and 52 respectively formed in two passes becomes more conspicuous. In other words, as the overall duty is lower, the uneven density is less noticeable, and there is often no problem even if the uneven density is not actively suppressed. The same applies to the individual duty. When the individual duty for a certain nozzle row 21 is high, shading unevenness when printing using the nozzle row 21 is likely to be noticeable.

  Also, depending on the type of ink used, there are cases where unevenness in density is easily noticeable and difficult to notice. For example, when black ink is used, streaky unevenness of density is easily noticeable, whereas when black ink is not used, that is, when only yellow, cyan, and magenta color inks are used, unevenness of density is less noticeable. . Therefore, by appropriately setting the use boundary position of the four-color nozzle row 21 according to the duty and the type of the nozzle row 21 to be used, it is possible to suppress an unnecessary increase in the printing time.

  FIG. 8 is a flowchart of shading unevenness suppression processing. In FIG. 8, Si (i = 1, 2, 3,...) Indicates each step. The flow of processing in the control device 6 when density unevenness suppression printing is performed is as follows. First, when a print command is input from the external device 29 or the operation panel 23, as shown in FIG. 8, the control device 6 acquires image data from the external device 29 via the communication unit 28 (S1). Next, image data processing such as color conversion processing and halftone processing is performed on the image data (S2). Further, provisional rasterization is performed from the processed data, and a setting of a pass for printing the image and a decision as to which pass from which nozzle 20 ejects ink are provisionally determined (S3). Here, since it is not yet determined whether the scanning areas 51 of two passes are partially overlapped, and if they are overlapped, they are referred to as “provisional rasterization”.

  Next, the setting regarding the use boundary position of each nozzle row 21 is performed in the overlapping range 50 where the scanning areas 51 of the two passes overlap (S4). First, based on the data after provisional rasterization, the used ink color (used nozzle row 21) and duty (overall duty, individual duty) in the overlapping range 50 of each pass are determined. Then, the setting regarding the use boundary position 30 of the four nozzle rows 21 is performed in the overlapping range 50 from the conditions of the used ink color and the duty. For example, the use boundary positions 30 among the four nozzle rows 21 are made different from each other, or at least a part thereof is matched, and if they are made different, the distance between them is determined. . Based on the setting relating to the use boundary position 30 in S4, rasterization is performed again to determine the setting of the pass such as the overlapping range 50 and the nozzle 20 from which ink is ejected in which pass (S5). Then, based on the result of rasterization in S5, an image is printed on the recording paper 100 (S6).

  Next, some specific examples will be given below regarding the setting of the use boundary position performed according to the duty and the type of the use nozzle row 21 in S4 of FIG.

Example 1
FIG. 9 is a diagram illustrating the setting of the use boundary position 30 in the first embodiment. In FIG. 9 and FIG. 10 of the second embodiment, the four colors of black (K), yellow (Y), cyan (C), and magenta (M) in the “use boundary position” column are different frames. When it enters, it shows that the use boundary position 30 is made different, and when it enters the same frame, it shows that the use boundary position 30 is matched.

  In the first embodiment, first, it is determined whether the overall duty Da is greater than or equal to a predetermined first threshold (High) or less than a first threshold (Low). When the overall duty Da is High, the use boundary positions 30 of the nozzle rows 21 to be used are made different from each other regardless of the type of the nozzle row 21 to be used. For example, when four colors of black (K), yellow (Y), cyan (C), and magenta (M) are used, if the overall duty is high, the use boundary position 30 of the nozzle row 21 of the four colors is set. Make it different. Similarly, when the nozzle rows 21 to be used are three colors or two colors, the use boundary position 30 is made different between the nozzle rows 21 of three colors or two colors.

  On the other hand, when the overall duty Da is Low, the setting of the use boundary position 30 is changed depending on the type of the nozzle row 21 to be used. Specifically, when the black nozzle row 21k is used, the use boundary position 30 between the black nozzle row 21k and the other nozzle rows 21y, 21c, and 21m is made different. However, the use boundary position 30 is matched between the nozzle rows 21y, 21c, and 21m of colors other than black. By matching the use boundary positions 30 of the nozzle rows 21 of two or more colors, the range 50 where the scanning regions of the nozzle rows 21 overlap between the two passes can be narrowed, so that one recording is performed. It is possible to reduce the number of passes required for printing on the paper 100.

(Example 2)
FIG. 10 is a diagram illustrating the setting of the use boundary position 30 in the second embodiment. In the second embodiment, when the overall duty Da is High, the use boundary position 30 of the nozzle row 21 to be used is different from that of the first embodiment. Further, when the overall duty Da is Low and the black nozzle row 21k is used, the use boundary position 30 between the black nozzle row 21k and the other nozzle rows 21y, 21c, and 21m is also different. Same as Example 1. However, in the second embodiment, when the overall duty Da is Low and the four-color nozzle row 21 is used, the yellow nozzle row 21y with low visibility has a black nozzle row 21k and a use boundary position 30. Are different in that they match.

(Example 3)
In the first and second embodiments, the use boundary position 30 of each nozzle row 21 is set by the overall duty Da, but the use boundary position 30 is set by using the individual duty for each nozzle row 21 to be used. May be. For example, it is assumed that the individual duty Dk for black is equal to or greater than a predetermined second threshold value, and the individual duties Dm for yellow, cyan, and magenta are each less than a predetermined value. In this case, the use boundary position 30 of the black nozzle row 21k having a high individual duty is made different from that of the other nozzle rows 21y, 21c, and 21m. On the other hand, the use boundary positions 30 of the nozzle rows 21y, 21c, and 21m for yellow, cyan, and magenta that have low individual duties are made to coincide with each other.

Example 4
Further, the above-described third embodiment may be combined with the determination of whether the overall duty Da is high or low. That is, when the overall duty Da is High, the use boundary positions 30 of the nozzle rows 21 to be used are made different from each other as in the first and second embodiments. On the other hand, when the overall duty Da is Low, the use boundary position 30 of the nozzle row 21 to be used is set depending on whether the individual duty is higher or lower than the second threshold.

  In the third and fourth embodiments, only the individual duty information is used in setting the use boundary position 30, and the use boundary position 30 is not changed depending on the type of the nozzle row 21 to be used. . That is, in the present invention, it is not always necessary to consider the type of nozzle row 21 to be used in setting the use boundary position 30.

(Example 5)
When the use boundary position 30 is determined using the individual duty as in the third and fourth embodiments, the individual duty itself is not compared with the second threshold value, but is set in advance for each ink with respect to the individual duty. The value obtained by multiplying the weight coefficient may be compared with the second threshold value. The weighting coefficient is a coefficient indicating how the ink affects the conspicuousness of the density unevenness. For example, in the case of black, black lines are conspicuous even if the individual duty is low, so the weighting coefficient is set larger than that of the color ink.

  Alternatively, instead of applying a weighting factor to the individual duty, the second threshold value serving as a reference for determining whether the individual duty is high or low between the nozzle rows 21 of the four colors is made different depending on the conspicuousness of the shading unevenness. Also good.

(Example 6)
For each of the individual duties of the four colors, a value obtained by applying a weighting factor set in advance for each ink may be added, and the total sum may be compared with a predetermined third threshold value. . The total sum is a value that can be said to be a correction value of the overall duty Da, which is corrected with respect to the overall duty Da in consideration of the conspicuous density unevenness. For example, when the sum of the above values is equal to or greater than the third threshold value, the use boundary position 30 is different between the nozzle rows 21 of the four colors as in the first and second embodiments (FIGS. 9 and 10). Make it.

(Reference example)
In the first to sixth embodiments, the use boundary position 30 of each nozzle row 21 is set using the duty (overall duty or individual duty). However, in the reference example of the present invention, the duty is used. Instead, the use boundary position 30 may be set only by the type of the nozzle row 21 to be used. For example, when the black nozzle row 21k is used, the use boundary position 30k of the black nozzle row 21k is different from the other nozzle rows 21y, 21c, and 21m regardless of the duty. On the other hand, when only the color ink nozzle rows 21y, 21c, and 21m are used, the use boundary positions 30 of the color ink nozzle rows 21y, 21c, and 21m are made to coincide with each other regardless of the duty.

(Example 7)
When the use boundary positions 30 of the two or more nozzle rows 21 are different from each other, the larger the separation distance between the use boundary positions 30 in the nozzle arrangement direction, the two image portions 52a and 52b formed in two passes, respectively. Since the shading between the two is dispersed, the shading unevenness becomes inconspicuous. Therefore, the separation distance between the use boundary positions 30 of the four nozzle rows 21 may be changed according to the duty and the type of the nozzle row 21 to be used. For example, in FIG. 6, the use boundary positions 30 (for example, the black use boundary position 30k and the yellow use boundary position 30y) of two different nozzle arrays 21 are separated by one nozzle (one dot). When the overall duty Da is higher than a certain level, the use boundary positions 30 of the two different nozzle arrays 21 may be separated by two or more nozzles. However, the larger the use boundary position 30 between different nozzle arrays 21, the larger the overlapping range 50 between the two passes, and the number of passes required to print one recording sheet 100. Will increase.

In addition, if the use boundary position 30 of each nozzle row 21 determined as in the first to seventh embodiments and the reference example is the same in any pass, the nozzle that is not used in any pass in each nozzle row 21. 20 will exist. Since such a nozzle 20 does not discharge ink at all during printing on the recording paper 100, the ink in the nozzle 20 tends to dry and thicken easily. Therefore, it is preferable that the use boundary position 30 of each nozzle row 21 is different between different passes.

  In the present embodiment described above, when printing an image on the recording paper 100 by a plurality of passes of the inkjet head 4, a part of the scanning region 51 of the nozzle row 21 is overlapped in the first and second passes. Let In addition, the use boundary positions 30 of the used nozzles and the non-use nozzles of the four nozzle rows 21 in each pass are individually set. Thereby, the use boundary position 30 can be varied among the four nozzle rows 21 for each pass. That is, in each pass, the positions of the dots at the ends of the four colors respectively formed by the four nozzle rows 21 can be intentionally dispersed in the transport direction so that they are not aligned with each other. As a result, even when the image portion 52a formed in the previous pass and the image portion 52b formed in the subsequent pass are relatively displaced in the transport direction, lightness and darkness is produced at the joint portion between the two image portions 52a and 52b. Since it is dispersed, the shading unevenness is less likely to be a streak and less noticeable.

  Further, in the present embodiment, the use boundary positions 30 of the four nozzle rows 21 are respectively set according to the duty at the time of image printing. As a result, when it is not necessary to positively suppress the uneven density, the use boundary position 30 is not shifted between the different nozzle rows 21, thereby increasing the number of passes and increasing the printing time. Can be prevented.

  In the embodiment described above, the recording paper 100 corresponds to the “recording medium” of the present invention. The transport mechanism 5 corresponds to the “transport section” of the present invention. The control device 6 corresponds to the “control unit” of the present invention. The nozzle row 21 corresponds to the “nozzle group” of the present invention. The communication unit 28 corresponds to the “image data acquisition unit” of the present invention. The left-right direction (scanning direction) in the embodiment corresponds to the “first direction” of the present invention, and the front-rear direction corresponds to the “second direction” of the present invention.

  Next, modified embodiments in which various modifications are made to the embodiment will be described. However, components having the same configuration as in the above embodiment are given the same reference numerals and description thereof is omitted as appropriate.

1] In the above embodiment, the nozzle row 21 that ejects one color of ink has a single row configuration. However, as shown in FIG. 11, even if there are two or more nozzle rows 21 that eject one color of ink. Good. In the case of this form, the nozzle group 61 composed of two or more nozzle rows 21 corresponds to the “nozzle group” in the present invention.

2] The plurality of nozzle groups according to the present invention in which the positions of the nozzles 20 in the nozzle arrangement direction coincide with each other are not limited to ejecting different colors of ink. For example, the plurality of nozzle groups are nozzle groups that eject ink of the same color, but the diameters of the nozzles 20 constituting each nozzle group may be different. In other words, the plurality of nozzle groups may have different ink droplet sizes. In this case, in particular, for the nozzle group having a large diameter of the nozzle 20, it is preferable to make the use boundary position 30 different from the other nozzle groups.

3] The use boundary position 30 may be set so that the use boundary position 30 of each nozzle group changes during one pass. In this way, by changing the use boundary position 30 of each nozzle group during one pass, the light and shade generated between the two image portions formed in the two passes are further dispersed. Less noticeable.

4] In the embodiment, the use boundary position 30 for each of the plurality of nozzle rows 21 (nozzle group) is set according to the duty. On the other hand, it is also possible to set the use boundary position 30 of each nozzle group according to the print setting information input from the external device 29 such as a PC via the communication unit 28. This print setting may be input from the operation panel 23 of the printer 1 by a user operation. The print setting information includes a condition related to at least one of the print speed and the print resolution, and is sometimes called a print mode.

  For example, in the high-speed printing mode, the printing speed is more important than the image quality deterioration due to the occurrence of shading unevenness between passes. On the other hand, in the high image quality printing mode, it is preferable to suppress the occurrence of streaky shading by actively performing the shading unevenness suppression printing even if the printing speed is somewhat slow. Therefore, when print settings such as print speed and print resolution are input from the external device 29 or the operation panel 23, the control device 6 determines each of the plurality of nozzle groups for each pass according to the print settings. The use boundary position 30 for is set.

  As a result, in the case of a print setting in which printing speed is emphasized, density unevenness suppression printing is not actively performed, and an unnecessary increase in the number of passes is prevented. On the other hand, in the case of a print setting that emphasizes the print resolution, light and shade unevenness suppression printing is actively performed to reliably suppress the occurrence of streaks and light and shade between image portions printed in two passes. To do. In this embodiment, the communication unit 28 for acquiring print settings input from the external device 29 or the operation panel 23 operated by the user corresponds to the print setting acquisition unit in the present invention.

5] Conventionally, not all dots are formed in one pass over the scanning range of the ink jet head on the recording paper, but each dot is formed by a plurality of passes having different dot formation patterns. Techniques are known. This method is also referred to as multi-pass printing, and is disclosed in JP 2004-42432 A, JP 2001-322262 A, JP 2004-256627 A, JP 2009-61774 A, and the like. The present invention can also be applied to the multipass printing described above. That is, in each pass, density unevenness may occur if the nozzles to be used match among the nozzle rows of a plurality of colors. Therefore, the nozzles (dot formation pattern) to be used between the nozzle rows of a plurality of colors. ).

DESCRIPTION OF SYMBOLS 1 Inkjet printer 4 Inkjet head 5 Conveyance mechanism 6 Control device 20 Nozzle 21 Nozzle row 23 Operation panel 28 Communication unit 29 External device 30 Use boundary position 50 Overlapping range 51 Scanning region 61 Nozzle group 100 Recording paper

Claims (9)

An inkjet head that ejects ink to a recording medium while moving in a first direction;
A transport unit that transports the recording medium in a direction that transports the recording medium in a second direction that intersects the first direction with respect to the inkjet head;
A control unit for controlling the inkjet head and the transport unit;
The inkjet head is
Having a plurality of nozzle groups composed of a plurality of nozzles arranged along the second direction,
Between the plurality of nozzle groups, the positions in the second direction of the nozzles constituting the nozzle group are the same,
The control unit is arranged so that a scanning region of each nozzle group on the recording medium partially overlaps between one pass and the next pass in the first direction of the inkjet head. In the overlapping range where the recording medium is transported by the transport unit between the two subsequent passes and the scanning areas of the two passes overlap, the previous pass and the subsequent pass in the second direction Let the inkjet head perform printing separately,
For each pass, the control unit sets, for each of the plurality of nozzle groups, a use boundary position between a use nozzle and a non-use nozzle within the overlapping range,
The controller is
An ink jet printer, wherein the use boundary positions of the plurality of nozzle groups are respectively set according to a duty at the time of printing on the recording medium. An inkjet head that ejects ink to a recording medium while moving in a first direction;
A transport unit that transports the recording medium in a direction that transports the recording medium in a second direction that intersects the first direction with respect to the inkjet head;
A control unit for controlling the inkjet head and the transport unit;
The inkjet head is
Having a plurality of nozzle groups composed of a plurality of nozzles arranged along the second direction,
Between the plurality of nozzle groups, the positions in the second direction of the nozzles constituting the nozzle group are the same,
The control unit is arranged so that a scanning region of each nozzle group on the recording medium partially overlaps between one pass and the next pass in the first direction of the inkjet head. In the overlapping range where the recording medium is transported by the transport unit between the two subsequent passes and the scanning areas of the two passes overlap, the previous pass and the subsequent pass in the second direction Let the inkjet head perform printing separately,
For each pass, the control unit sets, for each of the plurality of nozzle groups, a use boundary position between a use nozzle and a non-use nozzle within the overlapping range,
The controller is
An ink jet printer, wherein the use boundary positions of the plurality of nozzle groups are respectively set in accordance with the overall duty of the plurality of nozzle groups when printing on the recording medium. The controller is
When the overall duty is equal to or greater than a predetermined first threshold, the use boundary positions are made different among all of the plurality of nozzle groups,
3. The ink jet printer according to claim 2, wherein when the overall duty is less than the first threshold, the use boundary positions are made to coincide for at least two nozzle groups of the plurality of nozzle groups. . An inkjet head that ejects ink to a recording medium while moving in a first direction;
A transport unit that transports the recording medium in a direction that transports the recording medium in a second direction that intersects the first direction with respect to the inkjet head;
A control unit for controlling the inkjet head and the transport unit;
The inkjet head is
Having a plurality of nozzle groups composed of a plurality of nozzles arranged along the second direction,
Between the plurality of nozzle groups, the positions in the second direction of the nozzles constituting the nozzle group are the same,
The control unit is arranged so that a scanning region of each nozzle group on the recording medium partially overlaps between one pass and the next pass in the first direction of the inkjet head. In the overlapping range where the recording medium is transported by the transport unit between the two subsequent passes and the scanning areas of the two passes overlap, the previous pass and the subsequent pass in the second direction Let the inkjet head perform printing separately,
For each pass, the control unit sets, for each of the plurality of nozzle groups, a use boundary position between a use nozzle and a non-use nozzle within the overlapping range,
The controller is
An ink jet printer, wherein the use boundary positions of the plurality of nozzle groups are respectively set according to individual duties for the plurality of nozzle groups at the time of printing on the recording medium. The controller is
5. The use boundary position of a nozzle group is made different from the use boundary position of another nozzle group when the individual duty of a nozzle group is equal to or greater than a predetermined second threshold value. The inkjet printer described in 1. An image data acquisition unit for acquiring image data to be printed;
The ink jet printer according to claim 1, wherein the control unit determines the duty condition from the image data acquired from the image data acquisition unit.   The ink jet printer according to claim 1, wherein the control unit changes the use boundary position of each nozzle group between different passes.   The said control part sets the said use boundary position so that the said use boundary position of each nozzle group may change in the middle of one pass, The Claim 1 characterized by the above-mentioned. Inkjet printer. An inkjet head that ejects ink to a recording medium while moving in a first direction;
A transport unit that transports the recording medium in a direction that transports the recording medium in a second direction that intersects the first direction with respect to the inkjet head;
A control unit for controlling the inkjet head and the transport unit;
A print setting acquisition unit that acquires print setting information including conditions related to at least one of a print speed and a print resolution when printing on the recording medium using the inkjet head and the transport unit;
The inkjet head is
Having a plurality of nozzle groups composed of a plurality of nozzles arranged along the second direction,
Between the plurality of nozzle groups, the positions in the second direction of the nozzles constituting the nozzle group are the same,
The control unit is arranged so that a scanning region of each nozzle group on the recording medium partially overlaps between one pass and the next pass in the first direction of the inkjet head. In the overlapping range where the recording medium is transported by the transport unit between the two subsequent passes and the scanning areas of the two passes overlap, the previous pass and the subsequent pass in the second direction Let the inkjet head perform printing separately,
For each pass, the control unit sets, for each of the plurality of nozzle groups, a use boundary position between a use nozzle and a non-use nozzle within the overlapping range,
The ink jet printer, wherein the control unit sets the use boundary positions of the plurality of nozzle groups according to the print setting information acquired by the print setting acquisition unit.

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